Synthesis of acylated SOD derivatives which bind to the biomembrane lipid surface and dismutate extracellular superoxide radicals

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Abstract
Involvement of oxygen radicals in the pathogenesis of various inflammatory diseases has been the focus of recent attention. Since lipid peroxidation of cell membranes is postulated to be one of the major reasons for radical-induced tissue injury, inhibition of oxygen toxicity at or near plasma membranes is important. To metabolize extracellular superoxide radicals effectively at or near cell membranes, we synthesized amphipathic superoxide dismutase (SOD) derivatives (AC-SOD) by covalently linking hydrophobic fatty acids with different chain lengths, such as caprylic acid, capric acid, lauric acid and myristic acid, to the lysyl amino groups of the enzyme. When incubated with erythrocytes or polymorphonuclear leukocytes (PMNs), AC-SOD, but not SOD, bound to plasma membranes of these cells. When topically instilled to the eye, AC-SOD also bound to corneal epithelial cell surface. Upon activation by phorbolmyristyl acetate, extracellular cytochrome c was rapidly reduced by PMNs which were pretreated with SOD. In contrast, PMNs preincubated with AC-SOD failed to catalyze the reduction of cytochrome c under the same experimental conditions. These results suggested that AC-SOD bound to cell membranes and effectively dismutated superoxide radicals at or on the outer surface of plasma membranes.