Targeting mitochondrial cardiolipin and the cytochrome c/cardiolipin complex to promote electron transport and optimize mitochondrial ATP synthesis

BACKGROUND AND PURPOSE

Cardiolipin plays an important role in mitochondrial respiration and cardiolipin peroxidation is associated with age-related diseases. Hydrophobic interactions between cytochrome c and cardiolipin converts cytochrome c from an electron carrier to a peroxidase. In addition to cardiolipin peroxidation, this impedes electron flux and inhibits mitochondrial ATP synthesis. SS-31 (D-Arg-dimethylTyr-Lys-Phe-NH2 ) selectively binds to cardiolipin and inhibits cytochrome c peroxidase activity. Here, we examined whether SS-31 also protected the electron carrier function of cytochrome c.

EXPERIMENTAL APPROACH

Interactions of SS-31 with cardiolipin were studied using liposomes and bicelles containing phosphatidylcholine alone or with cardiolipin. Structural interactions were assessed by fluorescence spectroscopy, turbidity and nuclear magnetic resonance. Effects of cardiolipin on electron transfer kinetics of cytochrome c were determined by cytochrome c reduction in vitro and oxygen consumption using mitoplasts, frozen and fresh mitochondria.

KEY RESULTS

SS-31 interacted only with liposomes and bicelles containing cardiolipin in about 1:1 ratio. NMR studies demonstrated that the aromatic residues of SS-31 penetrated deep into cardiolipin-containing bilayers. SS-31 restored cytochrome c reduction and mitochondrial oxygen consumption in the presence of added cardiolipin. In fresh mitochondria, SS-31 increased state 3 respiration and efficiency of ATP synthesis.

CONCLUSIONS AND IMPLICATIONS

SS-31 selectively targeted cardiolipin and modulated its interaction with cytochrome c. SS-31 inhibited the cytochrome c/cardiolipin complex peroxidase activity while protecting its ability to serve as an electron carrier, thus optimizing mitochondrial electron transport and ATP synthesis. This novel class of cardiolipin therapeutics has the potential to restore mitochondrial bioenergetics for treatment of numerous age-related diseases.

Rapid reactive oxygen species (ROS) generation induced by curcumin leads to caspase-dependent and -independent apoptosis in L929 cells

Evidence that curcumin may have anticancer activities has renewed interest in its potential to prevent and treat disease. In this study, we show that curcumin-mediated rapid generation of reactive oxygen species (ROS) leads to apoptosis by modulating different apoptotic pathways in mouse fibroblast L929 cells. We show for the first time that curcumin-induced rapid ROS generation causes the release of apoptosis inducing factor (AIF) from the mitochondria to the cytosol and nucleus, hence, leading to caspase 3-independent apoptosis. However, our studies also show that curcumin induces the release of cytochrome c from mitochondria, causing activation of caspase 3, and concomitant PARP cleavage, which is the hallmark of caspase-dependent apoptosis. Furthermore, curcumin-induced ROS generation leads to the induction of the proapoptotic protein p53 and its effector protein p21 and down-regulation of cell cycle regulatory proteins such as Rb and cyclin D1 and D3. Both glutathione (GSH) and N-acetylcysteine (NAC) pretreatment resulted in the complete inhibition of curcumin-induced ROS generation, AIF release from mitochondria, and caspase activation. Additionally, pretreatment of L929 cells with these antioxidants completely blocked the induction of p53-dependent p21 accumulation. In conclusion, our data show that in addition to caspase 3 activation, curcumin-induced rapid ROS generation leads to AIF release, and the activation of the caspase-independent apoptotic pathway.

Adriamycin-induced, TNF-α-mediated central nervous system toxicity

The clinical effectiveness of adriamycin (ADR), a potent chemotherapeutic, is known to be limited by severe cardiotoxic side effects. However, the effect of ADR on brain tissue is not well understood. It is generally thought that ADR is not toxic to the brain because ADR does not pass the blood-brain barrier. The present study demonstrates that ADR autofluorescence was detected only in areas of the brain located outside the blood-brain barrier, but a strong tumor necrosis factor (TNF) alpha immunoreactivity was detected in the cortex and hippocampus of ADR-treated mice. Systemic injection of ADR led to a decline in brain mitochondrial respiration via complex I substrate shortly after ADR treatment (P < 0.05). Cytochrome c release, increased caspase 3 activity, and TUNEL-positive cell death all were suggestive of apoptosis in brain following systemic ADR treatment. The levels of the known pro-apoptotic proteins, p53 and Bax, were increased in brain mitochondria at 3 h following ADR treatment and declined by 48 h. In contrast, the anti-apoptotic protein, Bcl-xL, was increased later at 6 h post-ADR treatment and was sustained throughout 72 h. Furthermore, p53 migrated to mitochondria and interacted with Bcl-xL, supporting the hypothesis that mitochondria are targets of ADR-induced CNS injury. Neutralizing antibodies against circulating TNF completely abolished both the increased TNF in the brain and the observed mitochondrial injury in brain tissues. These results are consistent with the notion that TNF is an important mediator by which ADR induces central nervous system (CNS) injury. This study, the first to provide direct biochemical evidence of ADR toxicity to the brain, revealed novel mechanisms of ADR-induced CNS injury and suggests a potential therapeutic intervention against circulating TNF-induced CNS effects.

