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B A Nexø

Publications and source records attributed to B A Nexø.

At least 19 recordsLinked to original sources
PubMed2001

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.

Adult↗
PubMed2000

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.

Alleles↗
PubMed2000

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.

Alkylating Agents↗
PubMed1999

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.

Adult↗
PubMed1999

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.

Adenine↗
PubMed1998

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.

Blood Cell Count↗
PubMed1998

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.

Animals↗
PubMed1997

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.

Cell Survival↗
PubMed1996

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.

Environmental Monitoring↗
PubMed1995

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.

Air Pollution, Indoor↗
PubMed1990

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.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1985

Spontaneous expression of C-type virus in DBA/2 mice is associated with an increased rate of mortality, independent of neoplastic disease.

Ecotropic C-type retroviruses isolated from both normal and dimethylbenzanthracene-treated DBA/2 mice could be classified into three major groups, Ea, Eb, and Ec, that differed in structure and biology. Weanling DBA/2 mice were generally free of viruses, but a fraction of adult individuals became virus positive and were apparently selectively associated with a high expression of the Eb viruses. Some of the ecotropic viruses from DBA/2 mice acted as exogenous pathogens. They caused viremia and a moderate incidence of leukemia when injected into C3H and ST/a mice. In addition, they caused an appreciable number of early deaths without signs of malignancy. To evaluate the natural role of the viruses, we studied the survival of spontaneously viremic and nonviremic DBA/2 mice. The viremic animals as a group were characterized by a significantly reduced life-span that was not related to neoplasia. These observations indicated that endogenous C-type retroviruses can be pathogenic without preselection of the host for disease. They also emphasize that endogenous viruses, like their exogenous counterparts, can have a broader pathogenic spectrum than normally appreciated.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1982

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.

Animals↗
PubMed1981

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.

Animals↗