Endothelin 1 transcription is controlled by nuclear factor-kappaB in AGE-stimulated cultured endothelial cells

The challenge of type 1 diabetes mellitus

Diabetes mellitus is a heterogeneous group of diseases characterized by high blood glucose levels due to defects in insulin secretion, insulin action, or both. With the number of cases expected to increase rapidly in the years to come, diabetes is a growing health challenge worldwide. Of the approximately 16 million diabetics in the United States, about 1.5 million suffer from type 1 diabetes. In this catabolic disorder afflicting predominantly young individuals, blood insulin is almost completely absent, leading to hyperglycemia and alterations in lipid metabolism. Type 1 diabetes is thought to be induced by a toxic or infectious insult that occurs in genetically predisposed individuals. With recent advances in the understanding of the involved immunology and cellular and molecular mechanisms, researchers strive to battle the disease with new preventive and corrective strategies.

In response to protein load podocytes reorganize cytoskeleton and modulate endothelin-1 gene: implication for permselective dysfunction of chronic nephropathies

Effacement of podocyte foot processes occurs in many proteinuric nephropathies and is accompanied by rearrangement of the actin cytoskeleton. Here, we studied whether protein overload affects intracellular pathways, leading to cytoskeletal architecture changes and ultimately to podocyte dysfunction. Mouse podocytes bound and endocytosed both albumin and IgG via receptor-specific mechanisms. Protein overload caused redistribution of F-actin fibers instrumental to up-regulation of the prepro-endothelin (ET)-1 gene and production of the corresponding peptide. Increased DNA-binding activity for nuclear factor (NF)-kappaB and Ap-1 nuclear proteins was measured in nuclear extracts of podocytes exposed to excess proteins. Both Y27632, which inhibits Rho kinase-dependent stress fiber formation, and jasplakinolide, an F-actin stabilizer, decreased NF-kappaB and Ap-1 activity and reduced ET-1 expression. This suggested a role for the cytoskeleton, through activated Rho, in the regulation of the ET-1 peptide. Focal adhesion kinase (FAK), an integrin-associated nonreceptor tyrosine kinase, was phosphorylated by albumin treatment via Rho kinase-triggered actin reorganization. FAK activation led to NF-kappaB- and Ap-1-dependent ET-1 expression. These data suggest that reorganization of the actin cytoskeletal network in response to protein load is implicated in modulation of the ET-1 gene via Rho kinase-dependent FAK activation of NF-kappaB and Ap-1 in differentiated podocytes. Increased ET-1 generation might alter glomerular permselectivity and amplify the noxious effect of protein overload on dysfunctional podocytes.

Calpain inhibition decreases endothelin-1 levels and pulmonary hypertension after cardiopulmonary bypass with deep hypothermic circulatory arrest*

OBJECTIVE

Cardiopulmonary bypass in infants and children can result in cardiopulmonary dysfunction through ischemia and reperfusion injury. Pulmonary hypertension and injury are particularly common and morbid complications of neonatal cardiac surgery. Inhibition of calpain, a cysteine protease, has been shown to inhibit reperfusion injury in adult organ systems. The hypothesis is that calpain inhibition can alleviate the cardiopulmonary dysfunction seen in immature animals following ischemia and reperfusion with cardiopulmonary bypass.

DESIGN

Animal case study.

SETTING

Medical laboratory.

SUBJECTS

Crossbred piglets (5-7 kg).

INTERVENTIONS

Piglets were cooled with cardiopulmonary bypass to 18 degrees C followed by deep hypothermic circulatory arrest for 120 mins. Animals were rewarmed to 38 degrees C on cardiopulmonary bypass and maintained for 120 mins. Six animals were administered calpain inhibitor (Z-Leu-Leu-Tyr-fluoromethyl ketone; 1 mg/kg, intravenously) 60 mins before cardiopulmonary bypass. Nine animals were administered saline as a control. Plasma endothelin-1, pulmonary and hemodynamic function, and markers of leukocyte activity and injury were measured.

MEASUREMENTS AND MAIN RESULTS

Calpain inhibition prevented the increased pulmonary vascular resistance seen in control animals (95.7 +/- 39.4 vs. 325.3 +/- 83.6 dyne.sec/cm, respectively, 120 mins after cardiopulmonary bypass and deep hypothermic circulatory arrest, p = .05). The attenuation in pulmonary vascular resistance was associated with a blunted plasma endothelin-1 response (4.91 +/- 1.72 pg/mL with calpain inhibition vs. 10.66 +/- 6.21 pg/mL in controls, p < .05). Pulmonary function after cardiopulmonary bypass was better maintained after calpain inhibition compared with controls: Po2/Fio2 ratio (507.2 +/- 46.5 vs. 344.7 +/- 140.5, respectively, p < .05) and alveolar-arterial gradient (40.0 +/- 17.2 vs. 128.1 +/- 85.2 mm Hg, respectively, p < .05). Systemic oxygen delivery was higher after calpain inhibition compared with controls (759 +/- 171 vs. 277 +/- 46 mL/min, respectively, p < .001). In addition, endothelial nitric oxide synthase activity in lung tissue was maintained with calpain inhibition.

CONCLUSIONS

The reduction in plasma endothelin-1 and maintenance of lung endothelial nitric oxide levels after cardiopulmonary bypass and deep hypothermic circulatory arrest with calpain inhibition were associated with reduced pulmonary vascular resistance. Improved gas exchange and higher systemic oxygen delivery suggest that calpain inhibition may be advantageous for reducing postoperative cardiopulmonary dysfunction commonly associated with pediatric heart surgery and cardiopulmonary bypass.

Circulating cytokines and chemokines in acute symptomatic parvovirus B19 infection: negative association between levels of pro-inflammatory cytokines and development of B19-associated arthritis

The aim of the study was to characterise the profile and clinical correlates (arthritis, rash, and fatigue) of cytokines, chemokines, and other mediators in symptomatic acute parvovirus B19 infection. Serum was examined from cases of acute B19 infection (as defined by serum anti-B19 IgM positivity) (n = 84), and in normal persons (n = 43) for B19 markers (serum B19 antibodies and DNA), rheumatoid factor (RF), and antinuclear antibody (ANA). A panel of cytokines/chemokines was measured in duplicate using the Bioplex Protein Array system (BioRad Hemel Hempstead, UK). These included interleukin-1 beta (IL-1 beta), IL-4, IL-5, IL-6, IL-8, IL-13, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), macrophage chemoattractant protein-1 (MCP-1), granulocyte-monocyte colony stimulating factor (GM-CSF), transforming growth factor-beta1 (TGF-beta 1), endothelin-1 (ET-1), and neopterin. Acute symptomatic infection was characterised by specific IgG positivity (83%), serum B19 DNA positivity (96%), and raised levels of IL-4, IL-6, IL-8, TNF-alpha, IFN-gamma, MCP-1, GM-CSF, TGF-beta 1, and ET-1. Patients with acute B19-associated arthritis were found to have lower levels of IL-6, TNF-alpha, and GM-CSF than patients without arthritis, while those with rash had lower levels of TGF-beta 1. It is concluded that cytokine levels following acute symptomatic infection with parvovirus B19 indicate a state of immune activation. The profile of circulating mediators may provide insights into the possible pathogenesis of particular clinical manifestations of this infection.

