Determination of Squalene and 6 Non-cholesterol Sterols in Human Serum by GC/MS

Besides cholesterol, a few of squalene and non-cholesterol sterols exist in human serum, which include cholesterol synthesis precursors (e.g. desmosterol and lathosterol) and plant sterols (e.g. campesterol, stigmasterol, sitosterol and cholestanol). In present studies, squalene and cholesterol precursors could be considered as cholesterol synthesis markers, which reflect synthesis efficiency of cholesterol, while plant sterols are considered as cholesterol absorption markers which reflect cholesterol absorption efficiency. Because of the similar molecule structure among cholesterol and non-cholesterol sterols, and the less content of non-cholesterol sterols, the present method, such as radioactive isotope, high-performance liquid chromatography (HPLC), and gas chromatography (GC), have some difficulties in the separation and quantification of non-cholesterol sterols.
In our studies, the method of sample preparation was improved, and the chemical derivation process was also optimized, and GC/MS were used in the quantitative determination of cholesterol and non-cholesterol sterols. Compared to GC method, our method has a better resolution and repeatability, and the accuracy is also good, so it is feasible to use the method in analysis for clinical individual difference of cholesterol metabolism. Serum of 30 patients of hyperlipemia were determined by our method, and the mean values of squalene and sterols are squalene 0.18 mg•dL^－1, cholestanol 0.69 mg•dL^－1, desmosterol 0.03 mg•dL^－1, lathosterol 0.31 mg•dL^－1, campesterol 0.27 mg•dL^－1, stigmasterol 0.05 mg•dL－1 and sitosterol 0.39 mg•dL^－1. The total content of squalene and non-cholesterol sterols is 1.53 mg•dL^－1, which is 0.89% of cholesterol.
Linear regression analysis is made between all kinds of sterols. Cholesterol has positive correlation with all 6 non-cholesterol sterols. Whereas, the positive correlations with cholestanol and stigmasterol are not significant probably due to the serum quantity is not enough. More serum data will need to obtain more representative results.