The production and distribution of IL-6 and TNF-a in subcutaneous adipose tissue and their correlation with serum concentrations in Welsh ponies with equine metabolic syndrome

Abstract

A main symptom of equine metabolic syndrome (EMS) in ponies is pathological obesity characterized by abnormal accumulation of fat deposits and inflammation. In this study, we analyzed the expression of two pro-inflammatory cytokines, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), in subcutaneous adipose tissue and the correlation with serum concentrations in peripheral blood of Welsh ponies. Based on clinical examination findings, the animals were divided into two groups: ponies affected with EMS (n = 8) and obese ponies (n = 8). The adipose tissue was examined using immunohistochemical analysis while concentrations IL-6 and TNF-a were measured using enzyme-linked immunosorbent assays (ELISAs). Additionally, histological characterization of the adipose tissue was performed. The results obtained showed that IL-6 expression in adipose tissue biopsies derived from animals with EMS was enhanced while TNF-α levels of both groups were comparable. Compared to the obese ponies, EMS animals also had significantly elevated levels of serum IL-6 and TNF-α. Histological analysis revealed macrophage infiltration and fibrosis in adipose tissue preparations from the EMS group. These data suggest that IL-6 may play a key role in the course of EMS in Welsh ponies. Our findings also demonstrated that analysis of pro-inflammatory cytokines levels in serum may serve as an additional tool for diagnosing EMS.

Keywords: equine metabolic syndrome; interleukin-6; leptin; subcutaneous adipose tissue; tumor necrosis factor-alpha.

Fig. 1. Histology and immunohistochemistry examination of adipose tissue collected from equine metabolic syndrome (EMS; group A; panels A, C, E, and G) and healthy (group B; panels B, D, F, and H) ponies. (A) Fibrotic changes associated with macrophage and lymphocyte infiltration were noted in samples from group A. (B) Adipose tissue in a normal histological section from group B. (C and D) Expression of tumor necrosis factor-alpha (TNF-α) in tissue sections from groups A and B, respectively. (E and F) Expression of interleukin-6 (IL-6) in tissue sections from groups A and B, respectively. (G) High infiltration of macrophages and lymphocytes in samples from group A. (H) No signs of inflammation in the sections from group B. 40× magnification, scale bar = 60 µm (A~H).

Fig. 2. The concentration of IL-6 in the serum from EMS and healthy ponies along with results of the statistical analysis (p < 0.05).

Fig. 3. The concentration of TNF-α in the serum from EMS and healthy ponies along with results of the statistical analysis (p < 0.05).

Fig. 4. The concentration of LEP in the serum from EMS and healthy ponies along with results of the statistical analysis (p < 0.05).