Adela Rovira

Impaired tyrosine-kinase activity of muscle insulin receptors from hypomagnesaemic rats

SummaryThe effect of magnesium deficiency on glucose disposal, glucose-stimulated insulin secretion and insulin action on skeletal muscle was investigated in rats which were fed a low magnesium-containing diet for 4 days. Control rats were fed a standard diet. Compared to the control rats, the rats fed with low magnesium diet presented: 1) lower serum magnesium levels (0.45±0.02 vs 0.78±0.01 mmol/l, p<0.001), 2) higher basal serum glucose (6.8±0.2 vs 5.5±0.2 mmol/l, p<0.05) and similar basal serum insulin, 3) 40% reduction (p<0.001) in the glucose disappearance rate after its i.v. administration, and 4) 45% reduction (p<0.05) in the glucose-stimulated insulin secretion. The insulin action upon the glucose uptake by skeletal muscle was determined by means of hindquarter perfusions. Compared with control rats, magnesium-deficient rats presented: 1) normal basal glucose uptake, 2) lower stimulatory effect on the glucose uptake by insulin at the concentrations of 5×10−10 mol/l (3.0±0.9 vs 5.4±0.6, p<0.05) and 5×10−9mol/l (6.3±0.5 vs 8.0±0.5, p<0.05), 3) normal glucose uptake at a maximal insulin concentration of 1×10−7 mol/l, and 4) 50% reduction in the insulin sensitivity (ED50: 1.3±0.3 vs 0.55±0.1 mol/l, p<0.05). In partially purified insulin receptors prepared from gastrocnemius muscle, 125I-insulin binding was similar in both groups of rats. However, the autophosphorylation of the Β-subunit of the insulin receptor was significantly reduced by 50% in magnesium-deficient rats and the tyrosine kinase activity of insulin receptors toward the exogenous substrate Poly Glu4: Tyr 1 was also reduced (p<0.05) by hypomagnesaemia. The abundance of the insulin-sensitive glucose transporter protein (muscle/fat GLUT4), measured by Western blot analysis using polyclonal antisera, was similar in muscles of control and hypomagnesaemic rats. These findings indicate that hypomagnesaemia has a deleterious effect on glucose metabolism due to an impairment of both insulin secretion and action. The insulin resistance observed in skeletal muscle of magnesium-deficient rats may be attributed, at least in part, to a defective tyrosine kinase activity of insulin receptors.

High-sensitivity C-reactive protein is a good marker of cardiovascular risk in obese children and adolescents.

OBJECTIVE We intend to assess the utility of the high-sensitivity C-reactive protein (hs-CRP) as a marker of cardiovascular risk in obese children and adolescents. METHODS The study included children and adolescents between 6 and 18 years of age with a body mass index (BMI) higher than 2 SDS. All the patients had their blood pressure taken and hs-CRP, hepatic function, lipid profile and uric acid were determined after 12 h of fasting. Likewise, an oral glucose tolerance test was performed, determining basal glucose and insulin levels, and after stimulus. We considered the presence of metabolic syndrome when the obese children and teenagers showed at least two of the following conditions: decreased high density lipoprotein (HDL)-cholesterol, hypertriglyceridemia, hypertension or alteration in glucose metabolism. RESULTS Out of the 115 obese children studied, 24% showed signs of metabolic syndrome. Those with metabolic syndrome presented higher levels of hs-CRP (mean: 3.8 mg/l; 95% CI: 2.8-4.8) in comparison with the obese patients who did not show signs of metabolic syndrome (mean: 2 mg/l; 95% CI: 1.5-2.5). After a multivariate analysis, the variables that appear to influence the changes in hs-CRP were BMI, triglycerides and HDL-cholesterol levels. CONCLUSION The hs-CRP is a useful tool for early diagnosis of cardiovascular risk in obese children and teenagers.

Increased glucose transporter (GLUT4) protein expression in hyperthyroidism

We have studied skeletal muscle glucose uptake by perfused hindquarter preparations from rats treated with thyroxine. Basal glucose uptake (in the absence of insulin) was approximately 2 fold higher in muscle of hyperthyroid rats compared to controls. Insulin (10(-7) M) stimulated glucose uptake 4.0 and 6.8 fold in the 10 day and 30 day controls rats, respectively. Maximal glucose uptake (10(-7) M insulin) was not different in control and hyperthyroid rats and thus insulin responsiveness in the hyperthyroid animals was reduced to 2.5 fold stimulation. The abundance of the insulin-sensitive glucose transporter protein (muscle/fat, GLUT-4), measured by Western blot analysis using polyclonal antisera, was higher in skeletal muscle from both groups of hyperthyroid rats. These studies indicate that thyroid hormones increase basal glucose uptake in skeletal muscle and this is due, at least in part, to an increment of GLUT-4 isoform. Increased expression of muscle glucose transporter proteins may be responsible for the increased peripheral glucose utilization seen in hyperthyroidism.

