The lignan-rich fractions of Fructus Schisandrae improve insulin sensitivity via the PPAR-γ pathways in in vitro and in vivo studies

Ethnopharmacological relevance: Fructus Schisandrae, the fruit of Schisandra chinensis (Turcz.) Baillon, has been traditionally used as a hypoglycemic agent in Asia and its extracts have been shown to improve insulin-stimulated glucose uptake in cell-based assays in previous studies. Aim of the study: We set out to determine which fractions of Fructus Schisandrae improved peroxisome proliferator-activated receptor (PPAR)-gamma activity and glucose-stimulated insulin secretion in cell-based experiments. The fractions that enhance glucose homeostasis were then tested for their hypoglycemic effects and mechanism was examined. Materials and methods: The fractions (FS-0, FS-20, FS-40, FS-60, FS-80, FS-100) were made by extracting Fructus Schisandrae with 70% ethanol followed by its fractionation with a XDA column with a different ratio of methanol and water. The insulin-stimulated glucose uptake and PPAR-gamma agonistic actions of each fraction were investigated in 3T3-L1 adipocytes and glucose-stimulated insulin secretion was determined in Min6 cells. The fraction(s) that were efficacious (200 mg/kg bw) were orally given to 90% pancreatectomized (Px) diabetic rats for 8 weeks to evaluate insulin sensitivity in euglycemic hyperinsulinemic clamp and insulin secretion at hyperglycemic clamp. Results: FS-60 contains schizandrin, gomisin A and angeloylgomisin H while FS-80 contains deoxyschizandrin, gamma-schizandrin, and gomisin N. A PPAR-gamma agonistic action was greater in the ascending order of the control. FS-80 and FS-60 in 3T3-L1 adipocytes. FS-60 increased the glucose disposal rates of Px rats as much as rosiglitazone during euglycemic hyperinsulinemic clamp while hepatic glucose output at hyperinsulinemic clamped states decreased in the descending order of the control, FS-80, FS-60 with potentiating insulin signaling. At hyperglycemic clamp only FS-60 potentiated first phase insulin secretion in diabetic animals; the second phase was not increased. Conclusions: FS-60, a lignan-rich fraction, improves glucose homeostasis by increasing glucose disposal rates and enhancing hepatic insulin sensitivity by working as a PPAR-gamma agonist in type-2 diabetic rats. (C) 2011 Elsevier Ireland Ltd. All rights reserved.