Circulating actin-gelsolin complexes following oleic acid-induced lung injury.

Plasma gelsolin is one of two extracellular proteins that bind actin, a major body protein, with high affinity. The authors performed a series of experiments to determine whether tissue injury leads to actin release and the formation of circulating actin-gelsolin complexes. Two functions of plasma gelsolin, filament-nucleating and filament-severing activity, were used to measure total and free gelsolin concentrations, respectively. Both gelsolin and gelsolin-actin complexes nucleate actin assembly, whereas only free gelsolin severs actin filaments. Therefore, nucleation reflects the total gelsolin concentration, severing, the free gelsolin concentration, and the difference, gelsolin-actin complexes. Injection of F-actin in the rat caused a reduction in the free, but not total, gelsolin levels, consistent with the formation of circulating actin-gelsolin complexes. Oleic acid (50 mg/kg) administered intravenously in rats, a treatment that causes acute hemorrhagic pulmonary necrosis, caused the free gelsolin concentration to fall to a greater extent than the total gelsolin concentration, which indicated the presence of circulating actin-gelsolin complexes. Lower doses (9-27 mg/kg) in rabbits caused a qualitatively similar but smaller change in the free gelsolin level. Plasma gelsolin was immunoprecipitated at times when actin-gelsolin complexes were present, as determined functionally, and bound actin was demonstrated by immunoblotting with an anti-actin antiserum. These studies show that considerable amounts of actin are released into the extracellular space during acute lung injury and that circulating actin-gelsolin complexes can be detected in the peripheral blood.