Increases in cerebrospinal fluid caffeine concentration are associated with favorable outcome after severe traumatic brain injury in humans

Caffeine, the most widely consumed psychoactive drug and a weak adenosine receptor antagonist, can be neuroprotective or neurotoxic depending on the experimental model or neurologic disorder. However, its contribution to pathophysiology and outcome in traumatic brain injury (TBI) in humans is undefined. We assessed serial cerebrospinal fluid (CSF) concentrations of caffeine and its metabolites (theobromine, paraxanthine, and theophylline) by high-pressure liquid chromatography/ultraviolet in 97 ventricular CSF samples from an established bank, from 30 adults with severe TBI. We prospectively selected a threshold caffeine level of > or = 1 micromol/L (194 ng/mL) as clinically significant. Demographics, Glasgow Coma Scale (GCS) score, admission blood alcohol level, and 6-month dichotomized Glasgow Outcome Scale (GOS) score were assessed. Mean time from injury to initial CSF sampling was 10.77+/-3.13 h. On initial sampling, caffeine was detected in 24 of 30 patients, and the threshold was achieved in 9 patients. Favorable GOS was seen more often in patients with CSF caffeine concentration > or = versus < the threshold (55.6 versus 11.8%, P=0.028). Gender, age, admission CGS score, admission blood alcohol level, and admission systolic arterial blood pressure did not differ between patients with CSF caffeine concentration > or = versus < the threshold. Increases in CSF concentrations of the caffeine metabolites theobromine and paraxanthine were also associated with favorable outcome (P=0.018 and 0.056, respectively). Caffeine and its metabolites are commonly detected in CSF in patients with severe TBI and in an exploratory assessment are associated with favorable outcome. We speculate that caffeine may be neuroprotective by long-term upregulation of adenosine A1 receptors or acute inhibition of A2a receptors.

Phospholipase C and Src modulate angiotensin II-induced cyclic AMP production in preglomerular microvascular smooth-muscle cells from spontaneously hypertensive rats

Our previous study indicates that the phospholipase C family (PLC) and Src kinase family (Src) modulate adrenoceptor-induced cAMP production in a negative and positive manner, respectively, in preglomerular vascular smooth-muscle cells (PGSMCs) obtained from spontaneously hypertensive rats (SHR). Because angiotensin II (Ang II) activates PLC and Src, and because PLC and Src inhibit and augment cAMP production, respectively, it is conceivable that the balance between these signal-transduction pathways determines whether Ang II increases or decreases cAMP production in SHR PGSMCs. In SHR PGSMCs, Ang II (500 nM) did not alter cAMP production in the absence or presence of PP1 (100 nM; inhibitor of Src). In the presence of U73122 (3 microM; inhibitor of PLC), Ang II stimulated cAMP production from 2.2 +/- 0.062 to 4.7 +/- 0.73 pmol/well. In another study in U73122-pretreated SHR PGSMCs, Ang II increased cAMP from 3.0 +/- 0.07 to 6.3 +/- 0.40 pmol/well, and this response was blocked by PP1. RT-PCR of 10 isoforms of Scr (Lck, Hck, Frk Fyn, Blk, Lyn, Fgr, Yes, Yrk, and c-Src) indicated that SHR PGSMCs preferentially express Frk, Fyn, Lyn, and c-Src. We conclude that in SHR PGSMCs, inhibition of PLC uncovers a stimulatory effect of Ang II on cAMP production that is mediated by Src family kinases, most likely Frk, Fyn, Lyn, and/or c-Src.

2-Methoxyestradiol, an estradiol metabolite, inhibits neointima formation and smooth muscle cell growth via double blockade of the cell cycle

2-Methoxyestradiol (2-ME), an endogenous metabolite of estradiol with no affinity for estrogen receptors, is a potent anticarcinogenic agent (in phase II clinical trials) and mediates the inhibitory effects of estradiol on smooth muscle cell (SMC) growth. Here we studied the intracellular mechanisms by which 2-ME inhibits SMC growth and whether 2-ME prevents injury-induced neointima formation. 2-ME concentrations that inhibit proliferation of cycling human aortic SMCs by >or=50% blocked cell-cycle progression in G(0)/G(1) and in G(2)/M phase, as determined by flow cytometry. Consistent with the cell-cycle effects, at a molecular level (Western blots), 2-ME inhibited cyclin D(1) and cyclin B(1) expression; cyclin-dependent kinase (cdk)-1 and cdk-2 activity; and retinoblastoma protein (pRb), extracellular signal-regulated kinase (ERK) 1/2, and Akt phosphorylation. 2-ME also upregulated the Cdk inhibitor p27 and interfered with tubulin polymerization. Moreover, 2-ME augmented COX-2 expression, suggesting that it may also inhibit SMC growth via prostaglandin formation. In rats, treatment with 2-ME abrogated injury-induced neointima formation; decreased proliferating SMCs; downregulated expression of proliferating-cell nuclear antigen (PCNA), c-myc, cyclin D(1), cyclin B(1), phosphorylated Akt, phosphorylated ERK1/2, p21, and pRb; inhibited cdk-1 and cdk-4 activity; and upregulated expression of cyclooxygenase (COX)-2 and p27. Caspase-3 cleavage assay and fluorescence-activated cell-sorting (FACS) analysis showed no evidence of apoptosis in 2-ME-treated SMCs, and TUNEL staining in carotid segments showed no evidence of 2-ME-induced apoptosis in vivo. The antimitotic effects of 2-ME on SMCs are mediated by the inhibition of key cell-cycle regulatory proteins and effects on tubulin polymerization and COX-2 upregulation. These effects of 2-ME most likely contribute to the antivasoocclusive actions of this endogenous compound.

cAMP-adenosine pathway in the proximal tubule

The "extracellular cAMP-adenosine pathway" refers to the conversion of cAMP to AMP by ecto-phosphodiesterase, followed by metabolism of AMP to adenosine by ecto-5'-nucleotidase, with all the steps occurring in the extracellular compartment. This study investigated whether the extracellular cAMP-adenosine pathway exists in proximal tubules. Freshly isolated proximal tubules rapidly converted basolaterally administered cAMP to AMP and adenosine. Proximal tubular cells in culture (first passage) rapidly converted apically administered cAMP to AMP and adenosine. In both freshly isolated proximal tubules and cultured proximal tubular cells, conversion of cAMP to AMP and adenosine was affected by a broad-spectrum phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine), an ecto-phosphodiesterase inhibitor (1,3-dipropyl-8-p-sulfophenylxanthine), and a blocker of ecto-5'-nucleotidase (alpha,beta-methyleneadenosine-5'-diphosphate) in a manner consistent with exogenous cAMP being processed by the extracellular cAMP-adenosine pathway. In cultured proximal tubular cells, but not freshly isolated proximal tubules, stimulation of adenylyl cyclase increased extracellular concentrations of cAMP, AMP, and adenosine plus inosine, and these changes were also modulated by the inhibitors in a manner consistent with the extracellular cAMP-adenosine pathway. Conversion of renal interstitial (basolateral) cAMP and AMP to adenosine in vivo was shown by microdialysis coupled with ion trap mass spectrometry. Western blot analysis showed A1, A2A, and A3 receptors on both apical and basolateral proximal tubular membranes, with A1 and A2A receptors more highly expressed on basolateral compared with apical membranes. We conclude that cAMP that reaches either the apical or basolateral membranes of proximal tubular cells is converted in part to adenosine that has ready access to adenosine receptors.

Adenosine inhibits PDGF-induced growth of human glomerular mesangial cells via A(2B) receptors

The objectives of the present study were to determine whether adenosine attenuates proliferation of glomerular mesangial cells (GMCs), which adenosine receptor (AR) mediates the antimitogeneic actions of adenosine, and the cellular mechanisms by which adenosine inhibits growth of GMCs. Studies were conducted in both human and rat GMCs. Platelet-derived growth factor (PDGF)-BB (25 ng/mL) increased DNA synthesis ([3H]thymidine incorporation), cellular proliferation (cell number), collagen synthesis ([3H]proline incorporation), and mitogen-activated protein kinase (MAPK) activity, and these effects were attenuated by 2-chloroadenosine (nonselective AR agonist) and 5'-N-methylcarboxamidoadenosine (MECA; nonselective AR agonist), but not by N6-cyclopentyladenosine (selective A1 AR agonist), AB-N-MECA (selective A3 AR agonist), or CGS21680 (selective A(2A) AR agonist). KF17837 (selective A(2A/B) AR antagonist) and 1,3-dipropyl-8-p-sulfophenylxanthine (nonselective AR antagonist), but not 8-cyclopentyl-1,3-dipropylxanthine (selective A1 AR antagonist), blocked the growth-inhibitory effects of 2-chloroadenosine and 5'-N-MECA. Antisense, but not sense or scrambled, oligonucleotides to the A(2B) receptor increased both basal and PDGF-induced DNA synthesis, cell proliferation, and collagen synthesis, and the growth-inhibitory effects of 2-chloroadenosine, 5'-N-MECA, and erythro-9-(2-hydroxy-3-nonyl)adenine (inhibitor of adenosine deaminase) plus iodotubercidin (inhibitor of adenosine kinase) were abolished by antisense, but not scrambled or sense, oligonucleotides to the A(2B) receptor. We conclude that adenosine causes inhibition of GMC growth by activating A(2B) receptors coupled to inhibition of MAPK activity. A(2B) receptors may play an important role in regulating glomerular remodeling associated with GMC proliferation. Pharmacological or molecular biologic activation of A(2B) receptors may prevent glomerular remodeling associated with glomerulosclerosis, renal disease, and abnormal growth associated with hypertension and diabetes.

Cytochromes 1A1/1B1- and catechol-O-methyltransferase-derived metabolites mediate estradiol-induced antimitogenesis in human cardiac fibroblast

We investigated the role of specific cytochrome P450s (CYP450s) and catechol-O-methyltransferase (COMT) in the growth inhibitory effects of estradiol in cardiac fibroblasts (CFs) expressing functional estrogen receptors. 3-Methylcholantherene, phenobarbital (broad-spectrum CYP450 inducers), and beta-naphthoflavone (CYP1A1/1A2 inducer) augmented, and 1-aminobenzotriazole (broad-spectrum CYP450 inhibitor) blocked, the inhibitory effects of estradiol on serum-induced CF growth (DNA synthesis, cell number, and collagen synthesis). Neither ketoconazole (3A4 inhibitor) nor furafylline (selective 1A2 inhibitor) altered the antimitogenic effects of estradiol on CF growth. In contrast, ellipticine (selective 1A1 inhibitor), pyrene (selective 1B1 inhibitor), and alpha-naphthoflavone (1A1>1A2 inhibitor) abrogated the antimitogenic effects of estradiol on CF growth. OR486 (COMT inhibitor) also blocked the antimitogenic effects of estradiol in both the presence and absence of the CYP450 inducers. ICI182780 (estrogen receptor antagonist) attenuated the growth inhibitory effects of estradiol, but only at concentrations that inhibit the metabolism of estradiol to hydroxyestradiols (precursors of methoxyestradiols). CFs expressed CYP1A1 and CYP1B1, isozymes that convert estradiol to hydroxyestradiols. Moreover, CFs metabolized estradiol to hydroxyestradiol, and 2-hydroxyestradiol to 2-methoxyestradiol. OR486 and quercetin (COMT inhibitor) blocked the conversion of 2-hydroxyestradiol to 2-methoxyestradiol in CFs. We conclude that the antimitogenic effects of estradiol on CF growth are mediated in part by conversion to hydroxyestradiols via CYP1A1 and CYP1B1, followed by metabolism of hydroxyestradiols to methoxyestradiols by COMT.

