Mechanistic relationships between hepatic genotoxicity and carcinogenicity in male B6C3F1 mice treated with polycyclic aromatic hydrocarbon mixtures

Association between urinary polycyclic aromatic hydrocarbons and risk of metabolic associated fatty liver disease

OBJECTIVE

To investigate the effect of urinary PAHs on MAFLD.

METHODS

The study included 3,136 adults from the National Health and Nutrition Examination Survey (NHANES) conducted between 2009 and 2016. Among them, 1,056 participants were diagnosed with MAFLD and were designated as the case group. The analysis of the relationship between monohydroxy metabolites of seven PAHs in urine and MAFLD was carried out using logistic regression and Bayesian kernel regression (BKMR) models.

RESULTS

In single-pollutant models, the concentration of 2-hydroxynaphthalene (2-OHNAP) was positively correlated with MAFLD (OR = 1.47, 95% CI 1.18, 1.84), whereas 3-hydroxyfluorene (3-OHFLU) and 1-hydroxypyrene (1-OHPYR) demonstrated a negative correlation with MAFLD (OR = 0.59, 95% CI 0.48 0.73; OR = 0.70, 95% CI 0.55, 0.89). Conversely, in multi-pollutant models, 2-OHNAP, 2-hydroxyfluorene (2-OHFLU), 2-hydroxyphenanthrene, and 3-hydroxyphenanthrene (2&3-OHPHE) displayed positive correlations with MAFLD (OR = 6.17, 95% CI 3.15, 12.07; OR = 2.59, 95% CI 1.37, 4.89). However, 3-OHFLU and 1-OHPYR continued to exhibit negative correlations with MAFLD (OR = 0.09, 95% CI 0.05, 0.15; OR = 0.62, 95% CI 0.43, 0.88). Notably, the BKMR analysis mixtures approach did not indicate a significant joint effect of multiple PAHs on MAFLD, but identified interactions between 3-OHFLU and 2-OHFLU, 1-OHPYR and 2-OHFLU, and 1-OHPYR and 3-OHFLU.

CONCLUSION

No significant association was found between mixed PAHs exposure and the risk of MAFLD. However, interactions were observed between 3-OHFLU and 2-OHFLU. Both 2-OHFLU and 2&3-OHPHE exposure are significant risk factors for MAFLD, whereas 3-OHFLU is a key protective factor for the disease.

Attenuation of Polycyclic Aromatic Hydrocarbon (PAH)-Induced Carcinogenesis and Tumorigenesis by Omega-3 Fatty Acids in Mice In Vivo

Lung cancer is the leading cause of cancer death worldwide. Polycyclic aromatic hydrocarbons (PAHs) are metabolized by the cytochrome P450 (CYP)1A and 1B1 to DNA-reactive metabolites, which could lead to mutations in critical genes, eventually resulting in cancer. Omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are beneficial against cancers. In this investigation, we elucidated the mechanisms by which omega-3 fatty acids EPA and DHA will attenuate PAH-DNA adducts and lung carcinogenesis and tumorigenesis mediated by the PAHs BP and MC. Adult wild-type (WT) (A/J) mice, Cyp1a1-null, Cyp1a2-null, or Cyp1b1-null mice were exposed to PAHs benzo[a]pyrene (BP) or 3-methylcholanthrene (MC), and the effects of omega-3 fatty acid on PAH-mediated lung carcinogenesis and tumorigenesis were studied. The major findings were as follows: (i) omega-3 fatty acids significantly decreased PAH-DNA adducts in the lungs of each of the genotypes studied; (ii) decreases in PAH-DNA adduct levels by EPA/DHA was in part due to inhibition of CYP1B1; (iii) inhibition of soluble epoxide hydrolase (sEH) enhanced the EPA/DHA-mediated prevention of pulmonary carcinogenesis; and (iv) EPA/DHA attenuated PAH-mediated carcinogenesis in part by epigenetic mechanisms. Taken together, our results suggest that omega-3 fatty acids have the potential to be developed as cancer chemo-preventive agents in people.