Preclinical studies of the pan-Bcl inhibitor obatoclax (GX015-070) in multiple myeloma

Bcl family members Bcl-2, Bcl-xL, and Mcl-1, are frequently expressed and implicated in the survival of myeloma cells. Obatoclax (GX015-070) is a novel, small-molecule antagonist of the BH3-binding groove of the Bcl family of proteins. We show that GX015-070 inhibits the binding of Bak to Mcl-1, up-regulates Bim, induces cytochrome c release, and activates capase-3 in human myeloma cell lines (HMCLs), confirming the predicted mechanism of action. Consequently, GX015-070 potently inhibited the viability of 15 of 16 HMCLs (mean IC50 of 246 nM), including those resistant to melphalan and dexamethasone. In combination studies, GX015-070 enhanced the antimyeloma activity induced by melphalan, dexamethasone, or bortezomib. Sensitivity to GX015-070 correlated with the absence or near absence of Bcl-xL. Coculture with interleukin-6 or adherence to bone marrow stroma conferred modest resistance; however, it did not overcome GX015-070–induced cytotoxicity. Of importance, GX015-070 as a single agent induced potent cytotoxic responses against patient-derived tumor cells. GX015-070 inhibited normal bone marrow–derived colony formation; however, cytotoxicity to human blood lymphocytes was not observed. Taken together, these studies describe a novel BH3 mimic with selectivity for Mcl-1, and support the therapeutic application of GX015-070 for diverse neoplasias including multiple myeloma.

Melatonin reduces the severity of anesthesia-induced apoptotic neurodegeneration in the developing rat brain

General anesthetics cause widespread apoptotic neurodegeneration in many regions of the developing rat brain. The activation of mitochondria-dependent apoptotic pathway is important in the early stages of anesthesia-induced developmental neuroapoptosis. To investigate potential means of protecting against this type of damage, we studied melatonin, a sleep-promoting agent and antioxidant known to inhibit apoptotic-type neuronal damage by improving mitochondrial homeostasis and stabilizing the inner mitochondrial membrane. When 7-day-old rats (the peak of synaptogenesis) were exposed to a commonly used and highly pro-apoptotic anesthesia cocktail (midazolam, isoflurane, nitrous oxide) in combination with the escalating doses of melatonin (from 1 to 20 mg/kg, s.c.), the severity of anesthesia-induced damage was reduced in a dose-dependent manner in two most vulnerable brain regions--the cerebral cortex and anterior thalamus. Melatonin-induced neuroprotection was mediated, at least in part, via the inhibition of mitochondria-dependent apoptotic pathway since melatonin caused an up-regulation of the anti-apoptotic protein, bcl-X(L), reduction in anesthesia-induced cytochrome c release into the cytoplasm and a decrease in anesthesia-induced activation of caspase-3, an important step in the activation of DNAses and the formation of the apoptotic bodies.

High susceptibility of neural stem cells to methylmercury toxicity: effects on cell survival and neuronal differentiation

Neural stem cells (NSCs) play an essential role in both the developing embryonic nervous system through to adulthood where the capacity for self-renewal may be important for normal function of the CNS, such as in learning, memory and response to injury. There has been much excitement about the possibility of transplantation of NSCs to replace damaged or lost neurones, or by recruitment of endogenous precursors. However, before the full potential of NSCs can be realized, it is essential to understand the physiological pathways that control their proliferation and differentiation, as well as the influence of extrinsic factors on these processes. In the present study we used the NSC line C17.2 and primary embryonic cortical NSCs (cNSCs) to investigate the effects of the environmental contaminant methylmercury (MeHg) on survival and differentiation of NSCs. The results show that NSCs, in particular cNSCs, are highly sensitive to MeHg. MeHg induced apoptosis in both models via Bax activation, cytochrome c translocation, and caspase and calpain activation. Remarkably, exposure to MeHg at concentrations comparable to the current developmental exposure (via cord blood) of the general population in many countries inhibited spontaneous neuronal differentiation of NSCs. Our studies also identified the intracellular pathway leading to MeHg-induced apoptosis, and indicate that NSCs are more sensitive than differentiated neurones or glia to MeHg-induced cytotoxicity. The observed effects of MeHg on NSC differentiation offer new perspectives for evaluating the biological significance of MeHg exposure at low levels.

