Photoreactivation of ultraviolet radiation-induced release of arachidonic acid from marsupial cells

Arachidonic acid metabolites mediate the radiation-induced increase in glomerular albumin permeability

Radiation-induced renal injury is characterized by proteinuria, hypertension, and progressive decline in renal function. We have previously shown that in vivo or in vitro irradiation of glomeruli with a single dose of radiation (9.5 Gy) increases glomerular albumin permeability (P(alb)) within 1 hr. The current studies tested the hypothesis that this early radiation-induced increase in P(alb) is caused by the release of arachidonic acid and by the generation of specific arachidonic acid metabolites. Glomeruli obtained from WAG/Rij/MCW rats and cultured rat glomerular epithelial and mesangial cells were studied after irradiation (9.5 Gy, single dose). Arachidonic acid release and eicosanoid synthesis by glomeruli or cultured glomerular cells were measured after irradiation, and the effect of inhibitors of phospholipase A2 (PLA2) and cyclooxygenase (COX) on the irradiation-induced increase in P(alb) was assessed. Arachidonic acid release was demonstrated within 10 mins of irradiation of isolated glomeruli and monolayer cultures of glomerular epithelial and mesangial cells. Prostaglandin F(2alpha) (PGF(2alpha)) and PGE2 release was increased after irradiation of isolated glomeruli. Blocking arachidonic acid release or COX activity before irradiation completely prevented the increase in P(alb). COX inhibition immediately after irradiation also diminished the radiation-induced increase in P(alb). We conclude that arachidonic acid and its COX metabolites play an essential role in the early cellular changes that lead to the radiation-induced increase in P(alb). Understanding of the early epigenetic effects of irradiation may lead to new intervention strategies against radiation-induced injury of normal tissues.

The protective effect of indomethacin on photocarcinogenesis in hairless mice

Orally administered indomethacin at 10-600 micrograms per mouse per day has been shown to inhibit UV radiation-induced erythema dose responsively. At the higher doses tested (200-600 micrograms) there was evidence of drug toxicity. Indomethacin administered orally at 20 micrograms per mouse daily during photocarcinogenesis induction both increased the probability of remaining tumour free and reduced the average tumour multiplicity. When indomethacin was administered only during the UV irradiation period (initiation), a reduction in tumour multiplicity and in the progression of tumours to malignant squamous cell carcinomas was observed; when administered only during the post-irradiation promotion period, there was a significant increase in the probability of remaining tumour free. Thus both tumour initiation and promotion by UV radiation appear to be indomethacin-sensitive, possibly affected by different mechanisms.

Modulation of interferon-gamma-induced HLA-DR expression on the human keratinocyte cell line SCC-13 by ultraviolet radiation

Cell surface expression of major histocompatibility determinants on epidermal keratinocytes is a characteristic feature of a number of inflammatory dermatoses and in all likelihood is caused by diffusion of human leukocyte antigen (HLA)-DR-inducing cytokines from cells present in the dermal mononuclear cell infiltrate. Many of these same disorders respond to ultraviolet (UV) radiation phototherapy. Using the human SCC-13 keratinocyte cell line as a model, UV radiation was found to inhibit interferon-gamma-induced HLA-DR expression. Inhibition correlated closely with decreased steady-state levels of HLA-DR mRNA. These findings provide evidence that the therapeutic effect of UV radiation phototherapy may be mediated by its capacity to down-regulate cytokine-induced keratinocyte HLA-DR expression.