Human biomonitoring and reference values of urinary 1-hydroxypyrene among Iranian adults population

Polycyclic aromatic hydrocarbons (PAHs) are one of the most important environmental pollutants. Urinary concentrations of 1-hydropyren metabolites of PAHs have been used as biomarkers of these chemicals' exposure in humans. This cross-sectional study was conducted on 468 healthy Iranian adults over 25 years old and non-smokers in six provinces who were selected based on the clustering method. Fasting urine sampling and body composition and demographic measurements were performed. Urine samples were analyzed by GC-MS. The analysis included descriptive statistics and analytical statistics using multiple linear regression by Python software. 1-Hydroxypyrene was found in 100% of samples, and the mean (Reference Value 95%) concentration of 1-hydroxypyrene was 6.12 (RV 95%: 20) μg/L and 5.95 (21) μg/gcrt. There was a direct relationship between the amount of body composition (body fat, visceral fat), BMI, and age with the urinary concentrations of 1-hydropyren metabolites, and this relationship was significant for BMI with urinary concentrations of 1-hydropyren metabolites (P = 0.045). The amount of 1-hydroxypyrene in healthy Iranian adults has been higher than in similar studies in other countries. These results provide helpful information regarding the exposure of Iranian adults to 1-hydroxypyrene, and these data can be used to supplement the national reference values of human biomonitoring for the interpretation of biomonitoring results.

Aryl Hydrocarbon Receptor in Oxidative Stress as a Double Agent and Its Biological and Therapeutic Significance

The aryl hydrocarbon receptor (AhR) has long been implicated in the induction of a battery of genes involved in the metabolism of xenobiotics and endogenous compounds. AhR is a ligand-activated transcription factor necessary for the launch of transcriptional responses important in health and disease. In past decades, evidence has accumulated that AhR is associated with the cellular response to oxidative stress, and this property of AhR must be taken into account during investigations into a mechanism of action of xenobiotics that is able to activate AhR or that is susceptible to metabolic activation by enzymes encoded by the genes that are under the control of AhR. In this review, we examine various mechanisms by which AhR takes part in the oxidative-stress response, including antioxidant and prooxidant enzymes and cytochrome P450. We also show that AhR, as a participant in the redox balance and as a modulator of redox signals, is being increasingly studied as a target for a new class of therapeutic compounds and as an explanation for the pathogenesis of some disorders.

Attenuation of Polycyclic Aromatic Hydrocarbon (PAH)-Mediated Pulmonary DNA Adducts and Cytochrome P450 (CYP)1B1 by Dietary Antioxidants, Omega-3 Fatty Acids, in Mice

Numerous human and animal studies have reported positive correlation between carcinogen-DNA adduct levels and cancer occurrence. Therefore, attenuation of DNA adduct levels would be expected to suppress tumorigenesis. In this investigation, we report that the antioxidants omega 3-fatty acids, which are constituents of fish oil (FO), significantly decreased DNA adduct formation by polycyclic aromatic hydrocarbons (PAHs). B6C3F1 male mice were fed an FO or corn oil (CO) diet, or A/J male mice were pre-fed with omega-3 fatty acids eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA). While the B6C3F1 mice were administered two doses of a mixture of seven carcinogenic PAHs including benzo(a)pyrene (BP), the A/J mice were treated i.p. with pure benzo[a]pyrene (BP). Animals were euthanized after 1, 3, or 7 d after PAH treatment. DNA adduct levels were measured by the ³²P-postlabeling assay. Our results showed that DNA adduct levels in the lungs of mice 7 d after treatment were significantly decreased in the FO or EPA/DHA groups compared with the CO group. Interestingly, both qPCR and Western blot analyses revealed that FO, DHA and EPA/DHA significantly decreased the expression of cytochrome P450 (CYP) 1B1. CYP1B1 plays a critical role in the metabolic activation of BP to DNA-reactive metabolites. qPCR also showed that the expression of some metabolic and DNA repair genes was induced by BP and inhibited by FO or omega-3 fatty acids in liver, but not lung. Our results suggest that a combination of mechanism entailing CYP1B1 inhibition and the modulation of DNA repair genes contribute to the attenuation of PAH-mediated carcinogenesis by omega 3 fatty acids.

