Title

Gender and hormonal status modulate the effects of psyllium on the mechanisms determining plasma lipids and lipoprotein metabolism

Date of Completion

January 2002

Keywords

Health Sciences, Nutrition

Degree

Ph.D.

Abstract

These studies were conducted to identify the secondary mechanisms by which psyllium affects lipoprotein metabolism, and to examine how gender and hormonal status might influence these effects. The trial consisted of a crossover intervention in which 24 men, 23 pre-menopausal women and 21 postmenopausal women were randomly assigned to a fiber supplement (15 g psyllium/day) or a control, provided via cookies. Fasting plasma lipids, apo B, apo CI, apo CIII, and apo E, and cholesteryl ester transfer protein (CETP) and lecithin:cholesterol acyl transferase (LCAT) activities were measured at the end of each 30-day period. Mononuclear cell mRNA abundance of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase, LDL receptor and lipoprotein lipase (LPL) was measured in a representative subset of samples. Compared to control, psyllium intake decreased plasma LDL cholesterol by an average of 8% (P < 0.0001) without affecting HDL cholesterol concentrations. While LCAT activity was unaffected, CETP activity was 18% lower after psyllium supplementation (P < 0.0001), suggesting modifications of the intravascular processing of lipoproteins. There was an increase in mononuclear cell HMG-CoA reductase mRNA abundance (P < 0.05), whereas LDL receptor gene expression was unaffected with psyllium. Therefore, the psyllium-mediated hypocholesterolemic effects might have influenced cholesterol metabolism in peripheral tissues at the gene expression level. There was a psyllium-gender/hormonal status interaction on VLDL metabolism. Men had a 17% decrease in TG, while postmenopausal women had a 16% increase (P < 0.01). Plasma apo C III and apo E concentrations followed the same pattern and decreased by an average of 12% in men (P < 0.05) but increased by 10% in postmenopausal women (P < 0.05). While psyllium intake induced a 24% increase in mononuclear cells LPL mRNA abundance in men, postmenopausal women experienced a 23% decrease (P < 0.05). These results suggest an increased peripheral removal of TG in men while in PMW the increases in apoproteins may be related to an enhanced VLDL production and decreased TG removal by LPL. Parameters associated with VLDL metabolism were unaffected in pre-menopausal women, which could be associated with the protective effect of estrogen. Overall, these results indicate an important role of gender and hormonal status in determining the effects of psyllium on lipoprotein metabolism. ^