Formation of DNA-damaging nitroso compounds by interaction of drugs with nitrite. A preliminary screening for detecting potentially hazardous drugs

Mutagenicity and genotoxicity evaluation of 15 nitrosamine drug substance-related impurities in human TK6 cells

Nitrosamine drug substance-related impurities (NDSRIs) are a sub-category of N-nitrosamine drug impurities that share structural similarity to the corresponding active pharmaceutical ingredient. The mutagenicity of NDSRIs is poorly understood. We previously tested a series of NDSRIs using the Enhanced Ames Test (EAT). In this follow-up study, we further examined the genotoxicity and mutagenicity of 15 of these NDSRIs in human TK6 cells. Seven EAT-positive NDSRIs, including N-nitroso-nortriptyline, N-nitroso-fluoxetine, N-nitroso-desmethyl-diphenhydramine, N-nitroso-duloxetine, N-nitroso-lorcaserin, N-nitroso-varenicline, and N-nitroso-sertraline, induced concentration-dependent increases in micronuclei after bioactivation with hamster liver S9. These NDSRIs were also mutagenic in the TK and HPRT gene mutation assays, consistent with their positive EAT results. In the presence of hamster liver S9, the eight EAT-negative NDSRIs were negative in the micronucleus assay and negative for mutation induction. Using TK6 cells endogenously expressing a single human cytochrome P450 (CYP), we found that CYP2C19, CYP2B6, CYP2A6, and CYP3A4 are key enzymes activating the genotoxicity and mutagenicity of these NDSRIs. Overall, the hamster S9-mediated TK6 cell mutagenicity results agreed with those observed in the EAT, indicating consistency in the mutagenic responses produced by NDSRIs across different testing systems. These data support the use of EAT for hazard identification and safety assessment of NDSRIs.

Regulatory Experiences with Root Causes and Risk Factors for Nitrosamine Impurities in Pharmaceuticals

N-Nitrosamines (also referred to as nitrosamines) are a class of substances, many of which are highly potent mutagenic agents which have been classified as probable human carcinogens. Nitrosamine impurities have been a concern within the pharmaceutical industry and by regulatory authorities worldwide since June 2018, when regulators were informed of the presence of N-nitrosodimethylamine (NDMA) in the angiotensin-II receptor blocker (ARB) medicine, valsartan.  Since that time, regulatory authorities have collaborated to share information and knowledge on issues related to nitrosamines with a goal of promoting convergence on technical issues and reducing and mitigating patient exposure to harmful nitrosamine impurities in human drug products. This paper shares current scientific information from a quality perspective on risk factors and potential root causes for nitrosamine impurities, as well as recommendations for risk mitigation and control strategies.

Nitrosatable drug exposure during the first trimester of pregnancy and selected congenital malformations

BACKGROUND

Nitrosatable drugs can react with nitrite in the stomach to form N-nitroso compounds, and results from animal studies suggest that N-nitroso compounds are teratogens. With data from the National Birth Defects Prevention Study, the relation between prenatal exposure to nitrosatable drugs and limb deficiencies, oral cleft, and heart malformations in offspring was examined.

METHODS

Maternal reports of drugs taken during the first trimester of pregnancy were classified with respect to nitrosatability for mothers of 741 babies with limb deficiencies, 2774 with oral cleft malformations, 8091 with congenital heart malformations, and 6807 without major congenital malformations. Nitrite intake was estimated from maternal responses to a food frequency questionnaire.

RESULTS

Isolated transverse limb deficiencies and atrioventricular septal defects were associated with secondary amine drug exposures (adjusted odds ratios [aORs], 1.51; 95% confidence limit [CI], 1.11-2.06 and aOR, 1.97; 95% CI, 1.19-3.26, respectively). Tertiary amines were associated with hypoplastic left heart syndrome (aOR, 1.50; 95% CI, 1.10-2.04) and single ventricle (aOR, 1.61; 95% CI, 1.06-2.45). These two malformations were also significantly associated with amide drugs. For several malformations, the strongest associations with nitrosatable drug use occurred among mothers with the highest estimated dietary nitrite intake, especially for secondary amines and atrioventricular septal defects (highest tertile of nitrite, aOR, 3.30; 95% CI, 1.44-7.58).

