ZINC ATTENUATES UVA-DEPENDENT LABILE IRON INCREASE IN HUMAN DERMAL FIBROBLASTS: IMPLICATIONS FOR SKIN AGEING

Introduction To protect the cell from damaging oxidative stress induced by Fenton reactions, the cytosolic labile iron pool (LIP) is normally kept low and tightly regulated. These reactions are initiated by interactions between iron and hydrogen peroxide and can be prolonged and increased with ascorbate. The source of cytosolic labile iron is unclear. It has been suggested that lysosomes are the main source of iron, since protease inhibitors reduce leakage of lysosomal contents including iron after UVA (ultraviolet light) exposure. However, the time resolution of the changes in enzyme activity required to assess lysosomal leakage is too long to establish whether lysosomal damage occurs due to secondary response to iron release from other sources, particularly ferritin. Other methods are therefore required to clarify the source of cytosolic labile iron. Zinc is a redox-inert metal that has anti-oxidant, anti-inflammatory and anti-proliferative properties which is notably reduced in patients with subclinical carotid atherosclerosis, acute coronary syndrome and heart failure. Zinc is known to block iron diffusion via ferritin threefold channels and can therefore be used as a tool to examine UV-induced iron release from ferritin. Methods A fluorescence probe (FeRhoNox-1) specific for ferrous ion was used to determine the time dependent changes in human fibroblasts following exposure to UVA irradiation. Since it is known that low concentrations of zinc block iron diffusion via ferritin threefold channels, we reasoned that pre-incubating skin cells with low concentrations of ZnCl2 would inhibit iron release from ferritin after photo-activation by UVA. Confluent monolayers of human dermal fibroblasts were incubated overnight with 10 µM FeSO4 and 0, 10 and 40 µM ZnCl2, before being loaded with FeRhoNox-1 and exposed to UVA (360 nm) for 1–10 min (8–80 J/m2), with fluorescent readings gathered at 1 min intervals. Results The control cell iron dependent fluorescent signal increased by approximately 100% after 10 min UVA irradiation compared to pre-UV baseline (p Conclusions These Results suggest that UVA causes a significant increase in skin fibroblast LIP and hence oxidative stress which may exacerbate the ageing phenotype of dermal cells. This LIP is likely to be sourced mainly from ferritin since this is completely blocked by relatively low concentrations of extracellular ZnSO4.