Biomedical subjects

F L Chung

Publications and source records attributed to F L Chung.

113 records · Page 7Linked to original sources

PubMedDate not supplied

Formation of the acrolein-derived 1,N2-propanodeoxyguanosine adducts in DNA upon reaction with 3-(N-carbethoxy-N-nitrosamino)propionaldehyde.

3-(Methylnitrosamino)propionaldehyde (MNPA) is a carcinogenic nitrosamine formed by nitrosation of arecoline, a major alkaloid in areca nut which is a constituent of betel quid. While DNA adducts of its analogue, 3-(methylnitrosamino)propionitrile, have been characterized, little is known about the structures of DNA adducts by MNPA. In this paper, we report that the acrolein-derived 1,N2-propanoguanine adducts are formed upon incubating deoxyguanosine or DNA with 3-(N-carbethoxy-N-nitrosamino)propionaldehyde, a stable carbamate precursor of the metabolically activated MNPA. The identities of these adducts were confirmed by HPLC co-migration, by their NMR and UV spectra, and by chemical properties as compared with those of the synthetic standards. Analogous results were obtained from the reaction of the carbamate with calf thymus DNA. Upon acid or enzyme hydrolysis of the carbamate-modified DNA, acrolein-guanine adducts were detected, and the levels were quantitated. Again, the identities of the adducts were verified by co-chromatography with the standards, by UV spectroscopy, or by the ring-opening with NaOH/NaBH4. Consistent with its ability to modify DNA, the carbamate was found to be mutagenic in Salmonella tester strains. These results show that acrolein is a likely metabolite from the activation of MNPA and that the formation of 1,N2-propanoguanine adducts may contribute to the mutagenicity of the carbamate of MNPA.

Acrolein↗

PubMedDate not supplied

Formation of etheno adducts in reactions of enals via autoxidation.

4-Hydroxy-2-nonenal (HNE) and crotonaldehyde (CA) are alpha,beta-unsaturated aldehydes (enals) produced by lipid peroxidation. Previous studies have shown that enals form tricyclic propano adducts with purine nucleosides. When epoxidized by tert-butyl hydroperoxide, enals yield the more reactive epoxy aldehydes which are capable of modifying adenine and guanine in DNA by forming etheno adducts. The epoxides are considerably more mutagenic and tumorigenic than the parent aldehydes. In this study, we found that, in addition to the propano adducts, etheno adducts are detected upon incubation of enals with deoxyadenosine (dAdo) or deoxyguanosine (dGuo) at 37 degrees C (pH 7.4). When carried out under oxygen-enriched atmosphere, the reaction of HNE with dAdo yielded 1,N6-ethenodeoxyadenosine (1,N6-EdAdo) and 7-(1',2'-dihydroxyheptyl)-1,N6-EdA in 0.03% and 0.48% yield. The reaction with dG gave 0.19% 1,N2-ethenodeoxyguanosine (1,N2-EdGuo) and 0.79% 7-(1',2'-dihydroxyheptyl)-1,N2-EdGuo. In the case of CA, the reaction with dAdo produced 7-(1'-hydroxyethyl)-1,N6-EdAdo in 0.67% yield, while the reaction with dGuo yielded 0.34% 1,N2-EdGuo and 0.97% 7-(1'-hydroxyethyl)-1,N2-EdGuo, respectively. When the above reactions were carried out under nitrogen, yields of etheno adducts were significantly reduced. These results provide evidence for a pathway by which the etheno adducts may be formed by enals via autoxidation.

Aldehydes↗

PubMedDate not supplied

Epoxidation of trans-4-hydroxy-2-nonenal by fatty acid hydroperoxides and hydrogen peroxide.

In this study, we reported that fatty acid hydroperoxides and hydrogen peroxide are capable of epoxidizing 4-hydroxy-2-nonenal, a lipid peroxidation product, to the mutagenic epoxide. The evidence of its formation is provided (i) by trapping with [8-3H]deoxyadenosine for the formation of 7-(1',2'-dihydroxyheptyl)-1,N6-ethenodeoxyadenosine as a pair of diastereomers, (ii) by derivatization with (2,4-dinitrophenyl)hydrazine in acidic methanol, and (iii) by comparing its 1H-nuclear magnetic resonance and mass spectra to those of the authentic standard. After incubating 4-hydroxy-2-nonenal with 9- or 13-linoleic acid hydroperoxide at 37 degrees C for 24 h, the epoxide was produced in 13.4% or 12.5% yield, and with hydrogen peroxide, the yield was 21.5%. In the presence of fatty acid (linoleic acid, gamma-linolenic acid, or arachidonic acid) and lipoxygenase, the epoxide of 4-hydroxy-2-nonenal was formed in 15.3%, 7.2%, or 6.2% yield, respectively. The xanthine/xanthine oxidase/superoxide dismutase system generated the epoxide in 1.2% yield. These yields are estimated on the basis of a standard curve obtained from reactions of deoxyadenosine and epoxide. These results show that 4-hydroxy-2-nonenal is epoxidized by biological oxidants, suggesting a plausible endogenous pathway for the in vivo formation of etheno adducts.

Aldehydes↗

PubMedDate not supplied

A/J mouse lung tumorigenesis by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and its inhibition by arylalkyl isothiocyanates.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is an important carcinogen found in tobacco and tobacco smoke. It is a potent lung tumorigen in rodents and appears to be involved in human cancer induced by tobacco products. NNK induces lung tumors in A/J mice after a single dose; tumor multiplicity is higher when the mice are maintained on an AIN-76A diet than when they are maintained on NIH-07 diet. This paper reviews our recent research using this single-dose model. Bioassays of deuterium substituted analogues of NNK have demonstrated that methylation of DNA by NNK is an important step in lung tumor induction. Arylalkyl isothiocyanates inhibit the metabolic activation of NNK and consequently inhibit its DNA binding and tumorigenesis. Structure activity studies have demonstrated that increasing alkyl chain length leads to increasing efficacy in prevention of NNK tumorigenesis. Thus, 3-phenylpropyl isothiocyanate and 4-phenylbutyl isothiocyanate blocked NNK induced lung tumor formation in A/J mice. Lower doses of longer chain arylalkyl isothiocyanates were even more effective as chemopreventive agents.

Animals↗

PubMedDate not supplied

Quantitation of human uptake of the anticarcinogen phenethyl isothiocyanate after a watercress meal.

Our previous studies showed that phenethyl isothiocyanate (PEITC), a cruciferous vegetable constituent, inhibited the lung tumorigenesis induced by a potent tobacco-specific carcinogenic nitrosamine in animals. These results implicate dietary PEITC as a risk-reducing factor of lung cancers induced by smoking. To define the effect of dietary PEITC on human cancers, a method of measuring its uptake is needed. Since watercress is rich in gluconasturtiin, a glucosinolate precursor of PEITC, it was chosen to be the source of PEITC. Four individuals were asked to eat watercress as part of a breakfast meal, and 24-h urine samples were collected. A urinary metabolite was found, and its identity was confirmed as the N-acetylcysteine conjugate of PEITC by comparison with the synthetic standard using nuclear magnetic resonance and mass spectrometry. A dose-dependent excretion of this conjugate was observed. These results clearly showed that PEITC was released in the human body upon ingestion of watercress and suggest that the N-acetylcysteine conjugate of PEITC may be a useful marker for quantitating human exposure to this anticarcinogen as a tool for epidemiological investigations.

Animals↗