A specific chromosomal deletion in murine leukemic cells induced by radiation with different qualities.

G-banded metaphase chromosomes prepared from 14 male CBA/Ca mice with histologically confirmed myeloid leukemia (ML) were studied in an effort to identify specific chromosomal changes associated with radiation leukemogenesis. The chromosome studies were undertaken as part of a larger investigation of radiation carcinogenesis, in which mice were exposed to radiation of several different qualities, i.e., x-rays, gamma-rays and "monoenergetic" fast neutrons of 5 mean energies ranging from 0.2 to 14 MeV. The 14 ML cases showed no histologically phenotypic differences and they were transplantable in syngeneic mice. We detected a specific chromosomal deletion in 1 copy of mouse chromosome 2 at regions D-E in all radiation-induced ML cells, regardless of radiation quality. Our results strongly implicate the involvement of genes within or close to regions D-E of chromosome 2 in radiation leukemogenesis. In addition to the specific deletion in chromosome 2, loss or gain of the Y chromosome was also detected in some cells from 6 ML cases. Because this hypo- or hyperploidy occurred in only a small fraction of leukemic cells, a causative role in radiation leukemogenesis appears unlikely.

Understanding cancer development processes after HZE-particle exposure: roles of ROS, DNA damage repair and inflammation.

During space travel astronauts are exposed to a variety of radiations, including galactic cosmic rays composed of high-energy protons and high-energy charged (HZE) nuclei, and solar particle events containing low- to medium-energy protons. Risks from these exposures include carcinogenesis, central nervous system damage and degenerative tissue effects. Currently, career radiation limits are based on estimates of fatal cancer risks calculated using a model that incorporates human epidemiological data from exposed populations, estimates of relative biological effectiveness and dose-response data from relevant mammalian experimental models. A major goal of space radiation risk assessment is to link mechanistic data from biological studies at NASA Space Radiation Laboratory and other particle accelerators with risk models. Early phenotypes of HZE exposure, such as the induction of reactive oxygen species, DNA damage signaling and inflammation, are sensitive to HZE damage complexity. This review summarizes our current understanding of critical areas within the DNA damage and oxidative stress arena and provides insight into their mechanistic interdependence and their usefulness in accurately modeling cancer and other risks in astronauts exposed to space radiation. Our ultimate goals are to examine potential links and crosstalk between early response modules activated by charged particle exposure, to identify critical areas that require further research and to use these data to reduced uncertainties in modeling cancer risk for astronauts. A clearer understanding of the links between early mechanistic aspects of high-LET response and later surrogate cancer end points could reveal key nodes that can be therapeutically targeted to mitigate the health effects from charged particle exposures.

Protein expression profiles in pediatric multiple sclerosis: potential biomarkers.

The diagnosis of pediatric multiple sclerosis (MS) is challenging due to its low frequency and the overlap with other acquired childhood demyelinating disorders of the central nervous system. To identify potential protein biomarkers which could facilitate the diagnosis, we used two-dimensional gel electrophoresis (2-DE) in combination with mass spectrometry to identify proteins associated with pediatric MS. Plasma samples from nine children with MS and nine healthy subjects, matched in aggregate by age and gender, were analyzed for differences in their patterns of protein expression. We found 12 proteins that were significantly up regulated in the pediatric MS group: alpha-1-acid-glycoprotein 1, alpha-1-B-glycoprotein, transthyretin, apoliprotein-C-III, serum amyloid P component, complement factor-I, clusterin, gelsolin, hemopexin, kininogen-1, hCG1993037-isoform, and vitamin D-binding protein. These results show that 2-DE in combination with mass spectrometry is a highly sensitive technique for the identification of blood-based biomarkers. This proteomic approach could lead to a new panel of diagnostic and prognostic markers in pediatric MS.

Advantages of the CBA mouse in leukemogenesis research.

