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

Effect of Vagotomy and Sympathectomy on the Feeding Responses Evoked by Intra-Aortic Cholecystokinin-8 in Adult Male Sprague Dawley Rats

The vagus nerve and the celiaco-mesenteric ganglia (CMG) are required for reduction of meal size (MS) and prolongation of the intermeal interval (IMI) by intraperitoneal (ip) sulfated cholecystokinin-8 (CCK-8). However, recently we have shown that the gut regulates these responses. Therefore, reevaluating the role of the vagus and the CMG in the feeding responses evoked by CCK is necessary because the gut contains the highest concentration of enteric, vagal and splanchnic afferents and CCK-A receptors, which are required for reduction of food intake by this peptide, compared to other abdominal organs. To address this necessity, we injected sulfated CCK-8 (0, 0.1, 0.5, 1 and 3 nmol/kg) in the aorta, near the gastrointestinal sites of action of the peptide, in three groups of free-feeding rats (n = 10 rats per group), subdiaphragmatic vagotomy (VGX), celiaco-mesenteric ganglionectomy (CMGX) and sham-operated, and recorded seven feeding responses. In the sham group, CCK-8 reduced MS (normal chow), prolonged the intermeal interval (IMI, time between first and second meals), increased satiety ratio (SR, IMI/MS), shortened duration of first meal, reduced total (24 hrs) food intake and reduced number of meals relative to saline vehicle. Vagotomy attenuated all of the previous responses except IMI length and SR, and CMGX attenuated all of those responses. In conclusion, the feeding responses evoked by sulfated CCK-8 require, independently, the vagus nerve and the CMG.

Cholecystokinin-33, but not cholecystokinin-8 shows gastrointestinal site specificity in regulating feeding behaviors in male rats

Two separate experiments were performed to localize the gastrointestinal sites of action regulating meal size (MS), intermeal interval (IMI) length and satiety ratio (SR, IMI/MS) by cholecystokinin (CCK) 8 and 33. Experiment 1: CCK-8 (0, 0.05, 0.15, 0.25nmol/kg) was infused in the celiac artery (CA, supplies stomach and upper duodenum) or the cranial mesenteric artery (CMA, supplies small and part of the large intestine) prior to the onset of the dark cycle in free feeding, male Sprague Dawley rats and MS (normal rat chow), IMI and SR were recorded. Experiment 2: CCK-33 (0, 0.05, 0.15, 0.25nmol/kg) were infused in the CA or the CMA, under the same experimental conditions above, and MS, IMI and SR were recorded. Experiment 1 found that CCK-8 reduces MS, prolongs the IMI and increases the SR at sites supplied by both arteries. Experiment 2 found that CCK-33 reduces MS and increases the SR at sites supplied by the CMA. We conclude that in male rats the feeding behaviors evoked by CCK-33, but not CCK-8, are regulated at specific gastrointestinal sites of action.

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.

Obesity as an Early Symptom of the AMIS Syndrome

We review evidence that the AMIS (Absence of Meal-induced Insulin Sensitization) syndrome describes a paradigm fundamental to development of obesity. The hypoglycemic response to a pulse of insulin is doubled after a meal as a result of Hepatic Insulin Sensitizing Substance (HISS), released from the liver to act selectively on muscle, heart and kidney. In the absence of HISS action, the hypoglycemic response to insulin is the same as in the fasted state, and only half of what it should be. Postprandial hyperglycemia ensues, with compensatory hyperinsulinemia, resultant hyperlipidemia and elevated free radical stress. Storage of nutrient energy shifts from glycogen in muscle to fat. Chronic AMIS results in adiposity, occurs with age, is accelerated with sucrose supplement, and prevented by a synergistic antioxidant. Exercise reverses AMIS, as do pharmaceuticals that mimic the "feeding signals". The AMIS syndrome develops as a sequence of pathologies based on the consequences of absence of HISS action, including adiposity as the earliest symptom. Cardiac dysfunction, hypertension, hypercholesterolemia, and fatty liver are related to lack of HISS action. The AMIS syndrome hypothesis is mechanistic-based and accounts for the major pathologies associated with prediabetes, obesity, diabetes and metabolic syndrome. AMIS can be diagnosed, prevented and treated.

Identification of PPARγ ligands with One-dimensional Drug Profile Matching

Introduction

Computational molecular database screening helps to decrease the time and resources needed for drug development. Reintroduction of generic drugs by second medical use patents also contributes to cheaper and faster drug development processes. We screened, in silico, the Food and Drug Administration-approved generic drug database by means of the One-dimensional Drug Profile Matching (oDPM) method in order to find potential peroxisome proliferator-activated receptor gamma (PPARγ) agonists. The PPARγ action of the selected generics was also investigated by in vitro and in vivo experiments.

Materials and methods

The in silico oDPM method was used to determine the binding potency of 1,255 generics to 149 proteins collected. In vitro PPARγ activation was determined by measuring fatty acid-binding protein 4/adipocyte protein gene expression in a Mono Mac 6 cell line. The in vivo insulin sensitizing effect of the selected compound (nitazoxanide; 50–200 mg/kg/day over 8 days; n = 8) was established in type 2 diabetic rats by hyperinsulinemic euglycemic glucose clamping.

