The Effect of Microstructural Changes on Mechanical and Electrochemical Corrosion Properties of Duplex Stainless Steel Aged for Short Periods.

This work reports the effects of microstructural changes due to the secondary phases, in particular sigma (σ), on the mechanical properties and electrochemical behavior of thermally aged duplex stainless steel (DSS). Structural, morphological, mechanical, and electrochemical characterizations were performed. Sigma phase content increased with increasing aging treatment time. It had a net-like shape, as observed by electron backscatter diffractometry (EBSD). Its presence directly damaged mechanical properties. The corrosion assessment included electrochemical impedance spectroscopy (EIS) in 1 M NaCl solution at temperatures of 25, 40, and 65 °C. EIS results demonstrate that an increase in the σ phase content decreased the corrosion resistance (21.1-0.8, 3.5-0.3, and 3.1-0.2 kΩ cm2 at 25, 40, and 60 °C, respectively).

Polymorphic MLH1 and risk of cancer after methylating chemotherapy for Hodgkin lymphoma.

BACKGROUND AND OBJECTIVE: Methylating agents are effective chemotherapy agents for Hodgkin lymphoma, but are associated with the development of second primary cancers. Cytotoxicity of methylating agents is mediated primarily by the DNA mismatch repair (MMR) system. Loss of MLH1, a major component of DNA MMR, results in tolerance to the cytotoxic effects of methylating agents and persistence of mutagenised cells at high risk of malignant transformation. We hypothesised that a common substitution in the basal promoter of MLH1 (position -93, rs1800734) modifies the risk of cancer after methylating chemotherapy. METHODS: 133 patients who developed cancer following chemotherapy and/or radiotherapy (n = 133), 420 patients diagnosed with de novo myeloid leukaemia, 242 patients diagnosed with primary Hodgkin lymphoma, and 1177 healthy controls were genotyped for the MLH1 -93 polymorphism by allelic discrimination polymerase chain reaction (PCR) and restriction fragment length polymorphism assay. Odds ratios and 95% confidence intervals for cancer risk by MLH1 -93 polymorphism status, and stratified by previous exposure to methylating chemotherapy, were calculated using unconditional logistic regression. RESULTS: Carrier frequency of the MLH1 -93 variant was higher in patients who developed therapy related acute myeloid leukaemia (t-AML) (75.0%, n = 12) or breast cancer (53.3%. n = 15) after methylating chemotherapy for Hodgkin lymphoma compared to patients without previous methylating exposure (t-AML, 30.4%, n = 69; breast cancer patients, 27.2%, n = 22). The MLH1 -93 variant allele was also over-represented in t-AML cases when compared to de novo AML cases (36.9%, n = 420) and healthy controls (36.3%, n = 952), and was associated with a significantly increased risk of developing t-AML (odds ratio 5.31, 95% confidence interval 1.40 to 20.15), but only in patients previously treated with a methylating agent. CONCLUSIONS: These data support the hypothesis that the common polymorphism at position -93 in the core promoter of MLH1 defines a risk allele for the development of cancer after methylating chemotherapy for Hodgkin lymphoma. However, replication of this finding in larger studies is suggested.

Deregulation of homologous recombination DNA repair in alkylating agent-treated stem cell clones: a possible role in the aetiology of chemotherapy-induced leukaemia.

