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Biomedical subjects

F L Chung

Publications and source records attributed to F L Chung.

At least 109 records · Page 6Linked to original sources
PubMed1987

Investigations on the molecular dosimetry of tobacco-specific N-nitrosamines.

Approaches for assessing molecular dosimetry of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in humans by measurement of haemoglobin or DNA adducts are discussed. NNK and NNN form haemoglobin adducts in Fischer 344 rats. Acid or base hydrolysis of the globin gives 4-hydroxy-1-(3-pyridyl)-1-butanone, which can be detected in rat blood up to six weeks after injection of NNK; it may be a useful marker for assessing uptake and metabolic activation of NNK and NNN in tobacco consumers. NNK and its major metabolite, 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanol (NNAI), methylated DNA of rat liver, lung and nasal mucosa to similar extents. NNAI is formed in human tissues from NNK, but immunoassays for O6-methyldeoxyguanosine (O6-medGuo) in exfoliated oral cells from snuff-dippers have been negative. NNK is also expected to form pyridyloxobutyl adducts in DNA; 32P-postlabelling assays for these adducts are being developed and appear to hold promise for detecting NNK- or NNN-DNA adducts in vivo.

Animals↗
PubMed1986

Induction of liver tumors in F344 rats by crotonaldehyde.

The tumorigenic activities in F344 rats of crotonaldehyde, a representative alpha, beta-unsaturated carbonyl compound, and N-nitrosopyrrolidine, which could produce crotonaldehyde upon metabolism, were compared. Groups of rats were treated with either crotonaldehyde (0.6 mM or 6.0 mM) or N-nitrosopyrrolidine (0.6 mM) in their drinking water for 113 or 84 weeks, respectively. At the 0.6 mM dose, crotonaldehyde induced neoplastic lesions of the liver in 9 of 27 rats; 2 rats had hepatocellular carcinomas, and 9 rats had neoplastic nodules. It also caused altered liver cell foci in 23 of 27 rats. The incidences of tumors and foci were significantly higher than those of the control group. N-Nitrosopyrrolidine induced hepatocellular carcinomas in 20 of 23 rats, liver neoplastic nodules in 16 of 23 rats, and altered liver cell foci in 23 of 23 rats. Thus, crotonaldehyde appears to be a weaker tumorigen than N-nitrosopyrrolidine. At the 6.0 mM dose, crotonaldehyde treatment caused moderate to severe liver damage in 10 of 23 rats. No preneoplastic or neoplastic lesions were observed in these rats. The remaining 13 rats of this group developed altered liver cell foci. The tumorigenicity of crotonaldehyde suggests that alpha, beta-unsaturated carbonyl compounds, which are ubiquitous in the human environment and can be formed endogenously, may be an important class of potential carcinogens.

Adenoma, Bile Duct↗
PubMed1986

Formation of cyclic nucleic acid adducts from some simple alpha, beta-unsaturated carbonyl compounds and cyclic nitrosamines.

To determine the structures of the DNA adducts of two cyclic nitrosamines, N-nitrosopyrrolidine and N-nitrosomorpholine, the model compounds, alpha-acetoxy-N-nitrosopyrrolidine, 4-(carbethoxynitrosamino)butanal and 2-(carbethoxynitrosamino)ethoxyacetaldehyde, were allowed to react with deoxyguanosine in the presence of porcine liver esterase or base. These model compounds are stable precursors of intermediates formed upon metabolic alpha-hydroxylation of N-nitrosopyrrolidine and N-nitrosomorpholine. The major adducts formed in these reactions were isolated and characterized, on the basis of ultraviolet absorption, mass spectrometry, proton nuclear magnetic resonance and chromatographic properties, as structurally unique 1,N2-cyclic deoxyguanosine adducts. Reaction of crotonaldehyde and glyoxal with deoxyguanosine at 37 degrees C, pH 7, also led to the formation of 1,N2-cyclic deoxyguanosine adducts identical to those formed from the model compounds for alpha-hydroxylation of N-nitrosopyrrolidine and N-nitrosomorpholine, respectively. The 1,N2-cyclic deoxyguanosine adducts were also formed in DNA, upon incubation with N-nitrosopyrrolidine and rat liver microsomes. Acrolein, the simplest alpha, beta-unsaturated carbonyl compound, reacted readily with deoxyguanosine to form three major adducts. These adducts were characterized as cyclic 1,N2-propanodeoxyguanosine adducts resulting from Michael addition of acrolein to the 1- and N2-positions of deoxyguanosine followed by ring closure. One of these adducts, as well as the corresponding crotonaldehyde adduct, was formed in calf thymus DNA upon reaction with acrolein or crotonaldehyde under physiological conditions. The level of modification of DNA by acrolein was considerably higher than that by either crotonaldehyde or N-nitrosopyrrolidine.

