Oxidative stress and cyclooxygenase-2 induction mediate cyanide-induced apoptosis of cortical cells

Cyanide (KCN)-induced generation of reactive oxygen species (ROS) involves cyclooxygenase-2 (COX-2)-mediated reactions in some neurons. The present study examines the extent to which COX isoforms are involved in KCN-induced apoptotic cell death processes of cultured cortical cells. After treatment with KCN (10-300 microM), COX-2 was expressed in a time- and concentration-dependent manner increasing markedly over a 4-h period. However, no significant changes were observed in COX-1 levels at any cyanide concentration. Correlated with COX-2 up-regulation, KCN induced a time-dependent apoptotic death. TUNEL staining showed that the COX-2 inhibitor NS-398 (30 microM) blocked KCN-induced apoptosis, whereas the selective COX-1 inhibitor valeryl salicylate did not affect the level of apoptotic cell death. Exposure of cells to KCN (300 microM) for 24 h resulted in DNA fragmentation, which was also reduced by NS-398. Prostaglandin E(2) (PGE(2)) accumulation in cell culture supernatants was increased by KCN and NS-398 blocked PGE(2) generation. PCR studies further confirmed that COX-2 expression was increased by KCN. Antioxidants phenyl-N-test-butylnitrone, superoxide dismutase, and catalase significantly inhibited KCN-induced COX-2 up-regulation and subsequent apoptosis. N(G)-nitro-L-arginine methylester an inhibitor of nitric oxide synthase, blocked KCN-induced PGE(2) production and apoptosis, but not COX-2 expression. Increased nitric oxide levels caused by cyanide may directly activate the COX-2 enzyme. These data show that cyanide treatment of cortical cells involves increased COX-2 expression, PGE(2) accumulation, and ROS generation, resulting in apoptotic cell death.     

Mechanism of ricin-induced apoptosis in human cervical cancer cells

The mechanism of ricin-induced apoptosis in human cervical cancer cell line HeLa was studied. The present study demonstrated that ricin induces apoptosis of human cervical cancer cells (HeLa) in a time dependent manner with an IC(50) for cell viability of 1 microg/ml. Ricin treatment resulted in a time dependent increase in LDH leakage, DNA fragmentation, percent apoptotic cells, generation of reactive oxygen species and depletion of intracellular glutathione levels. DNA agarose gel electrophoresis showed typical oligonucleosomal length DNA fragmentation. Additionally, DNA diffusion assay was performed to confirm DNA damage and apoptosis. Ricin activated caspase-3 as evidenced by both proteolytic cleavage of procaspase-3 into 20 and 18 kDa subunits, and increased protease activity. Caspase activity was maximum at 4h and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the 85 kDa cleavage product. Ricin-induced caspase-3 activation also resulted in cleavage of DNA fragmentation factor-45 (DFF45/ICAD) and DFF40 or caspase-activated DNase in HeLa cells. Activation of caspase-3, cleavage of PARP and DNA fragmentation was blocked by pre-treatment with caspase-3 specific inhibitor Ac-DEVD-CHO (100 microM) and broad-spectrum caspase inhibitor Z-VAD-FMK (40 microM). Ricin-induced DNA fragmentation was inhibited by pre-treatment with PARP inhibitors 3-aminobenzamide (100 microM) and DPQ (10 microM). Our results indicate that ricin-induced cell death was mediated by generation of reactive oxygen species and subsequent activation of caspase-3 cascade followed by down stream events leading to apoptotic mode of cell death.     