Catecholamines block the antimitogenic effect of estradiol on human coronary artery smooth muscle cells

Sequential conversion of estradiol to catecholestradiols and methoxyestradiols by cytochrome-P(450) (CYP450) and catechol-O-methyltransferase (COMT), respectively, contributes to the antimitogenic effects of estradiol on vascular smooth muscle cell (SMC) growth via estrogen receptor-independent mechanisms. Because catecholamines are also substrates for COMT, we hypothesize that catecholamines may abrogate the vasoprotective effects of estradiol by competing for COMT and inhibiting methoxyestradiol formation. To test this hypothesis, we investigated the antimitogenic/inhibitory effects of estradiol on human coronary artery SMC growth (cell number, DNA synthesis, collagen synthesis, and SMC migration) and ERK1/2 phosphorylation in the presence and absence of catecholamines. Norepinephrine, epinephrine, isoproterenol, and OR486 (COMT inhibitor) abrogated the inhibitory effects of estradiol on SMC growth and ERK1/2 phosphorylation. The interaction of catecholamines with estradiol was not affected by phentolamine or propanolol, alpha- and beta-adrenoceptor antagonists, respectively. The antimitogenic effects of 2-hydroxy-estradiol, but not 2-methoxyestradiol, were abrogated by epinephrine, isoproterenol, and OR486. Catecholamines inhibited the conversion of both estradiol and 2-hydroxy-estradiol to 2-methoxyestradiol, and SMCs expressed CYP1A1 and CYP1B1. Our findings suggest that catecholamines within the coronary arteries may abrogate the antivasoocclusive effects of estradiol by blocking the conversion of catecholestradiols to methoxyestradiols. The interaction between catecholamines and estradiol metabolism may importantly define the cardiovascular effects of estradiol therapy in postmenopausal women.

Differential regulation of estrogen receptor subtypes alpha and beta in human aortic smooth muscle cells by oligonucleotides and estradiol

We investigated the mechanisms regulating estrogen receptor (ER) expression in human aortic smooth muscle cells (HASMCs) and the mechanisms by which estradiol inhibits HASMC growth. The autologous down-regulation pathway involves binding of liganded ER to the ER gene, thus suppressing transcription. Blockade of this pathway with sense and AS-OLIGOs to ERs up-regulated the expression of ERalpha but not ERbeta. Activation of the autologous down-regulation pathway with ER agonists down-regulated the expression of ERalpha but not ERbeta. The proteasomal degradation pathway entails ubiquination of liganded ER, followed by proteasome-mediated degradation. Blockade of the proteasomal degradation pathway increased the expression of ERbeta. Up-regulation of ERalpha by AS-OLIGOs did not increase the antimitogenic effects of estradiol on HASMCs; the estradiol metabolites 2-hydroxyestradiol and 2-methoxyestradiol were more potent inhibitors of HASMC growth, compared with estradiol; and blockade of metabolism of estradiol to hydroxyestradiols and methoxyestradiols abrogated the inhibitory effects of estradiol on HASMC growth. We conclude that, in HASMCs: 1) the expression of ERalpha is regulated by the autologous downregulation pathway; 2) the expression of ERbeta is governed by the proteasomal degradation pathway; and 3) the antigrowth effects of estradiol are not mediated by ERalpha, but rather by metabolism of estradiol to methoxyestradiols.

Tibolone and its metabolites induce antimitogenesis in human coronary artery smooth muscle cells: role of estrogen, progesterone, and androgen receptors

Tibolone, a hormone replacement drug, protects postmenopausal women against osteoporosis and climacteric symptoms without inducing adverse effects on the endometrium and breast. Compared with other estrogens, little is known about the cardiovascular effects of tibolone. Because abnormal growth of smooth muscle cells (SMCs) is a prerequisite for coronary artery disease, here we investigated the effects of tibolone on SMC growth. We examined the effects of tibolone and its metabolites on human arterial SMC growth (DNA synthesis, cellular proliferation, cell migration, collagen synthesis) and MAPK expression. Fetal calf serum-induced SMC growth, phosphorylated MAPK expression, and platelet-derived growth factor-induced SMC-migration were concentration-dependently inhibited by tibolone and its endogenous estrogenic and progestogenic/androgenic metabolites in the following order of potency: Delta 4-tibolone>3 beta-OH-tibolone congruent with 3 alpha-OH-tibolone. The antimitogenic effects of tibolone were partially blocked by ER antagonist (ICI182780), progesterone receptor antagonist (RU486) but not by the androgen receptor antagonist (flutamide); moreover, RU486 was more potent than ICI182780. The antimitogenic effects of tibolone were completely blocked by RU486 plus ICI182780. In addition, the inhibitory effects of equimolar concentrations of the three tibolone metabolites summed up to the inhibitory effects of tibolone. In conclusion, tibolone inhibits SMC growth and MAPK phosphorylation via both its estrogenic and progestogenic metabolites, and these inhibitory effects involve both progesterone and ERs. Hence, tibolone may induce antivasoocclusive actions and protect women against coronary artery disease.

Methoxyestradiols mediate the antimitogenic effects of 17beta-estradiol: direct evidence from catechol-O-methyltransferase-knockout mice

BACKGROUND

Studies using pharmacological agents suggest but do not prove that the antimitogenic effects of estradiol are caused by conversion of estradiol to hydroxyestradiols (mediated by CYP450s) followed by methylation of hydroxyestradiols to methoxyestradiols (mediated by catechol-O-methyltransferase, COMT).

METHODS AND RESULTS

To test this hypothesis more rigorously, we used aortic smooth muscle cells (SMCs) from mice lacking COMT (COMT-KO). Wild-type (WT) but not COMT-KO SMCs efficiently converted 2-hydroxyestradiol to 2-methoxyestradiol. Both WT and COMT-KO SMCs expressed estrogen receptors. Estradiol and 2-hydroxyestradiol concentration-dependently inhibited serum-induced DNA synthesis, cell numbers, and collagen synthesis in WT but not COMT-KO SMCs. 2-Methoxyestradiol inhibited DNA synthesis, cell numbers, and collagen synthesis in both WT and COMT-KO SMCs.

CONCLUSIONS

These data provide strong evidence that the vascular antimitogenic effects of estradiol are estrogen receptor-independent and involve the sequential conversion of estradiol to hydroxyestradiols and then to methoxyestradiols.

Catecholamines block the antimitogenic effect of estradiol on human glomerular mesangial cells

Local sequential conversion of estradiol to hydroxyestradiols and methoxyestradiols by CYP450 and catechol-O-methyltransferase, respectively, contributes to the antimitogenic effects of estradiol on glomerular mesangial cell growth via estrogen receptor-independent mechanisms. Catecholamines are also substrates for catechol-O-methyltransferase and therefore, might abrogate the renoprotective effects of estradiol by inhibiting formation of methoxyestradiols. To test this hypothesis, we investigated the antimitogenic effects of estradiol on human glomerular mesangial cell proliferation and collagen synthesis in the presence and absence of catecholamines. Norepinephrine, epinephrine, and isoproterenol abrogated the inhibitory effects of estradiol on cell number, DNA synthesis, and collagen synthesis. For example, serum-induced DNA synthesis was inhibited from 100% to 62+/-1.9% by 0.1 micromol/L estradiol, and these inhibitory effects were reversed to 91+/-1.9% by 1 micromol/L epinephrine, 90.7+/-3.3% by 1 micromol/L isoproterenol, 87.5+/-2.8% by 10 micromol/L norepinephrine, and 92+/-1% by 10 micromol/L OR486 (catechol-O-methyltransferase inhibitor). The interaction of catecholamines with estradiol was not affected by phentolamine or propanolol, alpha- and beta-adrenoceptor antagonists, respectively. Similar to estradiol, the antimitogenic effects of 2-hydroxyestradiol were abrogated by epinephrine, isoproterenol, and OR486. In contrast to estradiol and 2-hydroxyestradiol, the antimitogenic effects of 2-methoxyestradiol were not attenuated by epinephrine, isoproterenol, or OR486. Norepinephrine, epinephrine, and isoproterenol inhibited the conversion of both estradiol and 2-hydroxyestradiol to 2-methoxyestradiol. Our findings suggest that catecholamines within the glomeruli might abrogate the antimitogenic effects of estradiol by blocking the conversion of 2-hydroxyestradiol to 2-methoxyestradiol.

CYP450- and COMT-derived estradiol metabolites inhibit activity of human coronary artery SMCs

The purpose of this study is to test the hypothesis that the inhibitory effects of estradiol in human coronary vascular smooth muscle cells are mediated via local conversion to methoxyestradiols via specific cytochrome P450s (CYP450s) and catechol-O-methyltransferase (COMT). The inhibitory effects of estradiol on serum-induced cell activity (DNA synthesis, cell number, collagen synthesis, and cell migration) were enhanced by 3-methylcholantherene, phenobarbital (broad-spectrum CYP450 inducers), and beta-naphthoflavone (CYP1A1/1A2 inducer) and were blocked by 1-aminobenzotriazole (broad-spectrum CYP450 inhibitor). Ellipticine, alpha-naphthoflavone (selective CYP1A1 inhibitors), and pyrene (selective CYP1B1 inhibitor), but not ketoconazole (selective CYP3A4 inhibitor) or furafylline (selective CYP1A2 inhibitor), abrogated the inhibitor effects of estradiol on cell activity, a profile consistent with a CYP1A1/CYP1B1-mediated mechanism. The inhibitory effects of estradiol were blocked by the COMT inhibitors OR486 and quercetin. The estrogen receptor antagonist ICI 182,780 blocked the inhibitory effects of estradiol, but only at concentrations that also blocked the metabolism of estradiol to hydroxyestradiols (precursors of methoxyestradiols). Western blot analysis revealed that coronary smooth muscle cells expressed CYP1A1 and CYP1B1. Moreover, these cells metabolized estradiol to hydroxyestradiols and methoxyestradiols, and the conversion of 2-hydroxyestradiol to 2-methoxyestradiol was blocked by OR486 and quercetin. These findings provide evidence that the inhibitory effects of estradiol on coronary smooth muscle cells are largely mediated via CYP1A1- and CYP1B1-derived hydroxyestradiols that are converted to methoxyestradiols by COMT.

Methoxyestradiols mediate estradiol-induced antimitogenesis in human aortic SMCs

Estrogen receptors (ERs) are considered to mediate the ability of 17beta-estradiol (estradiol) to reduce injury-induced proliferation of vascular smooth muscle cells (VSMCs), leading to vascular lesions. However, the finding that estradiol attenuates formation of vascular lesions in response to vascular injury in knockout mice that lack either ER-alpha or ER-beta challenges this concept. Our hypothesis is that the local metabolism of estradiol to methoxyestradiols, metabolites of estradiol with little affinity for ERs, mediates the ER-independent antimitogenic effects of estradiol on VSMCs. In human VSMCs, 2-methoxyestradiol and 2-hydroxyestradiol were more potent than was estradiol in inhibiting DNA synthesis (3[H]-thymidine incorporation), collagen synthesis (3[H]-proline incorporation), cell proliferation (cell number), and cell migration (movement of cells across a polycarbonate membrane). The inhibitory effects of estradiol on VSMCs were enhanced by cytochrome-P450 (CYP450) inducers 3-methylcholanthrene and phenobarbital. Moreover, the inhibitory effects of estradiol were blocked in the presence of the CYP450 inhibitor 1-aminobenzotriazole and the catechol-O-methyltransferase inhibitors quercetin and OR486. Both OR486 and quercetin blocked the conversion of 2-hydroxyestradiol to 2-methoxyestradiol; moreover, they blocked the antimitogenic effects of 2-hydroxyestradiol but not of 2-methoxyestradiol. The ER antagonist ICI182780 blocked the inhibitor effects of estradiol on VSMCs, but only at concentrations (>50 micromol/L) that also inhibit the metabolism of estradiol to hydroxyestradiols (precursors of methoxyestradiols). In conclusion, the inhibitory effects of locally applied estradiol on human VSMCs are mediated via a novel ER-independent mechanism involving estradiol metabolism. These findings imply that vascular estradiol metabolism may be an important determinant of the cardiovascular protective effects of estradiol and that nonfeminizing estradiol metabolites may confer cardiovascular protection regardless of gender.

