Polymorphisms in the Toll-Like Receptor and the IL-23/IL-17 Pathways Were Associated with Susceptibility to Inflammatory Bowel Disease in a Danish Cohort

BACKGROUND

The inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), result from the combined effects of susceptibility genes and environmental factors. Previous studies have shown that polymorphisms in the Toll-like receptor (TLR), the apoptosis, the IL-23/IL-17 and the interferon gamma (IFNG) pathways are associated with risk of both CD and UC.

METHODS

Using a candidate gene approach, 21 functional single nucleotide polymorphisms (SNPs) in 15 genes were assessed in a clinical homogeneous group of severely diseased ethnic Danish patients consisting of 624 patients with CD, 411 patients with UC and 795 controls. The results were analysed using logistic regression.

RESULTS

The polymorphisms TLR5 (rs5744174) and IL12B (rs6887695) were associated with risk of CD, and TLR1 (rs4833095) and IL18 (rs187238) were associated with risk of both CD and UC (p<0.05). After Bonferroni correction for multiple testing, the homozygous variant genotype of TLR1 743 T>C (rs4833095) was associated with increased risk CD (OR: 3.15, 95% CI: 1.59-6.26, p = 0.02) and CD and UC combined (OR: 2.96, 95% CI: 1.64-5.32, p = 0.005).

CONCLUSION

Our results suggest that genetically determined high activity of TLR1 and TLR5 was associated with increased risk of both CD and UC and CD, respectively. This supports that the host microbial composition or environmental factors in the gut are involved in risk of IBD. Furthermore, genetically determined high activity of the IL-23/IL-17 pathway was associated with increased risk of CD and UC. Overall, our results support that genetically determined high inflammatory response was associated with increased risk of both CD and UC.

Effectiveness of anti-tumour necrosis factor-α therapy in Danish patients with inflammatory bowel diseases

INTRODUCTION

The objective of this study was to evaluate the outcome of anti-tumour necrosis factor-α (anti-TNF) treatment in a large cohort of patients with inflammatory bowel diseases (IBD), including Crohn's disease (CD) and ulcerative colitis (UC) in clinical practice and to establish a cohort for future studies of genetic markers associated with treatment response.

METHODS

A national, clinically based cohort of previously naïve anti-TNF treated patients from 18 medical departments was established. The patients were screened for tuberculosis prior to treatment initiation. By combining the unique personal identification number of Danish citizens (the CPR number) from blood samples with data from the National Patient Registry, patients with International Classification of Diseases, Version 10 (ICD-10) codes K50-K63 were identified. Treatment efficacy reflected the maximum response within 22 weeks.

RESULTS

Among 492 patients with CD and 267 patients with UC, 74%/13%/14% and 65%/12%/24% were responders, partial responders and non-responders to anti-TNF therapy, respectively. More patients with UC than with CD were non-responders (odds ratio (OR) = 1.96, 95% confidence interval (CI): 1.34-2.87, p = 0.001). Young age was associated with a beneficial response (p = 0.03), whereas smoking ≥ 10 cigarettes/day was associated with non-response among patients with CD (OR = 2.33, 95% CI: 1.13-4.81, p = 0.03).

CONCLUSION

In this clinically based cohort of Danish patients with IBD treated with anti-TNF, high response rates were found. Heavy smoking was associated with non-response, whereas young age at treatment initiation was associated with a beneficial response among patients with CD. Thus, the results obtained in this cohort recruited from clinical practice were similar to those previously obtained in clinical trials.

FUNDING

The work was funded by Health Research Fund of Central Denmark Region, Colitis-Crohn Foreningen and the University of Aarhus (PhD grant).

TRIAL REGISTRATION

Clinicaltrials NCT02322008.

Polymorphisms in the inflammatory pathway genes TLR2, TLR4, TLR9, LY96, NFKBIA, NFKB1, TNFA, TNFRSF1A, IL6R, IL10, IL23R, PTPN22, and PPARG are associated with susceptibility of inflammatory bowel disease in a Danish cohort

BACKGROUND

The inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), result from the combined effects of susceptibility genes and environmental factors. Polymorphisms in genes regulating inflammation may explain part of the genetic heritage.

METHODS

Using a candidate gene approach, 39 mainly functional single nucleotide polymorphisms (SNPs) in 26 genes regulating inflammation were assessed in a clinical homogeneous group of severely diseased patients consisting of 624 patients with CD, 411 patients with UC and 795 controls. The results were analysed using logistic regression.