Acetaldehyde↗
PubMed1986

Effects of butylated hydroxyanisole on the tumorigenicity and metabolism of N-nitrosodimethylamine and N-nitrosopyrrolidine in A/J mice.

Female A/J mice were maintained on NIH-07 diet or on NIH-07 diet containing butylated hydroxyanisole (BHA, a mixture of 2- and 3-tert-butyl-4-hydroxyanisole), 5 mg/g, for 1 week prior to and during 10 weeks of treatment with N-nitrosodimethylamine (NDMA) or N-nitrosopyrrolidine (NPYR), administered in the drinking water. Twenty weeks after nitrosamine treatment ended, mice were sacrificed and lung adenomas were counted. BHA inhibited NDMA tumorigenesis but enhanced NPYR tumorigenesis. Treatment of A/J mice for three weeks with BHA (5 mg/g) added to semisynthetic diet increased whole lung microsomal alpha-hydroxylation of NDMA and NPYR, as measured by aldehyde production, and increased lung and hepatic glutathione-S-transferase activities. No evidence was found for formation of S-methylglutathione in incubations with NDMA and hepatic supernatants obtained from BHA treated or control mice. Four h after gavage of NDMA, levels of 7-methylguanine in the lung DNA of mice treated with BHA were higher than in the lung DNA of control mice, but levels of O6-methylguanine in the two groups were the same. The results of this study indicate that BHA treatment increases the microsomal metabolic alpha hydroxylation of both NDMA and NPYR, but has differential effects on their tumorigenic activities.

Animals↗
PubMed1985

Formation of the cyclic 1,N2-glyoxal-deoxyguanosine adduct upon reaction of N-nitroso-2-hydroxymorpholine with deoxyguanosine.

N-nitroso-2-hydroxymorpholine, a mutagenic metabolite of N-nitrosomorpholine and N-nitrosodiethanolamine, reacted with deoxyguanosine at pH 7, 37 degrees C, to give 3-(2-deoxy-beta-D-erythropentofuranosyl)-6,7-dihydro-6,7-dihydr oxyimidazo- [1,2-a]purine-9(3H)one, which is also formed by reaction of deoxyguanosine with glyoxal. The results suggest that this adduct might be involved in DNA binding by N-nitrosomorpholine and N-nitrosodiethanolamine.

Chemical Phenomena↗
PubMed1985

Effects of dietary indoles and isothiocyanates on N-nitrosodimethylamine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone alpha-hydroxylation and DNA methylation in rat liver.

Dietary-related indoles, isothiocyanates, and the allyl isothiocyanate glucosinolate, sinigrin, were administered to F344 rats in the diet for 2 weeks (chronic protocol) or by gavage 2 h before sacrifice (acute protocol) and the effects of these pretreatments on the alpha-hydroxylation of two carcinogenic nitrosamines, N-nitrosodimethylamine (NDMA) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), were evaluated. alpha-Hydroxylation was measured in vitro by quantitation of formaldehyde formation upon incubation of the nitrosamines with liver microsomes, and in vivo by quantitation of levels of 7-methylguanine and O6-methylguanine in hepatic DNA, 4 h after nitrosamine treatment. Compounds shown to be inhibitory in the in vitro assay were selected to be further evaluated using the in vivo assay. The results of the in vitro assays showed that indoles were inducers of the demethylation of both nitrosamines. Indole, L-tryptophan and indole-3-carbinol were strong inducers of NDMA and NNK demethylation, respectively. In contrast, isothiocyanates such as phenethyl isothiocyanate and phenyl isothiocyanate demonstrated a wide range of inhibitory activities toward demethylation of these nitrosamines in both the acute and chronic studies. Chronic, but not acute, pretreatment with sinigrin also caused a significant decrease in the demethylation of NDMA and NNK. In view of their promising inhibitory activities, the effects of phenethyl isothiocyanate, phenyl isothiocyanate and sinigrin on the in vivo methylation of DNA by NDMA and NNK were evaluated. The results were parallel to those obtained in the in vitro assays. Phenethyl isothiocyanate, phenyl isothiocyanate and sinigrin generally inhibited the formation of 7-methylguanine and O6-methylguanine in rat hepatic DNA. The results of this study suggest that these compounds could be anticarcinogenic to NDMA and NNK.

