Differential assay and biological significance of poly(ADP-ribose) polymerase activity in isolated liver nuclei

Expression of antioxidant defense and poly(ADP-ribose) polymerase-1 in rat developing Sertoli cells

Sertoli cells play an essential role in the development of a functional testis. ROS (reactive oxygen species) are normally produced by the developing testicular cells and may be dangerous to spermatogenesis. The aim of this study was to investigate the developmental expression of genes involved in antioxidant defense as well as in the DNA damage response in rat Sertoli cells. As revealed by quantitative RT-PCR analysis, the expression pattern of the antioxidant enzymes GST (glutathione-S-transferase), CAT (catalase) and SOD (superoxide dismutase) showed a progressive decrease from birth to puberty. The expression level of the oncosuppressor p53 revealed a net reduction as well. We next focused on PARP-1 [poly(ADP-ribose) polymerase-1], a 'guardian of the genome' that combats stress conditions. At both the mRNA and protein level, PARP-1 expression was low at the early stage of development and increased later on. Maximal PARP-1 expression was preceded by a rise in the transcript level for MTs (metallothioneins), which provide zinc to zinc-dependent enzymes and proteins, including PARP-1. Our results showed an increased expression of PARP-1 during Sertoli cell development, together with a decrease in the expression of antioxidant enzymes. In conclusion, a role of PARP-1 in protecting the testicular differentiation is suggested.

Induction of hepatic poly(ADP-ribose) polymerase by peroxisome proliferators, non-genotoxic hepatocarcinogens

Two peroxisome proliferators, [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (Wy-14,643) or di(2-ethylhexyl) phthalate (DEHP), were given orally to male F-344 rats for up to 78 or 97 weeks. At 1 week, the activity of poly(ADP-ribose) polymerase (pADPRP) was increased 2- and 1.8-fold in the liver of rats treated with Wy-14,643 and DEHP, respectively. The induction of the activity was maintained at 2.5- or 2-fold for up to 52 weeks. The immunoblot and Northern blot analyses revealed that the induction of pADPRP activity would be responsible for the increase in the amount of mRNA. In addition, in the liver tumor induced by Wy-14,643 and DEHP, the pADPRP mRNA level increased 3.6- or 3.7-fold. The magnitude of the increase in the mRNA level was higher than that in the non-tumor portion. These findings suggest that the induction of pADPRP may play an important role in the hepatocarcinogenesis induced by peroxisome proliferators.

DNA strand breaks and poly (ADP-ribose) polymerase activation induced by crystalline nickel subsulfide in MRC-5 lung fibroblast cells

Nickel compounds are potent carcinogens. Their carcinogenicity is believed to be associated with their solubility and cellular uptake. In the present study, we assessed the in vitro genotoxic effect of a water-insoluble nickel compound, crystalline nickel subsulfide (alpha-Ni3S2) on human embryo lung fibroblast cell line (MRC-5 cells). DNA strand breaks was evaluated using single cell gel electrophoresis, or comet assay. The alpha-Ni3S2 induction of poly (ADP-ribose) polymerase (PADPRP), a nuclear enzyme associated with DNA damage and repair was also studied. Hydrogen peroxide (H2O2) was used as a reference compound. A dose-response relationship was found between alpha-Ni2S2 concentrations (2.5 micrograms/cm2 to 20 micrograms/cm2) and the comet tail length. The increase of PADPRP activity of alpha-Ni2S2 treated MRC-5 cells was also significant and dose-dependent within the concentration range of 2.5 micrograms/ cm2 to 10 micrograms/cm2. Close associations have been found between the comet length and PADPRP level for H2O2 (r = 0.98) and alpha-Ni3S2 (r = 0.97). These results clearly suggest that alpha-Ni3S2 is a potent agent in inducing DNA strand breaks, which may be closely related to its carcinogenic effects. Data from the present study also suggest that both comet assay and PADPRP determination are sensitive techniques for quantitative evaluation of DNA damage induced by nickel compounds.

N-acetylcysteine: pharmacological considerations and experimental and clinical applications

The diversity of application of the thiol drug NAC in both the experimental setting, as a tool for the study of the mechanisms and consequences of oxidative stress, and the clinical setting, as a therapeutic agent, clearly reflects the central role played by the redox chemistries of the group XVI elements, oxygen and sulfur, in biology. As our understanding of such redox processes increases, particularly their roles in specific pathophysiological processes, new avenues will open for the use of NAC in the clinical setting. As a drug, NAC represents perhaps the ideal xenobiotic, capable of directly entering endogenous biochemical processes as a result of its own metabolism. Thus, it is hoped that the experience gained with this unique agent will help in future efforts to design antioxidants and chemoprotective principles which are able to more accurately utilize endogenous biochemical processes for cell- or tissue-specific therapy.

