Intracellular calcium and pH alterations induced by tri-n-butyltin chloride in isolated rainbow trout hepatocytes: a flow cytometric analysis

The effects of tri-n-butyltin chloride (TBT) on ionic homeostasis on isolated trout hepatocytes were investigated by flow cytometry (FCM), using the Ca(2+)-sensitive and pH-sensitive fluorescent probes Indo-1 and SNARF-1, respectively. Cell viability was monitored concurrently. Treatment of hepatocytes with 1 and 5 microM TBT caused a rapid and sustained elevation of cytosolic free Ca2+ concentration [Ca2+]i and an important cytoplasmic acidification. These changes were dependent upon TBT concentration and were maintained over 60 min, the maximum exposure period investigated. At 0.5 microM TBT, there was a slight but not significant increase in [Ca2+]i and a significant reduction in intracellular pH (pHi) only after 60 min of exposure. A rise in [Ca2+]i and cytoplasmic acidification were observed before loss of viability was detectable. Experiments carried out in Ca(2+)-free medium suggest that TBT mainly mobilizes Ca2+ from intracellular stores in trout hepatocytes. The cytoplasmic acidification following TBT exposure seems to be caused by the combination of intracellular Ca2+ mobilization and by direct action of TBT. The present results suggest that ionic homeostasis perturbations could be early events in the mechanism of cell injury by TBT.     

Temporal relationships between de novo protein synthesis, calpain and caspase 3-like protease activation, and DNA fragmentation during apoptosis in septo-hippocampal cultures

Caspase 3-like proteases are key executioners in mammalian apoptosis, and the calpain family of cysteine proteases has also been implicated as an effector of the apoptotic cascade. However, the influence of upstream events on calpain/caspase activation and the role of calpain/caspase activation on subsequent downstream events are poorly understood. This investigation examined the temporal profile of apoptosis-related events after staurosporine-induced apoptosis in mixed glial-neuronal septo-hippocampal cell cultures. Following 3 hr exposure to staurosporine (0.5 microM), calpain and caspase 3-like proteases processed alpha-spectrin to their signature proteolytic fragments prior to endonuclease-mediated DNA fragmentation (not evident until 6 hr), indicating that endonuclease activation is downstream from calpain/caspase activation. Cycloheximide, a general protein synthesis inhibitor, completely prevented processing of alpha-spectrin by calpains and caspase 3-like proteases, DNA fragmentation and cell death, indicating that de novo protein synthesis is an upstream event necessary for activation of calpains and caspase 3-like proteases. Calpain inhibitor II and the pan-caspase inhibitor Z-D-DCB each inhibited their respective protease-specific processing of alpha-spectrin and attenuated endonuclease DNA fragmentation and cell death. Thus, activation of calpains and caspase 3-like proteases is an early event in staurosporine-induced apoptosis, and synthesis of, as yet, unknown protein(s) is necessary for their activation.     

Activation of caspase-3-like enzymes in non-apoptotic T cells

The activation of the caspase family of cysteine proteases is a key step in the implementation of apoptotic cell death leading to further downstream effects such as DNA fragmentation. In cultured tumor cells, caspase activity appears only when cells are undergoing apoptosis. Here we show that human and murine T lymphocytes acquire high intracellular activities of cell death-specific caspases upon activation by mitogens and IL-2 without evidence that apoptosis is proceeding. The highest activity is seen when cells are mitogen activated for 3 days. On a per cell basis, caspase activity in activated T cells is much higher than in tumor cells induced to undergo apoptosis. In the presence of exogenously added IL-2 cells stay alive and maintain a high level of caspase activity while IL-2 withdrawal results in cell death and decline of caspase activity. Caspase activity can also be measured in extracts from spleen and lymph nodes from mice injected with superantigen. While in tumor cell lines caspase activity correlates with cleavage of poly(ADP)-ribose polymerase (PARP) and DNA fragmentation, in activated T cells cleavage products of cellular PARP can be detected whereas DNA fragmenting activity appears only upon IL-2 withdrawal which coincides with cell death. These data show that caspase activation in intact cells does not necessarily lead to cell death and argue for a checkpoint in the apoptotic pathway downstream of caspases. Furthermore, they provide a molecular correlate for the high susceptibility of activated T cells for apoptosis.     

