Changes in Oxidative Status Biomarkers in Saliva and Serum in the Equine Gastric Ulcer Syndrome and Colic of Intestinal Aetiology: A Pilot Study

SIMPLE SUMMARY: Gastric ulcers and colic of intestinal aetiology (CIE) are highly prevalent diseases in domestic horses, with a negative impact on equine sport and breeding life. Therefore, the studies investigating possible biomarkers for their diagnosis or clarifying their pathophysiology are of high interest. Oxidative status changes have been reported in both diseases, but only in the blood. However, saliva may be a relevant source of oxidative status biomarkers not yet assessed in horses with interesting advantages, owing to its non-invasive collection. Hence, this study aimed to validate in both saliva and serum automated assays for the measurement of oxidative status biomarkers and assess them in horses suffering gastric ulcer diseases (squamous and/or glandular) and CIE, studying their possible relationship with their inflammatory and immunity status. It was found that horses with glandular mucosa ulcers showed higher levels of some antioxidant and oxidative biomarkers in saliva correlating with a marker of the immune system such as salivary adenosine deaminase. Horses suffering from CIE had increases in serum uric acid associated with their systemic inflammatory response and outcome of the disease. In conclusion, some oxidative status analytes can be automatically measured in horses’ saliva and serum and may potentially be assessed as biomarkers of gastric ulcers and CIE. ABSTRACT: Changes in the oxidative status of the blood of horses suffering from gastric ulcers and colic of intestinal aetiology (CIE) have been reported. However, saliva can also be a source of biomarkers of oxidative status. Therefore, this study aims to validate automated assays for the measurement of oxidative status biomarkers (ferric reducing ability of saliva/serum—FRAS/FRAP, cupric reducing antioxidant capacity—CUPRAC, the Trolox equivalent antioxidant capacity—TEAC, uric acid, and advanced oxidation protein products—AOPP) in the saliva and serum of horses, to assess their changes in the different ulcer gastric diseases (squamous—ESGD and glandular—EGGD) and CIE, and to evaluate their relationship with serum amyloid A (SAA), adenosine deaminase (ADA), and the systemic inflammatory response syndrome (SIRS) status. The assays showed a low imprecision and good linearity with enough sensitivity in both fluids. In EGGD, higher levels of FRAS, uric acid, and AOPP in saliva were observed compared to the healthy group, correlating with the salivary ADA levels. Horses with CIE showed increases in uric acid concentrations in serum associated with their SIRS status and outcome of the disease. In conclusion, analytes related to the oxidative status can be measured in the saliva and serum from horses by automated assays, and some of them can potentially be assessed as biomarkers in horses with gastric ulcers and CIE.