[The investigation into dynamics of depression level and the quality of life in the patients after myocardial infarction under the influence of the program of physical rehabilitation]

The evaluation of the psychological condition of the patients who survived myocardial infarction and its correction taking into consideration the peculiar features of the individual reaction to the disease are the indispensable components of physical rehabilitation. The present article was designed to report the results of the study on the influence of the authors' physical rehabilitation program on the prevalence of depression and the life quality characteristics of the patients treated after myocardial infarction during the follow-up period.

MATERIAL AND METHODS

The patients of the main group (n=30) were enrolled in the original physical rehabilitation program. Those comprising the group of comparison (n=30) were given a course of rehabilitation in accordance with the scheme that had been recommended by the leading scientists and generally accepted in the Ukraine for the patients recovering after myocardial infarction under conditions of the out-patient clinics, spa and health resort facilities or convalescent centers.

RESULTS AND DISCUSSION

The study has demonstrated that the patients of both groups exhibited positive dynamics of their clinical condition (e.g. the decrease in the number of depressed subjects); however, this tendency was more pronounced in the main group where the number of the patients experiencing depression decreased by 61% at the end of the observation period (р<0,05). The analysis of the causes of anxiety associated with this pathology in the individual patients has demonstrated that the main factors responsible for the deterioration of the quality of life were the necessity of treatment, the limitations on the everyday physical activity, and the feeling of emotional tension. Moreover, the positive dynamics of the characteristics being evaluated was documented in the patients of the main group which gives reason to conclude that the program of physical rehabilitation proposed by the authors for the treatment of the patients after myocardial infarction is highly efficient during the follow-up period. Suffice it to say that 23 (76,7%) patients of the main group did not consider their lives as of poor quality by the end of the study period (р<0,01). There were only 18 such patients in the control group (р<0,05).

CONCLUSION

The results of the present study provide a basis for recommending the proposed authors' program of physical rehabilitation for the patients treated after myocardial infarction with the emphasis on the necessity to do special dynamic exercises for the cervical and thoraco-cervical spine segments to be supplemented by the relevant educational program.

Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry

Although marine oysters contain abundant amounts of ether-linked aminophospholipids, the structural identification of the various molecular species has not been reported. We developed a normal-phase silica liquid chromatography/negative-ion electrospray ionization/quadrupole multiple-stage linear ion-trap mass spectrometric (NPLC-NI-ESI/Q-TRAP-MS(3)) method for the structural elucidation of ether molecular species of serine and ethanolamine phospholipids from marine oysters. The major advantages of the approach are (i) to avoid incorrect selection of isobaric precursor ions derived from different phospholipid classes in a lipid mixture, and to generate informative and clear MS(n) product ion mass spectra of the species for the identification of the sn-1 plasmanyl or plasmenyl linkages, and (ii) to increase precursor ion intensities by "concentrating" lipid molecules of each phospholipid class for further structural determination of minor molecular species. Employing a combination of NPLC-NI-ESI/MS(3) and NPLC-NI-ESI/MS(2), we elucidated, for the first time, the chemical structures of docosahexaenoyl and eicosapentaenoyl plasmenyl phosphatidylserine (PS) species and differentiated up to six isobaric species of diacyl/alkylacyl/alkenylacyl phosphatidylethanolamine (PE) in the US pacific oysters. The presence of a high content of both omega-3 plasmenyl PS/plasmenyl PE species and multiple isobaric molecular species isomers is the noteworthy characteristic of the marine oyster. The simple and robust NPLC-NI-ESI/MS(n)-based methodology should be particularly valuable in the detailed characterization of marine lipid dietary supplements with respect to omega-3 aminophospholipids.

Succinobucol induces apoptosis in vascular smooth muscle cells

Probucol inhibits the proliferation of vascular smooth muscle cells in vitro and in vivo, and the drug reduces intimal hyperplasia and atherosclerosis in animals via induction of heme oxygenase-1 (HO-1). Because the succinyl ester of probucol, succinobucol, recently failed as an antiatherogenic drug in humans, we investigated its effects on smooth muscle cell proliferation. Succinobucol and probucol induced HO-1 and decreased cell proliferation in rat aortic smooth muscle cells. However, whereas inhibition of HO-1 reversed the antiproliferative effects of probucol, this was not observed with succinobucol. Instead, succinobucol but not probucol induced caspase activity and apoptosis, and it increased mitochondrial oxidation of hydroethidine to ethidium, suggestive of the participation of H(2)O(2) and cytochrome c. Also, succinobucol but not probucol converted cytochrome c into a peroxidase in the presence of H(2)O(2), and succinobucol-induced apoptosis was decreased in cells that lacked cytochrome c or a functional mitochondrial complex II. In addition, succinobucol increased apoptosis of vascular smooth muscle cells in vivo after balloon angioplasty-mediated vascular injury. Our results suggest that succinobucol induces apoptosis via a pathway involving mitochondrial complex II, H(2)O(2), and cytochrome c. These unexpected results are discussed in light of the failure of succinobucol as an antiatherogenic drug in humans.

