Abstract
There is a continuous flux of the oxysterol 27-hydroxycholesterol (27-OHC) from the circulation across the blood-brain barrier (BBB) into the brain. The major metabolite of 27-OHC in the brain is 7α-hydroxy-3-oxo-4-cholestenoic acid (7-HOCA). We confirm a recent report describing the presence of this metabolite in cerebrospinal fluid (CSF) at a relatively high concentration. A simple and accurate method was developed for assay of 7-HOCA in CSF based on isotope dilution-mass spectrometry and use of (2)H4-labeled internal standard. The concentration of this metabolite was found to be markedly increased in CSF from patients with a dysfunctional BBB. There was a high correlation between the levels of 7-HOCA in CSF and the CSF/serum albumin ratio. The concentration of 7-HOCA in CSF was not significantly affected by neurodegeneration. Our findings suggest that 7-HOCA could be used as a diagnostic marker for conditions with a dysfunctional BBB.
Highlights
There is a continuous flux of the oxysterol 27hydroxycholesterol (27-OHC) from the circulation across the blood-brain barrier (BBB) into the brain
In the previous assay of 7␣-hydroxy-3-oxo-4cholestenoic acid (7-HOCA) in plasma or serum (1–5), two chromatographic steps had to be included in the assay prior to quantitation by combined gas chromatography-mass spectrometry (GC-MS) of the methyl ester TMS derivative. 14C-labeled 3-oxocholanoic acid was used as a recovery marker in the method described by Axelson and Sjövall (3)
The levels of 7-HOCA in plasma have been reported to be about 130 ng/ml (4), about 9-fold higher than the normal levels in cerebrospinal fluid (CSF) found in the present work
Summary
There is a continuous flux of the oxysterol 27hydroxycholesterol (27-OHC) from the circulation across the blood-brain barrier (BBB) into the brain. The major metabolite of 27-OHC in the brain is 7␣-hydroxy-3-oxo-4cholestenoic acid (7-HOCA). A simple and accurate method was developed for assay of 7-HOCA in CSF based on isotope dilution-mass spectrometry and use of 2H4-labeled internal standard The concentration of this metabolite was found to be markedly increased in CSF from patients with a dysfunctional BBB. Based on measurements of arteriovenous concentration differences in catheterization experiments, it was shown that there is a continuous flux of 7-HOCA from the human brain into the circulation (2). The magnitude of this flux is about 2 mg/24 h
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