Oxidant-induced cytotoxicity: a challenge for metabolic modulation

Hepatoprotective effect of Caesalpinia gilliesii and Cajanus cajan proteins against acetoaminophen overdose-induced hepatic damage

This study aims to evaluate two proteins derived from the seeds of the plants Cajanus cajan (Leguminosae) and Caesalpinia gilliesii (Leguminosae) for their abilities to ameliorate the toxic effects of chronic doses of acetoaminphen (APAP) through the determination of certain biochemical parameters including liver marker enzymes: alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and total bilirubin. Also, total protein content and hepatic marker enzyme, lactate dehydrogenase were studied. Moreover, liver antioxidants, glutathione (GSH), nitric oxide, and lipid peroxides were determined in this study. Hepatic adenosine triphosphatase (ATPase), adenylate energy charge (ATP, adenosine diphosphate, adenosine monophosphate, and inorganic phosphate), and phosphate potential, serum interleukin-6, tumor necrosis factor-α, and myeloperoxidase were also examined in the present study. On the other hand, histopathological examination of intoxicated and liver treated with both proteins was taken into consideration. The present results show disturbances in all biochemical parameters and hepatic toxicity signs including mild vascular congestion, moderate inflammatory changes with moderate congested sinusoids, moderate nuclear changes (pyknosis), moderate centrilobular necrosis, fatty changes, nuclear pyknosis vascular congestion, and change in fatty centrilobular necrosis liver. Improvement in all biochemical parameters studied was noticed as a result of treatment intoxicated liver with C. gilliesii and C. cajan proteins either paracetamol with or post paracetamol treatment. These results were documented by the amelioration signs in rat's hepatic architecture. Thus, both plant protein extracts can upregulate and counteract the inflammatory process, minimize damage of the liver, delay disease progression, and reduce its complications.

Effect of PJ-34 PARP-Inhibitor on Rat Liver Microcirculation and Antioxidant Status

BACKGROUND

Ischemia-reperfusion (I-R) injury during liver resection leads to the production of toxic free radicals and oxidants that influence the microcirculation. DNA single-strand breaks can be induced by these reactive species. In response to excessive DNA damage, PARP [poly(ADP-ribose) polymerase] becomes overactivated, which can lead to cellular ATP depletion and cell death. The aim of our study was to evaluate whether PARP is expressed in post-ischemic liver, and to examine the effect of the administration of PJ-34 PARP inhibitor on liver function, histopathology, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) reaction, and the oxidative state of the liver after injury.

METHODS

Male Wistar rats (weighing 250 g) underwent 60 min of normothermic, segmental liver ischemia followed by 30 min of reperfusion. The animals (n = 45) were divided into three groups: sham operated; I-R (control) treated with saline; and PJ-34 pre-treated (10 mg/kg i.v.). Hepatic microcirculation was monitored by a laser Doppler flowmeter. The reperfusion was characterized as the integral of the reperfusion area (RA) and the maximal plateau (PM). Histological alterations, TUNEL-reaction, serum, and liver tissue antioxidant levels, as well as serum ALT and AST levels were measured.

RESULTS

Upon reperfusion, the PJ-34 group had significantly (P < 0.05) higher flow rates than control groups (PM(PJ-34): 58%, PM(control): 37%; RA(PJ-34.): 48%, RA(control): 25%). At the end of the 30 min reperfusion, PJ-34 resulted in significantly (P < 0.05) lower serum ALT and AST levels and chemiluminescent intensity (free radicals) of the liver. The liver's free SH-group concentration and H-donor ability of the plasma was elevated in the PARP-inhibitor treated group. Positive staining for TUNEL, after PJ-34 pre-treatment was significantly increased (P < 0.05); in contrast, the control tissues were less positively stained for TUNEL but necrotic tissue was abundant.

CONCLUSION

PARP plays a pathogenetic role in the deterioration of the hepatic microcirculation and promotes hepatocellular necrosis in liver reperfusion injury.

Poly (ADP-ribose) polymerase activation and circulatory shock

Sepsis is associated with increased production of reactive oxidant species. Oxidative and nitrosative stress can lead to activation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP), with subsequent loss of cellular functions. Activation of PARP may dramatically lower the intracellular concentration of its substrate, NAD thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. In addition, PARP enhances the expression of various pro-inflammatory mediators, via activation of NF-kappaB, MAP kinase and AP-1 and other signal transduction pathways. Preclinical studies in various rodent and large animal models demonstrate that PARP inhibition or PAR deficiency exerts beneficial effects on the haemodynamic and metabolic alterations associated with septic and haemorrhagic shock. Recent human data also support the role of PARP in septic shock: In a retrospective study in 25 septic patients, an increase in plasma troponin level was related to increased mortality risk. In patients who died, significant myocardial damage was detected, and histological analysis of heart showed inflammatory infiltration, increased collagen deposition, and derangement of mitochondrial criptae. Immunohistochemical staining for poly(ADP-ribose) (PAR), the product of activated PARP was demonstrated in septic hearts. There was a positive correlation between PAR staining and troponin I; and a correlation of PAR staining and LVSSW. Thus, there is significant PARP activation in animal models subjected to circulatory shock, as well as in the hearts of septic patients. Based on the interventional studies in animals and the correlations observed in patients we propose that PARP activation may be, in part responsible for the cardiac depression and haemodynamic failure seen in humans with severe sepsis. Interestingly, recent studies reveal that the protective effects of PARP inhibitors are predominant in male animals, and are not apparent in female animals. Oestrogen, by providing a baseline inhibitory effect on PARP activation, may be partially responsible for this gender difference.

Pyruvate improves recovery after PARP-1-associated energy failure induced by oxidative stress in neonatal rat cerebrocortical slices