RESULTS

Sixteen polymorphisms in 13 genes involved in regulation of inflammation were associated with risk of CD and/or UC (p ≤ 0.05). The polymorphisms TLR2 (rs1816702), NFKB1 (rs28362491), TNFRSF1A (rs4149570), IL6R (rs4537545), IL23R (rs11209026) and PTPN22 (rs2476601) were associated with risk of CD and the polymorphisms TLR2 (rs1816702), TLR4 (rs1554973 and rs12377632), TLR9 (rs352139), LY96 (rs11465996), NFKBIA (rs696), TNFA (rs1800629), TNFRSF1A (rs4149570), IL10 (rs3024505), IL23R (rs11209026), PTPN22 (rs2476601) and PPARG (rs1801282) were associated with risk of UC. When including all patients (IBD) the polymorphisms TLR2 (rs4696480 and rs1816702), TLR4 (rs1554973 and rs12377632), TLR9 (rs187084), TNFRSF1A (rs4149570), IL6R (rs4537545), IL10 (rs3024505), IL23R (rs11209026) and PTPN22 (rs2476601) were associated with risk. After Bonferroni correction for multiple testing, both the homozygous and the heterozygous variant genotypes of IL23R G>A(rs11209026) (OR(CD,adj): 0.38, 95% CI: 0.21-0.67, p = 0.03; OR(IBD,adj) 0.43, 95% CI: 0.28-0.67, p = 0.007) and PTPN22 1858 G>A(rs2476601) (OR(CD,unadj) 0.54, 95% CI: 0.41-0.72, p = 7*10-4; OR(IBD,unadj): 0.61, 95% CI: 0.48-0.77, p = 0.001) were associated with reduced risk of CD.

CONCLUSION

The biological effects of the studied polymorphisms suggest that genetically determined high inflammatory response was associated with increased risk of CD. The many SNPs found in TLRs suggest that the host microbial composition or environmental factors in the gut are involved in risk of IBD in genetically susceptible individuals.

Associations between functional polymorphisms in the NFκB signaling pathway and response to anti-TNF treatment in Danish patients with inflammatory bowel disease

Antitumor necrosis factor-α (TNF-α) is used for treatment of severe cases of inflammatory bowel diseases (IBD), including Crohn's disease (CD) and ulcerative colitis (UC). However, one-third of the patients do not respond to the treatment. Genetic markers may predict individual response to anti-TNF therapy. Using a candidate gene approach, 39 mainly functional single nucleotide polymorphisms (SNPs) in 26 genes regulating inflammation were assessed in 738 prior anti-TNF-naive Danish patients with IBD. The results were analyzed using logistic regression (crude and adjusted for age, gender and smoking status). Nineteen functional polymorphisms that alter the NFκB-mediated inflammatory response (TLR2 (rs3804099, rs11938228, rs1816702, rs4696480), TLR4 (rs5030728, rs1554973), TLR9 (rs187084, rs352139), LY96 (MD-2) (rs11465996), CD14 (rs2569190), MAP3K14 (NIK) (rs7222094)), TNF-α signaling (TNFA (TNF-α) (rs361525), TNFRSF1A (TNFR1) (rs4149570), TNFAIP3(A20) (rs6927172)) and other cytokines regulated by NFκB (IL1B (rs4848306), IL1RN (rs4251961), IL6 (rs10499563), IL17A (rs2275913), IFNG (rs2430561)) were associated with response to anti-TNF therapy among patients with CD, UC or both CD and UC (P ⩽ 0.05). In conclusion, the results suggest that polymorphisms in genes involved in activating NFκB through the Toll-like receptor (TLR) pathways, genes regulating TNF-α signaling and cytokines regulated by NFκB are important predictors for the response to anti-TNF therapy among patients with IBD. Genetically strong TNF-mediated inflammatory response was associated with beneficial response. In addition, the cytokines IL-1β, IL-6 and IFN-γ may be potential targets for treating patients with IBD who do not respond to anti-TNF therapy. These findings should be examined in independent cohorts before these results are applied in a clinical setting.

(Some) cellular mechanisms influencing the transcription of human endogenous retrovirus, HERV-Fc1

DNA methylation and histone acetylation are epigenetic modifications that act as regulators of gene expression. DNA methylation is considered an important mechanism for silencing of retroelements in the mammalian genome. However, the methylation of human endogenous retroviruses (HERVs) is not well investigated. The aim of this study was to investigate the transcriptional potential of HERV-Fc1 proviral 5'LTR in more detail, and examined the specific influence of CpG methylation on this LTR in number of cell lines. Specifically, the role of demethylating chemicals e.g. 5-aza-2' deoxycytidine and Trichostatin-A, in inducing or reactivating expression of HERV-Fc1 specific sequences and the mechanisms were investigated. In our present study, 5-aza-dC is shown to be a powerful inducer of HERV-Fc1, and at the same time it strongly inhibits methylation of DNA. Treatment with this demethylating agent 5-aza-dC, results in significantly increased levels of HERV-Fc1 expression in cells previously not expressing HERV-Fc1, or with a very low expression level. The extent of expression of HERV-Fc1 RNAs precisely correlates with the apparent extent of demethylation of the related DNA sequences. In conclusion, the results suggest that inhibition of DNA methylation/histone deacetylase can interfere with gene silencing mechanisms affecting HERV-Fc1 expression in human cells.

