Damaging effect of subzero temperature (-4 degrees C) on rabbit renal function

The efficacy of ice recrystallization inhibitors in rat lung cryopreservation using a low cost technique for ex vivo subnormothermic lung perfusion

Although lung transplant remains the only option for patients with end-stage lung failure, short preservation times result in an inability to meet patient demand. Successful cryopreservation may ameliorate this problem; however, very little research has been performed on lung cryopreservation due to the inability to prevent ice nucleation or growth. Therefore, this research sought to characterize the efficacy of a small-molecule ice recrystallization inhibitor (IRI) for lung cryopreservation given its well-documented ability to control ice growth. Sprague-Dawley heart-lung blocks were perfused at room temperature using a syringe-pump. Cytotoxicity of the IRI was assessed through the subsequent perfusion with 0.4% (w/v) trypan blue followed by formalin-fixation. Ice control was assessed by freezing at a chamber rate of -5 °C/min to -20 °C and cryofixation using a low-temperature fixative. Post-thaw cell survival was determined by freezing at a chamber rate of -5 °C/min to -20 °C and thawing in a 37 °C water bath before formalin-fixation. In all cases, samples were paraffin-embedded, sliced, and stained with eosin. The IRI studied was found to be non-toxic, as cell membrane integrity following perfusion was not significantly different than controls (p = 0.9292). Alveolar ice grain size was significantly reduced by the addition of this IRI (p = 0.0096), and the addition of the IRI to DMSO significantly improved post-thaw cell membrane integrity when compared to controls treated with DMSO alone (p = 0.0034). The techniques described here provide a low-cost solution for rat ex vivo lung perfusion which demonstrated that the ice control and improved post-thaw cell survival afforded by IRI-use warrants further study.

Current techniques and the future of lung preservation

Although lung transplant remains the only option for patients suffering from end-stage lung failure, donor supply is insufficient to meet demand. Static cold preservation is the most common method to preserve lungs in transport to the recipient; however, this method does not improve lung quality and only allows for 8 h of storage. This results in lungs which become available for donation but cannot be used due to failure to meet physiologic criteria or an inability to store them for a sufficient time to find a suitable recipient. Therefore, lungs lost due to failure to meet physiological or compatibility criteria may be mitigated through preservation methods which improve lung function and storage durations. Ex situ lung perfusion (ESLP) is a recently developed method which allows for longer storage times and has been demonstrated to improve lung function such that rejected lungs can be accepted for donation. Although greater use of ESLP will help to improve donor lung utilization, the ability to cryopreserve lungs would allow for organ banking to better utilize donor lungs. However, lung cryopreservation research remains underrepresented in the literature despite its unique advantages for cryopreservation over other organs. Therefore, this review will discuss the current techniques for lung preservation, static cold preservation and ESLP, and provide a review of the cryopreservation challenges and advantages unique to lungs.

Subzero nonfreezing storage of isolated rat hepatocytes in University of Wisconsin solution

BACKGROUND

Various cryopreservation techniques have been investigated to elongate preservation time, however, most have failed to be clinically induced because of damage due to ice crystal formation. Subzero nonfreezing conditions could theoretically reduce organ metabolism without damage due to ice crystal formation. We evaluated the superiority of subzero nonfreezing storage compared with conventional hypothermic storage using isolated rat hepatocytes stored in University of Wisconsin (UW) solution without cryoprotectants.

METHODS

Hepatocytes of Wistar rats isolated by collagenase digestion were suspended in UW solution and divided into the following three groups: subzero nonfreezing group (-4 degrees C), zero nonfreezing group (0 degrees C), and control group (4 degrees C). They were stored for 48 hr at the temperatures indicated. After 24 and 48 hr of storage, we carried out a trypan blue exclusion test and a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, and measured lactate dehydrogenase release, lactic acid, ATP content, and the ability of hepatocytes to synthesize urea. After 48 hr of storage, morphological differences between the control group and the subzero nonfreezing group were investigated by scanning and transmission electron microscopy.

RESULTS

Significant improvements of the trypan blue exclusion test and ATP contents in the subzero nonfreezing group were observed. Lactic acid production was also significantly suppressed in the subzero nonfreezing group compared with that in the control group. The MTT assay value was significantly better at -4 degrees C than at 4 degrees C. The rate of urea synthesis at -4 degrees C was higher than that at 4 degrees C. Electron microscopy revealed that subzero nonfreezing delayed the lethal bleb-forming process of stored hepatocytes, which was followed by mitochondrial swelling, compared with the control group.

CONCLUSIONS

Subzero nonfreezing storage (-4 degrees C) in UW solution could provide better preservability for isolated rat hepatocytes with protection against hypoxic cell injury compared with conventional hypothermic storage (4 degrees C).

Introduction and removal of cryoprotective agents with rabbit kidneys: assessment by transplantation

Rabbit kidneys were perfused with up to 4 M glycerol or propane-1,2-diol (propylene glycol, PG) in three vehicle solutions: one normokalemic and made hypertonic with mannitol (HP5), one hyperkalemic but without mannitol (HP6), and one hyperkalemic and with mannitol (HP7). Subsequent function was assessed by autotransplantation. Up to 3 M glycerol in HP5 was well tolerated but not in HP6 or HP7. Conversely, up to 3 M PG in HP7 was compatible with excellent post-transplant function, but the same concentration in HP5 was severely damaging. PG (4 M) in either solution was severely injurious and no kidneys survived perfusion with this concentration. Vascular resistance was well controlled by the vehicle solutions with mannitol, but it was generally higher during perfusion with the hyperkalemic HP7 compared with the normokalemic HP5. No kidneys perfused with 3 M solutions of either of the cryoprotective agents and cooled briefly to -6 degrees C without freezing had any post-transplant function, and neither did kidneys perfused with 3 M PG or 4 M glycerol tolerate slow cooling to -80 degrees C and warming. The need to optimize perfusate composition for the CPA being used is clear, and the dramatic increase in toxicity of PG when the concentration exceeds 3 M supports the suggestion that mixtures of PG and glycerol should be considered. The observation of damage at high subzero temperatures, before freezing has occurred, requires further detailed study.

Beneficial effect of low concentrations of cryoprotective agents on short-term rabbit kidney perfusion

This report describes observations concerning the influence of the addition of 0.3 M cryoprotective agents (propylene glycol or glycerol) to Ringer's albumin solution used for rabbit kidney perfusion for periods of less than 4 and 24 hr. Endogenous creatinine clearance during short-term parabiotic perfusion on a shunt was used to evaluate function after perfusion. The findings were (A) Perfusion for less than 4 hr resulted in a significant loss of function by comparison with 1 hr ice-stored controls. (B) Continuing the perfusion for 24 hr resulted in a further significant fall in function. Much of the early perfusional injury seen in these two groups could be avoided by including 0.3 M cryoprotective agents in the perfusate.