Comparison of Incubation Solutions Prior to the Purification of Porcine Islet Cells

Excellent Islet Yields after 18-h Porcine Pancreas Preservation by Ductal Injection, Pancreas Preservation with MK Solution, Bottle Purification, and Islet Purification Using Iodixanol with UW Solution and Iodixanol with MK Solution

Successful islet isolation is the key to successful islet transplantation. Our group recently modified the islet isolation protocol to include pancreatic ductal injection of the preservation solution, pancreas storage in modified extracellular-type trehalose-containing Kyoto (MK) solution, and use of an iodixanol-based purification solution and bottle purification. In this study, we applied these methods to porcine islet isolation after 18-h pancreas preservation and compared two solutions with different compositions in bottle purification. Islet yield before purification was 651,661 ± 157,719 islet equivalents (IE) and 5576 ± 1538 IE/g pancreas weight. An IU solution was made by adding iodixanol to University of Wisconsin solution and an IK solution was made by adding iodixanol to MK solution. The efficacy of the two solutions for islet isolation was compared. There were no significant differences between the two purification methods with regard to islet yield, survival rate, purity, score, or stimulation index. These results indicate that our isolation protocol produces efficient islet yields from prolonged cold-stored pancreas and that IU and IK solutions are equally useful for islet purification.

Comparison of Tissue Loading Before and After the Creation of a Continuous Density Gradient in Porcine Islet Purification

The purification step is one of the most important and difficult procedures in islet isolation for pancreatic islet transplantation. We previously reported that a purification method using large plastic bottles effectively achieved a high yield of islets from the porcine pancreas. In this study, we evaluated the impact of the timing of tissue loading on porcine islet purification using large plastic bottles. One method involved loading digested tissue after creating a continuous density gradient (tissue after gradient [TAG]). The other method involved loading digested tissue before creating a continuous density gradient (tissue before gradient [TBG]). There were no significant differences between TAG and TBG in terms of the islet yield, rates of viability and purity, score, and in the stimulation index after purification. Furthermore, there were no marked differences in the attainability or suitability of post-transplantation normoglycemia. Our study shows the equivalency of these two methods of islet purification.

A Comparison of Pancreatic Islet Purification using Iodixanol with University of Wisconsin Solution and with Na-Lactobionate and Histidine Solution

Purification of pancreatic islets is an important step in islet isolation for islet transplantation. In this study, to investigate how a solution composed mainly of Na-lactobionate and histidine (HL) influences the purification of islets, iodixanol was added to a purified solution for porcine islet isolation. A solution (IU) made by adding iodixanol to University of Wisconsin solution and a solution (IHL) made by adding iodixanol to HL solution were used to evaluate the islet isolation performance. We noted no significant differences between the two purification methods with regard to the islet yield, survival rate or purity, score, or stimulation index. These results show that IHL solution is as useful as IU solution for islet purification.

Evaluation of Islet Purification Methods for Making a Continuous Density Gradient and Loading Tissue

Islet purification is one of the most important steps of islet isolation for pancreatic islet transplantation. We previously reported that a purification method using large plastic bottles effectively achieved a high yield of islets from porcine pancreas. In this study, we evaluated the methods for making a continuous density gradient and loading tissue. One method involved loading digested tissue on top of a continuous density gradient (top loading). The other method involved mixing digested tissue with low-density solution and then making a continuous gradient (mixed loading). There were no significant differences between the 2 purification methods in terms of the islet yield, rate of viability or purity, score, or in the stimulation index after purification. Furthermore, there were no marked differences in the attainability or suitability of posttransplantation normoglycemia. Our study shows the equivalency of these 2 methods of islet purification.

Comparison of Purification Solutions With Different Osmolality for Porcine Islet Purification

The osmolality of the purification solution is one of the most critical variables in human islet purification during islet isolation. We previously reported the effectiveness of a combined continuous density/osmolality gradient for the supplemental purification of human islets. We herein applied a combined continuous density/osmolality gradient for regular purification. The islets were purified with a continuous density gradient without osmolality preparation [continuous density/normal osmolality (CD/NO)] or continuous density/osmolality solution with osmolality preparation by 10× Hank's balanced salt solution (HBSS) [continuous density/continuous osmolality (CD/CO)]. The osmolality of the low-density solution was 400 mOsm/kg in both groups and that of the high-density solution was 410 mOsm/kg in the CD/NO group and 500 mOsm/kg in the CD/CO group. Unexpectedly, we noted no significant differences between the two solutions in terms of the islet yield, rate of viability and purity, score, stimulation index, or the attainability and suitability of posttransplantation normoglycemia. Despite reports that the endocrine and exocrine tissues of pancreata have distinct osmotic sensitivities and that high-osmolality solutions result in greater purification efficiency, the isolation and transplant outcomes did not markedly differ between the two purification solutions with different osmolalities in this study.

The Evaluation of Islet Purification Methods That Use Large Bottles to Create a Continuous Density Gradient

Islet purification is one of the most important steps of islet isolation for pancreatic islet transplantation. The most common method of islet purification is density gradient centrifugation using a COBE 2991 cell processor. However, this method can damage islets mechanically through its high shearing force. We recently reported that a new purification method using large plastic bottles effectively achieves a high yield of islets from the porcine pancreas. In the present study, we evaluated the methods of making a continuous density gradient. The gradient was produced with a gradient maker and two types of candy cane-shaped stainless steel pipes. One method was to use a "bent-tipped" stainless steel pipe and to load from a high-density solution to a low-density solution, uploading the stainless steel pipe. The other method was to use a regular stainless steel pipe and to load from a low-density solution to a high-density solution, leaving the stainless steel pipe in place. There were no significant differences between the two solutions in terms of the islet yield, rate of viability or purity, score, or the stimulation index after purification. Furthermore, there were no differences in the attainability or suitability of posttransplantation normoglycemia. Our study shows the equivalency of these two methods of islet purification.