Differences in the kinetics of gamma-H2AX fluorescence decay after exposure to low and high LET radiation.
OBJECTIVE
In order to obtain more insight into heavy ion tumour therapy, some features of the underlying molecular mechanisms controlling the cellular response to high linear energy transfer (LET) radiation are currently analysed.


METHODS
We analysed the decay of the integrated fluorescence intensity of gamma-H2AX (phosphorylated histone H2AX) which is thought to reflect the repair kinetics of radiation-induced DNA double-strand breaks (DSB) using Laser-Scanning-Cytometry. Asynchronous human HeLa cells were irradiated with a single dose of either 1.89 Gy of 55 MeV carbon ions or 5 Gy of 70 kV X-rays.


RESULTS
Measurements of the gamma-H2AX-intensities from 15-60 min resulted in a 16 % decrease for carbon ions and in a 43 % decrease for X-rays. After 21 h, the decrease was 77 % for carbon ions and 85 % for X-rays. The corresponding time-effect relationship was fitted by a bi-exponential function showing a fast and a slow component with identical half-life values for both radiation qualities being 24 +/- 4 min and 13.9 +/- 0.7 h, respectively. Apparent differences in the kinetics following high and low LET irradiation could completely be attributed to quantitative differences in their contributions, with the slow component being responsible for 47 % of the repair after exposure to X-rays as compared to 80 % after carbon ion irradiation.


CONCLUSIONS
gamma-H2AX loss kinetics follows a bi-exponential decline with two definite decay times independent of LET. The higher contribution of the slow component determined for carbon ion exposure is thought to reflect the increased amount of complex DSB induced by high LET radiation.
Schmid
Thomas E
TE
Klinikum rechts der Isar, Department of Radiation Oncology, Technische Universität München, München, Germany. T.E.Schmid@lrz.tu-muenchen.de
Dollinger
Günther
G
Beisker
Wolfgang
W
Hable
Volker
V
Greubel
Christoph
C
Auer
Susanne
S
Mittag
Anja
A
Tarnok
Attila
A
Friedl
Anna A
AA
Molls
Michael
M
Röper
Barbara
B
D002244:Carbon; D002453:Cell Cycle; D053903:DNA Breaks, Double-Stranded; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D020450:Heavy Ions; D006657:Histones / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D018499:Linear Energy Transfer
C468783:H2AX protein, human; D006657:Histones; D002244:Carbon