Formation of DNA adducts in the skin of psoriasis patients, in human skin in organ culture, and in mouse skin and lung following topical application of coal-tar and juniper tar

Plant sources, techniques of production and uses of tar: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Throughout history, Humans have always used tar for different purposes such as gluing materials, waterproofing, and conserving wood, but today, it is also used in medicines and cosmetics. Many countries around the world, Norway and Morocco to name a few, obtain tar from endemic trees. In a process of dry distillation, the organic material, endemic trees in this case, is exposed to a high temperature with a restricted amount of oxygen. Eventually, it cracks the large molecules in the matter and turns it into tar.

AIM OF THE REVIEW

This review article sheds light on tar production and the species that have been used in the process. Equal emphasis is placed on its uses, chemical composition, and toxicity.

MATERIALS AND METHODS

Meta-analysis (PRISMA) guidelines have been used to review this article. The review is put together from various articles, theses, documents in "Science Direct", "Hal (Archive ouvert)", "Web of knowledge" without limitation date.

RESULTS

It turns out that tar can be produced by 18 tree taxonomic families, notably Cupressaceae, Pinaceae, and Betulaceae. As for the production techniques, two methods are considered: Per ascensum and Per descensum, which can take different forms. The chemical composition of tar consists of acids, phenols, and aromatic hydrocarbons. The uses of tar have changed over time, while its toxicity is strongly related to its chemical composition.

CONCLUSIONS

The different species used in tar production have been highlighted in this research review. Equal importance has been given to its methods of extraction, uses and its chemical components. We hope that future studies will focus more on these species used to produce tar in other biological activities.

The Concept of "Cancer Stem Cells" in the Context of Classic Carcinogenesis Hypotheses and Experimental Findings

In this Commentary, the operational definition of cancer stem cells or cancer initiating cells includes the ability of certain cells, found in a heterogeneous mixture of cells within a tumor, which are able to sustain growth of that tumor. However, that concept of cancer stem cells does not resolve the age-old controversy of two opposing hypotheses of the origin of the cancer, namely the stem cell hypothesis versus the de-differentiation or re-programming hypothesis. Moreover, this cancer stem concept has to take into account classic experimental observations, techniques, and concepts, such as the multi-stage, multi-mechanism process of carcinogenesis; roles of mutagenic, cytotoxic and epigenetic mechanisms; the important differences between errors of DNA repair and errors of DNA replication in forming mutations; biomarkers of known characteristics of normal adult organ-specific stem cells and of cancer stem cells; and the characteristics of epigenetic mechanisms involved in the carcinogenic process. In addition, vague and misleading terms, such as carcinogens, immortal and normal cells have to be clarified in the context of current scientific facts. The ultimate integration of all of these historic factors to provide a current understanding of the origin and characteristics of a cancer stem cell, which is required for a rational strategy for prevention and therapy for cancer, does not follow a linear path. Lastly, it will be speculated that there exists evidence of two distinct types of cancer stem cells, one that has its origin in an organ-specific adult stem cell that is 'initiated' in the stem cell stage, expressing the Oct4A gene and not expressing any connexin gene or having functional gap junctional intercellular communication (GJIC). The other cancer stem cell is derived from a stem cell that is initiated early after the Oct4A gene is suppressed and the connexin gene is expressed, which starts early differentiation, but it is blocked from terminal differentiation.

Treatment Strategies Against Psoriasis: Principle, Perspectives and Practices

BACKGROUND

Psoriasis is a genetically predisposed autoimmune disease mediated by cytokines released by the activated immune cells. It manifests inflammatory, scaly red or white silvery flaky skin which may be a fluid-filled lesion with soreness and itchiness. The prevalence rate of psoriasis is increasing day by day. Despite having such a high prevalence rate, the treatment of psoriasis is still limited. Hence, there is a need to rethink the various treatment strategies available in the allopathic as well as in the alternative systems of medicine.

METHODS

Various bibliographic databases of previously published peer-reviewed research papers were explored and systematic data culminated in terms of various treatment strategies used for the management of psoriasis. The prime focus is given towards modern as well as alternative systems of medicine such as phototherapy, a combination of phototherapy with pharmacotherapy such as Ayurveda, Yoga and naturopathy, Unani, Siddha, and Homeopathy to treat psoriasis.

RESULTS

A comprehensive review of 161 papers, including both research and review articles, was carried out to make the article readily understandable. The pathogenesis including inflammatory mediators and type of psoriasis is discussed before the treatment strategies to understand the pathophysiology of the disease. The uniqueness, procedure, advantages, and limitations of conventional, advanced, and traditional systems of medicine to treat psoriasis are discussed in detail. Emphasis has also been given towards marine sources such as fish oil, marine sponges, and algae.

