Transendothelial Perforations and the Sphere of Influence of Single-Site Sonoporation

Acoustically driven gas bubble cavitation locally concentrates energy and can result in physical phenomena including sonoluminescence and erosion. In biomedicine, ultrasound-driven microbubbles transiently increase plasma membrane permeability (sonoporation) to promote drug/gene delivery. Despite its potential, little is known about cellular response in the aftermath of sonoporation. In the work described here, using a live-cell approach, we assessed the real-time interplay between transendothelial perforations (∼30-60 s) up to 650 µm², calcium influx, breaching of the local cytoskeleton and sonoporation resealing upon F-actin recruitment to the perforation site (∼5-10 min). Through biophysical modeling, we established the critical role of membrane line tension in perforation resealing velocity (10-30 nm/s). Membrane budding/shedding post-sonoporation was observed on complete perforation closure, yet successful pore repair does not mark the end of sonoporation: protracted cell mobility from 8 µs of ultrasound is observed up to 4 h post-treatment. Taken holistically, we established the biophysical context of endothelial sonoporation repair with application in drug/gene delivery.

Nanoparticle Mediated Tumor Vascular Disruption: A Novel Strategy in Radiation Therapy

More than 50% of all cancer patients receive radiation therapy. The clinical delivery of curative radiation dose is strictly restricted by the proximal healthy tissues. We propose a dual-targeting strategy using vessel-targeted-radiosensitizing gold nanoparticles and conformal-image guided radiation therapy to specifically amplify damage in the tumor neoendothelium. The resulting tumor vascular disruption substantially improved the therapeutic outcome and subsidized the radiation/nanoparticle toxicity, extending its utility to intransigent or nonresectable tumors that barely respond to standard therapies.

Thrombomodulin contributes to gamma tocotrienol-mediated lethality protection and hematopoietic cell recovery in irradiated mice

Systemic administration of recombinant thrombomodulin (TM) confers radiation protection partly by accelerating hematopoietic recovery. The uniquely potent radioprotector gamma tocotrienol (GT3), in addition to being a strong antioxidant, inhibits the enzyme hydroxy-methyl-glutaryl-coenzyme A reductase (HMGCR) and thereby likely modulates the expression of TM. We hypothesized that the mechanism underlying the exceptional radioprotective properties of GT3 partly depends on the presence of endothelial TM. In vitro studies confirmed that ionizing radiation suppresses endothelial TM (about 40% at 4 hr after 5 Gy γ-irradiation) and that GT3 induces TM expression (about 2 fold at the mRNA level after 5 μM GT3 treatment for 4 hr). In vivo survival studies showed that GT3 was significantly more effective as a radioprotector in TM wild type (TM+/+) mice than in mice with low TM function (TMPro/-). After exposure to 9 Gy TBI, GT3 pre-treatment conferred 85% survival in TM+/+ mice compared to only 50% in TMPro/-. Thus, GT3-mediated radiation lethality protection is partly dependent on endothelial TM. Significant post-TBI recovery of hematopoietic cells, particularly leukocytes, was observed in TM+/+ mice (p = 0.003), but not in TMPro/- mice, despite the fact that GT3 induced higher levels of granulocyte colony stimulating factor (G-CSF) in TMPro/- mice (p = 0.0001). These data demonstrate a critical, G-CSF-independent, role for endothelial TM in GT3-mediated lethality protection and hematopoietic recovery after exposure to TBI and may point to new strategies to enhance the efficacy of current medical countermeasures in radiological/nuclear emergencies.

Novel drugs to ameliorate gastrointestinal normal tissue radiation toxicity in clinical practice: what is emerging from the laboratory?

PURPOSE OF REVIEW

To give an overview of promising novel agents under development for the prevention and reduction of gastrointestinal radiation injury.

RECENT FINDINGS

Currently, several novel agents are being tested as drugs to prevent or reduce gastrointestinal radiation injury. These drugs may not only prevent injury, but also mitigate toxicity, that is, reduce injury after radiation exposure has occurred. Promising novel agents include the somatostatin analogue SOM230, growth factors, agents acting on the toll-like receptor 5 pathway, endothelial protectants, and the vitamin E analogue γ-tocotrienol.

SUMMARY

Gastrointestinal radiation injury is the most important dose-limiting factor during radiotherapy of the abdomen or pelvis. It may severely affect the quality of life both during radiotherapy treatment and in cancer survivors. To date, there are no agents that can prevent or reduce intestinal radiation injury. Hence, there is an urgent need for the development of novel drugs to ameliorate intestinal toxicity during and after radiotherapy. This review summarizes the several agents that have been shown to reduce intestinal radiation injury in animals. Further research is needed to investigate their safety and efficacy in patients receiving radiotherapy for abdominal or pelvic tumours.

Early and long-term effects of radiation on intercellular adhesion molecule 1 (ICAM-1) expression in mouse urinary bladder endothelium

The aim was to assess the effect of irradiation on intercellular adhesion molecule 1 (ICAM-1) expression in endothelial cells of vessels in mouse urinary bladder and to compare endothelial ICAM-1 expression with changes in bladder function (storage capacity) during the early and late radiation response phases. Female C3H/Neu mice were irradiated with doses of either 20 or 0 Gy. For assessment of ICAM-1 expression, which was measured by the intensity of the immunohistochemical staining signal in bladder endothelium, an arbitrary semiquantitative score (0 - 3) was applied. Bladder storage function was assessed by transurethral cystotonometry. A positive functional radiation response, defined as a reduction in bladder capacity by > 50%, between days 0 and 15 or 16 and 30 was found in 40 and 64% of the animals, respectively. A late functional response was observed in 71% of the animals sacrificed after day 180. Minor constitutive expression of ICAM-1 was observed in bladder endothelial cells. After irradiation, an increase in staining signal by day 2, with a maximum on day 4, and on days 16 - 28 was found, which preceded the functional radiation effects. A permanent increase in ICAM-1 staining signal was observed in the late phase on top of an age-related rise. ICAM-1 expression was significantly higher in animals with a positive late response on day 90, i.e. during the initial late phase. Irradiation induces significant early and chronic variations in ICAM-1 expression in bladder endothelium, which preceded the functional response. This suggests that endothelial ICAM-1 is involved in the pathogenesis of both the early and late phases of radiation-induced urinary bladder effects.

[Role of endothelium in radiation-induced normal tissue damages]

More than half of cancers are treated with radiation therapy alone or in combination with surgery and/or chemotherapy. The goal of radiation therapy is to deliver enough ionising radiation to destroy cancer cells, without exceeding the level that the surrounding healthy cells can tolerate. Unfortunately, radiation-induced normal tissue injury is still a dose limiting factor in the treatment of cancer with radiotherapy. Early and late side-effects not only limit radiation dose escalation, but might also affect the patient's quality of life. Vascular injury is one of the most common effects of radiotherapy on normal tissues. Radiation-induced fibrogenesis is characterized by an orchestrated pathological wound-healing response in which the radiation-induced endothelium dysfunction plays a critical role. Irradiated endothelial cells acquire a proinflammatory, procoagulant and prothrombotic phenotype. The knowledge of molecular mechanisms involved in endothelium dysfunction following radiation is needed to identify therapeutic targets and develop strategies to prevent and /or reduce side-effects of radiation therapy.

