Levels of manganese superoxide dismutase activity are increased in tears from patients with thyroid-associated ophthalmopathy

Abstract

Oxygen free radicals and their derivatives are second messengers of various traumatic, inflammatory and autoimmune processes and play a role in the tissue damage of autoimmune disorders. As free radicals are produced in the course of tissue inflammation scavenger enzymes such as superoxide dismutase (SOD), are activated. The lacrimal gland may play a role in the autoimmune reactions of thyroid-associated ophthalmopathy (TAO). The tears, which are produced mainly by the lacrimal gland, contain specific IgA class antibodies and oxygen free radical scavenger enzymes, in particular SOD, and may provide information about the orbital inflammatory process. The authors have measured total and manganese SOD activities in tears from patients with TAO, and control patients and subjects, correlating with clinical parameters of the ophthalmopathy. Levels of total SOD activity were increased in 40% of patients with TAO, 35.7% with Graves' hyperthyroidism without ophthalmopathy, 38.5% with other ocular disorders, 45.5% of patients with other thyroid disorders and in 5.6% of normal subjects. The specificity of Mn SOD measurement was much better; levels of Mn SOD activity were increased in 52.6% of patients with TAO, but in only 23.1% of those with Graves' hyperthyroidism without ophthalmopathy and 12.5% of patients with other orbital disorders. The possible relationship between SOD levels and parameters of the immune reaction against eye muscle and lacrimal autoantigens is discussed. Measurement of Mn SOD levels in tears may provide a simple clinical test for eye disease activity.

Key Words:

• Superoxide dismutase
• Graves' disease
• thyroid-associated ophthalmopathy
• lacrimal secretions (tears)
• eye muscle
• oxygen free radicals