Risk assessment of N-nitrosodiethylamine (NDEA) and N-nitrosodiethanolamine (NDELA) in cosmetics

N-nitrosamines and their precursors found in cosmetics may be carcinogenic in humans. Thus the aim of this study was to carry out risk assessment for N-nitrosamines (N-nitrosodiethanolamine [NDELA], N-nitrosodiethylamine [NDEA]) and amines (triethanolamine [TEA], diethanolamine [DEA]) levels in cosmetics determined using validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) procedures. NDELA and NDEA concentrations were present at levels of "not detected" (N.D.) to 596.5 μg/kg and N.D. to 40.9 μg/kg, respectively. TEA and DEA concentrations ranged from N.D. to 860 μg/kg and N.D. to 26.22 μg/kg, respectively. The nitrite concentration (3-2250 mg/l), number of nitrosating agents to a maximum 5, and pH (3.93-10.09) were also assessed. The impact of N-nitrosamine formation on the levels of TEA, DEA, nitrite, and other nitrosating agents was also examined. N-nitrosamine concentrations correlated with the number of nitrosating agents and nitrite concentrations. Data demonstrated that higher nitrite concentrations and a greater number of nitrosating agents increased NDELA and NDEA yields. Further, the presence of TEA and DEA exerted a significant influence on N-nitrosamine formation. Risk assessments, including the margin of exposure (MOE) and lifetime cancer risk (LCR) for N-nitrosamines and margin of safety (MOS) for amines, were calculated using product type, use pattern, and concentrations. Exposure to maximum amounts of NDELA and NDEA resulted in MOE > 10,000 (based upon the benchmark dose lower confidence limit 10%) and LCR <1 × 10^-5, respectively. In addition, TEA and DEA concentrations in cosmetic samples resulted in MOS values >100. Therefore, no apparent safety concerns were associated with cosmetic products containing NDELA, NDEA, TEA, and DEA in this study. However, since amines and nitrosating agents produce carcinogenic nitrosamines, their use in cosmetics needs to be minimized to levels as low as technically feasible.

Formation and inhibition of N-nitrosodiethanolamine in cosmetics under pH, temperature, and fluorescent, ultraviolet, and visual light

N-nitrosodiethanolamine (NDELA), a type of nitrosamine, is a possible human carcinogen that may form in cosmetic products. The aim of this study was to examine the formation and inhibition of NDELA through chemical reactions of secondary amines including mono-ethanolamine, di-ethanolamine (DEA), and tri-ethanolamine (TEA), and sodium nitrite (SN) under varying conditions such as pH, temperature, and fluorescent, ultraviolet (UV), and visual light (VIS) using liquid chromatography-mass spectroscopy. In a mixture of TEA and SN under acidic conditions pH 2, residual NDELA concentrations rose significantly under various storage conditions in the following order: 50°C > 40°C > UV (2 W/m²) > VIS (4000 lux) > fluorescent light > 25°C > 10°C. In a mixture of DEA and SN under the same acidic pH 2 conditions, NDELA formation was significantly elevated in the following order: UV (2 W/m²) > VIS (4000 lux) > 50°C > 40°C > fluorescent light > 25°C > 10°C. Inhibition of NDELA formation by d-mannitol, vitamin C (Vit C), or vitamin E (Vit E) was determined under varying conditions of pH, temperature, and fluorescent, UV, and VIS. At high concentrations of 100 or 1000 µg/ml, Vit E significantly decreased residual NDELA compared with control levels under acidic pH 2, but not under basic pH 6. Among various antioxidants, Vit E reacted more effectively with many nitrosating agents such as nitrate and nitrite found in cosmetic products. Therefore, to reduce NDELA, it is recommended that cosmetics be stored under cool/amber conditions and that Vit E or Vit C inhibitors of nitrosation be optimally added to cosmetic formulations at concentrations between 100 and 1000 µg/ml.

NDELA and nickel modulation of triazine disposition in skin

Cutting fluids can become contaminated with metals (e.g., nickel, Ni) and nitrosamines (e.g., N-nitrosodiethanolamine, NDELA) and there is concern that these classes of contaminants can modulate dermal disposition and ultimately the toxicity of cutting fluid additives, such as irritant biocides (e.g., triazine). Biocides are added to these formulations to prevent bacterial degradation of commercial cutting fluids. The purpose of this study was to assess the dermal absorption and skin deposition of 14C-triazine when topically applied to porcine skin in an in vitro flow-through diffusion cell system as aqueous soluble oil (mineral oil, MO) or aqueous synthetic (polyethylene glycol, PEG) mixtures. 14C-Triazine mixtures were formulated with NDELA and/or Ni, or with a combination of three additional cutting fluid additives; namely, 5% linear alkylbenzene sulfonate (LAS), 5% triethanolamine (TEA) and 5% sulfurized ricinoleic acid. Neither Ni nor NDELA was absorbed during these 8-h studies. However, 14C-triazine absorption ranged from 2.72 to 3.29% dose in MO and 2.29-2.88% dose in PEG with significantly greater triazine absorption in MO than PEG when all additives and contaminates were present. The difference between these two diluents was most pronounced when NDELA and/or Ni were present in cutting fluids. These contaminants also enhanced triazine deposition on the skin surface and skin tissues especially with PEG-based mixtures. In essence, the dermal disposition of irritant biocides could be dependent on whether the worker is exposed to a soluble oil or synthetic fluid when these contaminants are present. Workers should therefore not only be concerned about dermatotoxicity of these contaminants, but also the modulated dermal disposition of cutting fluid additives when these contaminants are present in cutting fluid formulations.

Modification of carcinogenesis by antioxidants and other compounds

Studies were made on the effects of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), sodium L-ascorbate (SA), ethoxyquin (EQ) and acetaminophen (AAF) on the induction of neoplastic lesions in the liver, kidney or urinary bladder of rats initiated by N-ethyl-N-hydroxyethylnitrosamine (EHEN), diethylnitrosamine (DEN) or N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). The number and area of histochemical gamma-glutamyltranspeptidase-positive (gamma-GT+) foci per unit area of liver section in rats given BHA, BHT, EQ or AAP, but not SA, were significantly less than in rats given EHEN or DEN alone. Similarly, the number of hyperplastic nodules (HN) in groups given BHA or AAP and their area in groups given BHA, EQ or AAP were significantly less than in control groups. Induction of hepatocellular carcinoma (HCC) was also clearly inhibited by these three chemicals. In contrast, the incidence and quantitative values of preneoplastic lesions and renal cell adenoma in the group given EHEN were significantly increased in groups given BHA, EQ or AAP administration. For assesing the influence of BHA and BHT on urinary bladder carcinogenesis, rats received BHA or BHT after treatment with BBN. The incidences and the number per unit length of basement membrane of papilloma and carcinomas were significantly increased in rats given BHA. BHT also showed significant increase but values were less than with BHA. These results clearly demonstrated that BHA, BHT, EQ and AAP inhibit the development of gamma-GT+ foci, or HN and HCC, whereas BHA, EQ and AAP enhance the appearance of preneoplastic and neoplastic lesions in the kidney, BHA and BHT also enhancing urinary bladder carcinogenesis.

Mutagenicity of N-nitrosodiethanolamine in a V79-derived cell line expressing two human biotransformation enzymes

N-nitrosodiethanolamine (NDELA) has demonstrated carcinogenic activity in various rodent models. However, it is negative or only weakly active in standard in vitro genotoxicity assays. This poor response might be due to the requirement of specific enzymes for its activation. Previous work indicated that cytochrome P450 (CYP) 2E1, alcohol dehydrogenases and sulphotransferases (SULTs) can convert NDELA into reactive metabolites. We report here that NDELA induces concentration-dependent gene mutations (at the hprt locus) in V79-hCYP2E1-hSULT1A1 cells, engineered for expression of human CYP2E1 and human SULT1A1, but is inactive in parental V79 cells. Mutagenicity of NDELA in V79-hCYP2E1-hSULT1A1 cells was abolished by the CYP2E1 inhibitor 1-aminobenzotriazole, but unaffected by the SULT1A1 inhibitor pentachlorophenol. The efficiency and specificity of these inhibitors was demonstrated in gene mutation assays using SULT- and CYP2E1-dependent reference mutagens, 2-nitropropane and N-nitrosodimethylamine, respectively. In this study, it is documented for the first time that NDELA can induce gene mutations in mammalian cells. Whereas human CYP2E1 was required for its activation, human SULT1A1 was not involved either in its activation or its inactivation in our cell model.

