Increasing hepatic glycogen moderates the diabetic phenotype in insulin-deficient Akita mice

Porphyra haitanensis glycoprotein regulates glucose homeostasis: targeting the liver

In this study, we investigated the effects of glycoprotein (PG)-mediated regulation of Porphyra haitanensis on liver glucose metabolism in hyperglycemic mouse models, and sought to establish the underlying mechanism, as determined by the changes in liver gene expression and metabolic profiles. The results showed that 30-300 mg kg-1 PG upregulated the expression of the liver genes Ins1, Ins2, Insr, Gys2, Gpi1, Gck, and downregulated the expression of G6pc, G6pc2, and G6pc3, in a concentration-dependent manner. 300 mg kg-1 PG downregulated the concentrations of glucose-related metabolites in the liver, but upregulated lactic acid, 2-aminoacetic acid, and glucose-1-phosphate concentrations. It was assumed that PG regulated liver glucose metabolism by enriching insulin secretion, glycolysis/gluconeogenesis, and the AMPK signaling pathway, and promoting insulin secretion, glycogen synthesis, and glycolysis. Our findings supported the development of P. haitanensis and its glycoproteins as novel natural antidiabetic compounds that regulated blood glucose homeostasis.

Phosphoenolpyruvate carboxykinase-1 targeted siRNA promotes wound healing in type 2 diabetic mice by restoring glucose homeostasis

It is well-accepted that the liver plays a vital role in the metabolism of glucose and its homeostasis. Dysregulated hepatic glucose production and utilization, leads to type 2 diabetes (T2DM). In the current study, RNA sequencing and qRT-PCR analysis of nanoformulation-treated T2DM mice (TGthr group) revealed beneficial crosstalk of PCK-1 silencing with other pathways involved in T2DM. The comparison of precise genetic expression profiles of the different experimental groups showed significantly improved hepatic glucose, fatty acid metabolism and several other T2DM-associated crucial markers after the nanoformulation treatment. As a result of these improvements, we observed a significant acceleration in wound healing and improved insulin signaling in vascular endothelial cells in the TGthr group as compared to the T2DM group. Enhanced phosphorylation of PI3K/Akt pathway proteins in the TGthr group resulted in increased angiogenesis as observed by the increased expression of endothelial cell markers (CD31, CD34) thereby improving endothelial dysfunctions in the TGthr group. Additionally, therapeutic nanoformulation has been observed to improve the inflammatory cytokine profile in the TGthr group. Overall, our results demonstrated that the synthesized therapeutic nanoformulation referred to as GPR8:PCK-1siRNA holds the potential in ameliorating hyperglycemia-associated complications such as delayed wound healing in diabetes.

Phloretamide Prevent Hepatic and Pancreatic Damage in Diabetic Male Rats by Modulating Nrf2 and NF-κB

This study examined the effect of phloretamide, a metabolite of phloretin, on liver damage and steatosis in streptozotocin-induced diabetes mellitus (DM) in rats. Adult male rats were divided into two groups: control (nondiabetic) and STZ-treated rats, each of which was further treated orally with the vehicle phloretamide 100 mg or 200 mg. Treatments were conducted for 12 weeks. Phloretamide, at both doses, significantly attenuated STZ-mediated pancreatic β-cell damage, reduced fasting glucose, and stimulated fasting insulin levels in STZ-treated rats. It also increased the levels of hexokinase, which coincided with a significant reduction in glucose-6 phosphatase (G-6-Pase), and fructose-1,6-bisphosphatase 1 (PBP1) in the livers of these diabetic rats. Concomitantly, both doses of phloretamide reduced hepatic and serum levels of triglycerides (TGs) and cholesterol (CHOL), serum levels of low-density lipoprotein cholesterol (LDL-c), and hepatic ballooning. Furthermore, they reduced levels of lipid peroxidation, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), mRNA, and total and nuclear levels of NF-κB p65, but increased mRNA levels, total and nuclear levels of Nrf2, as well as levels of reduced glutathione (GSH), superoxide dismutase (SOD-1), catalase (CAT), and heme-oxygenase-1 (HO-1) in the livers of diabetic rats. All of these effects were dose-dependent. In conclusion, phloretamide is a novel drug that could ameliorate DM-associated hepatic steatosis via its powerful antioxidant and anti-inflammatory effects. Mechanisms of protection involve improving the β-cell structure and hepatic insulin action, suppressing hepatic NF-κB, and stimulating hepatic Nrf2.