Increased mRNA expression levels of ERCC1, OGG1 and RAI in colorectal adenomas and carcinomas

BACKGROUND

The majority of colorectal cancer (CRC) cases develop through the adenoma-carcinoma pathway. If an increase in DNA repair expression is detected in both early adenomas and carcinomas it may indicate that low repair capacity in the normal mucosa is a risk factor for adenoma formation.

METHODS

We have examined mRNA expression of two DNA repair genes, ERCC1 and OGG1 as well as the putative apoptosis controlling gene RAI, in normal tissues and lesions from 36 cases with adenomas (mild/moderat n = 21 and severe n = 15, dysplasia) and 9 with carcinomas.

RESULTS

Comparing expression levels of ERCC1, OGG1 and RAI between normal tissue and all lesions combined yielded higher expression levels in lesions, 3.3-fold higher (P = 0.005), 5.6-fold higher (P < 3.10-5) and 7.7-fold higher (P = 0.0005), respectively. The levels of ERCC1, OGG1 and RAI expressions when comparing lesions, did not differ between adenomas and CRC cases, P = 0.836, P = 0.341 and P = 0.909, respectively. When comparing expression levels in normal tissue, the levels for OGG1 and RAI from CRC cases were significantly lower compared to the cases with adenomas, P = 0.012 and P = 0.011, respectively.

CONCLUSION

Our results suggest that increased expression of defense genes is an early event in the progression of colorectal adenomas to carcinomas.

Polymorphisms of the XRCC1, XRCC3 and XPD genes and risk of colorectal adenoma and carcinoma, in a Norwegian cohort: a case control study

Background

Genetic polymorphisms in DNA repair genes may influence individual variation in DNA repair capacity, which may be associated with risk of developing cancer. For colorectal cancer the importance of mutations in mismatch repair genes has been extensively documented. Less is known about other DNA repair pathways in colorectal carcinogenesis. In this study we have focused on the XRCC1, XRCC3 and XPD genes, involved in base excision repair, homologous recombinational repair and nucleotide excision repair, respectively.

Methods

We used a case-control study design (157 carcinomas, 983 adenomas and 399 controls) to test the association between five polymorphisms in these DNA repair genes (XRCC1 Arg¹⁹⁴Trp, Arg²⁸⁰His, Arg³⁹⁹Gln, XRCC3 Thr²⁴¹Met and XPD Lys⁷⁵¹Gln), and risk of colorectal adenomas and carcinomas in a Norwegian cohort. Odds ratio (OR) and 95% confidence interval (95% CI) were estimated by binary logistic regression model adjusting for age, gender, cigarette smoking and alcohol consumption.

Results

The XRCC1 280His allele was associated with an increased risk of adenomas (OR 2.30, 95% CI 1.19–4.46). The XRCC1 399Gln allele was associated with a reduction of risk of high-risk adenomas (OR 0.62, 95% CI 0.41–0.96). Carriers of the variant XPD 751Gln allele had an increased risk of low-risk adenomas (OR 1.40, 95% CI 1.03–1.89), while no association was found with risk of carcinomas.

Conclusion

Our results suggest an increased risk for advanced colorectal neoplasia in individuals with the XRCC1 Arg²⁸⁰His polymorphism and a reduced risk associated with the XRCC1 Arg³⁹⁹Gln polymorphism. Interestingly, individuals with the XPD Lys⁷⁵¹Gln polymorphism had an increased risk of low-risk adenomas. This may suggest a role in regression of adenomas.

GPX Pro198Leu and OGG1 Ser326Cys polymorphisms and risk of development of colorectal adenomas and colorectal cancer

Little is known about genetic risk factors for colorectal cancer. We assessed the association between polymorphisms in two genes involved in DNA repair of oxidative stress, GPX and OGG1, and risk of colorectal carcinoma or adenomas. We studied 166 cases with adenocarcinoma, 974 with adenomas and 397 controls recruited from the Norwegian cohort NORCCAP. No associations were found between the polymorphism GPX Pro198Leu and risk of colorectal adenomas or carcinomas. Carriers of the variant allele OGG1 Ser326Cys polymorphism had a lowered risk of colorectal cancer, OR=0.56 (95% confidence interval 0.33-0.95), while no association were found with risk of adenomas. This indicates that a low repair capacity of oxidative DNA damage may not be a risk factor for development of colorectal adenomas or carcinoma.

