Metabolic aspects of oryzanol in rats

Using a rat model, this study compared the bioavailability of three forms of oryzanol, a compound extracted from rice bran oil that has been associated with improved cholesterol levels. Various methods of extracting lipids from serum and liver were explored to determine oryzanol absorption. Cholesterol levels were obtained via enzymatic colorimetric assay and GCMS. Sprague Dawley retired female breeder rats were sustained for 11 weeks on a cholesterol-free diet to which either no oryzanol was added (n = 19) or 2.8 g/kg of oryzanol was added as: 7% oryzanol rice bran oil (RO, n = 8), crystalline oryzanol (CO, n = 8), or crystalline oryzanol dissolved in tocopherol-stripped corn oil (DO, n = 9). The percentage of dietary oryzanol recovered in the feces of rats fed the CO diet (41.9 ± 2.21, mean ± SEM) was significantly higher compared to the RO (28.3 ± 3.54) and DO (27.8 ± 2.63) groups (P \u3c 0.05), suggesting that bioavailability of crystalline oryzanol is lower relative to the oil forms. Oryzanol was not detected during GCMS analysis of serum following hexane extraction. Similarly, hexane extractions of liver analyzed via HPLC and GCMS did not reveal oryzanol. Hexane may not be an appropriate solvent for extracting oryzanol, or perhaps the compound is metabolized prior to its entry into the liver or bloodstream. Although serum cholesterol levels determined by colorimetric enzymatic assay did not differ significantly among the groups, levels were highest in the RO group, followed in sequence by the DO, CO, and oryzanol-free controls. It is likely that a cholesterol-enriched diet is required for the hypolipidemic effect of oryzanol to be realized. Additionally, it is plausible that the cholesterol values from the oryzanol-fed animals were inflated by phytosterols in the serum. Hexane extractions of serum analyzed via GCMS resulted in unintelligible data, suggesting that hexane is not a suitable solvent for the extraction of cholesterol from serum. Although a 2:1 chloroform:methanol mixture (Folch et al., 1956) resulted in more uniform values, it appeared that the extraction of total cholesterol from lipoproteins was incomplete. (Supported by USDA IFAFS 2000-04222