Inhibition of PARS attenuates endotoxin-induced dysfunction of pulmonary vasorelaxation

The poly(adenosine diphosphate-ribose) polymerase inhibitor PJ34 reduces pulmonary ischemia-reperfusion injury in rats

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Background

Ischemia-reperfusion (I/R) injury after lung transplantation causes alveolar damage, lung edema, and acute rejection. Poly(adenosine diphosphate-ribose) polymerase (PARP) is a single-stranded DNA repair enzyme that induces apoptosis and necrosis after DNA damage caused by reactive oxygen species. We evaluated tissue protective effects of the PARP inhibitor (PARP-i) PJ34 against pulmonary I/R injury.

Methods

Rats (total n=45) underwent a thoracotomy with left hilar isolation and saline administration (sham group) or thoracotomy with hilar clamping and saline administration (I/R group) or PJ34 administration (PARP-i group). Parameters were measured for 7 days after reperfusion.

Results

Pathologic analysis revealed that reperfusion injury was drastically suppressed in the PARP-i group 2 days after reperfusion. Terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick-end labeling–positive cells were significantly decreased in the PARP-i group compared to the I/R group (P<0.05). Accordingly, the wet-to-dry lung ratio in the I/R group was significantly higher compared with the PARP-i group (P=0.025). Four hours after reperfusion, serum tissue necrosis factor-α and interleukin-6 were significantly suppressed in the PARP-i group compared with the I/R group (P<0.05). Serum derivatives of reactive oxygen metabolites increased quickly and remained high in the I/R and PARP-i groups from 4 hr until 7 days after reperfusion. Interestingly, the serum biologic antioxidant potential in the PARP-i group was significantly higher than that in the I/R group from day 2 until day 7.

Conclusion

The PARP-i decreased inflammation and tissue damage caused by pulmonary I/R injury. These beneficial effects of the PARP-i may be correlated with its antioxidative efficacy.

Niacinamide mitigated the acute lung injury induced by phorbol myristate acetate in isolated rat's lungs

BACKGROUND

Phorbol myristate acetate (PMA) is a strong neutrophil activator and has been used to induce acute lung injury (ALI). Niacinamide (NAC) is a compound of B complex. It exerts protective effects on the ALI caused by various challenges. The purpose was to evaluate the protective effects of niacinamide (NAC) on the PMA-induced ALI and associated changes.

METHODS

The rat's lungs were isolated in situ and perfused with constant flow. A total of 60 isolated lungs were randomized into 6 groups to received Vehicle (DMSO 100 μg/g), PMA 4 μg/g (lung weight), cotreated with NAC 0, 100, 200 and 400 mg/g (lung weight). There were 10 isolated lungs in each group. We measured the lung weight and parameters related to ALI. The pulmonary arterial pressure and capillary filtration coefficient (Kfc) were determined in isolated lungs. ATP (adenotriphosphate) and PARP [poly(adenosine diphophate-ribose) polymerase] contents in lung tissues were detected. Real-time PCR was employed to display the expression of inducible and endothelial NO synthases (iNOS and eNOS). The neutrophil-derived mediators in lung perfusate were determined.

RESULTS

PMA caused increases in lung weight parameters. This agent produced pulmonary hypertension and increased microvascular permeability. It resulted in decrease in ATP and increase in PARP. The expression of iNOS and eNOS was upregulated following PMA. PMA increased the neutrophil-derived mediators. Pathological examination revealed lung edema and hemorrhage with inflammatory cell infiltration. Immunohistochemical stain disclosed the presence of iNOS-positive cells in macrophages and endothelial cells. These pathophysiological and biochemical changes were diminished by NAC treatment. The NAC effects were dose-dependent.

CONCLUSIONS

Our results suggest that neutrophil activation and release of neutrophil-derived mediators by PMA cause ALI and associated changes. NO production through the iNOS-producing cells plays a detrimental role in the PMA-induced lung injury. ATP is beneficial, while PARP plays a deteriorative effect on the PMA-induced ALI. NAC exerts protective effects on the inflammatory cascade leading to pulmonary injury. This B complex compound may be applied for clinical usage and therapeutic regimen.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism

Defending cellular integrity against disturbances in intracellular concentrations of ATP ([ATP](i)) is predicated on coordinating the selection of substrates and their flux through metabolic pathways (metabolic signaling), ATP transfer from sites of production to utilization (energetic signaling), and the regulation of processes consuming energy (cell signaling). Whereas NO and its receptor, soluble guanylyl cyclase (sGC), are emerging as key mediators coordinating ATP supply and demand, mechanisms coupling this pathway with metabolic and energetic signaling remain undefined. Here, we demonstrate that sGC is a nucleotide sensor whose responsiveness to NO is regulated by [ATP](i). Indeed, ATP inhibits purified sGC with a K(i) predicting >60% inhibition of NO signaling in cells maintaining physiological [nucleotide](i). ATP inhibits sGC by interacting with a regulatory site that prefers ATP > GTP. Moreover, alterations in [ATP](i), by permeabilization and nucleotide clamping or inhibition of mitochondrial ATP synthase, regulate NO signaling by sGC. Thus, [ATP](i) serves as a "gain control" for NO signaling by sGC. At homeostatic [ATP](i), NO activation of sGC is repressed, whereas insults that reduce [ATP](i,) derepress sGC and amplify responses to NO. Hence, sGC forms a key synapse integrating metabolic, energetic, and cell signaling, wherein ATP is the transmitter, allosteric inhibition the coupling mechanism, and regulated accumulation of cGMP the response.

