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Prolonged saturated fat–induced, glucose-dependent insulinotropic polypeptide elevation is associated with adipokine imbalance and liver injury in nonalcoholic steatohepatitis: dysregulated enteroadipocyte axis as a novel feature of fatty liver

¹ From the Gradenigo Hospital, Turin, Italy (GM); the Department of Internal Medicine, University of Turin, Turin, Italy (RG, FDM, and MC); and the Metabolic Unit, Institute of Biomedical Engineering, National Research Council, Padua, Italy (GP).

² Supported by the Piedmont Region Funds Comitato Interministeriale per la Programmazione Economica 2008.

³ Reprints not available. Address correspondece to G Musso, Gradenigo Hospital, C.so Regina Margherita 8, 10132 Torino, Italy. E-mail: giovanni_musso{at}yahoo.it.

Background: Genetic and acquired mechanisms underlying the association of nonalcoholic fatty liver disease (NAFLD) with diabetes are unknown. Glucose-dependent insulinotropic polypeptide (GIP) was recently linked to adipocyte metabolism and obesity-related metabolic disorders, including NAFLD, induced by an excess of saturated fatty acids (SFAs), but its role in vivo, as well as underlying mechanisms, is unknown. We hypothesized that altered GIP secretion may contribute to the pathogenesis of NAFLD.

Objective: We assessed GIP response to SFA ingestion and its effect on glucose and lipid metabolism and on liver injury in patients with nonalcoholic steatohepatitis (NASH).

Design: Thirty-two nonobese, nondiabetic patients with NASH and 32 healthy controls matched for age, body mass index, and sex underwent a 7-d dietary record, an oral-glucose-tolerance test (OGTT), and a high–fat-load test. OGTT-derived indexes of glucose homeostasis were calculated; circulating lipoproteins, total antioxidant status, GIP, adiponectin, resistin, and cytokeratin-18 fragments (markers of hepatocyte apoptosis) after a high-fat meal were assessed. All subjects were genotyped for transcription factor 7–like 2 (TCF7L2) polymorphism.

Results: Patients with NASH exhibited a prolonged GIP elevation after fat ingestion. GIP response correlated directly with hepatic steatosis, postprandial resistin, and free fatty acid (FFA) increase and inversely with β cell function and incretin effect. Dietary polyunsaturated:saturated fatty acid ratio and TCF7L2 polymorphism independently predicted postprandial GIP response. Cytokeratin-18 fragments increased significantly postprandially in both groups but more consistently in patients with NASH; their increase was predicted by postprandial adiponectin and FFA responses.

Conclusions: GIP response to SFA ingestion is prolonged in nondiabetic patients with NASH and is correlated with liver disease, an unfavorable dynamic adipokine profile, and β cell dysfunction, which provides a rationale for GIP antagonism in these subjects.