CONCLUSION

Prenatal exposure to nitrosatable drugs may be associated with several congenital malformations, especially with higher nitrite intake. The possible interaction between nitrosatable drugs and dietary nitrite on risk of congenital malformations warrants further attention.

Nitrosatable drug exposure during early pregnancy and neural tube defects in offspring: National Birth Defects Prevention Study

Nitrosatable drugs, such as secondary or tertiary amines and amides, form N-nitroso compounds in the presence of nitrite. Various N-nitroso compounds have been associated with neural tube defects in animal models. Using data from the National Birth Defects Prevention Study, the authors examined nitrosatable drug exposure 1 month before and 1 month after conception in 1,223 case mothers with neural tube defect-affected pregnancies and 6,807 control mothers who delivered babies without major congenital anomalies from 1997 to 2005. Nitrite intakes were estimated from mothers' responses to a food frequency questionnaire. After adjustment for maternal race/ethnicity, educational level, and folic acid supplementation, case women were more likely than were control women to have taken tertiary amines (odds ratio = 1.60, 95% confidence interval (CI): 1.31, 1.95). This association was strongest with anencephalic births (odds ratio = 1.96, 95% CI: 1.40, 2.73); odds ratios associated with tertiary amines from the lowest tertile of nitrite intake to the highest tertile were 1.16 (95% CI: 0.59, 2.29), 2.19 (95% CI: 1.25, 3.86), and 2.51 (95% CI: 1.45, 4.37), respectively. Odds ratios for anencephaly with nitrosatable drug exposure were reduced among women who also took daily vitamin supplements that contained vitamin C. Prenatal exposure to nitrosatable drugs may increase the risk of neural tube defects, especially in conjunction with a mother's higher dietary intake of nitrites, but vitamin C might modulate this association.

Prevalence and patterns of nitrosatable drug use among U.S. women during early pregnancy

BACKROUND

Experimental evidence indicates that certain drugs, that are secondary or tertiary amines or amides, form N-nitroso compounds in the presence of nitrite in an acidic environment. Nitrosatable drugs have been associated with birth defects in a few epidemiologic studies. This study describes the prevalence and patterns of nitrosatable drug use among U.S. women during early pregnancy and examines maternal factors associated with such use.

METHODS

Data were analyzed from the National Birth Defects Prevention Study and included 6807 mothers who gave birth to babies without major congenital malformations during 1997 to 2005. Information was collected by telephone interview about medication use, demographic factors, and maternal health. Drugs taken during the first trimester were classified according to nitrosatability, amine and amide functional groups, and primary indication of use.

RESULTS

Approximately 24% of the women took one or more nitrosatable drugs during the first trimester, including 12.4%, 12.2%, and 7.6% who respectively took secondary amines, tertiary amines, or amides. Five of the ten most commonly taken drugs were available over the counter. Women who were non-Hispanic white (29.5%), with 1 year or more college education (27.3%) or 40 years or older (28.8%) had the highest prevalence of use. Supplemental vitamin C, an inhibitor of nitrosation, was not taken by 41.6% and 19.3% of nitrosatable drug users during the first and second months of pregnancy, respectively.

CONCLUSIONS

In this U.S. population, ingestion of drugs classified as nitrosatable was common during the first trimester of pregnancy, especially among non-Hispanic white, more educated, and older mothers. Birth Defects Research (Part A) 2011. © 2011 Wiley-Liss, Inc.