Gliclazide treatment of streptozotocin diabetic rats restores GLUT4 protein content and basal glucose uptake in skeletal muscle

This study examined whether the treatment of streptozotocin (STZ)-diabetic rats with gliclazide (5 mg/kg body weight twice daily orally) increases muscle glucose uptake. Rats were treated (group G, n = 10) or untreated (group D, n = 11) for 12 days. Normal rats served as controls (group C, n = 11). At the end of the treatment, both basal and insulin-stimulated glucose uptake by the perfused hindquarters were measured. In gastrocnemious muscles, the protein content of GLUT4 and the insulin binding and tyrosine kinase activity of partially purified solubilized insulin receptors were measured. Group G had a lower mean glycemic value during the treatment period than group D (mean +/- SEM, 17 +/- 0.6 v 19.7 +/- 0.5 mmol/L, P < .05), without differences in serum insulin levels. Basal glucose uptake by the hindquarters was significantly higher in group G versus group D (2.8 +/- 0.3 v 1.3 +/- 0.2 mumol/g/h, P < .05), and was not different versus group C (3.6 +/- 0.2 mumol/g/h). Insulin-stimulated glucose uptake was higher (P < .05) in group C compared with the two groups of diabetic rats. Glucose uptake at 10(-7) mol/L insulin was higher in group G than in group D (9.2 +/- 0.6 v 7.0 +/- 0.6 mumol/g/h, P < .05). Both insulin binding and tyrosine kinase activity were similar in muscle insulin receptors from both groups of diabetic rats. The GLUT4 protein content was higher in group G than in group D (95 +/- 10 v 57 +/- 7 arbitrary units [AU]/microgram protein, P < .05) and similar to that of group C (113 +/- 13 AU/microgram protein). In conclusion, gliclazide has a glucose-lowering effect in STZ-diabetic rats that could be attributed to an increase in muscle glucose clearance by a post-insulin receptor mechanism, probably related to a normalization of GLUT4 content.

Circulating kisspeptin levels exhibit sexual dimorphism in adults, are increased in obese prepubertal girls and do not suffer modifications in girls with idiopathic central precocious puberty.

The system KISS1-KISS1R is one of the main regulators of the hypothalamic-pituitary-gonadal axis and constitutes a link between metabolism and reproduction through its interaction with leptin. The aim of this study was to clarify the possible utility of kisspeptin as a pubertal marker and/or the possible influence of nutritional status in kisspeptin levels. To this end, we have studied kisspeptin plasma levels throughout sexual development and in prepubertal obese girls and girls affected by idiopathic central precocious puberty (CPP). Plasma kisspeptin concentrations were analyzed by RIA. An increase in kisspeptin levels was observed in adult females compared to healthy prepubertal and pubertal girls (p<0.001) and to adult males (p<0.001). Additionally, kisspeptin was increased in prepubertal obese girls compared to healthy prepubertal girls (p<0.01) and girls with idiopathic CPP (p<0.05). As revealed by the regression analysis, in prepubertal healthy and obese girls and girls with idiopathic CCP, the parameters that influenced kisspeptin levels were BMI (R(2)=0.10, p<0.05) and leptin levels (R(2)=0.14, p<0.01). In conclusion, kisspeptin levels do not seem to be a good pubertal marker. The results obtained in prepubertal and idiopathic CCP girls point to a relationship between leptin, BMI and kisspeptin at least in this group, and suggest a possible role for adipose tissue in the modulation kisspeptin synthesis.

Sulphonylurea stimulates glucose uptake in rats through an ATP-sensitive K § channel dependent mechanism

SummaryWe studied the effect of gliclazide, a second-generation sulphonylurea, on rat skeletal muscle glucose uptake using perfused hindquarter muscle preparations. Gliclazide at concentrations of 10 to 1000 Μg/ml increased (p<0.05) the basal glucose uptake. The effect of gliclazide on glucose uptake was immediate and dose-dependent, reaching a plateau at a concentration of 300 Μg/ml; the half-maximal effect was obtained between 25 and 50 Μg/ml. The glucose uptake stimulated by gliclazide (300–1000 Μg/ ml) did not differ from that achieved by 10−9 mol/l insulin, and was lower (p<0.05) than that obtained with 10−7 mol/l insulin. The combination of gliclazide (300 Μg/ml) and 10−9 mol/l insulin produced an increase in glucose uptake (7.7±0.6 Μmol · g−1 · h−1, n=8, mean±SEM) which was higher (p<0.05) than that achieved with 10−9 mol/l insulin (5.6±0.7 Μmol · g−1 · h−1, n=11) and not different from that obtained with 10−7 mol/l insulin (9.8±1.0 Μmol · g−1 · h−1, n=11). Diazoxide (100 Μmol/l), an ATP-sensitive K+ channel opener, reversed the stimulatory effect of gliclazide (100 Μg/ml) on muscle glucose uptake from 3.1±0.4 to 0.5±0.2 Μmol · g−1 · h−1, (n=7, p<0.001). The addition of diazoxide prior to gliclazide into the perfusion medium blocked the gliclazide-induced glucose uptake by the hindquarter muscle preparations. In conclusion, gliclazide alone has an immediate stimulatory effect on glucose uptake by skeletal muscle and together with insulin has an additive effect on muscle glucose uptake. The effect of gliclazide on muscle glucose uptake seems to be due to the inhibition of ATP-sensitive K+ channels.

