Effects of acetaldehyde on the automaticity of the guinea pig sinus node

Role of autophagy and regulatory mechanisms in alcoholic cardiomyopathy

Alcoholism is accompanied with a high incidence of cardiac morbidity and mortality due to the development of alcoholic cardiomyopathy, manifested as dilation of one or both ventricles, reduced ventricular wall thickness, myofibrillary disarray, interstitial fibrosis, hypertrophy and contractile dysfunction. Several theories have been postulated for the etiology of alcoholic cardiomyopathy including ethanol/acetaldehyde toxicity, mitochondrial production of reactive oxygen species, oxidative injury, apoptosis, impaired myofilament Ca²⁺ sensitivity and protein synthesis, altered fatty acid extraction and deposition, as well as accelerated protein catabolism. In particular, buildup of long-lived or dysfunctional organelles has been reported to contribute to cardiac structural and functional damage following alcoholism. Removal of cell debris and defective organelles by autophagy is essential to the maintenance of cardiac homeostasis in physiological and pathological conditions. However, insufficient understanding is currently available with regards to the involvement of autophagy in the pathogenesis of alcoholic cardiomyopathy. This review summarizes the recent findings on the pathophysiological role of dysregulated autophagy in one set and development of alcoholic cardiomyopathy. A thorough understanding of how autophagy is affected in alcoholism, and subsequently, contributes to the pathogenesis of alcoholic heart injury, will offer therapeutic guidance towards the management of alcoholic cardiomyopathy.

Mitochondria as a source and target of lipid peroxidation products in healthy and diseased heart

The heart is a highly oxidative organ in which cardiomyocyte turnover is virtually absent, making it particularly vulnerable to accumulation of lipid peroxidation products (LPP) formed as a result of oxidative damage. Reactive oxygen and nitrogen species are the most common electrophiles formed during lipid peroxidation and lead to the formation of both stable and unstable LPP. Of the LPP formed, highly reactive aldehydes are a well-recognized causative factor in ageing and age-associated diseases, including cardiovascular disease and diabetes. Recent studies have identified that the mitochondria are both a primary source and target of LPP, with specific emphasis on aldehydes in cardiomyocytes and how these affect the electron transport system and Ca(2+) balance. Numerous studies have found that there are functional consequences in the heart following exposure to specific aldehydes (acrolein, trans-2-hexanal, 4-hydroxynonenal and acetaldehyde). Because these LPP are known to form in heart failure, cardiac ischaemia-reperfusion injury and diabetes, they may have an underappreciated role in the pathophysiology of these disease processes. Lipid peroxidation products are involved in the transcriptional regulation of endogenous anti-oxidant systems. Recent evidence demonstrates that transient increases in LPP may be beneficial in cardioprotection by contributing to mitohormesis (i.e. induction of anti-oxidant systems) in cardiomyocytes. Thus, exploitation of the cardioprotective actions of the LPP may represent a novel therapeutic strategy for future treatment of heart disease.

ALDH2 in alcoholic heart diseases: molecular mechanism and clinical implications

Alcoholic cardiomyopathy is manifested as cardiac hypertrophy, disrupted contractile function and myofibrillary architecture. An ample amount of clinical and experimental evidence has depicted a pivotal role for alcohol metabolism especially the main alcohol metabolic product acetaldehyde, in the pathogenesis of this myopathic state. Findings from our group and others have revealed that the mitochondrial isoform of aldehyde dehydrogenase (ALDH2), which metabolizes acetaldehyde, governs the detoxification of acetaldehyde formed following alcohol consumption and the ultimate elimination of alcohol from the body. The ALDH2 enzymatic cascade may evolve as a unique detoxification mechanism for environmental alcohols and aldehydes to alleviate the undesired cardiac anomalies in ischemia-reperfusion and alcoholism. Polymorphic variants of the ALDH2 gene encode enzymes with altered pharmacokinetic properties and a significantly higher prevalence of cardiovascular diseases associated with alcoholism. The pathophysiological effects of ALDH2 polymorphism may be mediated by accumulation of acetaldehyde and other reactive aldehydes. Inheritance of the inactive ALDH2*2 gene product is associated with a decreased risk of alcoholism but an increased risk of alcoholic complications. This association is influenced by gene-environment interactions such as those associated with religion and national origin. The purpose of this review is to recapitulate the pathogenesis of alcoholic cardiomyopathy with a special focus on ALDH2 enzymatic metabolism. It will be important to dissect the links between ALDH2 polymorphism and prevalence of alcoholic cardiomyopathy, in order to determine the mechanisms underlying such associations. The therapeutic value of ALDH2 as both target and tool in the management of alcoholic tissue damage will be discussed.

