Abstract
BackgroundFeline hyperthyroidism, the most common endocrinopathy in older cats, provides a spontaneous model for human thyrotoxicosis. Human thyrotoxicosis is associated with redox unbalance, which may result in organ damage. The redox status of hyperthyroid cats is largely unknown. The aims of the present study were to compare the redox status of cats with hyperthyroidism with that of healthy cats and cats with chronic non-thyroidal illness.ResultsForty cats with untreated hyperthyroidism (group H), 45 chronically ill cats with non-thyroidal illness (group I), and 39 healthy cats (group C) were recruited for this observational cross-sectional study. All cats were screened for redox status markers. Determinable reactive oxygen metabolites (d-ROMs) were used as oxidative stress markers. Antioxidant status was determined using the OXY-Adsorbent test to quantify the plasma barrier to oxidation. The Oxidative Stress index (OSi) was calculated as the ratio of d-ROMs and OXY-Adsorbent test values. Data were compared by ANOVA with Tukey’s multiple comparisons post-hoc test. The dROMs of group H (193 ± 47 CarrU) were significantly higher (p < 0.001) than those of the healthy cats (103 ± 17 CarrU). The OXY-Adsorbent test results in group H (265 ± 68 μmol HClO/ml) were significantly lower than those in healthy cats (390 ± 83 μmol HClO/ml; p < 0.01) and chronically ill cats (306 ± 45 μmol HClO/ml, p < 0.05). Moreover, the Osi value in group H (0.8 ± 0.2 CarrU/μmol HClO/ml) was significantly higher (p < 0.001) than that of the healthy cats (0.3 ± 0.1 CarrU/μmol HClO/ml).ConclusionsAs described in humans with hyperthyroidism, feline hyperthyroidism is associated with redox unbalance. Free radical production is increased in hyperthyroid cats and their antioxidant depletion seems to be more severe than in cats with non-thyroidal illnesses. Our results support the rationale for a clinical trial investigating the potential positive effects of antioxidant supplementation to cats with hyperthyroidism.
Highlights
Feline hyperthyroidism, the most common endocrinopathy in older cats, provides a spontaneous model for human thyrotoxicosis
The cats were categorized as hyperthyroid, chronically ill or healthy according to their history, physical examination, results of complete blood biochemical profile, urinalysis, serum total thyroxine (TT4) concentration, thoracic radiographic findings, and abdominal and/
30 of the 154 serum samples stored for redox status assessment were discarded before analysis because of flocculation, defrosting or hemolysis, leaving complete data for 124 cats
Summary
The most common endocrinopathy in older cats, provides a spontaneous model for human thyrotoxicosis. Feline hyperthyroidism (FH) is the most common endocrinopathy in middle-aged and geriatric cats [1, 2]. Feline hyperthyroidism most often results from benign adenomatous nodules of the thyroid tissue, making it pathologically similar to Plummer’s disease (toxic nodular goitre) in humans. Pharmacotherapy with thyroid peroxidase inhibitors, so-called anti-thyroid drugs, is often the sole treatment option when radioiodine therapy is unavailable or when concurrent geriatric problems are likely to increase the risk of anesthesia-related complications of thyroidectomy [4]. Side-effects are a well-known complication in cats treated with anti-thyrotoxic agents [5, 6]
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