Iohexol-based measurement of intestinal permeability in birds

Iohexol is an intestinal permeability marker in broilers under coccidiosis challenge

Intestinal integrity losses have been identified as a main driver for poor performance in broilers. The oral administration of markers such as iohexol is a major asset for measuring intestinal permeability (IP) alterations. The aim of the current study was to evaluate oral iohexol administration and serum levels as a quantitative measure for IP in Ross 308 broilers and to identify possible associations with histologic measurements. A total of 40, day-old broiler chickens were randomly divided into 4 groups of 10 broilers and a coccidiosis model was used to induce IP. Three challenge groups received a mixture of different field strains and concentrations of Eimeria acervulina and Eimeria maxima at d 16, and 1 group operated as an uninfected control group. On d 20, 5 birds per group were orally administered the permeability marker iohexol at a dose of 64.7 mg/kg body weight and blood was taken 60 min after the oral gavage. On d 21 these 5 birds per group were euthanized. On d 21, 5 other birds per group were given iohexol where after blood was taken. These birds were euthanized on d 22. During necropsy, birds were scored for coccidiosis lesions and a duodenal segment was taken for histology. The Eimeria challenge had a significant impact on the villus length, crypt depth, villus-to-crypt ratio and CD3⁺ T-lymphocytes area percentage. Challenged birds had a significant higher concentration of serum iohexol on both sampling days, as compared to the uninfected controls. A significant correlation could be found between the serum iohexol concentration and the histologic parameters (villus length, crypt depth and villus-to-crypt ratio) on the first sampling day. This suggests that iohexol may be used as a gut permeability marker in broilers under Eimeria challenge.

Current experimental models, assessment and dietary modulations of intestinal permeability in broiler chickens

Maintaining and optimising the intestinal barrier (IB) function in poultry has important implications for the health and performance of the birds. As a key aspect of the IB, intestinal permeability (IP) is mainly controlled by complex junctional proteins called tight junction proteins (TJ) that link enterocytes together. The disruption of TJ is associated with increased gut leakage with possible subsequent implications for bacterial translocation, intestinal inflammation, compromised health and performance of the birds. Despite considerable data being available for other species, research on IP in broiler chickens and in general avian species is still an understudied topic. This paper reviews the available literature with a specific focus on IP in broiler chickens with consideration given to practical factors affecting the IP, current assessment methods, markers and nutritional modulation of IP. Several experimental models to induce gut leakage are discussed including pathogens, rye-based diets, feed deprivation and stress-inducing agents such as exogenous glucocorticoids and heat stress. Although various markers including fluorescein isothiocyanate dextran, expression of TJ and bacterial translocation have been widely utilized to study IP, recent studies have identified a number of excreta biomarkers to evaluate intestinal integrity, in particular non-invasive IP. Although the research on various nutrients and feed additives to potentially modulate IP is still at an early stage, the most promising outcomes are anticipated for probiotics, prebiotics, amino acids and those feed ingredients, nutrients and additives with anti-inflammatory properties. Considerable research gaps are identified for the mechanistic mode of action of various nutrients to influence IP under different experimental models. The modulation of IP through various strategies (i.e. nutritional manipulation of diet) may be regarded as a new frontier for disease prevention and improving the health and performance of poultry particularly in an antibiotic-free production system.

Urinary Excretion of Iohexol as a Permeability Marker in a Mouse Model of Intestinal Inflammation: Time Course, Performance and Welfare Considerations

Simple Summary

In mammals, different diseases are associated with intestinal changes that may cause an increase in gut permeability. Intestinal permeability tests allow the evaluation of intestinal damage in humans, veterinary patients and laboratory animal models. When used in mouse models, these tests require that animals are singly housed in metabolic cages with a wire-grid floor to collect urine samples. This raises welfare concerns. Iohexol meets several criteria for an ideal intestinal permeability marker and has recently been used in several species. Here, we examined the performance of an intestinal permeability test using iohexol administered by mouth and following excretion over 24 h in urine. As a model, we chose immunodeficient mice with intestinal inflammation induced by adoptive transfer of effector/memory T cells. We collected urine samples at seven time points to profile the urinary excretion of iohexol, in addition to intestinal tissue samples for histological assessment. We conclude that a 6 h cumulative urine sample may be sufficient to evaluate small intestinal permeability in this mouse model and increased urinary excretion of iohexol is correlated with increased severity of duodenitis. The welfare of mice housed in metabolic cages could be improved by reducing the cage periods from 24 to 6 h.

Abstract

Intestinal permeability (IP) tests are used to assess intestinal damage in patients and research models. The probe iohexol has shown advantages compared to ⁵¹Cr-EDTA or absorbable/nonabsorbable sugars. During IP tests, animals are housed in metabolic cages (MCs) to collect urine. We examined the performance of an iohexol IP test in mice. Rag1-/- (C57BL/6) mice of both sexes were divided into controls or treatment groups, the latter receiving injections of effector/memory T cells to induce intestinal inflammation. After two, four and five weeks (W), a single dose of iohexol was orally administered. Urine was collected seven times over 24 h in MCs. Iohexol concentration was measured by ELISA. Intestinal histological damage was scored in duodenal sections. In control and treated mice of both sexes, urinary excretion of iohexol peaked at 4 h. From W2 to W4/W5, urinary iohexol excretion increased in treated mice of both sexes, consistent with development of duodenitis in this model. Positive correlations were observed between the urinary excretion of iohexol in W4/W5 and the histological severity of duodenitis in treated male mice. We conclude that a 6 h cumulative urine sample appears sufficient to evaluate small IP to iohexol in this mouse model, improving animal welfare by reducing cage periods.

Prolonged exposure to high humidity and high temperature environment can aggravate influenza virus infection through intestinal flora and Nod/RIP2/NF-κB signaling pathway

Seasonal influenza is an acute viral infection caused by influenza virus, which is often prevalent in the summer and winter. The influenza virus can infect pigs and poultry. Some literature reports that the influenza virus has an outbreak in summer. The summer climate is characterized by a high humidity and high temperature environment, which is the same as many animal feeding and growing environments. We established a flu animal model under a high temperature and humidity environment during the day to observe the impact of high humidity and high temperature environment on the mice after contracting the influenza virus. Our results indicate that the intestinal flora of 16 s rDNA cultured in High humidity and high temperature environment changes, the intestinal mucosal permeability increases, the expression of pIgR, sIgA, and IgA in the intestinal mucosal immune system decreases, and the NLR immune recognition signaling pathway NOD1 is activated. The expression of related genes such as NOD2, NF-κB, and pIgR increases, which leads to the increase of related inflammatory factors in the vicinity of the intestines, aggravating local inflammation. High humidity and high temperature environment can cause the expression of inflammatory cytokines in the body to rise, causing Th17/Treg immune imbalance, inhibiting Treg maturation and differentiation, and increasing the expression of IL-2, IL-6, and other cytokines, while the expression of IFN-γ and IL-17A decreases. This condition worsens after infection with the influenza virus. Overall, our study found that High humidity and high temperature environment affect the intestinal flora and the body's immune status, thereby aggravating the status of influenza virus infection.