Rim Khlifi

Head and neck cancer due to heavy metal exposure via tobacco smoking and professional exposure: A review

Chronic exposures to heavy metals via tobacco smoking and professional exposure may increase the risk of head and neck cancer, although the epidemiologic evidence is limited by problems of low study power and inadequate adjustment for tobacco and professional exposure use. Numerous scientific reviews have examined the association of various heavy metals exposure with respiratory cancer as well as other cancer types, but few have been published on head and neck cancer. The purpose of this paper, therefore, is to review the head and neck tract cancer-related data on exposure to heavy metals via smoking and working exposure and to study the major mechanisms underlying some toxic metals carcinogenesis.

Arsenic, cadmium, chromium and nickel in cancerous and healthy tissues from patients with head and neck cancer

Chronic exposure to heavy metals has long been recognized as being capable to increase head and neck cancer incidence among exposed human populations. Head and neck cancer is a significant public health issue in Tunisia. The aim of the present study was to evaluate the concentrations of As, Cd, Cr and Ni in healthy and tumor tissues of head and neck cancer patients. Metal concentrations were determined in tumor and healthy tissues of 101 head and neck cancer patients, using Atomic Absorption Spectrometry. The As, Cd, Cr, and Ni levels in tumor tissues were 3.4, 2.5, 1.3 and 1.5 times higher than those of healthy tissues (p<0.05), respectively. Tumor tissue metal levels were higher in men than in women. As and Cd levels in tumor and healthy tissue samples of patients smokers are significantly higher than those of non-smokers (p<0.05). A strong effect of cumulative smoking as expressed in the number of pack per year, and tumor tissue Cd levels were positively associated with three groups of age (<40, 51-60 and >60 years) in both never-smokers and ever-smokers (<20 and ≥20 pack per year). Healthy tissue Cd levels were negatively associated with age in those three groups of smokers. The highest Cd and Cr concentrations among both workers and non-workers were observed in tumor tissues. The Cd and Cr in tissues of farmers, bricklayers and painters were all significantly higher among the workers as compared with the non-workers group. Tissue metal levels have increased due to smoking and occupational exposure. Heavy metal exposure via tobacco smoking and occupational exposures may increase the risk of head and neck in the Tunisian population.

Polymorphisms in the Human Cytochrome P450 and Arylamine N-Acetyltransferase: Susceptibility to Head and Neck Cancers

The occurrence of head and neck cancer (HNC) is associated with smoking and alcohol drinking. Tobacco smoking exposes smokers to a series of carcinogenic chemicals. Cytochrome P450 enzymes (CYP450s), such as CYP1A1, CYP1B1, and CYP2D6, usually metabolize carcinogens to their inactive derivatives, but they occasionally convert the chemicals to more potent carcinogens. In addition, via CYP450 (CYP2E1) oxidase, alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Furthermore, two N-acetyltransferase isozymes (NATs), NAT1 and NAT2, are polymorphic and catalyze both N-acetylation and O-acetylation of aromatic and heterocyclic amine carcinogens. Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of HNC. It has been suggested that such polymorphisms may be linked to cancer susceptibility. In this paper, we select four cytochrome P450 enzymes (CYP1A1, CYP1BA1, CYP2D6, and CYP2E1), and two N-acetyltransferase isozymes (NAT1 and NAT2) in order to summarize and analyze findings from the literature related to HNC risk by focusing on (i) the interaction between these genes and the environment, (ii) the impact of genetic defect on protein activity and/or expression, and (iii) the eventual involvement of race in such associations.

Polymorphisms in human DNA repair genes and head and neck squamous cell carcinoma

Genetic polymorphisms in some DNA repair proteins are associated with a number of malignant transformations like head and neck squamous cell carcinoma (HNSCC). Xeroderma pigmentosum group D (XPD) and X-ray repair cross-complementing proteins 1 (XRCC1) and 3 (XRCC3) genes are involved in DNA repair and were found to be associated with HNSCC in numerous studies. To establish our overall understanding of possible relationships between DNA repair gene polymorphisms and development of HNSCC, we surveyed the literature on epidemiological studies that assessed potential associations with HNSCC risk in terms of gene–environment interactions, genotype-induced functional defects in enzyme activity and/or protein expression, and the influence of ethnic origin on these associations. We conclude that large, well-designed studies of common polymorphisms in DNA repair genes are needed. Such studies may benefit from analysis of multiple genes or polymorphisms and from the consideration of relevant exposures that may influence the likelihood of HNSCC when DNA repair capacity is reduced.

