Radiation-induced Apoptosis: Its Role in a MADCaT (Mitosis-opoptosis-differentiation-calcium Toxicity) Scheme of Cytotoxicity Mechanisms

Antiapoptotic and proliferative activity of curcumin on ovarian follicles in mice exposed to whole body ionizing radiation

The aim of this study was to evaluate the antiapoptotic and proliferative activity of curcumin (Cur) on the ovarian follicles in mice exposed to whole body ionizing radiation (Rd). The mice were exposed to 8.3 gray whole body Rd, and Cur groups were given as a daily dose of 100 mg/kg of Cur for 10 days (10 days before Rd). The ovaries were collected 3 and 12 h after irradiation. To date, no such studies have been performed on antiapoptotic and proliferative activity of Cur on the ovarian follicles in mice exposed to whole body Rd. Analysis of mice ovary after exposure to Rd by terminal-deoxynucleotidyl-transferase-mediated dUTP nick end labeling showed that there were apoptotic cells both in the follicular wall and the antrum, and that the number of follicles showing early atresic features was high 3 h after Rd. On the other hand, analysis of mice ovary 12 h after exposure to Rd showed that the number of follicles containing apoptotic cells with advanced atresic features was significantly higher when compared to the 3-h Rd exposure group. The proliferating cell nuclear antigen -positive granulosa cells were decreased in association with follicular atresia. The groups given treatment were observed to have some benefit from Cur against the damage caused by Rd. The results of this study demonstrate that Cur prevents follicular atresia in Rd-induced apoptosis in ovarian follicles.

Frequency of background and radiation-induced apoptosis in leukocytes of individuals with alpha-thalassemia variants, assessed by the neutral comet assay

To study effects of ionizing radiation on apoptosis induction in leukocytes of alpha-thalassemia (alpha-thal) variants compared to normal controls, venous blood samples were obtained from 10 healthy volunteers and 30 alpha-thal patients. Different types alpha-thal were diagnosed by multiplex polymerase chain reaction (PCR). Blood samples were irradiated with three Gy gamma rays, used for comet assay, immediately or 48 h after irradiation. Results show that the frequency of background as well as apoptosis in silent alpha-thal carriers, alpha-thal carriers and controls was similar but there was a significant difference between Hb H patients and other groups in the study. The increased apoptosis in Hb H patients might suggest that accumulation of beta-globin and oxidative stresses are effective in causing apoptosis, and cells from these patients are more vulnerable to damage from radiation-induced toxic substances. Therefore, from alpha-thal patients, those with Hb H disease might be considered as radiosensitive in terms of apoptosis formation.

Acid ceramidase upregulation in prostate cancer cells confers resistance to radiation: AC inhibition, a potential radiosensitizer

Radiation resistance in a subset of prostate tumors remains a challenge to prostate cancer radiotherapy. The current study on the effects of radiation on prostate cancer cells reveals that radiation programs an unpredicted resistance mechanism by upregulating acid ceramidase (AC). Irradiated cells demonstrated limited changes of ceramide levels while elevating levels of sphingosine and sphingosine-1-phosphate. By genetically downregulating AC with small interfering RNA (siRNA), we observed radiosensitization of cells using clonogenic and cytotoxicity assays. Conversely, AC overexpression further decreased sensitivity to radiation. We also observed that radiation-induced AC upregulation was sufficient to create cross-resistance to chemotherapy as demonstrated by decreased sensitivity to Taxol and C(6) ceramide compared to controls. Lower levels of caspase 3/7 activity were detected in cells pretreated with radiation, also indicating increased resistance. Finally, utilization of the small molecule AC inhibitor, LCL385, sensitized PPC-1 cells to radiation and significantly decreased tumor xenograft growth. These data suggest a new mechanism of cancer cell resistance to radiation, through upregulation of AC that is, in part, mediated by application of the therapy itself. An improved understanding of radiotherapy and the application of combination therapy achieved in this study offer new opportunities for the modulation of radiation effects in the treatment of cancer.

