The effects of antihypertensive agents on atherosclerosis-related parameters of human aorta intimal cells

Testing of serum atherogenicity in cell cultures: questionable data published

In a large series of studies was reported that culturing of smooth muscle cells with serum from atherosclerosis patients caused intracellular lipid accumulation, while serum from healthy controls had no such effect. Cultures were used for evaluation of antiatherogenic drugs. Numerous substances were reported to lower serum atherogenicity: statins, trapidil, calcium antagonists, garlic derivatives etc. On the contrary, beta-blockers, phenothiazines and oral hypoglycemics were reported to be pro-atherogenic. Known antiatherogenic agents can influence lipid metabolism and cholesterol synthesis, intestinal absorption or endothelium-related mechanisms. All these targets are absent in cell monocultures. Inflammatory factors, addressed by some antiatherogenic drugs, are also not reproduced. In vivo, relationship between cholesterol uptake by cells and atherogenesis must be inverse rather than direct: in familial hypercholesterolemia, inefficient clearance of LDL-cholesterol by cells predisposes to atherosclerosis. Accordingly, if a pharmacological agent reduces cholesterol uptake by cells in vitro, it should be expected to elevate cholesterol in vivo. Validity of clinical recommendations, based on serum atherogenicity testing in cell monocultures, is therefore questionable. These considerations pertain also to the drugs developed on the basis of the cell culture experiments.

Amlodipine and carvedilol prevent cytotoxicity in cortical neurons isolated from stroke-prone spontaneously hypertensive rats

We previously reported that vitamin E prevents apoptosis in neurons during cerebral ischemia and reperfusion in stroke-prone spontaneously hypertensive rats (SHRSP). In this paper, we analyzed the effects of antihypertensives as well as vitamin E, which were added to neuron cultures after reoxygenation (20% O2) following hypoxia (1% O2). When added after hypoxia before reoxygenation, vitamin E conferred significant protection to neuronal cells. It was also shown that vitamin E conferred complete protection from neural cell death when added hypoxia and again before reoxygenation. At higher concentrations of vitamin E, strong neuroprotection was observed. Moreover, we verified that pretreatment with either amlodipine, carvedilol or dipyridamole consistently prevented cell death during hypoxia and reoxygenation (H/R). On the other hand, nilvadipine, a dihydropyridine-type calcium entry blocker, had no apparent effect on neuroprotection during H/R. The order of neuroprotective potency was vitamin E > dipyridamole > carvedilol > or = amlodipine > nilvadipine. In parallel experiments, we examined whether these antihypertensive agents were more effective when combined with vitamin E and dipyridamole. The results suggested that in our in vitro model system, antioxidants were the most important agents for the reduction of oxygen-free radical damage in cortical neurons. These findings suggest that amlodipine and carvedilol, with their antioxidant properties and antihypertensive activity, would be useful to inhibit neuronal cell death in the treatment of cerebrovascular stroke and neurodegenerative diseases in hypertensive patients.

Increased expression and activity of RhoA are associated with increased DNA synthesis and reduced p27(Kip1) expression in the vasculature of hypertensive rats

We have previously shown that the function of the small G protein Rho is required for vascular smooth muscle cell proliferation and migration. We hypothesized that changes in Rho or Rho signaling might contribute to enhanced vascular proliferative responses associated with hypertension. Western blot analysis revealed that total RhoA expression was approximately 2-fold higher in aortas, tail arteries, and aortic smooth muscle cells (ASMCs) obtained from adult male spontaneously hypertensive rats (SHR) compared with those from Wistar Kyoto rats (WKY). An increase in active GTP-bound RhoA was detected in aortic homogenates by affinity precipitation with the RhoA effector rhotekin and by examining RhoA-[(35)S]GTPgammaS binding. RhoA protein and activity were also increased in vessels from rats treated with N-nitro-L-arginine methyl ester to increase blood pressure. Thrombin-stimulated RhoA activation was also significantly greater in ASMCs from SHR. As a functional correlate of these changes in Rho signaling, thrombin-stimulated DNA synthesis was enhanced in tail arteries and ASMCs from SHR. Expression of the cyclin-dependent kinase inhibitor p27(Kip1) was decreased by two thirds in SHR, and this decrease was mimicked in ASMCs by expression of a constitutively active (GTPase-deficient) mutant of RhoA. Wortmannin (10 nmol/L) fully inhibited the decrease in p27(Kip1) induced by RhoA, and a membrane-targeted catalytic subunit of phosphatidylinositol-3 kinase (PI3K [p110(CAAX)]) decreased p27(Kip1) expression, suggesting that RhoA signals through PI3K. These data provide evidence that RhoA brings about changes in DNA synthesis through reduced expression of p27(Kip1), mediated in part via PI3K, and suggest that increases in RhoA expression and activity contribute to the enhanced vascular responsiveness observed in hypertension.

The hyperlipemic hamster - a model for testing the anti-atherogenic effect of amlodipine

Male Golden Syrian hamsters were subjected to a hyperlipemic diet. At intervals ranging from 2 to 14 weeks, the animals were examined for changes in serum constituents and structural modifications of lesion-prone areas: the cardiac valves, coronary arteries and aortic arch. Serum was characterized by a gradual increase in cholesterol, triglycerides and a decrease in total peroxyl-radical trapping potential. The sequence of modifications of the endothelial cells, smooth muscle cells, and migrating plasma monocytes as well as of the extracellular matrix were established. Amlodipine treatment of hyperlipemic hamster was assessed. Amlodipine exhibited an athero-protective effect, acting as antioxidant, reducing the LDL uptake by the vessel wall and consequently, limiting the size and extent of lesioned areas. The hyperlipemic hamster is a reliable model to unravel the cellular alterations leading to atheroma formation, and for testing the effect of drugs in this process.