Cell death induced in a murine mastocytoma by 42-47 degrees C heating in vitro: evidence that the form of death changes from apoptosis to necrosis above a critical heat load

Calcium ionophores can induce either apoptosis or necrosis in cultured cortical neurons

Cultured cortical neurons exposed for 24 h to low concentrations of the Ca2+ ionophores, ionomycin (250 nM) or A-23187 (100 nM), underwent apoptosis, accompanied by early degeneration of neurites, cell body shrinkage, chromatin condensation and internucleosomal DNA fragmentation. This death could be blocked by protein synthesis inhibitors, as well as by the growth factors brain-derived neurotrophic factor or insulin-like growth factor I. If the ionomycin concentration was increased to 1-3 microM, then neurons underwent necrosis, accompanied by early cell body swelling without DNA laddering, or sensitivity to cycloheximide or growth factors. Calcium imaging with Fura-2 suggested a possible basis for the differential effects of low and high concentrations of ionomycin. At low concentrations, ionomycin induced greater increases in intracellular Ca2+ concentration in neurites than in neuronal cell bodies, whereas at high concentrations, ionomycin produced large increases in intracellular Ca2+ concentration in both neurites and cell bodies. We hypothesize that the ability of low concentrations of Ca2+ ionophores to raise intracellular Ca2+ concentration preferentially in neurites caused early neurite degeneration, leading to loss of growth factor availability to the cell body and consequent apoptosis, whereas high concentrations of ionophores produced global cellular Ca2+ overload and consequent necrosis.

DNA-dependent protein kinase protects against heat-induced apoptosis

Purified heat shock transcription factor 1 (HSF1) binds to both the regulatory and catalytic components of the DNA-dependent protein kinase (DNA-PK). This observation suggests that DNA-PK may have a physiological role in the heat shock response. To investigate this possibility, we performed a comparison of cell lines that were deficient in either the Ku protein or the DNA-PK catalytic subunit versus the same cell lines that had been rescued by the introduction of a functional gene. DNA-PK-negative cell lines were up to 10-fold more sensitive to heat-induced apoptosis than matched DNA-PK-positive cell lines. There may be a regulatory interaction between DNA-PK and HSF1 in vivo, because constitutive overexpression of HSF1 sensitized the DNA-PK-positive cells to heat but had no effect in DNA-PK-negative cells. The initial burst of hsp70 mRNA expression was similar in DNA-PK-negative and -positive cell lines, but the DNA-PK-negative cells showed an attenuated rate of mRNA synthesis at later times and, in some cases, lower heat shock protein expression. These findings provide evidence for an antiapoptotic function of DNA-PK that is experimentally separable from its mechanical role in DNA double strand break repair.

Changes in the noninvasive, in vivo electrical impedance of three xenografts during the necrotic cell-response sequence

PURPOSE

To investigate the noninvasive, in vivo use of electrical impedance spectroscopy (EIS) as a method for observing the real-time, cellular-level responses of a volume of tissue to therapies. Here, we studied the EIS response during the development and progression of hyperthermia-induced coagulative necrosis in three diverse human xenografts.

METHODS AND MATERIALS

A necrotic cell response sequence was selectively induced in three types of subcutaneously-grown human tumor xenografts by applying hyperthermia at 44.5 degrees C. The electrical impedance of the tumors was measured from 100 Hz to 10 MHZ, noninvasively, in vivo during the treatments. From the full spectrum EIS, ratios between resistivities at selected frequencies (p-ratios) were used as indicators of the changes in the electrical impedance spectra of each tumor's cell population.

RESULTS

The rho-ratios consistently demonstrated characteristic, early, rapid increases which coincided with cell and organelle swelling typical of early necrosis. These increases subsequently slowed, but no decrease began before the end of treatment, unlike previous, similarly treated, thermo-sensitive EMT6 mouse tumors. This was consistent with the xenograft histology, which revealed ubiquitous, early-stage coagulative necrosis, with no gross plasma membrane damage at the end of treatment. The extent of both the necrosis and p-ratio changes were similar to those seen early in the EMT6 tumor treatment. Within several days after treatment, the xenograft volumes regressed nearly completely, suggesting completion of the cell populations' necrotic response (lysing) during this period. Consistent with this, extended EIS measurements over a 24-h posttreatment period allowed tracking of the necrotic response sequence through this lysing phase for one type of xenograft.

CONCLUSION

The change in the electrical impedance of a volume of tumor tissue which occurs during and/or after a hyperthermia treatment can be correlated with the extent of necrosis observed histologically in the cell population.

Apoptosis and expression of p53 response proteins and cyclin D1 after cortical impact in rat brain

We measured the temporal profile and cellular identification of apoptosis in rat brain after cortical contusion injury. Double staining immunohistochemistry was also used to investigate the relationship between apoptotic cell death and selective protein expression associated with DNA damage and repair (p53, Bax, MDM2, WAF1, Gadd45, PCNA) and cell cycle protein, Cyclin D1, in male Wistar rats 48 h after injury. Cortical contusion was induced in male Wistar rats with a pneumatic impactor device. The animals were sacrificed at different times after trauma (1, 2, and 14 h and 1, 2, 4, 7 and 14 days; n=4 per time point). Sham-operated rats (n=4) and normal rats not subjected to any surgical procedure (n=4) were used as controls for temporal profile determination. Additional 11 rats were used for study of protein expression. Coronal brain sections were analyzed using an in situ terminal deoxynucleotdyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling (TUNEL), hematoxylin, and immunohistochemical double staining methods. Apoptotic cells were observed as early as 2 h after the impact. Apoptotic cell death peaked at 2 days, gradually tapering off afterward, although scattered apoptotic cells were detected at 2 weeks after the impact. The number of apoptotic cells at 2 days far exceeded their number at other times (p=0.009). Apoptotic cells were observed primarily in the cortex adjacent to the site of injury. In addition, apoptotic cells in conjunction with few injured cells were present in the ipsilateral hippocampus and localized to the granule layer of dentate gyrus. Our data indicate that DNA fragmentation is present in nearly all neurons subacutely after cortical contusion and persists for at least 2 weeks thereafter. Apoptosis is also present in neurons localized to the hilus of the dentate gyrus at a site remote from the area of injury suggesting a selective role for apoptosis in promoting secondary brain damage and dysfunction after traumatic brain injury. Using double staining, we were able to show that a great majority of apoptotic cells (>95%) were neurons and the rest were astrocytes and endothelial cells. Proteins associated with DNA damage and repair (p53, Bax, MDM2, WAF1, Gadd 45, PCNA) were expressed in the cytoplasm of normal cells of naive and sham rats. These proteins were translocated to the nuclei of apoptotic and injured cells at 48 h after cortical contusion. Cyclin D1 was not present in apoptotic cells. The differential expression of proteins associated with DNA damage, repair and the cell cycle protein Cyclin D1 in the contused brain suggest a potential role for these proteins in cell survival and apoptosis after cortical contusion.

