Formation of muconaldehyde, an open-ring metabolite of benzene, in mouse liver microsomes: an additional pathway for toxic metabolites.

Abstract

It has been proposed that a ring-opened form may be responsible for the toxicity of benzene. The present studies demonstrate that incubation of ("C]benzene with liver microsomes (obtained from male CD-1 mice treated with benzene) in the presence of NADPH results in the formation of a ring-opened product. Evidence for the identity of this product was obtained by derivatizing with 2-thiobarbituric acid (TBA), which resulted in the formation of an adduct with a 490-nm absorbance maximum. This ''maximum is identical to that observed after authentic trans,trans-muconaldehyde has reacted with TBA. Separation of muconaldehyde, both with and without trapping with TBA, from other benzene metabolites in the incubation mixture was accomplished by HPLC. The radioactivity profile of fractions collected during HPLC analysis contained peaks that eluted with muconaldehyde and the muconaldehyde-TBA adduct. The structure of the ring-opened product was confirmed by mass spectrometry, studies in whic~h the HPLC peak from the microsomal incubation mixture that eluted at the retention time of authentic muconaldehyde was collected and derivatized with 2,4-dinitrophenylhydrazine. The high-resolution mass spectrum of this sample contained an Ion with an m/z of 291.0729, corresponding to muconaldehyde mono-dinitrophenylhydrazone. These results indicate that benzene is metabolized in vitro to a ring-opened product identified as muconaldehyde.

A Method for In Vitro Culture of Rat Zymbal Gland: Use in Mechanistic Studies of Benzene Carcinogenesis in Combination with 32 P-Postlabeling

“…5 and 6) are consistent with the data of Rushmore et al (27), who have observed different Sephadex LH-20 column proflles of dG adducts in 3H-GMP-prelabeled DNA of rabbit bone marrow mitoplasts exposed in vitro to HQ, BQ, phenol, catechol, and BT. Although phenol or other metabolites of benzene induced relatively high levels of adducts, benzene itself produced adducts at levels barely detectable by the 32P-postlabeling assay. This could result from a) less efficient conversion of benzene to phenol in the Zymbal gland cultures; b) the high volatility of benzene, reducing the effective dose reaching Zymbal glands in the culture medium; and/or c) the metabolism of benzene predominantly to a ring-opened derivative (28), which may form polar adducts not detectable by postlabeling under the (29) to generate (3 'OH)benzetheno(N1,N2)dG as the major derivative on the basis of HPLC and NMR analysis. In comparison with this data, adduct 6, which was detected as the major product of the interaction of BQ with DNA or dGp ( Analysis of AAF adducts here (Fig.…”

Reactive Ring-Opened Aldehyde Metabolites in Benzene Hematotoxicity

“…Muconaldehyde was initially demonstrated to be formed in a mouse liver microsomal system supplemented with reduced nicotinamide adenine dinucleotide phosphate (NADPH) (6). A number of pathways can be postulated to lead to ringopening and the formation of muconaldehyde, as shown in Figure 2.…”

“…The results from hydroxyl radical and singlet oxygen scavenger studies suggest that reactive oxygen species may participate in the ring-opening of benzene in the microsomal system. The formation of muconaldehyde from benzene in liver microsomes (6,21) and the finding of muconic acid in perfusate of rat liver perfused with benzene (22) suggest that the liver is a site of ring opening in vivo.…”

Investigation of the DNA Adducts Formed in B6C3F1 Mice Treated with Benzene: Implications for Molecular Dosimetry

“…Results from microsomal activation systems and in vivo pharmacokinetic studies have shown that the principal metabolites of benzene are phenol, hydroquinone (HQ), muconaldehyde, and catechol (CAT) (8)(9)(10). HQ and CAT accumulate in the bone marrow (11,12), where they are further activated to exert their myelotoxic effects (6).…”