Resveratrol sensitization of DU145 prostate cancer cells to ionizing radiation is associated to ceramide increase

Radiotherapy is an established therapeutic modality for prostate cancer. Since it is well known that radiotherapy is limited due to its severe toxicity towards normal cells at high dose and minimal effect at low dose, the search for biological compounds that increase the sensitivity of tumors cells to radiation may improve the efficacy of therapy. Resveratrol, a natural antioxidant, was shown to inhibit carcinogenesis in animal models, and to block the process of tumor initiation and progression. The purpose of this study was to examine whether or not resveratrol can sensitize DU145, an androgen-independent human prostate cancer cell line, to ionizing radiation. We report here that DU145 cells are resistant to ionizing radiation-induced cell death, but pretreatment with resveratrol significantly enhances cell death. Resveratrol acts synergistically with ionizing radiation to inhibit cell survival in vitro. Resveratrol also potentiates ionizing radiation-induced ceramide accumulation, by promoting its de novo biosynthesis. This confirms ceramide as an effective mediator of the anticancer potential induced by resveratrol.

Radiosurgery of isolated cerebral vessels following administration of paclitaxel in the rat

Object

Progressive obliteration occurs in arteriovenous malformations (AVMs) after radiosurgery; however, the risk of hemorrhage remains until the obliteration process is complete. The authors sought to enhance the radiation effect and reduce the risk of hemorrhage by facilitating faster vessel obliteration. To that end, a combination of a lower radiation dose with the addition of a radiosensitizing agent was compared with the effect of a higher radiation dose alone.

Methods

Using a method described by Mulvany and Halpern, isometric myography measurements were made on isolated rat middle cerebral artery specimens. The vessels were treated with 200 Gy, 80 Gy, 50 Gy, 25 Gy, 20 Gy, or 15 Gy by using Gamma Knife surgery. Taxol (paclitaxel 3 mg/kg/body weight) was administered intravenously to the animals. Survival times posttreatment were 24 hours, 6 weeks, 12 weeks, 12 months, or 18 months. After dissection, the middle cerebral arteries were mounted on a small-vessel myograph, and contraction and relaxation studies were performed.

In a second series of experiments these results were validated in human fibroblast culture. When the cultures were 75 to 80% colonized, the samples were treated in vitro with 60Co gamma radiation in similar doses with or without paclitaxel.

Conclusions

Constriction responses were generally decreased in the paclitaxel-treated vessels. Differences were significant at 6 weeks (p < 0.05) and at 1 year (p < 0.05). After 1 year, in the paclitaxel-treated groups vascular reactivity was completely abolished in vessels receiving 50 Gy. In comparison, it took 6 months longer (18 months) for this reaction to be abolished in vessels without paclitaxel treatment.

In tissue cultures Giemsa staining and immunohistochemical reactions for p53, Ki-67, CD-34, and SMA antigens revealed marked fibroblast hypertrophy in all of the paclitaxel-treated groups. Paclitaxel-treated vessels demonstrated decreased reactivity at significantly earlier stages than vessels that had not been treated. It would appear that paclitaxel causes acceleration in the time course of the late biological effect of gamma radiation. This beneficial effect could be used in Gamma Knife surgery in patients with AVMs, thus reducing the risk of posttreatment hemorrhage.

