Comparison of six different methods to assess UVA cytotoxicity on reconstructed epidermis. Relevance of a fluorimetric assay (the calcein-AM) to evaluate the photoprotective effects of α-tocopherol

Novel fluorescence assay using calcein-AM for the determination of human erythrocyte viability and aging

BACKGROUND

A highly sensitive, fast, and simple flow cytometric assay to assess human red blood cell (RBCs) viability and aging is reported.

METHODS

The assay described in this report is based on the use of acetoxymethyl ester of calcein (calcein-AM), a fluorescein derivative and nonfluorescent vital dye that passively crosses the cell membrane of viable cells and is converted by cytosolic esterases into green fluorescent calcein, which is retained by cells with intact membranes and inactive multidrug resistance protein. The loss of calcein can be easily determined by flow cytometry, and the cytosolic localization of esterases was demonstrated by spectrofluorometric analyses.

RESULTS

We found that RBCs incubated with Ca(2+), which induces a rapid and modulated self-death that shares several features with apoptosis (Bratosin et al., Cell Death Differ 2001;8:1143-1156), externalized phosphatidylserine and lost calcein staining and cytosolic adenosine triphosphate content. Double labeling using phycoerythrin-labeled annexin-V and calcein-AM showed that the decrease of esterase activity is an early event that precedes the externalization of phosphatidylserine residues. In addition, this assay allowed us to distinguish young and aged RBCs isolated by ultracentrifugation in a self-forming Percoll gradient and can be considered as a reliable marker of RBC aging.

CONCLUSIONS

Calcein-AM assay may represent a wide application for assessing RBC viability, particularly in blood banks.

Monitoring the cellular activity of a cultured single cell by scanning electrochemical microscopy (SECM). A comparison with fluorescence viability monitoring

The respiratory activities of cultured HeLa cells were monitored at a single cell level using scanning electrochemical microscopy (SECM) that produces images of the localized distribution of oxygen around the cell. The change in the cellular activity was traced after exposures to KCN, ethyl alcohol and the antibiotic drug, Antimycin A. The results were compared with those from the conventional fluorescence monitoring using Calcein-AM that is sensitive to deformation of the cell membrane. The SECM-based measurement follows the decrease in the cellular activity upon exposure to KCN and Antimycin A more rapidly than the fluorescence-based measurements, demonstrating that SECM is suitable for studying the cellular influence of respiration inhibitors.

Anethole dithiolethione regulates oxidant-induced tyrosine kinase activation in endothelial cells

Interaction between neutrophils and endothelial cells is one of the first steps in the functional response of polymorphonuclear neutrophils (PMN), and is necessary for their migration toward damaged tissues. PMN activation, leading to their adhesion to and migration between endothelial cells, is part of a complex phenomenon that can be altered in pathological situations such as the ischemia-reperfusion syndrome, in which large numbers of PMN are recruited to the tissue and release reactive oxygen species (ROS) near the vessel wall. ROS have been implicated in the pathogenesis of various inflammatory diseases. The increased adhesion of PMN to ROS-stimulated endothelial cells involves an increase in tyrosine phosphorylation of a tyrosine kinase focal adhesion kinase (p125FAK) and several cytoskeleton proteins, including paxillin and p130 cas. We examined the role of glutathione (GSH) in the regulation of this adhesion phenomenon and in the increased tyrosine phosphorylation induced by ROS. For this purpose we used anethole dithiolthione (ADT), which increases the glutathione synthesis by activating gamma-glutamyl-cysteine synthetase. We found that ADT reduced both PMN adhesion to ROS-stimulated human umbilical vein endothelial cells (HUVEC) and tyrosine phosphorylation of p125FAK and paxillin. ADT increased redox status by increasing intracellular GSH content in oxidized cells. These results show that GSH can reverse the effect of oxidation on tyrosine kinase activation and phosphorylation, and thus plays an important role in cell signaling. They also confirm the antioxidant activity of ADT.

Effects of all-trans retinoic acid on UVB-irradiated human skin substitute

Retinoids are frequently used for treatment of photodamaged skin. We wished to find out whether photodamage could be attenuated by applying all-trans retinoic acid (RA) during repetitive irradiation. For this purpose, we used human cutaneous cells and tissue: pure monolayer cultures containing either keratinocytes or fibroblasts, and human skin substitute (SS) containing both cell types. All cultures were exposed to 8 mJ/cm(2) of UVB and were immediately treated with RA (0, 1.5, or 3 microM). The irradiation and RA treatment protocol was repeated until the cells of the nonirradiated culture had reached confluence. In the irradiated SS, RA preserved the structure (epidermal stratification and differentiation) and ultrastructure (well-organized intermediate filaments and desmosomes) in a state comparable to that observed in nonirradiated SS. As well RA maintained secretion of basement membrane components (laminin and type-IV collagen). Following irradiation, cutaneous cells also displayed more proliferative capacity when SS was treated. In the irradiated monolayer cultures, RA maintained the proliferative capacity of fibroblasts and decreased their differentiation whereas the opposite effect was seen on keratinocytes. In conclusion, RA clearly helps protect human skin against photodamage induced by repeated exposure to UVB.

Applications of reconstructed skin models in pharmaco-toxicological trials

The development of new cosmetic formulations requires precise assessment of their safety and efficacy. Today, legislation demands quality control combined with severe safety measures, as well as a limited use of animals for such testing (European Community directive 93/35/EEC). Consequently, safety assessment protocols are oriented towards in vivo tests on human volunteers and in vitro alternative methods to animal use, especially tissue engineered skin substitutes. In this paper, dermal and skin equivalents developed in the laboratory are described. The applications of reconstructed epidermis and skin substitutes for pharmaco-toxicological trials are also discussed. These tissue models have been shown to be very useful tools to assess cutaneous irritation, phototoxicity, photoprotection and to perform efficacy tests of cosmetic molecules and finished products. In conclusion, the authors are confident that these in vitro models can contribute to reduce animal use for routine toxicity testing.