Elevation of a Putative Bacterial Metabolite in a Pediatric ASD Population

Background:

It was previously shown that changes in the gut microbiome (dysbiosis) and increased intestinal permeability (IP) are present in the “maternal immune activation” (MIA) mouse model of autism spectrum disorder (ASD), a model that recapitulates key features of the autism phenotype, including increased anxiety, stereotypic behaviors, and decreased vocalizations and social behaviors. In addition, elevated levels of the putative bacterial metabolite 4-ethylphenylsulfate (4-EPS) were found by untargeted serum metabolomics in this model vs. controls, and this elevation was thought to be driven by dysbiosis and/or increased IP. Oral treatment with Bacteroides fragilis, a human commensal gut bacterial species, resulted in restoration of gut microbial profiles, decreased IP, and markedly reduced serum concentrations of 4-EPS. Several tryptophan metabolites were also altered in the MIA model, and their levels were normalized by B. fragilis treatment. Remarkably, this treatment was also observed to increase vocalization, reduce anxiety-like features and correct stereotyped behaviors. Finally, causality between 4-EPS and anxiety-like behaviors was established by parenterally administering 4-EPS to naïve mice and demonstrating that such treatment resulted in the development of an anxiety phenotype similar to that observed in the MIA model.

Objectives:

The objectives of the current study was to extend the preclinical results by determining whether elevations in serum 4-EPS can also be found in children diagnosed with ASD.

Methods:

• A targeted analysis of 4-EPS and several other putative biomarkers was performed on a cohort of 50 subjects and controls via ultra-performance liquid chromatography-tandem mass spectrometry.
• A non-targeted analysis encompassing ~1,000 analytes was performed on 129 children aged 3-12yo diagnosed with ASD and 101 age matched controls (cohorts from the “Childhood Autism Risks from Genetics and the Environment” study ongoing at the Univ. of California Davis)

Results:

In the targeted analysis in 50 pediatric subjects, elevated serum 4-EPS concentrations were found in the ASD children vs. controls. This finding was replicated in the non-targeted serum metabolomics study involving 230 children, wherein the mean concentration of 4-EPS was found to be elevated by ~6-fold in the ASD vs. control children. Several tryptophan metabolites were also altered, including indolelactate, which was one of the metabolites most strongly associated with ASD in the non-targeted analysis.

Conclusions:

4-EPS concentrations, as well as several other microbial products, were found to be elevated in children with ASD vs. healthy controls in replicate analyses. The impact of this elevation on behavior and the impact of treatment with B. fragilis will be the subject of subsequent studies.