Previous neuron and glial cell culture studies of excessive poly (ADP-ribose) polymerase (PARP-1) activation found NAD(+) depletion, glycolytic arrest, and cell death that could be avoided by exogenous tricarboxylic acid cycle (TCA) metabolites, especially pyruvate (pyr). Pyruvate neuroprotection has been attributed to cytosolic NAD(+) replenishment, TCA metabolism, and antioxidant activity. We investigated the first two mechanisms in respiring cerebrocortical slices after a 1-h H(2)O(2) exposure to activate PARP-1. H(2)O(2) was followed by a 4-h recovery with oxy-artificial cerebrospinal fluid superfusion having either: (1) no glucose (glc) or pyruvate; (2) 10 mmol/L glc only; (3) 10 mmol/L pyruvate only; (4) both 10 mmol/L glc and 10 mmol/L pyruvate. Poly-ADP-ribosylation was quantified from Western blots and immunohistochemistry. Perchloric acid extracts were quantified with 14.1 T (31)P nuclear magnetic resonance spectroscopy. Just after H(2)O(2) exposure, ATP and NAD(+) decreased by approximately 50%, PCr decreased by 75%, and the ADP/ATP ratio approximately doubled. ATP and NAD(+) changes, but not PCr changes, were nearly eliminated if PARP inhibitors accompanied the H(2)O(2). Recovery with both pyruvate and glc was better than with glc alone, having higher ATP (0.161 versus 0.075, P<0.01) and PCr levels (0.144 versus 0.078, P<0.01), and higher viable cell counts in TUNEL and Fluoro-Jade B staining. Two-dimensional [(1)H-(13)C] HSQC spectra showed metabolism during recovery of (13)C glc or pyr. Pyruvate metabolism was primarily via pyruvate dehydrogenase, with some via pyruvate carboxylation. Pyruvate superfusion of PARP-injured brain slices helps replenish NAD(+) while providing metabolic fuel. Although this augments recovery, a strong antioxidant role for pyruvate has not been ruled out.

Poly(ADP-ribose) polymerase activation by reactive nitrogen species--relevance for the pathogenesis of inflammation

Oxidative and nitrosative stress triggers DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP). Nitrogen-derived reactive oxidant species capable of involving DNA single strand breakage and PARP activation include peroxynitrite (the reaction product of nitric oxide and superoxide), but not nitric oxide per se. Activation of PARP may dramatically lower 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. Here we review the role of reactive nitrogen species in the process of PARP activation, followed by the effect of pharmacological inhibition or genetic inactivation of PARP on the course of various forms of inflammation.

Poly (ADP) ribose synthetase inhibition reduces obliterative airway disease in rat tracheal allografts

BACKGROUND

Obliterative bronchiolitis (OB) is the major long-term complication affecting lung transplant recipients, and is characterized pathologically by chronic inflammatory and fibroproliferative airway disease. Based on studies revealing anti-inflammatory and anti-apoptotic properties of poly (ADP)-ribose synthetase (PARS) inhibitors, we hypothesized that their administration would be protective in a heterotopic model of experimental OB.

METHODS

We transplanted rat tracheas from Brown-Norway donors into Lewis recipients, and treated 2 groups with a novel PARS inhibitor, INO-1001. One group received 14 days of treatment, whereas a second received delayed treatment beginning on Day 7 post-transplant. Tracheas were analyzed by light microscopy and computerized morphometry. Effects on cytokine transcription, nuclear transcription factor activation and cellular death were assessed by in situ hybridization for tumor necrosis factor-alpha (TNF-alpha), electromobility shift assays for nuclear factor-kappaB (NF-kappaB) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays, respectively.

RESULTS

PARS inhibition significantly decreased luminal obstruction (p < 0.001) and enhanced preservation of epithelial lining (p < 0.001) at 14 days post-transplant. Day 7 controls confirmed the development of an obstructive lesion in the lumen, averaging 28% occlusion. Delayed treatment (beginning on Day 7) arrested (p < 0.001) progression of the established lesion. Allograft airways treated with INO-1001 demonstrated attenuated NF-kappaB nuclear translocation, reduced transcription of TNF-alpha mRNA, and decreased cellular death on TUNEL and caspase 3 staining.

CONCLUSIONS

PARS inhibition is anti-inflammatory, protects against experimental OB, and is associated with enhanced preservation of respiratory epithelium and decreased cellular death. Delayed treatment with INO-1001 arrests progression of the lesion developed by Day 7. These studies suggest that activation of PARS plays a critical role in the development of airway obliterative disease.

Nicotinamide increases systemic vascular resistance in ovine endotoxemia

OBJECTIVE

The nuclear enzyme Poly(ADP-Ribose)-Polymerase (PARP) has been hypothesized as playing a major role in various forms of inflammation. PARP activation is induced by DNA strand breakage and can result in intracellular energy depletion and, ultimately, cell death. Further, it is thought to influence cardiovascular function and organ failure in endotoxemia. Here, we investigated the effect of the PARP inhibitor nicotinamide on cardiovascular and liver function in healthy and chronically endotoxemic sheep.

DESIGN

Prospective controlled trial.

SETTING

University research laboratory.

SUBJECTS

12 female adult sheep.

INTERVENTIONS

Six healthy sheep, instrumented for chronic study, received nicotinamide intravenously as a bolus of 40 mg/kg followed by a continuous infusion of 10 mg.kg(-1).h(-1); six animals received the vehicle. One hour after bolus application, a continuous infusion of endotoxin ( Salmonella typhosa, 10 ng.kg(-1).min(-1)) was started. Hemodynamic parameters were determined before and during endotoxemia.

MEASUREMENTS AND RESULTS

Treatment with nicotinamide resulted in a significantly higher systemic vascular resistance index and lower cardiac index in endotoxemic animals, but not in controls. It also attenuated endotoxin-induced increase in gamma-glutamyl transferase.

CONCLUSIONS

The PARP inhibitor nicotinamide attenuates impairment of cardiovascular function during endotoxemia. In addition, PARP activation may be involved in endotoxin-induced liver injury.

Evidence of nitric oxide synthase 2 activity in swine naturally infected with Actinobacillus pleuropneumoniae

Evidence of nitric oxide synthase (NOS) 2 activity was determined by formation of nitrotyrosine (a reaction product of peroxynitrite) and by activation of poly(ADP-ribose) synthetase (PARS) in NOS2-expressed pleuropneumonic lungs from 20 pigs naturally infected with Actinobacillus pleuropneumoniae using immunohistochemistry. Intense immunostaining for nitrotyrosine residue was seen within the lung lesions from A. pleuropneumoniae-infected pigs, but it was minimal in the unaffected parts of the lung from A. pleuropneumoniae-infected pigs and in the normal lung from control pigs. Staining was especially strong in neutrophils and macrophages in the periphery of the lesions and within the alveolar spaces. There was close cell-to-cell correlation when serial sections were examined by immunohistochemistry for NOS2 and nitrotyrosine in each of the 20 lung samples. Expression of PARS was always present within inflammatory lesions but was minimal in the unaffected lung of A. pleuropneumoniae-infected pigs. Macrophages in alveolar spaces frequently exhibited strong staining for PARS. Colocalization of nitrotyrosine and PARS antigen was especially prominent in macrophages in the periphery of lesions. NOS2 expression in pleuropneumonic areas associated with protein nitrosation and PARS suggests that NOS2 is functionally active during infections caused by A. pleuropneumoniae.

