ALTERATIONS IN PLASMA DIPEPTIDYL PEPTIDASE-IV ENZYME-ACTIVITY IN DEPRESSION AND SCHIZOPHRENIA - EFFECTS OF ANTIDEPRESSANTS AND ANTIPSYCHOTIC-DRUGS

Recently, our laboratory reported that the activity of dipeptidyl-pept idase IV (DPP IV) was significantly lower in the peripheral blood of m ajor depressed patients than in normal controls. The present study exa mines plasma DPP IV activity in 43 major depressed and 13 schizophreni c subjects versus 21 normal controls and the effects of antidepressant s and antipsychotic drugs on plasma DPP IV activity. DPP IV activity w as significantly lower in major depressed subjects than in normal cont rols and schizophrenic subjects. There was a trend towards higher DPP IV activity in schizophrenic patients than in normal controls. There w ere no signficant effects of antidepressants or neuroleptics on plasma DPP IV activity in depressed and schizophrenic patients, respectively . There were no significant relationships between plasma DPP IV activi ty and plasma cortisol or immune-inflammatory markers, such as serum i nterleukin-6 (IL-6) or soluble IL-2 receptor. A significant and positi ve correlation was found between plasma DPP IV and prolyl endopeptidas e (PEP) enzyme activity in the study group as a whole and in schizophr enic subjects. The results support the hypothesis that lower and highe r plasma DPP IV activities are trait markers of major depression and s chizophrenia, respectively. It is concluded that alterations in the en zyme activity of peptidases, such as DPP IV and PEP, play a role in th e pathophysiology of major depression and schizophrenia.