Radical medicine: treating ageing to cure disease

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

The mitochondrial antioxidants MitoE(2) and MitoQ(10) increase mitochondrial Ca(2+) load upon cell stimulation by inhibiting Ca(2+) efflux from the organelle

Mitochondrial reactive oxygen species (ROS) production is recognized as a major pathogenic event in a number of human diseases, and mitochondrial scavenging of ROS appears a promising therapeutic approach. Recently, two mitochondrial antioxidants have been developed; conjugating alpha-tocopherol and the ubiquinol moiety of coenzyme Q to the lipophilic triphenylphosphonium cation (TPP+), denominated MitoE(2) and MitoQ(10), respectively. We have investigated the effect of these compounds on mitochondrial Ca(2+) homeostasis, which controls processes as diverse as activation of mitochondrial dehydrogenases and pro-apoptotic morphological changes of the organelle. We demonstrate that treatment of HeLa cells with both MitoE(2) and MitoQ(10) induces (albeit with different efficacy) a major enhancement of the increase in matrix Ca(2+) concentration triggered by cell stimulation with the inositol 1,4,5-trisphosphate-generating agonist histamine. The effect is a result of the inhibition of Ca(2+) efflux from the organelle and depends on the TPP+ moiety of these compounds. Overall, the data identify an effect independent of their antioxidant activity, that on the one hand may be useful in addressing disorders in which mitochondrial Ca(2+) handling is impaired (e.g., mitochondrial diseases) and on the other may favor mitochondrial Ca(2+) overload and thus increase cell sensitivity to apoptosis (thus possibly counteracting the benefits of the antioxidant activity).

Mitochondria-targeted antioxidants in the treatment of disease

Mitochondrial oxidative damage is thought to contribute to a wide range of human diseases; therefore, the development of approaches to decrease this damage may have therapeutic potential. Mitochondria-targeted antioxidants that selectively block mitochondrial oxidative damage and prevent some types of cell death have been developed. These compounds contain antioxidant moieties, such as ubiquinone, tocopherol, or nitroxide, that are targeted to mitochondria by covalent attachment to a lipophilic triphenylphosphonium cation. Because of the large mitochondrial membrane potential, the cations are accumulated within the mitochondria inside cells. There, the conjugated antioxidant moiety protects mitochondria from oxidative damage. Here, we outline some of the work done to date on these compounds and how they may be developed as therapies.

Antioxidant activity of growth hormone-releasing hormone antagonists in LNCaP human prostate cancer line

Hypothalamic growth hormone-releasing hormone (GHRH) controls the release of growth hormone and acts as a growth factor in various tumors. Potent antagonistic analogues of GHRH have been synthesized that strongly suppress the growth of diverse cancers through several mechanisms. However, the influence of GHRH antagonists on the redox (reduction/oxidation) status of cancers has not been investigated. Cellular generation of reactive oxygen species (ROS) is central to redox signaling and is implicated in the initiation, development, and progression of cancer. In this study, we evaluated by Western blot the effects in vitro of GHRH and its antagonist JMR-132 on proliferating cell nuclear antigen, tumor suppressor protein p53, transcription factor NF-kappaB p50 and its phosphorylated form, caspase 3, and cleaved caspase 3 in the LNCaP human prostate cancer cell line. GHRH stimulated and GHRH antagonist inhibited the expression of the major antioxidant enzymes, as well as the expression of COX 2 and cytochrome c oxidase IV, which are enzymes involved in the generation of ROS. GHRH augmented and GHRH antagonist suppressed lipid and protein oxidative stress markers, as well as the intracellular generation of ROS. In all these tests, GHRH antagonists exerted strong antioxidant activity. Because the metabolism of ROS and oxidative stress have been associated with initiation and progression of not only prostate tumors but also other malignancies, our findings reinforce previous experimental evidence that GHRH antagonists could be useful for cancer therapy.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

Rapid and extensive uptake and activation of hydrophobic triphenylphosphonium cations within cells

