Alkaloid products in the metabolism of alcohol and biogenic amines

Pharmacological activators of ALDH2: A new strategy for the treatment of alcohol use disorders

In mammals, ethanol is metabolized to acetaldehyde mainly by the liver alcohol dehydrogenase (ADH), and acetaldehyde is subsequently oxidized to acetate by mitochondrial aldehyde dehydrogenase (ALDH2). The presence of an inactive variant of ALDH2 or the use of inhibitors of this enzyme leads to an accumulation of acetaldehyde after ethanol consumption, generating an aversive reaction that inhibits subsequent alcohol intake. However, experimental evidence shows that acetaldehyde has potent rewarding effects at the central level, suggesting that acetaldehyde would be responsible for the addictive effect of alcohol. Alda-1 is an organic molecule that acts as a pharmacological activator of ALDH2. Studies in animal models of alcohol use disorders (AUD; i.e. alcoholism) have shown that Alda-1 can inhibit the acquisition, the chronic intake, and the relapse of alcohol consumption. These effects are reversible without any effects on water consumption or other natural reinforcer such as saccharin. It has also been reported that Alda-1 can act as a protective agent from the toxic effects on various tissues and organs mediated by ethanol-derived acetaldehyde, including liver damage, cancer, and central nervous system (CNS) alterations. Using in silico tools such as molecular docking the identification of important molecular interactions between Alda-1 and ALDH2 has been demonstrated, identifying new molecules with higher pharmacological features. Thus, there is now preclinical evidence supporting the use of activators of ALDH2 as a pharmacological strategy for the treatment of AUD.

Elucidating the biological basis for the reinforcing actions of alcohol in the mesolimbic dopamine system: the role of active metabolites of alcohol

The development of successful pharmacotherapeutics for the treatment of alcoholism is predicated upon understanding the biological action of alcohol. A limitation of the alcohol research field has been examining the effects of alcohol only and ignoring the multiple biological active metabolites of alcohol. The concept that alcohol is a "pro-drug" is not new. Alcohol is readily metabolized to acetaldehyde within the brain. Acetaldehyde is a highly reactive compound that forms a number of condensation products, including salsolinol and iso-salsolinol (acetaldehyde and dopamine). Recent experiments have established that numerous metabolites of alcohol have direct CNS action, and could, in part or whole, mediate the reinforcing actions of alcohol within the mesolimbic dopamine system. The mesolimbic dopamine system originates in the ventral tegmental area (VTA) and projects to forebrain regions that include the nucleus accumbens (Acb) and the medial prefrontal cortex (mPFC) and is thought to be the neurocircuitry governing the rewarding properties of drugs of abuse. Within this neurocircuitry there is convincing evidence that; (1) biologically active metabolites of alcohol can directly or indirectly increase the activity of VTA dopamine neurons, (2) alcohol and alcohol metabolites are reinforcing within the mesolimbic dopamine system, (3) inhibiting the alcohol metabolic pathway inhibits the biological consequences of alcohol exposure, (4) alcohol consumption can be reduced by inhibiting/attenuating the alcohol metabolic pathway in the mesolimbic dopamine system, (5) alcohol metabolites can alter neurochemical levels within the mesolimbic dopamine system, and (6) alcohol interacts with alcohol metabolites to enhance the actions of both compounds. The data indicate that there is a positive relationship between alcohol and alcohol metabolites in regulating the biological consequences of consuming alcohol and the potential of alcohol use escalating to alcoholism.

Copper, biogenic amines, and amine oxidases

Amine oxidases have been classified in the past on the basis of either (a) the structural requirements in the substrate or (b) the tissue (or species) of origin, or both. As knowledge about the chemistry of these enzymes grows, their classification on the basis of chemical structure is becoming possible. Currently, many amine oxidases can be categorized according to whether they contain riboflavin (e.g. the monoamine oxidases -- EC 1.4.3.4) or copper (e.g. the amine oxidases of plasma and the diamine oxidases EC 1.4.3.6 -- found prominently in pig kidney cortex, placenta, and pea seedlings). The copper-linked oxidases are inhibited by cyanide and by semicarbazide. The nature of the carbonyl compound(s) in the various enzyme molecules is not yet known. Nutritional deficiencies of copper and treatment of animals with copper-chelating agents are reflected in reduced activity of one or more of these enzymes. The ultimate effects of copper deficiency and copper excess on amine metabolism in vivo are described.