Berberine induces apoptosis in SW620 human colonic carcinoma cells through generation of reactive oxygen species and activation of JNK/p38 MAPK and FasL

Berberine is the major constituent of Coptidis Rhizoma with multiple pharmacological activities, including anti-inflammation, promotion of apoptosis and anticancer potential effect. Mitogen-activated protein kinase (MAPK) and reactive oxygen species (ROS) may contribute to the causal relationship between tumorigenesis and pro-apoptotic function. Berberine is studied for the mechanism of its action in apoptotic pathway in human colonic carcinoma cell. Treatment of SW620 cells with 50 microM berberine resulted in activation of the caspase 3 and caspase 8, cleavage of poly ADP-ribose polymerase (PARP) and the release of cytochrome c; whereas, the expression of BID and anti-apoptosis factor c-IAP1, Bcl-2, and Bcl-(XL) were decreased markedly. Berberine-induced, dose-dependent induction of apoptosis was accompanied by sustained phosphorylation of JNK and p38 MAPK, as well as generation of the ROS. Furthermore, the induction of apoptosis was alleviated by inhibitors specific for JNK and p38. In addition, there was an increase in the cellular levels of phospho-c-Jun, FasL and t-BID in the berberine-induced apoptosis via the activation of JNK and p38 signaling modules. NAC administration, a scavenger of ROS, reversed berberine-induced apoptosis effects via inhibition of JNK, p38 and c-jun activation, and FasL and t-BID expression. These results leads us to speculate that berberine may play an apoptotic cascade in SW620 cells by activation of the JNK/p38 pathway and induction of ROS production, providing a new mechanism for berberine-induced cell death in human colon cancer cells.

The hierarchical relationship between MAPK signaling and ROS generation in human leukemia cells undergoing apoptosis in response to the proteasome inhibitor Bortezomib

The hierarchy of events accompanying induction of apoptosis by the proteasome inhibitor Bortezomib was investigated in Jurkat lymphoblastic and U937 myelomonocytic leukemia cells. Treatment of Jurkat or U937 cells with Bortezomib resulted in activation of c-Jun-N-terminal kinase (JNK) and p38 MAPK (mitogen-activated protein kinase), inactivation of extracellular signal-regulating kinase 1/2 (ERK1/2), cytochrome c release, caspase-9, -3, and -8 activation, and apoptosis. Bortezomib-mediated cytochrome c release and caspase activation were blocked by the pharmacologic JNK inhibitor SP600125, but lethality was not diminished by the p38 MAPK inhibitor SB203580. Inducible expression of a constitutively active MEK1 construct blocked Bortezomib-mediated ERK1/2 inactivation, significantly attenuated Bortezomib lethality, and unexpectedly prevented JNK activation. Conversely, pharmacologic MEK/ERK1/2 inhibition promoted Bortezomib-mediated JNK activation and apoptosis. Lastly, the antioxidant N-acetyl-l-cysteine (LNAC) attenuated Bortezomib-mediated reactive oxygen species (ROS) generation, ERK inactivation, JNK activation, mitochondrial dysfunction, and apoptosis. In contrast, enforced MEK1 and ERK1/2 activation or JNK inhibition did not modify Bortezomib-induced ROS production. Together, these findings suggest that in human leukemia cells, Bortezomib-induced oxidative injury operates at a proximal point in the cell death cascade to antagonize cytoprotective ERK1/2 signaling, promote activation of the stress-related JNK pathway, and to trigger mitochondrial dysfunction, caspase activation, and apoptosis. They also suggest the presence of a feedback loop wherein Bortezomib-mediated ERK1/2 inactivation contributes to JNK activation, thereby amplifying the cell death process.

In vitro effect of manganese chloride exposure on reactive oxygen species generation and respiratory chain complexes activities of mitochondria isolated from rat brain

Manganese (Mn) is known to induce mitochondrial dysfunction in excessive dose; however the mechanisms underlying its action are not elucidated clearly. To determine if Mn2+ can act directly on mitochondria or indirectly by producing reactive oxygen species (ROS), isolated mitochondria were exposed to different concentration of Mn2+ (5, 50, 500, 1000 microM). ROS generation, respiratory control ratio (RCR), mitochondrial membrane potential (MMP) and respiratory chain complexes activities were investigated. Dose-dependent inhibition of respiratory chain complexes and induction of ROS were observed; these changes were paralleled by decreasing of respiratory control ratio (RCR) both with succinate or glutamate + malate. Further investigation indicated that the membrane potential determined by Rhodamine123 release decreased after MnCl2 exposure at 1000 microM. In addition, effects of the antioxidants NAC (500 microM), GSH (500 microM) and Vitamin C (500 microM) were studied at 500 microM Mn2+. The results indicate that the effect of Mn2+ exposure on respiratory chain is not site-specific, and antioxidants can protect the mitochondria function by reducing the formation of free radicals.