CONCLUSION

Although there are many modern and alternative treatment strategies available to treat psoriasis, none of them have been proven to provide complete relief to patients. Moreover, they are associated with certain side effects. In order to overcome them, novel drug delivery systems have been utilized and found effective; however, their stability and safety become the major impediments towards their successful positioning. Traditional and alternative treatment strategies have found to be safe and effective but their use is localized to certain areas. In a nutshell, to achieve successful treatment of psoriasis, there is a need to focus on the development of stable and non-toxic novel drug delivery systems or the promotion of traditional systems to treat psoriasis.

Applications of Human Peripheral Blood Lymphocytes in Genotoxicity and Cytotoxicity

A number of features make peripheral blood lymphocytes an excellent system for studying both genotoxicity and cytotoxicity in humans. They are an abundant and readily accessible source of somatic cells, mostly in a non-proliferative state, but able to be stimulated by mitogens to enter the cell cycle. The blastocyte transformation of lymphocytes is a useful model for investigating the mechanisms which regulate cell-cycle progression in mammalian cells. By stimulating lymphocytes in vitro, it is possible to detect the genetic damages they have sustained in vivo, which become manifest as chromosomal aberrations, sister-chromatid exchanges or gene mutations. The metabolic properties of lymphocytes have been extensively studied, especially with reference to their characteristic collection of enzymes involved in nucleotide turnover, which makes them exquisitely sensitive to changes in intracellular levels of DNA precursors. The data collected on the ability of lymphocytes to metabolise xenobiotics show a marked quantitative difference between resting and proliferating lymphocytes, and minor qualitative differences between lymphocytes and other cell types, e.g. hepatocytes. An indirect approach to detect the metabolism of genotoxic xenobiotics by lymphocytes is the analysis of DNA adducts in their chromatin after in vivo or in vitro exposure. Lymphocytes can be employed to identify the (cyto)genetic consequences of in vivo genotoxic exposure and inter-individual variation in sensitivity to genotoxic agents. The analysis of mutations at the hgprt locus in lymphocytes is a promising approach for the study of somatic-cell mutations in humans and of the possible mechanisms of in vivo selection against mutants.

In the field of cytotoxicity, the applications of lymphocytes are, as yet, still few: the main effect measured is the impairment of the proliferative response to mitogens. But lymphocytes can be employed as primary human cells to be treated in vitro with mutagenic or toxic chemicals in standard genotoxicity and cytotoxicity assays, and offer the advantage of avoiding the problems of inter-species extrapolation of results by testing in a human system. Moreover, the (geno)toxic effects detected in lymphocytes after treatments in vitro may give information on the spontaneous or environmentally-determined susceptibility of the individual donors to xenobiotics.

Development and validation of a direct sandwich chemiluminescence immunoassay for measuring DNA adducts of benzo[a]pyrene and other polycyclic aromatic hydrocarbons

We have developed and validated a sandwich chemiluminescence immunoassay (SCIA) which measures polycyclic aromatic hydrocarbon (PAH)-DNA adducts combining high throughput and adequate sensitivity, appropriate for evaluation of adduct levels in human population studies. Fragmented DNA is incubated with rabbit antiserum elicited against DNA modified with r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and subsequently trapped by goat anti-rabbit IgG bound to a solid surface. Anti-single-stranded (ss) DNA antibodies binds in a quantity proportional to the adduct levels and is detected by chemiluminescence. The BPDE-DNA SCIA has a limit of detection of 3 adducts per 10(9) nucleotides with 5 μg DNA per well. We have validated the BPDE-DNA SCIA using DNA modified in vitro, DNA from benzo[a]pyrene (BP)-exposed cultured cells and mice. The levels of adduct measured by SCIA were lower (30-60%) than levels of bulky DNA adducts measured in the same samples by (32)P-postlabelling. The BPDE-DNA SCIA also detected adducts produced in vivo by PAHs other than BP. When blood DNA samples from maternal/infant pairs were assayed by BPDE-DNA SCIA, the adduct levels obtained were significantly correlated. However, there was no correlation between (32)P-postlabelling and SCIA values for the same samples. The SCIA can be extended to any DNA adduct and is expected to provide, when fully automated, a valuable high-throughput approach in large-scale population studies.

