NMDA receptor activation: critical role in oxidant tissue injury.

The excitatory amino acid glutamate serves important neurologic functions, but overactivation of its N-methyl-D-aspartate (NMDA) receptor is toxic to neurons (excitotoxicity). We report that NMDA receptor blocker MK-801 (dizocilpine maleate) attenuated oxidant injury induced by paraquat or by xanthine oxidase. We conclude that excitotoxicity may be a key factor in oxidant tissue injury.

Vasoactive intestinal peptide enhances lung preservation.

The outcome of lung transplantation is often dependent on the quality of the donor lungs. To explore a way to improve lung preservation, vasoactive intestinal peptide (VIP) was added to pneumoplegic solutions. The 4 solutions tested were Krebs solution, Krebs solution with VIP, University of Wisconsin solution, and the University of Wisconsin solution with VIP. The lungs of 8 male Sprague-Dawley rats were flushed and stored in these solutions for 24 hr. At regular intervals, tissue was sampled and examined by light, scanning, and transmission electron microscopy. Casts of the vasculature were made after 4 hr and viewed by a scanning electron microscope. Lungs appeared well preserved by light microscopy at all intervals. Although inflammatory cells around arteries, arterial constriction, bronchiolar epithelial detachment, peribronchiolar edema, and alveolar size inhomogeneity were greater with time, there was no significant difference among the 4 groups by light microscopy. Scanning microscopy of tissue at 24 hr confirmed the information found on light microscopy but did not allow separation of the groups. The vascular casts showed that edema around large vessels was less in the lungs treated with VIP (P < 0.01). Transmission electron microscopy showed that lungs stored in the solutions with VIP had significantly more normal-shaped mitochondria, less mitochondrial edema, less distortion of mitochondrial cristae, thinner basal lamina, and less aggregation of nuclear chromatin at most intervals sampled after 4 hr. We conclude that VIP added to certain pneumoplegic solutions improves the ultrastructure of rat lung stored in the cold for up to 24 hr. VIP may be an important additive to pneumoplegic solutions to improve preservation of lung before transplantation.

N-methyl-D-aspartate receptors outside the central nervous system: activation causes acute lung injury that is mediated by nitric oxide synthesis and prevented by vasoactive intestinal peptide.

N-methyl-D-aspartate receptors, found throughout the mammalian brain, are a component of the major excitatory transmitter system. Strong evidence exists that N-methyl-D-aspartate receptors, by promoting excessive entry of Ca2+ into neurons, play a role in neuronal damage that follows head injury, strokes, and epileptic seizures, and is associated with degenerative diseases such as Alzheimer's disease. Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We have investigated whether N-methyl-D-aspartate receptors exist in peripheral neurons, and, if so, whether their activation may result in tissue injury. We report that N-methyl-D-aspartate receptors exist in the lung, that their activation triggers acute injury, and that, as in toxicity to central neurons, this injury is associated with stimulation of nitric oxide synthesis, and can be attenuated by inhibition of this synthesis. Finally, vasoactive intestinal peptide, which protects the lung and heart against oxidant injury and promotes neuronal survival and differentiation also prevented N-methyl-D-aspartate lung injury, apparently by inhibiting a key neurotoxic action of nitric oxide, but not its production. The findings suggest that N-methyl-D-aspartate receptors exist in the peripheral nervous system and that activation of these receptors, resulting in damage to peripheral neurons, may be a novel mechanism of lung and other organ injury.

Nitric oxide mediates oxidant tissue injury caused by paraquat and xanthine oxidase.

In both paraquat and X/XO models of lung injury, the injury, previously attributed to the generation of reactive oxygen species, was related to the induction of NO. synthesis, and was totally preventable by inhibition of this synthesis. The results support the view that the NO. radical itself is an essential intermediary in the pathogenesis of at least some forms of oxidant tissue damage. Another form of oxidant injury, caused by prolonged perfusion of the lung ex vivo, is not mediated by NO. however.

VIP enhances and nitric oxide synthase inhibitor reduces survival of rat lungs perfused ex vivo.

