Crilvastatin, a new 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, inhibits cholesterol absorption in genetically hypercholesterolemic rats

The Impact of Egg Nutrient Composition and Its Consumption on Cholesterol Homeostasis

Nutrient deficiencies and excess are involved in many aspects of human health. As a source of essential nutrients, eggs have been used worldwide to support the nutritional needs of human societies. On the other hand, eggs also contain a significant amount of cholesterol, a lipid molecule that has been associated with the development of cardiovascular diseases. Whether the increase of egg consumption will lead to elevated cholesterol absorption and disruption of cholesterol homeostasis has been a concern of debate for a while. Cholesterol homeostasis is regulated through its dietary intake, endogenous biosynthesis, utilization, and excretion. Recently, some research interests have been paid to the effects of egg consumption on cholesterol homeostasis through the intestinal cholesterol absorption. Nutrient components in eggs such as phospholipids may contribute to this process. The goals of this review are to summarize the recent progress in this area and to discuss some potential benefits of egg consumption.

Regulation of Intestinal Cholesterol Absorption

The identification of defective structures in the ATP-binding cassette (ABC) transporters ABCG5 and ABCG8 in patients with sitosterolemia suggests that these two proteins are an apical sterol export pump promoting active efflux of cholesterol and plant sterols from enterocytes back into the intestinal lumen for excretion. The newly identified Niemann-Pick C1-like 1 (NPC1L1) protein is also expressed at the apical membrane of enterocytes and plays a crucial role in the ezetimibe-sensitive cholesterol absorption pathway. These findings indicate that cholesterol absorption is a multistep process that is regulated by multiple genes at the enterocyte level and that the efficiency of cholesterol absorption may be determined by the net effect between influx and efflux of intraluminal cholesterol molecules crossing the brush border membrane of the enterocyte. Combination therapy using cholesterol absorption (NPC1L1) inhibitor (ezetimibe) and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors (statins) provides a powerful novel strategy for the prevention and treatment of hypercholesterolemia.

Effect of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor on sterol absorption in hypercholesterolemic subjects

To investigate the potential effects of high-dose 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor on plasma phytosterol, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG), hypercholesterolemic subjects received 40 or 80 mg/d simvastatin in a 24-week prospective clinical trial. Plasma lipid levels were analyzed enzymatically, and plasma phytosterol concentrations were determined using gas-liquid chromatography. The change in the plasma phytosterol-campesterol level was used as an indicator of cholesterol absorption in humans. Simvastatin treatment reduced plasma campesterol (-24%, P = .017) but did not affect circulating stigmasterol and sitosterol levels. A dose of 80 mg/d simvastatin produced a larger decrease (P = .050) in plasma campesterol (0.1680 mmol/L) than 40 mg/d (0.0237 mmol/L) versus baseline. There was a positive correlation between plasma campesterol and TC both before (r = .54, P = .027) and after (r = .63, P = .009) treatment. Plasma TC and TG levels did not differ between groups receiving 40 or 80 mg/d simvastatin. Simvastatin treatment reduced circulating TC, LDL-C, and TG by 40%, 50%, and 33% (P<.007), respectively. There was no significant effect of simvastatin on plasma HDL-C, but the HDL-C/LDL-C ratio increased 1.3-fold (P<.0001). In conclusion, this HMG-CoA reductase inhibitor reduces the plasma campesterol level, a marker of cholesterol absorption, which may contribute to the mechanism by which simvastatin decreases circulating cholesterol levels.

Reduced cholesterol absorption in hamsters by crilvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Crilvastatin, a new drug from the pyrrolidone family, has been previously shown to inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, in vitro and in vivo, to reduce the absorption of dietary cholesterol and to stimulate the activity of cholesterol 7 alpha-hydroxylase in the rat. The aim of this study was to evaluate the effects of crilvastatin on cholesterol and bile acid metabolism in the hamster. In hamsters fed on a lithogenic diet for 8 weeks, crilvastatin treatment (200 mg/day per kg body weight) did not change plasma lipid levels, failed to improve bile parameters and did not prevent gallstone formation. In hamsters fed on a basal cholesterol-rich (0.2%) diet for 8 weeks, crilvastatin at the same dose reduced the cholesterol level in the plasma by 20%, with a decrease of both low-density and high-density lipoprotein cholesterol. The drug did not significantly stimulate the biliary secretion of bile acids but significantly decreased the activity of acyl coenzyme A:cholesterol acyltransferase in the small intestine by 64%. This effect was enhanced when cholestyramine, a bile acid-sequestering resin, was given in combination with crilvastatin. Crilvastatin alone did not change the activity of cholesterol 7 alpha-hydroxylase in the liver, despite the marked reduction in both hepatic cholesterogenesis and intestinal absorption of dietary cholesterol (the absorption coefficient was 44 +/- 2% in treated hamsters vs. 61 +/- 7% in controls).