Chemotherapeutic regimes involving alkylating agents, such as methylators and crosslinking nitrogen mustards, represent a major risk factor for acute myeloid leukaemia. A high frequency of microsatellite instability and evidence of MSH2 loss in alkylating chemotherapy-related acute myeloid leukaemia (t-AML) suggests that DNA mismatch repair (MMR) dysfunction may be an initiating event in disease evolution. Subsequent accumulation of secondary genetic changes as a result of DNA MMR loss may ultimately lead to the gross chromosomal abnormalities seen in t-AML. Homologous recombination repair (HRR) maintains chromosomal stability by the repair of DNA double-strand breaks, and is therefore a possible target for deregulation in MMR dysfunctional t-AML. In order to test this hypothesis Msh2- proficient and -deficient murine embryonic stem (ES) cells were used to examine the effects of MMR status and methylating agent treatment on cellular expression of DNA double-strand break repair genes. HRR gene expression was significantly deregulated in Msh2 null ES cell clones compared to wild-type clones. Furthermore, some Msh2 null clones expressed high levels of Rad51 specifically, a critical component of HRR. Such Rad51 superexpressing clones were also observed when expression was determined in monocytic myeloid cells differentiated from ES cells. A deregulated HRR phenotype could be partially recapitulated in MMR-competent wild-type cells by treatment with the methylating agent, N-methyl-N-nitrosourea. Furthermore, treatment with melphalan, a leukaemogenic DNA crosslinking chemotherapy nitrogen mustard predicted to elicit HRR, selected against cells with deregulated HRR. These data suggest a t-AML mechanism whereby DNA MMR loss promotes the emergence of HRR gene superexpressing clones, with concomitant chromosomal instability. However, melphalan selection against clones with deregulated HRR suggests that persistence and expansion of unstable clones may require additional genetic alterations that promote cell survival.

A genome-wide association study identifies risk loci for childhood acute lymphoblastic leukemia at 10q26.13 and 12q23.1.

Genome-wide association studies (GWASs) have shown that common genetic variation contributes to the heritable risk of childhood acute lymphoblastic leukemia (ALL). To identify new susceptibility loci for the largest subtype of ALL, B-cell precursor ALL (BCP-ALL), we conducted a meta-analysis of two GWASs with imputation using 1000 Genomes and UK10K Project data as reference (totaling 1658 cases and 7224 controls). After genotyping an additional 2525 cases and 3575 controls, we identify new susceptibility loci for BCP-ALL mapping to 10q26.13 (rs35837782, LHPP, P=1.38 × 10-11) and 12q23.1 (rs4762284, ELK3, P=8.41 × 10-9). We also provide confirmatory evidence for the existence of independent risk loci at 9p21.3, but show that the association marked by rs77728904 can be accounted for by linkage disequilibrium with the rare high-impact CDKN2A p.Ala148Thr variant rs3731249. Our data provide further insights into genetic susceptibility to ALL and its biology.

Mammalian 3-methyladenine DNA glycosylase protects against the toxicity and clastogenicity of certain chemotherapeutic DNA cross-linking agents.

DNA repair status is recognized as an important determinant of the clinical efficacy of cancer chemotherapy. To assess the role that a mammalian DNA glycosylase plays in modulating the toxicity and clastogenicity of the chemotherapeutic DNA cross-linking alkylating agents, we compared the sensitivity of wild-type murine cells to that of isogenic cells bearing homozygous null mutations in the 3-methyladenine DNA glycosylase gene (Aag). We show that Aag protects against the toxic and clastogenic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea and mitomycin C (MMC), as measured by cell killing, sister chromatid exchange, and chromosome aberrations. This protection is accompanied by suppression of apoptosis and a slightly reduced p53 response. Our results identify 3-methyladenine DNA glycosylase-initiated base excision repair as a potentially important determinant of the clinical efficacy and, possibly, the carcinogenicity of these widely used chemotherapeutic agents. However, Aag does not contribute significantly to protection against the toxic and clastogenic effects of several chemotherapeutic nitrogen mustards (namely, mechlorethamine, melphalan, and chlorambucil), at least in the mouse embryonic stem cells used here. We also compare the Aag null phenotype with the Fanconi anemia phenotype, a human disorder characterized by cellular hypersensitivity to DNA cross-linking agents, including MMC. Although Aag null cells are sensitive to MMC-induced growth delay and cell cycle arrest, their sensitivity is modest compared to that of Fanconi anemia cells.

c-MYC is a radiosensitive locus in human breast cells.