Induction of apoptosis by isoegomaketone from Perilla frutescens L. in B16 melanoma cells is mediated through ROS generation and mitochondrial-dependent, -independent pathway

We have demonstrated for the first time the mechanism underlying ROS-mediated mitochondria-dependent apoptotic cell death triggered by isoegomaketone (IK) treatment in melanoma cells. We showed that IK induced apoptotic cell death and tumor growth inhibition using tissue culture and in vivo models of B16 melanoma. Furthermore, we observed that IK effectively induced apoptotic cell death, including sub-G1 contents up-regulation, nuclei condensation, DNA fragmentation, and caspase activation in B16 melanoma cells. Pretreatment with caspase inhibitor increased the survival rate of IK-treated B16 cells, implying that caspases play a role in IK-induced apoptosis. Furthermore, IK treatment generated ROS in melanoma cells. We also determined whether or not IK-induced cell death is due to ROS production in B16 cells. N-acetyl cysteine (NAC) inhibitedIK-induced Bcl-2 family-mediated apoptosis. This result indicates that IK-induced apoptosis involves ROS generation as well as up-regulation of Bax and Bcl-2 expression, leading to release of cytochrome c and AIF. Our data suggest that IK inhibits growth and induces apoptosis in melanoma cells via activation of ROS-mediated caspase-dependent and -independent pathways.     

The role of p38 MAPK activation in auranofin-induced apoptosis of human promyelocytic leukaemia HL-60 cells

In a previous study, we reported an antileukaemic activity of auranofin (AF), demonstrating its dual effects: on the induction of apoptotic cell death and its synergistic action with retinoic acid on cell differentiation. In this study, we investigated the downstream signalling events of AF-induced apoptosis to determine the molecular mechanisms of AF activity. Treatment of HL-60 cells with AF induced apoptosis in a concentration- and time-dependent manner. Western blot analysis showed that AF-induced apoptosis was accompanied by the activation of caspase-8, caspase-9, and caspase-3, and the release of cytochrome c from the mitochondria. The phosphorylation and kinase activities of p38 mitogen-activated protein kinase (p38 MAPK) increased gradually until 12 h after AF (2 microM) treatment, and p38 MAPK was also activated concentration-dependently. Pretreatment with SB203580, a specific inhibitor of p38 MAPK, significantly blocked DNA fragmentation and the cleavage of procaspase-8, procaspase-3, and poly-ADP-ribose polymerase (PARP), whereas SB203580 alone had no effect. Reactive oxygen species (ROS) were also detected within 1 h after AF treatment, and the antioxidant N-acetyl-L-cysteine (NAC) effectively protected the cells from apoptosis by inhibiting the phosphorylation of p38 MAPK and the activation of caspases. These results suggest that ROS generation and the subsequent activation of p38 MAPK are essential for the proapoptotic effects of AF in human promyelocytic leukaemia HL-60 cells.     

Protection from apoptotic cell death by cilostazol, phosphodiesterase type III inhibitor, via cAMP-dependent protein kinase activation.

This study aimed to elucidate whether the effect of cilostazol to suppress apoptotic cell death is directly coupled to cAMP-dependent protein kinase activation in human umbilical vein endothelial cells (HUVECs). After exposure of HUVECs to LPS (1 microgml(-1)) for 18 h, the endothelial cells irregularly aggregated with loss of cobblestone appearance, which was reversed by cilostazol (1-100 microM), as well as by cilostamide (cilostazol analog), and cilostazol metabolites (OPC-13015 and OPC-31213), respectively. LPS-stimulated production of reactive oxygen species (ROS) was significantly reduced by cilostazol (0.1-10 microM). In line with these, LPS (1 microgml(-1))- and TNF-alpha (200 ngml(-1))-induced DNA fragmentation, assessed by agarose gel electrophoresis, was significantly reduced by treatment with cilostazol (10 microM) as well as by dibutyryl cAMP (100 microM). This effect was reversed by cAMP-dependent protein kinase inhibitor, Rp-cAMPs (200 microM). Further, LPS (1 microgml(-1))-induced decrease in Bcl-2 and increase in Bax protein expression were fully reversed by cilostazol (10 microM) and dibutyryl cAMP (100 microM), all of which were antagonized by Rp-cAMPs (200 microM). Taken together, cilostazol effectively protected HUVECs from LPS- and TNF-alpha-induced cell death associated with oligonucleosomal DNA fragmentation via activation of cAMP-dependent protein kinase.     

