The Promising Role of Probiotics in Managing the Altered Gut in Autism Spectrum Disorders

Abstract

Gastrointestinal symptoms (GIS) have been reported repeatedly in people with autism spectrum disorder (ASD) and studies have reported interesting correlations between severity of behavioral and gastrointestinal symptoms. Growing evidence indicates that the gut microbiota in ASD is altered with various shifts described at different taxonomic levels, pointing to the importance of considering the gut-brain axis in treatment of these disorders. Probiotics are live beneficial bacteria that are ingested as food or customized pills. These beneficial bacteria, when added in sufficient amounts, can correct the dysbiosis. Because probiotics have shown success in treating irritable bowel syndrome (IBS), it is plausible to investigate whether they can induce alleviation of behavioral symptoms as well. Probiotics show, in some clinical studies, their potential benefits (1) in improving gastrointestinal dysfunction, (2) in correcting dysbiosis, (3) in consequently reducing the severity of ASD symptoms. This review compiles data from selected studies that investigate these benefits and the mechanisms that mediate these effects, which include the production of metabolites, hormones, and neurotransmitters and the regulation of pro-inflammatory and regulatory cytokines. Future research based on more randomized, controlled studies with a larger population size and standardized use of strains, concentration of probiotics, duration of treatments, and methods of DNA extraction is still needed in this area, which may lead to more robust results.

Keywords: ASD; dysbiosis; gut microbiota; inflammation; probiotics.

Figure 1

The bi-directional relationship between the gut and the brain and its players. The brain can influence the gut microbiota through changes in gastrointestinal motility, intestinal permeability, blood flow, and the release of molecules in the lamina propria. The gut microbiota, in turn, influences the brain neural as well as immune system’s communication and active metabolites. The gut microbiota affects the brain through the enteric nervous system (ENS), which communicates with the autonomic and central nervous systems.

Figure 2

Summary diagram illustrating the effect of probiotics as a potential safe therapy in treating ASD symptoms. Probiotics may colonize the gut and shift the bacterial populations within this system to the so-called good bacteria. Probiotics include supplementation of bacterial-produced amino acids SCFAs (short-chain fatty acids) and other metabolites that might be beneficial by (1) affecting the GI symptoms, (2) affecting the gut microbiota population, and (3) changing the microbial signals. All these will change the neuroendocrine signaling as well as the cytokine immune signaling. As a consequence, the central nervous system will be affected and most of the neurological ASD symptoms will be alleviated.