Opposite role of changes in mitochondrial membrane potential in different apoptotic processes

[Ca2+]i oscillations in human sperm are triggered in the flagellum by membrane potential-sensitive activity of CatSper

STUDY QUESTION

How are progesterone (P4)-induced repetitive intracellular Ca2+ concentration ([Ca2+]i) signals (oscillations) in human sperm generated?

SUMMARY ANSWER

P4-induced [Ca2+]i oscillations are generated in the flagellum by membrane potential (Vm)-sensitive Ca2+-influx through CatSper channels.

WHAT IS KNOWN ALREADY

A subset of human sperm display [Ca2+]i oscillations that regulate flagellar beating and acrosome reaction. Although pharmacological manipulations indicate involvement of stored Ca2+ in these oscillations, influx of extracellular Ca2+ is also required.

STUDY DESIGN, SIZE, DURATION

This was a laboratory study that used >20 sperm donors and involved more than 100 separate experiments and analysis of more than 1000 individual cells over a period of 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen donors and patients were recruited in accordance with local ethics approval from Birmingham University and Tayside ethics committees. [Ca2+]i responses and Vm of individual cells were examined by fluorescence imaging and whole-cell current clamp.

MAIN RESULTS AND THE ROLE OF CHANCE

P4-induced [Ca2+]i oscillations originated in the flagellum, spreading to the neck and head (latency of 1-2 s). K+-ionophore valinomycin (1 µM) was used to investigate the role of membrane potential (Vm). Direct assessment by whole-cell current-clamp confirmed that Vm in valinomycin-exposed cells was determined primarily by K+ equilibrium potential (EK) and was rapidly 'reset' upon manipulation of [K+]o. Pre-treatment of sperm with valinomycin ([K+]o = 5.4 mM) had no effect on the P4-induced [Ca2+] transient (P = 0.95; eight experiments), but application of valinomycin to P4-pretreated sperm suppressed activity in 82% of oscillating cells (n = 257; P = 5 × 10-55 compared to control) and significantly reduced both the amplitude and frequency of persisting oscillations (P = 0.0001). Upon valinomycin washout, oscillations re-started in most cells. When valinomycin was applied in saline with elevated [K+], the inhibitory effect of valinomycin was reduced and was dependent on EK (P = 10-25). Amplitude and frequency of [Ca2+]i oscillations that persisted in the presence of valinomycin showed similar sensitivity to EK (P < 0.01). The CatSper inhibitor RU1968 (4.8 and 11 µM) caused immediate and reversible arrest of activity in 36% and 96% of oscillating cells, respectively (P < 10-10). Quinidine (300 µM) which blocks the sperm K+ current (IKsper) completely, inhibited [Ca2+]i oscillations.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was an in-vitro study and caution must be taken when extrapolating these results to in-vivo regulation of sperm.

WIDER IMPLICATIONS OF THE FINDINGS

[Ca2+]i oscillations in human sperm are functionally important and their absence is associated with failed fertilisation at IVF. The data reported here provide new understanding of the mechanisms that underlie the regulation and generation (or failure) of these oscillations.

STUDY FUNDING/COMPETING INTEREST(S)

E.T.-N. was in receipt of a postgraduate scholarship from the CAPES Foundation (Ministry of Education, Brazil). E.M-M received travel funds from the Programa de Apoyo a los Estudios de Posgrado (Maestria y Doctorado en Ciencias Bioquimicas-Universidad Autonoma de Mexico). SGB and CLRB are recipients of a Chief Scientist Office (NHS Scotland) grant TCS/17/28. The authors have no conflicts of interest.

Antiproliferative chromone derivatives induce K562 cell death through endogenous and exogenous pathways

A series of furoxan derivatives of chromone were prepared. The antiproliferative activities were tested against five cancer cell lines HepG2, MCF-7, HCT-116, B16, and K562, and two normal human cell lines L-02 and PBMCs. Among them, compound 15a exhibited the most potent antiproliferative activity. It was also found 15a produced more than 8 µM of NO at the peak time of 45 min by Griess assay. Generally, antiproliferative activity is positively related to NO release to some extent. Further in-depth studies on apoptosis-related mechanisms showed that 15a caused S-phase cell cycle arrest in a concentration-dependent manner and induced apoptosis significantly through mitochondria-related pathways. Human apoptosis protein array assay also demonstrated 15a increased the expression levels of pro-apoptotic Bax, Bad, HtrA2 and Trail R2/DR5. The expression of catalase and cell cycle blocker claspin were similarly up-regulated. In balance, 15a induced K562 cells death through both endogenous and exogenous pathways.

Mitochondrial oxidative stress and dysfunction induced by single- and multiwall carbon nanotubes: A comparative study

With the ever-increasing use of carbon nanotubes (CNTs) in health-related and engineering applications, the hazardous risks of this material have become a major concern. It is well known that CNTs accumulate with cytotoxic and genotoxic levels within vital organs. It has also been shown that treating cell cultures with CNTs resulted in cell-cycle arrest and increased apoptosis/necrosis. The goal of this pilot study is to perform a comprehensive comparative study on the toxicity of single-wall (SW) and multiwall (MW) CNTs in rat skin cells. Our results confirm a dose-dependent toxicity of SWCNTs and MWCNTs due to the loss of mitochondrial activity, increase in mitochondrial reactive oxygen species (ROS) formation, and mitochondrial membrane potential collapse before mitochondrial swelling. Moreover, disturbance in the oxidative phosphorylation is observed by a decrease in ATP level. These events induced the release of cytochrome c via outer membrane rupture or MPT pore opening and subsequently programmed cell death of all doses compared to control group. Our results demonstrate that although MWCNTs can be very toxic, SWCNTs cause more mitochondrial damage to the cells. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2047-2055, 2017.

