Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice

Abstract

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

Keywords: biliary cholesterol; cholesterol/absorption; cholesterol/biosynthesis; intestine; liver; transintestinal cholesterol excretion.

Fig. 1.

Lipoprotein profile in plasma analyzed by FPLC. Total cholesterol concentrations were measured in FPLC fractions of 0.5 ml. Data are presented from pool of n = 7 mice per group.

Fig. 2.

Cholesterol synthesis is increased in statin-treated mice. A: Statin treatment leads to increased total body cholesterol synthesis measured by the incorporation of ¹³C-acetate into the cholesterol molecule over a period of 72 h. B: Hepatic cholesterol synthesis is highly increased after statin treatment, compared with the proximal, middle, and distal parts of the small intestine using deuterium water. C: mRNA levels of Hmgcr in the liver are increased, however, not in the small intestine. D: Hepatic HMGCR protein concentrations were increased after statin treatment. n = 6–7 animals per group. * P < 0.05 compared with control. AS, atorvastatin; CTRL, control; LS, lovastatin; RS, rosuvastatin.

Fig. 3.

Plasma cholesterol precursor concentrations do not reflect cholesterol synthesis in mice. A: Hepatic HMG levels are increased upon statin treatment. B: Statin treatment increases gene expression of the regulator of cholesterol synthesis Srebp2 and of enzymes acting downstream in the cholesterol synthesis pathway. C: Minor changes in the concentrations of the cholesterol synthesis precursors lathosterol, lanosterol, and desmosterol were observed upon statin treatment. n = 7 animals per group. * P < 0.05 compared with control.

Fig. 4.

Atorvastatin and lovastatin treatment increases fecal neutral sterol excretion. A: After 2 weeks of statin treatment, fecal neutral sterols are increased. The increase of fecal neutral sterols could not be explained by changes in dietary cholesterol (B) or fractional cholesterol absorption (C) but is largely due to the contribution of biliary cholesterol (D) and slightly to TICE (E). n = 7 animals per group. * P < 0.05 compared with control.

Fig. 5.

Increased fecal bile acids in atorvastatin-treated mice. A: Hepatic gene expression levels of Cyp7a1 and Cyp8b1. Cyp7a1 is increased in mice treated with atorvastatin. B: Biliary bile acids in feces are increased in atorvastatin-treated mice. n = 7 animals per group. * P < 0.05 compared with control.