Hypothermic perfusion preservation of the isolated dog lung

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

Implementation of an experimental isolated lung perfusion model on surgically resected human lobes

Isolated lung perfusion (ILP) is an ideal model to study treatment effects on a variety of pathologies. As published research mostly relies on rejected donor lungs or animal organs, this study investigates the use of surgically resected human lobes as an alternative and novel model for personalized experimental research. Ten surgically resected lobes were perfused in acellular and normothermic condition. The indication for surgery was lung cancer. Perfusion and ventilation were adapted to the size of the lobes and both functional and metabolic parameters were assessed during ILP. Patients (age 67.5 y (59–81)|♀n = 3|♂n = 7) underwent anatomic pulmonary lobectomy. Ischemic time between arterial ligation and ILP was 226 minutes (161–525). Median duration of ILP was 135 (87–366) minutes. Gas exchange and mechanical respiratory parameters remained steady during ILP (pulmonary venous pO₂ 196(151–219) mmHg | peak AWP: 14.5(11–22) cmH₂O). Metabolism stayed constant during ILP (Glucose consumption: 1.86 mg/min/L_TLC (95%CI: −2.09 to −1.63) | lactate production: 0.005 mmol/min/ L_TLC (95%CI: 0.004 to 0.007)). ILP of surgically resected human lobes is a feasible and promising method. By maintaining a near physiological setting, this model may pave the way for future experimental lung research including cancer research, transplantation, physiology, pharmacology and mechanical ventilation.

Lung protection during total cardiopulmonary bypass by isolated lung perfusion: preliminary results of a novel perfusion strategy

BACKGROUND

The present pilot study was conducted to evaluate the effect of isolated short-term lung perfusion during cardiopulmonary bypass (CPB) on inflammatory response and oxygenation.

METHODS

A total of 24 patients undergoing elective cardiac surgery with routine CPB were prospectively assigned to three groups. Group I (n = 7), control subjects receiving neither lung perfusion nor ultrafiltration; group II (n = 9), patients undergoing lung perfusion; and group III (n = 8), patients undergoing lung perfusion plus ultrafiltration. Lung perfusion consisted of single-shot hypothermic pulmonary artery perfusion with oxygenated blood. Proteins indicative of leukocyte activation and lung injury were measured in plasma and bronchoalveolar lavage fluid (BALF). The alveolar-arterial oxygen gradient (A-aDO2) and the oxygenation index (PO2/FiO2) were also determined.

RESULTS

Oxygenation values were best preserved in group III, followed by group II. After CPB, elastase-alpha1-proteinase inhibitor complex had increased in plasma in all groups; in BALF it increased in groups I and II, but not in group III. Alpha2-macroglobulin increased significantly in BALF in group I but not in groups II and III.

CONCLUSIONS

These preliminary results provide some evidence that single-shot hypothermic lung perfusion with oxygenated blood at the beginning of CPB may have a protective effect on the lungs, especially when combined with ultrafiltration.

Extended lung preservation with the use of hibernation trigger factors

BACKGROUND

The complications of preserving lungs for transplantation are well known, with successful transplantation only being assured by preservation times of 5 to 6 hours or less. If a new method of consistent lung preservation could be identified, lung transplantation could be extended to many patients. We have previously reported lung preservation times averaging 14.8 hours using a multiorgan autoperfusion block infused with physiologic saline solution as a model. When plasma from deeply hibernating woodchucks (Marmota monax) or the delta opioid DADLE was infused into the multi-organ block, lung preservation times increased threefold to 45 hours.

METHODS

In this study, we examined the effect of infusing plasma containing the hibernation induction trigger molecule on lung preservation for transplantation using a multiorgan autoperfusion block.

RESULTS

This study demonstrated that successful orthotopic transplantation of single canine lungs is possible after 24 to 33 hours of preservation when the lung has been maintained with plasma containing the hibernation induction trigger molecule.

CONCLUSIONS

Theoretically, hibernation induction trigger could be administered to donors before lung harvest in an effort to extend lung preservation times.

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.

Lung preservation techniques

Some of the barriers to successful lung transplantation include the lack of acceptable methods for ischemic protection and the absence of reliable systems for preservation. The lung response to 60 minutes of warm ischemia basically consists of alveolar-capillary edema and disruption, mitochondria swelling, interstitial hemorrhage, significantly depressed pulmonary function, elevation of pulmonary vascular resistance, and considerable drop in levels of glucose, phospholipids, and adenosine triphosphate. The tolerance to warm ischemia increases to several hours with the use of different systems of ventilatory assistance with or without positive end-expiratory pressure. Several methods of preservation have been attempted: hypothermia, hyperbaria, and hypothermic pulsatile or nonpulsatile perfusion. Hypothermic pulsatile perfusion appears to offer longer periods of protection than the other methods. Longer periods of ischemia and extended preservation may be made possible by advances in the use of drug protection during warm ischemia and the utilization of intracellular colloid or noncolloid solutions for hypothermic storage or hypothermic pulsatile perfusion.

Prevention of acute pulmonary edema during isolated perfusion for 24 hours

Fifty-nine canine lungs were perfused with cryoprecipitated plasma, silica gel fraction, or modified silica gel fraction (MSGF) af different perfusate pressures for periods up to 24 hours under hypothermic conditions. High perfusate pressures accounted for all poor perfusion results. The use of MSGF at a low perfusate pressure protected all the lungs from the appearance of pulmonary edema during perfusion, and the morphology was consistently maintained for 24 hours.