Smoking-related O4-ethylthymidine formation in human lung tissue and comparisons with bulky DNA adducts

Tobacco smoke contains many alkylating agents that can react with DNA to produce O(4)-ethylthymidine (O(4)-etT) and several other types of promutagenic base modifications. Our aims were (i) to confirm results of a pilot study (Godschalk, R., Nair, J., Schooten, F. J., Risch, A., Drings, P., Kayser, K., Dienemann, H. and Bartsch, H. (2002) Comparison of multiple DNA adduct types in tumor adjacent human lung tissue: effect of cigarette smoking. Carcinogenesis, 23, 2081-2086) on the formation of O(4)-etT in smokers' lung; (ii) to explore associations between levels of O(4)-etT and smoking status and (iii) to investigate whether a correlation exists between levels of O(4)-etT and bulky (polycyclic aromatic hydrocarbons-derived) DNA adducts. Archived DNA samples originated from histologically normal peripheral lung tissues of 64 Hungarian lung cancer patients, who underwent lung resection. O(4)-etT was determined by an immunoenriched (32)P-postlabelling-high-performance liquid chromatography method. Levels of bulky DNA adducts were determined by the nuclease P1 adduct-enriched (32)P-postlabelling. O(4)-etT levels ranged from 0.01 to 3.91 adducts/10(8) thymidines. In the combined group of subjects who smoked until surgery or gave up smoking at most 1 year before it, the mean level of O(4)-etT was 1.7-fold (P = 0.015) and of bulky DNA adducts 2.2-fold (P < 0.0001) higher than in long-term ex-smokers (LES) and never-smokers (NS) combined. We found no significant correlation between the individual levels of the two DNA adduct types. No dose-response was detected between O(4)-etT formation and smoking dose. In one-third of LES, O(4)-etT levels were above the 2.0-fold mean level of adducts found in NS, indicating its high persistence. Our results confirm the smoking-related formation of O(4)-etT in human lung DNA that should be explored as biomarker. Its long persistence in target tissue implicates a role of this potentially miscoding lesion in tobacco smoking-associated cancers.

Recovery of bulky DNA adducts by the regular and a modified 32P-postlabelling assay; influence of the DNA-isolation method

Bulky DNA adducts are widely used as biomarkers of human exposure to complex mixtures of environmental genotoxicants including polycyclic aromatic hydrocarbons. The 32P-postlabelling method is highly sensitive for the detection of bulky DNA adducts, but its relatively low throughput poses limits to its use in large-scale molecular epidemiological studies. The objectives of this study were to compare the impact of DNA-sample preparation with a commercial DNA-isolation kit or with the classical phenol-extraction procedure on the measurement of bulky DNA adducts by 32P-postlabelling, and to increase the throughput of the 32P-postlabelling method--whilst maintaining radio-safety--by reducing the radioisotope requirement per sample. The test DNA samples were prepared from MCF-7 cells treated with benzo[a]pyrene and from human peripheral blood lymphocytes, buffy coat, and peripheral lung tissue. The modified 32P-postlabelling procedure involved an evaporation-to-dryness step after the enzymatic digestions of the DNA, and radio-labelling with a reduced amount of [γ-32P]ATP substrate in a reduced reaction volume compared with the regular method. Higher levels of DNA adducts were measured in the MCF-7 cells and in the lung-tissue samples after isolation with the kit than after solvent extraction. A seven-fold higher level of adducts was detected in the buffy-coat DNA samples isolated with the kit than with the phenol extraction procedure (p<0.001). Reduction of the amount of [γ-32P]ATP from 50 μCi to 25 μCi (>6000 Ci/mmol specific radioactivity) per sample in the modified 32P-postlabelling procedure was generally applicable without loss of adduct recovery for all test samples prepared with both DNA isolation methods. The difference between the bulky DNA-adduct levels resulting from the two DNA-isolation procedures requires further systematic investigation. The modified 32P-postlabelling procedure allows a 50% reduction of radioisotope requirement per sample, which facilitates increased throughput of the assay whilst maintaining radio-safety.

Scalp psoriasis: European consensus on grading and treatment algorithm

The scalp is a common site of involvement of psoriasis and, for many patients, is a challenging aspect of their disease. This can be attributed not only to the scaling, itching and cosmetic embarrassment that go with scalp psoriasis, but also to the fact that the scalp skin is relatively inaccessible, making topical therapies difficult to apply. The proximity of sensitive facial skin can also limit the use of potentially irritating topical treatments. Nevertheless, the specific challenges of scalp psoriasis are often neglected by treatment guidelines. This paper summarizes the discussions that took place at an international conference of experts convened in Geneva, Switzerland, in March 2008. The objective of the meeting was to review the available treatments for scalp psoriasis in terms of efficacy, safety, convenience, and the implications for patient compliance with treatment. In addition, definitions of mild, moderate and severe scalp psoriasis were agreed. This paper presents a treatment algorithm that includes recommendations for patients in all three categories. It considers the role of potent topical corticosteroids, vitamin D3 derivatives, salicylic acid preparations, and photo- and radiotherapy, as well as systemic therapies, including newer biological agents, for patients with widespread psoriasis with scalp involvement. Data from clinical trials indicate that a potent topical corticosteroid in a short-contact formulation is the most appropriate treatment for most patients with scalp psoriasis.

