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

Lipid biosynthesis in cultured arterial smooth muscle cells is related to their phenotype

During the atherogenic process in vivo, arterial smooth muscle cells (SMC) undergo changes in their phenotype. In the present study, rat SMC from primary cultures and from subcultures before 10 and after 200 passages, showing contractile-like, synthetic and transformed phenotypes, respectively, were compared in regard to their lipid content and biosynthesis. The rationale for comparing these phenotypes rests in the similar changes in phenotype of SMC that occur in the formation and progression of atherosclerotic lesions. Phenotype changes were shown to be associated with changes in the phospholipid content of SMC. Phospholipid levels increased, but not as significantly as did cholesterol levels when passing from contractile to synthetic and transformed cells (1.23 +/- 0.18, 2.28 +/- 0.26 and 3.25 +/- 0.23 micrograms/10(6) cells, respectively). Cholesterol normalized in respect to cell protein was increased to the same extent. Lipid synthesis as judged by [14C]acetate incorporation was increased 3- to 12-fold in the synthetic and transformed cells, respectively, compared to contractile cells. After thin-layer chromatography, radioactivity was shown to be markedly increased in most of the lipid fractions, but label in the cholesterol fraction of synthetic and transformed cells was increased by 7- and 21-fold, respectively. Thus, SMC in vitro were shown to drastically increase cholesterol biosynthesis associated with phenotype changes. Such changes are known to occur in vivo and might represent a critical step in the deposition of excess cholesterol within foam cells.

Interactions between the monocyte/macrophage and the vascular smooth muscle cell. Stimulation of mitogenesis by a soluble factor and of prostanoid synthesis by cell-cell contact

The effect of soluble factors from the monocyte/macrophage (M phi) on cell proliferation and the functional effects of cell-cell contact on the arachidonic acid (AA) cascade were studied with vascular smooth muscle cells (SMCs). Peripheral blood M phi s were isolated by adherence or in a Percoll gradient, and alveolar M phi s were obtained by lavage. Conditioned medium (CM) was prepared by preincubating M phi s with medium alone or by separating SMC and M phi cocultures by a membrane insert. Cell proliferation (image analysis) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha, radioimmunoassay) were measured in SMCs. Labeled prostanoids and other eicosanoid metabolites were isolated by high-performance liquid chromatography from SMCs prelabeled with 14C-AA. M phi s did not synthesize 6-keto-PGF1 alpha. The CM enhanced proliferation but did not stimulate 6-keto-PGF1 alpha synthesis in SMCs. However, cell-cell contact in cocultures of SMCs with the same concentration of M phi s used to generate CM resulted in increased 6-keto-PGF1 alpha synthesis by SMCs. Since the stimulatory effect of cell contact was not blocked by butylated hydroxytoluene, it could not be attributed to an oxidative burst from M phi s. Functional studies showed that the stimulatory effect of cell contact was enhanced by exogenous free AA and by endogenous AA release through A23187. Release of total radioactivity from prelabeled SMCs was enhanced by cell contact, and this effect was blocked by indomethacin (IM). Cell contact did not increase the release of free AA from prelabeled SMCs, even in the presence of IM. Finally, cell contact only stimulated the formation of prostanoids (IM-sensitive eicosanoid metabolites) from prelabeled SMCs. Lipoxygenase and other products of AA were not formed through cell-cell contact. These data showed that M phi s express a soluble factor that enhances SMC proliferation without affecting prostanoid synthesis. Subsequent cell contact between SMCs and M phi s stimulates prostanoid synthesis, which may possibly serve as a local and focal homeostatic mechanism for the regulation of uncontrolled SMC proliferation in atherogenesis.

