Barna Peitl

Improvement of insulin sensitivity by a novel drug candidate, BGP-15, in different animal studies

BACKGROUND Insulin resistance has been recognized as the most significant predictor of further development of type 2 diabetes mellitus (T2DM). Here we investigated the effect of a heat shock protein (HSP) co-inducer, BGP-15, on insulin sensitivity in different insulin-resistant animal models and compared its effect with insulin secretagogues and insulin sensitizers. METHODS Insulin sensitivity was assessed by the hyperinsulinemic euglycemic glucose clamp technique in normal and cholesterol-fed rabbits and in healthy Wistar and Goto-Kakizaki (GK) rats in dose-ranging studies. We also examined the effect of BGP-15 on streptozotocin-induced changes in the vasorelaxation of the aorta in Sprague-Dawley rats. RESULTS BGP-15 doses of 10 and 30 mg/kg increased insulin sensitivity by 50% and 70%, respectively, in cholesterol-fed but not in normal rabbits. After 5 days of treatment with BGP-15, the glucose infusion rate was increased in a dose-dependent manner in genetically insulin-resistant GK rats. The most effective dose was 20 mg/kg, which showed a 71% increase in insulin sensitivity compared to control group. Administration of BGP-15 protected against streptozotocin-induced changes in vasorelaxation, which was similar to the effect of rosiglitazone. CONCLUSION Our results indicate that the insulin-sensitizing effect of BGP-15 is comparable to conventional insulin sensitizers. This might be of clinical utility in the treatment of T2DM.

Involvement of cholecystokinin in baseline and post-prandial whole body insulin sensitivity in rats

The objective of the study was to investigate the role of cholecystokinin (CCK) on the food-induced insulin sensitization phenomenon in healthy Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats. Whole body insulin sensitivity determined by hyperinsulinaemic euglycaemic glucose clamping and the rapid insulin sensitivity test served as endpoints. Determinations were done in both fasted and re-fed animals. The involvement of CCK in post-prandial insulin sensitization was assessed by using proglumide, a CCK receptor blocker, by assessment of hypothalamic CCK-1/CCK-2 receptor expression by rt-PCR technique and by plasma insulin immunoreactivity determinations by means of radioimmunoassay as pharmacological, genetic and analytical approaches, respectively. The body weight of the OLETF rats and the amount of food consumed much exceeded those seen with LETO rats. The post-prandial increase in insulin sensitivity was marked in LETO, but not in OLETF rats. Intravenous proglumide attenuated post-prandial insulin sensitivity in LETO rats, with no effect in OLETF rats. Nevertheless, baseline insulin sensitivity was much lower in OLETF than in LETO rats. Treatment with rosiglitazone increased baseline insulin sensitivity of OLETF rats and evoked an increase in CCK-1 receptor gene expression in LETO rats. The results provide evidence for the involvement of CCK receptors in adjustment of both fasting and post-prandial insulin sensitivity. The data obtained with OLETF rats strongly suggest the predominant role of CCK-1 receptors.

Diet-induced obesity alters dural CGRP release and potentiates TRPA1-mediated trigeminovascular responses

Background Clinical studies suggest a link between obesity and the primary headache disorder migraine. In our study we aimed to reveal the effect of obesity on meningeal nociceptor function in rats receiving a high-fat, high-sucrose diet. Methods Transient receptor potential ankyrin 1 (TRPA1) receptor activation-induced changes in meningeal blood flow, release of calcitonin gene-related peptide (CGRP) from trigeminal afferents and TRPA1 protein expression in the trigeminal ganglia were measured in control and obese rats. Metabolic parameters of the animals were assessed by measuring glucose and insulin homeostasis as well as plasma cytokine concentrations. Results The present experiments revealed an enhanced basal and TRPA1 receptor agonist-induced CGRP release from meningeal afferents of obese insulin-resistant rats and an attenuated CGRP release to potassium chloride. Obesity was also associated with an augmented vasodilatation in meningeal arteries after dural application of the TRPA1 agonist acrolein, a reduction in TRPA1 protein expression in the trigeminal ganglia and elevations in circulating proinflammatory cytokines IL-1β and IL-6 in addition to increased fasting blood glucose and insulin concentrations. Conclusions Our results suggest trigeminal sensitisation as a mechanism for enhanced headache susceptibility in obese individuals after chemical exposure of trigeminal nociceptors.

