Eicosanoids in regulation of arterial smooth muscle cell phenotype, proliferative capacity, and cholesterol metabolism

Role of progesterone on the regulation of vascular muscle cells proliferation, migration and apoptosis

The purpose of this study was to investigate the effect of progesterone (Pg) on cellular growth, migration, apoptosis, and the molecular mechanism of action displayed by the steroid. To that end, rat aortic vascular smooth muscle cell (VSMC) cultures were employed. Pg (10nM) significantly increased [(3)H]thymidine incorporation after 24h of treatment. The enhancement in DNA synthesis was blunted in the presence of an antagonist of Pg receptor (RU486 compound). The mitogenic action of the steroid was suppressed by the presence of the compounds PD98059 (MEK inhibitor), chelerythrine (PKC inhibitor), and indomethacin (cyclooxygenase antagonist) suggesting that the stimulation of DNA synthesis involves MAPK, PKC, and cyclooxygenase transduction pathways. The proliferative effect of the hormone depends on the presence of endothelial cells (EC). When muscle cells were incubated with conditioned media obtained of EC treated with Pg, the mitogenic action of the steroid declined. Wounding assays shows that 10nM Pg enhances VSMC migration and motility. The role of the steroid on programmed cell death was measured using DNA fragmentation technique. Four hours of treatment with 10nM Pg enhanced DNA laddering in a similarly extent to the apoptotic effect induced by the apoptogen hydrogen peroxide (H(2)O(2)). In summary the results presented provide evidence that Pg enhances cell proliferation, migration, and apoptosis of VSMC. The modulation of cell growth elicited by the steroid involves integration between genomic and signal transduction pathways activation.

Cyclooxygenase-2 induction by lysophosphatidylcholine in cultured rat vascular smooth muscle cells: involvement of the p38MAPK pathway

Lysophosphatidylcholine (lysoPC) stimulates the release of prostaglandins (PGs) in various cells and tissues. Cyclooxygenase (COX)-2 has recently emerged as a key regulator of PG synthesis. We investigated whether lysoPC regulates COX-2 expression in cultured rat vascular smooth muscle cells (VSMCs). LysoPC strongly increased the expression of COX-2 mRNA in a time- and dose-dependent manner. COX-2 protein expression also was increased by lysoPC. The p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 significantly suppressed lysoPC-induced COX-2 mRNA and protein expression, but not a p42/44MAPK kinase (MEK-1) inhibitor, PD98059. LysoPC did not increased the transcription of the COX-2 gene, as assayed with a COX-2 promoter/luciferase chimeric plasmid and suppressed the decay of COX-2 mRNA. SB203580 markedly enhanced the decay of COX-2 mRNA induced by lysoPC, implying that p38MAPK activated by lysoPC helps to regulate COX-2 by stabilizing its mRNA. The COX-2 specific inhibitor NS-398 attenuated lysoPC-stimulated DNA and protein synthesis as well as PGE(2) production by VSMCs. These results suggest that in rat VSMCs lysoPC regulates COX-2 expression and PG production and also modulates cell proliferation through p38MAPK-mediated signaling pathways.

Protective Effect of Policosanol on Endothelium and Intimal Thickness Induced by Forceps in Rabbits

Policosanol is a cholesterol-lowering drug isolated from sugar cane wax with concomitant antiplatelet effects that prevents lipofundin-induced atherosclerotic lesions in rabbits and rats, including foam cell formation, and also reduces foam cell formation in carrageenan-induced granulomas in rats, while it inhibits proliferation of smooth muscle cells induced in rabbit cuffed artery. This study was undertaken to determine whether policosanol prevents endothelium damage and increase in arterial wall thickness in rabbits with arterial walls damaged with a forceps. Artery forceps were placed over the central artery of the right ear of all rabbits, and each artery was injured eight times. Animals were randomly distributed into four groups: a positive control group treated with Tween 20/H2O vehicle, two groups treated with policosanol (5 and 25 mg/kg, respectively), and a group treated with aspirin (8 mg/kg). Treatments were given for 30 days. Damaged arteries were examined by light and electron (transmission and scanning) microscopy. To evaluate intimal thickening, areas of intima were measured, and a significant reduction in policosanol-treated animals was observed. The endothelial surface, studied with scanning electron microscopy, revealed several types of damage. In control group, the endothelial surface was severely damaged. De-endothelialized areas were reduced in policosanol-treated animals. Platelet adhesion to subendothelium was seen in all animals of the control group, whereas policosanol-treated groups exhibited significantly reduced platelet adhesion. Policosanol also reduced, dose-dependently, the platelet sequestration induced in the damaged vessel wall, partially preventing the reduction in platelet count. It is concluded that policosanol prevents endothelium injury and reduces significantly intimal thickness of rabbit arteries damaged with forceps.

Regulation of cholesteryl ester hydrolases

Recent developments in understanding the biochemical and molecular nature of the CE hydrolases and their impact on cellular cholesterol trafficking have further defined the enzyme's mechanism of action with reasonable clarity. The availability of the cDNA probe for the human lysosomal acid lipase/CE hydrolase and the hormone-sensitive lipase now makes it possible to study CE hydrolase gene regulation and expression in human tissue; and it can now be stated with more assurance that the cytoplasmic CE hydrolase (NCEH) is most likely activated through phosphorylation by the cyclic AMP-dependent protein kinase. Evidence also shows that the NCEH is most likely identical to the hormone-sensitive lipase and that it plays an important role in cholesterol efflux properties of the cell. Recent advances in the discovery of the role of the eicosanoid/cytokine network in the regulation of CE hydrolysis, highlighted in Figure 10, further emphasize the interesting but complex nature of the cholesterol trafficking processes in cells, particularly under pathophysiological conditions such as cell injury, repair, and inflammation. It can be speculated that in several years, when the crystal structure of the CE hydrolase is known, the structure-function properties of this enzyme's catalytic domain, as it relates to the physical state of the CE substrates, should further clarify the precise role of this enzyme in intracellular cholesterol mobilization and trafficking under a variety of cellular conditions.

Effect of D-003 on intimal thickening and circulating endothelial cells in rabbit cuffed carotid artery

D-003 is a mixture of very-high-molecular-weight aliphatic primary acids purified from sugar-cane (Saccharum officinarum L.) wax, in which octacosanoic acid is the most abundant component. Previous experimental studies have shown that D-003 not only shows cholesterol-lowering and anti-platelet effects, but also reduces thromboxane B2 and increases prostacyclin levels. It acts by inhibiting cholesterol biosynthesis. The positioning of a non-occlusive silicone collar around the rabbit carotid artery results in the formation of a neointima. Collars were placed around the left carotid for 15 days. The contralateral artery was sham-operated. We included three experimental groups: A control group received vehicle, and two others received D-003 at 5 and 25 mg/kg until sacrificed. Samples of arteries were examined by light microscopy. To evaluate intimal thickening the cross-sectional areas of intima and media were measured. Neointima was significantly reduced in D-003-treated animals compared with controls. Furthermore, the circulating endothelial cell has been studied in this experimental model with endothelium damage. The results demonstrate the protective effect of D-003 on vascular endothelium of the studied rabbits. It is concluded that the protective effect of D-003 against neointima formation and circulating endothelial cells in this experimental model could represent potential beneficial pleiotropic effects in the anti-atherogenic profile of this substance, beyond its cholesterol-lowering and anti-platelet effects independently demonstrated.

