Natural inhibitors of poly(ADP-ribose) polymerase-1.

Poly(ADP-ribose) polymerases (PARPs) are enzymes that catalyze the transfer of ADP-ribose units from ß-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.

Inhibition of poly(ADP-ribose) polymerase-1 attenuates the toxicity of carbon tetrachloride.

Carbon tetrachloride (CCl(4)) is routinely used as a model compound for eliciting centrilobular hepatotoxicity. It can be bioactivated to the trichloromethyl radical, which causes extensive lipid peroxidation and ultimately cell death by necrosis. Overactivation of poly(ADP-ribose) polymerase-1 (PARP-1) can rapidly reduce the levels of ß-nicotinamide adenine dinucleotide and adenosine triphosphate and ultimately promote necrosis. The aim of this study was to determine whether inhibition of PARP-1 could decrease CCl(4)-induced hepatotoxicity, as measured by degree of poly(ADP-ribosyl)ation, serum levels of lactate dehydrogenase (LDH), lipid peroxidation, and oxidative DNA damage. For this purpose, male ICR mice were administered intraperitoneally a hepatotoxic dose of CCl(4) with or without 6(5H)-phenanthridinone, a potent inhibitor of PARP-1. Animals treated with CCl(4) exhibited extensive poly(ADP-ribosyl)ation in centrilobular hepatocytes, elevated serum levels of LDH, and increased lipid peroxidation. In contrast, animals treated concomitantly with CCl(4) and 6(5H)-phenanthridinone showed significantly lower levels of poly(ADP-ribosyl)ation, serum LDH, and lipid peroxidation. No changes were observed in the levels of oxidative DNA damage regardless of treatment. These results demonstrated that the hepatotoxicity of CCl(4) is dependent on the overactivation of PARP-1 and that inhibition of this enzyme attenuates the hepatotoxicity of CCl(4).

Toxicology and human health assessment of decabromodiphenyl ether.

We evaluated the available pharmacokinetic data and human and animal toxicity data for 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209) (CASRN 1163-19-5) with the objective of deriving a reference dose (RfD) based on the best available science. The available studies for deriving an RfD were first screened using the Klimisch criteria and further evaluated using the United States Environmental Protection Agency's general assessment factors for data quality and relevance (i.e., soundness, applicability and utility, clarity and completeness, uncertainty and variability, and evaluation and review). The chronic 2-year dietary feeding study conducted by the United States National Toxicology Program ( NTP, 1986 , Technical Report Series No. 309) was selected for RfD derivation. Hepatocellular degeneration in male rats was chosen as the critical endpoint in the development of an RfD. For dose-response characterization, we applied benchmark-dose modeling to animal data and determined a point of departure (the 95% lower confidence limit for a 10% increase in hepatocellular degeneration) of 419 mg/kg-day for oral exposures. Based on the similar pharmacokinetic characteristics of BDE-209 across species, this value was converted to a human equivalence dose of 113 mg/kg-day by applying a dosimetric adjustment factor based on body weight scaling to the (3/4) power. An oral RfD of 4 mg/kg-day was calculated by using a composite uncertainty factor of 30, which consisted of 10 for intraspecies uncertainty, 3 for interspecies uncertainty (i.e., 3 for toxicodynamics x 1 for toxicokinetics), and 1 for deficiencies with the database. We consider the RfD to be adequately protective of sensitive subpopulations, including women, their fetuses, children, and people with hepatocellular diseases.