X irradiation induces the proapoptotic state independent of the loss of clonogenic ability in Chinese hamster V79 cells

The clonogenic ability (reproductive cell death) of Chinese hamster V79 cells was measured after treatment with X radiation and a newly developed anti-cancer drug, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS106). Amplification in the loss of clonogenicity was observed compared to that obtained for cells exposed to X rays alone. Addition of benzyloxycarbonyl-val-ala-asp-fluoromethylketone (Z-VAD-FMK), a broad-spectrum caspase inhibitor, attenuated the increased lethality, but the dose-response curve obtained was found to merely revert to that obtained for cells exposed to X rays alone. Flow cytometric analysis showed that the number of cells arrested at the G2/M phase by X irradiation was decreased by co-treatment with TAS106, and instead the number of cells in the sub-G1 phase increased. Western blot analysis proved that TAS106 treatment down-regulated the expression of the G2/M arrest-related proteins cyclin B1, phospho-CDC2 and WEE1. From these results, it was concluded that (1) no apoptosis was included in the dose-response curve obtained from cells exposed to X rays alone, (2) X radiation induced a potentially apoptotic (proapoptotic) state in cells independent of the loss of their clonogenic ability, and (3) TAS106 enhanced the loss of their clonogenic ability by converting the proapoptotic cells to apoptotic cells through the abrogation of arrest at the G2/M phase.

Suppression of apoptosis and clonogenic survival in irradiated human lymphoblasts with different TP53 status

The influence of radiation-induced apoptosis on radiosensitivity was studied in a set of closely related human lymphoblastoid cell lines differing in TP53 status. The clonogenic survival of irradiated TK6 cells (expressing wild-type TP53), WTK1 cells (overexpressing mutant TP53), and TK6E6 cells (negative for TP53 owing to transfection with HPV16 E6) was assessed in relation to the induction of apoptosis and its suppression by caspase inhibition or treatment with PMA as well as after treatment with caffeine. Measurements using the alkaline comet assay and pulsed-field electrophoresis of the induction and repair of DNA strand breaks showed similar kinetics of the processing of early DNA damage in these cell lines. The cytochalasin B micronucleus assay revealed identical levels of residual damage in the first postirradiation mitosis of these cells. Abrogation of TP53-dependent apoptosis in TK6E6 cells resulted in a distinct increase in radioresistance. Further suppression of apoptosis as observed in WTK1 cells overexpressing mutant TP53 apparently was not responsible for the high radioresistance of WTK1 cells, since other means of highly efficient suppression of apoptosis (caspase inhibition or PMA treatment) increased the clonogenic survival of irradiated TK6 cells only to levels similar to those of TK6E6 cells with abrogated TP53-dependent apoptosis. Considering the similar levels of residual chromosomal damage in TK6E6 cells and WTK1 cells, a hitherto unknown mechanism of tolerance needs to be inferred for these TP53 mutant cells. This residual damage tolerance, however, appears to require an intact G2/M-phase checkpoint function since the relative radioresistance of the WTK1 cells was completely lost upon caffeine treatment, which also resulted in a failure of the TK6 and TK6E6 cells to execute apoptosis. In this situation, the cellular response seems to be dominated entirely by TP53-independent mitotic failure.

Experimental stereotactic gamma knife radiosurgery. Vascular contractility studies of the rat middle cerebral artery after chronic survival

In vitro isometric small vessel myograph experiments and pathological investigations were performed on rat middle cerebral arteries. Thirty-four animals provided 68 normal vessels, six further rats had the endothelial layer mechanically removed from their 12 arteries. Eighteen animals received gamma knife irradiation to the middle cerebral arteries. Fifteen of these received 50 Gray, and three 25 Gray dose to the 50% isodose and the contralateral vessels offered 20 Gray and 15 Gray irradiated specimens. Survival times varied from 12 weeks to 18 months. In the acute stage, abolition of potassium-induced relaxation occurred as early as 24 h after irradiation whilst in one year this reaction seemed to recover and remained active to 18 months. The contraction response to prostaglandin F2 alpha was diminished at six weeks in the 50 Gray-irradiated vessels. However, from one year further reduction was seen and by 18 months this response was totally abolished. We demonstrated reduction of contractile capability of the irradiated normal vessels while the vessels remained patent. When using low irradiation dose there were no pathological changes even at 18 months, but marked physiological changes could be demonstrated. Different vessel wall functions appear to have different radiosensitivity, time course and capability for regeneration.