Mitochondria-targeted molecules comprising the lipophilic TPP (triphenylphosphonium) cation covalently linked to a hydrophobic bioactive moiety are used to modify and probe mitochondria in cells and in vivo. However, it is unclear how hydrophobicity affects the rate and extent of their uptake into mitochondria within cells, making it difficult to interpret experiments because their intracellular concentration in different compartments is uncertain. To address this issue, we compared the uptake into both isolated mitochondria and mitochondria within cells of two hydrophobic TPP derivatives, [3H]MitoQ (mitoquinone) and [3H]DecylTPP, with the more hydrophilic TPP cation [3H]TPMP (methyltriphenylphosphonium). Uptake of MitoQ by mitochondria and cells was described by the Nernst equation and was ∼5-fold greater than that for TPMP, as a result of its greater binding within the mitochondrial matrix. DecylTPP was also taken up extensively by cells, indicating that increased hydrophobicity enhanced uptake. Both MitoQ and DecylTPP were taken up very rapidly into cells, reaching a steady state within 15 min, compared with ∼8 h for TPMP. This far faster uptake was the result of the increased rate of passage of hydrophobic TPP molecules through the plasma membrane. Within cells MitoQ was predominantly located within mitochondria, where it was rapidly reduced to the ubiquinol form, consistent with its protective effects in cells and in vivo being due to the ubiquinol antioxidant. The strong influence of hydrophobicity on TPP cation uptake into mitochondria within cells facilitates the rational design of mitochondria-targeted compounds to report on and modify mitochondrial function in vivo.

Targeting lipophilic cations to mitochondria

Mitochondrial function and dysfunction contributes to a range of important aspects of biomedical research. Consequently there is considerable interest in developing approaches to modify and report on mitochondria in cells and in vivo. One approach has been to target bioactive molecules to mitochondria by conjugating them to lipophilic cations. Due to the large mitochondrial membrane potential, the cations are accumulated within mitochondria inside cells. This approach had been used to develop mitochondria-targeted antioxidants that selectively block mitochondrial oxidative damage and prevent some types of cell death and also to develop probes of mitochondrial function. Here we outline some of the background to the development of these compounds.

Age-dependent endothelial dysfunction is associated with failure to increase plasma nitrite in response to exercise

Age-dependent alterations of the vessel wall may predispose older individuals to increased cardiovascular pathology. Aging is associated with an impaired bioactivity of nitric oxide (NO). Plasma nitrite reflects NO-synthase activity under fasting conditions and is an important storage pool of NO. To test the hypothesis that aging is associated with an impaired capacity of the vasculature to increase plasma nitrite during exercise, 29 young and 28 old healthy individuals (25 +/- 1 years and 58 +/- 2 years; P < 0.001) without major cardiovascular risk factors were enrolled. Exercise stress was similar in both groups. Baseline nitrite did not differ (107 +/- 8 vs. 82 +/- 10 nmol/l, young vs. old; n.s.) although a trend toward higher nitrite levels in young individuals was seen. In young subjects, exercise increased plasma nitrite by 38 +/- 7% (P < 0.001) compared to only 13 +/- 8% (P = n.s.) in older subjects. L-NMMA blocked increases of nitrite. Endothelial function, as defined by flow-mediated-dilation (FMD) of the brachial artery via ultrasound, was impaired in older subjects (5.4 +/- 0.4% vs. 6.7 +/- 0.3%; P < 0.01). Multivariate analysis showed that age (P = 0.007), BMI (P = 0.010), and LDL (P = 0.021) were independent predictors of nitrite increase. The fact that aging is associated with an impaired capacity of the vasculature to adequately increase nitrite to physiological stimuli may contribute to attenuated maintenance and further deterioration of vascular homeostasis with aging.

