Arachidonic metabolism and radiation toxicity in cultures of vascular endothelial 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.

Effects of Lipochromin and Levosinum in the modulation of radiation-induced injury to pig skin

Pig skin was used as a model to study the effectiveness of two topically applied creams, Lipochromin and Levosinum, in modifying the development of both early and late radiation damage to pig skin. Irradiated skin sites that received daily topical application of Levosinum or Lipochromin after exposure were compared with sites on the contralateral flank of the same animal that received irradiation only. Irradiation was with graded doses of 90Sr/90Y beta-rays. Incidence of moist desquamation (acute) and ischaemic dermal necrosis (late) were used as end-points. The latency period for the development of moist desquamation and its healing time was also assessed. The latency period for the development of moist desquamation in this model ranged from 4.00-6.75 weeks. There was no significant difference between the cream treatment and control sites. Application of Levosinum shortened the healing time of moist desquamation at each dose level by 5-10 days. In three out of four dose levels used, this shortening of the healing time was statistically significant (p < 0.03). Treatment with these topical applications also reduced the incidence of late dermal necrosis and increased the ED50 values for the incidence of dermal necrosis. This increase in ED50 values was equivalent to a dose modification factor of 1.11-1.13.

Initiation of non-neoplastic late effects: the role of endothelium and connective tissue

While early radiation lesions might be a direct consequence of parenchymal cell loss, late-radiation injury most probably develops as a consequence of functional perturbations that may involve both parenchymal and nonparenchymal elements. Damage to blood vessels and consequent perturbations in blood flow and endothelial physiology play an important role in the development of late effects. The development of late-radiation damage has been studied in three different tissue systems: the skin, kidney and central nervous system. The results suggested that damage to vascular tissue played a major role in the development of radiation-induced late effects.

Amelioration of both early and late radiation-induced damage to pig skin by essential fatty acids

PURPOSE

To evaluate the possible role of essential fatty acids, specifically gamma-linolenic and eicosapentaenoic acid, in the amelioration of early and late radiation damage to the skin.

METHODS AND MATERIALS

Skin sites on the flank of 22-25 kg female large white pigs were irradiated with either single or fractionated doses (20 F/28 days) of beta-rays from 22.5 mm diameter 90Sr/90Y plaques at a dose rate of approximately 3 Gy/min. Essential fatty acids were administered orally in the form of two 'active' oils, So-1100 and So-5407, which contained gamma-linolenic acid and a mixture of that oil with eicosapentaenoic acid, respectively. Oils (1.5-6.0 ml) were given daily for 4 weeks prior, both 4 weeks prior and 10-16 weeks after, or in the case of one single dose study, just for 10 weeks after irradiation. Control animals received a 'placebo' oil, So-1129, containing no gamma linolenic acid or eicosapentaenoic acid over similar time scales before and after irradiation. Acute and late skin reactions were assessed visually and the dose-related incidence of a specific reaction used to compare the effects of different treatment schedules.

RESULTS

A reduction in the severity of both the early and late radiation reactions in the skin was only observed when 'active' oils were given over the time course of the expression of radiation damage. Prior treatment with oils did not modify the radiation reaction. A 3.0 ml daily dose of either So-1100 or So-5407 given prior to, but also after irradiation with single and fractionated doses of beta-rays produced the most significant modification to the radiation reactions, effects consistent with dose modification factors between 1.06-1.24 for the acute reactions of bright red erythema and/or moist desquamation, and of 1.14-1.35 for the late reactions of dusky/mauve erythema and dermal necrosis. There was the strong suggestion of an effect produced by the 'placebo' oil, So-1129, after higher daily doses of oil.

CONCLUSIONS

Essential fatty acids can modulate normal tissue reactions when given over the time when radiation damage is normally expressed. Dose modification factors suggest that a > or = 10% higher dose is required to produce the same level of normal tissue injury. Clinical application of selected essential fatty acids at appropriate doses may lead to a significant increase in the therapeutic gain in patients treated for cancer by radiotherapy.

Membrane-derived second messenger regulates x-ray-mediated tumor necrosis factor alpha gene induction

Cells adapt to adverse environmental conditions through a wide range of responses that are conserved throughout evolution. Physical agents such as ionizing radiation are known to initiate a stress response that is triggered by the recognition of DNA damage. We have identified a signaling pathway involving the activation of phospholipase A2 and protein kinase C in human cells that confers x-ray induction of the tumor necrosis factor alpha gene. Treatment of human cells with ionizing radiation or H2O2 was associated with the production of arachidonic acid. Inhibition of phospholipase A2 abolished radiation-mediated arachidonate production as well as the subsequent activation of protein kinase C and tumor necrosis factor alpha gene expression. These findings demonstrate that ionizing radiation-mediated gene expression in human cells is regulated in part by extranuclear signal transduction. One practical application of phospholipase A2 inhibitors is to ameliorate the adverse effects of radiotherapy associated with tumor necrosis factor alpha production.

