Pathophysiological mechanisms underlying gastrointestinal symptoms in patients with COVID-19

May 27, 2021World journal of gastroenterology

How COVID-19 may cause digestive symptoms

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Abstract

Elevated plasma serotonin levels and high fecal calprotectin are observed in COVID-19 patients with diarrhea.

Gastrointestinal symptoms such as diarrhea, abdominal pain, vomiting, and anorexia are common in COVID-19 patients.
SARS-CoV-2 infection may impair barrier function by downregulating ACE2 receptors in intestinal cells.
The B0AT1/ACE2 complex in the intestinal epithelium regulates gut microbiota composition and function.
Disruptions to the B0AT1/ACE2 complex may lead to microbial dysbiosis and increased immune responses.
Altered serotonin metabolism is suggested as a potential cause of GI disorders like diarrhea.
Positive rectal swabs for SARS-CoV-2 after respiratory clearance indicate stronger viral shedding from the GI tract.

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Gastrointestinal (GI) symptoms, such as diarrhea, abdominal pain, vomiting, and anorexia, are frequently observed in patients with coronavirus disease 2019 (COVID-19). However, the pathophysiological mechanisms connecting these GI symptoms to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections remain elusive. Previous studies indicate that the entry of SARS-CoV-2 into intestinal cells leads to downregulation of angiotensin converting enzyme 2 (ACE2) receptors resulting in impaired barrier function. While intestinal ACE2 functions as a chaperone for the amino acid transporter B0AT1, the B0AT1/ACE2 complex within the intestinal epithelium acts as a regulator of gut microbiota composition and function. Alternations to the B0AT1/ACE2 complex lead to microbial dysbiosis through increased local and systemic immune responses. Previous studies have also suggested that altered serotonin metabolism may be the underlying cause of GI disorders involving diarrhea. The findings of elevated plasma serotonin levels and high fecal calprotectin in COVID-19 patients with diarrhea indicate that the viral infection evokes a systemic inflammatory response that specifically involves the GI. Interestingly, the elevated proinflammatory cytokines correlate with elevated serotonin and fecal calprotectin levels further supporting the evidence of GI inflammation, a hallmark of functional GI disorders. Moreover, the finding that rectal swabs of COVID-19 patients remain positive for SARS-CoV-2 even after the nasopharynx clears the virus, suggests that viral replication and shedding from the GI tract may be more robust than that of the respiratory tract, further indicating fecal-oral transmission as another important route of viral spread. This review summarized the evidence for pathophysiological mechanisms (impaired barrier function, gut inflammation, altered serotonin metabolism and gut microbiota dysbiosis) underlying the GI symptoms in patients with COVID-19.

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Pathophysiological mechanisms underlying gastrointestinal symptoms in patients with COVID-19

Abstract

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