Final safety assessment of Coal Tar as used in cosmetics

Coal Tar is a semisolid by-product obtained in the destructive distillation of bituminous coal, which functions in cosmetic products as a cosmetic biocide and denaturant--antidandruff agent is also listed as a function, but this is considered an over-the-counter (OTC) drug use. Coal Tar is a nearly black, viscous liquid, heavier than water, with a naphthalene-like odor and a sharp burning taste, produced in cooking ovens as a by-product in the manufacture of coke. Crude Coal Tar is composed of 48% hydrocarbons, 42% carbon, and 10% water. In 2002, Coal Tar was reported to the Food and Drug Administration (FDA) to be used in four formulations, all of which appear to be OTC drug products. Coal Tar is monographed by the FDA as Category I (safe and effective) OTC drug ingredient for use in the treatment of dandruff, seborrhoea, and psoriasis. Coal Tar is absorbed through the skin of animals and humans and is systemically distributed. In short-term studies, mice fed a diet containing Coal Tar found it unpalatable, but no adverse effects were reported other than weight loss; rats injected with Coal Tar experienced malaise in one study and decreased water intake and increased liver weights in another; rabbits injected with Coal Tar residue experienced eating avoidance, respiratory difficulty, sneezing, and weight loss. In a subchronic neurotoxicity study using mice, a mixture of phenols, cresols, and xylenols at concentrations approximately equal to those expected in Coal Tar extracts produced regionally selective effects, with a rank order of corpus striatum > cerebellum > cerebral cortex. Coal Tar applied to the backs of guinea pigs increases epidermal thickness. Painting female rabbits with tar decreases the absolute and relative weights of the ovaries and decreased the number of interstitial cells in the ovary. Four therapeutic Coal Tar preparations used in the treatment of psoriasis were mutagenic in the Ames assay. Urine and blood from patients treated with Coal Tar were genotoxic in bacterial assays. Coal Tar was genotoxic in a mammalian genotoxicity assay and induced DNA adducts in various tissue types. Chronic exposure of mice to Coal Tar significantly decreased survival and liver neoplasms were seen in a significant dose-related trend; in other studies using mice lung tumors and perianal skin cancers were found. Coal Tar was comedogenic in three small clinical studies. Folliculitis is associated with the prolonged use of some tars. Several published reports describe cases of contact sensitivity to Coal Tar. Polycyclic aromatic hydrocarbons, which make up Coal Tar, are photosensitizers and cause phototoxicity by an oxygen-dependent mechanism. A retrospective study of the reproductive toxicity of Coal Tar in humans compared exposed women to controls and found little difference in spontaneous abortion and congenital disorders. Cancer epidemiology studies of patients who have received Coal Tar therapy of one form or other have failed to link treatment with an increase in the risk of cancer. Although the Cosmetic Ingredient Review (CIR) Expert Panel believes that Coal Tar use as an antidandruff ingredient in OTC drug preparations is adequately addressed by the FDA regulations, the Panel also believes that the appropriate concentration of use of Coal Tar in cosmetic formulations should be that level that does not have a biological effect in the user. Additional data needed to make a safety assessment include product types in which Coal Tar is used (other than as an OTC drug ingredient), use concentrations, and the maximum concentration that does not induce a biological effect in users.

Myeloperoxidase--463A variant reduces benzo[a]pyrene diol epoxide DNA adducts in skin of coal tar treated patients

The skin of atopic dermatitis patients provides an excellent model to study the role of inflammation in benzo[a]pyrene (BaP) activation, since these individuals are often topically treated with ointments containing high concentrations of BaP. In this study we have determined, by HPLC with fluorescence detection, the BaP diol epoxide (BPDE)-DNA adduct levels in human skin after topical treatment with coal tar and their modulation by the -463G-->A myeloperoxidase (MPO) polymorphism, which reduces MPO mRNA expression. BPDE-DNA adduct levels were 2.2 and 14.2 adducts/10(8) nt for MPO-463AA/AG and -463GG, respectively. The predominant BaP tetrol observed was tetrol I-1, which is derived after hydrolysis of the anti-BPDE-DNA adduct. The tetrol I-1/II-2 ratio, corresponding to the anti/syn ratio, was 6.7. The (32)P-post-labeling assay was also performed and thin layer chromatograms showed a major spot with a chromatographic location corresponding to BPDE-DNA. The mean values of the BPDE-DNA adduct spots were 3.8 +/- 2.4 per 10(8) nt for MPO-463AA/AG (n = 3) and 18.4 +/- 11.0 per 10(8) nt for MPO-463GG (n = 7), respectively (P = 0.03). One individual with the homozygous mutant genotype (-463AA) even had a 13-fold lower adduct level (1.4 per 10(8) nt) as compared to MPO-463GG subjects. In conclusion, these data show for the first time: (i) the in vivo formation of BPDE-DNA adducts in human skin treated with coal tar; (ii) that the MPO-463AA/AG genotype reduced BPDE-DNA adduct levels in human skin.