[Proapoptotic antibodies as new therapeutic agents for tumor treatment]

To convert the concept already successful in mice into clinical practice and commercialize it, a human anti-CD95-antibody must be produced. In a second step experiments must be performed on various normal healthy cells and tissues to determine whether these human anti-CD95-antibodies administered in very low doses have any effect on human cells (particularly hepatocytes) or at least cause only minimal side effects. If these studies yield positive results, then clinical trials can be conducted in which increasing doses are given to exclude an acute hepatotoxic effect and then the effect exerted by the antibody in combination with irradiation on tumor growth can be investigated.The advantage of this concept lies in the fact that systemic stimulus (low doses of anti-CD95-antibodies) is highly intensified by local radiotherapy and only then initiates cell death. Since the anti-CD95-antibodies trigger apoptosis primarily in tumor endothelia, this approach could be employed not only for prostate cancer and melanomas, which have already been tested, but also for many other tumors.

Interactions between endothelia of the trabecular meshwork and of Schlemm's canal: a new insight into the regulation of aqueous outflow in the eye

PURPOSE

To test the hypothesis that trabecular meshwork endothelial cells (TMEs) regulate aqueous outflow by actively releasing ligands that upon binding to Schlemm's canal endothelial cells (SCEs) increase transendothelial flow, thereby facilitating the egress of aqueous.

METHODS

We tested our hypothesis by (1) activating the TMEs in vitro using a laser procedure known to increase aqueous outflow in vivo; (2) demonstrating that lasered TMEs become activated at the genome-wide level and synthesize ligands; (3) ascertaining that media conditioned by laser-activated TMEs and ligands therein increase transendothelial flow when added to SCEs; and (4) determining that ligands identified as synthesized by TMEs increase permeability when added to SCEs.

RESULTS

We find that adding either media conditioned by lasered TMEs or ligands synthesized by TMEs to naïve control SCEs increases permeability. Adding media boiled, diluted, or conditioned by nonlasered TMEs abrogates these permeability effects. Media conditioned by either lasered TMEs or SCEs (TME-cm/SCE-cm), when added to untreated controls of each cell type, induce congruous gene expression and flow effects: TME-cm induces far more differentially expressed genes (829 in control TMEs and 1,120 in control SCEs) than does the SCE-cm (12 in control TMEs and 328 in control SCEs), and TME-cm also increases flow much more (more than 11-fold in control TMEs and more than fourfold in control SCEs) than does the SCE-cm (fivefold in control TMEs and twofold in control SCEs).

CONCLUSIONS

As postulated, the TMEs release factors that regulate SCE permeability. Derangement of this TME-driven process may play an important role in the pathogenesis of glaucoma. Ligands identified, which regulate permeability, have potential use for glaucoma therapy.

Radiation enteropathy and leucocyte-endothelial cell reactions in a refined small bowel model

BACKGROUND

Leucocyte recruitment and inflammation are key features of high dose radiation-induced tissue injury. The inflammatory response in the gut may be more pronounced following radiotherapy due to its high bacterial load in comparison to the response in other organs. We designed a model to enable us to study the effects of radiation on leucocyte-endothelium interactions and on intestinal microflora in the murine ileum. This model enables us to study specifically the local effects of radiation therapy.

METHOD

A midline laparotomy was performed in male C57/Bl6 mice and a five-centimetre segment of ileum is irradiated using the chamber. Leucocyte responses (rolling and adhesion) were then analysed in ileal venules 2 - 48 hours after high dose irradiation, made possible by an inverted approach using intravital fluorescence microscopy. Furthermore, intestinal microflora, myeloperoxidase (MPO) and cell histology were analysed.

RESULTS

The highest and most reproducible increase in leucocyte rolling was exhibited 2 hours after high dose irradiation whereas leucocyte adhesion was greatest after 16 hours. Radiation reduced the intestinal microflora count compared to sham animals with a significant decrease in the aerobic count after 2 hours of radiation. Further, the total aerobic counts, Enterobacteriaceae and Lactobacillus decreased significantly after 16 hours. In the radiation groups, the bacterial count showed a progressive increase from 2 to 24 hours after radiation.

CONCLUSION

This study presents a refinement of a previous method of examining mechanisms of radiation enteropathy, and a new approach at investigating radiation induced leucocyte responses in the ileal microcirculation. Radiation induced maximum leucocyte rolling at 2 hours and adhesion peaked at 16 hours. It also reduces the microflora count, which then starts to increase steadily afterwards. This model may be instrumental in developing strategies against pathological recruitment of leucocytes and changes in intestinal microflora in the small bowel after radiotherapy.

Radiation injury and the protein C pathway

OBJECTIVE

To summarize current knowledge regarding the role of the thrombomodulin (TM)-protein C system in acute and chronic radiation responses in normal tissues.

DATA SOURCE

Studies published in the biomedical literature during the past three decades and cited in PubMed and unpublished clinical and laboratory data from our own research program. STUDY SUMMARY: The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. Microvascular injury is a prominent feature of normal tissue radiation injury and plays a critical role in both acute (inflammatory) and chronic (fibrotic) radiation responses. Evidence from our own and other laboratories strongly suggests that dysfunction of the TM-protein C system plays a key role in the pathogenesis of radiation-induced injury to normal tissue. Exposure of normal tissues to ionizing radiation causes a pronounced, sustained deficiency of endothelial TM. This is likely to be due to a combination of initial inactivation of TM by reactive oxygen species, reduced transcription of TM, and release of TM into the circulation. Deficient levels of endothelial TM cause loss of local vascular thrombo-resistance, excessive activation of protease-activated receptor-1 by thrombin, and insufficient activation of protein C. These changes are presumed to be critically involved in many aspects of acute radiation toxicity and in sustaining the fibroproliferative processes that lead to chronic radiation-induced organ dysfunction and clinical complications.

CONCLUSION

Injury of vascular endothelium may be key to the acute responses of normal tissues to ionizing radiation and to the progressive nature of chronic radiation fibrosis. Restitution of the TM-protein C pathway is an appealing strategy by which to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

Gamma knife irradiation increases cerebral endothelial expression of intercellular adhesion molecule 1 and E-selectin

OBJECTIVE

Alterations in multiple functions of the microvasculature occur in response to gamma irradiation and are thought to contribute to radiation-induced end organ damage by inducing inflammatory responses, particularly leukocyte infiltration into the affected area. Endothelial cell adhesion molecules (ECAMs) mediate leukocyte adhesion and migration. Here, we validate a method to study the effect of Leksell gamma knife stereotactic radiosurgery on the expression of ECAMs on human cerebral endothelium at 0, 24, 48, and 72 hours after irradiation.

METHODS

A human brain endothelial cell line (IHEC) was cultured on 12-mm coverslips and subjected to 50 Gy of collimated gamma irradiation with the Leksell gamma knife (Elekta Instruments, Inc., Atlanta, GA). Lactate dehydrogenase release was measured at 24, 48, and 72 hours after irradiation and caspase-3 at 24, 48, 72, 96, and 120 hours. ECAM expression was measured at postirradiation intervals of 0, 24, 48, and 72 hours by cell enzyme-linked immunoabsorbent assay. We used a cell irradiator composed of two chambers. The upper chamber holds the coverslips firmly in place while they are immersed in media. The lower chamber is connected to a peristaltic pump, which pumps water into the chamber and maintains the media in the upper chamber at 37 degrees C through convection.

RESULTS

None of the ECAMs tested was significantly elevated compared with the control basally. Twenty-four hours after irradiation, intercellular adhesion molecule 1 was significantly elevated on brain endothelial cells but there was no significant elevation of E-selectin. Vascular cell adhesion molecule 1 was increased slightly but not significantly and decreased at 48 hours. At 72 hours, E-selectin expression was significantly increased; intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 were not altered relative to sham controls.

CONCLUSION

Increased ECAM expression and lactate dehydrogenase release support the idea that the cerebral microvasculature undergoes an inflammatory response after Leksell gamma knife stereotactic radiosurgery.

