Human mesenchymal stem cells promote cancer motility and cytokine secretion in vitro.

Interactions of human mesenchymal stem cells (hMSC) with tumors are controversially discussed since there is evidence for both tumor progression as well as tumor inhibition by hMSC. The objective of the present study is to investigate whether hMSC support cell motility and cytokine secretion in a head and neck squamous cell carcinoma cell line (HLaC 78). A spheroid model was generated in which the ultrastructure of spheroids was analyzed using scanning electron microscopy (SEM). The migration capability was monitored in a monolayer as well as in a spheroid model. The variation in migration and secretion of interleukin (IL)-6, IL-8 and vascular endothelial growth factor (VEGF), as well as the expression of the multidrug resistance gene (MDR-1) was investigated. Finally, the alteration in the cell cycle was analyzed by flow cytometry. SEM showed a tight cell-cell contact with extensive secretion of extracellular matrix. The migration and invasion capability of HLaC 78 was enhanced by hMSC. Cancer cell motility was also increased by hMSC as well as secretion of the cytokines IL-6, IL-8 and VEGF. hMSC did not induce the expression of MDR-1 in HLaC 78, and there was no alteration in the cell cycle of HLaC 78 after cocultivation with hMSC. Our results confirm the important role of hMSC in cancer biology since both an enhancement of cell motility as well as cytokine secretion could be shown. However, based on these findings and those in the current literature, caution must be applied when using hMSC as a carrier for tumor therapy in cancer treatment.

DiI labeling of human adipose-derived stem cells: evaluation of DNA damage, toxicity and functional impairment.

INTRODUCTION: Adipose tissue-derived stem cells (ASCs) have become the primary focus of tissue engineering research. To understand their functions and behavior in in vitro and in vivo models, it is mandatory to track the implanted cells and distinguish them from the resident or host cells. A common labeling method is the use of fluorescent dyes, e.g. the lipophilic carbocyanine dye, DiI. This study aimed to analyze potential DNA damage, toxicity and impairment of the functional properties of human ASCs after labeling with DiI. METHODS: Cytotoxicity was measured using the MTT assay and DNA damage was determined by means of the comet assay. Potential apoptotic effects were determined using the annexin V-propidium iodide test. Differentiation potential was evaluated by trilineage differentiation procedures in labeled and unlabeled ASCs. Proliferation as well as migration capability was analyzed, and the duration and stability of DiI labeling in ASCs during in vitro expansion was observed over a period of 35 days. RESULTS: DiI labeling did not cause genotoxic effects 15, or 30 min or 24 h after the labeling procedure, and there were no cytotoxic effects until 72 h afterwards. No impairment of proliferation or migration capability or differentiation potential could be determined. However, after 35 days, only 37% of labeled cells could be detected using the fluorescence microscope, which indicates a decrease in staining stability during in vitro expansion. CONCLUSION: DiI is a convenient method for ASCs labeling which causes no toxic effects and does not impair the proliferation, migration or differentiation potential of ASCs after the labeling procedure.

Aspects of nitrogen dioxide toxicity in environmental urban concentrations in human nasal epithelium.

Cytotoxicity and genotoxicity of nitrogen dioxide (NO(2)) as part of urban exhaust pollution are widely discussed as potential hazards to human health. This study focuses on toxic effects of NO(2) in realistic environmental concentrations with respect to the current limit values in a human target tissue of volatile xenobiotics, the epithelium of the upper aerodigestive tract. Nasal epithelial cells of 10 patients were cultured as an air-liquid interface and exposed to 0.01 ppm NO(2), 0.1 ppm NO(2), 1 ppm NO(2), 10 ppm NO(2) and synthetic air for half an hour. After exposure, genotoxicity was evaluated by the alkaline single-cell microgel electrophoresis (Comet) assay and by induction of micronuclei in the micronucleus test. Depression of proliferation and cytotoxic effects were determined using the micronucleus assay and trypan blue exclusion assay, respectively. The experiments revealed genotoxic effects by DNA fragmentation starting at 0.01 ppm NO(2) in the Comet assay, but no micronucleus inductions, no changes in proliferation, no signs of necrosis or apoptosis in the micronucleus assay, nor did the trypan blue exclusion assay show any changes in viability. The present data reveal a possible genotoxicity of NO(2) in urban concentrations in a screening test. However, permanent DNA damage as indicated by the induction of micronuclei was not observed. Further research should elucidate the effects of prolonged exposure.

The differentiation of hMSCs counteracts their migration capability and pro-angiogenic effects in vitro.