Animals↗
PubMed1984

Photoaddition of chlorpromazine to DNA.

Chlorpromazine, 2-chloro-N-(3-dimethylaminopropyl)phenothiazine (CPZ), is a frequently prescribed antipsychotic drug that causes cutaneous photosensitivity in man. CPZ is also phototoxic and photomutagenic in vitro. We have investigated the photoaddition of CPZ to DNA as a possible mechanism for these photobiologic effects. Prior to irradiation, CPZ binds non-covalently to double-stranded calf thymus DNA. At high nucleotide to CPZ ratios, the CPZ absorption maximum shifts from 305 nm to 340 nm with an isosbestic point at 323 nm and 90% of the CPZ fluorescence at 455 nm is quenched. The excitation and emission spectra for the unquenchable fluorescence are the same as those for unbound CPZ. The absorption and fluorescence spectra of unbound CPZ are restored at 0.1 mM magnesium acetate or 100 mM sodium acetate. Non-covalent binding of CPZ to heat-denatured DNA does not shift the CPZ absorption spectrum but quenches 65% of the CPZ fluorescence. Photolytic decomposition of CPZ was inhibited by binding to DNA. In the presence of high concentrations of double-stranded DNA or denatured DNA the photolysis rates were reduced by greater than 98% and 65%, respectively, compared to free CPZ. Formation of covalent photoadducts between CPZ and denatured DNA was 10-fold more efficient than photoadduct formation with double-stranded DNA. Approximately 10% of the CPZ which photodecomposed upon irradiation at 323 nm photoadded to denatured DNA. These results indicate that formation of a complex between CPZ and double-stranded DNA absorbing at 340 nm protects CPZ from photodecomposition and inhibits covalent photoadduct formation.

Animals↗
PubMed1984

Formation of cyclic 1,N2-propanodeoxyguanosine adducts in DNA upon reaction with acrolein or crotonaldehyde.

Acrolein reacted with deoxyguanosine at pH 7 and 37 degrees to give three major products, Adducts 1 to 3, which were separated by high-performance liquid chromatography. They were identified by their ultraviolet, mass, and nuclear magnetic resonance spectra, by the spectra of the corresponding guanine derivatives, and by chemical transformations. Adducts 1 and 2 were two rapidly equilibrating diastereomers of 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-6- hydroxypyrimido [1,2-a]purine-10(3H)one, and Adduct 3 was 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8- hydroxypyrimido [1,2-a]purine-10(3H)one. Adducts 1 and 2 were formed by Michael addition of N-1 of deoxyguanosine to C-3 of acrolein, followed by ring closure between N2 of deoxyguanosine and C-1 of acrolein. Adduct 3 was formed by ring closure in the opposite direction. Adduct 3 was analogous to the major crotonaldehyde-deoxyguanosine adducts which were previously characterized. Adduct 3 (0.2 mmol/mol DNA-P) or the corresponding crotonaldehyde adduct (0.03 mmol/mol DNA-P) was formed when either acrolein or crotonaldehyde was allowed to react with DNA at pH 7 and 37 degrees. These results demonstrate that cyclic 1,N2-propanodeoxyguanosine adducts are formed by reaction of acrolein and crotonaldehyde with DNA.

Acrolein↗
PubMed1984

Carcinogenicity and metabolic activation of tobacco-specific nitrosamines: current status and future prospects.

Over the past decade, research on the carcinogenicity and metabolism of tobacco-specific nitrosamines has provided a basis for understanding their possible roles in human cancer. 4-(N-Nitrosomethylamino)-1-(3-pyridyl)-1-butanone appears to be the most important tobacco-specific nitrosamine, because of its strong carcinogenicity. A large population of smokers and snuff dippers is exposed to significant quantities of this and the other tobacco-specific nitrosamines on a daily basis. Further research should now focus on the relationship between human exposure to tobacco-specific nitrosamines and the risk of developing tobacco-related cancers. Several important areas can be identified: we need to develop sensitive assays that can be used routinely to quantify the levels of tobacco-specific nitrosamines or their metabolites in human blood, and the levels of their DNA adducts in human tissues; we need to establish, through comparative metabolic and DNA-binding studies, the relationships between the organospecificity of tobacco-specific nitrosamines in experimental animals and that in humans; we may also be enabled to identify naturally-occurring substances that can inhibit carcinogenesis by tobacco-specific nitrosamines. These research approaches will hopefully lead to a reduction in the incidence of tobacco-related cancers.