Adenovirus-Encoded Hammerhead Ribozyme to PDGF A-Chain mRNA Inhibits Neointima Formation after Arterial Injury

To develop a strategy for gene therapy of restenosis following coronary angioplasty, we examined the effects of a recombinant adenovirus vector encoding a hammerhead ribozyme specific for rat platelet-derived growth factor (PDGF) A-chain mRNA (Ad. Ribozyme) and a control recombinant adenovirus vector encoding the Escherichia coli LacZ gene (Ad.LacZ) on neointima formation in rat carotid artery after balloon injury. Ad. Ribozyme (10(8) PFU/ml) markedly reduced the increased expression of PDGF A-chain mRNA and protein. Ad. Ribozyme significantly decreased the intima/media ratio (68%) of the injured artery, whereas Ad.LacZ had no effect on the intima/media ratio. Most carotid arteries developed thrombi by 14 days after balloon injury, whereas Ad. Ribozyme completely inhibited thrombus formation. Expression of thromboxane A2 (TXA2) receptor mRNA was significantly increased after balloon injury. Ad. Ribozyme significantly decreased the levels of TXA2 receptor. Expression of prostaglandin I2 (PGI2) synthase mRNA was significantly decreased after balloon injury. Ad. Ribozyme significantly increased levels of PGI2 synthase mRNA after balloon injury. The observation that adenovirus-encoded ribozyme to PDGF A-chain inhibits neointima formation may serve as a novel strategy to prevent restenosis after coronary angioplasty. Inhibition of growth factors by genetic approaches may yield new insights into the mechanisms underlying responses to vascular injury and lead to new therapeutic applications.

PGE(2) stimulates vascular smooth muscle cell proliferation via the EP2 receptor

Prostaglandins released by injured vascular tissue can modulate smooth muscle cell (SMC) proliferation. The mechanism of action of PGE(2) was investigated with porcine coronary artery SMCs obtained by explant culture. DNA and RNA syntheses exhibited a concentration-dependent increase following treatment of quiescent SMCs with PGE(2), while PGI(2) had no effect. PGE(2) also elevated PCNA expression, bromodeoxyuridine incorporation, and cell number, indicative of a hyperplastic growth response. Furthermore, induction of c-fos expression required activation of both phosphatidylinositol 3-kinase and mitogen-activated protein kinase. Contrary to these data, treatment of proliferating cells with PGE(2) caused a reduction in DNA synthesis. A role for PKA in either growth stimulation or inhibition was excluded. Interestingly, only quiescent SMCs expressed EP2 receptors, and the selective EP2 receptor agonist butaprost confirmed that this receptor was essential for growth stimulation and possibly inhibition. These data suggest that the growth state-dependent actions of PGE(2) on SMC proliferation may be mediated via the EP2 receptor.

Inflammation, endothelial dysfunction, and the risk of high blood pressure: epidemiologic and biological evidence

In spite of its high impact on cardiovascular and renal disease, knowledge on risk factors for the development of high blood pressure (HBP) is limited. Mild chronic inflammation may play a significant role in the incidence of HBP. A persistent low-grade inflammation state could be associated with high but within the 'normal range' cytokine plasma concentration. By impairing the capacity of the endothelium to generate vasodilating factors, particularly nitric oxide (NO), elevated cytokines may lead to the development of endothelial dysfunction, chronic impaired vasodilation, and HBP. These alterations in the L-arginine : NO pathway may play a major role in the development of HBP in young subjects, with inflammation-related alterations in the production of cyclo-oxygenase-derived vasoconstrictors becoming more prominent with advanced age. Cross-sectional independent associations between HBP and plasma levels of C-reactive protein, interleukin-6, and tissue necrosis factor alpha have been reported, but no prospective evidence of these associations is currently available.

Arsenite stimulates cyclooxygenase-2 expression through activating IkappaB kinase and nuclear factor kappaB in primary and ECV304 endothelial cells

Epidemiological studies have shown that chronic exposure to arsenic can result in liver injury, peripheral neuropathy, arteriosclerosis, and an increased incidence of cancer of the lung, skin, bladder, and liver. The overexpression of inducible cyclooxygenase-2 (Cox-2) has been associated with vascular inflammation and cellular proliferation. However, the effect of arsenite on Cox-2 gene expression in endothelial cells was left to be investigated. Western Blot analysis of HUVECs revealed a two-fold induction of Cox-2 protein by arsenite. This induction was associated with a two-fold increase of prostaglandin E2 in the media. Furthermore, the level of Cox-2 mRNA was correspondingly elevated as demonstrated by both Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses. Transfection of an immortalized human endothelium cell line (ECV304) with Cox-2 reporter gene constructs demonstrated that the transcription of Cox-2 gene was enhanced by arsenite. This induction was attenuated by pyrrolidine dithiocarbamate (PDTC), an inhibitor of NFkappaB. In addition, electrophoretic mobility shift assays indicated that NFkappaB activity was induced by arsenite. The kinase activity assay also indicated that IkappaB kinase (IKK) activity was induced by arsenite. These findings indicated that the induction of Cox-2 gene transcription by arsenite was through the stimulation of NFkappaB activity. Arsenite could induce IKK activity, which leads to the phosphorylation and degradation of IkappaB in ECV304 cells. Therefore, it appears that IKK signaling pathway is involved in arsenite-mediated Cox-2 expression.

In vitro bleeding test with PFA-100-aspects of controlling individual acetylsalicylic acid induced platelet inhibition in patients with cardiovascular disease

OBJECTIVES

This study investigated the usefulness and practicability of a platelet function analyzer (PFA-100(TM), DADE-Behring, Germany) to determine individual platelet inhibition in patients treated with acetylsalicylic acid (ASA).

BACKGROUND

Patients with coronary artery disease (CAD) routinely and during angioplasty (PTCA) receive standard doses of ASA to avoid acute coronary syndromes and abrupt vessel closures without information of the individual efficacy of platelet inhibition.

METHODS

With the PFA-100(TM) a standardized bleeding time is measured. Whole-blood anticoagulated with 3.2% sodium citrate is aspirated through a capillary ( solidus in circle 200 microm) and through an aperture ( solidus in circle 147 microm). The time until occlusion of the aperture (closure time, CT) by a stable platelet plug induced by shear stress, collagen and epinephrine (COLL/EPI-CT) or shear stress, collagen and adenosine 5'-diphosphate (COLL/ADP-CT) is determined. To examine the usefulness of the PFA-100(TM) as a rapid bedside test and the individual effect of ASA, closure time was measured in healthy individuals (n=17), in patients with stable CAD (n=19) and in patients undergoing PTCA (n=8).

RESULTS

Patients with stable CAD and regular medication with 100 mg ASA per day for at least 3 month showed shorter COLL/ADP-CT in comparison to healthy individuals who took only one single dose of 100 mg ASA. Of the patients with CAD 63% had a COLL/EPI-CT within normal range suggesting a low or no response to ASA. Also only 50% of the patients undergoing PTCA reached the expected COLL/EPI-CT>300 s after an additive single dose of 500 mg ASA intravenously. Neither heparin, phenprocoumon, sex nor different blood sampling methods seem to influence the measurements relevantly.

CONCLUSIONS

This pilot study indicates that with the PFA-100(TM) test device a simple and quick measurement of an in vitro bleeding time is possible. It is able to detect an increase in the bleeding time after a single dose of ASA 100 mg in healthy subjects, reflecting a sensitive detection of ASA induced changes in platelet inhibition respective activation. Differences in the individual response to ASA could be observed in healthy subjects, patients with stable CAD and patients undergoing PTCA. Further studies should validate the PFA-100(TM) with standard methods to determine ASA response in patients with cardiovascular disease and investigate implications for treatment and outcome in this patient group.

