Fiber is an essential nutrient that has been linked to weight loss, healthy blood sugar levels, and lower cholesterol. Now, in a new study from the University of Campinas in Brazil, researchers have found evidence that fiber may also play an important role in controlling the inflammation associated with COVID-19.
The experts report that compounds produced by gut microbiota during the fermentation of insoluble fiber have the potential to limit the severity of COVID-19. These compounds were found to reduce the expression of a gene that plays a key role in viral cell entry and a cytokine receptor that favors inflammation.
Meanwhile, the molecules did not affect the ability of the novel coronavirus SARS-CoV-2 to enter and replicate in cells lining the intestines.
As many as half of all COVID-19 patients experience gastrointestinal symptoms such as diarrhea and abdominal pain. These symptoms have been detected in 17.6 percent of severe cases, and are partly associated with viral entry into intestinal cells that alters their normal functions.
Furthermore, recent studies have found evidence of major changes in the gut microbiota of COVID-19 patients, including a decrease in levels of bacteria that secrete short-chain fatty acids (SCFAs) by fermenting dietary fiber. These fatty acids are important to colon health and to maintaining the integrity of the intestinal barrier.
The researchers set out to investigate whether SFCAs directly influence the infection of intestinal cells by SARS-CoV-2.
“In earlier research, we found in animals that compounds produced by gut microbiota help protect the organism against respiratory infection,” said Patrícia Brito Rodrigues.
“The model used there was respiratory syncytial virus (RSV), which causes bronchiolitis and frequently infects children. Similar results have been obtained by other research groups in studies of different respiratory diseases.”
For the current study, healthy colon tissue and epithelial cells were infected with SARS-CoV-2 in the lab and subjected to a battery of tests.
“Viral load wasn’t reduced and was the same in cells and tissue treated with SCFAs and in untreated samples,” explained Professor Raquel Franco Leal. “However, treated intestinal biopsy samples displayed a significant decrease in expression of the gene 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 expression of the protein TMPRSS2, which is important to viral cell entry.”
Tissue and cell samples were treated with a mixture of compounds that are produced by gut microbiota during the metabolization of the SCFAs present in dietary fiber. The treatments did not alter viral load in colon biopsies or cells, and there were no changes in cell wall permeability and integrity.
“That doesn’t exclude the possibility of significant action by SCFAs on infection by SARS-CoV-2. The antiviral effects could depend on interaction with other cells in the organism,” explained Rodrigues.
“We’ll continue our investigation in animal models since the action of these compounds on the infection could depend on a more complete system than the samples we used in vitro (isolated cells and tissues).”
The study is published in the journal Gut Microbes.