Elena Giné

Stimulation of Islet Protein Kinase C Translocation by Palmitate Requires Metabolism of the Fatty Acid

The secretory, metabolic, and signaling aspects of glucose/ palmitate interaction on β-cell function have been studied on rat islets. Palmitate potentiated the glucose-induced insulin response of perifused islets at suprathreshold (>3 mmol/1) sugar concentrations. This potentiating effect could be suppressed by 8-bromocGMP, which also blocks palmitate metabolism. Palmitate did not modify glucose utilization, but it slightly reduced glucose oxidation and concomitantly increased lactate production. The very low rate of palmitate oxidation (80-fold lower than that of 20 mmol/l glucose) might explain its lack of effect on glycolysis and hence that the glucose/fatty acid cycle is inoperative in islet cells. However, glucose determines the metabolic fate of exogenous palmitate, which is mainly diverted toward lipid synthesis at high sugar concentrations and might then generate lipid messengers for cell signaling. Palmitate did not increase glucose-induced production of inositol-l,4,5-trisphosphate, but it stimulated the translocation of protein kinase C activity from a cytosolic to a particulate fraction at 20 but not at 3 mmol/l glucose. This increased translocation was partially or completely blocked by hydroxycitrate or 8-bromo-cGMP, respectively, which are agents interfering with palmitate metabolism (inhibiting lipid synthesis). The metabolic interaction between glucose and palmitate might generate lipid messengers (diacylglycerol, phosphatidylserine) necessary for the activation of islet protein kinase C, which would in turn result in a potentiation of glucose-induced insulin secretion.

Common single nucleotide variants underlying drug addiction: more than a decade of research.

Drug‐related phenotypes are common complex and highly heritable traits. In the last few years, candidate gene (CGAS) and genome‐wide association studies (GWAS) have identified a huge number of single nucleotide polymorphisms (SNPs) associated with drug use, abuse or dependence, mainly related to alcohol or nicotine. Nevertheless, few of these associations have been replicated in independent studies. The aim of this study was to provide a review of the SNPs that have been most significantly associated with alcohol‐, nicotine‐, cannabis‐ and cocaine‐related phenotypes in humans between the years of 2000 and 2012. To this end, we selected CGAS, GWAS, family‐based association and case‐only studies published in peer‐reviewed international scientific journals (using the PubMed/MEDLINE and Addiction GWAS Resource databases) in which a significant association was reported. A total of 371 studies fit the search criteria. We then filtered SNPs with at least one replication study and performed meta‐analysis of the significance of the associations. SNPs in the alcohol metabolizing genes, in the cholinergic gene cluster CHRNA5‐CHRNA3‐CHRNB4, and in the DRD2 and ANNK1 genes, are, to date, the most replicated and significant gene variants associated with alcohol‐ and nicotine‐related phenotypes. In the case of cannabis and cocaine, a far fewer number of studies and replications have been reported, indicating either a need for further investigation or that the genetics of cannabis/cocaine addiction are more elusive. This review brings a global state‐of‐the‐art vision of the behavioral genetics of addiction and collaborates on formulation of new hypothesis to guide future work.

Taurine Levels and Localization in Pancreatic Islets

Taurine is present in most mammalian tissues including the pancreas. In this organ, taurine appears to be specifically concentrated in the islets as was reported 25 years ago using semi-quantitative techniques2. Experiments confirming these data or studies on the implications of taurine on pancreatic physiology have been scarce. It has been shown, for instance, that taurine administration strongly suppresses glucose-stimulated secretion of insulin from isolated mice islets15, and also that intraperitoneal injection of taurine inhibits the increase in serum insulin induced by glucose administration8. On the contrary, it has been reported very recently that taurine enhances glucose-stimulated insulin release by cultured rat fetal islets4. Clinical studies linking taurine and pancreatic pathological situations are almost absent. It has been shown, however, that taurine plasma levels are low in diabetic patients and that supplementation with this amino acid reduces the increased tendency towards platelet aggregation in these patients5. These data indicate possible functional roles of taurine in the pancreas, and thus, a re-evaluation of its presence and cellular distribution in the islet needs to be carried out. The aim of this study was to determine taurine levels in the pancreatic islets by using a quantitative biochemical method, and also to localize the taurine distribution among the different cell types of the rat pancreas by immunohistochemical techniques.