Differences in leucocyte-endothelium interactions between normal and adenocarcinoma bearing tissues in response to radiation

Previously, we demonstrated that the interaction between leucocytes and endothelial cells in tumour tissues is greatly diminished compared with normal tissues under several induced inflammatory conditions. Radiation has been reported to cause release of inflammatory mediators and to promote neutrophil adhesions to cultured endothelial monolayers. In this study, we tested the hypothesis that radiation would cause increased leucocyte rolling and adhesion in both tumour and normal tissues. We examined these two parameters in response to 6 Gy of gamma-radiation in mammary adenocarcinomas implanted into rat skinfold window chambers as well as normal (i.e. non-tumour-bearing) preparations. Leucocyte rolling and adhesion were measured in terms of flux of rolling leucocytes (F(rolling)) and density of adhering leucocytes (D(adhering)) in microvessels. F(rolling) and D(adhering) were measured in two groups of preparations: irradiated and control. In normal preparations, F(rolling) and D(adhering) were both increased significantly by radiation. In contrast, in adenocarcinoma-bearing preparations, F(rolling) and D(adhering) were either unchanged (in the tumour centre) or reduced (in tumour periphery and the normal tissue surrounding the tumour) by radiation. Radiation did not cause changes in haemodynamics in these preparations, thus the observed changes in leucocyte rolling and adhesion could not be accounted for by haemodynamic factors. These results indicate that: (1) in normal preparations, radiation could cause inflammation as manifested by increased leucocyte rolling and adhesion; and (2) in tumour-bearing preparations, radiation caused changes in the vascular surface properties such that they became less adhesive to leucocytes. Such differences in radiation response may have important implications for radiation therapy and provide new insights into the unique features of tumours.

The modulation of radiation-induced damage to pig skin by essential fatty acids

The ability of essential fatty acids (EFAs) to modulate radiation-induced normal tissue injury was assessed in pig skin. Female Large White pigs (approximately 25 Kg) received 3 ml/day orally of either an 'active' oil [So-1100, containing 9% gamma-linolenic acid (GLA)] or a 'placebo' oil (So-1129) for just 4 weeks before or for 4 weeks before and for 16 weeks after irradiation; localised irradiation of skin was with single doses of beta-rays from 22.5 mm diameter 90Sr/90Y plaques. The severity of the acute reaction, assessed in terms of erythema or moist desquamation, was significantly less in those pigs that received So-1100 both before and after irradiation, as compared with those receiving that oil only prior to irradiation and the 'placebo' groups. Dose modification factors (DMFs) of between 1.13-1.24 were obtained. A similar reduction in the severity of acute skin injury was seen in pigs receiving So-1100 for only 10 weeks after irradiation. Late skin damage, assessed in terms of late erythema or dermal necrosis, was also reduced with So-1100, with DMFs of 1.14-1.51. No such modification was observed if So-1100 was only administered for 4 weeks prior to irradiation. No adverse side-effects were apparent as a result of EFA administration. So-1100 may represent a safe and valuable method of increasing the therapeutic gain in radiotherapy.

Cancer cell interactions with injured or activated endothelium

Blood vessels and lymphatics are the most important pathways for dissemination of cancer cells but the entry and exit of these cells into and from the vasculature requires that they pass through barriers formed by the endothelium and its basement membrane. This review summarizes evidence that this step in metastasis can be regulated by microenvironmental influences which alter the properties of this barrier. These phenomena can be attributed to both 'passive' and 'active' responses of the endothelium. The microvasculature is susceptible to perturbation from environmental agents, host cells and cancer cells. There is clinical and experimental evidence that this can upregulate the metastatic process. Using established animal models of pulmonary microvascular injury it has been shown that endothelial damage promotes the localization and metastasis of circulating cancer cells to the lung and that this effect is lost after endothelial repair. Oxidative stress is an effector of vascular damage in several of the experimental models. While endothelial cells appear to be directly susceptible to free radical attack, basement membranes are not. However, oxidative injury of endothelial cells causes release of proteases which can then degrade the basement membrane. This event is associated with generation of tumor cell chemoattractants and enhances cancer cell invasion of vascular basement membranes in vitro. Vascular endothelial cells are also susceptible to stimulation by systemic mediators including cytokines, thrombin, or endotoxin which induce a series of active responses in the vessel wall. These perturbed endothelial cells synthesize and express cell surface adhesion molecules which can interact with cancer cells. They also release chemoattractants which stimulate cancer cell motility. We postulate that such responses endow the vessel wall with the potential to act as a determinant of metastatic rate.

Increase in plasma thrombomodulin and decrease in plasma von Willebrand factor after regular radiotherapy of patients with cancer

In this study, we investigated plasma levels of thrombomodulin (TM) and von Willebrand factor (vWF) in 51 patients suffering from cancer or tumor undergoing 60 cobalt radiotherapy. Plasma TM and vWF antigen were measured by immunoradiometric assay and ELISA, respectively. During radiotherapy, an increase in plasma TM in patients was observed, which was radiation-dose dependent and there was a positive correlation between plasma TM level and radiation doses. However, the level of plasma vWF in the patients was decreased during radiotherapy and there was an inverse correlation between the amount of plasma vWF and radiation doses. Our data indicate that plasma TM is an useful molecular marker for early detection of radiation injury to endothelial cells in patients undergoing radiotherapy.