Effects of dietary defatted squid on cholesterol metabolism and hepatic lipogenesis in rats

Male Sprague-Dawley rats were fed a cholesterol-free (Exp. 1) or cholesterol-supplemented (Exp. 2) diet containing 20% casein (control group) or 15% defatted squid and 5% casein (defatted squid group), as protein, for 14 d. Serum and hepatic cholesterol concentrations were lower in rats fed defatted squid than in those fed casein in both cholesterol-free (-20%, P < 0.05 and -15%, P < 0.05, respectively) and cholesterol-supplemented (-25%, P < 0.05 and -15%, P < 0.05, respectively) diets. Hepatic triglyceride concentration was lower in the defatted squid than in the control groups in both cholesterol-free (-51%, P < 0.05) and cholesterol-supplemented diets (-38%, P < 0.01). The activities of cytosolic fatty acid synthase and the NADPH-generating enzymes, malic enzyme and glucose-6-phosphate dehydrogenase, in the liver were lower in the defatted squid than in the control groups in both cholesterol-free (-21%, P < 0.01, -33%, P < 0.05, and -33%, P < 0.01, respectively) and cholesterol-supplemented diets (-34%, P < 0.05, -57%, P < 0.05, and -67%, P < 0.05, respectively). The activity of mitochondrial carnitine palmitoyltransferase in the liver was comparable between the control and defatted squid groups. The activity of Mg²⁺-dependent phosphatidate phosphohydrolase in the liver cytosol was lower in the defatted squid (-9%, P < 0.05) than in the control groups only in the cholesterol-free diet. Fecal excretion of total steroids was stimulated by the feeding of defatted squid in both cholesterol-free (+77%, P < 0.005) and cholesterol-supplemented diets (+29%, P < 0.01). These results suggest that the nonlipid fraction of squid exerts a hypocholesterolemic effect by increasing the excretion of total steroids in feces. The fraction also induces a triglyceride-lowering activity in the liver by decreasing hepatic lipogenesis.