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Quantitation of γH2AX Foci in Tissue Samples
Published on: June 28, 2010
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Comparison of different techniques for γH2AX/pH3 biomarkers quantification for chemical genotoxicity assessment
Cynthia Recoules1, Chloé Huertas1, Julien Vignard1
1Toxalim, INRAE, INP-ENVT, INP-EI-Purpan, Université de Toulouse 3 Paul Sabatier, Toulouse, France.
Summary
Histone modifications like gamma-H2AX and phospho-H3 are key genotoxicity biomarkers. This study compared quantification methods, finding gamma-H2AX foci best for clastogens and global intensity useful for detecting subtle changes.
Area of Science:
- Biomarkers and Genotoxicity Testing
- In vitro toxicology
- Chemical risk assessment
Background:
- In vitro genotoxicity tests are crucial for chemical risk assessment.
- Histone modifications, specifically gamma-H2AX (phosphorylated H2AX) and phospho-H3 (pH3), are emerging as sensitive biomarkers for detecting DNA damage.
- Optimizing the quantification of these histone modifications is essential for accurate genotoxicity assessment.
Purpose of the Study:
- To compare the sensitivity and reliability of different quantification parameters for gamma-H2AX and pH3 biomarkers across various cell lines and chemical exposures.
- To identify the most suitable methods for detecting genotoxicity induced by different classes of hazardous substances.
- To evaluate the impact of apoptosis on gamma-H2AX measurements and assess the risk of false positives.
Main Methods:
- Comparison of three gamma-H2AX parameters (global intensity, nuclear intensity, foci number) and two pH3 parameters (global intensity, % cell in mitosis).
- Exposure of three cell lines (U2OS, HepG2, IEC-6) to four reference chemicals: nocodazole, etoposide, benzo[a]pyrene, and tunicamycin.
- Utilized the Benchmark Concentration (BMC) approach to determine the sensitivity of each method.
Main Results:
- The sensitivity of the tested methods varied significantly based on the chemical compound and cell line used.
- Gamma-H2AX foci analysis demonstrated higher sensitivity for clastogenic compounds (e.g., etoposide, benzo[a]pyrene).
- For aneugenic compounds (e.g., nocodazole), global intensity and the proportion of mitotic cells showed comparable sensitivity.
- Tunicamycin-induced apoptosis did not interfere with gamma-H2AX global intensity or foci number, but increased nuclear intensity in U2OS cells, minimizing false positives.
- Global intensity measurements were most effective in detecting weaker fold inductions of the biomarkers.
Conclusions:
- The choice of quantification method for gamma-H2AX and pH3 biomarkers is critical and depends on the type of genotoxic agent and the cell line.
- Gamma-H2AX foci and global intensity are valuable parameters for assessing clastogenic and aneugenic effects, respectively.
- Global intensity offers a sensitive approach for detecting low-level genotoxic responses and is less affected by apoptosis, reducing false positives.
