Adult stem cells--perspectives in treatment of metabolic diseases.

There is currently great excitement and expectation concerning the differential potential of adult stem cells or adult cells with capacity of differentiation. As the body of work concerning transdifferentiation of somatic stem cells and bone marrow derived stem cells grows, the number of critics increases steadily questioning the reliability of reported findings. So scientists are now challenged more and more to prove that resulting differentiated somatic cells originated from somatic adult stem cell through a transdifferentiation process. Phenomenons such as fusion of cells have to be ruled out and the origin of the differentiated cell has to be determined by specific techniques i.e. in situ hybridisation. Cellular mimicry through uptake of specific factors out of the medium is questioned to be the reason for cells staining positive for Insulin. Some multipotent adult stem cells can cross lineage boundaries and differentiate into somatic cells of other lineages after being relocated. Bone marrow cells have been described to have the greatest plasticity among adult stem cells regenerating damaged liver or myocardium. It has been proposed that the differentiation of bone marrow derived adult stem cells occurs naturally even in healthy organs as a physiologic process of tissue-regeneration. Others believe that organ damage is essential to induce transdifferentiation by release of organ specific microenvironmental factors. We here try to constitute necessary data which should be demonstrated to give substantial evidence for transdifferentiation of newly characterized cells including exclusion of fusion, phagocytosis or DNA uptake, description of the outset cell, differentiation into all three germ layers and functional parameters.