Results

After examining the closest neighbors of each of the reference set’s members and counting their most abundant neighbors, ten generic drugs were selected with oDPM. Among them, four enhanced fatty acid-binding protein/adipocyte protein gene expression in the Mono Mac 6 cell line, but only bromfenac and nitazoxanide showed dose-dependent actions. Induction by nitazoxanide was higher than by bromfenac. Nitazoxanide lowered fasting blood glucose levels and improved insulin sensitivity in type 2 diabetic rats.

Conclusion

We demonstrated that the oDPM method can predict previously unknown therapeutic effects of generic drugs. Nitazoxanide can be the prototype chemical structure of the new generation of insulin sensitizers.

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.

Block by nitrate tolerance of meal-induced insulin sensitization in conscious rabbits

PURPOSE

Hemodynamic nitrate tolerance has been shown to result in an insulin-resistant state. We studied whether nitrate tolerance induced by a 7-day continuous exposure to transdermal nitroglycerin influenced the meal-induced insulin sensitization phenomenon in rabbits.

METHODS

Changes in insulin sensitivity in response to feeding in conscious rabbits were determined by rapid insulin sensitivity test, in both nitrate-tolerant and nitrate-intolerant animals. In a separate series of experiments with anesthetized rabbits with or without nitrate tolerance, the hyperinsulinemic euglycemic glucose clamping methods was used to study the effect of intraportal infusion of cholecystokinin (CCK) on whole-body insulin sensitivity.

RESULTS

Rabbits with normal feeding exhibited a 46 ± 6% increase in insulin sensitivity as compared with their matching fasting controls. A 7-day period of treatment with patches releasing 0.07 mg of nitroglycerin per hour yielded nitrate tolerance and a state of insulin resistance and no increase in insulin sensitivity in response to food. Intraportal infusion of CCK8 (0.3-3.0 μg/kg over 20 minutes) resulted in a dose-dependent increase in insulin sensitivity in normal but not in nitrate-tolerant, fasted anesthetized animals.

CONCLUSIONS

Nitrate tolerance blocks both the meal-induced insulin sensitization phenomenon and the insulin-sensitizing effect of intraportal CCK.

Roles of dorsomedial hypothalamic cholecystokinin signaling in the controls of meal patterns and glucose homeostasis

A role for dorsomedial hypothalamus (DMH) cholecystokinin (CCK) signaling in feeding control has been proposed. Administration of CCK into the DMH reduces food intake and OLETF rats lacking CCK1 receptors (CCK1R) become hyperphagic and obese. We hypothesized that site specific replenishment of CCK1R in the DMH of OLETF rats would attenuate aspects of their feeding deficits. Recombinant vectors of adeno-associated viral (AAV)-mediated expression of CCK1R (AAVCCK1R) were bilaterally delivered into the DMH of OLETF. OLETF rats with AAVCCK1R injections demonstrated a 65% replenishment of Cck1r mRNA expression in the DMH relative to lean LETO control rats. Although this level of replenishment did not significantly affect overall food intake or body weight through 14 weeks following viral injections, meal patterns were partially normalized in OLETF rats receiving AAVCCK1R with a significant decrease in dark cycle meal size and a small but significant decrease in daily food intake in the meal analysis chambers. Importantly, the elevation in blood glucose level of OLETF rats was attenuated by the AAVCCK1R injections (p=0.03), suggesting a role for DMH CCK signaling in glucose homeostasis. In support of this role, administration of CCK into the DMH of intact rats enhanced glucose tolerance, as this occurred through activation of CCK1R but not CCK2R signaling. In conclusion, partial replenishment of CCK1R in the DMH of OLETF rats, although insufficient for altering overall food intake and body weight, normalizes meal pattern changes and reduces blood glucose levels. Our study also shows a novel role of DMH CCK signaling in glucose homeostasis.

Impaired insulin secretion and enhanced insulin sensitivity in cholecystokinin-deficient mice

OBJECTIVE

Cholecystokinin (CCK) is released in response to lipid intake and stimulates insulin secretion. We hypothesized that CCK deficiency would alter the regulation of insulin secretion and glucose homeostasis.

RESEARCH DESIGN AND METHODS

We used quantitative magnetic resonance imaging to determine body composition and studied plasma glucose and insulin secretion of CCK gene knockout (CCK-KO) mice and their wild-type controls using intraperitoneal glucose and arginine infusions. The area of anti-insulin staining in pancreatic islets was measured by immunohistochemistry. Insulin sensitivity was assessed with euglycemic-hyperinsulemic clamps.

RESULTS

CCK-KO mice fed a low-fat diet had a reduced acute insulin response to glucose but a normal response to arginine and normal glucose tolerance, associated with a trend toward greater insulin sensitivity. However, when fed a high-fat diet (HFD) for 10 weeks, CCK-KO mice developed glucose intolerance despite increased insulin sensitivity that was associated with low insulin secretion in response to both glucose and arginine. The deficiency of insulin secretion in CCK-KO mice was not associated with changes in β-cell or islet size.

CONCLUSIONS

CCK is involved in regulating insulin secretion and glucose tolerance in mice eating an HFD. The impaired insulin response to intraperitoneal stimuli that do not typically elicit CCK release suggests that this hormone has chronic effects on β-cell adaptation to diet in addition to acute incretin actions.