Biomarkers of increased intestinal permeability in chickens

Abstract

Enterocytes comprising the single layer of epithelial cells in the intestine are linked together by a series of proteins known as tight junction proteins (TJP). TJP absorb nutrients through selective permeability and act as a barrier between intestinal contents and blood. When the barrier function is compromised this is known as increased intestinal permeability (IP). The aim of the thesis was to investigate biomarkers of increased IP in chickens. Increased IP has been studied extensively in rats, pigs and humans. In contrast, this is a relatively a new area in chickens (Chapter 2). Based on published studies in rats and pigs, lipopolysaccharide (LPS), an endotoxin produced by Gram-negative bacteria, was selected as a method for increasing IP in chickens. Three experiments were conducted utilizing LPS to increase IP in chickens (Chapter 3). These studies concluded that LPS failed to increase IP as measured by permeability of lactulose, rhamnose and mannitol sugars (LMR) and fluorescein isothiocyanate dextran (FITC-d) across the epithelial barrier. However, this work generated useful data and indicated for the first time that 90 minutes post-oral gavage was the optimal time-point for blood sampling. Since fasting for 19.5 hours was applied in the protocol of LPS administration (Chapter 3), a second experiment was conducted with fasting for 19.5 hours and dextran sodium sulphate ingestion along with the LMR sugars and FITC-d (Chapter 4). Additional biomarkers such as intestinal fatty acid binding protein, fecal antitrypsin inhibitor, diamine oxidase and d-lactate were also utilized. This paper concluded that 19.5 hours fasting increased IP that could be evaluated by LMR sugar and FITC-d methods. However, DSS ingestion did not show any IP increase in chickens. Since fasting is routinely applied in the chicken meat industry, fasting and its effects on IP were further investigated (Chapter 5). This study revealed that fasting for as little as 4.5 and 9 hours also increased IP in chickens. The study also confirmed that both methods (LMR sugars and FITC-d) could be utilized to evaluate increased IP. Chapter 6 focused on delayed feeding at the time of chicken placement at the farm. However, this study revealed that delayed feeding did not alter IP in very young chickens. Finally, as short-term fasting also increased IP in older chickens, a further study was conducted to investigate whether mRNA expression of gut barrier associated genes was altered (Chapter 7). This study showed that mRNA expression of claudin-3 only was significantly different from control for 9 and 19.5 hours fasting. This thesis has identified several biomarkers that could be utilized to evaluate increased IP in chickens. Some of these biomarkers such as fecal antitrypsin inhibitor, fatty acid binding protein, diamine oxidase and d-lactate could not detect IP changes induced by fasting in the current studies, they could potentially eliminate the need for oral gavage which is required in the FITC-d and LMR sugar tests. Nonetheless, this research project has shown that permeation of LMR sugars and FITC-d across the intestinal epithelium was able to demonstrate IP changes in chickens.