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Activation of liver tryptophan pyrrolase mediates the decrease in tryptophan availability to the brain after acute
Abdulla A-B Badawy1, Donald M Doughrty, Dawn M Marsh-Richard
1Cardiff School of Health Sciences, University of Wales Institute Cardiff (UWIC), Wales, UK. ABadawy@uwic.ac.uk
Alcohol and Alcoholism (Oxford, Oxfordshire)
|February 10, 2009
Summary
Acute ethanol consumption depletes circulating tryptophan (Trp) by activating liver Trp pyrrolase. This study confirms that alcohol intake increases kynurenine pathway metabolites, reducing brain Trp availability.
Area of Science:
- Biochemistry
- Neuroscience
- Pharmacology
Background:
- Acute ethanol consumption may reduce brain tryptophan availability.
- This reduction is hypothesized to be mediated by the activation of liver tryptophan pyrrolase.
- The kynurenine pathway is the primary route for tryptophan degradation.
Purpose of the Study:
- To investigate the effect of acute ethanol consumption on plasma levels of tryptophan metabolites.
- To further examine the hypothesis that alcohol activates liver tryptophan pyrrolase.
- To assess the impact of varying ethanol doses on tryptophan and kynurenine pathway metabolites.
Main Methods:
- Ten healthy subjects participated in a placebo-controlled, dose-escalation study.
- Subjects received ethanol doses ranging from 0.2 to 0.8 g/kg body weight.
- Plasma samples were analyzed for tryptophan, competing amino acids, and kynurenine metabolites 2 hours post-ingestion.
Main Results:
- Ethanol consumption led to a dose-dependent depletion of plasma tryptophan.
- Plasma kynurenine levels and the kynurenine/tryptophan ratio increased with ethanol intake.
- These findings suggest increased activity of the tryptophan pyrrolase enzyme.
Conclusions:
- Acute ethanol consumption activates liver tryptophan pyrrolase.
- This activation results in decreased plasma tryptophan availability to the brain.
- The kynurenine pathway plays a significant role in mediating alcohol's effect on tryptophan metabolism.
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