Association between low self-rated health and heterozygosity for -110A > C polymorphism in the promoter region of HSP70-1 in aged Danish twins

We have studied the possible association between the -110A > C polymorphism in the promoter region of one of the heat shock protein genes HSP70-1 with human longevity in a cohort of aged Danish twins. This cohort includes individuals aged between 70 and 91 years (mean = 75.6 years), who are categorized according to the presence or absence of various diseases and according to the various, age-related parameters for which a genetic component has already been defined. Four hundred DNA samples from the cohort were genotyped using real-time PCR. Aging phenotypes (diseases, physical and cognitive functioning) were compared with regard to genotype. Of all the aging phenotypes studied, self-rated health and relative self-rated health, which represent an individual's overall sense of physical well-being and which have been shown to be both predictors of survival at older ages and better indicators of future survival than objectively measured health status, were associated with the polymorphism. An association was found between low self-rated health and heterozygosity for -110A > C polymorphism in the promoter region of HSP70-1 in aged Danish twins.

Twelve single nucleotide polymorphisms on chromosome 19q13.2-13.3: linkage disequilibria and associations with basal cell carcinoma in Danish psoriatic patients

The genetic susceptibility to basal cell carcinoma (BCC) among Danish psoriatic patients was investigated in association studies with 12 single nucleotide polymorphisms on chromosome 19q13.2-3. The results show a significant association between BCC and the A-allele of a polymorphism in ERCCI exon4 (Odds ratio 12;95% Confidence Interval 1.17-124; p(chi2, two-side) = 0.019) and to a lesser extent with XPD exon6 (p = 0.06). This is in accordance with recent studies of a different group of BCC cases (Rockenbauer et al. (in press) Carcinogenesis; Yin et al. (manuscript submitted for publication). Cancer Epidemiol. Biomarkers Prev), which places two highly influential markers between these two genes. The analysis also confirmed that considerable linkage disequilibrium exists between SNPs both within genes and between genes in this region. The combined studies suggest that genetic variation in nucleotide excision repair is of importance for the development of BCC.

Polymorphisms of the DNA repair gene XPD: correlations with risk of basal cell carcinoma revisited

The XPD gene product has a dual function in basal transcription and in nucleotide excision repair. We have previously reported that two polymorphisms in the gene, one silent mutation in codon 156 of exon 6 and one giving rise to a Lys-->Gln substitution in codon 751 of exon 23, showed signs of being associated with basal cell carcinoma in a Scandinavian study group of psoriasis patients and non-psoriatics with and without basal cell carcinoma [Dybdahl, Vogel, Frentz, Wallin and Nexø (1999) Cancer Epidemiol. Biomark. Prev., 8, 77-81]. In both polymorphisms, the CC genotype appeared to be protective against basal cell carcinoma. Here, we have genotyped an American study group of basal cell carcinoma patients and controls without skin cancer for the two polymorphisms. In addition, we studied an A-->G polymorphism in codon 312 of exon 10, which results in an Asp-->Asn substitution in a conserved region of XPD. In the whole study group, subjects carrying the AA and AC genotype in exon 6 were at 1.9-fold higher risk of basal cell carcinoma (P = 0.062, CI 0.96-3.75). If only subjects without a family history of non-melanoma skin cancer were included, subjects carrying AA or AC genotype were at 3.3-fold higher risk of basal cell carcinoma (P = 0.007, CI 1.35-8.18). Among subjects with a family history of non-melanoma skin cancer, subjects with an AG or AA genotype in codon 312 of exon 10 were at 5.25-fold increased risk of basal cell carcinoma (P = 0.027, CI 1.15-23.93). A protective effect of the CC genotype in exon 23 could not be confirmed. Cases with a family history of skin cancer had statistically significantly different allele frequencies of the polymorphisms in exon 6 and exon 10 from cases without family history of non-melanoma skin cancer. Our results indicate that the exon 6(A) allele is a risk factor in basal cell carcinoma.

