Effect of hyonate® administration on pulmonary function and indices of oxidative stress in COPD horses in clinical remission at rest and after exercise

Pulmonary function tests, bronchoalveolar lavages, and venous blood samplings were performed 24 hours before and one hour after a standardized strenuous treadmill exercise test on six horses suffering from chronic obstructive pulmonary disease (COPD) in clinical remission. Pulmonary function test consisted of the measurement of the mechanics of breathing and arterial blood gases analyses. During the exercise tests, heart and respiratory rates, and venous plasma lactate, pH and packed cell volume were controlled. Venous blood was analyzed for some markers of the oxidative stress, i.e., hemolysate glutathione redox ratio and oxidized glutathione, and plasma uric acid. BAL was analyzed for cell cytology as well as for markers of oxidative stress, i.e., glutathione redox ratio, and isoprostanes concentration. The procedure was repeated twice, i.e., before and after two IV injections of 40mg hyaluronate administered at seven day intervals. The results were compared to assess a possible influence of the treatment on the pulmonary and systemic inflammatory and/or oxidative status of these horses. Hyaluronate did not influence the pulmonary function test or the physiological parameters recorded during exercise. There was a decrease in the percentage of BAL neutrophils after the treatment, suggesting a possible antiinflammatory effect at the pulmonary level. As well, the concentration of isoprostanes in the pulmonary epithelium lining fluid was significantly lower after the treatment, which might be either a consequence of the decrease of the BAL neutrophils, or related to a possible antioxidant effect of the treatment. Lastly, the exercise-induced increase in plasma uric acid was significantly less marked after the treatment, which could be due to a systemic antioxidant effect of the hyaluronate. In conclusion, this preliminary study brings some evidence that hyaluronate could have some antiinflammatory and antioxidant effects at the pulmonary - and systemic - level in COPD horses in remission. However, it does not help to understand the possible mechanisms underlying these observations. Further studies are now necessary to better understand its action, to assess the effect of the product on the pulmonary function of horses suffering from other respiratory problems as well as to assess the efficiency of other ways of administration, i.e., nebulization.