Cyclo-oxygenase-1 and cyclo-oxygenase-2 and cardiovascular system

Prostaglandins play important roles in the pathophysiological mechanism of action of platelets and endothelial cells in the cardiovascular system. The two isoforms of cyclo-oxygenase, respectively cyclo-oxygenase-1 and cyclo-oxygenase-2, are differently expressed in these cells. Activated platelets show a relatively large amount of cyclo-oxygenase-1, whereas endothelial cells have the gene for cyclo-oxygenase-2, the expression of which follows cell activation. In the atherosclerosis lesion, prostaglandin synthesis is mainly mediated by the inducible cyclo-oxygenase-2 expressed in macrophages/foam cells, smooth muscle cells and endothelial cells. Aspirin, a selective platelet cyclo-oxygenase-1 inhibitor still remains the most extensively studied antiplatelet agent, even though there is growing evidence that many other compounds could be valuable either in association, or alternatives in antithrombotic therapy.

A comparative study of policosanol vs lovastatin on intimal thickening in rabbit cuffed carotid artery

Policosanol is a cholesterol-lowering drug isolated from sugar cane wax, which acts by inhibiting cholesterol biosynthesis. Previous studies have demonstrated that policosanol inhibited smooth muscle cell (SMC) proliferation in the cuffed carotid artery of the rabbit and in arterial wall damage induced by forceps in the central artery of the ear of rabbits. The present study was undertaken to compare the effects of policosanol and lovastatin on SMC proliferation in the cuffed carotid artery of rabbits. Collars were placed around the left carotid for 7 and 15 days. The contralateral artery was sham operated. We studied eight experimental groups: two controls groups receiving vehicle for 7 and 15 days, respectively, a satellite sham operated control group, four groups treated with policosanol at 5 and 25 mg kg(-1)for 7 and 15 days and a reference group receiving lovastatin at 20 mg kg(-1)for 15 days. Samples of arteries were examined by light and electron microscopy. To evaluate intimal thickening the cross-sectional areas of intima and media were measured. Neointima was significantly reduced in treated animals compared with controls, but the reduction in lovastatin animals was significantly lower than in policosanol-treated groups. The SMC proliferation was studied by the immunohistochemical detection of proliferating cell nuclear antigen and the reduction observed in policosanol-treated rabbits was significantly larger than in lovastatin-treated animals. It is concluded that the protective effect of policosanol against neointima formation in this experimental model was slightly better than that of lovastatin.

Cytokines induce upregulation of vascular P2Y(2) receptors and increased mitogenic responses to UTP and ATP

P2Y(2) receptors, which mediate contractile and mitogenic effects of extracellular nucleotides in vascular smooth muscle cells (VSMCs), are upregulated in the synthetic phenotype of VSMCs and in the neointima after balloon angioplasty, suggesting a role in the development of atherosclerosis. Because released cytokines in atherosclerotic lesions mediate multiple effects on gene transcription in VSMCs, we speculated that cytokines could be involved in the regulation of P2Y(2) receptor expression. Using a competitive reverse transcription-polymerase chain reaction, we detected that interleukin (IL)-1beta induced a time- and dose-dependent upregulation of P2Y(2) receptor mRNA, which was dramatically enhanced when combined with interferon-gamma or tumor necrosis factor-alpha. Lipopolysaccharide also significantly increased the expression of P2Y(2) receptor mRNA. The upregulation of P2Y(2) receptor mRNA was paralleled at the functional level because IL-1beta significantly increased the UTP-stimulated DNA synthesis and the release of intracellular Ca(2+). Actinomycin D completely blocked the upregulation of P2Y(2) receptor mRNA expression by IL-1beta, indicating de novo mRNA synthesis. There was no cAMP accumulation in the cells stimulated with IL-1beta. The cyclooxygenase inhibitor indomethacin and the protein kinase C inhibitor RO-31-8220 inhibited IL-1beta-induced upregulation of P2Y(2) receptor mRNA expression, whereas rapamycin and PD098059 had no effects. Furthermore, neither P38 mitogen-activated protein kinase inhibitor SB20358 alone nor its combination with PD098059 blocked the effect of IL-1beta on the expression of P2Y(2) receptor mRNA. Our results demonstrate that inflammatory mediators upregulate vascular P2Y(2) receptors at the transcriptional and at the functional level through protein kinase C and cyclooxygenase but not cAMP, extracellular signal-regulated kinases 1 and 2, or P38-dependent pathways. This may result in increased growth-stimulatory or contractile effects of extracellular UTP and ATP, which may be of importance in the development of vascular disease.

Induction of cyclooxygenase-2 by angiotensin II in cultured rat vascular smooth muscle cells

Angiotensin II (Ang II) stimulates the release of prostaglandins (PGs) in various cells and tissues. Recently, cyclooxygenase-2 (COX-2) emerged as a new key regulator for PG synthesis. In the present study, we investigated whether Ang II regulates COX-2 expression in cultured rat vascular smooth muscle cells (VSMCs). Ang II markedly increased the expression of COX-2 mRNA in a time- and dose-dependent manner. This effect was completely blocked by the Ang II type 1 receptor antagonist losartan but not by the Ang II type 2 receptor antagonist PD123319. The p42/44 mitogen-activated protein kinase (MAPK) kinase-1 inhibitor PD98059 and the p38 MAPK inhibitor SB203580 significantly suppressed Ang II-induced COX-2 mRNA and protein expression. Ang II did not increase transcription of the COX-2 gene, as examined with a COX-2 promoter/luciferase chimeric plasmid construct. Instead, it suppressed the degradation of COX-2 mRNA. PD98059 and SB203580 markedly enhanced the decay of COX-2 mRNA induced by Ang II, implying that p42/44 and p38 MAPK activated by Ang II play a role in the regulation of COX-2 through stabilization of its mRNA. The COX-2-specific inhibitor NS-398 attenuated Ang II-stimulated DNA and protein synthesis, as well as PGE(2) production by VSMCs. These results suggest that Ang II regulates COX-2 expression and PG production and modulates cell proliferation through MAPK-mediated signaling pathways in rat VSMCs.

Human prostacyclin synthase gene and hypertension : the Suita Study

BACKGROUND

Prostacyclin (prostaglandin I(2)) is a strong vasodilator that inhibits the growth of vascular smooth muscle cells and is also the most potent endogenous inhibitor of platelet aggregation. Therefore, it has been considered to play an important roles in cardiovascular disease. On the basis of the hypothesis that variations of the prostacyclin synthase gene may also play an important role in human cardiovascular disease, we performed a screening for variations in the human prostacyclin synthase gene.

METHODS AND RESULTS

We have detected a repeat polymorphism in the promoter region of the human prostacyclin synthase gene. The number of 9-bp (CCGCCAGCC) repeats in the promoter region, which encodes a tandem repeat of Sp1 transcriptional binding sites, varied between 3 and 7 in Japanese subjects. Luciferase reporter analysis indicated that the alleles of 3 and 4 repeats (R3 and R4, respectively) had less promoter activity in cultured human umbilical vein endothelial cells. We then investigated the possible association of this repeat polymorphism with blood pressure in a large population-based sample (the Suita Study), which consisted of 4971 Japanese participants. Multivariate models indicated that participants with the R3R3, R3R4, or R4R4 genotype (SS genotype, n=80) had significantly higher systolic pressure (P=0.0133) and pulse pressure (P=0.0005). The odds ratio of hypertension (140/90 mm Hg) for the SS genotype was 1.942 (95% confidence interval 3.20 to 1.19, P=0.0084).