Smooth muscle cells and the pathogenesis of the lesions of atherosclerosis

In this review we have tried to identify the characteristic features of SMCs in developing lesions of atherosclerosis and the extracellular factors that may be involved in regulating these altered features. Though the list seems long and complex there is probably a great deal of interplay among the different regulatory mechanisms. The function and activities of SMCs in the artery are dependent on the milieu created by the surrounding cells and the components of the extracellular matrix. In the normal, uninjured media of the artery, SMC phenotype and function seem to be in large part determined by the extracellular matrix in which they are embedded and by diffusible factors, in particular from endothelial cells. Endothelial cell injury, infiltration of monocytes and lymphocytes, and ultimately, thrombosis and platelet release, as seen in developing lesions of atherosclerosis, dramatically alter the balance of growth-regulatory and vasoactive factors present in the local environment. These extracellular factors (table and figure) can alter both SMC phenotype, and thus responsiveness, and SMC migration, proliferation, and synthesis of the extracellular matrix. A better understanding of how specific factors mediate these responses, should make it possible to determine the ways in which the SMC response can be modulated. Though growth regulatory molecules seem to be key to this process, the challenge for the future is to understand their regulation in the environment of the artery wall and the interplay between growth-regulatory molecules, extracellular matrix, and vasoactive agents.

Role of cholesterol-accumulating macrophages on vascular smooth muscle cell proliferation

The proliferation of vascular smooth muscle cells (VSMC) was stimulated by co-incubation with macrophages. Further stimulation was observed when co-incubated macrophages were supplied with LDL or cholesterol. However, the stimulation of VSMC proliferation did not result from co-incubation with macrophages supplemented with acetylated LDL or delipidated LDL. The addition of anti-PDGF antibody partially abolished the stimulation of VSMC proliferation induced by co-incubation with macrophages supplemented with LDL or cholesterol. A high concentration of prostaglandin E2 inhibited the proliferation of VSMC stimulated by PDGF and plasma-derived serum when they were at the G0/G1 stage. However, the inhibitory effect of prostaglandin E2 on proliferation was not observed when cells were incubated with macrophages supplemented with LDL or cholesterol in spite of the promotion under these conditions of prostaglandin E2 production. These results suggest that cholesterol-accumulating macrophages may exert a regulatory effect on the proliferation of VSMC through the synthesis and secretion of platelet-derived growth factor (PDGF) and prostaglandin E2, besides foam-cell formation.

The influence of fish oil supplementation on plasma lipoproteins and arterial lipids in vervet monkeys with established atherosclerosis

There is controversy about whether supplementing diets with marine fish oil can regress, promote or prevent atherosclerosis. Therefore the effects of an Atlantic pilchard oil (FO) supplement and dietary change were measured in a proven atherosclerosis model. Vervet or African Green monkeys were fed an atherogenic diet (AD) for long enough to ensure progression before treatments started. Matched groups were then treated for 20 months, either by adding FO to the AD (AD/FO), or by changing to a therapeutic diet with FO (TD/FO). Control treatments consisted of supplementing with sunflower oil (SO) instead of FO, so that treatments were AD/SO and TD/SO. The same total polyunsaturates were supplied by the FO and SO and the dose of FO was realistic (2.5% of total energy). A reference group (R) received the TD with no oil supplements. Supplementing with FO did not change the concentrations of total, low or high density lipoprotein cholesterol in plasma. After The AD/FO the intimas of aortas contained more total (p < or = 0.001), free (p < or = 0.05) and esterified (p < or = 0.05) cholesterol, total phospholipid (p < or = 0.01) and sphingomyelin (p < or = 0.05) than after the AD/SO. After FO supplementation eicosapentaenoic acid was significantly higher and arachidonic acid significantly lower in the plasma and aorta intima phosphatidylcholine. None of these changes was anti-atherogenic in terms of atherosclerosis measured in the same individuals (1). Nor did FO increase the efficacy of the TD.

Modulation of prostacyclin production by cytokines in vascular endothelial cells

The data presented in this review clearly show that many different cytokines regulate the synthesis of PGI2 in vascular EC (Tables 1 & 2). Since these agents are synthesized, stored, and/or released from platelets, leukocytes and cells present in the vascular wall (Fig.), they are to be found at sites of vascular injury and may, through their effect on the synthesis of PGI2 and other prostanoids, regulate thrombogenesis and atherogenesis. Despite the mass of detailed data, the picture is still fragmentary. Very little, for instance, is known about the 'orchestral effects' of different combinations of cytokines. In addition, it seems that the regulation of PGI2 synthesis by cytokines varies with the species and with the type of vasculature from which the cells originated. However, discrepancies may also be due to the use of different culture conditions. Moreover, we must remember that the present data are almost exclusively from in vitro studies, and the representativeness of these results in in vivo situations remains to be clarified.

