Mulberry leaves ameliorate diabetes via regulating metabolic profiling and AGEs/RAGE and p38 MAPK/NF-κB pathway

Abstract

Ethnopharmacological relevance: Mulberry leaves have been used as traditional hypoglycemic medicine-food plant for thousand years in China. According to traditional Chinese medicine theory, type 2 diabetes mellitus (T2DM) belongs to the category of XiaoKe. Presently, the research of mulberry leaf hypoglycemic and lipid-lowering direction is mature, but the curative effects of alkaloids, flavonoids, polysaccharides, and other bioactive ingredients and the related mechanism is still unclear.

Aim of the study: This paper aims to study the efficacy and mechanism of alkaloids, flavonoids, polysaccharides, and other bioactive components in mulberry leaves in the treatment of T2DM individually.

Materials and methods: The determination of levels of fasting blood glucose (FBG), triglyceride (TG) and total cholesterol (T-Cho), and pyruvate kinase (PK), hexokinase (HK), and alanine aminotransferase (ALT/GPT) of in plasma of diabetic mice. Urine metabolomics was analyzed by UPLC-QTOF/MS to evaluate differential metabolites from multiple metabolic pathways. The glucose uptake of HepG2 cells and 3T3-L1 cells. Expression of Caspase-3 and caspase-9, inflammatory injury and p38MAPK/NF-κB signaling pathway in GLUTag cells.

Results: Our study revealed alkaloids, flavonoids, and polysaccharides in mulberry leaf could increase the levels of PK, HK, and ALT/GPT, and decrease the levels of TG and T-Cho significantly, and regulate glucose, amino acid, and lipid metabolism. Furthermore, 1-deoxynojirimycin (DNJ) and isoquercitrin (QG) both could increase glucose uptake and promote differentiation of HepG2 cells, increase PPARγ, C/EBPα and SREBP-l expression in 3T3-L1 cells, and inhibit AGEs-induced injury and apoptosis in GLUTag cells, reduce the expression of proteins related to AGEs/RAGE and p38MAPK/NF-κB pathway. Notably, isoquercitrin exhibited more pronounced anti-diabetic efficacy.

Conclusions: The alkaloids, flavonoids, and polysaccharides from mulberry leaf exhibited hypoglycemic activity through the regulation of glucose, amino acid, and lipid metabolism. 1-DNJ and QG increased glucose uptake and promoted differentiation of HepG2 cells, increased PPARγ, C/EBPα and SREBP-l expression in 3T3-L1 cells, and inhibited AGEs-induced injury and apoptosis in GLUTag cells via the AGEs/RAGE and p38 MAPK/NF-κB pathway.

Keywords: 1-deoxynojirimycin; Diabetes mellitus; Glucose metabolism; Insulin resistance; Isoquercitrin; Lipid metabolism; Morus alba L..