Hypoglycemic and hypolipidemic effect of pentaamino acid fullerene C60 derivative in rats with metabolic disorder

Pentaamino acid fullerene C₆₀ derivative is a promising nanomaterial, which exhibited antihyperglycemic activity in high-fat diet and streptozotocin-induced diabetic rats. This study investigates the effect of pentaaminoacid C₆₀ derivative (PFD) in rats with metabolic disorders. Rats were assigned to 3 groups (of 10 rats each) as follows: Group 1 (normal control), group 2 included the protamine-sulfate-treated rats (the untreated group of animals with the model metabolic disorder); group 3 (Protamine sulfate + PFD) included the protamine-sulfate-treated model rats that received an intraperitoneal injection of PFD. Metabolic disorder in rats was initiated by protamine sulfate (PS) administration. The PS + PFD group was injected intraperitoneally with PFD solution (3 mg/kg). Protamine sulfate induces biochemical changes (hyperglycemia, hypercholesterolemia, and hypertriglyceridemia) in the blood and morphological lesions in rat liver and pancreas. The potassium salt of fullerenylpenta-N-dihydroxytyrosine in protamine sulfate-induced rats normalized blood glucose level and the serum lipid profile and improved hepatic function markers. Treatment with PFD restored pancreas islets and liver structure of protamine sulfate-induced rats compared to the untreated group. PFD is a promising compound for further study as a drug against metabolic disorders.

Whole grains-derived functional ingredients against hyperglycemia: targeting hepatic glucose metabolism

Type 2 diabetes mellitus (T2DM) is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycemia. However, concerns have been raised about the safety and efficacy of current hypoglycemic drugs due to undesirable side effects. Increasing studies have shown that whole grains (WG) consumption is inversely associated with the risk of T2DM and its subsequent complications. Thus, dietary strategies involving functional components from the WG provide an intriguing approach to restoring and maintaining glucose homeostasis. This review provides a comprehensive understanding of the major functional components derived from WG and their positive effects on glucose homeostasis, demonstrates the underlying molecular mechanisms targeting hepatic glucose metabolism, and discusses the unclear aspects according to the latest viewpoints and current research. Improved glycemic response and insulin resistance were observed after consumption of WG-derived bioactive ingredients, which are involved in the integrated, multi-factorial, multi-targeted regulation of hepatic glucose metabolism. Promotion of glucose uptake, glycolysis, and glycogen synthesis pathways, while inhibition of gluconeogenesis, contributes to amelioration of abnormal hepatic glucose metabolism and insulin resistance by bioactive components. Hence, the development of WG-based functional food ingredients with potent hypoglycemic properties is necessary to manage insulin resistance and T2DM.

Active Glycogen Synthase in the Liver Prevents High-Fat Diet-Induced Glucose Intolerance, Decreases Food Intake, and Lowers Body Weight

Many lines of evidence demonstrate a correlation between liver glycogen content and food intake. We previously demonstrated that mice overexpressing protein targeting to glycogen (PTG) specifically in the liver-which have increased glycogen content in this organ-are protected from high-fat diet (HFD)-induced obesity by reduced food intake. However, the use of PTG to increase liver glycogen implies certain limitations. PTG stimulates glycogen synthesis but also inhibits the enzyme responsible for glycogen degradation. Furthermore, as PTG is a regulatory subunit of protein phosphatase 1 (PP1), which regulates many cellular functions, its overexpression could have side effects beyond the regulation of glycogen metabolism. Therefore, it is necessary to determine whether the direct activation of glycogen synthesis, without affecting its degradation or other cellular functions, has the same effects. To this end, we generated mice overexpressing a non-inactivatable form of glycogen synthase (GS) specifically in the liver (9A-MGS^Alb mice). Control and 9a-MGS^Alb mice were fed a standard diet (SD) or HFD for 16 weeks. Glucose tolerance and feeding behavior were analyzed. 9A-MGS^Alb mice showed an increase in hepatic glycogen in fed and fasting conditions. When fed an HFD, these animals preserved their hepatic energy state, had a reduced food intake, and presented a lower body weight and fat mass than control animals, without changes in energy expenditure. Furthermore, 9A-MGS^Alb animals showed improved glucose tolerance when fed an SD or HFD. Moreover, liver triacylglycerol levels that were increased after HFD feeding were lower in these mice. These results confirm that increased liver glycogen stores contribute to decreased appetite and improve glucose tolerance in mice fed an HFD. On the basis of our findings, strategies to preserve hepatic glycogen stores emerge as potential treatments for obesity and hyperglycemia.

Protein Targeting to Glycogen (PTG): A Promising Player in Glucose and Lipid Metabolism

Protein phosphorylation and dephosphorylation are widely considered to be the key regulatory factors of cell function, and are often referred to as "molecular switches" in the regulation of cell metabolic processes. A large number of studies have shown that the phosphorylation/dephosphorylation of related signal molecules plays a key role in the regulation of liver glucose and lipid metabolism. As a new therapeutic strategy for metabolic diseases, the potential of using inhibitor-based therapies to fight diabetes has gained scientific momentum. PTG, a protein phosphatase, also known as glycogen targeting protein, is a member of the protein phosphatase 1 (PP1) family. It can play a role by catalyzing the dephosphorylation of phosphorylated protein molecules, especially regulating many aspects of glucose and lipid metabolism. In this review, we briefly summarize the role of PTG in glucose and lipid metabolism, and update its role in metabolic regulation, with special attention to glucose homeostasis and lipid metabolism.

