Action of an HMG CoA reductase inhibitor, lovastatin, on apoptosis of untransformed and ts-SV40 transformed human smooth muscle cells derived from saphenous vein

Calcium channel regulation in vascular smooth muscle cells: synergistic effects of statins and calcium channel blockers

In the Anglo-Scandinavian Cardiac Outcomes Trial-Lipid Lowering Arm (ASCOT-LLA) we have reported a positive interaction between atorvastatin and amlodipine-based antihypertensive strategy in terms of the prevention of coronary events. In cellular and molecular studies on human vascular smooth muscle cells (VSMC) we have reported that transformation from a differentiated to a synthetic or dedifferentiated phenotype is associated with loss of function of L-type calcium channels and hence loss of potential responsiveness to calcium channel blockers (CCB). Statins directly inhibit cell cycle progression and dedifferentiation of VSMC due to their ability to inhibit the synthesis of isoprenoid cholesterol intermediates. We hypothesize that statins promote a more differentiated VSMC phenotype that results in upregulation of L-type calcium channels and restoration of a CCB-sensitive calcium influx pathway in VSMC, favourably affecting the balance that exists between VSMC proliferation, apoptosis and matrix metalloproteinase production with an associated increase in stability of atheromatous plaques.

Ezetimibe is an inhibitor of tumor angiogenesis

Epidemiological and preclinical observations have suggested a role for one or more products of the mevalonate/cholesterol biosynthesis pathway in the progression of prostate cancer. In this study, we used ezetimibe (Zetia), a specific, FDA-approved, cholesterol uptake-blocking drug, in combination with either a hyper- or hypocholesterolemic diet, to show that elevated circulating cholesterol levels promote, whereas a reduction in circulating cholesterol levels retard, the growth of human prostate cancer xenograft tumors in mice. Circulating cholesterol levels also modified tumor angiogenesis; higher cholesterol levels increased microvessel density and other indicators of vascularity. Consistent with these data, the reduction of cholesterol levels also increased the levels of the angiogenesis inhibitor thrombospondin-1 in the xenografts. Our results thus suggest that hypercholesterolemia directly accelerates the growth of prostate carcinomas, and that the pharmacological reduction of serum cholesterol levels may retard prostate cancer growth by inhibiting tumor angiogenesis.

Reduction of protein synthesis and statin-induced cardiomyocyte cell death

The objective of this study was to determine whether an HMG Co A reductase inhibitor (statin) reduces protein synthesis in cardiomyocytes and whether this action maybe an underlying mechanism for statin-induced cell death. Cardiomyocytes from embryonic chick heart were maintained in culture. Cells exposed to lovastatin for 4 h showed a concentration dependent reduction in protein synthesis as assessed by [3H] leucine incorporation and [35S] methionine incorporation. Compared to control, lovastatin 100 microM, which produced a 25% increase in cell death, induced a three-fold reduction in methionine incorporation. [35S] methionine autoradiography showed little (new) protein synthesis at concentrations of lovastatin of 70 microM or higher; an effect that was not limited to specific proteins. Cardiomyocytes treated with lovastatin showed morphologic changes in the nucleoli consistent with insufficient protein synthesis. These cardiomyocytes manifested cell death under conditions of reduced protein synthesis. Interruption of protein synthesis with cycloheximide, a ribosomal RNA transcription inhibitor or reduction in protein substrate availability by lowering the media concentration of fetal calf serum was associated with a concentration-dependent reductions in cell viability. Importantly, stimulation of protein synthesis by higher concentrations of fetal calf serum limited lovastatin-induced cell death. These data suggest that statin-induced inhibition of protein synthesis is an underlying mechanism for statin-induced cell death.

HMG-CoA reductase inhibitors induce apoptosis in pericytes

Pericytes, which surround endothelial cells in precapillary arterioles, capillaries, and postcapillary venules, are important for the development, maturation, and maintenance of the vascular system. Pericytes are also pluripotent cells that can differentiate into a variety of mesenchymal cells including smooth muscle cells and osteoblasts. Possibly because of their vasculature regulating activities and ability to differentiate in situ, pericytes are implicated in several diseases with vascular complications, including diabetic retinopathy, as well as Reynaud's Syndrome, central nervous system dementias, and vascular calcification among others. Statin drugs, which block the conversion of HMG-CoA to mevalonate in the cholesterol synthesis pathway, are known to have apoptotic and growth inhibitory effects on cells in vitro and complex pleiotropic effects on cells and tissues in vivo. Recently, evidence has emerged that statin drug use in human patients results in a significant 20% reduction in cancer incidence. It is not known whether these results are due to direct statin action on normal tissue, growth inhibitory/pro-apoptotic effects on tumor cells, and/or effects on angiogenesis. Because of the role of pericytes in angiogenesis and the effects of statins on cancer incidence, we tested the direct effects of statins on pericytes. Specifically, we demonstrate that 3 statins, simvastatin, lovastatin, and mevastatin induce dose-dependent apoptosis in the TR-PCT1 pericyte cell line, that simvastatin (empirically shown to be the most potent of the 3 statins) induces similar levels of apoptosis in freshly isolated pericytes, and that simvastatin-induced apoptosis in pericytes is cholesterol, caspase-3, and caspase-7 mediated.