CONCLUSIONS

Repeat polymorphism of the human prostacyclin synthase gene seems to be a risk factor for higher pulse pressure and is consequently a risk factor for systolic hypertension in the Japanese population.

Mechanism of SNAP potentiating antiproliferative effect of calcitonin gene-related peptide in cultured vascular smooth muscle cells

We previously showed that CGRP inhibits cell proliferation which correlates with an elevation of cAMP levels in rabbit aortic vascular smooth muscle cells (VSMCs). The present study determined the effects of S-nitroso-N-acetylpenicillamine (SNAP, a nitric oxide donor) on CGRP-induced antiproliferative effects and cellular mechanism in cultured rabbit aortic VSMCs. The cells (in fifth-sixth passage) were exposed to 2.5% fetal bovine serum for 24 h in the presence or absence of SNAP, hCGRP or both.(3)H-thymidine incorporation was used to measure DNA synthesis. The results showed that SNAP (60-100 microm) significantly inhibited the proliferation and elevated cGMP levels in cultured rabbit aortic VSMCs. In combination, however, SNAP (30 microm) potentiated hCGRP (10-100 n m)-induced antiproliferation. SNAP (30 microm) and hCGRP (10-100 n m) or forskolin (10 microm), an activator of adenylate cyclase, caused more than additive cAMP elevations, but not cGMP elevations, in these cells. Quazinone, an inhibitor of cGMP-inhibited-phosphodiesterase (cGI-PDE, PDE3), or SNAP plus quazinone caused a similar potentiation as SNAP of the hCGRP-induced elevations of cAMP levels. The data indicate that SNAP-induced potentiation of CGRP's effects likely involves inhibition of cGI-PDE, thus allowing enhanced accumulation of cAMP that mediates the antiproliferative effects of hCGRP in cultured rabbit aortic VSMCs.

Cyclooxygenase-2 is widely expressed in atherosclerotic lesions affecting native and transplanted human coronary arteries and colocalizes with inducible nitric oxide synthase and nitrotyrosine particularly in macrophages

Inflammation appears to have a major role in the development of atherosclerotic lesions affecting native and transplanted coronary arteries. The subsequent risk of plaque rupture and acute ischemic events correlates with the degree of inflammation and may be modified by aspirin, an anti-inflammatory cyclooxygenase inhibitor. Cyclooxygenase-2 (Cox-2) and inducible nitric oxide synthase (iNOS) are involved in the inflammatory response via the rapid and exaggerated production of prostanoids and nitric oxide, both of which may have proatherosclerotic effects. These effects may be mediated by the formation of peroxynitrite in the case of nitric oxide and involve "cross talk" between the two enzyme systems. This study aimed to investigate native and transplant atherosclerosis for the presence and distribution of Cox-2 and iNOS. Immunocytochemical studies were performed on atherosclerotic lesions from patients with native (n=12) and transplant (n=5) coronary disease by using antibodies to Cox-2, iNOS, and nitrotyrosine (an indicator of peroxynitrite production). Control tissue was obtained from unused donor hearts and at the time of autopsy. Cox-2 and iNOS colocalized predominantly in macrophages/foam cells in both types of atherosclerosis. Cox-2 expression was also detected in medial smooth muscle cells and endothelial cells, including those of the vasa vasorum. Nitrotyrosine was found in the same distribution as that of iNOS and was colocalized with Cox-2 in macrophages. Cox-2 and iNOS are coexpressed in native and transplant atherosclerosis, possibly allowing for interaction between the enzymes and suggesting an alternative mechanism for the benefits of aspirin via inhibition of Cox-2 activity.

Prevention of neointimal formation by a serine protease inhibitor, FUT-175, after carotid balloon injury in rats

BACKGROUND AND PURPOSE

In vivo and vitro studies revealed the activation of thrombin and the complement system in vascular lesion formation during the process of atherosclerosis, along with pathological proliferation of smooth muscle cells. We examined the effect of the synthetic serine protease inhibitor FUT-175 (developed as a potent inhibitor of thrombin and the complement system) on vascular lesions using balloon dilatation-induced neointimal formation in the carotid artery of rats.

METHODS

Sprague-Dawley (SD) rats underwent balloon dilatation injury of the left carotid artery to induce neointimal formation. Three groups of these rats (n=8, each) were treated with daily intraperitoneal injections of 1 of the following doses of FUT-175: 0.5, 1.0, or 2.0 mg/d in 1 mL of saline for 7 consecutive days. The control group (n=8) was similarly treated with 1 mL of saline for 7 days. The injections were started immediately after balloon injury. Two weeks after the injury, the left carotid arteries were perfusion-fixed, and the areas of the neointimal and medial layer were analyzed under a microscope.

RESULTS

A morphometric analysis revealed that there were significant differences in the intima-media ratio between the 4 groups treated with vehicle (saline) or a low, medium, or high dose of FUT-175 (1.45+/-0.11, 1.08+/-0.06, 0.71+/-0.04, or 0.32+/-0.04, respectively). This suppression was achieved in a dose-dependent manner by the administration of FUT-175 after balloon injury. In the histological study, it was demonstrated that FUT-175 suppresses the production of platelet-derived growth factor (PDGF)-BB in the neointima and the medial smooth muscle cell layer.

CONCLUSIONS

After balloon injury activated proteases that were inhibited by FUT-175 were demonstrated to have an essential role in the development of the pathological thickening of the arterial wall.

Gene transfer of human prostacyclin synthase prevents neointimal formation after carotid balloon injury in rats

BACKGROUND AND PURPOSE

A disordered proliferative process in the vascular wall is thought to underlie the pathogenesis of restenosis after percutaneous transluminal angioplasty and carotid endarterectomy. A growth inhibitory property of overexpressed prostacyclin (PGI2) synthase (PGIS) was recently implicated in the pathological proliferation of vascular smooth muscle cells (VSMC) in vitro. Here, we investigated the effects of increased PGI2 synthesis on the pathological proliferation of VSMCs.

METHODS

The cDNA encoding human PGIS was transfected into endothelium-denuded rat carotid arteries after arterial balloon injury with the use of hemagglutinating virus Japan (HVJ). HVJ liposome vector complex without PGIS cDNA was used for vehicle control. The level of 6-keto PGF1alpha, a stable hydrolyzed metabolite of PGI2, the histological distribution of the immunoreactivity for human PGIS and the ratio of neointimal/medial area were analyzed.

RESULTS

In the analyses of 6-keto PGF1alpha, the level in the carotid arteries was significantly elevated 3 days after PGIS expression-vector transfection compared with that in the arteries after vehicle transfection. Seven days after human PGIS expression-vector transfection, the PGIS cDNA-transfected neointimal cells were strongly positive for human PGIS immunoreactivity in 81% sections examined. Fourteen days after the injury, the ratio of neointimal/medial area was 1.2+/-0.4 in the PGIS expression-vector transfected group, which was significantly smaller than that of the vehicle control group, 1.7+/-0.5; P<0.01.

CONCLUSIONS

It was thus demonstrated that the gene transfer of human PGIS expression-vector into rat carotid arteries resulted in the increased production of human PGI2 in the vascular wall, the expression of human PGIS in the developing neointima and significantly inhibited the neointimal formation generated after balloon injury.

