Molecular mechanisms of apoptosis induced by cytotoxic chemicals

Artichoke polyphenols induce apoptosis and decrease the invasive potential of the human breast cancer cell line MDA-MB231

The human breast cancer cell line, estrogen receptor negative, MDA-MB231, was used to evaluate the antitumor effect of polyphenolic extracts from the edible part of artichokes (AEs). Treatment of cancer cells reduced cell viability and inhibited cell growth in a dose-dependent manner. Importantly, AEs did not have any effect on normal breast epithelial cell line, MCF10A. Chlorogenic acid (ChA), the most representative component of the polyphenolic fraction of artichoke, had no prominent effects on the cell death rate of MDA-MB231 cells. The addition of AEs to the cells, rather than ChA, triggered apoptosis via a mitochondrial and a death-receptor pathway, as shown by the activation of caspase-9 and caspase-8, respectively. Furthermore, an increase of the Bax:Bcl2 ratio and up-regulation of cyclin-dependent kinase inhibitor, p21(WAF1), crucial apoptotic players, were documented. According to our data on activation of caspase-9, a loss of mitochondrial transmembrane potential (Ψ(m)) was shown. Cell motility and invasion capabilities were remarkably inhibited by AEs-treatment in highly invasive MDA-MB231 cells. In addition, a significant decrease of proteolytic activity of metalloproteinase-2 protein (MMP-2), involved in degrading components of the extracellular matrix, was detected. Our findings indicate that AEs reduced cell viability, inhibited cell growth, triggered apoptotic mechanisms, and showed inhibitory properties against the invasive behavior of MDA-MB231 cancer cell line. Altogether, these data indicate the potential chemopreventive activity of artichoke polyphenolic extracts.

Role of calcium and mitochondria in MeHg-mediated cytotoxicity

Methylmercury (MeHg) mediated cytotoxicity is associated with loss of intracellular calcium (Ca²⁺) homeostasis. The imbalance in Ca²⁺ physiology is believed to be associated with dysregulation of Ca²⁺ intracellular stores and/or increased permeability of the biomembranes to this ion. In this paper we summarize the contribution of glutamate dyshomeostasis in intracellular Ca²⁺ overload and highlight the mitochondrial dysfunctions induced by MeHg via Ca²⁺ overload. Mitochondrial disturbances elicited by Ca²⁺ may involve several molecular events (i.e., alterations in the activity of the mitochondrial electron transport chain complexes, mitochondrial proton gradient dissipation, mitochondrial permeability transition pore (MPTP) opening, thiol depletion, failure of energy metabolism, reactive oxygen species overproduction) that could culminate in cell death. Here we will focus on the role of oxidative stress in these phenomena. Additionally, possible antioxidant therapies that could be effective in the treatment of MeHg intoxication are briefly discussed.

Safrole induces cell death in human tongue squamous cancer SCC-4 cells through mitochondria-dependent caspase activation cascade apoptotic signaling pathways

Safrole is one of important food-borne phytotoxin that exhibits in many natural products such as oil of sassafras and spices such as anise, basil, nutmeg, and pepper. This study was performed to elucidate safrole-induced apoptosis in human tongue squamous carcinoma SCC-4 cells. The effect of safrole on apoptosis was measured by flow cytometry and DAPI staining and its regulatory molecules were studied by Western blotting analysis. Safrole-induced apoptosis was accompanied with up-regulation of the protein expression of Bax and Bid and down-regulation of the protein levels of Bcl-2 (up-regulation of the ratio of Bax/Bcl-2), resulting in cytochrome c release, promoted Apaf-1 level and sequential activation of caspase-9 and caspase-3 in a time-dependent manner. We also used real-time PCR to show safrole promoted the mRNA expressions of caspase-3, -8, and -9 in SCC-4 cells. These findings indicate that safrole has a cytotoxic effect in human tongue squamous carcinoma SCC-4 cells by inducing apoptosis. The induction of apoptosis of SCC-4 cells by safrole is involved in mitochondria- and caspase-dependent signal pathways.

Antitumor activity of celastrol nanoparticles in a xenograft retinoblastoma tumor model

Background

Celastrol, a Chinese herbal medicine, has shown antitumor activity against various tumor cell lines. However, the effect of celastrol on retinoblastoma has not yet been analyzed. Additionally, the poor water solubility of celastrol restricts further therapeutic applications. The goal of this study was to evaluate the effect of celastrol nanoparticles (CNPs) on retinoblastoma and to investigate the potential mechanisms involved.

Methods

Celastrol-loaded poly(ethylene glycol)-block-poly(ɛ-caprolactone) nanopolymeric micelles were developed to improve the hydrophilicity of celastrol. The 2-(2-methoxy-4- nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulf-ophenyl)-2H tetrazolium monosodium salt (WST-8) assay was used to determine the inhibitory effect of CNPs on SO-Rb 50 cell proliferation in vitro. Immunofluorescence was used to evaluate the apoptotic effect of CNPs on nuclear morphology, and flow cytometry was used to quantify cellular apoptosis. The expression of Bcl-2, Bax, NF-κB p65, and phospo-NF-κB p65 proteins was assessed by Western blotting. A human retinoblastoma xenograft model was used to evaluate the inhibitory effects of CNPs on retinoblastoma in NOD-SCID mice. Hematoxylin and eosin staining was used to assess the apoptotic effects of CNPs on retinoblastoma.

Results

CNPs inhibit the proliferation of SO-Rb 50 cells in a dose- and time-dependent manner with an IC₅₀ of 17.733 μg/mL (celastrol-loading content: 7.36%) after exposure to CNPs for 48 hours. CNPs induce apoptosis in SO-Rb 50 cells in a dose-dependent manner. The expression of Bcl-2, NF-κB p65, and phospo-NF-κB p65 proteins decreased after exposure to CNPs 54.4 μg/mL for 48 hours. Additionally, the Bax/Bcl-2 ratio increased, whereas the expression of Bax itself was not significantly altered. CNPs inhibit the growth of retinoblastoma and induce apoptosis in retinoblastoma cells in mice.