Induction of poly(ADP-ribosyl)ation in the kidney after in vivo application of renal carcinogens

Dichlorovinylcysteine, the key metabolite thought to be responsible for the nephrocarcinogenicity of trichloroethene and dichloroacetylene, induces DNA double-strand breaks followed by increased poly(ADP-ribosyl)ation of nuclear proteins in cultured renal cells (Vamvakas et al., 1992, Biochem. Pharmacol. 44, 1131-1138). Poly(ADP-ribosyl)ation represents a post-translational modification of nuclear proteins involved in DNA repair, DNA replication, and modulation of gene expression. The present study investigates the induction of DNA double-strand breaks and poly(ADP-ribosyl)ation in the renal cortex after in vivo administration of several renal carcinogens to male Wistar rats, and the temporal relationship between these two processes. Dichlorovinylcysteine caused a time-dependent increase in the amount of poly(ADP-ribosyl)conjugates in the kidney cortex, which was preceded by increased formation of DNA double-strand breaks. Potassium bromate and ferric nitrilotriacetate, whose nephrocarcinogenicity is thought to result from increased formation of reactive oxygen species, both induced poly(ADP-ribosyl)ation with the concomitant formation of DNA double-strand breaks. Dimethylnitrosamine, an indirect acting methylating agent, and trimethylpentane, a non-genotoxic renal carcinogen, failed to induce poly(ADP-ribosyl)ation or a significant increase in DNA double-strand breaks in the renal cortex. The results indicate that nephrocarcinogens capable of inducing DNA fragmentation also induce post-translational modification of renal proteins via increased poly(ADP-ribosyl)ation.

Relationship between poly(ADP-ribose) polymerase activity and DNA damage induced by zinc dithiocarbamates in mouse and rat liver

The genotoxic effects due to in vivo treatment with zinc dithiocarbamates were evaluated in rat and mouse liver. The two pesticides Zineb and Ziram, belonging to this chemical class, induced an increase in single-strand DNA breaks, as measured by the alkaline elution technique. The nuclear enzyme poly(ADP-ribose) polymerase (pADPRP), a chromatin-bound catalytic protein, utilizing NAD+ as a substrate, was tested by a radiometric procedure. A close relationship between the increased extent of DNA damage and the enhanced level of endogenous pADPRP activity was obtained in rat liver, whereas both parameters remained unchanged in mouse liver.

Influence of poly(ADP ribose) polymerase depletion on promotion of liver carcinogenesis

In previous studies we demonstrated that liver poly(ADP ribose) polymerase (pADPRP) activity was lost in animals exposed to N-2-acetylaminofluorene (2AAF) according to the Teebor and Becker experimental model (Cancer Res 31:1-3, 1971). In addition, we used the resistant hepatocyte model of Solt and Farber (Nature 263:702-703, 1976) to further investigate pADPRP activity during the multistep process of liver carcinogenesis. A marked depletion of the catalytic protein was evidenced after 2AAF exposure, confirming previous results and indicating a specific effect of 2AAF on this nuclear enzyme that controls conformational changes of chromatin and regulates several catalytic activities in the nucleus. The levels of pADPRP mRNA, measured by northern blot analysis using both experimental models, indicate that the enzyme depletion is not due to a loss of transcript. Moreover, these data indicate that pADPRP depletion, caused by 2AAF, was also maintained during liver compensatory growth, which is known to induce a rapid and marked increase in pADPRP activity and protein level. Treatment of 2AAF-exposed animals with N-acetyl-L-cysteine not only efficiently protected against DNA damage, but also prevented a rapid depletion of the catalytic protein. Interestingly, these data indicate that the marked loss of liver pADPRP occurred during the promotion step induced by 2AAF feeding and that this loss was observed using different models for experimental hepatocarcinogenesis. This phenomenon can be ascribed to a highly defective transcript that cannot be correctly translated into the specific protein or to a rapid degradation of the translated protein.

Antioxidant activity and other mechanisms of thiols involved in chemoprevention of mutation and cancer

Our studies provide evidence that thiols, such as N-acetyl-L-cysteine, inhibit both spontaneous mutations and induced mutations in bacteria, prevent the in vivo formation of carcinogen-DNA adducts, and suppress or delay the development of tumors or preneoplastic lesions in rodents. N-Acetylcysteine and other thiols exert antioxidant activity toward superoxide anion, hydrogen peroxide, and singlet oxygen, assessed in bacterial genotoxicity models. In addition, several other mechanisms were shown to contribute to their antimutagenic and anticarcinogenic activities, in the extracellular environment and in nontarget or target cells. These mechanisms include blocking of electrophilic metabolites and of direct-acting compounds, either of endogenous or exogenous source, modulation of several xenobiotic-metabolizing pathways, and protection of DNA-dependent nuclear enzymes. Chemoprevention of mutation and cancer by thiols is particularly useful under conditions of reduced glutathione (GSH) depletion due to toxic agents or to cancer-associated viral diseases, such as acquired immunodeficiency syndrome (AIDS) or viral hepatitis B.