Pentoxifylline rescue preserves lung function in isolated canine lungs injured with phorbol myristate acetate

Acute lung injury and acute respiratory distress syndrome: experimental and clinical investigations

Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) can be associated with various disorders. Recent investigation has involved clinical studies in collaboration with clinical investigators and pathologists on the pathogenetic mechanisms of ALI or ARDS caused by various disorders. This literature review includes a brief historical retrospective of ALI/ARDS, the neurogenic pulmonary edema due to head injury, the long-term experimental studies and clinical investigations from our laboratory, the detrimental role of NO, the risk factors, and the possible pathogenetic mechanisms as well as therapeutic regimen for ALI/ARDS.

Acute respiratory distress syndrome and lung injury: Pathogenetic mechanism and therapeutic implication

To review possible mechanisms and therapeutics for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). ALI/ARDS causes high mortality. The risk factors include head injury, intracranial disorders, sepsis, infections and others. Investigations have indicated the detrimental role of nitric oxide (NO) through the inducible NO synthase (iNOS). The possible therapeutic regimen includes extracorporeal membrane oxygenation, prone position, fluid and hemodynamic management and permissive hypercapnic acidosis etc. Other pharmacological treatments are anti-inflammatory and/or antimicrobial agents, inhalation of NO, glucocorticoids, surfactant therapy and agents facilitating lung water resolution and ion transports. β-adrenergic agonists are able to accelerate lung fluid and ion removal and to stimulate surfactant secretion. In conscious rats, regular exercise training alleviates the endotoxin-induced ALI. Propofol and N-acetylcysteine exert protective effect on the ALI induced by endotoxin. Insulin possesses anti-inflammatory effect. Pentobarbital is capable of reducing the endotoxin-induced ALI. In addition, nicotinamide or niacinamide abrogates the ALI caused by ischemia/reperfusion or endotoxemia. This review includes historical retrospective of ALI/ARDS, the neurogenic pulmonary edema due to head injury, the detrimental role of NO, the risk factors, and the possible pathogenetic mechanisms as well as therapeutic regimen for ALI/ARDS.

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.

The involvement of nitric oxide, nitric oxide synthase, neutrophil elastase, myeloperoxidase and proinflammatory cytokines in the acute lung injury caused by phorbol myristate acetate

Phorbol myristate acetate (PMA) causes acute lung injury (ALI). The present study was designed to elucidate the role of nitric oxide (NO), inducible NO synthase (iNOS), neutrophil elastase (NE) and other mediators in the ALI caused by PMA. In isolated rat's lungs, PMA at various doses (1, 2 and 4 mug/g lung weight) was added into the lung perfusate. Vehicle group received dimethyl sulfoxide (the solvent for PMA) 100 mug/g. We measured the lung weight changes, pulmonary arterial pressure, capillary filtration coefficient, exhaled NO, protein concentration in bronchoalveolar lavage (PCBAL) and Evan blue dye leakage. Nitrate/nitrite, methyl guanidine, proinflammatory cytokines, NE and myeloperoxidase (MPO) in lung perfusate were determined. Histopathological examination was performed. We detected the iNOS mRNA expression in lung tissue. PMA caused dose-dependent increases in variables for lung changes, and nitrate/nitrite, methyl guanidine, proinflammatory cytokines, NE and MPO in lung perfusate. The pathology was characterized by alveolar hemorrhagic edema with inflammatory cell infiltration. Scanning electron microscopy revealed endothelial damage. PMA upregulated the expression of iNOS mRNA. Our results suggest that neutrophil activation by PMA causes release of NE, upregulation of iNOS and a series of inflammatory responses leading to endothelial damage and ALI.

N-acetylcysteine attenuates the acute lung injury caused by phorbol myristate acetate in isolated rat lungs

Acute lung injury (ALI) caused by phorbol myristate acetate (PMA) is characterized by pulmonary edema and inflammatory cells infiltration. PMA-activated neutrophils in vivo and in vitro to release free radicals, pro-inflammatory cytokines, nitric oxide (NO) and other mediators. These mediators may be the causes of pulmonary hypertension and increased microvascular permeability. In the present study, we used isolated perfused rat lungs from Sprague-Dawley (SD) rats. The purpose was to evaluate the effects of pretreatment of N-acetylcysteine (NAC) on the PMA-induced ALI and associated changes. PMA (2 microg kg(-1)) was introduced into the lung perfusate. NAC (150 mg kg(-1)) was administered 10 min before PMA. Thirty isolated lungs were randomly assigned to receive vehicle (dimethyl sulfoxide, DMSO, the solvent for PMA, 100 microg g(-1)), PMA alone and PMA with NAC pretreatment. There were 10 lungs in each group. We measured the lung weight (LW) to body weight (BW) ratio (LW/BW), LW gain (LWG), exhaled nitric oxide (NO) and protein concentration in bronchoalveolar lavage (PCBAL). The pulmonary arterial pressure (PAP) and microvascular permeability (K(fc)) were assessed. The concentration of nitrate/nitrite, methyl guanidine (MG), tumor necrosis factor(alpha) (TNF(alpha)) and interleukin-1(beta) (IL-1(beta)) in lung perfusate were determined. In addition, we also evaluate the lung injury by histopathological examination and by grading system for the lung injury score (LIS). PMA caused severe ALI as evidenced by the marked increases in LW changes, exhaled NO, PCBAL, histopathological changes, and LIS. It also increased the nitrate/nitrite, MG, TNF(alpha), and IL-1(beta) in lung perfusate. Pretreatment with NAC significantly attenuated these changes and abrogated the extent of ALI. Our results suggest that NAC exerts strong protective effects on the PMA-induced ALI and associated alterations. The mechanisms are possibly attributable to its antioxidant actions, inhibition of pro-inflammatory cytokines, and restoration of glutathione enzymes.

