Improved lung preservation using a dimethylthiourea flush

Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes

This article deals with a class of ruthenium-BIAN-derived complexes, [Ru(II)(tpm)(R-BIAN)Cl]ClO4 (tpm = tris(1-pyrazolyl)methane, R-BIAN = bis(arylimino)acenaphthene, R = 4-OMe ([1a]ClO4), 4-F ([1b]ClO4), 4-Cl ([1c]ClO4), 4-NO2 ([1d]ClO4)) and [Ru(II)(tpm)(OMe-BIAN)H2O](2+) ([3a](ClO4)2). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([N-(phenyl)imino]acenapthenone)-derived complex [Ru(II)(tpm)(BIAO)Cl]ClO4 ([2]ClO4). The redox-sensitive bond parameters involving -N═C-C═N- or -N═C-C═O of BIAN or BIAO in the crystals of representative [1a]ClO4, [3a](PF6)2, or [2]ClO4 establish its unreduced form. The chloro derivatives 1a(+)-1d(+) and 2(+) exhibit one oxidation and successive reduction processes in CH3CN within the potential limit of ±2.0 V versus SCE, and the redox potentials follow the order 1a(+) < 1b(+) < 1c(+) < 1d(+) ≈ 2(+). The electronic structural aspects of 1a(n)-1d(n) and 2(n) (n = +2, +1, 0, -1, -2, -3) have been assessed by UV-vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru(II) → Ru(III)) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex 3a(2+) undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru(II)-H2O}/{Ru(III)-OH} and {Ru(III)-OH}/{Ru(IV)═O}, respectively. The chloro (1a(+)-1d(+)) and aqua (3a(2+)) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI(OAc)2 as oxidant in CH2Cl2 at 298 K, though the analogous 2(+) remains virtually inactive. The detailed experimental analysis with the representative precatalyst 1a(+) suggests the involvement of the active {Ru(IV)═O} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations.

Microvascular permeability of the non-heart-beating rabbit lung after warm ischemia and reperfusion: role of neutrophil elastase

BACKGROUND

The duration of warm ischemia and reperfusion injury is a major limiting factor in the setting of lung transplantation with non-heart-beating donors (NHBD). We hypothesized that reperfusion with neutrophil elastase inhibitor or leukocyte-depleted blood has an inhibitory effect on the ischemia-reperfusion injury of NHBD rabbit lungs.

METHODS

To assess the lung injury, we used a perfused rabbit lung model and measured the hemodynamic parameters and filtration coefficient. The rabbit lungs after hypoxic cardiac arrest for 30, 50, and 60 minutes were harvested at room temperature, and ventilated lungs were reperfused for 1 hour at a constant flow (120 mL/min). The group with 60 minutes of warm ischemia and hypoxia was further divided into three groups to determine the effects of leukocyte-depleted reperfusion or neutrophil elastase inhibitor, (1) no other special treatment, (2) reperfusion with leukocyte-depleted blood, and (3) administration of 10 mg of specific neutrophil elastase inhibitor. The lungs reperfused immediately after harvest from the heart-beating donor were regarded as the control.

RESULTS

Sixty minutes of warm ischemia and hypoxia resulted in an increase in filtration coefficient (0.68+/-0.20 g x min(-1) x cm H2O(-1) per 100 g) compared with the control values of 0.13+/-0.03 g x min(-1) x cm H2O(-1) per 100 g. The increase in filtration coefficient after 60 minutes of warm ischemia and hypoxia in NHBD was remarkably suppressed by leukocyte depletion (0.23+/-0.07) and by neutrophil elastase inhibitor (0.21+/-0.08). The shunt fraction and histology results were also near normal.

CONCLUSIONS

These results suggested that leukocyte depletion or treatment with neutrophil elastase inhibitor during reperfusion reduces alveolar-capillary damage caused by lung ischemia-reperfusion injury in the NHBD lung transplantation setting. This effect might be mediated by inhibition of neutrophil elastase activity or sequestration, and thus may lead to the increased availability of NHBD lungs.