Xanthoangelol D Isolated from the Roots of Angelica keiskei Inhibits Endothelin-1 Production through the Suppression of Nuclear Factor-.KAPPA.B

Transcription factor nuclear factor-kappa B (NF-kappaB) has been demonstrated to be important in regulating various gene expressions such as cytokines, adhesion molecules, and endothelin-1 (ET-1) in vascular endothelial cells. In the present study, we show the effects of xanthoangelol, xanthoangelol D, E, and F, which isolated from the root of Angelica keiskei KOIDZUMI (Umbelliferae), on NF-kappaB activation and ET-1 gene expression in cultured porcine aortic endothelial cells (PAECs). Treatments of xanthoangelol D but not xanthoangelol, xanthoangelol E and F markedly suppressed both of basal and tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation in PAECs. To clarify the mechanism of xanthoangelol D-induced suppression on NF-kappaB activation, we evaluated the effects of xanthoangelol D on phosphorylation and degradation of IkappaBalpha, an inhibitory protein bound to NF-kappaB, and obtained evidence that xanthoangelol D selectively suppresses the phosphorylation of IkappaBalpha rather than the degradation of phosphorylated IkappaBalpha. In addition, xanthoangelol D significantly attenuated basal and TNF-alpha-induced prepro ET-1 mRNA expression in PAECs. These results suggest that xanthoangelol D may be useful for the treatment of various vascular diseases involved NF-kappaB activation.

Effects of ETAReceptor Antagonism on Proinflammatory Gene Expression and Microcirculation Following Hepatic Ischemia/Reperfusion

BACKGROUND

The objective of this study was to investigate the effect of a specific endothelin(A) receptor antagonist (ET(A)-RA) on mRNA expression of genes encoding vasoactive mediators and proinflammatory cytokines and on the microhemodynamics (assessed by measurement of laser Doppler flow and tissue blood gases) following complete vascular exclusion of the porcine liver.

STUDY DESIGN

Sixteen adult German landrace pigs were subjected to 120 min of warm hepatic ischemia by total vascular exclusion. To avoid portal congestion, a passive porto-femoro/jugular bypass was implanted. The animals were divided into 2 groups: the control group received saline solution and the therapy group was given the selective ET(A)-RA BSF 208075. Hepatic microcirculation was evaluated by p(O(2)) and p(CO(2)) measurement with the Paratrend sensor and by laser Doppler flow measurement. Liver tissue samples were collected 1 h after reperfusion and quantitative mRNA expression for prepro-ET-1, pro-IL-1beta, pro-IL-6, pro-TNF-alpha, eNOS was analyzed using the TaqMan system. Additionally, immunohistochemical analysis using a semiquantitative score for ET-1 was performed. Postischemic liver damage was monitored by measurement of liver enzymes and assessed by histological analysis using a semiquantitative scoring classification.

RESULTS

Partial oxygen pressure in the hepatic tissue and laser Doppler flow were significantly improved in the therapy group. One hour after reperfusion, quantitative RT-PCR revealed significantly lower expression of prepro-ET-1, eNOS, pro-TNF-alpha, and pro-IL-6 in the therapy group compared to controls. Immunohistochemical analysis demonstrated significantly reduced ET-1 immunostaining after therapy. Furthermore, blockade of ET(A) receptors prevents tissue damage.

CONCLUSIONS

Treatment with the selective ET(A)-RA BSF 208075 has protective effects on microcirculation after 120 min liver ischemia and reperfusion. The authors were able to show that ET(A)-RA not only affects the expression of vasoactive genes, but also decreases gene expression of proinflammatory cytokines such as TNF-alpha and IL-6.

Advanced glycation and endothelial functions: a link towards vascular complications in diabetes

The formation of advanced glycation end-products (AGEs), also called the Maillard reaction, occurs ubiquitously and irreversibly in patients with diabetes mellitus, and its consequences are especially relevant to vascular dysfunctions. The interaction of AGEs with their receptors (RAGE) has been implicated in the development of vascular complications. This interaction elicits remarkable vascular cell changes analogous to those observed in diabetes mellitus, including angiogenic and thrombogenic responses of endothelial cells, increased oxidative stress, and functional alterations in vascular tone control. This review focuses on AGEs formation, the interaction with their specific receptors and how the triggered intracellular events determine functional alterations of vascular endothelium. Finally, some potential pharmacological approaches undertaken to circumvent the deleterious effects of AGEs are also discussed.

Extracellular signal-regulated kinase (ERK) in glucose-induced and endothelin-mediated fibronectin synthesis

Increased extracellular matrix protein deposition and basement membrane thickening are important features of diabetic angiopathy. One key matrix protein that has been shown to be instrumental in basement membrane thickening is fibronectin (FN). We have previously demonstrated that glucose-induced increased expression of endothelin-1 (ET-1), may in part, be responsible for increased FN expression via nuclear factor-kappaB (NF-kappaB) and activating protein (AP-1) activation. The present study was aimed at elucidating the mechanism of ET-1 with respect to mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway activation and glucose-induced FN upregulation. Human endothelial cells were exposed to either low (5 mM) or high (25 mM) glucose levels. Cells in low glucose were also treated with ET-1 peptide (5 nM). In addition, we treated cells exposed to high glucose levels with specific MAPK/ERK inhibitor PD098059 (50 microM), dual ET-receptor antagonist, bosentan (10 microM), and PKC blocker, chelerythrine (1 microM). Following incubation period, RNA and total proteins were extracted for RT-PCR for FN and immunoblot analysis of MAPK/ERK activation. Confocal microscopy was performed for analysis of FN protein and nuclear localization of activated Elk. Electrophoretic mobility shift assay was carried out to detect NF-kappaB and AP-1 activation. Our data demonstrates that high glucose-induced upregulation of FN messenger RNA and protein levels occur via activation of MAPK/ERK pathway, which was prevented by treatment of cells with bosentan, PD098059 and PKC blocker chelerythrine. Confocal microscopy demonstrated nuclear localization of phospho-Elk protein. Glucose-induced FN expression was also associated with protein kinase C, NF-kappaB, and AP-1 activation. These results suggested that glucose-induced, ET- and PKC-dependent, upregulation of FN is, in part, mediated via MAPK/ERK activation.

Air pollutants increase gene expression of the vasoconstrictor endothelin-1 in the lungs

Inhalation of urban pollutants elevates the circulating levels of the vasoactive peptides endothelin (ET)-1 and ET-3 in rats. This effect could explain the association between episodic variations of urban pollutants and acute cardiopulmonary morbidity and mortality documented in epidemiological studies. Because the lungs are the primary source of circulating ET-1 and the main site of clearance from circulation, we investigated the response of endothelin system genes in the lungs of Fischer-344 rats after 4-h nose-only inhalation of 0.8 ppm ozone plus 49 mg/m(3) EHC-93 (Ottawa particles). The mRNA levels for preproET-1, preproET-3, endothelin-converting enzyme (ECE)-1, and ET receptor subtypes A and B were determined at 2 h, and 1, 2, 3, 7, and 14 days after exposure. The pollutants induced preproET-1 and ECE-1 (P<0.05) after 2 h, consistent with the notion of increased synthesis and conversion of the peptide ET-1 in lung endothelial cells. PreproET-3 mRNA was down-regulated at 2 h post-exposure (P<0.05), and returned to control levels by 24 h, indicating that induction of ET-3 in the lungs is not responsible for the sustained elevation of ET-3 in plasma reported after inhalation of pollutants. Our results indicate that lung endothelin system genes respond rapidly and transiently to inhalation of urban pollutants, consistent with the dynamics of urban pollutant health effects in the human population.

Nuclear factor kappa B—molecular biomedicine: the next generation

Nuclear factor kappa B (NFkappaB) as a transcription factor plays an important integrating role in the intracellular regulation of immune response, inflammation and cell cycle regulation. Nouvelle insights into the structure and regulation of activation of NFkappaB have brought a detailed picture of the function of this transcription factor. In this review the findings of interactions of NFkappaB with its inhibitors, tumour necrosis factor alpha and glucocorticoids are presented. The results from the latest in vivo studies show the capability of specific NFkappaB inhibitors in the clinical use. This article summarizes the most important facts regarding NFkappaB participation in the pathogenesis of diseases and its potential as a target of pharmacological agents.

