Inhibition of vascular smooth muscle cell proliferation by the calcium antagonist clentiazem: role of protein kinase C

Metabolic Stress

Mitochondria regulate major aspects of cell function by producing ATP, contributing to Ca²⁺ signaling, influencing redox potential, and controlling levels of reactive oxygen species. In this review, we will discuss recent findings that illustrate how mitochondrial respiration, Ca²⁺ handling, and production of reactive oxygen species affect vascular smooth muscle cell function during neointima formation. We will review mitochondrial fission/fusion as fundamental mechanisms for smooth muscle proliferation, migration, and metabolism and examine the role of mitochondrial mobility in cell migration. In addition, we will summarize novel aspects by which mitochondria regulate apoptosis.

Calcium-sensing receptor, calcimimetics, and cardiovascular calcifications in chronic kidney disease

Renal function impairment goes along with a disturbed calcium, phosphate, and vitamin D metabolism, resulting in secondary hyperparathyroidism (sHPT). These mineral metabolism disturbances are associated with soft tissue calcifications, particularly arteries, cardiac valves, and myocardium, ultimately associated with increased risk of mortality in patients with chronic kidney disease (CKD). sHPT may lead to cardiovascular calcifications by other mechanisms including an impaired effect of parathyroid hormone (PTH), and a decreased calcium-sensing receptor (CaR) expression on cardiovascular structures. PTH may play a direct role on vascular calcifications through activation of a receptor, the type-1 PTH/PTHrP receptor, normally attributed to PTH-related peptide (PTHrP). The CaR in vascular cells may also play a role on vascular mineralization as suggested by its extremely reduced expression in atherosclerotic calcified human arteries. Calcimimetic compounds increasing the CaR sensitivity to extracellular calcium efficiently reduce serum PTH, calcium, and phosphate in dialysis patients with sHPT. They upregulate the CaR in vascular cells and attenuate vascular mineralization in uremic states. In this article, the pathophysiological mechanisms associated with cardiovascular calcifications in case of sHPT, the impact of medical and surgical correction of sHPT, the biology of the CaR in vascular structures and its function in CKD state, and finally the role played by the CaR and its modulation by the calcimimetics on uremic-related cardiovascular calcifications are reviewed.

PKC isozymes in chronic cardiac disease: possible therapeutic targets?

Cardiovascular disease is the leading cause of death in the United States. Therefore, identifying therapeutic targets is a major focus of current research. Protein kinase C (PKC), a family of serine/threonine kinases, has been identified as playing a role in many of the pathologies of heart disease. However, the lack of specific PKC regulators and the ubiquitous expression and normal physiological functions of the 11 PKC isozymes has made drug development a challenge. Here we discuss the validity of therapeutically targeting PKC, an intracellular signaling enzyme. We describe PKC structure, function, and distribution in the healthy and diseased heart, as well as the development of rationally designed isozyme-selective regulators of PKC functions. The review focuses on the roles of specific PKC isozymes in atherosclerosis, fibrosis, and cardiac hypertrophy, and examines principles of pharmacology as they pertain to regulators of signaling cascades associated with these diseases.

Inhibition of Mitogen-Mediated Proliferation of Rat Vascular Smooth Muscle Cells by Labedipinedilol-A through PKC and ERK 1/2 Pathway

Labedipinedilol-A is a novel 1, 4-dihydropyridine type calcium antagonist with alpha-receptor blocking activity. This study investigates the effects of labedipinedilol-A on mitogen-induced proliferation of rat vascular smooth muscle cells (VSMCs). Labedipinedilol-A's inhibition on cell proliferation was measured by the tetrazolium salt (XTT) test. Labedipinedilol-A dose-dependently inhibited mitogen-induced DNA synthesis, determined by the incorporation of 5-bromo-2'-deoxyuridine (BrdU). Labedipinedilol-A was also found capable of inhibiting the migration of VSMCs induced by PDGF-BB with an IC50 value of 5.6 microM. In accordance with these findings, labedipinedilol-A revealed blocking of the FBS-inducible progression through G0/G1 to S phase of the cell cycle in synchronized cells. Labedipinedilol-A appeared to cause inhibition of mitogens-induced PKC translocation, suggesting the probable involvement of protein kinase C (PKC) in this cellular response. Labedipinedilol-A reduced both intracellular Ca and the phosphorylation of extracellular signal-regulated protein kinase 1/2 in PDGF-BB-stimulated VSMCs. It also suppressed the levels of proliferative cell nuclear antigen (PCNA) in VSMCs both time- and dose-dependently. These results indicate that labedipinedilol-A may inhibit cell proliferation by attenuating activation of the ERK 1/2 pathway, which is regulated by PKC and Ca, suggesting that it may have great potential in the prevention of progressive atherosclerosis.

Antiatherosclerotic effects of calcium channel blockers

Over the past 30 years, a considerable body of experimental and clinical evidence has accumulated to support the suggestion that calcium channel blockers (CCBs) have significant antiatherosclerotic effects that are independent of their hypotensive effects. Early research using animal models of atherosclerosis and CCBs in concentrations that exceeded the normal therapeutic dose range showed definite antiatherosclerotic effects, especially in the development of new lesions. Investigations of these effects in humans have used quantitative coronary angiography and B-mode ultrasonography and have demonstrated some antiatherosclerotic effects. This article reviews the currently available evidence of antiatherosclerotic effects of CCBs in animal models and in clinical trials.

