Oxygen Scavengers in Simple Bone Cysts

Abstract

Simple bone cyst is a fluid-filled, cystic lesion that occurs in the metaphysis of the long bones of children and adolescents. The chemical characteristics of the cyst fluid of the simple bone cyst are similar to those of serum. The existence of the cyst fluid itself may be an obstacle to cyst healing, and, in part, this may be because the cyst fluid contains bone destructive factors. Oxygen-free radicals, which are cytotoxic and cause connective tissue damage, are known to be generated under ischemic conditions. Blockage to the drainage of interstitial fluid within the metaphysis has been suggested as the possible primary cause of simple bone cyst, thus causing an ischemic state in which free radicals are generated. The precise measurement of free radical levels is difficult to obtain because of their extremely short half-lives. High levels of oxygen-free radicals induce high levels of oxygen scavengers locally to protect cells from the harmful effects of the free radicals. Therefore, the activity of the oxygen scavengers, superoxide dismutase and catalase, was measured in the cyst fluid of 9 cases of simple bone cyst as an indicator of high oxygen-free radical content in the cyst. Serum from the patients with simple bone cyst and joint fluid from patients with osteoarthritis were used for comparison with the intracystic levels of oxygen scavengers. Superoxide dismutase activity was directly measured at room temperature using an electron spin resonance spin-trapping technique with 5,5′ -dimethyl- 1-pyrroline-N-oxide as a trapping agent. Catalase was measured with a spectrophotometer. Superoxide dismutase activity in cyst fluid was 15-fold greater than in the patients' serum, and catalase activity was 5.5-fold higher. These values were also significantly higher than those in joint fluid from osteoarthritis patients. These results suggest that high activity of oxygen radicals may exist in cyst fluid of simple bone cyst and may contribute to bone destruction.