A newly developed solution enhances thirty-hour preservation in a canine lung transplantation model

Ischemia and reperfusion cause the production of oxygen free radicals. These damage grafts or disrupt normal vascular homeostatic mechanisms, with a parallel reduction in endothelial nitric oxide and adenosine 3',5'-cyclic monophosphate levels. We hypothesized that lung preservation failure may be related to these events. To improve lung preservation, we prepared a new ET-Kyoto solution, which contains N-acetylcysteine (a radical scavenger), nitroglycerin (to elevate the nitric oxide level), and dibutyryl adenosine 3',5'-cyclic monophosphate (to elevate the adenosine 3',5'-cyclic monophosphate level) and examined its efficacy in a canine single-lung transplantation model. Lungs were flushed with new ET-Kyoto solution (group I, n = 9), basal ET-Kyoto solution (group II, n = 6), basal ET-Kyoto solution plus ethanol and propylene glycol (solvents of nitroglycerin; group III, n = 6), or low-potassium dextran glucose solution (group IV, n = 6), and stored at 4 degrees C for 30 hours. After left single-lung transplantation, the right main bronchus and right pulmonary artery were ligated and the functions of the transplanted lung were assessed for 6 hours. Arterial oxygen tension was significantly higher in group I than in groups II, III, and IV (p < 0.05). Peak inspiratory pressure and wet-to-dry lung weight ratio were significantly lower in group I than in groups II and IV (p < 0.01). Histologic and ultrastructural studies showed better preservation in group I than in groups II, III, and IV. We conclude that the new ET-Kyoto solution provides enhanced 30-hour lung preservation.

Potentiation of oxidant-induced toxicity in hamster lung slices by dimethylthiourea

Dimethylthiourea (DMTU) is an effective scavenger of reactive oxygen metabolites. This property has been successfully exploited, experimentally, in the protection of cells and tissues against oxidative damage. In this study, however, we have observed that levels of nonprotein sulfhydryls (NPSH) in hamster lung slices were markedly decreased by incubation with 10 or 40 mM DMTU. These changes were associated with morphological signs of injury, increased levels of oxidised glutathione (GSSG), and an increased activity of the pentose phosphate pathway (PPP), suggesting that the loss of NPSH was due to their oxidation. Incubation with 40 mM, but not 10 mM DMTU, also resulted in a decreased ability to oxidise [6-14C]glucose or to synthesise proteins, suggesting that at the high concentration, DMTU may cause functional impairment of the tissue. Furthermore, the ability of the slices to accumulate putrescine decreased after incubation with the oxidative toxins paraquat (PQ), tert-butyl hydroperoxide (t-BOOH) or hydrogen peroxide (H2O2) and was further decreased by co-incubation with DMTU. Putrescine uptake, a function specific to the alveolar type I and II epithelial cells, was not affected by incubation with DMTU alone. DMTU did not exacerbate the effect of the nonoxidative toxin iodoacetamide (IAA) on putrescine uptake but it did affect markers of general cell damage or dysfunction. We suggest, therefore, that the toxicity of oxidants toward lung tissue is potentiated in alveolar epithelial cells by DMTU.

Changes in vascular permeability with ischemic time, temperature, and inspired oxygen fraction in isolated rabbit lungs

The capillary filtration coefficient (Kf) is one of the most accurate measures of change in pulmonary vascular permeability and has been used in various models of acute lung injury. To evaluate the isolated effects of ischemia on Kf, we have developed an ex vivo rabbit lung model in which the influences of reperfusion are eliminated. The current study was designed to validate this model by determining the effect of cold flushing with low-potassium-dextran solution containing 1% glucose (LPDG), ischemic time, temperature, and inspired oxygen fraction on Kf. On completion of the ischemic period, the ventilated lungs, with the heart still attached, were suspended from a strain-gauge force transducer. After the lungs were flushed with 50 mL hetastarch solution (6% hetastarch solution with physiologic saline solution), the left atrial drainage cannula was occluded and the pulmonary artery pressure was incrementally increased by elevation of the reservoir. The Kf was calculated as the slope of the line relating the weight gain rate and pulmonary capillary pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung preservation: a review of current practice and future directions

During the past 10 years, pulmonary transplantation has emerged as a successful mode of surgical therapy for suitable patients with end-stage lung disease. Current preservation techniques of donor lungs for subsequent transplantation include core-cooling and single flush perfusion. The relative merits of these are described. These methods are essentially restricted to 6 hours of ischemia. Research in lung preservation is aimed not only at extending the safe period of ischemia but also at improving the quality of preservation. Areas of interest include the ideal composition of the perfusate, relevant pharmacologic additives, and the best conditions for preservation and harvesting. Advantages and disadvantages of the various animal models are listed in addition to the methods used in assessing the quality of preservation. There have been major advances in experimental lung preservation during the past 10 years, and we are possibly on the threshold of incorporating some of these into clinical practice. Among the most important are the adoption of colloid-based perfusates, the more widespread use of free radical scavengers, and the use of leukocyte depletion.

