Induction of cytotoxicity and mutagenesis is facilitated by fatty acid hydroperoxidase activity in Chinese hamster lung fibroblasts (V79 cells)

Final Report on the Safety Assessment of Arachidonic Acid

Arachidonic Acid is an essential, polyunsaturated, fatty acid that is used as a surfactant-cleansing agent and a surfactant-emulsifying agent in cosmetic formulations. Arachidonic Acid is well absorbed from the gastrointestinal tract and the circulatory system; it distributes rapidly into the lipid compartment of the body and is rapidly converted to phospholipid by the liver.

Arachidonic Acid may alter the cutaneous immune response; in one study, the effect was more pronounced at lower test concentrations than at higher. Application of Arachidonic Acid to mouse skin produced edema and inflammation, with high dosages possibly causing ulceration of the skin. Arachidonic Acid has mutagenic potential. In a 24 h single insult patch test, a formulation containing 0.04% Arachidonic Acid was not a skin irritant.

The safety of use of this ingredient in cosmetic products has not been documented and substantiated. It cannot be concluded that Arachidonic Acid is safe for use in cosmetic products until the needed additional safety test data have been obtained and evaluated. If the requested skin absorption data indicate that absorption occurs, immunomodulatory data, carcinogenicity and photocarcinogenicity data, human irritation, sensitization, and photosensitization data may also be required.

N-acetylation of three aromatic amine hair dye precursor molecules eliminates their genotoxic potential

N-acetylation has been described as a detoxification reaction for aromatic amines; however, there is only limited data available showing that this metabolic conversion step changes their genotoxicity potential. To extend this database, three aromatic amines, all widely used as precursors in oxidative hair dye formulations, were chosen for this study: p-phenylenediamine (PPD), 2,5-diaminotoluene (DAT) and 4-amino-2-hydroxytoluene (AHT). Aiming at a deeper mechanistic understanding of the interplay between activation and detoxification for this chemical class, we compared the genotoxicity profiles of the parent compounds with those of their N-acetylated metabolites. While PPD, DAT and AHT all show genotoxic potential in vitro, their N-acetylated metabolites completely lack genotoxic potential as shown in the Salmonella typhimurium reversion assay, micronucleus test with cultured human lymphocytes (AHT), chromosome aberration assay with V79 cells (DAT) and Comet assay performed with V79 cells. For the bifunctional aromatic amines studied (PPD and DAT), monoacetylation was sufficient to completely abolish their genotoxic potential. Detoxification through N-acetylation was further confirmed by comparing PPD, DAT and AHT in the Comet assay using standard V79 cells (N-acetyltransferase (NAT) deficient) and two NAT-proficient cell lines,V79NAT1*4 and HaCaT (human keratinocytes). Here we observed a clear shift of dose-response curves towards decreased genotoxicity of the parent aromatic amines in the NAT-proficient cells. These findings suggest that genotoxic effects will only be found at concentrations where the N-acetylation (detoxifying) capacity of the cells is overwhelmed, indicating that a 'first-pass' effect in skin could be taken into account for risk assessment of these topically applied aromatic amines. The findings also indicate that the use of liver S-9 preparations, which generally underestimate Phase II reactions, contributes to the generation of irrelevant positive results in standard genotoxicity tests for this chemical class.

Unexpected DNA damage caused by polycyclic aromatic hydrocarbons under standard laboratory conditions