Mechanisms of alcoholic heart disease

Compromised heart function is regularly seen in patients with chronic alcohol ingestion and is often manifested as cardiomegaly, reduced myocardial contractility (with concomitant reductions in ejection fraction and stroke volume), myocardial fibrosis, enhanced risk of stroke and hypertension, and disruptions in the myofibrillary structure. A number of mechanisms including oxidative damage, deposition of triglycerides, altered fatty acid extraction, decreased myofilament Ca(2+) sensitivity, and impaired protein synthesis have been proposed for the development of alcoholic cardiomyopathy. Nonetheless, the underlying mechanism(s) has not been delineated. Several alcohol metabolites have been identified as specific toxins of myocardial tissue, including ethanol, its first and major metabolic product--acetaldehyde--and fatty acid ethyl esters. Acetaldehyde directly impairs cardiac contractile function, disrupts cardiac excitation-contraction coupling and promotes oxidative damage and lipid peroxidation. Unfortunately, the most direct approach to studying this (direct administration of acetaldehyde) is impossible, since direct intake of acetaldehyde is highly toxic and unsuitable for chronic studies. In order to overcome this obstacle, transgenic mice have recently been produced to artificially alter ethanol/acetaldehyde metabolism, resulting in elevated acetaldehyde levels after ethanol ingestion. This review will summarize some of the postulated mechanisms for alcoholic cardiomyopathy, with special emphasis on animal models.

Ethanol and acetaldehyde in alcoholic cardiomyopathy: from bad to ugly en route to oxidative stress

Alcoholic cardiomyopathy is characterized by cardiomegaly, disruptions of myofibrillary architecture, reduced myocardial contractility, decreased ejection fraction, and enhanced risk of stroke and hypertension. Although several mechanisms have been postulated for alcoholic cardiomyopathy, including oxidative damage, accumulation of triglycerides, altered fatty acid extraction, decreased myofilament Ca(2+) sensitivity, and impaired protein synthesis, neither the mechanism nor the ultimate toxin has been unveiled. Primary candidates acting as specific toxins of myocardial tissue are ethanol; its first and major metabolic product, acetaldehyde; and fatty acid ethyl esters. Acetaldehyde has been demonstrated to impair directly cardiac contractile function, disrupt cardiac excitation-contractile coupling, and contribute to oxidative damage and lipid peroxidation. Acetaldehyde-elicited cardiac dysfunction may be mediated through cytochrome P450 oxidase, xanthine oxidase, and the stress-signaling cascade. Unfortunately, the most direct approach that can be used to examine toxicity is hampered by the fact that direct intake of acetaldehyde is highly toxic and unsuitable for long-term study. To overcome this obstacle, transgenic mice have been used to alter artificially ethanol/acetaldehyde metabolism, resulting in elevated acetaldehyde concentrations after ethanol ingestion. In this review, we summarize results obtained with the use of transgenic animal models to elucidate the role of acetaldehyde in the mechanism of action in alcoholic cardiomyopathy.

Ethanol and hormesis

This article provides a detailed assessment of the toxicological and pharmacological literature concerning alcohol-induced biphasic dose-response relationships. The assessment reveals that alcohol-induced hormetic-like dose-response relationships are commonly observed, highly generalizeable according to model and endpoint and quantitative feature of the dose response. These findings have important implications affecting study design, animal model, and endpoint selection as well as clinical applications.

Influences of changes in calcium concentrations, cocaine and clonidine on the cardiac effect of acetaldehyde in rat isolated atria

1. Cardiovascular responses to acetaldehyde (AChO) were investigated in rat isolated atria. 2. Results show that two different doses of AChO (0.29 and 0.88 mM) induce positive inotropic effects on rat atria, and express Ca2+ dependence when analyzed at three external Ca2+ concentrations (0.6, 1.1, 2.2 mM). 3. Cocaine (3.5 and 35 microM) produced significant potentiation of the AChO-positive (0.29 and 0.88 mM) inotropic effect in 1.1 mM Ca2+ medium. 4. Clonidine (40 microM) increased the peak tension developed (PTD) induced by AChO (both 0.29 and 0.88 mM) only 1.1 mM Ca2+ medium. 5. It is suggested that the positive inotropic effect produced by AChO involves a Ca2(+)-dependent mechanism, which can be potentiated by the additional stimulation of alpha-adrenergic receptors.

