Non-Genotoxic Carcinogens.Approaches to Their Risk Assessment

Epidemiological studies support the idea that most human cancers are related to chemicals present in the human environment. In turn, chemicals are believed to cause cancer via either genotoxic or non-genotoxic mechanisms. There were described in literature several simple, rapid and inexpensive short term tests to reasonably predict the genotoxic nature of chemicals but in contrast, there is no reliable test or battery of tests available to predict the carcinogenicity of non-genotoxic compounds and this poses a major problem to their risk assessment. In addition, there are conflictive opinions about risk assessment needs for both classes of carcinogens. Some workers believe that for non-genotoxic carcinogens, thresholds for exposure can be drawn while others do not. In this review, the reasons behind both of these opinions and the present hypotheses about the mechanism of action of non-genotoxic carcinogens are described and analyzed in relation to future needs.

Role of Oxidative Stress in Non-genotoxic Carcinogenesis with Special Reference to Liver Tumors Induced by Peroxisome Proliferators

Peroxisome proliferators (POPs), such as hypolipidemic drugs or industrial phthalate ester plasticizers, are widely known as non-genotoxic hepatocarcinogens in rodents. As one of the possible mechanisms of POP-induced carcinogenesis, the 'Oxidative Stress' theory has been postulated. In this review, in order to reconsider the significance of 'Oxidative Stress' to POP-induced carcinogenesis, we focus on in vivo studies examining formation of 8-hydroxydeoxyguanosine (8-OH -dG), a marker of oxidative DNA damage with mutagenic potential, after treatment of rodents with POPs. Some studies clearly demonstrated that 8-OH-dG levels in the liver DNA were increased by POP-treatments. These findings suggest that 'Oxidative Stress' could contribute as one factor to POP-induced carcinogenesis. Furthermore, we refer to other multiple biological changes caused by POP-treatment presumably contributing to the carcinogenic mechanisms, and consider possible roles of 'Oxidative Stress' in the carcinogenesis process

Interactions of chemical carcinogens and genetic variation in hepatocellular carcinoma

In the etiology of hepatocellular carcinoma (HCC), in addition to hepatitis B virus and hepatitis C virus infections, chemical carcinogens also play important roles. For example, aflatoxin B 1 (AFB 1 ) epoxide reacts with guanine in DNA and can lead to genetic changes. In HCC, the tumor suppressor gene p53 codon 249 mutation is associated with AFB 1 exposure and mutations in the K -ras oncogene are related to vinyl chloride exposure. Numerous genetic alterations accumulate during the process of hepatocarcinogenesis. Chemical carcinogen DNA-adduct formation is the basis for these genetic changes and also a molecular marker which reflects exposure level and biological effects. Metabolism of chemical carcinogens, including their activation and detoxification, also plays a key role in chemical hepatocarcinogenesis. Cytochrome p450 enzymes, N -acetyltransferases and glutathione S -transferases are involved in activating and detoxifying chemical carcinogens. These enzymes are polymorphic and genetic variation influences biological response to chemical carcinogens. This genetic variation has been postulated to influence the variability in risk for HCC observed both within and across populations. Ongoing studies seek to fully understand the mechanisms by which genetic variation in response to chemical carcinogens impacts on HCC risk.

CHEMICAL“CARCINOGENS”,AS MODULATORS OF INTER-CELLULAR COMMUNICATION,ARE MITOGENS,NOT MUTAGENS.

Although mutations clearly play a role in themulti-stage process of carcinogenesis,a challengewll be made to the paradigm that most chemical"carcinogens" act via mutagenic activity("carcinogens as mutagens").Control ofproliferation and differentiation within andbetween tissues is mediated by

A SEQUENTIAL TESTING PROGRAM FOR PREDICTING AND IDENTIFICATING CARCINOGENS AND ITS APPLICATION

In this paper our studies about the sequential testing program for predicting and identificating carcinogens, sequential discriminant method and cost- effectiveness analysis are summarized. The analysis of our database of carcinogeniclty and genotoxicity of chemicals demonstrates the uncertainty . of short- term tests ( STTs ) to predict carcinogens and the results of most routine STTs are statistically dependent. We recommend the sequential testing program combining STTs and carclnogenicity assay, the optimal STT batteries, the rules of the sequential discrimination and the preferal choices of STTs tor specific chemical class. For illustrative pmposes the carclnogenicity prediction of several sample chamicals is presented. The results of cost-effectiveness analysis suggest that this program has vast social-economic effectiveness.