Meal-induced enhancement in insulin sensitivity is not triggered by hyperinsulinemia in rats

Several reports confirmed the phenomenon of postprandial increase in whole-body insulin sensitivity. Although the initial step of this process is unknown, the pivotal role of postprandial hyperinsulinemia has strongly been suggested. The aim of the present study was to determine whether hyperinsulinemia per se induces insulin sensitization in healthy male Wistar rats. Rapid insulin sensitivity test (RIST) were performed in fasted, anesthetized rats before and during stable hyperinsulinemia achieved by hyperinsulinemic euglycemic glucose clamping (HEGC) with insulin infused either through the jugular vein (systemic HEGC) or into the portal circulation (portal HEGC) at a rate of 3 mU/(kg min). Insulin sensitivity expressed by the rapid insulin sensitivity (RIST) index (in milligrams per kilogram) was characterized by the total amount of glucose needed to maintain prestudy blood glucose level succeeding an intravenous bolus infusion of 50 mU/kg insulin over 5 minutes. In fasted animals, the RIST index was 37.4 +/- 3.1 mg/kg. When hyperinsulinemia mimicking the postprandial state was achieved by systemic HEGC, the RIST index (39.7 +/- 10.6 mg/kg) showed no significant changes as compared with the pre-HEGC values. Hyperinsulinemia achieved by portal insulin infusion also failed to modify the RIST index (35.7 +/- 4.3 mg/kg). The results demonstrate that acute hyperinsulinemia, no matter how induced, does not yield any sensitization to the hypoglycemic effect of insulin.

Impairment of neurogenic inflammatory and anti-inflammatory responses in diabetic rats.

The effect was studied of a primary (preconditioning) neurogenic inflammatory challenge induced by electrical stimulation of the peripheral stump of the sciatic nerve (20 V, 0.5 ms, 5 Hz, for 5 min) on neurogenic oedema (5 min later) induced by stimulation of the contralateral sciatic nerve. Plasma extravasation due to the second stimulation was decreased by 52.7+/-3.1% (P<0.01) in normal animals and by 29.7+/-2.2 and 18.1+/-1.5% with 50 mg/kg streptozotocin pretreatment i.v. 4 and 8 weeks previously, respectively. Subsequently, bilateral sciatic nerve stimulation increased baseline plasma somatostatin levels from 6.4+/-0.3, 11. 7+/-1.4, and 16.8+/-3.8 to 28.3+/-2.9 (P<0.01), 17.9+/-3.7, and 25. 1+/-1.7 pmol/l in normal, and 4- and 8-week diabetic animals, respectively. We conclude that experimental diabetes impairs the capability of a preconditioning neurogenic inflammatory episode to elicit a systemic anti-inflammatory effect. This is accompanied by a deficiency in elevation of the plasma somatostatin level in response to nerve stimulation, although the baseline plasma somatostatin level increases proportionally to the duration of experimental diabetes.

Insulin resistance occurs in parallel with sensory neuropathy in streptozotocin-induced diabetes in rats: differential response to early vs late insulin supplementation

We investigated whether progressive sensory neuropathy was accompanied by changes in whole-body insulin sensitivity (WBIS) in rats made diabetic by streptozotocin (STZ). The effects of early and late insulin supplementation were also studied. The STZ-treated rats failed to gain weight and exhibited stable hyperglycemia and low plasma insulin levels with a decrease in nerve conduction velocity (NCV) measured in A and C fibers of the saphenous nerve. A decreased sensory neuropeptide (SNP) release such as that of substance P, somatostatin, and calcitonin gene-related peptide determined from organ fluid of tracheal preparations subjected to electrical field stimulation also occurred in diabetic animals. These features were accompanied by a decrease in WBIS measured by hyperinsulinemic-euglycemic glucose clamping and a decrease in insulin-stimulated glucose uptake in cardiac and gastrocnemius muscle. When insulin supplementation with slow-release implants (2 IU/d) was started 4 weeks after STZ injection, blood glucose level normalized. Both insulin sensitivity and sensory nerve function reflected in either NCV or SNP release completely recovered by the 12th post-STZ week. When the insulin implants were applied from the eighth post-STZ week, both WBIS and glucose uptake remained significantly decreased, with a seriously impaired NCV and SNP release with strong hyperglycemia. Late insulin supplementation, however, even by using double implantation from the 10th post-STZ week, was unable to restore blood glucose, WBIS, NCV, and SNP release by the 12th week. Insulin resistance occurs in parallel with sensory neuropathy in STZ-diabetic rats. Both can be improved by early but not late insulin supplementation.

Development of insulin resistance by nitrate tolerance in conscious rabbits.