Conclusion

CNPs inhibit the growth of retinoblastoma in mouse xenograft model by inducing apoptosis in SO-Rb 50 cells, which may be related to the increased Bax/Bcl-2 ratio and the inhibition of NF-κB. CNPs may represent a potential alternative treatment for retinoblastoma.

Sodium deoxycholate inhibits chick duodenal calcium absorption through oxidative stress and apoptosis

High concentrations of sodium deoxycholate (NaDOC) produce toxic effects. This study explores the effect of a single high concentration of NaDOC on the intestinal Ca(2+) absorption and the underlying mechanisms. Chicks were divided into two groups: 1) controls and 2) treated with different concentrations of NaDOC in the duodenal loop for variable times. Intestinal Ca(2+) absorption was measured as well as the gene and protein expressions of molecules involved in the Ca(2+) transcellular pathway. NaDOC inhibited the intestinal Ca(2+) absorption, which was concentration dependent. Ca(2+)-ATPase mRNA decreased by the bile salt and the same occurred with the protein expression of Ca(2+)-ATPase, calbindin D(28k) and Na(+)/Ca(2+) exchanger. NaDOC produced oxidative stress as judged by ROS generation, mitochondrial swelling and glutathione depletion. Furthermore, the antioxidant quercetin blocked the inhibitory effect of NaDOC on the intestinal Ca(2+) absorption. Apoptosis was also triggered by the bile salt, as indicated by the TUNEL staining and the cytochrome c release from the mitochondria. As a compensatory mechanism, enzyme activities of the antioxidant system were all increased. In conclusion, a single high concentration of NaDOC inhibits intestinal Ca(2+) absorption through downregulation of proteins involved in the transcellular pathway, as a consequence of oxidative stress and mitochondria mediated apoptosis.

Effects of camptothecin and hydroxycamptothecin on insect cell lines Sf21 and IOZCAS-Spex-II

BACKGROUND

In recent years, concerns over the potential impact of synthetic pesticides on the environment have made the discovery and development of environmentally friendly pesticides a more pressing issue. Camptothecin (CPT) and its derivatives have attracted much attention owing to their unique mechanisms of action against insects. In this paper, two insect cell lines, Sf21 and IOZCAS-Spex-II, were used to conduct a preliminary investigation of the potential of CPT and hydroxycamptothecin (HCPT) as inducers of apoptosis in insect cell lines, and to illustrate the mechanism of action of CPT on insects at the cellular level.

RESULTS

The results showed that both CPT and HCPT demonstrate potent cytotoxic effects to the tested insect cell lines in a time- and dose-dependent manner. The DNA fragmentation, activation of caspases and cytochrome c release were observed in both IOZCAS-Spex-II and Sf21 treated with CPT and HCPT. There is no significant difference in cytotoxicity and caspase-3 activation (P < 0.05, except when treated for 2 h) between CPT and HCPT, although the caspase-3 activation was slightly stronger when treated with HCPT in both Sf21 and IOZCAS-Spex-II.

CONCLUSION

The results confirm the existence of the mitochondrial-dependent pathway of apoptosis induced by CPT and HCPT in Sf21 and IOZCAS-Spex-II cell lines. Further investigations are required to reveal the mitochondrial mechanisms and regulation of caspase activation during apoptosis. These studies will provide basic knowledge needed to understand the mechanisms of action of CPT and to develop CPT and its derivatives as insecticides.

Ellagic acid protects human keratinocyte (HaCaT) cells against UVA-induced oxidative stress and apoptosis through the upregulation of the HO-1 and Nrf-2 antioxidant genes

UV radiation from the sun is a potent environmental risk factor in the pathogenesis of skin damage. Much of the skin damage caused by ultraviolet A (UVA) irradiation from the sun is associated with oxidative stress. The aim of this study was to investigate the protective role of ellagic acid (25-75 μM), a natural antioxidant, against UVA (5-20 J/cm(2))-induced oxidative stress and apoptosis in human keratinocyte (HaCaT) cells and to reveal the possible mechanisms underlying this protective efficacy. Ellagic acid pre-treatment markedly increased HaCaT cell viability and suppressed UVA-induced ROS generation and MDA formation. Moreover, ellagic acid pre-treatment prevented UVA-induced DNA damage as evaluated by the comet assay. Ellagic acid treatment also significantly inhibited the UVA-induced apoptosis of HaCaT cells, as measured by a reduction of DNA fragmentation, mitochondria dysfunction, ER stress, caspase-3 activation, and Bcl-2/Bax deregulation. Notably, the antioxidant potential of ellagic acid was directly correlated with the increased expression of HO-1 and SOD, which was followed by the downregulation of Keap1 and the augmented nuclear translocation and transcriptional activation of Nrf2 with or without UVA irradiation. Nrf2 knockdown diminished the protective effects of ellagic acid. Therefore, ellagic acid may be useful for the treatment of UVA-induced skin damage.