Obstruction stimulates COX-2 expression in bladder smooth muscle cells via increased mechanical stretch

Studies were performed to investigate the regulatory mechanism of bladder cyclooxygenase-2 (COX-2) expression after outlet obstruction. In situ hybridization of murine bladder tissues using COX-2-specific riboprobes demonstrated that COX-2 expression was induced predominantly in the bladder smooth muscle cells after outlet obstruction. To study the effect of increased mechanical stretch on COX isoform expression, cultured rat bladder smooth muscle cells were grown on silicone elastomer-bottomed plates coated with collagen type I and were subjected to continuous cycles of stretch/relaxation for variable duration. COX-1 mRNA levels did not change with stretch. COX-2 expression increased in a time-dependent manner after stretch, with maximal mRNA and protein levels occurring after 4 h. PGE2 levels increased more than 40-fold in the culture media after stretch, consistent with increased COX activity, and this was reduced to near completion in the presence of a COX-2 inhibitor, NS-398. Exposure to stretch over a 48-h period induced a 4.7 +/- 0.6-fold increase in tritiated thymidine incorporation rate. This increase in DNA synthesis was markedly suppressed when the cells were stretched in the presence of NS-398. We conclude that in bladder obstruction COX-2 activation occurs predominantly in the smooth muscle cells in response to mechanical stretch. Our findings also suggest that stretch-activated COX-2 expression may participate in bladder smooth muscle cell proliferation and thereby play a role in pathological bladder wall thickening after obstruction.

Effect of policosanol on intimal thickening in rabbit cuffed carotid artery

We studied the effect of policosanol on smooth muscle cell proliferation in the cuffed carotid artery of the rabbit. Policosanol is a mixture of higher aliphatic primary alcohols isolated from sugar cane wax, with cholesterol lowering effects proved in experimental models and patients with type II hypercholesterolemia. It acts by inhibiting cholesterol biosynthesis. The positioning of a nonocclusive silicone collar around the rabbit carotid artery results in the formation of a neointima. We wished to determine whether policosanol orally administered prevented intimal thickening. Collars were placed around the left carotid for 15 days. The contralateral artery was sham operated. We included three experimental groups: a control received vehicle and two others policosanol at 5 and 25 mg Kg until sacrificed. Samples of arteries were examined by light and electron microscopy. To evaluate intimal thickening the cross-sectional area of intima and media were measured. Neointima was significantly reduced in policosanol-treated animals compared with controls. The smooth muscle cell proliferation was studied by the immunohistochemical detection of proliferating cell nuclear antigen and a significant reduction was observed in policosanol treated rabbits. It is concluded that policosanol has a protective effect on the neointima formation in this experimental model.

Tolerance development to antimitogenic actions of prostacyclin but not of prostaglandin E1 in coronary artery smooth muscle cells

This study compares the antimitogenic effects of iloprost and prostaglandin E1 on platelet-derived growth factor-BB stimulated DNA synthesis ([3H]thymidine incorporation) in bovine coronary artery smooth muscle cells. When added 20-24 h after stimulation with platelet-derived growth factor-BB (20 ng/ml), both iloprost and prostaglandin E1, concentration-dependently (IC50 3-5 nM) inhibited DNA synthesis. However, when added together with the growth factor (0-24 h), the inhibition of DNA synthesis by iloprost was markedly attenuated, indicating tolerance development. In contrast, no tolerance to antimitogenic effects of prostaglandin E1 or forskolin were observed. When added to iloprost-tolerant cells, both prostaglandin E1 and forskolin, still inhibited DNA synthesis. There was no evidence for transcriptional down-regulation of prostacyclin receptor gene by iloprost. The data demonstrate a tolerance development to antimitogenic actions of prostacyclin but not of prostaglandin E1 and suggest that the receptors, mediating the antiproliferative actions of these prostaglandins, may be different.

Serum amyloid A (SAA) protein enhances formation of cyclooxygenase metabolites of activated human monocytes

As serum amyloid A (SAA), an apolipoprotein associated with HDL during the acute-phase reaction may induce Ca2+ mobilization in human monocytes we raised the question whether SAA1 the predominant isoform of human acute-phase SAA is able to alter eicosanoid formation. In resting monocytes SAA1 was without effect on the secretion of cyclooxygenase metabolites while in calcium ionophore A23187- (0.5 and 2.5 microM) stimulated cells SAA1 led to a pronounced dose-dependent increase of TXA2, PGE2, and PGF2alpha. In addition a time-dependent increase of cyclooxygenase metabolites in between 1.5- and 3-fold in the presence of SAA1 was observed; apo A-I, the main HDL-apolipoprotein under non-acute-phase conditions, had no effect. Using sequence-specific anti-human SAA1 peptide (40-63) F(ab)2 fragments we could show that the proposed Ca2+-binding tetrapeptide Gly48-Pro49-Gly50-Gys51 of SAA1 is not responsible for enhanced biosynthesis of cyclooxygenase metabolites. Finally, we could demonstrate that human SAA1 is unable to bind Ca2+-ions, suggesting that SAA1 does not directly enhance eicosanoid biosynthesis via Ca2+ mobilization leading to enhanced phospholipase A2 activity.

Suppression of smooth-muscle alpha-actin expression by platelet-derived growth factor in vascular smooth-muscle cells involves Ras and cytosolic phospholipase A2

Platelet-derived growth factor (PDGF), which is a potent mitogen for vascular smooth-muscle cells (VSMC), also inhibits the expression of specific smooth-muscle proteins, including smooth-muscle alpha-actin (SM-alpha-actin), in these cells. The goal of this study was to identify signalling pathways mediating these distinct effects. In rat aortic VSMC, PDGF caused a rapid activation of Ras and Raf, leading to the activation of mitogen-activated protein kinases (ERKs). Cells stably transfected with constitutively active Ras (H-Ras) expressed low levels of SM-alpha-actin protein. Arginine vasopressin, which stimulated SM-alpha-actin promoter activity in wild-type cells or controls (Neo; transfected with a plasmid lacking an insert), failed to do so in cells transiently expressing H-Ras. The effects of Ras on suppression of SM-alpha-actin expression were not mediated by the Raf/ERK pathway, since cells stably expressing constitutively active Raf (BxB-Raf) had normal levels of SM-alpha-actin protein, and stimulation of SM-alpha-actin promoter activity by vasopressin was unaffected in cells transiently expressing BxB-Raf. Furthermore a specific inhibitor of ERK activation had no effect on SM-alpha-actin expression. Exposure of wild-type VSMC to PDGF, or stable expression of Ras but not Raf, also resulted in constitutive increases in prostaglandin E2 production and cytosolic phospholipase A2 (cPLA2) activity, which was mediated by an increased expression of cPLA2 protein. Transient expression of cPLA2 in wild-type VSMC inhibited the stimulation of SM-alpha-actin promoter activity by vasopressin. These results suggest that PDGF-induced inhibition of SM-alpha-actin expression is mediated through a Ras-dependent/Raf independent pathway involving the induction of cPLA2 and eicosanoid production.