Biomarkers of Human Exposure to Carcinogens: An Overview

Environmental, occupational, or dietary exposure to certain chemicals has been shown to be associated with carcinogenesis in humans. In the 18th century, for example, Percival Pott (1775) noted a high incidence of scrotal cancer in chimney sweeps, which he attributed to their exposure to soot and a concomitant lack of bathing. Subsequent epidemiological studies have identified a number of additional carcinogenic agents, including aromatic amine-based dyes (Case et al., 1954), cigarette smoke (Wynder and Graham, 1950), asbestos (Doll, 1955), vinyl chloride (Creech and

Pitfalls in Assessing Risks from Carcinogens

The decision to classify a chemical as a human carcinogen must depend upon agreed conclusions from epidemiology, bioassays, and some short-term corroborating tests; information from only one of these disciplines is inadequate. Most pitfalls appear in interpreting the results from animal bioassays; this report will concentrate on them. Often the conclusion is accepted that a chemical is an animal carcinogen without a critical appraisal of the experimental design. By manipulating the experiment, 90 + % of all chemicals can induce some tumor in a rodent. Pitfalls encountered in bioassays result from not specifying the exact agent under test and how it relates to human exposure, using inappropriate routes of administration unrelated to humans, administering illogically high doses, or concluding that a cancer was induced without adequate histopathological description of the lesion. Importance of animal husbandry is often overlooked. Pitfalls are also related to short-term tests. Finally, a major pitfall in assessing carcinogenic risk from chemicals is drawing global conclusions about the carcinogenicity of an agent after the detection of only one or two tumors in the treated group.

New development in risk assessment of genotoxic carcinogens in foods

The no-observed-effect level (NOEL) in a study of carcinogenicity for compounds that are both genotoxic and carcinogenic represents the limit of detection in that bioassay, rather than an estimate of a possible threshold. Therefore, for those genotoxic and carcinogenic contaminants (e.g. acrylamides, PAHs, etc.) in foods it is not possible to develop health-based guidance values (e.g. ADI or PTWI) using the traditional NOEL and safety/uncertainty factors.

Relative carcinogenicity of tacrolimus vs mycophenolate after solid organ transplantation and its implications for liver transplant care

BACKGROUND De novo malignancy is a leading cause of late morbidity and mortality in liver transplant recipients.Cumulative immunosuppression has been shown to contribute to post-transplant malignancy(PTM)risk.There is emerging evidence on the differential carcinogenic risk profile of individual immunosuppressive drugs,independent of the net effect of immunosuppression.Calcineurin inhibitors such as tacrolimus may promote tumourigenesis,whereas mycophenolic acid(MPA),the active metabolite of mycophenolate mofetil,may limit tumour progression.Liver transplantation(LT)is relatively unique among solid organ transplantation in that immunosuppression monotherapy with either tacrolimus or MPA is often achievable,which makes careful consideration of the risk-benefit profile of these immunosuppression agents particularly relevant for this cohort.However,there is limited clinical data on this subject in both LT and other solid organ transplant recipients.AIM To investigate the relative carcinogenicity of tacrolimus and MPA in solid organ transplantation.METHODS A literature search was conducted using MEDLINE and Embase databases using the key terms“solid organ transplantation”,“tacrolimus”,“mycophenolic acid”,and“carcinogenicity”,in order to identify relevant articles published in English between 1st January 2002 to 11th August 2022.Related terms,synonyms and explosion of MeSH terms,Boolean operators and truncations were also utilised in the search.Reference lists of retrieved articles were also reviewed to identify any additional articles.Excluding duplicates,abstracts from 1230 records were screened by a single reviewer,whereby 31 records were reviewed in detail.Full-text articles were assessed for eligibility based on pre-specified inclusion and exclusion criteria.RESULTS A total of 6 studies were included in this review.All studies were large population registries or cohort studies,which varied in transplant era,type of organ transplanted and immunosuppression protocol used.Overall,there was no clear difference demonstrated between tacrolimus and MPA in de novo PTM risk following solid organ transplantation.Furthermore,no study provided a direct comparison of carcinogenic risk between tacrolimus and MPA monotherapy in solid organ transplantation recipients.CONCLUSION The contrasting carcinogenic risk profiles of tacrolimus and MPA demonstrated in previous experimental studies,and its application in solid organ transplantation,is yet to be confirmed in clinical studies.Thus,the optimal choice of immunosuppression drug to use as maintenance monotherapy in LT recipients is not supported by a strong evidence base and remains unclear.

