Leonotis leonurus: understanding the mechanism of anti-diabetic action and investigating a nano drug delivery system

• Main Authors: Odei-Addo, Frank, Levendal, Ruby-Ann
• Format: Others
• Language: English
• Published: Nelson Mandela Metropolitan University 2016
• Subjects: Diabetes; Plant extracts
• Online Access: http://hdl.handle.net/10948/13116

Diabetes mellitus is a metabolic disease characterised by hyperglycaemia resulting from defects in insulin secretion, insulin action, or both. The leaf extract of Leonotis leonurus and its active compound marrubiin, have been shown to possess anti-diabetic, antiplatelet, anti-inflammatory and anti-coagulation activity. In the present study, the mechanism by which L. leonurus and marrubiin exert their anti-diabetic properties, the cross-talk between the peripheral tissues and a nano drug delivery system were investigated. Marrubiin in the plant extract was effectively quantified by an optimised reversed phase highperformance liquid chromatography (HPLC) protocol using a pentafluorophenyl (PFP) column with water and acetonitrile (50:50) as mobile phase, and a flow rate of 1ml/min. The chemical structure was determined using liquid chromatography-tandem mass spectroscopy LC-MS/MS. Real-time quantitative polymerase chain reaction (RT-qPCR) gene expression of selected adipokines and proteins implicated in Type-2 diabetes (T2D) were investigated in specific peripheral tissues isolated from an in vivo obese rat model. An in vitro cell culture model was used to determine the crosstalk between the peripheral tissues and pancreatic (INS-1E) β-cells. Various nanoformulations of L. leonurus extract were prepared and their effect on cytotoxicity (in Chang liver and INS-1 cells), insulin-mediated glucose uptake (Change liver cells) and insulin secretion (INS-1) were investigated. The average yield of marrubiin from the plant extract was 10% (n=3), with a molecular mass of 333.20Da and a molecular formula of C20H29O4 +. Results from the in vivo study showed that the L. leonurus extract significantly (p<0.05) enhanced the gene expression of adiponectin, peroxisome proliferator-activated receptor gamma (PPAR-γ), glucokinase (GK), uncoupling protein-2 (UCP-2) and reduced leptin in adipose tissue, but resistin, glucose transporters (GLUT), fatty acid synthase (FAS), insulin receptor substrate -1 (IRS-1) and phosphoenolpyruvate carboxykinase (PEPCK) gene expression were not affected. Marrubiin decreased gene expression of leptin and resistin, and increased IRS-1 and glucokinase in adipose tissue. In liver and muscle tissues, marrubiin and the L. leonurus extract reduced gene expression of PPAR-γ, IRS-1, glucokinase and PEPCK. In the in vitro crosstalk study (under normoglycaemic and hyperglycaemic conditions), conditioned medium from 3T3-L1 cells significantly (p<0.01) enhanced insulin secretion. This was not observed in INS-1E cells exposed to muscle- and liver-conditioned medium, respectively. The in vitro studies using a nanostructured lipid formulation (NLC) of the plant extract was not cytotoxic to either INS-1 and Chang liver cells. The NLC formulation significantly (p<0.05) enhanced glucose uptake in Chang liver cells and improved chronic insulin release in INS-1 cells (p<0.05). Based on the above findings from the in vivo and in vitro studies, both L. leonurus and marrubiin exerted an insulinotropic effect via adipose tissue on pancreatic β-cells. The findings in the in vivo study showed that marrubiin and the L. leonurus extract were employing their major anti-diabetic action via the adipose tissue.