Modifying effects of menthol against benzo(a)pyrene-induced forestomach carcinogenesis in female Swiss mice

Benzo(a)pyrene (BaP) is a polycyclic aromatic hydrocarbon widespread in the environment and closely associated to tobacco use, which is an important risk factor for highly incident stomach cancer. Menthol, a monoterpene extracted from Mentha genus species, has multiple biological properties, including anti-inflammatory and gastroprotective properties, but its effects on carcinogenesis are still to be fully understood. Thus, we evaluated the modifying effects of Ment against BaP-induced forestomach carcinogenesis. Female Swiss mice received BaP by intragastrical (i.g.) administration (50 mg/kg of body weight [b wt], 2×/week), from weeks 1-5 weeks. Concomitantly, mice received Menthol at 25 (Ment25) or 50 (Ment50) mg/kg b wt (i.g, 3×/week). Animals were euthanized at weeks 5 (n = 5 mice/group) or 30 (n = 10 mice/group). At week 5, both Ment doses reduced peripheral leukocyte blood genotoxicity 4 h after the last BaP administration, but only Ment50 attenuated this biomarker 8 h after the last BaP administration. In accordance to these findings, both Ment interventions attenuated BaP-induced increase in the percentage of H2A.X-positive forestomach epithelial cells. Moreover, Ment50 reduced cell proliferation and apoptosis (i.e., Ki-67 and caspase-3, respectively) in forestomach epithelium but exerted no significant effects on NFκB, and Nrf2 protein levels. At week 30, Ment50 reduced by ~55% the incidence of BaP-induced forestomach diffuse hyperplasia and multiplicity of forestomach tumors (squamous cell papillomas and carcinomas). Our findings indicate that Ment50, administered during initiation phase, attenuates forestomach carcinogenesis by reducing early genotoxicity, cell proliferation, and apoptosis induced by BaP.

Serum lipids mediate the relationship of multiple polyaromatic hydrocarbons on non-alcoholic fatty liver disease: A population-based study

Polyaromatic hydrocarbons (PAHs) are recognized as organic pollutants with liver toxicity. However, the relationship between PAHs and nonalcoholic fatty liver disease (NAFLD) is unclear in humans. The aim of this study was to investigate the levels of PAHs in the US population and their association with the risk of NAFLD. We investigated urinary levels of nine PAHs in 2436 participants from the National Health and Nutrition Examination Survey (NHANES) between 2005 and 2012, including 1-Hydroxynapthalene (1-OHN), 2-Hydroxynapthalene (2-OHN), 3-Hydroxyfluorene (3-OHF), 2-Hydroxyfluorene (2-OHF), 3-Hydroxyphenanthrene (3-OHPhe), 1-Hydroxyphenanthrene (1-OHPhe), 2-Hydroxyphenanthrene (2-OHPhe), 1-Hydroxypyrene (1-OHPyr), 9-Hydroxyfluorene (9-OHF). Logistic regression models were used to estimate the relationship between single PAH and NAFLD. Assessment of the overall effect of multiple PAH mixtures on NAFLD using Bayesian kernel machine regression (BKMR) model. There were 698 participants diagnosed with NAFLD in the study group. After adjusting for related covariates such as sex, age, race, education, marital status, poverty income ratio (PIR), body mass index (BMI), total energy intake, smoking, hypertension, and diabetes, logistic regression analysis showed that compared to the low tertile (T1), the odds ratio of the high tertile (T3) was 1.70 (95%CI: 1.26-2.29, p = 0.001) for total PAHs, 1.50 (95%CI: 1.11-2.03, p = 0.008) for 2-OHN, 1.75 (95%CI: 1.31-2.34, p < 0.001) for 2-OHPhe, 1.59 (95%CI: 1.18-2.14, p = 0.002) for 9-OHF and 0.63 (95%CI: 0.46-0.87, p = 0.004) for 3-OHF. In the BKMR model, we found that the overall effect of the nine PAH mixtures was positively associated with the risk of NAFLD. Mediation analysis showed that HDL and TG mediated the association between PAHs and NAFLD. Our study suggests that multiple PAHs mixtures exposure may induce NAFLD by mediating serum lipids in human metabolism.