Animals↗
PubMed1984

Inhibition of target tissue activation of N'-nitrosonornicotine and N-nitrosopyrrolidine by dietary components.

Twenty-one dietary and related chemicals have been evaluated for their potential inhibitory activities against the tumorigenic effects of N-nitrosopyrrolidine and N'-nitrosonornicotine using in-vitro metabolic assays in the target tissues, namely, rat liver microsomes and cultured rat oesophagus, respectively. Compounds studied include phenols, cinnamic acids, coumarins, isothiocyanates and indoles. Isothiocyanates were the most potent inhibitors of both nitrosamines in the acute studies, but were less active in chronic studies. This difference may be explained by the pharmacokinetic properties of these compounds. Phenols, cinnamic acids, coumarins and indoles were primarily inducers of N-nitrosopyrrolidine metabolism. The results suggest that isothiocyanates, in general, are the most promising chemicals for future study as protective agents against the carcinogenic effects of these nitrosamines.

Animals↗
PubMed1984

Effects of dietary compounds on alpha-hydroxylation of N-nitrosopyrrolidine and N'-nitrosonornicotine in rat target tissues.

Male F344 rats were pretreated with various dietary compounds, and the effects of pretreatment on the in vitro alpha-hydroxylation of N-nitrosopyrrolidine or N'-nitrosonornicotine were determined in assays with liver microsomes or cultured esophagus, respectively. Dietary compounds included phenols, cinnamic acids, coumarins, indoles, and isothiocyanates. Pretreatments were carried out either by administering the compound by gavage 2 hr prior to sacrifice (acute protocol) or by adding the compound to the diet for 2 weeks (chronic protocol). Acute pretreatment with benzyl isothiocyanate, allyl isothiocyanate, phenethyl isothiocyanate, phenyl isocyanate, and benzyl thiocyanate but not sodium thiocyanate inhibited formation of alpha-hydroxylation products of both nitrosamines. When the chronic pretreatment protocol was used, only phenyl isothiocyanate and sodium thiocyanate inhibited formation of alpha-hydroxylation products of both nitrosamines. Pretreatments with butylated hydroxyanisole, p-methoxyphenol, or N-acetylcysteine had little, if any, effect on the alpha-hydroxylation of N-nitrosopyrrolidine or N'-nitrosonornicotine. Chronic pretreatment with p-hydroxycinnamic acid, 4-hydroxy-3- methoxycinnamic acid, coumarin, umbelliferone, limetine , indole, indole-3-carbinol, indole-3-acetonitrile, and L-tryptophan induced activity for the alpha-hydroxylation of N-nitrosopyrrolidine. The results of this study indicate that isothiocyanates are possible candidates for further study as potential inhibitors of carcinogenesis by N-nitrosopyrrolidine and N'-nitrosonornicotine.

Animals↗
PubMed1980

Synthesis of certain [6:5:6] linear tricyclic nucleosides as potential antitumor agents.

A new class of tricyclic nucleosides in which the aglycon has a linear [6:5:6] geometry has been synthesized using certain pyrrolo[2,3-d]pyrimidine nucleosides as the starting materials. An adenosine-adenosine analogue (12) has been prepared from 6-aminotoyocamycin using two different synthetic routes. An adenosine-guanosine analogue (4) and several adenosine-6-mercaptopurine ribonucleoside-type tricyclic nucleoside derivatives have also been synthesized. Structural assignments have been based on 1H NMR spectral studies, as well as an unequivocal chemical proof of structure. An interesting chemical shift for the 2' hydrogen of certain tricyclic nucleosides was observed and is discussed. The in vitro cytotoxicity of these nucleosides against leukemia L-1210 has been determined. The in vivo evaluation of these tricyclic nucleosides against mouse leukemia will also be discussed.

Animals↗
PubMedDate not supplied

Identification of crotonaldehyde as a hepatic microsomal metabolite formed by alpha-hydroxylation of the carcinogen N-nitrosopyrrolidine.