A strong genotoxic effect in mouse skin of a single painting of coal tar in hairless mice and in MutaMouse

The dorsal skin of C3H/Tif/hr hairless mice was painted with coal tar, pharmacological grade. Epidermal cells and hepatocytes were isolated after 4, 24, 48 and 96 h and DNA strand breaks were determined as tail moment by the alkaline comet assay. The tail moment of epidermal cells was significantly greater at the time points 4, 24, 48 and 96 h after exposure compared to the controls, with the most DNA strand breaks at 24 h. The DNA strand breaks in epidermal cells increased linearly with the dose of coal tar. In hepatocytes, no difference in DNA strand breaks was found between exposed animals and controls. DNA adducts were determined by the 32P-postlabeling assay. For epidermal cells, the mean DNA adduct level was 12-fold greater in coal tar painted mice after 24 h than in controls. Again, a linear dose/response relationship was seen 24 h after painting. For liver DNA, the mean DNA adduct level was 3-fold greater than for controls. The mutation frequency in epidermal and liver cells was examined in lambdalacZ transgenic mice (MutaMouse). Thirty-two days after painting, the mutation frequency in epidermal cells was 16-fold greater in coal tar treated mice compared to controls. No effect was detected in hepatocytes. We found that a single painting of coal tar resulted in strong genotoxic effects in the murine epidermis, evidenced by induction of DNA strand breaks and DNA adducts in hairless mice and lambdalacZ mutations in the MutaMouse. This demonstrates that it is possible to detect genotoxic effects of mixtures with high sensitivity in mouse skin by these end-points.

Polycyclic aromatic hydrocarbon-DNA and protein adducts in coal tar treated patients and controls and their relationship to glutathione S-transferase genotype

Coal tar treated psoriasis patients were used as a model population to evaluate a panel of immunoassays for monitoring exposure to benzo[a]pyrene (BP) and related polycyclic aromatic hydrocarbons (PAH). The assays included measurement of PAH diol epoxide-DNA adducts in white blood cells by competitive enzyme-linked immunosorbent assay (ELISA) with fluorescence endpoint detection, PAH-albumin adducts by competitive ELISA with color endpoint detection and serum levels of antibodies recognizing BP diol epoxide-DNA adducts by noncompetitive color ELISA. PAH-DNA adducts by ELISA were elevated in patients (mean 6.77 +/- 12.05/10(8)) compared to controls (4.90 +/- 8.81/10(8), p = 0.12). There was no difference in PAH-albumin adducts between patients (mean 0.61 +/- 0.31 fmol/micrograms) and controls (0.63 +/- 0.30 fmol/micrograms). Glutathione S-transferase M1 genotype was also determined but no relationship was found between presence of the gene and either DNA or protein adduct levels. About 30% of both patients and controls had measurable titer of antibodies recognizing BPDE-I-DNA adducts. Measurement of white blood cell DNA adducts by ELISA was the most sensitive method for detecting PAH exposure in coal tar-treated psoriasis patients.

Is dermatologic usage of coal tar carcinogenic? A review of the literature

BACKGROUND

Coal tar ointments have been used for decades in the treatment of various dermatoses, most notably eczema and psoriasis. Occupational exposure to coal tar poses an increased risk of developing cutaneous malignancies. The evidence of an increased risk of skin cancer in humans, as a result of dermatologic usage of tar, however, is conflicting.

OBJECTIVE

A consensus on the carcinogenicity of tar is sought.

METHODS

The existing literature (in vitro, animal, and human studies) on this subject is reviewed.

RESULTS

The carcinogenicity of coal tar has clearly been demonstrated by in vitro and animal studies, and appears to be potentiated by concomitant use of ultraviolet radiation. Systemic absorption of mutagens from topically applied tar has been demonstrated in humans. Epidemiologic studies in humans, however, have not definitively shown an increase in skin cancer with therapeutic use of tar.

CONCLUSIONS

Conclusive evidence for the carcinogenicity of tar used in dermatologic practice is lacking. Further controlled studies are necessary.