Neurotoxicity and metabolism of the catecholamine-derived 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde: the role of aldehyde dehydrogenase

Aldehydes are highly reactive molecules formed during the biotransformation of numerous endogenous and exogenous compounds, including biogenic amines. 3,4-Dihydroxyphenylacetaldehyde is the aldehyde metabolite of dopamine, and 3,4-dihydroxyphenylglycolaldehyde is the aldehyde metabolite of both norepinephrine and epinephrine. There is an increasing body of evidence suggesting that these compounds are neurotoxic, and it has been recently hypothesized that neurodegenerative disorders may be associated with increased levels of these biogenic aldehydes. Aldehyde dehydrogenases are a group of NAD(P)+ -dependent enzymes that catalyze the oxidation of aldehydes, such as those derived from catecholamines, to their corresponding carboxylic acids. To date, 19 aldehyde dehydrogenase genes have been identified in the human genome. Mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria, and pyridoxine-dependent seizures, most of which are characterized by neurological abnormalities. Several pharmaceutical agents and environmental toxins are also known to disrupt or inhibit aldehyde dehydrogenase function. It is, therefore, possible to speculate that reduced detoxification of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde from impaired or deficient aldehyde dehydrogenase function may be a contributing factor in the suggested neurotoxicity of these compounds. This article presents a comprehensive review of what is currently known of both the neurotoxicity and respective metabolism pathways of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde with an emphasis on the role that aldehyde dehydrogenase enzymes play in the detoxification of these two aldehydes.

A possible physiological role for cerebral tetrahydroisoquinolines

Tetrahydroisoquinolines present in the mammalian brain, 1,2,3,4-tetrahydroisoquinoline (TIQ) and salsolinol, suspected to cause neurodegeneration leading to Parkinson's disease, were investigated to find their possible physiological role. To this aim their behavioral and receptor effects induced after a single dose were tested in mice and rats. Both compounds do not affect significantly the basal locomotor activity, very effectively block hyperactivity induced by apomorphine (rats) and amphetamine (mice), only partially block hyperactivity induced by scopolamine, do not affect locomotor stimulation induced by cocaine, and strongly augment the running fit induced by morphine (mice). They do not produce extrapyramidal symptoms and do not potentiate haloperidol-induced catalepsy (rats). TIQ and salsolinol do not displace antagonists of several receptors (including D(1) and D(2)) from their binding sites, but displace the agonists of Alpha(2)-adrenoceptors, [(3)H]clonidine and of dopamine receptors, [(3)H]apomorphine. The results indicate that salsolinol and TIQ act as specific antagonists of agonistic conformation of dopamine receptors, and owing to that may play a role of endogenous feed-back regulators of the dopaminergic system. Those properties make tetrahydroisoquinolines potential antidopaminergic drugs devoid of extrapyramidal effects, with possible application in substance addiction disorder as anti-craving agents.

Alkaloids, alcohol and Parkinson's disease

Relatively early seminal investigations on 'mammalian alkaloid biosynthesis'-endogenous Pictet-Spengler condensations of catecholamines or indoleamines with aldehydes (such as acetaldehyde from ethanol metabolism) to form tetrahydroisoquinoline or beta-carboline alkaloids-and the roles of mammalian alkaloids in the CNS complications of chronic alcoholism were launched in Gerald Cohen's laboratory. While occasional studies on alcohol and the alkaloids continue today, the field of study has been expanded principally by others into Parkinson's disease. Certain mammalian or xenobiotic alkaloids have been examined by various laboratories as possible neurotoxic factors inducing mitochondrial energy depletion and/or oxidative stress in the nigrostriatum. In that regard, specific arguments for N-methylated 'MPP(+)-like' cationic alkaloids that can be generated centrally from beta-carbolines derived from the environment and diet are summarized.