G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 2. Role of protein kinase C-delta in the regulation of eicosanoid production

PGI2 generation by the vessel wall is an agonist for cyclic-AMP-dependent cholesteryl ester hydrolysis. The process of enhanced PGI2 synthesis is stimulated, in part, by G-protein-coupled receptor ligands. Cellular cholesterol enrichment has been hypothesized to alter G-protein-mediated PGI2 synthesis. In the studies reported herein, cells generated PGI2 in response to AlF4-, GTPgammaS, and ATP in a dose-dependent manner. G-protein agonists stimulated eicosanoid production principally by activating phospholipase A2, but not phospholipase C. This is in contrast to PDGF, which stimulated phospholipase A2 and PLCgamma activities. Galphai subunits mediate G-protein agonist-induced PGI2 synthesis, since ATP- and PDGF-induced PGI2 synthesis was inhibited by pertussis toxin. Although cholesterol enrichment reduced arachidonic acid- and PDGF-induced PGI2 synthesis, cholesterol enrichment enhanced PGI2 release in response to AlF4-, GTPgammaS, and ATP. The enhancement of PGI2 release in cholesterol-enriched cells was augmented by mevalonate, which inhibits the ability of cholesterol enrichment to reduce membrane-associated G-protein subunits. Since cholesterol enrichment inhibited PDGF and AlF4--induced MAP kinase activity [Pomerantz, K., Lander, H. M., Summers, B., Robishaw, J. D., Balcueva, E. A., & Hajjar, D. P. (1997) Biochemistry 36, 9523-9531] (the major mechanism by which phospholipase A2 is activated), these results suggest that cholesterol enrichment induces other alternative signaling pathways leading to phospholipase A2 activation. A PKC-dependent pathway is described herein that is involved in enhanced eicosanoid production in cholesterol-enriched cells. This conclusion is supported by two observations: (1) G-protein-linked PGI2 production is inhibited by calphostin, and (2) cholesterol enrichment augments the specific translocation of the delta-isoform of PKC from the cytosol to the plasma membrane following treatment of cells with phorbol ester. These data support the concept that, in cells possessing normal levels of cholesterol, MAP-kinase-dependent pathways mediate eicosanoid synthesis in response to G-protein activation; however, under conditions of high cellular cholesterol levels, augmented G-protein-linked eicosanoid production results from enhanced PKCdelta activity.

Cell-cell interaction between platelets and IL-1 beta-stimulated vascular smooth muscle cells in synthesis of thromboxane A2

Transcellular biosynthesis of thromboxane (Tx) A2 between vascular smooth muscle cells (SMC) and platelets has been investigated by using 14C-arachidonic acid (AA) radiolabeled rat SMC (or platelets) and the fate of the label in phospholipids and eicosanoid fractions was studied using radioimmunoassay (RIA) and thin-layer chromatography (TLC). Stimulation of SMC with interleukin-1 beta (IL-1 beta) resulted in production of cyclooxygenase metabolites (e.g. 6-keto-PGF1 alpha, PGE2, PGF2 alpha, PGD2), 15-, 11-, 5-HETE, and free AA1 with a coincident decline of phosphatidylcholine (PC) in SMC. IL-1 beta did not induce TXB2 production, a stable metabolite of TXA2 measured by TLC and radioimmunoassay, either in human platelets from 0.01-100 U/ml for 1 h or in SMC for 24 h. However, human platelets converted exogenous PGH2 to TXA2 despite cyclooxygenase inhibition or PGH2 receptor blockade. Furthermore, TXB2 was produced in large quantities during co-incubation of IL-1 beta-stimulated SMC with human platelets for 30 min in concert with a significant decrease of 6-keto-PGF1 alpha and eicosanoids (PGE2, PGF2 alpha and PGD2) compared with control (P < 0.01). Pretreatment of SMC with cycloheximide and actinomycin not only inhibited IL-1 beta-induced eicosanoid synthesis and phospholipid breakdown but also diminished TXB2 production when co-incubated with platelets. These data suggest that a cell-cell interaction, i.e. platelet utilizing SMC-derived endoperoxides for its TXA2 production, might cause an excess thromboxane A2 synthesis.

Endothelial cell injury in cardiovascular surgery: the intimal hyperplastic response

Arteries and veins respond to injury by a healing process that includes the development of a neointima. This response to injury is implicated as the primary cause of failure after arterial reconstruction. Because it is an integrator and transmitter of blood flow variations, inflammation, and growth stimuli, the endothelium is a potent regulator of long-term arterial wall mass changes. The contribution of the endothelium to intimal development depends on the type of arterial conduit. In arteries, the growth of the intima stops when the endothelium has regrown. In synthetic grafts, the endothelium stabilizes intimal growth. Hence, the mere presence of endothelial cells can influence intimal changes in arterial conduits. Understanding endothelial biology should help us define methods to prevent cell proliferation, extracellular matrix accumulation, intimal hyperplasia, and vessel narrowing.

Roles of vasodilatory prostaglandins in mitogenesis of vascular smooth muscle cells

Vasodilatory prostaglandins (PGI2, PGE1) and synthetic prostacyclin mimetics inhibit smooth muscle cell proliferation in vitro after stimulation by growth factors. Similar results are obtained in vivo after endothelial injury, suggesting that vasodilatory prostaglandins might also control smooth muscle cell proliferation in vivo. However, available data from clinical trials are conflicting and currently do not support the concept that these compounds might be successfully used to suppress excessive smooth muscle cell growth in response to tissue injury, specifically restenosis after PTCA. One possible explanation for these different results is an agonist-induced down-regulation of prostacyclin receptors in vascular smooth muscle cells. It is possible that enhanced endogenous prostacyclin biosynthesis, subsequent to induction of COX-2 and/or in relation to the formation of a neointima from media smooth muscle cells, might have a similar effect. There is still uncertainty regarding the cellular signal transduction pathways and their possibly complex interaction, although cAMP-dependent reactions are probably involved. In addition, vasodilatory prostaglandins might also interfere with the generation and action of other growth modulating factors, including PDGF, hepatocyte growth factor and nitric oxide. In conclusion, vasodilatory prostaglandins might be considered as growth modulating endogenous mediators in vascular smooth muscle cells.

Identification of vascular endothelial genes differentially responsive to fluid mechanical stimuli: cyclooxygenase-2, manganese superoxide dismutase, and endothelial cell nitric oxide synthase are selectively up-regulated by steady laminar shear stress

Early atherosclerotic lesions develop in a topographical pattern that strongly suggests involvement of hemodynamic forces in their pathogenesis. We hypothesized that certain endothelial genes, which exhibit differential responsiveness to distinct fluid mechanical stimuli, may participate in the atherogenic process by modulating, on a local level within the arterial wall, the effects of systemic risk factors. A differential display strategy using cultured human endothelial cells has identified two genes, manganese superoxide dismutase and cyclooxygenase-2, that exhibit selective and sustained up-regulation by steady laminar shear stress (LSS). Turbulent shear stress, a nonlaminar fluid mechanical stimulus, does not induce these genes. The endothelial form of nitric oxide synthase also demonstrates a similar LSS-selective pattern of induction. Thus, three genes with potential atheroprotective (antioxidant, antithrombotic, and antiadhesive) activities manifest a differential response to distinct fluid mechanical stimuli, providing a possible mechanistic link between endothelial gene expression and early events in atherogenesis. The activities of these and other LSS-responsive genes may have important implications for the pathogenesis and prevention of atherosclerosis.

Prevention of arterial thrombosis by adenovirus-mediated transfer of cyclooxygenase gene

BACKGROUND

Prostacyclin is an important vasoprotective molecule. It inhibits platelet aggregation, monocyte interaction with endothelium, and smooth muscle cell lipid accumulation. Vascular cyclooxygenase-1 (COX-1) is the rate-limiting step in prostacyclin synthesis. The objective of this study was to determine whether adenovirus-mediated transfer of COX-1 could restore COX-1 activity, augment prostacyclin synthesis, and prevent thrombus formation in a porcine carotid angioplasty model.