Cadmium-induced apoptosis and necrosis in human osteoblasts: role of caspases and mitogen-activated protein kinases pathways

Cadmium is a widespread environmental pollutant which induces severe toxic alterations, including osteomalacia and osteoporosis, likely by estrogen receptor-dependent mechanisms. Indeed, cadmium has been described to act as an endocrine disruptor and its toxicity is exerted both in vivo and in vitro through induction of apoptosis and/or necrosis by not fully clarified intracellular mechanism(s) of action. Aim of the present study was to further investigate the molecular mechanism by which cadmium might alter homeostasis of estrogen target cells, such as osteoblast homeostasis, inducing cell apoptosis and/or necrosis. Human osteoblastic cells (hFOB 1.19) in culture were used as an in vitro model to characterize the intracellular mechanisms induced by this heavy metal. Cells were incubated in the presence/ absence of 10-50 μM cadmium chloride at different times and DNA fragmentation and activation of procaspases- 8 and -3 were induced upon CdCl(2) treatment triggering apoptotic and necrotic pathways. Addition of caspase-8 and -3 inhibitors (Z-IETD-FMK and Z-DQMD-FMK) partially blocked these effects. No activation of procaspase-9 was observed. To determine the role of mitogen-activated protein kinases (MAPK) in these events, we investigated c-jun N-terminal kinase (JNK), p38 and extracellular signal-regulated protein kinase (ERK1/2) phosphorylation which were activated by 10 μM CdCl(2). Chemical inhibitors of JNK, p38, and ERK1/2, SP600125, SB202190, and PD98059, significantly reduced the phosphorylation of the kinases and blunted apoptosis. In contrast, caspase inhibitors did not reduce the cadmium-induced MAPK phosphorylation, suggesting an independent activation of these pathways. In conclusion, at least 2 pathways appear activated by cadmium in osteoblasts: a direct induction of caspase-8 followed by activation of caspase-3 and an indirect induction by phosphorylation of ERK1/2, p38, and JNK MAPK triggering activation of caspase-8 and -3.

2,4,8-trihydroxybicyclo [3.2.1]octan-3-one scavenges free radicals and protects against xenobiotic-induced cytotoxicity

Currently, there is a great deal of interest in the study of natural compounds with free-radical-scavenging activity because of their potential role in maintaining human health and preventing diseases. In this paper, we report the antioxidant and cytoprotective properties of 2,4,8-trihydroxybicyclo [3.2.1]octan-3-one (TBO) isolated from the aqueous extract of Decalepis hamiltonii roots. Our results show that TBO is a potent scavenger of superoxide (O(2)·-), hydroxyl (·OH), nitric oxide (·NO) and lipid peroxide (LOO·) - physiologically relevant free radicals with IC(50) values in nmolar (42-281) range. TBO also exhibited concentration-dependent secondary antioxidant activities such as reducing power, metal-chelating activity and inhibition of protein carbonylation. Further, TBO at nmolar concentration prevented CuSO(4)-induced human LDL oxidation. Apart from the in vitro free-radical-scavenging activity, TBO demonstrated cytoprotective activity in primary hepatocytes and Ehrlich ascites tumour (EAT) cells against oxidative-stress-inducing xenobiotics. The mechanism of cytoprotective action involved maintaining the intracellular glutathione (GSH), scavenging of reactive oxygen species (ROS) and inhibiting lipid peroxidation (LPO). Based on the results, it is suggested that TBO is a novel bioactive molecule with implications in both prevention and amelioration of diseases involving oxidative stress as well as in the general well-being.

14-aminotetradecanoic acid exhibits antioxidant activity and ameliorates xenobiotics-induced cytotoxicity

Natural compounds with free-radical scavenging activity have potential role in maintaining human health and preventing diseases. In this study, we report the antioxidant and cytoprotective properties of 14-aminotetradecanoic acid (ATDA) isolated from the Decalepis hamiltonii roots. ATDA is a potent scavenger of superoxide (O(2) (•-)), hydroxyl ((•)OH), nitric oxide ((•)NO), and lipid peroxide (LOO(•)) physiologically relevant free radicals with IC(50) values in nM (36-323) range. ATDA also exhibits concentration-dependent secondary antioxidant activities like reducing power, metal-chelating activity, and inhibition of protein carbonylation. Further, ATDA at nM concentration prevented CuSO(4)-induced human LDL oxidation. ATDA demonstrated cytoprotective activity in primary hepatocytes and Ehrlich ascites tumor cells against oxidative stress inducing xenobiotics apart from the in vitro free-radical scavenging activity. The mechanism of cytoprotective action involved maintaining the intracellular glutathione, scavenging of reactive oxygen species, and inhibition of lipid peroxidation. It is suggested that ATDA is a novel bioactive molecule with potential health implications.

Mitochondrial genetic background plays a role in increasing risk to asthma

A number of studies suggest that mitochondrial dysfunction plays a role in the pathogenesis of asthma. To shed light for the first time on the role of the mitochondrial genome in the etiology of asthma we analyzed the mitochondrial tRNA genes and part of their flanking regions in patients with asthma compared with a set of healthy controls. We found a total of 10 mutations in 56 out of 76 asthmatic patients. Four of these mutations were not found in the control group, five were observed at a significantly lower frequency in controls, but none of the combinations of mutations detected in asthma patients was observed in the controls. Furthermore, we observed that 27.6% of the asthma patients (vs. 4% of the controls) belonged to the haplogroup U (Fisher test P = 0.00) and a positive significant correlation was found between the occurrence of the haplogroup U and the severity of the disease (Fisher test P = 0.02). Whereas further studies in larger cohorts are needed to confirm these observations we suggest that the mitochondrial genetic background plays a key role in asthma development.

Methylmercury inhibits electron transport chain activity and induces cytochrome c release in cerebellum mitochondria

The involvement of oxidative stress has been suggested as a mechanism for toxicity caused by methylmercury (MeHg). One of the major critical sites for oxidative stress is the mitochondria. In this research, to clarify the target site in mitochondria affected by MeHg, the individual activities of the mitochondrial electron transport chain (ETC) (I∼IV) were examined in the liver, cerebrum and cerebellum of MeHg-intoxicated rats. In addition, to elucidate the mechanism underlying MeHg toxicity, cytochrome c release, caspase 3 activity and histological study were examined in the cerebrum and cerebellum. The cerebellum was found to be an exclusive tissue in which significant MeHg-induced alterations were observed. The complex II activity in the cerebellum mitochondria significantly decreased after MeHg exposure. Cytochrome c release from mitochondria increased only in the cerebellum by MeHg exposure. However, no significant alterations in caspase 3 activity or histological structure were found in brain tissues. These results suggest that MeHg acts on the constituents of complex II in the cerebellum, and induces mitochondrial dysfunction, leading to a release of cytochrome c from mitochondria. These events were considered to occur at the early stage of MeHg intoxication.