Metabolic stress in PC12 cells induces the formation of the endogenous dopaminergic neurotoxin, 3,4-dihydroxyphenylacetaldehyde

3,4-Dihydroxyphenylacetaldehyde (DOPAL) has been reported to be a toxic metabolite formed by the oxidative-deamination of dopamine (DA) catalyzed by monoamine oxidase. This aldehyde is either oxidized to 3,4-dihydroxyphenylacetic acid (DOPAC) by aldehyde dehydrogenase, an NAD-dependent enzyme or reduced to 3, 4-dihydroxyphenylethanol (DOPET) by aldehyde or aldose reductase. In the present study we examined whether levels of DOPAL are elevated by inhibition of the mitochondrial respiratory chain. Using inhibitors of mitochondrial complexes I, II, III and IV we found that inhibition of complex I and III increased levels of DOPAL and DOPET. Nerve growth factor-induced differentiation of PC12 cells markedly potentiated DOPAL and DOPET accumulation in response to metabolic stress. DOPAL was toxic to differentiated PC12 as well as to SK-N-SH cell lines. Because complex I dysfunction has been implicated in the pathogenesis of Parkinson's disease, the accumulation of DOPAL may explain the vulnerability of the dopaminergic system to complex I inhibition. The rapid appearance of DOPAL and DOPET after inhibition of complex I may be a useful early index of oxidative stress in DA-forming neurons.

Modulation of dihydroxyphenylacetaldehyde extracellular levels in vivo in the rat striatum after different kinds of pharmacological treatment

We recently identified the direct product of dopamine (DA) by monoamine-oxidase (MAO) activity, dihydroxyphenylacetaldehyde (DOPALD) in the trans-striatal dialysate. Based on these findings, in this work, we directly measured the variations in DOPALD levels after various kinds of pharmacological treatment in rat striatal extracellular fluid. Using both reversible and irreversible MAO inhibitors, we found that MAO-A inhibition suppressed, whereas MAO-B inhibition did not modify DOPALD levels in the dialysate. The vesicular DA uptake blocker Ro 4-1284 led to an increase in extracellular DA and DOPALD, whereas the increase in extracellular DA obtained after administration of the plasma membrane DA uptake blocker GBR-12909 occurred without concomitant changes in DOPALD extracellular levels. Microinfusions of DA through the dialysis probe or systemic administration of L-DOPA increased striatal DOPALD to a greater extent compared with other DA metabolites, both in intact and in 6-hydroxydopamine (6-OHDA)-lesioned striatum. This study indicates that the direct product of MAO activity within the rat striatum derives from the activity of the isoenzyme MAO-A. The assay of DOPALD, together with DOPAC, represents a reliable tool to measure directly, in freely moving animals, DA oxidative metabolism. As recent studies have shown that microinfusions of exogenous DOPALD might induce cell death, pharmacological modulation of DOPALD levels might also be relevant for an understanding of the mechanisms involved in DA neurotoxicity.

Formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines in human urine

Human urine samples were examined for the occurrence of formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines generated by condensation of the methanol oxidation product with biogenic amines. Positive results were obtained for the tryptamine condensation product 1,2,3,4-tetrahydro-beta-carboline and the serotonine condensation product 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline as well as for the condensation products with tyramine, dopamine, adrenaline and noradrenaline 1,2,3,4-tetrahydroisoquinoline, 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, 4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, and the metabolite 6-methoxy-7-hydroxy-1,2,3,4-tetrahydroisoquinoline. Negative results were obtained for N-methyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-1,2,3,4-tetrahydro-beta-carboline, 6-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in samples of chronic alcoholics as well as in the urine of healthy volunteers. No correlation between alcohol ingestion or state of alcoholization could be demonstrated.

Reduction of regional brain glucose metabolism following different durations of chronic ethanol consumption in mice: a selective effect on diencephalic structures

The effects of chronic alcohol consumption on regional brain glucose metabolism were examined in Balb/c mice using the [14C]2-deoxyglucose autoradiographic technique. Animals were given a solution of 12% v/v ethanol as their only source of fluid for either 6, 12 or 18 months and compared to control groups receiving either an isocaloric solution or saccharose or tap water. Alterations of cerebral brain glucose metabolism were assessed in mice who were returned to a non-alcoholic diet and allowed to freely explore a T-maze. The results showed that chronic ethanol consumption induced reductions of regional metabolic activity which were functions both of the duration of alcohol treatment and of the structure studied. Whereas a six month period of alcoholization did not induce any significant effects on metabolic activity, 12 months of treatment were necessary to induce the first observable and significant reductions in [14C]2-deoxyglucose labelling. These effects were mainly limited to diencephalic structures such as the lateral mammillary nuclei and the anterodorsal thalamic nuclei. The cerebellum was also affected but to a lesser degree. After 18 months of alcoholization, a generalized spread of the metabolic reduction to the entire mammillary complex (lateral, medial and posterior nuclei) and to the thalamic nuclei was observed. This same duration of treatment was necessary to induce the first detectable decrease of metabolic activity in the hippocampus. In agreement with data from human neuropathology, these findings confirm the particular vulnerability of diencephalic structures to ethanol and suggest that damage limited to diencephalic regions rather than to hippocampal or cortical areas could be primarily responsible for the memory disorders observed in Korsakoff's syndrome.