Arrhythmogenic and antiarrhythmic actions of substances of abuse: effects on triggered activity

Substances of abuse exert adrenergic and/or depressant actions on the cellular processes responsible for cytosolic calcium overload. This investigation attempted to determine whether substances of abuse, through catechol-mediated effects or cellular actions, elicit or inhibit the production of arrhythmias caused by delayed afterdepolarizations (DADs) and triggered activity (TA). The papillary muscles of rats and Purkinje fibers of dogs were superfused in vitro with Tyrode's solution at 37 degrees C. Intracellular microelectrodes were used to record membrane potentials. Overdrives failed to induce DADs and TA in the canine Purkinje fibers exposed to either Tyrode's solution alone, or containing ethanol or harmine. Instead, ethanol and harmine inhibited DADs and TA induced by overdrives in the presence of strophanthidin. On the contrary, in the presence of acetaldehyde and amphetamine, overdrives did produce TA, which was inhibited by propranolol. In conclusion, substances of abuse may either elicit or inhibit the production of DADs and TA, depending on the balance between adrenergic and depressant actions on the cellular mechanisms responsible for the calcium overload of the cytosol.

Mechanisms of the in vitro effects of amphetamine on rat sinus node automaticity and membrane potentials of atrial fibers

The main objective of this investigation was to clarify the mechanisms of the acute in vitro actions of amphetamine (AMP) on cardiac electrophysiology. Concentrations of AMP ranging from those considered clinically therapeutic to those considered toxic were tested in isolated rat sinoatrial tissues while recording membrane potentials with intracellular microelectrodes. In preparations beating spontaneously, 6.8 nM-2.71 microM AMP exerted a positive chronotropic action that was blocked by propranolol. The positive chronotropic action of 5.43 microM AMP was smaller than that of 2.7 microM AMP and was reversed by propranolol. Neither phentolamine nor atropine blocked this depressant action of AMP. It is concluded that the positive chronotropic action of AMP was beta-adrenergic and that beta-adrenergic block unmasked a negative chronotropic action of a high concentration of AMP, which was neither alpha-adrenergic nor muscarinic. In atrial fibers driven at a constant rate, 54.3 nM AMP prolonged the action potential duration (APD), without affecting the resting membrane potential (RMP), the action potential amplitude (APA), or the maximum velocity of phase 0, while 5.43 microM AMP reduced RMP, APA, and the maximum velocity of phase 0, and increased APD. The prolongation of APD, as well as the decreases of RMP and APA, was not abolished by propranolol, phentolamine, or 4-aminopyridine. Conversely, nifedipine abolished the effects of AMP on all three parameters. In general, AMP produced mainly a prolongation of the action potential. Only a high concentration of AMP decreased RMP and depressed phase 0 of the action potential. The effect of AMP on APD, RMP, and APA essentially involved increasing the influx of calcium through the L-type channels in the sarcolemma.

Cardiac chronotropic effects of nicotine and ethanol in the rat

The purpose of this research was to study the chronotropic effects of ethanol (ETOH) and nicotine (NIC), alone and in combination, on the heart. Rat sinoatrial preparations superfused with Tyrode's solution (37 degrees C) were used. The sinoatrial rate (SAR) was monitored using intracellular microelectrodes. NIC concentrations below and including 6.2 x 10(-5) M did not affect the SAR. NIC 6.2 x 10(-4) M and above depressed the SAR. This chronotropic effect of NIC was in part muscarinic. Acute in vitro exposure to ETOH diminished the chronotropic effect of NIC. Chronic ingestion of ETOH (35% of total caloric intake) for 24 weeks did not modify the effect of NIC on the SAR. In summary, there is no positive component in the chronotropic effect of NIC on the rat heart, which is probably due to absence of NIC receptors for the release of norepinephrine. Acute in vitro exposure to ETOH, but not chronic ingestion of ETOH, diminished the negative chronotropic action of NIC.

Effects of acetaldehyde on membrane potentials of sinus node pacemaker fibers

The experiments reported here were performed to characterize the effects of acetaldehyde on membrane potentials (MP) of sinus node subsidiary pacemaker fibers in the absence and presence of adrenergic and cholinergic blockade. Guinea pig sinoatrial preparations were superfused with Tyrode's solution at 37 degrees C while electrically stimulated at 5 Hz. Intracellular microelectrodes were used to record the MP of sinus node subsidiary pacemaker fibers. Acetaldehyde 3 x 10(-6) M and 3 x 10(-3) M had no effect on maximum diastolic potential (MDP), while 3 x 10(-5) M and 3 x 10(-2) M exerted a depolarizing effect on the MDP, without affecting the overshoot (OS). The fall in MDP was associated with a reduction in the amplitude of the action potential (AAP) and the maximum velocity of phase 0 (Vmax 0). The depressant effect of acetaldehyde on MDP was not abolished by adrenergic blockers or atropine. Concentrations of acetaldehyde between 3 x 10(-5) and 3 x 10(-2) M prolonged the action potential duration (APD). Acetaldehyde 3 x 10(-3) M did not affect MDP even in the presence of atropine or propranolol. The APD-prolonging effect of acetaldehyde was not abolished by adrenergic blockers. In summary, the actions of acetaldehyde on MDP and APD were independent of adrenergic and cholinergic mechanisms.