Role of oxidative stress and the mitochondrial permeability transition in methylmercury cytotoxicity

Oxidative stress has been implicated in the pathogenesis of methylmercury (MeHg) neurotoxicity. Studies of mature neurons suggest that the mitochondrion may be a major source of MeHg-induced reactive oxygen species and a critical mediator of MeHg-induced neuronal death, likely by activation of apoptotic pathways. It is unclear, however, whether the mitochondria of developing and mature neurons are equally susceptible to MeHg. Murine embryonal carcinoma (EC) cells, which differentiate into neurons following exposure to retinoic acid, were used to compare the differentiation-dependent effects of MeHg on ROS production and mitochondrial depolarization. EC cells and their neuronal derivatives were pre-incubated with the ROS indicator 2',7'-dichlorofluoroscein diacetate or tetramethylrhodamine methyl ester, an indicator of mitochondrial membrane potential, with or without cyclosporin A (CsA), an inhibitor of mitochondrial permeability transition pore opening, and examined by laser scanning confocal microscopy in the presence of 1.5 μM MeHg. To examine consequences of mitochondrial perturbation, immunohistochemical localization of cytochrome c (cyt c) was determined after incubation of cells in MeHg for 4 h. MeHg treatment induced earlier and significantly higher levels of ROS production and more extensive mitochondrial depolarization in neurons than in undifferentiated EC cells. CsA completely inhibited mitochondrial depolarization by MeHg in EC cells but only delayed this response in the neurons. In contrast, CsA significantly inhibited MeHg-induced neuronal ROS production. Cyt c release was also more extensive in neurons, with less protection afforded by CsA. These data indicate that neuronal differentiation state influences mitochondrial transition pore dynamics and MeHg-stimulated production of ROS.

Low doses of cadmium chloride and methallothionein-1-bound cadmium display different accumulation kinetics and induce different genes in cells of the human nephron

Background/Aims

The present study was conducted to investigate the renal tubular handling of inorganic cadmium (Cd²⁺) by exposing primary human tubular cell cultures to physiologically relevant doses of cadmium chloride (CdCl₂). Furthermore, the cellular accumulation of Cd²⁺ was compared to that of metallothionein-1-bound Cd (Cd7MT-1). Finally, this study aimed to investigate the effect of the accumulation of Cd (both Cd²⁺ and Cd7MT-1) in renal cells on the expression of genes relevant to nephrotoxic processes.

Methods

Cd concentration was measured using atomic absorption spectrometry. mRNA expression was evaluated by quantitative real-time RT-PCR.

Results

Cd²⁺ accumulated into human tubular cells in a concentration- and time-dependent way. Furthermore, cellular accumulation of Cd²⁺ was different from the cellular accumulation of Cd7MT-1, indicative for different uptake routes. Finally, mRNA expression of the genes encoding the anti-oxidative proteins metallothionein-1 (MT-1) and heme-oxygenase-1 (HO-1) as well as the pro-apoptotic Bcl-2-associated X protein (Bax) were upregulated by CdCl₂ and not by Cd7MT1.

Conclusion

In the presence of physiologically relevant Cd concentrations, tubular accumulation of the element in its inorganic form is different from that of Cd7MT-1. Furthermore, the tubular accumulation of inorganic Cd induces mRNA expression of genes of which the protein products may play a role in Cd-associated renal toxicity.

Molecular mechanisms involved in the adaptive response to cadmium-induced apoptosis in human myelomonocytic lymphoma U937 cells

We examined the molecular mechanisms involved in the adaptive response to cadmium (Cd)-induced apoptosis in human myelomonocytic lymphoma U937 cells. When U937 cells were treated with 50 μM cadmium chloride (CdCl2) for 12 h, significant apoptosis occurred. This was associated with an increase in intracellular reactive oxygen species (ROS), sustained phosphorylation of JNK, activation of caspase-3, a decrease in Mcl-1 (anti-apoptotic Bcl-2 proteins), and increases in Bim, Noxa and tBid (a pro-apoptotic protein under the Bcl-2 family). No apoptosis occurred when the cells were treated with 1 μM CdCl2 for 72 h. However, pretreatment with low-dose CdCl2 dramatically altered the sensitivity of the cells to 50 μM CdCl2 with inhibition of apoptosis. Concomitantly, there were significant decreases in the generation of intracellular ROS and the activation of JNK. Pretreatment with 1 μM CdCl2 also attenuated the decrease in Mcl-1 and the increases in Bim, Noxa and tBid induced by 50 μM CdCl2. In conclusion, pretreatment with low-dose Cd inhibited apoptosis induced by high-dose Cd. The mechanism involves inhibition of intracellular ROS generation and JNK activation, and modulating the balance between the expression of Mcl-1 and its binding partners, Bim, Noxa and tBid.