A comparative study of apoptosis and necrosis in HepG2 cells: oxidant-induced caspase inactivation leads to necrosis

Apoptosis and necrosis are two distinct forms of cell death that can occur in response to various agents. In the present study the HepG2 cell line was used for a comparative study of CD95-mediated apoptosis and menadione-induced necrosis. Apoptosis coincided with the release of cytochrome c from mitochondria, activation of caspases, cleavage of cellular proteins, and also involved nuclear condensation and DNA fragmentation. Necrosis was not accompanied by DNA fragmentation, caspase activation or cleavage of caspase target proteins, despite cytochrome c release from mitochondria. In fact, the addition of menadione to cells undergoing CD95-mediated apoptosis blocked their caspase activity. Inhibition of caspases coincided with an accumulation of reactive oxygen species (ROS) and ATP depletion. In order to determine the predominance of either of these events in the inhibition of caspase, cells were either co-incubated with antioxidant enzymes or their ATP level was manipulated to maintain it at a relatively high level during the experiments. Co-incubation with catalase, but not Cu/Zn superoxide dismutase, substantially reduced the levels of ROS and reversed the inhibitory effect of menadione on caspase activity. In contrast, increasing cellular ATP level had little effect on restoring caspase activity. These data suggest that menadione inhibits caspase activity by the generation of hydrogen peroxide through redox cycling and that caspase inactivation by this mechanism may prevent cell death by apoptosis in this oxidative-stress model.

Quantitative differentiation of both free 3'-OH and 5'-OH DNA ends between heat-induced apoptosis and necrosis

Cell death is roughly categorized as either apoptosis or necrosis. For better understanding of the differences in DNA cleavage between them, we performed quantitative analysis of both the 3'-OH and the 5'-OH ends of DNA strand breaks via in situ nick-end labeling (ISEL) combined with transmission electron microscopy (TEM) of both heat-induced apoptosis and necrosis in mouse B-cells derived from a lymphoma cell line. To detect the 5'-OH ends, the 3'-P ends located on the opposite side holding the 5'-OH ends were dephosphorylated into 3'-OH ends with alkaline phosphatase. As assessed by statistical analysis of both the 3'-OH and the 5'-OH ends, their labeling densities were significantly higher in both the apoptotic and the necrotic cells in the early stage than in control cells. The labeling densities increased during the apoptotic and necrotic processes, except for a decrease in the density of the 3'-OH ends in necrotic cells in the late stages. Therefore, DNA degradation in both necrosis and apoptosis provides early evidence for these processes, and both apoptosis and necrosis may share at least the first steps of DNA degradation pathways.

Glutamine reduces heat shock-induced cell death in rat intestinal epithelial cells

Glutamine supplementation is beneficial for preventing intestinal atrophy and maintaining mucosal functions in metabolically stressed patients. The mechanisms by which glutamine prevents mucosal atrophy remain unclear. In particular, the role of glutamine in the survival of cells under stress is unknown. Intestinal epithelial cells (IEC-6) were cultured in media with or without supplementation of L-glutamine. A low concentration of L-glutamine (1.0 mmol/L) was sufficient to minimize the percentage of floating cells under basal conditions. Heat shock at 43 degrees C for 90 min decreased (P < 0. 001) the number of attached cells, while increasing (P < 0.001) the number of floating cells, which is a measurement of the extent of cell death in these cultures. Glutamine enhanced attached cell count and diminished heat shock-induced cell death in a dose-dependent manner. Of note, 2 mmol/L was suboptimal in both respects, thus indicating that heat-shocked cells require higher concentrations of glutamine for optimal cell survival. Maximal effect was achieved with 8 mmol/L glutamine, which increased (P < 0.001) cell growth (indicated by the number of attached cells) and diminished (P < 0. 001) cell death (indicated by the number of floating cells). Further increase of L-glutamine concentration to 12 or 20 mmol/L did not provide additional benefit in minimizing cell death. Heat shock protein 70 (hsp 70) mRNA was induced by heat shock only in cultures supplemented with L-glutamine, and the induction was more consistent and greater in cultures containing higher concentrations of glutamine. Thus, glutamine supplementation reduced heat shock-induced cell death. This effect, together with the maintenance of cell growth, may play a key role in the prevention of intestinal mucosal atrophy.

Cadmium induces apoptosis differentially on immune system cell lines

We investigate the role of cadmium-induced apoptosis in the immune system, studying the apoptotic effect of Cd2+ in three human cell lines, the T-cell line CCRF-CEM, the B-cell line Raji and the lymphoblastoid cell line Molt-3. Cd2+ was found to be dose-dependently toxic for these cell lines, after 18 h incubation. The 50% lethal dose (LD50) for CCRF-CEM was 25 +/- 20 microM, for Molt-3 was 22.5 +/- 2.4 microM, and for Raji was 13.5 +/- 2.2 microM. DNA electrophoresis and quantitation of apoptosis after 18 h incubation with different Cd2+ concentrations was carried out. In CCRF-CEM cells, apoptosis was detected at 10 microM, reaching a maximum at 30 microM. In Molt-3, apoptosis was detected at 10 microM, increased thereafter and a plateau effect was observed from 30 to 50 microM Cd2+. In Raji, apoptosis was detected at 5 microM, while a plateau effect was observed from 20 to 30 microM Cd2+. The above results indicated that Raji cells were more sensitive to cadmium compared to both CCRF-CEM and Molt-3 cells, suggesting a differential Cd2+-induced apoptotic effect, which may disturb the immune system normal growth and development.

Therapeutic efficacy and apoptosis and necrosis kinetics of doxorubicin compared with cisplatin, combined with whole-body hyperthermia in a rat mammary adenocarcinoma

We have compared the therapeutic efficacy as well as the kinetics of treatment-induced apoptosis and necrosis of the maximum tolerated dose (MTD) of doxorubicin (DOX) or cisplatin (CDDP) combined with long-duration, low-temperature whole-body hyperthermia (LL-WBH, at 40.0 degrees C for 6 hr), with the combination of the MTDs of either DOX or CDDP with short-duration, high-temperature WBH (SH-WBH, at 41.5 degrees C for 2 hr), in a rat mammary adenocarcinoma (MTLn3). The MTD of LL-WBH + DOX resulted in increased therapeutic efficacy, compared with the MTD of DOX alone and SH-WBH + DOX. The MTD of LL-WBH + CDDP, however, did not increase therapeutic efficacy, when compared with the MTD of CDDP alone or SH-WBH + CDDP. The MTD of LL-WBH + DOX caused a significant delay in the development of spontaneous axillary lymph node (ALN) metastasis and tended to cause longer mean survival, compared with SH-WBH + DOX. The peak of treatment-induced apoptosis was higher for the MTD of DOX + LL-WBH, compared with SH-WBH + DOX, whereas the apoptosis peak of the MTD of SH-WBH + CDDP was higher than that of LL-WBH + CDDP. The most extensive levels of tumor necrosis appeared to occur earlier with SH-WBH alone and the MTD of SH-WBH + DOX or CDDP than with other groups. Our results suggest that LL-WBH + DOX may be a promising therapy for breast cancer, and the extent of treatment-induced tumor apoptosis appears to correlate with antitumor response for MTDs of LL-WBH + DOX and SH-WBH + DOX, but not for the MTDs of CDDP with SH-WBH or LL-WBH.