Effect of dietary supplementation with n-3 polyunsaturated fatty acids on physical properties and metabolism of low density lipoprotein in humans

The effects of marine n-3 polyunsaturated fatty acids were investigated in relation to the chemical and physical properties of low density lipoprotein (LDL) and how these changes affected LDL metabolism in humans. The subjects received supplements of six capsules daily, each capsule containing 1 g of either highly concentrated ethyl esters of n-3 fatty acids (85% eicosapentaenoic acid and docosahexaenoic acid) (n = 12) or corn oil (56% linoleic and 26% oleic acid) (n = 11). After 4 months of oil supplementation, the following changes were observed in the lipid moiety of the n-3-enriched LDL particles compared with LDL from the corn oil group: LDL cholesteryl ester, as well as the amount of total lipids of LDL, was significantly lower (0.97 +/- 0.12 versus 1.19 +/- 0.23 mg/mg protein and 1.88 +/- 0.40 versus 2.45 +/- 0.31 mg/mg, respectively; mean +/- SD, n = 6, p less than 0.05); the amount of eicosapentaenoic and docosahexaenoic acids and the unsaturation index increased (104.0 versus 29.4 micrograms/mg protein and 6.64 versus 5.49, respectively); and differential scanning calorimetry showed that LDL cholesteryl ester melting temperature was lowered by 2 degrees C (27.6 +/- 0.8 degrees versus 29.5 +/- 0.2 degrees C). The only effect observed on the protein moiety was an increase in the ratio of apolipoprotein (apo) B to cholesterol (0.66 +/- 0.17 versus 0.82 +/- 0.14 mg/mg cholesterol; p less than 0.05). Circular dichroism spectra of LDL indicated an alpha-helix content of 46 +/- 5% in apo B from both groups. No difference was observed by 13C nuclear magnetic resonance spectroscopy in the ratio of "active" to "normal" lysine residues of apo B. No detectable differences in the size of n-3 fatty acid-enriched LDL particles versus control LDL could be measured by either electron microscopy of negatively stained LDL (24.5 +/- 2.0 versus 25.0 +/- 1.5 nm) or dynamic light scattering (24.9 +/- 0.9 versus 24.9 +/- 0.4 nm). LDL from the fish oil and corn oil groups showed similar susceptibility to Cu(2+)-catalyzed lipid peroxidation, as indicated by the amount of lipid peroxides formed during the oxidation time, and degradation of oxidatively modified LDL in J774 macrophages as a function of Cu2+ oxidation time. No effect of n-3 fatty acids was observed on LDL metabolism. Specific uptake and degradation of n-3 fatty acid-enriched LDL were similar to those for control LDL in HepG2 cells as well as in human skin fibroblasts, and they showed the same ability to stimulate cholesteryl ester synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of ethanol on low density lipoprotein and platelet composition

The present study was designed to investigate the effect of ethanol (EtOH) dose on low density lipoprotein (LDL) and platelet composition. Male squirrel monkeys were divided into three groups designated Control, Low, and High EtOH, and fed isocaloric liquid diets containing 0%, 12%, and 24% of calories as EtOH, respectively. After four months of treatment, monkeys fed the 12% alcohol dose had LDL and platelet cholesterol concentrations similar to Controls. By contrast, platelet membranes from High EtOH animals contained significantly more cholesterol which was associated with higher levels of plasma LDL cholesterol and apolipoprotein B. Blood platelet count, size, and mass were similar for all groups and circulating platelet aggregates were absent in the two alcohol cohorts. Despite elevations in platelet cholesterol mass and thromboxane A2 (TXA2) precursor, phospholipid arachidonate, platelet responsiveness, measured as thromboxane formed in response to a collagen challenge in vitro, and the cholesterol/phospholipid molar ratio, were not significantly altered by high dose alcohol. Normal platelet activity in High EtOH monkeys may have resulted from a significant increase in the platelet phospholipid polyunsaturated/saturated fatty acid ratio and a non-significant increase in platelet phospholipid mass, both of which would have a fluidizing effect on platelet membranes. Our data indicate that low EtOH intake has no effect on platelet composition and function while unfavorable platelet cholesterol enrichment following consumption of high dose ethanol may arise from elevations in plasma LDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular free calcium concentration and thromboxane A2 formation of vascular smooth muscle cells are influenced by fish oil and n-3 eicosapentaenoic acid

