|Preliminary Large Animal Studies
In this section we present some of our early large animal experimental results from 1998 to 1999. The crucial test for any bio-artificial pancreas is the large animal allograft. For reasons we have explained we prefer the canine (dog) allograft. Between September, 1998 and June, 1999 we did five such experiments at the University of Chicago (Click here to read about the first such experiment). Two produced little useful data. But three of the experiments provided data crucial to improving sheet fabrication methods. Using these methods we began large animal preclinical studies in February, 2000 at the University of Cincinnati (click here for summary).
A summary of three canine allograft experiments follows. You can link to a more detailed report of each experiment.
Pre clinical animal experiment, Chicago 1, summary.
After sheet implantation the fasting plasma glucose levels gradually increased for 7 days. Plasma C-peptide levels rose fourfold before reaching a plateau at 0.18nmol/L. The sheets were explanted after 25 days, and were processed for histology. The animal was maintained for an additional three days, during which time there was no significant change in the fasting plasma glucose or C-peptide titers.
Histological examination of the explanted sheet showed the overcoats had delaminated from the core, exposing the islets within. There was an accumulation of fibroblasts surrounding the sheet. No attempt was made to measure residual islet function by in vitro assays.
From this experiment we confirmed successful encapsulation of islets without affecting their viability prior to implant. However the first attempts at making sheets with cells showed the cell-free overcoats did not sufficiently laminate them to the islet-containing core. We have since modified this chemistry to eliminate delamination.
Pre clinical animal experiment, Chicago 2, summary.
These sheets were not reinforced, and were found to roll up into a "Jelly roll" in the peritoneal cavity. The plasma glucose was not normalized, C-peptide production was negligible and histological evaluation of the explanted sheets showed evidence of fibroblast accumulation between the rolls of the sheet. Despite this, some of the encapsulated islets still contained insulin after 14 days in vivo.
From this experiment it was clear the sheet would have to be reinforced and sutured in place to keep it flat. It was also learned that the overcoats were well bonded to the core, completely and uniformly protecting the islets from direct exposure to the host cells.
Pre clinical animal experiment, Chicago 3, summary.
This dog maintained normal blood sugars for several days after implantation, during which significant C-peptide was detectable. These measures were not persistent, and progressively more injected insulin was required to control blood sugars.
After explantation, modest fibrosis was observed on several of the sheets. However, static incubation experiments showed one of these sheets produced insulin in response to the secretagogue caffeine. Insulin production was not increased in response to high glucose. This may reflect beta-cell dysfunction subsequent to sustained elevated plasma glucose levels.