Induction of a large deletion in mitochondrial genome of mouse cells by X-ray irradiation

Therapeutic effect of green tea extract on alcohol induced hepatic mitochondrial DNA damage in albino wistar rats

The present study principally sought to investigate the effect of green tea extract (GTE) supplementation on hepatic mitochondrial DNA (mtDNA) damage in alcohol receiving rats. MtDNA was isolated from hepatic tissues of albino wistar rats after alcohol treatment with and without GTE supplementation. Entire displacement loop (D-loop) of mtDNA was screened by PCR-Sanger's sequencing method. In addition, mtDNA deletions and antioxidant activity were measured in hepatic tissue of all rats. Results showed increased frequency of D-loop mutations in alcoholic rats (ALC). DNA mfold analysis predicted higher free energy for 15507C and 16116C alleles compared to their corresponding wild alleles which represents less stable secondary structures with negative impact on overall mtDNA function. Interestingly, D-loop mutations observed in ALC rats were successfully restored on GTE supplementation. MtDNA deletions were observed in ALC rats, but intact native mtDNA was found in ALC + GTE group suggesting alcohol induced oxidative damage of mtDNA and ameliorative effect of GTE. Furthermore, markedly decreased activities of glutathione peroxidise, superoxide dismutase, catalase and glutathione content were identified in ALC rats; however, GTE supplementation significantly (P < 0.05) restored these levels close to normal. In conclusion, green tea could be used as an effective nutraceutical against alcohol induced mitochondrial DNA damage.

Common Deletion (CD) in mitochondrial DNA of irradiated rat heart

The purpose of this study was to map the common deletion (CD) area in mtDNA and investigate the levels of this deletion in irradiated heart. The assays were developed in male Wistar rats that were irradiated with three different single doses (5, 10 or 15 Gy) delivered directly to the heart and the analyses were performed at various times post-irradiation (3, 15 or 120 days). The CDs area were sequenced and the CD quantified by real-time PCR. Our study demonstrated that the CD levels progressively decreased from the 3rduntil the 15th day after irradiation, and then increased thereafter. Additionally, it was observed that the levels of CD are modulated differently according to the different categories of doses (moderate and high). This study demonstrated an immediate response to ionizing radiation, measured by the presence of mutations in the CD area and a decrease in the CD levels.

Mitochondrial DNA point mutations and a novel deletion induced by direct low-LET radiation and by medium from irradiated cells

Radiation damage incurred by nuclear DNA is well documented and interest is increasing in the properties of 'bystander' factor(s) and their ability to induce radiation-like damage in cells never exposed to radiation. 'Bystander' and direct low-LET radiation effects on the mitochondria, and more particularly the mitochondrial genome are less well understood. In this study HPV-G cells (a human keratinocyte cell line derived from human neonatal foreskin transfected with the HPV-16 virus) were exposed to either gamma-radiation doses as low as 5 mGy and up to 5 Gy from a 60Co teletherapy unit, or to growth medium taken from similarly irradiated cells, i.e. irradiated cell conditioned medium (ICCM). Mutation and deletion analysis was performed on mitochondrial DNA (mtDNA) 4-96 h after exposure. Primers flanking the so-called mitochondrial 'common deletion' were employed to assess its possible induction. Single-strand conformation polymorphism (SSCP) analysis was conducted to identify induced point mutations. The relative mitochondrial number per cell was analysed by semi-quantitative PCR (sqPCR). Results indicate the induction of a relatively novel deletion in the mitochondrial genome as early as 12 h after direct exposure to doses as low as 0.5 Gy and 24 h after exposure to 0.5-Gy ICCM. SSCP analysis identified the induction of point mutations, in a non-consistent manner, in only the D-loop region of the mitochondrial genome and only in cells exposed to 5 Gy, and neither in cells exposed to lower doses of direct radiation nor in those exposed to ICCM. SqPCR also identified an increase in the number of mitochondria per cell after both exposure to low level gamma-radiation and ICCM, indicative of a possible mechanism to respond to mitochondrial stress by increasing the number of mitochondria per cell.