Hydrogen peroxide generation by monoamine oxidases in rat white adipocytes: role on cAMP production

In rat, white adipocytes monoamine oxidases (EC 1.4.3.4.) generate hydrogen peroxide (H2O2). Recent studies suggested that, in addition to its toxic f eatures, H2O2 may behave as a cell second messenger. In the present study, using fluorimetric and chemiluminescence (CL) assays, we showed that tyrami ne degradation by monoamine oxidases in intact adipocytes resulted in the c oncentration-dependent generation of H2O2. In addition, we found that, in t he presence of low tyramine concentrations, forskolin-dependent cAMP produc tion was significantly increased as compared to that of the control and thi s increase was prevented by the monoamine oxidase ;inhibitor pargyline or b y the H2O2 trapping system homovanillic acid-peroxidase. Finally, we demons trated that tyramine degradation by monoamine oxidases increased the abilit y of isoproterenol to induce cell lipolysis. Taken together, these data sug gest that H2O2 produced during substrate degradation by monoamine oxidases may participate in the regulation of adipocyte metabolism. (C) 2000 Elsevie r Science B.V. All rights reserved.