Catalytic generation of nitric oxide from S-nitrosothiols using organoselenium species and development of amperometric S-nitrosothiol sensors.

Abstract

Novel nitric oxide (NO) generating polymeric materials possessing organoselenium (RSe) catalysts have been developed with the goal of improving the biocompatibility of blood-contacting surfaces in biomedical devices. Low-molecular-weight diselenides were covalently linked to model polymeric materials, e.g., cellulose filter paper and polyethylenimine. Such RSe-derivatized polymers were shown to generate NO from S-nitrosothiols (RSNOs) in the presence of thiol reducing agents (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO liberation from RSNOs is suggested in the proposed catalytic cycle. The new RSe-polymers clearly exhibit the ability to generate NO from RSNO species even after prolonged contact with fresh animal plasma. Such NO generating capability could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood containing endogenous RSNOs, owing to NO's activity to inhibit platelet adhesion and activation. Efforts were also undertaken to utilize the new immobilized RSe catalysts to detect RSNO species. To apply a planar-type amperometric NO_(g) sensor for directly detecting RSNOs in biological samples (e.g., fresh blood), the NO selectivity was quantitatively examined over both ammonia and nitrite, and compared with other types of amperometric NO sensors. It was found that the NO selectivity coefficient of the planar-type NO sensor can be significantly enhanced up to a thousand fold by treating the porous gas-permeable membrane with a Teflon AF<super>RTM</super> solution. Finally, novel electrochemical devices for the direct detection of RSNO species were developed by modifying the selectivity-improved NO sensor with thin polymeric layers containing immobilized RSe- or copper-based catalysts. Such polymeric layers are capable of decomposing RSNOs to generate NO_(g) at the distal tip of the NO sensor. Under optimized conditions, these RSNO sensors were shown to reversibly and quantitatively detect various RSNO species in test solutions down to 0.1 muM concentration. Basic performance parameters (e.g., limit of detection and lifetime, etc.) and factors influencing sensor sensitivity were identified for both the RSe- and copper-based RSNO sensors. The new sensors were shown to be useful in assessing the NO-generating ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.