Effects of beta-blockers on the concentration and oxidizability of plasma lipids

Metabolic effects of manidipine

The calcium channel antagonists (CCAs) were originally introduced as vasodilators for the treatment of coronary heart disease, but are now also noted for their clinical efficacy in the management of hypertension. Data from large clinical studies have shown that CCAs are not associated with the undesirable metabolic effects (e.g. worsening of dyslipidemia and reduction of insulin sensitivity) seen with older agents such as thiazide diuretics and beta-adrenoceptor antagonists (beta-blockers) that are used to treat hypertension. Indeed, reductions in cardiovascular risk and rates of onset of new cases of diabetes mellitus have been reported in trials in patients with hypertension treated with CCAs. These beneficial effects extend beyond those expected to accompany reductions in BP. Until recently, the biochemical effects underlying these metabolic changes were only poorly understood, but pharmacologic studies have now started to shed more light on these issues. Of particular interest are studies with manidipine, some of which suggest that this agent may be associated with greater improvements in insulin sensitivity and may have better renal protective properties than other CCAs. Confirmation of potential differences among CCAs in terms of the relative magnitude of any beneficial metabolic effects requires further study. Ongoing research is expected to clarify further the action of these agents at the cellular level and to assist with the optimization of antihypertensive therapy, particularly in patients with elevated cardiovascular risk profiles.

Effect of antihypertensive therapy on serum lipids in newly diagnosed essential hypertensive men

The effect of antihypertensives on serum lipids in newly diagnosed male essential hypertensive patients was studied. The participants (n = 99) were randomly allocated to receive amlodipine, atenolol, enalapril, hydrochlorothiazide, and a combination of amlodipine and atenolol. Lipid parameters were estimated before and after 8 weeks of therapy. The atenolol and thiazide group showed a significant increase in triglycerides (TGs) and very-low-density lipoprotein cholesterol (VLDL-C). High-density lipoprotein cholesterol (HDL-C) and HDL-C to low-density lipoprotein cholesterol (LDL-C) ratio were significantly increased and TC to HDL-C ratio was significantly decreased in the amlodipine and amlodipine- atenolol combination groups. In the enalapril group, we found a significant reduction in TC, TGs, VLDL-C, non-HDL-C, and TG to HDL-C ratio after treatment. It can be concluded from the present study that some drugs have beneficial effects on the lipid status, whereas others adversely affect the lipid status in hypertension.

Potent Antioxidant Properties of 4-Hydroxyl-propranolol

The antioxidant properties of 4-HO-propranolol (4HOP), a major metabolite of propranolol, were studied and compared with that of propranolol and vitamin E (Trolox). When isolated hepatic microsomal membranes were peroxidized by an iron-catalyzed.OH-generating system [dihydroxyfumarate +Fe (III)], 4HOP potently and concentration-dependently inhibited lipid peroxidation; the IC50 value was 1.1 microM, whereas those for Trolox and propranolol were 4.3 and 168 microM, respectively. When isolated human low-density lipoprotein (LDL) was oxidized by 7.5 microM Cu(II) for 9 h, 4HOP at 3 microM delayed the lag phase significantly by 108 min, which was comparable with that of probucol (98-min delay) but was far greater than that provided by propranolol (6 min) or Trolox (47 min). At 1 microM 4HOP, the delay was 45 min. When confluent cultured bovine aortic endothelial cells were exposed to the Fe-catalyzed oxy-radical system, acute loss of glutathione occurred (55% decrease in 50 min). Pretreatment of the cells with 0.067 to 6.7 microM 4HOP for 30 min provided increasing degrees of protection against the glutathione loss; the EC50 value was 1.2 microM, whereas those for Trolox and propranolol were 7.9 and 49 microM, respectively. The loss of cell survival due to the radical stress was also effectively preserved by 4HOP. In separate experiments, when the endothelial glutathione was oxidatively depleted by a peroxynitrite-generating system (3-morpholinosydnonimine), 4HOP also provided potent protective activities. In conclusion, 4HOP is 4- to 8-fold more potent than vitamin E and >100-fold more active than propranolol as a "chain-breaking" antiperoxidatant against membrane and LDL oxidation and can provide superior endothelial cytoprotective efficacy against oxygen- or nitrogen-derived oxidant-mediated cell injury. Being a major metabolite in human and with its plasma level approaching that of propranolol, 4-HO-propranolol may contribute, in part, to the cardiovascular therapeutic benefits of propranolol.