Etiology of bromate-induced cancer and possible modes of action-studies in Japan

Renal cell tumors were significantly increased in male and female rats given potassium bromate at 250 and 500 mg/L in drinking water. In at least one other study renal cell tumors were produced in male rats at 125 mg/L. Among male mice given 750 mg/L of potassium bromate, there were no significant differences in renal cell tumors between treated and control groups after 88 weeks on test. In oxidative DNA damage tests 8-oxodeoxyguanosine (8-oxodG also referred to as 8-OH-dG) was induced in DNA in the male rat kidney in 1 week, and in females after 3 weeks at 500 mg/L, and also in both male and female rats at 250 mg/L, but not at 125 mg/L. DNA adducts are considered to be an initial step in the carcinogenesis process, however, the administered doses are not always sufficient to cause mutations, possibly due to DNA repair. In the two-step rat renal carcinogenesis model using N-ethyl-N-hydroxyethylnitrosamine (EHEN) as initiator, promotion activity by potassium bromate was measured using the BrdU labeling index. The promoting activity of bromate in male rats was much greater and extended to doses as low as 60 mg/L in male rats, whereas in females the response was limited to 250 and 500 mg/L. Therefore, it was concluded that the mechanisms contributing to cancer in the male rat were more complex than in the female rat. The accumulation of alpha2mu-globulin in the kidneys of male rats exposed to potassium bromate probably accounts for the greater labeling index in the male rat relative to the female rat. Accumulation of alpha(2mu)-globulin as a result of treatment with chemicals is unique to the male rat and does contribute to carcinogenic responses. Neither humans nor female rats display this response. Nevertheless, bromate must be considered carcinogenic because of the response of the female rats. The better correlation between 8-oxodG formation and tumor response indicates that dose-response information from the female rat would be much more relevant to human risk assessment. The fact that an elevation of BrdU-LI in the kidney of the female rat is consistent with the possibility that cell proliferation observed in female rats resulted from oxidative stress and/or cytotoxic responses in the kidney. Therefore, oxidative stress is most likely the mechanism of interest for cancer risk in humans.

Genotoxicity of glycidamide in comparison to (±)-anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide and α-acetoxy-N-nitroso-diethanolamine in human blood and in mammalian V79-cells

Genotoxic activity of glycidamide (GA) was investigated in comparison to that of the known carcinogens (+/-)-anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide ((+/-)-BPDE) and alpha-acetoxy-N-nitroso-diethanolamine (alpha-A-NDELA), using the hypoxanthine-phosphoribosyl-transferase (hPRT) gene mutation assay with V79 mammalian cells and modified alkaline single cell gel electrophoresis (alkaline comet assay with and without treatment of cells with formamido-pyrimidine-DNA-glycosylase (FPG)) in lymphocytes from human whole blood. As shown earlier, GA induced significant DNA damage in lymphocytes from treated whole blood at > or = 300 microM (4 h) (Baum et al., Mutat. Res. 2005, 580, 61-69). In the present study, using the alkaline comet assay with FPG treatment, increased formation of DNA strand breaks was observed in lymphocytes treated with GA (10 microM; 4 h). alpha-A-NDELA and (+/-)-BPDE were genotoxic at 10-30 microM (1 h). Genotoxic activity of these compounds was not enhanced after FPG treatment. FPG treatment thus offers an enhanced sensitivity of DNA damage detection for genotoxic compounds with preference for N(7)- resp. N(3)-purine alkylation. In the hPRT assay with V79 cells, mutagenic activity of (+/-)-BPDE became significant at > or = 3 microM (24 h). For alpha-A-NDELA significant activity was observed at greater, not dbl 10 microM (24 h). As previously observed, GA was considerably less effective, inducing significant mutagenicity roughly at about 80-300-fold higher concentrations (800 microM; 24 h) (Baum et al., Mutat. Res. 2005, 580, 61-69).

Investigation of the formation of N-nitrosodiethanolamine in B6C3F1 mice following topical administration of triethanolamine

To determine potential nitrosation of triethanolamine (TEA) to N-nitrosodiethanolamine (NDELA) at different physiological conditions of the GI tract, in vitro NDELA formation was examined in aqueous reaction mixtures at several pHs (2-10) adjusted with acetic, sulphuric or hydrochloric acids or in cultures of mouse cecal microflora incubated. In vivo NDELA formation was also determined in blood, ingesta, and urine of female B6C3F1 mice after repeated dermal, most relevant human route, or single oral exposure to 1000 mg/kg TEA in the presence of high oral dosages of NaNO(2). Appropriate diethanolamine (DEA) controls were included to account for this impurity in the TEA used. Samples were analyzed for NDELA using GC/MS. The highest degree of nitrosation of TEA to NDELA ( approximately 3%) was observed in the in vitro cultures at pH 4 and acetic acid with lower amounts obtained using sulphuric acid ( approximately 1.3%) and hydrochloric acid ( approximately 1.2%). At pH 7, <1% of the TEA was nitrosated to NDELA and at pH 2 (HCl) or pH 10 (NaOH) no NDELA was found above the limit of detection. In incubated cultures containing cecal microflora and nutrient broth, only 0.68% of TEA was nitrosated to NDELA. No NDELA was formed in rats repeatedly dermally dosed with TEA at the limits of detection in blood (0.001 microg/ml, ppm), ingesta (0.006 microg/ml, ppm), and urine (0.47 microg/ml, ppm). Levels of NDELA measured in blood and ingesta after a single oral dose of TEA and NaNO(2) were less than those in DEA controls. These findings in toto confirm the lack of any significant formation of NDELA from TEA in vivo.

Mass spectrometric methodology for the determination of glyoxaldeoxyguanosine and O6-hydroxyethyldeoxyguanosine DNA adducts produced by nitrosamine bident carcinogens

N-Nitrosodiethanolamine (NDELA) is a bident carcinogen that undergoes both P-450 mediated alpha-hydroxylation and beta-oxidation, leading ultimately to the formation of two prominent DNA adducts, glyoxaldeoxyguanosine (gdG) and O6-2-hydroxyethyldeoxyguanosine (OHEdG), in rat liver. HPLC coupled with electrospray ionization (ESI) and tandem mass spectrometry was used for both detection and quantification of gdG and OHEdG. The method, which is fast, sensitive, and unambiguous, is a significant improvement over the previous 32P-postlabeling methodology. A rapid procedure for the enzymatic hydrolysis of the DNA under acidic conditions preserved the integrity of the pH sensitive gdG adducts. Glyoxal and 3-nitroso-2-oxazolidinone generated gdG and OHEdG adducts, respectively, in calf thymus DNA (ct-DNA) in a concentration (range of 10(4)) dependent manner permitting optimization. Isotopomeric internal standards were prepared from the modified guanine derivatives by enzymatic trans-glycosylation. Quantitative HPLC-ESI-MS/MS analysis employing selective reaction monitoring (SRM) for the loss of the deoxyribose fragment was utilized. Both adducts could be detected in the liver DNA of rats that were administered NDELA in a dose range of 0.4-0.8 mmol/kg. At the highest dose, gdG adducts (4.4-11 adducts/10(6) nuc.) were more abundant than OHEdG adducts (0.35-0.87 adducts/10(6) nuc.). Conversely, OHEdG adducts were produced in higher yields in ct-DNA than were gdG adducts at the same reagent concentrations.

Determination of N-nitrosodiethanolamine in cosmetic products by LC?MS?MS

We have developed and validated in-house a liquid chromatography and mass spectrometry (LC-MS-MS) method for determination of N-nitrosodiethanolamine (NDELA) in cosmetics. The sample is diluted with water and then a C18 clean-up is performed. The average recovery of NDELA is 88.3%, range 48.3-112.7%, and the limit of detection is 22.8 microg kg-1. The repeatability is 7.6%, and the intermediate precision is 8.7%. Surveys were carried out in the Netherlands in September and October 2002 to determine the quantities of NDELA in cosmetics marketed in the Netherlands. The LC-MS-MS method was used to determine the NDELA content of 140 cosmetic products including shower gels, hair oils, shampoos and conditioners, cream and foam baths, mud baths, scrubs, creme and other soaps, and body washes. NDELA at levels ranging from 23 to 992 microg kg-1 was found in 35 cosmetic products.

