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

Identification of peptides from soybean protein, glycinin, possessing suppression of intracellular Ca2+ concentration in vascular smooth muscle cells

In this study, we challenged to identify vasoactive peptides in soybean 11S glycinin hydrolysate by thermolysin to regulate intracellular Ca(2+) concentration ([Ca(2+)]i) that can induce constrictive vascular tension. As a function of the inhibition of elevated [Ca(2+)]i by 10 μM angiotensin (Ang) II in vascular smooth muscle cells (VSMCs), eleven peptides were successfully identified from the hydrolysate, among which His-Gly-Lys exhibited the most potent inhibition against [Ca(2+)]i elevation in Ang II-stimulated VSMCs (inhibition at 300 μM: 46.5±8.0% vs. control). The biological capacity of His-Gly-Lys analogues as an [Ca(2+)]i inhibitor was also proven when His-Lys and His-Gly-Arg elicited a significant reduction in [Ca(2+)]i. In contrast, less reduction of [Ca(2+)]i by His-Gly-Ile and His-(3-methyl)-Gly-Lys indicated the importance of the imino proton in His, along with basic amino acids positioned at C-terminal for the effect.

Verapamil stereoisomers induce antiproliferative effects in vascular smooth muscle cells via autophagy

Calcium channel blockers (CCBs) are important in the management of hypertension and limit restenosis. Although CCB efficacy could derive from decreased blood pressure, other mechanisms independent of CCB activity also can contribute to antiproliferative action. To understand mechanisms of CCB-mediated antiproliferation, we studied two structurally dissimilar CCBs, diltiazem and verapamil, in cultured rat vascular smooth muscle cells (VSMC). To elucidate CCB-independent effects, pure stereoisomers of verapamil (R-verapamil, inactive VR; S-verapamil, active, VS) were used. The effects of CCB exposure on cell viability (MTT reduction), cell proliferation ((3)H-thymidine incorporation), VSMC morphology by light and transmission electron microscopy (TEM) and autophagy (LC3I/II, ATG5) were measured. In general, verapamil, VR or VS treatment alone (80 μM) appreciably enhanced MTT absorbance although higher concentrations (VR or VS) slightly decreased MTT absorbance. Diltiazem (140 μM) markedly decreased MTT absorbance (40%) at 120 h. VR or VS treatment inhibited (3)H-thymidine incorporation (24h) and induced cytological alterations (i.e., karyokinesis, enhanced perinuclear MTT deposition, accumulated perinuclear "vacuoles"). TEM revealed perinuclear "vacuoles" to be aggregates of highly laminated and electron-dense vesicles resembling autophagosomes and lysosomes, respectively. Increased autophagosome activity was confirmed by a concentration-dependent increase in LC3-II formation by Western blotting and by increased perinuclear LC3-GFP(+) puncta in verapamil-treated VSMC. Verapamil stereoisomers appeared to decrease perinuclear mitochondrial density. These observations indicate that antiproliferative effects of verapamil stereoisomers are produced by enhanced mitochondrial damage and upregulated autophagy in VSMC. These effects are independent of CCB activity indicating a distinct mechanism of action that could be targeted for more efficacious anti-atherosclerotic and anti-restenosis therapy.

LipoCardium: Endothelium-directed cyclopentenone prostaglandin-based liposome formulation that completely reverses atherosclerotic lesions

Atherosclerosis is a multifactorial inflammatory disease of blood vessels which decimates one in every three people in industrialized world. Despite the important newest clinical approaches, currently available strategies (e.g. nutritional, pharmacological and surgical) may only restrain the worsening of vascular disease. Since antiproliferative cyclopentenone prostaglandins (CP-PGs) are powerful anti-inflammatory agents, we developed a negatively charged liposome-based pharmaceutical formulation (LipoCardium) that specifically direct CP-PGs towards the injured arterial wall cells of atherosclerotic mice. In the blood stream, LipoCardium delivers its CP-PG contents only into activated arterial wall lining cells due to the presence of antibodies raised against vascular cell adhesion molecule-1 (VCAM-1), which is strongly expressed upon inflammation by endothelial cells and macrophage-foam cells as well. After 4 months in a high-lipid diet, all low-density lipoprotein receptor-deficient adult control mice died from myocardium infarction or stroke in less than 2 weeks, whereas LipoCardium-treated (2 weeks) animals (still under high-lipid diet) completely recovered from vascular injuries. In vitro studies using macrophage-foam cells suggested a tetravalent pattern for LipoCardium action: anti-inflammatory, antiproliferative (and pro-apoptotic only to foam cells), antilipogenic and cytoprotector (via heat-shock protein induction). These astonishing cellular effects were accompanied by a marked reduction in arterial wall thickness, neointimal hyperplasia and lipid accumulation, while guaranteed lifespan to be extended to the elderly age. Our findings suggest that LipoCardium may be safely tested in humans in a near future and may have conceptual implications in atherosclerosis therapy.

Pharmacological basis of different targets for the treatment of atherosclerosis

The development of atherosclerotic plaque is a highly regulated and complex process which occurs as a result of structural and functional alterations in endothelial cells, smooth muscle cells (SMCs), monocytes/macrophages, T-lymphocytes and platelets. The plaque formation in the coronary arteries or rupture of the plaque in the peripheral vasculature in latter stages of atherosclerosis triggers the onset of acute ischemic events involving myocardium. Although lipid lowering with statins has been established as an important therapy for the treatment of atherosclerosis, partially beneficial effects of statins beyond decreasing lipid levels has shifted the focus to develop newer drugs that can affect directly the process of atherosclerosis. Blockade of renin angiotensin system, augmentation of nitric oxide availability, reduction of Ca(2+) influx, prevention of oxidative stress as well as attenuation of inflammation, platelet activation and SMC proliferation have been recognized as targets for drug treatment to control the development, progression and management of atherosclerosis. A major challenge for future drug development is to formulate a combination therapy affecting different targets to improve the treatment of atherosclerosis.