The association between antihypertensive drug therapies and plasma lipid levels in the general population

OBJECTIVE

To assess the association between different antihypertensive drug regimens and plasma lipid levels in the general population.

METHODS

The Monitoring Project on Cardiovascular Risk Factors was conducted from 1987 to 1991 as a cross-sectional study in The Netherlands. Antihypertensive drug-users and untreated hypertensives were selected. After exclusion of users of cholesterol-lowering drugs 2997 subjects remained for the analysis. The plasma lipid concentrations of the users and non-users of antihypertensives were compared by multiple linear regression.

RESULTS

In the univariate analysis patients using beta-blockers had lower high-density lipoprotein (HDL) concentrations (1.13 mmol/l, P < 0.05) and higher cholesterol ratios (5.74, P < 0.05) than untreated hypertensives (Total cholesterol = 6.07 mmol/l, HDL = 1.20 mmol/l and ratio = 5.44). Patients using diuretics had higher total cholesterol levels (6.34 mmol/l) and higher HDL levels (1.26 mmol/l) compared to untreated hypertensives. After adjustment for possible confounders these differences were smaller and no longer statistically significant. After adjustment we found a significant lower HDL cholesterol (mean difference of -0.10 mmol/l, P < 0.05) for users of a combination of a beta-blocker and a diuretic.

CONCLUSIONS

Although randomised, controlled trials have demonstrated that antihypertensive drugs may influence plasma lipid levels we observed no substantial association for single antihypertensive drug therapy in the general population. The combination of a diuretic and a beta-blocker was associated with a worse lipid profile.

Low density lipoprotein oxidation, antioxidants, and atherosclerosis

Oxidized low density lipoproteins (LDLs) are believed to be the most atherogenic form of LDL. However, although a number of experimental data support this concept, the protective role of antioxidants that may prevent LDL oxidation in atherosclerosis is only partially confirmed by studies in humans. Observational and epidemiologic data as well as randomized trials failed to provide clear-cut indications because of mixed results on the protective role of antioxidants against cardiovascular diseases. In spite of the lack of a general consensus, recent data reinforce the concept that a regular intake of antioxidants present in food blocks the progression of atherosclerosis and that the reduced oxidisability of LDL may represent a good marker to follow the action of antioxidants. When it becomes possible to monitor the efficacy of any antioxidant therapy with validated markers of oxidation, the potential influence of vitamins and antioxidants on coronary artery disease will eventually be resolved.

Antioxidants and coronary artery disease

The protective role of antioxidants in experimental models of atherosclerosis is only partially confirmed by studies in man. Observational and epidemiologic data, as well as randomized trials failed to provide clear cut indications, because of mixed results on the protective role of antioxidants against cardiovascular diseases. In spite of the lack of a general consensus, recent data reinforce the concept that a regular intake of antioxidants present in food limits the progression of atherosclerosis. When it will be possible to monitor the efficacy of any antioxidant therapy with validated markers of oxidation, the potential influence of vitamins and antioxidants on coronary artery disease may eventually be resolved.

Antioxidants and coronary artery disease

Data on the protective role of antioxidants in models of atherosclerosis are only partially confirmed in man. Observational and epidemiological data, as well as randomized trials, provide no clear cut indications, because of positive and disappointing results on the use of antioxidants in cardiovascular protection. Despite the lack of a general consensus, recent data reinforce the concept that the regular intake of antioxidants present in food limits the progression of atherosclerosis. When it is possible to monitor the efficacy of any antioxidant therapy with validated markers of oxidation, the potential influence of vitamins and antioxidants on coronary artery disease may eventually be resolved.