Gastroesophageal reflux may increase risk of dying from COVID-19, study suggests

Analyses by Brazilian researchers suggest alterations to pH caused by stomach acid lead to increase in expression of ACE2 and make cells more susceptible to infection by novel coronavirus.

By Karina Toledo  |  Agência FAPESP – Digestive disorders such as gastroesophageal reflux disease and Barrett’s esophagus may be associated with a higher risk of death from COVID-19, according to a study supported by FAPESP and published on medRxiv, a preprint platform for new medical research that has not yet been peer-reviewed.

Damage to the esophagus from stomach acid appears to cause increased expression of ACE2, the enzyme receptor to which SARS-CoV-2 binds in order to penetrate human cells. Esophageal cells thereby become more susceptible to infection by the virus.

“Our data suggest that the change in the pH of esophageal tissue caused by this acid reflux favors an increase in viral load,” Helder Nakaya, a professor in the University of São Paulo’s School of Pharmaceutical Sciences (FCF-USP) in Brazil and principal investigator for the study, told Agência FAPESP. 

The discovery was accidental, Nakaya recalled, and was made when Leandro Jimenez, a PhD candidate whose research he supervised, and other members of his research group were analyzing transcriptomes from patients with Barrett’s syndrome. The transcriptome is the complete set of all RNA molecules expressed in a cell or cell population. Barrett’s syndrome, a chronic complication of gastroesophageal reflux disease, is characterized by alterations in the lining of the esophagus, which becomes similar to the lining of the intestine.

The initial analysis used bioinformatics techniques and data mined from the public repository Gene Expression Omnibus (GEO). At this point, the study had no bearing on the COVID-19 pandemic.

“We found increased expression of ACE2 in patients with Barrett’s esophagus, as well as alterations in signaling pathways associated with regulation of intracellular pH,” Nakaya said. “This suggested that cells submitted to acid pH might be more susceptible to SARS-CoV-2.”

Nakaya is a member of the Center for Research on Inflammatory Diseases (CRID), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP. CRID is hosted by the University of São Paulo’s Ribeirão Preto Medical School (FMRP-USP). He is also a member of the Institut Pasteur-USP Scientific Platform.

Experiments were conducted in vitro to test the hypothesis, with Pedro Moraes-Vieira collaborating. Moraes-Vieira is a professor at the University of Campinas’s Biology Institute (IB-UNICAMP) and a co-author of the article on the study.

Human monocytes (immune system blood cells) were placed in media with varying degrees of acidity and incubated with SARS-CoV-2. The pH ranged from 7.4 (normal for blood) to 6. After 24 hours the cells cultured in the most acid medium expressed the most ACE2 and produced the highest viral load.

The experiment was conducted in IB-UNICAMP’s Laboratory of Emerging Virus Studies (LEVE), a Biosafety Level III (BSL-3) facility led by José Luiz Proença Módena, a professor in IB-UNICAMP and also a co-author of the article. 

Clinical evidence

The next step was an analysis of data on two cohorts of patients hospitalized for treatment of complications associated with COVID-19 – 551 in Manaus, the capital of the state of Amazonas, and 806 in São José do Rio Preto, in the state of São Paulo. The aim of the analysis was to find out whether there was in fact a link between the severity of the disease and pre-existing digestive problems. 

This part of the study was conducted in collaboration with researchers at the Dr Heitor Vieira Dourado Tropical Medicine Foundation and São José do Rio Preto Medical School (FAMERP).

“On admission to hospital, patients were asked what medications they took regularly. We considered patients with digestive disorders to be those who continuously took proton pump inhibitors [omeprazole, pantoprazole etc.], which decrease the amount of acid produced in the stomach,” Nakaya explained. “It’s important to note that these drugs were merely a reference we used to identify patients who had digestive problems before contracting COVID-19. In themselves, the drugs had nothing to do with the severity of the viral infection. Nor do we know if the risk of death was higher for people who took these drugs and only had mild symptoms of COVID-19.”

A multivariate analysis, in which the results were adjusted to eliminate the influence of factors such as being over 60 and having comorbidities, showed that the risk of being admitted to a hospital intensive care unit was twice the normal risk for patients with acid reflux due to digestive problems. The risk of death was three times as high.

“Our findings suggest some gastric problems can be a risk factor for severe COVID-19 of which no one was aware until now. However, more research will be needed to confirm this,” Nakaya said.

Another hypothesis posed in the article is that the lung damage caused by SARS-CoV-2 and the resulting impairment of oxygen delivery to other organs led to acidification of the blood and increased expression of ACE2.

“It is possible that acidosis in the blood of some severe COVID-19 patients worsens the disease by increasing ACE2 levels and facilitating viral entry into cells. Hypoxia itself may help regulate ACE2”, the authors say.

FAPESP also supported the research via grants awarded to André Fujita (USP), Paola Minoprio (USP) and Maurício Lacerda Nogueira (FAMERP).

“It’s a most interesting study that opens up new perspectives from which to understand COVID-19 severity factors,” Nogueira said. “I should stress that it also shows the importance of collaborative studies in multiple institutions. The findings from Manaus and São José do Rio Preto were obtained independently and mirror each other, enhancing the credibility and soundness of the conclusions.”

The article “The influence of pH on SARS-CoV-2 infection and COVID-19 severity” can be retrieved from: www.medrxiv.org/content/10.1101/2020.09.10.20179135v1.