LIVER METABOLISM
David M. Gibson, Robert A. Harris in Metabolic Regulation in Mammals, 2001
Initiation of glycogen synthesis requires glycogemn (enzyme 1). which thereafter remains covalently attached to the glycogen molecule through the hydroxyl group of a specific tyrosine residue. Glycogenin glycosylates itself with UDP-glucose, creating a chain of about eight glucose residues. Once synthesis is initiated in this manner, a glycogen molecule grows by repeated addition of activated glucose residues (UDP-glucose) followed by branching of terminal chains. Glycogen synthase (enzyme 2) uses UDP-glucose to elongate terminal chains of glycogen by forming a-1,4-linkages between glucose residues. Branching enzyme (enzyme 3; amylo (1.4 ->1.6) transglucosytase) creates branches by transferring seven-residue segments to the 6-carbon hydroxyl of a glucose four residues from existing branches
Genetics of Endocrine Disorders and Diabetes Mellitus
George H. Gass, Harold M. Kaplan in Handbook of Endocrinology, 2020
Defective insulin-stimulated glycogen storage has been found in NIDDM,117 so the enzymes involved in glycogen synthesis are possible candidates for defects in NIDDM. Glycogen synthase catalyzes the addition of uridine diphosphate glucose (UDP glucose) to glycogen, an important step in the nonoxidative pathway of glucose metabolism. The glycogen synthase gene is found on chromosome 19.118,119 A restriction fragment length polymorphism, called Xbal RFLP A2, in the glycogen synthase gene was found to be associated with NIDDM in a Finnish population.118 The patients with this polymorphism had a higher likelihood of hypertension than NIDDM patients without the polymorphism.118 The association of this polymorphism and NIDDM was not found in a French population,120 a Japanese population,121 or a Swedish population.122 However, an association with the alternative allele, Xbal RFLP A1 allele, was found in the French subjects.120 Additionally, a simple tandem repeat polymorphism in the synthase gene was associated with NIDDM in a different group of Japanese NIDDM patients.123 The glycogen synthase locus was not linked to MODY in a study of 15 MODY families.82 Further studies are needed, but it appears there may be a real association with the glycogen synthase gene and NIDDM.
Medicinal Plants in Natural Health Care as Phytopharmaceuticals
Anil K. Sharma, Raj K. Keservani, Surya Prakash Gautam in Herbal Product Development, 2020
Studies have demonstrated the hypoglycaemic action and effects of coriander on carbohydrate metabolism. The effect of coriander seeds on carbohydrate metabolism was studied in rats that were fed with a fat-rich cholesterol diet. The spice exhibited noteworthy hypoglycemic action. There was an increase in the concentration of hepatic glycogen as was evident from the increased activity of glycogen synthase. Activities of glycogen phosphorylase and gluconeogenic enzymes revealed decreased rates of glycogenolysis and gluconeogenesis. The increased activities of glucose-6-phosphate dehydrogenase and glycolytic enzymes suggest the utilization of glucose by the pentose phosphate pathway and glycolysis. These observations clearly indicated that coriander seeds demonstrate good hypoglycemic activity through enhanced glycogenesis, glycolysis and decreased glycogenolysis and gluconeogenesis (Aissaoui et al., 2011).
Hesperidin, a citrus flavonoid ameliorates hyperglycemia by regulating key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic rats
Published in Toxicology Mechanisms and Methods, 2019
R. Sundaram, E. Nandhakumar, H. Haseena Banu
Glycogen is a branched polymer of glucose residues synthesized by the enzyme glycogen synthase (Naresh et al. 2012). It has direct expression of insulin action as insulin promotes intracellular glycogen deposition by stimulating glycogen synthase and inhibiting glycogen phosphorylase. There is an impaired synthesis of glycogen in the rat liver and skeletal muscles during diabetes due to enhanced catabolic processes such as glycogenolysis, lipolysis, and proteolysis (Hwang et al. 1996; Murali and Saravanan 2012). Therefore, the quantification of glycogen, the primary intracellular storage form of glucose in liver, can be considered as an important indicator of diabetes mellitus. Our results showed that the treatment with hesperidin and glibenclamide forbiddens the decrease of glycogen content in both liver and muscle tissues which could be due to insulin secretion.
Determination of histopathological effects and myoglobin, periostin gene-protein expression levels in Danio rerio muscle tissue after acaricide yoksorrun-5EC (hexythiazox) application
Published in Drug and Chemical Toxicology, 2023
Yücel Başımoğlu Koca, Serdar Koca, Zübeyde Öztel, Erdal Balcan
We found that following yoksorrun (hexythiazox) treatments, myoglobin level was increased, depending on the skeletal muscle atrophy. This can point at two things: firstly, the acaricide may have reduced the oxygen content of the water. Secondly, oxygen may be insufficient in the muscle tissue due to muscle damage. Therefore, the unknown myoglobin gene expression mechanisms may be induced in intact and/or slightly damaged muscle cells to obtain the required oxygen. On the other hand, previous reports suggested that this pesticide is highly toxic to larvae of Tetranychus urticae but not harmful for deutonymph and adults (Dekeyser 2005, Leviticus et al.2020). More recently, Demaeght et al. (2014) proposed that hexythiazox binds to central pore region of chitin synthase enzyme and block the chitin translocation (Demaeght et al.2014). In a recent study, the regulatory effect of glycogen synthase and glycogen phosphorylase on chitin biosynthesis was investigated (Zhang et al.2019). Glycogen synthase is a key glycosyltransferase in the glycogen biosynthesis. Muscle glycogen is an essential energy source during mechanical action. To evaluate the glycogen content in hexythiazox-treated zebrafish skeletal muscle, we performed PAS technique. Our results indicated that glycogen is decreased upon the pesticide treatment. These data suggest that hexythiazox is not only responsible for the loss of muscle mass in zebrafish but also responsible for the decreasing of glycogen deposits in the skeletal muscles.
Pueraria lobata root polysaccharide alleviates glucose and lipid metabolic dysfunction in diabetic db/db mice
Published in Pharmaceutical Biology, 2021
Dan Luo, Xiaokang Dong, Jie Huang, Chengcheng Huang, Guowei Fang, Yanqin Huang
The liver is one of the most important sites to regulate carbohydrate metabolism and plays an important role in maintaining blood glucose homeostasis (Han et al. 2019). It has been reported that insulin resistance affected the activity of carbohydrate metabolism-related enzymes, thus decreased the capacity of hepatic tissue to synthesis glycogen, utilize and decompose glucose. Eventually, more glucose is secreted into the blood. Our findings indicated that PLP could increase hepatic glycogen content in db/db mice, which implied that PLP could regulate hepatic glucose homeostasis. PEPCK and glucose-6-phosphatase (G6Pase) are the main rate-limiting enzymes involved in the regulation of liver gluconeogenesis. Glycogen synthase (GS) is one of the main rate-limiting enzymes involved in the regulation of hepatic glycogen synthesis (Ros et al. 2010). Our results indicated PLP treatment could suppress the activities of PEPCK and G6Pase enzyme, and downregulate the mRNA expression levels of PEPCK, G6PC, and FOXO1 in db/db mice, thus suppressing hepatic gluconeogenesis. This is consistent with a previous report (Valenti et al. 2008), we found that MOMA-IR index, and PEPCK and G6PC mRNA levels were positively correlated with FOXO1 mRNA level. Moreover, our findings also showed that PLP treatment could upregulate the mRNA expression level of GS, thus promoting glycogenesis. The above findings showed that the activities of carbohydrate metabolism-related enzymes were modulated to notably decrease blood glucose by PLP.
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