Small low-density lipoprotein particles in women with natural or surgically induced menopause

Abstract

Objective: To investigate the mechanism of the decrease in the size of low-density lipoprotein (LDL) particles in women with natural menopause and women with surgically induced menopause. Methods: We measured plasma levels of total cholesterol; triglycerides; high-density lipoprotein (HDL) cholesterol; apolipoproteins A-I, A-II, and B; and sex hormones in 45 women; 15 women were premenopausal, 15 were naturally postmenopausal, and 15 were surgically menopausal. Lipoprotein lipase and hepatic triglyceride lipase activities were measured in postheparin plasma. Concentrations of total cholesterol and of apolipoprotein B in LDL also were measured. Low-density lipoprotein particle diameter was determined by gradient gel electrophoresis. Results: Plasma levels of total cholesterol, triglycerides, apolipoprotein B, LDL-total cholesterol, LDL-apolipoprotein B, and the activity of postheparin plasma lipoprotein lipase were significantly higher and concentrations of estrone and estradiol were significantly lower in the naturally postmenopausal and surgically menopausal women than in the premenopausal women. Plasma levels of HDL cholesterol and apolipoproteins A-I and A-II and postheparin plasma hepatic triglyceride activity did not differ significantly between groups. The diameter of LDL particles was significantly reduced in the naturally (25.29 ± 0.19 nm) and surgically (25.29 ± 0.22 nm) menopausal women compared with the premenopausal women (25.88 ± 0.22 nm). Plasma triglyceride levels were negatively correlated with LDL particle diameter in all three groups (premenopausal group: r = −0.64, P < .01; naturally postmenopausal group: r = −0.62, P < .01; and surgically menopausal group: r = −0.76, P < .001). The prevalence of LDL subclass pattern B was significantly increased in the naturally (67%, P < .05) and surgically (60%, P < .05) menopausal women. Conclusion: The plasma concentration of LDL particles was increased after menopause, whether natural or surgically induced. An increase in plasma triglyceride levels in women with low levels of endogenous estrogen appeared to cause the size of LDL particles to be reduced.