Hydroxypropyl methylcellulose (HPMC), a semisynthetic, nonfermentable soluble dietary fiber, is not absorbed by the body, but its presence in the intestinal lumen increases fecal fat, sterol, and bile acid excretions and decreases intestinal cholesterol absorption, all of which may indirectly affect hepatic lipid metabolism. We measured the expression of hepatic genes involved in cholesterol, bile acid, and fatty acid metabolism in hamsters fed diets containing 39% of energy as fat and 5% of weight as HPMC or microcrystalline cellulose (control) for 4 wk. HPMC-fed hamsters gained significantly less body weight than the control group but did not differ in food intake. They had significantly lower plasma triglyceride and total-, VLDL-, HDL-, and LDL-cholesterol concentrations and hepatic total lipid, total and free cholesterol and triglyceride concentrations than controls. Compared with controls, HPMC-fed hamsters had greater levels of mRNA for CYP7A1 (cytochrome P450 7A1; 8-fold of control; P < 0.05), CYP51 (lanosterol 14alpha-demethylase; 5.3-fold of control; P < 0.05), and HMG-CoAR (3-hydroxy-3-methylglutaryl CoA reductase; 1.8-fold of control; P < 0.05). The plasma total cholesterol concentrations from both the control and HPMC groups were inversely correlated with expression of hepatic CYP7A1 (r = -0.54; P < 0.05), CYP51 (r = -0.79; P < 0.005), and HMG-CoAR (r = -0.75; P < 0.005) genes. This suggests that HPMC supplementation affected both cholesterol and bile acid synthesis. Our data confirm that altered hepatic expression of lipid metabolism-related genes, possibly due to modulation of fecal bile acid excretion and intestinal cholesterol absorption, contributes to the lipid-lowering effects of HPMC.

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F(2)-isoprostanes are a unique class of prostaglandin-like compounds formed in vivo, which have been established as biomarkers of oxidative stress. Accurate analysis has been challenging due to lack of specificity for the isoforms of isoprostanes and lengthy sample preparation procedures to enable trace quantitative analysis. A quantitative analytical method was developed for the determination of F(2)-isoprostanes in rat and hamster urine by online solid phase extraction (SPE) coupled with liquid chromatography and tandem mass spectrometry (LC-MS/MS). The online SPE LC-MS/MS procedure has significant advantages over alternative methods with respect to specificity, sensitivity, simplicity, and speed. The assay enables the detection of iPF(2alpha)-III, iPF(2alpha)-IV, and iPF(2alpha)-VI over a linear dynamic range of 0.1-50 ng/mL in rat urine samples. This range covers the basal levels of these F(2)-isoprostanes. The limit of quantitation (LOQ) for the standard isoprostanes was about 0.3 ng/mL. The average recoveries ranged from 73 to 115% depending upon the individual F(2)-isoprostane isomers in rat urine. Additionally, the method was used to determine increases of endogenous urine iPF(2alpha)-VI and iPF(2alpha)-III in hamsters challenged with either low-fat or high-fat diets.

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