7-Hydroxystaurosporine (UCN-01) induces apoptosis in human colon carcinoma and leukemia cells independently of p53

7-hydroxystaurosporine (UCN-01) is a more selective protein kinase C inhibitor than staurosporine. UCN-01 exhibits antitumor activity in experimental tumor models and is presently in clinical trials. Our study reveals that human myeloblastic leukemia HL60 and K562 and colon carcinoma HT29 cells undergo internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis after UCN-01 treatment. These three cell lines lack functional p53, and K562 and HT29 cells are usually resistant to apoptosis. DNA fragmentation in HT29 and K562 cells occurred after 1 day of treatment while it took less than 4 h in HL60 cells. Cycloheximide prevented UCN-01-induced DNA fragmentation in HT-29 cells, but not in HL60 and K562 cells, suggesting that macromolecular synthesis is selectively required for apoptotic DNA fragmentation in HT29 cells. UCN-01-induced DNA fragmentation was preceded by activation of cyclin B1/cdc2 kinase. Further studies in HL60 cells showed that UCN-01-induced apoptosis was associated with degradation of CPP32, PARP, and lamin B and that the inhibitor of caspases (ICE/CED-3 cysteine proteases), Z-VAD-FMK, and the serine protease inhibitor, DCI, protected HL60 cells from UCN-01-induced DNA fragmentation. However, only DCI and TPCK, but not Z-VAD-FMK, inhibited DNA fragmentation in the HL60 cell-free system, suggesting that serine protease(s) may play a role in the execution phase of apoptosis in HL60 cells treated with UCN-01. Z-VAD-FMK and DCI also inhibited apoptosis in HT29 cells. These data demonstrate that the protein kinase C inhibitor and antitumor agent, UCN-01 is a potent apoptosis inducer in cell lines that are usually resistant to apoptosis and lack p53 and that caspases and probably serine proteases are activated during UCN-01-induced apoptosis.     

Activin A and transforming growth factor-beta stimulate heart formation in axolotls but not rescue cardiac lethal mutants

The cytotoxicity of transforming growth factor beta 1 (TGF beta 1) was assessed in rat hepatocytes cultured under periportal (PP)-or pericentral (PC)-equivalent conditions. TGF beta 1 induced a 5-fold greater DNA fragmentation and LDH release in PC cultures than in PP cultures. At low exposure level (1 ng/ml TGF beta 1), albumin secretion and mitochondrial activity (rhodamine-123 uptake) were selectively reduced in PP cultures, whereas the incidence of apoptotic cells in PC cultures was about 10-fold higher than that in PP cultures. The time profiles of TGF beta 1-induced apoptotic and necrotic events and the concentration-response relationship differed in PC and PP cultures. In PC cultures the early appearance of cells with apoptotic nuclei was not associated with DNA fragmentation nor with an increase in LDH release or impaired mitochondrial function. At a high exposure level (5 ng/ml TGF beta 1), again cells with apoptotic nuclei were much more strongly induced in PC cultures but DNA fragmentation, LDH release, and impairment of mitochondrial activity all increased in an exposure-time dependent manner in both PP and PC cultures. At this exposure level 48 and 72% of the apoptotic cells detected in PC cultures after continuous exposure for 24 hr were induced within an exposure of 1 and 4 hr, respectively. Aurintricarboxylic acid (50 microM), an inhibitor of endonucleases, significantly inhibited the appearance of apoptotic cells and the progression in apoptosis. Clearly, TGF beta 1 preferentially induced apoptotic cell death in hepatocytes with PC-equivalent metabolism at low exposure levels. High exposure levels or prolonged exposure periods produced both apoptosis and necrosis.     