The genotoxicity of 15 polycyclic aromatic hydrocarbons was determined with the alkaline version of the comet assay employing V79 lung fibroblasts of the Chinese hamster as target cells. These cells lack the enzymes necessary to convert PAHs to DNA-binding metabolites. Surprisingly, 11 PAHs, i.e., benzo[a]pyrene (BaP), benz[a]anthracene, 7,12-dimethylbenz[a]anthracene, 3-methylcholanthrene, fluoranthene, anthanthrene, 11H-benzo[b]fluorene, dibenz[a,h]anthracene, pyrene, benzo[ghi]perylene and benzo[e]pyrene caused DNA strand breaks even without external metabolic activation, while naphthalene, anthracene, phenanthrene and naphthacene were inactive. When the comet assay was performed in the dark or when yellow fluorescent lamps were used for illumination the DNA-damaging effect of the 11 PAHs disappeared. White fluorescent lamps exhibit emission maxima at 334.1, 365.0, 404.7, and 435.8 nm representing spectral lines of mercury. In the case of yellow fluorescent lamps these emissions were absent. Obviously, under standard laboratory illumination many PAHs are photo-activated, resulting in DNA-damaging species. This feature of PAHs should be taken into account when these compounds are employed for the initiation of skin cancer. The genotoxicity of BaP that is metabolically activated in V79 cells stably expressing human cytochrome P450-dependent monooxygenase (CYP1A1) as well as human epoxide hydrolase (V79-hCYP1A1-mEH) could not be detected with the comet assay performed under yellow light. Likewise the DNA-damaging effect of r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BaPDE) observed with the comet assay was only weak. However, upon inhibition of nucleotide excision repair (NER), which is responsible for the removal of stable DNA adducts caused by anti-BaPDE, the tail moment rose 3.4-fold in the case of BaP and 12.9-fold in the case of anti-BaPDE. These results indicate that the genotoxicity of BaP and probably of other compounds producing stable DNA adducts are reliably detected with the comet assay only when NER is inhibited.

Oxidative stress response of rat testis to model prooxidants in vitro and its modulation

Understanding the effects of prooxidants on mammalian testis either in vitro or in vivo is important, since recent evidence shows that oxidative stress can play a vital role in the etiology of male infertility. In this investigation, we have examined the oxidative stress response of adult rat testis in vitro as induced by model prooxidants (tert-butyl hydroperoxide (t-bHP) and cumene hydroperoxide (cHP) deploying two models-testicular cell suspensions (TCS) and testicular explants (TE). Significant induction of oxidative stress was observed in both models as evidenced by increased thiobarbituric acid reactive substances (TBARS) levels on incubation with hydroperoxides. The response was both concentration and time dependent. At the highest concentration (200 microM), both hydroperoxides induced a 100% increase in the TE model, compared with a dramatic (380-560%) increase in the TCS model during a 30-min incubation. Further evidence of oxidative stress such as reduction in the GSH levels and alterations in the activity of antioxidant enzymes (catalase and glutathione peroxidase) were also obtained in the TE model. In the TE model, radical scavengers, namely thiourea, urea and mannitol, as well as antioxidants such as glutathione and catalase inhibited the t-bHP-induced lipid peroxidation response to varying degree. A similar degree of protection was also evident with known antioxidants such as ascorbic acid, butylated hydroxyanisole and butylated hydroxytoluene in the TE model. Further co-incubation of TE either with mercaptosuccinate (a potent glutathione peroxidase inhibitor) or 3-aminotriazole (an irreversible catalase inhibitor) resulted in a marked increase in t-bHP-induced lipid peroxidation, clearly suggesting the importance of both of these enzymic antioxidants in rat testis in vitro. These data suggest that the TE model may be further utilized to screen antioxidants in vitro and also investigate the prooxidant potency of xenobiotics in testicular cells.

Fanconi anemia, complementation group A, cells are defective in ability to produce incisions at sites of psoralen interstrand cross-links

The hypersensitivity of Fanconi anemia, complementation group A, (FA-A) cells to agents which produce DNA interstrand cross-links correlates with a defect in their ability to repair this type of damage. In order to more clearly elucidate this repair defect, chromatin-associated protein extracts from FA-A cells were examined for ability to endonucleolytically produce incisions in DNA at sites of interstrand cross-links. A defined 140 bp DNA substrate was constructed with a single site-specific monoadduct or interstrand cross-link produced by 4,5',8-trimethylpsoralen (TMP) plus long wavelength (UVA) light. Our results show that FA-A cells are defective in ability to produce dual incisions in DNA at sites of interstrand cross-links. Specifically, there is defective incision on the 3'- and 5'-sides of both the furan and pyrone sides of the cross-link. This defect is corrected in FA-A cells transduced with a retroviral vector expressing FANCA cDNA. At the site of a TMP monoadduct, FA-A cells can introduce incisions on both the 3'- and 5'-sides of the furan side monoadduct, but are defective in ability to produce these incisions on the pyrone side monoadduct. These studies also indicate that XPF is involved in production of the 5' incision by the normal extracts on these substrates. These results correlate with our previous work, which showed that FA-A cells are mainly defective in ability to repair psoralen interstrand cross-links with a lesser defect in ability to repair psoralen monoadducts. This defect in endonucleolytic incision at sites of TMP interstrand cross-links could be related to reduced levels of non-erythroid alpha spectrin (alphaSpIISigma*) in the extracts from FA-A cells. alphaSpIISigma* could act as a scaffold to align proteins involved in cross-link repair and enhance their interactions; a deficiency in alphaSpIISigma* could thus lead to reduced efficiency of repair and the decreased levels of incisions we observe at sites of interstrand cross-links in FA-A cells.

