Search

Although significant amounts of polymers associated with adverse health effects in oils are produced during frying, the chemical bonds forming these polymers are not well understood. This study revealed that ester bonds are responsible for the polymerization of soybean oil during frying and heating at 175 °C. The ester value of soybean oil increased during frying up to day 3 of the experiment and slightly decreased on day 4 of the experiment indicating that esterification and hydrolysis concomitantly occurred. The 13C NMR spectra showed further evidence of the formation of ester bonds. This study also examined unidentified chemical bonds in the polymer products, other than ester bonds, with NMR spectroscopy. No NMR signals indicating ether bonds were observed. The NMR study after the reaction of oxidized soybean oil with acetyl chloride clarified assignments of proton signals, confirming some previous assignments, and assigning a new proton signal as an alcohol.

The Ames assays strains TA98 and TA100 have been useful in characterizing complex mixtures from organic solvent extracts of particles from diesel-powered vehicles, ambient air, and other sources. In this paper we report preliminary experiments using TA102, a bacterial strain that detects compounds that can oxidize DNA, to characterize the mutagenicity of an ambient air sample collected in Ann Arbor, MI. Four sets of ambient air filters were collected in duplicate over a period of several days. The mutagenicities of methylene chloride extracts of these filters were compared using strains TA98, TA100 and TA102. The concentration-mutagenicity data for TA98 and TA100 were linear over the concentration range 0–200 μg extract/plate. The mutagenicity of the extracts using TA102 was much lower than the other two strains and was non-linear over the concentration range tested. These results suggest that it would be difficult to use TA102 to identify the oxidative mutagens present in an ambient air particulate extract.

In order to determine the efficiency of organic solvent extractions of fresh diesel-engine exhaust particles a series of Soxhlet extractions were set up using single and sequential extractions of fresh diesel particles with solvents of increasing polarities. Single extractions were carried out with methylene chloride, methanol, acetone and acetonitrile. A single filter was sequentially extracted with methylene chloride followed by methanol, acetone and acetonitrile. Methylene chloride extracted the most mutagenicity relative to the other three solvents. In addition, methylene chloride extracted 97% of the total extracted mutagenicity from a sequential series of extractions. Therefore, we conclude that of the solvents tested methylene chloride extracts the highest proportion of mutagens from fresh diesel exhaust and little mutagenicity is lost using methylene chloride as the only extraction solvent.

The mutagenicities of the five possible isomers of bromomethylfluoranthene, chloromethylfluoranthene, and hydroxymethylfluoranthene were determined in the Ames assay using strains TA100 and TA98 without the addition of rat-liver S9 tissue extract. The mutagenicities of the bromomethyl and chloromethylfluoranthenes ranged from 25 to 6000 rev./nmol. The most mutagenic compound was 8-chloromethylfluoranthene in strain TA98 (6000 rev./nmol). The reactivities of the bromomethylfluoranthenes and the chloromethylfluoranthenes were estimated from electronic structure calculations using the MNDO and the PM3 semi-empirical methods. The bromomethylfluoranthenes showed the smallest differences between the heats of formation of the carbocations and the heats of formation of the parent bromomethyl derivatives. Therefore, the bromomethylfluoranthenes were estimated to be the most reactive of the halomethylfluoranthenes studied. The compound that showed the largest change in heat of formation (the most stable halomethylfluoranthene) going from the halomethylfluoranthene to the carbocation was 2-chloromethylfluoranthene. However, neither the most reactive nor the most stable halomethylfluoranthenes were the most mutagenic in either strain of bacteria. These results are interpreted to suggest that the reactivity of the parent halomethylfluoranthene is not a critical factor in the mechanism by which these compounds are mutagenic, but some other factor, perhaps intercalation, must be a critical step in the mechanism of mutagenesis of these compounds.

In order to investigate the chemistry that leads to the formation of direct-acting mutagens in vehicle exhaust, we have sought a laboratory combustion system that would simulate the particle-associated organic compounds of vehicle exhaust

1-Nitropyrene is an unusually potent direct-acting (in the sense that tissue homogenate is not required for activation) mutagen in the Ames assay (Mermelstein et al., 1981). Recently, there has been considerable interest in 1-nitropyrene as an environmental mutagen because the compound has been found at low concentrations (1-100 ppm) in particles collected from ambient urban air (Gibson, 1982); from fireplace emissions (Gibson, 1982); and from diesel engine exhaust (Pederson and Siak, 1981; Salmeen et al., 1982). In some cases 1-nitropyrene accounted for a few to 10°70 of the direct-acting mutagenicities observed for organic solvent extracts of the particles (Gibson, 1982; Salmeen et al., 1982). Despite its potency in the Ames assay, 1-nitropyrene is not a direct-acting mutagen in mammalian cell culture assays so far tested (I(arpinski et al., 1982; Li and Dutcher, 1983; our data, unpublished). (It may be a weak mutagen for some cells with $9 activation (Li and Dutcher, 1983).) One conjecture to explain the difference between the mutagenicity of 1-nitropyrene in bacteria and in mammalian cells is that the bacteria have a unique nitroreductase activity (Karpinski et al., 1982; Mermelstein et ah, 1981). This conjecture was based on reasonably strong evidence that 1-nitropyrene reduction is necessary for the bacterial mutagenicity of the compound. Herein we describe experiments in which we tested this conjecture with measurements of nitropyrene reduction by intact Salmonella bacteria which are sensitive to mutation by 1-nitropyrene; by Salmonella bacteria which are resistant to mutation by 1-nitropyrene; and by two types of mammalian cells V79 Chinese hamster cells (not sensitive to mutation by 1-nitropyrene), and primary rat liver cells (non-dividing cells). We found that all of the bacterial strains and both types of mammalian cells reduced 1-nitropyrene to 1-aminopyrene. We conclude that reduction of nitropyrene is not unique to bacteria which are sensitive to mutation by 1-nitropyrene and that, although 1-nitropyrene reduction may be necessary, it is not sufficient, for the mutagenicity of 1-nitropyrene.

