Anti-hyperglycemic and anti-hyperlipidemic effects of a special fraction of Luohanguo extract on obese T2DM rats

Luohanguo (LHG), a traditional Chinese medicine, could clear heat, moisten the lung, soothe the throat, restore the voice, and lubricate intestine and open the bowels. LHG has been utilized for the treatment of sore throats and hyperglycemia in folk medicine as a homology of medicine and food. The hypoglycemic pharmacology of LHG has attracted considerable attention, and mogrosides have been considered to be active ingredients against diabetes mellitus. We have found that these mogrosides could be metabolized into their secondary glycosides containing 1–3 glucose residues in type 2 diabetes mellitus (T2DM) rats in previous studies. These metabolites may be the antidiabetic components of LHG in vivo. Thus far, no reports have been found on reducing blood glucose of mogrosides containing 1–3 glucose residues. The aim of this study was to confirm that mogrosides containing 1–3 glucose residues were the active components of LHG for antidiabetic effects and to understand their potential mechanisms of action. First, the special fraction of mogrosides containing 1–3 glucose residues was separated from a 50% ethanol extract of LHG, and the chemical components were identified by ultra-performance liquid chromatography (UPLC) and named low-polar Siraitia grosvenorii glycosides (L-SGgly). Second, the antidiabetic effects of L-SGgly were evaluated by HFD/STZ-induced (high-fat diet and streptozocin) obese T2DM rats by indexing fasting blood glucose (FBG), fasting insulin (FINS), and insulin resistance, and then compared with other fractions in the separation process. The changes in serum lipid levels were also detected. Finally, possible mechanisms of antidiabetic activity of L-SGgly were identified as increasing GLP-1 levels and activating liver AMPK in T2DM rats. The chemical analysis of L-SGgly showed that they contain 11-oxomogroside V, mogroside V, mogroside III, mogroside IIE, mogroside IIIA1, mogroside IIA1, and mogroside IA1, respectively. The total content of the mogrosides in L-SGgly was 54.4%, including 15.7% mogroside IIA1 and 12.6% mogroside IA1. L-SGgly showed excellent effects on obese T2DM rats compared with the other fractions of LHG extract, including significantly reducing the levels of FBG (p < 0.001) and modifying insulin resistance (p < 0.05). Meanwhile, they could significantly decrease the content of triglyceride (p < 0.01), total cholesterol (p < 0.01), low-density lipoprotein cholesterol (p < 0.01) and free fatty acid (p < 0.001) and increase the content of high-density lipoprotein cholesterol (p < 0.001) in serum of T2DM rats. Moreover, L-SGgly can significantly increase (p < 0.01) GLP-1 levels and decrease (p < 0.01) IL-6 levels in T2DM rat serum. AMPK-activating activity in T2DM rats was also upregulated by L-SGgly, but no statistical significance was shown. L-SGgly, fractions separated from LHG extract, were verified to have obvious anti-hyperglycemic and anti-hyperlipidemic effects on T2DM rats. Furthermore, L-SGgly regulated insulin secretion in T2DM rats by increasing GLP-1 levels. These findings provide an explanation for the antidiabetic role of LHG.