Role of bacteria in carcinogenesis, with special reference to carcinoma of the gallbladder

Carcinoma of the gallbladder (CaGB) is the fifth commonest gastrointestinal tract cancer and is endemic in several countries. The interplay of genetic susceptibility, infections, and life style factors has been proposed to be responsible for carcinogenesis of gallbladder. Persistence of infection leading to chronic inflammation, and production of certain toxins and metabolites with carcinogenic potentials, by certain bacteria has been speculated to be involved in the transformation of the gallbladder epithelium. Therefore, any bacteria that have evolved to acquire both of the above carcinogenic mechanisms can cause cancer. Salmonella typhi has been found to be prominently associated with CaGB. Chronic typhoid carriage (persistence) and production of mediators of chronic infl ammation and a genotoxic toxin (cytotoxic distending toxin, CdtB) are also known for this bacterium. Furthermore, the natural concentrating function of the gallbladder might amplify the carcinogenic effect of the mediators of carcinogenesis. In addition to S. typhi, certain species of Helicobacter (H. bilis and H. hepaticus) and Escherichia coli have also been implicated in carcinogenesis. As the isolation rate is verypoor with the presently available culture techniques, the existence of bacteria in a viable but non-cultivable state is quite likely; therefore, sensitive and specif ic molecular techniques might reveal the etiological role of bacterial infection in gallbladder carcinogenesis. If bacteria are found to be causing cancers, then eradication of such infections might help in reducing the incidence of some cancers.

Human papillomavirus does not have a causal role in colorectal carcinogenesis

AIM: To investigate the presence of human papillomavirus(HPV) DNA along with the integration,the quantification and the expression of the HPV16 in colorectal cancers.METHODS: A prospective series of colorectal tumors were genotyped for HPV DNA.The clinical and pathological variables of the HPV-positive tumors were compared to those of HPV-negative samples.The integration status of HPV16 was evaluated by calculating E2/E6 ng ratios.HPV16-positive tumors were also evaluated for(1) E2,E4,E5,E6 and E7 viral gene ng quantification;(2) relative quantification compared to W12 cells; and(3) viral E2,E4,E5,E6 and E7 mR NA transcripts by real-time polymerase chain reaction.RESULTS: HPV infection was detected in 16.9% of all tumors examined,and HPV16 was the most frequent type detected(63.6% of positive tissues).Notably,the clinical and pathological features of HPV-positive colorectal cancers were not significantly different than those of HPV-negative cancers(χ2 and t-test for all clinical and pathological features of HPV-positive vs HPV-negative colorectal cancers: p ns).HPV16 DNA was present exclusively in episomal form,and the HPV16 E2,E4,E5,E6 and E7 genes were detected in tracenanogram quantities.Furthermore,the HPV16 genes ranged from 10-3 to 10-9 compared to W12 cells at an episomal stage.Although the extractions were validated by housekeeping gene expression,all the HPV16 positive tissues were transcriptionally inactive for the E2,E4,E5,E6 and E7 mR NAs.CONCLUSION: Based on our results,HPV is unlikely involved in colorectal carcinogenesis.

Chemopreventive effect of oltipraz on AFB_1-induced hepatocarcinogenesis in tree shrew model

INTRODUCTIONHepatocellular carcinoma (HCC) is one of themajor cancers in the world with a mortality of morethan 250 000 cases yearly.More than 137 000 casesof HCC were diagnosed each year in China,whichacount approximately for more than 40 percent ofthe total number in the world.HCC has become thesecond major cause of death for cancer in

Maternal and Fetal Exposure to Four Carcinogenic Environmental Metals

Objective To examine maternal and fetal exposure levels to four carcinogenic metals, arsenic （As）, cadmium （Cd）, nickel （Ni）, and beryllium （Be）, and to investigate their environmental influences. Methods Metal concentrations in maternal and umbilical cord blood were measured by inductively coupled plasma-mass spectrometry （ICP-MS）. Environmental factors that might play a role in exposure were analyzed using Mann Whitney nonparametric U-tests and multiple linear regression. Results The concentrations of As, Cd, and Ni in umbilical cord blood （5.41, 0.87, and 139.54 gg/L） were significantly lower than those in maternal blood （6.91, 1.93, and 165.93 p.g/L）. There were significant positive correlations between the maternal and cord concentrations of each carcinogen. Our results showed that： （i） exposures to potentially harmful occupational factors during pregnancy were associated with high levels of maternal As, Cd, and Ni; （ii） living close to major transportation routes （〈500 m） or exposure to second-hand smoke during pregnancy increased the maternal Cd levels and （iii） living close to industrial chimneys induced high maternal Ni levels. Multiple linear regression analysis showed that these environmental factors remained significant in models of the influences of these four carcinogens. Conclusion Both mothers and fetuses had been exposed to As, Cd, Ni, and Be. The increased levels of these carcinogens in pregnant women were associated with some detrimental environmental factors, such as occupational exposure, contact with second-hand smoke and living close to major transportation routes or industrial chimneys.

