The effect of a hydrogen sulfide releasing molecule (Na2S) on the cold storage of livers from cardiac dead donor rats. A study in an ex vivo model.

Liver transplantation is currently the preferred treatment option for end-stage liver disease. Donation after cardiac death was a common practice in the early years of organ donation before brain death criteria were established. Those organs were subjected to variable periods of warm ischemia that might intensify cold ischemia/reperfusion injuries. In the present, shortage of brain dead donors has led to the reassessment of organ donation after cardiac death. Since many cytoprotective roles have been describe for H2S during ischemia/reperfusion on a variety of tissues, we hypothesized that graft exposure to this bioactive gas might improve preservation of non-heart beating donated organs. Therefore, to establish a rat model of donation post-cardiac arrest and using this approach to judge H2S delivery effects on graft hypothermic preservation, were the main objectives of this investigation. Cardiopulmonary arrest was induced in sedated rats by overload of potassium (K(+)). Livers were surgically removed and subsequently stored in HTK Solution (Histidine-tryptophan-ketoglutarate) at 0-4°C. After 24 h of hypothermic preservation, livers were rewarmed in an ex vivo model. Three experimental groups were established as follows: I--Livers procured before cardiac death and cold stored 24 h in HTK (BCD); II--Livers procured after cardiac death (45 min) and cold stored 24 h in HTK (ACD); III--Livers procured after cardiac death (45 min) and cold stored 24 h in HTK+10 µM Sodium Sulfide (Na2S) (ACD-SS). Data suggest that after 45 min of warm ischemia, viability parameters assessed during reperfusion in the ex vivo model were significantly impaired. Real time PCR revealed that after ex vivo reperfusion there is an increased expression of HO-1 and TNF-α and a modest drop in Bcl-2 mRNA, which could be interpreted as the cellular response to the hypoxic insult sustained during warm ischemia. On the other hand, warm ischemic livers exposed to H2S during cold storage, improved microcirculation, morphology and viability parameters during ex vivo reperfusion and showed significant modulation of HO-1 mRNA expression. In conclusion, HTK supplementation with Na2S arose as a potential treatment to recover non-heart beating harvested organs. Furthermore, an appropriate model of cardiac dead liver donors was successfully developed.

DESIGN OF A SIMPLE SLOW COOLING DEVICE FOR CRYOPRESERVATION OF SMALL BIOLOGICAL SAMPLES.

BACKGROUND: Slow cooling is a cryopreservation methodology where samples are cooled to its storage temperature at controlled cooling rates. OBJECTIVE: Design, construction and evaluation of a simple and low cost device for slow cooling of small biological samples. MATERIALS AND METHODS: The device was constructed based on Pye's freezer idea. A Dewar flask filled with liquid nitrogen was used as heat sink and a methanol bath containing the sample was cooled at constant rates using copper bars as heat conductor. RESULTS: Sample temperature may be lowered at controlled cooling rate (ranging from 0.4°C/min to 6.0°C/min) down to ~-60°C, where it could be conserved at lower temperatures. An example involving the cryopreservation of Neuro-2A cell line showed a marked influence of cooling rate over post preservation cell viability with optimal values between 2.6 and 4.6°C/min. CONCLUSION: The cooling device proved to be a valuable alternative to more expensive systems allowing the assessment of different cooling rates to evaluate the optimal condition for cryopreservation of such samples.

A modular perfused chamber for low- and normal-temperature microscopy of living cells.

An inexpensive modular perfused chamber (MPC) designed for low- and normal-temperature live-cell imaging is presented. The device consists of four lathed pieces of stainless steel assembled as a cylindrical open chamber that can hold either round or square glass coverslips. The chamber is connected to a thermal-bath operating with recirculation. For image acquisition at 4°C, cooled air is blown toward the coverslip surface to prevent condensation. Principal advantages of this device are thermal stability in the sample environment, rapid response to changes in temperature set point, and easy sample insertion. The device enables the study of dynamic processes in cells governed by large temperature differences such as those imposed by hypothermic preservation of cells (0-4°C) followed by rewarming to normothermia (37°C). The capabilities of the MPC were demonstrated by monitoring the internalization of fluorescent quantum dots (QDs) in rat hepatocytes after hypothermic storage and during rewarming with an inverted microscope.