DNA adducts in cervical tissue of smokers and non-smokers

Cervical biopsy samples were taken from 40 women, aged between 31 and 72, undergoing hysterectomies. Twenty-two of the women were smokers, four were ex-smokers and 14 were non-smokers. DNA was isolated and analysed using 32P-postlabelling, after butanol extraction or nuclease P1 digestion enhancement of the adducts. Resolution of the adducts was by thin-layer chromatography on polyethyleneimine (PEI)-cellulose. The pattern of adducts seen was similar to smoking-related adducts detected in other tissues and consisted mainly of a diagonal zone of radioactivity. With the butanol extraction enrichment method, the levels of adducts in DNA from the 22 smokers ranged from 1.65 to 6.04 adducts/10(8) nucleotides (mean = 3.70, SD = 1.36), in DNA from non-smokers from 1.16 to 3.98 (mean = 2.04, SD = 0.77) and in samples from ex-smokers from 2.57 to 3.35 (mean = 2.86, SD = 0.37). The increase in adduct levels in smokers compared with non-smokers was highly significant (Mann-Whitney test p = 0.0005, two-tailed). When analysed by the nuclease P1 digestion enhancement method, total adduct levels in samples from smokers (mean = 2.95, SD = 1.77) were not significantly different (p = 0.3, two-tailed) from levels in non-smokers (mean = 2.34, SD = 0.96). However, the level of a minor discrete adduct spot was significantly lower (p = 0.02, two-tailed) in smokers (mean = 0.19, SD = 0.36) than in non-smokers (mean = 0.39, SD = 0.41). The results indicate that some of the DNA adducts detected in cervical epithelium correlate with tobacco smoking and support the hypothesis that smoking-related cervical cancer results from exposure to genotoxic components of cigarette smoke that become activated to DNA-binding products in this tissue.

Tumorigenicity of a combination of psoriasis therapies

Coal tar, a tumour initiator, and dithranol, a tumour promoter, are used in the treatment of psoriasis. Topical treatment of mice with pharmaceutical formulations of these two agents, at therapeutic doses, induced skin papillomas in a classical two-stage carcinogenesis protocol, while treatment with either agent alone did not. This finding has implications for the use of both agents in combination in the treatment of psoriasis.

DNA adduct assay in cervical epithelium

Numerous epidemiological studies have shown that there is an association between smoking and cervical cancer. However, the essential evidence to show whether this relationship is casual or causal is lacking. The demonstration of DNA modification by tobacco components in the cervical epithelium would provide biochemical evidence to support a causal role. In this study, DNA from 39 cervical biopsies was analysed for the presence of DNA adducts using the 32P-postlabeling technique. A questionnaire on smoking habit and a urinary cotinine assay were used to identify smokers and nonsmokers. DNA samples from smokers [identified from questionnaire] were found to have significantly higher adduct levels than nonsmokers (Mann-Whitney one-tailed U-test, 95% CI > 0.339, P = 0.024). Exclusion of the women whose urinary cotinine levels did not confirm their self-reported smoking status (smoker or nonsmoker) increased this significance (95% CI > 0.508, P = 0.01). Women who had abnormal cervical smears had significantly higher DNA adduct levels than those with normal smears (95% CI > 0.439, P = 0.015). Monitoring of women with high DNA adduct levels may be a way of identifying women at risk of cervical cancer. These findings demonstrate that tobacco smoking by women leads to elevated levels of DNA adducts in cervical epithelium and provides the biochemical evidence to support the concept that smoking is a cause of cervical cancer.

Damage to DNA in cervical epithelium related to smoking tobacco

OBJECTIVE

To determine whether tobacco smoking causes increased DNA modification (adducts) in human cervical epithelium.

DESIGN

Comparison of DNA adducts measured by the technique of postlabelling with phosphorus-32 in normal ectocervical epithelium of smokers and non-smokers. A questionnaire on smoking habit and a urinary cotinine assay were used to identify smokers and non-smokers.

SETTING

Cytology unit in large teaching hospital.

SUBJECTS

39 women (11 current smokers, seven former smokers, and 21 who had never smoked) undergoing gynaecological treatment (colposcopy or hysterectomy). Nineteen members of staff who did not smoke as controls.

INTERVENTIONS

Biopsy of normal ectocervical epithelium. Urine sample.

MAIN OUTCOME MEASURES

Measurement of DNA adducts in cervical epithelial tissue of smokers and non-smokers. Smoking habit derived from results of questionnaire and urinary cotinine:creatinine ratio. Proportion of adducts in women with abnormal and normal results of cervical smear test.