Antioxidant and cytoprotective properties of 2-(hydroxymethyl)-3-methoxybenzaldehyde

Currently there is a great deal of interest in the study of natural compounds with free radical scavenging activity because of their potential role in maintaining human health and preventing diseases. In this paper, we report the antioxidant and cytoprotective properties of 2-(hydroxymethyl)-3-methoxybenzaldehyde (HMMB) isolated from the aqueous extract of Decalepis hamiltonii roots. Our results show that HMMB is a potent scavenger of superoxide (O2(-)), hydroxyl (OH), nitric oxide (NO), and lipid peroxide (LOO) physiologically relevant free radicals with IC50 values in the nmolar (5-214) range. HMMB also exhibited concentration dependent secondary antioxidant activities, such as reducing power, metal chelating activity, and inhibition of protein carbonylation. Further, HMMB at nmolar concentration prevented CuSO4-induced human LDL oxidation. Apart from the in vitro free radical scavenging activity, HMMB demonstrated cytoprotective activity in primary hepatocytes and Ehrlich Ascites Tumour (EAT) cells against oxidative stress inducing xenobiotics. The mechanism of cytoprotective action involved maintaining the intracellular glutathione (GSH), scavenging of reactive oxygen species (ROS), and inhibition of lipid peroxidation (LPO). Based on the results it is suggested that HMMB is a novel bioactive molecule with health implications in both prevention and amelioration of diseases involving oxidative stress, as well as in the general well being.

Complex methylmercury-cysteine alters mercury accumulation in different tissues of mice

Methylmercury (MeHg) can cause deleterious effects in vertebrate tissues, particularly in the central nervous system. MeHg interacts with sulfhydryl groups from low and high molecular weight thiols in the blood, which can facilitate MeHg uptake into different tissues. The purpose of this study was to examine the effect of MeHg-Cysteine (MeHg-Cys) complex administration on Hg-uptake in cerebral areas (cortex and cerebellum), liver and kidney of adult mice. Animals were divided into four groups: control (1 mL/kg distilled water), MeHg (2 mg/kg), Cys (2 mg/kg) and MeHg-Cys complex (0.8 molar ratio). Mice received one intraperitoneal injection per day for 60 consecutive days. Treatment with MeHg significantly increased mercury concentrations in all tissues analysed when compared with the control group. The accumulation of mercury in brain and in liver was further increased in animals that received MeHg-Cys complex when compared with the MeHg alone group. However, renal Hg decreased in MeHg-Cys treated mice, when compared with the group treated only with MeHg. In summary, the transport of MeHg-Cys complex was tissue-specific, and we observed an increase in its uptake by liver and brain as well as a decrease in kidney.

Dioxin toxicity, aryl hydrocarbon receptor signaling, and apoptosis-persistent pollutants affect programmed cell death

Exogenous ligands of the aryl hydrocarbon receptor (AhR) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related substances are highly toxic pollutants ubiquitously present in the environment. They cause a variety of toxic effects to different organs and tissues. Among other effects, TCDD exposure to laboratory animals leads to thymus atrophy and immunosuppression on the one hand, and to tumor formation on the other. Apoptosis appears to be involved in both these toxic effects: AhR activation by TCDD was discussed to induce apoptosis of immune cells, leading to the depletion of thymocytes and ultimately immunosuppression. This mechanism could help to explain the highly immunotoxic actions of TCDD but it is nevertheless under debate whether this is the mode of action for immunosuppression by this class of chemical substances. In other cell types, especially liver cells, TCDD inhibits apoptosis induced by genotoxic treatment. In initiation-promotion studies, TCDD was shown to be a potent liver tumor promoter. Among other theories it was hypothesized that TCDD acts as a tumor promoter by preventing initiated cells from undergoing apoptosis. The exact mechanisms of apoptosis inhibition by TCDD are not fully understood, but both in vivo and in vitro studies consistently showed an involvement of the tumor suppressor p53 in this effect. Various strings of evidence have been established linking apoptosis to the detrimental effects of exogenous activation of the AhR. Within this article, studies elucidating the effects of TCDD and related substances on apoptosis signaling, be it inducing or repressing, is to be reviewed.

Safrole induces apoptosis in human oral cancer HSC-3 cells

Phytochemicals have been used as potential chemopreventive or chemotherapeutic agents. However, there are data suggesting a mutagenic effect of some phytochemicals. We hypothesized that safrole would have anticancer effects on human oral squamous cell carcinoma HSC-3 cells. Safrole decreased the percentage of viable HSC-3 cells via induction of apoptosis by an increased level of cytosolic Ca(2+) and a reduction in the mitochondrial membrane potential (ΔΨ(m)). Changes in the membrane potential were associated with changes in the Bax, release of cytochrome c from mitochondria, and activation of downstream caspases-9 and -3, resulting in apoptotic cell death. In vivo studies also showed that safrole reduced the size and volume of an HSC-3 solid tumor on a xenograft athymic nu/nu mouse model. Western blotting and flow cytometric analysis studies confirmed that safrole-mediated apoptotic cell death of HSC-3 cells is regulated by cytosolic Ca(2+) and by mitochondria- and Fas-dependent pathways.

Roles of reactive oxygen species and mitochondria in cadmium-induced injury of liver cells

The roles of reactive oxygen species (ROS) and mitochondrial damage in the cadmium (Cd)-induced injury of liver cells were studied by using N-acetyl-L-cysteine (NAC) and acetyl-L-carnitine hydrochloride (ALCAR). After exposure of experimental rats to cadmium (Cd) for 16 h, mitochondrial membrane potential (MMP), ROS production, glutathione peroxidase (GSH-Px) activity, glutathione (GSH) content, malondialdehyde (MDA) content and DNA single-strand break (DNA-SSB) were analyzed. Loss of MMP, increase of ROS production, inhibition of GSH-Px activity, elevation of GSH content, rise of MDA content and DNA-SSB level suggest the participation of ROS and mitochondrion in Cd-induced injury of liver cell. NAC pretreatment attenuated oxidative stress, reversed the decline in GSH-Px activity and reduced GSH and MDA levels significantly. However, Cd-induced loss in MMP was significantly exacerbated by NAC. For another, ALCAR did not perform as well as NAC in terms of reducing ROS production, restoring GSH-Px activity and reducing GSH content. Nevertheless, it significantly improved the recovery of MMP and reduction of MDA content. In addition, conspicuous DNA damage was observed in the samples treated with NAC or ALCAR, indicating Cd could attack DNA through other pathways. These results suggest that oxidative stress or mitochondrial impairment plays a main role in different injuries respectively.