Suppression of apoptosis by gonadotropin, 17beta-estradiol, and epidermal growth factor in rainbow trout preovulatory ovarian follicles

In this study we present the first evidence for the occurrence of apoptotic cell death in ovarian follicles from teleost fish. Preovulatory ovarian follicles from mature hatchery-raised rainbow trout (Oncorhynchus mykiss) were collected and either immediately frozen in liquid nitrogen or incubated in serum-free medium at 18 degrees for 24 hr. The extent of ovarian apoptotic DNA fragmentation was determined using 3'-end labeling of DNA with [32P]dideoxy-ATP, size fractionation by agarose gel electrophoresis, and quantification of low-molecular-weight (<15 kb) DNA using autoradiography and liquid scintillation counting. The extent of apoptotic DNA fragmentation was eightfold greater in immediately frozen preovulatory follicles than in previtellogenic ovarian follicles collected from immature rainbow trout (P < 0.05), suggesting differences in the degree of apoptosis at different stages of follicular development. In preovulatory trout follicles, the extent of apoptotic DNA fragmentation was fivefold greater in follicles incubated for 24 hr. Treatment of incubated preovulatory follicles with either partially purified salmon gonadotropin SG-G100 (1 microg/ml) or epidermal growth factor (EGF; 100 ng/ml) suppressed apoptotic DNA fragmentation by 31 and 41%, respectively, in comparison to untreated incubated follicles (P < 0.01). Treatment of incubated follicles with 17beta-estradiol (1-100 ng/ml) caused a concentration-dependent suppression of apoptotic DNA fragmentation (P < 0.05). These results suggest that apoptosis is involved in teleost ovarian development and that several of the hormonal factors acting as follicle survival factors in mammalian and avian ovaries may play a similar role in teleost ovarian follicles.     

Antigen receptor-induced B lymphocyte apoptosis mediated via a protease of the caspase family

An extensive body of data, in a variety of systems, denoted the caspase family of proteases as a key player in the execution of programmed cell death. This family consists of cysteine proteases that cleave after asparagine-containing motifs. It is well established that the caspases are essential for the apoptosis mediated by Fas (CD95) and TNF receptor p55, molecules that contain the "death domain" in the cytoplasmic tail. However, little is known about the mechanisms underlying the antigen receptor-mediated cell death in B lymphocytes, a process instrumental in negative selection of potentially autoreactive B cells. Here, we investigated the involvement of caspases in cell death triggered via the antigen receptor in B lymphocytes (BCR) by using specific inhibitors. Initially, we used a well-established cell line, CH31, which is a model of B cell tolerance, to demonstrate that these proteases indeed participate in the BCR-induced apoptotic pathway. Next, we confirmed the physiological relevance of the caspase-mediated cell death pathway in splenic B cell populations isolated ex vivo that were induced to undergo apoptosis by extensive cross-linking of their BCR. Most interestingly, our data demonstrated that caspases regulate not only the nuclear DNA fragmentation, but also the surface membrane phosphatidylserine translocation as well as the degradation of a specific nuclear substrate. Taken together, this report supports the hypothesis that regulation of the caspase family is crucial in controlling the life/death decision in B lymphocytes mediated by the antigen receptor signal transduction.     

Gossypol-induced apoptotic DNA fragmentation correlates with inhibited protein kinase C activity in spermatocytes

After exposure of cultured rat spermatocytes to gossypol acetic acid for five hours, DNA fragmentation in a ladder pattern was found in the medium and supernatants of cell lysates. The concentrations of gossypol used for the induction of apoptosis ranged from 100 microM to 300 microM. Within this dose range, gossypol was also found to be effective at inhibiting protein kinase C (PKC) activity. This inhibitory effect was demonstrated by measuring the PKC residing in cytosolic and particulate fractions. However, the gossypol-induced inhibition of PKC activity was protected by phorbol 12,13-dibutyrate (PDBu), an activator of PKC. Furthermore, the presence of PDBu prevented gossypol-induced DNA fragmentation. These results suggest that spermatocyte apoptosis induced by gossypol is correlated with the reduction of PKC activity, and that maintenance of PKC basal activity is essential for protecting the spermatocyte from apoptosis.     

