Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Rates of insulin release, glucose utilization (measured as [(3)H]water formation from [5-(3)H]glucose) and glucose oxidation (measured as (14)CO(2) formation from [1-(14)C]- or [6-(14)C]-glucose) were determined in mouse pancreatic islets incubated in vitro, and were used to estimate the rate of oxidation of glucose by the pentose cycle pathway under various conditions. Rates of oxidation of [U-(14)C]ribose and [U-(14)C]xylitol were also measured. 2. Insulin secretion was stimulated fivefold when the medium glucose concentration was raised from 3.3 to 16.7mm in the absence of caffeine; in the presence of caffeine (5mm) a similar increase in glucose concentration evoked a much larger (30-fold) increase in insulin release. Glucose utilization was also increased severalfold as the intracellular glucose concentration was raised over this range, particularly between 5 and 11mm, but the rate of oxidation of glucose via the pentose cycle was not increased. 3. Glucosamine (20mm) inhibited glucose-stimulated insulin release and glucose utilization but not glucose metabolism via the pentose cycle. No evidence was obtained for any selective effect on the metabolism of glucose via the pentose cycle of tolbutamide, glibenclamide, dibutyryl 3':5'-cyclic AMP, glucagon, caffeine, theophylline, ouabain, adrenaline, colchicine, mannoheptulose or iodoacetamide. Phenazine methosulphate (5mum) increased pentose-cycle flux but inhibited glucose-stimulated insulin release. 4. No formation of (14)CO(2) from [U-(14)C]ribose could be detected: [U-(14)C]xylitol gave rise to small amounts of (14)CO(2). Ribose and xylitol had no effect on the rate of oxidation of glucose; ribitol and xylitol had no effect on the rate of glucose utilization. Ribose, ribitol and xylitol did not stimulate insulin release under conditions in which glucose produced a large stimulation. 5. It is concluded that in normal mouse islets glucose metabolism via the pentose cycle does not play a primary role in insulin-secretory responses.
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PMID:The pentose cycle and insulin release in mouse pancreatic islets. 456 19

Glucosamine, a potent inhibitor of glucokinase (hexokinase IV or D), was used to estimate the contribution of this enzyme to glucose phosphorylation in freshly isolated rat hepatocytes and its sensitivity to fructose 6-phosphate in situ. Experiments with radiolabelled glucosamine indicated that this amino sugar, at concentrations of 5 or 40 mM, readily penetrated hepatocytes to reach in 1 min a total (i.e., glucosamine+metabolites) intracellular concentration equal to 0.8-1.2-fold its extracellular concentration. In marked contrast, N-acetylglucosamine barely penetrated the cells. The detritiation of [2-3H]glucose, used to estimate glucose phosphorylation in intact cells, was inhibited by glucosamine much more potently than by N-acetylglucosamine, half-maximal effects being reached at about 2.5 and 30 mM respectively. Extrapolation of the data indicated that about 12% of the detritiation was resistant to glucosamine. Dihydroxyacetone (10 mM), lactate (10 mM) + pyruvate (1 mM), and glucagon (1 microM) increased up to 8-fold the concentration of hexose 6-phosphates (glucose 6-phosphate+fructose 6-phosphate) and, against expectations, modestly decreased the detritiation rate measured in the absence of glucosamine. In the presence of 40 mM glucosamine, these agents increased the detritiation rate, which then positively correlated with the concentration of hexose 6-phosphates. This hexose 6-phosphates-dependent detritiation was sensitive to inhibition by vanadate, and was also catalysed by gel-filtered cell-free extracts, as well as by liver microsomes in the presence of phosphoglucoisomerase; it can be explained by an exchange reaction catalysed by glucose-6-phosphatase. When this exchange reaction is taken into account, it appears that the rate of glucose detritiation attributable to glucokinase decreases when the concentration of hexose 6-phosphates increases. This is in agreement with the known effect of fructose 6-phosphate to potentiate the inhibition of glucokinase by its regulatory protein.
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PMID:Glucosamine-sensitive and -insensitive detritiation of [2-3H]glucose in isolated rat hepatocytes: a study of the contributions of glucokinase and glucose-6-phosphatase. 775 69