Catecholamines block 2-hydroxyestradiol-induced antimitogenesis in mesangial cells

Methylation of 2-hydroxyestradiol to 2-methoxyestradiol by catechol-O-methyl transferase (COMT) mediates the antimitogenic effects of 2-hydroxyestradiol on vascular smooth muscle cells. Moreover, 2-hydroxyestradiol inhibits growth of glomerular mesangial cells (GMCs). Because catecholamines are substrates for COMT, which is expressed in GMCs, we hypothesize that catecholamines may abrogate the antimitogenic effects of 2-hydroxyestradiol on GMCs by competing for COMT and inhibiting 2-methoxyestradiol formation. To test this hypothesis, we investigated the antimitogenic effects of 2-hydroxyestradiol on rat GMCs in the presence and absence of catecholamines. The capability of GMCs to methylate 2-hydroxyestradiol in the presence and absence of catecholamines was also evaluated. GMCs metabolized 2-hydoxyestradiol in a concentration-dependent manner with a V(max) of 12.03+/-0.32 pmol/10(6) cells/min and an apparent K(m) of 0.23+/-0.04 micromol/L. Norepinephrine (10 micromol/L) and epinephrine (10 micromol/L) significantly inhibited methylation of 0.25 micromol/L 2-hydroxyestradiol. Norepinephrine concentration-dependently abrogated the ability of 2-hydroxyestradiol to inhibit 3H-thymidine incorporation (index of DNA synthesis). In the presence of 5, 10, and 40 micromol/L norepinephrine, the inhibitory effect of 0.1 micromol/L 2-hydroxyestradiol on 3H-thymidine incorporation was reduced from 51+/-0.7% to 46+/-0.4%, 39+/-0.3%, and 25+/-0.7%, respectively. Similar to DNA synthesis, the inhibitory effects of 2-hydroxyestradiol on cell number and 3H-proline incorporation (index of collagen synthesis) on GMCs were abrogated by catecholamines. Our findings provide evidence that methylation of 2-hydroxyestradiol inhibits GMC proliferation and extracellular matrix synthesis and may in part protect against renal proliferative diseases. Moreover, catecholamines may abrogate the renoprotective effects of 2-hydroxyestradiol in the glomeruli by inhibiting COMT and 2-methoxyestradiol formation.

A(2B) adenosine receptors stimulate growth of porcine and rat arterial endothelial cells

The goal of this study was to determine which adenosine receptor subtype mediates growth stimulation by adenosine in arterial endothelial cells. In porcine coronary artery and rat aortic endothelial cells, 2-chloroadenosine (Cl-Ad), a metabolically stable analog of adenosine, stimulated DNA synthesis ((3)H-thymidine incorporation), cellular proliferation (cell number), collagen synthesis ((3)H-proline incorporation), and cell migration. The growth effects of adenosine and Cl-Ad were mimicked by the adenosine receptor agonist 5'-N-methylcarboxamidoadenosine but not by the adenosine receptor agonists N(6)-cyclopentyladenosine, 4-aminobenzyl-5'-N-methylcarboxamidoadenosine or CGS21680, an agonist profile consistent with an A(2B) receptor-mediated effect. The adenosine receptor antagonists KF17837 and 1,3-dipropyl-8-p-sulfophenylxanthine but not 8-cyclopentyl-1,3-dipropylxanthine blocked the growth-stimulatory effects of Cl-Ad and 5'-N-methylcarboxamidoadenosine, an antagonist profile consistent with an A(2) receptor-mediated action. Treatment of endothelial cells with erythro-9-(2-hydroxy-3-nonyl) adenine plus iodotubericidin (inhibitors of adenosine deaminase and adenosine kinase, respectively) induced endothelial cell growth, and these effects were blocked by 1,3-dipropyl-8-p-sulfophenylxanthine and KF17837 but not 8-cyclopentyl-1,3-dipropylxanthine, suggesting that endothelial cell-derived adenosine induces growth via A(2) receptors. The growth-stimulatory effects of Cl-Ad, 5'-N-methylcarboxamidoadenosine, and erythro-9-(2-hydroxy-3-nonyl) adenine plus iodotubericidin were abolished by antisense but not scrambled or sense oligonucleotides to the A(2B) receptor. Our findings strongly support the hypothesis that adenosine induces endothelial cell growth by activating A(2B) receptors. Thus, A(2B) receptors may play a critical role in regulating vascular remodeling associated with endothelial cell proliferation in angiogenesis, collateral vessel development, and recovery after vascular injury. Pharmacological or molecular biological activation of A(2B) receptors may be useful in modulating vascular remodeling.

Role of methoxyestradiols in the growth inhibitory effects of estradiol on human glomerular mesangial cells

Metabolism of locally applied 17beta-estradiol (estradiol) to methoxyestradiols contributes to the growth inhibiting effects of estradiol on vascular smooth muscle cells via an estrogen receptor (ER)-independent mechanism. Because vascular smooth muscle cells are phenotypically similar to glomerular mesangial cells, it is feasible that estradiol inhibits glomerular mesangial cell growth via a similar mechanism, and this possibility was investigated. In human glomerular mesangail cells, estradiol concentration dependently (1 to 100 nmol/L) inhibited serum-induced proliferation (cell number) and DNA ((3)[H]-thymidine incorporation) and collagen ((3)[H]-proline incorporation) synthesis. The inhibitory effects of estradiol were mimicked by 2-hydroxyestradiol and 2-methoxyestradiol, metabolites of estradiol with little affinity for ERs. 2-Hydroxyestradiol and 2-methoxyestradiol were more potent growth inhibitors than estradiol. The inhibitory effects of estradiol were enhanced by CYP450 inducers 3-methylcholanthrene (10 micromol/L) and phenobarbital (10 micromol/L) and blocked by the CYP450 inhibitor 1-aminobenzotriazole (10 micromol/L). The growth inhibitory effects of estradiol were also blocked by quercetin (10 micromol/L) and OR 486 (10 micromol/L) inhibitors of catechol-O-methyltransferase (converts catecholestradiols to methoxyestradiols). ICI182780 (ER antagonist with ER binding affinity similar to estradiol) blocked the growth inhibitory effects of estradiol (1 to 100 nmol/L) only at concentrations (>50 micromol/L) that inhibited estradiol metabolism to catecholestradiols. The growth inhibitory effects of 2-hydroxyestradiol were abrogated by quercetin and OR486 (two structurally dissimilar catechol-O-methyltransferase inhibitors), but not by ICI182780. However, the growth inhibitory effects of 2-methoxyestradiol were unaltered by catechol-O-methyltransferase inhibitors and ICI182780. In conclusion, our findings provide the first evidence that methoxyestradiols mediate the growth inhibitory effects of locally applied estradiol on glomerular mesangial cell growth via an ER-independent mechanism.

Methoxyestradiols mediate the antimitogenic effects of locally applied estradiol on cardiac fibroblast growth

Estradiol inhibits cardiac fibroblast growth and may protect against cardiac remodeling associated with heart disease. However, the mechanisms by which estradiol attenuates cardiac fibroblast growth remain unclear. Because cardiac fibroblasts express cytochrome P450s (CYP450s) and catechol-O-methyltransferase (COMT) capable of converting estradiol to hydroxyestradiols and methoxyestradiols, respectively, and because hydroxyestradiols and methoxyestradiols (estradiol metabolites with little affinity for estrogen receptors) are potent inhibitors of cardiac fibroblast growth, we hypothesized that the antimitogenic effects of estradiol are mediated via hydroxyestradiols and/or methoxyestradiols. The inhibitory effects of estradiol (1 to 100 nmol/L) on serum-stimulated (3)H-thymidine incorporation (DNA synthesis), (3)H-proline incorporation (collagen synthesis), and cell number (proliferation) were enhanced (P<0.005) by CYP450 inducers 3-methylcholanthrene (10 micromol/L) and phenobarbital (10 micromol/L). Moreover, the inhibitory effects of estradiol were blocked by the CYP450 inhibitor 1-aminobenzotriazole (10 micromol/L) and the COMT inhibitors quercetin (10 micromol/L) and OR486 (10 micromol/L). In contrast to estradiol, the modulators of CYP450 and COMT were poor ligands for estrogen receptors (binding affinity less-than-or-equal 0.0001% versus estradiol). In cardiac fibroblasts, both quercetin and OR486 inhibited the metabolism of hydroxyestradiol to methoxyestradiol and blocked the inhibitory effects of hydroxyestradiol on cardiac fibroblast proliferation and DNA and collagen synthesis. The abrogating effects of quercetin and OR486 on the metabolism and antimitogenic effects of 2-hydroxyestradiol were mimicked by 20 micromol/L norepinephrine and isoproterenol, substrates for COMT. Our findings provide evidence that estradiol can inhibit cardiac fibroblast growth via an estrogen receptor--independent pathway that involves the local metabolism of estradiol to methoxyestradiols.

Catecholamines abrogate antimitogenic effects of 2-hydroxyestradiol on human aortic vascular smooth muscle cells

Catechol-O-methyltransferase (COMT)-mediated methylation of 2-hydroxyestradiol (endogenous estradiol metabolite) to 2-methoxyestradiol (angiogenesis inhibitor) may be responsible for the antimitogenic effects of 2-hydroxyestradiol on vascular smooth muscle cells (VSMCs). Catecholamines are also substrates for COMT, and increased levels of catecholamines are associated with vasoocclusive disorders. We hypothesize that catecholamines may abrogate the vasoprotective effects of 2-hydroxyestradiol by competing for COMT and inhibiting 2-methoxyestradiol formation. To test this hypothesis, we investigated the antimitogenic effects of 0.001 to 0.1 micromol/L of 2-hydroxyestradiol on human aortic VSMC proliferation (cell number and DNA synthesis), collagen synthesis, and migration in the presence and absence of catecholamines. Norepinephrine, epinephrine, and isoproterenol concentration-dependently abrogated the inhibitory effects of 2-hydroxyestradiol on cell number, DNA synthesis, collagen synthesis, and cell migration. These modulatory/attenuating effects of catecholamines were not abrogated in the presence of the alpha- and beta-adrenergic receptor antagonists, phentolamine mesylate and propranolol, respectively. In contrast to 2-hydroxyestradiol, the antimitogenic effects of 2-methoxyestradiol (0.1 micromol/L) were not attenuated by isoproterenol (1 micromol/L) or quercetin (competitive inhibitor of COMT, 10 micromol/L). Norepinephrine, epinephrine, and isoproterenol concentration-dependently (10 to 500 micromol/L) inhibited the metabolism of 2-hydroxyestradiol (0.25 to 2 micromol/L) to 2-methoxyestradiol, and the potency of the catecholamines to reverse 2-hydroxyestradiol-induced inhibition of VSMC proliferation, collagen synthesis, and migration was correlated with their ability to inhibit 2-methoxyestradiol formation. Our findings suggest that catecholamines within the vasculature may abrogate the anti-vaso-occlusive effects of estradiol and 2-hydroxyestradiol by blocking 2-methoxyestradiol formation.

Endogenous cyclic AMP-adenosine pathway regulates cardiac fibroblast growth

Our previous studies show that cardiac fibroblasts express the extracellular "cAMP-adenosine pathway," that is, the generation of adenosine from extracelluar cAMP. The goal of this study was to assess whether activation of the cAMP-adenosine pathway by stimulation of endogenous cAMP synthesis regulates cardiac fibroblast growth. Cardiac fibroblasts in 3D cultures were used as the model system. Treatment of cardiac fibroblasts with forskolin, isoproterenol, or norepinephrine increased cAMP production and extracellular levels of adenosine, and these effects were prevented by inhibition of adenylyl cyclase (2',5'-dideoxyadenosine). Treatment with forskolin, isoproterenol, or norepinephrine for 24 hours inhibited DNA synthesis ((3)H-thymidine incorporation), and this effect was enhanced by combined inhibition of adenosine deaminase (erythro-9-[2-hydroxy-3-nonyl] adenine) plus adenosine kinase (iodotubercidin). Inhibition of adenylyl cyclase or adenosine receptors (1,3-dipropyl-8-p-sulfophenylxanthine or KF17837) prevented the effects of forskolin, isoproterenol, and norepinephrine on DNA synthesis. Forskolin also inhibited protein synthesis ((3)H-leucine incorporation) and cell proliferation, and these effects were blocked by adenosine receptor antagonism. Treatment of cardiac fibroblasts with norepinephrine for >48 hours but not <48 hours increased DNA synthesis, protein synthesis, and cell number. However, blockade of adenylyl cyclase or antagonism of adenosine receptors caused norepinephrine to induce proliferation in <48 hours. Our findings indicate that the endogenous cAMP-adenosine pathway regulates cardiac fibroblast growth.

