Defining the minimally effective dose and schedule for parenteral hydrogen sulfide: long-term benefits in a rat model of hindlimb ischemia

BACKGROUND Peripheral arterial disease (PAD) affects millions of Americans and leads to critical limb ischemia (CLI) in the most severe cases. Investigators have demonstrated the utility of hydrogen sulfide for restoring perfusion in rodent models of chronic ischemia. We sought to determine the minimum effective dose (MED) of sulfide necessary to restore perfusion in the rat hindlimb, to assess the persistence of limb perfusion after cessation of treatment, and to compare perfusion measurements between laser doppler and ultrasound methods. METHODS In 3 separate experiments, sodium sulfide (1.0, 0.5, or 0.25 mg/kg twice daily for 14 days, 0.25 mg/kg twice daily for 7 days, 0.5 mg/kg once daily for 7 days, or 0.25 mg/kg twice daily for 3 days) or vehicle was administered after left femoral artery ligation and transection. Hindlimb perfusion was assessed by laser doppler flowmetry and contrast enhanced ultrasound over the duration of each study, and cellular proliferation and vascular density were assessed by immunohistochemical means in the initial experiment. RESULTS Intravenous sodium sulfide at 0.25, 0.5, or 1.0 mg/kg twice daily for 2 weeks significantly enhanced the recovery of blood flow to the ischemic hindlimb by 7 days. The enhancement of blood flow with 1.0 mg/kg dosing was coincident with an increase in cellular proliferation and vascular density in the ischemic tissue. In a final experiment, i.v. administration of sodium sulfide at 0.5 mg/kg once daily for 7 days or 0.25 mg/kg twice daily for 7 days significantly elevated blood flow and skeletal muscle perfusion in the ischemic hindlimb, whereas 0.25 mg/kg twice daily for 3 days had no effect. This enhancement of blood flow appeared long lived, as blood flow remained elevated 3 weeks after cessation of treatment. CONCLUSIONS These data, together with other published observations, demonstrate the efficacy of hydrogen sulfide in restoring perfusion to chronically ischemic tissue and establish a minimum efficacious dose in the rat hindlimb model.