Presence of Cholesterol in Non-Animal Organisms: Identification and Quantification of Cholesterol in Crude Seed Oil from Perilla frutescens and Dehydrated Pyropia tenera

The importance of choosing the appropriate cholesterol quantification method: enzymatic assay versus gas chromatography

Cholesterol is a major lipid of the animal realm with many biological roles. It is an important component of cellular membranes and a precursor of steroid hormones and bile acids. It is particularly abundant in nervous tissues, and dysregulation of cholesterol metabolism has been associated with neurodegenerative diseases such as Alzheimer's and Huntington's diseases. Deciphering the pathophysiological mechanisms of these disorders often involves animal models such as mice and Drosophila. Accurate quantification of cholesterol levels in the chosen models is a critical point of these studies. In the present work, we compare two common methods, gas chromatography coupled to flame-ionization detection (GC/FID) and a cholesterol oxidase-based fluorometric assay to measure cholesterol in mouse brains and Drosophila heads. Cholesterol levels measured by the two methods were similar for the mouse brain, which presents a huge majority of cholesterol in its sterol profile. On the contrary, depending on the method, measured cholesterol levels were very different for Drosophila heads, which present a complex sterol profile with a minority of cholesterol. We showed that the enzyme-based assay is not specific for cholesterol and detects other sterols as well. This method is therefore not suited for cholesterol measurement in models such as Drosophila. Alternatively, chromatographic methods, such as GC/FID, offer the required specificity for cholesterol quantification. Understanding the limitations of the quantification techniques is essential for reliable interpretation of the results in cholesterol-related research.

Enzyme-assisted ReMALDI-MS assay for quantification of cholesterol in food

Cholesterol is a vital building block for animal cell membranes and participates in the synthesis of various hormones. Accurate quantitation of cholesterol in food is crucial for healthy diets. Here, we describe an enzyme-assisted reactive matrix-assisted laser desorption/ionization mass spectrometry (ReMALDI-MS) assay for the quantification of cholesterol in food. First, cholesterol was converted to 4-cholesten-3-one using the cholesterol oxidase, and then reacted with a reactive matrix, 4-hydrazinoquinazoline (4-HQ), to form a hydrazone bond. Utilizing 4-HQ significantly improved the ionization efficiency of cholesterol, which possesses poor ionization efficiency in MALDI-MS, and no additional tedious derivatization/purification steps were needed. Thus, the proposed assay was successfully used for the quantification of cholesterol in bovine milk and cream. The standard recovery tests show a recovery range of 95.3-103.0% with a relative standard deviation of 0.3-3.1%. Therefore, the proposed enzyme-assisted ReMALDI-MS assay has great potential for quantification of cholesterol in other foods.