5-Hydroxyindoleacetic acid and 5-hydroxytryptophol levels in rat brain: effects of ethanol, pyrazole, cyanamide and disulfiram treatment

Tryptophan metabolism in alcoholism

Acute and chronic alcohol (ethanol) intake and subsequent withdrawal exert major effects on tryptophan (Trp) metabolism and disposition in human subjects and experimental animals. In rats, activity of the rate-limiting enzyme of Trp degradation, liver Trp pyrrolase (TP), is enhanced by acute, but inhibited after chronic, ethanol administration, then enhanced during withdrawal. These changes lead to alterations in brain serotonin synthesis and turnover mediated by corresponding changes in circulating Trp availability to the brain. A low brain-serotonin concentration characterizes the alcohol-preferring C57BL/6J mouse strain and many alcohol-preferring rat lines. In this mouse strain, liver TP enhancement causes the serotonin decrease. In man, acute ethanol intake inhibits brain serotonin synthesis by activating liver TP. This may explain alcohol-induced depression, aggression and loss of control in susceptible individuals. Chronic alcohol intake in dependent subjects may be associated with liver TP inhibition and a consequent enhancement of brain serotonin synthesis, whereas subsequent withdrawal may induce the opposite effects. The excitotoxic Trp metabolite quinolinate may play a role in the behavioural disturbances of the alcohol-withdrawal syndrome. Some abstinent alcoholics may have a central serotonin deficiency, which they correct by liver TP inhibition through drinking. Further studies of the Trp and serotonin metabolic status in long-term abstinence in general and in relation to personality characteristics, alcoholism typology and genetic factors in particular may yield important information which should facilitate the development of more effective screening, and preventative and therapeutic strategies in this area of mental health.

Disulfiram effects on responses to intravenous cocaine administration

Disulfiram has been studied as a treatment for cocaine dependence. We report results of a randomized, double-blind, placebo-controlled, within-subject study to examine the interaction of disulfiram with intravenous cocaine.

METHODS

Non-treatment-seeking, cocaine-dependent, volunteers participated in serial experiments in which they received disulfiram placebo, 62.5 or 250 mg/day on days 1-6. On days 4-6, participants received a morning disulfiram dose 2 h prior to a scheduled session in which they were administered intravenous cocaine placebo, 0.25 mg/kg (n=9) or 0.5 mg/kg (n=3) over 1 min. Blood, cardiovascular and subjective measures were collected. Seven days of washout occurred between disulfiram conditions.

RESULTS

Following active disulfiram treatments and cocaine 0.25 mg/kg administration, plasma cocaine AUC (0-480 min) was increased (p=0.003 and 0.001) and cocaine clearance decreased (p<0.001). Disulfiram treatments also decreased cocaine clearance for the 0.5 mg/kg cocaine dose (p=0.002 and<0.001). Neither disulfiram dose with cocaine altered cardiovascular responses relative to cocaine alone. Following cocaine 0.25 mg/kg, 'any high' (p=0.021 and 0.019), 'cocaine high' (p=0.017 and 0.018) and 'rush' (p=0.013 and 0.047) significantly decreased with either disulfiram dose.

CONCLUSIONS

Disulfiram decreased cocaine clearance without toxicity. Cocaine 'high' and 'rush' were diminished. Disulfiram may be a promising pharmacotherapy in selected cocaine dependent individuals.

5-hydroxytryptophol as a marker for recent alcohol intake

AIMS

To review the mechanism behind the alcohol-induced shift in serotonin metabolism, and the use of urinary 5-hydroxytryptophol (5-HTOL) as a biochemical marker of acute alcohol consumption.

BACKGROUND

The serotonin metabolite 5-HTOL is a normal, minor constituent of urine and is excreted mainly in conjugated form with glucuronic acid. The formation of 5-HTOL increases dramatically after alcohol intake, due to a metabolic interaction, and the elevated urinary excretion remains for some time (>5-15 hours depending on dose) after ethanol has been eliminated. This biochemical effect can be used for detection of recent alcohol intake.

RESULTS

5-HTOL is determined by the gas chromatography-mass spectrometry (GC-MS) or liquid chromatography and mass spectrometry (LC-MS) techniques. A new ELISA method for 5-HTOL glucuronide provides a promising clinical assay. The most robust way to use the marker is by measuring the ratio of 5-HTOL to 5-hydroxyindoleacetic acid, because this compensates for urine dilution and dietary intake of serotonin. 5-HTOL is a very sensitive and specific indicator of recent alcohol consumption and, as such, a valuable complement to self-report. In clinical use, 5-HTOL is effective for monitoring lapses into drinking during out-patient treatment and for objective evaluation of treatment efforts. Other applications include detection of high-risk patients in elective surgery, monitoring of disulfiram treatment and a method to rule out artefactual ethanol formation in forensic toxicology. 5-HTOL can also be used as a sensitive reference method for validation of self-report data in clinical alcohol research.

