An improved perfusate for hypothermic renal preservation. I. Initial in vitro optimization based on tissue electrolyte transport

CPA toxicity screening of cryoprotective solutions in rat hearts

In clinical practice, donor hearts are transported on ice prior to transplant and discarded if cold ischemia time exceeds ∼5 h. Methods to extend these preservation times are critically needed, and ideally, this storage time would extend indefinitely, enabling improved donor-to-patient matching, organ utilization, and immune tolerance induction protocols. Previously, we demonstrated successful vitrification and rewarming of whole rat hearts without ice formation by perfusion-loading a cryoprotective agent (CPA) solution prior to vitrification. However, these hearts did not recover any beating even in controls with CPA loading/unloading alone, which points to the chemical toxicity of the cryoprotective solution (VS55 in Euro-Collins carrier solution) as the likely culprit. To address this, we compared the toxicity of another established CPA cocktail (VEG) to VS55 using ex situ rat heart perfusion. The CPA exposure time was 150 min, and the normothermic assessment time was 60 min. Using Celsior as the carrier, we observed partial recovery of function (atria-only beating) for both VS55 and VEG. Upon further analysis, we found that the VEG CPA cocktail resulted in 50 % lower LDH release than VS55 (N = 4, p = 0.017), suggesting VEG has lower toxicity than VS55. Celsior was a better carrier solution than alternatives such as UW, as CPA + Celsior-treated hearts spent less time in cardiac arrest (N = 4, p = 0.029). While we showed substantial improvement in cardiac function after exposure to vitrifiable concentrations of CPA by improving both the CPA and carrier solution formulation, further improvements will be required before we achieve healthy cryopreserved organs for transplant.

Cryopreservation of rat hippocampal slices by vitrification

Although much interest has attended the cryopreservation of immature neurons for subsequent therapeutic intracerebral transplantation, there are no reports on the cryopreservation of organized adult cerebral tissue slices of potential interest for pharmaceutical drug development. We report here the first experiments on cryopreservation of mature rat transverse hippocampal slices. Freezing at 1.2 degrees C/min to -20 degrees C or below using 10 or 30% v/v glycerol or 20% v/v dimethyl sulfoxide yielded extremely poor results. Hippocampal slices were also rapidly inactivated by simple exposure to a temperature of 0 degree C in artificial cerebrospinal fluid (aCSF). This effect was mitigated somewhat by 0.8 mM vitamin C, the use of a more "intracellular" version of aCSF having reduced sodium and calcium levels and higher potassium levels, and the presence of a 25% w/v mixture of dimethyl sulfoxide, formamide, and ethylene glycol ("V(EG) solutes"; Cryobiology 48, pp. 22-35, 2004). It was not mitigated by glycerol, aspirin, indomethacin, or mannitol addition to aCSF. When RPS-2 (Cryobiology 21, pp. 260-273, 1984) was used as a carrier solution for up to 50% w/v V(EG) solutes, 0 degree C was more protective than 10 degrees C. Raising V(EG) concentration to 53% w/v allowed slice vitrification without injury from vitrification and rewarming per se, but was much more damaging than exposure to 50% w/v V(EG). This problem was overcome by using the analogous 61% w/v VM3 vitrification solution (Cryobiology 48, pp. 157-178, 2004) containing polyvinylpyrrolidone and two extracellular "ice blockers." With VM3, it was possible to attain a tissue K(+)/Na(+) ratio after vitrification ranging from 91 to 108% of that obtained with untreated control slices. Microscopic examination showed severe damage in frozen-thawed slices, but generally good to excellent ultrastructural and histological preservation after vitrification. Our results provide the first demonstration that both the viability and the structure of mature organized, complex neural networks can be well preserved by vitrification. These results may assist neuropsychiatric drug evaluation and development and the transplantation of integrated brain regions to correct brain disease or injury.

Physical problems with the vitrification of large biological systems

Vitrification is an attractive potential pathway to the successful cryopreservation of mature mammalian organs, but modern cryobiological research on vitrification to date has been devoted mostly to experiments with solutions and with biological systems ranging in diameter from about 6 through about 100 microns. The present paper focuses on concerns which are particularly relevant to large biological systems, i.e., those systems ranging in size from approximately 10 ml to approximately 1.5 liters. New qualitative data are provided on the effect of sample size on the probability of nucleation and the ultimate size of the resulting ice crystals as well as on the probability of fracture at or below Tg. Nucleation, crystal growth, and fracture depend on cooling velocity and the magnitude of thermal gradients in the sample, which in turn depend on sample size, geometry, and cooling technique (environmental thermal history and thermal uniformity). Quantitative data on thermal gradients, cooling rates, and fracture temperatures are provided as a function of sample size. The main conclusions are as follows. First, cooling rate (from about 0.2 to about 2.5 degrees C/min) has a profound influence on the temperature-dependent processes of nucleation and crystal growth in 47-50% (w/w) solutions of propylene glycol. Second, fracturing depends strongly on cooling rate and thermal uniformity and can be postponed to about 25 degrees C below Tg for a 482-ml sample if cooling is slow and uniform. Third, the presence of a carrier solution reduces the concentration of cryoprotectant needed for vitrification (CV). However, the CV of samples larger than about 10 ml is significantly higher than the CV of smaller samples whether a carrier solution is present or not.