Increased 2-methoxyestradiol production in human coronary versus aortic vascular cells

Estradiol may be cardioprotective; however, the mechanisms involved remain unclear. Recent findings that estradiol attenuates neointima formation in estrogen receptor knockout mice suggest that the cardioprotective effects of estradiol may be mediated through estrogen receptor-independent mechanisms. Because 2-methoxyestradiol, an endogenous metabolite of estradiol with no affinity for estrogen receptors, is more potent than estradiol in inhibiting vascular smooth muscle cell growth, it is feasible that 2-methoxyestradiol mediates in part the cardioprotective effects of estradiol. To address this hypothesis, we examined the kinetics of 2-methoxyestradiol synthesis in vascular smooth muscle cells and endothelial cells. In human aortic smooth muscle cells, the V(max), K(m), and V(max)/K(m) ratio values for conversion of 2-hydroxyestradiol to 2-methoxyestradiol were 19+/-0.69 pmol. min(-1) per 10(6) cells, 0.52+/-0.085 micromol/L, and 44+/-4.9 pmol. min(-1). micromol/L per 10(6) cells, respectively. In human coronary artery vascular smooth muscle cells, the V(max), K(m), and V(max)/K(m) ratio values for conversion of 2-hydroxyestradiol to 2-methoxyestradiol were 16+/-0.59 pmol. min(-1) per 10(6) cells, 0.23+/-0.011 micromol/L, and 69+/-3.6 pmol. min(-1). micromol/L per 10(6) cells, respectively (all values significantly different compared with human aortic smooth muscle cells). Also, in human aortic versus coronary artery endothelial cells, the V(max) (33+/-0.24 versus 22+/-0.33 pmol. min(-1) per 10(6) cells, respectively), K(m) (0.20+/-0.010 versus 0.099+/-0.014 micromol/L, respectively), and V(max)/K:(m) (163+/-7.7 versus 243+/-41 pmol. min(-1). micromol/L per 10(6) cells, respectively) values were significantly different. Our results indicate that vascular smooth muscle and endothelial cells effectively metabolize 2-hydroxyestradiol to 2-methoxyestradiol. The lower K(m) and higher V(max)/K(m) ratio of human coronary versus aortic cells indicate a faster rate of local metabolism of 2-hydroxyestradiol to 2-methoxyestradiol in the coronary circulation at low levels of 2-hydroxyestradiol.

Dysregulation of extracellular adenosine levels by vascular smooth muscle cells from spontaneously hypertensive rats

-The objective of this investigation was to determine whether the regulation of extracellular adenosine levels by smooth muscle cells (SMCs) from conduit arteries (aorta) and resistance microvessels (renal arterioles) is different in spontaneously hypertensive rats (SHR) versus normotensive Wistar-Kyoto (WKY) rats. Basal extracellular adenosine levels were decreased in cultured aortic and arteriolar SHR SMCs, and the increase in extracellular adenosine levels induced by stimulation of the cAMP-adenosine pathway was less in aortic and arteriolar SHR SMCs. Extracellular adenosine levels were lower in SHR SMCs, however, even when the cAMP-adenosine pathway was inhibited with 3-isobutyl-1-methylxanthine. Inhibition of adenosine kinase with iodotubercidin and inhibition of adenosine deaminase with erythro-9-(2-hydroxy-3-nonyl) adenine increased extracellular adenosine; however, only inhibition of adenosine deaminase equalized extracellular adenosine levels in SHR versus WKY SMCs. Membrane-disrupted SHR SMCs metabolized exogenous adenosine faster than WKY SMCs did, and this difference was abolished by inhibition of adenosine deaminase but not adenosine kinase. SHR SMCs demonstrated a greater proliferative response than WKY SMCs. This enhanced proliferative response was not blocked by adenosine per se or inhibition of adenosine kinase but was blocked by inhibition of adenosine deaminase and by 2-chloroadenosine (adenosine deaminase-resistant adenosine analogue). We conclude that dysregulation of extracellular adenosine levels exists in SHR SMCs, that this dysregulation is not due to a defect in the cAMP-adenosine pathway but rather to enhanced activity of adenosine deaminase, and that the dysregulation of extracellular adenosine mediates the enhanced proliferative response of SHR SMCs.

Effects of estradiol and its metabolites on glomerular endothelial nitric oxide synthesis and mesangial cell growth

Reduced nitric oxide synthesis by glomerular endothelial cells and increased proliferation of glomerular mesangial cells is associated with glomerular remodeling that leads to accelerated glomerulosclerosis. Estradiol induces nitric oxide synthesis and slows the progression of renal disease. Because the estradiol metabolites 2-hydroxyestradiol and 2-methoxyestradiol are more potent than estradiol in inhibiting growth of vascular smooth muscle cells, which are phenotypically similar to mesangial cells, we compared the effects of estradiol, 2-hydroxyestradiol, and 2-methoxyestradiol on growth of glomerular mesangial cells and on basal nitric oxide synthesis by glomerular endothelial cells. In human glomerular mesangial cells, estradiol and its metabolites concentration-dependently (1 nmol/L to 10 micromol/L) inhibited serum (2.5%)-induced DNA synthesis, cell proliferation, and collagen synthesis with the order of potency being 2-methoxyestradiol > 2-hydroxyestradiol > estradiol. ICI182780 (100 micromol/L, an estrogen receptor antagonist) blocked the growth inhibitory effects of estradiol but not 2-hydroxyestradiol or 2-methoxyestradiol. Treatment with estradiol, but not 2-hydroxyestradiol and 2-methoxyestradiol, induced nitric oxide synthesis (P<0.05, assayed by the formation of (3)H-L-citrulline from (3)H-L-arginine) in human glomerular endothelial cells, and these effects were blocked by ICI182780 and L-NMA (a nitric oxide synthesis inhibitor). In conclusion, estradiol may attenuate glomerulosclerosis by inducing nitric oxide synthesis via an estrogen receptor-dependent mechanism and by conversion to 2-hydroxyestradiol and 2-methoxyestradiol, which inhibit glomerular mesangial cell proliferation independent of estrogen receptors.

A(2b) receptors mediate the antimitogenic effects of adenosine in cardiac fibroblasts

Adenosine inhibits growth of cardiac fibroblasts; however, the adenosine receptor subtype that mediates this antimitogenic effect remains undefined. Therefore, the goals of this study were to determine which adenosine receptor subtype mediates the antimitogenic effects of adenosine and to investigate the signal transduction mechanisms involved. In rat left ventricular cardiac fibroblasts, PDGF-BB (25 ng/mL) stimulated DNA synthesis ((3)H-thymidine incorporation), cellular proliferation (cell number), collagen synthesis ((3)H-proline incorporation), and MAP kinase activity. The adenosine receptor agonists 2-chloroadenosine and 5'-N-methylcarboxamidoadenosine, but not N(6)-cyclopentyladenosine, 4-aminobenzyl-5'-N-methylcarboxamidoadenosine, or CGS21680, inhibited the growth effects of PDGF-BB, an agonist profile consistent with an A(2B) receptor-mediated effect. The adenosine receptor antagonists KF17837 and 1,3-dipropyl-8-p-sulfophenylxanthine, but not 8-cyclopentyl-1,3-dipropylxanthine, blocked the growth-inhibitory effects of 2-chloroadenosine and 5'-N-methylcarboxamidoadenosine, an antagonist profile consistent with an A(2) receptor-mediated effect. Antisense, but not sense or scrambled, oligonucleotides to the A(2B) receptor stimulated basal and PDGF-induced DNA synthesis, cell proliferation, and collagen synthesis. Moreover, the growth-inhibitory effects of 2-chloroadenosine, 5'-N-methylcarboxamidoadenosine, and erythro-9-(2-hydroxy-3-nonyl) adenine plus iodotubericidin (inhibitors of adenosine deaminase and adenosine kinase, respectively) were abolished by antisense, but not scrambled or sense, oligonucleotides to the A(2B) receptor. Our findings strongly support the hypothesis that adenosine causes inhibition of CF growth by activating A(2B) receptors coupled to inhibition of MAP kinase activity. Thus, A(2B) receptors may play a critical role in regulating cardiac remodeling associated with CF proliferation. Pharmacologic or molecular biological activation of A(2B) receptors may prevent cardiac remodeling associated with hypertension, myocardial infarction, and myocardial reperfusion injury after ischemia.

Methoxyestradiols mediate the antimitogenic effects of estradiol on vascular smooth muscle cells via estrogen receptor-independent mechanisms

Estrogen receptors (ERs) are widely held to mediate the ability of 17 beta-estradiol (estradiol) to attenuate injury-induced proliferation of vascular smooth muscle cells (VSMCs) leading to vascular lesions. However, recent findings that estradiol prevents injury-induced vascular lesion formation in knock-out mice lacking either ER alpha or ER beta seriously challenge this concept. Here we report that the local metabolism of estradiol to methoxyestradiols, endogenous metabolites of estradiol with no affinity for ERs, is responsible for the ER-independent inhibitory effects of locally applied estradiol on rat VSMC growth. These finding imply that local vascular estradiol metabolism may be an important determinant of the cardiovascular protective effects of circulating estradiol. Thus, interindividual differences, either genetic or acquired, in the vascular metabolism of estradiol may define a given female's risk of cardiovascular disease and influence the cardiovascular benefit she receives from estradiol replacement therapy in the postmenopausal state. These findings also imply that nonfeminizing estradiol metabolites may confer cardiovascular protection in both women and men.

A2B Adenosine Receptors Mediate the Anti-Mitogenic Effects of Adenosine in Cardiac Fibroblasts

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Adenosine inhibits growth of CFs; however, the adenosine receptor subtype that mediates this anti-mitogenic effect remains undefined. Using specific ADE receptor antagonists and agonists and antisense oligonucleotides (OLIGO) against A2B receptors, we investigated the role of A2B receptors in inhibiting cardiac fibroblast growth. PDGF (25ng/ml)-induced DNA synthesis, cell number and collagen synthesis in CFs were inhibited by A2 (chloroadenosine [Cl-Ad]and MECA), but not by A1 (CPA), A2a ( CGS21680 ) or A3 (AB-MECA),receptor agonists.The inhibitory effects of 1μM MECA and Cl-Ad were reversed by A1/A2 (DPSPX; 10nM), but not by A1 (DPCPX; 10nM), receptor antagonists. In CFs treated with antisense, but not sense or scrambled, OLIGOs to the A2B receptor, both basal and PDGF-induced DNA synthesis was enhanced by 70±4% and 64±5% respectively. Moreover, the inhibitory effects of Cl-Ad and MECA were completely abolished in CFs treated with antisense, but not sense and scrambled, OLIGOs. In conclusion, A2B receptors mediate the anti-mitogenic effects of adenosine suggesting that A2B receptors are importantly involved in the regulation of CF biology. Thus, A2B receptors may play a critical role in regulating cardiac remodeling associated with CF proliferation.

