Low density lipoprotein metabolism in the normal to moderately elevated range of plasma cholesterol: comparisons with familial hypercholesterolemia

A suggestion for familial hypercholesterolemia (FH) heterozygosity clinical diagnosis based on epidemiological observations in a large Italian population

We selected 247 subjects from 29 large familial hypercholesterolemia (FH) kindreds from 550 probable FH subjects in Emilia Romagna (Italy) on the basis of LDL-cholesterol plasmatic levels and family trees, in order to define the best diagnostic criteria for heterozygous patients. Familial hypercholesterolemia is a monogenic disease of cholesterol metabolism inherited as an autosomal dominant trait and characterised by early cardiovascular disease. A low xanthomas and xanthelasmas prevalence was found (8.6%); coronary heart disease (CHD) death occurs very frequently in heterozygous males (72% of all deaths; mean age at death 52 years), while in females the primary cause of death was thrombotic stroke (55%; mean age 69 years). Total cholesterol (TC) mean values were 389.8 (m) and 373.3 mg/dl (f) for FH trait carriers, and 223.3 (m) and 228.8 (f) for healthy relatives. No age-related change in TC was found in heterozygotes, while unaffected relatives of FH families showed mean TC and LDL-C values, and a TC frequency distribution and a TC age-related increasing trend similar to the expected values for the Italian population. The TC frequency distribution curve appeared bimodal, with a mid-point between heterozygous and homozygous FH modal values of 280 mg/dl. To identify the FH patients, the final FH heterozygosity risk was evaluated in an unselected free-living population (from 0.07 to 0.8%, respectively, for TC between 265-274 and 295-304 mg/dl) and in hypercholesterolemic families (31 to 83%, and the same TC classes). Our conclusion is that the clinical picture is rarely pathognomonic, while the FH heterozygosity final risk evaluation and the 280 mg/dl cut-off point can be used to guide the practical clinical diagnosis and to select the patients destined for B-E receptor activity evaluation.

Atherogenic dyslipidemia: lipoprotein abnormalities and implications for therapy

Atherogenic dyslipidemia is a lipoprotein profile combining 4 specific abnormalities: borderline-high total cholesterol levels; high triglyceride concentrations; small, dense, low-density lipoprotein (LDL) particles; and low high-density lipoprotein (HDL) concentrations. It is a predisposing factor to premature coronary artery disease (CAD), although separating and calculating the contribution of each abnormality to the risk of CAD is difficult, especially since the abnormalities often appear in this combination. The ratio of total cholesterol to HDL cholesterol is currently the most powerful single predictor of risk in dyslipidemic patients. Therapy for atherogenic dyslipidemia includes dietary changes aimed at decreasing intake of cholesterol-raising fatty acids and achieving weight reduction; exercise, which confers many of the benefits of weight reduction; and, when those measures fail to correct the lipid and lipoprotein profile, drug therapy. Nicotinic acid reduces triglyceride and cholesterol levels while raising HDL concentrations, but up to half of patients cannot tolerate its adverse effects. Fibric acids effectively lower triglyceride levels and are generally well tolerated but have little beneficial effect on the cholesterol profile. Statins offer marked reductions in total, LDL, and very low-density lipoprotein cholesterol levels and cause modest increases in HDL concentration. Combination therapy can enhance the efficacy of the individual drugs.

Effects of postmenopausal estrogen replacement on the concentrations and metabolism of plasma lipoproteins

BACKGROUND

Postmenopausal estrogen-replacement therapy may reduce the risk of cardiovascular disease, and this beneficial effect may be mediated in part by favorable changes in plasma lipid levels. However, the effects on plasma lipoprotein levels of postmenopausal estrogens in the low doses currently used have not been precisely quantified, and the mechanism of these effects is unknown.

METHODS

We conducted two randomized, double-blind crossover studies in healthy postmenopausal women who had normal lipid values at base line. In study 1, 31 women received placebo and conjugated estrogens at two doses (0.625 mg and 1.25 mg per day), each treatment for three months. In study 2, nine women received placebo, oral micronized estradiol (2 mg per day), and transdermal estradiol (0.1 mg twice a week), each treatment for six weeks. The metabolism of very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) was measured by endogenously labeling their protein component, apolipoprotein B.