Receptor for advanced glycation endproduct (RAGE)-mediated nuclear factor-κB activation in vasculitic neuropathy

Binding of ligands to the receptor for advanced glycation endproducts (RAGE) results in activation of the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) and subsequent expression of NF-kappaB-regulated cytokines. In order to determine whether engagement of RAGE contributes to the pathogenesis of vasculitic neuropathy, we studied the presence of the RAGE ligand N(epsilon)-(carboxymethyl)lysine (CML), the receptor itself, NF-kappaB, and interleukin-6 (IL-6) in sural nerve biopsies of 12 patients with vasculitic neuropathies and 12 controls. In the patients, CML, RAGE, NF-kappaB, and IL-6 were localized in mononuclear cells, epineurial and endoneurial vessels and the perineurium. CML, RAGE, NF-kappaB, and IL-6 were expressed by CD4(+), CD8(+), and CD68(+) cells invading the nerves. Controls showed only weak staining. These data suggest that the RAGE pathway plays a critical proinflammatory role in vasculitic neuropathy.

Correlation between cardiovascular disease and diabetes mellitus: current concepts

Individuals exhibiting precursor symptoms of diabetes mellitus or reaching diagnostic thresholds for diabetes are at increased risk of death due to cardiovascular disease (CVD). Moreover, patients with diabetes alone, as well as those who have diabetes paired with established CVD, remain undertreated for cardiovascular risk factors. The clear correlation between these disease processes has led many to speculate that they share common pathogenetic processes. Recent research has made it increasingly evident that the core metabolic defects that mark diabetes, including impaired glucose tolerance, insulin resistance, and proinflammatory and prothrombotic states, lead to endothelial dysfunction and accelerate atherogenesis. Moreover, increases in sympathetic tone with diabetes are associated with changes in cardiac and vascular function that lead to hypertension, left ventricular dysfunction, and cardiac autonomic neuropathy; such changes set the stage for arrhythmia, silent infarction, and sudden death. Furthermore, diabetes-related changes in metabolic and autonomic functioning, as well as increases in inflammatory and thrombotic signaling, compromise the ability of myocardial and vascular tissue to remodel after injury and to recover and sustain functionality. Because potentiation of atherogenesis and cardiac dysfunction occurs in the presence of early diabetic symptoms as well as in the established disease, early implementation of strategies to reduce cardiovascular risk factors and to slow diabetes progression may help to improve long-term outcomes for at-risk individuals. Such interventions may include well-established treatments for hypertension and dyslipidemia, diet improvements, weight loss, and exercise as well as novel pharmacologic interventions aimed at newly identified therapeutic targets.

Ouabain stimulates endothelin release and expression in human endothelial cells without inhibiting the sodium pump

Ouabain, a sodium pump (Na+/ K+-ATPase) inhibitor, has been shown to act as a hormone and is possibly involved in the pathogenesis of hypertension. The mechanism by which ouabain may act was investigated using primary cultures of human umbilical artery endothelial cells (HUAECs), which are known to express and release the vasoconstrictive hormone endothelin (ET-1). Five minutes after application, low concentrations of ouabain induced Ca2+ oscillations and stimulated ET-1 release from endothelial cells into the medium. To investigate whether the observed effects were due to inhibition of the sodium pump, the effects of ouabain on the uptake of 86Rb+ by HUAECs were examined. Unexpectedly, ouabain concentrations below 10 nm stimulated 86Rb+ uptake by 15-20%, and in some experiments by 50%, results that are consistent with a stimulation of the pump. Within the concentration range 1-10 nm, ouabain induced a 2.5-fold stimulation (phosphorylation) of mitogen-activated protein kinase (MAP kinase). After incubation of HUAECs with ouabain for 12 h, the glycoside stimulated cell growth by 49 +/- 4%, as measured by cell number, with a maximum response at 5 nm. At similar concentrations, ouabain also increased ET-1 mRNA abundance by 19.5 +/- 3.1%. The results indicate that, by influencing ET-1 expression and release, ouabain may contribute to the regulation of vascular tone. The data also confirm that it is not a global inhibition of the sodium pump that is involved in the mechanism of action of this cardiac glycoside.

The receptor for advanced glycation end products (RAGE) is elevated in women with preeclampsia

A leading theory of the pathophysiology of preeclampsia is that oxidative stress induces vascular endothelial cell dysfunction. Advanced glycation end products (AGEs) form when aldose sugars react nonenzymatically with proteins under conditions of oxidative stress. AGEs are circulating molecules and can generate reactive oxygen species and vascular dysfunction (in diabetes and atherosclerosis) through an association with cell surface receptors (RAGE). RAGE is a multiligand receptor, expressed in vascular tissue, which is upregulated by its own ligands. Insulin resistance and obesity are risk factors for developing preeclampsia, as well as being conditions that would increase RAGE levels. Thus, we hypothesized that women with preeclampsia will have elevated levels of RAGE protein compared with normal pregnant women. Biopsies of nonlaboring myometrium as well as omentum were taken from normal pregnant and preeclamptic women. Nonpregnant samples were obtained at the time of hysterectomy. Tissue sections were immunostained with anti-RAGE as well as anti-alpha-actin and anti-von Willebrand factor (to identify blood vessels and intact endothelial cells). Staining intensity was qualitatively described as well as given an intensity score, with the identity of the section concealed. Nonpregnant myometrial and omental vessels showed very low to undetectable levels of RAGE staining. Pregnancy induced a significant increase in RAGE protein levels in both myometrium and omental vasculature. Blood vessels from women with preeclampsia consistently had intense staining for RAGE in both vessel beds. Thus, our data suggest that since RAGE activation can induce similar pathophysiologic changes to those observed in women with preeclampsia (including NFkappaB activation, increased TNFalpha and endothelin), elevated RAGE protein may be contributing to the vascular dysfunction in preeclampsia.

Role for nuclear factor-kappaB and signal transducer and activator of transcription 1/interferon regulatory factor-1 in cytokine-induced endothelin-1 release in human vascular smooth muscle cells

Endothelin-1 (ET-1) is a potent vasoconstrictor and growth-promoting mediator that is involved in the maintenance of vascular tone within the healthy circulation. However, a pathogenic role has been implicated by its overproduction in a number of cardiovascular diseases, which include pulmonary hypertension, congestive heart failure, atherosclerosis, and coronary vasospasm. ET-1 mRNA expression and peptide production in human vascular smooth muscle cells (HVSMCs) are markedly increased by exposure to tumor necrosis factor-alpha and interferon-gamma. The intracellular signaling mechanism involved in this pathway is not known. Because the transcription factors nuclear factor-kappaB (NF-kappaB), signal transducer and activator of transcription 1 (STAT1), and interferon regulatory factor-1 (IRF-1) often mediate the effects of cytokines in target cells the aim of this study was to determine whether the production of ET-1 after exposure of HVSMCs to cytokines depends upon synergism between NF-kappaB and STAT1/IRF-1. Immunoblotting showed that cytokine-stimulation of ET-1 release in VSMCs involves nuclear translocation of NF-kappaB and STAT1. Cytokines also induced an increase in IRF-1 protein expression. Antisense oligonucleotides to NF-kappaB, STAT1, and IRF-1 significantly inhibited cytokine induced ET-1 release. In conclusion, NF-kappaB, STAT1, and IRF-1 activation are involved in the stimulation by cytokines of ET-1 release from HVSMCs. However, nuclear run-on assays would provide definitive proof that ET-1 is regulated transcriptionally by cytokines. Because up-regulated production of ET-1 within VSMCs may underlie the causative role of ET-1 in a number of disease states, this finding indicates that NF-kappaB, STAT1, and IRF-1 within HVSMCs could be central to a number of vascular pathologies and that inhibition of this pathway could be of therapeutic benefit.