In utero exposure to decabromodiphenyl ethane causes rapid growth in mice cubs by activating glycogenolysis and lipid synthesis

Decabromodiphenyl ethane (DBDPE) as a novel brominated flame retardant is frequently detected in environmental media due to its widespread use. Studies have shown that exposure to environmental pollutants in utero could lead to weight loss in newborns and obesity in adulthood. However, the mechanisms of how the cubs grow rapidly from low birth weight to obesity remain unclear. Although it has been reported that perinatal DBDPE exposure caused obesity in the offspring of mice in adulthood, its metabolic changes in offspring juvenile are unknown. Here, we monitored changes of body weight in cubs following exposure to DBDPE in utero. Furthermore, ¹H NMR-based metabolomics was used to investigate the effects of in utero DBDPE exposure on the metabolic profile of neonates included days 1 and 25. Additionally, the expression levels of key genes in the relevant pathways were quantified. The results showed that exposure to high levels of DBDPE in utero caused cubs to be smaller at birth and grow rapidly during lactation. Metabolomics analysis showed that cubs in the exposed group consistently accelerated glycogenolysis and lipid synthesis to promote appetite and energy absorption, and achieved rapid growth in the subsequent lactation, which was further evidenced by the expression levels of genes related to glycolipid metabolism. These results reveal the mechanism for the first time how the weight loss of newborns in utero environmental pollutant exposure transformed into obesity in adulthood, although the exposures here were much higher than would be anticipated from the environment.

Combined treatment with niclosamide ethanolamine and artemether combination improves type 1 diabetes via the targeting of liver mitochondria

Type 1 diabetes (T1D) is characterized by dysregulated blood glucose and liver metabolism. In previous studies, niclosamide ethanolamine salt (NEN) and artemether (Art) displayed significant hypoglycemic effects. However, their combined therapeutic effects on the liver in T1D have remained elusive. In the present study, T1D mice were established and randomly allocated into groups. Following treatment, the physiological and metabolic parameters, including liver function, glycogen content, glucose-6-phosphatase (G6Pase) protein expression levels, mitochondrial biogenesis and mitochondrial metabolism were analyzed. Compared with the NEN or Art treatments alone, their combination improved glycometabolism and the symptoms of diabetes. Combined treatment with NEN and Art also significantly ameliorated liver injury and increased liver glycogen storage. Furthermore, combinatorial treatment significantly downregulated hepatic G6Pase protein expression levels and regulated mitochondrial biogenesis. NEN and Art increased the respiratory exchange rate and reduced mitochondrial phosphoenolpyruvate carboxykinase and branched-chain α-keto acid dehydrogenase complex protein expression levels, whereby the effects were obviously enhanced by their application as a combined treatment. In conclusion, the present study confirmed that combined treatment with NEN and Art improved glycometabolism and liver function in T1D mice and the therapeutic effects may be partially associated with the regulation of liver mitochondria.

Hepatic overexpression of protein targeting to glycogen attenuates obesity and improves hyperglycemia in db/db mice

Increased liver glycogen content has been shown to reduce food intake, attenuate obesity, and improve glucose tolerance in a mouse model of high-fat diet (HFD)-induced obesity. Here we studied the contribution of liver glycogen to the regulation of obesity and glucose metabolism in a model of type 2 diabetes and obesity, namely the db/db mouse. To this end, we crossed db/db mice with animals overexpressing protein targeting to glycogen (PTG) in the liver to generate db/db mice with increased liver glycogen content (db/db-PTG). Hepatic PTG overexpression reduced food intake and fat weight and attenuated obesity and hyperglycemia in db/db mice. Db/db-PTG mice showed similar energy expenditure and physical activity to db/db mice. PTG overexpression reduced liver phosphoenolpyruvate carboxykinase (PEPCK) protein levels and repressed hepatic glucose production in db/db mice. Moreover, increased liver glycogen elevated hepatic ATP content in these animals. However, lipid metabolism was not modified by PTG overexpression. In conclusion, increased liver glycogen content ameliorates the diabetic and obesity phenotype in db/db mice.

Increased liver glycogen levels enhance exercise capacity in mice

Muscle glycogen depletion has been proposed as one of the main causes of fatigue during exercise. However, few studies have addressed the contribution of liver glycogen to exercise performance. Using a low-intensity running protocol, here, we analyzed exercise capacity in mice overexpressing protein targeting to glycogen (PTG) specifically in the liver (PTG^OE mice), which show a high concentration of glycogen in this organ. PTG^OE mice showed improved exercise capacity, as determined by the distance covered and time ran in an extenuating endurance exercise, compared with control mice. Moreover, fasting decreased exercise capacity in control mice but not in PTG^OE mice. After exercise, liver glycogen stores were totally depleted in control mice, but PTG^OE mice maintained significant glycogen levels even in fasting conditions. In addition, PTG^OE mice displayed an increased hepatic energy state after exercise compared with control mice. Exercise caused a reduction in the blood glucose concentration in control mice that was less pronounced in PTG^OE mice. No changes were found in the levels of blood lactate, plasma free fatty acids, or β-hydroxybutyrate. Plasma glucagon was elevated after exercise in control mice, but not in PTG^OE mice. Exercise-induced changes in skeletal muscle were similar in both genotypes. These results identify hepatic glycogen as a key regulator of endurance capacity in mice, an effect that may be exerted through the maintenance of blood glucose levels.