The effect of fish oil and n-3 eicosapentaenoic acid (EPA) on intracellular free calcium concentration ([Ca2+]i) and thromboxane B2 (TXB2) formation in resting and stimulated cultured rat vascular smooth muscle cells (VSMC) was examined. In resting control cells [Ca2+]i was 147 +/- 15 nmol l-1 (mean +/- SEM, n = 4). After pretreatment of the cells with fish oil or EPA for 24 days the resting [Ca2+]i was decreased to 126 +/- 10 nmol l-1 and 84 +/- 8 nmol-1, respectively. After stimulation of untreated control cells with either 100 nmol l-1 angiotensin II (AII), 40 micrograms ml-1 low-density lipoprotein (LDL), or 100 ng ml-1 of recombinant platelet-derived growth factor (PDGFAB), [Ca2+]i was (in nmol l-1) 306 +/- 31, 217 +/- 25 and 213 +/- 16. Treatment of cells with fish oil or EPA reduced the stimulatory effect of the agonists, and the following [Ca2+]i values (in nmol l-1) were found: 199 +/- 21, 131 +/- 10, 148 +/- 13; and 175 +/- 11, 98 +/- 12, and 103 +/- 6, respectively. PDGFAB induced a four fold increase in TXB2-generation (270 +/- 28 pg mg-1 cell protein compared with 61 +/- 8.2 pg mg-1 in unstimulated control cells) within 6 min. In cells pretreated with fish oil or EPA, TXB2-formation was reduced by 54% and 44%, respectively.

IN CONCLUSION

in rat VSMC stimulated by a variety of vasoactive agonist, fish oil and EPA can markedly attenuate intracellular mechanisms related to changes of cytosolic calcium concentration and eicosanoid production.(ABSTRACT TRUNCATED AT 250 WORDS)

Reductions in serum thromboxane, prostacyclin, and leukotriene B4 levels in swine fed a fish oil supplement to an atherogenic diet

We have reported previously that fish oil rich in omega-3 fatty acids added to a butter-cholesterol atherogenic diet for swine resulted in marked retardation of the atherosclerotic process which many regard as largely an inflammatory response to injury by excessive lipids in the intima. In this report on the same swine we present serum levels of several eicosanoids derived from arachidonic acid via the cyclooxygenase and lipoxygenase pathways. The study involves six swine fed a high fat, high cholesterol diet (BT group) for 4 months, six swine fed the same diet but with 30 ml/day fish oil added (BT + FO), and five swine fed a low fat, low cholesterol mash diet (MA). The serum eicosanoids were measured by radioimmunoassay. Thromboxane B2 levels (ng/dl: means +/- SEM) were 543 +/- 49 for MA, 231 +/- 12 for BT, and 105 +/- 20 for BT + FO, and all differences were statistically highly significant, 6-Keto PGF1 alpha (a relatively stable prostacyclin metabolite) levels were 249 +/- 31 for MA, 184 +/- 12 for BT, and 101 +/- 10 for BT + FO, and all differences were significant. Leukotriene B4 levels at 4 months were 151 +/- 25 for MA, 112 +/- 11 for BT, and 84 +/- 11 for BT + FO. BT + FO was significantly different from both MA and BT, but BT was not significantly different from MA. Leukotriene C4 levels were not significantly different among the three groups. Of special interest was the effect of the BT diet without the FO additive in reducing several eicosanoid levels compared to MA values. The affected eicosanoid levels were reduced still further by the fish oil additive, indicating its ability to inhibit both the cyclooxygenase and the lipoxygenase pathways. The relation of the fish oil-induced inhibition to the observed retardation of atherogenesis is not as yet clear but there are several theoretical possibilities, including reduction in recruitment of monocytes and in proliferation of smooth muscle cells.

