Unusual oxidative pattern in thermo-oxidation of dry films of cholesterol [Patrón oxidativo inusual en la termo-oxidación de películas secas de colesterol]

Formation of cholesterol oxidation products (COPs) during dry heating of cholesterol films at 150°C for 48 h was studied. A method based on aminopropyl solid-phase extraction (SPE), followed by GC-MS analysis was employed for the identification and quantification of COPs. Two kinetic runs were performed: 60 min and 48 h of treatment. In the short run (60 min), 7-ketocholesterol and 25-hydroxycholesterol were detected in similar amounts after 30 and 15 min, respectively. Oxysterols present in higher amounts in the long run (48 h) were 7β-hydroxycholesterol (12.6 mg/g) and 5,6α-epoxycholesterol (13.4 mg/g). However, compounds whose formation is related to enzymatic oxidation and/or irradiation were detected, as 6-ketocholestanol (3.38 mg/g) and 4β-hydroxycholesterol (2.04 mg/g). 25-hydroxycholesterol (0.12 mg/g) was found after only 1 h, reaching 0.99 mg/g after 48 h of treatment. The results suggest that due to the physical state of cholesterol, the oxidative pattern was changed, favoring unusual routes, such as formation of 4β-OH and 6-keto from breakage of the epoxide ring. Regarding 25-hydroxycholesterol, it is assumed that the solid state favored exposure of the side chain, rendering it more susceptible to oxidation.