A role for increased mRNA stability in the induction of endothelin-1 synthesis by lipopolysaccharide

An association exists between infection and cardiovascular diseases, including atherosclerosis, stroke and myocardial infarction. This may involve endothelin-1 (ET-1) which has been implicated in these and other vascular pathologies. ET-1 synthesis is controlled primarily by the level of its mRNA and numerous stimuli, including infection, lead to elevated ET-1 levels. Here, we have investigated the regulation of ET-1 release and preproET-1 (ppET-1) mRNA in bovine aortic endothelial cells by lipopolysaccharide (LPS). ET-1 release from bovine aortic endothelial cells was stimulated by LPS and reporter gene assays implicated LPS-induced ppET-1 transcription. However, changes in transcription were modest compared to increases in ET-1 synthesis. Therefore, ppET-1 mRNA levels were measured by real-time reverse transcription-polymerase chain reaction. The effect of LPS on ppET-1 mRNA levels was more marked than on transcription (1.2-fold increase in transcription vs. 5.5-fold increase in ppET-1 mRNA). Analysis of ppET-1 mRNA stability by real-time reverse transcription-polymerase chain reaction showed that LPS increased its half-life by approximately 2-fold. Thus, upregulated ppET-1 mRNA and hence increased ET-1 synthesis may be due to both increased transcription and reduced mRNA degradation. These effects of LPS on mRNA stability may be a key mechanism in vascular pathologies through which many proteins are induced in response to infection.

Diabetes-induced overexpression of endothelin-1 and endothelin receptors in the rat renal cortex is mediated via poly(ADP-ribose) polymerase activation

We hypothesize that poly (ADP-ribosyl)ation, that is, poly (ADP-ribose) polymerase (PARP)-dependent transfer of ADP-ribose moieties from NAD to nuclear proteins, plays a role in diabetic nephropathy. We evaluated whether PARP activation is present and whether two unrelated PARP inhibitors, 3-aminobenzamide (ABA) and 1,5-isoquinolinediol (ISO), counteract overexpression of endothelin-1 (ET-1) and ET receptors in the renal cortex in short-term diabetes. The studies were performed in control rats and streptozotocin-diabetic rats treated with/without ABA or ISO (30 and 3 mg x kg(-1) x day(-1), intraperitoneally, for 2 weeks after 2 weeks of diabetes). Poly (ADP-ribose) immunoreactivity was increased in tubuli, but not glomeruli, of diabetic rats and this increase was corrected by ISO, whereas ABA had a weaker effect. ET-1 concentration (ELISA) was increased in diabetic rats, and this elevation was blunted by ISO. ET-1, ET(A), and ET(B) mRNA (ribonuclease protection assay), but not ET-3 mRNA (RT/PCR), abundance was increased in diabetic rats, and three variables were, at least, partially corrected by ISO. ABA produced a trend towards normalization of ET-1 concentration and ET-1, ET(A), and ET(B) mRNA abundance, but the differences with untreated diabetic group were not significant. Poly(ADP-ribosyl)ation is involved in diabetes-induced renal overexpression of ET-1 and ET receptors. PARP inhibitors could provide a novel therapeutic approach for diabetic complications including nephropathy, and other diseases that involve the endothelin system.

The role of nuclear factor-kappa B in the regulation of endothelin-1 production by nitric oxide

Nitric oxide (NO) has been reported to have an inhibitory effect on endothelin-1 production, but the detailed mechanisms are poorly understood. Our previous studies showed that a transcription factor nuclear factor-kappaB (NF-kappaB) plays an important role in endothelin-1 production. In the present study, we investigated the possible involvement of NF-kappaB in the inhibitory regulation of endothelin-1 production by NO. 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO), which is a well-known NO scavenger, remarkably increased both endothelin-1 production and NF-kappaB activation in cultured vascular endothelial cells. On the other hand, a spontaneous NO donor (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexanamide (FK409) significantly attenuated the basal and tumor necrosis factor-alpha-induced endothelin-1 production and NF-kappaB activation in endothelial cells. In addition, we found that FK409 suppressed NF-kappaB activation by the induction and stabilization of the inhibitory protein alpha, IkappaBalpha. Taken together, our results suggest that NO modulates the endothelial endothelin-1 production, possibly through the regulation of NF-kappaB activation.

RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain

Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.

Glimepiride reduces mononuclear activation of the redox-sensitive transcription factor nuclear factor-kappa B

AIMS

Glimepiride has the lowest ratio of insulin release to glucose decrease compared with other sulphonylureas. This prompted us to study in vitro and in vivo in a placebo-controlled study the effect of glimepiride on the redox-sensitive transcription factor nuclear factor-kappa B (NF-kappaB).

METHODS

Fifteen patients with type 2 diabetes on glibenclamide with a stable HbA1c over the last 6 months were included. After sampling for determination of baseline values, 10 patients were changed to an equivalent dose of glimepiride, while the placebo group was maintained at glibenclamide plus placebo. The glimepiride dose in these patients was adjusted so that no change in glucose control occurred, allowing for direct comparison. The others were kept on glibenclamide and received additional placebo. After 4 weeks of glimepiride or glibenclamide plus placebo, a second blood sample was taken. Mononuclear cells were isolated and assayed in a tissue-culture-independent electrophoretic mobility shift assay (EMSA)-based detection system for NF-kappaB binding activity, and by Western Blot for nuclear localization of NF-kappaB-p65, the cytoplasmic content of IkappaBalpha and the NF-kappaB-controlled haemoxygenase-1. Glimepiride dose-dependent inhibition of carboxymethyllysin (CML) albumin or tumour necrosis factor alpha (TNFalpha)- and H2O2-induced activation of NF-kappaB binding were determined, using isolated peripheral blood mononuclear cells from healthy volunteers, and transcriptional activity of bovine aortic endothelial cells either left untreated or induced with CML albumin incubated with or without glimepiride. Furthermore, in-vitro studies were implemented to demonstrate radical quenching properties of glimepiride in the cell-free 2,2'-azo-bis(2-aminopropane)-dihydrochloride system.

RESULTS

Baseline glucose and HbA1c remained stable in the patients switched from glibenclamide to a corresponding dose of glimepiride or kept on glibenclamide plus placebo. While in the group of patients only taking glibenclamide plus placebo the NF-kappaB binding activity did not change significantly (p = 0.58), the NF-kappaB binding activity in the group of patients taking glimepiride was reduced from 19.3 relative NF-kappaB-p65-equivalents to 15.5 relative NF-kappaB-p65-equivalents (p = 0.04). The nuclear translocation of NF-kappaB-p65 was reduced from 100% at baseline to 58% after 4 weeks (p = 0.04); the cytoplasmic localization of NF-kappaB-p65 increased from 100% to 129% (p = 0.03) and the cytoplasmic content of IkappaBalpha increased from 100% to 109% (p = 0.06). The redox-sensitive haemoxygenase-1 antigen was reduced from 100% to 82% (p = 0.04). To prove directly that glimepiride reduces NF-kappaB activation, we isolated peripheral blood mononuclear cells (PBMC) from healthy volunteers. In vitro, glimepiride reduced TNFalpha-(1 nmol/l) and CML albumin (800 nmol/l)-induced NF-kappaB activation dose dependently, being half maximal at 120 micromol/l. H2O2-mediated NF-kappaB activation was only partially reduced. In addition, glimepiride reduced NF-kappaB-dependent gene expression using a NF-kappaB-driven luciferase reporter system. Finally, a cell-free detection system showed that glimepiride has radical quenching properties.

