Molecules derived from the microbiota do not modify entry or replication of SARS-CoV-2 in intestinal cells

A study conducted at the University of Campinas (UNICAMP) in the State of São Paulo, Brazil, shows that the compounds produced by the gut microbiota (bacteria and other microorganisms) during the fermentation of insoluble fiber from raw materials food plants do not affect the ability of the novel coronavirus SARS-CoV-2 to enter and replicate in cells lining the intestines. However, while the in vitro treatment of cells with these molecules did not significantly influence local tissue infection, it reduced the expression of a gene that plays a key role in the entry of viral cells and a cytokine receptor that promotes inflammation.

An article reporting the results is published in the journal Intestinal microbes.

Up to 50% of patients with COVID-19 have gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain. Such symptoms are detected in 17.6% of severe cases. They are partly associated with viral entry into intestinal cells leading to alterations in their normal functions. Additionally, recent studies indicate major changes in patients’ gut microbiota, including decreased levels of bacteria that secrete short-chain fatty acids (SCFAs) by fermenting dietary fiber. SCFAs are important for colon health and maintaining the integrity of the intestinal barrier.

The researchers decided to confirm whether SFCA directly affects infection of intestinal cells with SARS-CoV-2. Previous studies had suggested alterations in the gut microbiota and its products could alter the immune response of an infected subject.

“In previous research, we found in animals that compounds produced by the gut microbiota help protect the body against respiratory infections. The model used was respiratory syncytial virus. [RSV], which causes bronchiolitis [inflammation of the small airways in the lung] and frequently infects children. Similar results have been obtained by other research groups in studies of different respiratory diseases, “said Patrícia Brito Rodrigues, who has a doctoral fellowship from FAPESP and is the first joint author of the article with the intern. Postdoctoral Fellow Livia Bitencourt Pascoal Rodrigues conducted her doctoral research at the Institute of Biology of UNICAMP (IB) with a grant from FAPESP.

In the latest study, healthy colon tissue and epithelial cells were infected with SARS-CoV-2 in the lab and subjected to a battery of tests.

“The viral load was not reduced and was the same in cells and tissues treated with SCFAs and in untreated samples. However, the treated intestinal biopsy samples showed a significant decrease in gene expression. . DDX58 [an innate immune system receptor that detects viral nucleic acids and activates a signaling cascade that results in production of pro-inflammatory cytokines] and the interferon-lambda receptor, which mediates antiviral activity. There was also a decrease in the expression of the TMPRSS2 protein, which is important for the entry of viral cells, ”said Raquel Franco Leal, professor at the Faculty of Medical Sciences at UNICAMP (FCM), argued by FAPESP and co-principal investigator of the study with Marco Aurélio Ramirez Vinolo, professor at IB-UNICAMP, also supported by FAPESP.

Protection against inflammation

The researchers took colon tissue samples from 11 patients without COVID-19. They also tested epithelial cells that line the intestines and come in close contact with the gut microbiota. Tissue and cell samples were infected with SARS-CoV-2 in the Emerging Viruses Laboratory (LEVE) of IB-UNICAMP, a Biosafety Level III (BSL-3) facility directed by José Luiz Proença Módena, professor at IB-UNICAMP and a co-author of the article.

Tissues and cells were treated with a mixture of acetate, propionate and butyrate, compounds produced by metabolization of the intestinal microbiota of SCFAs present in dietary fibers. The treatment did not change the viral load in colon biopsies or cells, and there was no change in the permeability and integrity of the cell wall.

This does not exclude the possibility of a significant action of SCFAs on infection with SARS-CoV-2. Antiviral effects may depend on the interaction with other cells in the body. We will continue our investigation on animal models since the action of these compounds on the infection could depend on a more complete system than the samples that we used in vitro. [isolated cells and tissues]. “

Patrícia Brito Rodrigues, co-first author

Other tests involving untreated infected biopsy samples showed increased expression of the gene DDX58, which encodes an important viral receptor, and interferon-beta (IFN-beta), a pro-inflammatory molecule that participates in the cytokine storm associated with severe cases of COVID-19.

“Alterations in genes associated with viral recognition and response during intestinal infection may be relevant to the onset of the inflammatory chain,” Leal said. “In this context, it will be important to further analyze the effects of SCFAs with these parameters, as this could be important in the severe stages of the disease.”