New strategies to reduce ischemia/reperfusion injury following lung allotransplantation by substitution of the NO/cGMP pathway

Background: Impairment of the NO/cGMP pathway accelerates ischemia/reperfus ion injury following lung transplantation (LTPL). Direct application of NO is not ideal because of its short half-life and toxic side effects. Tetrahy drobiopterin (BH4) is the essential coenzyme of the NO synthase. 8-Br-cGMP is a membrane permeable analogue of cGMP, second messenger of NO. We evalua ted the effect and several treatment modalities with these compounds on pos t-transplant lung ischemia/reperfusion injury in a large animal model. Methods: Unilateral left LTPL was performed in 25 weight matched outbred pi gs (all groups n = 5). Donor lungs were flushed with 1.5 1 cold LPD solutio n and preserved for 20 h at 1 degrees C. In group I and II recipients were treated with a bolus of BH4 (20 mg/kg) over 30 min, starting 15 min before reperfusion. In group II an additional continuous dose of BH4 (10 mg/kg) wa s given over the entire observation period. In group III 8-Br-cGMP (1 mg/kg ) was added to the flush solution and in group IV 8-Br-cGMP was given as co ntinuous infusion (0.2 mg/kg/h) over 5 h starting 15 min before reperfusion . Group V served as control. All donors (except group III) received 250 mu g PGE1 injected into the pulmonary artery prior to flush. One hour after re perfusion the recipient contralateral right pulmonary artery and bronchus w ere ligated to assess graft function only. Extravascular lung water index ( EVLWI) and hemodynamic parameters (PAP, PVR, CO) were assessed during a fiv e hour observation period. Lipid peroxidation (TBARS) and neutrophil migrat ion to the allograft (MPO activity) were measured at the end of the assessm ent. cGMP levels were determined in the pulmonary venous and arterial blood in all animals. Results: EVLWI (2 h after reperfusion), MPG, TBARS and cGMP at the end of t he assessment are summarized below. [GRAPHICS] No effect on pulmonary and systemic hemodynamic parameters with either trea tment could be detected. Conclusions: Our results show that substitution of the NO pathway by BH4 or 8-Br-cGMP respectively reduces post-transplant pulmonary edema, neutrophil migration, and lipid peroxidation in the allograft. Addition of 8-Br-cGMP to the flush solution is superior to PGE1. Based on pharmacologic considera tions of both substances and the presented results, administration of cGMP in the flush solution and BH4 during reperfusion seems to be very promising .