Summary: Although low density lipoprotein receptors have been described on oligodendrocytes, apolipoprotein B was thought to be absent or present in only very small amounts in cerebrospinal fluid (CSF). Several immunoassays have been used for the measurement of apolipoprotein B in serum. However, the majority of methods cannot be used to measure small amounts of apolipoprotein B in CSF. In this study, we describe a highly sensitive time resolved immunoftoorometric assay (TR-IFMA) using europium as label (detection limit: 0,3 g/l). The reliability of the TR-IFMA for the measurement of apolipoprotein B was first studied in serum. Serum and CSF apolipoprotein B concentrations were then determined in subjects free of neurological disorders and in patients with multiple sclerosis. Local intrathecal apolipoprotein B synthesis was calculated. Although the high sensitivity of the TR-IFMA allowed low amounts of apolipoprotein B in CSF to be detected (0.11 ± 0.06; 0.12 ± 0.06 mg/1 in controls and multiple sclerosis patients, respectively), no apolipoprotein B could be detected in CSF by electroimmunodiffusion. As suggested by the blood/CSF apolipoprotein B ratio (about 6000), no apolipoprotein B synthesis was observed by both using apolipoprotein B index and formula. This indicates its probable serum origin. Moreover, there was no difference between controls and multiple sclerosis patients in CSF, serum, blood/CSF, index, and local intrathecal apolipoprotein B synthesis. Finally, these results suggest that the role of apolipoprotein B in lipid transport in the central nervous system may be questionable.

A time-resolved immunofluorometric assay (TR-IFMA) was used for the measurement of glycated C3. The very high sensitivity of this technique allowed the direct measurement of glycated and non-glycated proteins (especially C3) in chromatography eluates. C3 glycation in vitro after incubation with 20 mmol/1 glucose was always less than 3.5% by day 5. As determined with the TR-IFMA, the means + standard deviations of glycated C3 were 0.20% + 0.04 for non-diabetic subjects and 0.88% ± 0.06 for insulindependent diabetic patients. The low percentages of glycated C3 in both our in vitro and in vivo studies show that this protein is subject to only moderate rates of glycation.

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