Regulation of plasma cholesterol esterification by sphingomyelin: effect of physiological variations of plasma sphingomyelin on lecithin-cholesterol acyltransferase activity

Although sphingomyelin (SM) is the most abundant phospholipid in the plasma, next to phosphatidylcholine (PC), its physiological function in plasma is unclear. Here we employed plasma from various genetic models of mice which naturally differ in their plasma SM/PC ratios, to study the role of SM as a modulator of LCAT, the enzyme responsible for HDL maturation and the synthesis of cholesteryl esters (CE) in normal plasma. Serine palmitoyltransferase deficient mice, and SM synthase deficient mice, both of which have below normal SM/PC ratios, showed significantly elevated LCAT activities when assayed with the endogenous substrates. On the other hand, LDL receptor knockout mice, and apo E knockout mice, both of which have high SM/PC ratios, had markedly reduced (-80%) LCAT activities. The LCAT levels in plasma, as assayed with an exogenous substrate, were similar in all groups, except for a 45% decrease in apo E knockout mice. Plasma samples with high SM/PC ratios had lower percentage of 20:4, 22:5, and 22:6 CE all of which are formed by LCAT, and a higher percentage of the atherogenic 18:1 CE which is mainly derived from the action of liver ACAT, showing that in vivo, the contribution of LCAT to plasma CE is reduced while that of liver ACAT is increased. These results show that SM is a physiological modulator of LCAT activity as well as plasma CE composition, and this may contribute to the previously reported pro-atherogenic effect of high plasma SM levels.

A manganese-porphyrin complex decomposes H(2)O(2), inhibits apoptosis, and acts as a radiation mitigator in vivo

Ionizing radiation triggers mitochondrial overproduction of H(2)O(2) with concomitant induction of intrinsic apoptosis, whereby clearance of H(2)O(2) upon overexpression of mitochondrial catalase increases radioresistance in vitro and in vivo. As an alternative to gene therapy, we tested the potential of Mn((III))-porphyrin complexes to clear mitochondrial H(2)O(2). We report that triphenyl-[(2E)-2-[4-[(1Z,4Z,9Z,15Z)-10,15,20-tris(4-aminophenyl)-21,23-dihydroporphyrin-5-yl]phenyl]iminoethyl]phosphonium-Mn((III)) compartmentalizes preferentially into mitochondria of mouse embryonic cells, reacts with H(2)O(2), impedes γ-ray-induced mitochondrial apoptosis, and increases the survival of mice exposed to whole body irradiation with γ-rays.

A mitochondria-targeted inhibitor of cytochrome c peroxidase mitigates radiation-induced death

The risk of radionuclide release in terrorist acts or exposure of healthy tissue during radiotherapy demand potent radioprotectants/radiomitigators. Ionizing radiation induces cell death by initiating the selective peroxidation of cardiolipin in mitochondria by the peroxidase activity of its complex with cytochrome c leading to release of haemoprotein into the cytosol and commitment to the apoptotic program. Here we design and synthesize mitochondria-targeted triphenylphosphonium-conjugated imidazole-substituted oleic and stearic acids that blocked peroxidase activity of cytochrome c/cardiolipin complex by specifically binding to its haem-iron. We show that both compounds inhibit pro-apoptotic oxidative events, suppress cyt c release, prevent cell death, and protect mice against lethal doses of irradiation. Significant radioprotective/radiomitigative effects of imidazole-substituted oleic acid are observed after pretreatment of mice from 1 h before through 24 h after the irradiation.

A high-throughput screening assay of ascorbate in brain samples

Ascorbate is a vital reductant/free radical scavenger in the CNS, whose content defines - to a large extent - the redox status and the antioxidant reserves. Quick, reliable and specific methods for its measurement in brain samples are highly desirable. We have developed a new high-throughput screening assay for measurements of ascorbate using a fluorescence plate-reader. This assay is based on a direct reaction of ascorbate with a nitroxide radical conjugated with a fluorogenic acridine moiety, 4-((9-acridinecarbonyl)-amino)-2,2,6,6-tetramethylpiperidine-1-oxyl radical (AC-TEMPO), yielding fluorescent hydroxylamine product (AC-TEMPO-H). The reaction was monitored over time using fluorescence and electron spin resonance techniques. The appearance of fluorescent AC-TEMPO-H was linear within the range of 3.75-75μM AscH(-) in the sample (0.5-10μM AscH(-) in the well). Assay was validated with high performance liquid chromatography method. The concentration of ascorbate in murine tissue samples, including brain samples after traumatic brain injury and hemorrhagic shock, was measured.

