Abstract
Cholesterol and α-tocopherol oxidations were studied in brain subcellular fractions isolated from cerebral hemispheres of 4-month-old, male Fischer 344 rats. The fractions were suspended in buffered media (pH 7.4, 37°C) and oxidized by adding (i) ferrous iron (Fe2+) with or without ascorbate or (ii) peroxynitrite (an endogenous oxidant produced by the reaction of superoxide and nitric oxide). Treatment of subcellular fractions with Fe2+ in the presence or absence of ascorbate produced primarily 7-keto- and 7-hydroxy-cholesterols and small amounts of 5α,6α-epoxycholesterol. Since brain contains high levels of ascorbate, any release of iron could result in oxysterol formation. Peroxynitrite oxidized α-tocopherol but not cholesterol. Hence, the toxicity of peroxynitrite or nitric oxide could not be due to cytotoxic oxysterols. When synaptosomes were incubated for 5 min in the presence of 0.5 to 2 μM Fe2+ and ascorbate, α-tocopherol was oxidized while cholesterol remained unchanged. Thus, α-tocopherol is functioning as an antioxidant, protecting cholesterol. Diethylenetriaminepentaacetic acid blocked production of oxysterols, whereas citrate, ADP and EDTA dit not. A significant percentage of mitochondrial cholesterol was oxidized by treatment with Fe2+ and ascorbate. Hence, mitochondrial membrane properties dependent on cholesterol could be particularly susceptible to oxidation. The oxysterols formed were retained within the membranes of synaptosomes and mitochondria. The 7-oxysterols produced are known to be inhibitors of membrane enzymes and also can modify membrane permeability. Hence, oxysterols may play an important role in brain tissue damage during oxidative stress.
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Abbreviations
- DTPA:
-
diethylenetriaminepentaacetic acid
- TMCS:
-
trimethylchlorosilane
- trivial names of sterols: cholest-5-ene-3β,7α-diol:
-
7α-hydroxycholesterol
- cholest-5-ene-3β,7β-diol:
-
7β-hydroxycholesterol
- 3β-hydroxycholest-5-ene-7-one:
-
7-ketocholesterol
- 5,6,α-epoxy-5α-cholestan-3β-ol:
-
5α,6α-epoxycholesterol
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Vatassery, G.T., Quach, H.T., Smith, W.E. et al. Oxidation of cholesterol in synaptosomes and mitochondria isolated from rat brains. Lipids 32, 879–886 (1997). https://doi.org/10.1007/s11745-997-0113-1
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DOI: https://doi.org/10.1007/s11745-997-0113-1