Amlodipine modulates THP-1 cell adhesion to vascular endothelium via inhibition of protein kinase C signal transduction

Inflammatory responses play an important role in atherosclerosis. To critically assess the effect of dihydropyridines in inflammatory reactions, we conducted a monocyte-endothelial adhesion assay with monocytic THP-1 cells treated with amlodipine under flow conditions in vitro. THP-1 cells were incubated in the presence of amlodipine (10 micromol/L) for 48 hours and then perfused over activated (interleukin-1beta, 10 U/mL, 4 hours) human umbilical vein endothelial cells. The adhesion of THP-1 cells was significantly reduced after amlodipine treatment (P<0.001); however, flow cytometric analysis reveled that the expression levels of integrins in THP-1 cells were not significantly altered. Furthermore, Western blotting analysis of THP-1 cell lysates revealed that translocation of RhoA from the cytosol to the membrane was significantly diminished after amlodipine treatment. In addition, activation of protein kinase C-alpha and -beta, as well as intracellular calcium influx, induced by phorbol 12-myristate 13-acetate, was diminished after amlodipine treatment. Pretreatment of THP-1 cells with calphostin C, a potent inhibitor of protein kinase C, significantly reduced THP-1 adhesion to vascular endothelium, whereas activation of beta1-integrin was reduced after amlodipine treatment in THP-1 cells, based on the immunoreactivity of an activation-specific antibody for beta1-integrin. Similar inhibitory effects were observed when we used freshly isolated peripheral blood mononuclear cells. These findings suggest a potential role for amlodipine in monocyte-endothelial interactions by modulation of protein kinase C- and RhoA-dependent mechanisms, which might account for its vascular protective effects.

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.

Effects of Cl- channel blockers on endothelin-1-induced proliferation of rat vascular smooth muscle cells

The effects of Cl- channel blockers on endothelin-1 (ET-1)-induced proliferation of rat aortic vascular smooth muscle cells (VSMC) were examined. We found ET-1 concentration-dependently increased cell count and [3H]-thymidine incorporation into VSMC, with EC50 values of 24.8 and 11.4 nM, respectively. Both nifedipine and SK&F96365 inhibited 10 nM ET-1-induced [3H]-thymidine incorporation into VSMC with the maximal inhibitory concentrations of 1 and 10 microM, respectively. DIDS inhibited 10 nM ET-1-induced increase in cell count and [3H]-thymidine incorporation into VSMC in a concentration-dependent manner, whereas other Cl- channel blockers including IAA-94, NPPB, DPC, SITS and furosemide did not produce these effects. 3 microM DIDS reduced 10 nM ET-1-induced sustained increase in cytoplasmic Ca2+ concentration ([Ca2+]) by 52%. Pretreatment of VSMC with 1 microM nifedipine completely inhibited the DIDS effect on 10 nM ET-1-induced [3H]-thymidine incorporation into VSMC and sustained increase in [Ca2+]i, whereas pretreatment with 10 microM SK&F96365 did not completely block these effects of DIDS. DIDS did not affect ET-1-induced Ca2+ release and 30 mM KCl-induced increase in [Ca2+]i. Our data suggest that DIDS-sensitive Cl- channels mediate VSMC proliferation induced by ET-1 by mechanisms related to membrane depolarization and Ca2+ influx through voltage-dependent Ca2+ channels.

Ouabain-induced signaling and vascular smooth muscle cell proliferation

The hypothesis of this study is that the sodium pump complex acts as an intracellular signal-transducing molecule in canine vascular smooth muscle cells through its interaction with other membrane and cytoskeletal proteins. We have demonstrated that 1 nm ouabain induced transactivation of the epidermal growth factor receptor (EGFR), resulting in increased proliferation and bromodeoxyuridine (BrdUrd) uptake. Immunoprecipitation and Western blotting showed that the EGFR and Src were phosphorylated within 5 min of 10(-9) m ouabain stimulation. Both ouabain-induced DNA synthesis (BrdUrd uptake) and MAPK42/44 phosphorylation were inhibited by the Src inhibitor PP2, the EGFR kinase inhibitor AG1478, the tyrosine kinase inhibitor genistein, and the MEK1 inhibitor PD98059. Ouabain concentrations higher than 1 nm had little or no stimulating effect on proliferation or BrdUrd uptake but did minimally activate ERK1/2. Thus, low concentrations of ouabain, which do not inhibit the sodium pump sufficiently to perturb the resting cellular ionic milieu, initiate a transactivational signaling cascade leading to vascular smooth muscle cell proliferation.

The calcium inhibitor SR33805 reduces intimal formation following injury of the porcine carotid artery

We studied the effect of SR33805, a calcium channel blocker, in vitro on the proliferation of vascular smooth muscle cells (SMC) stimulated by foetal calf serum, basic fibroblast growth factor and platelet derived growth factor, and in vivo with regard to SMC migration and proliferation which occurred following injury of the porcine carotid artery. The intimal lesion was induced by a silasten collar surgically positioned around the carotid artery and by a stenosis reducing blood flow by 50% for 30 days. Animals received SR33805 (5 mg/kg/day) 8 days before the induction of the lesion and up to 30 days after. In vitro, SR33805 inhibited in a dose-dependent manner growth factor-induced proliferation of SMC (0.20<IC(50)<0.46 microM). In vivo, SR33805 reduced the intima/media ratio of the cross sectional surface area (decrease of 60%, P<0.05) without affecting neointimal SMC density. The medial SMC density was 40% lower in treated than in control animals (upstream, P<0.05 and downstream to the stenosis, P<0.01). Thus, it appears that SR33805 significantly reduced intimal hyperplasia, which occurred after perivascular manipulation of the artery, an effect consistent with its in vitro proliferation inhibitory activity, suggesting that long-term treatment with SR33805 may reduce or delay SMC proliferation.

Lipophilic calcium antagonists in antiatherosclerotic therapy

Two key events in atherosclerotic plaque formation are the deposition of lipids in cells of the vascular wall, and migration and proliferation of arterial smooth muscle cells from the tunica intima toward the media. It has been shown that various calcium-channel antagonists may delay plaque formation in animal models. Among these, the new and highly lipophilic calcium antagonists, such as lacidipine and lercanidipine, display the most promising antiatherosclerotic activities. This paper will review and discuss these beneficial effects.

Calcium antagonists ameliorate ischemia-induced endothelial cell permeability by inhibiting protein kinase C

BACKGROUND

Dihydropyridines block calcium channels; however, they also influence endothelial cells, which do not express calcium channels. We tested the hypothesis that nifedipine can prevent ischemia-induced endothelial permeability increases by inhibiting protein kinase C (PKC) in cultured porcine endothelial cells.

METHODS AND RESULTS

Ischemia was induced by potassium cyanide/deoxyglucose, and permeability was measured by albumin flux. Ion channels were characterized by patch clamp. [Ca2+]i was measured by fura 2. PKC activity was measured by substrate phosphorylation after cell fractionation. PKC isoforms were assessed by Western blot and confocal microscopy. Nifedipine prevented the ischemia-induced increase in permeability in a dose-dependent manner. Ischemia increased [Ca2+]i, which was not affected by nifedipine. Instead, ischemia-induced PKC translocation was prevented by nifedipine. Phorbol ester also increased endothelial cell permeability, which was dose dependently inhibited by nifedipine. The effects of non-calcium-channel-binding dihydropyridine derivatives were similar. Analysis of the PKC isoforms showed that nifedipine prevented ischemia-induced translocation of PKC-alpha and PKC-zeta. Specific inhibition of PKC isoforms with antisense oligodeoxynucleotides demonstrated a major role for PKC-alpha.

