Effects of sodium butyrate on X-ray and bleomycin-induced chromosome aberrations in human peripheral blood lymphocytes

Bleomycin-induced genotoxicity in vitro in human peripheral blood lymphocytes evidenced as complex chromosome- and chromatid-type aberrations

Bleomycin is a chemotherapeutic and a radiomimetic drug which induces single and double-strand breaks in DNA by forming free radicals. We demonstrate in this study the capacity of bleomycin in inducing complex chromosome- and chromatid-type aberrations. Human peripheral blood was exposed to different concentrations of bleomycin (0, 10, 20, 30 and 40 μg/mL) and the aberrations induced were studied. The chromosomal-type aberrations studied were dicentrics, tricentrics, tetracentrics, centric rings and acentric fragments. The chromatid-type aberrations studied were double minutes, terminal lesions and terminal deletions. Though the overall trends that we obtained in the dose-dependent mitotic index and the chromosome- and chromatid-type aberrations conform to the reported literature, we could observe enhanced numbers and the types of such damages in this study. We could notice that chromosome-type aberrations were more than the chromatid-type aberrations. The enhanced numbers and the types of aberrations induced pave way for enhancing the sensitivity of genotoxic assays. Also, with more numbers and type of aberrations available, it would be useful to study the mechanisms of genotoxicity of drugs and in understanding phenomena such as "tolerance induction" to chronic exposure to such mutagens.

Evidence for intrathecal sodium butyrate as a novel option for leptomeningeal metastasis

INTRODUCTION

The prognosis for leptomeningeal metastasis (LM) remains extremely poor regardless of intrathecal chemotherapy with various drugs, and thus, new treatments are necessary. Butyrate is an endogenous 4-carbon saturated fatty acid, has been investigated as an anti-tumor agent because of its multiple suppressive effects on several tumors. In this study, we investigated the cellular basis of sodium butyrate (SB), a sodium salt compound of butyrate, in vitro and evaluated the clinical potential of intrathecal SB administration for LM in vivo.

METHODS

We examined SB's effects on Walker 256 rat mammary tumor cells with regard to cytotoxicity, cell morphology, colony formation, migration, and invasion. We also examined SB's neurotoxicity for primary neurons and primary astrocytes. We finally evaluated the potency of continuous intrathecal SB administration in rats with intrathecally transplanted breast tumors as an LM model.

RESULTS

Physiological SB concentrations (2-4 mM) induced growth suppression, morphological changes, and inhibition of migration and invasion, but did not exhibit neurotoxic effects on primary neurons and astrocytes. Continuous intrathecal SB administration in a rat LM model significantly increased survival periods with little neurotoxicity.

CONCLUSIONS

Continuous intrathecal SB administration significantly improved prognoses in a rat LM model, which suggests that SB is a promising therapy for LM.

Evaluation of γ-Hydroxybutyric Acid for Genotoxicity in the Mouse Micronucleus Assay

Gamma-hydroxybutyric acid (GHB) is an endogenous compound found in the brain and other tissues of mammals. Neurotransmitter/neuromodulator functions have been ascribed to GHB, which has lately become a drug of abuse. In this study, we tested GHB for genotoxicity by measuring its ability to induce micronuclei in polychromatic erythrocytes (reticulocytes) in the peripheral blood of mice. Intraperitoneal injection with a dose of 25 mg/kg/day for 3 days or 50 mg/kg/day x 3 days resulted in a significant (by Dunnett's test) increase of 1.9- to 2.1-fold in micronuclei. However, because increases were small and because no consistent dose-dependent increase in induced micronuclear frequency could be demonstrated, our results do not conclusively show that GHB is an in vivo genotoxicant in mammals.

Histone H2AX Phosphorylation as a Predictor of Radiosensitivity and Target for Radiotherapy

Based on the role of phosphorylation of the histone H2A variant H2AX in recruitment of DNA repair and checkpoint proteins to the sites of DNA damage, we have investigated gammaH2AX as a reporter of tumor radiosensitivity and a potential target to enhance the effectiveness of radiation therapy. Clinically relevant ionizing radiation (IR) doses induced similar patterns of gammaH2AX focus formation or immunoreactivity in radiosensitive and radioresistant human tumor cell lines and xenografted tumors. However, radiosensitive tumor cells and xenografts retained gammaH2AX for a greater duration than radioresistant cells and tumors. These results suggest that persistence of gammaH2AX after IR may predict tumor response to radiotherapy. We synthesized peptide mimics of the H2AX carboxyl-terminal tail to test whether antagonizing H2AX function affects tumor cell survival following IR. The peptides did not alter the viability of unirradiated tumor cells, but both blocked induction of gammaH2AX foci by IR and enhanced cell death in irradiated radioresistant tumor cells. These results suggest that H2AX is a potential molecular target to enhance the effects of radiotherapy.

Influence of sodium butyrate on the induction of radiation-induced chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary (CHO) cells

CHO cells were pre-treated with sodium butyrate (SB) for 24 h and then X-irradiated in G1. Metaphases were scored for the induction of chromosomal aberrations and sister chromatid exchanges (SCEs). The data were compared with those obtained after irradiation of cells not pre-treated with SB and showed that SB has different effects on the endpoints examined. The frequencies of dicentric chromosomes were elevated and of small acentric rings (double minutes, DMs) reduced. These results are discussed to be a consequence of conformational changes in hyperacetylated chromatin which could lead to more interchromosomal and to less intrachromosomal exchanges. SB itself induces a few SCEs but suppresses the induction of SCEs by X-rays. We assume that a minor part of radiation induced SCEs are 'false' resulting from structural chromosomal aberrations, such as inversions, induced in G1. Inversions are the symmetrical counterparts of DMs. If inversions are suppressed by SB treatment to a similar extent as DMs a small reduction of SCEs by SB can be expected.

Modulatory effect of sodium butyrate on AluI-induced chromosomal aberrations in CHO cells

Exponentially growing CHO cells exposed to millimolar concentrations of sodium butyrate (SB) for 24 h were treated with AluI using two methods of cell poration, i.e., electroporation and streptolysin O (SLO). Under both conditions, SB was found to induce a 2-4-fold increase in AluI-induced chromosomal aberrations. When cells in monolayer were treated with AluI/SLO, lower concentrations of SB (2.5 mM) and AluI (1-4 U/ml) were required to produce a similar effect as that observed for electroporated cells, demonstrating the differential sensitivity of the two methods. Furthermore, in AluI/SLO-treated cells, a higher percentage of cells was found to show increased frequencies of aberrations per cell, compared to AluI/electroporated cells. The mechanism by which SB modulates the cell response to AluI treatment might involve changes in chromatin configuration thereby increasing the accessibility of AluI to different parts of chromatin.