Crotonaldehyde (2-butenal), which reacts with DNA and is mutagenic and carcinogenic, was identified as a hepatic microsomal metabolite of the hepatocarcinogen N-nitrosopyrrolidine. Incubation mixtures of N-nitrosopyrrolidine, cofactors, and hepatic microsomes from Aroclor pretreated or control F344 rats were derivatized with (2,4-dinitrophenyl)hydrazine reagent and the resulting mixtures analyzed by high-performance liquid chromatography. Crotonaldehyde (2,4-dinitrophenyl)hydrazone was identified by its retention time in two different systems and by its ultraviolet and mass spectrum. The ratio of 4-hydroxybutyraldehyde, which has previously been identified as a metabolite of NPYR, to crotonaldehyde was 1.5-2 over a range of substrate concentrations. The approximate values of Km and nu max for crotonaldehyde were 5.8 mM and 0.6 nmol/min/mg of protein and for 4-hydroxybutyraldehyde 14.1 mM and 1.7 nmol/min/mg of protein, for substrate concentrations between 1 and 8 mM, with microsomes from Aroclor pretreated rats. The ratio of 4-hydroxybutyraldehyde to crotonaldehyde was 1.9 upon esterase-catalyzed solvolysis of alpha-acetoxy-N-nitrosopyrrolidine, a stable precursor to the initial product of N-nitrosopyrrolidine alpha-hydroxylation. These results demonstrate that crotonaldehyde is formed upon metabolic alpha-hydroxylation of N-nitrosopyrrolidine and suggest that it may be involved in N-nitrosopyrrolidine-macromolecule interactions.

Aldehydes↗
PubMedDate not supplied

Structural characterization of adducts formed in the reaction of 2,3-epoxy-4-hydroxynonanal with deoxyguanosine.

Six adducts were isolated by reverse-phase high-performance liquid chromatography from the reaction of deoxyguanosine at 50 degrees C in pH 7.0 buffer with the epoxide of trans-4-hydroxy-2-nonenal, a major alpha,beta-unsaturated aldehyde from lipid peroxidation. These adducts were designated as adducts 1-6. Structures of these adducts were fully characterized by spectroscopic methods such as UV, proton NMR, MS, and CD and by chemical reactions. Adduct 1 was previously identified as 1,N2-ethenodeoxyguanosine. Adducts 2, 3, 5, and 6 are four diastereomeric 1,N2-ethanodeoxyguanosine derivatives possessing two five-membered fused rings at the 1- and N2-positions of guanine. The systematic name of these adducts is 3-(2-deoxy-beta-D-erythropentofuranosyl)-3,5,5a,7,8,8a-hexahydro-8 -hydroxy-7- pentyl-10H-furo[2',3':4,5]imidazo[1,2-a]-purin-10-one. Acid hydrolysis of adducts 5 and 6 yielded the corresponding guanine products which were identical in all respects except having opposite CD. Similar results were obtained with adducts 2 and 3, suggesting they are two pairs of enantiomers. The stereochemical characteristics of these adducts were elucidated. Adduct 4 was characterized by spectroscopic methods and chemical reactions as 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-5,9-dihydro-7-(1,2- dihydroxyheptyl)-9H-imidazo[1,2-a]purin-9-one, a 1,N2-ethenodeoxyguanosine derivative. Upon mild base treatment, adducts 2, 3, 5, and 6 were readily converted to adduct 1. The mechanisms for the formation of these adducts and the conversion of adducts 2, 3, 5, and 6 to adduct 1 are discussed.

Aldehydes↗
PubMedDate not supplied

Formation of acyclic and cyclic guanine adducts in DNA reacted with alpha-acetoxy-N-nitrosopyrrolidine.

This paper describes the reaction of alpha-acetoxy-N-nitrosopyrrolidine with DNA to produce six adducts: two new acyclic adducts, 7-(4-oxobutyl)guanine (6) and 7-(3-carboxypropyl)guanine (7), and four cyclic adducts--the exocyclic 7,8-guanine adducts 5, 11, and 12 and an exocyclic 1,N2-guanine adduct 13--which we have previously characterized. The initial purpose of this study was to carry out an independent synthesis to verify the structure of adduct 5, which is formed in liver DNA of rats treated with N-nitrosopyrrolidine. This was accomplished by the reaction of 2',3',5'-triacetylguanosine with 4-iodobutyraldehyde. This reaction also produced 7-(4-oxobutyl)guanine (6), which underwent air oxidation to 7. The new adducts were characterized by their proton NMR, UV, and mass spectral properties, by chemical transformations, and by independent syntheses. The six adduct standards were used to develop HPLC systems for their analysis as products of the reaction of alpha-acetoxy-N-nitrosopyrrolidine with DNA. Studies on their rates of formation and stability in DNA were carried out. The major products were 7-(4-oxobutyl)guanine (6) and the exocyclic 7,8-guanine adduct 5, which apparently were both formed mainly by reaction with DNA of 4-oxobutanediazohydroxide (4). Their concentrations were maximal after 6 h and subsequently decreased due to depurination. Little evidence was obtained for cyclization of 6 to 5, at the base level or in DNA. The concentrations of adducts 11-13, which were formed by reaction with DNA of crotonaldehyde (10), increased gradually over the 36-h time period studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Differential effects of thiols on DNA modifications via alkylation and Michael addition by alpha-acetoxy-N-nitrosopyrrolidine.