Effect of dietary selenite on N-nitrosodiethylamine-induced and phenobarbital promoted multistage hepatocarcinogenesis in rat: reflection in some minerals

Selenium (Se), a dietary micronutrient, plays a vital role in cancer chemotherapy in many organs including the liver. We have studied the relationship between some minerals, which are essential in normal functioning of cells and anticancer effect of Se in N-nitrosodiethylamine (DEN) induced and phenobarbital (PB) promoted multistage hepatocarcinogenesis. Se (4 ppm through drinking water; as sodium selenite) was given to animals throughout the study, before initiation and during promotion phase of hepatocarcinogenesis, in a defined experimental protocol. Se, sodium, potassium, calcium and iron were measured either in hepatoma, or surrounding liver tissue or whole liver tissue and serum of experimental animals. DEN and PB treatment significantly (P < 0.001) increased potassium, calcium and iron levels in serum, while it decreased (P < 0.001) the Se and sodium levels when compared with control rats. We have also observed significantly increased (P < 0.001) sodium, calcium and iron levels in hepatoma and surrounding liver tissue, whereas, Se, and potassium level was found to be decreased (P < 0.001) when compared with control rats. Supplementation of selenite throughout the study, before initiation and during promotion stage significantly alters the above mineral content. Results showed that the most significant beneficial effect of selenium during hepatocarcinogenesis was exerted potentially in long-term continuous and/or before the initiation phase of carcinogenicity, rather than in the promotion phase. The present and previous results from our laboratory suggest that sub-optimal intake of a single trace mineral can have broad effects on chemotherapy, providing a framework for understanding the multiple beneficial effects of selenium in cancer chemoprevention.

N -Nitrosodiethanolamine urinary excretion in workers exposed to aqueous metalworking fluids

OBJECTIVE

This work was intended to clarify the extent of exposure of workers occupationally exposed to N-nitrosodiethanolamine (NDELA), a carcinogenic nitrosamine, while working with aqueous metalworking fluids (MWFs) formulated with ("nitrite-formulated") or without ("nitrite-free") nitrite and to study the relationships between the nitrite and NDELA content of the MWFs as well as between the concentration of NDELA in MWFs and in urine.

METHOD

Pre-shift and post-shift urine samples from 100 workers directly exposed to MWFs in 15 factories were analysed for NDELA with chemiluminescent detection (TEA) according to a previously described analytical procedure. The method was also applied to eight indirectly exposed workers and to 48 unexposed subjects. The NDELA and concentrations in 84 fluids used by the workers were also determined.

RESULTS

No detectable NDELA could be observed in the control group. The mean post-shift NDELA excretion in workers exposed to "nitrite-formulated" and "nitrite-free" MWFs were 44.6 and 0.4 microg/l, with maxima of 277 and 2.7 microg/l, respectively. According to the correlation between the nitrite and NDELA concentrations in "nitrite-free" MWFs, there is a low probability of fluids exceeding 5 mg/l NDELA when the nitrite content does not exceed 20 mg/l. The NDELA concentrations in the fluids and urine were found to be highly correlated, particularly after correction for creatinine (r=0.917 in post-shift samples). Cutaneous contact probably contributes, at least in part, to the overall body uptake of NDELA:

CONCLUSION

Due to clear evidence of urinary NDELA excretion in workers exposed to contaminated MWFs, and despite a lack of knowledge of the human risk following NDELA exposure, levels of NDELA in MWFs should be kept as low as possible. NDELA fluid concentrations of less than 1 mg/l must be considered as the objective to be attained, even if the limit of 5 mg/l is temporarily satisfactory and consistent with a nitrite limit of 20 mg/l that is easy to verify with inexpensive colorimetric tests. "Nitrite-formulated" fluids, still sometimes used, should be prohibited. Meanwhile, the material safety data sheets (MSDS) of commercially available products should be clearly labelled to indicate their nitrite content.

Investigating genotoxic and hematotoxic effects of N-nitrosodimethylamine, N-nitrosodiethylamine and N-nitrosodiethanolamine in the hen's egg-micronucleus test (HET-MN)

The hen's egg test for micronucleus induction (HET-MN) combines the use of the commonly accepted genetic endpoint "formation of micronuclei" with the well-characterized and complex model of the incubated hen's egg, which enables metabolic activation, elimination and excretion of xenobiotics including mutagens and promutagens and does not conflict with animal protection regulations and ethical aspects. N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) produced clearly positive, dose-dependent and reproducible results in this assay. NDMA revealed, in accordance with literature data, a much higher mutagenicity than NDEA. For both compounds the sensitivity of HETMN was to a large extent higher than published for the rodent micronucleus test, which is not capable of unequivocally identifying NDEA as positive. Additionally, NDEA induced severe anemia without obscuring the formation of micronucleated cells. N-nitrosodiethanolamine (NDELA), which in the literature is described as a non-mutagenic animal carcinogen, could clearly be confirmed as non-mutagenic in the HETMN without showing any disturbing effects on the formation of erythrocytes. The micronucleus frequencies of the concurrent negative controls of all experiments was in agreement with the historic negative control from 302 eggs and 412,532 cells. The same is true for the historic control of proliferation marker from 61 eggs and 13,020 cells. We interpret these results, which correspond well to published data from animal tests, as being further support for using the HET-MN as a reliable alternative genotoxicity assay system, which is physiologically closer to in vivo conditions than in vitro genotoxicity tests, and allows the observation of further local and systemic effects.

N-ethyl-N-hydroxyethylnitrosamine (EHEN)-induced renal and hepatocarcinogenesis in the tumor suppressor Tsc2 transgenic rat

Hereditary renal carcinomas (RCs) develop in Tsc2 gene mutant (Eker) rats around the age of 1 year. We previously reported that Tsc2 mutations were detected in chemically (N-ethyl-N-hydroxyethylnitrosamine (EHEN) and diethylnitrosamine)-induced non-Eker rat RCs, suggesting an involvement of Tsc2 alteration in rat RC development. In this study, we evaluated the effect of extra copies of the Tsc2 gene on renal and hepatocarcinogenesis that was induced by EHEN in vivo. The incidence of RCs in non-transgenic rats (2/17) is slightly higher than in transgenic rats (0/32), although it is statistically not significant. These results suggest the presence of other target RC gene(s) in chemically (EHEN)-induced renal carcinogenesis. We observed no difference in the numbers and areas of the hepatic glutathione S-transferase placental type positive foci.

Down-regulation of von Hippel-Lindau protein in N-nitroso compound-induced rat non-clear cell renal tumors

Non-clear cell rat kidney tumors, inducible by N-nitroso compounds but lacking mutations in the von Hippel--Lindau (VHL) coding sequence, were examined for other VHL alterations. Neither mutations nor DNA methylation was detected in a putative promoter region. By immunohistochemistry, however, VHL protein level was evidently reduced in six of the eight eosinophilic renal epithelial tumors and in all the ten nephroblastomas. Immunoblotting of normal kidney detected two VHL proteins of 20 and 22kDa in a 16-day-old fetal rat but only 20kDa protein in an adult rat. This is the first demonstration of VHL alteration at the protein level.

DNA adducts from N-nitrosodiethanolamine and related beta-oxidized nitrosamines in vivo: (32)P-postlabeling methods for glyoxal- and O(6)-hydroxyethyldeoxyguanosine adducts

The mechanism by which environmentally prevalent N-nitrosodiethanolamine (NDELA) and related 2-hydroxyethyl- or other beta-oxidized nitrosamines initiate the carcinogenic process has remained obscure. (32)P-Postlabeling assays for the pH sensitive glyoxal-deoxyguanosine (gdG) and the O(6)-2-hydroxyethyldeoxyguanosine (OHEdG) DNA adducts have been developed as probes in this mechanistic investigation and used in both in vitro and in vivo experiments. The ready cleavage of the glyoxal fragment from gdG at pH 7 and greater has required methods of optimization in order to achieve a detection limit of 0.05 micromol/mol of DNA. Nuclease P1 treatment enhances the detection of gdG adducts but does not increase the detection limit for OHEdG. For OHEdG, best results were achieved using fraction collection from HPLC (0.3 micromol/mol of DNA). Using radiochemical methods, both adducts could be detected either by HPLC or 2D TLC. NDELA, N-nitrosomorpholine (NMOR), N-nitrosomethyethanolamine (NMELA), and N-nitrosoethylethanolamine (NEELA) all produce both gdG and OHEdG adducts in rat liver DNA in vivo and are called bident carcinogens because fragments from both chains of the nitrosamine are incorporated into DNA. N-Nitroso-2-hydroxymorpholine (NHMOR), a metabolite of NDELA and NMOR, generates gdG in DNA in vitro and in vivo. gdG DNA adducts were found in the range 1.1-6.5 micromol/mol of DNA. OHEdG DNA adducts were produced from equimolar amounts of nitrosamines in rat liver in vivo over the range 4-25 micromol/mol of DNA and in the order NMELA > NEELA > NDELA > NMOR. Deuterated isotopomers of NDELA showed a marked isotope effect on DNA OHEdG adduct formation. alpha-Deuteration markedly decreased OHEdG adduct formation while beta-deuteration had the opposite effect. These data support the hypothesis that NDELA and related nitrosamines are activated by both enzyme mediated alpha-hydroxylation and beta-oxidation. The formation of OHEdG adducts from NDELA requires alpha-hydroxylation of the 2-hydroxyethyl chain, and formation of gdG necessitates a beta-oxidation as well. The bident nature of these carcinogens may explain why they are relatively potent carcinogens despite the fact that major proportions of doses are excreted unchanged.

