Cholesterol interaction with free radicals produced from carbon tetrachloride or bromotrichloromethane by either catalytic decomposition or via liver microsomal activation.
The reaction between cholesterol (Ch) and trichloromethyl or trichloromethyl peroxyl radicals was studied. The latter were generated from CCl4 either by benzoyl peroxide (BP) catalysis or via thermal activation or by liver microsomal NADPH-dependent biotransformation of CBrCl3. The structure of the products formed was elucidated by gas chromatography-mass spectrometry (GC/MS). Under aerobic conditions and using thermal activation of CCl4, the formation of 6 products was observed. Two (I and II) were dehydrated Ch derivatives (one also having a third double bond) (I). Another product was a delta(5)-3 ketone derivative of Ch (III). Two additional reaction products were determined as ketocholesterols (IV and V). One chloro Ch was also formed (VI). At low concentrations of BP, reaction was more extensive than under thermal activation, and the formation of peaks I to IV was also observed. When the reaction was conducted anaerobically and using thermal activation of CCl4 to generate radicals, only products I and II were formed in low yield. Under anaerobic conditions, but using catalyst, compounds I and III were produced plus two new isomeric ketocholesterol derivatives (VIII and IX) and also a compound having an extra hydroxyl group on the Ch structure (X). In order to check whether similar reactions are observable under biological experimental conditions, we used activation of CBrCl3 by liver microsomes. The incubation using only microsomes (without CBrCl3 or NADPH) showed two ketocholesterol peaks (A and B). In the presence of CBrCl3 we could detect peak B and hydroxycholesterol (C) and two others, ketocholesterols (D and E). D was the only peak showing close similarity (spectrum and retention time) to one of those observed in the chemical reaction system (V). The reaction of CBrCl3 in the presence of NADPH showed peaks B, C, D and E, in low abundance and a 7-ketocholesterol (F). If some of the reaction products reported here were formed during the intoxication with these haloalkanes, significant biological consequences might be expected.
Centro de Investigaciones Toxicológicas (CEITOX) CITEFA/CONICET, Pcia. de Buenos Aires, Argentina.
S L
SL
Fanelli
G D
GD
Castro
J A
JA
Castro
D000332:Aerobiosis; D000693:Anaerobiosis; D000818:Animals; D001711:Biotransformation; D001975:Bromotrichloromethane / Q000378:metabolism*; D002251:Carbon Tetrachloride / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D005609:Free Radicals; C025280:trichloromethyl free radical; D002784:Cholesterol; D002251:Carbon Tetrachloride; D001975:Bromotrichloromethane