Surprising inability of singlet oxygen-generated 6-hydroperoxycholesterol to induce damaging free radical lipid peroxidation in cell membranes.
Singlet oxygen attack on cholesterol (Ch), a prominent monounsaturated lipid of mammalian cell plasma membranes, gives rise to three hydroperoxide (ChOOH) isomers, 5alpha-OOH, 6alpha-OOH and 6beta-OOH, the latter two in lower yield than 5alpha-OOH, and 6alpha-OOH in lowest yield. A third possible positional isomer, 7alpha-OOH and 7beta-OOH, is produced by free radical attack. In the presence of iron and ascorbate (Fe/AH), 5alpha-OOH or 6beta-OOH in phosphatidylcholine/Ch/ChOOH (20:15:1 by mol) liposomes was reduced to its corresponding alcohol, the rate constant being approximately the same for both ChOOHs. Using [(14)C]Ch as an in situ probe, we found that liposomal 5alpha-OOH readily set off free radical-mediated (chain) peroxidation reactions when exposed to Fe/AH, whereas 6beta-OOH under the same conditions did not. Moreover, liposomal 5alpha-OOH triggered robust chain peroxidation in [(14)C]Ch-labeled L1210 cells, leading to cell death, whereas 6beta-OOH was essentially inert in this regard. Thus, 5alpha-OOH and 6beta-OOH undergo iron-catalyzed reductive turnover, but only the former can provoke toxic membrane damage. These novel findings have important implications for UVA-induced photodamage in Ch-rich tissues like skin and eye, where (1)O(2) often plays a major role.
Korytowski
Witold
W
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
Schmitt
Jared C
JC
Girotti
Albert W
AW
D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D002784:Cholesterol / Q000031:analogs & derivatives / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D015227:Lipid Peroxidation; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D051379:Mice; D010545:Peroxides / Q000737:chemistry; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D005609:Free Radicals; D008081:Liposomes; D010545:Peroxides; D026082:Singlet Oxygen; D002784:Cholesterol
J Photochem Photobiol B. 1992 Apr 30;13(2):105-18
1506985
Biochemistry. 1996 Jul 2;35(26):8670-9
8679629
Anal Biochem. 1991 Aug 15;197(1):149-56
1952058
J Org Chem. 1973 Oct 5;38(20):3639-42
4780829
CRC Crit Rev Biochem. 1983;14(1):47-92
6340956
Methods Enzymol. 1999;300:23-33
9919505
Free Radic Biol Med. 2008 Mar 15;44(6):956-68
18206663
J Biol Chem. 1990 Jan 5;265(1):454-61
2294113
Methods Enzymol. 2000;319:85-100
10907502
J Org Chem. 1973 May 4;38(9):1763-5
4709674
J Biol Chem. 2008 Jun 6;283(23):15521-5
18285330
Photochem Photobiol. 1999 Oct;70(4):484-9
10546545
J Biol Chem. 1995 Aug 11;270(32):18825-30
7642534
Arch Biochem Biophys. 2000 Aug 1;380(1):208-18
10900151
J Lipid Res. 1998 Aug;39(8):1529-42
9717713
Free Radic Biol Med. 1999 Aug;27(3-4):301-8
10468202
J Nutr Biochem. 2009 May;20(5):389-98
18656335
Anal Biochem. 1999 May 15;270(1):123-32
10328773