Restoration of direct pathway glycogen synthesis flux in the STZ-diabetes rat model by insulin administration

Abstract

-Type 1 diabetes subjects are characterized by impaired direct pathway synthesis of hepatic glycogen that is unresponsive to insulin therapy. Since it is not known whether this is an irreversible defect of insulin-dependent diabetes, direct and indirect pathway glycogen fluxes were quantified in streptozotocin (STZ)-induced diabetic rats and compared with STZ rats that received subcutaneous or intraperitoneal insulin (I-SC or I-IP). Three groups of STZ rats were studied at 18 days post-STZ treatment. One group was administered I-SC and another I-IP as two daily injections of short-acting insulin at the start of each light and dark period for days 9 -18. A third group did not receive any insulin, and a fourth group of nondiabetic rats was used as control. Glycogen synthesis via direct and indirect pathways, de novo lipogenesis, and gluconeogenesis were determined over the nocturnal feeding period using deuterated water. Direct pathway was residual in STZ rats, and glucokinase activity was also reduced significantly from control levels. Insulin administration restored both net glycogen synthesis via the direct pathway and glucokinase activity to nondiabetic control levels and improved the lipogenic pathway despite an inefficient normalization of the gluconeogenic pathway. We conclude that the reduced direct pathway flux is not an irreversible defect of insulindependent diabetes. indirect pathway; 2 H-nuclear magnetic resonance; glucokinase; de novo lipogenesis TYPE 1 DIABETES IS CHARACTERIZED by significant alterations in hepatic carbohydrate and lipid metabolism resulting from insulin insufficiency, and impairment of postprandial glycogen synthesis is among the best studied of these characteristics. Hepatic glycogen is synthesized via two pathways, the classical direct pathway from intact glucose units and the indirect pathway by which glucose is first metabolized to 3-carbon intermediates (pyruvate and further to lactate), followed by gluconeogenic resynthesis into glucose 6-phosphate (G6P) (Fig.

Effects of dietary carbohydrate on hepatic de novo lipogenesis in European seabass (Dicentrarchus labrax L.)

“…Given that high CHO intake promotes hepatic de novo lipogenesis (DNL) in mammals, it was hypothesized that, for farmed seabass, a diet with a high digestible starch (DS) content would also promote hepatic DNL activity and might, in part, explain the increased adiposity associated with dietary CHO supplementation. To test this hypothesis, we estimated DNL by measuring incorporation of deuterated water ( 2 H 2 O) into hepatic TG using 2 H NMR as previously described for mammals (15)(16)(17). For fish metabolic studies, 2 H 2 O can be conveniently incorporated into tank water without disturbing feeding and behavior (18,19).…”

Analysis of Mammalian Cell Proliferation and Macromolecule Synthesis Using Deuterated Water and Gas Chromatography-Mass Spectrometry

“…Following the administration of 2 H 2 O into the body water pool in vivo or into cell culture media in vitro, 2 H atoms become stably incorporated via enzyme catalyzed reactions into C-H bonds of nonessential amino acids, glycerol-3-phosphate, fatty acids, cholesterol, hexoses and pentoses (ribose and deoxyribose). Subsequent analysis of 2 H labelling of these constituents in macromolecules provides a highly sensitive measure of the rates of synthesis/turnover of lipids [15,16,17,18,19,20,21,22,23,24,25,26,27], proteins [15,28,29,30,31,32,33,34], DNA [15,35,36], RNA [15] and glucose/glycogen [25,26,37,38,39,40,41,42,43] and an objective assessment of fundamental cellular processes that include, but are not limited to, rates of cell and organelle proliferation, cell and tissue biomass turnover, de novo lipogenesis and gluconeogenesis. Such measurements have tremendous application to researchers in the field of cancer, immunology, cardiovascular disease, metabolism, diabetes, obesity, developmental biology, as well as the biotechnology and agricultural sectors.…”

Effect of β-anhydroicaritin on the expression levels of tumor necrosis factor-α and matrix metalloproteinase-3 in periodontal tissue of diabetic rats

“…All rats had free access to water and food, and were maintained under a 12:12 h light/dark cycle at 22±2°C and 65–69% relative humidity for 12 weeks. At week 12, the blood glucose, urine glucose and body weight were assessed (12). …”