Clinical evidence has been raised to suggest that transdermal nitroglycerin increases the sensitivity of peripheral tissues to the hypoglycemic effect of insulin. In this study we determined whether development of tolerance to the hypotensive effect of nitroglycerin also resulted in tolerance to the insulin-sensitizing effect in rabbits. Intravenous glucose disposal and hyperinsulinemic euglycemic glucose clamp studies were performed on naive and hemodynamic nitrate tolerant conscious New Zealand white rabbits. These rabbits were exposed to continuous “patch on” with nitroglycerin (0.07 mg/kg/h) or placebo patches over 7 days. Nitroglycerin treatment of 7 days produced a lack of hypotensive response to a single intravenous bolus of 30 &mgr;g/kg nitroglycerin, which caused a significant decrease in mean arterial blood pressure in control rabbits. A six-hour exposure to transdermal nitroglycerin significantly increased insulin sensitivity determined by hyperinsulinemic (100 &mgr;U/ml) euglycemic (5.5 mmol/l) glucose clamping as compared with that seen in rabbits treated with placebo patches. A significant decrease in insulin sensitivity was observed in the nitroglycerin patch-treated animals both in the presence and after the removal of the last patch when the patches were applied over 7 days. We conclude that acutely nitrate patches improve insulin sensitivity whereas a 7-day chronic treatment schedule that results in hemodynamic nitrate tolerance also produces insulin resistance.

Morphological, hemodynamical and hemorheological changes of mature artificial saphenous arterio-venous shunts in the rat model

Artificial femoral arterio‐venous (AV) shunts are widely used in rodent models for studying shunt maturation and to optimize various surgical techniques. However, little is known about complex circulatory, microcirculatory, and hemorheological effects of end‐to‐side saphenous AV shunts. We aimed to study these parameters in mature AV shunts. Studying these questions in CD rats, end‐to‐side anastomoses were made between the left saphenous artery and vein. On the right‐side the nonoperated saphenous vessels served as own control. Furthermore healthy control animals were also investigated. On the 8th to 12th postoperative week microcirculatory and blood flow measurements were performed and blood samples were taken both from the shunts arterial and venous limbs and from the nonoperated side vessels. Hematological parameters, erythrocyte aggregation, and deformability were determined. The entire shunt and the control vessels were removed for histological examinations. The skin microcirculation on shunt side slightly increased on thigh and decreased on paws versus the nonoperated side. Blood flow measurements made directly on the vessels showed that arterial to venous blood flow rate ratio was 1.59 ± 0.29 on nonoperated side and 1.2 ± 0.13 on the shunt side, and 1.49 ± 0.05 in control animals. Erythrocyte aggregation and deformability worsened on the shunt side. Histologically increased number of smooth muscle elements and connective tissue were found in venous limb of the shunts. The artificial AV shunt between the saphenous artery and vein seems to be a suitable model for further functional‐morphological and hemorheological examinations of hemodialysis in various states and diseases.

Diet-Induced Obesity Enhances TRPV1-Mediated Neurovascular Reactions in the Dura Mater.

Exploring the pathophysiological changes in transient receptor potential vanilloid 1 (TRPV1) receptor of the trigeminovascular system in high‐fat, high‐sucrose (HFHS) diet‐induced obesity of experimental animals.

Effect of long-term olanzapine treatment on meal-induced insulin sensitization and on gastrointestinal peptides in female Sprague–Dawley rats

Meal-induced insulin sensitization (MIS), an endogenous adaptive mechanism is activated post-prandially. Reduced MIS leads to diabetes, but its activation improves insulin sensitivity. MIS is preserved to single olanzapine administration, therefore we aimed to investigate the chronic effect of olanzapine on fasted-state insulin sensitivity and on MIS in female Sprague–Dawley rats. Daily food and water intake, stool and urine production and body weight were determined. The MIS was characterized by a rapid insulin sensitivity test. Fasting hepatic and peripheral insulin sensitivity were determined by a hyperinsulinaemic euglycaemic glucose clamping supplemented with radiotracer technique. Fasted and post-prandial blood samples were obtained for plasma insulin, leptin, ghrelin, amylin, GLP-1, GIP, PYY and PP determination. Adiposity was characterized by weighing intra-abdominal and inguinal fat pads. Olanzapine caused hepatic insulin resistance and a reduced metabolic clearance rate of insulin, but the MIS retained its function. Body weight and adiposity were enhanced, but olanzapine failed to increase food intake. Fasting insulin and leptin were elevated and the post-prandial reduction in ghrelin level was inhibited by olanzapine. The MIS remained functionally intact after long-term olanzapine treatment. Altered insulin, leptin and ghrelin levels indicate olanzapine-induced metabolic derangements. Pharmacological activation of MIS could potentially be exploited to treat or prevent olanzapine-induced insulin resistance.