Transcriptome Analysis Reveals the AhR, Smad2/3, and HIF-1α Pathways as the Mechanism of Ochratoxin A Toxicity in Kidney Cells

Ochratoxin A (OTA) is a mycotoxin occurring in foods consumed by humans. Recently, there has been growing global concern regarding OTA toxicity. The main target organ of OTA is the kidney, but the mechanism underlying renal toxicity is not well known. In this study, human-derived proximal tubular epithelial cells, HK-2 cells, were used for RNA-sequencing (RNA-seq) and transcriptome analysis. In total, 3193 differentially expressed genes were identified upon treatment with 200 nM OTA in HK-2 cells; of these, 2224 were upregulated and 969 were downregulated. Transcriptome analysis revealed that OTA significantly affects hypoxia, epithelial-mesenchymal transition (EMT), apoptosis, and xenobiotic metabolism pathways in kidney cells. Quantitative real-time PCR analysis showed gene expression patterns similar to RNA-seq analysis. Expression of EMT markers (E-cadherin and fibronectin), apoptosis markers (caspase-3 and Bax), and kidney injury molecule-1 (KIM-1) was suppressed by inhibiting AhR expression using siRNA, and the related transcription factors, Smad2/3, and HIF-1α were downregulated. Smad2/3 suppression with siRNA could inhibit fibronetcin, caspase-3, Bax, and KIM-1 expression. Fibronetcin, caspase-3, Bax, and KIM-1 expression could be increased with HIF-1α suppression with siRNA. Taken together, these findings suggest that OTA-mediated kidney toxicity via the AhR-Smad2/3-HIF-1α signaling pathways leads to induction of EMT, apoptosis, and kidney injury.

Polycyclic Aromatic Hydrocarbon-induced Pulmonary Carcinogenesis in Cytochrome P450 (CYP)1A1- and 1A2-Null Mice: Roles of CYP1A1 and CYP1A2

In 2019, lung cancer was estimated to be the leading cause of cancer deaths in humans. Polycyclic aromatic hydrocarbons (PAHs) are known to increase the risk of lung cancer. PAHs are metabolized by the cytochrome P450 (CYP)1A subfamily, comprised of the CYP1A1 and 1A2 monooxygenases. These enzymes bioactivate PAHs into reactive metabolites that induce mutagenic DNA adducts, which can lead to cancer. Past studies have investigated the role of CYP1A1 in PAH bioactivation; however, the individual roles of each CYP1A enzyme are still unknown. In this investigation, we tested the hypothesis that mice lacking the genes for Cyp1a1 or Cyp1a2 will display altered susceptibilities to PAH-induced pulmonary carcinogenesis. Wild-type, Cyp1a1-null (Cyp1a1-/-), and Cyp1a2-null (Cyp1a2-/-) male and female mice were treated with 3-methylcholanthrene for cancer initiation and tumor formation studies. In wild-type mice, CYP1A1 and 1A2 expression was induced by 3-methylcholanthrene. Cyp1a1-/- and Cyp1a2-/- mice treated with PAHs displayed a compensatory pattern, where knocking out 1 Cyp1a gene led to increased expression of the other. Cyp1a1-/- mice were resistant to DNA adduct and tumor formation, whereas Cyp1a2-/- mice displayed increased levels of both. UALCAN analysis revealed that lung adenocarcinoma patients with high levels of CYP1A2 expression survive significantly better than patients with low/medium expression. In conclusion, Cyp1a1-/- mice were less susceptible to PAH-induced pulmonary carcinogenesis, whereas Cyp1a2-/- mice were more susceptible. In addition, high CYP1A2 expression was found to be protective for lung adenocarcinoma patients. These results support the need to develop novel CYP1A1 inhibitors to mitigate human lung cancer.