Ionising radiation is a potent human carcinogen. Epidemiological studies have shown that adolescent and young women are at increased risk of developing breast cancer following exposure to ionising radiation compared with older women, and that risk is dose-dependent. Although it is well understood which individuals are at risk of radiation-induced breast carcinogenesis, the molecular genetic mechanisms that underlie cell transformation are less clear. To identify genetic alterations potentially responsible for driving radiogenic breast transformation, we exposed the human breast epithelial cell line MCF-10A to fractionated doses of X-rays and examined the copy number and cytogenetic alterations. We identified numerous alterations of c-MYC that included high-level focal amplification associated with increased protein expression. c-MYC amplification was also observed in primary human mammary epithelial cells following exposure to radiation. We also demonstrate that the frequency and magnitude of c-MYC amplification and c-MYC protein expression is significantly higher in breast cancer with antecedent radiation exposure compared with breast cancer without a radiation aetiology. Our data also demonstrate extensive intratumor heterogeneity with respect to c-MYC copy number in radiogenic breast cancer, suggesting continuous evolution at this locus during disease development and progression. Taken together, these data identify c-MYC as a radiosensitive locus, implicating this oncogenic transcription factor in the aetiology of radiogenic breast cancer.

Modulation of surface and bulk properties of biomedical polymers.

The surface and bulk modulation of polymeric biomedical devices allows the full range of material properties to be exercised as demanded by custom applications. Polymeric biomaterials are finding greater use as relatively inert and even transient options and so therefore will require thorough processing analyses and the transfer of technology from nonbiomedical applications to the biomedical industry.

Bone formation into surface phosphonylated polymeric implants.

Through the use of two animal models, the present study demonstrates the ability of phosphonylated surfaces to bind bone. In one model, surface-treated polypropylene (PP) and polyethylene (PE) were implanted in the medial cortex of the goat tibia. In the second model, surface-treated poly(ether-ether ketone) (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) were implanted through both cortices of the goat mandible. Selected rods of all material types were microtextured using crystallization induced microphase separation, a method for the formation of continuous, open-cell microporous surfaces in thermoplastic polymers. Microtextured and smooth rods were phosphonylated, and calcium was subsequently introduced to the phosphonylated surface by incubating the samples in a saturated solution of calcium oxide. For all substrate materials tested, phosphonylation and calcium posttreatment resulted in an increased propensity for bone binding and apposition, as measured by push out test. Microtextured PP, PE, and CFR-PEEK surfaces that were further phosphonylated and calcium treated resulted in test samples with an increased interfacial strength.

The Escherichia coli DNA repair protein UvrA can re-associate with the UvrB: aflatoxin B1-DNA complex in vitro.

The UvrA and UvrB proteins form part of the UvrABc endonuclease, which is responsible for nucleotide excision repair in Escherichia coli. Using a mobility shift gel assay we have studied the binding of UvrA dimer, UvrB monomer and UvA(2)B trimer complexes with 40, 50 and 136 bp (32)P-end-labelled DNA fragments adducted with aflatoxin B(1). UvrA was shown to re-associate with adduct specific UvrB: DNA complexes, a phenomenon which could be reversed by the addition of 500 mM potassium chloride or anti-UvrA anti-sera. Re-association was shown to be UvrA concentration dependent. Re-association of UvrA(2)B to the UvrB:DNA complex was not seen. We have also shown that the UvrB:DNA complex, in the case of aflatoxin B(1), is extremely stable with a half-life excess of 400 min and that fragment termini are not a specific substrate for UvrA binding.

Infusing a teacher preparation program in learning disabilities with assistive technology.

A recent trend in the fields of special education, rehabilitation, and technology is the development and implementation of assistive technology (AT) devices and services to assist individuals in compensating for disabilities and/or utilizing functional capabilities to meet environmental demands. AT devices and services have major implications for individuals with learning disabilities (LD) regarding life span issues, environmental and curricular accessibility, and compensatory strategies. Faculty members in higher education who are responsible for designing teacher preparation programs in LD must explore ways to structure curricula, methodologies, and practica to better prepare teachers to work with students who use AT devices to compensate for their specific learning disabilities. The purpose of this article is to describe curriculum design steps and barriers to and solutions for infusing LD teacher preparation programs with assistive technology.

Common genetic variation contributes significantly to the risk of childhood B-cell precursor acute lymphoblastic leukemia.

