Identification of defective binding of low density lipoprotein by the U937 proliferation assay in German patients with familial defective apolipoprotein B-100

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Abstract
Familial defective apolipoprotein B‐100 (FDB) is a dominantly inherited disorder characterized by decreased binding of low density lipoprotein (LDL) to the LDL receptor due to a substitution of glutamine for arginine in residue 3500 of apolipoprotein B‐100. We present the results of the U937 cell proliferation assay for the detection of familial defective apo B100 in 13 German FDB patients. Due to a defect in the pathway of cholesterol synthesis the human myelomonocytic tumour cell line U937 lacks the ability to synthesize cholesterol which makes proliferation of these cells dependent on the presence of exogenous LDL‐cholesterol. U937 cells were incubated with LDL from 13 FDB‐patients, 10 healthy normocholesterolaemic individuals (NC) and 26 patients with familial hypercholesterolaemia due to a defective LDL‐receptor (FH). At LDL‐cholesterol concentrations below 1 μg ml‐1 no proliferation occurred. In the presence of LDL from FDB patients at concentrations between 2·5 μg ml‐1 and 15·0 μg ml‐1, the proliferation was significantly reduced compared to LDL from FH‐patients and normocholesterolaemic controls. At 5 μg ml‐1 the reduction was 31–80% regardless of age, sex, apo E genotype, Lp (a)‐ and lipid levels. At concentrations above 25·0 μg ml‐1 no further differences were observed. The present results indicate that the U937 proliferation assay is a reliable test for the detection of defective LDL‐binding due to the 3500 mutation in FDB patients. It may be useful for the detection of defective binding of LDL due to other mutations in the apo B‐100 gene.

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