Dopamine-derived endogenous 1(R),2(N)-dimethyl-6,7-dihydroxy- 1,2,3,4-tetrahydroisoquinoline, N-methyl-(R)-salsolinol, induced parkinsonism in rat: biochemical, pathological and behavioral studies

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal) and related compounds were examined for their selective neurotoxicity to dopamine neurons by injection into the rat striatum. Among salsolinol analogs examined, only N-methyl-(R)- salsolinol (NM(R)Sal) induced behavioral changes very similar to those in Parkinson's disease: hypokinesia, stiff tail, limb twitching at rest and postural abnormality. Biochemical analysis showed that after NM(R)Sal injection, NM(R)Sal itself and its oxidation product, 1-2-dimethyl-6,7-dihydroxyisoquinolinium ion (DMDHIQ+) accumulated in the striatum, and also in the substantia nigra definite amount of DMDHIQ+ was detected. Dopamine and noradrenaline were reduced in the striatum and more markedly in the substantia nigra, whereas serotonin and its metabolite were not affected. Morphological analysis revealed selective reduction of tyrosine hydroxylase (TH)-containing neurons in the substantia nigra after continuous NM(R)Sal administration in the striatum. These results demonstrate the selective cytotoxicity of NM(R)Sal to the dopamine neurons in the substantia nigra, and the possible involvement of this 6,7-dihydroxy-isoquinoline in the pathogenesis of Parkinson's disease is discussed.

Influence of ethanol on the salsolinol excretion in healthy subjects

This report describes the change of salsolinol (SAL) levels in the urine of healthy subjects after ethanol ingestion. A new rapid method for SAL extraction from urine sample and a GC-MS assay were used to study the urinary SAL excretion in a group of adult males (n = 14) and females (n = 13) with and without ingestion of ethanol. The results of this study show that the urinary SAL output of all subjects is significantly influenced by the intake of ethanol. A decrease in the SAL level was found in the urine of most of the volunteers (n = 17), whereas only eight subjects showed an increase in the SAL level after administration of ethanol.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydroisoquinolines in human urine

A gas chromatographic-mass spectrometric method has been developed for the identification of 1,2,3,4-tetrahydroisoquinoline and six metabolites extracted from urine in the picogram range. The derivatization procedure for the substances, formed by reaction of formaldehyde with biogenic amines, employs propionic anhydride and can take place in aqueous medium. In this way artificial formation of these compounds via condensation of biogenic amines with aldehydes or alpha-keto acids during the work-up procedure is eliminated. The procedure results in hydrophobic compounds, which are quantitatively extractable by liquid-liquid extraction with organic solvents. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydro-beta-carbolines in human urine

A gas chromatographic-mass spectrometric method for the identification of 1,2,3,4-tetrahydro-beta-carboline and four metabolites extracted from urine is described. In a first step the substances, formed by reaction of formaldehyde with biogenic amines, were derivatized in aqueous solution with methyl chloroformate to eliminate an artificial formation of these compounds via condensation of endogenous indole ethylamines with aldehydes or alpha-keto acids during the work-up procedure. This initial derivatization formed stable hydrophobic compounds and improved the extractability for a liquid-liquid extraction. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns. The method can identify these compounds in the picogram range.

