Redox status of biomarkers in serum of dogs with hypothyroidism and its treatment with levothyroxine sodium

Ling Zhu ¹ Jinge Han ² Halihaxi Bahetijiang ¹ Gang Liu ¹ John P Kastelic ³ Xueying Zhou ^1* Bo Han ^1*

• ¹ China Agricultural University, Beijing, China
• ² Tianjin Agricultural University, Tianjin, Tianjin Municipality, China
• ³ University of Calgary, Calgary, Alberta, Canada

Information regarding canine hypothyroidism in China remains limited and redox status in dogs with hypothyroidism is unclear in China. Therefore, the objective of this study was to evaluate the redox status of dogs with hypothyroidism and how it changed after levothyroxine replacement therapy. Ten healthy dogs and 10 dogs with hypothyroidism (control and treatment groups, respectively) from China Agricultural University Veterinary Teaching Hospital were used. Redox status was determined in all 20 dogs. Thyroid profiles thyroxine (T4), free thyroxine (fT4) and thyroid stimulating hormone (TSH) and biomarkers of oxidative stress including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-px) and malondialdehyde (MDA) were assessed on day 0 in all dogs and on days 14 and 45 post-levothyroxine sodium treatment in dogs with hypothyroidism. Dogs with hypothyroidism had decreased serum T4 and fT4 concentrations and increased serum TSH concentrations. Based on SOD, CAT, GSH-px, and MDA, dogs with hypothyroidism had oxidative stress. However, following treatment with levothyroxine sodium (0.02 mg/kg orally twice a day for 45 days), antioxidant status was improved, with increases in SOD (60.2 to 76.7 U/mL), CAT (105.9 to 115.5 mU/mL) and GSH-px (from 10.2 to 8.4 U/mL), plus a decrease in MDA from 8.2 to 6.8 μmol on days 0 and 14, respectively, and on day 45, subsequent increases to 83.3, 132.9, and 9.7 U/mL, plus a decrease in MDA to 4.4 μmol. In conclusion: Increased serum TSH and MDA concentrations, plus decreases in serum T4 and fT4 concentrations and decreases in SOD and CAT activities indicated there was oxidative stress in dogs with hypothyroidism. However, there were significant improvements in the redox status of biomarkers in serum of dogs with hypothyroidism after treatment with levothyroxine sodium (0.02 mg/kg twice daily) for 45 days.