Modulation of the tumor vasculature functionality by ionizing radiation accounts for tumor radiosensitization and promotes gene delivery

The ultimate goal of radiotherapy is to induce irreversible damages in genetically unstable, fast-growing cancer cells while minimizing the cytotoxic effects on host tissues. The satus of the tumor vasculature is particular because it is located within the tumor but mostly arises from host cells. The aim of this study was to characterize the effects of low-dose irradiation on the function of endothelial cells lining tumor vessels. Using isolated arterioles mounted on a pressure myograph, we first documented that the nitric oxide (NO)-mediated vasorelaxation that was defective in tumor vessels was completely restored following local tumor irradiation. Immunoblot analyses revealed that this was attributable to an increase in the abundance of the endothelial NO synthase while the expression of its physiological inhibitor, caveolin-1, was reduced. We further showed that the potentiation of the NO-dependent pathway induced a marked increase in tumor blood flow and oxygenation that determined the higher sensitivity of the tumor to further irradiation. Finally, we documented that the NO-mediated effects of irradiation on the tumor vasculature increased the delivery and expression of a reporter gene into the tumor. Thus, low-dose irradiation of endothelial cells within a tumor is a key determinant of the effectiveness of radiotherapy and may offer a new strategy to increase gene and/or drug delivery to the tumor.

Apoptosis of human dermal endothelial cells as a potential side effect following therapeutic administration of UVA1 irradiation: preliminary results

Apoptosis is a highly selective form of cell suicide with characteristic morphological and biochemical features. UVA1 phototherapy has been introduced into the treatment of many T cell-derived skin diseases. The aim of our pilot study was to assess apoptosis of endothelial cells in relation to time after irradiation with medium-dose UVA1 using four different staining techniques. With in situ nick end labelling (ISEL) and Hoechst 33342 staining we investigated DNA degradation during apoptosis and used M30 CytoDEATH to selectively stain the cytoplasm of apoptotic cells. Additionally, the expression of the tumour suppressor gene p53 was determined. ISEL and Hoechst 33342 revealed only a few positive endothelial cells 3 h after UVA1 irradiation. After 6 h almost all vessels were positively stained. By 12 h after irradiation this peak concentration had lowered again. The first p53-positive endothelial cells were seen 6 h after UVA1 irradiation and reached a maximum at 12 h after irradiation. Fibroblasts of the lower dermis were positively stained after 6 and 12 h. M30-positive endothelial cells were found from 3 to 12 hours after irradiation. ISEL and Hoechst 33342 staining clearly revealed UVA1-induced apoptotic cell elimination predominantly restricted to endothelial cells as a possible side effect of UVA1 irradiation. The induction of apoptosis was specifically verified by M30 immunostaining of early caspase cleavage. Whereas the p53-positive endothelial cells underwent programmed cell death as demonstrated by M30, ISEL and Hoechst 33342, some fibroblasts seemed to accumulate the p53 antibody, but this did not induce apoptotic cascades.

Non-thermal activation of the hsp27/p38MAPK stress pathway by mobile phone radiation in human endothelial cells: molecular mechanism for cancer- and blood-brain barrier-related effects

We have examined whether non-thermal exposures of cultures of the human endothelial cell line EA.hy926 to 900 MHz GSM mobile phone microwave radiation could activate stress response. Results obtained demonstrate that 1-hour non-thermal exposure of EA.hy926 cells changes the phosphorylation status of numerous, yet largely unidentified, proteins. One of the affected proteins was identified as heat shock protein-27 (hsp27). Mobile phone exposure caused a transient increase in phosphorylation of hsp27, an effect which was prevented by SB203580, a specific inhibitor of p38 mitogen-activated protein kinase (p38MAPK). Also, mobile phone exposure caused transient changes in the protein expression levels of hsp27 and p38MAPK. All these changes were non-thermal effects because, as determined using temperature probes, irradiation did not alter the temperature of cell cultures, which remained throughout the irradiation period at 37 +/- 0.3 degrees C. Changes in the overall pattern of protein phosphorylation suggest that mobile phone radiation activates a variety of cellular signal transduction pathways, among them the hsp27/p38MAPK stress response pathway. Based on the known functions of hsp27, we put forward the hypothesis that mobile phone radiation-induced activation of hsp27 may (i) facilitate the development of brain cancer by inhibiting the cytochrome c/caspase-3 apoptotic pathway and (ii) cause an increase in blood-brain barrier permeability through stabilization of endothelial cell stress fibers. We postulate that these events, when occurring repeatedly over a long period of time, might become a health hazard because of the possible accumulation of brain tissue damage. Furthermore, our hypothesis suggests that other brain damaging factors may co-participate in mobile phone radiation-induced effects.

Effects of ionizing radiation on gene expression in cultured rat heart cells

PURPOSE

To determine the in vitro effect of ionizing radiation on TGF-beta1, FGF-2, IL-1beta, atrial natriuretic peptide (ANP) and procollagen types I and III gene expression in three different cell types of rat heart.

MATERIALS AND METHODS

Primary cell cultures of myocytes and fibroblasts and cultures of a rat heart endothelial cell line (RHEC) were irradiated with single doses of 2.0, 8.5 or 15 Gy. At different time-points after irradiation (4-336 h), gene expression was analysed using a competitive PCR technique.

RESULTS

Irradiation of cultured rat heart cells may lead to temporary changes in expression of the genes studied. Analysis of the radiation response of cultured myocytes, cardiac fibroblasts and rat heart endothelial cells reveals different responses with regard to (1) the dose necessary to evoke changes in mRNA expression, (2) the level of and (3) the duration of the 'induced' response. The changes observed were small and between parallel experiments the onset and time-course of the induced gene expression varied between 4 and 48 h. The average expression of TGF-beta1 mRNA between 4 and 48 h was significantly elevated in endothelial cells after a dose of 2.0 Gy, in fibroblasts after a dose of 8.5 Gy and in myocytes after a dose of 15 Gy. Down-regulation of TGF-beta1 mRNA in myocytes was observed after a dose of 8.5 Gy. FGF-2 and procollagen type-I mRNAs were significantly elevated in fibroblasts after a dose of 2.0 Gy. For all three cell types, no effect of dose on the timing or size of the gene expression was observed.

CONCLUSIONS

Although irradiation of cultured heart cells influences expression of genes involved in tissue remodelling, the observed differences were too small and too restricted in time and dose to explain the exact role of these cell types in processes leading to radiation-induced cardiac fibrosis.

[Functional and molecular aspects of anti-inflammatory effects of low-dose radiotherapy]

PURPOSE

Low-dose radiotherapy (LD-RT) with single fractions between 0.1 and 1.0 Gy is known to exert an antiinflammatory effect. Although different mechanisms for the clinical efficiency were proposed, only few experimental data are still available. This paper focuses on functional and molecular aspects of LD-RT.

METHODS AND RESULTS

The antiinflammatory efficiency of LD-RT in clinical studies could be confirmed in experimental models of osteoarthritis and rheumatoid arthritis. In a model of adjuvants arthritis, 5 x 1.0 Gy as well as 5 x 0.5 Gy, given at the maximum of the acute inflammation, could prevent clinically and histologically progression of the disease without affecting existing signs of inflammation. The effect of LD-RT on the adhesion of peripheral blood mononuclear cells (PBMC) and endothelial cells (EC) was analyzed in in-vitro assays. In the dose range between 0.3 and 0.7 Gy almost 4 hours after irradiation adherent cells reached a relative minimum of adhesion compared to unirradiated controls. In PBMC an discontinuous increase of apoptosis with a maximum between 0.3 and 0.5 Gy, the proteolytic shedding of L-selectin and an increased expression of the antiinflammatory cytokine interleukin 10 as well as downregulation of TNF alpha could be identified as potential mechanisms for the observed reduced adhesion. Conversely, reduced expression of E-selectin and an increased induction of transforming growth factor beta (TGF beta 1) with a maximum at 0.5 Gy could be observed in endothelial cells. Macrophages immigrating the site of inflammation are known to express inducible nitrix-oxide synthase (iNOS), which in turn mediates cytotoxic and immunmodulatory effects by producing nitric oxide (NO). LD-RT of stimulated macrophages within the dose range between 0.6 and 1.25 Gy reduced NO production and iNOS-protein expression without affecting iNOS-mRNA expression.