Brain and plasma tetrahydroisoquinolines in rats: effects of chronic ethanol intake and diet

Brain concentrations of salsolinol (SAL), a simple tetrahydroisoquinoline (sTIQ) condensation product of dopamine (DA) and acetaldehyde, are reported to increase in chow-fed rats drinking ethanol/H2O ad libitum. However, our analyses showed that rat chow contains traces of SAL and, as previously reported, appreciable 3,4-dihydroxyphenylalanine (DOPA), a sTIQ precursor. To examine the effect of consumption of ethanol in a DOPA- and SAL-free diet on endogenous sTIQs, we analyzed two brain regions and blood plasma of rats undergoing prolonged intake (3 weeks and 23 weeks) of liquid diet containing 6.6% ethanol or isocaloric carbohydrate. SAL and three other DA-related sTIQs were quantitated using capillary gas chromatography/mass spectrometry in the selected ion mode with deuterated standards. In accord with studies on ethanol/chow-fed rats, sTIQ concentrations in hypothalamus were elevated after 3 weeks of ethanol, although after 23 weeks, hypothalamic sTIQs were either unchanged or reduced (O-methylated SAL). Furthermore, sTIQ concentrations in corpus striatum and, with one exception, plasma were not altered by ethanol ingestion for either duration. (However, 23 weeks of ethanol intake significantly reduced the striatal concentrations of DA and its acid metabolite, presumably reflecting neurotoxicity.) Reasoning that DOPA in diet might underlie the reported ethanol-dependent increases in striatal sTIQs, we found that L-DOPA supplementation (500 micrograms/rat/day) of EtOH/liquid diet-fed rats for 13 weeks tended to increase striatal SAL. Overall, the data indicate that elevations in endogenous sTIQ concentrations due to prolonged ethanol intake depend on the brain region, duration of intake, and even associated dietary constituents. In that regard, the higher striatal SAL concentrations in rats drinking ethanol ad libitum could have been facilitated by DOPA and perhaps SAL consumed in lab chow.

Flumazenil but not nitrendipine reverses the increased anxiety during ethanol withdrawal in the rat

After 7 day's gradual introduction of ethanol, rats were maintained for a further 4 weeks on a liquid diet containing 10% ethanol (mean daily dose 11.8 +/- 0.2 g/kg/day). Control-treated rats received liquid diet alone. Pairs of rats were tested in the social interaction test of anxiety 8 h after withdrawal. Withdrawal from ethanol significantly reduced the time spent in social interaction compared with controls, indicating an anxiogenic withdrawal response. Nitrendipine (50 mg/kg) had no effect on, whereas flumazenil (4 mg/kg) significantly reversed, this withdrawal response. This reversal appeared to be long-lasting as there was still no evidence of increased anxiety when rats were again withdrawn after 3 more days of ethanol diet.

Human brain aldehyde dehydrogenase: activity with DOPAL and isozyme distribution

Aldehyde dehydrogenase (ALDH, EC 1.2.1.3), has been shown to be the most important enzyme for DOPAL metabolism in human brain (Agarwal et al.). In the present investigation cerebellum, corpus striatum and pons showed the highest ALDH activity. Most of the enzyme activity was found in the mitochondrial and microsomal fractions. Two activity bands on IEF gels and dual Km values indicate the presence of two distinct isozymes in all the fractions. Two cerebella from alcoholics yielded the same results as the control group regarding their total ALDH activity, subcellular distribution pattern and protein content. The presence of DOPAC (acid metabolite of DOPAL), pargyline, pyrazole or ethanol in the assay mixture did not alter the ALDH activity significantly.

Enhancement of voluntary alcohol consumption in rats by clofibrate feeding

Clofibrate is known to be an inducer of alcohol- and acetaldehyde dehydrogenase. Therefore, male rats were offered increasing amounts of alcohol over a period of three months. Eventually they could choose between a 30% alcohol solution and tap water which was available ad lib. Animals were sacrificed after further 1 1/2 months of clofibrate feeding. Before clofibrate feeding voluntary intake of alcohol was 3.47 g/kg per day and increased up to 7.77 g/kg per day, i.e., by 123% within the clofibrate feeding period while the alcohol intake of controls increased from 3.84 to 4.88 g/kg per day, i.e., by only 27%. Food consumption increased in the clofibrate control group, whereas in the alcohol drinking clofibrate group the total caloric intake increase was due mainly to the enhancement of alcohol consumption. Relative liver weight was increased by clofibrate in the non-drinking as well as in the drinking group by 59%. Measurements of triglycerides and cholesterol exhibited changes typical for clofibrate in ethanol drinking and non-drinking animals. Probably the clofibrate-alcohol interaction results in accelerated ethanol metabolism and increased metabolic tolerance by induction of the ethanol detoxifying system in the liver.

