title: The effects of Syzygium 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 STZ-induced 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.
authors.affiliation: Department of Human PhysiologyFaculty of Health Science, School of Medical Sciences, University of KwaZulu-Natal, Durban, South Africa.
authors.forename: Phikelelani S
authors.initials: PS
authors.lastname: Ngubane
authors.forename: Bubuya
authors.initials: B
authors.lastname: Masola
authors.forename: Cephas T
authors.initials: CT
authors.lastname: Musabayane
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism / Q000187:drug effects*; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy*; D005941:Glucokinase / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology; D009828:Oleanolic Acid / Q000302:isolation & purification / Q000494:pharmacology / Q000627:therapeutic use*; D008517:Phytotherapy; D010936:Plant Extracts / Q000494:pharmacology / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D027842:Syzygium / Q000737:chemistry*
chemical_list: D010936:Plant Extracts; D009828:Oleanolic Acid; D006003:Glycogen; D006593:Hexokinase; D005941:Glucokinase