Aging impairs the control of prefrontal cortex on the release of corticosterone in response to stress and on memory consolidation

This study investigated the role of the dorsomedial prefrontal cortex (dmPFC) on the activity of the hypothalamus-pituitary-adrenal axis and memory consolidation in young and aged rats. The messenger RNA (mRNA) expression of several gamma-aminobutyric acid (GABA) and glutamate receptor subunits were also evaluated in the prefrontal cortex (PFC) of young and aged rats. Microinjections of picrotoxin (GABA(A) antagonist), muscimol (GABA(A) agonist), or vehicle were performed into the dmPFC of young adult (3 months) and aged (27 months) male Wistar rats. Plasma corticosterone was measured under acute stress (30-minute restraint) conditions following microinjections. The retention of an inhibitory avoidance response was also evaluated in response of the same treatments. Picrotoxin microinjections into the dmPFC reduced the stress-induced corticosterone concentrations on young but not on aged animals. Aging did not modify the mRNA content of any of the receptor subunits analyzed. Picrotoxin into the dmPFC reduced inhibitory avoidance response in young but not aged animals. Muscimol treatment did not modify any of the parameters evaluated. These results suggest that prefrontal cortex loses its capacity to control hypothalamo-pituitary-adrenal (HPA) axis activity and the consolidation of emotional memory during aging.

Hypothyroidism decreases the biogenesis in free mitochondria and neuronal oxygen consumption in the cerebral cortex of developing rats

Thyroid hormone plays a critical role in mitochondrial biogenesis in two areas of the developing brain, the cerebral cortex and the striatum. Here we analyzed, in the cerebral cortex of neonatal rats, the effect of hypothyroidism on the biogenesis in free and synaptosomal mitochondria by analyzing, in isolated mitochondria, the activity of respiratory complex I, oxidative phosphorylation, oxygen consumption, and the expression of mitochondrial genome. In addition, we studied the effect of thyroid hormone in oxygen consumption in vivo by determining metabolic flow through (13)C nuclear magnetic resonance spectroscopy. Our results clearly show that in vivo, hypothyroidism markedly reduces oxygen consumption in the neural population of the cerebral cortex. This effect correlates with decreased free mitochondria biogenesis. In contrast, no effect was observed in the biogenesis in synaptosomal mitochondria. The parameters analyzed were markedly improved after T(3) administration. These results suggest that a reduced biogenesis and the subsequent reduction of respiratory capacity in free mitochondria could be the underlying cause of decreased oxygen consumption in the neurons of the cerebral cortex of hypothyroid neonates.

Developmental Hypothyroidism Increases the Expression of Kainate Receptors in the Hippocampus and the Sensitivity to Kainic Acid-Induced Seizures in the Rat

Thyroid hormones are essential for normal brain development, and multiple alterations at behavioral, cognitive, cellular, and molecular levels have been described in animals made hypothyroid during development. Here we analyzed the effect of developmental hypothyroidism in the rat on the sensitivity to kainic acid-induced limbic seizures and the expression of kainate receptors in the hippocampus. Our results show that hypothyroid rats are extremely sensitive to the proconvulsant and neurotoxic effects of kainic acid (KA). Hypothyroid rats entered in status epilepticus at a dose of KA three times lower than that required to reach status epilepticus in control animals. In accordance with this, high levels of glial activation and neuronal loss after low KA dose injections were observed only in the hippocampus of hypothyroid rats. These effects correlated with an increased expression of kainate receptor subunits, excluding GluR5, in the hippocampus of hypothyroid animals. The concentrations of GluR6, GluR7, KAR1, and KAR2 (ionotropic glutamate receptor subunits of the kainic acid subtype) mRNAs were increased between 50 and 250% in hypothyroid animals relative to the values in controls. In agreement with these results, Western blot and immunohistochemical analysis showed a clear increase in the hippocampal content of GluR6/7 proteins in hypothyroid animals.

Cocaine reverses the naltrexone-induced reduction in operant ethanol self-administration: The effects on immediate-early gene expression in the rat prefrontal cortex