EEG alpha activity increases during transient episodes of ethanol-induced euphoria

The effects of acute ethanol administration were studied in 18 men to determine the electroencephalographic (EEG) correlates of ethanol-induced behavioral changes. Subjects were instructed to operate an instrumental device to indicate changes in their subjective mood state while EEG activity and plasma ethanol levels were continuously measured. Three groups of 6 subjects consumed either placebo, 0.347 g/kg ethanol or 0.695 g/kg ethanol over a 15 min period. EEG and behavioral changes were directly correlated with plasma ethanol levels during the ascending limb of the plasma ethanol curve. Theta EEG activity increased proportionally as plasma ethanol levels increased during the 2 hr recording session. Alpha EEG activity increased during the first hour and then returned to control levels. The increased alpha activity was most prominent when subjects reported feeling intense pleasure or euphoria. Power spectral analysis of discrete samples of EEG activity revealed that transient increases in alpha activity paralleled the onset of ethanol-induced euphoria. These data suggest that ethanol-induced behavioral effects are associated with discrete changes in brain electrical activity.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Increased salsolinol levels in rat striatum and limbic forebrain following chronic ethanol treatment

Endogenous levels of salsolinol and its methylated metabolite were measured by combined gas chromatography and mass spectrometry in rats chronically exposed to ethanol for 150 days. The chronic ethanol administration produced a significant increase of salsolinol concentrations in dopamine-rich brain areas, e.g., the striatum and the limbic forebrain. A negative correlation was observed between plasma ethanol concentration and the level of salsolinol in the brain. A possible role for salsolinol in the regulation of ethanol drinking and/or in the development of ethanol dependence is discussed.

The route and significance of endogenous synthesis of alkaloids in animals

There is now substantial evidence that several TIQs and beta-carbolines are present in vivo and increase during certain pathological conditions. It still remains to be determined, however, precisely what roles they play in endogenous functions and whether or not they are critical for the expression of these pathological conditions. Accumulating biochemical information continues to support the notion that these compounds can act as false transmitters. The exciting new findings, which will certainly receive a great deal more attention, concern the interaction of some of the beta-carbolines with the benzodiazepine receptor. Determining if a beta-carboline is an endogenous receptor ligand will attract further research interest on the theoretical and specifically clinically-directed levels. Biochemical, morphological, and behavioral data indicate that some of the condensation products can act as neurotoxins. Very few experiments have included an examination of long-term effects of exposure to one of these alkaloids, so the amount of information on this issue is limited. Chronic rather than acute administration of an alkaloid is more likely to mimic the pathological states in which these compounds are hypothesized to play a role. Biochemically, both the dopaminergic and serotonergic systems have been shown to be affected by chronic treatments with certain alkaloids. Progressive and long-term behavioral alterations also have been reported. Such changes may reflect an adaptation to an increase or decrease in activity of particular systems or a neurotoxic action.

Metabolic interactions between opiates and alcohol

1. Acute preperfusion with ethanol does not alter significantly the initial hepatic extraction or subcellular distribution of narcotics, or the immediate biotransformation of the long-acting narcotic, methadone, using the isolated perfused rabbit liver. However, the acute administration of ethanol may alter distribution and/or impair hepatic drug metabolism in perfusion studies of longer duration, or in vivo, as has been suggested by others in studies of several drugs. 2. Following chronic treatment with both ethanol and methadone in the rat, plasma levels of unmetabolized methadone, determined by gas liquid chromatography, are significantly lowered. 3. Following chronic treatment with methadone alone, blood elimination rates of ethanol are accelerated to a greater extent than following chronic treatment with ethanol alone in the rat; following chronic treatment with both methadone and ethanol, rates of ethanol elimination are accelerated to a significantly more rapid rate than following treatment with either agent alone. 4. To date, clinical studies in patients on chronic steady-dose methadone maintenance treatment, without liver disease, polydrug abuse, or heavy use of ethanol, show no significant acute dispositional interactions between methadone and ethanol. 5. Clinical studies in patients on chronic steady-dose methadone maintenance treatment, without liver disease, polydrug abuse, or heavy use of ethanol, show no significant dispositional interactions between methadone and disulfiram (Antabuse) when the latter was given for one week for study purposes only. 6. Clinical studies of possible dispositional interactions between methadone and ethanol in methadone-maintained patients, who are also chronic abusers of alcohol, are now in progress.

