Vitamin D protects keratinocytes from deleterious effects of ionizing radiation.
BACKGROUND
Radiotherapy can induce severe skin responses that may limit the clinically acceptable radiation dose. The responses include erythema, dry and moist desquamation, erosions and dermal-epidermal blister formation. These effects reflect injury to, and reproductive failure of, epidermal cells and may also be due to dysregulation of the tissue remodelling process caused by excessive proteolytic activity. Calcitriol, the hormonally active vitamin D metabolite, protects keratinocytes from programmed cell death induced by various noxious stimuli.


OBJECTIVE
To examine whether calcitriol protects proliferating keratinocytes from the damage inflicted by ionizing radiation under conditions similar to those employed during radiotherapy.


METHODS
Autonomously proliferating HaCaT keratinocytes, used as a model for basal layer keratinocytes, were irradiated using a linear accelerator. Cell death was monitored by vital staining, executioner caspase activation, lactic dehydrogenase release and colony formation assay. Induction of matrix metalloproteinase-9 was assessed by gelatinase activity assay and mRNA determination. Levels of specific proteins were determined by immunoblotting.


RESULTS
Treatment with calcitriol inhibited both caspase-dependent and -independent programmed cell death occurring within 48 h of irradiation and increased the colony formation capacity of irradiated cells. These effects may be attributable to inhibition of the c-Jun NH(2)-terminal kinase cascade and to upregulation of the truncated antiapoptotic isoform of p63. Treatment with the hormone also attenuated radiation-induced increase in matrix metalloproteinase-9 protein and mRNA levels.


CONCLUSIONS
The results of this study suggest that active vitamin D derivatives may attenuate cell death and excessive proteolytic activity in the epidermis due to exposure to ionizing radiation in the course of radiotherapy.
Langberg
M
M
The Basil and Gerald Felsenstein Medical Research Center, Sackler Faculty of Medicine, Tel Aviv University, Beilinson Campus, Rabin Medical Center, Petah-Tikva 49100, Israel.
Rotem
C
C
Fenig
E
E
Koren
R
R
Ravid
A
A
D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death; D049109:Cell Proliferation / Q000528:radiation effects*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D066298:In Vitro Techniques; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism / Q000528:radiation effects; D012333:RNA, Messenger; D011832:Radiation Injuries / Q000517:prevention & control*; D011839:Radiation, Ionizing; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014807:Vitamin D / Q000378:metabolism / Q000494:pharmacology*; D014815:Vitamins / Q000494:pharmacology*
D012333:RNA, Messenger; D014815:Vitamins; D014807:Vitamin D; D053148:Caspase 3; D020780:Matrix Metalloproteinase 9