Oxytocin-Induced Increase in N,N-dimethylglycine and Time-Course of Changes in Oxytocin Efficacy for Autism Social Core Symptoms

Abstract

Background: Oxytocin is expected as a novel therapeutic agent for autism spectrum disorder (ASD) core symptoms. However, previous results on the efficacy of repeated administrations of oxytocin are controversial. Recently, we reported time-course changes in the efficacy of the neuropeptide underlying the controversial effects of repeated administration; however, the underlying mechanisms remained unknown. Methods: The current study explored metabolites representing the molecular mechanisms of oxytocin's efficacy using high-throughput metabolomics analysis on plasma collected before and after 6 week repeated intranasal administration of oxytocin (48 IU/day) or placebo in adult males with ASD (N=106) who participated in a multi-center, parallel-group, double-blind, placebo-controlled, randomized controlled trial.Results: Among the 35 metabolites measured, a significant increase in N,N-dimethylglycine was detected in the subjects administered oxytocin compared with those given placebo at a medium effect size (False discovery rate (FDR) corrected P=0.043, d=0.74, N=83). Furthermore, subgroup analyses of the participants displaying a prominent time-course change in oxytocin efficacy revealed a significant effect of oxytocin on N,N-dimethylglycine levels with a large effect size (PFDR=0.004, d=1.13, N=60). The increase in N,N-dimethylglycine was significantly correlated with oxytocin-induced clinical changes, assessed as changes in quantifiable characteristics of autistic facial expression, including both of improvements between baseline and 2 weeks (PFDR=0.006, r=-0.485, N=43) and deteriorations between 2 and 4 weeks (PFDR=0.032, r=0.415, N=37).Limitations: The metabolites changes caused by oxytocin administration were quantified using peripheral blood, and therefore may not directly reflect central nervous system changes. Conclusion: Our findings demonstrate an association of N,N-dimethylglycine upregulation with the time-course change in the efficacy of oxytocin on autistic social deficits. Furthermore, the current findings support the involvement of the N-Methyl-D-Aspartate receptor and neural plasticity to the time-course change in oxytocin’s efficacy.Trial registration: A multicenter, parallel group, placebo-controlled, double blind, confirmatory trial of intranasal oxytocin in participants with autism spectrum disorders. (The date registered: 30th Oct 2020; UMIN Clinical Trials Registry: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000017703) (UMIN000015264)