Psoriasis patients with basal cell carcinoma have more repair-mediated DNA strand-breaks after UVC damage in lymphocytes than psoriasis patients without basal cell carcinoma

We have investigated the formation of strand-breaks following UVC irradiation in lymphocytes from psoriasis patients with or without basal cell carcinoma (BCC). Isolated lymphocytes were irradiated with UVC light at a dose of 3.6 J/m(2), and the level of DNA strand-breaks were measured 25 min after the irradiation by the alkaline comet assay. The generation of strand-breaks following UVC irradiation indicates DNA-repair-mediated incisions, as UVC light does not generate strand-breaks per se. We found that psoriasis patients with BCC had more DNA-repair incisions than non-cancer patients. The incision level correlated to two polymorphisms of the XPD gene. At present, it is not clear if the association is a primary effect that is related to differences of the XPD protein. Genes encoding for other repair proteins, namely XRCC1, ERCC1, and LIG1 are located close to the XPD gene, and it is possible that the association is due to a cosegregation with a polymorphism in one of these genes.

Sensitivity to nitrogen mustard relates to the ability of processing DNA damage in Chinese hamster ovary cells

The hallmark of the excision repair pathways is the removal of DNA adducts by excision of the damaged nucleotides. In the course of repair, transient DNA strand breaks occur, which can be measured by the Comet assay. We have investigated the processing of DNA damage, mediated by nitrogen mustard, in wild-type AA8 Chinese hamster ovary cells, and in UV5, UV20 and UV41 DNA repair deficient cell lines. Whereas DNA repair could not be detected by unscheduled DNA synthesis at nitrogen mustard doses below 10 microM, processing of nitrogen mustard-mediated DNA damage was observed by the Comet assay at a 100-times lower concentration. Wild-type Chinese hamster ovary AA8 cells were able to process nitrogen mustard-mediated DNA damage within 4-24 hr depending on the dose of nitrogen mustard (0.1-10 microM). None of the repair-deficient cell lines was able to completely process the DNA damage induced by 10 microM nitrogen mustard. At nitrogen mustard doses that conferred 10% colony forming ability, the repair-deficient cells had an altered processing of nitrogen mustard-mediated DNA damage: In the AA8, UV20, and UV41 cells, the amplitude of strand breaks peaked early (within 4 hr), the level of strand breaks in the nitrogen mustard exposed UV20 and UV41 cells did not return to the baseline of the unexposed reference culture, and the peak in strand breaks in the UV5 cell line occurred after 4 hr. Our results indicate that the single cell gel electrophoresis (Comet) assay is suitable for assessing repair capability of DNA alkylations.

Low DNA repair is a risk factor in skin carcinogenesis: a study of basal cell carcinoma in psoriasis patients

We have studied DNA repair in patients with psoriasis aiming at investigating the importance of repair in chemically induced cancer. An increased risk of non-melanoma skin cancer has been observed in psoriasis patients extensively treated with tar, methotrexate and photochemotherapy (psoralen + UVA). We measured the DNA repair capacity (DRC) by a host cell reactivation (HCR) assay in lymphocytes from psoriasis patients with and without basal cell cancer and non-psoriatic persons with and without basal cell cancer (4 x 20 study persons). Among psoriasis patients we observed a significant lower DRC in patients with skin cancer compared to patients without skin cancer (P = 0.015; Mann-Whitney, one-sided). Using the median of the healthy control group (group 4) as a cutoff value to divide the psoriasis patients into groups of high and low repair, we found that individuals who had a low repair capacity had a 6.4-fold increased skin cancer risk compared to individuals with high repair (95% confidence interval (CI), 1.44-28.5). The level of DNA repair was correlated with the age at which the psoriasis patients got their first skin cancer. The lower the level of DNA repair, the earlier the psoriasis patients had their first skin tumor (P = 0.070 Spearman; one-sided). Psoriasis patients without BCC had marginally higher repair than healthy controls (P = 0.11, Mann-Whitney, two-sided). We found no difference between BCC patients without psoriasis and healthy controls. In conclusion, these findings suggest a protective role of DNA repair in a predominantly chemically induced cancer.

Polymorphisms in the DNA repair gene XPD: correlations with risk and age at onset of basal cell carcinoma