Assessment of Mitochondrial Membrane Potential in HEI-OC1 and LLC-PK1 Cells Treated with Gentamicin and Mitoquinone

Objective

To determine the effects of concurrent treatment with gentamicin and the mitochondria-targeted antioxidant mitoquinone (MitoQ; which may prevent gentamicin ototoxicity) on change in the mitochondrial membrane potential (Δψm), a precursor of apoptosis.

Study Design

Prospective and controlled.

Setting

Academic research laboratory.

Subjects and Methods

LLC-PK1 (Lilly Laboratories Culture–Pig Kidney Type 1) and HEI-OC1 (House Ear Institute Organ of Corti 1) cells—renal and auditory cell lines, respectively—were used in this study. Δψm was assessed by flow cytometry through the MitoProbe JC-1 Kit for Flow Cytometry in untreated LLC-PK1 and HEI-OC1 cells and cells exposed to low- (100µM) or high- (2000µM) dose gentamicin for 24 hours, with and without 0.5µM each of MitoQ or idebenone (IDB; an untargeted ubiquinone).

Results

Δψm was not different in untreated LLC-PK1 cells and cells coincubated with low-dose gentamicin and MitoQ or IDB ( P > .05). In HEI-OC1 cells, coincubation with low-dose gentamicin and MitoQ decreased Δψm ( P = .002). Coincubation of LLC-PK1 cells with high-dose gentamicin and DMSO, MitoQ, or IDB depolarized Δψm ( P < .0001), with MitoQ depolarizing the Δψm to a greater extent than that of IDB ( P = .03). In contrast, HEI-OC1 cells demonstrated a hyperpolarized Δψm when coincubated with high-dose gentamicin and DMSO, MitoQ, or IDB ( P < .001).

Conclusion

The combination of gentamicin and MitoQ holds the potential to disrupt Δψm. This suggests a heightened need to monitor for toxicity in patients receiving both agents.

U937 variant cells as a model of apoptosis without cell disintegration

The variant cell line U937_V was originally identified by a higher sensitivity to the cytocidal action of tumor necrosis factor alpha (TNFα) than that of its reference cell line, U937. We noticed that a typical morphological feature of dying U937_V cells was the lack of cellular disintegration, which contrasts to the formation of apoptotic bodies seen with dying U937 cells. We found that both TNFα, which induces the extrinsic apoptotic pathway, and etoposide (VP-16), which induces the intrinsic apoptotic pathway, stimulated U937_V cell death without cell disintegration. In spite of the distinct morphological differences between the U937 and U937_V cells, the basic molecular events of apoptosis, such as internucleosomal DNA degradation, phosphatidylserine exposure on the outer leaflet of the plasma membrane, caspase activation and cytochrome c release, were evident in both cell types when stimulated with both types of apoptosis inducer. In the U937_V cells, we noted an accelerated release of cytochrome c, an accelerated decrease in mitochondrial membrane potential, and a more pronounced generation of reactive oxygen species compared to the reference cells. We propose that the U937 and U937_V cell lines could serve as excellent comparison models for studies on the mechanisms regulating the processes of cellular disintegration during apoptosis, such as blebbing (zeiosis) and apoptotic body formation.

Toxicity of depleted uranium on isolated rat kidney mitochondria

BACKGROUND

Kidney is known as the most sensitive target organ for depleted uranium (DU) toxicity in comparison to other organs. Although the oxidative stress and mitochondrial damage induced by DU has been well investigated, the precise mechanism of DU-induced nephrotoxicity has not been thoroughly recognized yet.

METHODS

Kidney mitochondria were obtained using differential centrifugation from Wistar rats and mitochondrial toxicity endpoints were then determined in both in vivo and in vitro uranyl acetate (UA) exposure cases.

RESULTS

Single injection of UA (0, 0.5, 1 and 2mg/kg, i.p.) caused a significant increase in blood urea nitrogen and creatinine levels. Isolated mitochondria from the UA-treated rat kidney showed a marked elevation in oxidative stress accompanied by mitochondrial membrane potential (MMP) collapse as compared to control group. Incubation of isolated kidney mitochondria with UA (50, 100 and 200μM) manifested that UA can disrupt the electron transfer chain at complex II and III that leads to induction of reactive oxygen species (ROS) formation, lipid peroxidation, and glutathione oxidation. Disturbances in oxidative phosphorylation were also demonstrated through decreased ATP concentration and ATP/ADP ratio in UA-treated mitochondria. In addition, UA induced a significant damage in mitochondrial outer membrane. Moreover, MMP collapse, mitochondrial swelling and cytochrome c release were observed following the UA treatment in isolated mitochondria.

