Abstract 11633: Phosphodiesterase-5 (PDE-5) Inhibitor, Tadalafil, Activates NO/Sirt1/PGC-1 Signaling And Attenuates Mitochondrial Dysfunction In Type 2 Diabetic Hearts

Abstract

Background: Enhanced nitric oxide (NO) production is known to activate Sirt1, which is a histone deacetylase that regulates peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) -a master regulator of mitochondrial biogenesis and co-activator of transcription factors impacting energy homeostasis. Since phosphodiesterase-5 (PDE-5) inhibitors are known to increase NO production, we hypothesized that chronic treatment with long-acting PDE-5 inhibitor, tadalafil (TAD) would activate NO/Sirt1/PGC-1α signaling and protect against metabolic stress-induced mitochondrial dysfunction in diabetic hearts.

Methods and Results: Adult male diabetic db/db mice (n=24/group) were randomized to receive DMSO (10%, 0.2 ml, i.p.) or TAD (1 mg/kg, i.p.) for 8 weeks. C57BLKS/J mice treated with DMSO (10%, 0.2ml, i.p.) served as non-diabetic controls. The hearts were excised and homogenized for Sirt1 activity analysis. Mitochondrial function was determined by measuring oxidative-phosphorylation (OXPHOS) in isolated mitochondria using substrates that donate electrons to the complexes of electron transport chain. The generation of reactive oxygen species (ROS) and susceptibility to calcium-induced membrane permeability transition (MPT) was studied. TAD-treated mice demonstrated increased cardiac Sirt1 activity as compared to diabetic controls (p<0.001, n=6/group). In addition, TAD treatment enhanced plasma NO levels, myocardial Sirt1 and PGC-1α expression in the diabetic hearts (n=6/group, p<0.05). OXPHOS with the complex I substrate, glutamate, was decreased by 50% in diabetic hearts as compared to the non-diabetic controls (222±28 vs 441±43 nAO/min/mg protein, n=6/group p<0.05). Treatment with TAD protected OXPHOS with an improved glutamate state 3 respiration rates (358±20 nAO/min/mg protein, n=6/group, p<0.05). TAD- treatment did not affect the susceptibility of MPT to calcium. The increased ROS production from complex I in diabetic mice was significantly decreased by TAD treatment (227± 80 vs 123± 15 n=6/group, p<0.05).

Conclusion: Activation of NO-induced Sirt1/PGC-1α signaling by chronic treatment with TAD improves mitochondrial respiratory function and attenuates ROS production in type 2 diabetic hearts.