X-rays modulate extracellular matrix in vivo

X-rays have an antiangiogenic effect in the chicken embryo chorioallantoic membrane (CAM) model of in vivo angiogenesis. Our study demonstrates that X-rays induce an early apoptosis of CAM cells, modulate the synthesis and deposition of extracellular matrix (ECM) proteins involved in regulating angiogenesis and affect angiogenesis induced by tumour cells implanted onto the CAM. Apoptosis was evident within 1-2 hr, but not later than 6 hr after irradiation. Fibronectin, laminin, collagen type I, integrin alpha(v)beta3 and MMP-2 protein amounts were all decreased 6 hr after irradiation. In contrast, collagen type IV, which is restricted to basement membrane, was not affected by irradiation of the CAM. There was a similar decrease of gene expression for fibronectin, laminin, collagen type I and MMP-2, 6 hr after irradiation. The levels of mRNA for integrin alpha(v)beta3 and collagen type IV were unaffected up to 24 hr after irradiation. The decrease in both protein and mRNA levels was reversed at later time points and 48 hr after irradiation, there was a significant increase in the expression of all the genes studied. When C6 glioma tumour cells were implanted on irradiated CAMs, there was a significant increase in the angiogenesis induced by tumour cells, compared to that in non-irradiated CAMs. Therefore, although X-rays have an initial inhibitory effect on angiogenesis, their action on the ECM enhances new vessel formation induced by glioma cells implanted on the tissue.

Review article: new insights into the pathogenesis of radiation-induced intestinal dysfunction

Exposure of the abdomino-pelvic region to ionizing radiation, such as that received during radiotherapy, is associated with the development of a number of untoward symptoms which may limit the course of therapy or which may involve serious chronic intestinal disease. While the mucosal dysfunction surrounding acute radiation enteritis is generally ascribed to the effects of ionizing radiation on the cell cycle of epithelial stem cells of the intestinal crypts and subsequent epithelial loss, recent evidence suggests that other, earlier events also play a role. The severity of these early events may determine the incidence and severity of chronic enteritis. The mechanism for this is unclear, but may relate to radiation-induced compromise of host defence responses to luminal pathogens or antigens. This review will address the current state of knowledge of the pathogenesis of radiation-induced intestinal dysfunction, focusing on events which occur in the mucosa, and will discuss what the future may hold with respect to the treatment of radiation-associated diseases of the intestinal tract.

Overexpression of bax in human glioma cell lines

OBJECT

Cells that lose their ability to undergo apoptosis may promote the development of neoplasms and result in resistance to clinical treatment with DNA-damaging modalities such as radio- and chemotherapy. Four established human glioma cell lines that are resistant to apoptosis were transfected with the proapoptotic gene bax and assessed for their sensitivity to a proapoptotic stimulus.

METHODS

Two cell lines had a wild-type p53 genotype (U87 and D247MG) and two had mutant p53 genotypes (U138 and U373). Constitutive overexpression of murine bax was achieved in U138 and U373 only, which resulted in an increased sensitivity of these lines to the apoptosis-inducing effect of cytosine arabinoside (ara-C). Multiple attempts to produce constitutive overexpression of bax in U87 and D247MG cells resulted in spontaneous, near-complete cell loss. Vector-only control transfections were successful in all four cell lines. Inducible overexpression of bax was achieved in the U87 cells and elevated levels of BAX were observed as early as 6 hours after gene induction. This overexpression of BAX resulted in the spontaneous induction of apoptosis in these cells.

CONCLUSIONS

Overexpression of BAX in four human glioma cell lines resulted in increased sensitivity to apoptosis. In the two lines that had a wild-type p53 genotype, overexpression of BAX produced spontaneous apoptosis. In contrast, the lines that had mutant, nonfunctional P53 did not undergo spontaneous apoptosis, but they were rendered more sensitive to the apoptosis-inducing effect of ara-C. Modulation of BAX expression may be a useful therapeutic modality for gliomas, regardless of p53 genotype.