GENERAL SIGNIFICANCE

Both our in vivo and in vitro results showed that UA-induced nephrotoxicity is linked to the impairment of electron transfer chain especially at complex II and III which leads to subsequent oxidative stress.

Poly(caprolactone)-modified Pluronic P105 micelles for reversal of paclitaxcel-resistance in SKOV-3 tumors

Three poly(caprolactone)-modified Pluronic P105 polymers (P105/PCLs) were synthesized using commercially available ε-caprolactone monomers and Pluronic P105 copolymers. The chemical structures, compositions and molecular weights of the P105/PCLs were confirmed by FT-IR, (1)H NMR and GPC measurements. Three paclitaxel (PTX)-loaded P105/PCL polymeric micelles were then prepared, and they showed average diameters in the range of 30-150 nm, drug-loading coefficients of 0.15%-5.43%, and encapsulation ratios of 2.1%-76.53%. The in vitro cytotoxicity assay demonstrated that three PTX-loaded P105/PCL micelles were able to sensitize the resistant SKOV-3/PTX tumor cells. The PTX-loaded P105/PCL(50) micelle was then selected for an in vivo antitumor efficacy study. The tumor volumes in nude mice bearing s.c. resistant SKOV-3/PTX carcinoma treated with this micellar PTX were significantly less than the control group treated with Taxol. It was demonstrated that three PCL-modified P105 monomers and micelles inhibited P-gP efflux activity in the resistant SKOV-3/PTX cells via at least three intracellular events: 1) inhibition of ATPase of P-gP, 2) decrease of membrane microviscosity and 3) a loss of mitochondrial membrane potential and subsequent decrease of ATP levels at the concentration of monomers (0.001%) and/or micelles (0.01-1.0%). Considering other favorable characteristics, such as sustained PTX release in vitro, long-circulating time in vivo and increased PTX concentration in the tissues of ovaries and uterus in mice, the PCL-modified Pluronic P105 polymeric micelle system could have important clinical implications for delivery of paclitaxel and treatment of the resistant ovarian tumors.

Mitochondrial membrane potential measurement of H9c2 cells grown in high-glucose and galactose-containing media does not provide additional predictivity towards mitochondrial assessment

Drug-induced mitochondrial toxicity is a contributing factor to many organ toxicities. The fact that some, but not all members of a particular drug class can induce mitochondrial dysfunction has necessitated the need for predictive screens within the drug development process. One of these screens is a cell viability assay done in two types of media, one containing high-glucose, the other, galactose. Since galactose-grown cells are more susceptible to mitochondrial toxicants than high-glucose-grown cells, this assay distinguishes compounds that cause toxicity primarily through mitochondrial targets from those that cause multifactorial toxicity. However, the assay does not show if compounds that cause multifactorial toxicity cause impairment on mitochondria. To address this problem, we investigated if multiplexing the assay with mitochondrial membrane potential measurements using the fluorescent dye, JC-1, could provide further information. We tested 28 drugs in the multiplexed assay and found that, although mitochondrial toxicants could be detected, no additional information was revealed about compounds that caused multifactorial toxicity. Hence, measurements with JC-1 did not provide additional information beyond what was detected using the cell viability assay. We conclude that even though the multiplexed assay is useful for HTS applications, it provides no additional value over the high-glucose-galactose cell viability assay.

Apoptosis and its suppression in hepatocytes culture

In order to achieve the goal of developing extracorporeal liver support devices, it is necessary to optimise bioprocess environment such that viability and function are maximised. Optimising culture medium composition and controlling the constitution of the cellular microenvironment within the bioreactor have for many years been considered vital to achieving these aims. Coupled to this is the need to understand apoptosis, the prime suspect in the demise of animal cultures, including those of hepatocytes. Results presented here show that absent nutrients including glucose and amino acids play a substantial part in the induction of apoptosis. The use of chemical apoptosis inhibitors was utilised to investigate key components of hepatic apoptosis where caspases, predominantly caspase 8, were implicated in staurosporine (STS)-induced HepZ apoptosis. Caspase 9 and 3 activation although recorded was of less significance. Interestingly, these results were not consistent with those of mitochondrial membrane depolarisation where inhibition of caspase activation appeared to drive depolarisation. Inhibition of mitochondrial permeability transition and use of anti-oxidants was unsuccessful in reducing apoptosis, caspase activation and mitochondrial membrane depolarisation. In further studies, the anti-apoptotic gene bcl-2 was over-expressed in HepZ, resulting in a cell line that was more robust and resistant to death induced by glucose and cystine deprivation and treatment with STS. Bcl-2 did not however show significant cytoprotectivity where apoptosis was stimulated by deprivation of glutamine and serum. Overall, results indicated that although apoptosis can be curbed by use of chemical inhibitors and genetic manipulation, their success is dependent on apoptotic stimuli.

