Impact of Asymmetric Dimethylarginine on Coronary Physiology Early After Heart Transplantation

L-Arginine-Nitric Oxide-Asymmetric Dimethylarginine Pathway and the Coronary Circulation: Translation of Basic Science Results to Clinical Practice

By 1980, it was thought that we already knew most of the major mechanisms regulating vascular tone. However, after the somewhat serendipity discovery that endothelium is involved in mediation of relaxation to acetylcholine, a whole new world opened up and we had to rewrite our concept regarding vascular function and its regulation (not to mention many other fields). The new player was an endothelium derived relaxing factor, which molecular constitution has been identified to be nitric oxide (NO). This review summarizes the major molecular steps concerning how NO is synthetized from L-arginine. Also, the fate of L-arginine is described via the arginase and methylation pathways; both of them are affecting substantially the level and efficacy of NO. In vitro and in vivo effects of L-arginine are summarized and controversial clinical findings are discussed. On the basis of the use of methylated L-arginines, the vasomotor effects of endothelial NO released to agonists and increases in flow/wall shear stress (a major biological stimulus) is summarized. In this review the role of NO in the regulation of coronary vascular resistance, hence blood flow, is delineated and the somewhat questionable clinical use of NO donors is discussed. We made an attempt to summarize the biosynthesis, role, and molecular mechanisms of endogenously produced methylated L-arginine, asymmetric dimethylarginine (ADMA) in modulating vascular resistance, affecting the function of the heart. Additionally, the relationship between ADMA level and various cardiovascular diseases is described, such as atherosclerosis, coronary artery disease (CAD), ischemia/reperfusion injuries, and different types of coronary revascularization. A novel aspect of coronary vasomotor regulation is identified in which the pericardial fluid ADMA and endothelin play putative roles. Finally, some of the open possibilities for future research on L-arginine-NO-ADMA signaling are highlighted.

Usefulness of Asymmetric Dimethylarginine to Predict Outcomes After Heart Transplantation

Asymmetric dimethylarginine (ADMA) is a key mediator of vascular homeostasis and an independent predictor of the development of accelerated cardiac allograft vasculopathy after heart transplantation. However, its association with clinical outcomes in heart transplant recipients has not been described. Plasma levels of ADMA were assayed within 8 weeks following transplantation (baseline) using a competitive enzyme-linked immunosorbent assay. The primary end point was the composite of nonfatal myocardial infarction, percutaneous coronary intervention, retransplantation, or death at 5-year follow-up. Kaplan-Meier curves were generated to assess the association between baseline ADMA levels (stratified at 0.70 µM, a previously established cutoff) and cumulative event-free survival. Multivariate Cox regression was performed to adjust for other candidate predictors. In 69 heart transplant recipients at Stanford, the primary end point occurred in 11 patients (16%)-4 percutaneous coronary intervention, 1 retransplant, and 6 deaths-during 5-years follow-up. Patients with baseline ADMA ≥0.70 µM had lower cumulative 5-year event-free survival (77% vs 93%, p = 0.059). In multivariate Cox analysis, baseline ADMA was the only significant predictor of the primary end point (hazard ratio 1.33, 95% confidence interval 1.03 to 1.72 per 0.1 µM; p = 0.031). This association remained significant even after restricting the end point to death or retransplantation (hazard ratio 1.48, 95% confidence interval 1.12 to 1.97 per 0.1 µM; p = 0.006). In conclusion, elevated baseline plasma levels of ADMA independently predicted 5-year clinical outcomes after heart transplantation, suggesting that ADMA has potential prognostic value in the heart transplant arena.