CONCLUSION

Glimepiride can affect the activation of the redox-sensitive transcription factor NF-kappaB in vitro and in vivo.

Proteolysis, the ubiquitin-proteasome system, and renal diseases

Protein degradation is a critical process for the growth and function of cells. Proteolysis eliminates abnormal proteins, controls many cellular regulatory processes, and supplies amino acids for cellular remodeling. When substrates of proteolytic pathways are poorly recognized or there is mistiming of proteolysis, profound changes in cell function can occur. Based on these potential problems, it is not surprising that alterations in proteolytic enzymes/cofactors or in the structure of protein substrates that render them more or less susceptible to degradation are responsible for disorders associated with kidney cell malfunctions. Multiple pathways exist for protein degradation. The best-described proteolytic system is the ubiquitin-proteasome pathway, which requires ATP and degrades the bulk of cellular and some membrane proteins. This review will survey examples of renal abnormalities that are associated with defective protein degradation involving the ubiquitin-proteasome pathway. Loss of muscle mass associated with chronic renal failure, von Hippel-Lindau disease, Liddle syndrome, and ischemic acute renal failure will be discussed. These examples are indicative of the diverse roles of the ubiquitin-proteasome system in renal-associated pathological conditions.

Differential activation of NF-kappa B and AP-1 in increased fibronectin synthesis in target organs of diabetic complications

Increased extracellular matrix protein production leading to structural abnormalities is a characteristic feature of chronic diabetic complications. We previously showed that high glucose in endothelial cell culture leads to the upregulation of basement membrane protein fibronectin (FN) via an endothelin (ET)-dependent pathway involving activation of NF-kappaB and activating protein-1 (AP-1). To delineate the mechanisms of basement membrane thickening, we used an animal model of chronic diabetes and evaluated ET-dependent activation of NF-kappaB and AP-1 and subsequent upregulation of FN in three target organs of chronic diabetic complications. After 3 mo of diabetes, retina, renal cortex, and myocardium demonstrated increased FN mRNA and increased ET-1 mRNA expression. Increased FN expression was shown to be dependent on ET receptor-mediated signaling, as the increase was prevented by the dual ET receptor antagonist bosentan. NF-kappaB activation was most pronounced in the retina, followed by kidney and heart. AP-1 activation was also most pronounced in the retina but was similar in both kidney and heart. Bosentan treatment prevented NF-kappaB activation in the retina and heart and AP-1 activation in the retina and kidney. These data indicate that, although ETs are important in increased FN production due to diabetes, the mechanisms with respect to transcription factor activation may vary depending on the microenvironment of the organ.

Endothelins in chronic diabetic complications

Endothelins are widely distributed in the body and perform several vascular and nonvascular functions. Experimental data indicate abnormalities of the endothelin system in several organs affected in chronic diabetic complications. In support of this notion, it has been shown that endothelin-receptor antagonists prevent structural and functional abnormalities in target organs of diabetic complications in animal models. Alterations of plasma endothelin levels have also been demonstrated in human diabetes. This review discusses the role of endothelins in the pathogenesis of chronic diabetic complications. The current experimental evidence suggests that endothelin-receptor antagonism may potentially be an adjuvant therapeutic tool in the treatment of chronic diabetic complications.

Oleic acid induces endothelin-1 expression through activation of protein kinase C and NF-kappa B

This study investigated the effect of oleic acid on the expression levels of endothelin-1 (ET-1) and on the signaling pathways mediating it in human aortic endothelial cells (HAECs). ET-1 mRNA expression was significantly increased by oleic acid in a dose- and time-dependent manner. Elevation of ET-1 expression in response to oleic acid was inhibited by the protein kinase C (PKC) inhibitor, GF109203X, or the NF-kappa B inhibitor, pyrrolidine dithiocarbamate. In addition, both PKC and NF-kappa B activities were significantly increased by oleic acid. Immunoblot analysis revealed that conventional PKCs (PKC-alpha and -beta II isoforms) were significantly increased in the membranous fractions of HAECs treated with oleic acid. PKC inhibitor completely abolished oleic acid-induced NF-kappa B activation, suggesting that PKC activation is upstream of NF-kappa B activation in oleic acid-induced ET-1 expression. These data suggest that elevated plasma oleic acid levels observed in obese, insulin-resistant subjects result in endothelial dysfunction, at least in part, through an increase in ET-1 expression.

Acute hyperglycemia causes intracellular formation of CML and activation of ras, p42/44 MAPK, and nuclear factor kappaB in PBMCs

Twenty-three nondiabetic volunteers were divided into three groups. In group A (n = 9), the glucose infusion was adjusted to maintain blood glucose at 5 mmol/l (euglycemic clamp). In group B (n = 9), the glucose infusion was adjusted to maintain blood glucose at 10 mmol/l (hyperglycemic clamp) over 2 h. Group C consisted of five volunteers who were studied as the control group. Peripheral blood mononuclear cells (PBMCs) were isolated before and at the end of a 2-h clamp. In group C, PBMCs were isolated before and after 2 h without performing a clamp. The euglycemic clamp as well as "no clamp" had no effects on all parameters studied. In contrast, a significant increase in carboxymethyllysine (CML) content and p21(ras) and p42/44 mitogen-activated protein kinase (MAPK) phosphorylation was observed at the end of a 2-h hyperglycemic clamp. The nuclear factor (NF)-kappaB (but not Oct-1) binding activity increased significantly in the hyperglycemic clamp. Western blots confirmed NF-kappaB-p65-antigen translocation into the nucleus. IkappaBalpha did not change significantly in both groups. Hyperglycemia-mediated NF-kappaB activation and increase of CML content, p21(ras), and p42/44 MAPK phosphorylation was also seen in ex vivo-isolated PBMCs stimulated with 5 or 10 mmol/l glucose. Addition of insulin did not influence the results. Inhibition of activation of ras, MAPK, or protein kinase C blocked hyperglycemia-mediated NF-kappaB activation in ex vivo-isolated PBMCs stimulated with 10 mmol/l glucose. Similar data were obtained using an NF-kappaB-luciferase reporter plasmid. Therefore, we can conclude that an acute hyperglycemia-mediated mononuclear cell activation is dependent on activation of ras, p42/p44 MAPK phosphorylation, and subsequent NF-kappaB activation and results in transcriptional activity in PBMCs.

Vascular inflammation: a role in vascular disease in hypertension?

PURPOSE OF REVIEW

In this review, we summarize the more recent clinical evidence highlighting the importance of vascular inflammation in terms of clinical risk prediction, and the mechanisms mediating the upregulation of inflammatory mediators in cardiovascular disease and hypertension.

RECENT FINDINGS

Markers of inflammation have been shown to be upregulated in different forms of cardiovascular disease, and to correlate with vascular risk. Atherosclerosis is characterized by chronic inflammation of the vascular wall. The I-kappaB/nuclear factor-kappaB system is considered a major intracellular inflammatory pathway, mediating most of the vascular inflammatory responses. Increasing evidence indicates that hypertension, through the vasoactive peptides angiotensin and endothelin-1, promotes and accelerates the atherosclerotic process via inflammatory mechanisms. In animal and human studies proinflammatory properties of angiotensin II have been demonstrated in large conduit and small arteries, in the kidney as well as in the heart. The angiotensin II receptors involved in the inflammatory process and the interaction between angiotensin II and nitric oxide in mediating vascular inflammation have been identified. In addition, recent advances concerning the role of endothelin-1 as another important mediator of chronic inflammation in the vascular wall has been documented, and the relationship between endothelin-1 and angiotensin II on vascular inflammation demonstrated.