RESULTS

In study 1, the conjugated estrogens at doses of 0.625 mg per day and 1.25 mg per day decreased the mean LDL cholesterol level by 15 percent (95 percent confidence interval, 11 to 19 percent; P less than 0.0001) and 19 percent (95 percent confidence interval, 15 to 23 percent; P less than 0.0001), respectively; increased the HDL cholesterol level by 16 percent (95 percent confidence interval, 12 to 20 percent; P less than 0.0001) and 18 percent (95 percent confidence interval, 14 to 22 percent; P less than 0.0001), respectively; and increased VLDL triglyceride levels by 24 percent (95 percent confidence interval, 8 to 40 percent; P less than 0.003) and 42 percent (95 percent confidence interval, 26 to 58 percent; P less than 0.0001), respectively. In study 2, oral estradiol increased the mean concentration of large VLDL apolipoprotein B by 30 +/- 10 percent (P = 0.05) by increasing its production rate by 82 +/- 18 percent (P less than 0.01). Most of this additional large VLDL was cleared directly from the circulation and was not converted to small VLDL or LDL. Oral estradiol reduced LDL cholesterol concentrations by 14 +/- 3 percent (P less than 0.005), because LDL catabolism increased by 36 +/- 7 percent (P less than 0.005). The oral estradiol increased the HDL cholesterol level by 15 +/- 2 percent (P less than 0.0001). Transdermal estradiol had no effect.

CONCLUSIONS

The postmenopausal use of oral estrogens in low doses favorably alters LDL and HDL levels that may protect women against atherosclerosis, while minimizing potentially adverse effects on triglyceride levels. The decrease in LDL levels results from accelerated LDL catabolism; the increase in triglyceride levels results from increased production of large, triglyceride-rich VLDL.

Effects of MK-733 on plasma lipid and lipoprotein levels in subjects with hypercholesterolaemia

MK-733, which is a competitive inhibitor of the rate-limiting step in cholesterol biosynthesis, or a matching placebo was administered to 30 subjects with primary hypercholesterolaemia (who were already receiving dietary treatment) over a period of four weeks in a double-blind trial. Twenty-one subjects manifested heterozygous familial hypercholesterolaemia and nine subjects had polygenic hypercholesterolaemia. Five subjects received placebo, 15 subjects a low dose of MK-733 (2.5-10 mg/day) and 10 subjects received a high dose of MK-733 (20-80 mg/day). Plasma cholesterol levels in subjects who were receiving MK-733 declined significantly and in a dose-dependent fashion (31% reduction in plasma cholesterol levels with a high dose, 19% reduction with a low dose). Eight of 10 subjects who were receiving a high dose of MK-733 achieved better than a 30% reduction in plasma cholesterol levels after four weeks of treatment. The response was independent of the presence or absence of familial hypercholesterolaemia. High-density lipoprotein cholesterol levels did not change significantly, but there was a suggestive, dose-dependent reduction in plasma triglyceride levels after four weeks of treatment. MK-733 was well-tolerated, appeared to be safe, and may ultimately become an important drug in the management of more severe grades of hypercholesterolaemia.

Familial hypercholesterolaemia: effect of low density lipoproteins on esterification of cholesterol in lymphocytes from homozygous and heterozygous subjects

The effect of low density lipoproteins on esterification of cholesterol was studied in lymphocytes from patients with familial hypercholesterolaemia; results were compared with those obtained using cells from normal individuals. Freshly isolated lymphocytes were maintained in lipoprotein-deficient medium for 48 h and the rate of formation of [3H] cholesteryl oleate from [3H] oleate was then determined in the presence or absence of low density lipoproteins. In the absence of low density lipoproteins, incorporation of [3H] oleate was higher in heterozygote and homozygote cells than in normal lymphocytes. Incorporation in the presence of low density lipoproteins was increased relative to that measured in their absence for all of the subjects studied; heterozygotes and homozygotes showed marked changes in some cases but not in others.