Differential activity of caspase-3 regulates susceptibility of lung and breast tumor cell lines to Paclitaxel

Recent development of tumor resistance to paclitaxel presents a major problem to cancer treatment. An unsettled controversy in the cancer chemotherapy field, however, is whether caspases play a prominent role in paclitaxel-induced death in tumors. Previous studies suggest that cleavage of caspase-3 is not instrumental for the execution of death in tumors treated with paclitaxel, while other reports indicate that caspase-dependent pathways may be critical for paclitaxel cytotoxicity. In this study, we investigated the role of caspase-3 in breast and lung tumor cell line sensitivity to paclitaxel. Clonogenic survival and live/dead viability-assays, together with enzymatic activity and cell proliferation assays, reveal that the levels of paclitaxel-induced caspase-3 enzymatic activity in tumor cells correlate directly with tumor sensitivity to the drug.We observed a 2-fold increase in caspase-3 activity in 4T1-Luc breast tumor cells, but a 3-fold and 4-fold decrease in A549 and A427 lung tumor cell lines, respectively. Together, our results suggest that caspase-activation and activity levels are not only key determinants of paclitaxel-induced death in tumors but also serve as good indicators for tumor susceptibility to paclitaxel therapy. Our studies also indicate that within clinically relevant doses of paclitaxel, the ability to rid tumor populations of dormant tumor cells controls the rate of tumor recurrence.

Characterisation of serum-induced intracellular Ca2+ oscillations in primary bone marrow stromal cells

Intracellular Ca2+ signalling is pivotal to cell function and [Ca2+]i oscillations permit precise and prolonged modulation of an array of Ca2+-sensitive processes without the need for extended, global elevations in [Ca2+]i. We have studied [Ca2+]i signalling in primary rat marrow stromal cells exposed to foetal calf serum (FCS) constituents at concentrations up to those required to promote growth and differentiation in culture. Spontaneous [Ca2+]i signalling was not observed, but exposure to 1% FCS induced regular, sustained Ca2+ oscillations in 41 +/- 3% of cells. Incidence of FCS-induced oscillations was dose-dependent, saturating at 0.5%. These oscillations were arrested by disruption of Ca2+ stores with 100 nM-1 microM thapsigargin or discharge of mitochondrial membrane potential and were sensitive to blockade of IP3-receptors by 50 microM 2-amino-ethoxydiphenyl borate (2-APB) and inhibition of phospholipase C with 5 microM U73122. The oscillations decreased in frequency and amplitude following inhibition of Ca2+ influx with EGTA or La3+ but were poorly sensitive to nifedipine (1-10 microM) and Bay K 8644 (300 nM). The factor(s) responsible for inducing [Ca2+]i oscillations are heat stable, insensitive to disulphide bond reduction with 20 mM dithioerythritol and retained by a 30 kDa molecular weight filter. Serum is routinely present in culture medium at 10%-15% [v/v] and marrow stromal cells maintained under culture conditions exhibited sustained oscillations. This is the first demonstration of agonist-induced complex Ca2+ signals in marrow stromal cells. We conclude that Ca2+ oscillations occur constantly in these cells in culture and are potentially important regulators of cell proliferation and differentiation.

Characterization of cells with different mitochondrial membrane potential during apoptosis

BACKGROUND

Until now, the simultaneous analysis of several parameters during apoptosis, including DNA content and mitochondrial membrane potential (DeltaPsi), has not been possible because of the spectral characteristics of the commonly used dyes. Using polychromatic flow cytometry based upon multiple laser and UV lamp excitation, we have characterized cells with different DeltaPsi during apoptosis.

METHODS

U937 cells were treated with the flavonoid quercetin (Qu) and stained with JC-1 to detect DeltaPsi, propidium iodide (PI) for cell viability, Hoechst 33342 for DNA content, Annexin V conjugated with Alexa Fluor-647 for detection of phosphatidilserine (PS) exposure, marker of early apoptosis, or Mitotracker Deep Red for the determination of mitochondrial mass.

RESULTS

Treatment with Qu provoked the onset of three cell populations with different DeltaPsi: (1) healthy cells, with normal DeltaPsi, DNA content and physical parameters, high mitochondrial mass, PI- and Annexin V-negative; (2) cells with intermediate DeltaPsi and normal DNA content, but with physical parameters typical of apoptotic cells and low mitochondrial mass; most of them were PI+ and Annexin V+; (3) cells with collapsed DeltaPsi that had low mitochondrial mass and were Annexin-V+, PI+; half of them showed diminished DNA content. Similar results, i.e. the presence of cells with intermediate DeltaPsi, were observed in other models of apoptosis.

CONCLUSIONS

During Qu-induced apoptosis, loss of DeltaPsi, PS exposure, and decrease of mitochondrial mass are early events that precede permeability to PI and loss of DNA. Populations of cells with different DeltaPsi, as revealed by flow cytometry after JC-1 staining, differed also for other parameters associated to apoptosis. Thus, the simultaneous analysis of several parameters by polychromatic flow cytometry permits a better identification of many stages of cell death, and, more in general, allows to evaluate the eventual heterogenic sensibility of the population under study to a given compound.