IL-4 and interferon-gamma production in children with atopic disease

The mechanism by which 7,12-dimethylbenz[a]anthracene (DMBA) produces cytotoxicity in lymphocytes was investigated in these studies using the murine A20.1 B cell lymphoma. Results show that in vitro exposure of these cells to 10-30 microM DMBA for 4 hr produced an increase in intracellular Ca2+, DNA fragmentation, and subsequent cell death. Elevation of Ca2+ and DNA fragmentation induced by DMBA were greatly pronounced when the A20.1 cells were exposed at high cell density (10(7) cells/ml). DMBA-induced DNA fragmentation and cell death were inhibited by coexposure of A20.1 cells to a calcium chelator (EDTA), a general nuclease and polymerase inhibitor (aurintricarboxylic acid), and a protein synthesis inhibitor (cycloheximide). These agents have been previously shown to inhibit apoptosis in lymphocytes and other cells exposed to chemical agents. We also found that cyclosporin A, an inhibitor of Ca(2+)-dependent pathways of T and B cell activation, prevented apoptosis in the A20.1 cell line. These results demonstrate that DMBA induces programmed cell death (apoptosis) in the A20.1 murine B cell lymphoma by Ca(2+)-dependent pathways. The increased sensitivity of A20.1 at high cell density to Ca2+ elevation and DNA fragmentation suggests that cell to cell interactions may also be important in this process.     

Evidence of hepatocyte apoptosis in rat liver after the administration of carbon tetrachloride

In acute liver injury induced by the injection of CCl4, cell death has been attributed to the necrosis of hepatocytes in the centrilobular area. In the present study, we re-examined the hepatic injury evoked by CCl4 in rats and explored the possibility that apoptosis may also contribute to its pathogenesis. Apoptotic hepatocytes were identified and quantified by light and electron microscopy, the in situ immunohistochemical labeling of nuclear DNA fragmentation, flow cytometry, and DNA gel electrophoresis. We found that a substantial number of hepatocytes underwent apoptosis. Apoptotic changes were also observed in ballooned hepatocytes. Apoptotic hepatocytes increased in number at 3 hours and peaked at 6 hours after the CCl4 injection. Apoptotic bodies were sequestrated in the adjacent hepatocytes and sinusoidal cells. Double staining of the cells with immunostaining for phagocytes and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining for labeling of DNA fragmentation showed that the majority of apoptotic hepatocytes were phagocytosed by Kupffer cells and macrophages. The results indicated that apoptosis occurs in the ballooned and injured hepatocytes of the centrilobular area. What occurs after CCl4 administration may be important in reducing inflammation, shortening the course of acute hepatic injury, and preventing the development of fibrosis.     

Toxoplasma gondii-infected cells are resistant to multiple inducers of apoptosis

Infection with certain intracellular pathogens, including viruses and bacteria, may induce host cell apoptosis. On the other hand, infection with some viruses inhibits apoptosis. Complex protozoan parasites, including Toxoplasma gondii and members of Plasmodium, Leishmania, and Microsporidia, are also obligate intracellular pathogens, yet relatively little is known regarding their subversion of host cell functions. We now report that cells infected with T. gondii are resistant to multiple inducers of apoptosis, including Fas-dependent and Fas-independent CTL-mediated cytotoxicity, IL-2 deprivation, gamma irradiation, UV irradiation, and the calcium ionophore beauvericin. Inhibition of such a broad array of apoptosis inducers suggests that a mechanism common to many, or perhaps all, apoptotic pathways is involved. The inhibitory activity requires live intracellular parasite and ongoing protein synthesis. Despite T. gondii-mediated inhibition of DNA fragmentation, infected cells can still be lysed by CTL.     

Ca2+ channel blockers verapamil and nifedipine inhibit apoptosis induced by 25-hydroxycholesterol in human aortic smooth muscle cells

We have characterized the death of human aortic smooth muscle cells induced by 25-hydroxycholesterol, an oxidation product of cholesterol. Chromatin condensation characteristic of apoptosis was observed by enzymatic (TUNEL) staining of chromatin, and by electron microscopy. Fourteen percent of cells treated with 5 microg/ml of 25-hydroxycholesterol for 24 h displayed chromatin degradation as determined by positive TUNEL staining. Addition of TNF alpha (10 ng/ml) and IFN gamma (20 ng/ml) increased the proportion of TUNEL positive cells to 30%, whereas the cytokines alone were without effect. After 48 h, 40% of the cells treated with 5 microg/ml of 25-hydroxycholesterol were TUNEL positive, and 21% of the cells displayed chromatin condensation. Oligonucleosomal DNA fragmentation typical of apoptosis was demonstrated by agarose gel electrophoresis. Furthermore, activation of the ICE-like protease caspase 3 (CPP32) was observed in cells treated with 25-hydroxycholesterol. Addition of the Ca2+ entry blockers verapamil or nifedipine to the culture medium inhibited apoptosis by more than 70% and reduced cytotoxicity, while removal of Ca2+ from culture medium reduced apoptosis by 42%. Within a few minutes after addition, 25-hydroxycholesterol induced intracellular Ca2+ oscillations with a frequency of approximately 0.3-0.4 min(-1). Thus it appears that Ca2+ influx through plasma membrane channels is an important signal in oxysterol-induced apoptosis. Addition of TNF alpha and IFN gamma enhanced cytotoxicity and resulted in a higher proportion of apoptotic cells, suggesting that inflammatory cytokines can increase the cytotoxicity of lipid oxidation products.     

