The Effects ofSyzygium aromaticum-Derived Oleanolic Acid on Glycogenic Enzymes in Streptozotocin-Induced Diabetic Rats

Abstract

Studies indicate that the antihyperglycemic effects of Syzygium aromaticum-derived oleanolic acid (OA) are mediated in part through increased hepatic glycogen synthesis. Accordingly, this study assessed the influence of OA on the activity of glucokinase (GK) and hexokinase (HK) of skeletal muscle and liver tissues in streptozotocin (STZ)-induced diabetic rats. After 5 weeks of OA treatment, hepatic and gastrocnemius muscle glycogen concentrations and activities of GK and HK were measured spectrophotometrically in reactions where the oxidation of glucose-6-phosphate (G-6-PDH) formed was coupled to nicotinamide adenine dinucleotide phosphate (NADP + ) reduction catalyzed by G-6-PDH dehydrogenase. Rats treated with deionized water or standard hypoglycemic drugs acted as untreated and treated positive controls, respectively. STZ-induced diabetic rats exhibited depleted glycogen levels and low activities of glycogenic enzymes in muscle and hepatic tissues. OA administration restored these biochemical alterations to near normalcy. The combination of OA and insulin did not significantly alter the activities of HK and GK of STZinduced diabetic rats, suggesting that glycogen synthesis can also occur from precursors such as amino acids or fructose and lactate. The attenuation of the activities of glycogenic enzymes with concomitant increases of hepatic and muscle glycogen concentrations of STZ-induced diabetic rats provides a therapeutic strategy for diabetes treatment.

Antioxidant effects of maslinic acid in livers, hearts and kidneys of streptozotocin-induced diabetic rats: effects on kidney function

“…12,25,26 The spectra of the plant derived MA elucidated using 1 H-and 13 C-NMR compared with previously reported data of maslinic acid. 28,29 Streptozotocin used to induce diabetes mellitus selectively destroys pancreatic b-cells 30 and the systemic changes which occur after its injection are related to the induced diabetic state.…”

“…25 Briefly, liver and gastrocnemius muscle tissue samples (1-1.5 g) were homogenized in 2 mL of 30% potassium hydroxide solution and digested at 100 C for 30 min and then cooled in ice-saturated sodium sulphate. The glycogen was precipitated with ethanol, pelleted and resolubilized in deionized water.…”

“…The selection of these doses was based on the posology of other triterpenes used in our laboratory. 25,26 MA was freshly dissolved in dimethyl sulphoxide (DMSO, 2 mL) and normal saline (19 mL) before use in each case. 27 Rats treated with DMSO/saline (3 mL kg À1 , p.o.)…”

The Effects of Syzygium Aromaticum-Derived Triterpenes on Gastrointestinal Ghrelin Expression in Streptozotocin-Induced Diabetic Rats

“…Various medicinal plant extracts have been reported to significantly reduce food intake possibly through the reduction of plasma ghrelin levels (Bast et al, 2002;Fong, 2002). Studies conducted in our laboratory have shown that Syzygium aromaticum-derived oleanolic acid (OA) and maslinic acid (MA) reduce blood glucose concentrations in STZ-induced diabetic rats in sub-chronic studies through a variety of mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014;Musabayane et al, 2010;Ngubane et al, 2011). Furthermore, these triterpenes have previously been reported to reduce food intake through unknown mechanisms (Khathi et al, 2013;Mkhwanazi et al, 2014).…”

“…Experimental type 1 diabetes mellitus was induced in male Sprague-Dawley rats using a previously described protocol (Mapanga et al, 2009;Ngubane et al, 2011). Briefly, each animal was administered a single intraperitoneal injection of 60 mg/kg streptozotocin in freshly prepared 0.1M citrate buffer (pH 6.3).…”