The XPD protein has a dual function, both in nucleotide excision repair and in basal transcription. We have studied the role of two nucleotide substitutions in the XPD gene, one in exon 23 leading to an amino acid substitution (Lys751Gln) and one silent in exon 6 in relation to basal cell carcinoma (BCC). Both are two-allele polymorphisms, with the nucleobases A and C at the given positions. We genotyped psoriasis patients with and without BCC and nonpsoriatic persons with and without BCC (4 x 20 persons). The choice to study psoriasis patients was motivated by their high genotoxic exposure via treatment and their high relative rate of early BCC. Subjects carrying two A alleles (AA genotype) in exon 23 were at 4.3-fold higher risk of BCC than subjects with two C alleles (95% CI, 0.79-23.57). In addition, the mean age at first skin tumor for BCC cases with the AA genotype was significantly lower than the mean age for BCC cases with the AC or CC genotype (P = 0.012). Thus, the variant C-allele of exon 23 may be protective. The exon 6 genotype was associated with the risk of BCC among the psoriasis patients; psoriatics carrying two A alleles in exon 6 were at 5.3-fold higher risk of BCC than psoriatics with two C alleles (95% CI, 0.78-36.31). For the psoriatics, the mean age at onset of BCC for cases with the AA genotype was marginally lower than the mean age for cases with genotype AC or CC (P = 0.060). Our results raise the possibility that the polymorphisms in the XPD gene may be contributing factors in the risk of BCC development. They are, therefore, important candidates for future studies in susceptibility to cancer.

Proficient deoxyribonucleic acid repair of methylation damage in hamster ERCC-gene mutants

Three major pathways, nucleotide excision repair (NER), base excision repair (BER) and O6-methylguanine-DNA methyltransferase (MGMT), are responsible for the removal of most adducts to DNA and thus for the survival of cells influenced by deoxyribonucleic acid (DNA) adduct-forming chemicals. We have evaluated host cell reactivation and cell survival of wild type Chinese hamster ovary cells and of mutants in the NER-genes ERCC1, ERCC2, and ERCC4 after treatment with the methylating compounds dimethylsulfate and methylnitrosourea. No effect of the three genes could be demonstrated, i.e., survival and host cell reactivation after methylation damage in the mutants and the wild type cells were similar. Gene-specific repair experiments confirmed the proficient removal of methyl lesions. We conclude that the three nucleotide excision repair genes are immaterial to the repair of methylation damage. This suggests that NER does not play a role in the removal of methylation in mammalian cells and that BER and MGMT are responsible for the survival of such cells, when they are challenged with methylation of DNA.

Seasonal variation of DNA damage and repair in patients with non-melanoma skin cancer and referents with and without psoriasis

Quadruples of skin cancer patients with and without psoriasis and referents with and without psoriasis (4 x 20 study persons) were identified and examined for DNA damage by single cell gel electrophoresis (comet-assay) and DNA-repair by UV-induced unscheduled DNA synthesis (UDS) in mononuclear blood cells (lymphocytes and monocytes). DNA damage (strand breaks and alkaline labile sites) as assessed by the comet assay and DNA repair as assessed by UDS were significantly associated with the season in which blood sampling took place. This variation might be explained by an increased exposure to solar radiation. When the comet tail moment data were stratified by sampling period, an interaction between psoriasis and skin cancer was detected, with patients with psoriasis and skin cancer exhibiting more DNA damage. Patients with psoriasis and skin cancer also had lower UDS compared to healthy study persons, suggesting that the more DNA damage may be caused by a lower rate of DNA repair. In all study persons, the extent of UDS correlated positively with the amount of DNA damage determined by the comet assay.

Nitrogen mustard-mediated mutagenesis in human T-lymphocytes in vitro

The cytotoxic and mutagenic effect of the bifunctional alkylating agent nitrogen mustard (HN2) was examined. Primary human lymphocytes were exposed to graded doses of HN2 in vitro and relative survival was determined. Mutation induction at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus was measured by cloning the exposed T-cells in microtitre plates in the presence and absence of 6-thioguanine (TG). The IC50-value determined for 30 min exposure to HN2 was 1.34 microM. The mutant frequencies (MF) in exposed T-cell cultures were 10-fold (2 microM HN2) to 32-fold (4 microM HN2) higher than those of unexposed cultures (median values). Nitrogen mustard-mediated mutagenesis is discussed in terms of the current ideas about DNA damage and repair.

Somatic mutation detection in human biomonitoring

Somatic cell gene mutation arising in vivo may be considered to be a biomarker for genotoxicity. Assays detecting mutations of the haemoglobin and glycophorin A genes in red blood cells and of the hypoxanthine-guanine phosphoribosyltransferase and human leucocyte antigenes in T-lymphocytes are available in humans. This MiniReview describes these assays and their application to studies of individuals exposed to genotoxic agents. Moreover, with the implementation of techniques of molecular biology mutation spectra can now be defined in addition to the quantitation of in vivo mutant frequencies. We describe current screening methods for unknown mutations, including the denaturing gradient gel electrophoresis, single strand conformation polymorphism analysis, heteroduplex analysis, chemical modification techniques and enzymatic cleavage methods. The advantage of mutation detection as a biomarker is that it integrates exposure and sensitivity in one measurement. With the analysis of mutation spectra it may thus be possible to identify the causative genotoxic agent.