Cadmium-induced apoptosis in murine macrophages is antagonized by antioxidants and caspase inhibitors

Cadmium is a toxic heavy metal that accumulates in the environment and is commonly found in cigarette smoke and industrial effluents. This study was designed to determine the role of reactive oxygen species (ROS) generation, and its antagonism by antioxidants, in cadmium-mediated cell signaling and apoptosis in murine macrophage cultures. Cadmium-generated ROS production was observed in J774A.1 cells at 6 h, reverting to control levels at 16 and 24 h. The ROS production was concentration related between 20 and 500 microM cadmium. Activation of caspase-3 was observed at 8 h and DNA fragmentation at 16 h in the presence of 20 microM cadmium, suggesting that caspase-3 activation is a prior step to DNA fragmentation in cadmium-induced apoptosis. Inhibitors of caspase-3, -8, -9, and a general caspase inhibitor suppressed cadmium-induced caspase-3 activation and apoptosis indicating the importance of caspase-3 in cadmium-induced toxicity in these cells. Protection against the oxidative stress with N-acetylcysteine (NAC) and silymarin (an antioxidant flavonoid) blocked cadmium-induced apoptosis. Pretreatment of cells with NAC and silymarin prevented cadmium-induced cell injury, including growth arrest, mitochondrial impairment, and necrosis, and reduced the cadmium-elevated intracellular calcium ([Ca2+]i), suggesting that the oxidative stress is a source of increased [Ca2+]i. NAC inhibited cadmium-induced activation of mitogen-activated protein kinases, the c-Jun NH2-terminal protein kinase (JNK) and extracellular signal-regulated kinase (ERK). However, silymarin provided only a partial protection for JNK activation, and only at the low concentration did it inhibit cadmium-induced ERK activation. Inhibition of caspase-3 protected oxidative stress produced by cadmium, suggesting that the activation of caspase-3 also contributes to generation of reactive oxygen species (ROS). Results emphasized the role of ROS, Ca2+ and mitogen-activated protein kinases in cadmium-induced cytotoxicity in murine macrophages.     

Protective effects of fangchinoline and tetrandrine on hydrogen peroxide-induced oxidative neuronal cell damage in cultured rat cerebellar granule cells

The present study was performed to examine the neuroprotective effects of fangchinoline (FAN) and tetrandrine (TET), bis-benzylisoquinoline alkaloids, which exhibit the characteristics of Ca 2+ channel blockers, on H2O2 -induced neurotoxicity using cultured rat cerebellar granule neurons. H2O2 produced a concentration-dependent reduction of cell viability, which was blocked by (5 R,10 S)-(+)-5-methyl-10,11-dihydro-5 H-dibenzo[ a,d]cyclohepten-5,10-imine (MK-801), an N-methyl- D-aspartate (NMDA) receptor antagonist, verapamil, an L-type Ca 2+ channel blocker, and NG-nitro- L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor. Pretreatment with FAN and TET over a concentration range of 0.1 to 10 microM significantly decreased the H2O2 -induced neuronal cell death as assessed by a trypan blue exclusion test, a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and the number of apoptotic nuclei. In addition, FAN and TET inhibited the H2O2 -induced elevation of glutamate release into the medium, elevation of the cytosolic free Ca 2+ concentration ([Ca 2+] c ), and generation of reactive oxygen species (ROS). These results suggest that FAN and TET may mitigate the harmful effects of H2O2 -induced neuronal cell death by interfering with the increase of [Ca 2+] c, and then by inhibiting glutamate release and generation of ROS. Abbreviations. AP5:D(-)-2-amino-5-phosphonopentanoic acid DMSO:dimethyl sulfoxide FAN:fangchinoline H 2 DCF-DA:2',7'-dichlorodihydrofluorescin diacetate MK-801:(5 R,10 S)-(+)-5-methyl-10,11-dihydro-5 H-dibenzo[ a,d]cyclohepten-5,20-imine MTT:3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide L-NAME: NG-Nitro- L-arginine methyl ester NMDA: N-methyl- D-aspartate TET:tetrandrine     

Stimulation of 5-HT1A receptor with 8-OH-DPAT inhibits hydrogen peroxide-induced neurotoxicity in cultured rat cortical cells.