SUMMARY

Inflammatory mechanisms are important participants in the pathophysiology of hypertension and cardiovascular disease. The identification of useful markers of inflammation, of new therapeutic targets to interfere with these mechanisms, and the evaluation of the efficacy of antiinflammatory treatments will allow progress in our ability to combat cardiovascular disease and the complications of hypertension.

High glucose-induced, endothelin-dependent fibronectin synthesis is mediated via NF-kappa B and AP-1

Human endothelial cells cultured under high glucose (HG) conditions were shown before to upregulate several basement membrane proteins, including fibronectin (FN), thus mimicking effects of diabetes. Using human macrovascular (HUVEC) and microvascular (HMEC) endothelial cell lines, we evaluated in the present study some of the key molecular signaling events involved in HG-induced FN overexpression. This expression was shown to be dependent on endogenous endothelin (ET) receptor-mediated signaling. We also examined the roles played by protein kinase C (PKC) and the transcription factors nuclear factor kappaB (NF-kappaB) and activating protein (AP)-1 with respect to such changes. HG, PKC activators, and ETs (ET-1 and ET-3) that increased FN expression also caused activation of NF-kappaB and AP-1. Inhibitors of both NF-kappaB and AP-1 prevented HG- and ET-induced FN production. ET receptor blockade also prevented these HG- and ET-mediated changes. The results of this study indicate that glucose-induced increased FN production in diabetes may be mediated via ET-dependent NF-kappaB and AP-1 activation.

Activation of tubular epithelial cells in diabetic nephropathy

Previous studies have shown that renal function in type 2 diabetes correlates better with tubular changes than with glomerular pathology. Since advanced glycation end products (AGEs; AGE-albumin) and in particular carboxymethyllysine (CML) are known to play a central role in diabetic nephropathy, we studied the activation of nuclear factor kappaB (NF-kappaB) in tubular epithelial cells in vivo and in vitro by AGE-albumin and CML. Urine samples from healthy control subjects (n = 50) and type 2 diabetic patients (n = 100) were collected and tested for excretion of CML and the presence of proximal tubular epithelial cells (pTECs). CML excretion was significantly higher in diabetic patients than in healthy control subjects (P < 0.0001) and correlated with the degree of albuminuria (r = 0.7, P < 0.0001), while there was no correlation between CML excretion and HbA(1c) (r = 0.03, P = 0.76). Urine sediments from 20 of 100 patients contained pTECs, evidenced by cytokeratin 18 positivity, while healthy control subjects (n = 50) showed none (P < 0.0001). Activated NF-kappaB could be detected in the nuclear region of excreted pTECs in 8 of 20 patients with pTECs in the urine sediment (40%). Five of eight NF-kappaBp65 antigen-positive cells stained positive for interleukin-6 (IL-6) antigen (62%), while only one of the NF-kappaB-negative cells showed IL-6 positivity. pTECs in the urine sediment correlated positively with albuminuria (r = 0.57, P < 0.0001) and CML excretion (r = 0.55, P < 0.0001). Immunohistochemistry in diabetic rat kidneys and a human diabetic kidney confirmed strong expression of NF-kappaB in tubular cells. To further prove an AGE/CML-induced NF-kappaB activation in pTECs, NF-kappaB activation was studied in cultured human pTECs by electrophoretic mobility shift assays (EMSAs) and Western blot. Stimulation of NF-kappaB binding activity was dose dependent and was one-half maximal at 250 nmol/l AGE-albumin or CML and time dependent at a maximum of activation after 4 days. Functional relevance of the observed NF-kappaB activation was demonstrated in pTECs transfected with a NF-kappaB-driven luciferase reporter plasmid and was associated with an increased release of IL-6 into the supernatant. The AGE- and CML-dependent activation of NF-kappaBp65 and NF-kappaB-dependent IL-6 expression could be inhibited using the soluble form of the receptor for AGEs (RAGE) (soluble RAGE [sRAGE]), RAGE-specific antibody, or the antioxidant thioctic acid. In addition transcriptional activity and IL-6 release from transfected cells could be inhibited by overexpression of the NF-kappaB-specific inhibitor kappaBalpha. The findings that excreted pTECs demonstrate activated NF-kappaB and IL-6 antigen and that AGE-albumin and CML lead to a perpetuated activation of NF-kappaB in vitro infer that a perpetuated increase in proinflammtory gene products, such as IL-6, plays a role in damaging the renal tubule.

Advanced glycosylation end products induce NF-kappaB dependent iNOS expression in RAW 264.7 cells

Advanced glycosylation end products (AGEs) have been implicated in the pathogenesis of diabetic complications. Treatment of RAW 264.7 macrophages with bovine serum albumin (BSA)-derived AGEs caused dose- and time-dependent increases in nitrite production and inducible nitric oxide synthase (iNOS) expression. These effects were blocked by the nuclear factor-kappa B (NF-kappaB) inhibitor, pyrrolidone dithiocarbamate (PDTC). BSA-AGEs also stimulated the translocation of p65 NF-kappaB from cytosol to the nucleus. Electrophoretic mobility shift assay revealed that the NF-kappaB DNA-protein-binding activity was enhanced by AGEs. The tyrosine kinase inhibitor, genistein, the phosphatidylinositol-3-kinase (PI 3-K) inhibitor, LY 294002, the protein kinase C (PKC) inhibitor, Ro 31-8220, and the p38 mitogen-activated protein kinase (MAPK) inhibitor, SB 203580, all inhibited AGEs-stimulated iNOS expression, NO release, NF-kappaB translocation and NF-kappaB DNA binding activity. These results suggest that AGEs may activate NF-kappaB via an upstream signaling cascade composed of tyrosine kinase, PI 3-K, PKC, and p38 MAPK, resulting in the induction of iNOS expression in RAW 264.7 macrophages.

Activation of nuclear factor-kappaB induced by diabetes and high glucose regulates a proapoptotic program in retinal pericytes

To reconstruct the events that may contribute to the accelerated death of retinal vascular cells in diabetes, we investigated in situ and in vitro the activation of nuclear factor-kappaB (NF-kappaB), which is triggered by cellular stress and controls several programs of gene expression. The retinal capillaries of diabetic eye donors showed an increased number of pericyte nuclei positive for NF-kappaB, when compared with nondiabetic donors, whereas endothelial cells were negative. Microvascular cell apoptosis and acellular capillaries were increased only in the diabetic donors with numerous NF-kappaB-positive pericytes. Likewise, high glucose in vitro activated NF-kappaB in retinal pericytes but not in endothelial cells, and increased apoptosis only in pericytes. Studies with NF-kappaB inhibitors suggested that in pericytes, basal NF-kappaB has prosurvival functions, whereas NF-kappaB activation induced by high glucose is proapoptotic. Pericytes exposed to high glucose showed increased expression of Bax and of tumor necrosis factor-alpha, which were prevented by the NF-kappaB inhibitors and mimicked by transfection with the p65 subunit of NF-kappaB, and failed to increase the levels of the NF-kappaB-dependent inhibitors of apoptosis. Colocalization of activated NF-kappaB and Bax overexpression was observed in the retinal pericytes of diabetic donors. A proapoptotic program triggered by NF-kappaB selectively in retinal pericytes in response to hyperglycemia is a possible mechanism for the early demise of pericytes in diabetic retinopathy.

Advanced glycation end products and endothelial dysfunction in type 2 diabetes

OBJECTIVE

Data from experimental studies have suggested that the increased formation of advanced glycation end products (AGEs) is one of the causes of endothelial dysfunction in diabetes. This study was performed to investigate whether changes in endothelium-dependent vasodilation, a marker of endothelial function, were related to serum AGEs concentrations in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

For this study, 170 patients with type 2 diabetes and 83 healthy nondiabetic control subjects of similar age were recruited. Serum AGEs were assayed by competitive enzyme-linked immunosorbent assay. Endothelium-dependent and -independent vasodilation of the brachial artery was measured by high-resolution vascular ultrasound.

