Chronic treatment with an oral rho-kinase inhibitor restores erectile function by suppressing corporal apoptosis in diabetic rats.

Introduction: It has been suggested that the up-regulation of the contractile RhoA/Rho-kinase (ROCK) signaling pathway is one of the important mechanisms for diabetes-associated erectile dysfunction (ED). However, the exact role of RhoA/ROCK signaling in the pathogenesis of diabetes-related ED has not been fully delineated.

Aim: To determine whether the RhoA/ROCK pathway is involved in the regulation of corporal apoptosis and whether administration of insulin or fasudil, a specific ROCK inhibitor, could ameliorate ED in streptozotocin-induced diabetic rats.

Main Outcome Measures: At 16 weeks after diabetes induction, erectile function was assessed by cavernous nerve stimulation. Penile tissue was assessed for apoptosis with terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate (dUTP) nick end labeling assay. Expression of myosin phosphatase target subunit 1 (MYPT1), protein kinase B (Akt), and phospho-endothelial nitric oxide synthase (eNOS) were evaluated by Western blot. Immunohistochemical study was carried out for smooth muscle alpha-actin, B-cell leukemia/lymphoma 2 (Bcl-2), and Bcl-2-associated X Protein (Bax). Activity of caspase-3 and phosphatase and tensin homolog deleted on chromosome ten (PTEN) was also determined.

Methods: Male Sprague-Dawley rats (8 weeks old) were randomly divided into four groups: age-matched controls, diabetic controls, and diabetic rats treated with insulin (10 U/day, subcutaneous injection) or fasudil (30 mg/kg/day, oral) for the last 4 weeks of the 16 weeks after diabetes induction.

Results: Diabetic rats showed impairment of erectile function, increased MYPT1 phosphorylation, and corporal apoptosis. Expression of phospho-Akt, phospho-eNOS, and Bcl-2 were decreased, whereas activity of PTEN and caspase-3 and expression of Bax were increased. Treatment with fasudil normalized these molecular and histologic alterations, and restored erectile function. Insulin treatment showed similar effects to those of fasudil, however, the effects were smaller than fasudil.

Conclusions: This study indicates that up-regulation of the penile RhoA/ROCK pathway in diabetic rats enhances corporal apoptosis via the PTEN/Akt pathway resulting in ED, which could be prevented by chronic treatment with fasudil.