Effects of glucosamine on insulin-stimulated glucose metabolism in rat soleus muscle

Oxidative stress is responsible for maternal diabetes-impaired transforming growth factor beta signaling in the developing mouse heart

OBJECTIVE

Oxidative stress plays a causal role in diabetic embryopathy. Maternal diabetes induces heart defects and impaired transforming growth factor beta (TGFβ) signaling, which is essential for cardiogenesis. We hypothesize that mitigating oxidative stress through superoxide dismutase 1 (SOD1) overexpression in transgenic (Tg) mice reverses maternal hyperglycemia-impaired TGFβ signaling and its downstream effectors.

STUDY DESIGN

Day 12.5 embryonic hearts from wild-type (WT) and SOD1 overexpressing embryos of nondiabetic (ND) and diabetic mellitus (DM) dams were used for the detection of oxidative stress markers: 4-hydroxynonenal (4-HNE) and malondlaldehyde (MDA), and TGFβ1, 2, and 3, phosphor (p)-TGFβ receptor II (TβRII), p-phosphorylated mothers against decapentaplegic (Smad)2, and p-Smad3. The expression of 3 TGFβ-responsive genes was also assessed. Day 11.5 embryonic hearts were explanted and cultured ex vivo, with or without treatments of a SOD1 mimetic (Tempol; Enzo Life Science, Farmingdale, NY) or a TGFβ recombinant protein for the detection of TGFβ signaling intermediates.

RESULTS

Levels of 4-HNE and MDA were significantly increased by maternal diabetes, and SOD1 overexpression blocked the increase of these 2 oxidative stress markers. Maternal diabetes suppresses the TGFβ signaling pathway by down-regulating TGFβ1 and TGFβ3 expression. Consequently, phosphorylation of TβRII, Smad2, and Smad3, downstream effectors of TGFβ, and expression of 3 TGFβ-responsive genes were reduced by maternal diabetes, and these reductions were prevented by SOD1 overexpression. Treatment with Tempol or TGFβ recombinant protein restored high-glucose-suppressed TGFβ signaling intermediates and responsive gene expression.

CONCLUSION

Oxidative stress mediates the inhibitory effect of hyperglycemia in the developing heart. Antioxidants, TGFβ recombinant proteins, or TGFβ agonists may have potential therapeutic values in the prevention of heart defects in diabetic pregnancies.

Effects of oral glucosamine sulphate on serum glucose and insulin during an oral glucose tolerance test of subjects with osteoarthritis

BACKGROUND

and objective: Glucosamine is suggested to affect glucose transport and insulin resistance. The effects of oral glucosamine on serum glucose and insulin levels at the initiation and throughout the duration of a 3-h oral glucose tolerance test were examined.

METHODS

Sera from 16 patients with osteoarthritis, but with no other diagnosed medical condition who had fasted overnight, were obtained every 15-30 min during the 3 h of continued fasting and during the 3 h after ingestion of 75 g of glucose with or without ingestion of 1500 mg of glucosamine sulphate. Glucose was analysed by high-performance liquid chromatography using a Metrohm-Peak 817 Bioscan, and the area under the curve (AUC) for glucose was calculated. Insulin was measured by radioimmunoassay every 30 min for 2 h.

RESULTS

Three participants who were found to have previously undiagnosed abnormalities of glucose tolerance demonstrated significant (p = 0.04) incremental elevations in glucose levels after ingestion of glucosamine sulphate. The other 13 participants also had mean incremental elevations that were not significant (p = 0.20). Glucosamine sulphate ingestion had no effect on insulin levels.

CONCLUSION

The results suggest that glucosamine ingestion may affect glucose levels and consequent glucose uptake in patients who have untreated diabetes or glucose intolerance.

Acute glucosamine-induced insulin resistance in muscle in vivo is associated with impaired capillary recruitment

AIMS/HYPOTHESIS

Glucose toxicity and glucosamine-induced insulin resistance have been attributed to products of glucosamine metabolism. In addition, endothelial cell nitric oxide synthase is inhibited by glucosamine. Since insulin has endothelial nitric-oxide-dependent vasodilatory effects in muscle, we hypothesise that glucosamine-induced insulin resistance in muscle in vivo is associated with impaired vascular responses including capillary recruitment.

