Hypoxia and Hypercapnia Diminish Intestinal Barrier Integrity in a Human Enteroid Model System

Abstract

Warfighters are commonly exposed to unique physiologic stressors that affect their physical and mental performance, as well as their overall health. The adverse impact of these stressors may be in part due to effects on the microorganisms residing in the human gut, collectively known as the gut microbiome. Numerous studies have revealed the gut microbiome can influence multiple physiological process, including immunity, nutrient metabolism, and cognition. Hypoxia refers to a lack of oxygen in a given system and exists as a gradient in intestinal tissue, however, the intestine is sensitive to changes in oxygenation and can alter normal cellular process, such as inflammation and barrier function. Similarly, an excess of carbon dioxide (CO2), or hypercapnia, also affects intestinal tissue, as levels of CO2 are inversely coupled with the level of oxygen and are found to be elevated in hypoxic tissue. The GI tract is thought to have a low‐grade, albeit constant, level of inflammation and is home to multiple immune cell types. In addition, both epithelial and immune cells in the intestine can sense and respond to various stimuli including pathogens, and compromises to intestinal barrier integrity due to injury or stress can result. In this study, we sought to determine the extent to which hypoxia and hypercapnia degrade intestinal cellular integrity through inflammation‐mediated mechanisms. Intestinal epithelial organoids (enteroids) derived from the duodenum were exposed to hypoxic (0.5% O2) or hypercapnic (10%, 20% CO2) conditions for a period of 72 hours. Initial results indicated intestinal barrier integrity was compromised in hypoxia and 20% CO2 conditions as evidenced by transepithelial electrical resistance (TEER), with hypoxia (0.7 Ω) and 20% CO2 (0.85 Ω) being significantly lower than control (1.19 Ω; P < 0.05). The Quantigene Plex array system was used to interrogate a panel of intestinal and inflammatory markers. Preliminary results suggest alterations in tight‐junction markers as well as in genes involved in inflammatory response pathways. In addition, IL‐8, a macrophage‐mediated chemokine produced in intestinal epithelial cells and involved in the innate immune response, was found to be significantly downregulated in hypoxia (58.7 pg/mL) and hypercapnia (42.5 pg in 10% CO2, 49.7 pg/mL in 20% CO2) compared to control (190.7 pg/mL; P < 0.05). In sum, our data indicate hypoxic and hypercapnic conditions lead to alterations in molecules involved in the innate immune response pathway, tight‐junction markers, as well as compromised epithelial barrier integrity. Future experiments will be aimed at identifying the mechanism(s) responsible for diminished intestinal barrier function as well as identify potential preventative strategies.Support or Funding InformationFunding support provided by the Office of Naval Research award #N0001419MP00144 to SP FY18‐FY20.