Oxidative stress biomarkers in hypothyroid, non thyroid illness and euthyroid dogs

Abstract There are only a few numbers of published reports available on oxidative stress parameters in hypothyroidism and many of which are in the field of human medicine. Studies on hypothyroidism in dogs lack an assessment of oxidative stress and some are vague and inconclusive. So, the current study was formulated primarily to address variations in chief antioxidant parameters in dogs with hypothyroidism, non-thyroid illness and euthyroidism. Secondly, magnitude of oxidative stress was measured in hypothyroid dogs prior to and during the course of levothyroxine therapy, which were compared statistically. Evaluation of thyroid profile (TT4, fT4 and cTSH) was carried out prior to the assessment of oxidative stress biomarkers such as, serum malondialdehyde (MDA), superoxide dismutase (SOD), reduced glutathione (GSH) and catalase. A total of 45 dogs were employed in the study, that includes 19 dogs with hypothyroidism, 11 dogs with non-thyroid illness and 15 dogs with euthyroidism. These dogs were brought either to the dermatological unit or the immunization unit. Dogs were divided into three groups: group 1 represented hypothyroidism (low fT4 or low TT4 and high cTSH); group 2 represented non-thyroid disease (low or normal TT4 and low cTSH i.e., inconclusive levels of thyroid hormones); and group 3 represented dogs with normal thyroid levels (euthyroid dogs). Descriptive statistics and normality plots were carried out using SPSS software version 21. Assuming that the variances were unequal, P values were calculated and compared by one-way ANOVA, post hoc multiple comparison analysis using the Games-Howell test. The mean thyroid hormone levels of hypothyroid dogs before (Day 0) and after (Day 60) treatment was significantly different (P<0.05). Hypothyroid dogs (group 1) displayed significantly lower mean fT4 levels (0.56±0.07) and higher mean cTSH levels (8.14±1.17) when compared to other groups. The mean values of serum biochemical parameters showed significant differences among groups (P<0.01). Various biomarkers showed a significant alteration viz., there was a significant reduction in catalase, SOD, GSH and increase in MDA in hypothyroid dogs when compared with euthyroid dogs. However, following therapy for 60 days, catalase, SOD and GSH levels elevated and MDA level reduced significantly and reached nearly to that of euthyroid dogs. Further, there was no significant difference between NTI and euthyroid dogs which demonstrated the antioxidant defence against oxidative stress in hypothyroid dogs. As an outcome, antioxidant measures and serum biochemical tests can be employed as a diagnostic tool to rule out oxidative stress in hypothyroid dogs.