Protection from acetaminophen-induced liver damage by the synergistic action of low doses of the poly(ADP-ribose) polymerase-inhibitor nicotinamide and the antioxidant N-acetylcysteine or the amino acid L-methionine

Comparative study of the binding characteristics to and inhibitory potencies towards PARP and in vivo antidiabetogenic potencies of taurine, 3-aminobenzamide and nicotinamide

BACKGROUND

Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.

METHODS

PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.

RESULTS

3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.

CONCLUSIONS

At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.

Farnesyltransferase inhibitors reduce Ras activation and ameliorate acetaminophen-induced liver injury in mice

Hepatotoxicity due to overdose of the analgesic and antipyretic acetaminophen (APAP) is a major cause of liver failure in adults. To better understand the contributions of different signaling pathways, the expression and role of Ras activation was evaluated after oral dosing of mice with APAP (400-500 mg/kg). Ras-guanosine triphosphate (GTP) is induced early and in an oxidative stress-dependent manner. The functional role of Ras activation was studied by a single intraperitoneal injection of the neutral sphingomyelinase and farnesyltransferase inhibitor (FTI) manumycin A (1 mg/kg), which lowers induction of Ras-GTP and serum amounts of alanine aminotransferase (ALT). APAP dosing decreases hepatic glutathione amounts, which are not affected by manumycin A treatment. However, APAP-induced activation of c-Jun N-terminal kinase, which plays an important role, is reduced by manumycin A. Also, APAP-induced mitochondrial reactive oxygen species are reduced by manumycin A at a later time point during liver injury. Importantly, the induction of genes involved in the inflammatory response (including iNos, gp91phox, and Fasl) and serum amounts of proinflammatory cytokines interferon-gamma (IFNgamma) and tumor necrosis factor alpha, which increase greatly with APAP challenge, are suppressed with manumycin A. The FTI activity of manumycin A is most likely involved in reducing APAP-induced liver injury, because a specific neutral sphingomyelinase inhibitor, GW4869 (1 mg/kg), did not show any hepatoprotective effect. Notably, a structurally distinct FTI, gliotoxin (1 mg/kg), also inhibits Ras activation and reduces serum amounts of ALT and IFN-gamma after APAP dosing. Finally, histological analysis confirmed the hepatoprotective effect of manumycin A and gliotoxin during APAP-induced liver damage.

CONCLUSION

This study identifies a key role for Ras activation and demonstrates the therapeutic efficacy of FTIs during APAP-induced liver injury.

Metabonomics evaluation of urine from rats given acute and chronic doses of acetaminophen using NMR and UPLC/MS

Urinary metabolic perturbations associated with acute and chronic acetaminophen-induced hepatotoxicity were investigated using nuclear magnetic resonance (NMR) spectroscopy and ultra performance liquid chromatography/mass spectrometry (UPLC/MS) metabonomics approaches to determine biomarkers of hepatotoxicity. Acute and chronic doses of acetaminophen (APAP) were administered to male Sprague-Dawley rats. NMR and UPLC/MS were able to detect both drug metabolites and endogenous metabolites simultaneously. The principal component analysis (PCA) of NMR or UPLC/MS spectra showed that metabolic changes observed in both acute and chronic dosing of acetaminophen were similar. Histopathology and clinical chemistry studies were performed and correlated well with the PCA analysis and magnitude of metabolite changes. Depletion of antioxidants (e.g. ferulic acid), trigonelline, S-adenosyl-L-methionine, and energy-related metabolites indicated that oxidative stress was caused by acute and chronic acetaminophen administration. Similar patterns of metabolic changes in response to acute or chronic dosing suggest similar detoxification and recovery mechanisms following APAP administration.