CONCLUSIONS

Nifedipine exerts a direct effect on endothelial cell permeability that is independent of calcium channels. The inhibition of ischemia-induced permeability by nifedipine seems to be mediated primarily by PKC-alpha inhibition. Anti-ischemic effects of dihydropyridine calcium antagonists could be due in part to their effects on endothelial cell permeability.

Isradipine lowers human arterial low density lipoprotein retention in vivo

During the recent past it has been discussed that calcium antagonists may exert antiatherosclerotic actions at the vessel wall. Apolipoprotein B containing lipoproteins were isolated by immunoaffinity chromatography and radiolabeled with 123-iodine. The effect of 2 x 2.5 mg isradipine on the low density lipoproteins (LDL) entry into the carotid and femoral arteries of 12 hypertensive patients with primary hyperlipoproteinemia (total cholesterol >6.5 mmol/l [250 mg/dL) was examined. Cholesterol -1.7% (P< 0.05 664), high density lipoprotein (HDL) cholesterol +4.5% (P< 0.01 123), and LDL cholesterol -1% (P< 0.01 563) did not change, nor did any of the safety parameters. The types of entry kinetics reflecting vascular surface lining did not change while the LDL retention 20 h after tracer application was depressed by up to 23.5%. The data were comparable in the carotid and femoral artery segments, the significance level ranging up to 0.0009. These results indicate a decreased LDL retention in the arterial wall of hypertensive patients induced by isradipine. The clinical implications of the findings ought to be pursued in properly designed clinical trials.

Vascular smooth muscle cell migration, atherosclerosis, and calcium channel blockers

Calcium channel blockers have been studied widely for their potential ability to retard or even reverse atherosclerosis. Several potential cellular mechanisms have been proposed, including interactions with vascular smooth muscle cells: migration, inhibition of proliferation, or both. This paper reviews some of the signaling events involved in smooth muscle cell migration, including changes in intracellular calcium, and the inhibition of cell migration by calcium channel blockers. Finally, there is a discussion of preliminary experiments on human vascular smooth muscle cell migration using amlodipine.

Preservation of endogenous antioxidant activity and inhibition of lipid peroxidation as common mechanisms of antiatherosclerotic effects of vitamin E, lovastatin and amlodipine

OBJECTIVES

We sought to document the common mechanisms of the antiatherogenic effects of the cholesterol-lowering hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor lovastatin, the dihydropyridine Ca2+ blocker amlodipine and the antioxidant vitamin E.

BACKGROUND

Vitamin E, HMG-CoA reductase inhibitors and Ca2+ blockers each inhibit atherosclerosis in hypercholesterolemic animals.

METHODS

New Zealand White rabbits were fed regular chow (Group A), chow with 1% cholesterol (Group B), 1% cholesterol diet plus lovastatin (Group C), 1% cholesterol diet plus vitamin E (Group D) or 1% cholesterol diet plus amlodipine (Group E) for 12 weeks. The extent of aortic atherosclerosis was measured by planimetry of the sudanophilic area. Malondialdehyde (MDA) and superoxide dismutase (SOD) in blood were measured as indexes of lipid peroxidation and antioxidant activity, respectively.

RESULTS

Group A rabbits showed no atherosclerosis, whereas Group B rabbits had 17.4 +/- 9.3% (mean +/- SD) of the aorta covered with atherosclerosis, and Groups C, D and E rabbits had significantly less atherosclerosis. Plasma SOD activity was lower in Group B than in Group A (6.9 +/- 1.1 vs. 12.8 +/- 1.5 U/ml, p < 0.01) and was preserved in the groups given lovastatin, vitamin E or amlodipine with a high cholesterol diet. The serum MDA level was higher in Group B rabbits than Group A rabbits (12.1 +/- 2.6 vs. 1.2 +/- 0.1 nmol/ml, p < 0.01) and increased minimally in rabbits given lovastatin, vitamin E or amlodipine with a high cholesterol diet. In in vitro experiments, both lovastatin and amlodipine preserved SOD activity and reduced the oxidizability of low density lipoproteins by rabbit leukocytes.

CONCLUSIONS

This study suggests that a reduction in lipid peroxidation and preservation of SOD may be common mechanisms of antiatherosclerotic effects of lovastatin, vitamin E and amlodipine.

Serum calcium: a new, independent, prospective risk factor for myocardial infarction in middle-aged men followed for 18 years

BACKGROUND

Primary hyperparathyroidism (HPT) is a disease characterized by hypercalcemia, and associated with an increased mortality in cardiovascular diseases. However, serum calcium levels within the normal range have not been evaluated as a prospective cardiovascular risk factor.

METHODS

A cohort of males aged 50 (n = 2183) were investigated in 1970-1973 for serum calcium and known cardiovascular risk factors. They were then followed up over the next 18 years.

RESULTS

During the follow-up period, 180 subjects experienced a myocardial infarction (MI). The serum calcium levels were significantly elevated at the baseline (2.37 +/- 0.09 SD versus 2.35 +/- 0.09 mmol/l, p < 0.03) in the subjects who developed a MI when compared with the rest of the cohort. Also blood pressure, body mass index (BMI), fasting insulin, serum cholesterol, serum triglycerides, and the atherogenic index were significantly elevated in the MI group (p < 0.01), while HDL-cholesterol was lower at the baseline investigation (p < 0.01). Cox's proportional hazard analysis showed that only serum calcium (p < 0.01), BMI (p < 0.0003), diastolic blood pressure (p < 0.0009), and the atherogenic index (p < 0.002) were significantly independent risk factors for MI. The range of serum calcium levels from the mean value, -2 SDs to the mean value +2 SDs corresponds to a variation in estimated risk for MI ranging from 0.06 to 0.15.

CONCLUSIONS

Serum calcium was found to be an independent, prospective risk factor for MI in middle-aged males suggesting a role for extracellular calcium levels in the atherosclerotic process.