Risk assessment methodologies for carcinogenic compounds in indoor air

OBJECTIVES

The purpose of this study was to compare different methods for calculating maximal allowable concentrations of potentially carcinogenic substances in indoor air. Benzene, tetrachloroethylene, trichloroethylene, and vinyl chloride were selected as the model substances.

METHODS

Estimates were used of carcinogenic potency from quantitative risk assessment, lowest observable effect levels (LOEL) from animal experiments and epidemiologic studies combined with safety factors, and estimation from occupational exposure limits with safety factors. The estimates were compared with actual concentrations in buildings in Denmark.

RESULTS

Concentrations of benzene, tetrachloroethylene, trichloroethylene, and vinyl chloride of the order of 10, 20, 200, and 40 ppb, respectively, in indoor air were found to correspond to a 10(-4) lifetime risk of cancer.

CONCLUSIONS

The estimated maximal allowable concentrations of carcinogenic compounds obtained from indoor air by quantitative risk assessment using a lifetime risk of 10(-4) or using LOEL values and suitable safety factors appear to be comparable and reasonable. Calculations based on occupational exposure limits and safety factors generally give comparable or somewhat higher values. Using a lifetime risk of 10(-6) for quantitative risk assessment does not seem reasonable considering the risks associated with the activities of everyday life.

Mechanism of chemical activation of expression of the endogenous ecotropic murine leukemia provirus Emv-3

DBA/2 mice carry a single endogenous ecotropic murine leukemia provirus, Emv-3. This provirus is defective; it is very poorly expressed in young DBA/2 mice. The defect in Emv-3 is caused by a single base substitution in codon 3 of p15gag. The resulting amino acid substitution inhibits myristylation of the gag precursor and subsequent virus assembly. Despite this defect, percutaneous treatment of DBA/2 mice with the carcinogen and mutagen 7,12-dimethylbenz[a]anthracene (DMBA) induces ecotropic murine leukemia virus replication in virtually all treated mice. We hypothesized that this induction is the result of a DMBA-induced reverse mutation in codon 3 of p15gag which allows for efficient myristylation. We tested this hypothesis by isolating ecotropic viruses from DMBA-treated mice and determining the DNA sequences of selected regions of p15gag, including codon 3. In support of the above-described model, all of the viruses examined contained single nucleotide substitutions in codon 3. In addition, most of the replication-competent viruses that were sequenced appeared to result from simple mutation of Emv-3 rather than recombination with other endogenous murine leukemia viruses. These studies may provide a basis for development of a sensitive assay for the mutagenic activity of a variety of chemical carcinogens in vivo.

Murine xenotropic type C viruses. V. Biologic and structural differences among three cloned retroviruses isolated from kidney cells from one NZB mouse

Three xenotropic retroviruses have been biologically cloned from cells cultured from the kidney of a 3-month-old NZB female mouse. They were obtained by first cocultivating the kidney cells for several weeks with mink, dog, and human cells and then cloning them by endpoint dilution. The cloned viruses differ in their infectivity and replicative ability in a variety of heterologous cell lines. The mink cell line-derived virus (X-NZB/K-Mlc) reaches titers in culture of over 10(8) infectious viruses/ml, and is produced in high titer within 24 hr after infection of mink lung cells. The human and dog cell-derived NZB viruses (X-NZB/K-Huc and X-NZB/K-Dgc) grow to lower titers and are similar in many respects. They differ in their relative ability to replicate in dog and human cells and to transform mink S+L- cells. Peptide mapping studies indicate that the X-NZB/K-Mlc virus has a unique p15(E) protein which distinguishes it from the other two cloned NZB viruses. These results lend further support to the observation that several types of xenotropic virus are present in a mouse strain and that more than one virus can be expressed by one organ of a particular mouse.

Variants of type-C retroviruses from DBA/2 mice: protein-structural and biological properties

Ecotropic murine leukemia viruses isolated from normal and carcinogen-treated DBA/2 mice can be classified into three main groups that differ in structure and biology. Two groups, called Ea and Eb, consist of N-tropic viruses related to the standard endogenous ecotropic virus of AKR mice. Ea viruses replicate with reduced efficiency in cell lines derived from C3H mice, while Eb viruses essentially replicate normally in these cells. As elsewhere reported, Ea viruses appear apathogenic in C3H mice, while Eb viruses cause a moderate incidence of late leukemias. The biological differences are associated with modulations of the fine structure of the gag gene-encoded proteins. A third group of viruses, called Ec, is clearly more diverged. They differ extensively from Ea and Eb viruses in the products of the gag and env gene, and are related to Rauscher leukemia virus. Ec viruses are NB-ecotropic; they replicate efficiently in all mouse cells tested, and induce leukemias in C3H mice with shorter latency periods than Eb viruses. Since published nucleic acid hybridization data indicate that DBA/2 mice only carry one ecotropic provirus, we assume that the DBA/2 viruses represent a developmental series of variants evolving during the life of the animals.