Novel phenanthridinone inhibitors of poly (adenosine 5'-diphosphate-ribose) synthetase: potent cytoprotective and antishock agents

OBJECTIVE

To synthesize novel inhibitors of the nuclear enzyme poly(adenosine 5'-diphosphate [ADP]-ribose) synthetase (PARS), also known as poly(ADP-ribose) polymerase (PARP), and to test them in in vitro models of oxidant-induced cytotoxicity and in endotoxin and splanchnic occlusion-reperfusion-induced shock.

DESIGN

Randomized, prospective laboratory study.

SETTING

Research laboratory.

SUBJECTS

Murine macrophages, thymocytes, and endothelial cells; Balb/c mice and Wistar rats.

INTERVENTIONS

Macrophages and endothelial cells were treated with peroxynitrite and bleomycin to induce PARS activation, and thymocytes were treated with peroxynitrite to induce cell necrosis. Novel PARS inhibitors were synthesized and used to reduce PARS activation and to reverse cytotoxicity. Balb/c mice were subjected to splanchnic occlusion and reperfusion and were pretreated with various doses (1-10 mg/kg intraperitoneally) of PJ34, a selected, potent, water-soluble PARS inhibitor. The passage of fluorescein isothiocyanate-conjugated dextran (4 kDa) was analyzed in everted gut ileal sacs incubated ex vivo as an index of gut permeability. Wistar rats were subjected to Escherichia coli bacterial lipopolysaccharide (40 mg/kg intraperitoneally). PJ34 was also used at 10 mg/kg intraperitoneally, 1 hr before lipopolysaccharide or at 25 mg/kg intraperitoneally 1 hr after lipopolysaccharide treatment. Serum concentrations of indicators or multiple organ injury, concentrations of various proinflammatory mediators, and tissue concentrations of myeloperoxidase and malondialdehyde were measured. In addition, survival rates and vascular contractile and relaxant responses were recorded.

MEASUREMENTS AND MAIN RESULTS

Appropriate modifications of the phenanthridinone core structure yielded significant increases in the potency of the compounds, both as PARS inhibitors and as cytoprotective agents. The compound N-(6-oxo-5,6-dihydro-phenanthridin-2-yl) -N,N-dimethylacetamide (designated as PJ34) was one of the potent PARS inhibitors of the series, and it dose-dependently protected against thymocyte necrosis, with a half-maximal restoration of cell viability of 35 nM and complete protection at 200 nM. PARS activation also was visualized by immunohistochemistry and was dose-dependently suppressed by PJ34. The effect of PJ34 was dose-dependently reversed by excess nicotinamide adenine dinucleotide (oxidized). The PARS inhibitors dose-dependently suppressed proinflammatory cytokine and chemokine production and restored viability in immunostimulated macrophages. PJ34 was selected for the subsequent in vivo studies. PJ34 significantly protected against splanchnic reperfusion-induced intestinal hyperpermeability in the mouse. PJ34 reduced peak plasma concentrations of tumor necrosis factor-alpha, interleukin-1beta, and nitrite/nitrate in the plasma of lipopolysaccharide-treated rats. PJ34 ameliorated the lipopolysaccharide-induced increases in indexes of liver and kidney failure and concentrations of myeloperoxidase and malondialdehyde in the lung and gut. Lipopolysaccharide elicited vascular dysfunction, which was normalized by PJ34. Lipopolysaccharide-induced mortality was reduced by PJ34 (both pre- and posttreatment).

CONCLUSIONS

The novel series of phenanthridinone PARS inhibitors have potent cytoprotective effects in vitro and significant protective effects in shock and reperfusion injury in rodent models in vivo.

Poly(adenosine 5'-diphosphate) ribose polymerase activation as a cause of metabolic dysfunction in critical illness

Poly(adenosine 5'-diphosphate) ribose polymerase is a nuclear enzyme activated in response to genotoxic stress induced by a variety of DNA damaging agents. Several oxygen and nitrogen-centered free radicals, notably peroxynitrite, are strong inducers of DNA damage and poly(adenosine 5'-diphosphate) ribose polymerase activation in vitro and in vivo. Activation of this nuclear enzyme depletes the intracellular stores of its substrate nicotinamide adenine dinucleotide, slowing the rate of glycolysis, mitochondrial electron transport and adenosine triphosphate formation. This process triggers a severe energetic crisis within the cell, leading to acute cell dysfunction and cell necrosis. Poly(adenosine 5'-diphosphate) ribose polymerase also plays an important role in the regulation of inflammatory cascades, through a functional association with various transcription factors and transcription co-activators. Recent works identified this enzyme as a critical mediator of cellular metabolic dysfunction, inflammatory injury, and organ damage in conditions associated with overwhelming oxidative stress, including systemic inflammation, circulatory shock, and ischemia-reperfusion. Accordingly, pharmacological inhibitors of poly(adenosine 5'-diphosphate) ribose polymerase protect against cell death and tissue injury in such conditions, and may therefore represent novel therapeutic tools to limit multiple organ damage and dysfunction in critically ill patients.

Role of peroxynitrite and poly (ADP-ribosyl) synthetase activation in cardiovascular derangement induced by zymosan in the rat

Peritoneal administration of zymosan in the rat induced a severe inflammatory process characterised by an increase in the plasma levels of nitrite and nitrate, stable metabolites of nitric oxide (NO) and in the levels of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123, at 18 hours zymosan challenge. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the aorta of zymosan-shocked rats. In ex vivo experiments, thoracic aorta rings of zymosan-treated rats showed a reduced contraction to noradrenaline and reduced responsiveness to the relaxant effect to acetylcholine (vascular hyporeactivity and endothelial dysfunction, respectively). Treatment of zymosan-shocked rats with 3-aminobenzamide or Nicotinamide, inhibitors of poly ADP-ribosil synthetase (PARS) activity reduced the production of peroxynitrite and significantly prevented the cardiovascular dysfunction. Our data suggest that peroxynitrite and PARS activation play a role in the zymosan-induced cardiovascular derangements in the rat.

