Association between oxidative status and the composition of intestinal microbiota along the gastrointestinal tract

Studies have shown that the microbiota along the gastrointestinal tract (GIT) plays an important role when it comes to the maintenance of its proper functions. Many studies exist that have analyzed the composition of the bacterial community in the different regions of the GIT of humans and model animals. Microbial imbalance leads to several systemic disorders, including cardiovascular and renal disease. The imbalance between the production of reactive oxygen species (ROS) and their elimination by antioxidants leads to oxidative stress. Oxidative stress plays an important role in a variety of physiological processes, as well as disease. The continuous formation of ROS in the GIT is the result of the interaction between intestinal mucosa, symbiotic bacteria and dietary factors. It has also been proven that ROS play a role in the pathogenesis of several GI disorders, including IBD. We hypothesized that the levels of advanced glycation end products (AGEs) would be the highest in the ileum, caecum or colon, where the microbiota mostly consist of butyrate producing bacteria, Bacterioides, Clostridium, Ruminococcus or Bifidobacterium, which derive energy through carbohydrate fermentation. We also assumed that advanced oxidation protein products (AOPP) mostly act in the segments, where bacteria reside and which are responsible for the amino acid fermentation, such as caecum or colon. Lipid hydroxyperoxides are generated during digestion in the stomach, which contains absorbed oxygen and has a low pH. According to this we hypothesized that the highest concentration of thiobarbituric acid reacting substances (TBARS) could be in the stomach, which, however, has not been confirmed. Because Lactobacilli are able to produce catalase, an endogenous antioxidant, and are abundant in the small intestine, we hypothesized that antioxidant capacity (measured by ferric reducing ability) would be the highest here. The highest levels of AGEs were found in the caecum. The highest level of TBARS was found in the jejunum of the rats. The assessment of our hypothesis also revealed high levels of AOPP in the caecum. It has been shown that AOPP contributes to the progression of IBD. The ferric reducing ability of tissue was the lowest in the colon of the experimental animals, which is in accordance with previous studies that show that rat colon has a lower total antioxidant capacity than the small bowel. In summary, we offer some insight into the differences between the oxidative status along the GIT of rats and some advice concerning supportive antioxidant therapy of gastrointestinal diseases.