Abstract
Apolipoprotein (apo) B-48 is the only specific marker of intestinal lipoproteins. We evaluated a novel enzyme-linked immunosorbent assay (ELISA) standardized with recombinant apo B-48 to measure apo B-48 in plasma and triglyceride-rich lipoproteins (TRLs, density <1.006 g/mL). Coefficients of variation were less than 2.5%. Assay values correlated well (r = 0.82, P < .001) with values obtained by gel scanning of TRLs (n = 75 samples); however, the gel scanning method yielded values that were about 50% lower than ELISA values. About 60% to 70% of apo B-48 was found in TRLs. In 12 healthy subjects, median fasting plasma apo B-48 levels were 0.51 mg/dL and were increased by 121% to 147% in the fed state. In 63 obese subjects, median fasting apo B-48 values were 0.82 mg/dL; and feeding resulted in almost no change in total cholesterol, non-high-density lipoprotein cholesterol, or total apo B values, whereas triglyceride, remnant lipoprotein cholesterol, and apo B-48 levels were significantly higher (P < .05; by +73%, +58%, and +106%), and direct low-density lipoprotein cholesterol and direct high-density lipoprotein cholesterol were significantly lower (P < .001, by -13% and -20%) than fasting values. Relative to controls, 270 hyperlipidemic subjects had significantly higher (P < .001, +115%) fasting total apo B and higher apo B-48 values (P = .06, +37%). Our data indicate that the apo B-48 ELISA tested provides highly reproducible results and is excellent for research studies. Median apo B-48 values in healthy subjects are about 0.5 mg/dL and increase more than 100% in the fed state. Elevated levels are observed in obese and hyperlipidemic subjects.