Background Laparoscopic Roux-en-Y gastric bypass (RYGB) induces a more favorable metabolic profile than expected by weight loss alone. In this study, we investigated the effect of RYGB on serum bile acid levels and their relation to clinical outcomes. Methods We included 30 obese patients who underwent RYGB (BMI=46.1±5.9 kg/m2). Clinical measurements and laboratory determinations were performed before surgery and 1 year after surgery. Fasting serum bile acids were measured by an enzymatic method and individual bile acids were quantified by HLPC-tandem mass spectrometry. Indirect calorimetry was performed to measure the rates of energy expenditure and substrate oxidation. Results Fasting total serum bile acid levels increased twofold after RYGB (pre, 3.68±2.03 vs. post, 7.06± 9.65 μmol/l, +92 %, p=0.002). This increase in total bile acids was accompanied by a decrease in conjugated bile acids, which correlated with decreased glucose oxidation (r=0.571, p=0.002) and with increased lipid oxidation (r=−0.626, p=0.0004). The change in taurineconjugated bile acids correlated with altered DIO2 mRNA expression in adipose tissue (r=−0.498, p=0.013) potentially linking bile acid conjugation to substrate oxidation through DIO2. Conclusions Fasting serum bile acid levels increase after RYGB. More specifically, changes in bile acid conjugation after RYGB associate with altered energy metabolism.

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Lower levels of ketone bodies in individuals with NASH compared to individuals with simple steatosis suggest a decrease in ketone body metabolism in NASH.

Dysregulation of the cholesterol synthesis pathway and accumulation of cholesterol in the liver are linked to the pathogenesis of nonalcoholic steatohepatitis (NASH). Therefore, we investigated the association of serum and liver levels of cholesterol precursors with NASH. Liver histology was assessed in 110 obese patients (Kuopio Obesity Surgery Study [KOBS] study, age 43.7 6 8.1 years [mean 6 standard deviation, SD], body mass index [BMI] 45.0 6 6.1 kg/m 2 ). Serum and liver levels of cholesterol precursors were measured with gas-liquid chromatography. The association between cholesterol precursors and serum alanine aminotransferase (ALT), as a marker of liver disease, was also investigated in a population cohort of 717 men (Metabolic Syndrome in Men Study [METSIM] study, age 57.6 6 5.8 years, BMI 27.1 6 4.0 kg/m 2 ). Serum desmosterol levels and the desmosterol-tocholesterol ratio were higher in individuals with NASH, but not in individuals with simple steatosis, compared to obese subjects with normal liver histology (P 5 0.002 and P 5 0.003, respectively). Levels of serum and liver desmosterol correlated strongly (r 5 0.667, P 5 1 3 10 29 ), suggesting a shared regulation. Both serum and liver desmosterol levels correlated positively with steatosis and inflammation in the liver (P < 0.05). Serum desmosterol had a higher correlation with the accumulation of cholesterol in the liver than serum cholesterol. Serum desmosterol levels (P 5 2 3 10 26 ) and the serum desmosterol-tocholesterol ratio (P 5 5 3 10 25 ) were associated with serum ALT in the population study. Conclusion: Levels of desmosterol in serum and the liver were associated with NASH. These results suggest that serum desmosterol is a marker of disturbed cholesterol metabolism in the liver. Whether desmosterol has a more specific role in the pathophysiology of NASH compared to other cholesterol precursors needs to be investigated. (HEPATOLOGY 2013;58:976-982)