We investigated the effect of 8-hydroxy-2-(N,N-dipropylamino)tetralin (8-OH-DPAT), a specific 5-HT(1A) receptor agonist, on H(2)O(2)-induced neuronal cell death in cultured rat cortical cells. H(2)O(2) produced a concentration-dependent reduction of cell viability, which was significantly reduced by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801), an N-methyl-d-aspartate (NMDA) receptor antagonist. Pretreatment of 8-OH-DPAT over the concentration range of 1-100 microM significantly inhibited the H(2)O(2) (100 microM)-induced neuronal cell death as assessed by a MTT assay and the number of apoptotic nuclei, evidenced by Hoechst 33342 staining. The protective effect of 8-OH-DPAT (100 microM) was completely blocked by the simultaneous treatment of 1-(2-methoxyphenyl)-4-[4-(2-phthalimideo)butyl]piperazine (NAN-190, 10muM), a selective 5-HT(1A) receptor antagonist, but not in the presence of the dopamine receptor blocker spiperone (10 microM), indicating that the protective effect of 8-OH-DPAT was mediated via 5-HT(1A) receptors. In addition, 8-OH-DPAT inhibited the H(2)O(2)-induced elevation of glutamate release into the medium and cytosolic Ca(2+) concentration ([Ca(2+)](c)), generation of reactive oxygen species (ROS), and caspase-3 activity. These results suggest that the activation of 5-HT(1A) receptor with 8-OH-DPAT may ameliorate an oxydative stress-induced apoptosis of neuronal cell by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of ROS and caspase activity.     

Nonylphenol‐induced apoptotic cell death in mouse TM4 Sertoli cells via the generation of reactive oxygen species and activation of the ERK signaling pathway

Nonylphenol (NP), a representative endocrine disruptor, interferes with reproductive function in aquatic organisms and animals. Although many previous studies have focused on apoptotic cell death by NP, the fundamental mechanism of NP on apoptosis remains poorly understood. Here, we investigated the molecular mechanism on NP‐induced apoptotic cell death in mouse TM4 Sertoli cells. To evaluate NP treatment on cell viability, formazan and lactate dehydrogenase (LDH) assays were performed. Results indicate that NP reduced cell viability and increased the release of LDH in dose‐ and time‐dependent manners. The reduction of cell viability by NP treatment appeared to involve necrosis as well as apoptosis based on nuclear fragmentation, an increase in the sub G1 population, and the detection of poly(ADP ribose) polymerase and caspase‐3 cleavage. Additionally, the anti‐apoptotic protein Bcl‐2 diminished, whereas the pro‐apoptotic protein Bax increased in a time‐dependent manner. Note that NP‐induced apoptotic cell death was enhanced by the generation of reactive oxygen species (ROS) and activation of extracellular signal‐regulated kinase (ERK) signaling. Pretreatment with N‐acetylcysteine, an antioxidant, attenuated NP‐induced apoptotic cell death. Moreover, NP caused a transient activation of the MAPK pathway. In particular, NP‐induced cell death was significantly suppressed by U0126, a specific inhibitor of ERK. Taken together, our results suggest that NP induces apoptosis in mouse TM4 Sertoli cells via ROS generation and ERK activation. Copyright © 2013 John Wiley & Sons, Ltd.     

