The role of redox signaling in cardiac hypertrophy induced by experimental hyperthyroidism

Abstract

This study was conducted to test whether oxidative stress activates the intracellular protein kinase B (AKT1) signaling pathway, which culminates with cardiac hypertrophy in experimental hyperthyroidism. Male Wistar rats were divided into four groups: control, vitamin E, thyroxine (T(4)), and T(4)+vitamin E. Hyperthyroidism was induced by T(4) administration (12 mg/l in drinking water for 28 days). Vitamin E treatment was given during the same period via s.c. injections (20 mg/kg per day). Morphometric and hemodynamic parameters were evaluated at the end of the 4-week treatment period. Protein oxidation, redox state (reduced glutathione, GSH/glutathione dissulfide, GSSG), vitamin C, total radical-trapping antioxidant potential (TRAP), hydrogen peroxide (H2O2), and nitric oxide metabolites (NO(X)) were measured in heart homogenates. The p-AKT1/AKT1 ratio, p-glycogen-synthase kinase (GSK)3B/GSK3B ratio, FOS, and JUN myocardial protein expression were also quantified by western blot after 4 weeks. Increases in biochemical parameters, such as protein oxidation (41%), H2O2 (62%), and NO(X) (218%), and increase in the left ventricular end-diastolic pressure were observed in the T(4) group. T(4) treatment also caused a decrease in GSH/GSSG ratio (83%), vitamin C (34%), and TRAP (55%). These alterations were attenuated by vitamin E administration to the hyperthyroid rats. Expression of p-AKT1/AKT1, p-GSK3B/GSK3B, FOS, and JUN were elevated in the T(4) group (by 69, 37, 130, and 33% respectively), whereas vitamin E administration promoted a significant reduction in their expression. These results indicate that oxidative stress plays an important role in cardiac hypertrophy, and suggest redox activation of AKT1 and JUN/FOS signaling pathways with H2O2 acting as a possible intracellular mediator in this adaptive response to experimental hyperthyroidism.