Carbon nanotubes degraded by neutrophil myeloperoxidase induce less pulmonary inflammation

We have shown previously that single-walled carbon nanotubes can be catalytically biodegraded over several weeks by the plant-derived enzyme, horseradish peroxidase. However, whether peroxidase intermediates generated inside human cells or biofluids are involved in the biodegradation of carbon nanotubes has not been explored. Here, we show that hypochlorite and reactive radical intermediates of the human neutrophil enzyme myeloperoxidase catalyse the biodegradation of single-walled carbon nanotubes in vitro, in neutrophils and to a lesser degree in macrophages. Molecular modelling suggests that interactions of basic amino acids of the enzyme with the carboxyls on the carbon nanotubes position the nanotubes near the catalytic site. Importantly, the biodegraded nanotubes do not generate an inflammatory response when aspirated into the lungs of mice. Our findings suggest that the extent to which carbon nanotubes are biodegraded may be a major determinant of the scale and severity of the associated inflammatory responses in exposed individuals.

A mitochondria-targeted triphenylphosphonium-conjugated nitroxide functions as a radioprotector/mitigator

Removal of excessive mitochondrial reactive oxygen species by electron scavengers and antioxidants is a promising therapeutic strategy to reduce the detrimental effects of radiation exposure. Here we exploited triphenylphosphonium (TPP) cation as a means to target nitroxide radicals to mitochondria. We synthesized a library of TPP-conjugated nitroxides and tested their radioprotective effects in gamma-irradiated mouse embryo cells and human epithelial BEAS-2B cells. Cells were incubated with conjugates either before or after irradiation. We found that [2-(1-oxyl-2,2,6,6-tetramethyl-piperidin-4-ylimino)-ethyl]-triphenyl-phosphonium (TPEY-Tempo) significantly blocked radiation-induced apoptosis as revealed by externalization of phosphatidylserine on the cell surface and inhibition of cytochrome c release from mitochondria. Using electron paramagnetic resonance, we showed that TPEY-Tempo was integrated into cells and mitochondria, where it underwent one-electron reduction to hydroxylamine. TPEY-Tempo acted as an electron scavenger that prevented superoxide generation and cardiolipin oxidation in mitochondria. Finally, TPEY-Tempo increased the clonogenic survival rate of irradiated cells. The cellular integration efficiencies of nonradioprotective TPP conjugates, including Mito-Tempo (Alexis, San Diego, CA), were markedly lower, although these homologues were integrated into isolated succinate-energized mitochondria to a similar extent as TPEY-Tempo. We conclude that mitochondrial targeting of TPP-conjugated nitroxides represents a promising approach for the development of novel radioprotectors.

Heterolytic reduction of fatty acid hydroperoxides by cytochrome c/cardiolipin complexes: antioxidant function in mitochondria

Cytochrome c (cyt c), a mitochondrial intermembrane electron shuttle between complexes III and IV, can, upon binding with an anionic phospholipid, cardiolipin (CL), act as a peroxidase that catalyzes cardiolipin oxidation. H(2)O(2) was considered as a source of oxidative equivalents for this reaction, which is essential for programmed cell death. Here we report that peroxidase cyt c/CL complexes can utilize free fatty acid hydroperoxides (FFA-OOH) at exceptionally high rates that are approximately 3 orders of magnitude higher than for H(2)O(2). Similarly, peroxidase activity of murine liver mitochondria was high with FFA-OOH. Using EPR spin trapping and LC-MS techniques, we have demonstrated that cyt c/CL complexes split FFA-OOH predominantly via a heterolytic mechanism, yielding hydroxy-fatty acids, whereas H(2)O(2) (and tert-butyl hydroperoxide, t-BuOOH) undergo homolytic cleavage. Computer simulations have revealed that Arg(38) and His(33) are important for the heterolytic mechanism at potential FFA-OOH binding sites of cyt c (but not for H(2)O(2) or t-BuOOH). Regulation of FFA-OOH metabolism may be an important function of cyt c that is associated with elimination of toxic FFA-OOH and synthesis of physiologically active hydroxy-fatty acids in mitochondria.