The hepatocarcinogen NPYR is metabolically activated by alpha-hydroxylation mediated by cytochrome P-450 enzymes to yield a 4-oxobutylating agent and 2-butenal (crotonaldehyde). Both are reactive intermediates capable of modifying DNA with guanine either by simple alkylation or by Michael type addition, respectively. In order to assess the roles of these pathways in NPYR tumorigenesis, we are interested in identifying agents which can selectively modify one of these two pathways. In this study, we examined the effects of three thiols--(mesna), glutathione (Glu), and N-acetylcysteine (Nac)--on DNA adduct formation by alpha-acetoxyNPYR, a stable precursor of alpha-hydroxyNPYR. Calf thymus DNA isolated from incubation of alpha-acetoxyNPYR with or without thiol was hydrolyzed and analyzed for the adducts formed by alkylation (adducts 1 and 2) and Michael addition (adducts 3-5). The results showed that the addition of mesna completely blocked the formation of the crotonaldehyde-derived adducts 3-5, whereas it exerted little effect on the formation of the alkylated adducts 1 and 2. These results indicate the preferential conjugation of mesna with crotonaldehyde. In contrast, Nac had little selectivity on adduct formation; levels of adducts 1 to 5 were were reduced by 36-75%. These results suggest that Nac conjugated with both alkylating agent and crotonaldehyde. Similar to mesna, Glu blocked the formation of the crotonaldehyde-derived adducts (adducts 3-5) efficiently. However, unlike mesna, Glu inhibited the formation of adduct 1, while it did not inhibit the formation of adduct 2, although both adducts are presumably derived from the 4-oxobutylating agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗
PubMedDate not supplied

Reaction of alpha-acetoxy-N-nitrosopiperidine with deoxyguanosine: oxygen-dependent formation of 4-oxo-2-pentenal and a 1,N2-ethenodeoxyguanosine adduct.

The six-membered heterocyclic nitrosamine N-nitrosopiperidine (NPIP) is an esophageal carcinogen in the rat whereas its five-membered homologue N-nitrosopyrrolidine (NPYR) is a liver carcinogen. These contrasting organo-specificities may be due to differences between NPIP and NPYR in their metabolic activation to intermediates which bind to DNA. Previous studies have shown that the metabolic activation of NPYR to DNA binding products occurs through alpha-hydroxylation. DNA adducts of NPIP have not been characterized. Therefore, we began our studies by investigating the reaction of alpha-acetoxyNPIP with deoxyguanosine. A major adduct, detected by high-performance liquid chromatography with UV detection, was characterized by its UV, 1H-NMR, and MS as 7-(2-oxopropyl)-5,9-dihydro-9-oxo-3-beta-D-deoxyribofuranosylimidazo+ ++[1,2-a] purine. This 7-(2-oxopropyl)-substituted 1,N2-ethenodeoxyguanosine adduct was formed by reaction of 4-oxo-2-pentenal (3-acetylacrolein) with the 1 and N2 positions of deoxyguanosine. Since the formation of 4-oxo-2-pentenal from alpha-acetoxyNPIP was unexpected, we investigated the solvolysis of alpha-acetoxyNPIP in more detail. Major products formed in incubations of alpha-acetoxyNPIP for 7-24 h in phosphate buffer (pH 7.0) at 37 degrees C included 4-oxo-2-pentenal (11-21% yield), 4-hydroxypentanal (18-22%), and 5-hydroxypentanal (27-29%). The formation of 4-oxo-2-pentenal required O2. The results of this study demonstrate some unique features of the chemistry of alpha-acetoxyNPIP and the resulting deoxyguanosine adducts which may be related to the carcinogenic activity of NPIP.

Acrolein↗