5-Methylcytosine content of DNA in blood, synovial mononuclear cells and synovial tissue from patients affected by autoimmune rheumatic diseases.

The percentage of 5-methylcytosine (m5Cyt) has been determined in peripheral blood, synovial mononuclear cells and synovial tissue from patients affected by various rheumatic autoimmune diseases. The determination was performed by reversed-phase high-performance liquid chromatography. Fifteen controls were compared to twenty-one patients affected by rheumatoid arthritis and to nine patients affected by systemic lupus erythematosus. The mean percentage of m5Cyt in normal individuals was significantly higher than in the rheumatoid arthritis and systemic lupus erythematosus patients. In addition, patients with active disease showed lower values than patients in remission. This finding is in agreement with the hypothesis that DNA hypomethylation may play a role in the pathogenesis of the autoimmune diseases, resulting in altered oncogene expression. Therapy with cyclosporin A led to a decrease in the percentage of m5Cyt in three rheumatoid arthritis patients, but a rebound was observed when the cyclosporin A was suspended. The percentage of m5Cyt in the DNA of synovial tissue from four rheumatoid arthritis patients and five patients with osteoarthritis was similar; this observation confirms that, in addition to disease-specific and disease activity-specific variations, the percentage of m5Cyt may also show tissue-specific variations.