Mice Abundant in Muricholic Bile Acids Show Resistance to Dietary Induced Steatosis, Weight Gain, and to Impaired Glucose Metabolism

Abstract

High endogenous production of, or treatment with muricholic bile acids, strongly reduces the absorption of cholesterol. Mice abundant in muricholic bile acids may therefore display an increased resistance against dietary induced weight gain, steatosis, and glucose intolerance due to an anticipated general reduction in lipid absorption. To test this hypothesis, mice deficient in steroid 12-alpha hydroxylase (Cyp8b1-/-) and therefore abundant in muricholic acids were monitored for 11 weeks while fed a high fat diet. Food intake and body and liver weights were determined, and lipids in liver, serum and feces were measured. Further, responses during oral glucose and intraperitoneal insulin tolerance tests were evaluated. On the high fat diet, Cyp8b1-/- mice displayed less weight gain compared to wildtype littermates (Cyp8b1+/+). In addition, liver enlargement with steatosis and increases in serum LDL-cholesterol were strongly attenuated in Cyp8b1-/- mice on high fat diet. Fecal excretion of cholesterol was increased and there was a strong trend for doubled fecal excretion of free fatty acids, while excretion of triglycerides was unaltered, indicating dampened lipid absorption. On high fat diet, Cyp8b1-/- mice also presented lower serum glucose levels in response to oral glucose gavage or to intraperitoneal insulin injection compared to Cyp8b1+/+. In conclusion, following exposure to a high fat diet, Cyp8b1-/- mice are more resistant against weight gain, steatosis, and to glucose intolerance than Cyp8b1+/+ mice. Reduced lipid absorption may in part explain these findings. Overall, the results suggest that muricholic bile acids may be beneficial against the metabolic syndrome.

Fig 1. Cyp8b1^-/- (ko) mice show improved glucose tolerance and response to insulin on a high fat diet (HFD) as compared to Cyp8b1^+/+ (wt) mice.

Blood glucose levels in response to oral glucose tolerance test (OGTT) (A) and area under the curves (AUCs) (B). Blood glucose levels in response to intraperitoneal insulin tolerance test (IITT) (C), and as AUCs (D). Data is shown as mean ±SEM, n = 16 for all groups. *** = p<0.001 and ** = p<0.01.

Fig 2. Cyp8b1^-/- (ko) mice are protected from liver hypertrophy and fatty liver when exposed to high fat diet (HFD) and display improved lipoprotein profiles as compared to Cyp8b1^+/+ (wt) mice.

Liver weight (A), liver cholesterol (B) and liver triglycerides (TGs) (C). Serum cholesterol in VLDL (C), LDL (D), and HDL (E) lipoprotein fractions. Data is shown as mean ±SEM, n = (18–19) for all groups. *** = p<0.001, ** = p<0.01, and * = p<0.05.

Fig 3. Cyp8b1^-/- (ko) mice show improved resistance to body weight (BW) gain following exposure to a high fat diet (HFD) and display lowered food efficiency index than Cyp8b1^+/+ (wt) mice.

Body weight (A) and area under the curve (AUC) (B). The arrow denotes the time point at which a significant difference in body weight between Cyp8b1^-/- and Cyp8b1^+/+ mice on HFD first occurred, and this difference persisted throughout the experiment. Body weight gain shown as AUC (C), food intake (D) and food efficiency (E). Where indicated, data is shown as mean ±SEM, n = (17–19) for all groups. *** = p<0.001, ** = p<0.01, and * = p<0.05.

Fig 4. Cyp8b1^-/- (ko) mice have increased fecal excretion of cholesterol and free fatty acids (FFAs) when fed a high fat diet (HFD) as compared to Cyp8b1^+/+ (wt) mice.

Fecal excretion of FFAs, cholesterol, and triglycerides (A), serum campesterol levels, a marker of cholesterol absorption (B), and serum glucagon-like peptide-1 (GLP-1) levels (C). Where indicated, data is shown as mean ±SEM, n = (17–19) for all groups. *** = p<0.001, ** = p<0.01, and * = p<0.05.