Entry of murine retrovirus into mouse fibroblasts

We have studied the entry of murine retrovirus into mouse fibroblasts by following the fate of both radioactively (protein) labeled virus particles and infectious virus particles. Physical and infectious particles bound to the cell surface with a half time of 1.5-2 hr. Both types of particles were internalized with a half time of approximately 3 hr as measured by the resistance to externally added proteases. The binding proceeded both at 37 and 0 degrees, whereas the internalization was blocked at 0 degrees. The internalized physical particles followed two routes: they either were degraded or remained stable in the cell. Degradation was blocked by lysosomotropic bases and is therefore believed to occur in the lysosomes. Infection could also be inhibited by lysosomotropic bases when present in the first hours after the internalization, indicating that the infectious route also is leading through the lysosomes or another acidic compartment of the cell.

Structural homologies of cobalamin-binding proteins. Tryptic peptide mapping of intrinsic factor, transcobalamin and haptocorrin from man, hog and rabbit

We have explored the structural features of cobalamin binding proteins by peptide mapping. The present report is a comparison of the radioiodinated tryptic peptides of intrinsic factor, transcobalamin and haptocorrin from man, hog and rabbit. The results show that the homology between analogous proteins from different species is close for intrinsic factor and transcobalamin and weaker for haptocorrin. The results also suggest the existence of one or more regions which, with minor changes, are conserved among all proteins investigated. This implies a common evolutionary origin for all the cobalamin binding proteins studied.

Decay of Moloney leukemia virus production after enucleation of chronically infected mouse cells

The effect of enucleation of synthesis of Moloney leukemia virus was studied in chronically infected YACIR-A9 mouse hybrid cells. The synthesis of infectious virus decreased gradually until, 12 h after enucleation, virtually no infectious virus was produced. As determined by particle-bound p30 and reverse transcriptase, cytoplasts produced a low level of noninfectious viral particles. Thus, the assembly of virus particles does not appear to be wholly dependent on the presence of the cell nucleus. In contrast, production of infectious particles shows an absolute requirement for the cell nucleus.

Activation of C-type virus during chemically induced leukemogenesis in mice

Repeated percutaneous applications of 7,12-dimethylbenz(a)anthracene on weaning DBA/2 and ST/a mice induced 100% leukemias with short latency periods. Endogenous C-type viruses were activated during the treatment as evidenced by (a) increased expression of the murine leukemia virus major core protein, p30, in blood and spleens and (b) increased frequency of detection of ecotropic virus by cocultivation of the splenocytes with SC-1 cells. The treatment did not affect p30 expression in several nonlymphoid organs, and detection of xenotropic viruses in the splenocytes was decreased. Virus expression did not correlate with the progression of disease in that (a) high p30 levels were generally found in mice with relatively low spleen weights and (b) p30 levels had no obvious connection to survival of the individual. 7,12-Dimethylbenz(a)anthracene treatment had little influence on p30 expression in spleens and blood from C3H and BALB/c mice, which are less sensitive to 7,12-dimethylbenz(a)anthracene-induced leukemogenesis. The results indicate an association of C-type virus activation with chemical induction of leukemia but do not necessarily imply an etiological role of the virus in the disease.

C-type virus protein p30 in blood from inbred mice correlates with their later incidence of leukemia

The major core protein, p30, of mouse C-type viruses was quantitated radioimmunologically in lymphoid organs and blood from inbred strains of mice. The concentration of p30 in thymus and spleen had a weak and moderate correlation, respectively, to leukemia frequency. In contrast, the concentration of p30 in blood from mice with a high incidence of leukemia (strains AKR and C58) was 100-fold increased at 2 months of age compared with 10 strains with a low incidence of the disease. The SJL mice, which have a high incidence of reticulum cell neoplasms, showed generally elevated, but variable, values. The high concentration in AKR blood developed during the first weeks of life. Approximately one-third of the DBA/2 mice had elevated levels after 4 to 5 months, whereas the values from mice of the 129 strain were low irrespective in their age. The major part of p30 appeared to be associated with the erythrocytes. The concentration of p30 in the blood seems to reflect the presence of replicating virus in mice. It identifies among the inbred strains a high leukemia group one-half year prior to disease.