Effects of dietary intake of a fungal beta-D-glucan derivative on the level of DNA damage induced in primary rat hepatocytes by various carcinogens

Water-soluble derivative of chitin-glucan complex used in our study, carboxymethyl chitin-glucan (CM-CG), enables oral administration without harmful side-effects, which can occur upon parenteral administration of the insoluble fungal beta-D-glucans. The aim of this study was to determine in ex vivo experiments the effects of dietary CM-CG on the level of DNA lesions in primary rat hepatocytes induced by various indirectly acting carcinogens. Multiorgan carcinogen benzo[a]pyrene (BaP); two hepatocarcinogens, dimethyldibenzocarbazole (diMeDBC) and N-nitrosomorpholine (NMOR); as well as a complex mixture of organic compounds adsorbed on ambient air particles (TP-S) were used for this purpose. The amount of DNA lesions was assessed using the comet assay and the micronucleus test. In addition, the mitotic indexes and the frequencies of necrotic and apoptotic cells were evaluated as well. Our results showed that the diet enriched with CM-CG (200 mg/kg of body weight) during 21 days did not induce any negative effect on DNA nor did the mitotic indexes and the frequencies of necrotic and apoptotic cells differ statistically from the controls. On the other hand, the hepatocytes isolated from CM-CG fed animals were more resistant to the action of all genotoxins used in our study [BaP (5-20 microM), diMeDBC (0.2-2 microM), NMOR (3.4-10.2 mM), TP-S (5-20 microM)]. We can conclude that in addition to the known immunopotentiating activity of beta-D-glucans, they can efficiently inhibit the genotoxicity of carcinogens requiring metabolic activation in rat heptocytes.

Genotoxic and carcinogenic risk to humans of drug-nitrite interaction products

The large majority of N-nitroso compounds (NOC) have been found to produce genotoxic effects and to cause tumor development in laboratory animals; four NOC have been classified by the International Agency for Research on Cancer (IARC) as probably and another 15 as possibly carcinogenic to humans. A considerable fraction of drugs are theoretically nitrosatable due to the presence of amine, amide or other groups which by reacting with nitrite in the gastric environment, or even in other sites, can give rise to the formation of NOC, and in some cases other reactive species. This review provides a synthesis of information on the chemistry of NOC formation, the carcinogenic activity of NOC in animals and humans and the inhibitors of nitrosation reactions. It contains information on the drugs which have been tested for the formation of NOC by reaction with nitrite and the genotoxic-carcinogenic effects of their nitrosation products. In an extensive search we have found that 182 drugs, representing a wide variety of chemical structures and therapeutic activities, were examined in various experimental conditions for their ability to react with nitrite, and 173 (95%) of them were found to form NOC or other reactive species. Moreover, 136 drugs were examined in short-term genotoxicity tests and/or in long-term carcinogenesis assays, either in combination with nitrite or using their nitrosation product, in order to establish whether they produce genotoxic and carcinogenic effects; 112 (82.4%) of them have been found to give at least one positive response. The problem of endogenous drug nitrosation is largely unrecognized. Only a small fraction of theoretically nitrosatable drugs have been examined for the possible formation of genotoxic-carcinogenic NOC, guidelines for genotoxicity testing of pharmaceuticals do not indicate the need of performing the appropriate tests, and patients are not informed that the drug-nitrite interaction and the consequent risk can be reduced to a large extent by consuming the nitrosatable drug with ascorbic acid.

Comparative evaluation of DNA damage by genotoxicants in primary rat cells applying the comet assay

