Encapsulation of N-Nitroso-melatonin with Poly(lactide-co-glycolide)

Abstract

N-Nitrosomelatonin (NOMela) is well known for its capabilities to transnitrosate nucleophiles such as thiols and ascorbate thereby generating nitric oxide (NO)-releasing compounds. Like molsidomine, NOMela is one of the few NO-releasing substrates not inducing nitrate tolerance and may be therefore highly suitable as NO-therapeutical. As the physical and chemical properties of NOMela do not allow its direct application (oral or intravascular) in animals/ humans, the encapsulation with biodegradable poly(lactide-co-glycolide) (PLGA) polymers was performed and NOreleasing kinetics were studied. NOMela could be successfully encapsulated in PLGA (NOMela-PLGA) with an efficiency of 85% thereby prolonging its half-life time in aqueous solution (e.g. in the cytoplasm of endothelial and smooth muscle cells) about 3-fold. In the presence of “activated hydroxy compounds“ like vitamin C and thus under physiological conditions, NOMela-PLGA yielded two therapeutically relevant hormones, melatonin and nitric oxide, via reactions only known (until now) for unencapsulated, freely diffusing NOMela. Importantly, in the absence of any activated hydroxy compound the unwanted hydrolysis reaction of NOMela dominated, generating the non-functional nitrite (and not nitric oxide). These findings suggested that PLGA-encapsulated NOMela will be highly attractive as a novel NO-releasing drug lacking common side-effects of classical NO-releasing molecules such as glyceroltrinitrate.