RESULTS

Serum AGEs were increased in diabetic patients compared with control subjects (4.6 +/- 0.7 vs. 3.1 +/- 0.8 unit/ml; P < 0.01), and both endothelium-dependent (5.1 +/- 2.5 vs. 9.1 +/- 4.1%; P < 0.01) and endothelium-independent vasodilation (13.2 +/- 4.6 vs. 16.4 +/- 5.5%; P < 0.01) were impaired. On univariate analysis of all subjects, serum AGEs correlated with endothelium-dependent vasodilation (r = -0.51, P < 0.01); a weaker association was found with endothelium-independent vasodilation (r = -0.24, P < 0.01). On multiple regression analyses including age, sex, smoking status, and plasma lipids, only serum AGEs remained a significant independent determinant of endothelium-dependent vasodilation (r(2) = 0.34, P < 0.01).

CONCLUSIONS

Increased serum concentrations of AGEs in patients with type 2 diabetes is associated with endothelial dysfunction, independent of other cardiovascular risk factors. Further studies to determine whether treatment targeting AGEs will lead to an amelioration of endothelial dysfunction are warranted.

Diabetic vascular dysfunction: links to glucose-induced reductive stress and VEGF

A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. These involve either increased reductive or oxidative stress to the cell, or the activation of numerous protein kinase pathways, particularly protein kinase C and mitogen-activated protein kinases. As detailed below, there is tremendous crosstalk between these competing hypotheses. We propose that increased tissue glucose levels alter cytosolic coenzyme balance by increased flux of glucose through the sorbitol pathway increasing free cytosolic NADH levels. Increased NADH levels can generate reactive oxygen species via numerous mechanisms, lead to the formation of intracellular advanced glycation end products, and induce growth factor expression via mechanisms involving protein kinase C activation. The elevation in growth factors, particularly vascular endothelial growth factor (VEGF), is responsible for the vascular dysfunction via numerous mechanisms reported here in detail.

A nuclear factor-kappaB inhibitor BAY 11-7082 suppresses endothelin-1 production in cultured vascular endothelial cells

BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB), which prevents a step of the phosphorylation of inhibitory protein IkappaB bound to NF-kappaB, suppressed basal and tumor necrosis factor (TNF)-alpha-induced prepro endothelin (ET)-1 mRNA expression and NF-kappaB activation in cultured vascular endothelial cells. BAY 11-7082 significantly decreased basal and TNF-alpha-induced ET-1 release from endothelial cells. These results indicate that the inhibition of NF-kappaB activation contributes to the suppressive effect of BAY 11-7082 on ET-1 gene expression and ET-1 release, thereby suggesting that NF-kappaB plays an important role in the regulation of ET-1 production.

Leptin induces endothelin-1 in endothelial cells in vitro

Leptin, a protein encoded by the obese gene, is produced by adipocytes and released into the bloodstream. In obese humans, serum leptin levels are increased and correlate with the individual's body mass index and blood pressure. Elevated serum concentrations of endothelin-1 (ET-1), a potent vasoconstrictor and mitogen, were also observed in obese subjects. The pathomechanisms underlying this ET-1 increase in obesity are poorly understood. In the present study, we investigated the influence of the ob gene product leptin on the expression of ET-1 in human umbilical vein endothelial cells (HUVECs). Binding studies using (125)I-radiolabeled leptin revealed high- and low-affinity leptin binding sites on HUVECs (Kd1=13.1+/-3.1 nmol/L and Kd2=1390+/-198 nmol/L, respectively), mediating a time- and dose-dependent increase of ET-1 mRNA expression and protein secretion after incubation of HUVECs with leptin. This leptin-induced ET-1 expression was inhibited by preincubation of HUVECs with 0.75 micromol/L antisense phosphorothioate oligonucleotides directed against the leptin receptor Ob-Rb. Furthermore, after incubation with leptin, increased nuclear staining of c-fos and c-jun, the major components of the transcription factor AP-1, and increased AP-1 DNA binding were observed. Transient transfection studies with ET-1 promoter constructs showed that leptin-induced promoter activity was abolished in the absence of AP-1 binding sites or by cotransfection with a plasmid overexpressing a mutated jun, which is able to bind c-fos but not DNA. Thus, leptin upregulates ET-1 production in HUVECs via a mechanism potentially involving jun binding members of the bZIP family.

Reciprocal regulation of endothelin-1 and nitric oxide: relevance in the physiology and pathology of the cardiovascular system

The endothelium plays a crucial role in the regulation of cardiovascular structure and function by releasing several mediators in response to biochemical and physical stimuli. These mediators are grouped into two classes: (1) endothelium-derived constricting factors (EDCFs) and (2) endothelium-derived relaxing factors (EDRFs), the roles of which are considered to be detrimental and beneficial, respectively. Endothelin-1 (ET-1) and nitric oxide (NO) are the prototypes of EDCFs and EDRFs, respectively, and their effects on the cardiovascular system have been studied in depth. Numerous conditions characterized by an impaired availability of NO have been found to be associated with enhanced synthesis of ET-1, and vice versa, thereby suggesting that these two factors have a reciprocal regulation. Experimental studies have provided evidence that ET-1 may exert a bidirectional effect by either enhancing NO production via ETB receptors located in endothelial cells or blunting it via ETA receptors prevalently located in the vascular smooth muscle cells. Conversely, NO was found to inhibit ET-1 synthesis in different cell types. In vitro and in vivo studies have started to unravel the molecular mechanisms involved in this complex interaction. It has been clarified that several factors affect in opposite directions the transcription of preproET-1 and NO-synthase genes, nuclear factor-KB and peroxisome proliferator-activated receptors playing a key role in these regulatory mechanisms. ET-1 and NO interplay seems to have a great relevance in the physiological regulation of vascular tone and blood pressure, as well as in vascular remodeling. Moreover, an imbalance between ET-1 and NO systems may underly the mechanisms involved in the pathogenesis of systemic and pulmonary hypertension and atherosclerosis.

Protective effect of alpha-lipoic acid against ischaemic acute renal failure in rats

1. In the present study, we investigated whether treatment with alpha-lipoic acid (LA), a powerful and universal anti-oxidant, has renal protective effects in rats with ischaemic acute renal failure (ARF). 2. Ischaemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Blood urea nitrogen (BUN), plasma concentrations of creatinine (Pcr) and urinary osmolality (Uosm) were measured for the assessment of renal dysfunction. Creatinine clearance (Ccr) and fractional excretion of Na+ (FENa) were used as indicators of glomerular and tubular function, respectively. 3. Renal function in ARF rats decreased markedly 24 h after reperfusion. Intraperitoneal injection of LA at a dose of 10 mg/kg before the occlusion tended to attenuate the deterioration of renal function. A higher dose of LA (100 mg/kg) significantly (P < 0.01) attenuated the ischaemia/reperfusion-induced increases in BUN (19.1 +/- 0.7 vs 7.2 +/- 0.7 mmol/L before and after treatment, respectively), Pcr (290 +/- 36 vs 78.1 +/- 4.2 micromol/L before and after treatment, respectively) and FENa (1.39 +/- 0.3 vs 0.33 +/- 0.09% before and after treatment, respectively). Treatment with 100 mg/kg LA significantly (P < 0.01) increased Ccr (0.70 +/- 0.13 vs 2.98 +/- 0.27 mL/min per kg before and after treatment, respectively) and Uosm (474 +/- 39 vs 1096 +/- 80 mOsmol/kg before and after treatment, respectively). 4. Histopathological examination of the kidney of ARF rats revealed severe lesions. Tubular necrosis (P < 0.01), proteinaceous casts in tubuli (P < 0.01) and medullary congestion (P < 0.05) were significantly suppressed by the higher dose of LA. 5. A marked increase in endothelin (ET)-1 content in the kidney after ischaemia/reperfusion was evident in ARF rats (0.43 +/- 0.02 ng/g tissue) compared with findings in sham- operated rats (0.20 +/- 0.01 ng/g tissue). Significant attenuation (P < 0.01) of this increase occurred in ARF rats treated with the higher dose of LA (0.24 +/- 0.03 ng/g tissue). 6. These results suggest that administration of LA to rats prior to development of ischaemic ARF prevents renal dysfunction and tissue injury, possibly through the suppression of overproduction of ET-1 in the postischaemic kidney.

