Nostoc commune var sphaeroides Kutzing, a blue‐green alga, lowers plasma cholesterol levels by promoting fecal neutral sterol excretion in mice

Abstract

Intake of Nostoc commune var sphaeroides Kützing (N. Commune) has been shown to lower plasma cholesterol levels in rats, but the mechanisms behind the hypocholesterolemic effect have not been elucidated. To elucidate the mechanisms underlying the cholesterol‐lowering effect of N. commune, male C57BL/6 mice were fed the AIN93‐M diet with or without 5% whole N. Commune (wt/wt) supplementation for 4 weeks. N. commune supplementation significantly reduced total plasma cholesterol concentration by ~30 percent compared to controls (P = 0.0049). Hepatic lipids in N. commune fed mice were not significantly altered. However, quantitative Realtime PCR analysis revealed the expression of genes encoding cholesterol 7α‐hydroxylase, sterol regulatory element binding protein 2, and 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase was significantly decreased in mice fed N. commune (P < 0.030). Fecal neutral sterol output, measured by gas chromatography, increased 2‐fold in N. commune‐fed mice, while acidic sterol output remained unchanged. In addition, N. commune supplementation drastically altered mouse intestinal flora populations, demonstrated by denaturing gradient gel electrophoresis. In conclusion, N. commune supplementation exerted a hypocholesterolemic effect, largely in part, by promoting fecal neutral sterol excretion and by modifying the microflora of the intestinal environment.