Regulation of BAX and BCL-2 expression in breast cancer cells by chemotherapy

Optimizing chemotherapeutic drug delivery strategies relies, in part, on identification of the most clinically effective sequence, dose, and duration of drug exposure. The combination of dose intensive etoposide (VP-16) followed by cyclophosphamide has clinical efficacy in the treatment of advanced breast cancer. However, molecular mechanisms that underlie the effectiveness of this combination of chemotherapeutic agents have not been investigated. In this study we investigated regulation of BAX and BCL-2 expression by VP-16 and cyclophosphamide as a potential mechanism for the induction of breast cancer cell death induced by this regimen. There was a dose and time dependent increase in BAX expression in the breast cancer cell lines MCF-7, MDA-MB-435S, and MDA-MB-A231 following in vitro treatment with 50-100 microM VP-16. Elevation of BAX protein expression in the presence of VP-16 alone did not correlate with reduced viability or induction of apoptosis in MCF-7, MDA-MB-435S, or MDA-MB-A231. VP-16 did effectively block the breast cancer cell lines evaluated (MCF-7 and MDA-MB-435S) at G2/M phase of the cell cycle, confirming activity of the drug in vitro. MCF-7 and MDA-MB-435S cells that were pre-treated with VP-16 and subsequently exposed to 1.0-12.0 microg/ml 4-hydroperoxycyclophosphamide (4HC), an active metabolite of cyclophosphamide, had markedly reduced viability when compared to matched controls treated with either VP-16 or 4HC individually. Consistent with this loss of viability, exposure of all three cell lines to the combination of VP-16 and 4HC resulted in higher BAX protein levels than those observed following treatment with either single agent. This combination of chemotherapeutic agents also resulted in reduced BCL-2 expression. These observations suggest that combination chemotherapy may derive its efficacy, in part, through coordinated regulation of specific gene products associated with apoptosis. Characterization of molecular events that underlie susceptibility of specific tumor cells to combination chemotherapeutic regimens may lead to additional improvements in treatment strategies for this disease.

Distinctive inhibitory activity of docosahexaenoic acid against sphingosine-induced apoptosis

The effect of supplementation of docosahexaenoic acid (DHA) on the apoptosis of HL60 cells was examined using N-acetyl sphingosine (C2-ceramide) and sphingosine as apoptosis-inducing agents. Although C2-ceramide-induced apoptosis was not affected by DHA supplementation, sphingosine-induced apoptosis was reduced almost to the background level by preincubation with 10 microM DHA for 24 h. Among the fatty acids, only DHA appeared to be endowed with the ability to reduce sphingosine-induced apoptosis, whereas, other unsaturated fatty acids, such as arachidonic acid (AA) and eicosapentaenoic acid (EPA), did not show this activity. Incubation of HL60 with DHA within 6 h did not affect the apoptosis, suggesting that DHA probably expressed the inhibitory activity after modulation of the membrane fatty acid composition. DHA also attenuated the apoptosis induced by dimethylsphingosine and H-7, but not by calphostin C, indicating that enrichment of DHA in membranous phospholipid does not necessarily prevent all of the apoptosis associated with the inhibition of protein kinase C. The mechanism of the inhibition against sphingosine-induced apoptosis by DHA remains to be further explored. However, the inhibition of cytosolic phospholipase A2 (cPLA2) may be involved in the mechanism, because distinctive inhibitory activity of DHA against cPLA2 has been demonstrated [M. Shikano, Y. Masuzawa, K. Yazawa, K. Takayama, I. Kudo, K. Inoue, Biochim. Biophys. Acta, 1212, 1994, 211-216], and arachidonyl trifluoromethylketone, a specific inhibitor of cPLA2, attenuated the apoptosis induced by sphingosine.