Pretreatment with intraventricular aurintricarboxylic acid decreases infarct size by inhibiting apoptosis following transient global ischemia in gerbils

The goal of this study was to determine whether aurintricarboxylic acid (ATA), an endonuclease inhibitor known to inhibit apoptosis, could ameliorate cell damage in a gerbil model of transient ischemia. Transient ischemia was induced in gerbils by bilateral carotid artery occlusion for a period of 5 minutes. Four micrograms of ATA was administered intraventricularly 1 hour before ischemia, and the brains were assessed histologically 1 week later to quantitate cell loss in the vulnerable CA-1 subsector of the hippocampus. In a separate set of experiments, 4 microg of ATA was administered intraventricularly 1 hour before ischemia and the brains were assessed for evidence of DNA fragmentation by the TUNEL method. There was only a 16% cell loss compared with nonischemic controls in animals pretreated with ATA that was significantly less (p < 0.05) than the 48% cell loss in animals pretreated with saline alone. TUNEL-positive cells were first evident at 3 days and were still present at 7 days subsequent to ischemia. Maximal staining occurred at 4 days. Pretreatment with ATA virtually eliminated TUNEL staining at 4 days. These results support the hypothesis that the delayed cell death secondary to transient ischemia is, in part, apoptotic. Furthermore, ATA afforded significant neuronal protection and prevented DNA fragmentation.

Selenium, calcium channel blockers, and cancer risk--the Yin and Yang of apoptosis?

It is increasingly clear that apoptosis plays a crucial role in the promotional phase of cancer development. Initiated pre-neoplastic clones in rat liver experience a high rate of apoptosis, and this rate has an important impact on the survival and growth of these clones. Suppression of apoptosis appears to be a universal property of cancer promoters, suggesting conversely that agents which inhibit cancer induction during the promotional phase increase the rate of apoptosis in initiated cells. Modulation of apoptosis is a likely explanation for recent striking evidence that use of calcium channel blockers substantially increases, whereas supplemental selenium substantially decreases, human cancer incidence. Non-genotoxic measures which are likely to upregulate apoptosis in pre-neoplastic/neoplastic cells--and thus may be useful in prevention and/or therapy--include selenium, retinoids/carotenoids, green tea polyphenols, caloric restriction, downregulation of IGF-I activity, high-dose tamoxifen and other protein kinase C antagonists, withdrawal or blockade of trophic hormones, isoflavones, limonene, vitamin D and cholecalciferol analogs, dietary fiber/sodium butyrate, hyperthermia, benzaldehyde derivatives, and creatine.

Neuronal apoptosis and necrosis following spinal cord ischemia in the rat

We examined the characteristics of neuronal death induced by ischemia in the spinal cord. Spinal cord ischemia was induced in Long-Evans rats by occlusion of the descending aorta with a 2F Fogarty catheter for 20 min (model 1) or more limited aortic occlusion (15 min) coupled with blood volume reduction (model 2); rats were sacrificed 6 h-7 days later. The animals developed variable paraparesis in model 1 and reliable paraplegia in model 2. The extent of histopathological spinal cord damage, being maximal in the lumbar cord, correlated well with the severity of paraparesis. Two distinct types of spinal cord neuronal death were observed, consistent with necrosis and apoptosis. Neuronal necrosis was seen in gray matter laminae 3-7, characterized by the rapid (6 h) onset of eosinophilia on hematoxylin/eosin-stained sections, and gradual (1-7 days) development of eosinophilic ghosting. Although TUNEL positivity was present, disintegration of membranes and cytoplasmic organelles was seen under electron microscopy. Neuronal apoptosis was seen after 1-2 days in dorsal horn laminae 1-3, characterized by both TUNEL positivity and electron microscopic appearance of nuclear chromatin aggregation and the formation of apoptotic bodies. DNA extracted from the ischemic lumbar cord showed internucleosomal fragmentation (laddering) on gel electrophoresis. These data suggest that distinct spinal cord neuronal populations may undergo necrosis and apoptosis following transient ischemic insults.

DNA fragmentation follows delayed neuronal death in CA1 neurons exposed to transient global ischemia in the rat

Apoptosis is an active, gene-directed process of cell death in which early fragmentation of nuclear DNA precedes morphological changes in the nucleus and, later, in the cytoplasm. In ischemia, biochemical studies have detected oligonucleosomes of apoptosis whereas sequential morphological studies show changes consistent with necrosis rather than apoptosis. To resolve this apparent discrepancy, we subjected rats to 10 minutes of transient forebrain ischemia followed by 1 to 14 days of reperfusion. Parameters evaluated in the CA1 region of the hippocampus included morphology, in situ end labeling (ISEL) of fragmented DNA, and expression of p53. Neurons were indistinguishable from controls at postischemic day 1 but displayed cytoplasmic basophilia or focal condensations at day 2; some neurons were slightly swollen and a few appeared normal. In situ end labeling was absent. At days 3 and 5, approximately 40 to 60% of CA1 neurons had shrunken eosinophilic cytoplasm and pyknotic nuclei, but only half of these were ISEL. By day 14, many of the necrotic neurons had been removed by phagocytes; those remaining retained mild ISEL. Neither p53 protein nor mRNA were identified in control or postischemic brain by in situ hybridization with riboprobes or by northern blot analysis. These results show that DNA fragmentation occurs after the development of delayed neuronal death in CA1 neurons subjected to 10 minutes of global ischemia. They suggest that mechanisms other than apoptosis may mediate the irreversible changes in the CA1 neurons in this model.

Apoptosis induced by hyperthermia and verapamil in vitro in a human colon cancer cell line

The aim of this study was to determine the mechanisms responsible for the growth inhibitory effect of hyperthermia and verapamil in human colon cancer cell line HT-29. Apoptotic cell death was verified by flow cytometry analysis. The effect of treatment with hyperthermia and verapamil on the expression of apoptosis-associated proteins including Bcl-2, p53, bax, and c-Myc was studied by Western blot analysis. Changes in intracellular calcium homeostasis was analysed by fluorescence microscopy. The combination of 42 degrees C hyperthermia and verapamil caused a significant delay of human colon cancer cell proliferation as a result of apoptosis. Administration of these agents alone did not cause any cell inhibitory effect. Our experiments have shown that HT-29 cells constitutively express apoptosis-promoting proteins, such as Bax and c-Myc, while they fail to produce Bcl-2. Therefore, we hypothesize that HT-29 cells must have Bcl-2 independent pathways to protect cells against death-inducing signals. Also, apoptosis of HT-29 cells produced by hyperthermia in the presence of verapamil is a p53-independent process. Verapamil, when it did not act as a calcium channel blocker or inhibitor of release from intracellular storages under hyperthermic conditions, accelerated the increase of [Ca2+]i in HT-29 cells which resulted in programmed cell death (apoptosis).

Induction of thermotolerance in early postimplantation rat embryos is associated with increased resistance to hyperthermia-induced apoptosis

Previously we reported that hyperthermia (43 degrees C) induces cell death in neurulation stage rat embryos as part of the pathogenesis culminating in abnormal growth and development. We now show that hyperthermia-induced cell death occurs by a process termed apoptosis. DNA fragmentation, a hallmark of apoptosis, was noted as early as 2.5 hr after embryos were exposed to 43 degrees C. A smaller but significant increase in DNA fragmentation was also observed in embryos exposed to 42 degrees C, but only at the 5 hr time point. In control embryos, TUNEL-positive apoptotic bodies were consistently observed in the neuroepithelium at the point of neural tube closure and in the optic stalk. In embryos exposed to 43 degrees C, the number of TUNEL-positive apoptotic bodies was significantly increased. Using both gel electrophoresis and TUNEL, we also show that the induction of thermotolerance is associated with a significant reduction in DNA fragmentation. Together our results show that specific programmed cell death and hyperthermia-induced cell death correlate with internucleosomal DNA fragmentation characteristic of apoptosis. Finally, we show that the induction of thermotolerance in rat embryos is associated with a significant reduction in internucleosomal DNA fragmentation and associated apoptosis.

