Influence of ultraviolet C bystander effect on inflammatory response in A375 cell on subsequent exposure to ultraviolet C or hydrogen peroxide.

Ultraviolet C (UVC) irradiation (λ: 200-280 nm) causes release of several secretory cytokines responsible for inflammation. Our objective was to investigate whether inflammatory response was also induced in bystander cells. For this purpose, the conditioned medium containing the released factors from UVC irradiated A375 cells was used in this study to evaluate the expression of inflammatory markers, such as tumour necrosis factor alpha (TNFα), nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and p38 mitogen-activated protein kinase (p38 MAPK) in its bystander cells. Inflammatory responses in bystander cells subjected to further irradiation by UVC or other damaging agent like H2O2 were also examined. It was observed that TNFα, NFκB and p38 MAPK were not induced in UVC-bystander cells, but their expression was suppressed in the UVC-bystander cells treated with UVC or H2O2. This lowering in inflammatory response might be due to smaller depletion in the reduced glutathione (GSH) content present in these treated bystander cells. The study indicated that UVC-induced bystander effect was an intrinsic protective response in cells, capable of suppressing inflammation induced in cells on exposure to damaging agents.

Some UV-bystander effects are mediated through induction of antioxidant defense in mammalian cells.

Bystander effect is the communication of signals from irradiated to unexposed neighboring cells which is often mediated through factors released from irradiated cells. We have attempted to investigate whether UV-bystander phenomenon can modulate the sensitivity of A375 cells and its mechanism. For this purpose, the conditioned medium from UVC-irradiated cells, which contained these released factors, was used to treat non-exposed cells. These cells were then subsequently treated with UVC or another genotoxicant H2O2. Cell viability was determined by Trypan blue-exclusion assay, DNA damage by flow cytometry analysis, ROS production by flow cytometry and microscopic analysis. Lipid peroxidation and antioxidant defense were assayed biochemically. Our findings revealed that exposure of non-irradiated cells to these factors induced increased in SOD and catalase activities which reverted to normal levels by 8 h. During this period, the released factors-treated cells were resistant to killing by UVC or H2O2 and induced DNA damage and lipid peroxidation were also lowered. This protection from cell killing was not present 8 h after exposure to these released factors. Our results suggested UV-bystander effect increased viability of cells through induction of antioxidant defense. This indicated UV-bystander phenomenon triggers protective response in cells.

Suppression of apoptosis leads to cisplatin resistance in V79 cells subjected to chronic oxidative stress.

We derived V79C cells from V79 cell line through chronic oxidative stress by H2O2. These cells demonstrated transformation-like stable changes. Our objective was to see how V79C cells would respond to cisplatin treatment and also to understand the mechanism of cisplatin-resistance, because resistance towards various chemotherapeutic agents is major cause of concern in cancer therapeutics. The sensitivity to cisplatin in these cells was observed by comparing the viability with that of parental V79 cells from colonogenic assay. The role of apoptotic death was investigated microscopically by Hoechst staining and from nucleosomal ladder formation in agarose gel. Release of cytochrome c from the mitochondria was determined by Western blotting. Caspase 9 and caspase 3 activities were estimated through fluorimetric assay. We found that V79C cells exhibited lower sensitivity towards killing by cisplatin through suppression of apoptotic cell death. Quantifying the release of cytochrome c in the cytoplasm and assay of caspase 9 and caspase 3 activities revealed that cisplatin resistance was due to inhibition of caspase-dependent apoptotic death pathways. These findings may aid in understanding the mechanism of cisplatin resistance in tumors arising from oxidative stress. Exogenous caspases may facilitate apoptotic death to sensitize such resistant cells.