Increased 2-Methoxyestradiol Production in Human Coronary Artery Versus Aortic Smooth Muscle Cells: Potential Role in Mediating the Cardioprotective Effects of Estradiol

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Estradiol (E) protects premenopausal women against coronary artery disease (CAD), however, the mechanisms involved remain unclear. Recent findings that E protects neointima formation in α and β estrogen receptor(ER) knockout mice suggest that the effects may be mediated via an ER independent mechanism. Because 2-methoxyestradiol(2MeOE),an endogenous metabolite of E with no affinity for ER, is more potent than E in inhibiting vascular smooth muscle cell (SMC) growth, it is feasible that 2MeOE mediates the protective effects of E. Since formation of 2MeOE involves the methylation of 2-hydroxyestradiol (2OHE; major estradiol metabolite)by COMT, the protective effects of estradiol on the coronary circulation may be due in part to the efficient conversion of E and 2OHE to 2MeOE in coronary vascular SMCs. To test this hypothesis, we compared the kinetics of 2MeOE synthesis in human aortic (A) versus coronary artery (CA) SMCs. Incubation of human ASMCs and CASMCs with 10μM 2OHE resulted in a time-dependent formation of 2MeOE. As compared to ASMCs, CASMCs were twice as effective in metabolizing 2OHE to 2MeOE and the Vmax and Km were 15.7±.7 vs 38.3±.9 pmol 2MeOE/10 6 cells/min and .35±.07 vs .12±.02 μM, respectively. Rat ASMCs and porcine aortic endothelial cells (ECs) also metabolized 2OHE to 2MeOE, the Vmax being 17.1±.8 and 14.22±.3 pmol/10 6 cells/min, respectively, and Km of 0.48±.1 and 0.32±.04μM,respectively. Our findings indicate that vascular SMCs and ECs effectively metabolize 2OHE to 2MeOE and that as compared to ASMCs, CASMCs have increased COMT activity and 2MeOE formation.Thus, local metabolism of 2OHE to 2MeOE may mediate the anti-vasoocclusive effects of E via an ER-independent mechanism. Moreover, increased COMT activity may selectively protect the coronary artery by generating more 2MeOE and this may be responsible for the decreased incidence of CAD in premenopausal women.

Estradiol and Its Metabolites Differentially Induce NO Synthesis by Human Glomerular Endothelial Cells and Inhibit Glomerular Mesangial Cell Growth

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Reduced NO synthesis by glomerular endothelial cells (GECs) and increased proliferation of glomerular mesangial cells (GMCs) is associated with glomerular remodeling process leading to glomerosclerosis. Moreover, estradiol (E) slows the progression of renal disease. Because E induces NO synthesis and E metabolites are as potent as E in inhibiting growth of vascular smooth muscle cells, which are phenotypically similar to GMCs, we investigated whether E and its major endogenous metabolites (2-hydroxyestradiol[2OHE] and 2-methoxyestradiol [2MeOE])inhibit growth of GMCs and induce basal NO synthesis by GECs. E and its metabolites (1nM-10μM)inhibited serum (2.5%)-induced DNA synthesis, cell number and collagen synthesis in human GMCs concentration-dependently,and with the order of potency being 2MeOE > 2OHE > E. ICI182780, an estrogen receptor antagonist (100μM) blocked the growth inhibitory effects of E, but not 2OHE and 2MeOE. Treatment with E, but not 2OHE and 2MeOE, induced NO synthesis (P<.05; assayed by the formation of 3 H-L-citrulline from 3 H-L-arginine) in human GECs, and these effects were blocked by ICI182780 and L-NMA (NO synthesis inhibitor).In conclusion, E may protect glomerosclerosis by inducing NO synthesis via an estrogen receptor-dependent mechanism and via conversion to 2OHE and 2MeOE, which inhibit GMC proliferation independently of the estrogen receptor.

Catecholamines Abrogate the Anti-Mitogenic Effects of 2-Hydroxy Metabolite of Estradiol on Vascular Smooth Muscle Cells by Inhibiting Catechol-O-Methyltransferase (COMT) Activity and 2-Methoxyestradiol Formation

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Methylation of 2-hydroxyestradiol(2OHE; endogenous estradiol metabolite) to 2-methoxyestradiol (2MeOE; angiogenesis inhibitor)by COMT plays a key role in mediating the anti-mitogenic effects of 2OHE on vascular smooth muscle cell (SMC)growth. Catecholamines such as norepinephrine (NE) are also substrates for COMT and increased levels of NE are associated with vasoocclusive disorders. We hypothesize that increased endogenous synthesis/levels of NE under pathophysiological conditions may abrogate the vasoprotective effects of 2OHE by competing for COMT and inhibiting 2MeOE formation. To test this hypothesis we investigated the anti-mitogenic effects of .001-10μM 2OHE on 2.5% FCS-induced SMC growth (cell number, DNA synthesis [thymidine incorporation], collagen synthesis [proline incorporatio])in rat and human aortic SMCs in the presence and absence of NE (0.1-40μM). NE concentration-dependently abrogated the inhibitory effects of 2OHE on SMC growth and in the presence of 10μM NE the inhibitory curve of 2OHE on SMC growth was shifted to the right(P<.05). In the presence of 10μM NE, the inhibitory effect of 1μM 2OHE on DNA synthesis was reduced from 70±3% to 24±2% (P<.05), and this effect of NE was mimicked by isoproterenol (ISO) and epinephrine (EPI). Additionally, NE (0.5-2.5mM) inhibited the metabolism of 10μM 2OHE to 2MeOE in a concentration-dependent manner and the effects of NE were mimicked by ISO, EPI, metanephrine, normetanephrine and 3,4-dihydroxymandelic acid. At 0.5 mM ISO, NE and EPI inhibited 2MeoE formation by 70±4%,20±2% and 40±2%, respectively. Our findings suggest that increases in local synthesis of catecholamines within the vasculature may abrogate the anti-vasoocclusive effects of estradiol and 2OHE by blocking 2MeOE formation. In conclusion, the interaction between catecholamines and 2OHE may play a key role in the biology of vascular SMC growth.

Cardiac fibroblasts express the cAMP-adenosine pathway

The extracellular "cAMP-adenosine pathway" refers to the local production of adenosine mediated by cAMP egress into the extracellular space, conversion of cAMP to AMP by ectophosphodiesterase, and the metabolism of AMP to adenosine by ecto-5'-nucleotidase. The goal of this study was to assess whether the cAMP-adenosine pathway limits cardiac fibroblast growth. Studies were conducted in ventricular cardiac fibroblasts maintained in 3-dimensional cultures. Addition of exogenous cAMP to cardiac fibroblasts increased extracellular levels of AMP, adenosine, and inosine in a concentration-dependent and time-dependent manner. This effect was attenuated by blockade of total phosphodiesterase activity (3-isobutyl-1-methylxanthine), ectophosphodiesterase activity (high concentration of 1, 3-dipropyl-8-p-sulfophenylxanthine), or ecto-5'-nucleotidase (alpha, beta-methylene-adenosine-5'-diphosphate). Treatment with exogenous cAMP inhibited cell growth as assessed by DNA synthesis ((3)H-thymidine incorporation), cell proliferation (cell counts), and protein synthesis ((3)H-leucine incorporation). Antagonism of A(2) (KF17837) or A(1)/A(2) (low concentration of 1, 3-dipropyl-8-p-sulfophenylxanthine), but not A(1) (8-cyclopentyl-1, 3-dipropylxanthine), adenosine receptors blocked the growth-inhibitory effects of exogenous cAMP, but not the growth inhibitory effects of 8-bromo-cAMP (stable cAMP analogue). The growth-inhibitory effects of exogenous cAMP were enhanced by the combined inhibition of adenosine deaminase [erythro-9-(2-hydroxy-3-nonyl) adenine] and adenosine kinase (iodotubercidin). In conclusion, the extracellular cAMP-adenosine pathway exists in cardiac fibroblasts and attenuates cell growth. Pharmacological augmentation of this pathway could abate pathological cardiac remodeling in heart disease.

Clinically used estrogens differentially inhibit human aortic smooth muscle cell growth and mitogen-activated protein kinase activity

Some estrogenic compounds modify vascular smooth muscle cell (SMC) biology; however, whether such effects are mediated in part by estrogen receptors is unknown. The purpose of this study was to evaluate whether the actions of clinically used estrogens on human aortic SMC biology are mediated by estrogen receptors. We examined the effects of various clinically used estrogens in the presence and absence of ICI 182,780, an estrogen receptor antagonist, on cultured human aortic SMC DNA synthesis ([(3)H]thymidine incorporation), cellular proliferation (cell counting), cell migration (modified Boyden chamber), collagen synthesis ([(3)H]proline incorporation), and mitogen-activated protein kinase activity. FCS-induced DNA synthesis, cell proliferation, collagen synthesis, platelet-derived growth factor-induced SMC migration, and mitogen-activated protein kinase activity were significantly inhibited by physiological (10(-9) mol/L) concentrations of 17beta-estradiol and low concentrations (10(-8) to 10(-7) mol/L) of 17beta-estradiol, estradiol valerate, estradiol cypionate, and estradiol benzoate but not by estrone, estriol, 17alpha-estradiol, or estrone sulfate. The inhibitory effects of 17beta-estradiol and other inhibitory estrogens were completely reversed by 100 micromol/L ICI 182,780, and the rank-order potency of various estrogens to inhibit SMC biology matched their rank-order affinity for estrogen receptors. The inhibitory effects of estrogens on SMC biology are in part receptor-mediated. Because the cardioprotective effects of hormone replacement therapy are most likely mediated by modification of SMC biology, whether hormone replacement therapy protects a given postmenopausal woman against cardiovascular disease will depend partially on the affinity of the estrogen for estrogen receptors in vascular SMCs.

Estradiol inhibits smooth muscle cell growth in part by activating the cAMP-adenosine pathway

Estradiol inhibits smooth muscle cell growth; however, the mechanisms involved remain unclear. Because estradiol stimulates cAMP synthesis and adenosine inhibits cell growth, we hypothesized that the conversion of cAMP to adenosine (ie, the cAMP-adenosine pathway) mediates in part the inhibitory effects of estradiol on vascular smooth muscle cell growth. To test this hypothesis, we examined the effects of estradiol (0.001 to 1 micromol/L) on serum-induced DNA, collagen, and total protein synthesis and cell number in the absence and presence of 1, 3-dipropyl-8-p-sulfophenylxanthine (10 nmol/L; A(1)/A(2) adenosine receptor antagonist), KF17837 (10 nmol/L; selective A(2) adenosine receptor antagonist), 8-cyclopentyl-1,3-dipropylxanthine (10 nmol/L; selective A(1) adenosine receptor antagonist), and 2', 5'-dideoxyadenosine (10 micromol/L; adenylyl cyclase inhibitor). Estradiol inhibited all measures of cell growth, and the concentration-dependent inhibitory curves for estradiol were shifted to the right (P<0.05) by 1,3-dipropyl-8-p-sulfophenylxanthine, KF17837, and 2',5'-dideoxyadenosine but not by 8-cyclopentyl-1, 3-dipropylxanthine. Moreover, the inhibitory effects of estradiol were enhanced by stimulation of adenylyl cyclase with forskolin and by inhibition of adenosine metabolism with erythro-9-(2-hydroxy-3-nonyl)adenine plus iodotubericidin (adenosine deaminase and kinase inhibitors, respectively). Estradiol also increased levels of cAMP and adenosine, and these effects were blocked by 2',5'-dideoxyadenosine (P<0.05). Our results support the hypothesis that estradiol stimulates cAMP synthesis and cAMP-derived adenosine regulates smooth muscle cell growth via A(2) adenosine receptors. Thus, the cAMP-adenosine pathway may contribute importantly to the antivasooclusive effects of estradiol.