Augmented Ca2+ influx is involved in the mechanism of enhanced proliferation of cultured vascular smooth muscle cells from spontaneously diabetic Goto-Kakizaki rats

To investigate whether augmented calcium influx is involved in the mechanism of the enhanced proliferation of vascular smooth muscle cells (VSMCs) in diabetes, we studied the association between proliferation and cytosolic free calcium concentration ([Ca2+]i) in cultured aortic VSMCs from spontaneously diabetic Goto-Kakizaki (GK) and Wistar rats. Serum, angiotensin II and Bay K 8644, a voltage-dependent Ca2+ channel (VDC) agonist, stimulated the proliferation of VSMCs; the magnitude was greater in VSMCs from GK than Wistar rats. VDC blockers, verapamil and nicardipine, inhibited Bay K 8644-induced cell proliferation, and the difference in the proliferation of VSMCs between GK and Wistar rats disappeared. Angiotensin II-induced proliferation was only partially inhibited by VDC blockers, and enhanced proliferation of GK-VSMCs was still observed. Bay K 8644 and angiotensin II increased [Ca2+]i, and the increase was augmented in GK-VSMCs. Bay K 8644-induced [Ca2+]i increase was completely inhibited by pretreatment with verapamil or removal of extracellular Ca2+, suggesting that VDC is associated with this increase. Although angiotensin II-induced [Ca2+]i increase was not affected by verapamil, removal of extracellular Ca2+ slightly but significantly attenuated angiotensin II-induced [Ca2+]i increase, suggesting that VDC blocker-insensitive receptor-activated Ca2+ influx is involved. These results indicate that augmented Ca2+ influx via VDC and a receptor-activated pathway may be involved in the mechanism of the enhanced proliferation of VSMCs from GK rats.

Effect of isradipine on in-vivo platelet function

In animal studies calcium channel blockers (CCB's) and especially isradipine, a second generation dihydropyridine, interrupt the sequence of events culminating in the formation of atherosclerotic lesions. The effect of 4 weeks isradipine treatment (5mg daily) on blood pressure and in-vivo platelet function (measured with 111Indium-oxine labeled autologous platelets) were investigated in a randomized, double-blind and placebo controlled trial in 40 patients with mild to moderate hypertension and scintigraphically diagnosed active atherosclerotic lesions of the carotid arteries. The average supine systolic/diastolic blood pressure was significantly reduced at the end of the treatment period in the isradipine group (group 1; p < 0.0001) but remained unchanged in the placebo group (group P). The heart rate was not significantly altered in either group. There were no serious side effects. The platelet uptake ratio (PUR) measured over the atherosclerotic region of the carotid artery on 4 consecutive days before and after treatment decreased significantly in group I from 1.20 to 1.15 (within groups: p < 0.0001) but remained unchanged in group P. Platelet survival increased significantly in group I (mean 5.70 hours, lower quartile 4.50, upper quartile 4.50 hours, within groups: p < 0.0001) and remained unchanged in group P. Isradipine has a beneficial effect on in-vivo platelet function as evidenced by a decreased platelet deposition on vascular lesion sites and an associated prolonged platelet survival in patients with hypertension and active atherosclerotic lesions.

Impact of a combination of a calcium antagonist and a beta-blocker on cell- and copper-mediated oxidation of LDL and on the accumulation and efflux of cholesterol in human macrophages and murine J774 cells

Calcium antagonists and beta-blockers may retard or inhibit atherogenesis. In the absence of data pertaining to the potential cardioprotective action of an association of such agents, we have investigated the impact of nifedipine and atenolol, alone or in combination, on the capacity of monocyte-macrophages (ex vivo) and copper ions (in vitro) to oxidize LDL and on intracellular metabolism and efflux of free and esterified forms of cholesterol in human macrophages and foam cells. At concentrations up to 100 micromol/L, atenolol had no effect on the oxidative resistance of LDL; on the contrary, nifedipine displayed a significant dose-dependent capacity to protect LDL during copper-mediated oxidation (100 micromol/L; P<.001). Using a DPPH radical generating system, nifedipine was shown to exert free radical-trapping activity (molar ratio of scavenging activity, nifedipine:alpha-tocopherol, 1:114). The addition of atenolol to nifedipine was without effect on the antioxidant activity of the calcium antagonist. In experiments in which oxidative modification was mediated by monocyte-macrophages, nifedipine but not atenolol conserved its antioxidant capacity. Furthermore, we demonstrated that association of atenolol with nifedipine did not modify the antioxidant properties of nifedipine itself. Using a human monocyte-derived macrophage culture system, nifedipine, atenolol, or a combination of the two drugs was ineffective in inhibiting foam cell formation induced by acetylated LDL or oxidized LDL. However, atenolol (100 micromol/L) increased cellular accumulation of cholesteryl ester (+17%; P<.05), whereas nifedipine (100 micromol/L) decreased total cholesterol (-37.4%; P<.05) accumulation induced by acetylated LDL in the mouse macrophage cell line J774. A combination of the two drugs neutralized these antagonistic effects. None of these results were reproduced during the oxidized LDL-induced transformation of murine J774 cells into foam cells. Furthermore, cholesterol efflux from preloaded human macrophages was equally unaffected by the addition of the drugs alone or in combination. It therefore seems unlikely that the beneficial effect of atenolol on coronary heart disease is mediated by changes in either LDL oxidizability or cholesterol metabolism in human macrophages and foam cells. Our findings with nifedipine suggest, however, that this calcium antagonist may potentially exert antiatherosclerotic properties via a reduction of the oxidative modification of LDL, thereby affecting a reduction in foam cell formation and in the pathophysiological cellular activities of oxidized lipids, rather than by inducing a direct reduction in cholesterol accumulation in human foam cells of macrophage origin.

Effect of the new calcium antagonist lercanidipine and its enantiomers on the migration and proliferation of arterial myocytes

The in vitro effects were investigated of the new dihydropyridine calcium antagonist (CA) lercanidipine and its enantiomers on arterial myocyte (smooth muscle cell; SMC) migration and proliferation as related to L-type calcium channel inhibition. Lercanidipine and its enantiomers inhibited the replication and migration of arterial myocytes in concentration ranging from 10 to 50 microM. The antiproliferative effect of lercanidipine, evaluated as cell number, was dose dependent, with a potency similar to that of lacidipine and nifedipine, and was unrelated to the stereoselectivity of enantiomers to bind L-type calcium channels. The cell doubling time increased with drug concentration < or = 122 versus 38 h for controls. The cell growth inhibition induced by lercanidipine and its enantiomers was reversible. Lercanidipine dose dependently decreased [3H]thymidine incorporation into DNA; the (R)-enantiomer, displaying the lowest CA activity, was the most potent in this respect. The tested compounds were able to inhibit fibrinogen-induced myocyte migration in a dose-dependent manner, with the (R)-enantiomer showing the more pronounced effect. To directly rule out the role of calcium channels in the antiatherosclerotic properties of lercanidipine, we examined the effect of the compounds on serum-stimulated calcium influx in SMC. Fluorimetry of Fluo 3 was used to measure changes in free cytosolic Ca2+ concentration ([Ca2+]i) in SMC after long-term preincubation (24 h) with the tested CA. Lercanidipine and its enantiomers (25 microM) decreased the serum-induced elevation of [Ca2+]i in SMC with the (S)-enantiomer (69% inhibition) 2.4-fold more active than the counterpart and the racemate (29% inhibition). In conclusion, our in vitro results suggest that lercanidipine may directly interfere with events involved in atherogenesis. The studies performed with enantiomers of lercanidipine suggest that the observed effects are not related to the blockade of voltage-dependent Ca2+ channels and confirm at least in vitro a pharmacologic potential of the compound to negatively influence the process of atherogenesis.

