High-fiber diet may help control inflammation associated with COVID-19, study finds

Compounds produced by gut microbiota during fermentation of insoluble fiber from dietary plant matter do not affect the ability of the novel coronavirus (COVID-19) to enter and replicate in cells lining the intestines. However, while 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 viral cell entry and a cytokine receptor that favors inflammation, according to a new study published in the journal Gut Microbes.

Up to 50 percent of COVID-19 patients experience gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain, according to the researchers from the University of Campinas (UNICAMP) in the São Paulo, Brazil. Such symptoms are detected in 17.6 percent of severe cases. They are partly associated with viral entry into intestinal cells resulting in alterations to their normal functions, they said.

In addition, recent studies point to major changes in patients’ gut microbiota, including a decrease in levels of bacteria that secrete short-chain fatty acids (SCFAs) by fermenting dietary fiber. SCFAs are important to colon health and maintenance of intestinal barrier integrity.

The researchers decided to confirm whether SFCAs directly affected the infection of intestinal cells by SARS-CoV-2. Previous studies had suggested alterations in gut microbiota and its products could modify an infected subject’s immune response. In the latest study, healthy colon tissue and epithelial cells were infected with SARS-CoV-2 in the laboratory and subjected to a battery of tests.

The researchers took colon tissue samples from 11 patients without COVID-19. They also tested epithelial cells that line the intestines and are in close contact with gut microbiota. Tissue and cell samples were infected with SARS-CoV-2 in IB-UNICAMP’s Laboratory of Emerging Virus Studies (LEVE), a Biosafety Level III (BSL-3) facility.

The tissues and cells were treated with a mixture of acetate, propionate and butyrate, compounds produced by gut microbiota metabolization of SCFAs present in dietary fiber. The treatment did not alter viral load in colon biopsies or cells, nor were there any changes in cell wall permeability and integrity, according to the study.

Other tests involving non-treated infected biopsy samples showed an increase in expression of the gene DDX58, which encodes an important viral receptor, and of 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 virus recognition and response during intestinal infection may be relevant to the onset of the inflammatory chain,” said Raquel Franco Leal, PhD, co-principal investigator of the study and a professor at UNICAMP’s School of Medical Sciences (FCM), in a statement. “In this context, it will be important to deepen the analysis of the effects of SCFAs with these parameters, as this could be significant in severe stages of the disease.”

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