Some oxidized forms of
cholesterol (
oxysterols) are thought to be atherogenic and cytotoxic. Because
plant sterols are structurally related to
cholesterol, we examined whether oxidized
plant sterols (oxyphytosterols) could be identified in human serum and soy-based
lipid emulsions. We first prepared both deuterated and nondeuterated reference compounds. We then analyzed by gas-liquid chromatography-mass spectrometry the oxyphytosterol concentrations in serum from patients with
phytosterolemia or
cerebrotendinous xanthomatosis, in a pool serum and in two
lipid emulsions.
7-Ketositosterol, 7 beta-
hydroxysitosterol, 5 alpha, 6 alpha-epoxysitosterol, 3 beta,5 alpha,6 beta-sitostanetriol, and probably also 7 alpha-
hydroxysitosterol were present in markedly elevated concentrations in serum from phytosterolemic patients only. Also,
campesterol oxidation products such as 7 alpha-hydroxycampesterol and 7 beta-hydroxycampesterol were found. Interestingly,
sitosterol was oxidized for approximately 1.4% in phytosterolemic serum, which is rather high compared with the approximate 0.01% oxidatively modified
cholesterol normally seen in human serum. The same oxyphytosterols were also found in two
lipid emulsions in which the ratio of oxidized
sitosterol to
sitosterol varied between 0.038 and 0.041. In conclusion, we have shown that oxidized forms of
plant sterols are present in serum from phytosterolemic patients and two frequently used soy-based
lipid emulsions. Currently, it is unknown whether oxyphytosterols affect health, as has been suggested for
oxysterols. However,
7 beta-hydroxycholesterol may be one of the more harmful
oxysterols, and both
sitosterol and
campesterol were oxidized into 7 beta-
hydroxysitosterol and 7 beta-hydroxycampesterol. The relevance of these findings therefore deserves further exploration.