Mitochondrial reactive oxygen species regulate the temporal activation of nuclear factor kappaB to modulate tumour necrosis factor-induced apoptosis: evidence from mitochondria-targeted antioxidants

ROS (reactive oxygen species) from mitochondrial and non-mitochondrial sources have been implicated in TNFalpha (tumour necrosis factor alpha)-mediated signalling. In the present study, a new class of specific mitochondria-targeted antioxidants were used to explore directly the role of mitochondrial ROS in TNF-induced apoptosis. MitoVit E {[2-(3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-yl)ethyl]triphenylphosphonium bromide} (vitamin E attached to a lipophilic cation that facilitates accumulation of the antioxidant in the mitochondrial matrix) enhanced TNF-induced apoptosis of U937 cells. In time course analyses, cleavage and activation of caspase 8 in response to TNF were not affected by MitoVit E, whereas the activation of caspase 3 was significantly increased. Furthermore, there was an increased cleavage of the proapoptotic Bcl-2 family member Bid and an increased release of cytochrome c from mitochondria, in cells treated with TNF in the presence of MitoVit E. We considered several mechanisms by which MitoVit E might accelerate TNF-induced apoptosis including mitochondrial integrity (ATP/ADP levels and permeability transition), alterations in calcium homoeostasis and transcription factor activation. Of these, only the transcription factor NF-kappaB (nuclear factor kappaB) was implicated. TNF caused maximal nuclear translocation of NF-kappaB within 15 min, compared with 1 h in cells pretreated with MitoVit E. Thus the accumulation of an antioxidant within the mitochondrial matrix enhances TNF-induced apoptosis by decreasing or delaying the expression of the protective antiapoptotic proteins. These results demonstrate that mitochondrial ROS production is a physiologically relevant component of the TNF signal-transduction pathway during apoptosis, and reveal a novel functional role for mitochondrial ROS as a temporal regulator of NF-kappaB activation and NF-kappaB-dependent antiapoptotic signalling.

Low dose (-)deprenyl is cytoprotective: it maintains mitochondrial membrane potential and eliminates oxygen radicals

Hypoxia leads to a collapse in mitochondrial transmembrane potential (Deltapsi(M)), a fall in the ATP/ADP ratio, and finally cell death. Since (-)deprenyl directly modulates Deltapsi(M) and production of reactive oxygen species (ROS) by altering the respiratory function of mitochondria, we were interested in the dose-response relations of these effects. The changes in JC-1 red/green signal ratios {mitochondrial transmembrane potential}, and the changes in the cerium staining (intracellular ROS) in hypoxic and normoxic PC12 cell cultures were measured following 1 h of Argon hypoxia and 24 h of re-oxygenation in the absence and in the presence of various concentrations of (-)deprenyl. Deltapsi(M) shifted to lower values following hypoxia/re-oxygenation and all cells had decreased and uniform Deltapsi(M) levels. The amount of ROS increased. Following 24 h of treatment with various concentrations of (-)deprenyl during the re-oxygenation period, survival increased, the Deltapsi(M) shift caused by oxygen deprivation was reversed and the peroxy radical levels decreased except for at 10(-3) M.

The antipsoriatic drug anthralin accumulates in keratinocyte mitochondria, dissipates mitochondrial membrane potential, and induces apoptosis through a pathway dependent on respiratory competent mitochondria

Anthralin is a potent topical drug, inducing clearance of psoriatic plaques. Anthralin disrupts mitochondrial function and structure, but its mechanism of action remains undefined. This study aimed to determine whether anthralin induced keratinocyte apoptosis as well as to investigate molecular mechanisms and the role of mitochondria. We studied human keratinocytes and human 143B rho(0) cells, which lack mitochondrial DNA and a functional respiratory chain. We show that anthralin disrupts mitochondrial membrane potential (DeltaPsim) and causes endogenous cytochrome c release, resulting in the activation of caspase-3 and characteristic morphological changes of apoptosis. Disruption of DeltaPsim and cytochrome c release were independent of mitochondrial permeability transition or caspase activation. Human 143B rho(0) cells were resistant to anthralin-induced cell death, disruption of DeltaPsim, and cytochrome c release compared with the isogenic 143B rho+ cell line. Using the intrinsic fluorescence of anthralin, rapid accumulation within mitochondria was observed independent of DeltaPsim. Using assays that measure individual respiratory chain complexes, we show that anthralin specifically interacts with ubiquinone pool. These data indicate that anthralin induces apoptosis through a novel mitochondrial pathway dependent on oxidative respiration and involving electron transfer with the ubiquinone pool. These studies identify keratinocyte apoptosis as a potentially important mechanism involved in the clearance of psoriasis.

No effects of intermittent 50 Hz EMF on cytoplasmic free calcium and on the mitochondrial membrane potential in human diploid fibroblasts

The recently described increase in DNA strand breaks of cultured human diploid fibroblasts after intermittent exposure to extremely-low-frequency electromagnetic fields (ELF-EMF) of more than about 70 microT ELF-EMF is difficult to explain by a direct induction of covalent bond disruption. Therefore the hypothesis has been tested that ELF-EMF-induced DNA strand breaks might be mediated by cellular processes that cause alteration of the intracellular concentration of free calcium ([Ca2+]i) and/or the membrane potential (DeltaPsi(m)). [Ca2+]i was determined by the ratiometric fura-2 technique. Changes in DeltaPsi(m) were assessed by using the potential-dependent lipophilic cationic probe JC-1. Human fibroblasts were exposed to intermittent ELF-EMF (50 Hz, 1000 microT). Although exposure of fiboblasts to ELF-EMF resulted in a highly significant increase in DNA strand breaks as determined by the comet assay, no effect on JC-1 fluorescence emission or on [Ca2+]i has been observed when comparing exposed with sham-exposed cells. Therefore, it is suggested that ELF-EMF-induced DNA strand breaks are unlikely to be caused by intracellular changes that affect [Ca2+]i and/or DeltaPsi(m).

