Associação entre síndrome metabólica e estresse oxidativo/nitrosativo lamelar em equinos submetidos a dieta rica em carboidratos não estruturais

Abstract

Oxidative stress occurs when there is an imbalance between generation and removal of reactive oxygen species in metabolic processes, and its occurrence has already been documented in septic laminitis. The aim of this study was to evaluate oxidative stress on hoof blades and its relationship with clinical and laboratory alterations observed in Mangalarga Marchador horses submitted to a high calorie diet. Biological material and data from a previous experiment were used, in which 9 Mangalarga Marchador horses had an increase in weight and adiposity induced for 5 months. During this period, body morphometric and ultrasound measurements of subcutaneous fat, blood collections, dynamic low-dose oral glucose test, hooves biopsies and latero-medial radiographs were performed. Chapter 1 consists of a brief review of equine metabolic syndrome (EMS) causes and diagnostic methods. Chapter 2 describes the study of lamellar oxidative stress with immunostaining using superoxide dismutase 2 (SOD2) and 3-nitrotyrosine (NIT). Of the 9 animals, 4 had staining for 3-nitrotyrosine in the sample obtained at the end of the experimental period. The findings are unprecedented evidence for the occurrence of lamellar oxidative stress in horses in the absence of septic laminitis. The animals were then divided into two groups - NIT + (with nitrotyrosine staining) and NIT- (without nitrotyrosine staining) for the evaluations of the later chapters. In chapter 3, these groups were compared regarding body morphometric measurements and analytes obtained from blood collections (lipids, lipoproteins, fructosamine, IGF-1, fasting glucose and insulin), and results of dynamic low-dose oral glucose tests. In this chapter, proxies G: I, MIRG, HOMA-IR, RISQI and QUICKI were also calculated, and the IGF-1 correlation test was performed with the studied variables. The animals in the NIT + group showed lower height at the withers and developed a more pronounced increase in adiposity, indicators of insulin dysregulation (DI) and delipidemia. The results suggest that lamellar oxidative stress discriminated the animals most susceptible to metabolic and morphometric changes that could culminate in EMS development. IGF-1 levels correlated with insulin dysregulation and dyslipidemia indicators, corroborating the hypothesis that this hormone acts in EMS. In chapter 4, the lamellar histological parameters and radiographic data of hooves of the groups NIT + and NIT- were evaluated. Most pronounced changes in the hoof-phalanx relationship and in the epidermal lamina length in NIT + were observed. Thus, it can be concluded that the lamellar oxidative stress of these animals results from a greater propensity to the development of EMS associated laminitis. This study provides pioneering evidence that lamellar oxidative stress, identified by 3-nitrotyrosine labeling, is an important factor in the development of endocrinopathic laminitis in horses with EMS, and have potential to be a marker to identify susceptible animals, even before clinical signs presentation.