Pronounced proliferation of non-beta cells in response to beta-cell mitogens in isolated human islets of Langerhans

The potential to treat diabetes by increasing beta-cell mass is driving a major effort to identify beta-cell mitogens. Demonstration of mitogen activity in human beta cells is frequently performed in ex vivo assays. However, disparities in the efficacy of beta-cell mitogens between studies led us to investigate the sources of this variability. We obtained 27 male (16) and female (11) human islet batches from multiple centers covering a range of donor ages (18-65 years) and BMI (16.4-38.5). Islets were kept intact or dispersed into single cells and cultured in the presence of the beta-cell mitogens harmine, glucose, and heparin-binding epidermal growth factor-like growth factor (HB-EGF), and subsequently analyzed for cell proliferation by immunochemistry or flow cytometry. Harmine and HB-EGF promoted human beta-cell proliferation, whereas the effect of glucose was assay-dependent. In addition, harmine potently stimulated alpha-cell proliferation and both harmine and HB-EGF increased proliferation of insulin- and glucagon-negative cells, including cytokeratin 19-positive cells. These results suggest that assessment of beta-cell mitogens requires complementary approaches and rigorous identification of cell identity. This is better achieved by flow cytometry that eliminates the subjectivity of visual scoring and enables simultaneous assessment of several endocrine and proliferation markers in higher numbers of cells.