Characterization of plasma lipoproteins separated and purified by agarose-column chromatography

Radioimmunoassay for human plasma apolipoprotein B

We have developed a simplified double antibody radioimmunoassay for human apolipoprotein beta. The purified antigen, a narrow density subclass of beta lipoprotein (d 1.030-1.050 g/ml; was isolated by a combination of gel filtration and ultracentrifugationmthis material gave a single immunoprecipitin arc on crossed immunoelectrophoresis into an antibody to whole human serum. The antigen was radiolabelled using iodine monochloride at pH 10. The iodinated antigen was indistinguishable immunochemically from native material and eluted as a single radioactive peak from a Sephadex G-200 column. The lower limit of sensitivity of the assay was 15 ng protein, and the working range, 15-200 ng. The mean apolipoprotein B level (+/-1 S.D.) in 128 healthy control subjects was 86.6 +/- 29.6 mg/100ml and is in agreement the values published by other workers using unmodified assays.

Diagnosis of dyslipoprotein aemia by molecular sieve chromatography

Agarose gel molecular sieve chromatography has been used as a tool in the diagnosis of dyslipoproteinaemias. The elution profile from control plasma contained three peaks, corresponding to very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). These accounted for 9.5%, 23.5% and 67% of the total lipoprotein absorption at 280 nm. Elution patterns from dyslipoproteinaemic serum showed alterations, not only in peak area, but also in peak migration rate through the agarose gel. These variations were reproducible and of such magnitude as to permit the use of molecular sieve chromatography as a tool in the diagnosis of dyslipoprotein-aemias of Type I, II (a + b), III, IV and V.

Characterization of the Ehrlich ascites tumor plasma lipoproteins

1. The lipoproteins of the Ehrlich ascites tumor plasma were separated into 3 distinct fractions, very low density, low density and high density lipoproteins by preparative ultracentrifugation combined with agarose column chromatography. 2. High density lipoproteins contained 74% of the total protein in the lipoproteins. By contrast, most of the lipids were present in the very low density lipoprotein fraction. 3. The fatty acid compositions of the cholesteryl esters were appreciably different in the very low, low and high density lipoproteins, whereas phospholipid and triacylglycerol fatty acid compositions were quite similar in the 3 lipoprotein fractions. 4. Very low and high density apoprotein electrophoretic patterns on sodium dodecyl sulfate-acrylamide gels were similar to those observed in the corresponding lipoprotein fractions obtained from other mammalian species. The low density fraction, however, contained 7 apoprotein bands, and 32% of the low density apoprotein was soluble in tetramethyl urea. 5. The average molecular weights as determined by analytical ultracentrifugation were 2-10(7) (very low density), 6-10(6) (low density) and 4.4-10(5) (high density).

Decreased serum cholesterol-binding reserve in premature myocardial infarction

Incubation of human serum with crystalline cholesterol which had been pulverised by sonication resulted in a measurable uptake of cholesterol by the serum. This uptake was designated "serum cholesterol-binding reserve" (S.C.B.R.). Among more than 200 men and women examined, S.C.B.R. values varied from less than 10 to over 200 mg/dl, while the values from repeated determinations on two individuals over several months varied within 24 mg/dl. S.C.B.R. could be attributed to two serum-lipoprotein subfractions--S.F.V. separated from very-low-density lipoprotein and S.F.H. from high-density lipoprotein, by gel filtration. Without further purification, S.F.V. solubilised 4-5 mg and S.F.H. solubilised 0-36 mg of additional cholesterol/mg of protein, while the remaining bulk of the lipoproteins lacked this property. It is proposed that S.F.V. and S.F.H. have physiological roles in retarding atherogenesis by removing cholesterol from the arterial intima and carrying it back to the circulating serum. Accordingly, individuals who have low S.C.B.R. values, being deficient in S.F.V. and S.F.H., are at higher risk for the development of atherosclerosis and coronary heart-disease. This hypothesis was tested by comparing S.C.B.R. values of patients with premature myocardial infarction with values of controls. The results indicated a trend of increasing S.C.B.R. values with increasing levels of serum cholesterol and triglycerides among the controls, but this trend was virtually lost among the patients. The S.C.B.R. values also were lower among patients than controls, and the difference was statistically significant between patients and controls with serum-cholesterol above 250 mg/dl or fasting serum-triglycerides above 160 mg/dl. These results are consistent with the proposed hypothesis.