Various compounds known to cause DNA damage (hydrogen peroxide, visible light-excited methylene blue, N-nitrosomorpholine and benzo[a]pyrene) were tested with different primary rat cells (lymphocytes, testicular cells, type II pneumocytes and hepatocytes) to determine the range of induced DNA damage applying the comet assay. A dose-dependent increase of DNA breaks was observed after treatment with hydrogen peroxide in all cell types studied. The most prominent effect was observed in lymphocytes, whereas only a slight increase of DNA breaks was observed in hepatocytes. Visible light-excited methylene blue caused significant oxidative DNA damage, which did not significantly differ between the cell types used with the exception of hepatocytes, for which a lower level of DNA damage was observed. N-Nitrosomorpholine and benzo[a]pyrene induced a moderate but significant increase of DNA strand breaks in pneumocytes and hepatocytes while in lymphocytes no effect was observed. Our results clearly demonstrate that due to their differential function which is also expressed by the level of drug metabolizing and/or antioxidant enzymes, freshly isolated rat cells (lymphocytes, testicular cells, type II pneumocytes and hepatocytes) respond differently to the exposure to genotoxic agents as detected by comet assay.

An investigation of the genotoxic effects of N -nitrosomorpholine in mammalian cells

N-nitrosomorpholine (NMOR) is a well-known hepatocarcinogen. Since this compound is representative of the group of indirect-acting N-nitrosamines, its metabolic activation should be essential. However, the mechanism of NMOR-induced carcinogenesis is still not completely clear. In this paper we tried to further our understanding of the genotoxic effects of NMOR. The central aim of this study was to elucidate to what extent NMOR requires metabolic activation. For evaluation of the mutagenicity of NMOR, V79 cells were used either in the presence or absence of the microsomal S9 fraction in the mutation assay and formation of reactive oxygen/nitrogen species (ROS/RNS) in Caco-2 cells treated with NMOR was measured by a fluorescent assay. A very weak rise of 6-thioguanine resistant mutations was observed in both NMOR-treated model cells, V79/-S9 and V79/+S9. A significant difference between the level of mutations in V79/-S9 and V79/+S9 cells was recorded on the 7th day of expression only. Data obtained by the fluorescent assay confirmed that NMOR caused generation of ROS/RNS. In summary, the presented results showed that NMOR might induce DNA damage not only indirectly by its activation by drug-metabolizing enzymes but also via direct formation of ROS/RNS.

DNA lesions and cytogenetic changes induced by N-nitrosomorpholine in HepG2, V79 and VH10 cells: the protective effects of Vitamins A, C and E

INTRODUCTION

N-Nitrosomorpholine (NMOR), present in the workplace of tyre chemical factories, is a known hepatocarcinogen. This compound belongs to the group of N-nitrosamines, which are indirect-acting and require metabolic activation. However, the mechanism of its carcinogenic effect is not completely clear.

AIMS

The objective of this study was (i) to compare the DNA-damaging and clastogenic effects of NMOR in three cell lines (HepG2, V79 and VH10) with different levels of metabolizing enzymes and (ii) to determine the protective effects of Vitamins A, C and E against deleterious effects of NMOR.

METHODS

The exponentially growing cells were pre-treated with Vitamins A, C and E and treated with NMOR. Genotoxic effects of NMOR were evaluated by single-cell gel electrophoresis (SCGE, comet assay), while the chromosomal aberration assay was used for the study of clastogenic effects.

KEY RESULTS

NMOR-induced a significant dose-dependent increase of DNA damage as analyzed by SCGE, but the extent of DNA migration in the electric field was unequal in the different cell lines. Although the results obtained by SCGE confirmed the genotoxicity of NMOR in all cell lines studied, the number of chromosomal aberrations was significantly increased only in HepG2 and V79 cells, while no changes were observed in VH10 cells. In HepG2 cells pre-treated with Vitamins A, C and E we found a significant decrease of the percentage of tail DNA induced by NMOR. The reduction of the clastogenic effects of NMOR was observed only after pretreatment with Vitamins A and E; Vitamin C did not alter the frequency of NMOR-induced chromosomal aberrations under the experimental conditions of this study.

CONCLUSIONS

The fat-soluble Vitamins A and E, which are dietary constituents, reduce the harmful effects of N-nitrosomorpholine in human hepatoma cells HepG2, which are endowed with the maximal capacity for metabolic activation of several drugs.