Liposome-mediated transfection of fetal lung epithelial cells: DNA degradation and enhanced superoxide toxicity

Cationic liposomes, 1:1 (mol/mol) 1,2-dioleoyldimethylammonium chloride-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, were used to transfect primary cultures of distal rat fetal lung epithelial cells with pCMV4-based plasmids. A DNA-to-lipid ratio of 1:10 to 1:15 (wt/wt) optimized DNA uptake over a 24-h exposure. At a fixed DNA-to-lipid ratio of 1:15, chloramphenicol acetyltransferase (CAT) reporter gene expression declined at lipid concentrations > 2.5 nmol/cm2 cell surface area, whereas DNA uptake remained concentration dependent. CAT expression peaked 48 h after removal of the liposome-DNA complex, declining thereafter. Reporter gene expression was increased, and supercoiled cDNA degradation was reduced by the addition of 0.2 mM nicotinamide and 10 microM chloroquine. Rat fetal lung epithelial cells transfected with two different expression cassettes had an increased susceptibility to superoxide-mediated cytotoxicity. This could be attributed to a nonspecific delivery of exogenous DNA or some other copurified factor. The DNA-dependent increase in superoxide-mediated cytotoxicity, but not basal levels of cytotoxicity, was inhibited by the addition of 0.2 mM nicotinamide and 10 microM chloroquine.

Role of poly(ADP-ribose)synthetase in inflammation

Peroxynitrite and hydroxyl radicals are potent initiators of DNA single strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP-ribose)synthetase (PARS). Rapid activation of PARS depletes the intracellular concentration of its substrate, NAD+, slowing the rate of glycolysis, electron transport and ATP formation. This process can result in acute cell dysfunction and cell necrosis. Accordingly, inhibitors of PARS protect against cell death under these conditions. In addition to the direct cytotoxic pathway regulated by DNA injury and PARS activation, PARS also appears to modulate the course of inflammation by regulating the expression of a number of genes, including the gene for intercellular adhesion molecule 1, collagenase and the inducible nitric oxide synthase. The research into the role of PARS in inflammatory conditions is now supported by novel tools, such as novel, potent inhibitors of PARS, and genetically engineered animals lacking the gene for PARS. In vivo data demonstrate that inhibition of PARS protects against various forms of inflammation, including zymosan or endotoxin induced multiple organ failure, arthritis, allergic encephalomyelitis, and diabetic islet cell destruction. Pharmacological inhibition of PARS may be a promising novel approach for the experimental therapy of various forms of inflammation.

Poly(ADP-ribose) synthetase activation mediates increased permeability induced by peroxynitrite in Caco-2BBe cells

BACKGROUND & AIMS

Peroxynitrite induces cytotoxicity by generating DNA single-strand breaks and activating poly(ADP-ribose) synthetase (PARS), a nuclear enzyme that consumes oxidized nicotinamide adenine dinucleotide (NAD+) and depletes cellular adenosine triphosphate (ATP). The aim of this study was to examine this mechanism of injury in an intestinal epithelial cell model after exposure to exogenous peroxynitrite (ONOO-) and nitric oxide (NO).

METHODS

Caco-2BBe cell monolayers exposed to donors of peroxynitrite (3-morpholino-sydnonimine [SIN-1], 3 mmol/L) or NO (S-nitroso-N-acetyl penicillamine [SNAP]; 3 mmol/L) were analyzed for DNA strand breaks, [NAD+], [ATP], and transepithelial flux of fluorescein sulfonic acid.

RESULTS

SIN-1 but not SNAP induced DNA single-strand breakage. Both SIN-1 and SNAP reduced [ATP], but only SIN-1 reduced [NAD+]. Inhibition of PARS activity by the PARS inhibitors 5-iodo-6-amino 1,2-benzopyrone or 3-aminobenzamide prevented the SIN-1-induced reduction in [NAD+] and [ATP] but had no effect on the SNAP-induced reduction in [ATP]. PARS inhibition reduced SIN-1-but not SNAP-induced hyperpermeability.

CONCLUSIONS

Peroxynitrite but not NO increases transepithelial permeability by inducing DNA strand breaks that activate the PARS pathway and cause the depletion of intracellular energy stores. Inhibition of PARS activity may represent a novel strategy in ameliorating peroxynitrite-mediated epithelial injury during intestinal inflammation.

DNA damage induced by peroxynitrite: subsequent biological effects

Nitric oxide (NO) and superoxide rapidly react to yield peroxynitrite. Peroxynitrite is a potent oxidant which reacts with proteins, lipids, and DNA. The present paper overviews the various DNA modifications induced by exposure to peroxynitrite or NO and superoxide concurrently, with special reference to the formation of 8-nitroguanine and 8-oxoguanine as well as the induction of DNA single strand breakage. In addition, we review the secondary processes that may follow the process of DNA damage, such as activation of the nuclear enzyme, poly(ADP-ribose) synthetase, apoptosis, and carcinogenesis.

Role of peroxynitrite and activation of poly (ADP-ribose) synthase in the vascular failure induced by zymosan-activated plasma

1. Zymosan is a wall component of the yeast Saccharomyces Cerevisiae. Injection of zymosan into experimental animals is known to produce an intense inflammatory response. Recent studies demonstrated that the zymosan-induced inflammatory response in vivo can be ameliorated by inhibitors of nitric oxide (NO) biosynthesis. The cytotoxic effects of NO are, in part, mediated by the oxidant preoxynitrite and subsequent activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS). In the present in vitro study, we have investigated the cellular mechanisms of vascular failure elicited by zymosan-activated plasma and the contribution of peroxynitrite production and activation of PARS to the changes. 2. Incubation of rat aortic smooth muscle cells with zymosan-activated plasma (ZAP) induced the production of nitrite, the breakdown product of NO, due to the expression of the inducible isoform of NO synthase (iNOS) over 6 24 h. In addition, ZAP triggered the production of peroxynitrite in these cells, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123 and by nitrotyrosine Western blotting. 3. Incubation of the smooth muscle cells with ZAP induced DNA single strand breakage and PARS activation. These effects were reduced by inhibition of NOS with NG-methyl-L-arginine (L-NMA, 3 mM), and by glutathione (3 mM), a scavenger of peroxynitrite. The PARS inhibitor 3-aminobenzamide (1 mM) inhibited the ZAP-induced activation of PARS. 4. Incubation of thoracic aortae with ZAP in vitro caused a reduction of the contractions of the blood vessels to noradrenaline (vascular hyporeactivity) and elicited a reduced responsiveness to the endothelium-dependent vasodilator acetylcholine (endothelial dysfunction). 5. Preincubation of the thoracic aortae with L-NMA (1 mM), glutathione (3 mM) or by the PARS inhibitor 3-aminobenzamide (1 mM) prevented the development of vascular hyporeactivity in response to ZAP. Moreover, glutathione and 3-aminobenzamide treatment protected against the ZAP-induced development of endothelial dysfunction. The PARS-related loss of the vascular contractility was evident at 30 min after incubation in endothelium-intact, but not in endothelium-denuded vessels and also manifested at 6 h after incubation with ZAP in endothelium-denuded rings. The acute response is probably related, therefore, to peroxynitrite formation (involving the endothelial NO synthase), whereas the delayed response may be related to the expression of iNOS in the smooth muscle. 6. The data obtained suggest that zymosan-activated plasma causes vascular dysfunction by inducing the simultaneous formation of superoxide and NO. These radicals combine to form peroxynitrite, which, in turn causes DNA injury and PARS activation. The protective effect of 3-aminobenzamide demonstrates that PARS activation contributes both to the development of vascular hyporeactivity and endothelial dysfunction during the vascular failure induced by ZAP.