Comparison of effects of fish oil and corn oil supplements on hyperlipidemic diet induced atherogenesis in swine

The addition of a fish oil supplement rich in n - 3 unsaturated fatty acids to a high cholesterol, high saturated fat (BT) diet for swine has been shown previously to result in modest lowering of plasma cholesterol levels and in marked retardation of atherogenesis. It has been suggested that the effect was due to the change in polyunsaturated (PUFA) to saturated fatty acid ratios (P/S) and that a supplement of PUFA of the n - 6 series might have the same effect as the fish oil. We have tested this hypothesis in swine fed an atherogenic diet by comparing the effect of a fish oil supplement producing a P/S ratio of 0.28 to that of corn oil in the same amount producing a ratio of 0.46. The P/S ratio of the atherogenic diet without supplements was 0.16. Thirteen young male Yorkshire swine were fed either BT alone (n = 4), BT + cod liver oil (n = 4) or BT + corn oil (n = 5) for 6 months and then killed for quantitative studies of atherosclerosis in the aortas and coronary arteries including lesion areas, number of lesion cells, and number of monocytes attached to endothelium. Plasma cholesterol levels were determined periodically and lipoproteins were separated terminally by density gradient ultracentrifugation, Pevikon block electrophoresis and immunoelectrophoresis. The fish oil supplement resulted in a 30% reduction in time-weighted average plasma cholesterol levels, and a marked shift in terminal lipoprotein patterns from predominantly apo B and E containing ones to predominantly apo B only ones. Atherogenesis was reduced by the fish oil supplement as judged by several morphometric criteria including size of lesions, number of lesion cells, and number of monocytes attached to lesion endothelium. The corn oil supplement produced no significant reductions in any of these variables from those in swine fed the atherogenic BT diet without the supplement. We conclude that the n - 3 fatty acid rich fish oil supplemented diet retarded atherogenesis, but that this effect was not shared by the corn oil supplemented diet which had an even higher P/S ratio.

Effect of fish oil supplementation on the excretion of the major metabolite of prostaglandin E in healthy male subjects

We investigated the effect of fish oil supplementation on the synthesis of prostaglandin E (PGE) in vivo by measuring the excretion of its catabolite, PGE-M, in 24-hr urine by gas chromatography/mass spectrometry. Forty healthy male volunteers (24-57 years of age) consumed a controlled basal diet providing 40% of energy from fat (P/S ratio about 0.8:1), 130 mg/1000 kcal cholesterol, and a minimum of 22 mg/day of alpha-tocopherol (alpha-T), for three experimental periods lasting a total of 28 weeks. During period 1 (10 weeks) the diet was supplemented with placebo (PO) capsules (15 X 1 g/day) consisting of a blend of fats approaching the fatty acid profile of the basal diet. This was followed by a second 10-week period during which the subjects received 15 X 1 g/day capsules of fish oil concentrate (FOC). During period 3 (8 weeks) they continued the 15 g/day intake of FOC but received an additional 200 mg/day of alpha-T. PO and FOC capsules contained 1 mg alpha-T/g fat as antioxidant. A 14% reduction of PGE-M excretion was observed after 10 weeks of FOC supplementation (period 2), compared to an identical period of placebo supplementation (period 1), P = 0.009. PGE-M excretion during the last week of period 3 was not significantly different from that at the end of period 2. The reduction in PGE synthesis in response to the relatively high marine oil supplementation was large in many subjects participating in this study.

Native low-density lipoproteins stimulate leukotriene B4 production by human monocyte-derived macrophages

We have evaluated the effect of native low-density lipoproteins (LDL) on the production of leukotriene B4 (LTB4), a potent inflammatory and chemotactic factor, by human monocyte-derived macrophages. The capacity of LDL (d, 1.024-1.050 g/ml) to increase LTB4 secretion was dose-dependent with an optimal response at 100 micrograms LDL protein/ml, representing an approx. 7.5-fold stimulation over basal levels at 10 days of culture; the half-maximal response occurred at 20 micrograms/ml. The effect of LDL on LTB4 production was rapid (within 15 min) and was maintained for at least 21 h. The generation of LTB4 in response to LDL was partially inhibited (approx. 70% inhibition) by EDTA (5 mM) and by a monoclonal antibody (IgG-C7; 160 micrograms/ml) directed against the binding site of the cellular LDL receptor. In addition, the effects of native LDL and acetylated LDL were additive. These findings suggest that the specific interaction of LDL with its high affinity receptor represents a major component in the stimulation of the production of LTB4 by human monocyte-derived macrophages.