Microsome-mediated oxidation of N-nitrosodiethanolamine (NDELA), a bident carcinogen

N-Nitrosodiethanolamine (NDELA), an environmentally prevalent, potent carcinogen, undergoes competitive rat liver microsome-mediated oxidation at both the alpha (adjacent to N)- and beta-positions of the 2-hydroxyethyl chains. The former process, alpha-hydroxylation, is detected by the formation of glycolaldehyde (determined as its 2,4-dinitrophenylhydrazone DNP) that is assumed to arise from the decomposition of the corresponding alpha-hydroxynitrosamine, which is also the progenitor of the 2-hydroxyethyldiazonium ion. This finding refutes prior published work that states that the alpha-hydroxylation of NDELA does not occur. Competitive microsomal oxidation at the beta-position gives the hemiacetal N-nitroso-2-hydroxymorpholine (NHMOR) at a rate 1.5 times alpha-hydroxylation. Glycolaldehyde is oxidized in this system to glyoxal at a rate 39 times the conversion of NDELA to glycolaldehyde. The alpha-hydroxylation of NHMOR at either C-3 or C-5 to give glyoxal or glycolaldehyde, respectively, occurs at respective rates 3-6 times that of the alpha-hydroxylation of NDELA. Ethylene glycol, a hydrolysis product of the 2-hydroxyethyldiazonium ion is shown to undergo microsome mediate oxidation to glyoxal. Ethyl-2-hydroxyethylnitrosamine (NEELA) undergoes a similar set of microsome-mediated oxidations at alpha-position of the ethyl (fastest) and 2-hydroxyethyl groups, as well as beta-oxidation of the 2-hydroxyethyl group, a process which is slightly more rapid than alpha-hydroxylation of the same chain. Comparisons of oxidations rates of these substrates, as manipulated by preinducers, isoniazid, streptozocin, and phenobarbital, and enzyme inhibitors diethyldithiocarbamate and 4-methylpyrazole, with that of dimethylnitrosamine, a substrate for cytochrome P450 2E1, strongly suggest that this isozyme is also responsible for the oxidations reported here. alpha-Deuteration of NDELA practically eliminates its alpha-hydroxylation by microsomes from isoniazid induced rats, but doubles beta-oxidation, while beta-deuteration of this substrate significantly reduces beta-oxidation and enhances alpha-hydroxylation. Since both glyoxal-guanine and 2-hydroxyethyl-DNA base adducts are known to arise from the in vivo administration of NDELA and because this work demonstrates that these two fragments can come from the microsomal oxidation of a single nitrosamine molecule containing the 2-hydroxyethyl group, NDELA and related nitrosamines are bident (two-toothed) carcinogens, a process which is likely to enhance their carcinogenic potency.

Strain variation in renal carcinogenesis by N-ethyl-N-hydroxyethylnitrosamine in F1 (Wistar-Fischer) rats

The present study was conducted to compare the incidences of renal tumors in Wistar (W), Fischer (F) and F1 rats (WF: female Wistar rats x male Fischer rats; FW: female Fischer rats x male Wistar rats) induced by N-ethyl-N-hydroxyethylnitrosamine (EHEN). Levels of 8-OHdG in renal DNA were also investigated in Wistar and Fischer rats. After 2000 ppm of EHEN was administered orally for 2 weeks, the animals were fed basal diet until week 32. Wistar males and females demonstrated significantly higher sensitivity regarding induction of renal lesions, while both WF and FW rats had similar incidences, generally intermediate between those for the two parent strains. The formation of 8-OHdG was maximal 60-180 min after an intraperitoneal dose of 750 mg/kg to Wistar and Fischer rats, which correlates with the increase tending to the incidence of renal tumors in male and female Wistar and Fischer rats. The results suggest that EHEN induction of renal tumors is related to oxygen radical damage and that the genes in the Wistar strain responsible for the sensitivity are not inherited in a sex-dependent fashion, despite the male being more susceptible.

Specific genomic alterations in rat renal cell carcinomas induced by N-ethyl-N-hydroxyethylnitrosamine

To characterize genetic alterations occurring in renal tumorigenesis, EHEN-induced renal cell tumors were examined using restriction landmark genomic scanning (RLGS) analysis, an electrophoretic separation technique that detects gene amplifications and deletions. Comparison of DNAs from tumor against those from corresponding nontumorous kidney and/or EHEN-treated kidney without development of renal tumors yielded specific alterations in terms of both amplified and reduced DNA spots. Two amplified spots were detected only in renal cell tumors and an additional four spots were frequent in EHEN-treated kidneys. One reduced spot was common to all tumor samples, and another was frequently detected in the tumors analyzed but not in EHEN-treated kidneys. A subset of the altered spots thus appeared to be specific for EHEN-induced renal tumorigenesis.

Establishment and characterization of three new rat renal cell carcinoma cell lines from N-ethyl-N-hydroxyethylnitrosamine-induced basophilic cell tumors

Three new rat cell lines (designated as BP13, BP30 and BP36B), derived from rat basophilic-type renal cell carcinomas induced with N-ethyl-N-hydroxyethylnitrosamine, were established and characterized. Passaged up to 100 times in vitro for 3 years, each cell line forms epithelial monolayers with cell cycles for BP13, BP30 and BP36B of 29, 21 and 17 h, respectively. Positive glucose-6-phosphate dehydrogenase (G6PD) and gamma-glutamyltransferase (gamma-GT) activity in their cytoplasm, but negative succinate dehydrogenase (SD) and slightly positive carbonic anhydrase type II (CA) localization indicates an origin from proximal tubules. Ultrastructural examination showed the presence of variable numbers of mitochondria and many microvilli and intracellular junctions on the plasma membrane. BP13 and BP30 were found to be tetraploid and BP36B diploid. BP13 has one marker chromosome 15p+, and BP36B an isochromosome of 1q. Anchorage-independent growth and tumorigenicity in immunosuppressed nude mice of BP13 and BP36B, but not BP30, proved their neoplastic nature. These three cell lines should provide useful tools for studying the biological characteristics of renal cell tumors.

Prevention of renal cell carcinoma by active vitamin D3

We studied the serum levels of 1,25-dihydroxyvitamin D [1,25(OH)2D (Vit D)] in patients with renal cell carcinoma (RCC) and the influence of 1,25(OH)2D3 (Vit D3) on gap junctional intercellular communication (GJIC) during carcinogenesis. The serum Vit D levels were measured by a competitive protein-binding assay using the chromatographic method. Using the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay, noncytotoxic concentrations of Vit D3 and the tumor promoters N-nitrosodimethylamine (NDMA) and N-ethyl-N-hydroxyethylnitrosamine (EHEN) were tested against cultured human renal proximal tubular cells (HRPTCs). GJIC function was assayed by the scrape-loading dye transfer technique. Cx43 mRNA expression was also examined by the reverse transcriptase-polymerase chain reaction (RT-PCR). Serum Vit D levels in patients with RCC were lower than those in controls (p< 0.001). Patients with T3 to T4 (rapid-growth) tumors had lower levels of Vit D than did patients with T1 to T2 (slow-growth) tumors (p < 0.001). Vit D3 enhanced the GJIC function of HRPTCs (p < 0.05), whereas NDMA and EHEN suppressed it (p < 0.05). When the cells were treated with tumor promoters and Vit D3 simultaneously, the GJIC functions remained at pretreatment levels. We also demonstrated Cx43 mRNA expression in RPTECs treated with EHEN and VitD3 simultaneously. These data suggest that a decrease in the serum Vit D level is one of the risk factors for development and progression of RCC, and Vit D3 may prevent RCC by preserving GJIC during carcinogenesis.