Proinflammatory effects of angiotensin II and endothelin: targets for progression of cardiovascular and renal diseases

Angiotensin II and endothelin-1 can both be regulated by nuclear factor-kappaB. They are to varying degrees also capable of activating nuclear factor-kappaB and increasing the expression of nuclear factor-kappaB dependent genes. Angiotensin II related vascular effects are in part mediated by endothelin-1. Nitric oxide synthase inhibition facilitates angiotensin II related effects, which can be inhibited both by angiotensin II type 1 receptor blockers and by endothelin system inhibitors. This supports the notion that a combined therapeutic strategy of inhibiting angiotensin II and endothelin-1 generation or blocking their effects at the receptor level would be superior to either strategy alone. Animal studies are encouraging but not without conflicting results. Angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers have a superb track record in experimental animal models and in a host of clinical studies. Selective and nonselective blockers of the endothelin-1 receptors are important research tools and are also undergoing clinical trials. Inhibitors of the endothelin converting enzyme have been developed. The recent elucidation of the endothelin converting enzyme's physical structure should facilitate the development of still more novel compounds to inhibit endothelin-1 generation.

Diabetes-associated sustained activation of the transcription factor nuclear factor-kappaB

Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) has been suggested to participate in chronic disorders, such as diabetes and its complications. In contrast to the short and transient activation of NF-kappaB in vitro, we observed a long-lasting sustained activation of NF-kappaB in the absence of decreased IkappaBalpha in mononuclear cells from patients with type 1 diabetes. This was associated with increased transcription of NF-kappaBp65. A comparable increase in NF-kappaBp65 antigen and mRNA was also observed in vascular endothelial cells of diabetic rats. As a mechanism, we propose that binding of ligands such as advanced glycosylation end products (AGEs), members of the S100 family, or amyloid-beta peptide (Abeta) to the transmembrane receptor for AGE (RAGE) results in protein synthesis-dependent sustained activation of NF-kappaB both in vitro and in vivo. Infusion of AGE-albumin into mice bearing a beta-globin reporter transgene under control of NF-kappaB also resulted in prolonged expression of the reporter transgene. In vitro studies showed that RAGE-expressing cells induced sustained translocation of NF-kappaB (p50/p65) from the cytoplasm into the nucleus for >1 week. Sustained NF-kappaB activation by ligands of RAGE was mediated by initial degradation of IkappaB proteins followed by new synthesis of NF-kappaBp65 mRNA and protein in the presence of newly synthesized IkappaBalpha and IkappaBbeta. These data demonstrate that ligands of RAGE can induce sustained activation of NF-kappaB as a result of increased levels of de novo synthesized NF-kappaBp65 overriding endogenous negative feedback mechanisms and thus might contribute to the persistent NF-kappaB activation observed in hyperglycemia and possibly other chronic diseases.

NFkappaB polymorphisms and susceptibility to type 1 diabetes

Nuclear factor kappa B (NFkappaB) is an important transcription factor that is involved in the response to oxidative stress and inflammation. Recent studies suggest that it may be involved in the development of diabetic microvascular complications. A highly polymorphic (CA) dinucleotide repeat microsatellite has been identified in the regulatory region of the NFkappaB gene. The aim of this study was to investigate whether this polymorphic region was associated with susceptibility to type 1 diabetes, or its late complications. Genomic DNA was extracted from the peripheral blood of 217 patients with type 1 diabetes mellitus (T1DM) and 111 normal healthy controls. In our population 18 alleles (A1-A18) were identified. There was a highly significant decrease in the frequency of allele 146 bp (A14) in type 1 diabetes (0.03) compared with the normal controls (0.28) (chi(2) = 79.8, Pc = 0.00001). In contrast, the frequency of the allele 138 bp (A10) was significantly increased in patients with type 1 diabetes (0.17) compared with the normal controls (0.02) (chi(2) = 32.8, P < 0.00000). These results demonstrate that the NFkappaB gene may play a role in the susceptibility to type 1 diabetes: individuals with the A10 allele may be more likely to develop diabetes compared with the A14 allele.

Effects of alpha-lipoic acid on deoxycorticosterone acetate-salt-induced hypertension in rats

We investigated the potential of natural occurring antioxidant alpha-lipoic acid to prevent hypertension and hypertensive tissue injury induced by deoxycorticosterone acetate (DOCA) and salt in rats. Two weeks after the start of DOCA-salt treatment, the rats were given alpha-lipoic acid (10 or 100 mg/kg/day, s.c.) or its vehicle for 2 weeks. Uninephrectomized rats without DOCA-salt treatment served as sham-operated controls. In vehicle-treated DOCA-salt rats, systolic blood pressure increased markedly after 3-4 weeks. Daily administration of 100 mg/kg alpha-lipoic acid for 2 weeks suppressed the increase in systolic blood pressure, whereas 10 mg/kg alpha-lipoic acid did not affect the progression of DOCA-salt-induced hypertension. When the degree of vascular hypertrophy of the aorta was morphometrically evaluated at 4 weeks, there were significant increases in media cross-sectional area in vehicle-treated DOCA-salt rats compared with sham-operated rats. The development of vascular hypertrophy was markedly suppressed by alpha-lipoic acid at 100 mg/kg but not at 10 mg/kg. Histopathological examination of the kidney in vehicle-treated DOCA-salt rats revealed fibrinoid-like necrosis in glomeruli and thickening of small arteries. In these animals, creatinine clearance decreased, and fractional excretion of Na(+), urinary excretion of protein and N-acetyl-beta-glucosaminidase increased. Such renal lesions and dysfunctions were ameliorated in DOCA-salt rats given alpha-lipoic acid. In addition, a marked increase in endothelin-1 content in both the aorta and kidney was evident in vehicle-treated DOCA-salt rats compared with findings in sham-operated rats. Significant attenuation of this increase occurred in alpha-lipoic acid-treated DOCA-salt rats. These results suggest that administration of alpha-lipoic acid to DOCA-salt hypertensive rats lessens the increased blood pressure and protects against renal and vascular injuries, possibly through the suppression of renal and vascular endothelin-1 overproduction.

Therapeutic potential of endothelin receptor antagonists in diabetes

Endothelins (ETs) are widely distributed in the body and perform several vascular and non-vascular functions. Experimental evidence indicates that abnormalities of the ET system occur in several organs affected in chronic diabetic complications. Furthermore, ET antagonists were found to prevent structural and functional changes in the target organs of chronic diabetic complications in animal models. Abnormalities of plasma ET levels have also been demonstrated in human diabetes. This review discusses the role of ET in the pathogenesis of chronic diabetic complications. The current experimental evidence suggests that ET antagonism may potentially represent an adjuvant therapeutic tool in the treatment of chronic diabetic complications.