Mitochondrial targeting of electron scavenging antioxidants: Regulation of selective oxidation vs random chain reactions

Effective regulation of highly compartmentalized production of reactive oxygen species and peroxidation reactions in mitochondria requires targeting of small molecule antioxidants and antioxidant enzymes into the organelles. This review describes recently developed approaches to mitochondrial targeting of small biologically active molecules based on: (i) preferential accumulation in mitochondria because of their hydrophobicity and positive charge (hydrophobic cations), (ii) binding with high affinity to an intra-mitochondrial constituent, and (iii) metabolic conversions by specific mitochondrial enzymes to reveal an active entity. In addition, targeted delivery of antioxidant enzymes via expression of leader sequences directing the proteins into mitochondria is considered. Examples of successful antioxidant and anti-apoptotic protection based on the ability of targeted cargoes to inhibit cytochrome c-catalyzed peroxidation of a mitochondria-specific phospholipid cardiolipin, in vitro and in vivo are presented. Particular emphasis is placed on the employment of triphenylphosphonium- and hemi-gramicidin S-moieties as two effective vehicles for mitochondrial delivery of antioxidants.

Radioprotection by short-term oxidative preconditioning: role of manganese superoxide dismutase

Manganese superoxide dismutase (MnSOD) is vital to the protection of mitochondria and cells against oxidative stress. Earlier, we demonstrated that catalytically active homo-tetramer of MnSOD can be stabilized by oxidative cross-linking. Here we report that this effect may be translated into increased radioresistance of mouse embryonic cells (MECs) by pre-exposure to oxidative stress. Pre-treatment of MECs with antimycin A, rotenone or H(2)O(2) increased their survival after irradiation. Using MnSOD siRNA, we show that MECs with decreased MnSOD levels displayed a lowered ability to preconditioning. Thus oxidative preconditioning may be used for targeted regulation of MnSOD.

Cytochrome c/cardiolipin relations in mitochondria: a kiss of death

Recently, phospholipid peroxidation products gained a reputation as key regulatory molecules and participants in oxidative signaling pathways. During apoptosis, a mitochondria-specific phospholipid, cardiolipin (CL), interacts with cytochrome c (cyt c) to form a peroxidase complex that catalyzes CL oxidation; this process plays a pivotal role in the mitochondrial stage of the execution of the cell death program. This review is focused on redox mechanisms and essential structural features of cyt c's conversion into a CL-specific peroxidase that represent an interesting and maybe still unique example of a functionally significant ligand change in hemoproteins. Furthermore, specific characteristics of CL in mitochondria--its asymmetric transmembrane distribution and mechanisms of collapse, the regulation of its synthesis, remodeling, and fatty acid composition--are given significant consideration. Finally, new concepts in drug discovery based on the design of mitochondria-targeted inhibitors of cyt c/CL peroxidase and CL peroxidation with antiapoptotic effects are presented.

Mitochondria-targeted disruptors and inhibitors of cytochrome c/cardiolipin peroxidase complexes: a new strategy in anti-apoptotic drug discovery

The critical role of mitochondria in programmed cell death leads to the design of mitochondriotropic agents as a strategy in regulating apoptosis. For anticancer therapy, stimulation of proapoptotic mitochondrial events in tumor cells and their suppression in surrounding normal cells represents a promising paradigm for new therapies. Different approaches targeting regulation of components of mitochondrial antioxidant system such as Mn-SOD demonstrated significant antitumor efficiency, particularly in combination therapy. This review is focused on a newly discovered early stage of mitochondria-dependent apoptosis - oxidative lipid signaling involving a mitochondria-specific phospholipid cardiolipin (CL). Cytochrome c (cyt c) acts as a CL-specific peroxidase very early in apoptosis. At this stage, the hostile events are still secluded within the mitochondria and do not reach the cytosolic targets. CL oxidation process is required for the release of pro-apoptotic factors into the cytosol. Manipulation of cyt c interactions with CL, inhibition of peroxidase activity, and prevention of CL peroxidation are prime targets for the discovery of anti-apoptotic drugs acting before the "point-of-no-return" in the fulfillment of the cell death program. Therefore, mitochondria-targeted disruptors and inhibitors of cyt c/CL peroxidase complexes and suppression of CL peroxidation represent new strategies in anti-apoptotic drug discovery.

Mitochondria-targeted (2-hydroxyamino-vinyl)-triphenyl-phosphonium releases NO(.) and protects mouse embryonic cells against irradiation-induced apoptosis

Generation of reactive oxygen species by damaged respiratory chain followed by the formation of cytochrome c (cyt c)-cardiolipin (CL) complex with peroxidase activity are early events in apoptosis. By quenching the peroxidase activity of cyt c-CL complexes in mitochondria, nitric oxide can exert anti-apoptotic effects. Therefore, mitochondria-targeted pro-drugs capable of gradual nitric oxide radical (NO*) release are promising radioprotectants. Here we demonstrate that (2-hydroxyamino-vinyl)-triphenyl-phosphonium effectively accumulates in mitochondria, releases NO* upon mitochondrial peroxidase reaction, protects mouse embryonic cells from irradiation-induced apoptosis and increases their clonogenic survival after irradiation. We conclude that mitochondria-targeted peroxidase-activatable NO-donors represent a new interesting class of radioprotectors.