Apoptosis in primary lymphoid organs with aging

Age-associated changes in the immune system are responsible for an increased likelihood of infection, autoimmune diseases, and cancer in the elderly. Immunosenescence is characterized by reduced levels of the peripheral naive T cell pool derived from thymus and the loss of immature B lineage cells in the bone marrow. Primary lymphoid organs, i.e., bone marrow and thymus, exhibit a loss of cellularity with age, which is especially dramatic in the thymus. A summary of major changes associated with aging in primary lymphoid organs is described in this article. The participation of apoptosis in cell loss in the immune system, a change associated with age, as well as a description of molecular machinery involved, is presented. Finally, the involvement of different hormonal and non-hormonal agents in counteracting apoptosis in thymus and bone marrow during aging is explained. Here, we underlie the important role of glucocorticoids as immunodepressors and melatonin as an immunostimulatory agent.

The K+ channel openers diazoxide and NS1619 induce depolarization of mitochondria and have differential effects on cell Ca2+ in CD34+ cell line KG-1a

OBJECTIVE

Mitochondrial membrane potential (deltaPsim) and intracellular Ca2+ play a crucial role in growth and differentiation in hemopoiesis. Some potassium channel openers such as diazoxide have the capacity to elevate cytosolic Ca2+ and depolarize mitochondria in cardiomyocytes. To clarify if such substances have effects on hemopoietic cells we investigated the commonly used opener of the mitoK(ATP) channel, diazoxide, and the opener of BK channels, NS1619, for their potential to depolarize mitochondria, elevate cytosolic Ca2+, and induce apoptosis in the hemopoietic CD34+ cell line KG-1a.

METHODS

Fluorescent probes were used to investigate deltaPsim, free Ca2+, and apoptosis (JC-1, fluo-3-AM and annexin V-FITC) by flow cytometry. To measure deltaPsim with JC-1 in glycoprotein P+ cells we used an improved dye loading technique with verapamil.

RESULTS

NS1619 induced stronger dose-dependent mitochondrial depolarizations than diazoxide. Depolarization was independent from caspase activation and could also be induced when the driving force for K+ out of cells was near 0 mV. In Ca2+ free solutions NS1619 induced stronger Ca2+ elevations than diazoxide and elevated Ca2+ also after Ca2+ depletion of the endoplasmatic reticulum with caffeine. NS1619 did not enhance the Ca2+ elevation induced by ionophores (CCCP, valinomycin) that depolarize mitochondria. Both agents were weak inducers of apoptosis.

CONCLUSION

Diazoxide has similar effects in CD34+ cells as described for muscle or nerve cells. In accordance to the single channel conductance of mitoK(ATP) and BK channels, NS1619 is a more potent inducer of mitochondrial depolarization than diazoxide. NS1619 releases Ca2+ from an intracellular pool that is insensitive to caffeine but depends strongly on deltaPsim.

Age-dependent changes in the susceptibility to apoptosis of peripheral blood CD4+ and CD8+ T lymphocytes with virgin or memory phenotype

Susceptibility to apoptosis changes with age and most of the available data on lymphocytes refer to mitogen stimulated cells. We studied this susceptibility in quiescent, purified CD4+ or CD8+ T cells from a group of Italian old people compared with a group of young people. We found that an apoptotic agent such as 2-deoxy-D-ribose (dRib), which acts via glutathione depletion and oxidative stress, was more effective in CD4+ T cells from young donors, while no difference was found in CD8+ T cells. On the contrary, another agent such as TNF-alpha, which acts via receptor engagement, was more effective in CD8+ T cells from old subjects, and no difference was found in CD4+ T cells. When marker of activation-memory were investigated, no difference between young and old subjects was found when dRib was used. Differently, when TNF-alpha was used, memory and activated CD4+ T cells from old donors were less sensitive than younger counterparts, while memory CD8+ T cells from old donors were more sensitive than younger counterparts. This suggests that age-related changes in susceptibility to apoptosis of resting T cells largely depend on the type of the apoptotic stimulus which is used as well as on the memory phenotype of the cells. These results may also account, at least in part, for the deep remodelling of T cell repertoire that occurs during ageing.

Apoptosis-resistant phenotype in HL-60-derived cells HCW-2 is related to changes in expression of stress-induced proteins that impact on redox status and mitochondrial metabolism

The onset of resistance to drug-induced apoptosis of tumour cells is a major problem in cancer therapy. We studied a drug-selected clone of promyelocytic HL-60 cells, called HCW-2, which display a complex resistance to a wide variety of apoptosis-inducing agents and we found that these cells show a dramatic increase in the expression of heat shock proteins (Hsps) 70 and 27, while the parental cell line does not. It is known that stress proteins such as Hsps can confer resistance to a variety of damaging agents other than heat shock, such as TNF-alpha, monocyte-induced cytotoxicity, and also play a role in resistance to chemotherapy. This elevated expression of Hsps is paralleled by an increased activity of mitochondrial metabolism and pentose phosphate pathway, this latter leading to high levels of glucose-6-phosphate dehydrogenase and, consequently, of glutathione. Thus, the apoptotic-deficient phenotype is likely because of the presence of high levels of stress response proteins and GSH, which may confer resistance to apoptotic agents, including chemotherapy drugs. Moreover, the fact that in HCW-2 cells Hsp70 are mainly localised in mitochondria may account for the increased performances of mitochondrial metabolism. These observations could have some implications for the therapy of cancer, and for the design of combined strategies that act on antioxidant defences of the neoplastic cell.