The objectives of this review are to: (a) demonstrate that the male CBA/Ca mouse has several characteristics that make it an excellent animal for the study of leukemogenesis, (b) show that several of the genetic abnormalities observed in the male CBA/Ca mouse during the development of radiation induced acute myeloid leukemia (AML) are syntenic with those frequently detected in patients with myeloid disorders such as myelodysplastic syndrome and AML, (c) illustrate that leukemia-related chromosomal lesions are the indicators for high risk individuals.

Evidence for an uncommon microsatellite instability on mouse chromosomes 2 and 4 and its possible role in radiation leukemogenesis.

Although microsatellite instability (MSI), usually detected by DNA length polymorphisms, has been implicated in the induction of solid tumors in both humans and animals, its role in leukemogenesis is unclear. The goal of this study was to investigate whether there is an association between MSI and radiation leukemogenesis in CBA/Ca mice. Microsatellite lengths at 55 loci, mapped to eight different mouse chromosomes, were examined in two groups of DNA samples: 1) 10 normal DNA samples collected from the bone marrow cells of control male CBA/Ca mice, and 2) 17 DNA samples isolated from the spleens of mice that developed myeloid leukemia (ML) after exposure to neutrons, or X rays, or gamma rays. Microsatellite markers were amplified using the non-radioisotopic multiplex-touchdown PCR protocols developed in our laboratory, and the sizes of amplicons were examined on 6% non-denaturing polyacrylamide gels. Although no correlation between microsatellite length polymorphisms and radiation leukemogenesis was observed at the 55 CBA/Ca mouse loci tested in this study, an uncommon MSI, manifested as the absence of DNA bands after PCR amplification at 2 loci (D2MIT140 and D4MIT104), was observed in both control and ML samples. However, the frequency of ML samples showing this type of MSI is statistically significant (p<0.05). Although there is no direct evidence that this type of MSI predisposes mice to the development of leukemia, the results suggests that genes flanking the D2MIT140 and D4MIT104 are susceptible to spontaneous mutation and perhaps to damage caused by ionizing radiation.

N-ras mutations in radiation-induced murine leukemic cells.

N-ras mutations were examined in DNA samples extracted from the spleen of CBA/Ca mice that developed myeloid leukemia (ML) following exposure to radiations of different qualities. A total of 17 ML cases, i.e. 5 cases of neutron-induced and 12 cases of photon- (3 gamma-ray and 9 x-ray) induced ML were included in the study along with 12 DNA samples from the bone marrow cells of control mice. Polymerase chain reaction-single strand conformational polymorphisms (PCR-SSCP) and the direct sequencing of PCR products were used to analyze three regions of the N-ras gene: (i) a 120 base-pair (bp) long portion of exon I (codons 2-37); (ii) a 103 bp long portion of exon II (codons 48-82); and (iii) a 107 bp long portion of exon III (codons 118-150). PCR-SSCP mobility shifts indicated mutations within only exon II of the N-ras gene. Such mutations were more prevalent in samples from mice exposed to fast neutrons. The exact type and location of these mutations were then determined by direct DNA sequencing. Silent point mutations, i.e. base transitions at the third base of codons 57 (GAC-->GAT), 62 (CAA-->CAC), or 70 (CAG-->CAA) were present only in mice that developed ML after exposure to fast neutrons. A base transversion at the third base of codon 61 (CAA-->CAC) was also observed in some ML cases. DNA sequencing demonstrated that ML samples contained normal as well as mutated DNA sequences. The higher frequency of N-ras mutations in neutron-induced ML suggested that fast neutrons are more effective in inducing genomic instability at the N-ras region of the genome. More importantly, N-ras mutations are not the initiating event in radiation leukemogenesis. This conclusion was supported by the finding that N-ras mutations were detected only in mice with an overt leukemic phenotype but not in mice with minimal tissue infiltration of leukemic cells, suggesting that the disease may be present prior to the presence of N-ras mutations. Alternatively, N-ras may be present in these mice but a large number of normal spleen cells in these mice interferes with the detection of mutation in a small population of leukemic cells.