Beneficial effects of 3-aminobenzamide, an inhibitor of poly (ADP-ribose) synthetase in a rat model of splanchnic artery occlusion and reperfusion

1. Peroxynitrite, a potent cytotoxic oxidant formed by the reaction of nitric oxide with superoxide anion, and hydroxyl radical, formed in the iron-catalysed Fenton reaction, are important mediators of reperfusion injury. In in vitro studies, DNA single strand breakage, triggered by peroxynitrite or by hydroxyl radical, activates the nuclear enzyme poly (ADP-ribose) synthetase (PARS), with consequent cytotoxic effects. Using 3-aminobenzamide, an inhibitor of PARS, we investigated the role of PARS in the pathogenesis of splanchnic artery occlusion shock. 2. Splanchnic artery occlusion and reperfusion shock (SAO/R) was induced in rats by clamping both the superior mesenteric artery and the coeliac trunk for 45 min, followed by release of the clamp (reperfusion). At 60 min after reperfusion, animals were killed for histological examination and biochemical studies. 3. SAO/R rats developed a significant fall in mean arterial blood pressure, significant increase of tissue myeloperoxidase activity and marked histological injury to the distal ileum. SAO/R was also associated with a significant mortality (0% survival at 2 h after reperfusion). 4. There was a marked increase in the oxidation of dihydrorhodamine 123 to rhodamine (a marker of peroxynitrite-induced oxidative processes) in the plasma of the SAO/R rats, starting early after reperfusion, but not during ischaemia alone. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific 'footprint' of peroxynitrite, in the necrotic ileum in shocked rats, as measured at 60 min after the start of reperfusion. 5. In addition, in ex vivo studies in aortic rings from shocked rats, we found reduced contractions to noradrenaline and reduced responsiveness to a relaxant effect to acetylcholine (vascular hyporeactivity and endothelial dysfunction, respectively). 6. In a separate set of studies, using a 4000 Dalton fluorescent dextran tracer, we investigated the changes in epithelial permeability associated with SAO/R. Ten minutes of reperfusion, after 30 min of splanchnic artery ischaemia, resulted in a marked increase in epithelial permeability. 7. There was a significant increase in PARS activity in the intestinal epithelial cells, as measured 10 min after reperfusion ex vivo. 3-Aminobenzamide, a pharmacological inhibitor of PARS (applied at 10 mg kg(-1), i.v., 5 min before reperfusion, followed by an infusion of 10 mg kg(-1) h(-1)), significantly reduced ischaemia/reperfusion injury in the bowel, as evaluated by histological examination. Also it significantly improved mean arterial blood pressure, improved contractile responsiveness to noradrenaline, enhanced the endothelium-dependent relaxations and reduced the reperfusion-induced increase in epithelial permeability. 8. 3-Aminobenzamide also prevented the infiltration of neutrophils into the reperfused intestine, as evidenced by reduced myeloperoxidase activity. It improved the histological status of the reperfused tissues, reduced the production of peroxynitrite in the late phase of reperfusion and improved survival. 9. In conclusion, our study demonstrates that the PARS inhibitor 3-aminobenzamide exerts multiple protective effects in splanchnic artery occlusion/reperfusion shock. We suggest that peroxynitrite and/or hydroxyl radical, produced during the reperfusion phase, trigger DNA strand breakage, PARS activation and subsequent cellular dysfunction. The vascular endothelium is likely to represent an important cellular site of protection by 3-aminobenzamide in SAO shock.

Soluble selectins and ICAM-1 modulate neutrophil-endothelial adhesion and diapedesis in vitro

We observed that normal plasma dramatically reduces neutrophil-endothelial adhesion. Therefore, we identified factors in plasma which might limit PMN adhesion in vitro. We found that the anti-adhesive effect was not mediated by vasoactive lipids present in plasma. Immunoprecipitation of soluble adhesion molecules, P and E-selectins and ICAM-1 restored PMN adhesion to control values. We further examined whether soluble adhesion molecules in plasma might also regulate PMN endothelial migration in response to fMLP (10(-6) M). Plasma significantly reduced PMN migration, and this effect was prevented only by the simultaneous removal of soluble P and E selectins and ICAM-1 together, but not individually. These data show that soluble selectins and ICAM-1 may regulate PMN adhesion and diapedesis, and that alterations in the levels of these molecules may regulate PMN-endothelial interactions in vivo.

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

1. An array of therapeutically used analgetic and antirheumatic drugs cause severe liver damage. The present study investigates the hepatoprotective effects of inhibitors of NAD-dependent adenoribosylation reactions and of antioxidants in analgesic-induced hepatic injury. 2. Male NMRI mice were treated PO with 500 mg/kg of acetaminophen, and the activities of both glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) were determined in serum. 3. The acetaminophen-induced release of both GOT and GPT from injured liver cells could be inhibited in a dose-dependent manner, when mice were injected additionally either with increasing amounts (from (25 mg/kg to 100 mg/kg i.p.) of the PARP-inhibitor nicotinamide, with increasing amounts (from 25 mg/kg to 100 mg/kg i.p.) of the antioxidant N-acetylcysteine, or with increasing amounts (from 50 mg/kg to 300 mg/kg i.p.) of the amino acid L-methionine. 4. A combination of both nicotinamide and N-acetylcysteine (at the low dose of 12.5 mg/kg i.p. each) results in a complete protection from acetaminophen-induced release of GOT and GPT from injured liver cells. 5. A combination of both L-methionine and N-acetylcysteine or nicotinamide (at the low dose of 12.5 mg/kg IP each) resulted also in complete protection from acetaminophen-induced release of GOT and GPT.

