Hydroxylation of deoxyguanosine at 5' site of GG and GGG sequences in double-stranded DNA induced by carbamoyl radicals

Human circulating ribosomal DNA content significantly increases while circulating satellite III (1q12) content decreases under chronic occupational exposure to low-dose gamma- neutron and tritium beta-radiation

A single exposure to ionizing radiation (IR) results in an elevated cell-free DNA (cfDNA) content in the blood plasma. In this case, the cfDNA concentration can be a marker of the cell death in the organism. However, a chronic exposure to a low-dose IR enhances both the endonuclease activity and titer of antibodies to DNA in blood plasma, resulting in a decrease of the total concentration of circulating cfDNA in exposed people. In this case, the total cfDNA concentration should not be considered as a marker of the cell death in an exposed body. We assumed that a pool of the cfDNA circulating in the exposed people contains DNA fragments, which are resistant to a double-strand break formation in the environment of the elevated plasma endonuclease activity, and can be accumulated in the blood plasma. In order to test this hypothesis, we studied the content of GC-rich sequences (69%GC) of the transcribed region of human ribosomal repeat (rDNA), as well as the content of AT-rich repeat (63%AT) of satellite III (1q12) in the cfDNA samples obtained from 285 individuals. We have found that a chronic exposure to gamma-neutron radiation (N=88) and tritium β-radiation (N=88) evokes an increase of the rDNA content (RrDNA index) and a decrease of the satellite III content (RsatIII index) in the circulating cfDNA as compared with the cfDNA of non-exposed people (N=109). Such index that simultaneously displays both the increase of rDNA content and decrease of satellite III content in the cfDNA (RrDNA/RsatIII) can be recommended as a marker of chronic processes in the body that involve the elevated cell death rate and/or increased blood plasma endonuclease activity.

GC-Rich Extracellular DNA Induces Oxidative Stress, Double-Strand DNA Breaks, and DNA Damage Response in Human Adipose-Derived Mesenchymal Stem Cells

BACKGROUND

Cell free DNA (cfDNA) circulates throughout the bloodstream of both healthy people and patients with various diseases. CfDNA is substantially enriched in its GC-content as compared with human genomic DNA.

PRINCIPAL FINDINGS

Exposure of haMSCs to GC-DNA induces short-term oxidative stress (determined with H2DCFH-DA) and results in both single- and double-strand DNA breaks (comet assay and γH2AX, foci). As a result in the cells significantly increases the expression of repair genes (BRCA1 (RT-PCR), PCNA (FACS)) and antiapoptotic genes (BCL2 (RT-PCR and FACS), BCL2A1, BCL2L1, BIRC3, and BIRC2 (RT-PCR)). Under the action of GC-DNA the potential of mitochondria was increased. Here we show that GC-rich extracellular DNA stimulates adipocyte differentiation of human adipose-derived mesenchymal stem cells (haMSCs). Exposure to GC-DNA leads to an increase in the level of RNAPPARG2 and LPL (RT-PCR), in the level of fatty acid binding protein FABP4 (FACS analysis) and in the level of fat (Oil Red O).

CONCLUSIONS

GC-rich fragments in the pool of cfDNA can potentially induce oxidative stress and DNA damage response and affect the direction of mesenchymal stem cells differentiation in human adipose-derived mesenchymal stem cells. Such a response may be one of the causes of obesity or osteoporosis.