Polyphyllin D is a potent apoptosis inducer in drug-resistant HepG2 cells

In a search for new anticancer agents, we identified a novel compound polyphyllin D (PD) (diosgenyl alpha-L-rhamnopyranosyl-(1-->2)-(alpha-L-arabinofuranosyl)-(1-->4)]-[beta-D-glucopyranoside) that induced DNA fragmentation and phosphatidyl-serine (PS) externalization in a hepatocellular carcinoma cell line HepG2 derivative with drug resistance (R-HepG2). PD is a saponin originally found in a tradition Chinese medicinal herb Paris polyphylla. It has been used to treat liver cancer in China for many years. We evaluated the cell-killing mechanisms of this compound in R-HepG2 and its parental cells. The mitochondrial apoptotic pathway was found to be involved in the PD-induced apoptosis because PD elicited depolarization of mitochondrial transmembrane potential (DeltaPsim), generation of H2O2, as well as release of cytochrome c and apoptosis-inducing factor in a dose- and time-dependent manner. In conclusion, we show for the first time that PD is a potent anticancer agent that can overcome drug resistance in R-HepG2 cells and elicit programmed cell death via mitochondrial dysfunction.

The selection between apoptosis and necrosis is differentially regulated in hydrogen peroxide-treated and glutathione-depleted human promonocytic cells

Treatment with 0.2 mM hydrogen peroxide (H(2)O(2)) or with 0.5 mM cisplatin caused caspase-9 and caspase-3 activation and death by apoptosis in U-937 human promonocytic cells. However, treatment with 2 mM H(2)O(2), or incubation with the glutathione suppressor DL-buthionine-(S,R)-sulfoximine (BSO) prior to treatment with cisplatin, suppressed caspase activation and changed the mode of death to necrosis. Treatment with 2 mM H(2)O(2) caused a great decrease in the intracellular ATP level, which was partially prevented by 3-aminobenzamide (3-ABA). Correspondingly, 3-ABA restored the activation of caspases and the execution of apoptosis. By contrast, BSO plus cisplatin did not decrease the ATP levels, and the generation of necrosis by this treatment was not affected by 3-ABA. On the other hand, while all apoptosis-inducing treatments and treatment with 2 mM H(2)O(2) caused Bax translocation from the cytosol to mitochondria as well as cytochrome c release from mitochondria to the cytosol, treatment with BSO plus cisplatin did not. Treatment with cisplatin alone caused Bid cleavage, while BSO plus cisplatin as well as 0.2 and 2 mM H(2)O(2) did not. Bcl-2 overexpression reduced the generation of necrosis by H(2)O(2), but not by BSO plus cisplatin. These results indicate the existence of different apoptosis/necrosis regulatory mechanisms in promonocytic cells subjected to different forms of oxidative stress.

Apoptotic death of striatal neurons induced by human immunodeficiency virus-1 Tat and gp120: Differential involvement of caspase-3 and endonuclease G

Human immunodeficiency virus-1 (HIV-1) infection affects the striatum, resulting in gliosis and neuronal losses. To determine whether HIV-1 proteins induce striatal neurotoxicity through an apoptotic mechanism, mouse striatal neurons isolated on embryonic day 15 and the effects of HIV-1 Tat(1-72) and gp120 on survival were assessed in vitro. Mitochondrial release of cytochrome c, caspase-3 activation, and neuron survival, as well as an alternative apoptotic pathway involving endonuclease G (endo G), were assessed at 4 h, 24 h, 48 h, and/or 72 h using enzyme assays and immunoblotting. Both HIV-1 Tat and gp120 significantly increased caspase-3 activation in a concentration-dependent manner in striatal neurons at 4 h following continuous exposure in vitro. Tat(1-72) and gp120 caused significant neuronal losses at 48 h and/or 72 h. Tat(1-72) increased cytochrome c release, and caspase-3 and endo G activation at 4 h, 24 h, and/or 72 h. By contrast, gp120 increased caspase-3 activation, but failed to increase cytochrome c or endo G levels in the cytoplasm at 4 h, 24 h, and/or 72 h. The cell permeant caspase inhibitor Z-DEVD-FMK significantly attenuated gp120-induced, but not Tat(1-72)-induced, neuronal death, suggesting that gp120 acts in large part through the activation of caspase(s), whereas Tat(1-72)-induced neurotoxicity was accompanied by activating an alternative pathway involving endo G. Thus, although Tat(1-72) and gp120 induced significant neurotoxicity, the nature of the apoptotic events preceding death differed. Collectively, our findings suggest that HIV-1 proteins are intrinsically toxic to striatal neurons and the pathogenesis is mediated through separate actions involving both caspase-3 and endo G.

anthocyanins rich extract-induced apoptotic cell death in human promyelocytic leukemia cells