Cell density-dependent apoptosis in HL-60 cells, which is mediated by an unknown soluble factor, is inhibited by transforming growth factor beta1 and overexpression of Bcl-2

We report a novel mode of apoptosis induction observed in human leukemic HL-60 cells. These cells spontaneously underwent apoptosis in the course of proliferation when the cell density became higher than 1 x 10(6)/ml. This occurred under ordinary in vitro culture conditions, with or without fetal calf serum. Even the low density cells were committed to undergo apoptosis if they were cultured under artificially concentrated conditions. Replacement of the culture supernatant of the low density cells by that of the high density ones resulted in apoptosis induction in the former cells. This apoptosis-inducing activity of the high density cell culture supernatant was completely eliminated by the action of trypsin but was fully restored following ultrafiltration by 3-kDa pore-sized membrane. A strong apoptosis-inducing activity was recovered from the culture supernatant of the high density HL-60 cells at a specific fraction in reverse-phase column chromatography. Neither an interleukin-beta converting enzyme inhibitor nor CPP-32 inhibitor blocked the induction of cell density-dependent apoptosis in HL-60 cells, although overexpression of Bcl-2 protein markedly attenuated the induction of this mode. Surprisingly, transforming growth factor-beta1 and activin A did not induce but, rather, inhibited the induction of cell density-dependent apoptosis. These data suggest that HL-60 cells release an unknown low molecular weight peptide-containing factor in response to an increase in cell density to induce apoptosis in an autocrine manner and that the interleukin-beta converting enzyme-independent intracellular machinery for this mode of apoptosis is strongly affected by signaling events through the transforming growth factor-beta1 receptor and by the action of Bcl-2 oncoprotein.

Radiation-induced apoptosis in different pH environments in vitro

PURPOSE

The effect of environmental pH on the radiation-induced apoptosis in tumor cells in vitro was investigated.

METHODS AND MATERIALS

Mammary adenocarcinoma cells of A/J mice (SCK cells) were irradiated with gamma-rays using a 137Cs irradiator and incubated in media of different pHs. After incubation at 37 degrees C for 24-120 h the extent of apoptosis was determined using agarose gel electrophoresis, TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, flow cytometry, and release of 3H from 3H-thymidine labeled cells. The clonogenicity of the cells irradiated in different pH medium was determined, and the progression of cells through the cell cycle after irradiation in different pHs was also determined with flow cytometry.

RESULTS

Irradiation with 2-12 Gy of gamma-rays induced apoptosis in SCK cells in pH 7.5 medium within 48 h as judged from the results of four different assays mentioned. Radiation-induced apoptosis declined as the medium pH was lowered from 7.5 to 6.4. Specifically, the radiation-induced degradation of DNA including the early DNA breaks, as determined with the TUNEL method, progressively declined as the medium pH was lowered so that little DNA fragmentation occurred 48 h after irradiation with 12 Gy in pH 6.6 medium. When the cells were irradiated and incubated for 48 h in pH 6.6 medium and the medium was replaced with pH 7.5 medium, DNA fragmentation promptly occurred. DNA fragmentation also occurred even in pH 6.6 medium when the cells were irradiated and maintained in pH 7.5 medium for 8 h or longer post-irradiation before incubation in pH 6.6 medium. The radiation-induced G2 arrest in pH 6.6 medium lasted markedly longer than that in pH 7.5 medium.

CONCLUSION

Radiation-induced apoptosis in SCK cells in vitro is reversibly suppressed in an acidic environment. Taking the results of four different assays together, it was concluded that early step(s) in the apoptotic pathway, probably the DNA break or upstream of DNA break, is reversibly halted by an acidic environment in irradiated cells. Radiation-induced G2 arrest is prolonged in an acidic environment indicating that the suppression of radiation-induced apoptosis and prolongation of radiation-induced G2 arrest in an acidic environment are related.

Variation of heat shock protein 70 through the cell cycle in HL-60 cells and its relationship to apoptosis

Cells respond to a heat shock by synthesizing heat shock proteins, which help to protect the cells from further heating. Recent results indicate that heat shock protein 70 (hsp70) may help to protect cells from apoptosis. We have used flow cytometry to investigate the relationship between constitutive and inducible hsp70 and apoptosis through the cell cycle in HL-60 cells. Specific antibodies were used to measure hsp70 in cells costained with propidium iodide. In separate samples apoptosis was measured using the TdT assay. The apoptotic cells have a subdiploid DNA content, which allows them to be identified also in the bivariate histograms of heat shock protein vs DNA content. After HL-60 cells were heated at 45.0 degrees C for 7.5 min and incubated for various times at 37 degrees C, many of them underwent apoptosis. The level of inducible hsp70 (hsp72) was lower in the apoptotic cells than in the nonapoptotic population, but constitutive hsp70 (hsp73) was the same in both populations. Pretreatment with sodium vanadate increased the fraction of apoptotic cells twofold, slightly increased the level of hsp72 in the nonapoptotic cells, but did not affect hsp73. These results suggest that hsp72, but not hsp73, is involved in the development or prevention of apoptosis.

Non-invasive, in-vivo electrical impedance of EMT-6 tumours during hyperthermia: correlation with morphology and tumour-growth-delay

The electrical impedance at frequencies from 100 Hz to 40 MHz of EMT-6 tumours was measured non-invasively, in vivo, during hyperthermia using an apparatus constructed for this purpose. Histology and morphometry were performed on tumours harvested periodically during the heating. A ratio of conductivities at two frequencies (sigma (10MHz)/sigma (10kHz)), which minimizes the tissues temperature-coefficient effects, was used to correlate impedance changes with the histopathological changes. The bulk of the cell population followed a necrotic cell death sequence during heating. Initial increase of the sigma-ratio correlated with cell swelling, and a reversal of the rate of this increase correlated with the appearance of small membrane breaks and evidence of mitochondrial damage. A continued, slowing sigma-ratio increase to a maximum correlated with continued cell swelling accompanied by increasing membrane disruption. The subsequent decrease in sigma-ratio correlated with continued general cell lysing. Between the appearance of the first membrane breaks (sigma-ratio peak) and the evidence of general lysing (sigma-ratio peak), the tumour-growth-delay increased non-linearly. Because the sigma-ratio consistently discerned these events, these measurements were able to predict the fate of this cell population when subjected to hyperthermia. Knowledge of temperature or time of heating was not required.

Therapeutic hyperthermia

Those diseases that medicines do not cure, are cured by the knife, and those diseases that the knife cannot cure are cured by fire. And those diseases that fire does not cure are to be reckoned wholly incurable.