Paraquat induces oxidative stress and neuronal cell death; neuroprotection by water-soluble Coenzyme Q10

Neuronal cell death induced by oxidative stress is correlated with numerous neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and stroke. The causes of sporadic forms of age-related neurodegenerative diseases are still unknown. Recently, a correlation between paraquat exposure and neurodegenerative diseases has been observed. Paraquat, a nonselective herbicide, was once widely used in North America and is still routinely used in Taiwan. We have used differentiated Human Neuroblastoma (SHSY-5Y) cells as an in vitro model to study the mechanism of cell death induced by paraquat. We observed that paraquat-induced oxidative stress in differentiated SHSY-5Y cells as indicated by an increase in the production of cellular reactive oxygen species (ROS). Furthermore, apoptosis was evident as indicated by cellular and nuclear morphology and DNA fragmentation. Interestingly, pretreatment of SHSY-5Y cells with water-soluble Coenzyme Q10 (CoQ10) before paraquat exposure inhibited ROS generation. Pretreatment with CoQ10 also significantly reduced the number of apoptotic cells and DNA fragmentation. We also analyzed the effect of paraquat and CoQ10 on isolated mitochondria. Our results indicated that treatment with paraquat induced the generation of ROS from isolated mitochondria and depolarization of the inner mitochondrial membrane. Pretreatment with CoQ10 was able to inhibit ROS generation from isolated mitochondria as well as the collapse of mitochondrial membrane potential. Our results indicate that water-soluble CoQ10 can prevent oxidative stress and neuronal damage induced by paraquat and therefore, can be used for the prevention and therapy of neurodegenerative diseases caused by environmental toxins.     

Protective effect of fangchinoline on cyanide-induced neurotoxicity in cultured rat cerebellar granule cells

The present study was performed to examine the effect of fangchinoline, a bis- benzylisoquinoline alkaloid, which exhibits the characteristics of a Ca2+ channel blocker, on cyanide-induced neurotoxicity using cultured rat cerebellar granule neurons. NaCN produced a concentration-dependent reduction of cell viability, which was blocked by MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist, verapamil, L-type Ca2+ channel blocker, and L-NAME, a nitric oxide synthase inhibitor. Pretreatment with fangchinoline over a concentration range of 0.1 to 10 microM significantly decreased the NaCN-induced neuronal cell death, glutamate release into medium, and elevation of [Ca2+]i and oxidants generation. These results suggest that fangchinoline may mitigate the harmful effects of cyanide-induced neuronal cell death by interfering with [Ca2+]i influx, due to its function as a Ca2+ channel blocker, and then by inhibiting glutamate release and oxidants generation.     

15-Deoxy-delta 12,14-prostaglandin J2 induces apoptosis via JNK-mediated mitochondrial pathway in osteoblastic cells

The cyclopentenone prostaglandin 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cell types. However, the underlying mechanism of 15d-PGJ2-induced apoptosis is not fully understood. The present study was undertaken to determine the molecular mechanism by which 15d-PGJ2 induces apoptosis in MC3T3-E1 mouse osteoblastic cells. 15d-PGJ2 caused a concentration- and time-dependent apoptotic cell death. 15d-PGJ2 induced a transient activation of ERK1/2 and sustained activation of JNK. 15d-PGJ2-induced cell death was prevented by the JNK inhibitor SP6001, but not by inhibitors of ERK1/2 and p38. JNK activation by 15d-PGJ2 was blocked by antioxidants N-acetylcysteine (NAC) and GSH. 15d-PGJ2 caused ROS generation and 15d-PGJ2-induced cell death was prevented by antioxidants, suggesting involvement of ROS generation in 15d-PGJ2-induced cell death. 15d-PGJ2 triggered the mitochondrial apoptotic pathway indicated by enhanced Bax expression, loss of mitochondrial membrane potential, cytochrome c release, and caspase-3 activation. The JNK inhibitor blocked these events induced by 15d-PGJ2. Taken together, these results suggest that the 15d-PGJ2 induces cell death through the mitochondrial apoptotic pathway dependent of ROS and JNK activation in osteoblastic cells.     