Cellular processes in atherogenesis: potential targets of Ca2+ channel blockers

Atherosclerosis is characterized by increased endothelial permeability, monocyte infiltration, intimal smooth muscle cell (SMC) proliferation, platelet aggregation and the accumulation of lipids, calcium and extracellular matrix components in the vessel wall. In various animal studies and recently in humans it could be established that Ca2+ channel blockers delayed the progression of the atherosclerotic process at the stage of early lesions. This review surveys the interaction of Ca2+ channel blockers with various membrane proteins (purinergic receptors, nucleoside transporter, peripheral benzodiazepine receptors, multi-drug resistance protein) which are involved in signal transduction and their potential impact on the observed antiatherosclerotic effects. Although the precise mechanisms have yet to be fully elucidated, it has been clearly shown that these drugs inhibit smooth muscle cell proliferation and migration, improve cellular lipoprotein metabolism in vascular cells, alter phospholipid turnover, decrease platelet adhesion in the vessel wall, reduce extracellular matrix synthesis and protect against radical induced cell damage. Most of these effects are independent of Ca2+ flux across voltage-operated Ca2+ channels. However, all these processes are relevant to the pathogenesis of atherosclerosis and therefore the elucidation of the antiatherogenic mechanisms of Ca2+ channel blockers at the cellular level is of great interest. The future development of Ca2+ channel blockers with altered molecular structures optimized for their antiatherosclerotic targets may provide a useful tool in the therapy of atherosclerosis and risk factor intervention. The protective mechanisms are related to a stabilization of cell membrane integrity, the modulation of secretory activities and cell/cell communication processes rather than to a lowering of plasma lipoprotein levels.

Colchicine and antineoplastic therapy for the prevention of restenosis after percutaneous coronary interventions

The complexity of the events that culminate in intimal proliferation after arterial injury and similarities between this response and benign neoplasia suggest that conventional medical therapies will continue to be unsuccessful in preventing recurrent stenosis after percutaneous coronary revascularization. By preventing cell division after smooth muscle cell activation, antimitogenic therapy may inhibit the final common pathway in this complex chain of events and offset the apparent loss of local growth control. Colchicine, which causes metaphase arrest of cell division, has been shown in experimental studies to decrease the extent of atheromatous plaque formation and reduce the severity of arterial restenosis after balloon angioplasty. However, preliminary results from a randomized placebo-controlled clinical trial suggest that low dose colchicine (0.6 mg twice a day orally) does not prevent restenosis. The use of more potent antineoplastic agents is limited by the potential for life-threatening side effects. It is possible that these adverse effects can be averted by using novel drug delivery systems to administer antimitogenic therapy locally at the site of arterial injury or by using low dose synergistic combinations of antiproliferative agents. This review examines the potential role of antimitogenic therapy in the prevention of restenosis after coronary interventions and considers the possibility of an overlap of the therapeutic realms of interventional cardiology and medical oncology.

U-61,431F, a stable prostacyclin analogue, inhibits the proliferation of bovine vascular smooth muscle cells with little antiproliferative effect on endothelial cells

The effects of U-61,431F, ciprostene, a stable prostacyclin analogue, were examined on the proliferation of cultured quiescent bovine aortic endothelial cells (EC) and smooth muscle cells (SMC). After stimulation with 5% fetal calf serum, U-61,431F suppressed both the DNA synthesis and proliferation of SMC dose-dependently at the concentration of 3-100 microM, but had no effect on either of them in EC at a concentration of up to 30 microM. The inhibitory effect on DNA synthesis was greater in SMC than in EC at 3-50 microM. When SMC were stimulated with platelet-derived growth factor (PDGF) for 2 hrs followed by a 22-hr incubation with insulin, U-61,431F (1-50 microM) administered at the time of PDGF stimulation did not inhibit DNA synthesis. SMC initiated and terminated DNA synthesis at about 15-18 h and 24 h after stimulation with serum, respectively. Inhibition of DNA synthesis in serum-stimulated SMC as a function of the addition time of U-61,431F reduced at 3-12 h after the stimulation. U-61,431F raised the cyclic AMP (cAMP) content in SMC. Moreover, a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, and a more specific cAMP phosphodiesterase inhibitor, Ro 20-1724, augmented the inhibition of DNA synthesis in SMC concomitant with further elevation of cAMP level. These results suggest that U-61,431F inhibits DNA synthesis of SMC acting in the progression stage rather than in the competence stage, with little antiproliferative effect on EC. cAMP may play an important role in its antiproliferative action in SMC.