RESULTS

DNA samples from smokers (identified from questionnaire) had significantly higher median proportions of DNA adducts that non-smokers (4.62 (95% confidence interval 4.04 to 7.74) v 3.47 (2.84 to 4.78) adducts/10(8) nucleotides; p = 0.048). Exclusion of women whose urinary cotinine:creatinine ratio did not confirm their self reported smoking habit (smoker or non-smoker) increased this difference (4.7 (3.85 to 8.08) v 3.52 (2.32 to 4.95) adducts/10(8) nucleotides; p = 0.03). Women who had abnormal results of cervical smear tests had significantly higher proportions of adducts than those with normal results (4.7 (3.90 to 8.13) v 3.47 (3.06 to 5.36) adducts/10(8) nucleotides; p = 0.03).

CONCLUSIONS

Tobacco smoking by women leads to increased modification of DNA in cervical epithelium, suggesting biochemical evidence consistent with smoking as a cause of cervical cancer.

DNA adducts in human urinary bladder and other tissues

Tobacco smoking is associated with an increased risk of cancer in a number of organs, including bladder and lung. Tobacco smoke contains at least 50 known chemical carcinogens that exert their biological effects through their covalent binding to cellular DNA. Examining human DNA for the presence of altered nucleotides is a means of monitoring exposure to genotoxic chemicals. DNA isolated from 73 human bladder biopsies has been analyzed by 32P-postlabeling for the presence of aromatic/hydrophobic adducts. Butanol extraction of DNA digests resulted in up to a 3-fold greater recovery of adducts than nuclease P1 digestion. Among 16 nonsmokers, adduct levels were in the range 3.2-20.8/10(8) nucleotides (mean 9.7). Eight ex-smokers had values in the range 2.6-12.3 (mean 7.1). Thirteen smokers had adduct levels between 1.3 and 26.7 adducts/10(8) nucleotides (mean 9.5, not different from nonsmokers). Six cigar smokers had higher levels of adducts (mean 12.1, range 7.3-15.0), but pipe smokers did not (five samples, mean 8.6, range 2.9-12.7). A further 8 samples from nonsmokers and 17 from smokers were examined in more detail. Although most of the DNA binding appears not to be smoking related, the levels of one adduct were found to be on average 2-fold higher in smokers (p < 0.005, one-tailed t test). Studies on tissues of the respiratory tract demonstrate a correlation between DNA adduct levels and exposure to tobacco smoke. Evidence to date on the influence of smoking on adducts in peripheral blood cells is equivocal; some studies demonstrate a significant effect, whereas others do not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adducts to macromolecules in the biological monitoring of workers exposed to polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants. Human exposure occurs through diet, smoking, and polluted air. In some groups of workers exposed to PAHs, epidemiological studies have revealed an increased mortality risk for neoplasms. This paper reviews the principal methods that have been developed recently for the detection of PAH adducts to white blood cell DNA and blood proteins (hemoglobin, albumin) and summarizes observations made on occupationally exposed subjects.

Purification and characterization of glutathione transferase from psoriatic skin

The glutathione transferases (GSTs) comprise a family of enzymes that catalyze the conjugation of glutathione with certain hydrophobic compounds, bind various hydrophobic compounds, and have selenium-independent glutathione peroxidase activity. Of the four classes of GST, the pi class is the only one present in keratinocytes, and pi-class GST is elevated in psoriatic epidermis. We have purified and characterized GST from psoriatic scales. Immunoreactivity was observed with pi class antisera, and amino terminal sequencing showed identity with GST from human placenta and cultured human keratinocytes. We conclude that the majority of GST activity in psoriatic skin is due to a pi-class isoenzyme, and pi-class GST may represent an index for hyperproliferation.

32P-postlabelling and mass spectrometric methods for analysis of bulky, polyaromatic carcinogen-DNA adducts in humans

There has been significant recent progress toward the development of human carcinogen-DNA adduct biomonitoring methods. 32P-Postlabelling is a technique which has found wide application in human studies. 32P-Postlabelling involves enzymatic preparation and labelling of DNA samples, followed by chromatographic separation of carcinogen-nucleotide adducts from unadducted nucleotides. Thin-layer ion-exchange and high-performance liquid chromatography (HPLC) have been utilized. This paper critically reviews 32P-postlabelling methods for analysis of bulky, polyaromatic carcinogen-DNA adducts and details a strategy to optimize this technique for monitoring human samples. Development of a human carcinogen biomonitoring method requires that the biomarker meet certain criteria: that the biomarker be responsive to exposures known to increase human cancer risk, to reductions in those exposures, and to the influence of metabolic differences. In addition, reliable samples must be available by non-invasive means. The ability of 32P-postlabelling to meet these criteria is traced in the literature and discussed. Identification of specific carcinogen-DNA adducts is a difficult task due to the low (femtomole) levels in human target tissues. Because co-chromatography in thin-layer chromatography (TLC) is generally not considered to be proof of chemical identity, both synchronous fluorescence and HPLC in conjunction with 32P-postlabelling and TLC are used to confirm the identity of specific carcinogen-DNA adducts in human samples. Mass spectrometry is a highly specific method, the sensitivity of which has been improved to the point which may allow its use to confirm the identity of carcinogen-DNA adducts isolated by 32P-postlabelling and other methods. The literature relating to the use of mass spectral techniques in carcinogen-DNA adduct analysis is reviewed.

