1 Storr Liver Centre, Westmead Institute for Medical Research, Westmead Hospital and University of Sydney, Westmead, NSW, Australia.
2 Liver and Pancreatobiliary Diseases Research Center, Digestive Disease Research Institute, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
3 SAHMRI Infection and Immunity Theme, School of Medicine, Flinders University, Adelaide, Australia.
4 Division of Gastroenterology and Hepatology, Department of Medical Science, University of Turin, Turin, Italy.
5 Section of Gastroenterology and Hepatology, Dipartimento Biomedico di Medicina Interna e Specialistica (Di.Bi.M.I.S.), University of Palermo, Palermo, Italy.
6 Department of Medical and Surgical Sciences, Alma Mater University, Bologna, Italy.
7 Medical School, Sir Charles Gairdner Hospital Unit, University of Western Australia, Nedlands, WA, Australia.
Nonalcoholic fatty liver disease (NAFLD) affects a quarter of the adult population. A significant subset of patients are lean, but their underlying pathophysiology is not well understood. We investigated the role of bile acids (BAs) and the gut microbiome in the pathogenesis of lean NAFLD. BA and fibroblast growth factor 19 (FGF19) levels (a surrogate for intestinal farnesoid X receptor [FXR] activity), patatin-like phospholipase domain-containing 3 (PNPLA3) and transmembrane 6 superfamily member 2 (TM6SF2) variants, and gut microbiota profiles in lean and non-lean NAFLD were investigated in a cohort of Caucasian patients with biopsy-proven NAFLD (n = 538), lean healthy controls (n = 30), and experimental murine models. Patients with lean NAFLD had a more favorable metabolic and histological profile compared to those with non-lean NAFLD (P < 0.05 for all). BA levels were significantly higher in NAFLD with advanced compared to earlier stages of liver fibrosis. Patients with lean NAFLD had higher serum secondary BA and FGF19 levels and reduced 7-alpha-hydroxy-4-cholesten-3-one (C4) levels (P < 0.05 for all). These differences were more profound in early compared to advanced stages of fibrosis (P < 0.05 for both). Lean patients demonstrated an altered gut microbiota profile. Similar findings were demonstrated in lean and non-lean murine models of NAFLD. Treating mice with an apical sodium-dependent bile acid transporter inhibitor (ASBTi) (SC-435) resulted in marked increases in fgf15, a shift in the BA and microbiota profiles, and improved steatohepatitis in the lean model. CONCLUSION: Differences in metabolic adaptation between lean and non-lean NAFLDpatients, at least in part, explain the pathophysiology and provide novel options for therapy.