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

The proliferation of vascular smooth muscle cells has been implicated as a causative factor in atherogenesis. Calcium channel blockers have been shown to retard the progression of atherosclerosis. To elucidate the mechanism by which these drugs mediate such actions, we studied the effects of a new calcium antagonist, clentiazem, on the in vitro proliferation of vascular smooth muscle cells. PDGF-induced prolifertion of these cells is markedly inhibited by clentiazem. The probable involvement of protein kinase C (PKC) in this cellular response is suggested. Clentiazem appear to cause inhibition of PKC translocation that is induced by phorbol esters and PDGF-BB and the phosphorylation of the 80 kDa protein substrate of PKC in vascular smooth muscle cells. Moreover, treatment with clentiazem leads to a marked decrease in the number of specific phorbol ester binding sites. Analysis of the membrane bound isoenzymes of protein kinase C revealed that the inhibition was specific to delta enzymes. Arterial cholesterol ester hydrolysis is not significantly altered by clentiazem. Our results suggest that clentiazem may inhibit cell proliferation by regulating cytosolic PKC and preventing its membrane translocation and activation.

Calcium-dependent second-messenger regulation of low-density lipoprotein oxidation by human aortic smooth muscle cells

BACKGROUND

We postulated that the response of vascular smooth muscle cells (SMCs) to oxidized low-density lipoprotein (LDL) may be modulated through calcium and 3', 5' cyclic adenosine monophosphate (Ca+2-cAMP) second-messenger activity.

METHODS

Changes in cytosolic calcium [Ca+2]i in aortic SMCs exposed to native (N-) and oxidized (Ox-) LDL were measured with a Fura 2-AM indicator. The influence of cAMP on this response was determined by incubating the cells with either forskolin or 8-bromo-cAMP (stimulatory) or galanin (inhibitory). The cells were then activated by an initial preincubation with N- or Ox-LDL, and the subsequent cellular oxidation of N-LDL was measured. The effect of cAMP mediators alone or in conjunction with calcium antagonism was studied.

RESULTS

Exposure of SMCs to Ox-LDL resulted in a marked elevation of [Ca+2]i(306 +/- 12 nmol/L) compared with that in the control group (192 +/- 15 nmol/Liter; p < 10(-6)). This response was augmented by cAMP stimulation (406 +/- 8 nmol/L; p < 10(-6)) but reduced by cAMP inhibition (247 +/- 8 nmol/L; p < 10(-6)). The activation of intracellular signaling by initial Ox-LDL priming increased the subsequent oxidation of N-LDL (0.40 +/- 0.02 nmol malondialdehyde versus 0.24 +/- 0.02 nmol MDA control; p < 10(-4)). This response was enhanced by cAMP (0.45 +/- 0.03 nmol MDA; p < 10(-4)) and inhibited by galanin (0.26 +/- 0.02; p < 10(-4)). The cAMP effect was reversed by the blockade of calcium mobilization via membrane channels and reticular release.

CONCLUSIONS

Oxidized LDL-induced Ca+2-cAMP signaling modulates the cellular oxidation of N-LDL. This finding suggests a mechanism through which the scavenger uptake of modified LDL may potentially be regulated.

Modification of adrenergic reactivity in rat tail artery by dietary lipids and calcium channel antagonists

1. The antiatherosclerotic activity of dihydropyridines (DHP), potent calcium antagonists, was studied with respect to prevention of hypercontractility of perfused rat tail arteries. 2. Used for 1 month, atherogenic diet increased pressor responses to norepinephrine (NE) in Ca(2+)-free physiological salt solution (PSS), and PSS containing Ca(2+). 3. When nifedipine (NIF) or nitrendipine (NIT) was administered simultaneously with an atherogenic diet, the contractile activity of NE in Ca(2+)-free PSS was attenuated. Moreover, vasoconstrictor responses to NE in PSS containing Ca2+ were inhibited after 1-month treatment with NIT and nimodipine (NIM). 4. NIF, NIT and NIM prevented atherosclerosis-induced vascular hyperreactivity to alpha-adrenoceptor agonists in rat tail artery.

Inhibitory effect of calcium channel blockers on human mesangial cell growth: evidence for actions independent of L-type Ca2+ channels

Calcium channel blockers (CCB) are known to affect the outcome of glomerulosclerosis in vivo and to suppress mesangial cell proliferation and cytokine production in vitro. It is uncertain, however, whether (i) human adult mesangial cells (HMC) express L-type Ca2+ channels and (ii) whether the effect of CCB on HMC is mediated by inhibition of L-type Ca2+ channels. In single cell preparations of HMC, the L-type Ca2+ channel agonist Bay K 8644 and K+-depolarization of the cell membrane caused a transient increase of cytosolic free Ca2+ ([Ca2+]i) in 60 to 80% of the cells. The CCB verapamil and nifedipine partially inhibited the effect of Bay K 8644 and K+-depolarization on [Ca2+]i. Binding experiments confirmed these functional studies by showing specific binding at the phenylalkylamine binding site of L-Type Ca2+ channels. Quiescent HMC were stimulated with fetal calf serum (FCS) or growth factors (platelet derived growth factor A/B, epidermal growth factor, angiotensin II, endothelin 1) in the presence of various concentrations (10(-10) to 10(-5) M) of different CCB: either (R)-verapamil, (S)-verapamil or the raceme of verapamil, and nifedipine or diltiazem, respectively. In addition, the enantiomers of devapamil were studied, because their action on the L-type Ca2+ channel is more stereoselective than that of the enantiomers of verapamil. At high concentrations (10(-6) to 10(-5) M) (R,S)-verapamil decreased cell numbers in cultures of quiescent HMC, increased LDH in the supernatant, and caused loss of trypan blue exclusion (cytotoxicity). At lower concentrations (R,S)-verapamil showed no cytotoxicity, but had two effects: (1.) concentration dependent (down to 10(-8) M) inhibition of indices of cell proliferation, that is, (i) stimulated (FCS or growth factor) 3H-thymidine incorporation and (ii) increment in cell number; and (2.) inhibition of indices of cell or matrix protein synthesis, that is, (i) stimulated 3H-methionine incorporation and (ii) 3H-proline incorporation. At equimolar concentrations the dihydropyridine nifedipine was equipotent with verapamil, whereas the benzothiazepine diltiazem was conspicuously less effective. Even at the lowest effective concentration (10(-8) M) comparison of (R)- and (S)-verapamil showed no significant difference between the enantiomer with weak or with strong effect on L-type Ca2+ channels, and this was true even when the more stereoselective enantiomers of devapamil were tested. These observations argue against the notion that effects of CCB result from specific interaction with L-type Ca2+ channels. The data are more consistent with the idea that interactions with targets other than L-type Ca2+ channels are involved.