Chromium(III)-induced apoptosis of lymphocytes: death decision by ROS and Src-family tyrosine kinases

Apoptosis is an active process induced by a variety of physiological and external stimuli, in which elimination of damaged cells are effected through a genetically controlled process. In this study, we have examined the mechanism of chromium(III) [Cr(III)]-induced cytotoxicity with respect to its relationship to oxidative stress. Morphology, flow cytometry, and DNA fragmentation studies show that tris-(1,10-phenanthroline)chromium(III) [Cr(III)-phen], tris-(2,2'-bipyridyl)chromium(III) [Cr(III)-bpy], trans-diaqua[1,2-bis(salicylideneamino)ethanechromium(III)] [Cr(III)-salen], and trans-diaqua[1,3-bis(salicylideneamino)propanechromium(III)] [Cr(III)-salprn] induced apoptosis of lymphocytes. Pentaammineaquachromium(III) [Cr(III)-hpa] does not induce apoptosis. Apoptosis induced by these complexes involves the generation of reactive oxygen species (ROS) as seen by increased fluorescence of dichloroflourescein (DCF) observed through flow cytometry. Pretreatment of lymphocytes with antioxidants completely abrogate apoptosis. Cr(III) treatment also increased the expression and activation of Src-family tyrosine kinases viz. p56lck, p59fyn, and p53/56lyn, as seen by immunoblotting and immune complex kinase assay. PP2, a selective Src-family tyrosine kinase inhibitor, abolishes apoptosis, indicating that Src-family tyrosine kinases are directly involved in eliciting apoptosis. Interestingly, a one-to-one correlation between the expression of Src-family tyrosine kinases and ROS is observed, since antioxidants pretreatment inhibits the expression and the activation of these kinases. These results further indicate that Cr(III)-induced apoptosis is mediated through production of ROS, which in turn activates the Src-family tyrosine kinases. The increased activation of Src-family tyrosine kinases may be a mechanism involved in apoptosis of lymphocytes elicited by various other physiological stimuli that exploit ROS as a second messenger.

Permeability transition-independent release of mitochondrial cytochrome c induced by valinomycin

To examine whether valinomycin induces a mitochondrial permeability transition (PT), we investigated its effects on mitochondrial functions under various conditions. The acceleration of mitochondrial respiration and swelling, induced by valinomycin, were found to be insensitive to inhibitors of the ordinary PT, indicating that valinomycin does not induce the ordinary PT. Results of experiments using mitochondria isolated from transgenic mice expressing human bcl-2 also supported this conclusion. Furthermore, evidence for induction of PT pores by valinomycin was not obtained by either electron microscopic analysis of mitochondrial configurations or by measurement of the permeability of the inner mitochondrial membrane by use of polyethylene glycol. However, valinomycin did induce a significant release of cytochrome c, and thus it may be a nice tool to study the processes of mitochondrial cytochrome c release.

Mitochondria in the pathogenesis of lipodystrophy induced by anti-HIV antiretroviral drugs: actors or bystanders?

Effective therapies are now available that can stop the progression of HIV infection and significantly delay the onset of AIDS. The "highly active antiretroviral therapy" (HAART) is a combination of potent antiretroviral drugs such as viral protease inhibitors or nucleoside-analogue reverse-transcriptase inhibitors, that has a variety of serious side effects, including lipodystrophy, a pathology characterized by accumulation of visceral fat, breast adiposity, cervical fat-pads, hyperlipidemia, insulin resistance as well as fat wasting in face and limbs. There is still an open debate that concerns the precise responsibility of HAART as well as metabolic pathways and mechanisms that are involved in the onset of lipodystrophy. The similarities with multiple symmetric lipomatosis (MSL), in which mitochondria impairment plays a crucial role, lead to the hypothesis that drug-induced damages to mitochondrial DNA are able to alter mitochondria functionality to an extent that is similar to what occurs in MSL. In addition, several evidences indicate that HAART is also linked to a deregulated production of tumour necrosis factor-alpha, which uses mitochondria as intracellular targets. In this paper, we review data concerning the role of mitochondria in the pathogenesis of lipodystrophy, and advance a unifying hypothesis involving either direct or indirect effects of the drugs employed during HAART.