A calcium channel blocker, benidipine, inhibits intimal thickening in the carotid artery of mice by increasing nitric oxide production

OBJECTIVE

Recent studies suggest that several calcium channel blockers exert their protective effects against vascular disorders by increasing nitric oxide (NO) production from the endothelium. The purpose of this study was to clarify the effects of a long-lasting calcium channel blocker, benidipine, on vascular remodeling.

METHODS

The left common carotid arteries of mice were completely ligated just proximal to the carotid bifurcation. Treatment with benidipine (3 mg/kg per day) or vehicle was started 1 week before the carotid ligation, and continued throughout the experiments. Four weeks after the carotid ligation, these mice were killed and vascular remodeling was analyzed. Moreover, NO production and endothelial NO synthase (eNOS) expression were assessed.

RESULTS

At 4 weeks after ligation, the neointimal area in the vehicle-treated mice was 39,400 +/- 4,900 microm2 (n = 8), whereas that in the drug-treated mice was reduced to 18,300 +/- 3,800 microm2 (n = 10). Consequently, the luminal area was 35% larger in the drug-treated mice. Benidipine increased the basal as well as agonist-induced NO production from the endothelium, detected by Griess method or NOx analyzer. Endothelial NOS expression in vessels of the drug-treated mice was increased compared with that of the vehicle-treated mice.

CONCLUSION

Our data provide evidence that benidipine increases NO production via increment of eNOS protein in vessels and prevents intimal thickening in mice. These results show the possibility of benidipine as a protective tool against vascular remodeling independent of its effect on blood pressure.

Protein kinase C: modulation of vasopressin-induced calcium influx and release in A7r5 vascular smooth muscle cells

This study was guided by the hypothesis that specific isoforms of protein kinase C may participate in modulating increases in intracellular Ca2+ that are induced by stimulation of vascular smooth muscle cells with vasopressin. Immunoblot analysis revealed that A7r5 vascular smooth muscle cells expressed conventional (alpha), novel (delta and epsilon), and atypical (iota/lambda and mu) isoforms of protein kinase C. Stimulation of fura-2-loaded cells with 20 nM vasopressin induced a rapid transient increase in the intracellular concentration of calcium that was followed by a slowly declining component which was above baseline throughout the period of observation. Cell fractionation studies showed that the calcium response was associated with (a) transient translocation of the alpha and delta isoforms of protein kinase C from the cytosolic fraction to the particulate-membrane fraction, (b) sustained translocation of the epsilon isoform, and (c) no translocation of iota/lambda or mu isoforms. Ratiometric and isobestic fluorescence analysis showed that vasopressin-induced Ca2+ influx and release were markedly inhibited in cells that were preincubated with either 1 microM phorbol 12-myristate 13-acetate, or 10 microM 1, 2 dioctanoyl-sn-glycerol, two structurally different activators of protein kinase C. In contrast, vasopressin-induced increases in intracellular Ca2+ were not significantly altered following preincubation with either 1 microM 4alpha-phorbol or 4alpha-phorbol 12,13-didecanoate, analogs of phorbol 12-myristate 13-acetate that do not activate protein kinase C. Moreover, the inhibitory effects of phorbol 12-myristate 13-acetate were prevented by treatment with 1 microM GF109203X, a potent inhibitor of protein kinase C. Taken together, these results show that direct activation of protein kinase C can negatively modulate vasopressin-induced Ca2+ influx and release in cultured vascular smooth muscle cells. They also show that stimulation with vasopressin induces translocation of specific isoforms of protein kinase C, an observation suggesting that one or more of these isoforms may participate in modulation of vasopressin-induced increases in intracellular Ca2+.

Inhibition of PDGF-mediated proliferation of vascular smooth muscle cells by calcium antagonists

BACKGROUND AND PURPOSE

The mechanism by which calcium antagonists (CAs) inhibit proliferation in vascular smooth muscle cells (VSMCs) is not yet fully understood. We investigated the effects of four CAs (clentiazem, verapamil, diltiazem, and nifedipine) on signal transduction pathways activated by platelet-derived growth factor (PDGF). To determine these effects, the levels of inositol phosphates (IPs), protein kinase C (PKC), and the induction of the transcription factor activator protein-1 (AP-1) were measured.

METHODS

The mitogenic effect of PDGF on VSMCs was measured by [3H]thymidine incorporated into DNA. IP production was monitored by [3H]myo-inositol incorporation. PKC activation was determined by measurement of myristoylated, alanine-rich C kinase substrate (MARCKS) phosphorylation in digitonin-permeabilized VSMCs. The induction of AP-1 complex was detected by electrophoretic mobility shift assays.

RESULTS

Each CA significantly inhibited the [3H]thymidine incorporation into DNA in unstimulated cells. Similar significant decreases in [3H]thymidine incorporation by CAs were observed when cells were stimulated by rPDGF-BB. The phosphorylation of MARCKS mediated by rPDGF-BB was significantly reduced by each CA. Clentiazem and verapamil significantly reduced the expression of AP-I induced by rPDGF-BB (P < .01, P < .05). Clentiazem also significantly reduced the expression of AP-1 induced by rPDGF-AB (P < .05).

CONCLUSIONS

PDGF-mediated proliferation of VSMCs correlates with activation of PKC but not with induction of the AP-1 complexes. In addition, our results suggest that CAs block proliferation of VSMCs by inhibiting DNA synthesis, possibly via PKC.