Pentoxifylline reduces regional inflammatory and ventilatory disturbances in meconium-exposed piglet lungs

Neonatal meconium aspiration frequently produces severe respiratory distress, which is associated with patchy pulmonary neutrophil influx and inflammatory injury. To examine the effects of pentoxifylline (PTX), a potent anti-inflammatory agent, on regional pulmonary inflammation and ventilation after meconium aspiration, we studied 17 anesthetized and ventilated neonatal piglets (age <2 d) for 12 h. After unilateral intrapulmonary instillation of meconium, PTX treatment was started in nine animals, and eight untreated animals served as controls. Bronchoalveolar lavage (BAL) fluid and lung tissue were studied for inflammatory variables at the end of the study, and changes in regional ventilation were serially analyzed with a dynamic pulmonary x-ray imaging method. Meconium insufflation increased BAL fluid total cell, neutrophil, and macrophage counts and tumor necrosis factor-alpha (TNF-alpha) and protein concentrations as well as lung tissue myeloperoxidase activity in the instilled lungs, compared with the noninstilled side. PTX treatment prevented the increase of BAL fluid alveolar macrophage count and TNF-alpha and protein concentrations in the meconium-instilled lungs but had no significant effect on the pulmonary neutrophil accumulation. Ventilation of the meconium-insulted lung was initially disturbed similarly in both study groups, but PTX administration prevented the sustained local ventilatory perturbation at 4, 6, and 12 h after meconium instillation. The results thus indicate that PTX treatment may attenuate meconium-induced regional ventilation derangements, mainly through its effects on local alveolar macrophages and TNF-alpha production as well as alveolocapillary permeability rather than via significant prevention of accumulation of active neutrophils in the insulted lungs.

Novel protection strategy for pulmonary transplantation

BACKGROUND

Ischemia-reperfusion injury continues to represent a significant challenge to successful lung transplantation. Traditional pulmonary ischemic protection is performed using hypothermic hyperkalemic depolarizing solutions to reduce the metabolic demands of the ischemic organ. Measures to further reduce the effects of ischemic injury have focused on the reperfusion period. We tested the hypothesis that novel physiologic hyperpolarizing solutions-using ATP-dependent potassium channel (K(ATP)) openers-given at the induction of ischemia, will reduce cellular injury and provide superior graft function even after prolonged periods of ischemia.

METHODS

An isolated blood-perfused ventilated rabbit lung model was used to study lung injury. Airway, left atrial, and pulmonary artery pressures were measured continuously during the 2-h reperfusion period. Oxygenation, as a surrogate of graft function, was measured using intermittent blood gas analysis of paired left atrial and pulmonary artery blood samples. Graft function was measured by oxygen challenge technique (F(i)O(2) = 1.0). Wet-to-dry ratio was measured at the conclusion of the 2-h reperfusion period. Control (Group I) lungs were perfused with modified Euro-Collins solution (depolarizing) and reperfused immediately (no ischemia). Traditional protection lungs were perfused with modified Euro-Collins flush solution and stored for 4 h (Group II) or 18 h (Group III) at 4 degrees C before reperfusion. Novel protection (Group IV) lungs were protected with a hyperpolarizing solution containing 100 nM Aprikalim, a specific K(ATP) channel opener, added to the modified Euro-Collins flush solution and underwent 18 h of ischemic storage at 4 degrees C before reperfusion.

RESULTS

Profound graft failure was measured after 18 h of ischemic storage with traditional protection strategies (Group III). Graft function was preserved by protection with hyperpolarizing solutions even for prolonged ischemic periods (Group IV). Wet-to-dry weight ratio, airway, left atrial, and pulmonary artery pressures were not significantly different between the groups.

CONCLUSIONS

We have created a model of predictable lung injury. Membrane hyperpolarization with a K(ATP) channel opener (PCO) provides superior prolonged protection from ischemia-reperfusion injury in an in vitro model of pulmonary transplantation.