A(2B) receptors mediate antimitogenesis in vascular smooth muscle cells

Adenosine inhibits growth of vascular smooth muscle cells. The goals of this study were to determine which adenosine receptor subtype mediates the antimitogenic effects of adenosine and to investigate the signal transduction mechanisms involved. In rat aortic vascular smooth muscle cells, platelet-derived growth factor-BB (PDGF-BB) (25 ng/mL) stimulated DNA synthesis ([(3)H]thymidine incorporation), cellular proliferation (cell number), collagen synthesis ([(3)H]proline incorporation), total protein synthesis ([(3)H]leucine incorporation), and mitogen-activated protein (MAP) kinase activity. The adenosine receptor agonists 2-chloroadenosine and 5'-N-methylcarboxamidoadenosine, but not N(6)-cyclopentyladenosine or CGS21680, inhibited the growth effects of PDGF-BB, an agonist profile consistent with an A(2B) receptor-mediated effect. The adenosine receptor antagonists KF17837 and 1,3-dipropyl-8-p-sulfophenylxanthine, but not 8-cyclopentyl-1, 3-dipropylxanthine, blocked the growth-inhibitory effects of 2-chloroadenosine and 5'-N-methylcarboxamidoadenosine, an antagonist profile consistent with an A(2) receptor-mediated effect. Antisense, but not sense or scrambled, oligonucleotides to the A(2B) receptor stimulated basal and PDGF-induced DNA synthesis, cell proliferation, and MAP kinase activity. Moreover, the growth-inhibitory effects of 2-chloroadenosine, 5'-N-methylcarboxamidoadenosine, and erythro-9-(2-hydroxy-3-nonyl) adenine plus iodotubericidin (inhibitors of adenosine deaminase and adenosine kinase, respectively) were abolished by antisense, but not scrambled or sense, oligonucleotides to the A(2B) receptor. Our findings strongly support the hypothesis that adenosine causes inhibition of vascular smooth muscle cell growth by activating A(2B) receptors coupled to inhibition of MAP kinase activity. Pharmacological or molecular biological activation of A(2B) receptors may prevent vascular remodeling associated with hypertension, atherosclerosis, and restenosis following balloon angioplasty.

Role of adenosine A(1) receptors in modulating extracellular adenosine levels

The purpose of this investigation was to test the hypothesis that A(1) receptors modulate extracellular levels of adenosine in cardiovascular tissues. Rat cardiac fibroblasts and human aortic vascular smooth muscle cells were cultured to confluence and various pharmacological agents were applied to the cultures. The extracellular fluid was extracted and adenosine concentrations were measured by HPLC. Three selective A(1) receptor antagonists, namely 8-cyclopentyl-1,3-dipropylxanthine, xanthine amine congener, and N-0840, at a concentration of 10 nM significantly increased extracellular levels of adenosine in both rat cardiac fibroblasts and human aortic vascular smooth muscle cells. Further studies in rat cardiac fibroblasts revealed that the effects of A(1) receptor blockade on extracellular adenosine levels were concentration dependent and prevented by inhibition of G(i) proteins with pertussis toxin or blockade of ecto-5'-nucleotidase with alpha, beta-methyleneadenosine-5'-diphosphate. In cardiac fibroblasts in which the extracellular levels of endogenous adenosine were increased, the ability of A(1) receptor blockade to augment extracellular adenosine was attenuated. A time-course study revealed a time lag of several hours between blockade of A(1) receptors and increases in extracellular adenosine levels. These data suggest that A(1) receptors function to detect the long-term levels of extracellular adenosine, and appropriately adjust extracellular adenosine levels by a slow-onset mechanism involving G(i) proteins and ecto-5'nucleotidase.

Angiotensin receptor subtype 1 mediates angiotensin II enhancement of isoproterenol-induced cyclic AMP production in preglomerular microvascular smooth muscle cells

In a previous study, we found that angiotensin (Ang) II enhances beta-adrenoceptor-induced cAMP production in cultured preglomerular microvascular smooth muscle cells (PMVSMCs) obtained from spontaneously hypertensive rats. The purpose of the present investigation was to identify the Ang receptor subtypes that mediate this effect. In our first study, we compared the ability of Ang II, Ang III, Ang (3-8), and Ang (1-7) to increase cAMP production in isoproterenol (1 microM)-treated PMVSMCs. Each peptide was tested at 0.1, 1, 10, 100, and 1000 nM. Both Ang II and Ang III increased intracellular (EC50s, 1 and 11 nM, respectively) and extracellular (EC50s, 2 and 14 nM, respectively) cAMP levels in a concentration-dependent fashion. In contrast, Ang (3-8) and Ang (1-7) did not enhance either intracellular or extracellular cAMP levels at any concentration tested. In our second study, we examined the ability of L 158809 [a selective Ang receptor subtype 1 (AT1) receptor antagonist] to inhibit Ang II (100 nM) and Ang III (100 nM) enhancement of isoproterenol (1 microM)-induced cAMP production in PMVSMCs. L 158809 (10 nM) abolished or nearly abolished (p <.001) Ang II and Ang III enhancement of isoproterenol-induced intracellular and extracellular cAMP levels. In contrast, PD 123319 (300 nM; a selective AT2 receptor antagonist) did not significantly alter Ang II enhancement of isoproterenol-induced intracellular or extracellular cAMP levels. We conclude that AT1 receptors, but not AT2, Ang (3-8), nor Ang (1-7) receptors mediate Ang II and Ang III enhancement of beta-adrenoceptor-induced cAMP production in cultured PMVSMCs.

Estrogen and tamoxifen metabolites protect smooth muscle cell membrane phospholipids against peroxidation and inhibit cell growth

The goal of this study was to test the hypothesis that antioxidant estrogens, by a mechanism independent of the estrogen receptor, protect phospholipids residing in the plasma membrane of vascular smooth muscle cells from peroxidation and peroxidation-induced cell growth and migration. Peroxidation of membrane phospholipids was assessed by HPLC analysis of phospholipids extracted from rat aortic vascular smooth muscle cells prelabeled with cis-parinaric acid (a fatty acid that is susceptible to peroxidation, which quenches its fluorescent properties). Incubation of cells for 2 hours with the peroxyl radical donor 2,2'-azobis-2,4-dimethylvaleronitrile (AMVN) caused peroxidation of all measured membrane phospholipids. This effect was attenuated by pretreating cells for 15 minutes with 50 to 5000 ng/mL of 2-hydroxyestradiol (strong antioxidant but weak estrogen-receptor ligand) or 4-hydroxytamoxifen (strong antioxidant and potent estrogen-receptor ligand), but not by estrone or droloxifene (both weak antioxidants but potent estrogen-receptor ligands). Moreover, pretreatment of cells for 20 hours with physiological concentrations (0.3 ng/mL) of 2-hydroxyestradiol or pharmacologically relevant concentrations of 4-hydroxytamoxifen (40 ng/mL) also decreased AMVN-induced phospholipid peroxidation. Both 2-hydroxyestradiol and 4-hydroxytamoxifen were as effective as 2,2,5, 7,8-pentamethyl-6-hydrochromane (an antioxidant homolog of vitamin E) in attenuating AMVN-induced peroxidation of membrane phospholipids. Also, physiological concentrations of 2-hydroxyestradiol, but not estrone, and pharmacologically relevant concentrations of 4-hydroxytamoxifen attenuated AMVM-induced DNA synthesis, cell proliferation, and cell migration. These studies demonstrate in vascular smooth muscle cells that antioxidant estrogens via a non-estrogen receptor-dependent mechanism attenuate peroxidation of membrane phospholipids and peroxidation-induced cell growth and migration.

Phytoestrogens inhibit growth and MAP kinase activity in human aortic smooth muscle cells

-Estrogens are known to induce cardioprotective effects by inhibiting smooth muscle cell (SMC) growth and neointima formation. However, the use of estrogens as cardioprotective agents is limited by carcinogenic effects in women and feminizing effects in men. If noncarcinogenic and nonfeminizing estrogenlike compounds, such as natural phytoestrogens, afford cardioprotection, this would provide a safe method for prevention of cardiovascular disease in both men and women. Therefore, we evaluated and compared in human aortic SMCs the effects of phytoestrogens (formononetin, genistein, biochanin A, daidzein, and equol) on 2.5% fetal calf serum-induced proliferation (3H-thymidine incorporation and cell number), collagen synthesis (3H-proline incorporation), and total protein synthesis (3H-leucine incorporation) and on PDGF-BB (25 ng/mL)-induced migration (modified Boydens chambers). Moreover, the effects of phytoestrogens on PDGF-BB (25 ng/mL)-induced mitogen-activated protein kinase (MAP kinase) activity in SMCs was also studied. Phytoestrogens inhibited proliferation, collagen and total protein synthesis, migration, and MAP kinase activity in a concentration-dependent manner and in the following order of potency: biochanin A>genistein>equol>daidzein>formononetin. In conclusion, our studies provide the first evidence that in human aortic SMCs phytoestrogens inhibit mitogen-induced proliferation, migration and extracellular matrix synthesis and inhibit/downregulate MAP kinase activity. Thus, phytoestrogens may confer protective effects on the cardiovascular system by inhibiting vascular remodeling and neointima formation and may be clinically useful as a safer substitute for feminizing estrogens in preventing cardiovascular disease in both women and men.

Adenosine inhibits collagen and total protein synthesis in vascular smooth muscle cells

-The objective of this study was to characterize the effects of exogenous, drug-induced and cAMP-adenosine pathway-derived adenosine on collagen synthesis by and hypertrophy of vascular smooth muscle cells (SMCs). Confluent vascular SMCs were stimulated with 2.5% fetal calf serum in the presence and absence of adenosine receptor agonists [adenosine, 2-chloroadenosine, N6-cyclopentyladenosine, 5'-N-ethylcarboxamidoadenosine, 5'-N-methylcarboxamidoadenosine, and 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamino adenosine], drugs that increase levels of endogenous adenosine [erythro-9-(2-hydroxy-3-nonyl) adenine, dipyridamole, and iodotubericidin], and cAMP (increases adenosine by conversion to AMP and hence to adenosine via the cAMP-adenosine pathway). Adenosine receptor agonists inhibited fetal calf serum-induced collagen and total protein synthesis (as assessed by [3H]proline and [3H]leucine incorporation, respectively) with a relative potency profile consistent with the effects being mediated by adenosine A2B receptors. Erythro-9-(2-hydroxy-3-nonyl) adenine, dipyridamole, iodotubericidin, and cAMP also inhibited collagen and total protein synthesis. The effects of 2-chloroadenosine, erythro-9-(2-hydroxy-3-nonyl) adenine, iodotubericidin, and cAMP on collagen and total protein synthesis were attenuated by KF17837 and 1,3-dipropyl-8-p-sulfophenylxanthine (selective and nonselective A2 receptor antagonists, respectively) but not by 8-cyclopentyl-1, 3-dipropylxanthine (selective A1 receptor antagonist). These studies indicate that exogenous, drug-induced and cAMP-adenosine pathway-derived adenosine inhibit vascular SMC collagen synthesis and hypertrophy via A2B receptors. Thus, exogenous A2B receptor agonists and drugs that modulate endogenous adenosine levels may protect against vasoocclusive disorders by attenuating extracellular matrix synthesis by and cellular hypertrophy of vascular SMCs. Moreover, the cAMP-adenosine pathway may protect against vascular hypertrophy.

Cyclooxygenase inhibition reveals synergistic action of vasoconstrictors on mesangial cell growth

Since endogenous vasoconstrictors promote mesangial cell growth and increase the biosynthesis of antiproliferative prostaglandins, the effects of cyclooxygenase inhibition on mesangial cell proliferation should be strongly dependent on the prevailing levels of neuroendocrine vasoconstrictors. We compared the effects of indomethacin (10(-6) M), a cyclooxygenase inhibitor, on [3H]thymidine incorporation by cultured rat mesangial cells in the presence of various combinations of angiotensin II (10(-10) M), [Arg8]vasopressin (10(-11) M), (-)-norepinephrine (10(-8) M) and endothelin-1 (10(-11) M). Indomethacin did not enhance [3H]thymidine incorporation in cells treated with each individual vasoconstrictor, or in cells treated with two-way combinations with the exception of modestly increased [3H]thymidine incorporation in cells treated with angiotensin II + (-)-norepinephrine or [Arg8]vasopressin + (-)-norepinephrine. In contrast, in cells treated with any three-way or the four-way combination, indomethacin markedly increased [3H]thymidine incorporation. Importantly, a highly significant interaction (P<0.0001) was observed for thymidine incorporation between the number of vasoconstrictors present and indomethacin treatment, thus demonstrating that cyclooxygenase inhibition reveals a synergistic action of vasoconstrictors on the DNA synthesis in mesangial cells.