Apigenin induces apoptosis in human lung cancer H460 cells through caspase- and mitochondria-dependent pathways

Apigenin (4,5,7-trihydroxyflavone), a promising chemopreventive agent presented in fruits and vegetables, has been shown to induce cell cycle arrest and apoptosis in many types of human cancer cell lines. However, there is no available information to address the effects of apigenin on human lung cancer H460 cells. In the present studies, H460 cells were treated with apigenin for different time and then were analyzed for the morphological changes, induction of apoptosis, protein levels associated with apoptosis and results in dose-dependent induction of morphological changes, decrease in the percentage of viability, induced DNA damage and apoptosis; down-modulation of the protein expression of Bid, Bcl-2, procaspase-8; up-regulation of protein levels of Bax, caspase-3, AIF, cytochrome c, GRP78 and GADD153; decreased the levels of mitochondrial membrane potential and increased the productions of reactive oxygen species (ROS) and Ca2+ in H460 cells. Taken together, this is the first systematic in vitro study showing the involvement of apoptosis regulatory proteins as potential molecular targets of apigenin in human lung cancer H460 cells.

A bacterial biosensor for oxidative stress using the constitutively expressed redox-sensitive protein roGFP2

A highly specific, high throughput-amenable bacterial biosensor for chemically induced cellular oxidation was developed using constitutively expressed redox-sensitive green fluorescent protein roGFP2 in E. coli (E. coli-roGFP2). Disulfide formation between two key cysteine residues of roGFP2 was assessed using a double-wavelength ratiometric approach. This study demonstrates that only a few minutes were required to detect oxidation using E. coli-roGFP2, in contrast to conventional bacterial oxidative stress sensors. Cellular oxidation induced by hydrogen peroxide, menadione, sodium selenite, zinc pyrithione, triphenyltin and naphthalene became detectable after 10 seconds and reached the maxima between 80 to 210 seconds, contrary to Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and sodium arsenite, which induced the oxidation maximum immediately. The lowest observable effect concentrations (in ppm) were determined as 1.0 × 10⁻⁷ (arsenite), 1.0 × 10⁻⁴ (naphthalene), 1.0 × 10⁻⁴ (Cu²⁺), 3.8 × 10⁻⁴ (H₂O₂), 1.0 × 10⁻³ (Cd²⁺), 1.0 × 10⁻³ (Zn²⁺), 1.0 × 10⁻² (menadione), 1.0 (triphenyltin), 1.56 (zinc pyrithione), 3.1 (selenite) and 6.3 (Pb²⁺), respectively. Heavy metal-induced oxidation showed unclear response patterns, whereas concentration-dependent sigmoid curves were observed for other compounds. In vivo GSH content and in vitro roGFP2 oxidation assays together with E. coli-roGFP2 results suggest that roGFP2 is sensitive to redox potential change and thiol modification induced by environmental stressors. Based on redox-sensitive technology, E. coli-roGFP2 provides a fast comprehensive detection system for toxicants that induce cellular oxidation.

Apoptosis contributes to testicular toxicity induced by two isomers of bromopropanes

The aim of this study was to investigate the different testicular toxicity and the role of apoptosis in the possible mechanism induced by the two isomers of bromopropanes (BPs) in the same dosage. Following the 14-day treatment with a single dose of 1-BP and 2-BP (1 g/kg), male rats were killed and a series of experiments were performed. 1-BP and 2-BP both significantly decreased the epididymal sperm count, while only 2-BP induced an increase in sperms with abnormal heads. Morphological evaluation showed that 1-BP did not cause morphological changes in seminiferous epithelium, but 2-BP treatment resulted in the disappearance of spermatogonia, atrophy of the seminiferous tubules and degeneration of germ cells. 2-BP significantly increased the TUNEL-positive cells and the activation of caspase-3 and decreased the genes and proteins expression of Bax, Bcl-2 and p53. In contrast, there were no significant changes in the expression of apoptosis-related genes and proteins in 1-BP group, though the TUNEL-positive cells were significantly increased. Taken together, this study indicated that those two isomers both have toxicity in male rats, however, the testicular toxicity and the role of apoptosis in the toxic mechanism induced by 1-BP and 2-BP may be different.

The impact of methylmercury on 1,25-dihydroxyvitamin D3-induced transcriptomic responses in dolphin skin cells

The Atlantic bottlenose dolphin has been the focus of much attention owing to the considerable impact of environmental stress on its health and the associated implications for human health. Here, we used skin cells from the dolphin to investigate the protective role of the vitamin D pathway against environmental stressors. We previously reported that dolphin skin cells respond to 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive metabolite of vitamin D3, by upregulation of the vitamin D receptor (VDR) and expression of several genes. Methylmercury is a highly bioaccumulative environmental stressor of relevance to the dolphin. We currently report that in dolphin cells sublethal concentrations of methylmercury compromise the ability of 1,25D3 to upregulate VDR, to transactivate a vitamin D-sensitive promoter, and to express specific target genes. These results help elucidate the effects of vitamin D and methylmercury on innate immunity in dolphin skin and potentially in human skin as well, considering similarities in the vitamin D pathway between the two species.