Hibiscus sabdariffa Linne (Malvaceae), an attractive plant believed to be native to Africa, is cultivated in the Sudan and Eastern Taiwan. Anthocyanins exist widely in many vegetables and fruits. Some reports demonstrated that anthocyanins extracted from H. sabdariffa L., Hibiscus anthocyanins (HAs) (which are a group of natural pigments existing in the dried calyx of H. sabdariffa L.) exhibited antioxidant activity and liver protection. Therefore, in this study, we explored the effect of HAs on human cancer cells. The result showed that HAs could cause cancer cell apoptosis, especially in HL-60 cells. Using flow cytometry, we found that HAs treatment (0-4 mg/ml) markedly induced apoptosis in HL-60 cells in a dose- and time-dependent manner. The result also revealed increased phosphorylation in p38 and c-Jun, cytochrome c release, and expression of tBid, Fas, and FasL in the HAs-treated HL-60 cells. We further used SB203580 (p38 inhibitor), PD98059 (MEK inhibitor), SP600125 (JNK inhibitor), and wortmannin (phosphatidylinositol 3-kinase; PI-3K inhibitor) to evaluate their effect on the HAs-induced HL-60 death. The data showed that only SB203580 had strong potential in inhibiting HL-60 cell apoptosis and related protein expression and phosphorylation. Therefore, we suggested that HAs mediated HL-60 apoptosis via the p38-FasL and Bid pathway. According to these results, HAs could be developed as chemopreventive agents. However, further investigations into the specificity and mechanism(s) of HAs are needed.

Regulation of ATP/ADP in pancreatic islets

ATP and ADP levels are critical regulators of glucose-stimulated insulin secretion. In many aerobic cell types, the phosphorylation potential (ATP/ADP/P(i)) is controlled by sensing mechanisms inherent in mitochondrial metabolism that feed back and induce compensatory changes in electron transport. To determine whether such regulation may contribute to stimulus-secretion coupling in islet cells, we used a recently developed flow culture system to continuously and noninvasively measure cytochrome c redox state and oxygen consumption as indexes of electron transport in perifused isolated rat islets. Increasing substrate availability by increasing glucose increased cytochrome c reduction and oxygen consumption, whereas increasing metabolic demand with glibenclamide increased oxygen consumption but not cytochrome c reduction. The data were analyzed using a kinetic model of the dual control of electron transport and oxygen consumption by substrate availability and energy demand, and ATP/ADP/P(i) was estimated as a function of time. ATP/ADP/P(i) increased in response to glucose and decreased in response to glibenclamide, consistent with what is known about the effects of these agents on energy state. Therefore, a simple model representing the hypothesized role of mitochondrial coupling in governing phosphorylation potential correctly predicted the directional changes in ATP/ADP/P(i). Thus, the data support the notion that mitochondrial-coupling mechanisms, by virtue of their role in establishing ATP and ADP levels, may play a role in mediating nutrient-stimulated insulin secretion. Our results also offer a new method for continuous noninvasive measures of islet cell phosphorylation potential, a critical metabolic variable that controls insulin secretion by ATP-sensitive K(+)-dependent and -independent mechanisms.

Critical upstream signals of cytochrome C release induced by a novel Bcl-2 inhibitor

Cytochrome c release is a central step in the apoptosis induced by many death stimuli. Bcl-2 plays a critical role in controlling this step. In this study, we investigated the upstream mechanism of cytochrome c release induced by ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (HA14-1), a recently discovered small molecule inhibitor of Bcl-2. HA14-1 was found to induce cytochrome c release from the mitochondria of intact cells but not from isolated mitochondria. Cytochrome c release from isolated mitochondria requires the presence of both HA14-1 and exogenous Ca(2+). This suggests that both mitochondrial and extramitochondrial signals are important. In intact cells, treatment with HA14-1 caused Ca(2+) spike, change in mitochondrial membrane potential (Delta psi(m)) transition, Bax translocation, and reactive oxygen species (ROS) generation prior to cytochrome c release. Pretreatment with either EGTA acetoxymethyl ester or vitamin E resulted in a significant decrease in cytochrome c release and cell death induced by HA14-1. Furthermore pretreatment with RU-360, an inhibitor of the mitochondrial Ca(2+) uniporter, or with EGTA acetoxymethyl ester, but not with vitamin E, prevented the HA14-1-induced Delta psi(m) transition and Bax translocation. This suggests that ROS generation is an event that occurs after the Delta psi(m) transition and Bax translocation. Together these data demonstrate that the Ca(2+) spike, mitochondrial Bcl-2 presensitization, and subsequent Delta psi(m) transition, Bax translocation, and ROS generation are important upstream signals for cytochrome c release upon HA14-1 stimulation. The involvement of endoplasmic reticulum and mitochondrial signals suggests both organelles are crucial for HA14-1-induced apoptosis.