Beneficial effects of nicotinamide on alcohol-induced liver injury in senescence-accelerated mice

The deleterious effects of ethanol in senescence-accelerated prone 8 mice (SAMP8) and the protective role of nicotinamide (NAM) against ethanol-induced liver injury were examined. The mice were orally administered 2 g ethanol/kg BW and 200 mg or 500 mg NAM/kg BW three times/week for 10 weeks. Results showed that ethanol elevated activity of alanine aminotransferase (ALT) significantly. Ethanol also enhanced the formation of malondialdehyde (MDA) and protein carbonyls in the liver, whereas ethanol treatment resulted in significantly lower activity of hepatic glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD). Hematoxylin and eosin staining indicated moderate to severe fatty infiltration but not fibrosis. Administration of high NAM (500 mg/kg BW) led to markedly decreased levels of hepatic MDA, protein carbonyls, fatty infiltration and the activity of ALT, and increased activity of GPx, catalase and SOD in the ethanol-fed group. Thus, using SAMP8 as animal model for ethanol-induced liver injury in the aged mice, this study demonstrates that NAM is effective in protecting such damage.

L-methionine reduces oxidant stress in endothelial cells: role of heme oxygenase-1, ferritin, and nitric oxide

The amino acid L-methionine is known to exert antioxidant effects by as yet unidentified mechanisms. In the present study, L-methionine led to a concentration-dependent induction of the antioxidant proteins heme oxygenase-1 (HO-1) and ferritin in cultured endothelial cells (ECV 304). HO-1 protein expression was accompanied by an increased catalytic activity of the enzyme. Long-term pre-incubation of endothelial cells with L-methionine reduced NADPH-mediated radical formation by up to 60%. The antioxidant effect of L-methionine was mimicked by the HO-1 product bilirubin, which suppressed free radical formation almost completely. Reduction of superoxide generation by L-methionine was inhibited in the presence of the nitric oxide (NO) synthase inhibitor L-NMMA, suggesting the involvement of endogenous NO in L-methionine-dependent cytoprotection. These findings demonstrate that L-methionine reduces free radical formation in endothelial cells, possibly through induction of heme oxygenase-1 and ferritin. This novel, indirect antioxidant action might be relevant for the preventive potential of methionine and methionine rich diets under conditions of inflammation and oxidative stress.

Protective effects of N-acetylcysteine against carbon tetrachloride- and trichloroethylene-induced poisoning in rats

This research investigates the protective effect of N-acetylcysteine (NAC) against carbon tetrachloride (CCl(4))- and trichloroethylene (TCE)-induced hepatotoxicity in rats. A single dose of 1.25 ml/kg of 20% CCl(4) in corn oil, administered orally, or 20% TCE, administered intraperitoneally, produced significantly elevated levels of serum glutamic pyruvic transaminase (SGPT) and serum glutamic oxaloacetic transaminase (SGOT) activities. Histopathological examinations showed massive centrilobular necrosis and fat accumulation in CCl(4)-treated animals. In the curative test, especially in animals treated with higher dosages of NAC, there was significant reduction in SGPT and SGOT levels. Although there was no sign of abnormality in the livers of rats treated with TCE, NAC demonstrated its action against TCE-induced elevation of transaminases in the enzyme assays. Compared to the curative tests, the overall performance of NAC against toxin-induced toxicity in the preventive tests was poor. Even at the highest dosage applied, the effect was not as prominent as that achieved in the curative test. It is therefore concluded that NAC is effective for lowering chemical-induced elevated levels of SGPT and SGOT in the curative mode.

Human placenta hydrolases active on free ADP-ribose: an ADP-sugar pyrophosphatase and a specific ADP-ribose pyrophosphatase