Endocrine disruptor, dioxin (TCDD)-induced mitochondrial dysfunction and apoptosis in human trophoblast-like JAR cells

The endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been demonstrated to disrupt hormone signalling, reduce fertility, interfere with embryo development and cause spontaneous miscarriage in humans. The precise mechanisms of its effects on early implantation in humans are still unclear. In this study, we examined the relationship between mitochondrial function and dioxin-induced toxicity in JAR cells, a human trophoblast-like cell line. Several experiments were performed to address the effects of TCDD on cell viability, reactive oxygen species (ROS) generation, oxidative damage (indicated by the presence of lipoperoxides and oxidized DNA bases), mitochondrial DNA (mtDNA) copy number, ATP content, mtDNA mutations and the protein levels of p53, Bax, Bcl2, cytochrome c and caspase 3. Increased oxidative damage and mitochondrial dysfunction in TCDD-treated trophoblast-like cells was demonstrated. A 2.58-fold increase in lipid peroxides was detected in cells treated with 2 nM TCDD for 4 h. The oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine was significantly increased by TCDD treatment in a time-dependent manner. Meanwhile, reductions in mtDNA copy number and ATP content and an increase in mtDNA deletions were found. Furthermore, we observed increased apoptosis, p53 accumulation, Bax overexpression, cytochrome c release and sequential caspase 3 activation after TCDD exposure. These results indicate that oxidative damage and mitochondrial dysfunction may be responsible for the apoptotic effects of TCDD.

Cardiotoxin III induces c-jun N-terminal kinase-dependent apoptosis in HL-60 human leukaemia cells

Cardiotoxin III (CTX III), a basic polypeptide with 60 amino acid residues isolated from Naja naja atra venom, has been reported to have anticancer activity. The molecular effects of CTX III on HL-60 cells were dissected in the present study. We found that the antiproliferative action of CTX III on HL-60 cells was mediated through apoptosis, as characterized by an increase of sub G1 population, DNA fragmentation and poly(ADP-ribose) polymerase (PARP) cleavage. Upregulation of Bax, downregulation of Bcl-2, the release of mitochondrial cytochrome c to cytosol and the activations of capase-9 and -3 were noted, while CTX III had no appreciable effect on the levels of Bcl-X(L) and Bad proteins. Moreover, c-Jun N-terminal kinase (JNK) was activated shortly after CTX III treatment in HL-60 cells. Consistently, the SP600125 compound, an anthrapyrazolone inhibitor of JNK, suppressed apoptosis induced by CTX III. As expected, this JNK inhibitor also attenuated the modulation of Bax and Bcl-2, as well as the cytosolic appearance of cytochrome c and the activation of caspase-3 and caspase-9 that induced by CTX III. These findings suggest that CTX III can induce apoptosis in HL-60 cells via the mitochondrial caspase cascade and the activation of JNK is critical for the initiation of the apoptotic death of HL-60 cells.

Analysis of 8-hydroxydeoxyguanosine among workers exposed to diesel particulate exhaust: Comparison with urinary metabolites and PAH air monitoring

Oxidative DNA damage and repair, as measured by 8-hydroxy-2'-deoxyguanosine (8-OHdG) in urine and DNA samples were studied in association with work-related diesel exhaust exposure among garage and waste collection workers. Seasonal variations of the urinary 8-OHdG levels in pre- and two post-workshift urine samples of 29 exposed workers and 36 control persons were evaluated. The mean+/-SE levels of post-workshift 8-OHdG (mumol/mol crea) were 1.52+/-0.44 in winter and 1.61+/-0.33 in summer for the exposed workers, and 1.56+/-0.61 in winter and 1.43+/-0.49 in summer for the controls, respectively. No significant difference in the urinary 8-OHdG levels between exposed workers and control subjects in winter (p=0.923) and summer (p=0.350) was observed. A linear mixed model, adjusted for years of employment, age, ex/non-smoking and BMI, indicated no significant dose exposure-relationships between the urinary 8-OHdG and 15 PAH air concentrations nor between the 8-OHdG and 7 PAH monohydroxy-metabolites analyzed in the same workers. 8-OHdG was also analyzed in the mononuclear cell DNA of 19 exposed and 18 control subjects. The mean value of 8-OHdG/non-modified 2'-deoxyguanosine (8-OHdG/105 dG+/-SE) were 4.89+/-0.17 for the exposed and 4.11+/-0.16 for the control persons, which showed no correlation with the urinary 8-OHdG levels (r=0.01, n=28, P=0.96). The PAH exposure at workplaces was mainly composed of volatile compounds, particularly naphthalene, suggesting low exposure through the respiratory tract and a low effect of PAH in ROS induction.

Alisol B acetate induces apoptosis of SGC7901 cells via mitochondrial and phosphatidylinositol 3-kinases/Akt signaling pathways

AIM: To examine the effect of alisol B acetate on the growth of human gastric cancer cell line SGC7901 and its possible mechanism of action.

METHODS: The cytotoxic effect of alisol B acetate on SGC7901 cells was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Phase-contrast and electron microscopy were used to observe the morphological changes. Cell cycle and mitochondrial transmembrane potential (Δψm) were determined by flow cytometry. Western blotting was used to detect the expression of apoptosis-regulated gene Bcl-2, Bax, Apaf-1, caspase-3, caspase-9, Akt, P-Akt and phosphatidylinositol 3-kinases (PI3K).

RESULTS: Alisol B acetate inhibited the proliferation of SGC7901 cell line in a time- and dose-dependent manner. PI staining showed that alisol B acetate can change the cell cycle distribution of SGC7901, increase the proportion of cells in G0-G1 phase and decrease the proportion of S phase cells and G2-M phase cells. Alisol B acetate at a concentration of 30 &mgr;mol/L induced apoptosis after 24, 48 and 72 h incubation, with occurrence rates of apoptotic cells of 4.36%, 14.42% and 21.16%, respectively. Phase-contrast and electron microscopy revealed that the nuclear fragmentation and chromosomal condensed, cells shrank and attachment loss appeared in the SGC7901 treated with alisol B acetate. Apoptosis of SGC7901 cells was associated with cell cycle arrest, caspase-3 and caspase-9 activation, loss of mitochondrial membrane potential and up-regulation of the ratio of Bax/Bcl-2 and inhibition of the PI3K/Akt.

CONCLUSION: Alisol B acetate exhibits an anti-proliferative effect in SGC7901 cells by inducing apoptosis. Apoptosis of SGC7901 cells involves mitochondria-caspase and PI3K/Akt dependent pathways.

