Abstract P321: Clozapine-induced Hypertension: Role of the Dopamine Type 4 Receptor (D4R) in Human Renal Proximal Tubule Cells (RPTC)

Abstract

Clozapine (CLZ), a potent D 4 R antagonist that is an effective antipsychotic drug for the treatment of schizophrenia, is associated with hypertension. The hypertensive side effect of CLZ may be through inhibition of the D 4 R because germline deletion of D 4 R in mice causes hypertension. The hypertension caused by germline deletion of D 4 R may, in part, be due to increased renal expression of the angiotensin type 1 receptor (AT 1 R) and renal expression of sodium exchangers, transporters, and pumps, e.g., NHE3, NKCC2, NCC, and Na + K + /ATPase, α subunit. CLZ administered subcutaneously (20mg/kg/day/x3 days, n=5) in mice induced hypertension, shifted the pressure-natriuresis plot to the right, and increased the renal expressions of NCC and Na + K + /ATPase, α subunit, relative to vehicle-treated mice (n=5). Activation of D 4 R decreased AT 1 R expression and Na + K + /ATPase activity in rat renal proximal tubule cells (RPTCs). Therefore, we studied two groups: subjects 18 to 75 years old with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder treated with CLZ for >2 months (CLZ, N=32) and untreated healthy controls ( HC , N=20) without psychiatric illness. There were no significant differences in blood pressure (BP) between the two groups since more than half of the CLZ participants received antihypertensive medication. We studied RPTCs cultured from the participant’s urine (CLZ, N=18; HC, N=9) and treated those cells with 100 nM CLZ. CLZ decreased D 4 R expression in both HC and CLZ groups ( HC , VEH 1.04±0.17 vs CLZ 0.73±0.09, n=9, paired t-test, P<0.05; CLZ, VEH 1.02±0.09 vs CLZ 0.75±0.06, n=16, paired t-test, P<0.01). CLZ also increased reactive oxygen species (Rosstar550 assay) in the HC but not CLZ-treated group ( HC , VEH 0.92±0.07 vs CLZ 1.02±0.09, n=8, paired t-test , P<0.05; CLZ VEH 1.09±0.18 vs CLZ 1.07±0.18, n=14). The density of plasma membrane AT 1 R tended to be higher in CLZ-treated hypertensive (CLX HP) than the CLZ-treated normotensive participants (CLZ NP): ( HC , 0.28±0.08 n=8; CLZ NP, 0.10±0.02 n=4; CLZ HP, 0.81±0.31 n=7). Thus, CLZ may induce hypertension through a D 4 R/AT 1 R-mediated mechanism similar to that reported in D 4 R knockout mice. Additional studies will determine if CLZ increases sodium transport in human RPTCs.