CONCLUSION

Our experimental data have confirmed the antiinflammatory efficiency of LD-RT in vitro and in vivo, indicating effects on different cellular components and mechanisms of inflammation. The regulation of the adhesion between PBMC and endothelial cells and the effects on activated macrophages may mediate the antiinflammatory properties of LD-RT. Ongoing experiments will help to clarify the molecular mechanism.

Late effects of radiotherapy on oral mucosa in humans

In order to gain further understanding of the late effects of radiotherapy on oral mucosa, we analysed the histomorphological alterations, the cell populations in the subepithelial tissue, and the endothelial expression pattern of different adhesion molecules. Biopsies were taken from patients before irradiation, directly after 60 Gy, and 6-12 months after radiotherapy. Besides the histomorphological evaluation of the vessels, the endothelial expression of ICAM-1, VCAM-1 and E-selectin was determined as well as the distribution of LFA-1-, Mac-1-, VLA-4-, RM3/1-, 27E10- and 25F9-bearing cells in the subepithelial tissue. The expression of ICAM-1 was downregulated after radiotherapy, whereas the percentage of LFA-1- and VLA-4-bearing cells increased. VCAM-1 remained at low levels. The subepithelial infiltration was still dominated by RM3/1-positive macrophages. The number of vessels decreased, while the lumen of the remaining vessels increased. In conclusion, the late effects of radiotherapy are characterized by a decreased number of blood vessels and by significantly different expression patterns of the adhesion molecules studied, and of integrins and macrophage subpopulations, compared to the conditions before irradiation and directly after irradiation with 60 Gy.

Ultraviolet A1 radiation induces nitric oxide synthase-2 expression in human skin endothelial cells in the absence of proinflammatory cytokines

Skin exposure to ultraviolet radiation from sunlight causes erythema and edema formation as well as inflammatory responses. As some of these ultraviolet-induced effects are potentially mediated by nitric oxide synthases, we examined the role of cytokines and ultraviolet A1 radiation (340-400 nm) on the expression of the nitric oxide synthase-2 in endothelia of normal human skin biopsies during short-term organ culture as well as expression and activity of the nitric oxide synthase-2 in in vitro cell cultures of human dermal endothelial cells. Both, cytokine challenge (interleukin-1beta + tumor necrosis factor-alpha + interferon-gamma) but also ultraviolet A1 exposure (50 J per cm2) in the absence of cytokines led to the expression of nitric oxide synthase-2 in human skin organ cultures as shown by immunohistochemistry. Moreover, exposing human dermal endothelial cell cultures to proinflammatory cytokines but also to ultraviolet A1 radiation (6-24 J per cm2) in the absence of cytokines resulted in significant nitric oxide synthase-2 mRNA and protein expression as well as enzyme activity. Ultraviolet A1 irradiation of cytokine activated cells led to further increases in nitric oxide synthase-2 mRNA, protein expression, and enzyme activity. Moreover, a reporter gene assay using a human nitric oxide synthase-2 promoter construct provide evidence that ultraviolet A1, in the absence of cytokines, induces nitric oxide synthase-2 expression and activity, as previously shown for cytokines. Thus, the results presented here demonstrate for the first time that in dermal endothelia of human skin ultraviolet A1 radiation alone represents a proinflammatory stimulus sufficient to initiate nitric oxide synthase-2 expression as well as activity comparable with the respective response seen in the presence of proinflammatory cytokines.

Irradiation enhances the support of haemopoietic cell transmigration, proliferation and differentiation by endothelial cells

Endothelial cells (ECs) are a critical component of the bone marrow stroma in the regulation of haemopoiesis. Recovery of bone marrow aplasia after radiation exposure depends, in part, on the repair of radiation-induced endothelial damage. Therefore, we assessed the ability of an irradiated human bone marrow EC line (TrHBMEC) to support transmigration, proliferation and differentiation of CD34+ bone marrow cells either irradiated or not in transendothelial migration or co-culture models. Radiation-induced EC damage was reflected by an increased release of soluble intercellular adhesion molecule (sICAM)-1 and platelet endothelial cell adhesion molecule (PECAM)-1. Irradiation of TrHBMECs with a 10 Gy dose strongly enhanced the transmigration of CD34+ cells, granulo-monocytic progenitors (CFU-GM) and erythroid progenitors (BFU-E). While ICAM-1 and PECAM-1 expression on irradiated TrHBMECs was increased, only antibodies against PECAM-1 inhibited the radiation-induced enhanced transmigration of haemopoietic cells. Irradiation of TrHBMECs (5-15 Gy) also increased proliferation and differentiation towards the granulo-monocytic lineage of co-cultured CD34+ cells, as well as colony formation by those cells and the production of interleukin 6 (IL-6), IL-8, granulocyte colony-stimulating factor (CSF) and granulocyte-macrophage CSF. Irradiated TrHBMECs were more capable of stimulating irradiated (1,2 Gy) CD34+ cells and haemopoietic progenitors than non-irradiated TrHBMECs. Together, these results suggest that, despite the radiation-induced damage, irradiated ECs may favour haemopoietic reconstitution after radiation exposure.

In vivo radioprotection of mouse brain endothelial cells by Hoechst 33342

Radiation-induced loss of mouse brain endothelial cells has been examined in mice given an intravenous injection of the DNA-binding radioprotector Hoechst 33342 (80 mg kg-1). At the time of irradiation, 10 min after injection, Hoechst fluorescence in the brain was confined to the endothelial cells. Endothelial cell density was measured using a histochemical fluorescence technique that had been used previously to monitor post-irradiation changes in endothelial cell density in rat brain, in which it was shown that a sensitive subpopulation comprising about 15% of the endothelial cells was lost within 24 h of radiation exposure. The present study shows a similar dose-response for the control mice, with depletion of the sensitive subpopulation to 85% being almost complete after a dose of 2.5 Gy gamma-rays. However, in mice irradiated 10 min after Hoechst 33342 administration, doses between 12 Gy and 20 Gy were required to ablate these cells. The kinetics of cell loss and the rather large dose modification factor suggests that Hoechst 33342 may be suppressing an apoptotic response in this subpopulation. Whatever the mechanism involved, Hoechst 33342 clearly provides substantial protection against early radiation-induced endothelial cell loss. Further studies are necessary to determine the extent to which this initial protection translates into an improved long-term survival of the "protected" cells and, especially, to see whether this endothelial cell protection can ameliorate the later consequences of central nervous system irradiation, namely necrosis and paralysis.

Radioprotection of human endothelial cells with amifostine

MATERIALS AND METHODS

We studied the effect of amifostine on radiation sensitivity of human endothelial cells and several tumor cell lines (HeLa, MIA PaCa-2 and BxPC-3). The cells were incubated in medium with a concentration of 1 microgram/microliter amifostine and after 1 hour irradiated with 10 or 20 Gy single dose. Proliferation index was measured by BrdU assay after another 8 and 24 hours.

RESULTS

The results show a higher proliferation rate of endothelial cells following radiation plus amifostine, compared with radiation alone. Amifostine induced an increase of proliferation in the control/non-irradiated human endothelial cells. After irradiation with 10 Gy single dose the proliferation of amifostine treated human endothelial cells was still higher. Amifostine exerts no apparent proliferative effect on the tumor cells.

