Differential alterations in peripheral tryptophan pathways in methamphetamine versus MDMA users are linked to their contrasting psychiatric symptoms

Chronic users of methamphetamine (METH) and MDMA (Ecstasy) show distinct changes in blood metabolites derived from tryptophan, a building block for serotonin and other signaling molecules. METH use was linked to lower serotonin levels and broad activation of the kynurenine pathway, while MDMA use was associated with a specific increase in a different branch of that pathway. These metabolite changes correlated with the severity of depression and psychosis symptoms. The findings suggest that lasting alterations in tryptophan metabolism may help explain the different clinical effects of the two drugs and could point to new therapeutic targets.

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Abstract

Methamphetamine (METH, “Crystal Meth”) and 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) are two types of substituted amphetamines that share structural-chemical similarities but exhibit contrasting acute and chronic effects including addictive liability. Tryptophan (TRY) pathways are involved in pleiotropic physiological functions at the interface of brain-body connections. Preclinical evidence suggests that amphetamines may modulate these pathways and, thus, indirectly influence brain functions via persistent alterations of peripheral metabolites. However, little is known about alterations of TRY-related metabolites in the blood and their clinical implications in chronic users of MDMA and METH. Hence, we characterized serum levels of TRY-related metabolites in a comparative cross-sectional study including n=36 chronic MDMA users, n=33 chronic METH users, and n=71 sex-matched, stimulant-naïve healthy controls (Ntotal=140). An ultra– high performance liquid chromatography–mass spectrometry method was used to determine TRY metabolites. Combining metabolite levels, metabolic ratios, and network analysis we found robust evidence of divergent pathway alterations between METH and MDMA users. Chronic METH use was particularly associated with a depletion of serum TRY and serotonin levels, and a general activation of kynurenine pathways, while chronic MDMA use was linked to a selective activation of the OH-kynurenine metabolic branch. Metabolite changes were associated with the severity of psychopathology in the depression and psychosis domains across groups. Altogether, our findings demonstrate differential changes of serum TRY pathways in chronic MDMA and METH users. Persistent alterations of these pathways might contribute to the contrasting clinical profile of the substances and constitute a peripheral dimension of neurochemical plasticity with relevant implications for therapeutic targets.