MATERIALS AND METHODS

Glucosamine (6.48 mg kg(-1) min(-1) for 3 h) was infused with or without insulin (10 mU kg(-1) min(-1)) into anaesthetised rats under euglycaemic conditions.

RESULTS

Glucosamine infusion alone increased blood glucosamine (1.9+/-0.1 mmol/l) and glucose (5.4+/-0.2 to 7.7+/-0.3 mmol/l) (p<0.05) but not insulin. Glucosamine induced both hepatic and muscle insulin resistance as evident from measures of glucose appearance and disposal as well as hind-leg glucose uptake, which was inhibited by approx. 50% (p<0.05). Insulin-mediated increases in femoral arterial blood flow and capillary recruitment were completely blocked by glucosamine.

CONCLUSION/INTERPRETATION

Glucosamine mediates a major impairment of insulin action in muscle vasculature associated with the insulin resistance of muscle. Further studies will be required to assess whether the impaired capillary recruitment contributes to insulin resistance.

Effect of glucosamine supplementation on fasting and non-fasting plasma glucose and serum insulin concentrations in healthy individuals

OBJECTIVE

To test the hypothesis that glucose intolerance does not occur when healthy adults consume normal, recommended dosages of glucosamine sulfate.

METHODS

Healthy adults (N=19) ingested 1500 mg of glucosamine sulfate or placebo (double blind) each day for 12 weeks. Three-hour oral glucose tolerance tests (OGTT) were performed using 75 g of dextrose. These occurred before the start of supplementation, at 6 weeks, and at the completion of supplementation (12 weeks).

RESULTS

There were no significant differences between fasted levels of serum insulin or blood glucose. Glucosamine sulfate supplementation did not alter serum insulin or plasma glucose during the OGTT. There were no significant differences within or between treatments, ages or gender. Glycated hemoglobin measurements at the three time points showed no significant change over time, within or between treatments, ages or gender. The lack of significant changes may have been due to large standard deviations in the data.

CONCLUSION

The data suggests that glucosamine supplementation, with normal recommended dosages, does not cause glucose intolerance in healthy adults. This cannot be determined conclusively, however, until further studies are conducted using alternative types of testing.

Synthesis of cis-(1→3)-glycosides of allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside

Syntheses of allyl 2,3,4-tri-O-benzyl-alpha-D-gluco- and D-galactopyranosyluronate-(1-->3)-2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside via oxidation of the hydroxymethyl group of allyl 2,3,4-tri-O-benzyl-alpha-D-gluco- and D-galactopyranosyl-(1-->3)-2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside under Jones conditions are described. Structures of the title compounds were confirmed by (1)H and (13)C NMR spectroscopy.

Differential effects of troglitazone and D-chiroinositol on glucosamine-induced insulin resistance in vivo in rats

Troglitazone and D-chiroinositol have been shown to exert antidiabetic effects by either potentiating or mimicking insulin action. We studied whether pretreatment with these compounds can prevent the deleterious effects of glucosamine on insulin action that may play an important role in hyperglycemia-induced insulin resistance. Normal Wistar rats were pretreated with troglitazone (100 mg/kg/d), D-chiroinositol (100 mg/kg/d), or placebo (saline) for 7 days. Glucosamine (50 micromol/kg/min) was then infused for 210 minutes, and a euglycemic glucose clamp was performed during the last 120 minutes. Pretreatment with troglitazone or D-chiroinositol had no effect on fasting plasma glucose or insulin or basal hepatic glucose output (HGO). Under the euglycemic-hyperinsulinemic (956+/-93 pmol/L) clamp condition, HGO in glucosamine-infused placebo-treated rats was not suppressed, but instead was increased over the basal level, indicative of hepatic insulin resistance. In contrast, HGO failed to increase during glucosamine infusion in rats pretreated with troglitazone but was not normally suppressed. This may indicate a partial improvement in the hepatic insulin resistance. D-Chiroinositol pretreatment had no effect on the glucosamine-induced increase in HGO. The glucose disposal rate (GDR) was 25% lower in rats infused with glucosamine versus saline-infused rats (25.5+/-2.5 v 34.1+/-2.0 mg/kg/min), indicative of peripheral insulin resistance. Pretreatment with D-chiroinositol (34.5+/-2.3 mg/kg/min) prevented the glucosamine-induced decrease in the GDR, indicating an improvement in peripheral insulin resistance. Troglitazone (25.2+/-3.3 mg/kg/min) was without effect. In conclusion, (1) in normal control rats, glucosamine infusion induced hepatic and peripheral insulin resistance; (2) D-chiroinositol, but not troglitazone, pretreatment prevented glucosamine-induced peripheral insulin resistance; and (3) troglitazone, but not D-chiroinositol, partially blocked the glucosamine-induced hepatic insulin resistance. D-Chiroinositol may provide a novel pharmacological approach to hexosamine-induced peripheral insulin resistance.

