Studies on Arteriosclerosis : II. Deposition of β-Lipoprotein on the Aortic Wall

Abstract

It was reported in the preceding paper that serum β-lipoprotein could be conveniently determined by the dextran sulfate method utilizing the affinity between β-lipoprotein and acid muco-polysaccharides, and that the level of the substance in serum was elevated in atherosclerosis. In this paper, a few experiments on the mechanism of the deposition of serum β-lipoprotein in the aortic wall are described. Methods and Results 1 ) Preparation of Anti-β-lipoprotein Serum Pure β-lipoprotein isolated from human serum by the dextran sulfate method was injected into rabbits and guinea pigs repeatedly to prepare anti-human-β-lipoprotein sera. The anti-sera were tested by agar immunoelectrophoresis and agar gel double diffusion, and were found to react specifically with β-lipoprotein. 2) Pressure Test of β-lipoprotein Experiments were performed to let serum albumin and β-lipoprotein invade a segment of the aorta of a dog or a pig placed in a specially designed apparatus. When pressure was applied to the solution of serum albumin labeled with bromphenol blue, the substance was found to invade the aortic wall to a depth approximately proportional to the pressure Next, human serum rich in β-lipoprotein was substituted for the solution, and after the pressurization the piece of aorta was removed and homogenized at low temperatures, and its β-lipoprotein extracted with physiological saline. The usual precipitation reaction between the extract and the anti-β-lipoprotein serum mentioned above showed the precipitin value to be approximately proportional to the pressure. The quantity of β-lipoprotein extracted was also measured by the dextran sulfate method and was found also to be roughly proportional to the pressure. The following experiments were carried out to test if it was due to combination with the acid muco-polysaccharides pressent in the aortic wall that the, β-lipoprotein was deposited there. First, the adventitia was removed from a piece of human aorta obtained in autopsy, and the media and intima were minced and freed of fat with acetone and ethyl ether, and dried. Then the acid muco-polysaccharides were isolated and purified by modified Kirk and Dyrbye's method and dissolved in distilled water. When human serum rich in β-lipoprotein was added to the solution, it became turbid, indicating combination of the acid polysaccharides with the β-lipoprotein.