Evaluation of intestinal biomarkers in calves with experimental endotoxemia

Objective: The determination of changes in citrulline, intestinal fatty acid-binding protein (iFABP), zonulin concentrations and intestinal alkaline phosphatase (IAP) activity within the scope of intestinal biomarkers during the experimental endotoxemia process in calves. Materials and Methods: The animal material of the study consisted of 6 healthy male Holstein calves aged 1-4 weeks. To induce endotoxemia, Escherichia coli 0111:B4; lipopolysaccharide was dissolved in 100 ml of 0.9% NaCl solution at a dose of 1 µg/kg and administered intravenously in 5 minutes. Blood samples were taken from the calves at pre-application (0th hours) and at 0.5, 1, 2, 4, 8, 12, 24, 48th hours after administration. Clinical examinations included assessment of body posture, skin elasticity, mucous membranes, capillary refill time, position of the eye globe in the orbital cavity, heart and respiratory rates, body temperature, suckling reflex, mental reflex, ability to stand and fecal character. Laboratory analyses encompassed complete blood count, blood gases, routine serum biochemistry tests, along with evaluation of cytokines (interleukin 1-β, interleukin 6, tumor necrosis factor-alpha), acute-phase proteins (serum amyloid A, haptoglobin). As intestinal biomarkers, concentrations of citrulline, iFABP, zonulin, and IAP activity were determined. Results: Hematological parameters revealed significant decreases in WBC and PLT counts at various hours compared to the 0th hour (p<0.001). Although changes in blood gases and electrolyte parameters were observed over time, only differences in lactate concentration showed significance (p<0.01). Evaluation of routine biochemical tests indicated significant changes in glucose and urea concentrations, as well as AST and ALP enzyme activities at different times (p<0.01). When acute-phase proteins were assessed, SAA levels showed no significant differences over time, whereas haptoglobin concentration was higher at the 2nd, 8th, 12th, and 24th hours compared to the 0th hour (p<0.01). Concerning intestinal biomarkers, citrulline concentration was significantly lower from the 30th minute onwards compared to the baseline (0th hour) (p<0.05). The average iFABP concentration showed significant increases at 1st, 12th, and 24th hours compared to the 0th hour (p<0.01). Although changes over time were observed, differences in IAP and zonulin concentrations did not reach statistical significance. Conclusion: The concentration of citrulline was markedly decreased during the endotoxemia process, while iFABP concentration showed increases at different hours compared to baseline values. Although changes over time were observed, differences in IAP and zonulin concentrations did not reach statistical significance. Based on the obtained results, it is considered beneficial to conduct new studies involving larger populations, evaluating intestinal damage in calf diseases associated with intestinal injury or sepsis.