UV irradiation of a B-cell hybridoma increases expression of alkaline phosphatase: involvement in apoptosis

Expression of alkaline phosphatase (APase) by 7TD1 B-cell hybridoma was amplified by ultraviolet irradiation; cell growth was inhibited and cell death by apoptosis was increased. Irradiation induced high levels of APase activity in cycling as well as in apoptotic cells. In contrast, APase activity faded with time in nonirradiated cells and was no longer expressed in spontaneous apoptotic cells appearing after several days in culture. This was demonstrated by cell morphology, DNA fragmentation, and flow cytometry after simultaneous staining of DNA with Hoechst 33342 and APase with naphthol AS-TR phosphate - fast red RC fluorescent reagent. Levamisole, a specific inhibitor of APase activity, almost totally abrogated apoptosis induced by ultraviolet irradiation at doses that failed to affect 7TD1 cell survival. These data suggest that APase could play a role in the signalling cascade that mediates apoptosis in irradiated cells. Key words: alkaline phosphatase, apoptosis, flow cytometry, levamisole, UV irradiation.

Early plasma membrane events occurring in ultraviolet-B-induced apoptosis

Whereas nonsolar ultraviolet C radiation primarily affects nuclei (i.e., where it is absorbed by nucleic acids) of eukaryotic cells, ultraviolet radiation of long (320-380 nm) wavelengths (ultraviolet A) and intermediate (290-320 nm) wavelengths (ultraviolet B) primarily affects lipid membranes. We have previously demonstrated that ultraviolet B irradiation alters the surface architecture of human B cells and impairs expression of an erythroid growth factor on their surface and on extracellular vesicles. Here, we examined the effects of ultraviolet B irradiation on the capacity of Chinese hamster ovary cells to undergo the process of exfoliation, and on the capacity of Chinese hamster ovary cells transfected with flt3/flk2 cDNA to express the cytokine flt3/flk2. Our results indicate that the rate of release of shed vesicles from untransfected Chinese hamster ovary cells is decreased after one to two h, at a time when there is electron microscopic evidence for retention of vesicles at the cell surface. These changes at the cell surface precede all other apparent morphological changes (including DNA condensation in the nucleus, swelling of the mitochondria and appearance of apoptotic bodies). Furthermore, plasma membranes and shed extracellular vesicles from ultraviolet B irradiated Chinese hamster ovary cells that have been transfected with flt3/flk2 cDNA fail to express the protein.

Overexpression of adenovirus-encoded transgenes from the cytomegalovirus immediate early promoter in irradiated tumor cells

Efficient expression of therapeutic genes in irradiated tumor cells would facilitate the conversion of a malignant tumor nodule into a cancer vaccine in situ. We reported previously that transgene expression from an adenoviral vector could be markedly enhanced by treating transduced tumor cells with butyrate. In this study, we demonstrated that a similar butyrate effect could be achieved in irradiated tumor cells. In addition, irradiating cells at doses of 2-40 Gy prior to transduction could also amplify recombinant adenoviral transgene products in a cell-type-specific manner. This suggests that adenovirus-mediated gene therapy, radiation therapy, and butyrate-mediated cancer therapy may potentially be formulated into one synergistic protocol for cancer treatment.

bcl-2 over-expression delays radiation-induced apoptosis without affecting the clonogenic survival of human prostate cancer cells

