Temperature profiles of different cooling methods in porcine pancreas procurement

Abstract

Porcine islet xenotransplantation is a promising alternative to human islet allotransplantation. Porcine pancreas cooling needs to be optimized to reduce the warm ischemia time (WIT) following donation after cardiac death, which is associated with poorer islet isolation outcomes. This study examines the effect of four different cooling Methods on core porcine pancreas temperature (n = 24) and histopathology (n = 16). All Methods involved surface cooling with crushed ice and chilled irrigation. Method A, which is the standard for porcine pancreas procurement, used only surface cooling. Method B involved an intravascular flush with cold solution through the pancreas arterial system. Method C involved an intraductal infusion with cold solution through the major pancreatic duct, and Method D combined all three cooling Methods. Surface cooling alone (Method A) gradually decreased core pancreas temperature to <10 °C after 30 min. Using an intravascular flush (Method B) improved cooling during the entire duration of procurement, but incorporating an intraductal infusion (Method C) rapidly reduced core temperature 15-20 °C within the first 2 min of cooling. Combining all methods (Method D) was the most effective at rapidly reducing temperature and providing sustained cooling throughout the duration of procurement, although the recorded WIT was not different between Methods (P = 0.36). Histological scores were different between the cooling Methods (P = 0.02) and the worst with Method A. There were differences in histological scores between Methods A and C (P = 0.02) and Methods A and D (P = 0.02), but not between Methods C and D (P = 0.95), which may highlight the importance of early cooling using an intraductal infusion. In conclusion, surface cooling alone cannot rapidly cool large (porcine or human) pancreata. Additional cooling with an intravascular flush and intraductal infusion results in improved core porcine pancreas temperature profiles during procurement and histopathology scores. These data may also have implications on human pancreas procurement as use of an intraductal infusion is not common practice.

Keywords: cold preservation; islet xenotransplantation; organ cooling; pancreas procurement.

Figure 1

Illustration depicts the different core pancreas temperature profiles for each cooling Method: surface cooling alone (Method A, the current practice), intravascular (arterial) flush (Method B), intraductal infusion (Method C), and combined intravascular flush with intraductal infusion (Method D). Note the rapid cooling following an intraductal infusion of cold preservation solution (CPS), and the improved sustained cooling with an intravascular flush with CPS.

Figure 2

Calculated average amount of energy removed and estimated core temperature drop (ΔT) during the first 10 minutes of cold ischemia time in a standardized 350-gram pancreas procured using surface cooling only (Method A, n=4), surface cooling and an intravascular flush (Method B, n=13), surface cooling and an intraductal infusion (Method C, n=4) and combined method with surface cooling, an intravascular flush, and an intraductal infusion (Method D, n=3).

Figure 3

Representative histology from pancreata cooled by Methods A, B and D. Pancreatic tissue cooled using Method A (surface cooling) exhibited moderate features of autolysis and many of the islet cells have partially condensed nuclear chromatin. Pancreatic tissue cooled using Method C (intraductal infusion) showed mild autolysis, nuclear condensation or lysis and some islet cells exhibit cytoplasmic hypereosinophilia. Exocrine cells may present some pyknotic nuclei and cytoplasmic condensation. Pancreatic tissue cooled using Method D (surface cooling combined with an intravascular flush and an intraductal infusion) exhibited minimal autolysis. Furthermore, very few of the islet cells exhibited cytoplasmic hypereosinophilia and nuclear pyknosis, and cell morphological details are more easily distinguishable with exocrine granules being well-preserved in samples taken from pancreata cooled by Method D.

Figure 4

Plot of necrosis/autolysis scores from biopsies of pancreata cooled using Methods A, C and D. The scores were significantly worse in pancreata cooled only with surface cooling (Method A) as compared to pancreata cooled by intraductal infusion (Method C) or the combined approach (Method D). Lines and error bars represent the mean ± standard errors.