Contribution of protein kinase C and glutamate in Pb(2+)-induced cytotoxicity

Activation of protein kinase C (PKC) plays an important role in lead (Pb(2+))-induced cytotoxicity. The effects of low dose exposure to Pb(2+) on cytosolic free calcium (Ca(2+)), PKC activity and mechanisms involved in cell death were studied in PC12 cells. Exposure of PC12 cells to low dose Pb(2+) (0.01 microM) increased PKC activity, while exposure to a higher dose (10 microM) led to decreased PKC activity. Additionally, in normal extracellular medium, low concentration of Pb(2+) (0.01 microM) stimulated increase in cytosolic free calcium while the higher concentrations of Pb(2+) (10 microM) did not. However, the effect of low dose Pb(2+) (0.01 microM) was blocked by removing Ca(2+) from external medium. The role of Pb(2+)-induced changes in PKC activity and its relationship to oxidative stress and related cytotoxicity was also studied. Pb(2+) alone (0.01-10 microM) produced reactive oxygen species (ROS) dose dependently over the period of 24 h. Pb(2+)-induced ROS were potentiated in the presence of 500 microM glutamate. Furthermore, a correlation was observed between ROS generation and the levels of cytotoxicity, which was observed after 24 h exposures to Pb(2+) by trypan blue method, and the cytotoxicity was enhanced by glutamate co-treatment. Pb(2+)-induced cell death was blocked partially by staurosporine (PKC inhibitor, 100 nM) and NMDA antagonist, MK-801 (1 microM). It is concluded that, in Pb-induced cytotoxicity, modulation of PKC and intracellular calcium play significant roles in augmenting glutamate receptor mediated oxidative species formation and subsequent cell death.     

Kainic acid-induced neuronal cell death in cerebellar granule cells is not prevented by caspase inhibitors

1. We examined the role of non-NMDA receptors in kainic acid (KA)-induced apoptosis in cultures of rat cerebellar granule cells (CGCs). KA (1 - 500 microM) induced cell death in a concentration-dependent manner, which was prevented by NBQX and GYKI 52466, non-NMDA receptor antagonists. Moreover, AMPA blocked KA-induced excitotoxicity, through desensitization of AMPA receptors. 2. Similarly, KA raised the intracellular calcium concentration of CGCs, which was inhibited by NBQX and GYKI 52466. Again, AMPA (100 microM) abolished the KA (100 microM)-induced increase in intracellular calcium concentration. 3. KA-induced cell death in CGCs had apoptotic features, which were determined morphologically, by DNA fragmentation, and by expression of the prostate apoptosis response-4 protein (Par-4). 5. KA (500 microM) slightly (18%) increased caspase-3 activity, which was strongly enhanced by colchicine (1 microM), an apoptotic stimulus. However, neither Z-VAD.fmk, a pan-caspase inhibitor, nor the more specific caspase-3 inhibitor, Ac-DEVD-CHO, prevented KA-induced cell death or apoptosis. In contrast, both drugs inhibited colchicine-induced apoptosis. 5. The calpain inhibitor ALLN had no effect on KA or colchicine-induced neurotoxicity. 6. Our findings indicate that colchicine-induced apoptosis in CGCs is mediated by caspase-3 activation, unlike KA-induced apoptosis.     

Differential susceptibility of brain areas to cyanide involves different modes of cell death