Peroxidase mechanism of lipid-dependent cross-linking of synuclein with cytochrome C: protection against apoptosis versus delayed oxidative stress in Parkinson disease

Damage of presynaptic mitochondria could result in release of proapoptotic factors that threaten the integrity of the entire neuron. We discovered that alpha-synuclein (Syn) forms a triple complex with anionic lipids (such as cardiolipin) and cytochrome c, which exerts a peroxidase activity. The latter catalyzes covalent hetero-oligomerization of Syn with cytochrome c into high molecular weight aggregates. Syn is a preferred substrate of this reaction and is oxidized more readily than cardiolipin, dopamine, and other phenolic substrates. Co-localization of Syn with cytochrome c was detected in aggregates formed upon proapoptotic stimulation of SH-SY5Y and HeLa cells and in dopaminergic substantia nigra neurons of rotenone-treated rats. Syn-cardiolipin exerted protection against cytochrome c-induced caspase-3 activation in a cell-free system, particularly in the presence of H(2)O(2). Direct delivery of Syn into mouse embryonic cells conferred resistance to proapoptotic caspase-3 activation. Conversely, small interfering RNA depletion of Syn in HeLa cells made them more sensitive to dopamine-induced apoptosis. In human Parkinson disease substantia nigra neurons, two-thirds of co-localized Syn-cytochrome c complexes occurred in Lewy neurites. Taken together, these results indicate that Syn may prevent execution of apoptosis in neurons through covalent hetero-oligomerization of cytochrome c. This immediate protective function of Syn is associated with the formation of the peroxidase complex representing a source of oxidative stress and postponed damage.

Phosphatidylserine targets single-walled carbon nanotubes to professional phagocytes in vitro and in vivo

Broad applications of single-walled carbon nanotubes (SWCNT) dictate the necessity to better understand their health effects. Poor recognition of non-functionalized SWCNT by phagocytes is prohibitive towards controlling their biological action. We report that SWCNT coating with a phospholipid "eat-me" signal, phosphatidylserine (PS), makes them recognizable in vitro by different phagocytic cells - murine RAW264.7 macrophages, primary monocyte-derived human macrophages, dendritic cells, and rat brain microglia. Macrophage uptake of PS-coated nanotubes was suppressed by the PS-binding protein, Annexin V, and endocytosis inhibitors, and changed the pattern of pro- and anti-inflammatory cytokine secretion. Loading of PS-coated SWCNT with pro-apoptotic cargo (cytochrome c) allowed for the targeted killing of RAW264.7 macrophages. In vivo aspiration of PS-coated SWCNT stimulated their uptake by lung alveolar macrophages in mice. Thus, PS-coating can be utilized for targeted delivery of SWCNT with specified cargoes into professional phagocytes, hence for therapeutic regulation of specific populations of immune-competent cells.

Cardiolipin deficiency leads to decreased cardiolipin peroxidation and increased resistance of cells to apoptosis

Cardiolipin (CL), a unique mitochondrial phospholipid synthesized by CL synthase (CLS), plays important, yet not fully understood, roles in mitochondria-dependent apoptosis. We manipulated CL levels in HeLa cells by knocking down CLS using RNA interference and selected a clone of CL-deficient cells with approximately 45% of its normal content. ESI-MS analysis showed that the CL molecular species were the same in CL-deficient and CL-sufficient cells. CL deficiency did not change mitochondrial functions (membrane potential, reactive oxygen species generation, cellular ATP levels) but conferred resistance to apoptosis induced by actinomycin D (ActD), rotenone, or gamma-irradiation. During ActD-induced apoptosis, decreased CL peroxidation along with suppressed cytochrome (cyt) c release was observed in CL-deficient cells, whereas Bax translocation to mitochondria remained similar to that in CL-sufficient HeLa cells. The amounts of loosely bound cyt c (releasable under high ionic strength conditions) were the same in CL-deficient and CL-sufficient cells. Given that CL peroxidation during apoptosis is catalyzed by CL/cyt c complexes and CL oxidation products are essential for cyt c release from mitochondria, our results suggest that CL deficiency prevents adequate assembly of productive CL/cyt c complexes and CL peroxidation, resulting in increased resistance to apoptosis.

