Methane supplementation improves graft function in experimental heart transplantation

Abstract

Maintenance of cell viability during cold storage is a key issue in organ transplantation. Methane (CH4) bioactivity has recently been recognized in ischemia/reperfusion conditions; we therefore hypothesized that cold storage in CH4-enriched preservation solution can provide an increased defense against organ dysfunction during experimental heart transplantation (HTX). The hearts of donor Lewis rats were stored for 60 minutes in cold histidine-tryptophan-ketoglutarate (Custodiol [CS]) or CH4-saturated CS solution (CS-CH4) (n = 12 each). Standard heterotopic HTX was performed, and 60 minutes later, the left ventricular (LV) pressure-volume relationships LV systolic pressure (LVSP), systolic pressure increment (dP/dtmax), diastolic pressure decrement, and coronary blood flow (CBF) were measured. Tissue samples were taken to detect proinflammatory parameters, structural damage (by light microscopy), endoplasmic reticulum (ER) stress, and apoptosis markers (CCAAT/enhancer binding protein [C/EBP] homologous protein, GRP78, glycogen synthase kinase-3β, very low-density lipoprotein receptor, caspase 3 and 9, B-cell lymphoma 2, and bcl-2-like protein 4), whereas mitochondrial functional changes were analyzed by high-resolution respirometry. LVSP and dP/dtmax increased significantly at the largest pre-load volumes in CS-CH4 grafts as compared with the CS group (114.5 ± 16.6 mmHg vs 82.8 ± 4.6 mmHg and 3,133 ± 430 mmHg/s vs 1,739 ± 169 mmHg/s, respectively); the diastolic function and CBF (2.4 ± 0.4 ml/min/g vs 1.3 ± 0.3 ml/min/g) also improved. Mitochondrial oxidative phosphorylation capacity was more preserved (58.5 ± 9.4 pmol/s/ml vs 27.7 ± 6.6 pmol/s/ml), and cytochrome c release was reduced in CS-CH4 storage. Signs of HTX-caused myocardial damage, level of ER stress, and the transcription of proapoptotic proteins were significantly lower in CS-CH4 grafts. The addition of CH4 during 1 hour of cold storage improved early in vitro graft function and reduced mitochondrial dysfunction and activation of inflammation. Evidence shows that CH4 reduced ER stress-linked proapoptotic signaling.