Male-mediated dominant lethal mutations in mice following prooxidant treatment

This study's primary aim is to examine if prooxidant treatment has the propensity to induce dominant lethal (DL) type mutations in a randomly bred closed colony of CFT-Swiss mice. Initially, graded doses of both organic hydroperoxides viz., t-butyl hydroperoxide (tbHP), and cumene hydroperoxide (cHP) were administered (i.p.) to adult males and the mortality data was analysed to determine the LD(50) values. cHP was relatively more toxic compared to tbHP. The computed LD(50) values were 1500 and 3000 micromol (kg body weight)(-1) for cHP and tbHP, respectively. Subsequently, adult males were administered (i.p.) with 1/10 LD(50) doses of hydroperoxide (HP) (tbHP--30 micromol (100 g body weight)(-1) and cHP - 15 micromol (100 g body weight)(-1)) on 5 consecutive days and were mated with virgin females for a period of 5 weeks to characterise the male-mediated DL mutations. Male-based analysis of the three major variables viz., implantations, live embryos and dead implants (DI) were carried out to assess the DL-type response induction. While tbHP induced significant increases (2- to 5-fold) in the incidence of DI during the first 4 weeks, cHP induced a marginal increase only during the first week. These results suggest that prooxidants induce DL-type effect only in specific post-meiotic stages of spermatogenesis and stress the need to further investigate the implications of chronic oxidative stress on the male reproductive system.

Genetic toxicity of 2-acetylaminofluorene, 2-aminofluorene and some of their metabolites and model metabolites

2-Acetylaminofluorene and 2-aminofluorene are among the most intensively studied of all chemical mutagens and carcinogens. Fundamental research findings concerning the metabolism of 2-acetylaminofluorene to electrophilic derivatives, the interaction of these derivatives with DNA, and the carcinogenic and mutagenic responses that are associated with the resulting DNA damage have formed the foundation upon which much of genetic toxicity testing is based. The parent compounds and their proximate and ultimate mutagenic and carcinogenic derivatives have been evaluated in a variety of prokaryotic and eukaryotic assays for mutagenesis and DNA damage. The reactive derivatives are active in virtually all systems, while 2-acetylaminofluorene and 2-aminofluorene are active in most systems that provide adequate metabolic activation. Knowledge of the structures of the DNA adducts formed by 2-acetylaminofluorene and 2-aminofluorene, the effects of the adducts on DNA conformation and synthesis, adduct distribution in tissues, cells and DNA, and adduct repair have been used to develop hypotheses to understand the genotoxic and carcinogenic effects of these compounds. Molecular analysis of mutations produced in cell-free, bacterial, in vitro mammalian, and intact animal systems have recently been used to extend these hypotheses.

Linoleic acid hydroperoxide-induced peroxidation of endothelial cell phospholipids and cytotoxicity

Peroxidation of endothelial cell phospholipids was examined following treatments with linoleic acid hydroperoxide. The treatment effects were analyzed over a range of toxicities and exposure intervals as determined by cell plating efficiencies and survival. Over the concentration ranges where lipid peroxidation was evident (20-40 microM treatments in complete medium), significant cytotoxicity was apparent after 1 h of exposure. The extent of toxicity was dependent on the time interval between the end of peroxide treatment and replating of cells. Maximum toxicity was found when cells were replated 1-3 h after treatment. When cells were replated 4 h after treatment a linear increase in cell survival was found as a function of replating time following peroxide exposure. Analysis of cell phospholipids by HPLC after 1 h of exposure to linoleic acid hydroperoxide revealed that peroxidation (evidenced by conjugated diene content) had taken place among a number of phospholipid species with the most marked increases in phosphatidylcholine. Analysis of the fatty acyl composition of phospholipids also showed that the proportions of polyunsaturated fatty acids were reduced relative to saturated fatty acids, indicating peroxidative damage to phospholipids. Pretreatment of cells with vitamin E prevented the peroxidation of all phospholipids and blocked the cytotoxic action of linoleic acid hydroperoxide. These findings indicate that an immediate cytotoxic action of lipid hydroperoxide is associated with peroxidation of membrane phospholipids. This cytotoxicity is a transient effect, and cells surviving the acute injury display a time-dependent increase in plating efficiency representing a period of repair.

