Effect of triiodothyronine on reactive oxygen species generation by leukocytes, indices of oxidative damage, and antioxidant reserve

We have examined the effect of short-term triiodothyronine (T₃) administration on reactive oxygen species (ROS) generation by leukocytes in 9 euthyroid subjects. At a dose of 60 μg/d orally for 7 days, T₃ induced a significant increase in ROS generation by mononuclear cells (MNCs) from 183 ± 102 mV at baseline to 313 ± 111 mV on the seventh day (P <. 02), and by polymorphonuclear leukocytes (PMNLs) from 195 ± 94 mV at baseline to 302 ± 104 mV on the seventh day (P <. 02). There was also a significant increase in meta-tyrosine (P <. 001) and ortho-tyrosine (P <. 001), known indices of oxidative damage to proteins and amino acids. However, there was no increase in plasma thiobarbituric acid-reactive substances (TBARS), an index of oxidative damage to lipids, and in the level of carbonylated proteins, a less sensitive index to assess protein oxidation. There was no decrease in the level of antioxidants such as α-tocopherol, vitamin A, β-carotene, lycopene, and lutein/zeaxanthin. The stimulatory effect on ROS generation may reflect a generalized increase in metabolic activity or may be a specific effect on NADPH oxidase in leukocyte membranes. The absence of a significant change in TBARS, carbonylated proteins, α-tocopherol, vitamin A, β- carotene, lycopene, and lutein/zeaxanthin may reflect the short duration of the increased Res load.