Evaluation of a prostacyclin analog, iloprost, and a thromboxane A2 receptor antagonist, daltroban, in experimental intimal hyperplasia

This study evaluated the efficacy of a prostacyclin analog, iloprost, and a thromboxane A2 receptor antagonist, daltroban, as inhibitors of experimental intimal hyperplasia. The vascular injury model used is based on an endothelial injury induced by a brief infusion of air into an isolated segment of the common carotid artery in the rat. Iloprost and daltroban were administered by continuous IV infusion for two weeks. The infusion rates were 0.1 micrograms/kg/min for iloprost and 0.1 mg/kg/hr for daltroban; these dosing rates are associated with significant alterations in eicosanoid-related pharmacologic effects. The animals were sacrificed at two weeks and the carotid arteries fixed in situ for light microscopy. The myointimal thickening was measured as the intima to media area (I/M) ratio. The control animals developed marked intimal thickening, with an I/M ratio of 0.76 +/- 0.12 (mean +/- SEM; N = 7). There was no inhibition of intimal hyperplasia (P greater than 0.05) after either iloprost (I/M ratio: 1.04 +/- 0.13; N = 8) or daltroban (I/M ratio: 0.70 +/- 0.04; N = 6). It is concluded that neither of these two modulators of eicosanoid activity, iloprost and daltroban, inhibit intimal hyperplasia following experimental endothelial injury.

Cyclosporine A inhibits induction of DNA synthesis by PDGF and other peptide mitogens in cultured rat aortic smooth muscle cells and dermal fibroblasts

The immunosuppressive drug cyclosporine A was recently shown to inhibit smooth muscle proliferation in the vascular response to injury. To examine if this may be due to a direct effect of the drug on the smooth muscle cells (SMCs), we have studied its influence on the phenotypic modulation of rat aortic SMCs in primary cultures and on the induction of DNA synthesis by peptide mitogens in serum-starved subcultures. The results demonstrate that cyclosporine A does not interfere with the transition of the SMCs from a contractile to a synthetic phenotype, an early step in the preparation for cell division. On the other hand, it inhibits induction of DNA synthesis by recombinant platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and insulin-like growth factor-I (IGF-I). Maximum effect was obtained at a concentration of 1-3 micrograms/ml and the drug could be added 4-6 h after the growth factors with full inhibitory effect. No distinct effect on the stimulation of overall RNA and protein synthesis by PDGF-BB was observed, indicating that the drug was not of general cytotoxicity at the concentrations used. Throughout this part of the investigation, similar results were obtained with rat dermal fibroblasts. The findings indicate that cyclosporine A inhibits induction of DNA synthesis by peptide mitogens, and suggest that the inhibitory effect of cyclosporine A on smooth muscle proliferation in vivo at least in part may be due to a direct action on these cells.

Effect of growth factors on human vascular endothelial cell prostacyclin production