A characteristic feature of non-insulin-dependent diabetes mellitus (NIDDM) is the lack of an acute insulin response to intravenous glucose with maintenance of the response to other secretagogues. It has been hypothesized that impaired glucose sensing stems from defective beta-cell glucokinase. It remains unclear whether decreased pancreatic glucokinase activity will produce defects of insulin secretion similar to those observed in NIDDM. In this study, the effects of glucosamine on glucokinase activity and on islet function were assessed in vitro and in vivo. Glucosamine (5 mmol/l) reduced glucokinase activity in islet homogenate and diminished the insulin response to glucose (200 mg/dl) by isolated islets, whereas the response to arginine (20 mmol/l at 100 mg/dl glucose) was unaffected. In conscious normal rats, glucosamine lowered plasma insulin, followed by an increase in blood glucose. Administration of glucosamine 10 min before an infusion of glucose (10 mg.min-1. 15 min) reduced the insulin response. The primary effect was an attenuation of the first-phase insulin response relative to the decreased basal insulin levels. Arginine (10 mg.min-1.15 min) induced biphasic insulin release in both groups. Although glucosamine slightly reduced the absolute insulin response, it was normal relative to preinfusion levels. In all experiments, glucagon secretion was unaffected by glucosamine. The results indicate that glucosamine inhibits beta-cell glucokinase activity in vitro. In addition, glucosamine impairs glucose- but not arginine-induced insulin secretion. We conclude that glucosamine, probably via a reduction of glucokinase activity, impairs insulin secretion in a manner comparable to that seen in NIDDM.
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PMID:Glucosamine inhibits glucokinase in vitro and produces a glucose-specific impairment of in vivo insulin secretion in rats. 792 84

High doses of glucosamine have been known to induce apoptosis of pancreatic beta cells. The mechanism for this phenomenon has not been clearly elucidated. We aimed to explore the potential mechanisms for glucosamine toxicity in the rat insulinoma cell line INS-1 and in rat native beta cells. We also investigated whether glucagon-like peptide (GLP)-1 could be protective against glucosamine. Glucosamine exhibited dose-dependent inhibition of cell survival and an increase in the cell population at the sub-G1 phase. Glucosamine was revealed to inhibit cellular glucose uptake, resulting in the activation of AMP-activated protein kinase (AMPK). Accordingly, phosphorylation of P70S6K and ribosomal protein S6 (S6RP) was decreased. Protein glycosylation appeared not to be involved in this cytotoxicity. Pretreatment with GLP-1 alleviated glucosamine-mediated inhibition of glucose uptake and lessened AMPK activation, thus allowing recovery of the phosphorylation levels of P70S6K and S6RP. The effect of GLP-1 was blocked by the adenylyl cyclase inhibitor MDL12330A but not by the protein kinase A inhibitor H89. Taken together, these data demonstrate that glucosamine may inhibit beta-cell survival by diminishing cellular glucose uptake independent of glycosylation. This glucosamine toxicity can be blocked by GLP-1, which leads to recovery of the glucose uptake through a PKA-independent, cAMP-dependent mechanism.
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PMID:Protective role of glucagon-like peptide-1 against glucosamine-induced cytotoxicity in pancreatic beta cells. 2011 Jun 82

Bioenergetic deficits are considered a common cause of neurodegenerative diseases. Although creatine supplementation has been shown to be effective in certain neurodegenerative disorders, it is less effective in amyotrophic lateral sclerosis, a disease that primarily affects motor neurons. These neurons are particularly vulnerable to a cellular energy deficit. Using the ATP-depleting drug glucosamine, we evaluated whether the incretin hormone glucagon-like peptide (GLP)-1 protects motor neurons against glucosamine-induced cytotoxicity. Undifferentiated NSC-34 cells were differentiated into glutamate-sensitive motor neurons by a modified serum deprivation technique. Glucosamine inhibited the viability of differentiated NSC-34 cells in a time- and dose-dependent manner. Glucosamine also acutely reduced cellular glucose uptake, glucokinase activity and intracellular ATP levels. As a result, the activity of AMP-activated protein kinase as well as endoplasmic reticulum stress increased. Pretreatment with GLP-1 significantly alleviated glucosamine-mediated neurotoxicity by restoring cellular glucose uptake, glucokinase activity and intracellular ATP levels. The protective effect of GLP-1 was replicated by Exendin-4 but not Exendin-9, and not blocked by inhibitors of phosphoinositide-3 kinase, protein kinase A, cSrc, or epidermal growth factor receptor, but it was blocked by an adenylate cyclase inhibitor. A selective activator for exchange proteins directly activated by cAMP (Epac), but not a selective activator for protein kinase A, mimicked the GLP-1 effect. Therefore GLP-1 may exert its effect mainly through cAMP-dependent, Epac-mediated restoration of glucose uptake that is typically impaired by glucosamine. These findings indicate that GLP-1 could be employed therapeutically to protect motor neurons that are susceptible to bioenergetic deficits.
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PMID:Glucagon-like peptide-1 protects NSC-34 motor neurons against glucosamine through Epac-mediated glucose uptake enhancement. 2047 53