Apoptotic and non-apoptotic cell death induced by cis and trans analogues of a novel ammine(cyclohexylamine)dihydroxodichloroplatinum(IV) complex

It has been previously demonstrated that cisplatin induces apoptosis in the CH1 human ovarian carcinoma cell line. This study demonstrates that two novel platinum (Pt) analogues JM149 and JM335, which are the cis and trans geometry respectively of ammine(cyclohexylamine)dihydroxodichloroPt(IV), initiate apoptosis in this cell line at physiologically relevant concentrations (IC50 values 2 h drug exposure were 35.3 microM for JM149 and 18.7 microM for JM335). While at equimolar drug concentrations there was a 2-fold higher level of total platinum-DNA adducts following exposure to JM335 vs JM149, at equitoxic concentrations, levels were similar (80 vs 70 pmol Pt mg-1 DNA respectively). Following a 2 h incubation with 2 x IC50 of both drugs, cells rounded up and detached in a time-dependent manner but with the kinetics of apoptosis being more rapid for JM335. The majority of detached cells exhibited morphology associated with apoptosis which was further supported by the presence of a 50 kb fragment detected in DNA lysates prepared from these cells. JM149 induced apoptosis across a range of concentrations (2 x, 5 x and 10 x IC50) with a 50 kb DNA fragment being detected at all concentrations. However, in marked contrast to this, JM335 failed to cause apoptosis at 10 x IC50, the detached cells neither displaying apoptotic morphology nor a detectable 50 kb DNA fragment. Moreover, these detached cells showed evidence of extensive vesiculation while the DNA remained normal in appearance and thus appeared to have died by a non-apoptotic mode. Apoptosis also appeared to be induced to a lesser extent at 5 x IC50 of JM335 as demonstrated by a less intense 50 kb fragment compared with that seen at 2 x IC50. The main cell cycle effect of these drugs (at 2 x IC50) was a slowdown in S-phase traverse during which most but not all of the apoptosis appeared to occur. However, at 5 x IC50 of JM335 cells appeared frozen in all phases of the cell cycle with little progress from G1 to S accompanied by a build-up of cells in G2 indicative of a G2/M block. This difference in cell cycle effect may account for the reduced level of apoptosis at this concentration and a failure to engage apoptosis at higher concentrations. These data suggest that the nature of the platinum drug (and consequently, the nature of resultant DNA damage) may have important implications in determining the rate and mechanism of cell death in this cell line. The cell death effects observed with the trans complex JM335 may correlate with the induction of DNA single-strand breaks in this cell line.

Induction of apoptosis in human HaCaT keratinocytes

Although cell death by apoptosis has been recognized as an important control mechanism in the maintenance of tissue homeostasis and in the elimination of cells with damaged DNA, information on the induction and characteristics of apoptosis in keratinocytes is rather scarce. Apoptotic mechanisms may play an important role in normal and disturbed homeostasis of the skin. In the present study, we therefore investigated the effects of several potential inducers of apoptosis in the human keratinocyte cell line HaCaT. Apoptosis was assessed with respect to morphological changes by light and electron microscopic examinations and to DNA integrity by a specific ELISA. UVB irradiation induced the morphology and internucleosomal DNA fragmentation characteristic of apoptosis in a dose- and time-dependent manner. Interferon-gamma caused DNA cleavage at the linker regions without producing morphological features consistent with apoptotic cell death. In contrast, treatment with dithranol and NP-40 resulted in necrotic alterations in the keratinocytes. Treatment with the calcium ionophore A23187 caused morphological changes which were similar to the characteristics of 'nonapoptotic programmed cell death'. Dexamethasone, tumor necrosis factor-alpha, transforming growth factor-beta, TPA, retinoic acid, the podophyllin derivative etoposide, the thromboxane A2 analogue U46619, cycloheximide, and the nitric oxide donors sodium nitroprusside and S-nitroso-glutathione, which are all known to induce apoptosis in other cell types, did not affect HaCaT keratinocytes. These results demonstrate that apoptosis can be induced in keratinocytes in vitro but the apoptosis differs from that in other cell types, such as haematopoietic cells, with regard to the type of inducer and/or the sensitivity of the target cells. Since keratinocytes are affected by numerous external and internal stimuli, they might posses several protective mechanisms to prevent apoptosis and to ensure the structural integrity of the outermost barrier of the body.

Key morphologic changes and DNA strand breaks in human lymphoid cells: discriminating apoptosis from necrosis

Apoptosis is an important form of physiologic cell death displayed by an enormous variety of tissues under divergent conditions. The recent attention toward apoptosis in virtually all aspects of modern biology indicates that rapid and accurate differentiation between apoptosis and necrotic death is of considerable interest. Apoptosis is distinguishable from necrosis on the basis of several criteria. In this study, we undertook to examine the effects of mild hyperthermia (43 degrees C leading to apoptotic death) and severe hyperthermia (50 degrees C leading to necrotic killing) on associated DNA fragmentation. Using laser scanning and fluorescent microscopic evaluation of DNA "comets" in the single cell gel assay, we compared necrotic and apoptotic DNA damage in a variety of human leukemia and lymphoma cell lines at the level of the individual cell. We show that necrotic cells do display detectable DNA damage. We confirm our preliminary report that comet "tail moment" is sufficient to distinguish between necrotic and apoptotic DNA damage, while comet tail length may confuse the two forms. We report that a recovery period is necessary for expression of increasing apoptotic but not necrotic DNA damage. We show that apoptosis increases with prolonged hyperthermia and confirm that the mode of death changes from apoptosis to necrosis with higher heat loads, producing a greater fraction of cells showing damage. In addition, we show that for necrotic cells, DNA tail moment reflects sensitivity to prolonged exposure without a concomitant change in tail length.

Hyperthermia induces apoptosis in malignant fibrous histiocytoma cells in vitro

The effect of mild hyperthermia on a cultured rat malignant fibrous histiocytoma (MFH) cell line, MFH-2NR, was investigated. MFH cells in log-phase (growing phase) were heated at 41 degrees-44 degrees C for 1 hr. Hyperthermic treatment at 41 degrees C did not substantially affect cell proliferation and treatment at 44 degrees C caused necrosis. After hypothermic treatment at 42 degrees or 43 degrees C, proliferation of MFH cells was arrested and morphological changes characteristic of apoptosis, cell shrinkage accompanying apoptotic bodies and chromatin condensation, became apparent. Hyperthermia-induced apoptosis was further confirmed by terminal deoxynucleotidyl transferase staining and a ladder pattern on agarose gel electrophoresis. Flow cytometric analysis indicated that the population in the G1 phase of the cell cycle significantly decreased with a concomitant increase in apoptotic cells, indicating that apoptosis might occur mainly in the G1 phase population.

Regional differences in apoptosis in murine gliosarcoma (T9) induced by mild hyperthermia

There are several reports of apoptosis induced by mild hyperthermia both in vitro and in vivo. However, in tumour nodules, regional differences in apoptosis induced by hyperthermia have not been studied morphologically or quantified. In this study, apoptosis was identified on the basis of its characteristic morphology, and was quantified in different tumour regions (margin and centre) by light and electron microscopy and discussed the correlation with necrosis. Apoptosis was induced in solid nodules of gliosarcoma (T9) in vivo by heating for 30 min in a water bath at 43 degrees C. The gliosarcoma cells showed a rapid increase in the number of apoptotic cells following mild hyperthermia. There was a regional difference in the rate of apoptosis immediately after hyperthermia. Necrosis was markedly enhanced only in the centre of the tumour 3 and 6 h after hyperthermia. These combined responses of apoptosis and necrosis seem to be caused by the microenvironmental change in the intratumour location.