The cytochrome P450 suicide inhibitor, 1-aminobenzotriazole, sensitizes rats to zymosan-induced toxicity

Reduction in whole body cytochrome P450 (CYP 450) activity is evident in humans who develop trauma and sepsis-induced multiple organ failure (MOF). It is not known whether this has any deleterious or protective effect. Intraperitoneal injection of zymosan, the cell wall of Saccharomycoses A, induces dose-dependent inflammation with concomitant MOF in rats. High dose intraperitoneal zymosan (100 mg/100 g body weight) causes mortality and organomegaly in rats; low dose zymosan (20 mg/100 g body weight) does not. To study a role for CYP 450 in zymosan-induced toxicity, we examined the effect of the non-specific CYP 450 suicide inhibitor 1-aminobenzotriazole (1-ABT)(80 mg/kg/d), on rats treated with low dose zymosan. The 90% reduction in CYP 450 content achieved by this dose of 1-ABT was associated with 58% mortality in rats treated with low dose zymosan, in contrast to no mortality in rats treated with low dose zymosan alone (p < 0.01). In survivors, liver and lung organomegaly (p < 0.01), and polymorphonuclear leukocyte accumulation in the liver (p < 0.01) were increased after zymosan administration in rats treated with 1-ABT compared to those without 1-ABT. There was no effect of treatment with 1-ABT on the increased urinary excretion of nitric oxide byproducts observed after zymosan administration. These observations are consistent with the hypothesis that the CYP 450 enzyme system is an endogenous protectant in this experimental model of inflammation-induced MOF.

Modulation by angiotensin II of isoproterenol-induced cAMP production in preglomerular microvascular smooth muscle cells from normotensive and genetically hypertensive rats

The objectives of the present study were to determine whether angiotensin II (Ang II) modifies beta-adrenoceptor-induced cAMP production in preglomerular microvascular smooth muscle cells (PMVSMCs), to determine whether the Ang II/beta-adrenoceptor interaction on cAMP production differs in PMVSMCs from normotensive Wistar-Kyoto (WKY) rats vs. PMVSMCs from spontaneously hypertensive rats (SHR), and to elucidate the mechanism of Ang II/beta-adrenoceptor interactions on cAMP production in PMVSMCs. In cultured PMVSMCs, isoproterenol increased cAMP levels and this effect was markedly enhanced by Ang II. The Ang II enhancement of isoproterenol-induced cAMP was significantly greater in SHR PMVSMCs compared with WKY PMVSMCs. Neither inhibition of calcineurin with FK506, inhibition of calcium-calmodulin with W-7 and calmidazolium, nor inhibition of Gi proteins with pertussis toxin attenuated Ang II enhancement of isoproterenol-induced cAMP in PMVSMCs from either SHR or WKY rats. Moreover, the effect of Ang II on isoproterenol-induced cAMP was not mimicked by alpha-2 adrenoceptor stimulation. In contrast, chelation of intracellular calcium with BAPTA-AM attenuated, increasing intracellular calcium with A23187 augmented, and inhibition of protein kinase C with either calphostin C or chelerythrine chloride abolished Ang II enhancement of isoproterenol-induced cAMP. We conclude that in cultured PMVSMCs Ang II enhances the cAMP response to beta-adrenoceptor agonists via a mechanism that involves coincident activation of adenylyl cyclase by stimulatory G proteins and protein kinase C. Thus, protein kinase C-mediated activation of adenylyl cyclase may attenuate Ang II-induced vasoconstriction in the renal microcirculation by raising the intracellular levels of cAMP, and this mechanism may be augmented in genetic hypertension.

Adenosine inhibits collagen and protein synthesis in cardiac fibroblasts: role of A2B receptors

The objective of this study was to characterize the effects of exogenous and endogenous (cardiac fibroblast-derived) adenosine on [3H]proline and [3H]leucine incorporation, which are reliable markers of collagen and total protein synthesis, respectively, in rat left ventricular cardiac fibroblasts. Growth-arrested confluent cardiac fibroblast monolayers were stimulated with 2.5% fetal calf serum (FCS) in the presence and absence of adenosine, 2-chloroadenosine (stable adenosine analogue), or modulators of adenosine levels including (1) erythro-9-(2-hydroxy-3-nonyl) adenine (adenosine deaminase inhibitor), (2) dipyridamole (adenosine transport blocker), and (3) iodotubericidin (adenosine kinase inhibitor). All agents inhibited in a concentration-dependent fashion FCS-induced [3H]proline and [3H]leucine incorporation. These effects were blocked by KF17837 (selective A2 antagonist) and 1,3-dipropyl-8-(p-sulfophenyl)xanthine (A1/A2 receptor antagonist) but not by 8-cyclopentyl-1,3-dipropylxanthine (selective A1 antagonist), thus excluding the participation of A1 receptors. The lack of effect of CGS21680 (selective A2A agonist) excluded involvement of A2A receptors, thus suggesting a major role for A2B receptors. Comparisons of the inhibitory potencies of N6-cyclopentyladenosine (selective A1 agonist), 5'-N-ethylcarboxamidoadenosine (A1/A2 agonist), and 5'-N-methylcarboxamidoadenosine (A1/A2 agonist) were consistent with that of an A2B receptor subtype mediating the inhibitory effects. We conclude that adenosine inhibits FCS-induced collagen and total protein synthesis in cardiac fibroblasts via activation of A2B receptors. These studies suggest, but do not prove, that endogenous adenosine may protect against cardiac fibrosis.

Adenosine inhibits growth of human aortic smooth muscle cells via A2B receptors

Adenosine inhibits rat vascular smooth muscle cell (SMC) growth. However, the effects of adenosine on human vascular SMC proliferation and synthesis of extracellular matrix proteins, such as collagen, are unknown. The objective of this study was to characterize the effects of exogenous and endogenous (SMC-derived) adenosine on human aortic SMC proliferation and collagen synthesis. Growth-arrested SMCs were stimulated with 2.5% fetal calf serum (FCS) in the presence and absence of adenosine, 2-chloroadenosine (stable adenosine analogue), and with agents that increase endogenous adenosine levels, including erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), dipyridamole, and iodotubericidin. All of these agents inhibited in a concentration-dependent manner FCS-induced SMC proliferation as assessed by DNA synthesis (3H-thymidine incorporation) and cell counting, as well as collagen synthesis (3H-proline incorporation). EHNA, dipyridamole, and iodotubericidin increased extracellular levels of adenosine by 1.7-fold to 18-fold when added separately to SMCs, and EHNA+iodotubericidin and EHNA+iodotubericidin+dipyridamole increased extracellular adenosine levels by more than 392-fold. Both KF17837 (selective A2 antagonist) and DPSPX (A1/A2 antagonist), but not DPCPX (selective A1 antagonist), blocked the antimitogenic effects of 2-chloroadenosine, EHNA, and dipyridamole on DNA and collagen synthesis, suggesting the involvement of A2A and/or A2B, but excluding the participation of A1, receptors. The lack of effect of CGS21680 (selective A2A agonist), excluded involvement of A2A receptors and suggested a major role for A2B receptors. A comparison of the inhibitory potencies of 2-chloroadenosine, N6-cyclopentyladenosine (selective A1 agonist), NECA (A1/A2 agonist), and MECA (A1/A2 agonist) were consistent with an A2B receptor subtype mediating the inhibitory effects of adenosine on human aortic SMC proliferation. In conclusion, human aortic SMCs synthesize adenosine, and exogenous as well as endogenous (SMC-derived) adenosine inhibits SMC proliferation and collagen synthesis via activation of A2B receptors.

Cyclic AMP-adenosine pathway induces nitric oxide synthesis in aortic smooth muscle cells

The main purpose of this investigation was to evaluate whether the cyclic AMP-adenosine pathway, ie, the conversion of cAMP to AMP and, hence, to adenosine, is involved in the regulation of nitric oxide (NO) synthesis by vascular smooth muscle cells (SMCs). Treatment of confluent monolayers of SMCs with adenosine, 2-chloroadenosine (stable analog of adenosine), and agents that elevate endogenous (SMC-derived) adenosine (EHNA and iodotubericidin) increased nitrite/nitrate (stable metabolites of NO) levels in the medium and enhanced the conversion of 3H-L-arginine to 3H-L-citrulline by cytosolic extracts obtained from the pretreated SMCs. The stimulatory effects of adenosine were not mimicked by low (1 to 100 nmol/L) concentrations of CGS21680, an A2A receptor agonist, or CPA, a selective A1 receptor agonist. The stimulatory effects of 2-chloroadenosine and EHNA plus iodotubericidin were significantly inhibited by KF17837, a selective A2 receptor antagonist, and by DPSPX, an A1/A2 receptor antagonist, but not by DPCPX, a selective A1 receptor antagonist. DDA (adenylyl cyclase inhibitor) and Rp-cyclic AMP (protein kinase A inhibitor) did not block the effects of adenosine on NO synthesis. Incubation of SMCs with exogenous cyclic AMP, at concentrations previously shown to elevate levels ofadenosine in the medium, also increased nitrite/nitrate levels and 3H-L-citrulline formation, and the effects of cyclic AMP on NO synthesis were blocked by DPSPX and KF17837, but not by DPCPX. These findings provide evidence that exogenous and SMC-derived adenosine induce NO synthesis via A2B receptors linked to a pathway not involving adenylyl cyclase/protein kinase A. Moreover, extracellular cyclic AMP induces NO synthesis via conversion to adenosine and activation of A2B adenosine receptors. The cyclic AMP-adenosine pathway may be importantly involved in the vascular production of NO.

17Beta-estradiol, its metabolites, and progesterone inhibit cardiac fibroblast growth

Postmenopausal women (PMW) have increased incidence of cardiovascular disease, and estrogen substitution therapy has been shown to have cardioprotective effects. Since abnormal growth of cardiac fibroblasts (CFs) is associated with hypertension and myocardial infarction and estrogen inhibits vascular smooth muscle cell (SMC) growth, it is feasible that estrogen may attenuate cardiac remodeling by inhibiting CF growth, and this possibility was investigated by using cultured CFs. 17Beta-estradiol and progesterone, but not 17alpha-estradiol, estrone, or estriol, inhibited 2.5% FCS-induced proliferation (DNA synthesis and cell number) and collagen synthesis (3H-proline incorporation) in a concentration-dependent manner and to a similar extent in male and female CFs. Compared to 17beta-estradiol, its metabolites 2-hydroxyestradiol and 2-methoxyestradiol were more potent in inhibiting FCS-induced DNA synthesis, collagen synthesis, and cell proliferation. The inhibitory effects of 17beta-estradiol and its metabolites were enhanced in presence of progesterone and 4-hydroxytamoxifen (high-affinity estrogen receptor ligand). Moreover, like estrogens, the dietary phytoestrogens biochanin A and daidzein inhibited FCS-induced growth of CFs. In conclusion, 17beta-estradiol, its metabolites, and progesterone inhibit CF growth in a gender-independent fashion. Moreover, hormone replacement therapy using 17beta-estradiol and progesterone may protect PMW against cardiovascular disease by inhibiting CF growth and cardiac remodeling; whereas estrogens that do not inhibit CF growth may be less effective in protecting PMW against cardiovascular disease. Finally, our studies provide evidence that phytoestrogens inhibit CF growth and may be clinically useful as a substitute for feminizing estrogens in preventing cardiovascular disease in both women and men.

