Effect of dietary lipids on activities of hepatic steroid metabolizing enzymes (5α-reductase and aromatase) and composition of microsomes

The effects of dietary fat (saturated, ω-6 and ω-3 fatty acids) on the activities of two key steroid metabolizing enzymes, 5α-reductase and aromatase, were examined in the present study. These enzymes are widely speculated to be involved in the initiation of prostate and breast cancer. Weanling male Sprague Dawley rats were fed semi-purified diets containing 14% fat of either beef fat (BF), safflower oil (SO) or fish oil (FO) for 7 wks and enzyme activity and hepatic microsomal phospholipid fatty acid composition were analyzed. 5α-reductase and aromatase activities were differentially modulated by the dietary lipids. Animals fed the FO diet showed significantly higher 5α-reductase activity compared to those fed the BF diet. Rats fed the SO diet had the highest activity of microsomal aromatase compared to animals fed the BF or FO diet. Liver microsomal lipids of animals fed the BF diet had a higher percentage of saturated (stearic, 18:0) and monounsaturated (oleic, 18:1) fatty acids compared to those of SO and FO fed groups while microsomes of animals fed BF and SO diets contained higher percentages of ω-6 fatty acids compared with FO diet group. Feeding FO diet resulted in accumulation of significantly higher levels of ω-3 fatty acids (20:5, 22:5 and 22:6) in the microsomes compared to the BF or SO fed groups. The data suggest that dietary fatty acids may play a role in steroid hormone action through modulating the activities of these two steroid metabolizing enzymes.