Identification of cholesteryl ester of ferulic acid in human plasma by mass spectrometry.

Epidemiological data suggests that regular consumption polyphenol rich foods and beverages is associated with a reduced risk of certain pathological conditions. While the in vivo "per se" antioxidant benefit of polyphenols still has not been clearly demonstrated, it has been suggested that phenolic acids can be incorporated into low-density lipoproteins (LDL). In the present study, we hypothesized that esterification of phenolic acids - such as ferulic acid - with lipophilic substances such as cholesterol can occur in vivo. To prove this hypothesis, we have synthesized pure cholesteryl-ferulate standard and used gas- and liquid chromatography coupled with mass spectrometry to confirm the presence of endogenous form in human plasma. The detection and identification of cholesteryl ferulate was based on: (1) matching gas- and liquid chromatographic retention time with the reference standard; (2) accurate mass of the molecular ion; (3) matching electron ionization mass spectrum and (4) matching electrospray product ion spectrum. The identified cholesteryl ferulate demonstrated an in vitro antioxidant capacity in various assays. The present study confirmed that phenolic acid can be found in human plasma as lipophilic conjugates which exert antioxidant capacity. These molecules can potentially be involved in the protection of lipoproteins against oxidative damages.