Quantitative analysis of 4β- and 4α‑hydroxycholesterol in human plasma and serum by UHPLC/ESI-HR-MS.

Cholesterol oxidation product 4β‑hydroxycholesterol (4β‑OHC) may possibly be used as an endogenous biomarker of CYP3A enzyme activity and as CYP3A4 is involved in the metabolism of approximately 50% of the drugs in clinical use, the monitoring of CYP3A activity by 4β‑OHC plasma or serum levels, may be of clinical significance. The plasma and serum concentrations of 4α‑hydroxycholesterol (4α‑OHC), an isomer of 4β‑OHC, increase during uncontrolled storage conditions and therefore serve as an indicator of proper handling of samples.