We have demonstrated that cyanide (KCN) induces selective degeneration of dopaminergic neurons in mice and apoptotic cell death in cultured neurons. In the present study the mode of cyanide-induced cell death was determined in the susceptible brain areas. Mice were treated with KCN (6 mg/kg ip) or vehicle (saline) twice daily for 1 to 12 days. After 3 days of KCN treatment, two separate lesions were observed in coronal brain sections. Widespread DNA fragmentation in parietal and suprarhinal regions of the motor cortex was observed by the in situ terminal deoxynucleotide transferase nick-end labeling (TUNEL) technique. Pyknosis and chromatin condensation, morphological hallmarks of apoptotic cells, were observed in TUNEL-positive regions. On the other hand, in the substantia nigra (SN), KCN produced a progressive, bilateral necrotic lesion that was evident by 3 days of treatment. The SN lesion was circumscribed by a prominent ring of glial infiltration, as determined by glial-acidic fibrillary protein (GFAP) immunostaining. The extent of the SN lesion steadily increased with treatment duration, and DNA fragmentation was not observed over the 1- to 12-day period. On the other hand, cortical apoptosis was not associated with necrotic cell loss or astrogliosis. Pretreatment of animals with the antioxidant alpha-phenyl-tert-butyl nitrone (PBN) for 7 days prior to and during 3 days of KCN administration markedly reduced cortical DNA fragmentation whereas the PBN treatment did not influence the SN necrosis or astrocytic gliosis. Except for moderate GFAP immunostaining in corpus callosum, other brain areas were not affected by cyanide. It is concluded that KCN-induced neuronal loss involves selective activation of necrosis or apoptosis in different neuronal populations, and involves divergent mechanisms and sensitivity to antioxidants.     

Genipin-induced apoptosis in hepatoma cells is mediated by reactive oxygen species/c-Jun NH2-terminal kinase-dependent activation of mitochondrial pathway

Genipin, the aglycone of geniposide, exhibits anti-inflammatory and anti-angiogenic activities. Here we demonstrate that genipin induces apoptotic cell death in FaO rat hepatoma cells and human hepatocarcinoma Hep3B cells, detected by morphological cellular changes, caspase activation and release of cytochrome c. During genipin-induced apoptosis, reactive oxygen species (ROS) level was elevated, and N-acetyl-l-cysteine (NAC) and glutathione (GSH) suppressed activation of caspase-3, -7 and -9. Stress-activated protein kinase/c-Jun NH2-terminal kinase 1/2(SAPK/JNK1/2) but neither MEK1/2 nor p38 MAPK was activated in genipin-treated hepatoma cells. SP600125, an SAPK/JNK1/2 inhibitor, markedly suppressed apoptotic cell death in the genipin-treated cells. The FaO cells stably transfected with a dominant-negative c-Jun, TAM67, was less susceptible to apoptotic cell death triggered by genipin. Diphenyleneiodonium (DPI), an inhibitor of NADPH oxidase, inhibited ROS generation, apoptotic cell death, caspase-3 activation and JNK activation. Consistently, the stable expression of Nox1-C, a C-terminal region of Nox1 unable to generate ROS, blocked the formation of TUNEL-positive apoptotic cells, and activation of caspase-3 and JNK in FaO cells treated with genipin. Our observations imply that genipin signaling to apoptosis of hepatoma cells is mediated via NADPH oxidase-dependent generation of ROS, which leads to downstream of JNK.     

Dosage effects of curcumin on cell death types in a human osteoblast cell line.

Curcumin, the yellow pigment of Curcuma longa, is known to have antioxidant and anti-inflammatory properties, as well as their ability to either induce or prevent cell apoptosis. However, the precise molecular mechanisms of these effects are unknown. Here, we demonstrate that curcumin can induce apoptotic changes, including JNK activation, caspase-3 activation, and cleavage of PARP and PAK2, at treatment concentrations lower than 25 microM in human osteoblast cells. In contrast, treatment with 50-200 microM of curcumin does not induce apoptosis, but rather triggers necrotic cell death in human osteoblasts. Using the cell permeable dye 2',7'-dichlorofluorescin diacetate (DCF-DA) as an indicator of reactive oxygen species (ROS) generation, we found that while treatment with 12.5-25 microM curcumin directly increased intracellular oxidative stress, 50-200 microM curcumin had far less effect. Pretreatment of cells with N-acetyl cysteine or alpha-tocopherol, two well known ROS scavengers, attenuated the intracellular ROS levels increases and converted the apoptosis to necrosis induced by 12.5-25 microM curcumin. Moreover, we observed a dose-dependent decrease in intracellular ATP levels after treatment of osteoblast cells with curcumin and pretreatment of cells with antimycin or 2-deoxyglucose to cause ATP depletion significantly converted 12.5-25 microM curcumin-induced apoptosis to necrosis, indicating that ATP (a known mediator of apoptotic versus necrotic death) is most likely involved in the switching mechanism. Overall, our results signify that curcumin dosage treatment determines the possible effect on ROS generation, intracellular ATP levels, and cell apoptosis or necrosis in osteoblast cells.     