Variation of cooling rate and concentration of dimethyl sulfoxide on rabbit kidney function

Rabbit kidney function was assessed in vitro after cryoprotection with either 3 or 4 M dimethyl sulfoxide. The introduction and removal of the cryoprotectant was carried out in a stepwise progressive manner and the removal in a stepwise progressive manner with hypertonic mannitol solutions. This in vitro model can be shown to respond to various ischemic-like states resulting in poor or absent function. Active tubular transport can be demonstrated. It has been used by many authors as an intermediate step prior to the ultimate test of reimplant and contralateral nephrectomy. Variations in the rate of cooling at cryoprotection levels of 3 and 4 M dimethyl sulfoxide concentration (Me2SO) were carried out. In general, at 3 M concentration of Me2SO, creatinine clearance, sodium and glucose reabsorption are preserved with a fair degree of success after cooling to -10, -15, and -20 degrees C in our model, when the rate of cooling to these levels is 1.0 degree C/min. When a cooling rate of 0.5 degree C/min is used, renal function is significantly reduced whether the final temperature is -10, -15, or -20 degrees C. Control rabbit kidneys will tolerate 4 M concentration of Me2SO and give fairly good function. When cooled to -15 or -20 degrees C, there is poor function at 0.1 and 0.5 degrees C/min. Fair function is obtained at the rate of 1 degree C/min to -10 degrees C. Therefore, at cryoprotectant levels of 3 and 4 M Me2SO, kidney function as assayed by in vitro perfusion, is better when the cooling rate is 1.0 degree C/min.

Comparison of cold storage and perfusion of dog livers on function of tissue slices

We compared how two methods of hypothermic preservation affect physiological functions of tissue slices of dog liver. Livers were preserved by either (i) cold storage (CS) in Collins' solution or (ii) continuous perfusion (P) with a perfusate, containing hydroxyethyl starch, sodium gluconate, adenosine, and potassium phosphate, recently developed in our laboratory. Livers were cold stored for 6 to 8, 24, or 48 hr, and perfused for 24 or 72 hr. Tissue slices of preserved livers were incubated at 30 degrees C and analyzed for volume control, electrolyte-pump activity (K and Na), and adenine nucleotide concentration. Also, mitochondria were isolated after preservation to quantify respiratory activity. Slice functions of livers preserved for short periods (6 to 8 hr by CS and 24 hr by P) were similar to those for control livers. After normothermic incubation, the mean (+/- SD) water content of tissue (expressed per unit dry mass of tissue) was 2.3 +/- 0.3 kg/kg for control, 2.6 +/- 0.4 kg/kg for 6- to 8-hr CS, and 2.5 +/- 0.5 kg/kg for 24-hr P. Longer periods of preservation resulted in cell swelling, and water content was 3.3 +/- 0.4 kg/kg for 24- to 48-hr CS and 2.8 +/- 0.3 kg/kg for 72-hr P. The mean (+/- SD) K/Na ratio was nearly normal for livers preserved for short periods: 3.7 +/- 0.5 for control, 4.1 +/- 0.2 for 6- to 8-hr CS, and 3.3 +/- 0.4 for 24-hr P.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional preservation of the mammalian kidney. VI. Viability assessment of rabbit kidneys perfused at 25 degrees C with dimethyl sulfoxide in RPS-2

The study utilizes an ex vivo perfusion model to evaluate the effects of warm perfusion (25 degrees C) with two K+-rich vehicle solutions (RPS-2 and solution A) on whole rabbit kidneys. The suitability of the solutions as vehicles for introducing cryoprotectant concentrations (2.8 and 3.5 M) of dimethyl sulfoxide (Me2SO) and the effects of the addition of albumin to RPS-2 are also tested. Albumin (5 g/dl) does not appreciably improve the renal perfusion dynamics of RPS-2. Results indicate that both RPS-2 and solution A serve as effective vehicles for the introduction of 2.8 M Me2SO, and the continued investigation of the RPS-2/Me2SO protocol is advocated.

Factors influencing renal cryopreservation. I. Effects of three vehicle solutions and the permeation kinetics of three cryoprotectants assessed with rabbit cortical slices

A renal cortical slice model was used to assess the effects on viability of three vehicle solutions-Krebs-Henseleit (K-H), solution A, and RPS-2--at 25 degrees C. After 120 min incubation no differences in [K+]/[Na+] ratios were found. Tracer techniques were used to study the osmotic effects and permeation kinetics at 25 degrees C of three cryoprotectants (dimethyl sulfoxide (Me2SO), ethylene glycol, and glycerol) and the effect of the vehicle solution (K-H or RPS-2) on Me2SO kinetics. It was found that Me2SO was most permeable and ethylene glycol least, and that ethylene glycol had unusual effects which suggest that it may not act as a simple solute. Differences were found when Me2SO was introduced in K-H and RPS-2 that are believed to be related to the binding properties of Me2SO to cell constituents.

Experimental observations on the mode of action of "intracellular" flush solution

Experiments were conducted using rabbit kidneys stored on ice for 48 hr to elucidate the mode of action of "intracellular" flush solutions. Measurements were made of renal function on a shunt and they were correlated with blood flow and the efficiency of the mechanical expulsion of red cells. By comparison with unflushed, ice-stored kidneys, near complete mechanical expulsion of blood by 30 to 60 min of continuous perfusion with hypertonic Ringer's albumin resulted in significantly higher blood flow with little gain in function. Similarly, increasing the content of nonelectrolyte in Ringer's albumin improved blood flow but not function. A simple flush with a low ionic strength sodium solution (LIE), containing impermeant anions and glucose was superior to that with Ringer's albumin. A high-potassium version of the low ionic strength solution (LIC) was in turn significantly better than LIE for kidney preservation by simple flushing and ice storage. These results were interpreted to mean that whereas mechanical flushing is a relatively minor component of the action of flush solutions, the major benefit results from a reduced sodium and elevated potassium content in the presence of impermeant anions. The primary importance of prevention of cell swelling by the inclusion of nonelectrolytes in "extracellular" flush solutions, is questioned.