Biophysical inhibition of synthetic phospholipid-lung surfactant apoprotein admixtures by plasma proteins.

Biophysical activity and inhibition characteristics were studied for a series of synthetic surfactants composed of purified bovine lung surfactant proteins (SP)-B or -C combined with dipalmitoyl phosphatidylcholine (DPPC) and egg-phosphatidylglycerol (PG) in a weight ratio of 80:20:1 DPPC/PG/protein. Surfactant protein preparations included two isolates of SP-B, confirmed by amino terminal sequence analysis, three isolates of SP-C which were free of SP-B by ELISA and Western blot analysis, and two isolates containing both SP-B and -C. In oscillating bubble studies, mixtures of phospholipids with isolates containing pure SP-B or both SP-B and -C lowered surface tension to less than 1 mN/m within 2 min of pulsation at both 1.25 mg/ml and 2.5 mg/ml. Phospholipids combined with isolates of pure SP-C also had substantial activity, lowering surface tension to between 1 mN/m and 3 mN/m depending on the SP-C preparation used. The surface activity of synthetic phospholipid-apoprotein admixtures was decreased significantly by the plasma proteins albumin and fibrinogen, but with varying characteristics depending on the apoprotein preparation involved. At 1.25 mg/ml phospholipid, admixtures containing either isolate of SP-B were inhibited by 10 mg/ml of plasma proteins, as were those with one of the SP-C preparations. However, admixtures containing the two other pure SP-C preparations were not inhibited until 20-50 mg/ml of albumin or fibrinogen were present. The highest resistance to inhibition was shown by admixtures containing one of the apoprotein isolates having both SP-B and -C.(ABSTRACT TRUNCATED AT 250 WORDS)