Mitochondrial permeability transition induced by the anticancer drug etoposide

Etoposide (VP-16) is widely used for the treatment of several forms of cancer. The cytotoxicity of VP-16 has been assigned to the induction of apoptotic cell death but the signaling pathway for VP-16-induced apoptosis is essentially unknown. There is some evidence that this process depends on events associated with the loss of mitochondrial membrane potential (Delta Psi) and/or release of apoptogenic factors, putatively as a consequence of mitochondrial permeability transition (MPT) induction. This work evaluates the interference of VP-16 with MPT in vitro, which is characterized by the Ca(2+)-dependent depolarization of Delta Psi, the release of matrix Ca(2+) and by extensive swelling of mitochondria. Delta Psi depolarization and Ca(2+) release were measured with ion-selective electrodes, and mitochondrial swelling was monitored spectrophotometrically. Incubation of rat liver mitochondria with VP-16 results in a concentration-dependent induction of MPT, evidenced by an increased sensitivity to Ca(2+)-induced swelling, depolarization of Delta Psi, Ca(2+) release by mitochondria and stimulation of state 4 oxygen consumption. All of these effects are prevented by preincubating the mitochondria with cyclosporine A, a potent and specific inhibitor of the MPT. Therefore, VP-16 increases the sensitivity of isolated mitochondria to the Ca(2+)-dependent induction of the MPT. Together, these data provide a possible mechanistic explanation for the previously reported effects of VP-16 on apoptosis induction.

Extensive DNA fragmentation in oxyphilic cell lesions of the thyroid

The in situ end-labeling (ISEL) method demonstrates DNA fragmentation, commonly regarded as a marker of apoptosis. We investigated by the ISEL procedure a series of 52 thyroid lesions, including 24 lesions of mitochondrion-rich oxyphilic cells, both benign and malignant, and 28 non-oxyphilic control tumors. A high percentage of nuclear ISEL staining (approximating to 100% in most cases) was observed in the vast majority of oxyphilic cells from both adenomas and carcinomas, in the absence of morphological apoptotic changes and with no immunocytochemical evidence of caspase activation. This pattern of DNA fragmentation was not observed in non-oxyphilic lesions and was confirmed in total extracted DNA. Moreover, a peculiar cytoplasmic staining was also observed in oxyphilic cells from both benign and malignant lesions, probably related to abnormal fragmentation of mitochondrial DNA. Similar staining patterns were detected in oxyphilic cell tumors of other organs (parathyroids, salivary glands, and kidneys). These findings are consistent with an extensive DNA fragmentation peculiar to oxyphilic cells, which is not directly related to apoptosis and whose origin and biological significance are presently unknown.

Mitochondria, aging and longevity--a new perspective

A new perspective is emerging indicating that mitochondria play a critical role in aging not only because they are the major source and the most proximal target of reactive oxygen species, but also because they regulate stress response and apoptosis. Recent literature indicates that, in response to stress, a variety of molecules translocate to and localise in mitochondria. These molecules are likely to interact with each other, in order to mediate mitochondria/nucleus cross-talk and to regulate apoptosis. We surmise that an integration of signals in multimolecular complexes occurs at mitochondrial level. These phenomena can be of critical importance for human aging and longevity.

Relationship between cell cycle changes and variations of the mitochondrial membrane potential induced by etoposide

Etoposide, a clinically useful anticancer drug, is a potent inhibitor of topoisomerase II. The DNA strand breaks caused by this epipodophyllotoxin lead to apoptotic death of tumor cells. Flow cytometry was used to investigate the relationship between the effects of the drug on the cell cycle of human leukemia HL-60 cells and the variations of the mitochondrial transmembrane potential (DeltaPsi(mt)). Three cationic fluorescent probes, DiOC(6), JC-1, and TMRM, were used to measure drug-induced changes of DeltaPsi(mt). In all three cases, we found that the arrest in the G2/M phase of the cells treated with 0.5 microM etoposide is associated with an increase in the potential of mitochondrial membranes whereas treatment with a tenfold higher drug concentration trigger massive apoptosis and a collapse of DeltaPsi(mt). DNA fragmentation (TUNEL assay) and externalization of phosphatidylserine residues in the outer leaflet of the plasma membrane (annexin V binding) were measured to characterize the apoptotic cell population.

Mitochondrial heterogeneity during staurosporine-induced apoptosis in HL60 cells: analysis at the single cell and single organelle level

BACKGROUND

Apoptosis is a complex phenomenon during which several events occur. A growing interest exists on the role and functionality of mitochondria during this type of cell death. The responsibility of modifications in mitochondrial membrane potential (Delta Psi) in triggering apoptosis is under investigation.

METHODS

We evaluated Delta Psi changes in HL60 cells treated with staurosporine (STS). Flow cytometry and confocal microscopy have been used to analyze samples stained with two Delta Psi-sensitive probes, JC-1 and MitoTrackertrade mark Red CMXRos.

RESULTS

At the cellular level, we found heterogeneic behavior. Indeed, after STS treatment, some cells displayed typical markers of apoptosis and a collapse in Delta Psi. Others were apoptotic with no changes in Delta Psi, others changed Delta Psi without being apoptotic, and others were healthy. The same heterogeneic response to STS was found at the single organelle level. In a given cell, some mitochondria were depolarized whereas others were not.

CONCLUSION

In this model of apoptosis, changes in Delta Psi can be different among cells of the same type and among different organelles of the same cell. The collapse in Delta Psi is thus a heterogeneic phenomenon that seems to be an ancillary event following the irreversible phase of the apoptotic process.