(Chloromethyl)benzo[a]pyrenes (ClMeB[a]P) are among the most potent direct-acting mutagens (i.e., not requiring metabolic activation) detected by the Ames assay using strain TA98 and TA100. We wanted to determine if molecular quantum mechanics would yield insights into the reactivity and mutagenicity of these compounds. Calculations using the MNDO semiempirical method (MOPAC program) were carried out on a series of ClMeB[a]P. The experimental rates of solvolysis of ClMeB[a]P in 50% aqueous acetone correlated well (r = -0.95) with the differences between the calculated heats of formation of ClMeB[a]P and those of their respective carbocations, supporting the hypothesis that ClMeB[a]P react via carbocations. None of the calculated parameters correlated with mutagenicity. Thus, the prediction of mutagenicity of ClMeB[a]P in the Ames assay is more complex than the simple formation of carbocation intermediates.

The cytotoxic and mutagenic effect of aflatoxin B1-dichloride (AFB1-Cl2), a direct-acting carcinogen which is a model for the proposed ultimate reactive metabolite of AFB1 (the 2,3-epoxide), was compared in normal, repair-proficient, diploid human fibroblasts and in complementation Group A xeroderma pigmentosum cells (XP12BE) which are virtually incapable of excision repair of DNA damage induced by ultraviolet radiation, the 7,8-diol-9,10-epoxide of benzo[a]pyrene, and several reactive aromatic amide derivatives. The XP cells were significantly more sensitive than normal to the cytotoxic and mutagenic effects of AFB1-Cl2, not only as a function of concentration administered but also of the number of AFB1-Cl2 residues initially bound to DNA. Cytotoxicity was determined from survival of colony-forming ability; resistance to 6-thioguanine was the genetic marker used for mutagenicity. We compared the rate of loss of AFB1-Cl2-DNA adducts from cells treated and held in the non-dividing state (confluent) over several days, as well as their ability to recover from the potentially mutagenic and/or cytotoxic effects of the agent. AFB1-Cl2 residues were lost from both strains of cells and both exhibited a gradual increase in survival. However, the rate of loss of adducts from the DNA in the normal cells was more rapid than in XP cells and they exhibited recovery from higher doses of AFB1-Cl2 than XP cells. The major primary DNA adduct formed in the human cells and in isolated DNA was a chemically unstable guanine derivative which could undergo a change in structure with time posttreatment to form a more stable secondary adduct. The cytotoxic effect of AFB1-Cl2 was highly correlated with the presence of either of these guanine adducts. Evidence suggests that the primary adduct is an N7-guanine adduct. The kinetics of the loss of this guanine and its transformation into the more stable secondary adduct resembled that reported recently for the major primary DNA adduct formed by the reaction of AFB1 at the N-7 position of guanine in the DNA of normal and XP cells and its transformation into the putative AFB1-ring opened triamino pyrimidyl structure.

The chemical and mutagenic properties of a series of chloromethylbenzo[a]pyrenes (chloromethyl-BaP) (chloromethyl groups in position 1-, 4-, 5-, 6-, 10-, 11- or 12-) were studied in order to address the question of the importance of arylmethyl carbocations as possible ultimate carcinogens of methylated polycyclic aromatic hydrocarbons (PAH). The rates of solvolysis of the series of chloromethyl-BaP in 50% aqueous acetone decrease in the order: 6 greater than 1 much greater than 4 greater than 12 greater than 5 greater than 10 greater than 11. There is a rough correlation (r = -0.80, P less than 0.05) between rates of solvolysis and the carbon chemical shifts of the methylene carbons. There is a good correlation (r = 0.98, P less than 0.001) between the rates of solvolysis and the gas phase stabilities of the carbocations, (M+ -35), obtained from mass spectral analysis. The mutagenicities of the series of chloromethyl-BaP in the Ames assay with strains TA98 and TA100 showed strong to very strong mutagenicities for the 4-, 5-, 10-, 11- and 12-isomers and weak mutagenicities for the 1- and 6-isomers. The corresponding hydroxymethyl-BaP were not mutagenic. The mutagenicities of some of the chloromethyl-BaP are among the highest reported for direct-acting (not requiring microsomal activation) mutagens in the Ames assay.