Free ADP-ribose has a reducing ribose moiety and it is hazardous due to its nonenzymic reactivity toward protein side chains. ADP-ribose hydrolases are putative protective agents to avoid the intracellular accumulation of ADP-ribose. In mammalian sources, two types of enzymes with ADP-ribose hydrolase activity are known: (i) highly specific ADP-ribose pyrophosphatases, which in a Mg(2+)-dependent fashion hydrolyse only ADP-ribose and the nonphysiological analogue IDP-ribose, and (ii) less specific nucleoside diphosphosugar or diphosphoalcohol (NDP-X) pyrophosphatases, which besides A(I)DP-ribose hydrolyse also some nonreducing NDP-X substrates. So far, of these two enzyme types only the less specific one has been reported in human sources: an ADP-sugar pyrophosphatase purified from erythrocytes or expressed from cDNA clones. Here we report that human placenta extracts contain two ADP-ribose hydrolases, which were characterised after a near 1000-fold purification. One is an ADP-sugar pyrophosphatase: it hydrolysed ADP-ribose, ADP-glucose and ADP-mannose, but not e.g. UDP-glucose, at similar rates. It resembles the erythrocyte and recombinant enzyme(s), but showed a 5-20-fold lower K(m) for ADP-ribose (7 microM). The other enzyme is a highly specific ADP-ribose pyrophosphatase (the first of this kind to be reported in humans): it hydrolysed only ADP-ribose and IDP-ribose at similar rates, with a very low, 0.4 microM K(m) for the former. This is a major candidate to control the accumulation of free ADP-ribose in humans. It remains to be seen whether it belongs to the 'nudix' protein family, which includes several ADP-ribose hydrolases and other 'housecleaning' enzymes (M.J. Bessman, D.N. Frick, S.F. O'Handley, J. Biol. Chem. 271 (1996) 25059-25062).

Gene expression microarray data analysis for toxicology profiling

When dealing with thousands of genes, all potentially interesting, it is desirable to rank the genes according to their degree of participation in a physiological process. Therefore, genes with the highest Shannon entropy and ERL can be selected as the best toxicity target candidates, permitting preclinical scientists to focus their research and resources on those genes.

ADP-ribose pyrophosphatase-I partially purified from livers of rats overdosed with acetaminophen reveals enzyme inhibition in vivo reverted in vitro by dithiothreitol

Free ADP-ribose reacts nonenzymatically with proteins and can lead to intracellular damage. The low-Km ADP-ribose pyrophosphatase-I (ADPRibase-I) is well suited to control free ADP-ribose and nonenzymatic ADP-ribosylation. In vitro, the acetaminophen metabolite N-acetyl-p-benzoquinoneimine (NAPQI) decreases ADPRibase-I Vmax and increases Km, effects not reverted by dithiothreitol (DTT) and attributed to enzyme arylation. The present study was conducted to test whether acetaminophen overdose affected ADPRibase-I in vivo. Rats pretreated with 3-methylcholanthrene and L-buthionine-[S,R]-sulfoximine to potentiate acetaminophen toxicity received an intraperitoneal dose of either acetaminophen (800 mg/ kg; n = 5) or vehicle (n = 3). ADPRibase-I partially purified from acetaminophen-overdosed rats showed a decreased Vmax (0.32+/-0.09 versus 0.60+/-0.03 mU/mg of liver protein; p<0.01) not reverted by DTT and an increased Km for ADP-ribose (1.39+/-0.31 versus 0.67+/-0.05 microM; p<0.01) that, contrary to the in vitro NAPQI effect, was reverted by DTT. Incubation of partially purified ADPRibase-I from normal rat liver with oxidized glutathione elicited a time- and dose-dependent, DTT-reverted increase of Km, without change of Vmax. The results indicate that the activity of ADPRibase-I can be regulated by thiol exchange and that the increase of Km, elicited by acetaminophen overdosage was related to the oxidative stress caused by the drug. It remains to be seen whether an increase of free ADP-ribose concomitant to ADPRibase-I inhibition could contribute to the hepatotoxicity of acetaminophen.

