Dysfunction in endocannabinoids, palmitoylethanolamide, and degradation of tryptophan into kynurenine in individuals with depressive symptoms
Stefano Comai 1 2 3 4, Nicolas Nunez 5, Tobias Atkin 5, Maykel F Ghabrash 5, Rita Zakarian 5, Allan Fielding 6, Marie Saint-Laurent 6, Nancy Low 5 6, Garrett Sauber 7, Eugenio Ragazzi 8, Cecilia J Hillard 7, Gabriella Gobbi 9 10
- 1Department of Pharmaceutical and Pharmacological Sciences, University of Padua, Padua, Italy. stefano.comai@unipd.it.
- 2Department of Biomedical Sciences, University of Padua, Padua, Italy. stefano.comai@unipd.it.
- 3Department of Psychiatry, McGill University, Montreal, QC, Canada. stefano.comai@unipd.it.
- 4IRCCS San Raffaele Scientific Institute, Milan, Italy. stefano.comai@unipd.it.
- 5Department of Psychiatry, McGill University, Montreal, QC, Canada.
- 6Department of Psychiatry, McGill University Health Center, Montreal, QC, Canada.
- 7Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI, USA.
- 8Department of Pharmaceutical and Pharmacological Sciences, University of Padua, Padua, Italy.
- 9Department of Psychiatry, McGill University, Montreal, QC, Canada. gabriella.gobbi@mcgill.ca.
- 10Department of Psychiatry, McGill University Health Center, Montreal, QC, Canada. gabriella.gobbi@mcgill.ca.
Affiliationer
Background: The endocannabinoid (eCB) system and the serotonin (5-HT) are both implicated in the severity of the depression. 5-HT is synthesized from the amino acid tryptophan (Trp), which is also a precursor for kynurenine (Kyn) whose production is increased at the expense of 5-HT in depressed patients. No clinical studies have investigated the crosstalk between the eCB system and the Trp/5-HT/Kyn pathways. Here, we hypothesized that the eCB system is associated with an enhanced Kyn production in relation to the severity of depressive symptoms.
Methods: Eighty-two subjects (51 patients with a diagnosis of depressive disorder (DSM-5) and 31 healthy volunteers), were assessed with the Montgomery-Åsberg Depression Rating Scale (MADRS), Beck Depression Scale, and Global Clinical Impression. Serum concentrations of eCBs (N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG)); structurally related fatty acyl compounds 2-oleoylglycerol (2-OG), oleoylethanolamide (OEA), and palmitoylethanolamide (PEA); Trp, Kyn, Kyn/Trp ratio (an index of Trp degradation into Kyn) and 5-HT were also determined.
Results: Following a principal component analysis including the severity of depression, Kyn and the Kyn/Trp ratio appear to be directly associated with 2-AG, AEA, and PEA. Interestingly, these biomarkers also permitted to distinguish the population into two main clusters: one of individuals having mild/severe depressive symptoms and the other with an absence of depressive symptoms. Using parametric analysis, higher serum levels of 2-AG, Kyn, and the ratio Kyn/Trp and lower levels of Trp and 5-HT were found in individuals with mild/severe depressive symptoms than in those without depressive symptoms. While in asymptomatic people, PEA was directly associated to Trp, and OEA indirectly linked to 5-HT, in individuals with depressive symptoms, these correlations were lost, and instead, positive correlations between AEA and 2-AG, PEA and AEA, and PEA vs 2-AG and OEA concentrations were found.
Conclusions: Parametric and non-parametric analyses suggest a possible association between eCBs, tryptophan/kynurenine biomarkers, and severity of depression, confirming a likely interplay among inflammation, stress, and depression. The enhanced relationships among the biomarkers of the 2-AG and AEA pathways and related lipids seen in individuals with depressive symptoms, but not in asymptomatics, suggest an altered metabolism of the eCB system in depression.
Keywords: Biomarkers; Depression; Endocannabinoids; Kynurenine pathway; Serotonin.
