Oxidative Pattern from Fluorescent Light Exposition of Crystalline Cholesterol

Abstract

The photo-oxidation of crystalline cholesterol in the presence of hematoporphyrin was kinetically studied. Samples were exposed to fluorescent light at 12 °C for 48 h (Test-A) and 21 days (Test-B). A method based on aminopropyl solid-phase extraction (SPE), followed by GC-MS analysis was employed for the identification and quantification of cholesterol oxidative compounds (COPs). In early stages of photo-oxidation (Test-A), a hyperbolic behavior on peroxides value was found, but not quantifiable secondary products were detected. In Test-B, 58 % of cholesterol was remained after exposure, due probably to exhaustion of hematoporphyrin and/or physical state of sample. Type II photo-oxidation seemed to be quantitatively predominant, in respect to Type I. 3,6-dione and 6β-OH generated in highest amount, following by 5,6α-epoxy and 7α-OH. Oxidative pattern shows the formation of other minor compounds, such as 7-ketostanol, 6-ketostanol and 4β-OH. This last one was previously attributed only to enzymatic oxidation. Finally, the relationship between 7-keto and 25-OH were strongly shifted toward the side-chain product, due probably to the exposure of aliphatic chain in crystalline cholesterol. These results confirm the crucial importance of physical state of cholesterol during photo-oxidation, giving an interesting and more complex degradation behavior.