Intercellular communication and maintenance of islet cell mass--implications for islet transplantation

The major emphasis in islet transplantation has been the development of methods to enhance islet purity. This focus assumes that islets do not require support from other cellular elements of the pancreas. We chose to examine a possible duct-islet interaction because of the embryologic origin of islets from ductal epithelium.

Duct and islet cells were prepared by collagenization of hamster pancreas and purified on a bovine serum albumin gradient. Primary duct cultures were passaged twice. Duct-conditioned medium was collected from the tertiary cultures. Three groups of cultures were established: group 1, 100 islets/plate in minimal medium (Dulbecco's modified Eagle medium/F12); group 2, 100 islets + 40 duct fragments/plate in Dulbecco's modified Eagle medium/F12; and group 3, 100 islets/plate+duct-conditioned medium. After a 3-day incubation, tritiated thymidine (1 microCi/ml) was added for 24 hours. The islets were separated from the ducts by handpicking and then sonicated. DNA was measured (microgram) fluorometrically and tritiated thymidine incorporation, a measure of cell proliferation, was determined in trichloroacetic acid-precipitated material by liquid scintillation. Data (mean +/- SEM) were compared by two-tailed Student's t test.

Tritiated thymidine incorporation into islet cells in minimal medium (81.1 +/- 24.6 disintegrations per minute [dpm]/microgram DNA [n = 8 plates]) was less than 25% (p < 0.001) of that of islet cells cocultured with ducts (323.2 +/- 54.5 dpm/micrograms DNA [n = 6]) or with duct-conditioned medium (389.7 +/- 27.6 dpm/micrograms DNA [n = 5]).

Pancreatic duct epithelium can stimulate islet cell proliferation in a paracrine manner.