Phosphodiesterases in the rat renal vasculature

The objective this investigation was to determine the relative importance of type I, III, and IV phosphodiesterases in the regulation of cyclic adenosine monophosphate (cAMP) in the renal circulation. In the first experimental series, four groups of isolated rat kidneys perfused with Tyrode's solution were stimulated with isoproterenol (3 microM) and then treated with increasing concentrations (from the approximately IC50 to 30 times the approximately IC50 in threefold increments) of one of four phosphodiesterase inhibitors: group 1, 3-isobutyl-1-methylxanthine, a "broad-spectrum" phosphodiesterase inhibitor (10-300 microM); group 2, Ro 20-1724, a selective type IV phosphodiesterase inhibitor (3-100 microM); group 3, 8-methoxymethyl-3-isobutyl-1-methylxanthine, a selective type I phosphodiesterase inhibitor (3-100 microM); and group 4, milrinone, a selective type III phosphodiesterase inhibitor (0.3-10 microM). In the second experimental series, five groups of cultured preglomerular (interlobular and afferent arteriolar) vascular smooth-muscle cells were stimulated with isoproterenol (1 microM) and treated with vehicle or supramaximal concentrations (30 times IC50) of either 3-isobutyl-1-methylxanthine (300 microM), Ro 20-1724 (100 microM), 8-methoxymethyl-3-isobutyl-1-methylxanthine (100 microM), or milrinone (10 microM). In perfused kidneys and cultured pre-glomerular vascular smooth-muscle cells, 3-isobutyl-1-methylxanthine and Ro 20-1724 similarly increased renal cAMP release and total cellular (extracellular + intracellular) cAMP levels, respectively. In contrast, neither 8-methoxymethyl-3-isobutyl-1-methylxanthine nor milrinone affected renal cAMP release or total cellular cAMP levels. These data indicate that in the renal circulation, type IV phosphodiesterase is the predominant phosphodiesterase isozyme.

Exogenous and endogenous adenosine inhibits fetal calf serum-induced growth of rat cardiac fibroblasts: role of A2B receptors

BACKGROUND

Because proliferation of cardiac fibroblasts participates in cardiac hypertrophy/remodeling associated with hypertension and myocardial infarction, it is important to elucidate factors regulating cardiac fibroblast proliferation. Adenosine, a nucleoside abundantly produced by cardiac cells, is antimitogenic vis-à-vis vascular smooth muscle cells; however, the effect of adenosine on cardiac fibroblast proliferation is unknown. The objective of this study was to characterize the effects of exogenous and endogenous (cardiac fibroblast-derived) adenosine on cardiac fibroblast proliferation.

METHODS AND RESULTS

Growth-arrested cardiac fibroblasts were stimulated with 2.5% FCS in the presence and absence of adenosine, 2-chloroadenosine (stable adenosine analogue), or modulators of adenosine levels, including (1) erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; adenosine deaminase inhibitor); (2) dipyridamole (adenosine transport blocker); and (3) iodotubericidin (adenosine kinase inhibitor). All of these agents inhibited, in a concentration-dependent manner, FCS-induced cardiac fibroblast proliferation as assessed by DNA synthesis ([3H]thymidine incorporation) and cell counting. EHNA, dipyridamole, and iodotubericidin increased extracellular levels of adenosine by 2.3- to 5.6-fold when added separately to cardiac fibroblasts, and EHNA+iodotubericidin or EHNA+iodotubericidin+dipyridamole increased extracellular adenosine levels by >690-fold. Both KF17837 (selective A2 antagonist) and DPSPX (nonselective A2 antagonist) but not DPCPX (selective A1 antagonist) blocked the antimitogenic effects of 2-chloroadenosine, EHNA, and dipyridamole on DNA synthesis, suggesting the involvement of A2A and/or A2B but excluding the participation of A1 receptors. The lack of effect of CGS21680 (selective A2A agonist) excluded involvement of A2A receptors and suggested a major role for A2B receptors. This conclusion was confirmed by the rank order potencies of four adenosine analogues.

CONCLUSIONS

Cardiac fibroblasts synthesize adenosine, and exogenous and cardiac fibroblast-derived adenosine inhibits cardiac fibroblast proliferation via activation of A2B receptors. Cardiac fibroblast-derived adenosine may regulate cardiac hypertrophy and/or remodeling by modulating cardiac fibroblast proliferation.

Metabolism of cAMP to adenosine in the renal vasculature

We recently demonstrated that cAMP added to the perfusate increased the renal venous recovery of adenosine in the isolated rat kidney, an effect blocked by inhibition of ecto-phosphodiesterase and ecto-5'-nucleotidase. Although our previous study established the cAMP-adenosine pathway, i.e., the conversion of cAMP to adenosine, as a viable metabolic pathway within the kidney, that study did not determine whether conversion of arterial cAMP to adenosine recoverable in the venous effluent occurred in the tubules versus nontubular sites. In the current study, we addressed this issue by determining the effects of blocking cAMP transport into the renal tubules with probenecid (0.1, 0.3 and 1 mM) on the increase in renal venous output of adenosine induced by adding cAMP (30 microM) to the perfusate of isolated rat kidneys. Addition of cAMP to the perfusate caused a marked increase in renal venous secretion of adenosine, an effect that was augmented, rather than inhibited, by probenecid. To test the hypothesis that the renal vasculature supports a cAMP-adenosine pathway, cultured rat preglomerular vascular smooth muscle cells were incubated with cAMP (30 microM) for 1 hr in the presence and absence of 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor). Incubation with cAMP increased extracellular adenosine levels 41-fold, and this effect was abolished by 3-isobutyl-1-methylxanthine. In a third experimental series, addition of cAMP (0.3, 1, 3, 10 and 30 microM) to the perfusate of isolated rat kidneys and mesenteric vascular beds increased the renal venous, but not mesenteric venous, output of AMP, adenosine and inosine. We conclude that the renal vasculature supports a cAMP-adenosine pathway, that administering cAMP into the renal artery and measuring adenosine in the venous effluent of the perfused rat kidney most likely monitors primarily the renal vascular cAMP-adenosine pathway and that the quantitative importance of the cAMP-adenosine pathway is not equivalent in all vascular compartments.

Cyclic AMP-adenosine pathway inhibits vascular smooth muscle cell growth

In this study we determined whether cAMP is metabolized to adenosine in vascular smooth muscle cells and whether cAMP-derived adenosine modulates vascular smooth muscle cell growth. Confluent smooth muscle cells were exposed to cAMP (0.01 to 30 mumol/L) in the presence and absence of 3-isobutyl-1-methylxanthine (IBMX, 1 mmol/L; an inhibitor of both extracellular and intracellular phosphodiesterase), alpha, beta-methyleneadenosine 5'-diphosphate (AMP-CP, 100 mumol/L; an ecto-5'-nucleotidase inhibitor), and 1,3-dipropyl-8-p-sulfophenyl-xanthine (DPSPX, 100 mumol/L; a xanthine that can inhibit extracellular phosphodiesterase) for 0 to 60 minutes. Medium was then sampled and assayed for AMP, adenosine, and inosine. cAMP increased the amount of AMP, adenosine, and inosine in the medium in a time- and concentration-dependent manner. The conversion of cAMP to adenosine and inosine was inhibited by blockade of phosphodiesterase with IBMX, of ecto-phosphodiesterase with DPSPX, and of ecto-5'-nucleotidase with AMP-CP. To evaluate the physiological relevance of cAMP-derived adenosine in vascular smooth muscle cell proliferation, we studied the inhibitory effects of cAMP (10(-4) mol/L) and 8-bromo-cAMP (10(-4) mol/L) on fetal calf serum-induced DNA synthesis ([3H]thymidine incorporation) in the presence and absence of erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, an inhibitor of adenosine deaminase), dipyridamole (a blocker of adenosine transport), KF17837 (a selective A2 adenosine receptor antagonist), and DPSPX (a nonselective adenosine receptor antagonist). cAMP inhibited DNA synthesis, and both EHNA and dipyridamole enhanced this effect. Both KF17837 and DPSPX significantly reduced the inhibitory effects of cAMP on DNA synthesis; however, they did not reduce the inhibitory effects of 8-bromo-cAMP on DNA synthesis. These results indicate that vascular smooth muscle cells metabolize cAMP to adenosine via the sequential action of ecto-phosphodiesterase and ecto-5'-nucleotidase and provide the first evidence that cAMP-derived adenosine can inhibit vascular smooth muscle cell growth. Hence, this cAMP-adenosine pathway may importantly contribute to the regulation of vascular biology.

Adenosine inhibits growth of rat aortic smooth muscle cells. Possible role of A2b receptor

Abnormal growth of vascular smooth muscle cells (SMC) is frequently associated with hypertension and atherosclerosis, and homeostasis within a normal vessel is maintained by the balanced generation of both vasoconstrictors and vasodilators. Moreover, several endogenous vasoconstricting factors induce SMC growth, whereas several vasodilators inhibit SMC growth. Inasmuch as adenosine is a potent vasodilator, it is possible that it too could inhibit SMC growth. Hence, the effects of adenosine (10(-8) to 10(-3) mol/L), 2-chloroadenosine (a stable analogue of adenosine; 10(-8) to 10(-3) mol/L), and 8-bromo-cAMP (10(-8) to 10(-3) mol/L) on fetal calf serum (FCS; 2.5%)-induced growth of rat aortic SMC were evaluated. Growth was analyzed by assaying DNA synthesis (thymidine incorporation in SMC pulsed for 4 hours with 1 microCi/mL [3H]thymidine) and cell proliferation (change in cell number). Growth-arrested SMC were treated with 2.5% FCS in the presence and absence of adenosine, 2-chloroadenosine, or 8-bromo-cAMP for 24 hours for DNA synthesis or 4 days for cell proliferation. All three substances inhibited DNA synthesis and cell proliferation in a concentration-dependent manner. Compared with adenosine, 2-chloroadenosine was more potent in inhibiting growth. The inhibitory effects of 2-chloroadenosine were reversed by KF17837 (a specific A2 receptor antagonist) but not by DPCPX (a specific A1 receptor antagonist). Furthermore, the inhibitory effects of 2-chloroadenosine were not mimicked by CGS21680 (an A2a receptor agonist), and the effects of N6-cyclopentyladenosine (CPA; an A1 receptor agonist) were not markedly more potent than those of 2-chloroadenosine, suggesting that the inhibitory effects of adenosine are possibly mediated via A2b receptors. These studies provide evidence that adenosine inhibits SMC growth and suggest that a decrease in local levels of adenosine may initiate SMC growth and contribute to the vascular remodeling process observed in hypertension and atherosclerosis.

Smooth muscle cell-derived adenosine inhibits cell growth

Several endogenous factors generated within the vessel wall have been implicated in contributing to the vascular remodeling process associated with hypertension and atherosclerosis. Furthermore, substances generated by smooth muscle cells (SMCs) are known to regulate SMC proliferation in an autocrine fashion. Adenosine is a vasodilator synthesized by SMCs, and exogenous adenosine inhibits SMC proliferation. However, whether adenosine produced endogenously has antimitogenic effects is not known. Hence, we evaluated the effects of SMC-derived adenosine on 2.5% fetal calf serum-induced proliferation of rat aortic SMCs. SMC proliferation was assayed by measurement of DNA synthesis ([3H]thymidine incorporation) and cell counting. To determine the effects of endogenous adenosine on SMC proliferation, we stimulated growth-arrested SMCs with 2.5% fetal calf serum in the presence and absence of modulators of adenosine levels, including (1) erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA; inhibits adenosine deaminase), (2) dipyridamole (blocks adenosine transport and inhibits phosphodiesterase), (3) dipyridamole plus EHNA, and (4) adenosine with or without EHNA. [3H]Thymidine incorporation and cell number were measured after 24 and 96 hours, respectively. EHNA and dipyridamole inhibited both FCS-induced DNA synthesis and cell proliferation in a concentration-dependent manner. Furthermore, extracellular (in medium) adenosine levels were significantly increased when cultured cells were treated with EHNA, and the inhibitory effects of dipyridamole as well as exogenous adenosine were enhanced in the presence of EHNA. Additionally, the inhibitory effects of dipyridamole and EHNA on DNA synthesis were significantly reduced in the presence of KF17837, an A2 adenosine receptor antagonist. These results indicate that SMC-derived adenosine can inhibit SMC proliferation. Hence, it is possible that a defect in localized adenosine synthesis within the vessel wall could contribute to vascular thickening and neointima formation.