Effect of a free radical scavenger on cadaver lung transplantation

The pulmonary donor pool would increase substantially if lungs could be safely transplanted after cessation of circulation. To determine whether the addition of the free radical scavenger dimethylthiourea to the perfusate of cadaver lungs could improve graft function, canine donors were sacrificed, and lungs retrieved 2 hours after death. In a blinded fashion, dimethylthiourea was added to the modified Euro-Collins solution and infused into recipients (n = 9) perioperatively; a placebo was included in the perfusate of control animals (n = 9). Donor animals were ventilated with 100% oxygen only during flush and harvest. Recipients were rendered dependent upon the single left transplanted lung by occlusion of the right pulmonary artery and bronchus 1 hour after transplantation. Ventilation was maintained at a constant inspiratory oxygen fraction of 0.4. Recipients were followed up for 8 hours or until death. Three of 9 control animals survived the 8-hour observation period, whereas 6 of 9 recipients of cadaver lungs harvested with dimethylthiourea survived the observation period. Two deaths in the dimethylthiourea group occurred after 7 hours, implying that the effects of the ischemia and reperfusion injury were ameliorated by the use of this agent in this model. This study supports the notion that perfusate modification may improve the yield of cadaver lung retrieval and may allow for transplantation of lungs harvested from cadavers after cessation of circulation.

Oxygen radicals and lung injury

This article describes the formation of oxygen radicals and their biological effects, especially in relation to lung injury. Various recent experimental data are reviewed. The relationships between hydrostatic effects and permeability effects in producing injury and edema are stressed. Means of prevention and problems related to extrapolation to clinical situations are focused.

Enhanced pulmonary function using dimethylthiourea for twelve-hour lung preservation

Current preservation techniques for lung transplantation limit ischemic time to 6 hours. The purpose of this study was to evaluate the ability of dimethylthiourea, a low molecular weight free radical scavenger, to prolong this interval. An in vivo canine transplantation model was used to assess lung function. At harvest and after circulatory arrest, the donor lung was flushed with modified Euro-Collins solution (50 mL/kg). In a blinded fashion, dimethylthiourea (5 g) or saline solution was added to the flush solution at harvest and also infused (20 g over 2 hours) at reimplantation. Harvested lungs were stored for 12 hours at 4 degrees C. Allotransplantation was performed in recipient dogs ventilated with 40% O2. After 1 hour, the contralateral pulmonary artery was ligated, forcing the dog to be dependent on the transplanted lung. Twelve dogs were studied, with 6 randomly assigned to each treatment group in a blinded fashion. Measurements were recorded for 8 hours, keeping the inspired oxygen fraction constant at 0.40. All dimethylthiourea-treated dogs survived the observation period, whereas one third of the dogs that received saline solution died. Dimethylthiourea-treated dogs had significantly greater arterial oxygen tension and significantly less pulmonary vascular resistance compared with control animals. These results suggest that treatment of the lung with a free radical scavenger (dimethylthiourea) improves pulmonary function after reimplantation in a canine model after 12-hour hypothermic storage.

Reduction of canine myocardial infarct size by a diffusible reactive oxygen metabolite scavenger. Efficacy of dimethylthiourea given at the onset of reperfusion

A number of scavengers of reactive oxygen metabolites reduce myocardial injury when given before ischemia and reperfusion, but few, if any, have proven to be effective when given near the onset of reperfusion. This is particularly true when infarct size is measured after at least 48 hours of reperfusion, when the full extent of myocardial damage has become apparent. Dimethylthiourea (DMTU) is an extremely diffusible, potent scavenger of hydroxyl radical, hydrogen peroxide, and hypochlorous acid, with a long half-life of 43 hours. Sixteen chloralose-anesthetized dogs underwent 90 minutes of left anterior descending coronary artery (LAD) occlusion followed by 48 hours of reperfusion. Collateral flow was measured by radioactive microspheres. Infarct size and risk area were measured by a postmortem dual-perfusion technique using triphenyl tetrazolium chloride and Evan's blue dye. In eight dogs, therapy with DMTU (500 mg/kg i.v.) was given during the last 15 minutes of ischemia and the first 15 minutes of reperfusion. In eight control dogs, the same volume of 0.9% saline was given during the last 15 minutes of ischemia through the first 15 minutes of reperfusion. Infarct size as a percent of risk area was reduced in the DMTU-treated group compared with the saline-treated controls (DMTU = 42 +/- 4% versus saline = 59 +/- 4%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Critical care management of lung transplant recipients

In the last 10 years, lung transplantation has become an increasingly common procedure for patients with end-stage respiratory disease. Although long-term survival can be achieved, there is still significant morbidity within the first year. Early postoperative problems that may be anticipated include respiratory insufficiency, airway anastomotic problems, hemorrhage, infection, and episodes of acute rejection. These problems and others make the immediate perioperative period particularly challenging. With aggressive management, however, the probability of a successful outcome can be enhanced.