Dietary Nitrites and Nitrates, Nitrosatable Drugs, and Neural Tube Defects

BACKGROUND

Amine-containing (nitrosatable) drugs can react with nitrite to form N-nitroso compounds, some of which are teratogenic. Data are lacking on whether dietary intake of nitrates and nitrites modifies the association between maternal nitrosatable drug exposure and neural tube defects (NTDs) in offspring.

METHODS

We examined nitrosatable drug exposure and NTD-affected pregnancies in relation to dietary nitrite and total nitrite intake in a case-control study of Mexican American women. We interviewed 184 women with NTD-affected pregnancies and 225 women with normal live births, including questions on periconceptional drug exposures and dietary intake. For 110 study participants, nitrate was also measured in the usual source of drinking water.

RESULTS

Women who reported taking drugs classified as nitrosatable were 2.7 times more likely to have an NTD-affected pregnancy than women without this exposure (95% confidence interval [CI] = 1.4-5.3). The effect of nitrosatable drugs was observed only in women with higher intakes of dietary nitrite and total nitrite (dietary nitrite + 5% dietary nitrate). Women within the highest tertile (greater than 10.5 mg/day) of total nitrite were 7.5 times more likely to have an NTD-affected pregnancy if they took nitrosatable drugs (95% CI = 1.8-45.4). The association between nitrosatable drug exposure and NTDs was also stronger in women whose water nitrate levels were higher.

CONCLUSIONS

Findings suggest that effects of nitrosatable drug exposure on risk for neural tube defects in offspring could depend on the amounts of dietary nitrite and total nitrite intake.

Effect of dietary intake of vitamin A or E on the level of DNA damage, chromosomal aberrations, and micronuclei induced in freshly isolated rat hepatocytes by different carcinogens

Hepatocytes freshly isolated from male Wistar rats fed a common diet or a vitamin A- or vitamin E-supplemented diet (each for 21, 28, or 41 days) were assayed for sensitivity to DNA breakage and cytogenetic changes induced by carcinogens. Different indirectly acting carcinogens were assayed. N-nitrosomorpholine (NMOR) was the only agent that induced DNA breaks, chromosomal aberrations, and micronuclei in all experiments. Benzo[a]pyrene (B[a]p) and dimethyldibenzo [c,g]carbazole (diMeDBC) induced only DNA breaks in all experiments. Occasionally, B[a]P induced chromosomal aberrations and micronuclei, and diMeDBC induced micronuclei, but not chromosomal aberrations. These results demonstrated that the tested carcinogens assayed at concentrations highly effective in a hypoxanthine phosphoribosyltransferase/V79 system significantly increased DNA damage, while cytogenetic changes were less frequent. In hepatocytes from rats fed vitamin A, a reduction in the severity of all three end points was observed after NMOR treatment. After B[a]P treatment, we found a reduction in DNA breaks and chromosomal aberrations; after treatment with diMeDBC, we observed a reduction in DNA breaks. Treatment with vitamin E was less effective: it reduced DNA strand breaks induced by B[a]P and partially reduced those induced by diMeDBC and NMOR and the level of micronuclei induced by NMOR and B[a]P. Both vitamins reduced the level of DNA strand breaks induced by the oxidative effect of a visible light-excited photosensitizer.

Effects of vitamins C and E on cytotoxicity induced by N-nitroso compounds, N-nitrosomorpholine and N-methyl-N'-nitro-N-nitrosoguanidine in Caco-2 and V79 cell lines

Since N-nitroso compounds as strong carcinogens are closely related to food and nutrition, the cytotoxic effects of N-nitrosomorpholine (NMOR) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and their reduction by vitamins C and E were investigated in hamster V79 cells and human colon carcinoma Caco-2 cells. Cytotoxicity was evaluated by the trypan blue exclusion technique in Caco-2 cells and by the plating efficiency assay in V79 cells. NMOR caused a dose-dependent decline of viable cells in both cell lines; MNNG induced a dose-dependent cytotoxic effect only in V79 cells. Pretreatment of cells with vitamin C and vitamin E significantly reduced the cytotoxicity of NMOR, however, both vitamins had not effect on cytotoxicity induced by MNNG. These results suggest that different N-nitroso compounds react differently with cellular macromolecules. Measurement of the level of NMOR-induced DNA strand breaks and alkali-labile sites in both cell types using the alkaline comet assay also indicates a protective effect of both vitamins against the genotoxic effects of NMOR.