CONCLUSIONS

An elevated urinary 5-HTOL level can serve as a sensitive and reliable marker for recent alcohol intake with a number of clinical and forensic applications.

Elevated brain 5-hydroxytryptophol levels in experimental portal-systemic encephalopathy

Brain tissue levels of the two serotonin metabolites 5-hydroxytryptophol and 5-hydroxyindole-3-acetic acid (5-HIAA) were measured in porta-caval shunted rats, an in vivo model of portal-systemic encephalopathy. An intraperitoneal challenge of L-tryptophan (280 mg/kg body weight) to sham-operated rats was also instituted to increase the brain serotonin metabolism in these rats. The results revealed significant increases in 5-hydroxytryptophol (by 31% and 5-HIAA (by 87%) brain levels in porta-caval shunted rats as compared to sham-operated controls. The brain 5-hydroxytryptophol-to-5-HIAA ratio was lower in the porta-caval shunted rats. The 5-hydroxytryptophol levels in sham rats after the L-tryptophan challenge were intermediate between the porta-caval shunted and sham rats but not statistically significant for either group. These results suggest that increased brain 5-hydroxytryptophol levels might be associated with the pathogenesis of portal-systemic encephalopathy. Further, the elevated brain 5-hydroxytryptophol levels in experimental portal-systemic encephalopathy are probably a result of the increased brain serotonin metabolism prevailing in this condition rather than changes in the brain redox potential.

The regulation of alcohol consumption in rats: the role of alcohol-metabolizing enzymes-catalase and aldehyde dehydrogenase

Aldehyde dehydrogenase (ALDH) and catalase enzymatic activities in brain were assayed and compared to measures of alcohol consumption in two groups of animals screened and maintained on free-choice alcohol access under different conditions. In the first group of Long-Evans rats screened and maintained in home cages, mean alcohol intake was 3.49 g/kg/day with a range of 1.69-5.33 g/kg/day. When alcohol intake (g/kg), total ALDH, low K(m) ALDH, and catalase activities were entered in a multiple regression, a significant correlation of r = 0.51 (p < 0.05) was obtained. In the second group of rats consisting of Long-Evans, P, and NP rats screened using a drinkometer procedure, a multiple correlation between ALDH and catalase enzyme activities and alcohol intake of r = 0.42 (p < 0.05) was obtained. There was a strong relationship between the frequency of alcohol drinking bouts and the activities of catalase and ALDH (r = 0.68, p < 0.0001). The P rats had significantly higher catalase activities than either the NP or Long-Evans rats. The results of the present study confirmed earlier reports on the role of alcohol-metabolizing enzymes in the regulation of alcohol intake. The results also highlighted the fact that the activity of these alcohol-metabolizing enzymes may play a mediating role in patterns of alcohol intake displayed by animals selected for high and low alcohol drinking and also unselected animals.

Changes in serotonin metabolism during treatment with the aldehyde dehydrogenase inhibitors disulfiram and cyanamide

The effect of the aldehyde dehydrogenase inhibitors disulfiram (Antabuse) and cyanamide (calcium carbimide, Dipsan) on the metabolism of serotonin measured as relative amounts of the metabolites 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol in urine were studied in alcoholic patients. Sixteen out of 23 patients receiving drug therapy showed elevated excretion of 5-hydroxytryptophol. However, there was a marked, 15-fold, variability in 5-hydroxytryptophol excretion rate between patients. A high degree of variability was also seen in another group of patients studied before and after introduction of drug therapy. When patients were followed during the dose interval, a time-dependent response after each single dose could be observed. The disulfiram response lasted over the course of several days whereas the response to cyanamide lasted for less than 12 hr. It is concluded that treatment with disulfiram and cyanamide affects serotonin metabolism leading to increased production of 5-hydroxytryptophol, but there is a marked inter-individual variability in degree of response.

Ethanol alters monoamines in specific mouse brain regions

Ethanol (3.5 g/kg 60 min post-IP injection) produced the following changes in regional brain monoamine levels and in the respective metabolite/neurotransmitter ratios: for the noradrenergic system, MHPG was decreased in the amygdala and increased in the hypothalamus, while the MHPG/NE ratio was increased in the prefrontal cortex and the hypothalamus. For the dopaminergic system, DA was decreased in the olfactory tubercle, DOPAC was increased in the prefrontal cortex and septum, and DOPAC/DA was increased in the prefrontal cortex, septum, striatum, and hypothalamus. HVA was increased in the prefrontal cortex and septum, while HVA/DA was increased in the same regions plus the olfactory bulb. 3MT was decreased in the olfactory tubercle and striatum. The serotonergic system was not altered. The results demonstrate that ETOH produces selective regional changes in the concentration and utilization of monoamines in mouse brain with a predominant influence on dopaminergic systems and a lesser effect on noradrenergic activity.