In this study we evaluated the effect of over-expression of the bcl-2 gene, a potent apoptosis suppressor, on radiation-induced apoptotic cell death in 2 human prostate cancer cell lines, androgen-independent PC-3 cells and androgen-sensitive LNCaP cells. Cells were transfected with the bcl-2 gene and bcl-2 transfectant clones isolated under neomycin selection; bcl-2 gene integration and level of mRNA and protein expression in the cloned transfectants were examined by Southern, Northern and Western blot analyses, respectively. Parental, neo control and bcl-2-expressing cells were exposed to single or fractionated doses of ionizing irradiation, and the cellular response to radiation was determined at 24, 48 and 72 hr post-irradiation, on the basis of: (i) loss of cell viability, (ii) clonogenic survival and (iii) induction of apoptotic DNA fragmentation. At 24 hr post-irradiation all cell lines, i.e., parental and bcl-2 transfectants, failed to form colonies, though the majority of bcl-2-expressing cells did not exhibit apoptotic morphology; bcl-2 over-expression in both cell lines reduced apoptosis 48 hr post-irradiation from 20-25% to 5% at a dose of 2,000 cGy. By 72 hr, bcl-2 over-expression afforded a 3-fold protection from radiation-induced apoptosis. There was no significant difference, however, in the clonogenic survival of the parental and bcl-2-expressing cells. Furthermore, there was a 24 hr delay in induction of the apoptosis marker gene SGP-2/TRPM-2 in the bcl-2-expressing cells, co-incidental with the delay in apoptotic DNA fragmentation.

Acid sphingomyelinase-deficient human lymphoblasts and mice are defective in radiation-induced apoptosis

Stress is believed to activate sphingomyelinase to generate ceramide, which serves as a second messenger in initiating the apoptotic response. Conclusive evidence for this paradigm, however, is lacking. In the present study, we used a genetic approach to address this issue directly. We show that lymphoblasts from Niemann-Pick patients, which have an inherited deficiency of acid sphingomyelinase activity, fail to respond to ionizing radiation with ceramide generation and apoptosis. These abnormalities are reversible up on restoration of acid sphingomyelinase activity by retroviral transfer of human acid sphingomyelinase cDNA. Acid sphingomyelinase knockout mice also expressed defects in radiation-induced ceramide generation and apoptosis in vivo. Comparison with p53 knockout mice revealed that acid sphingomyelinase-mediated apoptosis and p53-mediated apoptosis are likely distinct and independent. These genetic models provide definitive evidence for the involvement of acid sphingomyelinase in one form of stress-induced apoptosis.

Effects of ultraviolet light in vascular cells in vitro and in intact atherosclerotic explants: potential role of apoptosis in vascular biology

Complex cell-to-cell interactions are known to participate during vascular injury and remodeling, resulting in smooth muscle cell proliferation. Mechanical interventions have yielded little benefit in limiting this process and several site-specific genetic therapies are not yet clinically available. The aim of this study was to delineate the effect of very short wavelength ultraviolet (UVC) light therapy on the viability of macrophage and smooth muscle cells. Vascular cells were both treated in vitro and in intact explanted atherosclerotic aortic segments ex vivo with UVC light. Brief exposure to short wavelength UVC light in the absence of photosensitizers elicited a differential temporal and functional response among treated cells. However, dramatic reduction in both cellular viability and proliferative capacity with eventual cell demise was observed in all UVC-treated cells. Flow cytometry and immunohistochemical analyses revealed the presence of extensive DNA fragmentation, suggestive of apoptosis as a predominant pathway of cell death in these cells exposed to UVC light. We hypothesize that selective induction of apoptosis, in contrast to necrosis, with UVC light may represent a beneficial approach to interdict the complex biologic cascade of messengers that participate in the restenotic response to vascular injury.

Radiation-induced apoptosis: relevance to radiotherapy

Radiation-induced apoptosis is reviewed in terms of: (a) the identification of apoptotic and necrotic cells, (b) observations in vitro and in vivo of radiation-induced apoptosis, (c) genes controlling apoptosis, (d) evidence that the target may be the plasma membrane or nuclear DNA, (e) quantitative comparisons of apoptotic death and reproductive (clonogenic) death, (f) the importance of radiation-induced apoptosis in radiotherapy, and (g) studies of radiation-induced apoptosis that are needed. High priority should be placed on determining the molecular pathways that are important in the expression and modulation of radiation-induced apoptosis. Specifically, the events that modulate the apoptosis that occurs in interphase before the cell can divide should be distinguished from the events before division that modulate the misrepair of DNA damage, that results in chromosomal aberrations observed in mitotic cells, which in turn cause the progeny of the dividing cell with aberrations to die by either apoptosis or necrosis. Then, molecular events that determine whether a cell that divides with or without a chromosomal aberration will produce progeny that apoptose or necrose need to be identified. These considerations are important for determining how modulation of radiation-induced apoptosis will affect the ultimate clonogenic survival, and possibly genomic instability in the surviving progeny.