Recent genome-wide association studies (GWAS) have provided the first unambiguous evidence that common genetic variation influences the risk of childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL), identifying risk single-nucleotide polymorphisms (SNPs) localizing to 7p12.2, 9p21.3, 10q21.2 and 14q11.2. The testing of SNPs individually for an association in GWA studies necessitates the imposition of a very stringent P-value to address the issue of multiple testing. While this reduces false positives, real associations may be missed and therefore any estimate of the total heritability will be negatively biased. Using GWAS data on 823 BCP-ALL cases by considering all typed SNPs simultaneously, we have calculated that 24% of the total variation in BCP-ALL risk is accounted for common genetic variation (95% confidence interval 6-42%). Our findings provide support for a polygenic basis for susceptibility to BCP-ALL and have wider implications for future searches for novel disease-causing risk variants.

Detection of DNA damage by Escherichia coli UvrB-binding competition assay is limited by the stability of the UvrB-DNA complex.

To investigate the use of UvrB-binding to detect DNA damage, mobility shift gel electrophoresis was used to detect binding of UvrB protein to a 136 bp DNA fragment that was randomly adducted with aflatoxin B1 8,9-epoxide and end-labelled with 32P. After polyacrylamide gel electrophoresis, the shifted band that contained DNA bound by UvrB was quantified as a percentage of total radioactive substrate DNA. This method was applied to analyse plasmid DNA that was adducted with various DNA modifying agents in vitro. These adducts competed for UvrB-binding to the labelled substrate. By competing for UvrB-binding with 10 ng of plasmid DNA that was adducted with known levels of aflatoxin B1, 2-amino-3-methylimidazo[4,5-f]quinoline, or benzo[a]pyrene diol epoxide, UvrB competition could be quantified for DNA adducted with between one adduct in 10(2) and one adduct in 10(5) normal nucleotides. However, plasmid DNA exposed to N-methyl-N-nitrosourea or methylene blue + visible light, did not compete for UvrB-binding, even though the presence of UvrABC sensitive sites were confirmed on this DNA by a UvrABC incision assay. Mono-adducted 96-bp DNA substrates, which contained an internal 32P-label and either a single apurinic site, aflatoxin B1-guanine adduct, O6-methylguanine, 8-oxo-deoxyguanosine or non-adducted guanine, were also used as substrates for UvrA- and UvrB-binding to examine the stability of UvrB-DNA complexes with specific adducts. Under similar conditions used for the competition assay, significant UvrB-binding was seen only for the aflatoxin adducted substrate. These results suggest that stability of UvrB-binding varies greatly between bulky and non-bulky adducts. It was also found that rat liver DNA from untreated rats inhibited UvrB-binding to the substrate DNA in the competition assay, to a degree that was equivalent to competition with plasmid adducted at one adduct in 10(3) normal nucleotides.

Spread of rotavirus within families: a community based study.

The spread of rotavirus infection was studied over four weeks in a sample of 28 families exposed to a child with rotavirus infection. The results showed a high incidence of intrafamilial infection, with 46% of members of these families developing rotavirus infections compared with none in another series of 18 families. Children in the families with an index case were more frequently affected than adults: 75% of the children developed rotavirus infection but only 33% of the adults. Children tended to suffer the infection in a more severe form. Intrafamily contact is clearly important in transmitting rotavirus infection, and preventive measures should aim at reducing the likelihood of such cross infection.

3-methyladenine DNA glycosylases: structure, function, and biological importance.

The genome continuously suffers damage due to its reactivity with chemical and physical agents. Finding such damage in genomes (that can be several million to several billion nucleotide base pairs in size) is a seemingly daunting task. 3-Methyladenine DNA glycosylases can initiate the base excision repair (BER) of an extraordinarily wide range of substrate bases. The advantage of such broad substrate recognition is that these enzymes provide resistance to a wide variety of DNA damaging agents; however, under certain circumstances, the eclectic nature of these enzymes can confer some biological disadvantages. Solving the X-ray crystal structures of two 3-methyladenine DNA glycosylases, and creating cells and animals altered for this activity, contributes to our understanding of their enzyme mechanism and how such enzymes influence the biological response of organisms to several different types of DNA damage.