Effect of serum withdrawal on the contribution of L-type calcium channels (CaV1.2) to intracellular Ca2+ responses and chemotaxis in cultured human vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) chemotaxis is fundamental to atherosclerosis and intimal hyperplasia. An increase in intracellular Ca2+ [Ca2+]i is an important signal in chemotaxis, but the role of L-type calcium channels (CaV1.2) in this response in human vascular smooth muscle cells (hVSMC) has not been examined. hVSMC were grown from explant cultures of saphenous vein. Confluent hVSMC at passage 3 were studied after culture in medium containing 15% foetal calf serum (FCS) (randomly cycling) or following serum deprivation for up to 7 days. Smooth muscle alpha-actin was measured by immunoblotting and immunofluorescence microscopy. [Ca2+]i was measured using fura 2 fluorimetry. Chemotaxis was measured using a modified Boyden chamber technique and cell attachment to gelatin-coated plates was also quantified. The number and affinity of dihydropyridine-binding sites was assessed using [5-methyl-3H]PN 200-110 binding. In randomly cycling cells, the calcium channel agonist, Bay K 8644a and 100 mM KCl did not affect [Ca2+]i. In addition, the rise in [Ca2+]i induced by platelet-derived growth factor-BB (PDGF) was unaffected by the CaV1.2 antagonists, amlodipine and verapamil. In randomly cycling cells amlodipine did not affect PDGF-induced migration. In serum-deprived cells, smooth muscle alpha-actin was increased and Bay K 8644a and 100 mM KCl increased [Ca2+]i. PDGF-induced rises in [Ca2+]i were also inhibited by amlodipine and verapamil. The ability of Bay K 8644a to increase [Ca2+]i and verapamil to inhibit PDGF-induced rises in [Ca2+]i was evident within 3 days after serum withdrawal. In serum-deprived hVSMC Bay K 8644a induced chemotaxis and amlodipine inhibited PDGF-induced migration. Cell attachment in the presence of PDGF was unaffected by amlodipine in either randomly cycling or serum-deprived hVSMC. Serum withdrawal was associated with a decrease in the maximum number of dihydropyridine-binding sites (B(max)) and a decrease in affinity (K(D)). Serum deprivation of hVSMC results in increased expression of smooth muscle alpha-actin, a marker of more differentiated status, and increased [Ca2+]i responses and chemotaxis mediated by CaV1.2. These observations may have important implications for understanding the therapeutic benefits of calcium channel antagonists in cardiovascular disease.

Antirestenotic Effects of a Locally Delivered Caspase Inhibitor in a Balloon Injury Model

BACKGROUND

The precise role of arterial barotrauma-mediated apoptosis in causing restenosis is unclear. The purpose of this study was to determine if a link exists between angioplasty-mediated medial smooth muscle cell apoptosis and subsequent neointimal hyperplasia.

METHODS AND RESULTS

Bilateral iliac artery angioplasty was performed in 25 male New Zealand White rabbits. Simultaneous with balloon injury, each artery was treated locally with either the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(Ome)-fluoromethylketone (ZVAD-fmk) or control. In the acute cohort that was survived to 4 hours (n=10, 7 high dose and 3 low dose), an apoptotic index was calculated using the terminal deoxynucleotidyl TUNEL method. In the intermediate cohort that was survived to 2 weeks (n=5), luminal reendothelialization was measured via CD-31 staining. In the chronic cohort that was survived to 4 weeks (n=10), neointimal area was measured. In the acute cohort, there was a 40% reduction in the apoptotic index with high-dose ZVAD-fmk (P=0.008) and a 33% reduction with low-dose ZVAD-fmk (P=0.08). At 2 weeks, there was no significant difference in the degree of luminal reendothelialization. However, at 4 weeks, there was a 33% (0.33+/-0.23 versus 0.22+/-0.20 mm2) (P<0.005) reduction in neointimal area in ZVAD-fmk-treated arteries.

CONCLUSIONS

The local delivery of ZVAD-fmk during balloon injury inhibits smooth muscle cell apoptosis. This corresponds to a significant reduction in neointimal proliferation seen at 4 weeks without a significant change in the degree of reendothelialization at 2 weeks.