Dexfenfluramine as a mitogen signals through the formation of superoxide anion

Abstract

ABSTRACT Fenfluramine and its isomer, dexfenfluramine (d‐Fen), have been used extensively as appetite suppressants and have been associated with pulmonary hypertension and cardiac valvular insufficiency. The findings have been linked to alteration in levels of serotonin (5‐HT), but these agents also directly influence K + channels and intracellular Ca 2+ . Our study shows for the first time that d‐Fen also produces a mitogenic effect on fibroblasts in culture. The mitogenic effect occurs at 10–100‐µM concentrations; includes both cellular hyperplasia (assayed by [ 3 H]‐thymidine incorporation and cell counts) and hypertrophy (assayed by [ 3 H]‐leucine incorporation and Coulter counter analysis); and is initiated by cell signaling through a rapid elevation of superoxide, protein tyrosine phosphorylation, and ERK1/ERK2 MAP kinase activation, similar to the cellular effects produced by 5‐HT. The enhanced [ 3 H]‐thymidine incorporation and ERK1/ERK2 MAP kinase activation are blocked by an antioxidant (Tiron), a NADPH oxidase inhibitor (DPI), a tyrosine phosphorylation inhibitor (tyrphostin), and a MAP kinase kinase inhibitor (PD 98059), which suggests that reactive oxygen species and the MAP kinase pathway play critical roles in the d‐Fen‐induced mitogenesis. Blockage of the effect by 5‐HT transporter inhibitors and 5‐HT receptor antagonists suggests that d‐Fen shares a common cellular ligand and signaling pathway with 5‐HT.