Isradipine increases vascular prostaglandin I2-formation while the thromboxane B2-synthesis is diminished

PGI2- and TXA2-synthesis from vascular tissue samples derived from cultured (endothelial and smooth muscle) cells, rabbit aorta and human bypass surgery were determined using specific radioimmunoassays for the stable derivatives (6-oxo-PGF1a and TXB2, respectively) of these compounds. Cultured cells were incubated in presence of isradipine, rabbits were pretreated for 4 weeks receiving 0.3 mg isradipine/kg*day, while patients were on isradipine (5-10 mg total dose/day, per os twice daily) since 6-19 weeks. In presence of isradipine, cultured cells produced significantly (p < 0.01) more 6-oxo-PGF1a and significantly less TXB2 (p < 0.05). 6-oxo-PGF1a-formation in rabbit aorta was significantly (p < 0.01) higher in isradipine treated normocholesterolemic animals while no significant changes were seen in isradipine treated hypercholesterolemic animals. TXB2 was significantly (p < 0.01) depressed in the abdominal and the thoracic aortic segment of isradipine treated hypercholesterolemic animals and was not significantly influenced in isradipine treated normocholesterolemic animals. Similarly, PGI2-synthesis in human arterial specimen was significantly (p < 0.01) enhanced as compared to the untreated controls. These findings indicate a beneficial behaviour of isradipine on vascular wall eicosanoid profile, which may contribute to a variety of antiatherosclerotic actions at the vascular wall level and to an improvement in hemostatic balance already described.

Effect of SR 33805 on arterial smooth muscle cell proliferation and neointima formation following vascular injury

The possible activity of SR 33805 ([[N-[dimethoxy-3,4-phenethyl]-N- methylamino-propoxyl]-4-benzenesulfonyl]-2-isopropyl-3-methyl-1-in dole), a novel Ca2+ channel blocker, in early atherogenesis was investigated. In vitro, SR 33805 strongly inhibited fetal calf serum-induced proliferation of cultured human aortic smooth muscle cells with an IC50 value of 0.3 +/- 0.1 microM (n = 3). In this respect, SR 33805 was several fold more active than the reference compounds: diltiazem, verapamil, nifedipine and fantofarone. SR 33805 was also a potent inhibitor of platelet-derived growth factor- or basic fibroblast growth factor-induced proliferation of human smooth muscle cells. SR 33805 inhibited serum-stimulated 45Ca2+ uptake in these cells, with an IC50 value of 47 +/- 18 nM. The effect of SR 33805 on intimal smooth muscle hyperplasia in rabbit carotid arteries subjected to air-drying endothelial injury was then investigated. After a 16-day treatment, SR 33805 (6.0 mg/kg/day p.o.) inhibited the development of intimal thickening. Under the same experimental conditions, nifedipine, verapamil, diltiazem (2 x 6 mg/kg/day p.o.--16 days) and fantofarone (12 mg/kg/day p.o.--16 days) were inactive. These results show that SR 33805, a novel and potent Ca2+ channel blocker, can reduce myointimal thickening following endothelial injury.

Propionyl-L-carnitine prevents the progression of atherosclerotic lesions in aged hyperlipemic rabbits

We have characterized the extent and the phenotype of total and proliferating cell population of aortic plaques in aged rabbits receiving a long-term low-dose cholesterol hyperlipemic diet, which represents an experimental model of atherosclerosis. For nine months, rabbits received the hypercholesterolemic diet alone or in addition to a treatment with propionyl-L-carnitine (PLC), a derivative of carnitine, an intramitochondrial carrier of fatty acids present in most cell types. We observed that, in both PLC-treated and control hyperlipemic rabbits, the ratio between proliferating macrophage-derived and smooth muscle cells was 2:1. PLC in addition to the hypercholesterolemic diet induced a marked lowering of plasma triglycerides, very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) triglycerides, while plasma cholesterol was slightly and transiently reduced. Moreover, PLC-treated hyperlipemic rabbits exhibited a reduction of plaque thickness and extent, a slight but significant reduction of the percentage of macrophage-derived cells as compared to control hyperlipemic animals and a reduction of the number of both proliferating macrophage- and smooth muscle cell-derived foam cells. Finally, both proliferating and non-proliferating plaque cells expressed large amounts of macrophage colony-stimulating factor protein, in particular macrophage-derived foam cells. These results indicate that a modification of plasma lipemic pattern obtained by a long-term oral administration of PLC was associated with a decrease of plaque cell proliferation and severity of aortic atherosclerotic lesions.

Evidence for lipid regression in humans in vivo performed by 123iodine-low-density lipoprotein scintiscanning

Radiolabeling of autologous LDL allows in vivo characterization of arterial wall lipid metabolism and LDL receptor imaging. Different kinetic types of arterial wall LDL entry reflect the de-, re-, and endothelialized segments in both animals and humans. In 36 male cholesterol-fed rabbits being treated with the calcium channel blocker isradipine (0.3 mg/kg daily), the retention of the radiolabeled (125I-LDL) was reduced, being related to the reduction in arterial wall cholesterol ester content and the decreased extent of Sudan III-positive areas. In parallel, a significant (p < 0.01) increase in vascular prostaglandin I2 (PGI2) generation was seen in endothelialized and reendothelialized segments of the abdominal aorta. These effects were completely abolished by concomitant treatment with acetylicsalicylic acid (ASA). These data could be confirmed in humans, too: a 4-week treatment with prostaglandin E1 (PGE1:5 ng/kg/min iv, 5 days/week, 6 h/day for 6 weeks) and isradipine (2 x 2.5 mg po daily for 4 weeks) did not change arterial 123I-LDL influx kinetics, which were examined over a total of 60 (PGE1) and 96 (isradipine) vascular regions. In contrast to this, the retention of the tracer was significantly diminished in different arterial segments. In isradipine-treated patients, 20 hours after reinjection of radiolabeled LDL, the quantitative LDL entry was reduced by at least 4.7% with a maximum of 23.5% (p < 0.01) in type I (n = 50 lesions) or type II lesions (n = 41). PGE1 treatment induced a 16.9% to 30.7% (p < 0.01) decrease of LDL retention in type I (n = 36 lesions) or type II lesions (n = 24), respectively. These findings support the hypothesis derived from earlier experimental studies that the antiatherosclerotic effects are likely to be due to the increase in PGE1 and/or PGI2 availability mediated by an increase in cAMP. The results demonstrate the potential of 123I-LDL scintigraphy for the characterization of vascular LDL kinetics and the monitoring of functional lipid lesion regression.