A mitochondria-targeted nitroxide/hemigramicidin S conjugate protects mouse embryonic cells against gamma irradiation

PURPOSE

To evaluate the in vitro radioprotective effect of the mitochondria-targeted hemigramicidin S-conjugated 4-amino-2,2,6,6-tetramethyl-piperidine-N-oxyl (hemi-GS-TEMPO) 5-125 in gamma-irradiated mouse embryonic cells and adenovirus-12 SV40 hybrid virus transformed human bronchial epithelial cells BEAS-2B and explore the mechanisms involved in its radioprotective effect.

METHODS AND MATERIALS

Cells were incubated with 5-125 before (10 minutes) or after (1 hour) gamma-irradiation. Superoxide generation was determined by using dihydroethidium assay, and lipid oxidation was quantitated by using a fluorescence high-performance liquid chromatography-based Amplex Red assay. Apoptosis was characterized by evaluating the accumulation of cytochrome c in the cytosol and externalization of phosphatidylserine on the cell surface. Cell survival was measured by means of a clonogenic assay.

RESULTS

Treatment (before and after irradiation) of cells with 5-125 at low concentrations (5, 10, and 20 mum) effectively suppressed gamma-irradiation-induced superoxide generation, cardiolipin oxidation, and delayed irradiation-induced apoptosis, evaluated by using cytochrome c release and phosphatidylserine externalization. Importantly, treatment with 5-125 increased the clonogenic survival rate of gamma-irradiated cells. In addition, 5-125 enhanced and prolonged gamma-irradiation-induced G(2)/M phase arrest.

CONCLUSIONS

Radioprotection/mitigation by hemi-GS-TEMPO likely is caused by its ability to act as an electron scavenger and prevent superoxide generation, attenuate cardiolipin oxidation in mitochondria, and hence prevent the release of proapoptotic factors from mitochondria. Other mechanisms, including cell-cycle arrest at the G(2)/M phase, may contribute to the protection.

Activation of NO donors in mitochondria: peroxidase metabolism of (2-hydroxyamino-vinyl)-triphenyl-phosphonium by cytochrome c releases NO and protects cells against apoptosis

In mitochondrial apoptosis, the formation of cytochrome c-cardiolipin complex ([CL-cyt c]) with peroxidase properties is an early event in the cascade of reactions that leads to cell death. Herein, we report the synthesis of a new prodrug, (2-hydroxyamino-vinyl)-triphenyl-phosphonium (HVTP), which compartmentalizes exclusively into mitochondria, undergoes a [CL-cyt c]-catalyzed bioactivation to nitric oxide (NO), inhibits peroxidase activity, and protects cells from apoptosis.

Interplay between bax, reactive oxygen species production, and cardiolipin oxidation during apoptosis

Bax/Bak activation and cardiolipin peroxidation are essential for cytochrome c release during apoptosis, yet, the link between them remains elusive. We report that sequence of events after exposure of mouse embryonic fibroblast (MEF) cells to actinomycin D followed the order: Bax translocation-->superoxide production-->cardiolipin peroxidation. Genetic ablation of Bax/Bak inhibited actinomycin D induced superoxide production and cardiolipin peroxidation. Rotenone caused robust superoxide generation but did not trigger cardiolipin peroxidation in Bax/Bak double knockout MEF cells. This suggests that, in addition to participating in ROS generation, Bax/Bak play another specific role in cardiolipin oxidation. In isolated mitochondria, recombinant Bax enhanced succinate induced cardiolipin oxidation and cytochrome c release. Mitochondrial peroxidase activity, likely involved in cardiolipin peroxidation, was enhanced upon incubation with recombinant Bax. Thus, cardiolipin peroxidation may be causatively and time-dependently related to Bax/Bak effects on ROS generation and peroxidase activation of cytochrome c.

Cardiolipin-Specific Peroxidase Reactions of Cytochrome c in Mitochondria During Irradiation-Induced Apoptosis

PURPOSE

To determine whether cytochrome c (cyt c) content and associated cardiolipin oxidation can be determinants of cell sensitivity to irradiation-induced apoptosis.

METHODS AND MATERIALS

The small interfering RNA (siRNA) approach was used to engineer HeLa cells with lowered contents of cyt c (14%, HeLa 1.2 cells). Cells were treated by gamma-irradiation (in doses of 5-40 Gy). Lipid oxidation was characterized by electrospray ionization mass spectrometry analysis and fluorescence high-performance liquid chromatography-based Amplex Red assay. Release of a proapoptotic factor (cyt c, Smac/DIABLO) was detected by Western blotting. Apoptosis was revealed by caspase-3/7 activation and phosphatidylserine externalization.