Role of poly-ADP ribosyltransferase activation in the vascular contractile and energetic failure elicited by exogenous and endogenous nitric oxide and peroxynitrite

Stimulation of vascular smooth muscle with bacterial lipopolysaccharide (LPS) and proinflammatory cytokines induces the expression of a distinct isoform of NO synthase (inducible NOS [iNOS]) contributing to the suppression of vascular contractility. We have obtained evidence of the involvement of an indirect pathway triggered by NO and its reaction product peroxynitrite (ONOO-) through the activation of the nuclear enzyme poly-ADP ribosyltransferase (PARS) in the pathogenesis of cellular energetic and contractile failure in vascular smooth muscle. Exposure of vascular smooth muscle cells caused DNA strand breaks, activation of PARS, depletion of NAD+, and inhibition of mitochondrial respiration. The NAD+ depletion and inhibition of mitochondrial respiration were reduced by pharmacological inhibition of PARS. Stimulation of vascular smooth muscle cells with LPS and interferon gamma (IFN-gamma) triggered the production of superoxide anion over 3 to 48 hours and NO and ONOO- over 24 to 48 hours and resulted in significant DNA strand breakage. The decrease in mitochondrial respiration in response to LPS and IFN-gamma stimulation was inhibited by the ONOO- scavenger uric acid (100 mumol/L) and by inhibitors of iNOS. The PARS inhibitors 3-aminobenzamide (1 mmol/L), nicotinamide (1 mmol/L), and PD 128763 (100 mumol/L) inhibited the reduction in cellular NAD+ and ATP and the suppression of mitochondrial respiration in response to LPS and IFN-gamma stimulation. Administration of 3-aminobenzamide also reduced PARS activation and vascular hyporeactivity of rat thoracic aortas exposed to ONOO- (300 mumol/L to 1.5 mmol/L) in vitro. 3-Aminobenzamide (10 mg/kg IP) preserved the ex vivo contractility of aortas obtained from endotoxic rats and improved survival in lethal murine endotoxic shock. These data suggest that PARS activation due to iNOS induction (1) is involved in the energetic depletion of vascular smooth muscle cells that express iNOS and (2) contributes to the pathogenesis of vascular energetic and contractile failure in endotoxic shock. Inhibition of PARS may be a novel concept of therapeutic potential in shock.

DNA strand breakage and activation of poly-ADP ribosyltransferase: a cytotoxic pathway triggered by peroxynitrite

Peroxynitrite is a reactive oxidant produced from nitric oxide (NO) and superoxide. Although its reactivity and decomposition are very much dependent on the constituents of the cellular environment, peroxynitrite is considered a potent oxidant that reacts with proteins, lipids, and DNA. Inasmuch as peroxynitrite is formed in many pathophysiological conditions that are associated with NO and/or superoxide overproduction, the investigation of the cytotoxic pathways triggered by peroxynitrite is of major importance. Here we review the evidence that peroxynitrite is a potent initiator of DNA strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly ADP ribosyl synthetase (PARS). We present an overview of experimental data that demonstrate or suggest that the peroxynitrite-PARS pathway, by leading to cell necrosis or apoptosis, contributes to cellular injury in a number of pathophysiological conditions including shock and inflammation, pancreatic islet cell destruction, and diabetes, stroke, and neurodegenerative disorders, as well as the toxic effects of various environmental oxidants or cytotoxic drugs.

Synthesis of poly(ADP-ribose) in asbestos treated rat pleural mesothelial cells in culture

To investigate the origin of DNA repair in rat pleural mesothelial cells (RPMC) exposed to asbestos fibers, poly(ADP-ribose) polymerase (PARP) activity was measured in the asbestos-treated cells. As bleomycin has been shown to activate poly(ADP-ribose) synthesis in several cell systems, the response to bleomycin with regard to PARP assay was first investigated. Bleomycin produced a dose-dependent increase of poly(ADP-ribose) synthesis in RPMC. Likewise both chrysotile and crocidolite fibers produced a concentration-dependent PARP activation indicating that the formation of DNA strand breaks is one type of damage produced by asbestos in RPMC. Enhancement of DNA repair, assessed by the measurement of [3H] methylthymidine incorporation in growth arrested cells, was not detectable in the presence of 3-methoxybenzamide (3-MBA), a PARP inhibitor, confirming a relation between PARP activation and DNA repair. The participation of DNA breakage in asbestos toxicity on RPMC was determined by the colorimetric 3-4(5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. There was no relationship between DNA breakage and cytotoxicity since the use of PARP inhibitors did not change cell viability. These results indicate that asbestos produce DNA damage that is repaired in RPMC.

Oxidative stress and living cells

The review deals with the effects of reactive oxygen species, both radical and nonradical (e.g. hydrogen peroxide), on cells and organisms. The chemical and biochemical aspects include description of individual reactive oxygen species, chemical reactions giving rise to them, their interconversions and interactions with metals (Fe2+, Cu2+, Cu+) and other substances (scavengers, antioxidants). The biological aspects concern the specific features and locations of cellular enzyme systems involved in radical production and/or removal. Major harmful effects of the species on the molecular (protein oxidation, lipid peroxidation, damage to DNA) and cellular level (effect on signal transduction, on cell membrane functions and on gene expression) are surveyed. Methods whereby cells and organisms cope with the onslaught of these reactive species are reviewed as well as implications for plant, animal and human health.

Alteration of adenosine triphosphate and other nucleotides after sublethal oxidant injury to rat type II alveolar epithelial cells

The alveolar epithelial cells of the lower respiratory tract are continuously exposed to injurious agents, including oxygen radicals. The type II alveolar epithelial cell is critically important to the normal function of the lung, because it is responsible for synthesis of surfactant and other essential duties. The present investigation measured the level of intracellular nucleotides and adenosine over time after exposure of type II cells to sublethal concentrations of physiologically relevant oxidants, hydrogen peroxide and hypochlorous acid (HOCl). Initially, it was determined that 250 microM HOCl or 250 microM hydrogen peroxide could each cause sublethal injury to the type II cells after exposure of up to 1 and 2 hours, respectively. After exposure to 250 microM hydrogen peroxide, the intracellular levels of adenosine, adenosine diphosphate, and adenosine triphosphate all initially increased in the first 1 to 15 minutes, but subsequently decreased significantly, ultimately reaching close to 40% below control levels. The level of adenosine monophosphate remained significantly elevated throughout the exposure until returning to control levels after 2 hours. Similar results occurred after the type II cells were exposed to 250 microM HOCl. This study demonstrates that adenosine triphosphate and other cellular nucleotides and nucleosides were decreased in type II cells before lethal injury and subsequent cell death.

