Crosstalk between COVID-19 and the gut-brain axis: a gut feeling

Abstract

The microbes in the gut are crucial for maintaining the body’s immune system and overall gut health. However, it is not fully understood how an unstable gut environment can lead to more severe cases of SARS-CoV-2 infection. The gut microbiota also plays a role in the gut-brain axis and interacts with the central nervous system through metabolic and neuroendocrine pathways. The interaction between the microbiota and the host’s body involves hormonal, immune, and neural pathways, and any disruption in the balance of gut bacteria can lead to dysbiosis, which contributes to pathogen growth. In this context, we discuss how dysbiosis could contribute to comorbidities that increase susceptibility to SARS-CoV-2. Probiotics and fecal microbiota transplantation have successfully treated infectious and non-infectious inflammatory-related diseases, the most common comorbidities. These treatments could be adjuvant therapies for COVID-19 infection by restoring gut homeostasis and balancing the gut microbiota.

COVID-19-associated encephalopathy: connection between neuroinflammation and microbiota-gut-brain axis

“…They exert protective effects against a spectrum of pathogens while exhibiting varied benefits based on their specific strains. Through their interaction with the host immune system, probiotics elicit a response involving the production of both anti-and proinflammatory cytokines such as IL-10, IL-12, IL-17, and interferon-α (IFN-α) upon encountering infectious agents ( Azad et al, 2018 ; Kalam and Balasubramaniam, 2024 ). This immunomodulatory action encompasses two pivotal mechanisms: an immunostimulatory effect activating IL-12 and promoting the activity of natural killer (NK) cells, T1 helper cells, and T2 helper cells (Th1 and Th2) against harmful pathogens and an immunoregulatory effect fostering the production of IL-10 and regulatory T cells (Tregs) by stimulating various immune cells, including Th-2 cells, B cells, dendritic cells (DCs), and monocytes, thereby orchestrating an adaptive immune response within the human host ( Chiba et al, 2010 ; Kalam and Balasubramaniam, 2024 ).…”

“…A clinical study was conducted to evaluate the effectiveness of a combination of probiotics in outpatients who tested positive for COVID-19 ( Kalam and Balasubramaniam, 2024 ). The mixture consisted of strains of Lactobacillus plantarum and Pediococcus acidilactici in equal proportions.…”

“…All participants exhibited favorable tolerance to the probiotics during the trial. It is worth mentioning that the treatment group demonstrated a significant decrease in viral load in the nasopharyngeal region, as well as a reduction in both gastrointestinal (GI) and non-GI symptoms, compared to the placebo group ( Kalam and Balasubramaniam, 2024 ). Interestingly, the individuals who received treatment exhibited elevated levels of antibodies specific to SARS-CoV-2 compared to those in the control group.…”

“…However, no significant changes were observed in the composition of the fecal microbiota in either group. The effectiveness of probiotics may primarily depend on their interaction with the immune system of the host rather than the overall composition of the microbiota ( Chiba et al, 2010 ; Kalam and Balasubramaniam, 2024 ).…”

“…Additionally, a study was conducted to evaluate the effectiveness of various strains of beneficial bacteria, including Lactobacillus , Bifidobacterium , and Enterococcus , in COVID-19 patients across a spectrum of disease severities. Patients received a dose of 1.0 × 10 7 CFU of probiotics alongside standard care ( Kalam and Balasubramaniam, 2024 ). The results revealed that patients supplemented with probiotics exhibited improved clinical outcomes and a shortened duration of hospitalization compared to those receiving standard care alone ( Zhang et al, 2021 ; Kalam and Balasubramaniam, 2024 ).…”