RESULTS

Irradiation caused selective accumulation of hydroperoxides in cardiolipin (CL) but not in other phospholipids. HeLa 1.2 cells responded by a lower irradiation-induced accumulation of CL oxidation products than parental HeLa cells. Proportionally decreased release of a proapoptotic factor, Smac/DIABLO, was detected in cyt c-deficient cells after irradiation. Caspase-3/7 activation and phosphatidylserine externalization were proportional to the cyt c content in cells.

CONCLUSIONS

Cytochrome c is an important catalyst of CL peroxidation, critical to the execution of the apoptotic program. This new role of cyt c in irradiation-induced apoptosis is essential for the development of new radioprotectors and radiosensitizers.

Cardiolipin switch in mitochondria: shutting off the reduction of cytochrome c and turning on the peroxidase activity

Upon interaction with anionic phospholipids, particularly mitochondria-specific cardiolipin (CL), cytochrome c (cyt c) loses its tertiary structure and its peroxidase activity dramatically increases. CL-induced peroxidase activity of cyt c has been found to be important for selective CL oxidation in cells undergoing programmed death. During apoptosis, the peroxidase activity and the fraction of CL-bound cyt c markedly increase, suggesting that CL may act as a switch to regulate cyt c's mitochondrial functions. Using cyclic voltammetry and equilibrium redox titrations, we show that the redox potential of cyt c shifts negatively by 350-400 mV upon binding to CL-containing membranes. Consequently, functions of cyt c as an electron transporter and cyt c reduction by Complex III are strongly inhibited. Further, CL/cyt c complexes are not effective in scavenging superoxide anions and are not effectively reduced by ascorbate. Thus, both redox properties and functions of cyt c change upon interaction with CL in the mitochondrial membrane, diminishing cyt c's electron donor/acceptor role and stimulating its peroxidase activity.

Structural Requirements for Optimized Delivery, Inhibition of Oxidative Stress, and Antiapoptotic Activity of Targeted Nitroxides

Suppression of mitochondrial production of reactive oxygen species is a promising strategy against intrinsic apoptosis typical of degenerative diseases. Stable nitroxide radicals such as 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPOL) and its analogs combine several important features, including recycleability, electron acceptance from respiratory complexes, superoxide dismutase mimicry, and radical scavenging. Although successful in antioxidant protection, their effective concentrations are too high for successful in vivo applications. Recently (J Am Chem Soc 127:12460, 2005), we reported that 4-amino 2,2,6,6-tetramethyl-1-piperidinyloxy, covalently conjugated to a five-residue segment of gramicidin S (GS), was integrated into mitochondria and blocked actinomycin D (ActD)-induced superoxide generation and apoptosis. Using a model of ActD-induced apoptosis in mouse embryonic cells, we screened a library of nitroxides to explore structure-activity relationships between their antioxidant/antiapoptotic properties and chemical composition and three-dimensional (3D) structure. High hydrophobicity and effective mitochondrial integration are necessary but not sufficient for high antiapoptotic/antioxidant activity of a nitroxide conjugate. By designing conformationally preorganized peptidyl nitroxide conjugates and characterizing their 3D structure experimentally (circular dichroism and NMR) and theoretically (molecular dynamics), we established that the presence of the beta-turn/beta-sheet secondary structure is essential for the desired activity. Monte Carlo simulations in model lipid membranes confirmed that the conservation of the d-Phe-Pro reverse turn in hemi-GS analogs ensures the specific positioning of the nitroxide moiety at the mitochondrial membrane interface and maximizes their protective effects. These new insights into the structure-activity relationships of nitroxide-peptide and -peptide isostere conjugates are instrumental for development of new mechanism-based therapeutically effective agents.

Peroxidase activity and structural transitions of cytochrome c bound to cardiolipin-containing membranes