Ethanol causes increases in excitation and inhibition in area CA3 of the dorsal hippocampus

The effects of ethanol on synaptic transmission in hippocampus were studied by changes in the response of CA3 pyramidal cells to stimulation of two afferent pathways, the dentate (mossy fiber) pathway, and the commissural pathway. Both sources produce an excitatory response as measured either by single unit spiking or by population spike followed by a period of post-stimulus inhibition (PSI). After the injection of 3 g/kg ethanol (i.p.), both the excitatory responses and the duration of PSI are significantly increased. Because these changes occur in both afferent pathways, they are not pathway specific, but may be the result of the local microcircuitry in area CA3. Although the change in excitatory and inhibitory responses can occur simultaneously, detailed statistical analyses show that neither the magnitude nor onset times are correlated. Thus, the two responses are functionally separable. In addition, the increase in the duration of PSI is related to the rate of rise of blood ethanol level and shows short-term tolerance. The maximum change in the PSI occurs after blood ethanol levels plateau suggesting a secondary process is necessary before neurophysiological effects are apparent.

A critical evaluation of tetrahydroisoquinoline induced ethanol preference in rats

It has been reported that certain tetrahydroisoquinoline compounds, especially salsolinol and tetrahydropaveroline (THP) when infused into the lateral ventricle of rats' brains results in increased preference for alcohol solutions. The effect is reported to be long-term, in that animals do not return to baseline drinking even months later. The current report provides a replicatin of the original experiments and also an extension of the work to complete dose-response curves for salsolinol and THP. Generally we have confirmed that rats of the Sprague-Dawley and Long-Evans strains do increase their alcohol intake in response to infused THP or salsolinol and that the effect is long lasting, up to 10 months. Such animals consume less alcohol at concentrations above 20% than below, in contrast to the previous reports where drinking was maintained at high concentrations of alcohol. While the animals will select alcohol in the face of a saccharin choice, they will not drink alcohol adulterated with quinine. We have failed to observe signs of dependence or withdrawal by these techniques and suggest that the original reports of these signs may have been a result of cellular damage caused by the long-term infusions. Additionally we have carried out extensive dose-response experiments with both salsolinol and THP. Doses of THP of 104 nmoles/day were inhibitory to alcohol drinking. We conclude that these compounds do shift these animals preference for alcohol relatively permanently, but not to the point of gross intoxication nor into the highly aversive range of alcohol concentration. We cannot confirm the reports that salsolinol or THP produce withdrawal symptoms when infused.

Fatty liver and sudden death. A review

Alcoholism is associated with increased mortality from violent and nonviolent causes. The increase in nonviolent deaths is usually ascribed, at least in part, to "cirrhosis." In the majority of these deaths this implies fatty liver rather than true Laennec's cirrhosis. Studies of sudden nonviolent deaths illustrate the largely unrecognized and frequent occurrence of sudden death with autopsy findings limited solely to fatty liver. The mechanism(s) of these sudden fatty liver deaths is unknown. Several attractive theories attribute such deaths to ethanol withdrawal induced hypoglycemia or hypomagnesemia, pulmonary fat embolization from fatty liver, or other facets of the alcohol withdrawal syndrome, including ethanol dependent maladaptive derangements of neurotransmitters. All the theories of fatty liver death remain essentially untested, however, owing to uncontrolled postmortem conditions and the lack of awareness of fatty liver deaths within the scientific community.

Neuroamine condensations in human subjects

Non-enzymatic products of neuroamines and endogenous carbonyl compounds are apparent "normal" products in human metabolism, and their levels become increased during pathological conditions. DA condensation products--salsolinol, its O-methylated derivative, and methylated derivatives of 1-carboxyl-THP--are found normally in human urine, and the last TIQ is in human brain. Potential beta-carboline condensation products also occur in (aging) human lens tissue. Chronic drinking in alcoholics causes significant increases in urinary salsolinol and O-methyl-salsolinol, presumably due to the increased AcH which is made available. L-DOPA therapy (in Parkinson's disease) elevates urinary and tissue levels of the carboxylated THP derivatives, as well as of salsolinol and THP itself; hyperphenylalaninemia during PKU also increases tissue levels of a DA/phenylpyruvate-derived TIQ and an imine condensate of phenylethylamine and vitamin B6. These unusual products may interfere with neural dynamic processes, and produce cytotoxic metabolites.

