Introduction: Current human islet culture methods are suboptimal and cannot sustain islets beyond a few days. This limits access to clinical islet transplantation (IT). Gastrin is a gut hormone with a wide range of salutary effects. Increased gastrin was associated with better glycemic control in individuals with diabetes. In an ongoing study, we found that gastrin treatment enhanced IT outcomes in individuals with type 1 diabetes. Herein, the ability of a gastrin analog, Gastrin-17, to sustain human islets cultured long-term was assessed.  

Method: Human islets (150-200 IEQ) were embedded in 3D hydrogel and cultured with CMRL1066 supplemented media containing Gastrin-17 (0-1000 nM) for four weeks (n=5 islet donor preparations). Islet mass recovery and viability were assessed. Islet survival was expressed as the survival index (recovery rate multiplied by viability) and normalized to the control group (without Gastrin-17). Islet mRNA expression was determined by RT-PCR and protein levels by Milo single-cell Western blot. Islet function was assessed using the static glucose-stimulated insulin secretion assay.

Results: Gastrin-17, in a dose-dependent manner, increased cell mass recovery and viability. The highest islet recovery was at a concentration of 500 nM (>70%) and the highest viability was at 250 nM (>90%). Islet survival increased by over 15% in the Gastrin-17 group compared to the controls (survival index 1.15±0.02 at 250 nM and 1.16±0.04 at 750 nM, P<0.001 and P<0.05 vs. control, respectively). The effect of Gastrin-17 on survival was especially marked in islets from donors with lower HbA1c levels (4.9-5.3%) (survival index 1.11±0.01 at 100 nM, P<0.005 vs. control, n=3). Gastrin-17 (100 nM) significantly decreased mRNA expression of inflammatory genes including IL1B, TNF, IL6, and IL8 (P<0.01) while mRNA and protein levels of endocrine genes remained stable. Noteworthy, high Gastrin-17 (500 nM) increased long-term cultured islet insulin release above fresh islets (stimulation index 2.3±0.2 vs. 1.5±0.2 respectively, P<0.05).

Conclusion: Gastrin-17 promoted the long-term survival and function of 3D-hydrogel cultured human islets. Gastrin-17 also suppressed inflammatory gene activity. Discreet concentration thresholds were noted for each specific beneficial effect of Gastrin-17.