Prostacyclin (PGI2) is an antithrombotic factor, which may prevent the initiation and the complications of arteriosclerosis. The most important site of PGI2 production is the vascular endothelium, but little is known about how this process is regulated. In this connection, there is special interest in the roles of various growth factors released from platelets, macrophages, vascular smooth muscle cells, and the endothelial cells themselves. We investigated the effects of transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), and acidic and basic fibroblast growth factors (aFGF and bFGF) on the PGI2 production of cultured human umbilical vein endothelial cells by measuring the stable metabolite of PGI2, 6-keto-prostaglandin F1 alpha, by radioimmunoassay. TGF-beta induced dose- and time-dependent stimulation of PGI2 production. The lowest stimulatory concentration of TGF-beta was 0.1 ng/ml, and the maximal response, a 2.1-fold rise, was obtained with 1.0 ng/ml. The effect of TGF-beta lasted 48 hours and was blocked by inhibitors of transcription, translation, and cyclooxygenase. Maximal stimulation by TGF-beta was enhanced by epidermal growth factor. PDGF and bFGF had no effect on PGI2 production, but aFGF inhibited it. This is the first demonstration that TGF-beta enhances PGI2 production by human vascular cells, and this phenomenon may be part of negative feedback mechanisms that prevent thrombosis and arteriosclerosis.

Prostaglandin I2 half-life regulated by high density lipoprotein is decreased in acute myocardial infarction and unstable angina pectoris

To investigate the prostaglandin I2 (PGI2) half-life regulated by high density lipoprotein (HDL) in patients with coronary artery disease (CAD), we determined the stability of PGI2 and serum apolipoprotein A-I (Apo A-I) and apolipoprotein A-II (Apo A-II) levels in four age-matched groups of patients: controls (n = 17), angina pectoris (n = 18), unstable angina pectoris (n = 17), myocardial infarction (n = 19) (acute phase, 3.6 +/- 1.7 hours from onset; subacute phase, 75 +/- 15 hours from onset in the same patients). Serum PGI2 half-life and total serum Apo A-I levels were lower in the CAD group than in the control group. PGI2 was least stable in patients with unstable angina and the acute phase of myocardial infarction. In these patients, the molar ratio of Apo A-I to Apo A-II and HDL-associated Apo A-I levels were decreased, and free Apo A-I levels were increased. After in vitro incubation of HDL with increasing amounts of Apo A-II, Apo A-I in HDL was displaced by Apo A-II, with the parallel decrease in stability of PGI2. Free Apo A-I cannot stabilize PGI2. HDL-associated Apo A-I, whose amount is affected by Apo A-II, stabilized PGI2 and correlated well with stability of PGI2 in patients with CAD and control patients. Decreased PGI2 half-life may play an important role in the pathogenesis of atherosclerosis and thrombus formation in the coronary arteries, especially thrombus formation during an acute coronary event.

Group II phospholipase A2 mRNA synthesis is stimulated by two distinct mechanisms in rat vascular smooth muscle cells

Two potent inflammatory mediators, interleukin 1 (IL-1) and tumor necrosis factor (TNF) as well as lipopolysaccharide (LPS) increased group II phospholipase A2 (PLA2) mRNA levels, which resulted in enhanced secretion of the PLA2 enzyme from rat smooth muscle cells. cAMP-elevating agents also stimulated the release of PLA2 and increased the mRNA, but IL-1, TNF and LPS did not affect cAMP levels. Furthermore, the effects of TNF and cAMP-elevating agents were not additive but synergistic. Therefore, we concluded that the level of rat group II PLA2 mRNA is controlled at least by two distinct mechanisms, one involves cAMP and the other is mediated by TNF, IL-1 and LPS. This study also suggests important roles of group II PLA2 in pathogenesis of vascular inflammation.

Stimulation of a neutral cholesteryl ester hydrolase by cAMP system in P388D1 macrophages

Cholesteryl ester laden foam cells in atherosclerotic lesions derive, in part, from macrophages. Mobilization of stored cholesteryl esters involves hydrolysis by a neutral cholesteryl ester hydrolase. Incubation of intact P388D1 macrophages with dibutyryl cAMP in the presence of 1-methyl-3-isobutylxanthine resulted in a dose-dependent increase in neutral cholesteryl ester hydrolase activity of up to 50% (ED50 = 0.1 mM). Incubation with prostaglandin E1 in the presence of 1-methyl-3-isobutylxanthine also increased neutral cholesterol ester hydrolase activity by about 50%. In cell-free preparation, cAMP-dependent protein kinase caused about a 2-fold activation of the neutral cholesteryl ester hydrolase. Activation was blocked by protein kinase inhibitor. These data suggest that the P388D1 macrophage may be a useful model for studying the hormonal regulation of cholesteryl ester mobilization in macrophage-derived foam cells.