DNA adducts in human and mouse skin maintained in short-term culture and treated with petrol and diesel engine lubricating oils

Human and mouse skin samples maintained in short-term organ culture were treated topically with used engine oils from petrol- and diesel-powered vehicles. Mice were also treated topically in vivo for comparison. DNA was isolated and analysed by 32P-postlabelling and the labeled DNA digests were resolved on polyethyleneimine-cellulose tlc sheets. A large number of radioactive adduct spots were observed in DNA from skin treated with the used petrol-engine oil, indicating the formation of adducts by many components of the complex oil mixture. Total adduct levels were similar in mouse skin (both in vivo and in vitro) and in human skin, although qualitative differences in the adduct maps were apparent between the human and mouse skin DNA. Treatment with the used diesel engine oil produced adduct levels no greater than that of control samples in mouse skin (in vivo and in vitro), although significant levels were found in human skin DNA from one donor. The results correlate well with the carcinogenic activity of these oils in experimental animals, helping to substantiate the conclusion that petrol engine oils (but not diesel engine oils) may present a carcinogenic risk to man if appropriate measures to minimise skin contact are not observed.

32P-postlabelling detection of aromatic DNA adducts in peripheral blood lymphocytes from aluminium production plant workers

Aluminium production plant workers are exposed to a great number of airborne polycyclic aromatic hydrocarbons and epidemiological studies suggest that these workers are at increased risk of lung and bladder cancer. Blood samples from 46 workers at 2 primary aluminium plants and from 29 occupationally unexposed control individuals were analysed. DNA was isolated from the peripheral blood lymphocytes and aromatic DNA adducts were detected by 32P-postlabelling assay using the nuclease P1 digestion procedure for the enrichment of the adducts. The total levels of DNA adducts of exposed individuals varied from the detection limit of about 0.5 adducts/10(8) nucleotides up to 7.1 adducts/10(8) nucleotides and control adduct levels were up to 2.42 adducts/10(8) nucleotides. There was no significant difference between the mean adduct levels of the control group and of the individuals of one plant. However, the mean DNA adduct level obtained from workers of the second plant was significantly higher than that of the controls (p less than 0.001) and of the first plant (p less than 0.01), respectively. This difference can be attributed to differences in the design of technology and different levels of exposure at the 2 plants. The results of this study encourage further investigations of the use of peripheral white blood cells as marker cells and of 32P-postlabelling analysis for monitoring occupational exposure to mixtures of environmental carcinogenic pollutants.

Influence of cigarette smoking on the levels of DNA adducts in human bronchial epithelium and white blood cells

The presence of carcinogen-DNA adducts in human tissues is evidence of exposure to carcinogens and may be an indicator of cancer risk. DNA was isolated from non-tumorous bronchial tissue of 37 cigarette smokers, 8 former smokers and 8 non-smokers and analyzed for the presence of aromatic and/or hydrophobic DNA adducts in the 32P-post-labelling assay. Adducts were detected as bands of radioactive material when 5'-32P-labelled deoxyribonucleoside 3',5'-bisphosphates were chromatographed on polyethyleneimine-cellulose tlc plates, and the patterns indicated the formation of adducts by a large number of compounds. Adduct levels detected in DNA from non-smokers, former smokers and current smokers were 3.45 +/- 1.62, 3.93 +/- 1.92 and 5.53 +/- 2.13 adducts/10(8) nucleotides, respectively. The differences in adduct levels between smokers and former and non-smokers were statistically significant (p less than 0.01); and among the smokers, significant correlations were found between adduct levels and both daily cigarette consumption and total cigarette consumption (daily consumption X number of years smoked). DNA was also isolated from the peripheral-blood leukocytes of 31 heavy smokers (greater than 20 cigarettes/day) and 20 non-smokers and analyzed by 32P-post-labelling. Adduct levels in the smokers' samples were not significantly different from levels in the non-smokers' samples (2.53 +/- 1.31 and 2.12 +/- 1.44 adducts/10(8) nucleotides, respectively). Thus, evidence for carcinogen exposure was found in human bronchial epithelium, a target tissue for tobacco-induced tumour formation, but not in peripheral-blood cells, indicating possible limitations in the use of the latter as a surrogate, non-target tissue source of DNA for monitoring human exposure to inhaled carcinogens.