Screening method for determining the presence of N-nitrosodiethanolamine in cosmetics by open-tubular capillary electrochromatography

The presence of the carcinogenic N-nitrosodiethanolamine (NDELA; CAS No. 1116-54-7) in cosmetic samples was determined using an etched, C18 modified capillary in the open-tubular capillary electrochromatography technique. A very simple extraction procedure leads to a sample matrix free from interferences. The calibration curve was created using UV detection at 214 nm. The detector response was linear in the range of 5-120 ppm total amount injected. Minimum detection limits (1 ppm NDELA injected on capillary) are suitable for screening a large number of cosmetic samples. Diethanolamine and triethanolamine precursors of nitrosamines are not detected at the wavelength used. Cosmetic samples were analyzed unspiked and after addition of 60 ppm of NDELA. In spiked samples recoveries varied from 94% (hand and body lotion) to 55% (lipstick sample). NDELA was found in unspiked samples of old (5-15 years old) cosmetics at concentrations of 14.0 ppm and 35.0 ppm.

Concurrent administration of fish meal and sodium nitrite does not promote renal carcinogenesis in rats after initiation with N-ethyl-N-hydroxyethylnitrosamine

The modifying effects of concurrent administration of fish meal and sodium nitrite on the development of renal tumors after initiation with N-ethyl-N-hydroxyethylnitrosamine (EHEN) were investigated. A total of 120 male 6-week-old Wistar rats were divided into six groups. Groups 1-3 (30 animals each) were given 1000 ppm EHEN in their drinking water for 3 weeks as an initiation treatment for renal cancer induction and thereafter fed respective diets containing 64, 32, and 8% (original concentration in the basal diet) fish meal, and simultaneously given 0.12% sodium nitrite in the drinking water for 33 weeks. Groups 4-6 (ten animals each) were similarly treated without the prior application of EHEN. At the end of the 37th experimental week, all surviving animals were autopsied and examined histopathologically for the existence of renal proliferative lesions. The incidences of dysplastic lesions, adenomas or adenocarcinomas of the kidney were not significantly different among groups 1-3. No renal proliferative lesions were found in groups 4-6. Chronic nephropathy was slightly but significantly enhanced in the 64 and 32% fish meal-treated groups as compared with group 3. Our results suggest that concurrent administration of fish meal and sodium nitrite does not affect the post-initiation phase of EHEN-induced renal carcinogenesis in the rat.

Potential mechanisms of tumorigenic action of diethanolamine in mice

Diethanolamine (DEA), a secondary amine found in a number of consumer products, reportedly induces liver tumors in mice. In an attempt to define the tumorigenic mechanism of DEA, N-nitrosodiethanolamine (NDELA) formation in vivo and development of choline deficiency were examined in mice. DEA was administered with or without supplemental sodium nitrite to B6C3F1 mice via dermal application (with or without access to the application site) or via oral gavage for 2 weeks. Blood levels of DEA reflected the dosing method used; oral greater than dermal with access greater than dermal without access. No NDELA was observed in the urine, blood or gastric contents of any group of treated mice. Choline, phosphocholine and glycerophosphocholine were decreased </=62-84% in an inverse relation to blood DEA levels. These data demonstrated a lack of NDELA formation in vivo at tumorigenic dosages of DEA but revealed a pronounced depletion of choline-containing compounds in mice. It is suggested that the latter effect may underlie DEA tumorigenesis in the mouse.

Glyoxal-guanine DNA adducts: detection, stability and formation in vivo from nitrosamines

The glyoxal-deoxyguanosine adduct (gG) is formed from alpha-nitrosamino aldehydes and dG in vitro and in vivo from nitrosamines carrying the 2-hydroxyethyl side-chain as well as from N-nitrosomorpholine. The structures of all of the diastereomeric forms of both the cis and trans isomers of the adduct have been investigated by ab initio calculations and with nuclear magnetic resonance spectroscopy at 500 MHz. The preferred orientation of the OH groups is trans, but at equilibrium a small amount of the cis isomer was observed. The pH-independent equilibrium constant for the hydrolysis of the gG adduct is K = 1.36 x 10(-4) mol/L, and its rate of formation at pH 7.3 is k = 5.3 min-1 mol-1. In acid (pH 2), the hydrolysis of the nucleosidic linkage is nearly twice as rapid as the hydrolysis of gG to glyoxal and dG. We used a gG analogue to explore a number of reductive methods for derivatization of the adduct, but all of the processes either gave low yields or product mixtures which rendered them impractical for derivatizing the adduct in DNA. A 32P-postlabelling method for detection of the pH-sensitive gG adduct has been developed, which permitted detection of the adduct in the liver DNA of male Wistar rats after administration of selected nitrosamines. The levels of adducts found were: N-nitrosodiethanolamine > 2-hydroxyethylmethynitrosamine > N-nitrosomorpholine > 2-hydroxyethyethylnitrosamine. In separate experiments, N-nitrosodiethanolamine gave greater adduct levels than its metabolite 2-hydroxy-N-nitrosomorpholine. Mechanistic pathways for the generation of gG adducts in vitro and in vivo are discussed.

In vitro DNA deamination by alpha-nitrosaminoaldehydes determined by GC/MS-SIM quantitation

The deamination of DNA bases by three alpha-nitrosaminoaldehydes, butylethanalnitrosamine, methylethanalnitrosamine, and N-nitroso-2-hydroxymorpholine (NHMOR), the direct metabolite of potent animal carcinogen N-nitrosodiethanolamine, was demonstrated by a set of in vitro experiments. The deamination of guanine, adenine, and cytosine bases in nucleotides, oligonucleotides, and calf thymus DNA gave xanthine, hypoxanthine, and uracil, respectively. The order of relative reactivities of the bases was as listed above. Deamination of cytosine to uracil was detected by the reaction of (32)P-labeled oligonucleotide ([5'-(32)P]CGAT) followed by enzymatic hydrolysis. Quantitative analysis of deamination of guanine and adenine in calf thymus DNA was performed by a gas chromatography/mass spectrometry-selected ion monitoring method. Both the extent and the rate of the deamination reactions which occur by transnitrosation from the alpha-nitrosaminoaldehyde to the base were determined for formation of xanthine and hypoxanthine. The deamination of guanine by NHMOR remained significant at low substrate levels.

Carcinogenic effects of N-ethyl-N-hydroxyethylnitrosamine and its metabolites in rats and mice

N-ethyl-N-hydroxyethylnitrosamine (EHEN), a member of the nitrosamine class of carcinogens induces renal cancer. However, since very little is known about the metabolic products of EHEN and their effects, these were investigated in rats and mice. EHEN, N-ethyl-N-formylmethylnitrosamine (EFMN) and N-ethyl-N-carboxymethyl-nitrosamine (ECMN) were administered in the drinking water for 2 weeks and the animals were then maintained until sacrifice at week 32. The urine of the rats was collected over the 2-week exposure period and analyzed by HPLC. The results showed that EHEN but not EFMN or ECMN induces tumors in the kidneys of rats. In mice the lungs were targeted not only by the parent compound but also by both metabolites. The findings suggest that the kidney is the most susceptible organ to EHEN effects in the rat while the lung is the most susceptible organ in mice. These results are consistent with inter-species variation in the metabolism of xenobiotics.

