L-arginine polymer mediated inhibition of graft coronary artery disease after cardiac transplantation

Background. Nitric oxide (NO) limits the development of graft coronary artery disease (GCAD) in transplanted hearts. We hypothesized that L-arginine polymers administered to cardiac allografts ex vivo would translocate across vascular cellular membranes, upregulate inducible nitric oxide synthase (iNOS) production of NO, and inhibit the development of GCAD. Methods. Three groups of PVG rat donor hearts were incubated with either 0.8 ml phosphate-buffered saline, (PBS, n=12) or 50 μM L-arginine polymer solutions of length five (R5, n=12) or nine (R9, n=12) prior to heterotopic transplantation into ACI recipients. Graft vessels were scored at POD 60 and 90 for percentage luminal narrowing (%LN), intima to media ratio (I/M), and percentage affected vessels (%AV). Translocation efficiency was determined by treatment with biotinylated polymers. NO production of treated aortic segments was determined in vitro by Griess reaction. Results. Translocation efficiencies were 89±19% (R9), 7±10% (R5), and 0±0% PBS (ANOVA, P<0.001) which corresponded to NO production in treated aortic segments of 0.175±0.17 (R9), 0.120±0.006 (R5), and 0.135±0.035 μM/mg (PBS), (ANOVA, P=0.002). GCAD scores at POD 60 were: %LN: 3.2±3.8% (R9), 12.6±6.7% (R5), 11.3±4.2% (PBS) (ANOVA, P=0.025); I/M: 0.03±0.04 (R9), 0.13±0.07 (R5), 0.12±0.05 (PBS) (ANOVA, P=0.037); %AV: 7±7% (R9), 19±7%(R5), 22±9%(PBS) (ANOVA, P=0.021). Reduction of GCAD parameters was maintained at POD 90. Conclusion. R9 efficiently translocated across cytoplasmic membranes, enhanced vascular NO production, and decreased neointimal hyperplasia. This ex vivo treatment may have a therapeutic role in preventing GCAD.