Peripheral blood monocytes can differentiate into efficient insulin-producing cells in vitro

Background: Recent studies provide evidence that peripheral blood monocytes have the ability to differentiate into mesenchymal-like cells. The ability of cultured monocytes to differentiate and produce insulin in vitro is analysed in the present study. Methods: Peripheral blood monocytes were isolated from healthy donors and cultivated for fourteen days. Growth factors and liraglutide were used to induce pancreatic differentiation in most of the cultures. The growth factors were: monocyte colonystimulating factor, interleukin-3, hepatocyte growth factor and epidermal growth factor. The rest of the cultures were cultivated only with nutrient medium and human serum. Insulin levels were measured by an enzyme-linked immunosorbent assay. Cellular morphology was observed using optical and electron microscopy. Cell membrane receptors were detected by flow cytometry. Results: Monocytes were able to synthesize and excrete high levels of insulin after seven days in culture. A further increase in the excretion of insulin was observed after fourteen days. Cells were also able to differentiate and synthesize insulin, even if no growth factors were added to the culture medium. Some of the cultures were able to excrete insulin in a glucose-dependent manner. Differentiated monocytes were connected to neighbouring cells with axons and resembled the morphology of mesenchymal, dendritic and myeloid-progenitor cells. Cells retained their mature receptors and simultaneously developed immature receptors on their membrane. Conclusions: Monocytes can acquire morphological properties of multipotent cells when they are cultivated under specific conditions in vitro. Differentiated monocytes are able to synthesize and excrete insulin.