Mitochondrial compartment: a possible target of cadmium effects on breast epithelial cells

Cadmium-breast epithelial cell interactions were studied by analyzing some mitochondria-related aspects of stress response. We treated immortalized non-tumor breast cells with 5 or 50 microM CdCl(2) for 24 or 96 h demonstrating that the exposure did not cause a significant mitochondrial proliferation, while it induced a significant increase in the respiratory activity and mitochondrial polarization. In addition, we found that hsp60 was up-regulated while hsp70 and COXII and COXIV were down-regulated. The mRNA for hsp70 remained constant and only the inducible form of the 70-kDa heat shock protein was over expressed. The mRNAs for COXII and COXIV remained constant after 24 h and increased after longer incubations while the respective proteins decreased. These findings provide additional information on the cellular and molecular aspects of the interaction between Cd and epithelial cells, and on alterations of mitochondria as early events in Cd cytotoxicity.

Time-dependent effects of imatinib in human leukaemia cells: a kinetic NMR-profiling study

The goal of this study was to evaluate the time course of metabolic changes in leukaemia cells treated with the Bcr-Abl tyrosine kinase inhibitor imatinib. Human Bcr-Abl⁺ K562 cells were incubated with imatinib in a dose-escalating manner (starting at 0.1 μM with a weekly increase of 0.1 μM imatinib) for up to 5 weeks. Nuclear magnetic resonance spectroscopy and liquid-chromatography mass spectrometry were performed to assess a global metabolic profile, including glucose metabolism, energy state, lipid metabolism and drug uptake, after incubation with imatinib. Initially, imatinib treatment completely inhibited the activity of Bcr-Abl tyrosine kinase, followed by the inhibition of cell glycolytic activity and glucose uptake. This was accompanied by the increased mitochondrial activity and energy production. With escalating imatinib doses, the process of cell death rapidly progressed. Phosphocreatine and NAD⁺ concentrations began to decrease, and mitochondrial activity, as well as the glycolysis rate, was further reduced. Subsequently, the synthesis of lipids as necessary membrane precursors for apoptotic bodies was accelerated. The concentrations of the Kennedy pathway intermediates, phosphocholine and phosphatidylcholine, were reduced. After 4 weeks of exposure to imatinib, the secondary necrosis associated with decrease in the mitochondrial and glycolytic activity occurred and was followed by a shutdown of energy production and cell death. In conclusion, monitoring of metabolic changes in cells exposed to novel signal transduction modulators supplements molecular findings and provides further mechanistic insights into longitudinal changes of the mitochondrial and glycolytic pathways of oncogenesis.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

Morphological alteration in mitochondria following diclofenac and ibuprofen administration

This study was conducted to identify and to compare the mitochondrial morphological alterations in livers of rats treated with various doses of diclofenac and ibuprofen. Hundred and forty-four male Sprague Dawley rats were dosed with 3, 5 and 10 mg kg(-1) diclofenac and ibuprofen in saline via intraperitoneal injection for 15 days. The control group was administered with saline in a similar manner. Four rats were euthanised every 3 days until day 15. While 200 mg kg(-1) diclofenac and ibuprofen-treated rats (n = 4) were euthanized 10 h posttreatment. The livers were removed, cleaned and a section across the right lobe was taken and fixed in 4% (v/v) glutaraldehyde for electron microscopy analysis and the remaining samples were kept at -80 degrees C for Western blot analysis. Five milligram per kilogram and 10 mg kg(-1) diclofenac-administered rats for 15 days revealed the presence of enlarged mitochondria, irregular and ruptured mitochondrial membranes. While rats administered with 10 mg kg(-1) ibuprofen also showed the presence of mitochondria with irregular membrane structure and ruptured membranes. Western blotting analysis of mitochondrial fractions revealed the expression of cytochrome c in all samples and complete absence of cytochrome c expression in the cytosolic fraction of all samples after day 15. Analysis in 200 mg kg(-1) diclofenac and ibuprofen-treated groups, revealed expression of cytochrome c in both mitochondrial and cytosolic fractions. This observation indicates that both diclofenac and ibuprofen may alter the morphology of mitochondria, leading to cytochrome c release into the cytosol. Further studies needs to be conducted to investigate on the activity of the mitochondria following both treatments.

Involvement of both endoplasmic reticulum- and mitochondria-dependent pathways in cardiotoxin III-induced apoptosis in HL-60 cells

Cardiotoxin (CTX) III, a basic polypeptide with 60 amino acid residues isolated from Naja naja atra venom, has been reported to have anticancer activity. In the present study, we investigated the mechanisms underlying the anticancer activity of CTX III in human leukaemia (HL-60 cells). Cardiotoxin III activated the endoplasmic reticulum (ER) pathway of apoptosis in HL-60 cells, as indicated by increased levels of calcium and glucose-related protein 78 (Grp78), and triggered the subsequent activation of micro-calpain and caspase 12. In addition, CTX III initiated the mitochondrial apoptotic pathway in HL-60 cells, as evidenced by an increased Bax/Bcl-2 ratio, the release of cytochrome c and activation of caspase 9. In the presence of 50 micromol/L Z-ATAD-FMK (a caspase 12 inhibitor) and 100 micromol/L Z-LEHD-FMK (a caspase 9 inhibitor), the CTX III-mediated activation of caspase 9 and caspase 3 was significantly reduced. There was no significant effect of the caspase 12 inhibitor Z-ATAD-FMK on mitochondrial cytochrome c release. Cardiotoxin III-mediated activation of caspase 12 was not abrogated in the presence of the caspase 9 inhibitor Z-LEHD-FMK, indicating that caspase 12 activation was not downstream of caspase 9. These results indicate that CTX III induces cell apoptosis via both ER stress and a mitochondrial death pathway.