Modifying effects of phytic acid and gamma-oryzanol on the promotion stage of rat carcinogenesis

The modifying effects of phytic acid and gamma-oryzanol on the promotion stage of carcinogenesis were investigated using several two stage carcinogenesis models in rats. In a multi-organ carcinogenesis model, male F344 rats were given combined treatment with 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN), N-ethyl-N-hydroxyethylnitrosamine (EHEN) and 3,2'-dimethyl-4-aminobiphenyl (DMAB) during the initial 3 weeks as initiators, and then treated with dietary 2% phytic acid (50% in water), 1% gamma-oryzanol or basal diet alone for 32 weeks. Although the appearance of hepatic tumors was suppressed, the incidence of urinary bladder papillomas was increased by phytic acid. In addition, the incidence and multiplicity of lung tumors were significantly increased by gamma-oryzanol. Esophagus, colon, pancreas, kidney and thyroid lesion development was not influenced by these compounds. In a gamma-oryzanol dose response experiment using DHPN in the drinking water as an initiator, enhancing effects on lung were observed at a dose of 1% but not at 0.5% or lower. When the modifying effects of phytic acid, and its sodium (Na-PA), potassium (K-PA) and magnesium (Mg-PA) salt were further examined in rats pretreated with the bladder carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), a clear increase in the incidences of bladder tumors was noted, with only Na-PA, phytic acid itself being without effect. Finally, examination of the modifying potential of phytic acid and gamma-oxyzanol on mammary carcinogenesis in female Sprague Dawley rats pretreated with a single intragastric dose of 7,12-dimethylbenz(a)anthracene (DMBA) revealed no significant differences in the final incidences and multiplicities of mammary tumors, but the average tumor diameter was significantly reduced and the average survival time was increased with phytic acid. gamma-Oryzanol tended to decrease the size of the tumor but without significant difference. These results indicate that phytic acid inhibits hepatic and mammary carcinogenesis, while its Na-salt is a promoter of bladder carcinogenesis. The effect of phytic acid itself on urinary bladder carcinogenesis is equivocal. gamma-Oryzanol is a promoter of lung carcinogenesis but its effect is weak and exerted only at a very high dose level.

[Genotoxic effect on human mucous membrane biopsies of the upper aerodigestive tract]

BACKGROUND

In numerous epidemiologic studies, environmental and occupational substances such as sodium dichromate (Na2Cr2O7), benzo[a]pyren (B(a)P), and N'nitroso-diethanolamine (NDELA) have been shown to be of potential carcinogenic risk on human epithelial cells in the upper aerodigestive tract.

METHODS

Using the alkaline microgel electrophoresis technique (comet assay). mucosal cells isolated from biopsies of the upper aerodigestive tract (nose, paranasal sinuses, mouth, pharynx, larynx, and tonsils) were used to analyze target sites for different genotoxic substances and specific sensitivities of each donor. The cells were freshly isolated by enzymic digestion. 0.5-1 x 10(6) cells per donor were obtained with viabilities between 80-100%. After in vitro incubation, the cells were subsequently subjected to the single cell microgel electrophoresis assay. Results were evaluated regarding the personal history of each donor, focusing on previous exposure to tobacco, alcohol, and occupational compounds.

RESULTS

Na2Cr2O7 induced strong genotoxic damage in the nasal and paranasal sinus epithelia as well as in mucosa cells of the larynx. NDELA caused significant damage in mouth cavity epithelia and showed also to be harmful towards mucosa of pharynx and larynx. B(a)P induced fewer DNA strand breaks in mucosal cells of mouth, pharynx and larynx. Significant differences between individuals were apparent for tissue samples from different donors. The genotoxic damage induced in cells of donors with a history of chronic alcohol consumption was significantly higher than in cells of patients without chronic abuse of alcohol.

CONCLUSIONS

The data shows that DNA damage in human epithelial cells of the upper aerodigestive tract induced by environmental and occupational substances can be demonstrated using the microgel electrophoresis technique. The influence of chronic alcohol consumption on the genotoxic effects of substances such as NDELA and B(a)P showed the importance of evaluating preexisting compounding factors.

Effect of polyphenon-60 on the development of renal cell tumors in rats treated with N-ethyl-N hydroxyethylnitrosamine

Green tea consumed as a beverage in Asia contains polyphenols, which contain about a 15% mixture of catechins. The present paper reports the effect of polyphenon-60 (60% pure catechin) on the development of renal cell neoplasms in Wistar rats pretreated with N-ethyl-N-hydroxyethylnitrosamine (EHEN): 0.1% polyphenon-60 in block diet was given over a period of 30 weeks while EHEN was given in drinking water for 2 weeks. The results appears to show a tendency for green tea catechins (GTC) to decrease the incidence of renal cell tumors greater than 3 mm in diameter in Wistar rats but not tumors that are less than 3 mm in diameter. Polyphenon-60 did not affect EHEN initiation in the kidneys of rats. It is postulated that free radicals induced by EHEN may be suppressed by GTC, resulting in a lowering of the tendency for tumor growth.

Probing the mechanism of the carcinogenic activation of N-nitrosodiethanolamine with deuterium isotope effects: in vivo induction of DNA single-strand breaks and related in vitro assays

A series of bioassays, including in vivo induction of DNA single-strand breaks (SSB) and cytotoxicity in cytochrome P450 2E1-transfected cells, were utilized with N-nitrosodiethanolamine (NDELA), its deuterated isotopomers (alpha-D4NDELA and beta-D4NDELA), N-nitroso-2-hydroxymorpholine (NHMOR), and two of its deuterated isotopomers (2-D-NHMOR and 5,5-D2-NHMOR) to probe the mechanism of carcinogenic activation of NDELA and the role of its metabolite NHMOR. DNA samples, taken from the livers of male Wistar rats 4 h after the administration of NDELA, exhibited dose-dependent DNA SSB levels over the range of 0.08-0.75 mmol/kg (body weight), with the greatest SSB level at the highest dose. Deuterium isotope effects on DNA SSB levels were inversely dependent on dose: alpha-D4NDELA, 3. 22-1.37; and beta-D4NDELA, 1.38-0.79. At the lowest dose of 0.15 mmol/kg (body weight), 5,5-D2-NHMOR gave an isotope effect for DNA SSB of 2.8 while that for 2-D-NHMOR was 0.7. NDELA and beta-D4NDELA were equally cytotoxic to human P450 2E1-transfected V79 Chinese hamster cells, while alpha-D4NDELA was not. Significant DNA SSB levels were observed in these cells for NDELA and beta-D4NDELA but not for alpha-D4NDELA. A kinetic deuterium isotope effect of 2.6 for Vmax/Km was observed for the horse liver alcohol dehydrogenase-mediated oxidation of beta-D4NDELA to NHMOR, while kH/kD for alpha-D4NDELA was 1.05. These data provide the first definitive evidence for the activation of NDELA by a pathway involving the scission of the alpha-CH bond and are consistent with P450 2E1-mediated alpha-hydroxylation of NDELA producing the corresponding reactive alpha-hydroxynitrosamine.

Biallelic mutations of the Tsc2 gene in chemically induced rat renal cell carcinoma

A number of cancer genes have been identified by the study of hereditary human cancers and shown to be involved in sporadic genesis of the same tumors. We have identified a germline mutation in the rat homologue of the human tuberous sclerosis (TSC2) predisposing gene in the Eker rat model. In this study, we searched for mutations of the Tsc2 gene in chemically induced non-Eker rat renal cell carcinomas (RCs). N-ethyl-N-hydroxyethylnitrosamine (EHEN)- and diethylnitrosamine (DEN)-induced non-Eker rat primary RCs were subjected to polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis using specific primers covering all exons of the Tsc2 gene (41 coding exons and 1 non-coding exon). We simultaneously searched for mutations in the Vhl gene, a rat homologue of von Hippel-Lindau disease (VHL) gene, as well as the Tsc2 gene. Mutations in the Vhl gene were not detected in any rat RCs (0/8). In contrast, Tsc2 gene mutations were detected at a high frequency in EHEN-induced RCs (2/3) and DEN-induced RCs (3/5) (total 5/8) (p < 0.05). By a direct cloning approach utilizing PCR analysis in 2 applicable cases, we could demonstrate the presence of intragenic somatic mutations in both alleles of the Tsc2 gene. Our results suggest that Tsc2 gene inactivation plays an important role in EHEN- and DEN-induced RCs as well as in Eker rat RCs.

Determination of diethanolamine and N-nitrosodiethanolamine in fatty acid diethanolamides

Diethanolamine (DEA) is a precursor of N-nitrosodiethanolamine (NDELA), an animal carcinogen. A gas chromatographic (GC) method was developed for determining DEA in fatty acid diethanolamides that are commonly used in cosmetic products. Methanolic solutions of the amides were analyzed by GC with flame ionization detection on either a wide-bore methyl silicone (Rtx-1) or 95% dimethyl--5% diphenyl polysiloxane (SPB-5) capillary column. Recovery of DEA from fatty acid dialkanolamides at fortification levels of 0.50, 1.00, and 5.00% ranged from 94 to 100%. In a survey of commercial fatty acid diethanolamides, DEA was found at levels ranging from 1.1 to 14.0%, and most were in good agreement with manufacturer's DEA specifications. Fatty acid diethanolamides also were anlayzed for NDELA by liquid chromatography interfaced to a thermal energy analyzer. Recovery of NDELA from fatty acid diethanolamides at fortification levels of 50, 100, and 200 ppb averaged 95%. No NDELA was found in any of the fatty acid diethanolamide samples analyzed.