3-Aminobenzamide enhances dexamethasone-mediated mouse thymocyte depletion in vivo: implication for a role of poly ADP-ribosylation in the negative selection of immature thymocytes

3-Aminobenzamide (3-ABAm), an inhibitor of poly ADP-ribosylation, was here found to remarkably enhance the dexamethasone (Dex)-mediated depletion of total mouse thymocytes within 24 h post-injection, when given i.p. in combination with Dex. After treatment the total thymocytes were fractionated by Percoll gradient centrifugation into two mitogen-unresponsive (high- and medium-density) and one mitogen-reactive (low-density) subpopulations and these were analyzed for the phenotypic expression of CD4 and CD8 antigens. Treatment with Dex alone most extensively depleted the high- and medium-density thymocytes and also those expressing both CD4 and CD8 double positive (DP) phenotypes in all three subpopulations. The CD4+ and CD8+ single positive (SP) and CD4-CD8- double negative (DN) subsets, in the low-density subpopulation in particular, were most resistant to the Dex-mediated depletion, thus giving rise to an enrichment of SP (2-fold) and particularly DN subset in the medium- and low-density populations (5-fold) recovered. 3-ABAm, which alone increased the total thymocyte number up to 2-fold, had no effect on the distribution of phenotypic subsets. However, the inhibitor, when given in combination with Dex, additionally depleted all four phenotypic subsets up to one-third of the levels with Dex alone, except for those of medium-density subpopulation. Because the non-inhibitor, 3-aminobenzoate, had no potentiating effect, our present results, together with our previous in vitro studies, indicate a role for the DNA repair cofactor poly ADP-ribose in the intrathymic death by apoptosis and depletion of thymocytes, especially those of DP subset in the high-density, functionally immature population.

Acute pneumocyte injury, poly(ADP-ribose) polymerase activity, and pyridine nucleotide levels after in vitro exposure of murine lung slices to cyclophosphamide

Cyclophosphamide (CYC) is a metabolically activated, DNA-alkylating, antitumor agent that causes pulmonary fibrosis. BALB/cN (B) mice are sensitive and C57Bl/6N (C) mice are resistant to CYC-induced fibrosis. Pulmonary bioactivation may contribute to strain sensitivity. Therefore, we tested the intrinsic susceptibility of murine lung slices to cell injury by direct exposure to CYC for 2-8 hr. Injury was measured by release of lactate dehydrogenase (LDH). DNA damage activates the nuclear enzyme poly(ADP-ribose) polymerase (PAP, EC 2.4.2.30), causing depletion of its substrate, NAD. NAD can also be decreased by phosphorylation to NADP, as seen with oxidative stress. Depletion of NAD can lead to loss of ATP. Thus, we measured LDH release, PAP activation, NAD, NADP and ATP in slices incubated with or without the PAP-inhibitor, 3-aminobenzamide (3-AB). CYC (0.1 to 1.0 mg/mL for 4-8 hr) caused LDH release in slices from both murine strains, but LDH release was significantly greater in B lung slices than in C slices. After an 8-hr incubation 63.9 +/- 3.7% (mean +/- SEM) of total LDH was released from B lung slices with 1.0 mg CYC/mL, whereas only 45.8 +/- 2.6% was released from C lung slices (P < 0.05). 3-AB reduced LDH release to 44.7 +/- 2.4% in B slices and 28.1 +/- 2.0% in C slices (P < 0.05 vs CYC only). PAP activity in nuclei isolated from CYC-treated B lung slices was increased 2- to 4-fold after 2 hr of incubation with 0.5 and 1.0 mg CYC/mL. PAP activation was delayed and reduced with incubation in 3-AB. PAP was activated 2-fold in nuclei from C slices treated with 0.5 mg CYC/mL for 2 hr. NAD was decreased at 2 and 4 hr in B slices treated with 0.5 and 1.0 mg CYC/mL, and at 4 hr with 0.1 mg CYC/mL. NAD depletion occurred only at 4 hr in the resistant C slices treated with 1.0 mg CYC/mL. CYC increased NADP by a similar extent in B and C lung slices. In B slices, NAD losses were approximately 4 times the increases in NADP. CYC did not decrease ATP in B slices and ATP dropped 25% only after 4 hr in the resistant C slices. We conclude that CYC is directly toxic to lung tissue and observe that strain sensitivity in vitro mirrors the sensitivity to fibrosis in vivo. PAP activation and oxidative stress may contribute to this toxicity.

NAD depletion after in vitro exposure of murine lung slices to bleomycin

Bleomycin (BLM), a DNA-cleaving, antitumor antibiotic, causes pulmonary fibrosis. It also causes cell injury and activates the nuclear enzyme poly(ADP-ribose) polymerase (PAP; EC 2.4.2.30) in lung slices exposed to the drug in vitro. 3-Aminobenzamide (3-AB), a PAP inhibitor, prevents enzyme activation and cell injury. We have examined the potential role of ATP and NAD depletion in injury of BLM-sensitive C57B1/6N and -resistant BALB/cN murine lung slices treated with BLM or deprived of glucose, the major metabolic substrate of lung. Lung slices either were treated for 45 min with injurious concentrations of BLM (10-500 micrograms/mL) or were incubated without glucose, in the presence or absence of 2.5 mM 3-AB. Only the highest concentration of BLM, 500 micrograms/mL, caused any ATP depletion, and this 35% decrease was transient, occurring at 220 min in C57B1/6N slices. In contrast, glucose deprivation caused 50-70% ATP depletion in slices from both strains. BLM alone at 100 and 500 micrograms/mL caused a sustained 30-70% NAD depletion from 75 min through 400 min in C57B1/6N mouse lung slices. In the resistant BALB/cN lung slices, NAD depletion by BLM was only seen at 400 min. 3-AB almost completely antagonized NAD depletion in slices from both strains. In contrast to BLM, glucose deprivation did not decrease NAD levels unless 3-AB was present in C57B1/6N slices. Thus, ATP depletion may play a role in the injurious effects of glucose deprivation, but does not appear to be a major factor in pneumocyte injury caused by BLM. NAD depletion or other effects of PAP activation appear to account for the strain-selective, injurious effect of BLM on lung tissue.

3-aminobenzamide protects the mouse thymocytes in vitro from dexamethasone-mediated apoptotic cell death and cytolysis without changing DNA strand breakage

Exposure of mouse thymocytes to 1 microM dexamethasone (Dex) resulted in a dramatic increase in the degree of DNA strand breakage up to 80% between 4 to 6 h postincubation. During incubation a marked decrease in the number of total and viable cells as well as an increase in the release of lactate dehydrogenase into medium were detectable, indicating a strong cytotoxicity of Dex on the mouse thymocytes. Agarose gel electrophoresis of DNA from cells exposed to Dex for 6 h clearly demonstrated an increased laddering of DNA fragments multiple of approx. 200 base pairs as a characteristic feature of an apoptosis or programmed cell death. The cytotoxicity of Dex, as judged by the decrease in the viability and increase in the cell lysis, was effectively prevented by 3-aminobenzamide, a potent inhibitor of poly(ADP-ribose) synthesis. Furthermore, the lowering of intracellular NAD levels, which was observable in the present study most probably as a result of activation of poly(ADP-ribose) synthesis due to Dex-mediated DNA strand breakage, was also specifically prevented by the inhibitor, although the DNA strand breakage itself was not affected under these conditions. Our present results indicate that the Dex-mediated thymocyte death and cytolysis and probably intrathymic apoptotic thymocytolysis could be attributable primarily to the loss of intracellular NAD.

