Stable
nitroxyl radicals (nitroxides) are potential
antioxidant drugs, and we have previously reported that linking
nitroxide to
biological macromolecules can improve therapeutic activity in at least two ways. First, polynitroxylated compounds such as polynitroxyl
human serum albumin (PNA) are a novel class of high molecular weight, extracellular
antioxidants. Second, compounds such as PNA can prolong the half-life of free (unbound, low molecular weight) nitroxides such as 4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl (
Tempol) in vivo. Unlike PNA,
Tempol can readily access the intracellular compartment. Thus PNA can act alone in the extracellular compartment, or in concert with
Tempol, to provide additional
antioxidant protection within cells. In this study, we compared the abilities of PNA,
Tempol, and the combination of PNA +
Tempol to prevent lung microvascular injury secondary to prolonged gut
ischemia (I, 120 min) and reperfusion (R, 20 min) in the rat. Pulmonary capillary filtration coefficient (K(f,c)) and lung neutrophil retention (tissue
myeloperoxidase activity, MPO) were measured in normal, isolated rat lungs perfused with blood harvested from I/R rats. Blood donor rats were treated with
drug during
ischemia. Gut I/R resulted in a marked increase in pulmonary capillary coefficient and lung MPO. PNA +
Tempol, but not PNA alone or
Tempol alone, at the doses used, prevented the development of lung leak. None of the treatments had an effect on lung neutrophil retention. Anti-inflammatory therapeutic activity appeared to correlate with blood
Tempol level: in the presence of PNA, blood
Tempol levels were maintained in the 50-100 microM range vs. essentially undetectable levels shortly after
Tempol was administered alone. In this model of
lung injury secondary to prolonged gut I/R, lung capillary leak was prevented when the membrane-permeable compound
Tempol was maintained in its active,
free radical state by PNA.