METHODS AND RESULTS

Human COX-1 cDNA driven by a cytomegalovirus promoter was constructed into a replication-defective adenovirus 5 vector by homologous recombination. Recombinant adenovirus without a foreign gene (Ad-RR) and buffer were included as controls. Recombinant Ad-LacZ was used for marking the transfected cells in vivo. In the in vitro experiments, cultured human endothelial cells (ECs) and porcine arterial smooth muscle cells (SMCs) were incubated with Ad-COX-1 for 2 hours and 6-keto-PGF(1 alpha) level and the transgene expression were determined 72 hours after infection. In the in vivo experiments, recombinant adenoviruses were directly instilled into angioplasty-injured porcine carotid arteries for 30 minutes. Cyclic flow changes were monitored for 10 days and thrombus formation was examined histologically thereafter. Transgene expression and prostaglandin I2 (PGI2) synthesis by the injured arteries were determined. Cultured ECs infected with Ad-COX-1 produced a fivefold to eightfold increase in PGI2, and the transgene expression in cultured porcine SMCs was demonstrated by Northern analysis. Direct administration of Ad-COX-1 at a dose of 3 x 10(10) pfu completely inhibited carotid cyclic flow changes and thrombus formation accompanied by a fourfold increase in PGI2 synthesis by the injured arteries 10 days after infection, whereas Ad-COX-1 at a lower dose, 5 x 10(9) pfu, had no antithrombotic effects when compared with Ad-RR vector and buffer controls.

CONCLUSIONS

Adenovirus-mediated transfer of COX-1 to angioplasty-injured carotid arteries was efficacious in augmenting PGI2 synthesis and was associated with an inhibition of thrombosis when a relatively high titer of adenovirus was instilled.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Induction of cyclooxygenase-2 in human umbilical vein endothelial cells by lysophosphatidylcholine

Lysophosphatidylcholine (lysoPC), a component of atherogenic lipoproteins and atherosclerotic lesions, has been recently suggested to play a role in atherogenesis. LysoPC is known to induce several endothelial genes involved in leukocyte recruitment, mitogenesis, and inflammation. Cyclooxygenases (prostaglandin H2 synthases) are rate-limiting enzymes involved in the endothelial synthesis of prostacyclin, an antiplatelet, vasorelaxant, and vasoprotective molecule. We investigated the effect of lysoPC on the endothelial expression of cyclooxygenases. Our results demonstrate that, in cultured human umbilical vein endothelial cells, lysoPC induces cyclooxygenase-2 mRNA and protein levels. Increased expression of cyclooxygenase-2 is accompanied by the enhancement of both basal- and calcium ionophore A23187-induced synthesis of prostacyclin. Nuclear runoff experiments demonstrated an increased rate of transcription of the cyclooxygenase-2 gene by lysoPC. In contrast, lysoPC did not affect the expression of constitutive cyclooxygenase-1. Our results suggest that the induction of endothelial cyclooxygenase-2 by lysoPC may be an important vasoprotective mechanism that limits progression of atherosclerotic lesions and promotes their regression.

Dietary gamma-linolenic acid modulates macrophage-vascular smooth muscle cell interactions. Evidence for a macrophage-derived soluble factor that downregulates DNA synthesis in smooth muscle cells

Macrophages and smooth muscle cells (SMCs) are two of the major reactive cell types in atherosclerosis, a disease characterized by uncontrolled proliferation of SMCs. The present study was designed to determine how dietary oils containing gamma-linolenic acid (GLA) (primrose oil [PO]) and long-chain n-3 fatty acids (fish oil) influence the ability of macrophages to modulate SMC DNA synthesis in vitro. Mice were fed one of four diets containing 10% (wt/wt) corn oil (CO), PO, fish oil-CO mix (FC; 9:1, wt/wt), or fish oil-PO mix (FP; 1:3, wt/wt) for 2 weeks. Resident peritoneal macrophages were isolated from these mice and seeded on a semipermeable membrane with a 30-kDa cutoff. Macrophages were preincubated with or without 50 mumol/L indomethacin (a cyclooxygenase inhibitor) or 50 mumol/L L655,238 (a 5-lipoxygenase inhibitor) for 30 minutes and subsequently cocultured with naive murine aortic SMCs grown on culture dishes. DNA synthesis in SMCs and prostaglandin formation in coculture supernatants were measured at the end of a 39-hour incubation period. SMC DNA synthesis was inhibited by 28% and 60% in PO and FP diets containing 10.1% and 8.2% GLA, respectively, relative to the control CO diet containing no GLA or long-chain n-3 fatty acid. A fourfold increase in the levels of PGE1, a potent antiproliferative eicosanoid derived from GLA, was observed in the PO and FP groups relative to the control CO group.(ABSTRACT TRUNCATED AT 250 WORDS)

A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

This report is the continuation of two earlier reports that defined human arterial intima and precursors of advanced atherosclerotic lesions in humans. This report describes the characteristic components and pathogenic mechanisms of the various advanced atherosclerotic lesions. These, with the earlier definitions of precursor lesions, led to the histological classification of human atherosclerotic lesions found in the second part of this report. The Committee on Vascular Lesions also attempted to correlate the appearance of lesions noted in clinical imaging studies with histological lesion types and corresponding clinical syndromes. In the histological classification, lesions are designated by Roman numerals, which indicate the usual sequence of lesion progression. The initial (type 1) lesion contains enough atherogenic lipoprotein to elicit an increase in macrophages and formation of scattered macrophage foam cells. As in subsequent lesion types, the changes are more marked in locations of arteries with adaptive intimal thickening. (Adaptive thickenings, which are present at constant locations in everyone from birth, do not obstruct the lumen and represent adaptations to local mechanical forces). Type II lesions consist primarily of layers of macrophage foam cells and lipid-laden smooth muscle cells and include lesions grossly designated as fatty streaks. Type III is the intermediate stage between type II and type IV (atheroma, a lesion that is potentially symptom-producing). In addition to the lipid-laden cells of type II, type III lesions contain scattered collections of extracellular lipid droplets and particles that disrupt the coherence of some intimal smooth muscle cells. This extracellular lipid is the immediate precursor of the larger, confluent, and more disruptive core of extracellular lipid that characterizes type IV lesions. Beginning around the fourth decade of life, lesions that usually have a lipid core may also contain thick layers of fibrous connective tissue (type V lesion) and/or fissure, hematoma, and thrombus (type VI lesion). Some type V lesions are largely calcified (type Vb), and some consist mainly of fibrous connective tissue and little or no accumulated lipid or calcium (type Vc).

A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

This report is the continuation of two earlier reports that defined human arterial intima and precursors of advanced atherosclerotic lesions in humans. This report describes the characteristic components and pathogenic mechanisms of the various advanced atherosclerotic lesions. These, with the earlier definitions of precursor lesions, led to the histological classification of human atherosclerotic lesions found in the second part of this report. The Committee on Vascular Lesions also attempted to correlate the appearance of lesions noted in clinical imaging studies with histological lesion types and corresponding clinical syndromes. In the histological classification, lesions are designated by Roman numerals, which indicate the usual sequence of lesions progression. The initial (type I) lesion contains enough atherogenic lipoprotein to elicit an increase in macrophages and formation of scattered macrophage foam cells. As in subsequent lesion types, the changes are more marked in locations of arteries with adaptive intimal thickening. (Adaptive thickenings, which are present at constant locations in everyone from birth, do not obstruct the lumen and represent adaptations to local mechanical forces). Type II lesions consist primarily of layers of macrophage foam cells and lipid-laden smooth muscle cells and include lesions grossly designated as fatty streaks. Type III is the intermediate stage between type II and type IV (atheroma, a lesion that is potentially symptom-producing). In addition to the lipid-laden cells of type II, type III lesions contain scattered collections of extracellular lipid droplets and particles that disrupt the coherence of some intimal smooth muscle cells. This extracellular lipid is the immediate precursor of the larger, confluent, and more disruptive core of extracellular lipid that characterizes type IV lesions. Beginning around the fourth decade of life, lesions that usually have a lipid core may also contain thick layers of fibrous connective tissue (type V lesion) and/or fissure, hematoma, and thrombus (type VI lesion). Some type V lesions are largely calcified (type Vb), and some consist mainly of fibrous connective tissue and little or no accumulated lipid or calcium (type Vc).