VIP delayed the onset of edematous lung injury in isolated perfused rat lungs by 64%, and was more effective than PGI2 in prolonging lung survival ex vivo. While PGI2 increased survival by 37 min versus Krebs/BSA only, VIP increased it by 2 h and 17 min. On the other hand, inhibition of NO. synthase, which protected the lung against oxidant injury caused by paraquat or X/XO,3 actually hastened the onset of injury caused by prolonged perfusion ex vivo, suggesting opposite roles for NO. in different forms of oxidant injury.

Glutamate toxicity in the lung and neuronal cells: prevention or attenuation by VIP and PACAP.

VIP, which has been demonstrated to reduce or prevent oxidant injury in the lungs and other organs, is shown here to protect against excitotoxic injury of the lung and excitotoxic death of cortical neuronal cells in primary culture. Glutamate killing of neuron-like PC-12 cells, attributable to oxidant stress rather that to excitotoxicity, is also reduced or prevented by VIP and by the closely related peptide PACAP. The exact mechanisms of this protection remain to be determined, but appear to include antioxidant and anti-apoptotic actions, and suppression of glutamate-induced upregulation of its own receptor. Both VIP and PACAP offer the promise of novel and nontoxic means of defending against NMDA and glutamate toxicity.

Excitotoxicity in the lung: N-methyl-D-aspartate-induced, nitric oxide-dependent, pulmonary edema is attenuated by vasoactive intestinal peptide and by inhibitors of poly(ADP-ribose) polymerase.

Excitatory amino acid toxicity, resulting from overactivation of N-methyl-D-aspartate (NMDA) glutamate receptors, is a major mechanism of neuronal cell death in acute and chronic neurological diseases. We have investigated whether excitotoxicity may occur in peripheral organs, causing tissue injury, and report that NMDA receptor activation in perfused, ventilated rat lungs triggered acute injury, marked by increased pressures needed to ventilate and perfuse the lung, and by high-permeability edema. The injury was prevented by competitive NMDA receptor antagonists or by channel-blocker MK-801, and was reduced in the presence of Mg2+. As with NMDA toxicity to central neurons, the lung injury was nitric oxide (NO) dependent: it required L-arginine, was associated with increased production of NO, and was attenuated by either of two NO synthase inhibitors. The neuropeptide vasoactive intestinal peptide and inhibitors of poly(ADP-ribose) polymerase also prevented this injury, but without inhibiting NO synthesis, both acting by inhibiting a toxic action of NO that is critical to tissue injury. The findings indicate that: (i) NMDA receptors exist in the lung (and probably elsewhere outside the central nervous system), (ii) excessive activation of these receptors may provoke acute edematous lung injury as seen in the "adult respiratory distress syndrome," and (iii) this injury can be modulated by blockade of one of three critical steps: NMDA receptor binding, inhibition of NO synthesis, or activation of poly(ADP-ribose) polymerase.

Vasoactive intestinal peptide prevents lung injury due to xanthine/xanthine oxidase.

Reactive oxygen species mediate injury and inflammation in many tissues. The addition of xanthine and xanthine oxidase to perfused rat lungs led to increases in peak airway pressure and perfusion pressure, pulmonary edema, and increased protein content in bronchoalveolar lavage fluid. Treatment with 1-10 micrograms.kg-1.min-1 of vasoactive intestinal peptide (VIP), a widely distributed neuropeptide, markedly reduced or totally prevented all signs of injury. Simultaneously, VIP also diminished or abolished the associated generation of arachidonate products. Similar protection was provided by catalase (100 micrograms/ml) but not by the VIP-related peptides secretin or glucagon. The pulmonary vasodilator papaverine (0.15 mg/ml) was also ineffective. Injured lungs that were not treated with VIP released large amounts of this peptide in the perfusate. The results indicate that VIP has potent protective activity against injury triggered by xanthine/xanthine oxidase and may be a physiological modulator of inflammatory tissue damage associated with toxic oxygen metabolites.

Paraquat-induced lung injury: prevention by vasoactive intestinal peptide and related peptide helodermin.

