Albumin as a Nitric Oxide-Traffic Protein: Characterization, Biochemistry and Possible Future Therapeutic Applications

Nitric oxide (NO) is a ubiquitous molecule involved in multiple cellular functions. Inappropriate production of NO may lead to disease states. To date, pharmacologically active compounds that release NO within the body, such as organic nitrates, have been used as therapeutic agents, but their efficacy is significantly limited by rapid NO release, toxicity and induction of tolerance. Therefore, novel NO donors with better pharmacological and phamacokinetic properties are highly desirable. The S-nitrosothiol fraction in plasma is largely composed of S-nitrosylated human serum albumin (SNO-HSA) and that is why we are testing whether this albumin form can be used as a NO traffic protein. We have found that oleate and other endogenous ligands increase SNO-HSA formation in vitro. The cytoprotective effect of SNO-HSA in a ischemia/reperfusion model and its antiapoptotic effect on HepG2 cells treated with anti-Fas antibody were pronounced and could be enhanced by binding of oleate. The enhancement of S-transnitrosation to the HepG2 cells could be completely blocked by filipin III, a caveolae inhibitor. These findings indicate that a clinical application of SNO-HSA is expected as potent NO supplementary therapy and that fatty acids may serve as novel types of mediators for S-transnitrosation.