Toxicity and Carcinogenicity of Ozone in Combination with 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone and Dibutyl Phthalate in B6C3F1 Mice for 16 and 32 Weeks

Objective To evaluate the toxic and carcinogenic potential of ozone alone or in combination with 4-（N-methyl-N-nitrosamino）-1-（3-pyridyl）-1-butanone （NNK） and/or dibutyl phthalate （DBP）. Methods Male and female B6C3F1 mice were exposed, through inhalation, intravenous administration and diet, to 0.5 ppm of ozone, 1.0 mg/kg of NNK and 5000 ppm of DBP, individually and in combination for 16 and 32 weeks. Results No treatment-related death was seen, but significant differences in body and organ weights between control and treated mice were observed during the study. No incidence of lung tumor incidence was recorded in mice exposed to either ozone alone or combined treatment. Oviductal carcinomas were observed in female mice exposed to ozone or DBP alone for 16 weeks and ozone in combination with NNK and DBP for 32 weeks. Conclusion Although ozone alone and in conjunction with NNK and/or DBP does not induce lung cancer under our experimental conditions, they induce oviductal carcinomas in B6C3F1 mice.

Relationship between Structures and Carcinogenicities of Heterocyclic Amines

Semi-empirical molecular orbital calculations were performed on heterocyclic aromatic amines(HCAs). The relationship between the structures and the carcinogenicities can be rationally elucidated by the models based on the metabolism of HCAs and the Di-region theory. The degree of easiness for the formation of Di-region electrophilic centers determines the carcinogenic activity. There is a good linear relationship between the observed carcinogenicities and the PM3 calculated parameters, with r=0.973 and F=29.8>F ** 0.01 .

Opisthorchis viverrini:The carcinogenic human liver fluke

Opisthorchiasis caused by Opisthorchis viverrini remains a major public health problem in many parts of Southeast Asia, including Thailand, Lao PDR, Vietnam and Cambodia. The infection is associated with a number of hepatobiliary diseases, including cholangitis, obstructive jaundice, hepatomegaly, cholecystitis and cholelithiasis. Multi-factorial etiology of cholangiocarcinoma, mechanical damage, parasite secretions, and immunopathology may enhance cholangiocarcinogenesis. Moreover, both experimental and epidemiological evidences strongly implicate liver fluke infection as the major risk factor in cholangiocarcinoma, cancer of the bile ducts. The liver fluke infection is induced by eating raw or uncooked fish products that is the tradition and popular in the northeastern and northern region, particularly in rural areas, of Thailand. The health education programs to prevent and control opisthorchiasis are still required in the high-risk areas.

MUTAGENICITY AND CARCINOGENICITY OF FISH SAUCE FROM A COUNTY WITH THE HIGH RISK FOR GASTRIC CANCER IN CHINA

The mutagenicity and carcinogenicity of fish sauce (FS) sample from Changle County, a high gastric cancer mortality (113.20/105) area, were investigated with the biologic short-term tests and laboratory animal experiment. The results showed that the extract of FS was markedly direct mutagenic toward S. typhimurium TA100, induced high sister chromatid exchanges (SCE) and micronucleus (MN) in V79 cells after nitrosation with sodium nitrite. But the non-nitrosated FS did not. The nitrosated fish sauce (NFS) also induced SOS in E. coli PQ37 and alkylation of calfthymus DNA. The potency of NFS to induce unscheduled DNA synthesis (UDS) in human normal gastric mucosal cells was increased about fivefold compared with FS. When the NFS extract was given to newborn rats by gavage, dys-plasia and adenocaroinoma were induced in the glandular stomach in the 4th and 16th experimental week, respectively. N-nitrosamides were also found in NFS, which may account for the mutagenicity and carcinogenicity of NFS. It is indicated that FS, a traditional daily eaten seasoning, may contribute to the causes of the high gastric cancer mortality for the local residents.

