Molecular Tolerance of Voltage-Gated Calcium Channels is Evident After Short Exposures to Alcohol in Vasopressin-Releasing Nerve Terminals

Association between Triglyceride Glucose Index and Corrected QT Prolongation in Chinese Male Steelworkers

Objectives: Increased triglyceride glucose (TyG) index appears to be linked to carotid and coronary atherosclerosis and calcifications and possesses an elevated future risk of developing cardiovascular disease. Corrected QT (QTc) interval prolongation is associated with ventricular arrhythmias and sudden cardiac death, and a high prevalence of prolonged QTc interval was previously reported in blue-collar workers. The purpose of this study was to find the possible causal inter-relationship between TyG index and QTc interval in a large population of Chinese male steelworkers. Methods: A total of 3189 male workers from two steel plants were enrolled. They responded to a cross-sectional questionnaire on basic attributes and lifestyle, including sleep patterns. All workers in the two plants underwent periodic health checkups, including twelve-lead electrocardiography. Structural equation modeling (SEM) was used to assess the direct and indirect effects of TyG index on QTc interval. Results: With increasing TyG index tertile, the male steelworkers had an increased QTc interval. Applying multivariate analysis, TyG index was associated independently with the odds of QTc prolongation (adjusted odds ratio = 2.73, 95% confidence interval = 1.39–5.24, p = 0.004). SEM revealed that TyG index, hypertension, obesity, lifestyle, white blood cell (WBC) count, and liver function had statistically significant direct effects on QTc interval. Furthermore, TyG index also had an indirect effect on QTc interval through hypertension, obesity, WBC count, and liver function. Moreover, lifestyle had an indirect effect on QTc interval through TyG index. The final model explained 14% of the variability in QTc interval. Conclusions: An increased TyG index was associated with QTc interval prolongation in this study, and SEM delineated possible causal pathways and inter-relationships of the risk factors contributing to the occurrence of QTc prolongation among Chinese male steelworkers.

Alcohol Regulates BK Surface Expression via Wnt/β-Catenin Signaling

It has been suggested that drug tolerance represents a form of learning and memory, but this has not been experimentally established at the molecular level. We show that a component of alcohol molecular tolerance (channel internalization) from rat hippocampal neurons requires protein synthesis, in common with other forms of learning and memory. We identify β-catenin as a primary necessary protein. Alcohol increases β-catenin, and blocking accumulation of β-catenin blocks alcohol-induced internalization in these neurons. In transfected HEK293 cells, suppression of Wnt/β-catenin signaling blocks ethanol-induced internalization. Conversely, activation of Wnt/β-catenin reduces BK current density. A point mutation in a putative glycogen synthase kinase phosophorylation site within the S10 region of BK blocks internalization, suggesting that Wnt/β-catenin directly regulates alcohol-induced BK internalization via glycogen synthase kinase phosphorylation. These findings establish de novo protein synthesis and Wnt/β-catenin signaling as critical in mediating a persistent form of BK molecular alcohol tolerance establishing a commonality with other forms of long-term plasticity.

SIGNIFICANCE STATEMENT

Alcohol tolerance is a key step toward escalating alcohol consumption and subsequent dependence. Our research aims to make significant contributions toward novel, therapeutic approaches to prevent and treat alcohol misuse by understanding the molecular mechanisms of alcohol tolerance. In our current study, we identify the role of a key regulatory pathway in alcohol-induced persistent molecular changes within the hippocampus. The canonical Wnt/β-catenin pathway regulates BK channel surface expression in a protein synthesis-dependent manner reminiscent of other forms of long-term hippocampal neuronal adaptations. This unique insight opens the possibility of using clinically tested drugs, targeting the Wnt/β-catenin pathway, for the novel use of preventing and treating alcohol dependency.

P/Q-type voltage-gated calcium channels mediate the ethanol and CRF sensitivity of central amygdala GABAergic synapses

The central amygdala (CeA) GABAergic system is hypothesized to drive the development of alcohol dependence, due to its pivotal roles in the reinforcing actions of alcohol and the expression of negative emotion, anxiety and stress. Recent work has also identified an important role for the CeA corticotropin-releasing factor (CRF) system in the interaction between anxiety/stress and alcohol dependence. We have previously shown that acute alcohol and CRF each increase action potential-independent GABA release in the CeA via their actions at presynaptic CRF type 1 receptors (CRF₁s); however, the shared mechanism employed by these two compounds requires further investigation. Here we report that acute alcohol interacts with the CRF/CRF₁ system, such that CRF and alcohol act via presynaptic CRF₁s and P/Q-type voltage-gated calcium channels to promote vesicular GABA release and that both compounds occlude the effects of each other at these synapses. Chronic alcohol exposure does not alter P/Q-type voltage-gated calcium channel membrane abundance or this CRF₁/P/Q-type voltage-gated calcium channel mechanism of acute alcohol-induced GABA release, indicating that alcohol engages this molecular mechanism at CeA GABAergic synapses throughout the transition to dependence. Thus, P/Q-type voltage-gated calcium channels, like CRF₁s, are key regulators of the effects of alcohol on GABAergic signaling in the CeA.

