Diabetes results from diminished functional β-cell mass. Small molecule inhibitors of Dual Specificity Tyrosine Phosphorylation Regulated Kinase 1A (DYRK1A) markedly increase human β-cell replication in vitro and in vivo. Furthermore, combination of DYRK1A inhibitors such as Harmine (H) with widely clinically used glucagon-like peptide 1 receptor agonists such as Exendin-4 (E) further enhance human β-cell proliferation. However, whether H+E combination increases human β-cell mass and improves glucose homeostasis in diabetic immunosuppressed mice transplanted with a marginal number of human islets is unknown. Human islets from 5-6 different adult healthy donors were transplanted under the kidney capsule (200 islets per kidney) of streptozotocin-induced diabetic immunodeficient Rag1-/- mice. At the time of transplantation, osmotic Alzet minipumps were implanted for continuous delivery of vehicle V, H, E and H+E for a period of 12 weeks. At the end of the study, human islet-bearing kidneys were harvested, labeled with insulin antisera and cleared using a modification of the iDISCO+ method. Imaging and analysis of the β-cell volume was done using the Light-sheet Ultramicroscope II and Imaris software. Transplanted diabetic mice who received the combination of H+E showed a significant increase of human β-cell volume up to 600% compared with mice treated with V or the drugs alone. This increase correlated with a significant increase in plasma human insulin levels, sustained normalization of blood glucose levels and significantly improved glucose tolerance. Our studies provide unequivocal documentation that treatment with the harmine and exendin-4 combination can lead to actual increases in human β-cell mass in diabetic conditions suggesting that β-cell replenishment might be possible in humans with diabetes. Disclosure K.A.Beliard: None. S.Stanley: None. A.Garcia-ocana: Consultant; Sun Pharmaceutical Industries Ltd. C.Rosselot: None. Y.Li: None. A.Alvarsson: None. P.Wang: None. K.Thakkar: None. D.Guevara: None. R.J.Devita: None. A.F.Stewart: None. Funding NIH/NIDDK 1R01DK105015-05.