Atherosclerosis and thrombosis. Old and new drugs

Thanks to the increasing knowledge of the pathogenesis of atherosclerosis, much effort has been made in the last years to develop new drugs aimed at controlling risk factors correlated with the disease as well as to investigate more deeply their mechanism of action. In particular, this brief review will describe some new aspects of the mechanism of action of drugs widely used in the control of risk factors like hyperlipemia, hypertension and blood viscosity. Among drugs active on plasma lipid profile, HMG-CoA reductase inhibitor are, at present, under study for their promising activity in the modulation of the interaction between the cells of the arterial wall and circulating blood elements. Indeed, these compounds have been found to control the proliferation of smooth muscle cells and other events related to the formation of atheroma. As far as antithrombotic drugs are concerned, the efficacy of low doses of aspirin has emerged by recent clinical trials. The successful use of low doses of aspirin has been possible following the comprehension of the mechanism by which this compound inhibits TXA-dependent platelet function, thus allowing a dose-dependent dissociation of the antithrombotic activity from other undesirable effects. Also for calcium antagonist an antiatherogenic effect which deserves further investigations has been recently clarified. Indeed it has been demonstrated that calcium antagonists have a protective effect against vascular lesions because they inhibit smooth muscle cell proliferation, lipid uptake by macrophages and the production of collagen and elastin. Another class of drugs which represents a new approach in the control of some risk factors is represented by n-3 fatty acids. Besides their activity on triglycerides, these compounds exert a positive effect on hemostatic and thromboembolic event, by reducing platelet aggregation and blood viscosity. Also for those molecules which appear to exert promising antiatherosclerotic and antithrombotic action, further studies will define their exact mechanism of action.

Effect of calcium antagonists on isolated aorta from hypercholesterolemic Yoshida rats of different ages

1. The in vitro thoracic aorta, precontracted with norepinephrine, KCl or PGF2 alpha of hypercholesterolemic Pittsburg-Yoshida (YOS) and normolipidemic Brown-Norway (BN) rats of two age groups (2 and 18 months), was relaxed by the calcium antagonists verapamil and nifedipine without any difference between age-matched YOS and BN rats. 2. The relaxant activity of verapamil was impaired in aged rats of both strains and with the different contractile agents. Conversely, no variation with aging of the nifedipine relaxing effect was observed on KCl-induced contraction was the nifedipine relaxant effect differently affected by age, both in YOS and BN rats. 3. In conclusion, prolonged exposure to hypercholesterolemia in YOS rat does not affect aortic response to nifedipine and verapamil. Only the aging process was able to affect vascular relaxation to calcium antagonists.

Modulation of dihydropyridine receptors in vascular smooth muscle cells by membrane potential and cell proliferation

We have studied binding of isradipine to A7r5 vascular smooth muscle cells as a function of membrane potential and cell proliferation. Consistent with a voltage-modulated receptor model, two classes of binding sites were detected in confluent cultures: high-affinity sites under depolarizing (50 mM K+) conditions (Kd = 45 +/- 3 pM), and lower affinity sites under resting (5 mM K+) conditions (Kd = 181 +/- 20 pM). However, proliferating cells also displayed the high-affinity state at rest (Kd = 29 +/- 9 pM) in addition to a low-affinity site (Kd = 869 +/- 383 pM). Analysis of dissociation rates also revealed two receptor classes during proliferation. Proliferating cells showed a single class of high-affinity sites (Kd = 39 +/- 6 pM) when depolarized, similar to confluent cells. Receptor density in confluent monolayers increased from 15 +/- 3 fmol/10(6) cells at 5 days to 72 +/- 6 fmol/10(6) cells after 10 days. These results suggest (i) that some L-type Ca2+ channels are spontaneously active in proliferating vascular smooth muscle cells, but require depolarization to activate in a confluent monolayer, and (ii) that the density of dihydropyridine receptors increases after a monolayer becomes confluent.

Intralesional verapamil injection for the treatment of Peyronie's disease

Peyronie's disease remains a therapeutic dilemma for the practicing urologist. Multiple nonoperative therapies have been offered with variable suboptimal response rates. Calcium channel blockers have been shown to alter the metabolism of fibroblasts, resulting in decreased extracellular matrix secretion of collagen as well as increased collagenase activity. In this nonrandomized dose-escalating format study 14 men received biweekly injections of verapamil into the Peyronie's plaques for 6 months. Subjectively, there was significant improvement in plaque-associated penile narrowing (100%) and curvature (42%). Objectively, a decreased plaque volume of greater than 50% was noted in 30% of the subjects. Plaque softening was noted in all patients, while 83% noticed that plaque-related changes in erectile function had arrested or improved. There was no toxicity nor did symptoms recur when improvement was noted. This preliminary study suggests that intralesional calcium antagonist (verapamil) therapy offers an economical and sensible nonoperative approach to the treatment of Peyronie's disease.

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.

Nutrition, endothelial cell metabolism, and atherosclerosis

The vascular endothelium that forms an interface between the blood and the surrounding tissues is continuously exposed to both physiologic and pathophysiologic stimuli. These stimuli are often mediated by nutrients that can contribute to the overall function of the endothelial cell in the regulation of vascular tone, coagulation and fibrinolysis, cellular growth and differentiation, and immune and inflammatory responses. Therefore, nutrient-mediated functional changes of the endothelium and the underlying tissues may be significantly involved in the atherosclerotic disease process. There is evidence that individual nutrients or nutrient derivatives may either provoke or prevent metabolic and physiologic perturbations of the vascular endothelium. Preservation of nutrients that exhibit antiatherogenic properties may, therefore, be a critical issue in the preparation and processing of foods. This review focuses on selected nutrients as they affect endothelial cell metabolism and their possible implications in atherosclerosis.