Anti-carcinogenic properties of curcumin on colorectal cancer

Curcumin has been used in traditional Indian medicine for many centuries for its anti-inflammatory and anticarcinogenic properties.There has been some promising research concerning curcumin as a safe therapeutic agent for many cancers,colorectal cancer being among them.This has been shown through research in cell cultures,animal models,and humans.At this time,it appears that curcumin’s anti-carcinogenic properties are most likely due to its effects on multiple molecular targets,such as nuclear factorκ-light-chain-enhancer of activated B cells(NF-κB)and activator protein 1(AP-1).NF-κB and AP-1 are both major transcription factors that regulate inflammation and thus affect cell proliferation,differentiation and even apoptosis.Curcumin has also been shown to affect a variety of other key players involved in carcinogenesis,such as cyclooxygenase-2,matrix metallopeptidases 2 and 9 and tumor necrosis factorαinduced vascular cell adhesion molecule,just to name a few.Although many molecular targets are involved,curcumin has been well tolerated in many studies:doses up to 8 g a day have been confirmed to be safe for humans.In this brief review,we will examine the current studies and literature and touch upon many molecular pathways affected by curcumin,and demonstrate the exciting possibility of curcumin as a chemopreventive agent for colorectal cancer.

Carcinogenic potential of duodenal reflux juice from patients with long-standing postgastrectomy

AIM: To determine whether study on the carcinogenic potential of reflux juice from patients with remote gastrectomy could clarify the inherent relationship between duodenal reflux and gastric stump cancer. METHODS: A total of 37 reflux juice samples (13 Billroth I, 24 Billroth II) were employed in the present study. A two-stage transformation assay using BALB/c 3T3 cells was carried out to test the initiating or promoting activity of these samples. RESULTS: Two of 18 (11.1%) reflux samples exerted initiating activities, whereas 9/19 (47.4%) samples enhanced the MNNG-initiating cell transformation, suggesting the duodenal reflux juice might more frequently possess the tumor-promoter activity (P = 0.029). In addition, there was no difference in initiating activities of the samples irrespective of surgical procedures (P = 0.488), while Billroth II samples exhibited stronger tumor-promoter activity than Billroth I samples (P = 0.027). Furthermore, the promoter activities were well correlated with the histological changes of the stomas (r(s) = 0.625, P = 0.004), but neither their cytotoxicities nor initiating activities had this correlation (Probabilities were 0.523 and 0.085, respectively). CONCLUSION: The duodenal reflux juice from patients with remote postgastrectomy did have carcinogenic potential, and suggested that tumor-promoting activity should principally account for the high incidence of gastric cancer in gastrectomy patients. In contrast, it is difficult to explain the high stump-cancer incidence with the N-nitroso compounds theory-a popular theory for the intact stomach carcinogenesis, and it seemed to be justified to focus chemo-prevention of this cancer on the tumor-promoting potential of reflux juice.

Studies on the Mutagenicity and Teratogenicity of Kuianchun and Its Potential Carcinogenicity Prediction

Kuianchun is a newly synthesized antibacterial and growth-promoting drug. This paper selected a battery of three short-term tests, including Ames test, micronucleus test and sperm abnormality test, to detect the mutagenicity of Kuianchun. The carcinogenicity prediction and battery selection method (CPBS method) was used to determine the probability of carcinogenicity of Kuianchun based upon the results of short-term tests mentioned above. In addition, traditional teratogenic test was selected to study teratogenicity of Kuianchun. In Ames test, Kuianchun showed mutagenic for Salmonella typhimurium strains TA98 and TA100 in the absence and presence of microsomal metabolic activation system (S9-mix). However, the mutagenicity was reduced by the addition of S9-mix. In micronucleus test, Kuianchun was administered intra-peritoneally to male mouse 30 hours and 6 hours before they were killed respectively. The result indicated that there was no significant difference on the number of micronucleated polychromatic erythrocytes (PCEs) in the mouse bone marrow induced by Kuianchun compared with the negative contrast (50% DMSO) (P>0.05). In sperm abnormality test, Kuianchun was administered through a gastric incubation to male mouse as a suspension in 2% Tween-80. The dosage levels were 450, 750, 1000 and 1500mg/kg per day for 5 days. The result indicated that the percentage of abnormal sperms induced by Kuianchun was not significant compared with the negative contrast (P > 0.05). In traditional teratogenic test, Kuianchun was given orally to pregnant mouse at 1730, 1/20 and 1/15 LD50 during 6 - 15days of pregnancy period (the LD50 = 9000mg/kg). No toxicity was found either on mother and embryo in mouse, and teratogenic effects were also not observed at all tested dosages.The probability of carcinogenicity of Kuianchun is 23.8%(6 = 0.238). The result demonstrated that Kuianchun is a non-carcinogen.