Antioxidant Status in Hyperthyroid Cats before and after Radioiodine Treatment

Abstract

Background: Reversible antioxidant depletion is found in hyperthyroid humans, and antioxidant depletion increases the risk of methimazole toxicosis in rats.Objectives: To determine whether abnormalities in concentrations of blood antioxidants or urinary isoprostanes were present in hyperthyroid cats, and were reversible after radioiodine treatment. To determine whether or not antioxidant abnormalities were associated with idiosyncratic methimazole toxicosis.Animals: Hyperthyroid cats presented for radioiodine treatment (n = 44) and healthy mature adult control cats (n = 37).Methods: Prospective, controlled, observational study. Red blood cell glutathione (GSH), plasma ascorbate (AA), plasma free retinol (vitamin A), a-tocopherol (vitamin E), and urinary free 8-isoprostanes in hyperthyroid cats were compared to healthy cats and to hyperthyroid cats 2 months after treatment.Results: Blood antioxidants were not significantly different in hyperthyroid cats (mean GSH 1.6 ± 0.3 mM; AA 12.8 ± 4.9 lM, and vitamin E, 25 ± 14 lg/mL) compared to controls (GSH 1.4 ± 0.4 mM; AA 15.0 ± 6.6 lM, and vitamin E, 25 ± 17 lg/mL). Urinary isoprostanes were increased in hyperthyroid cats (292 ± 211 pg/mg creatinine) compared to controls (169 ± 82 pg/mg; P = .006), particularly in hyperthyroid cats with a USG < 1.035. Plasma free vitamin A was higher in hyperthyroid cats (0.54 ± 0.28 lg/mL versus 0.38 ± 0.21 in controls; P = .007). Both abnormalities normalized after radioiodine treatment. No association was found between oxidative status and prior idiosyncratic methimazole toxicosis.Conclusion and Clinical Importance: Increased urinary isoprostane could reflect reversible renal oxidative stress induced by hyperthyroidism, and this requires additional evaluation.

Evaluation of Antioxidant Supplementation on Redox Unbalance in Hyperthyroid Cats Treated with Methimazole: A Blinded Randomized Controlled Trial

“…Although the link between MMI-SE and redox unbalance has been acknowledged in both humans and laboratory animal models [6,7], comparative studies in domestic species are scarce. Signalment, thyroid status, and hemato-biochemical values of cats of the present trial were consistent with previous data [13,16]. With respect to the OS induced by hyperthyroidism, our findings were consistent with previous studies both in veterinary and human medicine [2,4].…”

“…Inclusion criteria were total plasma thyroxine (tT4) concentrations > 54 nmol/L or 4.3 µg/dL, as previously described, and owner agreement to administer the treatments and to attend all the scheduled appointments during the study [4]. Exclusion criteria were concurrent systemic diseases, such as congestive heart failure, renal failure (IRIS Stage 3 or 4) [15], systemic neoplasia, chronic liver disease, immune-mediated disease, or systemic infection [16], suspected nutritional deficiencies, antioxidant supplementation within 3-months, and administration of iodine-restricted food or commercial diet enriched with patented antioxidant formula [4].…”

Feline Hyperthyroidism

“…Heinz bodies are a more common finding on evaluation of the blood film in hyperthyroid cats than in control cats. Depletion of antioxidants and excessive fat and protein catabolism has been proposed as the reason for Heinz body formation in hyperthyroid cats (Christopher, 1989;Branter et al, 2012). Depletion of antioxidants and excessive fat and protein catabolism has been proposed as the reason for Heinz body formation in hyperthyroid cats (Christopher, 1989;Branter et al, 2012).…”

Characterization of feline serum–cobalt binding

“…A prospective study, however, with samples collected specifically for %CB, rather than stored samples as used in this study, might allow discovery of a viable method to normalize %CB values for serum albumin concentrations. A prospective study, centered on diseases known to cause oxidative stress, and which is confirmed by an independent marker of oxidative stress, such as isoprostanes could also be useful to determine the diagnostic utility of SCB in cats.…”

“…Hence, analysis of altered cobalt binding by serum has potential as a screening test for increased tissue ischemia and serum free radicals in the clinical setting, beyond its more limited original role. Domestic cats are susceptible to developing a number of diseases that have been associated with tissue ischemia and free radical production, such as infectious, cerebrovascular, and thromboembolic diseases, obesity, hyperthyroidism, and ketoacidosis in diabetes mellitus . This led us to develop an SCB test for use with feline serum.…”