Biochemistry of oxidative stress

The terms 'antioxidant', 'oxidative stress' and 'oxidative damage' are widely used but rarely defined. This brief review attempts to define them and to examine the ways in which oxidative stress and oxidative damage can affect cell behaviour both in vivo and in cell culture, using cancer as an example.

Offspring's leukocyte telomere length, paternal age, and telomere elongation in sperm

Leukocyte telomere length (LTL) is a complex genetic trait. It shortens with age and is associated with a host of aging-related disorders. Recent studies have observed that offspring of older fathers have longer LTLs. We explored the relation between paternal age and offspring's LTLs in 4 different cohorts. Moreover, we examined the potential cause of the paternal age on offspring's LTL by delineating telomere parameters in sperm donors. We measured LTL by Southern blots in Caucasian men and women (n=3365), aged 18-94 years, from the Offspring of the Framingham Heart Study (Framingham Offspring), the NHLBI Family Heart Study (NHLBI-Heart), the Longitudinal Study of Aging Danish Twins (Danish Twins), and the UK Adult Twin Registry (UK Twins). Using Southern blots, Q-FISH, and flow-FISH, we also measured telomere parameters in sperm from 46 young (<30 years) and older (>50 years) donors. Paternal age had an independent effect, expressed by a longer LTL in males of the Framingham Offspring and Danish Twins, males and females of the NHLBI-Heart, and females of UK Twins. For every additional year of paternal age, LTL in offspring increased at a magnitude ranging from half to more than twice of the annual attrition in LTL with age. Moreover, sperm telomere length analyses were compatible with the emergence in older men of a subset of sperm with elongated telomeres. Paternal age exerts a considerable effect on the offspring's LTL, a phenomenon which might relate to telomere elongation in sperm from older men. The implications of this effect deserve detailed study.

Molecular mechanism of proton translocation by cytochrome c oxidase

Cytochrome c oxidase (CcO) is a terminal protein of the respiratory chain in eukaryotes and some bacteria. It catalyzes most of the biologic oxygen consumption on earth done by aerobic organisms. During the catalytic reaction, CcO reduces dioxygen to water and uses the energy released in this process to maintain the electrochemical proton gradient by functioning as a redox-linked proton pump. Even though the structures of several terminal oxidases are known, they are not sufficient in themselves to explain the molecular mechanism of proton pumping. Thus, additional extensive studies of CcO by varieties of biophysical and biochemical approaches are involved to shed light on the mechanism of proton translocation. In this review, we summarize the current level of knowledge about CcO, including the latest model developed to explain the CcO proton-pumping mechanism.

Hydrogen peroxide inhibits caspase-dependent apoptosis by inactivating procaspase-9 in an iron-dependent manner

Apoptosis represents a physiological form of cell death, the perturbation of which may contribute to the development of several diseases connected with accumulation of unwanted cells or excessive cell loss. We have previously shown that the continuous presence of low concentrations of H2O2 (generated by the action of glucose oxidase) was able to inhibit caspase-mediated apoptosis in Jurkat cells. The main purpose of the present study was to elucidate the exact molecular mechanism(s) underlying this inhibitory action of H2O2. The results presented show that events like outer mitochondrial membrane permeabilization, release of cytochrome c from mitochondria, oligomerization of Apaf-1, and recruitment of procaspase-9 to apoptosomes were taking place normally, but further advancement toward activation of the execution caspases was interrupted when H2O2 was present during the apoptotic process. From the results presented in this work, it emerges that the inhibition of procaspase-9 autoactivation was probably due to the reversible oxidation of sensitive cysteine residues in this molecule. Remarkably, caspase-9 activation and the ensuing caspase cascade proceeded normally in the presence of H2O2 under conditions of iron deprivation, indicating that the inhibition of procaspase-9 activation was an iron-dependent process. Collectively, these results highlighted the potential role of available intracellular iron ions in signaling mechanisms related to apoptotic cell death.