We earlier showed that the neuropeptide vasoactive intestinal peptide (VIP) reduces or prevents acute injury produced in rat lungs by xanthine and xanthine oxidase. We have now examined whether VIP can protect against lung injury induced by paraquat, a prooxidant pesticide. Isolated guinea pig lungs were perfused for 60 min with Krebs-4% albumin and mechanically ventilated with 95% O2-5% CO2. Infusion of paraquat (100 mg/kg) into the pulmonary artery (n = 9 observations) increased peak airway pressure from 10.1 +/- 0.6 to 54.7 +/- 6.5 cmH2O, perfusion pressure from 8.0 +/- 0.5 to 14.9 +/- 3.0 cmH2O, wet-to-dry lung weight ratio to 7.17 +/- 0.37, and bronchoalveolar lavage protein content to 2.70 +/- 0.83 mg/ml (P < 0.01). Pretreatment with 1-3 micrograms.kg-1 x min-1 VIP markedly attenuated or prevented all abnormalities. Of the related peptides tested, helodermin was as effective as VIP, but secretin and glucagon were ineffective. The results demonstrate that VIP and helodermin protect perfused guinea pig lungs against paraquat-induced injury and support the view that VIP has antioxidant activity.

Paraquat-induced lung injury: prevention by N-tert-butyl-alpha-phenylnitrone, a free-radical spin-trapping agent.

The herbicide paraquat causes lung injury that is believed to be oxygen-radical mediated. To further characterize this injury and explore new methods of preventing it, we used the spin-trapping agent N-tert-butyl-alpha-phenylnitrone (PBN) to identify the paraquat radical in lung tissue and to reduce the injury resulting from the subsequent generation of reactive oxygen species. The formation of a paraquat free radical by guinea pig lung was detected under anaerobic conditions by electron paramagnetic resonance spectrometry. Infused (25, 50, or 100 mg/kg) into guinea pig lungs (perfused at constant flow with Krebs solution containing 4% bovine serum albumin and ventilated with 95% O2-5% CO2), paraquat produced dose-dependent increases in peak airway pressure (Paw), mean pulmonary arterial perfusion pressure (Ppa), and wet-to-dry (W/D) lung weight ratio. At 100 mg/kg, paraquat increased Paw by 589.6 +/- 59.8% (mean +/- SE, n = 8) and W/D ratio from 5.33 +/- 0.07 to 6.29 +/- 0.11 (P less than 0.001). Pulmonary vascular leak index increased from 0.40 +/- 0.09 to 1.96 +/- 0.45 (P less than 0.02), without changes in pulmonary microvascular pressure. Perfusate concentrations of thromboxane B2 and 6-ketoprostaglandin F1 alpha increased, but indomethacin did not reduce the injury. PBN (2.3 mM) markedly attenuated all evidence of lung injury, which was also reduced by catalase, mannitol, ethanol, and vitamin E.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide as a mediator of oxidant lung injury due to paraquat.

At low concentrations, nitric oxide is a physiological transmitter, but in excessive concentrations it may cause cell and tissue injury. We report that in acute oxidant injury induced by the herbicide paraquat in isolated guinea pig lungs, nitric oxide synthesis was markedly stimulated, as evidenced by increased levels of cyclic GMP in lung perfusate and of nitrite and L-citrulline production in lung tissue. All signs of injury, including increased airway and perfusion pressures, pulmonary edema, and protein leakage into the airspaces, were dose-dependently attenuated or totally prevented by either NG-nitro-L-arginine methyl ester or N omega-nitro-L-arginine, selective and competitive inhibitors of nitric oxide synthase. Protection was reversed by excess L-arginine but not by its enantiomer D-arginine. When blood was added to the lung perfusate, the paraquat injury was moderated or delayed as it was when paraquat was given to anesthetized guinea pigs. The rapid onset of injury and its failure to occur in the absence of Ca2+ suggest that constitutive rather than inducible nitric oxide synthase was responsible for the stimulated nitric oxide synthesis. The findings indicate that nitric oxide plays a critical role in the production of lung tissue injury due to paraquat, and it may be a pathogenetic factor in other forms of oxidant tissue injury.