Effects of aliphatic alcohols and aldehydes on fluidity of spin-labeled synaptosomal plasma membranes

Synaptosomal plasma membranes from Swiss-Webster mice were spin-labeled with 5-doxylstearic acid. By electron paramagnetic resonance techniques an order parameter was measured. A decrease in the order parameter reflected an increase in membrane fluidity. In confirmation of our previous work, ethanol decreased membrane order. Pentanol also showed a concentration-related decrease in the order parameter in the range of 23 to 87 mM. At equimolar concentrations, pentanol was about 9 times more effective than ethanol. Acetaldehyde had no effect on membrane fluidity at concentrations that might be found in vivo during ethanol oxidation (23 or 227 microM) but a very high concentration, 2.3 mM, produced a small decrease in the order parameter comparable to the effect of an intoxicating concentration of ethanol. Valeraldehyde also had a slight fluidizing effect and appeared very roughly three times more potent than acetaldehyde. This study shows that the fluidizing effects of ethanol are not shared by its aldehyde metabolite at relevant concentrations. The fluidizing effects of aldehydes are slight but they increase with concentration and with chain length.

Acetaldehyde hydrate and carbonic anhydrase: possible roles in the inhibition of brain aldehyde dehydrogenase

One biochemical explanation for the chronic and addictive effects of ethanol involves a relationship between biogenic aldehydes, brain aldehyde dehydrogenase and acetaldehyde, the principal metabolic product of ethanol. We suggest here the possibility that acetaldehyde hydrate may act as an especially strong inhibitor of aldehyde dehydrogenase. Aldehyde hydrates are known to strongly inhibit aldehyde dehydrogenase as well as a number of other aldehyde oxidizing enzymes and it may be that acetaldehyde hydrate acts as a transition state or activated intermediate inhibitor. It is also suggested that carbonic anhydrase, which catalyzes the very rapid equilibrium between acetaldehyde and its hydrate, may play a role in this process.

Dopamine-related tetrahydroisoquinolines: significant urinary excretion by alcoholics after alcohol consumption

Concentrations of dopamine-related tetrahydroisoquinolines (salsolinol and O-methylated salsolinol) were significantly higher in the daily urine samples of alcoholic subjects admitted for alcohol detoxification than in the daily urine samples of nonalcoholic control subjects. Salsolinol concentrations in alcoholic subjects appeared to drop to trace (control) values 2 to 3 days after admission, following the disappearance of ethanol and its reactive metabolite acetaldehyde from the blood. These results indicate that physiologically active tetrahydroisoquinolines increase in humans during long-term alcohol consumption, presumably because of acetaldehyde's direct condensation with catecholamines. The presence of these or similar condensation products in the urine could be useful as clinical indicators of prior blood acetaldehyde concentrations in chronic alcoholics.

Interaction of salsolinol and tetrahydropapaveroline with catecholamines

Formation of aberrant amine metabolites, tetrahydroisoquinolines (TIQs) has been hypothesized to account for some of the effects of ethanol. These compounds have been shown to interact with catecholamine neurons in a variety of ways by in vitro techniques. The most interesting facet of these alkaloids, however, is the fact that they cause an increase in preference for and voluntary consumption of ethanol when administered into the ventricle of the rat in exceedingly low amounts. Investigation of the neurochemical effects in vivo of two of the TIQs tetrahydropapaveroline (THP) and salsolinol, indicates that they influence several aspects of presynaptic catecholamine function when examined acutely. The mechanism of action responsible for the radical long-lasting behavioral effects of these substances has yet to be defined.

Intraventricular self-administration of acetaldehyde, but not ethanol, in naive laboratory rats

For 11 consecutive days, naive rats were maintained in operant chambers where they were given the opportunity to self-administer acetaldehyde (1,2, or 5% v/v), ethanol (2 or 10% v/v), or pH control solutions directly into the cerebral ventricles. Only the animals that had access to the 2 and 5% acetaldehyde solutions showed rates of lever pressing significantly higher than controls. It is suggested that acetaldehyde rather than ethanol itself may mediate the positive reinforcing effects of ethanol in the brain.