Relation of Heavy Alcohol Consumption to QTc Interval Prolongation

Until now, few studies have examined QT intervals in subjects who consume alcohol. We performed this study to evaluate the associations between alcohol consumption and the QTc interval based on a general population. A total of 11,269 adults were examined using a multistage cluster sampling method to select a representative sample of subjects aged ≥35 years. Participants were asked to provide information about their alcohol consumption, and all participants received electrocardiograms and echocardiograms. A prolonged QTc interval was defined according to the national guidelines, which specify thresholds of ≥460 ms in women and ≥450 ms in men. Patients were divided into 3 categories, based on the amount of alcohol they consumed: heavy drinkers (>15 g/day for women and >30 g/day for men), moderate drinkers (≤15 g/day for women and ≤30 g/day for men), and nondrinkers (0 g/day). The results showed that the heavy drinkers had longer QTc intervals than did the nondrinkers. Multivariate logistic regression analyses revealed that men who were heavy drinkers had approximately 1.4-fold higher odds of having a prolonged QTc interval (odds ratio 1.431, 95% confidence interval [CI] 1.033 to 1.982, p = 0.031) than nondrinkers; in women, heavy drinkers had ∼2.3-fold higher odds of having a prolonged QTc interval (odds ratio 2.344, 95% CI 1.202 to 4.571, p = 0.012) than nondrinkers. Neither men nor women who were moderate drinkers exhibited a significant increase in risk for prolonged QTc interval. In conclusion, heavy alcohol consumption was found to be a risk factor for a prolonged QTc interval.

Further characterization of the effect of ethanol on voltage-gated Ca(2+) channel function in developing CA3 hippocampal pyramidal neurons

Developmental ethanol exposure damages the hippocampus, a brain region involved in learning and memory. Alterations in synaptic transmission and plasticity may play a role in this effect of ethanol. We previously reported that acute and repeated exposure to ethanol during the third trimester-equivalent inhibits long-term potentiation of GABAA receptor-dependent synaptic currents in CA3 pyramidal neurons through a mechanism that depends on retrograde release of brain-derived neurotrophic factor driven by activation of voltage-gated Ca(2+) channels (Zucca and Valenzuela, 2010). We found evidence indicating that voltage-gated Ca(2+) channels are inhibited in the presence of ethanol, an effect that may play a role in its mechanism of action. Here, we further investigated the acute effect of ethanol on the function of voltage-gated Ca(2+) channels in CA3 pyramidal neurons using Ca(2+) imaging techniques. These experiments revealed that acute ethanol exposure inhibits voltage-gated Ca(2+) channels both in somatic and proximal dendritic compartments. To investigate the long-term consequences of ethanol on voltage-gated Ca(2+) channels, we used patch-clamp electrophysiological techniques to assess the function of L-type voltage-gated Ca(2+) channels during and following ten days of vapor ethanol exposure. During ethanol withdrawal periods, the function of these channels was not significantly affected by vapor chamber exposure. Taken together with our previous findings, our results suggest that 3(rd) trimester-equivalent ethanol exposure transiently inhibits L-type voltage-gated Ca(2+) channel function in CA3 pyramidal neurons and that compensatory mechanisms restore their function during ethanol withdrawal. Transient inhibition of these channels by ethanol may be, in part, responsible for the hippocampal abnormalities associated with developmental exposure to this agent.

Oral or intraperitoneal binge drinking and oxidative balance in adolescent rats

Oxidative imbalance is one of the most important mechanisms of alcohol-induced injury. Acute alcohol exposure induces a significant amount of reactive oxygen species during its hepatic metabolism via the microsomal ethanol oxidizing system. During adolescence, the physiological development is still taking place; therefore, ethanol's effects differ in adolescents compared to that in adults. Because binge drinking is the most important model of ethanol intake used by adolescents and because little is known about its effects on the liver, we have used two routes of acute ethanol administration (oral and intraperitoneal) in adolescent rats in order to analyze the oxidative damage caused in the periphery and liver. Here, it has been demonstrated for the first time that binge drinking in adolescents causes peripheral oxidation of lipid and DNA as well as lipid and protein hepatic oxidation, which are related to lower glutathione peroxidise (GPx) activity, higher catalase (CAT) activity, and higher expression of NADPHoxidase, contributing to hepatic damage. In addition, it is shown that the intraperitoneal administration route results in increased oxidative damage, which is probably related to the resulting general stress response that causes higher DNA and protein oxidation due to higher NADPHoxidase expression and higher CAT and superoxide dismutase (SOD) activities. According to these results, it is concluded that binge drinking induces hepatic damage during adolescence, at least in part, as consequence of oxidative stress because the antioxidant response was insufficient to avoid liver oxidation. Alcohol administered intraperitoneally provoked more DNA oxidation than that from the oral alcohol exposure model.