Role of proteolysis in apoptosis: involvement of serine proteases in internucleosomal DNA fragmentation in immature thymocytes

Three chemically distinct serine, but not cysteine, protease inhibitors (phenylmethylsulphonyl fluoride, N-tosyl-L-phenylalanylchloromethyl ketone and 3,4-dichloroisocoumarin) prevented, in a dose-dependent manner, the characteristic apoptotic internucleosomal DNA cleavage (DNA ladder) typically observed in thymocytes in response to dexamethasone and teniposide VM-26. This effect was not the result of a direct inhibition of the Ca2+,Mg(2+)-dependent endonuclease, since oligonucleosomal DNA cleavage occurred in the presence of these inhibitors in isolated nuclei. The proteolytic step occurred at a very early stage of apoptosis, and preincubation of thymocytes with the inhibitors before dexamethasone or teniposide VM-26 were added irreversibly suppressed ladder formation. This implied that the cellular effector(s) of these compounds preexisted and were not resynthesized in response to the inducers of apoptosis. Serine protease inhibitors also suppressed apoptotic cell shrinkage and complete nuclear collapse, suggesting that these morphological changes were directly related to internucleosomal fragmentation of DNA. However, the serine protease inhibitors did not prevent high molecular weight DNA cleavage (> 50 kilobases) that preceded the ladder formation and thymocytes still died by apoptosis. This supported the view that internucleosomal DNA cleavage, considered to be the biochemical marker of apoptosis, might in fact be a late and dispensable step and that the newly described high molecular weight DNA cleavage might be a better indicator of apoptosis.     

Anatomical basis of a congenital hearing impairment: basilar papilla dysplasia in the Belgian Waterslager canary

We studied the role of proteases in apoptosis using a cell-free system prepared from a human leukemia cell line. HL60 cells are p53 null and extremely sensitive to a variety of apoptotic stimuli including DNA damage induced by the topoisomerase I inhibitor, camptothecin. We measured DNA fragmentation induced in isolated nuclei by cytosolic extracts using a filter elution assay. Cytosol from camptothecin-treated HL60 cells induced internucleosomal DNA fragmentation in nuclei from untreated cells. This fragmentation was suppressed by serine protease inhibitors. Serine proteases (trypsin, endoproteinase Glu-C, chymotrypsin A, and proteinase K) and papain by themselves induced DNA fragmentation in naive nuclei. This effect was enhanced in the presence of cytosol from untreated cells. Cysteine protease inhibitors (E-64, leupeptin, Ac-YVAD-CHO [ICE inhibitor]) did not affect camptothecin-induced DNA fragmentation. The apopain/Yama inhibitor, Ac-DEVD-CHO, and the proteasome inhibitor, MG-132, were also inactive both in the cell-free system and in whole cells. Interleukin-1 beta converting enzyme (ICE) or human immunodeficiency virus protease failed to induce DNA fragmentation in naive nuclei. Together, these results suggest that DNA damage activates serine protease(s) which in turn activate(s) nuclear endonuclease(s) during apoptosis in HL60 cells.     