Neuroprotective effects of tetramethylpyrazine on hydrogen peroxide-induced apoptosis in PC12 cells

In the present study, we investigated the effects of tetramethylpyrazine (TMP) on hydrogen peroxide (H2O2)-induced apoptosis in PC12 cells. The apoptosis in H2O2-induced PC12 cells was accompanied by a decrease in Bcl-2/Bax protein ratio, release of cytochrome c to cytosol and the activation of caspase-3. TMP not only suppressed the down-regulation of Bcl-2, up-regulation of Bax and the release of mitochondrial cytochrome c to cytosol, but also attenuated caspase-3 activation and eventually protected against H2O2-induced apoptosis. These results indicated that TMP blocked H2O2-induced apoptosis by the regulation of Bcl-2 family members, suppression of cytochrome c release, and caspase cascade activation in PC12 cells.

Norcantharidin-induced apoptosis in oral cancer cells is associated with an increase of proapoptotic to antiapoptotic protein ratio

Norcantharidin (NCTD), the demethylated analogue of cantharidin, has been used to treat human cancers in China since 1984. It was recently found to be capable of inducing apoptosis in human colon carcinoma, hepatoma and glioblastoma cells by way of an elusive mechanism. In this study, we demonstrated that NCTD also induces apoptosis in human oral cancer cell lines SAS (p53 wild-type phenotype) and Ca9-22 (p53 mutant) as evidenced by nuclear condensation, TUNEL labeling, DNA fragmentation and cleavage of PARP. Apoptosis induced by NCTD was both dose- and time-dependent. We found NCTD did not induce Fas and FasL, implying that it activated other apoptosis pathways. Our data showed that NCTD caused accumulation of cytosolic cytochrome c and activation of caspase-9, suggesting that apoptosis occurred via the mitochondria mediated pathway. NCTD enhanced the expression of Bax in SAS cells consistent with their p53 status. Moreover, we showed that NCTD downregulated the expression of Bcl-2 in Ca9-22 and Bcl-XL in SAS. Our results suggest that NCTD-induced apoptosis in oral cancer cells may be mediated by an increase in the ratios of proapoptotic to antiapoptotic proteins. Since oral cancer cells with mutant p53 or elevated Bcl-XL levels showed resistance to multiple chemotherapeutic agents, NCTD may overcome the chemoresistance of these cells and provide potential new avenues for treatment.

3,3'-Diindolylmethane enhances chemosensitivity of multiple chemotherapeutic agents in pancreatic cancer

Clinical management of pancreatic cancer is a major problem, which is in part due to both de novo and acquired resistance to conventional therapeutics. Here, we present in vitro and in vivo preclinical evidence in support of chemosensitization of pancreatic cancer cells by 3,3-diindolylmethane (DIM), a natural compound that can be easily obtained by consuming cruciferous vegetables. DIM pretreatment of pancreatic cancer cells led to a significantly increased apoptosis (P < 0.01) with suboptimal concentrations of chemotherapeutic agents (cisplatin, gemcitabine, and oxaliplatin) compared with monotherapy. It is known that resistance to chemotherapy in pancreatic cancer is associated with constitutively activated nuclear factor-kappaB (NF-kappaB), which becomes further activated by chemotherapeutic drugs. Our data provide mechanistic evidence for the first time showing that DIM potentiates the killing of pancreatic cancer cells by down-regulation of constitutive as well as drug-induced activation of NF-kappaB and its downstream genes (Bcl-xL, XIAP, cIAP, and survivin). Most importantly, using an orthotopic animal model, we found reduction in tumor size (P < 0.001) when DIM was given in combination with oxaliplatin compared with monotherapy. This was accompanied by loss of phospho-p65 and down-regulation of NF-kappaB activity and its downstream genes (Bcl-xL, survivin, and XIAP), which correlated with reduced cell proliferation (as assessed by Ki-67 immunostaining of tumor specimens) and evidence of apoptosis [as assessed by poly(ADP-ribose) polymerase cleavage and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining]. These results provide strong in vivo evidence in support of our hypothesis that DIM could abrogate chemotherapeutic drug (cisplatin, gemcitabine, and/or oxaliplatin)-induced activation of NF-kappaB, resulting in the chemosensitization of pancreatic tumors to conventional therapeutics.

Catalpol inhibits apoptosis in hydrogen peroxide-induced PC12 cells by preventing cytochrome c release and inactivating of caspase cascade

In the present study, using a rat pheochromocytoma (PC12) cell line, the effect of catalpol on H2O2-induced apoptosis was studied. The apoptosis in H2O2-induced PC12 cells was accompanied by down-regulation of Bcl-2, up-regulation of Bax, the release of mitochondrial cytochrome c to cytosol and sequential activation of caspase-1 and caspase-3 then leading to cleavage of poly-ADP-ribose polymerase (PARP). Catalpol not only suppressed the down-regulation of Bcl-2, up-regulation of Bax and the release of mitochondrial cytochrome c to cytosol, but also attenuated caspase-3 activation, PARP cleavage, and eventually protected against H2O2-induced apoptosis. Taken together, these results suggest that treatment of PC12 cells with catalpol can block H2O2-induced apoptosis by the regulation of Bcl-2 family members, as well as suppression of cytochrome c release and caspase cascade activation.