CONCLUSIONS

The results presented indicate that amifostine acts as an activation of proliferation of the human endothelial cells in a simple in-vitro system and indicate that amifostine supplementation prior to radiation therapy might exert a radioprotective effect to healthy tissue without spurring tumor growth.

A novel potential application for 99mTc-HMPAO: endothelial cell labeling for in vitro investigation of cell-biomaterial interactions

Good adherence of endothelial cells (ECs) seeded on vascular prostheses and cell retention under flow conditions are important factors to consider in the use of functionalized prostheses in vascular surgery. Because 111In-oxine radiolabeling presents disadvantages, we wondered whether, because of its well-known physical properties, 99mTc-hexamethyl propyleneamine oxime (HMPAO or exametazime) could be used.

METHODS

The cytotoxicity of unlabeled HMPAO and 99mTc-HMPAO at increasing concentrations and activities was tested on monolayers of the EC line EA-hy-926. The influence of temperature and time on tracer incorporation into cells was also tested. The optimal labeling conditions were applied to evaluate the retention of ECs seeded on polyester grafts under flow conditions by gamma camera detection.

RESULTS

The activity of 10 MBq/10(6) cells corresponding to 4.5 microg/10(6) cells of unlabeled HMPAO, applied for 3 h at 37 degrees C (cellular uptake = 18%), was the best compromise between the maintenance of cell viability and metabolic activity and efficient detection by the gamma camera. Spontaneous leakage was observed and analyzed by high-performance liquid chromatography. A cell loss of 13% after 180-min exposure to shear stress was obtained.

CONCLUSION

Our data thus indicate the feasibility of using such a radiolabeling technique to investigate EC-biomaterial interactions.

Antiangiogenic radioimmunotherapy of human solid tumors in SCID mice using (125)I-labeled anti-endoglin monoclonal antibodies

Endoglin (CD105), which is a component of the TGF-beta receptor complex, is highly expressed at the surface of proliferating human endothelial cells such as those of tumor vessels. In the present study, we tested the antitumor efficacy of (125)I-labeled anti-endoglin monoclonal antibodies (MAbs), SN6f and SN6j, against s. c. tumors of MCF-7 human breast cancer cells in SCID mice by i.v. administration. SN6f and SN6j cross-react weakly with mouse endothelial cells, but show no significant reactivity with MCF-7 tumor cells. These MAbs are effectively internalized into the cells after binding to the cell surface antigen of endothelial cells. Four groups of SCID mice (n = 10 or 9 in each group) inoculated s.c. with 8 x 10(6) MCF-7 cells were treated with (125)I-SN6f (10 microCi), (125)I-SN6j (10 microCi), a (125)I-labeled isotype-matched control IgG (10 microCi) or PBS. The systemic therapy was performed in 2 series, i.e., on days 3, 5, 7 and days 58, 60, 62. Both (125)I-SN6f and (125)I-SN6j showed significant growth suppression of the tumors, whereas the (125)I-labeled control IgG did not show any significant antitumor efficacy. No significant toxicity or weight loss was observed in mice treated with either (125)I-SN6f or (125)I-SN6j. After 100 days of observation, autopsies revealed no significant organ damage. Our results show the possible usefulness of antiangiogenic radioimmunotherapy using (125)I-labeled anti-endoglin MAbs.

Radiation induced endothelial cell retraction in vitro: correlation with acute pulmonary edema

We determined the effects of low dose radiation (<200 cGy) on the cell-cell integrity of confluent monolayers of pulmonary microvascular endothelial cells (PMEC). We observed dose- and time-dependent reversible radiation induced injuries to PMEC monolayers characterized by retraction (loss of cell-cell contact) mediated by cytoskeletal F-actin reorganization. Radiation induced reorganization of F-actin microfilament stress fibers was observed > or =30 minutes post irradiation and correlated positively with loss of cell-cell integrity. Cells of irradiated monolayers recovered to form contact inhibited monolayers > or =24 hours post irradiation; concomitantly, the depolymerized microfilaments organized to their pre-irradiated state as microfilament stress fibers arrayed parallel to the boundaries of adjacent contact-inhibited cells. Previous studies by other investigators have measured slight but significant increases in mouse lung wet weight >1 day post thoracic or whole body radiation (> or =500 cGy). Little or no data is available concerning time intervals <1 day post irradiation, possibly because of the presumption that edema is mediated, at least in part, by endothelial cell death or irreversible loss of barrier permeability functions which may only arise 1 day post irradiation. However, our in vitro data suggest that loss of endothelial barrier function may occur rapidly and at low dose levels (< or =200 cGy). Therefore, we determined radiation effects on lung wet weight and observed significant increases in wet weight (standardized per dry weight or per mouse weight) in < or =5 hours post thoracic exposure to 50 200 cGy x-radiation. We suggest that a single fraction of radiation even at low dose levels used in radiotherapy, may induce pulmonary edema by a reversible loss of endothelial cell-cell integrity and permeability barrier function.

Arterial changes following single-dose irradiation

In this reported experiment, the serial morphologic changes in the rabbit ear central artery, following a single dose of 45 Gy 60Co gamma-ray irradiation, were investigated using light and scanning electron microscopy. Under light microscopy, mild intimal proliferation, disorganization of smooth muscle, and severe perivascular fibrosis were observed. These appeared to be caused by increased intimal cell death and lower repair capability after large single-dose irradiation. Under scanning electron microscopy, the endothelial cells did not show significant morphologic changes during the first 4 weeks. At 6 and 10 weeks after irradiation, the endothelial cells shrank in all directions and detached from the basement membrane. These changes accord with the theory that radiation damage following therapeutic dosage occurs within the DNA of the cell, and that there is no significant change until the cell attempts to divide.

Rearrangement of human cell homologous chromosome domains in response to ionizing radiation

Chromosomes are located within the interphase nucleus in regions called domains. Using fluorescence in situ hybridization with whole chromosome paints, a pain of homologous chromosomes can be visualized as two discrete domains and their relative spatial location determined. This study examines the effects of an ionizing radiation exposure on the relative spatial location of chromosome 7 and 21 domains in human skin fibroblasts and lung endothelial cells. The distance between homologous chromosome domains was assessed for each nucleus, before and after exposure to ionizing radiation, using conventional epifluorescence and confocal laser scanning microscopy. Results from conventional microscopy indicated that homologous chromosome domains were re-positioned closer to each other within interphase nuclei after exposure to radiation. Analysis of three-dimensional data obtained from confocal microscopy confirmed these results. In control cells, and in cells examined immediately after irradiation, 66.2% +/- 2.1% of the homologous chromosome 21 domains within endothelial cell nuclei were located greater than 4.0 microns apart (33.8% +/- 1.9% were less than 4.0 microns apart). However, when cells were examined 2 h after a 4.0 Gy gamma-ray exposure, only 30.5% +/- 2.1% of the homologous chromosome domains were greater than 4.0 microns apart (69.5% +/- 2.1% were less than 4.0 microns apart). Similar results were obtained for chromosomes 7 and 21 in skin fibroblast nuclei. The results indicate that homologous chromosome domains rearranged and became closer together within the interphase nuclei in response to ionizing radiation. The exact mechanism of this response is unknown, but it may be related to DNA repair processes. It is speculated that chromosome domains are re-positioned to permit repair of radiation-induced DNA damage.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Low energy laser irradiation fails to modulate the inflammatory function of human monocytes and endothelial cells

BACKGROUND AND OBJECTIVE

In view of the important regulatory role of cytokines in wound healing and inflammation, we investigated the effects of low energy laser irradiation on cytokine release by human peripheral blood monocytes (M phi) and human umbilical vein endothelial cells (HUVEC) in vitro. Also, the effects of laser light on the expression of endothelial adhesion molecules, another important feature of inflammatory and regenerative responses, were assessed.