Induction and persistence of cytogenetic damage in mouse splenocytes following whole-body X-irradiation analysed by fluorescence in situ hybridization. I. Dicentrics and translocations

Chromosome translocations (stable aberrations) can persist longer during cellular proliferation than dicentrics (unstable aberrations). It is important to know the kinetics of the elimination of dicentrics and to what extent translocations persist in an in vivo cell population after irradiation. The female Swiss mouse were used to study the induction and persistence of dicentrics and translocations in splenocytes up to 112 days after exposure to 2 Gy whole-body X-irradiation. Metaphase spreads at different time intervals were analyzed by fluorescence in situ hybridization (FISH) using chromosome-specific DNA libraries for chromosomes 1, 11 and 13. The frequencies of dicentrics and translocations appear to be equal immediately after irradiation. Frequencies of dicentrics decreased exponentially with time according to the relationship D = ae(-kt). The rate of elimination was faster in the early period (days 0-14) than in the later period (> or = 14 days). The frequency of translocations was constant in the period 0-7 days and then decreased linearly or exponentially. For the whole period, the trend is highly significant. As mouse chromosome painting probes are becoming available and by using FISH, an in vivo mouse model for the analysis of translocations has become feasible. As translocations are involved in carcinogenesis and genetic disorders, risk estimation for induction of translocations by ionizing radiation can be made with greater confidence and extrapolated to the human situation.

Effect of intracellular acidity and ionomycin on apoptosis in HL-60 cells

The aim was to investigate in detail the influence of intracellular pH (pHi) and intracellular Ca2+ concentration ([Ca2+]i) on apoptosis in HL-60 human promyelocytic leukaemia cells. The pHi was controlled by changing the pH of media as well as by interfering with the pHi regulatory mechanisms with 3-amino-6-chloro-5-(1-homopiperidyl)-N-(diaminomethylene) pyrazincarboxamide (HMA; an inhibitor of Na+/H+ antiport), 4-diiosothiocyanatostilbene-2,2'disulfonic acid, (DIDS; an inhibitor of Na(+)-dependent HCO3-/Cl- exchange) and nigericin (a K+ ionophore). The [Ca2+]i was increased with ionomycin, a Ca2+ ionophore. The apoptosis of HL-60 cells was measured with conventional agarose gel electrophoresis for DNA fragmentation and also with the release of 3H from 3H-thymidine-labelled DNA. Based on the magnitude of DNA fragmentation and 3H release at different pHi, it was shown that apoptosis occurred in HL-60 cells when the pHi was lowered from normal pHi of 7.4 to about 7.2-6.7 with a peak increase at pHi 6.8-6.9. Addition of 4 microM ionomycin to RPMI 1640 medium, which contained 615 microM Ca2+, elevated the apoptosis in the cells. Such an increase in apoptosis by ionomycin in HL-60 cells appeared to result from both an increase in [Ca2+]i and from a decline in pHi. The results indicate that the acidic intratumour environment may greatly affect the response of neoplastic tissues to hyperthermia, radiation and chemotherapeutic drugs which cause apoptosis.

Loss and shedding of surface markers from the leukemic myeloid monocytic line THP-1 induced to undergo apoptosis

Previous studies have established that a relationship exists between apoptosis and cell surface (ecto-) peptidase activity. Thus dose-dependent increases were found both in ectopeptidase activities and in the proportion of cells undergoing apoptosis in HeLa cell monolayers after exposure to UV and other perturbants causing arrest of DNA synthesis (indirectly or directly as a result of DNA damage). The nature of the correlation made no distinction as to whether an increase in peptidase activity was causal of, or consequential to apoptosis, nor whether the increase was a general response by all cells. As a wider approach to understanding the possible role played by ectopeptidases in apoptosis, we report the effect on expression of a known ectopeptidase, aminopeptidase N (CD13), by a myelomonocytic cell line induced to undergo apoptosis. Using THP-1 cultures exposed to low concentrations of ethanol, we used FACS technology to sort for early apoptotic cells that have an increased ability to sequester the vital dye Hoechst 33342 while excluding nonvital dyes. Apoptosis was verified by light, fluorescence, and transmission electron microscopy, and the presence of DNA fragmentation. These early apoptotic cells showed a significant loss in CD13 labeling. Another surface marker, CD33, behaved similarly, whereas CD14 was lost globally, and not just by the apoptotic cells. Peptidase assays confirmed that an aminopeptidase was shed into the bathing media and that this activity was inhibitable both by bestatin and by a CD13 neutralizing monoclonal antibody. In treated cells, there was no evidence for an increase in cell surface protease activity directed toward a highly aliphatic nonapeptide substrate used as a model for TGF-alpha scission from its precursor form. However, other cell surface proteases of different specificity are presumably responsible for the observed shedding of CD13.

Ultrastructural damage and neuritic beading in cold-stressed spinal neurons with comparisons to NMDA and A23187 toxicity

While exposure of cultured spinal neurons to mild hypothermia provides some protection from physical trauma (dendrotomy), profound cooling (< 17 degrees C) causes unrelated neuronal injury and death, which can be prevented by treatment with NMDA receptor antagonists. To investigate the mechanism of hypothermic neuronal injury we examined the ultrastructure of cultured spinal neurons after 2 h of cooling to 17 degrees C or 10 degrees C, with or without the presence of the NMDA receptor antagonist D-2-amino-5-phosphonovalerate, and with or without rewarming to 37 degrees C. These groups were compared to cultures exposed to NMDA or to the calcium ionophore A23187. Patterns of ultrastructural change, involving cytoskeletal disruption, mitochondrial abnormalities and vacuolization of the cytoplasm, suggest a common mechanism of injury in all treatment groups, involving an elevation of intracellular calcium. Some neurons exposed to hypothermia, NMDA or ionophore developed beaded dendrites. Microtubules were fragmented in varicosities but not in the intervening constrictions; other organelles were largely excluded from the constrictions. Varicosities may form when organelles and cytoplasm accumulate as the result of disruption of transport and membrane stabilizing proteins by proteases activated by calcium influx via NMDA mediated channels. The periodic nature of the swellings may reflect inherently discontinuous distribution of molecular subunits of the cytoskeleton.