Tetramethylpyrazine protects rat renal tubular cell apoptosis induced by gentamicin

BACKGROUND

Gentamicin, a widely used antibiotic for the treatment of bacterial infection, can cause nephrotoxicity. Tetramethylpyrazine (TMP) is a compound purified from the rhizome of Ligusticum wallichi (Chuanxiong) and has been found to protect against ischaemia-reperfusion injury, nephritis and alcohol-induced toxicity in rat kidneys.

METHODS

We used rat renal tubular cells (RTCs), NRK-52E, in this study. The cytotoxicity of gentamicin was checked with transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) staining, and the generation of reactive oxygen species was measured using the fluorescent probe 2,7-dichlorofluorescein. We evaluated several apoptotic parameters: cleaved caspase levels, tumour necrosis factor (TNF-alpha) excretion and nuclear factor Kappa B (NF-kappaB) activity. We also examined the TMP protective effect on gentamicin-induced apoptosis in rat kidneys.

RESULTS

The results of this study showed that gentamicin was found to markedly induce apoptosis in NRK-52E cells in a dose-dependent manner; that TMP expressed a dose-dependent protective effect against gentamicin-induced apoptosis; that pre-treatment of the cells with 50 or 100 microM of TMP effectively decreased the reactive oxygen species formation induced by gentamicin; that TMP was found to inactivate the gentamicin-stimulated activities of caspase-3, caspase-8 and caspase-9, to inhibit gentamicin-induced release of cytochrome c, as well as to raise the expression of Bcl-x(L); that TMP inhibited the gentamicin-induced TNF-alpha excretion, and inactivated the transcription factor NF-kappaB; and that the TMP treatment significantly reduced apoptotic injury in rat RTCs.

CONCLUSIONS

Based on the results of this study, we suggest that TMP can attenuate gentamicin-induced oxidative stress and apoptotic injury in rat RTCs, and that its character may have therapeutic potential for patients with renal diseases.

Involvement of cathepsin D in chemotherapy-induced cytochrome c release, caspase activation, and cell death

Treatment of cells with chemotherapy drugs activates the intrinsic mitochondrial pathway of apoptosis and the caspase protease cascade. Recently, the lysosomal protease cathepsin D has been implicated in apoptosis caused by oxidative stress, inhibition of protein kinase C, and stimulation of the TNFR1 and Fas death receptors. However, the role of cathepsin D in chemotherapy-induced cell death has remained largely unexplored. In this report, we show that treatment of U937 leukemia cells with the chemotherapy drug etoposide (VP-16) results in cathepsin D release into the cytosol within 4 hours after initiation of drug treatment. VP-16-induced cathepsin D release was not inhibited by z-VAD-FMK or pepstatin A, suggesting that it occurred independently of the activities of caspase proteases or cathepsin D. Down-regulation of cathepsin D expression in suspension U937 cells or adherent HeLa cells using cathepsin D small interfering RNA partially inhibited cell death resulting from treatment of cells with tumor necrosis factor-alpha, tumor necrosis factor-related apoptosis inducing ligand, or the chemotherapy drugs VP-16, cisplatin, and 5-fluorouracil. Moreover, cathepsin D down-regulation significantly delayed cytochrome c release and caspase-3 activation in response to chemotherapy treatment. Incubation of isolated mitochondria with cathepsin D-treated cytosolic extracts resulted in potent release of cytochrome c, indicating that a cytoplasmic substrate mediates the effects of cathepsin D on mitochondria. Together, these findings show that cathepsin D plays an important role in chemotherapy-induced cell death, and that cathepsin D lies upstream of cytochrome c release and caspase-3 activation in the chemotherapy-induced execution pathway.

Formation of the molten globule-like state of cytochrome c induced by n-alkyl sulfates at low concentrations

The molten globule state of cytochrome c is the major intermediate of protein folding. Elucidation of the thermodynamic mechanism of conformational stability of the molten globule state would enhance our understanding of protein folding. The formation of the molten globule state of cytochrome c was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS, at low concentrations. The refolding states of the protein were monitored by spectroscopic techniques including circular dichroism (CD), visible absorbance and fluorescence. The effect of n-alkyl sulfates on the structure of acid-unfolded horse cytochrome c at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of the molten globule state. The addition of n-alkyl sulfates to the unfolded state of cytochrome c appears to support the stabilized form of the molten globule. The m-values of the refolded state of cytochrome c by SOS, SDeS, SDS, and STS showed substantial variation. The enhancement of m-values as the stability criterion of the molten globule state corresponded with increasing chain length of the cited n-alkyl sulfates. The compaction of the molten globule state induced by SDS, as a prototype for other n-alkyl sulfates, relative to the unfolded state of cytochrome c was confirmed by Stokes radius and thermal transition point (T(m)) measured by microviscometry and differential scanning calorimetry (DSC), respectively. Thus, hydrophobic interactions play an important role in stabilizing the molten globule state.