STUDY DESIGN/MATERIALS AND METHODS

Cells were irradiated with a pulsed GaAs-laser (904 nm) at energy densities 0 (= sham), 0.3, 3.0, or 9.0 J/cm2 and subsequently incubated in absence or presence of endotoxin (M phi) or the proinflammatory cytokines TNF alpha and IL-1 beta (HUVEC).

RESULTS

Irradiation at any of the dosages used did not significantly affect spontaneous or endotoxin-induced release of TNF alpha, IL-6, and IL-8 by M phi. Similarly, secretion of IL-6 and IL-8 by resting or cytokine-activated HUVEC after either single or repeated laser treatment was unchanged as compared to sham-irradiated controls. Moreover, laser treatment did not induce de novo expression or upregulation of the endothelial adhesion molecules E-selectin, ICAM-1, and VCAM-1, and it failed to modify their expression in response to stimulation with TNF alpha or IL-1 beta.

CONCLUSION

We conclude that with the specific laser parameters and dose-regimen used, low energy laserlight does not affect the inflammatory function of human monocytes and endothelial cells in vitro.

Ionizing radiation induces human intercellular adhesion molecule-1 in vitro

Intercellular adhesion molecule-1 (ICAM-1) plays a central role in various inflammatory reactions and its expression is readily induced by inflammatory stimuli such as cytokines or ultraviolet irradiation. We have investigated the effect of ionizing radiation (IR) on human ICAM-1 expression in human cell lines and skin cultures. ICAM-1 mRNA levels in HL60, HaCaT, and HeLa cells were elevated at 3-6 h after irradiation and increased with doses from 10-40 Gy. The rapid induction of ICAM-1 occurred at the level of transcription, was independent of de novo protein synthesis, and did not involve autocrine stimuli including tumor necrosis factor-alpha and interleukin-1. IR also induced ICAM-1 cell surface expression within 24 h. Immunohistologic analysis of cultured human split skin revealed ICAM-1 upregulation on epidermal keratinocytes and dermal microvascular endothelial cells 24 h after exposure to 6 Gy. In conclusion, we propose ICAM-1 as an important radiation-induced enhancer of immunologic cell adhesion, which contributes to inflammatory reactions after local and total body irradiation.

Lectin staining of the endothelial cell membrane is more sensitive to ultraviolet radiation than the epidermal cell staining in guinea-pig skin

Ultraviolet radiation (UVR)-induced alterations in lectin stainings of both endothelial and epidermal cells were histochemically analysed in guinea-pig skin using Bandeiraea simplicifolia agglutinin-I and Ricinus communis agglutinin-I. The endothelial cell staining with both lectins was more sensitive to a single exposure to middle-wave UVR (UVB) and topical psoralen plus long-wave UVR (UVA) (PUVA) than the epidermal cell staining. More remarkable changes were seen following PUVA radiation than UVB radiation. No significant alterations were induced by UVA radiation alone or psoralen alone. The results suggest that the endothelial cell is a susceptible target for UVB and PUVA radiation.

Endothelial cell proliferation is induced by radiation in cultured explants of human urothelium and oesophageal mucosa

Normal oesophageal mucosa obtained during upper abdominal surgery or urothelium obtained from kidney transplants was placed in explant culture and exposed to 60Co gamma radiation after 48 h. Cultures were maintained for two to six weeks after exposure and were monitored at various intervals for the development of features associated with malignant transformation. Endpoints examined included proliferation rate, frequency of proliferating cells, cell type distribution and degree of differentiation of the different cell types. The results indicate that following exposure to gamma rays (2.5-10 Gy) an increased overall growth rate of the surviving cells can be observed 2-4 weeks later. Analysis of the results using autoradiography confirms that a higher level of cell proliferation occurs in treated cultures than in the control untreated cultures. When the distribution of different cell types in the culture is examined, the increase in growth can be seen to be due to greatly increased numbers of endothelial cells. These proliferated over the surface of the epithelial cells and are more strongly positive for endothelial cells markers than endothelial cells occurring in control cultures. The degree of differentiation of endothelial cells into capillary like structures is also more apparent in carcinogen treated cultures. Foci expressing both epithelial and endothelial markers also occur. The results suggest that exposure of tissue fragments to radiation stimulates the growth and development of endothelial cells in resulting cell cultures. The effect may be due to a direct action of the treatment on the endothelial cells but it is more likely that it results from a secondary effect mediated by traumatic response of damaged epithelial cells.

Ultrasound as a novel method for selective damage of endocardial endothelium

Damage of endocardial endothelium by mechanochemical methods in isolated cardiac muscle induces typical changes in the contractile performance of the myocardium. Functional and morphological features of isolated cat papillary muscles treated with ultrasound, a new technique for in vitro damage of endocardial endothelium, were compared with damage by Triton X-100. Treatment with either short bursts of continuous wave ultrasound (25 W; 1.05 MHz) or with 1-s immersion in 0.5% Triton X-100 resulted in an irreversible abbreviation of twitch contraction with concomitant decrease in total peak twitch tension but without significant changes in maximal unloaded velocity of shortening. Decrease of total peak isometric tension was significantly more pronounced after Triton X-100 administration. Scanning electron microscopy showed an extracted endothelium following immersion in Triton X-100 and a nearly complete desquamated surface after ultrasound. Fluorochromes in muscles treated with Triton X-100 or ultrasound did not enter myocytes, which maintained a normal ultrastructure. After Triton X-100, more endocardial fibroblasts were labeled and showed ultrastructural damage than after ultrasound. Ultrasound constitutes a powerful technique for selective in vitro damage of endocardial endothelium. The technique is also suitable for experimental in vivo intracardiac application.

Endothelial cell population dynamics in rat brain after local irradiation

The dynamics of the endothelial cell population was investigated in the rat brain after local irradiation with different doses of X rays. A fluorescent-histochemical technique was used for the visualization of the cells. A decrease in endothelial cell number was observed within 1 day of irradiation with doses of 5-200 Gy. At this time the endothelial cell number had decreased by up to 15% compared with the pre-treatment values. This early dose-independent loss in cell number was maintained for up to 1 month after irradiation. This was then followed by a slow dose-independent decrease in cell density up to 6 months after exposure. Subsequently the depletion of the endothelial cell population exposed to 40 and 60 Gy continued. After a dose of 25 Gy an abortive recovery of cell numbers occurred followed by an abrupt depletion of the endothelial cell population. The possible mechanisms of such changes are discussed.

[Consequences of radiation on tissues]

Tissular and cellular radiation-induced injuries. The authors examine morphological, tissular and cellular radiation-induced injuries utilizing anatomo-clinical case reports and experiments in the pig. One must distinguish early and delayed tissular lesions. In the latter, appearing in general after at least six months, vasculo-connective changes are the most important, leading to sclerosis. Indeed, because of the vascular damages the histo-haematic barrier is enlarged leading to a decrease of tissular resistance to injury, long and difficult tissular repairs after a surgical operation. At the end the authors mention some special morphological features concerning the site of lesions.