The insulin sensitizing effects of PPAR-γ agonist are associated to changes in adiponectin index and adiponectin receptors in Zucker fatty rats.

The adiponectin high molecular weight isoform (HMW-adp) and its relation with the other adiponectin isoforms (adiponectin index, S(A)), have been identified as essential for the adiponectin insulin sensitizing effects. The objective of this study is to gain further insight on the effect of the insulin sensitizing agents, PPAR-γ agonists, on the distribution of the adiponectin isoforms and the adiponectin receptors, adipoR1 and adipoR2 in an animal model of obesity and insulin resistance. To achieve the objective, Zucker fatty rats were treated with pioglitazone, rosiglitazone or placebo for six weeks. At the end of the treatment, total adiponectin, adiponectin isoforms and adiponectin receptors expression were measured. In order to see the possible relation with insulin sensitivity parameters, HOMA-IR, muscle insulin-stimulated glucose transport, muscle GLUT4 and plasma free fatty acids were also measured. The two glitazones improved insulin sensitivity and both muscle insulin-stimulated glucose transport and GLUT4 total content. Total plasma adiponectin and visceral fat HMW-adp were increased only by pioglitazone. On the other hand, both glitazones changed the distribution of adiponectin isoforms in plasma, leading to an increase in the S(A) of 21% by pioglitazone and 31% by rosiglitazone. Muscle adipoR1 expression was increased by both glitazones whereas liver adipoR2 expression was increased by rosiglitazone and tended to increase in the pioglitazone group. The insulin sensitizing action of glitazones is mediated, at least in part, by their effect on muscle insulin-stimulated glucose transport and by their direct influence on the adiponectin index and the adiponectin receptors expression.

Glucose tolerance, insulin secretion, insulin sensitivity and glucose effectiveness in normal and overweight hyperthyroid women

OBJECTIVE Inter‐relationships between insulin sensi‐tivity and body weight in patients with hyperthyroidism remain incompletely understood. We have examined whether a mild excess of body weight exacerbates the metabolic abnormalities of spontaneous hyperthyroidism.

Effect of short- and long-term experimental hyperthyroidism on plasma glucose level and insulin secretion during an intravenous glucose load and on insulin binding, insulin receptor kinase activity, and insulin action in adipose tissue☆

Glucose disposal, insulin secretion, and insulin action in adipose tissue were measured in rats treated for 10 or 30 days with high doses of thyroxine (T4). Acutely induced hyperthyroidism produced a high rate of glucose disposal after an intravenous glucose tolerance test (IVGTT), accompanied by a high glucose-stimulated insulin secretion. In addition, in these rats the following phenomena were observed: (1) high insulin binding to isolated adipocytes due to an increase in the insulin receptor number; (2) high insulin binding to partially purified fat insulin receptors; (3) normal tyrosine kinase activity of fat insulin receptors; and (4) high insulin action in isolated adipocytes, such as glucose transport and lipogenesis. Chronically induced hyperthyroidism produced high rates of glucose disposal after an IVGTT, accompanied by an increase of basal and glucose-stimulated insulin secretion. These rats showed (1) normal insulin binding to either isolated adipocytes or partially purified insulin receptors; (2) normal tyrosine kinase activity of fat insulin receptors; (3) normal insulin action in isolated adipocytes. In conclusion, exogenous hyperthyroidism induced an increase in glucose disposal, probably due in part to high insulin secretion. In short-term T4-treated rats an additional increase of insulin action in adipocytes was also observed.

The influence of puberty on vitamin D status in obese children and the possible relation between vitamin D deficiency and insulin resistance

Abstract Background: Puberty can affect vitamin D levels. Objectives: The goal of this study was to analyze the relation between vitamin D deficiency and puberty in obese Spanish children, along with the possible interrelation between vitamin D status and degree of insulin resistance. Methods: A cross-sectional study was carried out, in which clinical and biochemical data were gathered from 120 obese and 50 normal weight children between January 2011 and January 2013. Results: Mean vitamin D levels were 19.5 and 31.6 ng/mL in obese pubertal and obese prepubertal children, respectively. About 75% of the obese pubertal subjects and 46% of the obese prepubertal subjects had vitamin D deficiency. Vitamin D levels were significantly lower in pubescent subjects compared with pre-pubescent subjects in summer, fall, and winter. There was no apparent relation between vitamin D levels and homeostasis model assessment index for insulin resistence (expressed in standard deviation score for sex and Tanner stage) in either puberty or pre-puberty. Conclusion: Puberty may be a risk factor for the vitamin D deficiency commonly found in the obese child population. This deficiency is not associated with higher insulin resistance in obese pubertal children compared with obese prepubertal children.