Structures and Biological Properties of DNA Adducts Derived from N-Nitroso Bile Acid Conjugates

Abstract

A kind of N-nitrosobile acid conjugate, N-nitrosotaurocholic acid (NO-TCA), was incubated with calf thymus DNA, and formation of an adduct was detected by the 32P-postlabeling method under nuclease P1 conditions. To examine the nucleotides containing the adduct from NO-TCA, each of 2'-deoxyribonucleotide 3'-monophosphates (3'-dAp, 3'-dGp, 3'-dCp, or 3'-Tp) was incubated with NO-TCA. The same adduct spot was detected in the reaction of NO-TCA with 3'-dCp. The structure of this adduct was determined to be 3-ethanesulfonic acid-dC by several spectrometry techniques. Moreover, bulky adducts containing bile acid moiety were also produced from the reaction of NO-TCA with 3'-dCp and 3'-dAp. From comparison with spectral data for authentic compounds, these adducts were concluded to be N4-cholyl-dC and N6-cholyl-dA. N4-Cholyl-dC and N6-cholyl-dA were also detected in calf thymus DNA treated with NO-TCA. In addition, 3-ethanesulfonic acid-dC and N4-deoxycholyl-dC were found to be produced from N-nitrosotaurodeoxycholic acid (NO-TDCA) with dC. NO-TCA and NO-TDCA induced mutations in Salmonella typhimurium TA100 but not in TA98. Mutational spectrum analysis revealed that NO-TCA induced G to A transitions predominantly. When NO-TCA (250 mg/kg) was singly administered to male Wistar rats by gavage, both ethanesulfonic acid-dC and N4-cholyl-dC could be detected in the glandular stomach and colon. The levels of ethanesulfonic acid-dC were 0.22-0.29 per 10(6) nucleotides, but values for N4-cholyl-dC were about 500-fold lower. These observations suggest that N-nitroso bile acid conjugates, NO-TCA and NO-TDCA, may induce G to A base substitutions in genes via DNA adduct formation, producing ethanesulfonic acid- and/or (deoxy)cholic acid-DNA and, therefore, may be related to human carcinogenesis as endogenous mutagens.

Detection of N‐nitroso‐bile acids at 285 nm in reverse‐phase HPLC

“…In addition, some previous researchers strongly suggested that the major source of nitrosable amides in the human body is the conjugated bile acids, and some bile acids might be Nnitrosated in the stomach or intestines to form potentially mitogenic compounds [7][8][9][10]. It is also suggested that DNA adducts might be derived from N-nitroso-bile acid conjugates and related to human carcinogenesis as endogenous mutagens [11]. Chemically synthesized Nnitroso-bile acids also strongly caused a mutant fraction in a human lymphoblast assay [12].…”

Reaction mixtures formed by nitrite and selected sulfa-drugs showed mutagenicity in acidic medium

“…36 N-nitroso bile acid conjugates induced revertants on TA100, which detects base pairs change mutations, but not with TA98, a detector of frame-shift mutations. 37 With the "C" reaction mixture, the behavior was different from "A" and "B" systems: R.C. exceeded the value of 2.00 only for the TA98 strain.…”

Evaluation of the genotoxic effects of thyroxine using in vivo cytogenetic test on Swiss albino mice

“…Therefore, they increase in number each year. However, there is an increasing evidence that some substances which are normally present in the human or animal bodies may, under certain circumstances, exhibit genotoxic effects, therefore acting as endogenous mutagenic agents (Lutz, 1990;Totsuka et al, 2005). Probably the best studied endogenous mutagenic agents are oestrogenic hormones Schallreuter et al, 2006).…”