Background-Ezetimibe has been shown to inhibit cholesterol absorption in animal models, but studies on cholesterol absorption in humans have not been performed thus far. Methods and Results-The effect of ezetimibe (10 mg/d) on cholesterol absorption and synthesis, sterol excretion, and plasma concentrations of cholesterol and noncholesterol sterols was investigated in a randomized, double-blind, placebo-controlled, crossover study in 18 patients with mild to moderate hypercholesterolemia. Treatment periods lasted 2 weeks with an intervening 2-week washout period. Fractional cholesterol absorption rates averaged 49.8Ϯ13.8% on placebo and 22.7Ϯ25.8% on ezetimibe, indicating a reduction of 54% (geometric mean ratio; PϽ0.001). Cholesterol synthesis increased by 89% from 931Ϯ1027 mg/d on placebo to 1763Ϯ1098 mg/d on ezetimibe (PϽ0.001), while the ratio of lathosterol-to-cholesterol, an indirect marker of cholesterol synthesis, was increased by 72% (PϽ0.001). Bile acid synthesis was insignificantly increased (placebo: 264Ϯ209 mg/d, ezetimibe: 308Ϯ184 mg/d; Pϭ0.068). Mean percent changes from baseline for LDL and total cholesterol after ezetimibe treatment were Ϫ20.4% and Ϫ15.1%, respectively (PϽ0.001 for both), whereas campesterol and sitosterol were decreased by Ϫ48% and Ϫ41%, respectively. Conclusion-In humans, ezetimibe inhibits cholesterol absorption and promotes a compensatory increase of cholesterol synthesis, followed by clinically relevant reductions in LDL and total cholesterol concentrations. Ezetimibe also reduces plasma concentrations of the noncholesterol sterols sitosterol and campesterol, suggesting an effect on the absorption of these compounds as well.

Differences in fat cell size and function among adipose tissue depots are well known and may be important in the pathophysiology of the metabolic and cardiovascular complications of obesity. Since the newly discovered adipocyte hormone leptin is thought to be a central factor in the regulation of energy homeostasis, it may be interesting to know if there are regional differences in leptin production. The aim of this study was to compare the level of leptin expression in the omental and subcutaneous abdominal adipose tissue from obese humans. Adipose tissue samples were collected from 25 severely obese adults (mean BMI: 48.9 +/- 9.7 kg/m2) undergoing vertical gastric banding. Semi-quantitative determination of leptin mRNA by the RT-PCR technique showed significantly lower leptin expression in omental compared to subcutaneous abdominal adipose tissue (leptin/Sp1 ratio in omental vs. subcutaneous fat: 1.53 +/- 0.89 vs. 3.02 +/- 1.58, p < 0.01). Identical results were obtained when Northern blotting was applied in a subgroup. Leptin expression increased with age in omental adipose tissue (r = 0.42, p < 0.05), but not in subcutaneous tissue. No correlation was found between BMI or waist/hip ratio (WHR) and leptin expression in omental or subcutaneous adipose tissue. The regional difference in leptin expression was similar in the patients with impaired glucose tolerance/type-2 diabetes and those with normal glucose tolerance. In conclusion, the results of this study indicate that leptin expression is lower in omental than subcutaneous adipose tissue, possibly due to differences in fat cell size and/or sympathetic innervation.

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA)-reductase inhibitors (statins) are mainly considered for long-term use and often constitute part of a multiple-drug regime. Besides common adverse drug effects, such as nausea, abdominal discomfort and headaches, all statins harbour the risk of myopathy and fatal rhabdomyolysis. Usually, the frequency of myopathy is low but the incidence increases during concomitant drug therapy. Statins do not differ in their pharmacodynamic property. Therefore, the differences in their pharmacokinetic profiles, i.e. affinity for metabolising enzymes, constitute the rationale for choosing a specific statin especially for combination therapy. In order to point out harmful combinations of therapeutics, this review summarises the pharmacokinetic data of six clinically used statins (atorvastatin, cerivastatin, fluvastatin, lovastatin, pravastatin and simvastatin) with special regard to metabolism and drug interactions. In summary, statins that lack a significant hepatic metabolism, i.e. pravastatin, or that are metabolised by more than one cytochrome P450 isoenzyme, i.e. fluvastatin, or whose metabolism is taken over by other cytochrome P450 isoenzymes in case of blockage of the main metabolising enzyme, i.e. cerivastatin, are the least prone to drug interactions. Nevertheless, in case of a specific concomitant drug therapy known to be associated with a higher risk of adverse events, i.e. cyclosporin A and statin, clinical symptoms of myopathy and biochemical data, such as increasing serum creatine phosphokinase, should be monitored carefully.

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The recent identification of the aberrant transport proteins ABCG5 and ABCG8 resulting in sitosterolemia suggests that intestinal uptake of cholesterol is an unselective process, and that discrimination between cholesterol and plant sterols takes place at the level of sterol efflux from the enterocyte. Although plant sterols are structurally very similar to cholesterol, differing only in their side chain length, they are absorbed from the intestine to a markedly lower extent. In order to further evaluate the process of discrimination, three different sterols (cholesterol, campesterol, sitosterol) and their corresponding 5 ␣ -stanols (cholestanol, campestanol, sitostanol) were compared concerning their concentration in the proximal small intestine, in serum, and in bile after a single oral dose of deuterated compounds. The data obtained support the hypothesis that i ) the uptake of sterols and stanols is an extremely rapid process, ii ) discrimination probably takes place on the level of reverse transport back into the gut lumen, iii ) plant stanols are taken up, but not absorbed to a measurable extent, and iv ) the process of discrimination probably also exists at the level of biliary excretion. The range of structural alterations that decrease intestinal absorption and increase biliary excretion is: 1 ) campesterol, 2 ) cholestanol-sitosterol, and 3 ) campestanol-sitostanol. Investigators have been intrigued for more than a decade with the concept that there is a protein-mediated transport system responsible for intestinal uptake of cholesterol (1). The recent identification of the molecular defects underlying phytosterolemia (2, 3) and the lines of evidence supporting the existence of a specific transport protein located in the brush border membrane that possibly mediates intestinal sterol absorption (4-6) has shed new light on the cellular transport of cholesterol and plant sterols. Based on the characterization of sterol uptake in brush border membranes, it is currently hypothesized that the process of intestinal sterol uptake is protein mediated and that the pumping of sterols from the intestine into the enterocyte is unselective. In phytosterolemia, a rare autosomal recessive disorder caused by mutations in the tandem ABC genes, either ABCG5 or ABCG8, affected individuals hyperabsorb and retain not only cholesterol but also plant sterols (7-11). Consequently, it is hypothesized that the ABC transporters G5 and G8 are able to discriminate between cholesterol and other sterols. They are pumping the noncholesterol sterols out of the intestinal cell back into the gut lumen and also into bile, and they are differentiating between the side-chain length and probably also between the stereoselective 5 ␣ saturation of the ⌬ 5 double bond to stanols (12, 13).Plant sterols are structurally related to cholesterol and differ in their chemical structure only due to the presence of an additional methyl (campesterol) or ethyl (sitosterol) group at the C-24 position of the side chain. Stanols differ from the corre...