Human mesenchymal stem cells (hMSCs) have been applied therapeutically in numerous clinical trials. The pro-angiogenic effects of hMSCs, as well as their strong tumor tropism, have been shown both in vitro and in vivo. Some studies suggest using hMSCs as potential drug-carriers for tumor therapy. In previous investigations by our group, the pro-tumorigenic effects of hMSCs on head and neck squamous cell carcinoma (HNSCC) were shown. However, the influence of hMSCs on tumor vascularization as well as the possibility of its inhibition are yet to be elucidated. The cytokine patterns of the HNSCC cell line FaDu, native hMSCs (hMSCs-nat), hMSCs differentiated into adipocytes (hMSCs-adip) and osteocytes (hMSCs-ost) were evaluated. Human umbilical vein endothelial cells (HUVECs) were co-cultured with FaDu cells, hMSCs-nat, hMSCs-adip and hMSCs-ost. The capillary tube formation assay was applied. Furthermore, the migration capability of hMSCs-nat, hMSCs-adip and hMSCs-ost towards FaDu cells was measured in a Transwell system. Spheroids were cultured from hMSCs-nat, FaDu cells and DiI-labeled HUVECs. FaDu cells, hMSCs-nat, hMSCs-adip and hMSCs-ost released a wide range of cytokines and growth factors, e.g., IL-6, IL-8, IL-10, GRO and MCP. In the capillary tube formation assay, HUVECs generated significantly longer tubes after co-cultivation with hMSCs-nat as compared to HUVECs alone and FaDu. Differentiation into adipocytes and osteocytes counteracted the tube formation. The adipogenic differentiation did not alter hMSC motility, whereas osteogenic differentiation significantly inhibited hMSC migration. Generation of multi-cellular spheroids from hMSCs-nat, FaDu cells and DiI-labeled HUVECs was possible. Florescence microscopy revealed that all HUVECs were present in the spheroid core. Taken together, hMSCs-nat have a pro-angiogenic effect. The effects are counteracted by the differentiation of hMSCs towards osteogenic and adipogenic lineages. The differentiation of stem cells into different lineages may be a promising solution to generating carriers for cancer therapy without pro-tumorigenic properties.

Effects of salinomycin on human bone marrow-derived mesenchymal stem cells in vitro.

Various hypotheses on the origin of cancer stem cells (CSCs) exist, including that CSCs develop from transformed human bone marrow mesenchymal stem cells (hBMSC). Since the polyether antibiotic salinomycin selectively kills CSCs, the present study aims to elucidate the effects of salinomycin on normal hBMSC. The immunophenotype of hBMSC after salinomycin exposure was observed by flow cytometry. The multi-differentiation capacity of hBMSC was evaluated by Oil Red O and van Kossa staining. Cytotoxic effects of salinomycin were monitored by the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) assay. Furthermore, spheroid formation and migration capacity were assessed. There were no differences in the immunophenotype and multi-differentiation capacity of hBMSC induced by salinomycin treatment. Cytotoxic effects were observed at concentrations of 30 µM and above. Neither the migration capability nor the ability to form spheroids was affected. Essential functional properties of hBMSC were unaffected by salinomycin. However, dose-dependent cytotoxicity effects could be observed. Overall, low dose salinomycin showed no negative effects on hBMSC. Since mesenchymal stem cells from various sources respond differently, further in vitro studies are needed to clarify the effect of salinomycin on tissue-specific stem cells.

Ex vivo toxicity of nitrogen dioxide in human nasal epithelium at the WHO defined 1-h limit value.

Current pollution limits indicating potential harm to human health caused by nitrogen dioxide have prompted a variety of studies on the cytotoxicity and genotoxicity of nitrogen dioxide (NO2) in vitro. The present study focuses on toxic effects of NO2 at the WHO defined 1-h limit value of 200 µg NO2/m(3) air, equivalent to 0.1 ppm NO2. Nasal epithelial mucosa cells of 10 patients were cultured as an air-liquid interface and exposed to 0.1 ppm NO2 for 0.5 h, 1 h, 2 h and 3 h and synthetic air as negative control. After exposure, analysis of genotoxicity was performed by the alkaline single cell microgel electrophoresis (comet) assay and by the micronucleus test. Depression of proliferation and cytotoxic effects were checked by the micronucleus assay and the trypan blue exclusion assay. The experiments demonstrated significant DNA fragmentation even at the shortest exposure duration of half an hour in the comet assay. The amount of DNA fragmentation significantly increased with extended NO2 exposure durations. The amount of DNA fragmentation increased with extended exposure durations to synthetic air at a significantly lower level as compared to NO2 exposure. Micronucleus inductions were seen only at the longest exposure duration of 3h. There were no changes in proliferation seen in the micronucleus assay under any experimental setup. Moreover, no signs of necrosis, apoptosis or changes in viability were detected. Data demonstrate genotoxicity of NO2 at concentrations found in the urban atmosphere during short exposure durations. DNA alterations in the micronucleus assay at an exposure time of 3h indicate a significant DNA alteration possibly being hazardous to humans.