Effect of estrogen, hydralazine and ultraviolet ray on DNA methyltransferase-1 activity in patients with systemic lupus erythematosus.

Objective To explore the mechanism underlying the induction of systemic lupus erythematosus (SLE) by estrogen, hydralazine and ultraviolet irradiation. Methods Peripheral blood mononuclear cells (PBMCs) were harvested from 10 patients with SLE and 9 normal human controls, and cultured with or without the intervention with estrogen, hydralazine or ultraviolet irradiation. The DNA methyltransferase-1 (DNMT1) activity of PBMCs was quantified by using DNMT activity/inhibition assay kit. Results No statistical difference was observed in DNMT1 activity between patients with SLE and normal controls (0.36 ± 0.24 vs 0.46 ± 0.17, P ＞ 0.05). A significant decrease was noted in DNMT1 activity in PBMCs from patients with SLE after intervention with estrogen (0.32 ± 0.18 vs 0.46 ± 0.17, t = 1.725, P ＜ 0.05), hydralazine (0.33 ±0.13 vs 0.46 ± 0.17, t = 1.739, P ＜ 0.05) and ultraviolet irradiation (0.30 ± 0.14 vs 0.46 ± 0.17, t = 1.739,P ＜ 0.05 ) compared with that from normal human controls. The treatment with hydralazine also induced an attenuation of DNMT1 activity in PBMCs from normal human controls (0.38 ± 0.12 vs 0.46 ± 0.17, P＜ 0.05).Conclusion Estrogen, hydralazine and ultraviolet irradiation can inhibit the DNMT1 activity of SLE patients,indicating that they may induce the initiation of SLE by altering the activity of DNMT1. Key words: Lupus erythematosus, systemic;  Estrogens;  Hydralazine;  Ultraviolet rays