MRE11-RAD50-NBS1 complex alterations and DNA damage response: implications for cancer treatment

Genome instability is a hallmark of cancer cells and can be accelerated by defects in cellular responses to DNA damage. This feature of malignant cells opens new avenues for tumor targeted therapy. MRE11-RAD50-NBS1 complex plays a crucial role in sensing and repair of DNA damage. Through interacting with other important players of DNA damage response, MRE11-RAD50-NBS1 complex is engaged in various DNA damage repair pathways. Mutations in any member of this complex may lead to hypersensitivity to genotoxic agents and predisposition to malignancy. It is assumed that the defects in the complex may contribute to tumorigenesis and that treatments targeting the defect may be beneficial to cancer patients. Here, we summarized the recent research findings of the role of MRE11-RAD50-NBS1 complex in tumorigenesis, cancer treatment and discussed the potential approaches of targeting this complex to treat cancer.

A metabolomics study on effects of polyaromatic compounds in oil sand extracts on the respiratory, hepatic and nervous systems using three human cell lines

Polyaromatic compounds (PACs) are by-products of combustion and are the major pollutants from the oil and gas industry. However, the mechanism of PACs induced toxicity still remains elusive. The aim of this study was to elucidate the effects of a typical mixture of PACs found in oil sand extract (OSE) on the respiratory, hepatic and nervous systems in humans using in vitro cell culture models followed by non-targeted metabolomics analysis. OSE collected from Alberta, Canada was fractionated into PAC and alkane fractions, and their effects after 24 h exposure on the cell viability measured by MTT assay in three human cell lines (A549, HepG2, and SK-N-SH) were studied. The PAC fractions showed significant dose-dependent cytotoxicity. A549 cells showed the highest sensitivity to OSE extracts, followed by SK-N-SH and HepG2. In contrast, the alkane fractions showed no effects on cell viability. The three human cell lines were further exposed with the PACs at 10% and 20% lethal concentration for 24 h. Metabolomics analysis of the cell extracts indicated that PACs treatments showed different disruptions on possible metabolic pathways on the three cell lines. PACs altered the sex steroid hormone metabolism and regulated the levels of leukotrienes metabolites in all three cell types. The amino acids L-cysteine, L-glutamine, L-tyrosine that are known to cause respiratory effects were significantly up-regulated in A549 cells. The PACs treated HepG2 cells showed down-regulation in metabolites responsible for the inflammatory mediation. Treatment of the differentiated SK-N-SH cells showed up-regulated metabolites involved with butanoate, fatty acid, and pyrimidine metabolism. Leukotriene metabolites were found to be significantly increased in all PACs treated cells. In conclusion, our results showed that PACs in OSE can alter the metabolism of the human lung, liver and neuronal cells and may induce toxicity in multiple target organs.

Key characteristics of 86 agents known to cause cancer in humans

Since the inception of the International Agency for Research on Cancer (IARC) in the early 1970s, the IARC Monographs Programme has evaluated more than 1000 agents with respect to carcinogenic hazard; of these, up to and including Volume 119 of the IARC Monographs, 120 agents met the criteria for classification as carcinogenic to humans (Group 1). Volume 100 of the IARC Monographs provided a review and update of Group 1 carcinogens. These agents were divided into six broad categories: (I) pharmaceuticals; (II) biological agents; (III) arsenic, metals, fibers, and dusts; (IV) radiation; (V) personal habits and indoor combustions; and (VI) chemical agents and related occupations. Data on biological mechanisms of action (MOA) were extracted from the Monographs to assemble a database on the basis of ten key characteristics attributed to human carcinogens. After some grouping of similar agents, the characteristic profiles were examined for 86 Group 1 agents for which mechanistic information was available in the IARC Monographs up to and including Volume 106, based upon data derived from human in vivo, human in vitro, animal in vivo, and animal in vitro studies. The most prevalent key characteristic was "is genotoxic", followed by "alters cell proliferation, cell death, or nutrient supply" and "induces oxidative stress". Most agents exhibited several of the ten key characteristics, with an average of four characteristics per agent, a finding consistent with the notion that cancer development in humans involves multiple pathways. Information on the key characteristics was often available from multiple sources, with many agents demonstrating concordance between human and animal sources, particularly with respect to genotoxicity. Although a detailed comparison of the characteristics of different types of agents was not attempted here, the overall characteristic profiles for pharmaceutical agents and for chemical agents and related occupations appeared similar. Further in-depth analyses of this rich database of characteristics of human carcinogens are expected to provide additional insights into the MOA of human cancer development.