Apoptosis overview emphasizing the role of oxidative stress, DNA damage and signal-transduction pathways

Apoptosis (programmed cell death) is a central protective response to excess oxidative damage (especially DNA damage), and is also essential to embryogenesis, morphogenesis and normal immune function. An understanding of the cellular events leading to apoptosis is important for the design of new chemotherapeutic agents directed against the types of leukemias and lymphomas that are resistant to currently used chemotherapeutic protocols. We present here a review of the characteristic features of apoptosis, the cell types and situations in which it occurs, the types of oxidative stress that induce apoptosis, the signal-transduction pathways that either induce or prevent apoptosis, the biologic significance of apoptosis, the role of apoptosis in cancer, and an evaluation of the methodologies used to identify apoptotic cells. Two accompanying articles, demonstrating classic apoptosis and non-classic apoptosis in the same Epstein-Barr virus-transformed lymphoid cell line, are used to illustrate the value of employing multiple criteria to determine the type of cell death occurring in a given experimental system. Aspects of apoptosis and programmed cell death that are not covered in this review include histochemistry, details of cell deletion processes in the sculpting of tissues and organs in embryogenesis and morphogenesis, and the specific pathways leading to apoptosis in specific cell types. The readers should refer to the excellent books and reviews on the morphology, biochemistry and molecular biology of apoptosis already published on these topics. Emphasis is placed, in this review, on a proposed common pathway of apoptosis that may be relevant to all cell types.

Radiation-induced apoptosis in human sarcoma and glioma cell lines

Six human soft-tissue sarcoma and 14 glioma cell lines, exhibiting considerable differences in radioresponsiveness and histological grade of differentiation of the parental tumour, were examined with respect to apoptosis development after irradiation with 60Co gamma-rays. After test doses of 6 and 25 Gy, significant changes characteristic of apoptosis occurring within 6 to 30 hr were exhibited by only 2 differentiated sarcoma cell lines, EL7 and ESS2. The characteristic internucleosomal fragmentation of DNA was detected as early as 6 hr after exposure of subconfluent monolayer cultures to 6 Gy. It was limited to cells that had detached from the culture plate, whereas adherent cells showed random degradation of DNA, namely after higher doses (25Gy) or longer incubation times (30 hr). As assessed by fluorescence microscopy of unfixed cultures stained with Hoechst 33342 and propidium iodide, the proportion of cells showing apoptotic bodies in non-irradiated controls was < 0.1% and 0.3% for EL7 and ESS2, respectively. The dose-response relationship for apoptosis was determined at 9 hr post-irradiation. After 2 Gy, the percentage of apoptotic cells was elevated to 3.4% in EL7 and 4.5% in ESS2 cultures. Saturation was obtained above 6 Gy, with 8.4% apoptosis in EL7 and 15% in ESS2 after 25 Gy. Taken together, rapid ionizing-radiation-induced apoptosis seems to be limited to a subgroup of sarcomas and is unlikely to occur in gliomas.

Induction of apoptosis and cathepsin D in limbs exposed in vitro to an activated analog of cyclophosphamide

Apoptosis, a form of active cell death, plays a role during normal limb development. The present study was done to test the hypothesis that the teratogen cyclophosphamide, an alkylating agent and commonly used anticancer drug, produces malformations by disturbing the regulation of apoptosis in the limb. The effects of a preactivated analog of cyclophosphamide, 4-hydroperoxycyclophosphamide, on limb development and on apoptosis in the limb were determined in vitro. Cathepsin D is a lysosomal protease which is induced in tissues undergoing destruction by apoptosis. To further examine the process of apoptosis in the limb, the effects of 4-hydroperoxycyclophosphamide exposure on cathepsin D protein concentration and on the immunolocalization of cathepsin D in limb buds were assessed. Limb buds from gestational day 12 mice were excised and cultured in roller bottles in a chemically defined medium for up to 6 days. The addition of 4-hydroperoxycyclophosphamide (1 or 10 micrograms/ml) to the culture medium produced time- and concentration-dependent limb malformations. Electrophoresis of the DNA extracted from both control and treated limbs revealed a DNA fragmentation pattern characteristic of apoptosis. Limbs cultured in the control medium showed a "DNA ladder" only after 72 hours in vitro; however, those in the drug-treated groups showed fragmentation within 12 hours of drug exposure. Acridine orange staining and examination of cell ultrastructure with the electron microscope further confirmed that apoptotic cell death in the interdigital areas was accelerated in drug-exposed limbs. The relative abundance of cathepsin D in limbs exposed to 4-hydroperoxycyclophosphamide for 24 hours was increased compared to control limbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed cell death and N-acetoxy-2-acetylaminofluorene-induced apoptosis in the rat embryo

N-acetoxy-2-acetylaminofluorene (N-Ac-AAF) is an alkylating agent that forms DNA adducts at C-8 in guanine and causes single strand breaks. It has previously been shown to be embryotoxic, but the mechanisms by which it causes abnormal development have not been investigated. Previous studies have indicated that other DNA alkylating agents cause cell death during embryonic development although the types of cell death were not characterized. Using a whole embryo culture system, gestation day 10 rat embryos were exposed to several concentrations (5, 50, and 200 micrograms/ml) of N-Ac-AAF. At several time points after exposure was begun (5, 10, and 24 hours), the embryos were removed from culture and examined to identify location, type and quantity of cell death, relative to programmed cell death observed in control embryos. Vital staining with Nile blue sulphate revealed that the location of N-Ac-AAF-induced cell death included the forebrain region, tail, and areas of programmed cell death. Examination of tissue sections from both control and treated embryos indicated that the location of apoptotic cell death revealed by in situ DNA nick end-labelling was generally consistent with the cell death pattern observed by vital staining of whole embryos. Agarose gel analyses indicated that all concentrations of N-Ac-AAF caused DNA fragmentation, and quantification demonstrated a dose response. Examination of treated embryos (50 and 200 micrograms/ml) by transmission electron microscopy revealed that, by 5 hours after exposure, cells with classic, ultrastructural features of apoptosis were present. In conclusion, multiple methods have all indicated that, regardless of exposure level, apoptosis was the predominant form of cell death. Because apoptosis also occurs in developmental cell death, it is possible that apoptosis induced by N-Ac-AAF is due to an alteration in cell fate via premature or ectopic induction of the cell death program.

Calcium chelators induce apoptosis--evidence that raised intracellular ionised calcium is not essential for apoptosis

A moderate sustained rise in intracellular ionised calcium has been observed to be associated with apoptosis occurring in many experimental systems. The application of extracellular and intracellular chelators of calcium has been reported to produce a decrease in apoptosis, while the addition of calcium ionophores often increases apoptosis. These findings, together with the observation of calcium-induced internucleosomal DNA cleavage in isolated nuclei, have suggested that DNA cleavage (and apoptosis) is a calcium-dependent process. However, a number of studies have shown that apoptosis is not always associated with a rise in the level of intracellular ionised calcium. In the present study, calcium chelators were found to induce apoptosis in cultured cells, concomitant with a decrease in both intracellular ionised calcium and total cell calcium content. Decreased intracellular ionised magnesium was also induced by extracellular chelators. These findings provide further evidence that a raised intracellular ionised calcium is not universally present during the induction of apoptosis. It is proposed that loss of calcium homeostasis, rather than a sustained rise in cytosolic calcium, is a determining factor in cell death by apoptosis.

