Decreased eNOS Protein Expression in Involuting and Propranolol-Treated Hemangiomas

Objective: To examine the location and degree of endothelial nitric oxide synthase (eNOS) protein expression in hemangioma growth, involution, and during propranolol therapy. Design: Cross-sectional study. Setting: University hospital. Patients: Pediatric patients with hemangiomas. Interventions: Fresh human hemangioma specimens at various stages of development were harvested. Effective propranolol therapy had been implemented in some patients. Quantitative assessment and localization of eNOS protein expression was performed on each specimen by Western blot analysis and immunohistochemical analysis, respectively. Results: Hemangiomas in a proliferative phase (group 1: n=4; mean [SD] age, 4.25 [2.06] months), an early involuting phase (group 2: n=6; 12.00 [1.64] months), and a late involuting phase (group 3: n=6; 23.30 [1.97] months) were harvested. The mean (SD) eNOS protein expression was 0.88 (0.41) in group 1, 0.26 (0.26) in group 2, and 0.15 (0.08) in group 3, respectively. A statistically significant decrease in eNOS protein expression was observed between proliferating and involuting hemangiomas (group 1 vs group 2 and group 3; P <=.01) but not between early and late phases of involution (P=.17). In a separate propranolol treatment group (n=7), the eNOS protein level was significantly lower than in age-matched controls (n=7; 0.08 [0.1] vs 0.45 [0.45]; P=.03). Immunohistochemical analysis demonstrated eNOS to be predominately in endothelial cells lining mature blood vessels. Conclusion: Expression of eNOS protein decreases during the hemangioma lifecycle. Propranolol may suppress hemangioma growth by inhibiting expression of eNOS protein and subsequent production of nitric oxide.