Development of a database on key characteristics of human carcinogens

A database on mechanistic characteristics of human carcinogenic agents was developed by collecting mechanistic information on agents identified as human carcinogens (Group 1) by the International Agency for Research on Cancer (IARC) in the IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. A two-phase process is described for the construction of the database according to 24 toxicological endpoints, derived from appropriate test systems that were acquired from data obtained from the mechanisms sections of the IARC Monographs (Section 4) and a supplementary PubMed search. These endpoints were then aligned with 10 key characteristics of human carcinogens that reflect the broader attributes of these agents relating to the development of cancer in humans. The considerations involved in linking of toxicological endpoints to key characteristics are described and specific examples of the determination of key characteristics for six specific agents (tamoxifen, hepatitis B virus, arsenic, ultraviolet and solar radiation, tobacco smoking, and dioxin) are provided. Data for humans and animals were tabulated separately, as were results for in-vivo and for in-vitro sources of information. The database was constructed to support a separate analysis of the expression of these endpoints by 86 Group 1 carcinogens, in-vivo and in-vitro along with an analysis of the key characteristics of these agents.

Integration of micronucleus tests with a gene mutation assay in F344 gpt delta transgenic rats using benzo[a]pyrene

Reduction of the number of animals used in in vivo genotoxicity tests is encouraged. For this purpose, we conducted integrated toxicity tests combining gene mutation assays with multiple-organ micronucleus (MN) tests (peripheral blood, bone marrow, liver, and colon) in F344 gpt delta transgenic (Tg) rats. Seven-week-old male F344 gpt delta rats were orally administered 62.5 or 125 mg/kg/day benzo[a]pyrene (B[a]P) for 28 days. One day after the final day of treatment (day 29) and three days after the final treatment (day 31), bone marrow, liver, and colon samples were collected, and mutation assays and MN tests were performed. The gpt mutant frequency (MF) significantly increased in bone marrow, liver and colon but MN induction was only significant in bone marrow but not in liver and colon. Similarly MN induction was only observed in bone marrow in non-Tg F344 rats. In peripheral blood obtained on day 4, 15, 29, 31, a time-dependent increase was observed in reticulocyte MN frequency during the treatment. Thus, our integrated method successfully detected both gene mutations and MN induction caused by B[a]P. In addition, no significant differences were observed between sampling times (day 29 versus 31), suggesting that sampling on day 29 is also valid to evaluate gene mutations. On the other hand, MN results in bone marrow and peripheral blood were different depending on the sampling day. An appropriate sampling day should be designated according to which assays are integrated. We confirmed that integration of the MN test with a gene mutation assay using F344 gpt delta Tg rats is useful to evaluate different endpoints related to genotoxicity using the same animals and to reduce animal use.

Benzo(a)pyrene in Cigarette Smoke Enhances HIV-1 Replication through NF-κB Activation via CYP-Mediated Oxidative Stress Pathway

Smoking aggravates HIV-1 pathogenesis and leads to decreased responses to antiretroviral therapy. In this study, we aim to find a molecular mechanism that would explain smoking-induced HIV-1 replication. Benzo(a)pyrene (BaP), a major carcinogen in cigarette, requires metabolic activation through cytochrome P450s (CYPs) to exert its toxic effects. We hypothesized that CYP-mediated BaP metabolism generates reactive oxygen species (ROS), and the resultant oxidative stress aggravates HIV-1 replication. As expected, we observed ~3 to 4-fold increase in HIV-1 replication in U1 cells and human primary macrophages after chronic BaP exposure. We also observed ~30-fold increase in the expression of CYP1A1 at mRNA level, ~2.5-fold increase in its enzymatic activity as well as elevated ROS and cytotoxicity in U1 cells. The knock-down of the CYP1A1 gene using siRNA and treatment with selective CYP inhibitors and antioxidants significantly reduced HIV-1 replication. Further, we observed a nuclear translocation of NF-κB subunits (p50 and p65) after chronic BaP exposure, which was reduced by treatment with siRNA and antioxidants/CYP inhibitors. Suppression of NF-κB pathway using specific NF-κB inhibitors also significantly reduced HIV-1 replication. Altogether, our results suggest that BaP enhances HIV-1 replication in macrophages by a CYP-mediated oxidative stress pathway followed by the NF-κB pathway.