Effect of hexachloro-1,3-butadiene on renal carcinogenesis in male rats pretreated with N-ethyl-N-hydroxyethylnitrosamine

Hexachloro-1,3-butadiene (HCBD) is a potent nephrotoxicant that selectively damages the straight portion (pars recta) of the proximal tubule in the rat. To determine its effects on carcinogenesis. HCBD was administered for 30 wk at a concentration of 0.1% by weight in basal diet to male Wistar rats previously given 0.1% N-ethyl-N-hydroxyethylnitrosamine (EHEN) in the drinking water for 2 wk. The combined treatment resulted in a significantly higher incidence of renal cell tumors than when EHEN was administered alone. This chronic exposure and a short course of a 0.2% HCBD diet for 3 wk caused marked increase in the numbers of bromodeoxyuridine-incorporating cells or proliferating cell nuclear antigen-positive cells in the outer stripe of the kidney. The ability of HCBD to promote EHEN-initiated renal tumorigenesis in rats thus appears to be associated intimately with linked nephropathy and subsequent cell proliferation.

Formation of 8-hydroxydeoxyguanosine in rat kidney DNA after administration of N-ethyl-N-hydroxyethylnitrosamine

N-Ethyl-N-hydroxyethylnitrosamine (EHEN) is known to induce renal and liver tumors in rodents. Recent reports have indicated the formation of 8-hydroxydeoxyguanosine (8-OHdG), an oxidative DNA product, induced by various carcinogens. In the present study, to examine whether oxygen radicals are involved in tumorigenesis induced by EHEN, we investigated the formation and localization of 8-OHdG in kidney, liver and lung of rats. The effects of reduced glutathione (GSH) and diethylmaleate on these responses were also studied. Multiple doses of EHEN administrations (250, 500 or 750 mg/kg, i.p.) resulted in a significant elevation of the 8-OHdG level in kidney DNA in a dose-dependent manner and the formation of 8-OHdG reached the maximal level at 1-2 h after EHEN injection and recovered to the control level at 4 h. On the other hand, no increase in the 8-OHdG level was observed in the DNA of liver and lung. Combined pre- and post-treatment of rats with 2 x 800 mg/kg of GSH i.p. inhibited the elevation of the 8-OHdG level induced by EHEN. Pre-treatment with 0.3 ml/kg of diethylmaleate i.p. increased the formation of 8-OHdG. In the immunohistochemical examinations of rats treated with EHEN (750 mg/kg, i.p.), nuclear expression of 8-OHdG was detected in the epithelial cells of renal cortex, while no induction was observed in liver and lung. These findings suggest that the formation of 8-OHdG by active oxygen species may be an important factor in the initiation of EHEN-induced kidney carcinogenesis.

Studies of initiation and promotion of carcinogenesis by N-nitroso compounds

Complete carcinogens must possess both initiating and promoting properties. Most N-nitroso compounds are mutagens and are considered to be initiators, but some are not mutagenic and yet are complete carcinogens. To investigate the two activities, brief treatments of male F344 rats with each of three mutagens, nitrosodimethylurea, nitrosodiethylurea and nitrosobis-(2-oxopropyl)-amine, were followed by chronic treatment (40 weeks) with one of four non-mutagens, nitrosomethyl-3-carboxypropylamine, nitrosodiethanolamine, nitrosomethyl-2-hydroxypropylamine or phenobarbital, the last being a well-known promotor of liver tumors in rats. Each treatment group consisted of 18 animals and there were control groups of 15 animals without initiation and 15 animals without promotion. All surviving rats were sacrificed at week 78. There were almost no tumors in untreated controls or in groups treated with the promotors, other than bladder tumors in one group. Certain tumors were numerous in the initiated groups, but there were only a few instances of increased incidences after treatment with the promotors. The action of the initiators appeared to be the dominant factor and there was scant indication in this experiment of the induction of tumors by the promotors of promotion of initiated cells in most organs (e.g. the liver). This indicates that it is unlikely that non-genotoxic carcinogens induce tumors by promotion of already-initiated cells, but that some other mechanism prevails.

Experimental model of renal tumors in polycystic kidneys: effects of long-term 2-amino-4,5-diphenylthiazole administration in rats treated with N-ethyl-N-hydroxyethylnitrosamine

We previously reported that treatment of Fischer-344 rats with 2-amino-4,5-diphenylthiazole (DPT) results in renal cystic changes. The present study was undertaken to examine the effects of long-term DPT treatment after initiation of kidney carcinogenesis with N-ethyl-N-hydroxyethylnitrosoamine (EHEN) in Wistar rats. One hundred forty-four 6-wk-old male Wistar rats were divided into 6 equal receiving groups: 1000 ppm EHEN or normal tap water for 2 wk followed by 1.06% DPT or basal diet for the subsequent 14 or 30 wk. Controls were maintained without treatment throughout. Subgroups of 6 animals from each group were sacrificed after 8, 16, 24, and 32 wk for histopathological assessment of lesion development in the kidneys and liver. Animals treated with DPT first developed cystic changes of the kidneys (primarily at the corticomedullary border) after 8 wk of treatment, and these changes progressed with time thereafter. In the groups in which DPT treatment was discontinued after 14 wk, cysts then gradually decreased in size. All tumors detected in the kidneys were histopathologically diagnosed as renal cell adenomas. The tumor multiplicity after 32 wk of treatment was significantly higher in Group I, receiving EHEN + DPT for 30 wk (6.33 +/- 4.46), and Group III, receiving EHEN + DPT for 14 wk (3.83 +/- 1.57), than in Group V, EHEN alone (1.00 +/- 0.58) (p < 0.05). Renal cell tumors within cysts were only seen in Groups I and III. The general bromodeoxyuridine labeling indices for the kidneys at week 32 were significantly higher in Group I (55.94 +/- 21.08 cells/mm2) and Group III (53.75 +/- 12.38 cells/mm2) than in Group V (22.38 +/- 6.98 cells/mm2) (p < 0.05). In conclusion, DPT caused cystic changes in rat kidneys, which, however, gradually decreased in size after the treatment was discontinued, suggesting a reversible nature. DPT clearly also promotes renal tumor development after EHEN initiation, and this effect persists, to a certain extent, even after the insult is removed.

Somatic mutation of the tuberous sclerosis (Tsc2) tumor suppressor gene in chemically induced rat renal carcinoma cell

PURPOSE

von Hippel-Lindau (VHL) gene mutations are detected in noninherited, sporadic human renal cell carcinomas (RCs) at a high frequency. We recently identified a germline mutation in the rat homologue of the human tuberous sclerosis (TSC2) predisposing RC gene in the Eker rat model, and in this study we searched for mutations of the Tsc2 gene in chemically induced non-Eker rat RCs.

MATERIALS AND METHODS

Chemically [N-ethyl-N-hydroxyethylnitrosamine (EHEN)]-induced non-Eker rat RC lines (designated as BP13 and BP36B) were subjected to PCR-single strand conformation polymorphism (PCR-SSCP) analysis using specific primers covering entire exons of Tsc2 gene (41 coding exons and one non-coding exon). We simultaneously searched for mutations of Vhl gene, a rat homologue of von Hippel-Lindau disease gene (VHL) as well as Tsc2 gene.

RESULTS

BP36B showed an abnormal mobility shift from the normal tissue of the same rat in exon 35 on analysis by PCR-SSCP. This mutation was confirmed by direct sequencing and found to be a T-to-C transition at the second position of codon 1470, resulting in an amino acid change from leucine to proline (missense mutation).

CONCLUSIONS

This is the first demonstration of Tsc2 gene somatic mutation in non-Eker rat RCs. Our present findings call attention to further investigation of the role of Tsc2 gene mutations in rat renal carcinogenesis and possible Tsc2 gene mutations in human RCs, especially of the non-clear cell type, which are not related to the VHL gene.