DNA repair gene polymorphisms and risk of head and neck cancer in the Tunisian population.

Altered activity of DNA repair enzymes may be involved in modulating cancer susceptibility and pathogenesis of head and neck cancer (HNC). We conducted a case-control study to test the association between three common single-nucleotide polymorphisms of XRCC1, ERCC2, and ERCC3 genes with HNC risk in Tunisian patients. To the best of our knowle dge, this is the first report on polymorphisms in XRCC1, ERCC2, and ERCC3 and susceptibility to HNC in our population. The genotype analyses of XRCC1 Arg399Gln, ERCC2 Lys751Gln, and ERCC3 7122 A>G polymorphisms for 169 HNC patients, and 261 controls were performed using the PCR-based restriction fragment length polymorphism. Stratification of the populations according to smoking and drinking habits and occupational exposure highlighted the importance of tobacco, alcohol, and toxic substance as three risk co-factors for the development of HNC. Our study suggests that only the XRCC1 Arg399Gln polymorphism was associated with the risk of HNC in the Tunisian population (OR = 2.04; P = 0.001). Furthermore, the risk of HNC was associated with XRCC1 Arg399Gln polymorphism stratified by occupational exposure status (OR = 2.29; P = 0.024). However, no statistically significant association was observed between the risk of developing HNC and the ERCC2 Lys751Gln and ERCC3 A>G polymorphisms. These data suggest that the XRCC1 Arg399Gln polymorphism is associated with an increased risk of developing HNC, because it correlates with occupational exposure in Tunisian population.

Cytogenetic damage in the oral mucosa cells of bladder cancer patients exposed to tobacco in Southern Tunisia

Bladder cancer was associated to exposure to several pollutants which can be absorbed, inhaled, or possibly ingested. We analyzed the frequency of micronuclei (MNC) and binucleated cells (BNC) in exfoliated cells of the oral mucosa of 24 bladder cancer (BC) patients and 48 controls residing in Southern Tunisia. An assessment was carried out on the incidence of MNC and BNC in 1,000 cells per individual. The data were analyzed with SPSS, using the chi-square and the Mann-Whitney U test, α = 0.05. The frequency of MN cells in BC cases was 2.5-fold higher, than in the control group (P < 0.001), while the difference for BNC between both groups was not significant. The smoking habits, age, and gender significantly influenced the MN but not the BNC alterations. The results of our study showed significantly increased frequencies of MN but not of BNC in exfoliated oral cells of BC patients associated with the smoking status, sex, and age. This study provides preliminary evidence that the frequency of MN in oral mucosa could be a predictive biomarker for cancers in parts of the body other than the upper aerodigestive tract, such as BC. Further scrupulous investigations are certainly warranted in order to implement this assay as a routine test in the planning and validation of cancer surveillance and prevention programs.

Cytogenetic Abnormality in Exfoliated Cells of Buccal Mucosa in Head and Neck Cancer Patients in the Tunisian Population: Impact of Different Exposure Sources

Chromosome/DNA instability could be one of the primary causes of malignant cell transformation. The objective of the present study was to evaluate the spontaneous genetic damages in exfoliated cells of buccal mucosa of head and neck cancer (HNC) by counting micronucleus (MN) and binucleated (BN) cells frequencies. MN and BN frequencies were significantly increased in HNC patients compared with controls (5.53 ± 3.09/1000 cells, 5.63 ± 2.99/1000 cells versus 2.36 ± 2.11/1000 cells, 3.09 ± 1.82/1000 cells, P < 0.001). Regarding the gender and the age, the frequencies of the MN and BN were significantly higher than those of controls (P < 0.01). The evaluation of the MN and BN frequencies revealed a significant increase (P < 0.001) in the cases in relation to the control group after controlling the risk factors (tobacco smoking and chewing and occupational exposure) of HNC. Moreover, MN and BN frequencies were significantly increased in smokers and chewers compared with nonsmokers and nonchewers among patients (P < 0.05). MN frequency was significantly (P = 0.014) different between patients occupationally exposed (6.99 ± 3.40/1000 cells) and nonexposed (4.70 ± 2.48/1000 cells) among HNC group. The logistic regression model illustrated that HNC was significantly associated with frequencies of MN (OR = 8.63, P < 0.0001) and BN (OR = 5.62, P = 0.001). Our results suggest that increased chromosome/DNA instabilities may be associated with HNC.

