Immunochemical determination of apolipoprotein a I in human serum

Determination of human apolipoproteins A-I, B, and E by laser nephelometry

A laser immunonephelometric procedure for the determination of human apolipoproteins A-I, B, and E in serum and lipoproteins was developed. Coefficients of variation were 2.3%-3.4% within-run, 4.7%-4.9% between-run. Serum apolipoprotein A-I values were similar in normal and hyperlipoproteinaemic subjects with a correlation coefficient of r = 0.585 to HDL-cholesterol levels. LDL-apolipoprotein B values were highly (r = 0.935), VLDL-apolipoprotein B values less strongly (r = 0.472) correlated to the corresponding cholesterol levels. Serum apolipoprotein E concentrations were distinctly elevated in Type III and not correlated to cholesterol values.

Changes in very low and low density lipoproteins with dietary fat modification

Since VLDL and LDL are involved in atherogenesis, their response to dietary modification was studied in 15 normal male prisoners. A 3-month reference diet (P/S ratio 0.3, daily cholesterol intake 370 mg) was compared with a modified fat diet (P/S 1.0, 250 mg) given for further 3 months. The decrement in serum cholesterol by 32 mg/dl reflected a decrease in VLDL and LDL. It was associated with a decrease in serum apolipoprotein B by 16 mg/dl and in serum apolipoprotein E by 1.2 mg/dl. The decrement in VLDL cholesterol was paralleled by a lowered VLDL apolipoprotein E content. Serum and VLDL triglycerides, HDL cholesterol and the serum apolipoproteins A-I and A-II did not change significantly. One beneficial result of a conventional dietary regimen is lowered LDL with unaffected HDL. Another effect is the apparent modification of VLDL with a decrement of cholesterol and apolipoprotein E-enriched particles.

High density lipoproteins unaffected by dietary fat modification

Since diets containing a high P/S ratio have been reported to have detrimental effects on HDL, the effect of a moderately modified fat diet (P/S ratio 1.0, cholesterol content 250 mg/day) was investigated in 30 healthy male volunteers, divided into 2 groups. They were either given a modified fat diet or an isocaloric control diet (P/S ratio 0.3, cholesterol content 370 mg/day) for 3 months each in a cross-over design. After 3 months of the polyunsaturated fat diet LDL cholesterol was significantly lowered by 19 and 13%, respectively, in both groups. This effect was already apparent after 4 weeks. Apo A-I and cholesterol in serum and the subfractions HDL2 and HDL3 remained unchanged. Consequently, the ratio LDL/HDL cholesterol was decreased by this diet. Dietary adherence was good according to the typical changes of the linoleic acid content in serum cholesteryl esters, to the dietary recalls and to the constant body weight. We conclude that a moderately modified fat diet supplied from mixed general food is acceptable for longer periods, effectively lowers LDL cholesterol, even in normolipoproteinemic subjects, and has no detrimental effects on HDL.

[The apolipoproteins in man ]

Twelve different apolipoproteins have been described in human serum. Apo A-I and apo A-II are essential for the structure of the HDL particles and for the function of LCAT activity. Apo B is the main protein in LDL but does also occur in the triglyceride-rich particles. Apo B represents the binding protein for the LDL-receptor pathway. The C-apolipoproteins are located on the surface of VLDL. They are transferred to HDL throughout the catabolism of VLDL and affect lipoprotein lipase activity. This enzyme is also affected by the E-apolipoproteins which occur in the triglyceride-rich particles as well as in HDL. Apo E is the binding site for another specific cell receptor. The concentration and metabolism of apolipoproteins is affected by diet, drugs, hormones, body weight, alcohol, cigarettes, physical exercises, liver and renal diseases. There is a close relation between apolipoproteins and atherosclerosis.

Effects of etiroxate on low density and high density lipoproteins in hypercholesterolemic patients

Six female patients with a primary hyperlipoproteinemia type IIa received 40 mg/day etiroxate for 2 months. Serum lipids, low density and high density lipoprotein cholesterol, the apolipoproteins B and A-I, and cholesterol and apolipoprotein A-I in ultracentrifuged HDL2 and HDL3 were analysed before and after the treatment. Etiroxate caused a significant reduction in serum cholesterol, LDL-cholesterol, and serum apolipoprotein B. Concerning the HDL, there was a significant decrease in HDL-cholesterol. The analysis of HDL subfractions revealed a uniform fall in HDL2-cholesterol and HDL2-apolipoprotein A-I. It is concluded that detailed information about lipoproteins leads to a better understanding of the relationships between drug treatment and the possible prevention of atherosclerotic diseases.