Genotoxic effects of the o-phenylphenol metabolites phenylhydroquinone and phenylbenzoquinone in V79 cells

o-Phenylphenol (OPP) and its sodium salt, sodium o-phenylphenate are broad spectrum fungicides and disinfectants with widespread usage. Both chemicals have been reported to induce cancer in the kidney and urinary bladder of Fischer 344 rats. Recently it has been proposed that the metabolic activation of OPP occurs via a two-step process involving the cytochrome P450-mediated formation of phenylhydroquinone (PHQ) in the liver and a prostaglandin H synthase-mediated oxidation of PHQ to phenylbenzoquinone (PBQ) in the urinary tract. In order to further investigate the metabolic activation and genotoxic effects of OPP, we have investigated the ability of PHQ and PBQ to induce micronuclei and mutations at the HGPRT locus in a prostaglandin H synthase-containing V79 Chinese hamster lung fibroblast cell line. In arachidonic acid-supplemented V79 cells, PHQ induced a significant increase in micronuclei whereas no increase was observed in cells in the absence of arachidonic acid supplementation. Immunofluorescent labeling of centromeric proteins with the CREST antibody indicated that the arachidonic acid-dependent induction of micronuclei by PHQ was due almost entirely to micronuclei containing whole chromosomes which had failed to segregate properly during mitosis. The induction of micronuclei by PHQ was significantly inhibited by treatment of the cells with indomethacin, aspirin, ascorbic acid, dithiothreitol and reduced glutathione supporting a role for prostaglandin H synthase in the genotoxic effects of PHQ. No increase in 6-thioguanine-resistant cells was observed in cells treated with PHQ or PBQ. This arachidonic acid-dependent conversion of PHQ to a genotoxic species is consistent with the hypothesis that a prostaglandin H synthase-mediated activation of PHQ may be involved in OPP- and SOPP-induced urinary tract carcinogenesis and also suggests that the induction of aneuploidy may play an important role in OPP-induced tumorigenesis.

Role of oxygen radicals in the chromosomal loss and breakage induced by the quinone-forming compounds, hydroquinone and tert-butylhydroquinone

The mechanisms by which two quinone-forming compounds, hydroquinone (HQ) and tert-butyl-hydroquinone (tBHQ), induce chromosomal loss and breakage in a prostaglandin H synthase-containing V79 cell line have been investigated using the cytokinesis-block micronucleus assay with CREST antibody staining. Increased frequencies of CREST-positive micronuclei (indicating chromosome loss) and CREST-negative micronuclei (indicating chromosome breakage) were observed following exposure of cells to HQ and tBHQ. The formation of micronuclei by HQ, but not tBHQ, was dependent on arachidonic acid supplementation, indicating activation by prostaglandin H synthase. Since the oxidation of hydroquinones can result in the generation of oxygen radicals, the contribution of oxygen radicals to the formation of chromosomal alterations induced by HQ and tBHQ was investigated. In the presence of a superoxide-generating system consisting of hypoxanthine and xanthine oxidase, a significant increase in micronucleated cells was observed. These induced micronuclei consisted exclusively of CREST-negative micronuclei and their formation was completely inhibited by pretreatment with catalase. Catalase also significantly inhibited the CREST-negative micronuclei induced by HQ and tBHQ. In addition, glutathione treatment inhibited both CREST-positive and negative micronuclei induced by these phenolic compounds. These results indicate that both chromosome loss and breakage are induced by these two quinone-forming agents. Reactive oxygen species contribute to the chromosomal breakage induced by HQ and tBHQ but the observed chromosomal loss appears to result from other mechanisms such as an interference of quinone metabolites with spindle formation.

