RESUMO
Omicron B.1.1.529 became the predominant SARS-CoV-2 variant in early 2022, causing a new wave of public anxiety. Compared to the ancestral strain, Omicron has 50 mutations, with over 30 mutations in the spike protein. These differences likely underlie the changes in Omicron biology noted in other studies, including an attenuation in the lung parenchyma, compared to the ancestral SARS-CoV-2 strain and other variants, as well as a preference for endosomal entry, in place of the TMPRSS2-mediated membrane fusion pathway. This raises questions on Omicron tropism and infectivity in various target organ systems, including the gastrointestinal (GI) tract. Up to 70% of COVID-19 patients report GI symptoms, including nausea, vomiting, and diarrhea. Here, we show that in the context of donor intrinsic genetic heterogeneity, the SARS-CoV-2 Omicron variant infects human colonoids similarly, if not less effectively, than the ancestral WT (WA1) strain or the Delta variant. Additionally, we note a higher ratio of viral RNA to infectious virus titer, which may suggest that Omicron is potentially less infectious in the intestine. This study lays the foundation for further work defining mechanisms mediating intestinal infection and pathogenesis by Omicron.
RESUMO
IntroductionCoronavirus Disease 2019 (COVID-19) is an ongoing public health crisis that has sickened or precipitated death in millions. The etiologic agent of COVID-19, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), infects the intestinal epithelium, and can induce GI symptoms similar to the human inflammatory bowel diseases (IBD). An international surveillance epidemiology study (SECURE-IBD) reported that the standardized mortality ratio trends higher in IBD patients (1.5-1.8) and that mesalamine/sulfasalazine therapy correlates with poor outcome. The goal of our study was to experimentally address the relationship between mesalamine and SARS-CoV-2 entry, replication, and/or pathogenesis. MethodsViral infection was performed with a chimeric vesicular stomatitis virus expressing SARS-CoV-2 spike protein and EGFP (VSV-SARS-CoV-2) and SARS-CoV-2 virus derived from an infectious cDNA clone of 2019n-CoV/USA_WA1/2020. Primary human ileal spheroids derived from healthy donors were grown as 3D spheroids or on 2D transwells. We assessed the effect of 10 mM mesalamine (Millipore Sigma) on viral RNA levels, as well as the expression of the SARS-CoV-2 receptor angiotensin II-converting enzyme 2 (ACE2), Transmembrane Serine Protease 2 (TMPRSS2), TMPRSS4, Cathepsin B (CTSB) and CTSL by qRT-PCR. 8-12 week old K18-ACE2 were treated orally with PBS or mesalamine at 200 mg/kg daily. Mice were inoculated intranasally with 1x103 FFU of SARS-CoV-2. Mice were weighed daily and viral titers were determined 7 days post infection (dpi) by qRT-PCR. For the intestinal viral entry model, VSV-SARS-CoV-2 was injected into a ligated intestinal loop of anesthetized K18-ACE2 mice and tissues were harvested 6 hours post-infection. ResultsWe found no change in viral RNA levels in human intestinal epithelial cells in response to mesalamine. Expression of ACE2 was reduced following mesalamine treatment in enteroids, while CTSL expression was increased. Mice receiving mesalamine lost weight at similar rates compared to mice receiving vehicle control. Mesalamine treatment did not change viral load in the lung, heart, or intestinal tissues harvested at 7 dpi. Pretreatment with mesalamine did not modulate intestinal entry of the chimeric VSV-SARS-CoV-2 in K18-ACE2 mice. ConclusionsMesalamine did not alter viral entry, replication, or pathogenesis in vitro or in mouse models. Mesalamine treatment reduced expression of the viral receptor ACE2 while concurrently increasing CTSL expression in human ileum organoids.