Naltrexone is a clinically approved medication for alcoholism. We aimed to investigate the effectiveness of naltrexone co-administered with cocaine and the association of these substances with immediate-early gene expression in the rat prefrontal cortex. We used chronic operant ethanol self-administration and oral treatments prescribed for alcoholism and available in pharmacies to maximise the predictive validity in humans. We performed real-time PCR analysis to determine gene expression levels in the prefrontal cortex. Only the highest dose of naltrexone (1, 3, and 10 mg/kg, p.o.) reduced the response to ethanol. Cocaine increased ethanol self-administration in a dose-dependent manner (2.5, 10, 20 mg/kg, i.p.) and reversed the naltrexone-induced reduction. Naltrexone failed to prevent the cocaine-induced increase in locomotor activity observed in these animals. Chronic self-administration of ethanol reduced the expression of the C-fos gene 4- to 12-fold and increased expression of the COX-2 (up to 4-fold) and Homer1a genes in the rat prefrontal cortex. Chronic ethanol self-administration is prevented by naltrexone, but cocaine fully reverses this effect. This result suggests that cocaine may overcome naltrexones effectiveness as a treatment for alcoholism. The ethanol-induced reduction in C-fos gene expression in the prefrontal cortex reveals an abnormal activity of these neurons, which may be relevant in the compulsive consumption of ethanol, the control of reward-related areas and the behavioural phenotype of ethanol addiction.

Lactate Production in Pancreatic Islets

Lactate production, glucose utilization, glucose oxidation, and insulin release were studied in islets from rat and ob/ob mice. Lactate was determined with a highly sensitive method, based on esterification, subsequent separation, and quantitation with high-performance liquid chromatography. There was a significant lactate production in the absence of glucose, which increased with glucose concentrations up to 3 mmol/l, reaching its half-maximal rate in the presence of 0.2–1.0 mmol/l glucose in both species. Glucose utilization displayed a wider glucose concentration dependence, with a KQ 5 value between 3 and 10 mmol/l glucose. The rates of glucose utilization and lactate production were similar at 3 mmol/l glucose in rat islets and at about 6 mmol/l glucose in ob/ob mice islets. Saturation of lactate production at low glucose concentrations is probably contributing to the observed preferential stimulation of oxidative metabolism at higher concentrations. D-Mannoheptulose caused a marked inhibition of glucose utilization and glucose oxidation at 20 mmol/l glucose in islets from rat or ob/ob mice, as would be expected from a competitive inhibition of glucokinase. By contrast, D-mannoheptulose reduced only marginally the islet metabolism at 3 mmol/l glucose, which is consistent with an effective mannoheptulose-induced inhibition of the glucokinase-dependent, minor part of glucose phosphorylation at this low glucose concentration.

Effects of topiramate on ethanol‐cocaine interactions and DNA methyltransferase gene expression in the rat prefrontal cortex

Recent and ongoing clinical studies have indicated that topiramate (Topamax®) could be effective in treating ethanol or cocaine abuse. However, the effects of topiramate on the co‐administration of ethanol and cocaine remain largely unknown.

Multiple organ inflammatory response to portosystemic shunt in the rat.

Portosystemic shunt surgery is the best procedure to prevent recurrent bleeding of esophageal varices, but carries a high risk of postoperative inflammatory complications, including hepatic encephalopathy. Thus, portosystemic shunting procedures could induce a systemic inflammatory response with multiple organ dysfunction syndrome, including hepatic encephalopathy. To verify this hypothesis we used male Wistar rats at 6 weeks of postoperative evolution: Control (CR; n=14), Sham-operated (SO; n=8) and rats with end-to-side portacaval shunt (PCS; n=15). TNF-α, IL-1β and IL-10 were assayed by ELISA techniques, the expression of the endothelial constitutive nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), constitutive and inducible heme-oxygenase (HO-1 and HO-2) were assayed by Western-blot. mRNA levels of HO-1, HO-2, TNF-α, IL-1β and IL-10 were quantified by reverse transcriptase polymerase chain reaction amplification (RT-PCR) in the small bowel, liver, spleen and lungs. Portacaval shunting in the rat produces an interorgan imbalance of pro- and anti-inflammatory mediators. TNF-α mRNA expression is decreased in the liver (0.69±0.28, p<0.05). The hepatic production of IL-Iβ (204.13±71.90 pg/100 g; p<0.001) and IL-10 (4505.47±337.97 pg/100 g; p<0.001) is also decreased. However, the intestinal pro-inflammatory (TNF-α: 1471.86±153.62 pg/100 g, p<0.001; IL-1β: 48.35±9.84 pg/100 g, p<0.001 and iNOS: 0.59±0.01, p<0.01) and anti-inflammatory (IL-10: 1503.39±53.5 pg/100 g, p<0.001 and HO-1: 2.23±0.16, p<0.001) mediators are increased. Total portacaval shunting in the rat induces impairments of pro- and anti-inflammatory mediators in the splanchnic-lung axis that could be associated with a multiple organ dysfunction syndrome. Therefore, the complications after portosystemic shunts could be integrated into a systemic inflammatory response of possible intestinal origin.