Aging and induced senescence as factors in the pathogenesis of lung emphysema

Classically, the development of emphysema in chronic obstructive pulmonary disease is believed to involve inflammation induced by cigarette smoke and leukocyte activation, including oxidant-antioxidant and protease-antiprotease imbalances. While there is substantial evidence for this, additional aspects have been suggested by a number of clinical and experimental observations. Smokers exhibit signs of premature aging, particularly obvious in the skin. The link between aging and chronic disease is well-known, e.g., for the brain and musculoskeletal or cardiovascular system, as well as the clinical link between malnutrition and emphysema, and the experimental link to caloric restriction. Interestingly, this intervention also increases lifespan, in parallel with alterations in metabolism, oxidant burden and endocrine signaling. Of special interest is the observation that, even in the absence of an inflammatory environment, lung fibroblasts from patients with emphysema show persistent alterations, possibly based on epigenetic mechanisms. The importance of these mechanisms for cellular reprogramming and response patterns, individual risk profile and therapeutic options is becoming increasingly recognized. The same applies to cellular senescence. Recent findings from patients and experimental models open novel views into the arena of gene-environment interactions, including the role of systemic alterations, cellular stress, telomeres, CDK inhibitors such as p16, p21, pRb, PI3K, mTOR, FOXO transcription factors, histone modifications, and sirtuins. This article aims to outline this emerging picture and to stimulate the identification of challenging questions. Such insights also bear implications for the long-term course of the disease in relation to existing or future therapies and the exploration of potential lung regeneration.

Molecular mechanisms of DNA damage induced by procarbazine in the presence of Cu(II)

Procarbazine [N-isopropyl-alpha-(2-methylhydrazino)-p-toluamide], a hydrazine derivative, which has been shown to have effective antineoplastic activity, induces cancer in some experimental animals and humans. To clarify a new mechanism for its carcinogenic effect, we examined DNA damage induced by procarbazine in the presence of metal ion, using 32P-5'-end-labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. Procarbazine plus Cu(II) induced piperidine-labile and formamidopyrimidine-DNA glycosylase-sensitive lesions at the 5'-ACG-3' sequence, complementary to a hotspot of the p53 gene, and the 5'-TG-3' sequence. Catalase partially inhibited DNA damage, suggesting that not only H(2)O(2) but also other reactive species are involved. Procarbazine plus Cu(II) significantly increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, which was completely inhibited by calatase. Electron spin resonance spin-trapping experiments revealed that methyl radicals were generated from procarbazine and Cu(II). On the basis of these findings, it is considered that procarbazine causes DNA damage through non-enzymatic formation of the Cu(I)-hydroperoxo complex and methyl radicals. In conclusion, in addition to alkylation, oxidative DNA damage may play important roles in not only antitumor effects but also mutagenesis and carcinogenesis induced by procarbazine.

Carcinogenic semicarbazide induces sequence-specific DNA damage through the generation of reactive oxygen species and the derived organic radicals

Semicarbazide, a hydrazine derivative, is carcinogenic to mice but shows no or little mutagenicity in the Salmonella-microsome test. To clarify whether or not the genotoxic mechanism contributes to the non-mutagenic carcinogenicity of semicarbazide, we investigated DNA damage induced by semicarbazide using 32P-5'-end-labeled DNA fragments obtained from the c-Ha-ras-1 protooncogene and the p53 tumor suppressor gene. Semicarbazide caused DNA damage frequently at the thymine and cytosine residues in the presence of Cu(II). Catalase and bathocuproine partially inhibited DNA damage, suggesting that hydrogen peroxide plus Cu(I) participates in DNA damage. When a high concentration of semicarbazide was used in the presence of catalase, DNA damage was induced, especially at G in 5'-AG and slightly at 5'-G in GG and GGG sequences. An electron paramagnetic resonance (EPR) spectroscopic study has confirmed that the reaction of semicarbazide with Cu(II) produces carbamoyl radicals (z.rad;CONH(2)), possibly generated via the nitrogen-centered radicals of semicarbazide. Azodicarbonamide also produced carbamoyl radicals and induced DNA damage frequently at 5'-G in GG and GGG sequences, suggesting that carbamoyl radicals participate in this sequence-specific DNA damage by semicarbazide. On the basis of our previous reports, we consider that the sequence-specific DNA damage at G in 5'-AG in the present study is due to the nitrogen-centered radicals. This study has shown that semicarbazide induces DNA damage in the presence of Cu(II) through the formation of hydrogen peroxide and Cu(I). In addition, semicarbazide-derived free radicals participate in DNA damage. DNA damage induced by these reactive species may be relevant to the carcinogenicity of semicarbazide.