Induction of apoptotic DNA fragmentation and c-jun downregulation in human myeloid leukemia cells by the permeant Ca2+ chelator BAPTA/AM

The permeant Ca2+ chelator acetoxymethyl-1,2-bis(2-aminopheoxy)ethane- N,N,N',N'-tetraacetic acid (BAPTA/AM), an agent previously used to characterize drug-induced apoptosis in neoplastic cells, has been examined with respect to induction of DNA fragmentation and cytotoxicity in the human leukemia cell lines HL-60 and U937. Exposure of cells to various concentrations of BAPTA/AM for 6 h resulted in a biphasic induction of internucleosomal DNA cleavage, with maximal damage occurring at 10-microM concentrations. Higher BAPTA/AM concentrations were associated with the loss of internucleosomal cleavage products, but with the appearance of larger (i.e., 50-kilobase) fragments on pulsed-field gel electrophoresis. Cells exposed to 10 microM BAPTA/AM exhibited classic apoptotic morphology, whereas cells exposed to 50-microM concentrations displayed atypical features (e.g., cell swelling, chromatin clumping); in each case, substantial cytotoxicity was noted. The actions of BAPTA/AM did not depend upon the presence of extracellular Ca2+, nor were they affected by impermeant Ca2+ chelators. Measurement of cytosolic Ca2+ by Fura-2/AM or Indo-1 revealed late but not early increases in intracellular Ca2+ in BAPTA/AM-treated cells. Finally, BAPTA/AM-induced apoptosis was accompanied by the concentration-dependent downregulation of the immediate early response gene c-jun. These findings suggest a complex role for Ca2+ chelators such as BAPTA/AM in the regulation of human myeloid leukemic cell apoptosis, and indicate that this agent may selectively antagonize internucleosomal DNA fragmentation without interfering with other aspects of the apoptotic response and/or cell lethality.     

The proliferative effect of vascular endothelial growth factor requires protein kinase C-alpha and protein kinase C-zeta

The heparin-binding protein vascular endothelial growth factor (VEGF) is a highly specific growth factor for endothelial cells. VEGF binds to specific tyrosine kinase receptors, which mediate intracellular signaling. We investigated 2 hypotheses: (1) VEGF affects intracellular calcium [Ca2+]i regulation and [Ca2+]i-dependent messenger systems; and (2) these mechanisms are important for VEGF's proliferative effects. [Ca2+]i was measured in human umbilical vein endothelial cells using fura-2 and fluo-3. Protein kinase C (PKC) activity was measured by histone-like pseudosubstrate phosphorylation. PKC isoform distribution was observed with confocal microscopy and Western blot. Inhibition of PKC isoforms was assessed by specific antisense oligonucleotides (ODN) for the PKC isoforms. VEGF (10 ng/mL) induced a transient increase in [Ca2+]i followed by a sustained elevation. The sustained [Ca2+]i plateau was abolished by EGTA. Pertussis toxin also abolished the plateau phase, whereas the initial peak was not affected. The PKC isoforms alpha, delta, epsilon, and zeta were identified in endothelial cells. VEGF induced a translocation of PKC-alpha and PKC-zeta toward the nucleus and the perinuclear area, whereas cellular distribution of PKC-delta and PKC-epsilon was not influenced. Cell exposure to TPA led to a down-regulation of PKC-alpha and reduced the proliferative effect of VEGF. VEGF-induced endothelial cell proliferation also was reduced by the PKC inhibitors staurosporine and calphostin C. Specific down-regulation of PKC-alpha and PKC-zeta with antisense ODN reduced the proliferative effect of VEGF significantly. Our data show that VEGF induces initial and sustained Ca2+ influx. VEGF leads to the translocation of the [Ca2+]i-sensitive PKC isoform alpha and the atypical PKC isoform zeta. Antisense ODN for these PKC isoforms block VEGF-induced proliferation. These findings suggest that PKC isoforms alpha and zeta are important for VEGF's angiogenic effects.     

