The use of peptide-delivery to protect human adipose-derived adult stem cells from damage caused by the internalization of quantum dots

Label of human bone mesenchymal stem cells with CdSe/ZnS quantum dots (QDs) had been demonstrated to impair cell functions and activities. In the present study, QDs delivered by two different routes, Pep-1-labeled QDs (LQ) and PolyFect transfected QDs (TQ), were utilized to assess the effects of delivery mechanisms on various cellular responses of the QDs-internalized human adipose-derived adult stem cells (hADAS). Examination of labeled cells by flow cytometry and laser scanning confocal microscopy showed that LQ had higher fluorescence intensity due to the cluster formation and their distribution in cytoplasma while TQ were preferentially accumulated at perinuclear regions. The fluorescence intensity of the LQ group was still higher than that of the TQ group at 28 days after labeling, though cellular LQ were partitioned after initial cell division. Pep-1 but not PolyFect delivery facilitated QDs to escape from lysosome degradation. Pep-1 delivery of QDs rescued the cells from the negative effects caused by the internalized QDs on cell proliferation and on the expressions of CD29 and CD105 as well as osteogenic and chondrogenic-associated lineage markers. The same effect was also observed in the expression of alkaline phosphatase activity, calcium deposition and secretion of chondrogenic matrices (GAG and collagen type II) in micromass culture. These indicated that Pep-1-delivered QDs may serve appropriately to track the hADAS employed in cell therapy/tissue engineering applications. The results also suggested that the endo-/lysosome degradation of QDs may depend on different surface coatings and critically influence the differentiation of hADAS. (c) 2007 Elsevier Ltd. All rights reserved.