Biological Effects of Oxysterols

Guardiola, F., Codony, R., Addis, P.B., Rafecas, M., Boatella, J. 1996. Biological effects of oxysterols current status. Food Chem. Toxicol. 34, 193-211. 

FIGURE 1.3 The diversity of biological effects of oxidatively modified lipids. A generalized scheme showing both the beneficial and deleterious effects that oxidized lipids can have overall, including the effects of oxidized phospholipids, oxidized FAs, oxysterols, haloge-nated phospholipids, and nitrated lipids. It should be remembered that not all oxidized lipids have these effects and indeed different individual oxidized species may have opposing effects. 

Variable amounts of 7a-hydroxycholesterol (10-20 ng/ml), and various oxidized sitosterol forms are found (in ratio of oxidized sitosterol to sitosterol of about 0.04) in soybean oil based lipid emulsions that are frequently used for intravenous feeding. Cholesterol oxides have also been detected at ppm levels in dehydrated foods, potatoes fried in tallow (Chapter 12) and cured animal products. However, there is no adequate evidence of any harmful biological effects on the amounts ingested in a normal diet and on the degree of absorption and metabolism of oxysterols found in foods. One of the most atherogenic oxysterols is 7)5-hydroxycholesterol, but its possible harmful effects in humans are unknown. 

A voluminous literature has been published on a wide range of oxidation products of cholesterol because of their potential adverse effects on health and in compromising the safety of various food products (Chapters 12 and 13). This section is limited to the initial hydroperoxides serving as precursors to a complex mixture of oxygenated products, also referred to either as oxysterols or as cholesterol oxides. These products formed either enzymatically or non-enzymatically in biological and food systems will be discussed fiuther in Chapters 11 to 13. 

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