Protein phosphatase 2A subunit PR70 interacts with pRb and mediates its dephosphorylation

The retinoblastoma tumor suppressor protein (pRb) regulates cell proliferation and differentiation via phosphorylation-sensitive interactions with specific targets. While the role of cyclin/cyclin-dependent kinase complexes in the modulation of pRb phosphorylation has been extensively studied, relatively little is known about the molecular mechanisms regulating phosphate removal by phosphatases. Protein phosphatase 2A (PP2A) is constituted by a core dimer bearing catalytic activity and one variable B regulatory subunit conferring target specificity and subcellular localization. We previously demonstrated that PP2A core dimer binds pRb and dephosphorylates pRb upon oxidative stress. In the present study, we identified a specific PP2A-B subunit, PR70, that was associated with pRb both in vitro and in vivo. PR70 overexpression caused pRb dephosphorylation; conversely, PR70 knockdown prevented both pRb dephosphorylation and DNA synthesis inhibition induced by oxidative stress. Moreover, we found that intracellular Ca(2+) mobilization was necessary and sufficient to trigger pRb dephosphorylation and PP2A phosphatase activity of PR70 was Ca(2+) induced. These data underline the importance of PR70-Ca(2+) interaction in the signal transduction mechanisms triggered by redox imbalance and leading to pRb dephosphorylation.

[Does youth mean vigorous and age, feeble biological repair mechanisms?]

All living creatures are subject to aging, but our understanding of what governs aging is limited. In the course of a lifetime, with the constant renewal of the organic substance of living creatures errors arise, e.g. in the formation, disposal, and reproduction of DNA, proteins and lipids or in the constant substitution of aging cells in the organs. These errors are recognized and generally counterbalanced by appropriate repair mechanisms. This process is obviously determined partly by environmental influences (e.g. UV radiation, oxidizing influences, thermal shock) and genetic factors (such as the significance of so-called survival genes and gene mutations). In this paper the authors both explain and test the hypothesis that the aging of organs and organisms is the consequence of and not the reason for a progressive weakening of the repair mechanisms throughout life.

Alzheimer's disease: a lesson from mitochondrial dysfunction

Extensive literature exists supporting a role for mitochondrial dysfunction and oxidative damage in the pathogenesis of Alzheimer's disease. Mitochondria are a major source of intracellular reactive oxygen species and are particularly vulnerable to oxidative stress. This review discusses evidence supporting the notion that mitochondrial dysfunction is intimately associated with Alzheimer's disease pathogenesis. Furthermore, the potential connection between mitochondrial dysfunction/oxidative stress and autophagy in Alzheimer's disease is also discussed. As a result of insufficient digestion of oxidatively damaged macromolecules and organelles by autophagy, neurons progressively accumulate lipofuscin (biological garbage) that could exacerbate neuronal dysfunction. The knowledge that mitochondrial dysfunction has a preponderant role in several pathological conditions instigated the development of mitochondrial antioxidant therapies. Mitochondria-targeted antioxidant treatments are briefly discussed in this review.

p66(ShcA) and oxidative stress modulate myogenic differentiation and skeletal muscle regeneration after hind limb ischemia

Oxidative stress plays a pivotal role in ischemic injury, and p66(ShcA)ko mice exhibit both lower oxidative stress and decreased tissue damage following hind limb ischemia. Thus, it was investigated whether tissue regeneration following acute hind limb ischemia was altered in p66(ShcA)ko mice. Upon femoral artery dissection, muscle regeneration started earlier and was completed faster than in wild-type (WT) control. Moreover, faster regeneration was associated with decreased oxidative stress. Unlike ischemia, cardiotoxin injury induced similar skeletal muscle damage in both genotypes. However, p66(ShcA)ko mice regenerated faster, in agreement with the regenerative advantage upon ischemia. Since no difference between p66(ShcA)wt and knock-out (ko) mice was found in blood perfusion recovery after ischemia, satellite cells (SCs), a resident population of myogenic progenitors, were examined. Similar SCs numbers were present in WT and ko mice. However, in vitro cultured p66(ShcA)ko SCs displayed lower oxidative stress levels and higher proliferation rate and differentiated faster than WT. Furthermore, when exposed to sublethal H(2)O(2) doses, p66(ShcA)ko SCs were resistant to H(2)O(2)-induced inhibition of differentiation. Finally, myogenic conversion induced by MyoD overexpression was more efficient in p66(ShcA)ko fibroblasts compared with WT. The present work demonstrates that oxidative stress and p66(ShcA) play a crucial role in the regenerative pathways activated by acute ischemia.

