Isolation and characterization of a cellular protein-lipid complex from ascites fluid caused by various neoplasms.

High concentrations of lipids in ascites fluid caused by peritoneal carcinomatosis have been described recently. Since their nature has not yet been clarified, we isolated ascitic lipids from 25 patients with various neoplasms for further characterization. After chromatography on Sephadex G-100 gels, the ascitic lipids were fractionated on a Biogel A-5m column in three peaks. The second and third peaks were identified as low and high density lipoproteins, which were most likely of plasmatic origin, and represented the major amounts of ascitic lipids. The first peak was eluted in the void volume, indicating a molecular weight over 5 million. It consisted, on the average, of 65.3% protein, 16.2% triglycerides, 7.4% phospholipids, and 7.0% cholesterol. In a CsCl gradient, this protein-lipid complex floated in the density range from 1.128 to 1.181 g/ml. Sodium dodecyl sulfate: polyacrylamide gel electrophoresis separated up to 11 protein subunits (Mr 29,000 to 97,000), and electron microscopy revealed globular particles of 36 to 64 nm in diameter. The macromolecular complex showed no immunological reaction against anti-alpha- and anti-beta-lipoproteins, but a single precipitation line against anti-liver-specific lipoprotein was seen. The biochemical characteristics of this protein-lipid complex proved to have a close relationship to liver-specific lipoprotein. It is most likely derived from cell membranes of the peritoneum detached by carcinomatosis.