INCREASED MONOAMINE-OXIDASE-A ACTIVITY IN THE EPIDERMIS OF PATIENTS WITH VITILIGO

Human keratinocytes under in vitro conditions synthesize norepinephrin e and epinephrine, whereas melanocytes lack this capacity, Keratinocyt es established from lesional and nonlesional skin of patients with vit iligo synthesized four and two times more norepinephrine, respectively , than controls. Epinephrine synthesis was similar in keratinocytes fr om uninvolved epidermis and controls, but cells from involved skin had 6.5-fold less epinephrine than controls, indicative of low phenylehta nolamine-N-methyl transferase (PNMT) activity, Similar results were ob tained in five patients with vitiligo who showed low epinephrine level s in involved epidermis, Both human keratinocytes and melanocytes expr essed significant levels of monoamine oxidase A (MAO-A) activities as shown using C-14-labelled 5-hydroxytryptamine as substrate and immunoh istochemical staining with mouse monoclonal antibody, MAO-A activities in the total epidermis of patients with vitiligo were increased five- to ten-fold compared with skin of type-matched controls, Similar incr eases in MAO-A activities were also found in both keratinocytes and me lanocytes established in vitro from vitiliginous epidermis, Based on t hese results, it can be concluded that defective catecholamine synthes is in the epidermis of patients with vitiligo leads to increased level s of norepinephrine with a concomitant increase in MAO-A activity.