Bench-to-bedside review: Cytopathic hypoxia

The rate of oxygen consumption by certain tissues is impaired when mice or rats are injected with lipopolysaccharide. A similar change in the rate of oxygen consumption is observed when Caco-2 human enterocyte-like cells are incubated in vitro with cytomix, a cocktail of cytokines containing tumor necrosis factor, IL-1beta, and IFN-gamma. The decrease in the rate of oxygen consumption is not due to a change in oxygen delivery (e.g. on the basis of diminished microvascular perfusion), but rather to an acquired intrinsic defect in cellular respiration, a phenomenon that we have termed 'cytopathic hypoxia'. A number of different biochemical mechanisms have been postulated to account for cytopathic hypoxia in sepsis, including reversible inhibition of cytochrome a,a3 by nitric oxide, and irreversible inhibition of one or more mitochondrial respiratory complexes by peroxynitrite. Recently, however, our laboratory has obtained data to suggest that the most important mechanism underlying the development of cytopathic hypoxia is depletion of cellular stores of nicotinamide adenine dinucleotide (NAD+/NADH) as a result of activation of the enzyme, poly(ADP-ribose) polymerase-1. If cytopathic hypoxia is important in the pathophysiology of established sepsis and multiorgan dysfunction syndrome, then efforts in the future will need to focus on pharmacological interventions designed to preserve normal mitochondrial function and energy production in sepsis.

Activation of poly(ADP-Ribose) polymerase-1 is a central mechanism of lipopolysaccharide-induced acute lung inflammation

Recent studies demonstrated that activation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) by oxidant-mediated DNA damage is an important pathway of tissue injury in conditions associated with oxidative stress. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ-34, we now demonstrate an essential role of PARP-1 in the development of pulmonary inflammation induced by lipopolysaccharide (LPS). PARP-1+/+ and PARP-1-/- mice received an intratracheal instillation of LPS (50 microg), followed after 24 h by bronchoalveolar lavage to measure the cytokines TNF-alpha, IL-1beta, and IL-6, the chemokines MIP-1alpha and MIP-2, leukocyte counts and myeloperoxidase activity (neutrophil accumulation), protein content (high permeability edema), and nitrite/ nitrate (nitric oxide production). Malondialdehyde (an index of lipid peroxidation) was measured in lung tissue. Similar experiments were conducted in BALB/c mice treated with PJ-34 or vehicle. The absence of functional PARP-1 reduced LPS-induced increases of cytokines and chemokines, alveolar neutrophil accumulation, lung hyperpermeability, NO production, and lipid peroxidation. Histological analysis revealed attenuated lung damage after PARP inhibition. Our findings support a mechanistic role of PARP-1 in the regulation of LPS-induced lung inflammation. Pharmacological inhibition of PARP may be useful in clinical conditions associated with overwhelming lung inflammation.

Activation of poly(ADP-ribose) polymerase in severe hemorrhagic shock and resuscitation

This study examines activation of poly(ADP-ribose) polymerase (PARP) in the ileum during hemorrhage and resuscitation and determines if inhibition of PARP reduces organ dysfunction and metabolic acidosis. Awake, nonheparinized rats were hemorrhaged (40 mmHg, 60 min). Resuscitation used Ringer's solution (2 1/3 x shed volume) and packed red blood cells (2/3 shed volume). Ileal PARP activity was elevated at the end of hemorrhage (3.6-fold) and 10 min of resuscitation (5-fold). The subsequent decline in PARP activity observed after 60 min of resuscitation was not due to cleavage by caspase-3. Ileum permeability increased 10-fold and circulating liver enzymes increased 4- to 6-fold following 60 min of resuscitation in animals pretreated with 3-aminobenzoic acid, a structural analog that does not inhibit PARP. Pretreatment with 3-aminobenzamide (3-AB), a PARP inhibitor, reduced these changes, whereas posttreatment with a bolus of 3-AB was ineffective. Metabolic acidosis, accumulation of lactate, and base deficit was reduced by pretreatment with 3-AB. PARP is activated in the ileum by hemorrhage and by resuscitation. Activation of PARP contributes to organ dysfunction in the ileum and liver and appears to be central to the development of metabolic acidosis.

L-arginine attenuates lipopolysaccharide-induced lung chemokine production

Chemokines stimulate the influx of leukocytes into tissues. Their production is regulated by nuclear factor-kappaB (NF-kappaB), an inducible transcription factor under the control of inhibitory factor kappaB-alpha (IkappaB-alpha). We have previously demonstrated that L-arginine (L-Arg) attenuates neutrophil accumulation and pulmonary vascular injury after administration of lipopolysaccharide (LPS). We hypothesized that L-Arg would attenuate the production of lung chemokines by stabilizing IkappaB-alpha and preventing NF-kappaB DNA binding. We examined the effect of L-Arg on chemokine production, IkappaB-alpha degradation, and NF-kappaB DNA binding in the lung after systemic LPS. To block nitric oxide (NO) production, a NO synthase inhibitor was given before L-Arg. LPS induced the production of chemokine protein and mRNA. L-Arg attenuated the production of chemokine protein and mRNA, prevented the decrease in IkappaB-alpha levels, and inhibited NF-kappaB DNA binding. NO synthase inhibition abolished the effects of L-Arg on all measured parameters. Our results suggest that L-Arg abrogates chemokine protein and mRNA production in rat lung after LPS. This effect is dependent on NO and is mediated by stabilization of IkappaB-alpha levels and inhibition of NF-kappaB DNA binding.