Radiation-induced pulmonary endothelial dysfunction and hydroxyproline accumulation in four strains of mice

C57BL mice exposed to 14 Gy of whole-thorax irradiation develop significant histologic lung fibrosis within 52 weeks, whereas CBA and C3H mice do not exhibit substantial fibrosis during this time. The purpose of the present study was to determine whether this strain-dependent difference in radiation histopathology is associated with genetic differences in pulmonary endothelial metabolic activity or in endothelial radioresponsiveness. C57BL/6J, C57BL/10J, CBA/J, and C3H/HeJ mice were sacrificed 12 weeks after exposure to 0 or 14 Gy of 300-kV X rays to the whole thorax. Lung angiotensin converting enzyme (ACE) activity and plasminogen activator (PLA) activity were measured as indices of pulmonary endothelial function; and lung hydroxyproline (HP) content served as an index of pulmonary fibrosis. Lung ACE and PLA activities in sham-irradiated C57BL/6J and CB57BL/10J mice were only half as high as those in sham-irradiated CBA/J and C3H/HeJ mice. Exposure to 14 Gy of X rays produced a slight but nonsignificant reduction in lung ACE and PLA activity in the C57BL strains, and a significant reduction in the CBA/J and C3H/HeJ mice. Even after 14 Gy, however, lung ACE and PLA activities in CBA/J and C3H/HeJ mice were higher than those in sham-irradiated C57BL/6J and C57BL/10J mice. Lung HP content in all four strains increased significantly after irradiation, but this increase was accompanied by an increase in lung wet weight. As a result, HP concentration (per milligram wet weight) remained constant or increased slightly in both C57BL strains and actually decreased in the CBA/J and C3H/HeJ mice. These data demonstrate significant genetic differences in both intrinsic pulmonary endothelial enzyme activity and endothelial radioresponsiveness among the four strains of mice. Specifically, strains prone to radiation-induced pulmonary fibrosis (C57BL/6J, C57BL/10J) exhibit only half as much lung ACE and PLA activity as do strains resistant to fibrosis (CBA and C3H).

Structure-function analysis of angiotensin-converting enzyme inhibitors as modifiers of radiation-induced pulmonary endothelial dysfunction in rats

We have previously demonstrated that thiol-containing collagen antagonists (penicillamine) and angiotensin-converting enzyme (ACE) inhibitors (Captopril and CL242817) ameliorate endothelial dysfunction in irradiated rat lung. The purpose of the present study was to determine whether the non-thiol ACE inhibitor CGS13945 also modifies radiation-induced pulmonary endothelial dysfunction in rats sacrificed 2 months after a single dose (0-30 Gy) of 60 Co gamma rays to the right hemithorax. The CGS13945 was administered in the feed continuously after irradiation at a regimen of 30 mg (kg body weight)-1 day-1. Four markers of lung endothelial function were monitored: ACE activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Right lung ACE and PLA activities decreased with increasing radiation dose, and CGS13945 significantly ameliorated both responses. Dose-reduction factors (DRF) for the inhibitor were 1.80 for ACE activity and 1.41 for PLA activity (p less than 0.05). In contrast, lung PGI2 and TXA2 production increased with increasing radiation dose, and CGS13945 did not influence either response significantly. Thus the ACE inhibitor CGS13945 modifies radiation-induced pulmonary endothelial dysfunction in rats, indicating that the presence of a thiol group is not essential for therapeutic efficacy in this class of compounds. On the other hand, CGS13945 exhibits a differential sparing of radiation-induced pulmonary endothelial dysfunction, as does penicillamine. A structure-function analysis of the present and previous data indicates that all of the ACE inhibitors tested (Captopril, CL242817 and CGS13945) spare the radiation-induced suppression in lung ACE and PLA activity; all of the thiol compounds tested (penicillamine, Captopril and CL242817) spare the radiation-induced elevation in lung PGI2 and TXA2 production; and the thiol ACE inhibitors (Captopril and CL242817) spare all four endothelial responses. These data confirm a novel and potentially important application for ACE inhibitors as modifiers of radiation-induced lung injury, and suggest that there are at least two components to their mechanism of therapeutic action in this model.

Radiation-induced endothelial dysfunction and fibrosis in rat lung: modification by the angiotensin converting enzyme inhibitor CL242817

The purpose of this study was to evaluate the angiotensin converting enzyme (ACE) inhibitor CL242817 as a modifier of radiation-induced pulmonary endothelial dysfunction and pulmonary fibrosis in rats sacrificed 2 months after a single dose of 60Co gamma rays (0-30 Gy) to the right hemithorax. CL242817 was administered in the feed continuously after irradiation at a regimen of 60 mg/kg/day. Pulmonary endothelial function was monitored by lung ACE activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Pulmonary fibrosis was evaluated by lung hydroxyproline (HP) content. Lung ACE and PLA activities decreased with increasing radiation dose, and cotreatment with CL242817 significantly ameliorated both responses. CL242817 dose-reduction factors (DRF) were 1.3-1.5 for ACE and PLA activity. Lung PGI2 and TXA2 production increased with increasing radiation dose, and CL242817 almost completely prevented both radiation responses. The slope of the radiation dose-response curves in the CL242817-treated rats was essentially zero, precluding calculation of DRF values for PGI2 and TXA2 production. Lung HP content also increased with increasing radiation dose, and CL242817 significantly attenuated this response (DRF = 1.5). These data suggest that the ability of ACE inhibitors to ameliorate radiation-induced pulmonary endothelial dysfunction is not unique to captopril [Ward et al., Int. J. Radiat. Oncol. Biol. Phys. 15, 135-140 (1988)], rather it is a therapeutic action shared by other members of this class of compounds. These data also provide the first evidence that ACE inhibitors exhibit antifibrotic activity in irradiated rat lung.

Unscheduled DNA synthesis in various types of cells of the mouse brain in vivo

Very low incorporation of 3H-thymidine (TdR) into neurons and non-proliferating glial and endothelial cells in various brain areas of the adult mouse after 3H-TdR injection and subsequent X-irradiation of the head with 45 Gy has been demonstrated autoradiographically after exposure times of 250 days. In accordance with biochemical studies this incorporation of 3H-TdR represents DNA repair synthesis or UDS (unscheduled DNA synthesis). However, 3H-TdR incorporation into nuclear DNA of non-proliferating cells in the brain was not only found in X-irradiated but also in sham-irradiated mice. This suggests that spontaneous UDS also occurs. Up to now spontaneous UDS has been shown only in HeLa cells in vitro. Nearly all the various types of brain cells tested exhibited UDS after X-irradiation as well as spontaneous UDS. After correcting the mean grain numbers per nucleus not only for background but also for beta-self-absorption, substantial differences became apparent in the extent of UDS between the individual types of cells. After X-irradiation, UDS was highest in Purkinje cells and hippocampal granular cells but comparable UDS was also found in endothelial cells, regardless of the different brain areas studied. The extent of spontaneous UDS is also quite different in the various cell types, being highest in neurons of different sites and considerably lower in endothelial and glial cells.

Radiation-induced pulmonary endothelial dysfunction in rats: modification by an inhibitor of angiotensin converting enzyme

The ability of the angiotensin converting enzyme (ACE) inhibitor Captopril to modify radiation-induced pulmonary endothelial dysfunction was determined in male rats sacrificed 2 months after a single dose of 10-30 Gy of 60Co gamma rays to the right hemithorax. Half of each dose group consumed feed containing 0.12% w/w Captopril (60 mg/kg/day) continuously after irradiation, and half consumed control feed. Four markers of endothelial function were monitored: ACE activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. All data were plotted as dose-response curves, and subjected to linear regression analysis. The Captopril modifying effect was expressed as the ratio of isoeffective doses at a common intermediate response (DRF), or as the ratio of the response curve slopes. Right lung ACE and PLA activity decreased linearly, and PGI2 and TXA2 production increased linearly with increasing radiation dose. Captopril exhibited DRF values of 1.4-2.1, and slope ratios of 1.4-5.1 for all four functional markers (p less than 0.05). Thus, the ACE inhibitor Captopril ameliorates radiation-induced pulmonary endothelial dysfunction in rats sacrificed 2 months postirradiation. Although the mechanism of Captopril action is not clear at present, these data suggest a novel application for this class of compounds as injury-modifying agents in irradiated lung.

