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Are probiotics effective adjuvant therapeutic choice in patients with COVID-19?

we read very carefully the Editorial of Gao et al1 about the effort needed to be put to patients with COVID-19 with an initial presentation of gastrointestinal symptoms. On December 31, 2019, the Chinese health authorities announced the presence of an outbreak of febrile syndrome, associated with lungs of unknown origin2. The pathogen is a new β-coronavirus, called SARS-CoV-2, due to the genetic concordance (89.1%) with coronaviruses similar to SARS. The disease caused by the new virus was called COVID-19. The main symptoms are fever, cough and wheezing3. Patients in critical condition rapidly develop Acute Respiratory Distress Syndrome (ARDS), respiratory failure, multiple organ failure, even deaths4. Moreover, COVID-19 interact with GUT microbiota since about 5-10% of patients show diarrhea and gastrointestinal symptoms. SARS-CoV peak S protein trimers bind a hydrophobic pocket of the extracellular catalytic domain of Angiotensin-Converting Enzyme 2 (ACE2), accounting the possible route for COVID-195. ACE2 is expressed in endothelial cells of the vasculature and also in the epithelia of the lungs, intestine, and it plays a major role in acute lung injury and ARDS6. Following SARS-CoV entry, ACE2 increased Angiotensin II levels, providing a molecular explanation for the development of ARDS. Given the presence of ACE2 in the intestine, there may be the possibility of a cross-talk between lung and gut. The presence of viral nucleic acids in the fecal samples and anal swabs of patients with COVID-197], could explain the diarrhea (2%-10.1%) observed in COVID-19, related to a more serious clinical course of the disease. Moreover, ACE2 regulates amino acid transport in the intestine, and reduced tryptophan levels lead to reduced mTOR pathway activity in the small intestine8. The aberrant activation of mTOR causes an altered expression of antimicrobial peptides from small intestinal Paneth cells, which in turn alters the composition of the intestinal microbiota, with a vicious cycle. As most patients had a good prognosis, while some were in critical condition, especially those with chronic underlying diseases, the immune response is essential for the control and resolution of COVID-19. It has been shown that rebalancing the gut microbiota can reduce enteritis and ventilator-associated pneumonia9. In different pathological situations, including COVID-19, the loss of homeostatic equilibrium between TREG cells (IL-10) and Th17 cells (IL-17) was observed. Therefore, it is possible to hypothesize the therapeutic use of probiotics and their metabolites, such as propionic acid, to restore the innate and adaptive immunity10. It is conceivable to use probiotics, as Lactobacillus rhamnosus and Bifidumbacterium lactis HN019, that exhibit anti-inflammatory effects, to maintain the balance of intestinal microecology and prevent secondary bacterial infection in patients with COVID-19. Moreover, as hypo-nutrition aggravates the impaired immunity in COVID-19, we suggest for a correct immunomodulation a prebiotic, probiotic, postbiotic, polyphenols, and zinc supplementation, that are able to restore innate and adaptive immunity and may be an adjuvant therapeutic choice of COVID-19.