DNA damage and stress protein synthesis induced by oxidative stress proceed independently in the human premonocytic line U937

Heat shock proteins (HSPs) function as stress-inducible molecular chaperones and exert protective effects against cellular injury. The induction of the HSPs is considered to be mediated by the presence of abnormal proteins within the cell and/or by classical second messengers. Several lines of evidence have however suggested a relationship between DNA damage, HSP induction and thermotolerance. We investigated whether DNA alterations could represent a common signal for the induction of stress protein synthesis during heat shock or exposure to reactive oxygen species in the human premonocytic line U937. We measured, in parallel, DNA damage (both strand breaks and fragmentation) and HSP synthesis (by biometabolic labeling and Western blotting) after exposure to heat shock, hydrogen peroxide, bleomycin, cadmium or erythrophagocytosis. Heat shock induced DNA alterations along with HSP synthesis. In contrast, exposure to hydrogen peroxide or bleomycin induced DNA damage, but no HSP synthesis, suggesting that oxidation-induced DNA damage and HSP synthesis proceed independently in U937 cells. Erythrophagocytosis and cadmium induced the classical HSPs but no detectable DNA damage. Since these latter stresses also induced the oxidation-specific stress protein heme oxygenase, we suggest a protective role for heme oxygenase against oxidative 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.

Arrhenius relationships from the molecule and cell to the clinic

There are great differences in heat sensitivity between different cell types and tissues. However, for an isoeffefct induced in a specific cell type or tissue by heating for different durations at different temperatures varying from 43-44 degrees C up to about 57 degrees C, the duration of heating must be increased by a factor of about 2 (R value) when the temperature is decreased by 1 degrees C. This same time-temperature relationship has been observed for heat inactivation of proteins, and changing only one amino acid out of 253 can shift the temperature for a given amount of protein denaturation from 46 degrees C to either 43 or 49 degrees C. For cytotoxic temperatures < 43-44 degrees C, R for mammalian cells and tissues is about 4-6. Many factors change the absolute heat sensitivity of mammalian cells by about 1 degrees C, but these factors have little effect on Rs, although the transition in R at 43-44 degrees C may be eliminated or shifted by about 1 degrees C. R for heat radiosensitization are similar to those above for heat cytotoxicity, but Rs for heat chemosensitization are much smaller (usually about 1.1-1.2). In practically all of the clinical trials that have been conducted, heat and radiation have been separated by 30-60 min, for which the primary effect should be heat cytotoxicity and not heat radiosensitization. Data are presented showing the clinical application of the thermal isoeffect dose (TID) concept in which different heating protocols for different times at different temperatures are converted into equiv min at 43 degrees C (EM43). For several heat treatments in the clinic, the TIDs for each treatment can be added to give a cumulative equiv min at 43 degrees C, viz., CEM43. This TID concept was applied by Oleson et al. in a retrospective analysis of clinical data, with the intent of using this approach prospectively to guide future clinical studies. Considerations of laboratory data and the large variations in temperature distributions observed in human tumours indicate that thermal tolerance, which has been observed for mammalian cells for both heat killing and heat radiosensitization, probably is not very important in the clinic.(ABSTRACT TRUNCATED AT 400 WORDS)

Apoptosis. Its significance in cancer and cancer therapy

Apoptosis is a distinct mode of cell death that is responsible for deletion of cells in normal tissues; it also occurs in specific pathologic contexts. Morphologically, it involves rapid condensation and budding of the cell, with the formation of membrane-enclosed apoptotic bodies containing well-preserved organelles, which are phagocytosed and digested by nearby resident cells. There is no associated inflammation. A characteristic biochemical feature of the process is double-strand cleavage of nuclear DNA at the linker regions between nucleosomes leading to the production of oligonucleosomal fragments. In many, although not all of the circumstances in which apoptosis occurs, it is suppressed by inhibitors of messenger RNA and protein synthesis. Apoptosis occurs spontaneously in malignant tumors, often markedly retarding their growth, and it is increased in tumors responding to irradiation, cytotoxic chemotherapy, heating and hormone ablation. However, much of the current interest in the process stems from the discovery that it can be regulated by certain proto-oncogenes and the p53 tumor suppressor gene. Thus, c-myc expression has been shown to be involved in the initiation of apoptosis in some situations, and bcl-2 has emerged as a new type of proto-oncogene that inhibits apoptosis, rather than stimulating mitosis. In p53-negative tumor-derived cell lines transfected with wild-type p53, induction of the gene has, in rare cases, been found to cause extensive apoptosis, instead of growth arrest. Finally, the demonstration that antibodies against a cell-surface protein designated APO-1 or Fas can enhance apoptosis in some human lymphoid cell lines may have therapeutic implications.

Analysis of mitotic cell death caused by radiation in mouse leukaemia L5178Y cells: apoptosis is the ultimate form of cell death following mitotic failure

The appearance of various abnormal cells after irradiation was investigated in growing mouse leukaemia L5178Y cells. Morphologically defined apoptotic cells started to emerge at 10 h after irradiation and the frequency reached a peak at around 48 h being similar to the frequency of other abnormal cells, i.e. micronucleated, multinucleated and giant cells. Necrotic cells were rarely seen. The frequency of apoptosis and other abnormal cells depended on the radiation dose. The typical DNA ladder pattern for apoptosis was observed in the agarose gel electrophoretic analysis of the cells at 24-96 h postirradiation. A decline in the frequency of apoptotic cells occurred with longer incubation, which was associated with a sharp increase in cloning efficiency. Changes in the growth rate of the irradiated cell population during the postirradiation period could be reasonably well described by a simple model using the frequencies of apoptosis and other abnormal cells. The results suggest that apoptosis is the ultimate form of cell death via mitotic failure caused by relatively small doses of radiation in L5178Y cells.

Cytotoxic manifestations of the interaction between hyperthermia and TNF: DNA fragmentation

The relationship of DNA fragmentation to the greatly enhanced cytotoxicity seen in vitro against tumour cells when recombinant human tumour necrosis factor-alpha (TNF-alpha) is combined with hyperthermia was investigated. The TNF-alpha-sensitive L929 and -resistant EMT6 cells were treated with 8.8 and 16 ng of TNF-alpha per ml, respectively, and then heated at 40.5 degrees C for 24 h (L929) or at 43 degrees C for 1 h (L929) or 1.5 h (EMT-6) beginning 1 h later. For both cell lines at both temperatures, the addition of heating to the TNF-alpha treatment significantly decreased viability and increased DNA fragmentation at earlier time points than seen with either TNF-alpha or heat alone. DNA fragmentation was further studied using agarose gel electrophoresis to examine the size distribution of the DNA fragments and the ability of intracellular calcium buffering agents BAPTA and quin-2 to inhibit fragmentation. At 4.5 h after L929 cells were treated with TNF-alpha at 43 degrees C, the size distribution of DNA fragments more closely resembled the oligonucleosome sized apoptotic DNA fragmentation, as seen in irradiated rat thymocytes, than the spectrum of DNA fragments seen in necrotic fragmentation. However, while BAPTA and quin-2 inhibited the calcium-dependent apoptotic fragmentation seen in thymocytes they did not inhibit the DNA fragmentation in L929 cells. In addition, the loss of membrane integrity in both L929 and EMT-6 cells preceded or approximated the appearance of DNA fragmentation, whereas loss of membrane integrity usually follows DNA fragmentation in apoptosis. However, morphological studies showed that apoptotic bodies were present in L929 cell cultures treated with TNF-alpha and heat, and were distinguishable from necrosing cells. We conclude that both types of DNA fragmentation are operant in some cell lines exhibiting a cytotoxic response to TNF-alpha and heat treatments, and that increased fragmentation reflects the greatly enhanced cytotoxic interactions seen with combination treatments in those cells.