Mercuric chloride-induced apoptosis is dependent on protein synthesis.

Apoptosis is a mode of cell death with morphologic and biochemical features that distinguish it from necrosis. Recent studies demonstrating that mercury compounds initiate apoptosis in cultured cells did not elucidate if the biochemical mechanism of apoptosis involved a dependence on macromolecular synthesis post-insult, i.e. programmed cell death. The objectives of this in vitro study were (1) to determine if HgCl2 cytotoxicity includes an apoptotic component, and (2) to determine if apoptosis is dependent on protein synthesis, i.e. proceeds by an inducible mechanism. Suspensions of mouse lymphoma (L5178Y-R) cells were exposed to 0, 1, 5, or 10 microM HgCl2 and apoptosis was evaluated utilizing qualitative and quantitative methods. At 24 h after exposure, transmission electron microscopy revealed a concentration-related increase in morphologic changes typical of apoptosis: margination of condensed chromatin to the nuclear membrane, dilation of the rough endoplasmic reticulum, cytoplasmic condensation and vacuolation, nuclear dissolution, and plasma membrane blebbing. An increase in Hg-induced DNA fragmentation (DNA 'ladder') was observed using agarose gel electrophoresis. Time- and concentration-dependent increases in the percent of apoptotic cells were observed at 1, 6, 12, and 24 h after HgCl2 exposure using a flow cytometric method that discriminates between cells according to size and granularity. Pretreatment of cells with cycloheximide (CHX), an inhibitor of translation, prior to HgCl2 exposure resulted in a 25-50% reduction in apoptotic cells 24 h after exposure to 10 and 20 microM HgCl2, and concomitantly reduced the overall cytotoxicity compared to HgCl2 alone. These results, although limited to a single cell line, support the hypothesis that HgCl2 induces apoptosis that is dependent, at least in part, upon protein synthesis.     

Veratridine induces apoptotic death in bovine chromaffin cells through superoxide production

The molecular mechanisms involved in veratridine-induced chromaffin cell death have been explored. We have found that exposure to veratridine (30 microM, 1 h) produces a delayed cellular death that reaches 55% of the cells 24 h after veratridine exposure. This death has the features of apoptosis as DNA fragmentation can be observed. Calcium ions play an important role in veratridine-induced chromaffin cell death because the cell permeant Ca(2+) chelator BAPTA-AM and extracellular Ca(2+) removal completely prevented veratridine-induced toxicity. Following veratridine treatment, there is a decrease in mitochondrial function and an increase in superoxide anion production. Veratridine-induced increase in superoxide production was blocked by tetrodotoxin (TTX; 10 microM), extracellular Ca(2+) removal and the mitochondrial permeability transition pore blocker cyclosporine A (10 microM). Veratridine-induced death was prevented by different antioxidant treatments including catalase (100 IU ml(-1)), N-acetyl cysteine (100 microM), allopurinol (100 microM) or vitamin E (50 microM). Veratridine-induced DNA fragmentation was prevented by TTX (10 microM). Veratridine produced a time-dependent increase in caspase activity that was prevented by Ca(2+) removal and TTX (10 microM). In addition, calpain and caspases inhibitors partially prevented veratridine-induced death. These results indicate that chromaffin cells share with neurons the molecular machinery involved in apoptotic death and might be considered a good model to study neuronal death during neurodegeneration.