Filling the gap between chemical carcinogenesis and the hallmarks of cancer: A temporal perspective

BACKGROUND

Cancer is believed to arise through the perturbation of pathways and the order of pathway perturbation events can enhance understanding and evaluation of carcinogenicity. This order has not been examined so far, and this study aimed to fill this gap by attempting to gather evidence on the potential temporal sequence of events in carcinogenesis.

DESIGN

The methodology followed was to discuss first the temporal sequence of hallmarks of cancer from the point of view of pathological specimens of cancer (essentially branched mutations) and then to consider the hallmarks of cancer that one well-known carcinogen, benzo(a)pyrene, can modify.

RESULTS

Even though the sequential order of driving genetic alterations can vary between and within tumours, the main cancer pathways affected are almost ubiquitous and follow a generally common sequence: resisting cell death, insensitivity to antigrowth signals, sustained proliferation, deregulated energetics, replicative immortality and activation of invasion and metastasis. The first 3 hallmarks can be regarded as almost simultaneous while angiogenesis and avoiding immune destruction are perhaps the only hallmarks with a varying position in the above sequence.

CONCLUSIONS

Our review of hallmarks of cancer and their temporal sequence, based on mutational spectra in biopsies from different cancer sites, allowed us to propose a hypothetical temporal sequence of the hallmarks. This sequence can add molecular support to the evaluation of an agent as a carcinogen as it can be used as a conceptual framework for organising and evaluating the strength of existing evidence.

Desert Vegetation Forty Years after an Oil Spill

Deserts are the most frequent locations of terrestrial crude oil contaminations. Nevertheless, the long-term effects of petroleum hydrocarbons on desert ecosystems are still unknown, which makes risk assessment and decision making concerning remediation difficult. This study examined the long-term effects of petroleum hydrocarbons on perennial desert vegetation. The study site was a hyper-arid area in the south of Israel, which was contaminated by a crude oil spill in 1975. The contaminated area was compared to uncontaminated reference areas. The composition of perennial plants 40 yr after the oil spill was not significantly affected by the contamination. However, the size distribution of the two most dominant shrub species, Baker and (Moq.) Iljin., and the only tree species, Savi and (Forssk.) Hayne, were different from the reference. These differences can be explained by decreased recruitment. The estimated recruitment of in the last 40 yr post oil spill was 74% less than recruitment in the reference area. Low recruitment of may in the future lead to the loss of tree cover, which would change the entire ecosystem, as are keystone species on which a number of microorganisms, plants, and animals rely. Remediation of oil spills and preventative measures are recommended.

Environmental carcinogenesis and pH homeostasis: Not only a matter of dysregulated metabolism

According to the World Health Organization, around 20% of all cancers would be due to environmental factors. Among these factors, several chemicals are indeed well recognized carcinogens. The widespread contaminant benzo[a]pyrene (B[a]P), an often used model carcinogen of the polycyclic aromatic hydrocarbons' family, has been suggested to target most, if not all, cancer hallmarks described by Hanahan and Weinberg. It is classified as a group I carcinogen by the International Agency for Research on Cancer; however, the precise intracellular mechanisms underlying its carcinogenic properties remain yet to be thoroughly defined. Recently, the pH homeostasis, a well known regulator of carcinogenic processes, was suggested to be a key actor in both cell death and Warburg-like metabolic reprogramming induced upon B[a]P exposure. The present review will highlight those data with the aim of favoring research on the role of H⁺ dynamics in environmental carcinogenesis.