Nutritional value of ganoderma extract and assessment of its genotoxicity and antigenotoxicity using comet assays of mouse lymphocytes

The nutritive composition of a hot aqueous extract of wild Ganoderma fruit bodies was determined. This extract was assessed for cytotoxicity and in vivo genotoxicity by both acute and subchronic exposure of mice (given by mouth at a dose equivalent to extract of 220g fresh Ganoderma fruit body/kg body weight). To test any alleged protection against mutagens by Ganoderma treatments, the mice were injected intraperitoneally with the radiomimetic mutagen ethyl methanesulfonate (EMS), and after 24hr of treatment their lymphocytes were examined using the comet assay. Ganoderma extract consisted of Folin-positive material (68.9% of dry weight), but protein comprised only 7.3% of dry weight. Glucose accounted for 11. 1% and metals 10.2% of dry weight (K, Mg and Ca being the major components with Ge (often touted as being of value in sales literature for Ganoderma preparations) having the fifth highest metal concentration at 489 microg/g). In comparison to rodent chow, Ganoderma extract was a modest dietary supplement. No evidence was found for genotoxic chromosomal breakage nor cytotoxic effects by Ganoderma extract in the mouse, nor did it protect against the effects of ethyl methanesulfonate. We found no support in this study for the extract having any value in protecting against the test mutagen.

Studies on the ADP-ribose pyrophosphatase subfamily of the nudix hydrolases and tentative identification of trgB, a gene associated with tellurite resistance

Four Nudix hydrolase genes, ysa1 from Saccharomyces cerevisiae, orf209 from Escherichia coli, yqkg from Bacillus subtilis, and hi0398 from Hemophilus influenzae were amplified, cloned into an expression vector, and transformed into E. coli. The expressed proteins were purified and shown to belong to a subfamily of Nudix hydrolases active on ADP-ribose. Comparison with other members of the subfamily revealed a conserved proline 16 amino acid residues downstream of the Nudix box, common to all of the ADP-ribose pyrophosphatase subfamily. In this same region, a conserved tyrosine designates another subfamily, the diadenosine polyphosphate pyrophosphatases, while an array of eight conserved amino acids is indicative of the NADH pyrophosphatases. On the basis of these classifications, the trgB gene, a tellurite resistance factor from Rhodobacter sphaeroides, was predicted to designate an ADP-ribose pyrophosphatase. In support of this hypothesis, a highly specific ADP-ribose pyrophosphatase gene from the archaebacterium, Methanococcus jannaschii, introduced into E. coli, increased the transformant's tolerance to potassium tellurite.

Nicotinamide and methionine reduce the liver toxic effect of methotrexate

Methotrexate is widely used as a therapeutic agent in different diseases. This therapy is connected with various side effects, including liver toxicity. We have developed a mouse model to demonstrate the toxic effects of methotrexate: mice were given 50 mg/kg acetaminophen, which itself has no effect on the liver. If, additionally, methotrexate is applied, there is an increase in the death rate, as well as in glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) activities. If methotrexate is administered in conjunction with either nicotinamide or methionine, the rise in the death rate and in GOT and GPT activities associated with methotrexate application is markedly reduced. On the basis of these results, it can be concluded that methotrexate therapy should be combined with either nicotinamide or methionine, respectively.

Role of poly(ADP-ribose) synthetase in inflammation and ischaemia-reperfusion

Oxidative and nitrosative stress can trigger DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) synthetase (PARS). This enzyme has also been termed poly(ADP-ribose) polymerase (PARP) or poly(ADP-ribose) transferase (pADPRT). Rapid activation of the enzyme depletes the intracellular concentration of its substrate, nicotinamide adenine dinucleotide, thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. In this article, Csaba Szabó and Valina Dawson overview the impact of pharmacological inhibition or genetic inactivation of PARS on the course of oxidant-induced cell death in vitro, and in inflammation and reperfusion injury in vivo. A major trigger for DNA damage in pathophysiological conditions is peroxynitrite, a cytotoxic oxidant formed by the reaction between the free radicals nitric oxide and superoxide. The pharmacological inhibition of poly(ADP-ribose) synthetase is a novel approach for the experimental therapy of various forms of inflammation and shock, stroke, myocardial and intestinal ischaemia-reperfusion, and diabetes mellitus.