Study of N-nitrosomorpholine-induced DNA strand breaks in Caco-2 cells by the classical and modified comet assay: influence of vitamins E and C

We have studied the genotoxic effects of the well-known heterocyclic liver carcinogen N-nitrosomorpholine (NMOR), an N-nitroso compound, which was prepared in our laboratory by nitrosation of the secondary amine morpholine with NaNO2. NMOR induced DNA strand breaks in human colon carcinoma Caco-2 cells. The concentration-dependent DNA-damaging effects of NMOR were proved by the comet assay. We further characterized DNA strand breaks induced by NMOR as follows: 1) We pretreated cells with vitamins E and C, which are able to eliminate oxidative DNA damage. 2) We varied the pH of the comet assay (12.1 and 13). In general, alkali-labile sites are stable until pH is raised to 12.5. 3) We used the site-specific repair enzymes exonuclease III and formamidopyrimidine-DNA glycosylase in the modified comet assay. Results showed that NMOR-induced DNA strand breaks have their origin exclusively in alkali-labile sites. Nevertheless, vitamins E and C decreased the level of DNA strand breaks. These results showed that antioxidants may have biological activities other than free radical scavenging that relate to their cancer-prevention properties. Our conceptions about reduction of NMOR-induced DNA lesions in Caco-2 cells by vitamins E and C are presented in this work.

Review of the genotoxic properties of chlorpromazine and related phenothiazines

Chlorpromazine and related phenothiazine drugs have been used in human and veterinary medications for more than 40 years, predominantly as psychotropic agents. Genotoxicity reports are in many cases of relatively antiquated test design. Overall there appears to be no genotoxic activity associated with these drugs when tested under standard conditions. Limited evidence for the potential to form mutagenic nitrosation products and some indication for the ability to modulate the genotoxic action of various mutagens have been presented in the literature. UV irradiation of chlorpromazine and other chlorinated derivatives produces reactive free radicals which possess DNA damaging properties. Induction of gene mutation and chromosomal aberrations have been observed in appropriately designed photomutagenesis experiments. Enhancement but also reduction of UV induced skin tumour formation by chlorpromazine have been found. The decisive factor for the discrepant actions has not been recognized. It is clearly advisable to avoid extensive UV exposure during therapy with these drugs.

Genotoxicity of N-nitrosochlordiazepoxide in cultured mammalian cells

Chlordiazepoxide, a benzodiazepine derivative commonly used for the treatment of anxiety, was found to react with sodium nitrite in HCl aqueous solution yielding, at pH ranging from 0.5 to 5,N-nitrosochlordiazepoxide (NO-CDE). In the absence of a metabolic activation system, a dose-dependent frequency of DNA single-strand breaks was revealed by the alkaline elution technique in V79 cells exposed to subtoxic NO-CDE concentrations ranging from 33 to 330 microM. DNA lesions were only partially repaired within 48 hr, and their promutagenic character was demonstrated by the induction of 6-thioguanine resistance in the same cells. The genotoxicity of NO-CDE was confirmed by results obtained in metabolically competent primary cultures of both rat and human hepatocytes, which displayed similar dose-related amounts of DNA fragmentation and of DNA repair synthesis after treatment with concentrations ranging from 33 to 1000 microM. In conclusions similar to those which might occur in the stomach of a patient taking chlordiazepoxide the concentration of NO-CDE in the reaction mixture (50 microM) was of the same order as the concentrations found to induce a genotoxic effect in cultured mammalian cells.