Comparable beneficial effects of defibrotide and nifedipine in calcium induced atherosclerosis

The present study demonstrates the antiatherosclerotic property of Defibrotide (DFT) in an experimental model in which the pathology is secondary to calcium deposition in the vessel wall and various organs. Rats were treated by gavage for 21 consecutive days with Vitamin D3 and/or, twice a day, with DFT or Nifedipine (N). The calcium contents of aorta, heart and kidney were determined by atomic absorption spectrometry. Specimens of these tissues were examined histologically. DFT or N administered alone did not modify the calcium contents of aorta, heart or kidney. On the contrary, Vitamin D3 caused a huge increase in the calcium concentration in the aorta and in the kidney, whereas the heart content was only double that of control animals. In rats treated with Vitamin D3, contemporaneous administration of DFT or N sharply and highly significantly reduced the aorta calcium concentration and there were less striking, although still significant, reductions in the other two tissues. Histological examination paralleled these data; the effect of DFT or N in reducing the mineralization of aorta and heart was very evident, and more pronounced for DFT. These results confirm that DFT, even though not belonging to the class of the calcium antagonists, has comparable antiatherosclerotic properties, possibly due to its endothelial protective efficacy, as evidenced by the lesser amount of calcium in the aortic tissue.

Tissue selectivity of hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors

Hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors are a class of lipid-lowering medications, with a major activity on plasma cholesterol levels, now enjoying a vast popularity among physicians and patients. These drugs, affecting a very early and key step of sterol biosynthesis, differ to a large extent in their physicochemical properties, tissue distribution and side effects in animals, possibly in humans. Some of these agents (namely lovastatin and simvastatin) are strikingly lipophilic and require enzymatic conversion from the lactone to the open-ring forms, whereas pravastatin, active per se, is hydrophilic. Liver uptake of pravastatin is regulated by a carrier-mediated mechanism. Other HMG CoA reductase inhibitors have been designed, with the objective of obtaining high levels of hepato-selectivity. Evaluation of available data in terms of potential advantages in tissue, namely liver selectivity, of HMG CoA reductase inhibitors, suggests, that, indeed, altered sterol biosynthesis in a number of tissues may potentially result in the appearance of significant side effects. While there is no clear-cut relationship between tissue selectivity and lipophilicity, the presence of this latter feature seems, in general, to dictate a lesser absorption to peripheral tissues vs the liver. At present, the toxicological profile of major HMG CoA reductase inhibitors appears safe; it is, however, possible that in selected patient groups liver selectivity may offer a considerable therapeutic advantage.

Calcium channel blockers in current medical practice: an update for 1993

Calcium channel blocking drugs (CCB) have been used to lower blood pressure since 1970. Three classes are currently available, the phenylalkylamines, the benzothiazepines, and the dihydropyridines. The structure of the L-type, voltage dependent calcium channel has been elucidated with molecular techniques and the different binding sites of the various CCB described. CCB have specific effects at the site of target organs. In the kidney, all classes produce natriuresis. Their action appears independent of the level of salt intake. CCB may favorably influence the course of chronic renal disease; the results of a trial comparing nifedipine to the converting enzyme inhibitor captopril showed no difference between the two drugs. CCB may impede the progression of atherosclerosis in the coronary arteries; a prospective study of nifedipine on coronary artery morphology supports this view. In the brain, nimodipine improves the outcome of patients with stroke from subarachnoid hemorrhage. Positive effects on patients with ischemic stroke have not been corroborated. CCB are approved primary treatment for patients with hypertension and are readily combined with other antihypertensive agents. They are well tolerated and have no adverse metabolic side effects. The advent of molecular pharmacology will advance current efforts to develop new CCB, which are highly selective in their site and mode of action.

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.

Dual Ca2+ requirement for optimal lipid peroxidation of low density lipoprotein by activated human monocytes

The oxidative modification of LDL seems a key event in atherogenesis and may participate in inflammatory tissue injury. Our previous studies suggested that the process of LDL oxidation by activated human monocytes/macrophages required O2- and activity of intracellular lipoxygenase. Herein, we studied the mechanisms involved in this oxidative modification of LDL. In this study, we used the human monocytoid cell line U937 to examine the role of Ca2+ in U937 cell-mediated lipid peroxidation of LDL. U937 cells were activated by opsonized zymosan. Removal of Ca2+ from cell culture medium by EGTA inhibited U937 cell-mediated peroxidation of LDL lipids. Therefore, Ca2+ influx and mobilization were examined for their influence on U937 cell-mediated LDL lipid peroxidation. Ca2+ channel blockers nifedipine and verapamil blocked both Ca2+ influx and LDL lipid peroxidation by activated U937 cells. The inhibitory effects of nifedipine and verapamil were dose dependent. TMB-8 and ryanodine, agents known to prevent Ca2+ release from intracellular stores, also caused a dose-dependent inhibition of LDL lipid peroxidation by activated U937 cells while exhibiting no effect on Ca2+ influx. Thus, both Ca2+ influx through functional calcium channels and Ca2+ mobilization from intracellular stores participate in the oxidative modification of LDL by activated U937 cells. 45Ca2+ uptake experiments revealed profound Ca2+ influx during the early stages of U937 cell activation, however, the Ca2+ ionophore 4-bromo A23187 was unable to induce activation of U937 cells and peroxidation of LDL lipids. Release of intracellular Ca2+ by thapsigargin only caused a suboptimal peroxidation of LDL lipids. Our results indicate that although increases in intracellular Ca2+ levels provided by both influx and intracellular Ca2+ mobilization are required, other intracellular signals may be involved for optimal peroxidation of LDL lipids by activated human monocytes.

Inhibition of lipid deposition in the hypercholesterolemic rat by clentiazem, a calcium channel blocker

We studied the effects of clentiazem, a calcium channel blocker (1) on the accumulation of lipid in the aorta, (2) on the level of plasma lipids, and (3) on the number of adherent intimal monocytes and foam cells. Seventy Wistar rats were assigned to one of the following groups: (1) regular diet, (2) an atherogenic diet consisting of regular chow with 2% cholesterol, 1% cholic acid, and 0.5% thiouracil (CCT), (3) CCT supplemented with 5 mg/kg/day clentiazem, and (4) CCT with 25 mg/kg/day clentiazem. Animals were sacrificed after 6 or 12 weeks of diet. Aortas were studied by light microscopy after staining with oil red O (ORO) and/or hematoxylin. ORO staining was quantified in both abdominal and thoracic regions of the aorta. The aortas of the clentiazem groups demonstrated significantly less ORO staining than CCT diet controls in thoracic aorta after 6 weeks and abdominal aorta after 12 weeks. There was no significant difference in the plasma lipid concentrations. The clentiazem-treated groups had fewer numbers of adherent monocytes and foam cells. We conclude that clentiazem inhibits lipid deposition in cholesterol-fed rats without lowering plasma lipid concentrations and that the number of intimal monocytes and foam cells is decreased in the presence of this calcium antagonist.

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.