Improved lung preservation with cold air storage

Conventional topical slush cooling limits lung transport to 4 to 6 hours. For this canine study of an alternate air cooling system, 37 canine lungs were removed: 24 were placed in plastic bags, and inserted in a Transplanthermm container at core air temperatures (n = 6 lungs each) of (A) 4 degrees C, (B) 8 degrees C, (C) 12 degrees C, and (D) 20 degrees C; 6 were stored conventionally in ice slush (E); and 7 were transplanted immediately (F). After 8 hours, the stored lungs were transplanted and the contralateral pulmonary artery was ligated. Survival, arterial oxygen tension, and extravascular lung water were monitored at 15 minutes and every hour for 4 hours. Four-hour survival was 100% in groups A, B, and F; 83% in group C, 50% in group D, and 17% in group E. The mean arterial oxygen tension at 1 hour was lower in group E (6.4 +/- 2.4 kPa) than in group A (39.8 +/- 13.2 kPa) (p = 0.0002) or in group F (42.0 +/- 16.2 kPa) (p = 0.0035). Extravascular lung water in group E was higher at 15 minutes (15.44 +/- 5.63 mL/kg) than in group A (3.76 +/- 0.63 mL/kg) (p = 0.0001) and group F (4.69 +/- 1.65 mL/kg) (p = 0.003). Cold air storage appears to provide better lung preservation than hypothermic immersion in ice slush.

Improved heart and lung preservation in a rat model

We investigated the efficacy of four different preservation solutions in a heart-lung model in the rat. The heart and lungs of the donor were perfused under standardised conditions of temperature, pressure and flow. We studied 4 groups: group 1 received Stanford solution to heart and lung; group 2 received St. Thomas' solution to heart and Papworth solution to lung; group 3 received University of Wisconsin solution to heart and lung; and group 4 received University of Wisconsin solution to heart and Papworth solution to lung. Lung function assessed by arterial pO2 at a standardised FIO2 was significantly better in groups 2 and 4 than in other groups. However, cardiac function as assessed by cardiac output, stroke work index and minute work index was significantly better in group 4 than in any other group. Overall, the combination of solutions in group 4 provided the most effective preservation in this model.

Oxygen free radical scavengers decrease reperfusion injury in lung transplantation

An in vivo canine model was used to assess the ability of an oxygen free radical scavenger to decrease reperfusion injury in lung transplantation. In 12 dogs, the left lungs were transplanted after they had been preserved for 24 hours at 4 degrees C after pulmonary artery flushing with modified Eurocollins solution. In 6 dogs, dimethylthiourea, a potent oxygen free radical scavenger, was added to the flush solution and was also given to the recipients just before reperfusion. In all animals, the contralateral pulmonary artery and bronchus were ligated and lung function was assessed for 12 hours or until death. Three dogs died prematurely in the control group, whereas only 1 dog died prematurely in the dimethylthiourea group. This resulted in a statistically significant difference in the average length of survival (p less than 0.05). Pulmonary artery and right atrial pressures were significantly lower in the dimethylthiourea group during the first 6 hours (p less than 0.05). Treatment with dimethylthiourea resulted in a significantly higher arterial oxygen tension at 4 hours, and intrapulmonary shunt tended to be lower. Thus, it would appear that dimethylthiourea has a protective effect on lungs preserved for 24 hours before transplantation in dogs.

Lung transplantation

The supply of donor organs remains extremely limited, and improved methods of maintaining the lungs of potential donors to allow for transplantation must be developed. Currently the upper limit of donor lung ischemic even with our "best" preservation techniques is approximately 4 to 6 hours. Improved methods for preservation will increase the supply of suitable lungs and will considerably simplify the logistics of transplantation just as has occurred with liver transplantation. Efficient use of donor organs remains of paramount importance. We recently performed two single-lung transplants utilizing lungs from one donor. Likewise, there is no reason why a lung could not be sent to another center for transplantation if the harvesting group uses only one lung. Sufficient progress has been achieved to date to warrant continued application of lung transplantation for end-stage pulmonary disease. With increasing experience, one can anticipate refinement of techniques and broader application of these procedures. Single lung transplantation, initially restricted to patients with end-stage pulmonary fibrosis, has now been successfully applied to patients with emphysema, pulmonary hypertension, and other conditions. Although transplantation currently can offer real benefit only to a limited number of persons, it serves to create hope for many others. An additional benefit may prove to be the interest and attention that transplantation focuses on patients with end-stage lung disease and on the pathophysiology of chronic respiratory failure. Knowledge gained may ultimately result in the prevention of many of the disorders for which lung transplantation currently offers the only hope.