Amount and Distribution of Collagen in the Pancreas Have No Effect on Porcine Islet Isolation Outcome

Xenotransplantation of porcine islets of Langerhans is considered to be a possible alternative for clinical islet transplantation. However, porcine islet isolation procedures have been shown to produce highly variable yields between pigs with similar backgrounds. One of the variables that could account for this is the collagen substrate within the pancreas. We determined the amount and distribution of collagen within porcine pancreata as they determined islet isolation outcomes. This study involved the histological examination of 140 porcine pancreata (64 juvenile and 76 adult) and islet isolation from 58 adult organs. To quantify the amount of collagen, tissue samples were stained with Sirius Red. Collagen distribution was determined by assessing the presence of collagen in the endocrine-exocrine interface (the “islet capsule”), in tissue samples double-stained with Sirius Red and anti-insulin. Strong variation in total collagen was observed in both adult and juvenile pigs. The mean collagen content in the juvenile group was significantly lower than that in the adult group. Apparently, the pancreas undergoes a process of fibrosis as pigs age. The vast majority of islets from both adult and juvenile pancreata had no or only a limited collagen capsule. However, islet encapsulation was highly variable between pancreata. We observed no significant correlation between total collagen content or the percentage islet encapsulation and islet yield. Although total collagen content and islet encapsulation show great variability between pancreata, neither the amount nor the distribution of collagen affected porcine islet isolation outcome.