What do we know about covid-19’s effects on the gut?

Dear Editor

We would like to discuss “What do we know about covid-19’s effects on the gut?". The main underlying pathogenic mechanism of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with the surface spike protein, which binds to the Angiotensin-Converting-Enzyme-2 (ACE2) in the human cells and causes infection. ACE2 is not only expressed in lung cells but also present in the gastrointestinal (GI) tract cells (1, 2). The GI microbiota and SARS-CoV-2 balance can affect how the virus replicates in the mucosal layer of the digestive tract. The gut microbiota diversity and concentration are decreased by SARS-CoV-2 due to interactions between the respiratory and digestive tract, also known as the gut-lung axis (3-5). This GI tropism led to understanding of the relationship between SARS-CoV-2 and the gut microflora; this attracted the scientists to propose the use of the gut microbiota in the form of nutritional supplements as an adjunctive therapy for SARS-CoV-2 infection. Indeed, probiotics use became the topic of discussion as soon as the coronavirus disease 2019 (COVID-19) presented with atypical symptoms like GI manifestations (6).

The article we are responding to is a valuable reminder of how the gut microbiome can prevent inflammatory and infectious diseases. The tendency to traditional methods for managing various diseases has increased considerably in recent years. One of these modalities includes the therapeutic use of beneficial microorganisms in the form of non-chemical products for infectious diseases. These beneficial microorganisms, known as microbiota, are largely present on various surfaces of the body, including the skin and mucosal membranes of the oropharyngeal, GI and vaginal tracts, with no pathogenic effect. They live in a commensal condition with the humans and in an equilibrium with the pathogenic microorganisms. The greatest concentrations of microbiota live in the respiratory and GI tract, which constitute the largest surface area of the body. The human GI tract has a variety of microbiota, with a primary focus on Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. These commensals affect the human health by maintaining immune and metabolic homeostasis and combating against pathogenic microorganisms. Any changes in the composition of the GI microbiota may lead to certain GI infections or disorders (7, 8).

Probiotics are products containing the beneficial microbiota, which can correct the imbalance that occurs during infections. In fact, they are effective in preventing or treating several infectious and
noninfectious diseases, most prominently in the GI tract (9).

Probiotics have several mechanisms of action, all of which are associated with bacterial interference; this means that the beneficial microorganisms act in a way that inhibits the activity of the pathogenic ones. These mechanisms include competition for nutrients or space, lactose digestion, production of antimicrobial agents, vitamins, antioxidants and defensins against pathogenic microorganism, and immunomodulation. In fact, they function through reinforcing the mucosal innate immunity, decreasing intestinal permeability, inhibiting bacteria adhesion, and regulating the immune response through activation of anti-anti-inflammatory cytokines and exerting anti-inflammatory effects (10, 11).

The beneficial use of probiotics in the management of SARS-CoV-2 infection is not limited to GI infections; rather, they have been quite useful in COVID-19 with pulmonary involvement. In fact, probiotics can enhance the immune response, regulate the systemic inflammation and decrease the endothelial damage which is efficient in combating respiratory viruses like SARS-CoV-2. Furthermore, these agents have ability to regulate the exaggerated cytokine cascade which is the main cause of severe SARS-CoV-2 infection. They have been shown to decrease hospitalization, the time to recovery and mortality in COVID-19 patients. Thus, probiotics serve as immunomodulators and do favor in conditions in where no specific therapeutic option is available (12-14).

References
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2. Mohseni Afshar Z, Tavakoli Pirzaman A, Karim B, Rahimipour Anaraki S, Hosseinzadeh R, Sanjari Pireivatlou E, et al. SARS-CoV-2 omicron (B. 1.1. 529) variant: a challenge with COVID-19. Diagnostics. 2023;13(3):559.
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14. Infusino F, Marazzato M, Mancone M, Fedele F, Mastroianni CM, Severino P, et al. Diet supplementation, probiotics, and nutraceuticals in SARS-CoV-2 infection: a scoping review. Nutrients. 2020;12(6):1718.
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