Oral psoralen with UV-A therapy releases circulating growth factor(s) that stimulates cell proliferation

Background: The mechanism by which oral psoralen with UV-A (PUVA) stimulates melanocyte proliferation in vitiligo is unknown. This study was conducted to examine the hypothesis that it does so by stimulating the release of growth factors that stimulate melanocyte proliferation. Design: We examined the effect of serum samples obtained from patients with vitiligo before and following 2 and 4 months of PUVA therapy, and from non-PUVA-treated patients with vitiligo and normal individuals on the growth of melanocytes in vitro. Setting: Outpatient clinic in referral center. Patients: The study was conducted on serum samples obtained from 18 patients with vitiligo, 8 of whom were treated with PUVA, and from 10 normal individuals. Intervention: Treatment with PUVA. Main Outcome Measure: Ability of serum samples to stimulate the growth of melanocytes in culture. Results: Proliferation of melanocytes in serum collected after 4 months of PUVA therapy was on the average 3-fold greater than that in serum samples collected from the same patients prior to therapy with PUVA. This circulating growth factor was absent in serum samples of non-PUVA-treated patients with vitiligo and normal individuals. The effect was nonspecific, as it also stimulated the proliferation of fibroblasts. Conclusions: These findings suggest that PUVA treatment results in the release into the circulation of growth factor(s) that can stimulate a proliferation of melanocytes and of other cells. This could account for the repigmentation of vitiligo by PUVA treatment. As the growth factor(s) also stimulated the growth of other cells, it could also explain the thickening of the epidermis that occurs following exposure to UV light.