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An Automated Microscopic Scoring Method for the &#947;-H2AX Foci Assay in Human Peripheral Blood Lymphocytes

Ionizing radiation is a potent inducer of DNA damage and a well-documented carcinogen. Biological dosimetry comprises the detection of biological effects ...

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The lack of information on how biological systems respond to low-dose and low dose-rate exposures makes it difficult to accurately assess the carcinogenic risks. This is of critical importance to space radiation, which remains a serious concern for long-term manned space exploration. In this study, the γ-H2AX foci assay was used to follow DNA double-strand break (DSB) induction and repair following exposure to neutron irradiation, which is produced as secondary radiation in the space environment. Human lymphocytes were exposed to high dose-rate (HDR: 0.400 Gy/min) and low dose-rate (LDR: 0.015 Gy/min) (66)/Be(40) neutrons. DNA DSB induction was investigated 30 min post exposure to neutron doses ranging from 0.125 to 2 Gy. Repair kinetics was studied at different time points after a 1 Gy neutron dose. Our results indicated that γ-H2AX foci formation was 40% higher at HDR exposure compared to LDR exposure. The maximum γ-H2AX foci levels decreased gradually to 1.65 ± 0.64 foci/cell (LDR) and 1.29 ± 0.45 (HDR) at 24 h postirradiation, remaining significantly higher than background levels. This illustrates a significant effect of dose rate on neutron-induced DNA damage. While no significant difference was observed in residual DNA damage after 24 h, the DSB repair half-life of LDR exposure was slower than that of HDR exposure. The results give a first indication that the dose rate should be taken into account for cancer risk estimations related to neutrons.

The Impact of Dose Rate on DNA Double-Strand Break Formation and Repair in Human Lymphocytes Exposed to Fast Neutron Irradiation.

The radiosensitivity of haematopoietic stem and progenitor cells (HSPCs) to neutron radiation remains largely underexplored, notwithstanding their potential role as target cells for radiation-induced leukemogenesis. New insights are required for radiation protection purposes, particularly for aviation, space missions, nuclear accidents and even particle therapy. In this study, HSPCs (CD34CD38 cells) were isolated from umbilical cord blood and irradiated with Co γ-rays (photons) and high energy p(66)/Be(40) neutrons. At 2 h post-irradiation, a significantly higher number of 1.28 ± 0.12 γ-H2AX foci/cell was observed after 0.5 Gy neutrons compared to 0.84 ± 0.14 foci/cell for photons, but this decreased to similar levels for both radiation qualities after 18 h. However, a significant difference in late apoptosis was observed with Annexin-V/PI assay between photon and neutron irradiation at 18 h, 43.17 ± 6.10% versus 55.55 ± 4.87%, respectively. A significant increase in MN frequency was observed after both 0.5 and 1 Gy neutron irradiation compared to photons illustrating higher levels of neutron-induced cytogenetic damage, while there was no difference in the nuclear division index between both radiation qualities. The results point towards a higher induction of DNA damage after neutron irradiation in HSPCs followed by error-prone DNA repair, which contributes to genomic instability and a higher risk of leukemogenesis.

DNA damage response of haematopoietic stem and progenitor cells to high-LET neutron irradiation.

The objective of this study was to elucidate the proteomic mechanisms of drug resistance in HIV-infected African patients. Cell membrane fractions from forty oral  isolates isolated from African HIV-positive patients were analysed using HPLC-MS with the aim of identifying proteins associated with their pathogenicity and drug resistance. Heat shock proteins that mediate the fungicidal activity of salivary peptides were found in all tested  fractions, with pH-responsive proteins associated with increased pathogenicity only being present in the three most commonly isolated species. ABC multidrug transporter efflux pumps and estrogen binding proteins were only found in  fractions, while ergosterol biosynthesis proteins were identified in four species. The combination of various adherence, invasion, upregulation and efflux pump mechanisms appear to be instrumental for the  host colonization and drug resistance emergence in HIV-infected individuals.

Randall Fisher

Radiation Biophysics Division,
Nuclear Medicine Department,
Radiation Biophysics Division, Nuclear Medicine Department

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An Automated Microscopic Scoring Method for the γ-H2AX Foci Assay in Human Peripheral Blood Lymphocytes

Randall Fisher

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Radiation Biophysics Division,Nuclear Medicine Department,Radiation Biophysics Division, Nuclear Medicine Department

iThemba LABS

An Automated Microscopic Scoring Method for the γ-H2AX Foci Assay in Human Peripheral Blood Lymphocytes

Radiation Biophysics Division,
Nuclear Medicine Department,
Radiation Biophysics Division, Nuclear Medicine Department