Response to comment of Dr Kamal Chaouachi on “Shisha Smoking, Nickel and Chromium Levels in Tunisia”

Dear Editor,We have been informed of Dr. Kamal Chaouachi’s com-ments on our study published previously in the Environmen-tal Science and Pollution Research journal (Chaouachi2013; Khlifi et al. 2013). First, we wish to thank him forhis interest in our work and the time he took to carefullyanalyse some complex details, particularly in relation totobacco smoking in Tunisia.No doubt that his comments show that he is an interna-tional expert in this field and for this reason also we apolo-gise for our misquotation of his work in our study. Weconfirm that the right reference about shisha smoking andoral cancer was the important article he published with hiscolleague Dr. Sajid in the Medical Hypotheses journal(Chaouachi and Sajid 2010).On another level, we also appreciated very much hisproposals to enhance the methodology of our future studiesandinparticularthe issue ofthequestionnaire. Afterenquiryhere in Tunisia, we can say that he is quite right about theneed to distinguish between different smoking products(jurak, tobamel, etc.) and the different ways to prepare them(with aluminium or not, etc.) in order to avoid confusion byexcessive simplification. Finally, the pioneering studiesabout heavy metals (Saudi Arabia and Egypt) that we didnot know, unfortunately, and in which he was involved,deserve in our view great attention (Khater et al. 2010).References

Cytotoxicity and genotoxicity effects of arsenic trioxide on SQ20B human laryngeal carcinoma cells

This study investigates the cytotoxicity and the genotoxicity induced by arsenic trioxide As2O3in human laryngeal SQ20B carcinoma cell line. SQ20B cells were exposed to graded concentrations of arsenic trioxide (2 and 5μM) for 48h. Comet assay and γ-H2AX foci formation were used for measuring DNA damages, flow cytometry was used to identify cell cycle alterations and apoptosis, while cell morphology was visualized using transmission electron microscopy. The results show a dose-dependent induction of DNA damages and double strand breaks, alterations in cell cycle and morphologic alterations of cells. These results prove that As2O3 is highly cytotoxic and genotoxic at the micromolar range ina human laryngeal carcinoma cell line.

Inter-ethnic differences in genetic polymorphisms of xenobiotic-metabolizing enzymes (CYP1A1, CYP2D6, NAT1 and NAT2) in healthy populations: correlation with the functional in silico prediction

Several studies have shown that many polymorphisms of the xenobiotic-metabolizing enzymes (XME) affect either enzymatic functions or are associated with various aspects of human health. Owing to the presence of these single nucleotide variants (SNVs), differences in detoxification capacity have been observed between many ethnicities. The aim of this investigation was to study the prevalence of four polymorphisms in XME among various ethnic groups. Attention was focused on polymorphisms of CYP2D6 (rs1058172, G>A, p.Arg365His), CYP1A1 (rs4646421, c.-26-728C>T), NAT1 (rs4921880, c.-85-1014T>A) and NAT2 (rs1208, A>G, p.Arg268Lys). These polymorphisms were analyzed in 261 healthy Tunisians individuals in comparison with different ethnic backgrounds from hapmap database. In addition, in silico functional prediction was also performed to determine the loss of function variants. Our results demonstrated that population’s origins widely affect the genetic variability of XME enzymes and Tunisians show a characteristic pattern. In silico predictions showed a deleterious effect for p.Arg268Lys substitution on CYP2D6 function, findings confirmed its key role played in cancer susceptibility. These data show that detoxification genes structures depend on the studied population. This suggests that ethnic differences impact on disease risk or response to drugs and therefore should be taken into consideration in genetic association studies focusing on XME enzymes. Our results provide the first report on these SNV in Tunisian population and could be useful for further epidemiological investigations including targeted therapy.