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Neuronal cells injured by ischemia and reperfusion to a certain extent are committed to death in necrotic or apoptotic form. Necrosis is induced by gross ATP depletion or 'energy crisis' of the cell, whereas apoptosis is induced by a mechanism still to be defined in detail. Here, we investigated this mechanism by focusing on a DNA damage-sensor, poly(ADPribose) polymerase-1 (PARP-1). A 2-h oxygen and glucose deprivation (OGD) followed by reoxygenation (Reox) induced apoptosis, rather than necrosis, in rat cortical neurons. During the Reox, PARP-1 was much activated and autopoly(ADPribosyl)ated, consuming the substrate, NAD + . Induction of apoptosis by OGD/Reox was suppressed by overexpression of Bcl-2, indicating mitochondrial impairment in this induction process. Mitochondrial permeability transition (MPT), or membrane depolarization, and a release of proapoptotic proteins, i.e. cytochrome c, apoptosis-inducing factor and endonuclease G, from mitochondria were observed during the Reox. These apoptotic changes of mitochondria and the nucleus were attenuated by PARP-1 inhibitors, 1,5-dihydroxyisoquinoline and benzamide, and also by small interfering RNA specific for PARP-1. These results indicated that PARP-1 plays a principal role in inducing mitochondrial impairment that ultimately leads to apoptosis of neurons after cerebral ischemia. Keywords: apoptosis, apoptosis-inducing factor, cerebral ischemia, cytochrome c, endonuclease G, NAD Poly(ADP-ribose) polymerase-1 (PARP-1) [also called poly(ADP-ribose) synthetase] (EC 2.4.2.30) is a nuclear enzyme that catalyzes formation of (ADP-ribose) n chains from NAD + on acceptor proteins, including histones and PARP-1 itself (Hayaishi and Ueda 1977;Ueda and Hayaishi 1985). One molecule of the enzyme is present per approximately 1000 base pairs of DNA. PARP-1 is termed a 'guardian of the genome', because it senses DNA damage and helps its repair. The enzyme is activated by DNA strand breaks to produce poly(ADP-ribose) on multiple automodification sites; the polyanionic structure thus formed counteracts the inhibitory effect of histones on DNA ligase (Ueda and Hayaishi 1985). On the other hand, excessive activation of PARP-1 and exhaustion of NAD + after severe DNA damage are known to cause cell death by ATP depletion, or 'energy crisis' (Szabó and Dawson 1998;Pieper et al. 1999). Address correspondence and reprint requests to Dr Seigo Tanaka, Laboratory of Molecular Clinical Chemistry, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan. E-mail: seigo@scl.kyoto-u.ac.jpAbbreviations used: AIF, apoptosis-inducing factor; CAT, chloramphenicol acetyltransferase; COX I, cytochrome c oxidase subunit I; CTF, carboxy-terminal fragment; cyt c, cytochrome c; DAPI, 4¢,6-diamidino-2-phenylindole; DHIQ, 1,5-dihydroxyisoquinoline; EndoG, endonuclease G; FITC, fluorescein isothiocyanate; JC-1, 5,5¢,6,6¢-tetrachloro-1,1¢,3,3¢-tetraethylbenzimidazolylcarbocyanine iodide; KD, knockdown; mAb, monoclonal antibody; MNNG, N-methyl-N'-nitro-Nnitrosoguanidine; ...

Recent public concern has focused on potential reproductive and developmental effects from exposure to low levels of bisphenol A (BPA, CAS number 80-05-7). Two previous published reviews (Gray et al., 2004a; Goodman et al., 2006) conducted weight-of-evidence evaluations of in vivo reproductive/developmental toxicity from BPA exposure < or = 5 mg/kg-d based on studies published through February 2006. Here, an update of those analyses presents additional relevant studies that were published through July 25, 2008, and a weight-of-evidence analysis of the studies evaluated in all three reviews. As with the earlier literature, positive findings: (1) are countered by null findings in more numerous studies; (2) have not been replicated; (3) do not exhibit coherence and plausibility; (4) do not show consistency across species, doses, and time points; and/or (5) were from studies using non-oral exposure routes. Owing to the lack of first-pass metabolism, results from non-oral studies are of limited relevance to human exposure. Exposure levels in most of the low-dose oral and non-oral animal studies are generally much higher than those experienced by even the most exposed people in the general population. The weight of evidence does not support the hypothesis that low oral doses of BPA adversely affect human reproductive and developmental health.

Poly(ADP-ribose) polymerases (PARPs) are enzymes that catalyze the transfer of ADP-ribose units from β-nicotinamide adenine dinucleotide (NAD(+)) to acceptor proteins. PARP-1 is responsible for more than 90 % of protein poly-ADP-ribosylation in the brain and may play a role as a molecular switch for cell survival and death. The functional roles of PARP-1 are largely mediated by its activation after binding to damaged DNA. Upon binding, PARP-1 activity increases rapidly and cleaves NAD(+) into ADP-ribose and nicotinamide. Increased activity of PARP-1 can promote DNA repair and its interaction with several transcription factors, whereas hyperactivation of PARP-1 can result in poly(ADP-ribose) accumulation and depletion of NAD(+) and ATP which may lead to caspase independent apoptotic or necrotic cell death, respectively. Excessive PARP-1 activity has been implicated in the pathogenesis of numerous clinical conditions such as stroke, myocardial infarction, inflammation, diabetes, and neurodegenerative disorders. Therefore, it is not surprising that the search for PARP-1 inhibitors with specific therapeutic uses (e.g., brain ischemia, cancer) has been an active area of research. Beyond medicinal uses, naturally occurring PARP-1 inhibitors may also offer a unique preventative means at attenuating chronic inflammatory diseases through dietary supplementation. This possibility has prompted research for specific, naturally occurring inhibitors of PARP-1. Though fewer investigations focus on identifying endogenous inhibitors/modulators of PARP-1 activity in vivo, these activities are very important for better understanding the complex regulation of this enzyme and the potential long-term benefits of supplementation with PARP-1 inhibitors. With this in mind, the focus of this article will be on providing a state-of-the-science review on endogenous and naturally occurring compounds that inhibit PARP-1.