Recent advances in radiation oncology

Radiotherapy remains an important component of the management of malignant disease. Especially when combined with cytotoxic chemotherapy, limited surgical excision, or both, irradiation has been shown to control disease in the primary site and regional nodes without the need for surgical extirpation as frequently as in past years. New developments in three-dimensional treatment planning and the precise delivery of high-dose radiation promise to increase the benefit of radiation treatment. Finally, molecular studies of the cell's response to radiation and the phenomena of DNA damage and repair are providing explanations for heretofore unexplained radiobiologic observations. Such research is laying the groundwork for targeted manipulation of the cell's response to radiation, which will be tested in the near future.

Ionizing radiation-induced cell death

Selected aspects of radiation-induced cell death, connected with signal transduction pathways are reviewed. Cell death is defined as insufficiency of the cellular signal transducing system to maintain the cell's physiological functions. The insufficiency may be due to impaired signal reception and/or transduction, lack or erroneous transcription activation, and eventual cellular 'misexpression' of the signal. The molecular basis of this insufficiency would be damage to genomic (but also other cellular) structures and closing of specific signalling pathways or opening of others (like those leading to apoptosis). I describe experimental data that suggest an important role of RAS/NF1 and p53/p105 Rb proteins in cell cycle control-coupled responses to DNA damage.

Ionizing radiation acts on cellular membranes to generate ceramide and initiate apoptosis

Recent investigations provided evidence that the sphingomyelin signal transduction pathway mediates apoptosis for tumor necrosis factor alpha (TNF-alpha) in several hematopoietic and nonhematopoietic cells. In this pathway, TNF-receptor interaction initiates sphingomyelin hydrolysis to ceramide by a sphingomyelinase. Ceramide acts as a second messenger stimulating a ceramide-activated serine/threonine protein kinase. The present studies show that ionizing radiation, like TNF, induces rapid sphingomyelin hydrolysis to ceramide and apoptosis in bovine aortic endothelial cells. Elevation of ceramide with exogenous ceramide analogues was sufficient for induction of apoptosis. Protein kinase C activation blocked both radiation-induced sphingomyelin hydrolysis and apoptosis, and apoptosis was restored by ceramide analogues added exogenously. Ionizing radiation acted directly on membrane preparations devoid of nuclei, stimulating sphingomyelin hydrolysis enzymatically through a neutral sphingomyelinase. These studies provide the first conclusive evidence that apoptotic signaling can be generated by interaction of ionizing radiation with cellular membranes and suggest an alternative to the hypothesis that direct DNA damage mediates radiation-induced cell kill.

Radiation response of mouse lymphoid and myeloid cell lines. Part III. Different signals can lead to apoptosis and may influence sensitivity to killing by DNA double-strand breakage

We have examined the timing of gamma-irradiation-induced death in relation to cell cycle progression using a panel of mouse lymphoid or myeloid cell lines. Death was found to occur immediately after irradiation ('rapid interphase' death), or after arrest in G2 phase ('delayed interphase' death). In part II of this series of papers we demonstrated the occurrence of radiation-induced apoptosis in all these cell lines. This suggests that different signals can lead to apoptosis in these cell lines. DNA double-strand breakage appeared to directly stimulate the destruction of cell lines susceptible to rapid interphase death, whilst the signal for delayed interphase and mitotic death, whilst the signal for delayed interphase and mitotic death appeared to be chromosomal aberrations. Several of the cell lines showed different timing of death dependent upon the radiation dose used. These differences in the timing of radiation-induced death are shown to be useful indicators of the relative radiosensitivity of haematopoietic cell lines.