Lymphocytes of psoriatic patients have higher level of DNA damage. Effect of treatment with coal tar

We applied the modified comet assay for detection of strand breaks and oxid ised bases in lymphocytes of psoriatic patients before and after the treatm ent with therapeutic coal tar. Ten psoriatic patients were treated for 14-2 1 days. Lymphocytes of psoriatic patients taken before the treatment had si gnificantly higher levels of DNA strand breaks compared with matched contro ls. Moreover, after the treatment, DNA breaks as well as oxidised bases in lymphocytes were significantly elevated compared with levels of DNA damage before the treatment. The frequencies of chromosomal aberrations in the sam e group of patients were also higher after the treatment compared with no t reatment. Patients who smoke had more DNA damage than non-smokers; this eff ect seems stronger after the treatment with coal tar. Numbers of strand bre aks in all patients correlated with range of disease (size of damaged skin) , both before (r=0.677; p=0.035) and after the treatment (r=0.697; p=0.025) .