Glucosamine regulation of glucose metabolism in cultured human skeletal muscle cells: divergent effects on glucose transport/phosphorylation and glycogen synthase in non-diabetic and type 2 diabetic subjects

Chronic exposure (48 h) to glucosamine resulted in a dose-dependent reduction of basal and insulin-stimulated glucose uptake activities in human skeletal muscle cell cultures from nondiabetic and type 2 diabetic subjects. Insulin responsiveness of uptake was also reduced. There was no change in total membrane expression of either GLUT1, GLUT3, or GLUT4 proteins. While glucosamine treatment had no significant effects on hexokinase activity measured in cell extracts, glucose phosphorylation in intact cells was impaired after treatment. Under conditions where glucose transport and phosphorylation were down regulated, the fractional velocity (FV) of glycogen synthase was increased by glucosamine treatment. Neither the total activity nor protein expression of glycogen synthase were influenced by glucosamine treatment. The stimulation of glycogen synthase by glucosamine was not due totally to soluble mediators. Reflective of the effects on transport/phosphorylation, total glycogen content and net glycogen synthesis were reduced after glucosamine treatment. These effects were similar in nondiabetic and type 2 cells. In summary: 1) Chronic treatment with glucosamine reduces glucose transport/phosphorylation and storage into glycogen in skeletal muscle cells in culture and impairs insulin responsiveness as well. 2) Down-regulation of glucose transport/phosphorylation occurs at a posttranslational level of GLUTs. 3) Glycogen synthase activity increases with glucosamine treatment. 4) Nondiabetic and type 2 muscle cells display equal sensitivity and responsiveness to glucosamine. Increased exposure of skeletal muscle to glucosamine, a substrate/precursor of the hexosamine pathway, alters intracellular glucose metabolism at multiple sites and can contribute to insulin resistance in this tissue.

Amylin-mediated inhibition of insulin-stimulated glucose transport in skeletal muscle

We examined the effects of amylin on 3-O-methyl-D-glucose (3-O-MG) transport in perfused rat hindlimb muscle under hyperinsulinemic (350 microU/ml, 2,100 pmol/l) conditions. Amylin at 100 nmol/l concentration inhibited 3-O-MG transport relative to control in all three basic muscle fiber types. Transport decreased in slow-twitch oxidative (from 5.65 +/- 1.13 to 3.46 +/- 0.71 micromol . g-1 . h-1), fast-twitch oxidative (from 6.84 +/- 0.90 to 4.84 +/- 0.76 micromol . g-1 . h-1), and fast-twitch glycolytic (from 1.27 +/- 0.20 to 0.60 +/- 0.05 micromol . g-1 . h-1) muscle. Amylin inhibition of insulin-stimulated glucose transport in skeletal muscle was accompanied by a 433 +/- 72% increase in intracellular glucose 6-phosphate (G-6-P) despite the absence of extracellular glucose. The source of hexose units for the formation and maintenance of G-6-P was likely glycogen. Amylin increased glycogenolysis, increased lactate formation, and decreased glycogen synthase activity. Furthermore, the kinetics of glycogen synthase suggest that this enzyme may control intracellular G-6-P concentration. Despite the large increase in G-6-P, no detectable increase in uridine diphosphate-N-acetylhexosamines occurred, suggesting that the proposed glucosamine pathway may not be involved in transport inhibition. However, decreases in uridine diphosphate hexoses were detected. Therefore, uridine or hexosamine-based metabolites may be involved in amylin action.