Intestinal ischemia-reperfusion injury causes pulmonary endothelial cell ATP depletion

Intestinal ischemia-reperfusion is a common clinical event associated with both clinical and experimental distant organ injury. In particular, the pulmonary microvasculature appears to be susceptible to injury resulting from systemic inflammatory mediator activation. This study was designed to evaluate the hypothesis that noncellular humoral factors associated with intestinal ischemia-reperfusion result in pulmonary endothelial cell adenosine triphosphate (ATP) depletion. Male Sprague-Dawley rats had intestinal ischemia induced by microvascular clip occlusion of the superior mesenteric artery (SMA) for 120 minutes. Reperfusion resulted from superior mesenteric artery clip removal. After reperfusion for 0, 15, or 30 minutes, plasma samples were obtained from the portal vein. Monolayers of cultured rat pulmonary artery endothelial cells then were incubated with the plasma samples. Adenosine triphosphate levels were determined using a luciferin-luciferase assay. A 51Cr-release assay using labeled endothelial cells was performed under identical conditions to assess cytotoxicity. Potential mechanisms of ATP depletion were evaluated by analysis of cellular energy charge and assessment of microfilament architecture. Endothelial cell ATP levels decreased from 2.23 +/- 0.16 x 10(-11) moles/microgram DNA in sham preparations to 1.23 +/- 0.09 x 10(-11) moles/microgram DNA (p < 0.001) after 4 hours in plasma from animals undergoing 120 minutes of intestinal ischemia. For plasma obtained after 15 minutes of reperfusion, the decrease in cellular ATP concentration persisted (1.23 +/- 0.27 x 10(-11) moles/microgram DNA, p < 0.001 vs. sham). After 30 minutes' reperfusion, cellular ATP levels increased only slightly after the 4-hour incubation (1.39 +/- 0.26 x 10(-11) moles/microgram DNA, p < 0.005 vs. sham). No significant cytotoxic injury occurred in any group when compared with controls. Cellular energy charge was unchanged, and microfilament architecture was preserved. These data confirm the hypothesis that humoral factors, independent of the neutrophil, result in endothelial cell ATP depletion without metabolic inhibition or cell death. Depletion of energy stores by noncellular humoral factors may represent an early event that predisposes the cell to more severe injury by other mediators of the endogenous inflammatory response.

Role of the neutrophil in adult respiratory distress syndrome

Adult respiratory distress syndrome (ARDS) remains a significant cause of morbidity and mortality in surgical practice. Despite the continued advance of surgical technique and therapy, the mainstay of treatment of ARDS remains supportive. In the past decade cytokines have been found to be primary chemical mediators of the host response to inflammatory disease. The polymorphonuclear leucocyte has also emerged as a possible cellular mediator of the end-organ damage that characterizes these inflammatory processes. The role of the neutrophil as the primary cellular mediator of alveolar capillary membrane injury in ARDS remains controversial. This article reviews the relevant current literature and considers the implications of the prevailing evidence on future management of this syndrome.

Induction of fibronectin gene expression by transforming growth factor beta-1 is attenuated in bronchial epithelial cells by ADP-ribosyltransferase inhibitors

Transforming growth factor-beta (TGF-beta) exerts several effects on cultured airway epithelial cells including inhibition of proliferation and stimulation of fibronectin gene expression. ADP-ribosylation is one potential regulatory mechanism of gene expression by TGF-beta. We tested this possibility by exposing cultured bovine bronchial epithelial cells to the chemical inhibitor of ADP-ribosyl transferase enzymes, 3-aminobenzamide (3-AB) and, for comparison, 3-aminobenzoic acid (3-ABA), which is structurally similar to 3-AB but which does not inhibit ADP-ribosyl transferases. Exponential cell growth rate (1.2 doublings/day) or cellular morphology observed by phase contrast microscopy were not affected by 3 mM 3-AB or 3-ABA. Neither compound antagonized inhibition of cell division or induction of squamous morphology by TGF-beta 1. In contrast, the sixfold stimulation of fibronectin production by exposure of cells to 30 pM TGF-beta 1 for 48 h was reduced by 50% in the presence of 3 mM 3-AB, whereas 3 mM 3-ABA had no effect. The antagonistic effect was augmented by administration of 3-AB 24 h prior to induction by TGF-beta 1. Northern blot hybridization analyses demonstrated that 3-AB, but not 3-ABA, attenuated the induction of fibronectin mRNA by TGF-beta 1 by up to 50%. These observations may implicate a role of cellular ADP-ribosylation in the regulation of some gene expression by TGF-beta.

Alterations in DNA Synthesis and Cellular Constituents in Mouse Lung following Bleomycin Injections

Changes in the DNA synthesis and cellular constituents of mouse lung following repeated bleomycin (BLM) injections were studied. ICR mice were administered BLM subdermally for 10 days. Wet lung weight was increased 1.36 times on day 5 after the final administration compared with control mice receiving an identical volume of saline only for 10 days. The total number of cells in the bronchoalveolar lavage fluid of the BLM group reached a maximum on day 14, and histologic investigation of the lungs revealed marked cellular infiltrations. The labeling index obtained by the antibromodeoxyuridine monoclonal antibody method for cells was increased from days 5 to 14 in the BLM group. By day 28, these inflammatory changes had subsided and fibrotic remodeling had occurred. DNA polymerase activity in the lung tissue reached its maximal level on day 5 and remained unchanged until day 14. This phenomenon occurred in parallel with increases in DNA content and synthesis. During this period, an increase in DNA polymerase-beta activity and new induction of DNA polymerase-alpha activity were observed by phosphocellulose column chromatography. From these observations, it is concluded that: (1) repeated injections of BLM cause DNA injury in lung cells; (2) there is a subsequent increase in the DNA repair function as supported by the finding of an increase in DNA polymerase-beta activity; and (3) these lead further to cell proliferation as supported by the increase in both DNA polymerase-alpha activity and DNA content. Thus, a close relationship between morphologic changes and altered DNA synthesis was observed in the lungs of mice after BLM injections.