An in vivo micronucleus assay for detecting the clastogenic effect in rat kidney cells

A micronucleus assay in vivo has been developed that is based on the use of freshly isolated kidney cells from mononephrectomized rats. In this validation study, a statistically significant increase in the frequency of micronucleated cells was detected in rats given i.p. a single dose of four kidney carcinogens, N-nitrosodimethylamine, N-nitrosodiethylamine, N-ethyl-N-hydroxyethylnitrosamine and N-nitroso-N-methylurea. The clastogenic effect was more marked when the same dose was injected for 3 successive days. As compared to controls, treated rats displayed a reduction in the frequency of binucleated cells, presumably due to a toxicity-induced inhibition of cellular proliferation. The proposed method should be suitable for the detection of the clastogenic effect of procarcinogens biotransformed into reactive species in the kidney.

Effects of n-tritriacontane-16,18-dione, curcumin, chlorphyllin, dihydroguaiaretic acid, tannic acid and phytic acid on the initiation stage in a rat multi-organ carcinogenesis model

The modifying effects of the naturally occurring antioxidants n-tritriacontane-16,18-dione (TTAD), curcumin, dihydroguaiaretic acid (DHGA), chlorophyllin, tannic acid and phytic acid on the initiation stage in a rat multi-organ carcinogenesis model were examined in male F344 rats. Animals were initiated with two i.p. injections of 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN), followed by two i.g. administrations of N-ethyl-N-hydroxyethylnitrosamine (EHEN), and then three s.c. injections of 3,2'-methyl-4-aminobiphenyl (DMAB) during the first 3 weeks. Starting 1 day before the first carcinogen application, groups of rats received diet containing one of the antioxidants (0.2% TTAD, the others at 1% each) until 1 week after the last carcinogen exposure. Surviving animals were killed and complete autopsies were performed at the end of week 36. Histological examination revealed no inhibitory effects in terms of the multiplicities and/or incidences of neoplastic lesions in any of the organs examined, other than a significant increase in seminal vesicle atypical hyperplasia observed in rats treated with tannic acid. Thus, the antioxidants, with the exception of tannic acid, did not show any modifying effects on the initiation stage in the present multi-organ carcinogenesis model and at the present dose levels applied.

Decreased connexin32 and a characteristic enzyme phenotype in clofibrate-induced preneoplastic lesions not shared with spontaneously occurring lesions in the rat liver

Two different types of focal preneoplastic lesions, tentatively named Type I and II lesions, were recognized in the liver of rats chronically treated with clofibrate for 104 weeks. Type I lesions were characterized by mostly negative glucose-6-phosphate dehydrogenase (G6PD) activity (6 out of 10, 60%) and positive expression of succinate dehydrogenase (10 out of 10, 100%), in addition to the previously documented complete lack of expression of glutathione S-transferase, placental form (GST-P) and gamma-glutamyl transpeptidase (GGT). Furthermore, most importantly, Type I lesions exhibited a clear decrease in immunohistochemically demonstrated connexin32 (Cx32) spot counts on their hepatocyte membranes, similarly to nitrosamine-induced lesions. In contrast, Type II lesions, mostly small in size and positively expressing GST-P and/or GGT and G6PD, similarly to their previously reported nitrosamine-induced counterparts, did not exhibit a significant decrease in Cx32 count. In addition, spontaneously occurring lesions, again sharing the same enzyme phenotype, did not show a decrease in Cx32. The results indicate that: (i) a clear distinction between the two lesions, with Type I being involved in clofibrate-induced tumors and Type II being more likely to be spontaneous in nature; (ii) a decrease in Cx32 is closely linked to lesion development and possibly stage of progression, irrespective of the enzyme phenotype and the applied carcinogen; (iii) the unaltered condition of Cx32 may suggest a slow growing or non-progressive nature.

Effects of low dose mixtures of four N-nitroso compounds on hepatic foci development in the rat

Potential synergism between four N-nitroso compounds (nitrosomorpholine, nitrosodimethylamine, nitrosodiethanolamine, nitroso-oxazolidine) in rat liver carcinogenesis was examined in the medium-term bioassay. Male F344 rats were initially given diethylnitrosamine (DEN, 200 mg/kg, ip) and beginning 2 weeks later received test chemicals for 6 weeks individually at a full or 1/4 dose of that proven to be carcinogenic individually or in combination. All animals were subjected to partial hepatectomy at week 3 and killed at week 8. Induction of immunohistochemically-demonstrated glutathione S-transferase placental form (GST-P) positive foci was evaluated. The numbers and size of GST-P positive foci were significantly higher than the control levels by the treatment with each nitrosamine at full (1/1) and one quarter doses (1/4), excepting nitrosodiethanolamine and by combination of the four chemicals at 1/4 and 1/16. Because the dose-response curves were considered non-linear for most nitrosamines, synergistic effects were not apparent for the 1/4 mixture. Interestingly, however, the values for rats treated with these four chemicals in combination at the 1/4 dose level were almost the same as the average of four individual treatments at the full dose, and those for the 1/16 dose mixture were almost the same as the average of 1/4 individual treatment groups. These results indicate that these nitrosamines worked additively, rather than synergistically, in rat liver carcinogenesis.

Cx32 gene mutation in a chemically induced rat liver tumour

Cx32 is a major gap junction protein of the liver and is often aberrantly expressed in liver tumours. We have studied mutation of the Cx32 gene during chemically induced hepatocarcinogenesis. DNA from 12 rat liver tumours induced by diethylnitrosamine or N-ethyl-N-hydroxyethylnitrosamine (EHEN) was analysed by the PCR/SSCP method. One tumour induced by EHEN harboured a G--> A transition mutation at codon 220, substituting His for Arg. When the mutant DNA was transfected into HeLa cells, which are deficient in gap junctional intercellular communication (GJIC), GJIC recovered, as in HeLa cells transfected with the wild-type Cx32 gene. Moreover, GJIC was modulated by cAMP, 12-O-tetradecanoylphorbol-13-acetate and lysophosphatidic acid similarly in mutant and wild-type Cx32 transfectants. These results suggest that Cx32 gene mutations are rarely involved in rat hepatocarcinogenesis and that the mutation found in a tumour may be functionally silent.

Biological monitoring of workers exposed to N-nitrosodiethanolamine in the metal industry

Biological monitoring of occupational hazards was performed in workers using cutting fluids containing N-nitrosodiethanolamine (NDELA). The study involved a group of 25 male subjects from some metal factories in central Italy who used cutting fluids with an NDELA content of > or = 5 mg/l (high-exposure group) and a group of 37 males exposed to cutting fluids with an NDELA content < 5 mg/l (low-exposure group). For comparison, we recruited a control group consisting of 37 subjects living in the same area. For all subjects, internal dose (urinary excretion of NDELA, mutagens, and thioethers), early biological effects (sister chromatid exchanges in blood peripheral lymphocytes), and urinary excretion of D-glucaric acid (DGA) as an endpoint product in the glucuronidation pathway were assessed. The results showed that only the workers using cutting fluids with NDELA concentrations of > or = 5 mg/l excreted trace amounts of NDELA in their urine. Urine excretion of mutagens was similar in the two exposure groups and in the controls. High-exposure subjects had a higher mean value of urinary thioethers than low-exposure and control subjects, but no differences were found in urinary DGA or lymphocyte sister chromatid exchange among the three groups. Smoking status increased the mean values of all the biomarkers, and coffee drinking was associated with urinary DGA excretion.

Detection of primary DNA damage: applicability to biomonitoring of genotoxic occupational exposure and in clinical therapy

The biological effect of putative genotoxic chemicals in the work place environment was monitored in peripheral mononuclear blood cells of exposed workers. DNA strand breaks, alkali-labile sites of DNA and DNA cross-links were measured using the alkaline filter elution method. A dose dependent increase in DNA damage was found in sterilization workers exposed to ethylene oxide and metal workers with exposure towards N-nitrosodiethanolamine. Two subpopulations with different response to the external exposure were found in nonsmoking sterilization workers. Nurses handling antineo-plastic agents without adequate safety provisions showed a statistically significantly higher rate of DNA strand breaks compared to other nurses handling cytostatic drugs with recommended safety equipment and also compared to not exposed controls. Also in several other occupational groups such as fire fighters possibly exposed to several genotoxic chemicals after an accident in a chemical plant, roofers and petrol pump attendants a significantly higher amount of DNA damage was found compared to controls. No statistically significant differences in the amount of DNA strand breaks were found in cabinet makers and car mechanics compared to controls. In peripheral mononuclear blood cells of ovarial carcinoma patients as well as of patients with Morbus Hodgkin an increased DNA strand break rate was found after application of cytostatic drugs. The individual patients showed a very different response after drug intake. The increase in DNA damage after drug application is possibly related to the success of the chemotherapy.