Split-dose sparing of gamma-ray-induced pulmonary endothelial dysfunction in rats

The purpose of this study was to determine whether radiation-induced pulmonary endothelial dysfunction exhibits split-dose sparing. Rats were sacrificed 2 months after a range of 60Co gamma-ray doses (0-40 Gy) delivered to the right hemithorax in either a single fraction or in two equal fractions separated by 24 h. Pulmonary angiotensin converting enzyme (ACE) activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production served as indices of lung endothelial function. There were dose-dependent decreases in ACE and PLA activity and increases in PGI2 and TXA2 production after both single and split-dose exposures. The D2-D1 values determined from the two-fraction minus single-fraction isoeffective doses were 3.9 Gy for ACE activity, 7.2 Gy for PLA activity, 4.8 Gy for PGI2 production, and 4.7 Gy for TXA2 production. Thus these data demonstrate that over the present range of radiation doses approximately 4-7 Gy is repairable as subeffective endothelial damage during the 24-h interval between fractions. These values agree with previously published estimates of split-dose sparing in mouse lung based on lethality and breathing rate assays.

Functional responses of the pulmonary endothelium to thoracic irradiation in rats: differential modification by D-penicillamine

Male rats were sacrificed 2 or 6 months after a range of single doses of gamma rays (0-30 Gy) to the right hemithorax. Half of each dose group consumed control feed continuously after irradiation, and half consumed feed containing the collagen antagonist D-penicillamine (10 mg/rat/day). Four markers of pulmonary endothelial function were monitored: angiotensin converting enzyme (ACE) activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Bronchoalveolar lavage (BAL) fluid also was obtained from the right lung, and was analyzed for macrophage number, and PGI2 and TXA2 concentration. Right lung ACE and PLA activities decreased linearly with increasing dose at both 2 and 6 months postirradiation, and penicillamine had no significant effect on either response. In contrast, PGI2 and TXA2 production by the right lung increased linearly with increasing radiation dose at both autopsy times. Penicillamine significantly ameliorated the increase in PGI2 production at 2 months, and the increase in TXA2 production at both 2 and 6 months postirradiation. Penicillamine dose-reduction factors (DRF) for PGI2 and TXA2 production were 1.3-1.4, and the response curve slope ratios were 1.7-2.5 (p less than 0.05). Penicillamine also ameliorated the dose-dependent increase in TXA2 concentration in the BAL fluid at 2 months. These data indicate that the four "markers" of radiation-induced pulmonary endothelial dysfunction do not respond identically to penicillamine dose-modification. Of the four markers, TXA2 production exhibits the most significant and widespread penicillamine sparing. TXA2 is a potent vasoconstrictor, promoter of platelet aggregation, and mediator of inflammation, and partial prevention of the radiation-induced hyperproduction of this eicosanoid may account in part for penicillamine's therapeutic action in this model.

WR 2721 modification of type II cell and endothelial cell function in mouse lung after single doses of radiation

The ability of WR 2721 to protect endothelial cells and Type II cells in mouse lung after single doses of X rays was studied using specific assays of cell function to assess damage. The whole thorax of mice was exposed to a range of single doses of X rays either alone or 30 minutes after an i.p. injection of 400 mg/kg of WR 2721. Endothelial cell function was assayed by angiotensin converting enzyme (ACE) and Type II cell function by phosphatidylcholine and total protein present in lavage fluid 28 days after radiation. Similar protection factors (PFs) were found for the functional activity of both cell types, 1.2 and 1.24 for ACE and phosphatidylcholine respectively. These values were somewhat less than the PF of 1.37 for lethality from pneumonitis 7 to 9 months after irradiation for this mouse strain. The lack of a clear difference between the PFs for the functional activity of these two cell types suggests that neither the endothelial cell nor the Type II cell can be accepted or excluded as the target cell for radiation pneumonitis in lung.

Recovery of prostacyclin capacity of irradiated endothelial cells and the protective effect of vitamin C

Ionizing irradiation has been reported to affect prostacyclin (PGI2) production by intact blood vessels and cultured endothelial cells (EC) due to damage of enzymes of the arachidonate cascade. In the present study, we investigated whether EC can recover from radiation injury and regain their capacity to produce PGI2. Bovine aortic EC were exposed to radiation doses of 3 and 6 Gy and their capacity to produce PGI2 in response to stimulation with arachidonic acid was tested, at various times after irradiation. The results of these experiments showed clearly that EC exposed to single or fractionated irradiation could recover their capacity to produce PGI2 depending on the radiation dose and the time period following radiation. Radiation damage is associated with oxidant stress and the production of free radicals. We therefore tested the ability of an oxygen radical scavenger, vitamin C, to protect the capacity of irradiated EC to produce PGI2. Pretreatment of EC with low concentrations of vitamin C inhibited the radiation induced release of PGI2 to the culture medium. Vitamin C also enhanced the capacity of irradiated EC to produce PGI2 following short stimulation with arachidonic acid. Treatment with this scavenger however, did not protect the cells against the cytopathic effects of radiation.

The effects of ionizing radiation on the pulmonary vasculature of intact rats and isolated pulmonary endothelium

We studied the effects of ionizing radiation on the morphology of the pulmonary circulation using an in vivo rat model and an in vitro pulmonary artery endothelial cell model. Gamma radiation was given as either an acute (30 Gy) or fractionated (5 X 6 Gy) dose to one hemithorax of rats. An acute 30-Gy dose delivered resulted in a 70% decrease in pulmonary arterial perfusion, using technetium-99m microaggregated albumin (99mTc-MAA), in the irradiated lung by 2-3 weeks after irradiation. Pulmonary microradiographs, using a barium sulfate perfusion method, obtained 2-3 weeks after irradiation demonstrated widespread loss of capillary filling and segmentation of the vessels. Histologic examination demonstrated intact capillaries, suggesting that the alterations in pulmonary perfusion were at the precapillary level. Similar abnormalities in lung perfusion and morphology were found after delivery of fractionated doses of radiation, but the onset of the changes was delayed, occurring 4-6 weeks postirradiation. Using cultured pulmonary endothelial cell monolayers, cell sloughing and retraction from the surface substrate were observed within 24 h after in vitro delivery of 30 Gy. Similar findings occurred in monolayers given fractionated doses (5 X 6 Gy) of radiation 2-3 days after the final dose. The in vivo animal and in vitro endothelial cell models offer a useful means of examining the morphologic alterations involved in radiation lung vascular damage.

Pulmonary endothelial dysfunction induced by unilateral as compared to bilateral thoracic irradiation in rats

Rats were sacrificed 2 months after a single dose of 10-30 Gy of 60Co gamma rays delivered to either a right unilateral or a bilateral thoracic port. Four indices of lung endothelial function were measured: the activities of angiotensin-converting enzyme (ACE) and plasminogen activator (PLA) and the production of prostacyclin (PGI2) and thromboxane (TXA2). The number of macrophages recovered by bronchoalveolar lavage (BAL) and the degree of right ventricular hypertrophy (an index of pulmonary hypertension) also were determined. Right lung ACE and PLA activity decreased linearly, and PGI2 and TXA2 production increased linearly with increasing radiation dose. The response curves for right unilateral and bilateral thoracic irradiation were not significantly different. In contrast, bilateral irradiation was more toxic than unilateral, since rats exposed to the former exhibited decreased body weight, an increased incidence of pleural effusions, an increase in the number of macrophages recovered by BAL, and right ventricular hypertrophy. These data demonstrate that pulmonary endothelial dysfunction induced by hemithorax irradiation represents a direct response of the endothelium to radiation injury and is not secondary to other phenomena such as shunting of function to the shielded lung.