Nanoparticle-Mediated Delivery of Mitochondrial Division Inhibitor 1 to the Myocardium Protects the Heart From Ischemia-Reperfusion Injury Through Inhibition of Mitochondria Outer Membrane Permeabilization: A New Therapeutic Modality for Acute Myocardial Infarction

BACKGROUND

Mitochondria-mediated cell death plays a critical role in myocardial ischemia-reperfusion (IR) injury. We hypothesized that nanoparticle-mediated drug delivery of mitochondrial division inhibitor 1 (Mdivi1) protects hearts from IR injury through inhibition of mitochondria outer membrane permeabilization (MOMP), which causes mitochondrial-mediated cell death.

METHODS AND RESULTS

We formulated poly (lactic-co-glycolic acid) nanoparticles containing Mdivi1 (Mdivi1-NP). We recently demonstrated that these nanoparticles could be successfully delivered to the cytosol and mitochondria of cardiomyocytes under H2O2-induced oxidative stress that mimicked IR injury. Pretreatment with Mdivi1-NP ameliorated H2O2-induced cell death in rat neonatal cardiomyocytes more potently than Mdivi1 alone, as indicated by a lower estimated half-maximal effective concentration and greater maximal effect on cell survival. Mdivi1-NP treatment of Langendorff-perfused mouse hearts through the coronary arteries at the time of reperfusion reduced infarct size after IR injury more effectively than Mdivi1 alone. Mdivi1-NP treatment also inhibited Drp1-mediated Bax translocation to the mitochondria and subsequent cytochrome c leakage into the cytosol, namely, MOMP, in mouse IR hearts. MOMP inhibition was also observed in cyclophilin D knockout (CypD-KO) mice, which lack the mitochondrial permeability transition pore (MPTP) opening. Intravenous Mdivi1-NP treatment in vivo at the time of reperfusion reduced IR injury in wild-type and CypD-KO mice, but not Bax-KO mice.

CONCLUSIONS

Mdivi1-NP treatment reduced IR injury through inhibition of MOMP, even in the absence of a CypD/MPTP opening. Thus, nanoparticle-mediated drug delivery of Mdivi1 may be a novel treatment strategy for IR injury.

Synthesis of apoptosis-inducing iminophosphorane organogold(III) complexes and study of their interactions with biomolecular targets

New stable cationic organogold(III) complexes containing the "pincer" iminophosphorane ligand (2-C(6)H(4)-PPh(2)=NPh) have been prepared by reaction of the previously described [Au{kappa(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}Cl(2)] 1 and a combination of sodium or silver salts and appropriate ligands. The presence of the P atom in the PR(3) fragment has been used as a "spectroscopic marker" to study the in vitro stability (and oxidation state) of the new organogold complexes in solvents like dimethyl sulfoxide and water. Compounds with dithiocarbamato ligands and water-soluble phosphines of the general type [Au{kappa(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}(S(2)CN-R(2))]PF(6) (R = Me 2; Bz 3) and [Au{kappa(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}(PR(3))(n)Cl]PF(6) (PR(3) = P{Cp(m-C(6)H(4)-SO(3)Na)(2)} n = 1 4, n = 2 TPA {1,3,5-triaza-7-phosphaadamantane} 5) have been synthesized and characterized in solution and in the solid state (the crystal structure of 2 has been determined by X-ray diffraction studies). Complexes 1-5 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and Jurkat-T acute lymphoblastic leukemia cells. Compounds 2 and 3 are quite cytotoxic for these two cell lines. There is a preferential induction of apoptosis in HeLa cells after treatment with 1-5. However in the case of the more cytotoxic complex (2), cell death is activated because of both apoptosis and necrosis. The interactions of 1-5 with Calf Thymus DNA have been evaluated by Thermal Denaturation methods. All these complexes show no or little (electrostatic) interaction with DNA. The interaction of 2 with two model proteins (cytochrome c and thioredoxin reductase) has been analyzed by spectroscopic methods (vis-UV and fluorescence). Compound 2 manifests a high reactivity toward both proteins. The mechanistic implications of these results are discussed here.

2-methoxyestradiol induces apoptosis and cell cycle arrest in human chondrosarcoma cells

2-Methoxyestradiol (2ME) is an endogenous metabolite with estrogen receptor-independent anti-tumor activity. The current study seeks to determine the mechanism of anti-tumor activity of 2ME on human chondrosarcoma. 2ME caused a time- and dose-dependent cytotoxity in chondrosarcoma cells, while primary chondrocytes were minimally affected. Cells accumulated in G0/G1 phase in response to 2ME and DAPI stain indicated an induction of apoptosis. Bax, Cytochrome C, and Caspase-3 protein expression were increased, while p53 expression was decreased. A higher Bax/Bcl-2 ratio followed 2ME treatment. 2ME has a potentially promising role as a systemic therapy of chondrosarcoma when the mechanism of action is better delineated.