Effect of training and feeding on saliva concentrations of cartilage oligomeric matrix protein neo-epitope (COMP664) and neuropeptide Substance P in horses

Abstract: Osteoarthritis (OA) is a low-grade inflammatory disease associated with subsequent lameness and chronic joint pain. Lameness caused by degenerative joint disorders is perceived as one of the most common clinical problems for the equine athlete, advocating the severity of OA as a welfare and clinical issue. Despite an incomplete understanding around onset of the disease and multifactorial aetiology, consensus prevails regarding progression of disease through intensive and repeated loading during training. To this point, diagnostic tools have been inadequate in early detection of reversible biochemical changes within the joint, consequently leading to a late definite diagnosis. Research on equine OA biomarkers have identified promising diagnostic prospects in this field. Aim: This study aimed to quantify and document the change in saliva concentration of cartilage oligomeric matrix protein neo-epitope OA specific biomarker COMP664 and neuropeptide Substance P in response to exercise. The influence of feeding and training intensity was also investigated in these horses. The objective was to study the acute and delayed peaks in saliva biomarker con-centration, previously described by others to evaluate the impact of exercise induced load/overload in the joints. The influence of age and presumed OA burden of the joints in the individual horses was also investigated. The results from this study will contribute to develop current knowledge on the subject further guiding the construction of a larger study aiming to enable the interpretation of normal and deleterious responses in healthy joints and distinguish these from pathological responses in diseased joints. Method: The quantification of biomarkers was carried out using saliva as sampling material. The saliva was sampled from two different cohorts. Cohort 1 included sampling in conjunction with feeding in research horses owned by the university (N=5) and privately owned horses (N=2) to interpret the influence of feeding on biomarkers conducting the following training study. Cohort 2 included sampling in conjunction to a short-term training study (before, during and 2 hours after training) in privately owned horses (N=6). A competitive ELISA was used to determine the levels of COMP664 and Substance P concentrations in saliva. Heart rate and speed measurements were recorded during cohort 2 accounting for the effect of training intensity on biomarker levels. Results: Cohort 1: results obtained from the feeding study showed individual fluctuating differences in both biomarkers, however no significant changes were observed. Cohort 2: results obtained from the short-term training program showed an acute increase of COMP664 concentration in saliva at T2 followed by a delayed peak observed after training between T6-T8, however the data was not significantly different. The amplitude, magnitude and time point of these peaks variates when afterwards dividing the horses into young with no lameness history and old horses with known history of lameness and joint treatment. This was done with the hypothesis that the young horses had a healthy joint status and the older horses a presumable OA burden. The concentration of Substance P showed a similar pattern as COMP664 in response to training. Pulse measurements: training intensity measured by pulse and speed was interpreted as equal between horses, providing comparable results. Training intensity is increased during the acute peak of biomarkers but not the delayed. Conclusion: The data presented in this pilot study show an acute concentration peak of biomarkers associated with initiated training followed by an indicated delayed peak with different onset in time depending on the age and presumable joint health status. The different patterns of these peaks suggest the use when evaluating impact of training and early disease changes. This contributes with knowledge guiding future research to further investigate and categorize biomarker response to exercise into physiological and pathological.