Metabolism of cytotoxic hydroxysterols in cultured cells. Chemical characterization of metabolites

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

7 beta-hydroxycholesterol and 7 beta-hydroxycholesteryl-3-esters reduce the extent of reactive gliosis caused by an electrolytic lesion in rat brain

Electrolytic lesions performed in brain cortex of six-day-old or adult rats resulted in the appearance of many reactive astrocytes around the injury site after a postoperative delay of eight days. They were revealed by immunohistochemistry using antibodies against glial fibrillary acidic protein. Injection of tritiated thymidine 24 h prior to autopsy indicated that, in neonates, 50% of the reactive astrocytes were proliferating. Infusion of 2 microliters of liposome suspension made of phosphatidylcholine and a monosialoganglioside, in the injury site, immediately after the electrolytic lesion did not modify the extent of the reactive gliosis. Liposomes containing 3 nmol of either 7 beta-hydroxycholesterol, 7 beta-hydroxycholesteryl-3-stearate or 7 beta-hydroxycholesteryl-3-oleate reduced by about 50% the intensity of the reactive gliosis in the frontal cortex of six-day-old rats and by 40% the number of dividing astrocytes. In the adult rat cortex the intensity of the glial reaction was also decreased by 30% by 15 nmol 7 beta-hydroxycholesteryl-3-oleate. Further investigations demonstrated that it is the 7 beta-hydroxy function which is needed for the biological activity of these oxysterols. These findings, which demonstrate anti-proliferative and anti-inflammatory properties of 7 beta-hydroxycholesterol on astrocytes, facilitate the future investigation of the influence of reactive gliosis on functional recovery following brain injury. This anti-proliferative property could also be used in other kinds of pathologies involving glial cell proliferation, such as glioblastomas.

Polyoxygenated sterols and triterpenes: chemical structures and biological activities

Cholesterol and other sterols are precursors of many hormones of vertebrates (pregnane, androstane, estrane derivatives), invertebrates (ecdysteroids) and even of plants (brassinoids). The normal biosynthetic processes which begin by a series of oxidations lead to a family of compounds, some of which exhibit a wide variety of biological activities. Among the latter, those well-established are their inhibitory effect on the biosynthesis of cholesterol in mammalian cells, their toxic effect on tumor cells and their ability to modify some immunological responses. None of the members of this family has all of the activities just mentioned. The intensity of the effect depends markedly upon the specific structure of each compound.

Difference in cytotoxicity of (22R)-cholest-5-ene-3 beta,7 alpha,22-triol and (22R)-cholest-5-ene-3 beta,7 beta,22-triol is not explained by different patterns of metabolites

Ehrlich ascites tumor cells in suspension culture were incubated with the plant-derived sterol isomers (22R)-cholest-5-ene-3 beta,7 alpha,22-triol and (22R)-cholest-5-ene-3 beta,7 beta,22-triol. Both sterols were 7-dehydroxylated by the neoplastic cells, and the product was identified as (22R)-22-hydroxycholesta-4,6-dien-3-one. At sub-toxic sterol concentrations the conversion of the 7 alpha-hydroxy compound was about 5 times higher than that of the 7 beta-isomer. At higher sterol concentrations the 7 beta-hydroxy compound caused growth inhibition of the Ehrlich ascites cells, whereas the 7 alpha-hydroxylated sterol was ineffective. The rate of 7 alpha-dehydroxylation was, however, too low to be considered a likely pathway for detoxification. No other lipid-extractable products were detected, and no water-soluble products with influence on cell proliferation were present. Thus, the cytotoxicity is probably attributed to a property of the 7 beta-hydroxyl group of the (22R)-cholest-5-ene-3 beta,7 beta,22-triol.

Effect of 7 beta-hydroxycholesterol on astrocyte primary cultures and derived spontaneously transformed cell lines: cytotoxicity and metabolism

The lethal effect of 7 beta-hydroxycholesterol (7 beta-OHC) on neonatal rat astrocyte primary cultures and spontaneously transformed cell lines derived from them was investigated. Confluent astrocyte primary cultures were not affected by 30 microM 7 beta-OHC over a period of 72 h. In contrast, spontaneously transformed cells were killed by 20 microM 7 beta-OHC within the first 48 h. Further studies indicated that the cell lines metabolized 7 beta-OHC to a product the polarity of which was less than that of 7 beta-OHC. The metabolite was identified as 7 beta-OHC esterified on C-3 by naturally occurring fatty acids. Incubation of the cell lines with 0.5 microM metabolite markedly affected the cells within 24 h. These observations suggest that the 7 beta-OHC metabolite is implicated in the mechanism of action of 7 beta-OHC cytotoxicity on spontaneously transformed cells.