Chronic Exposure to Arsenite Enhances Influenza Virus Infection in Cultured Cells

Arsenic is a ubiquitous environmental toxicant that has been associated with various human diseases. Chronic, low dose arsenic exposure has been linked to greater morbidity from cancer, cardiovascular diseases, diabetes mellitus, neurological diseases, skin lesions (keratosis), and respiratory diseases. The primary route of arsenic exposure in humans is through inhalation and ingestion. It has been reported that millions of people are exposed to arsenic in drinking water worldwide. Recent epidemiological and experimental studies show that arsenic exposure is associated with enhanced influenza virus infection in vivo. The respiratory epithelium, which is the primary target of infection, plays an important role in innate immune defense by serving as a barrier against infection. Arsenic exposure has been shown to alter the epithelial barrier function by disrupting tight junction formation. Despite the strong link between arsenic exposure and respiratory infection, there are no reports investigating the effects of arsenic exposure on influenza virus infection in vitro. Therefore, we hypothesized that the effect of arsenic exposure on epithelial cells could enhance influenza virus infection. In this study we characterized influenza A virus A/WSN/33 (H1N1) infection in arsenite-exposed Madin-Darby Canine Kidney (MDCK) epithelial cells. We also characterized influenza A virus A/Udorn/72(H3N2) infection in human bronchial epithelial cells (BEAS-2B), and adenocarcinomic human alveolar basal epithelial cells (A549) in order to uncover novel molecular mechanisms mediating arsenic enhanced influenza virus infection in vitro. We found that chronic exposure to sodium arsenite enhanced influenza A virus A/WSN/33 (H1N1) infection in MDCK cells. We observed increased viral matrix (M2) protein expression, increased viral mRNA quantity, and increased plaque area in the arsenite-exposed MDCK cells. Similarly, we also found that chronic arsenite exposure enhanced influenza A virus A/Udorn/72 (H3N2) infection in BEAS-2B and A549 cells. We demonstrated that arsenite exposure resulted in significantly reduced cell viability and increased cytotoxicity in virus infected BEAS-2B and A549 cells. The first step of influenza virus infection is the binding of the virus to the host surface receptors. Therefore, to determine the molecular mechanisms mediating arsenic-enhanced influenza virus infection in vitro, we quantified the amount of α-2,3-linked and α-2,6-linked sialic acids-containing receptors in MDCK cells and BEAS-2B cells. We found that exposure to sodium arsenite resulted in increased α-2,3-linked sialic acid expression, leading to increased virus attachment and enhanced infection in MDCK cells. On the contrary, we did not observe a significant change in α-2,3-linked sialic acid expression in BEAS-2B cells. In conclusion, these studies show that exposure to sodium arsenite enhances influenza virus infection in vitro. This is consistent with previous reports showing that arsenite exposure enhances influenza virus infection in vivo. Furthermore, we uncover novel potential molecular mechanisms mediating arsenic-enhanced infection in vitro