Impact of porcine islet size on cellular structure and engraftment after transplantation: adult versus young pigs.

OBJECTIVES: To study the impact of porcine islet size on structural properties and cellular engraftment. METHODS: The endocrine structure and collagen/vascular localization in pig islets were studied before and after enzymatic isolation on the pancreas from 6 young and 6 adult Landrace pigs. Isolated islets from both pig types were transplanted under the kidney capsula of diabetic nude rats to assess cellular engraftment. RESULTS: In comparison with adult pig pancreata, a significantly greater number of small beta cells (<100 microm) were observed before and after isolation (82% vs. 32%, respectively, P < 0.005) from young pig pancreata. Small islets (<100 microm) showed a peripheral vascular structure, whereas large islets showed a more centralized vascular organization, thereby providing protection during the enzymatic digestion procedure. The islet endocrine structure was not affected by the islet size, but a loss of glucagon cells (-7.9%, P < 0.005) was observed in large isolated islets. The purity of islet preparation was better with pancreata from adult than young donors (86% vs. 64%, respectively, P < 0.05). A lack of engraftment was observed for small islets from young pig donors as compared with large islets from adult donors. CONCLUSIONS: Large and well-structured islets, mainly found in adult pig pancreata, probably possess a better potential for cellular engraftment due to centralized vascularization and collagen distribution.