Light-induced apoptosis: differential timing in the retina and pigment epithelium

Apoptosis is a genetically regulated form of cell death. Individual cells show condensed nuclear chromatin and cytoplasm, and biochemical analysis reveals fragmentation of the DNA. Ensuing cellular components, apoptotic bodies, are removed by macrophages or neighboring cells. Genes involved in the regulation of apoptosis as well as stimuli and signal transduction systems, are only beginning to be understood in the retina. Therefore, we developed a new in vivo model system for the investigation of events leading to apoptosis in the retina and the pigment epithelium. We induced apoptosis in retinal photoreceptors and the pigment epithelium of albino rats by exposure to 3000 lux of diffuse, cool white fluorescent light for short time periods of up to 120 minutes. Animals were killed at different time intervals during and after light exposure. The eyes were enucleated and the lower central retina was processed for light- and electron microscopy. DNA fragmentation was analysed in situ by TdT-mediated dUTP nick-end labeling (TUNEL) or by gel electrophoresis of total retinal DNA. We observed that the timing of apoptosis in the photoreceptors and pigment epithelium was remarkably different, the pigment epithelium showing a distinct delay of several hours before the onset of apoptosis. In photoreceptors, apoptosis was induced within 90 minutes of light exposure, with the morphological appearance of apoptosis preceding the fragmentation of DNA. In the pigment epithelium, the morphological appearance of apoptosis and DNA fragmentation were coincident. Different regulative mechanisms may lead to apoptotic cell death in the retinal photoreceptors and pigment epithelium. This in vivo model system will allow measurement of dose-responses, a potential spectral dependence and the molecular background of apoptotic mechanisms in the retina.     

Deficits in finite verb morphology: some assumptions in recent accounts of specific language impairment

Multiple aspartate-specific cysteine proteases have been identified and specific members of this family have been implicated in the apoptotic death of many mammalian cell types. Caspase-3-like proteases seem to play a pivotal role in neuronal apoptosis since mice with germline inactivation of the caspase-3 gene manifest profound alterations in neurogenesis. Moreover, inhibitors of caspase-3-related proteases have been shown to inhibit neuronal apoptosis. Here we extend recent work from our laboratory on the mechanisms mediating the neurotoxic actions of 1-methyl-4-phenylpyridinium using ventral mesencephalon cultures containing dopamine neurons. We demonstrate that low concentrations of 1-methyl-4-phenylpyridinium induce apoptosis in dopamine neurons by morphological and biochemical criteria. Moreover, pretreatment of ventral mesencephalon cultures with the tetrapeptide inhibitors of the caspase-3-like proteases zVAD-FMK or Ac-DEVD-CHO specifically inhibit death of dopamine neurons induced by low concentrations of 1-methyl-4-phenylpyridinium, whereas the caspase-1-like inhibitor Ac-YVAD-CHO was without effect. Our data indicate that exposure of cultured ventral mesencephalon dopamine neurons to low concentrations of 1-methyl-4-phenylpyridinium results in apoptotic death and that caspase-3-like proteases may mediate the neurotoxic apoptotic actions of 1-methyl-4-phenylpyridinium.     

Diterpenoids from germander, an herbal medicine, induce apoptosis in isolated rat hepatocytes

BACKGROUND & AIMS: Germander was withdrawn from the market after its use for weight control caused an epidemic of hepatitis. Its toxicity was shown to be caused by diterpenoids and their cytochrome P4503A-mediated metabolic activation into electrophilic metabolites that deplete cellular thiols. The aim of the present study was to determine the mechanisms of cell death. METHODS: Isolated rat hepatocytes were incubated for 2 hours with germander diterpenoids (100 micrograms/mL). RESULTS: Diterpenoids decreased cell glutathione, increased cytosolic [Ca2+], activated Ca(2+)-dependent tissue transglutaminase forming a cross-linked protein scaffold, and caused internucleosomal DNA fragmentation and the ultrastructural features of apoptosis. Cell death was prevented by decreasing metabolic activation (with troleandomycin), preventing depletion of glutathione (with cystine), blocking activation of Ca(2+)-modulated enzymes (with calmidazolium), or inhibiting internucleosomal DNA fragmentation (with aurintricarboxylic acid). Apoptosis was increased and diterpenoids caused overexpression of p53 and interleukin 1 beta-converting enzyme in rats treated with dexamethasone (cytochrome P4503A inducer). Apoptosis was also increased by a diet deficient in sulfur amino acids. CONCLUSIONS: The germander furano diterpenoids cause apoptosis within 2 hours in isolated rat hepatocytes. Electrophilic metabolites may stimulate apoptosis by decreasing thiols, increasing [Ca2+], and activating Ca(2+)-dependent transglutaminase and endonucleases.