Linoleate-dependent co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol by rat cytosolic lipoxygenase

1. Co-oxygenation of 14C-labelled benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol was studied in rat lung cytosol, using linoleic acid as a co-substrate. Covalently bound and soluble metabolites were quantified by radiometry and h.p.l.c., respectively. 2. The co-oxygenation resulted in the production of reactive metabolites capable of protein binding as well as a series of soluble derivatives. 3. Co-oxygenation of benzo(a)pyrene yielded primarily a significant amount of benzo(a)pyrene-6,12-dione while benzo(a)pyrene-7,8-dihydrodiol led to a significant amount of benzo(a)pyrene-trans-anti-tetrol. 4. Their production was abolished by addition of 25 microM of the lipoxygenase inhibitor and antioxidant NDGA. 5. It is postulated that the linoleic acid peroxyl radicals, formed by rat lung lipoxygenase, initiate the one-electron oxidation of benzo(a)pyrene to its quinones, and epoxidation of benzo(a)pyrene-7,8-diol to the ultimate carcinogenic benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide.

Effect of vitamin E on arachidonic acid peroxidation and its binding to Chinese hamster V79 cell DNA

Following 24 h incubation in standard culture medium (containing 2 microM of arachidonic acid, AA), and 10 and 20 microM supplemented AA, approx. 55, 40 and 33%, respectively, of the fatty acid was incorporated into Chinese hamster V79 cell lipids. The AA content of cells increased 5 to 7-fold with the 10 and 20 microM supplementations of AA and, there was a correspondingly marked decrease in the proportion of AA incorporated into phospholipids (94 vs. 50 and 32%), whereas an increased percentage of AA was recovered in triacylglycerols (1 vs. 30 and 50%) and free fatty acids (1 vs. 3 and 8%). AA at 12 and 22 microM induced a 50 and 80% increase, respectively, in cellular content of thiobarbituric acid reactive substances (TBARS), an indication of increased peroxidation of cell lipids. This formation of TBARS was inhibited by vitamin E but not by indomethacin or SKF-525. Binding of [3H]AA-derived counts to DNA increased in parallel to the levels of cellular lipid peroxidation. Vitamin E added to the culture medium at 10(-4) M was readily taken up by the cells within 48 h and significantly reduced both lipid peroxidation and binding of AA-derived counts to DNA, without affecting AA uptake. Cell vitamin E content was significantly reduced following 24 h incubation in the presence of 10 and 20 microM supplemented AA. This study indicates that products of lipid peroxidation can bind to DNA in cultured cells, and points to a potential cyto- and geno-toxic risk posed by increased cellular AA content relative to anti-oxidant defenses.

Ferrylmyoglobin-catalyzed linoleic acid peroxidation

The addition of linoleic acid (18:2) to a solution containing oxymyoglobin (MbIIO2), metmyoglobin (MbIII), or metmyoglobin-azide complex (MbIII-N3-) resulted in the formation of a common complex with identical absorption spectral properties. The addition of H2O2 to a MbIII/linoleic acid mixture revealed a spectral profile with lambda max at 530 nm and different from that observed in the reaction of MbIII with H2O2 and identical to that of ferrylmyoglobin. This was accompanied by a progressive decrease in the absorption in the visible region, indicating heme degradation during the lipid peroxidation process. The oxidation products of linoleic acid during the MbIII/18:2/H2O2 interaction were assessed by HPLC under anaerobic and aerobic conditions. In both instances, the chromatograms at lambda 234 nm revealed the formation of a main peak with a retention time of 11.1 min, which cochromatographed with a standard of 9-hydroperoxide of linoleic acid. The latter adduct was not degraded by the oxoferryl complex of myoglobin. The conclusions originating from this research are two-fold. On the one hand, the identical spectral properties exhibited by the product originating from the reaction of either MbIIO2 or MbIII with linoleic acid bridge the apparent discrepancy between the different reactivities of MbIIO2 and MbIII toward H2O2 and their ability to promote lipid peroxidation. On the other hand, the pattern of oxidation products of linoleic acid observed during the MbIII/H2O2 interaction, i.e., the formation of a 9-hydroperoxide adduct as a major product, points to a specific binding character and a regioselectivity of the oxoferryl complex in the oxidation of unsaturated fatty acids or a catalytic preference for decomposition of the various isomeric hydroperoxides over that of the 9-hydroperoxide.