Cell loss in isolated human islets occurs by apoptosis

Abstract

Purified islet allografts have largely failed to maintain long-term glucose homeostasis in human recipients, and the reasons for this are unclear. It is noteworthy, however, that islet isolation destroys or removes cellular and noncellular elements of the pancreas that could play an important role in supporting islet survival. The purpose of this study was to determine whether human islet isolation leads to the induction of programmed cell death. Human islets were enzymatically isolated from cadaveric donor pancreata using Liberase or Collagenase P, purified over a discontinuous BSA gradient, then cultured in RPMI 1640 at 37°C in 5% CO2 for ≤7 days. Islets were examined daily by routine histology and immunocytochemistry for islet hormones, DNA fragmentation [cell death; enzyme-linked immunosorbent assay (ELISA) and TUNEL assay] and for transglutaminase (TG) activity, two indicators of apoptosis. TG activity and DNA fragmentation increased by 1,000% and 1,890%, respectively (p < 0.05). This corresponded to the appearance of pyknotic nuclei on light microscopy, the presence of apoptotic bodies on electron microscopy, and the demonstration of TUNEL-positive cells. These were present primarily in a distribution that corresponded to the insulin-immunoreactive cells. At 5 days, 31.4 ± 2.2% of islet cells were TUNEL positive. In summary, apoptosis of islet cells appears soon after islet isolation, and involves primarily the β cell. This is the first report of apoptosis of islet cells after human islet isolation. The loss of β-cell mass could be implicated in the failure of islet transplantation and merits further investigation.