During apoptosis, cytochrome c (cyt c) is released from intermembrane space of mitochondria into the cytosol where it triggers the caspase-dependent machinery. We discovered that cyt c plays another critical role in early apoptosis as a cardiolipin (CL)-specific oxygenase to produce CL hydroperoxides required for release of pro-apoptotic factors [Kagan, V. E., et al. (2005) Nat. Chem. Biol. 1, 223-232]. We quantitatively characterized the activation of peroxidase activity of cyt c by CL and hydrogen peroxide. At low ionic strength and high CL/cyt c ratios, peroxidase activity of the CL/cyt c complex was increased >50 times. This catalytic activity correlated with partial unfolding of cyt c monitored by Trp(59) fluorescence and absorbance at 695 nm (Fe-S(Met(80)) band). The peroxidase activity increase preceded the loss of protein tertiary structure. Monounsaturated tetraoleoyl-CL (TOCL) induced peroxidase activity and unfolding of cyt c more effectively than saturated tetramyristoyl-CL (TMCL). TOCL/cyt c complex was found more resistant to dissociation by high salt concentration. These findings suggest that electrostatic CL/cyt c interactions are central to the initiation of the peroxidase activity, while hydrophobic interactions are involved when cyt c's tertiary structure is lost. In the presence of CL, cyt c peroxidase activity is activated at lower H(2)O(2) concentrations than for isolated cyt c molecules. This suggests that redistribution of CL in the mitochondrial membranes combined with increased production of H(2)O(2) can switch on the peroxidase activity of cyt c and CL oxidation in mitochondria-a required step in execution of apoptosis.

Mechanisms of cardiolipin oxidation by cytochrome c: relevance to pro- and antiapoptotic functions of etoposide

Execution of apoptotic program in mitochondria is associated with accumulation of cardiolipin peroxidation products required for the release of proapoptotic factors into the cytosol. This suggests that lipid antioxidants capable of inhibiting cardiolipin peroxidation may act as antiapoptotic agents. Etoposide, a widely used antitumor drug and a topoisomerase II inhibitor, is a prototypical inducer of apoptosis and, at the same time, an effective lipid radical scavenger and lipid antioxidant. Here, we demonstrate that cardiolipin oxidation during apoptosis is realized not via a random cardiolipin peroxidation mechanism but rather proceeds as a result of peroxidase reaction in a tight cytochrome c/cardiolipin complex that restrains interactions of etoposide with radical intermediates generated in the course of the reaction. Using low-temperature and ambient-temperature electron paramagnetic resonance spectroscopy of H(2)O(2)-induced protein-derived (tyrosyl) radicals and etoposide phenoxyl radicals, respectively, we established that cardiolipin peroxidation and etoposide oxidation by cytochrome c/cardiolipin complex takes place predominantly on protein-derived radicals of cytochrome c. We further show that etoposide can inhibit cytochrome c-catalyzed oxidation of cardiolipin competing with it as a peroxidase substrate. Peroxidase reaction of cytochrome c/cardiolipin complexes causes cross-linking and oligomerization of cytochrome c. With nonoxidizable tetraoleoyl-cardiolipin, the cross-linking occurs via dityrosine formation, whereas bifunctional lipid oxidation products generated from tetralinoleoyl-cardiolipin participate in the production of high molecular weight protein aggregates. Protein aggregation is effectively inhibited by etoposide. The inhibition of cardiolipin peroxidation by etoposide, however, is realized at far higher concentrations than those at which it induces apoptotic cell death. Thus, oxidation of cardiolipin by the cytochrome c/cardiolipin peroxidase complex, which is essential for apoptosis, is not inhibited by proapoptotic concentrations of the drug.

Mitochondrial targeting of selective electron scavengers: synthesis and biological analysis of hemigramicidin-TEMPO conjugates

Synthetic hemigramicidin S-peptidyl TEMPO conjugates are effectively delivered into cells and mitochondria, where they act as electron scavengers and exert protection against apoptosis. Our delivery approach is based on the use of specific structural signaling features recognizable by cells as mitochondria targeting sequences and offers considerable therapeutic anti-apoptotic potential.

Cytochrome c acts as a cardiolipin oxygenase required for release of proapoptotic factors

Programmed death (apoptosis) is turned on in damaged or unwanted cells to secure their clean and safe self-elimination. The initial apoptotic events are coordinated in mitochondria, whereby several proapoptotic factors, including cytochrome c, are released into the cytosol to trigger caspase cascades. The release mechanisms include interactions of B-cell/lymphoma 2 family proteins with a mitochondria-specific phospholipid, cardiolipin, to cause permeabilization of the outer mitochondrial membrane. Using oxidative lipidomics, we showed that cardiolipin is the only phospholipid in mitochondria that undergoes early oxidation during apoptosis. The oxidation is catalyzed by a cardiolipin-specific peroxidase activity of cardiolipin-bound cytochrome c. In a previously undescribed step in apoptosis, we showed that oxidized cardiolipin is required for the release of proapoptotic factors. These results provide insight into the role of reactive oxygen species in triggering the cell-death pathway and describe an early role for cytochrome c before caspase activation.

[Risk assessment for the development of occupational diseases among railroad workers]

An attempt was made to asses the actual risk of occupational diseases among various railway specialists having harmful and adverse working conditions. The risk was found to be high, suggesting that there are harmful and extremely harmful working conditions and high undetection of patients with occupational diseases.