Suppression of pseudointimal hyperplasia by a novel prostacyclin analogue: beraprost

The aim of this study was to evaluate the effect of a novel prostaglandin I2 analogue, beraprost (BPT), on the pseudointimal hyperplasia (PIH) of polytetrafluoroethylene (PTFE) prostheses. A total of 12 rabbits were equally divided into three groups. The control group was given a placebo daily, group 1 was given BPT orally 2 mg/kg per day, and group 2 was given BPT orally 4 mg/kg b.i.d. Exactly 1 cm of the inferior vena cava was resected and replaced by a 3-cm PTFE tube graft. All the grafts were patent when harvested 4 weeks after implantation, but the lumens were narrowed to various extents by PIH. PIH, determined by the dry weight of the intraluminal tissue deposit, was significantly (P < 0.01) suppressed in groups 1 and 2 compared with the control group. High-magnification light microscopy with various staining methods revealed the PIH to be composed mainly of smooth muscle cells (SMCs) and collagen fibrils in all three groups. Transmission electron microscopy revealed that the majority of SMCs in groups 1 and 2 were contractile in form, in contrast with the synthetic form seen in the control group. In conclusion, BPT attenuated the PIH of PTFE grafts by inhibiting the phenotype change in the SMCs.

Signal transduction in atherosclerosis: second messengers and regulation of cellular cholesterol trafficking

The data summarized in this review demonstrate that the regulation of intracellular cholesterol trafficking is mediated not only by extracellular lipoprotein concentrations and transcriptional responses to alterations in intracellular free cholesterol content. Rather, the modulation of cholesterol trafficking is also regulated by the products synthesized following activation of signal transduction pathways originating at the cell surface. Furthermore, we have identified those cell-derived factors which utilize these signal transduction pathways to elicit alterations in cholesterol trafficking, and demonstrated the importance of the generation of second messengers, most notably eicosanoids, and cyclic AMP in promoting a modulatory influence on specific pro-atherogenic effects of mitogens.

Mechanical stretch/relaxation of cultured rat mesangial cells induces protooncogenes and cyclooxygenase

In cultured rat glomerular mesangial cells, continuous cycles of stretching and relaxation (stretch/relaxation) stimulate cell proliferation, protein synthesis, and prostaglandin production. We examined regulation of gene expression that may underlie these alterations in cell functions. Stretch/relaxation caused time-dependent induction of the immediate early genes, c-fos and zif 268/egr-1, with maximal increases occurring between 15 and 30 min. The mitogen-inducible prostaglandin G2/H2 synthase (PGH2S-2) gene was also induced within 30 min of stretch/relaxation, with concomitant increases in the immunoreactive PGH2S-2 protein. These gene inductions were preceded by transient translocation of protein kinase C activity from cytosol to membrane as well as by increases in 45Ca2+ uptake and total cellular calcium content. The stretch/relaxation-induced expression was suppressed by protein kinase C inhibition, whereas less profound inhibition was observed with inhibition of calcium influx in low (100 nM) calcium buffer. These findings indicate that in mesangial cells mechanical stress induces expression of the protooncogenes and the mitogen-inducible cyclooxygenase primarily through protein kinase C-dependent mechanisms.

Adenylate and guanylate cyclase activity in the penis and aorta of the diabetic rat: an in vitro study

OBJECTIVE

To investigate the role of adenylate and guanylate cyclases in the mediation of erection in diabetic rats.

MATERIALS AND METHODS

Hyperglycaemic diabetes mellitus was induced in 35 rats using streptozotocin. Two months later the penises and aortae of these rats were excised and cut into rings or segments before being treated with varying concentrations of acetylcholine (Ach), sodium nitroprusside (NaNP), prostaglandin E1 (PGE1) and adrenaline (AD). The levels of adenosine 3'5'-cyclic monophosphate (cAMP) and guanosine 3'5'-cyclic monophosphate (cGMP) so generated were measured by radioimmunoassay and the results compared with those from seven age-matched control rats that had not been given streptozotocin.

RESULTS

Ach-stimulated cGMP synthesis was impaired in the aortae in diabetic rats. Ach-stimulated cGMP synthesis was undetectable in the penis. NaNP-stimulated cGMP and PGE1-stimulated cAMP synthesis was enhanced in both the penises and aortae in diabetic rats compared with controls. AD-stimulated cAMP synthesis was enhanced in the aorta in diabetic rats compared with controls, but AD had no effect on cAMP synthesis in the penis.

CONCLUSION

Ach-stimulated nitric oxide (NO) synthesis is impaired in the vasculature of diabetic rats and an Ach-NO axis may not be present in the penis of the rat. The enhanced capacity of the penis and vasculature to generate cAMP and cGMP may constitute an adaptive response to counteract the reduction in receptor-linked NO release. Impaired adenylate or guanylate cyclase activity does not contribute to erectile dysfunction in diabetic rats.

Interactions between cultured bovine arterial endothelial and smooth muscle cells; effects of modulated low density lipoproteins on cell proliferation and prostacyclin release

We exposed bovine aortic endothelial cells in culture to native LDL (n-LDL) and LDL modulated by dimethylsulfoxide (DMSO-LDL), dimethylsulfoxide-soluble particles from cigarette smoke (DSP-LDL) or Cu2+ (Cu(2+)-LDL) to explore the hypothesis that these LDL-forms might influence interactions between endothelial and smooth muscle cells. It was shown that 3H-thymidine incorporation into endothelial cells was decreased by DMSO-LDL, DSP-LDL and Cu(2+)-LDL compared to n-LDL, while it was higher by DSP-LDL compared to its control i.e. DMSO-LDL. These effects could be transferred by conditioned medium to smooth muscle cell cultures. DSP-LDL or Cu(2+)-LDL decreased total cellular protein of endothelial cells. Initial (15 min) prostacyclin release from endothelial cells was increased by all LDL preparations compared to medium without LDL, most pronounced for Cu(2+)-LDL. If n-LDL was control, only Cu(2+)-LDL significantly increased the release of prostacyclin during 15 min and during 24 h. The release of prostacyclin assayed after 24 h was depressed by DSP-LDL compared to DMSO-LDL. This study demonstrated that interactions between endothelial and smooth muscle cells could be influenced by LDL treated by dimethylsulfoxide-soluble particles from cigarette smoke or by Cu2+, and their effects were not similar. DSP-LDL, in contrast to Cu(2+)-LDL, significantly decreased the release of prostacyclin by endothelial cells after 24 h incubations and via endothelial cell conditioned medium stimulated smooth muscle cell proliferation judged by increased 3H-thymidine incorporation. The results might be of relevance for atherogenesis.