The researchers found that the labeling efficiency in each of the (U) SPIOs varied significantly when different populations of stem cells were compared. "This means that the labeling methods are likely to need to be optimized for each cell type," said Dr. Crabbe. "Over time we saw a dilution of the (U) SPIOs and a decrease of iron in cells." the non-invasive imaging plays an important role in post-transplant stem cell research, but questions whether the contrast agents used to track transplanted stem cells in vivo by MRI has an impact on the cells had largely gone unanswered to this study. On the question of whether (U) SPIO labeling biological affects the cells, the researchers found that "any significant alteration" of the phenotypes of cells and that the label "does not significantly alter the differentiation of stem cells." "Sinerem ® decreased proliferation of MMSC while Sinerem ® and ® Endorem affected rMAPC proliferation rate, although prolonged culture up to seven days, led to the restoration of the proliferation rate," said Dr. Crabbe. "We also found that increasing concentrations of Sinerem ® and ® Endorem were necessary for cell labeling to accomplish similar detectability of MRI." The researchers concluded that it will be necessary to evaluate the effectiveness of labeling cells for each combination of new contrast agent intended to be followed in vivo by MRI. In addition, the effect on the biological behavior of cells must be examined. They noted that their results were limited to examining the effects of labeling on the proliferation, not differentiation. "Although the labeling of stem cells with MRI is promising, there are some limitations," concluded Dr. Crabbe. "The optimal particle is necessary that can be taken without the need for potentially toxic agents. There is also the problem of the dilution of particles over time, the cells divide. When the grafted cells continue to proliferate, the signal loss is produced. " According to Dr. Julio Voltarelli, professor of clinical medicine and clinical immunology at the University of Sao Paulo, Brazil and section editor of cell transplantation has been a lack of knowledge of survival and distribution of stem cell populations used in vivo therapy. "Many studies have tried to close this gap by radioactive or nonradioactive labeling of cells to follow their fate in the body," said Dr. Voltarelli. "However, this work shows that the labeling may alter the behavior of stem cells, such as proliferative potential, and provide biased information, compared with nonlabeled cells."