Molecular and structural basis for redox regulation of beta-actin

An essential consequence of growth factor-mediated signal transduction is the generation of intracellular H(2)O(2). It operates as a second messenger in the control of actin microfilament dynamics, causing rapid and dramatic changes in the morphology and motile activity of stimulated cells. Little is understood about the molecular mechanisms causing these changes in the actin system. Here, it is shown that H(2)O(2) acts directly upon several levels of this system, and some of the mechanistic effects are detailed. We describe the impact of oxidation on the polymerizability of non-muscle beta/gamma-actin and compare with that of muscle alpha-actin. Oxidation of beta/gamma-actin can cause a complete loss of polymerizability, crucially, reversible by the thioredoxin system. Further, oxidation of the actin impedes its interaction with profilin and causes depolymerization of filamentous actin. The effects of oxidation are critically dependent on the nucleotide state and the concentration of Ca(2+). We have determined the crystal structure of oxidized beta-actin to a resolution of 2.6 A. The arrangement in the crystal implies an antiparallel homodimer connected by an intermolecular disulfide bond involving cysteine 374. Our data indicate that this dimer forms under non-polymerizing and oxidizing conditions. We identify oxidation of cysteine 272 in the crystallized actin dimer, likely to a cysteine sulfinic acid. In beta/gamma-actin, this is the cysteine residue most reactive towards H(2)O(2) in solution, and we suggest plausible structural determinants for its reactivity. No other oxidative modification was obvious in the structure, highlighting the specificity of the oxidation by H(2)O(2). Possible consequences of the observed effects in a cellular context and their potential relevance are discussed.

Triterpenoids and rexinoids as multifunctional agents for the prevention and treatment of cancer

Synthetic oleanane triterpenoids and rexinoids are two new classes of multifunctional drugs. They are neither conventional cytotoxic agents, nor are they monofunctional drugs that uniquely target single steps in signal transduction pathways. Synthetic oleanane triterpenoids have profound effects on inflammation and the redox state of cells and tissues, as well as being potent anti-proliferative and pro-apoptotic agents. Rexinoids are ligands for the nuclear receptor transcription factors known as retinoid X receptors. Both classes of agents can prevent and treat cancer in experimental animals. These drugs have unique molecular and cellular mechanisms of action and might prove to be synergistic with standard anti-cancer treatments.

Sirt1 regulates aging and resistance to oxidative stress in the heart

Silent information regulator (Sir)2, a class III histone deacetylase, mediates lifespan extension in model organisms and prevents apoptosis in mammalian cells. However, beneficial functions of Sir2 remain to be shown in mammals in vivo at the organ level, such as in the heart. We addressed this issue by using transgenic mice with heart-specific overexpression of Sirt1, a mammalian homolog of Sir2. Sirt1 was significantly upregulated (4- to 8-fold) in response to pressure overload and oxidative stress in nontransgenic adult mouse hearts. Low (2.5-fold) to moderate (7.5-fold) overexpression of Sirt1 in transgenic mouse hearts attenuated age-dependent increases in cardiac hypertrophy, apoptosis/fibrosis, cardiac dysfunction, and expression of senescence markers. In contrast, a high level (12.5-fold) of Sirt1 increased apoptosis and hypertrophy and decreased cardiac function, thereby stimulating the development of cardiomyopathy. Moderate overexpression of Sirt1 protected the heart from oxidative stress induced by paraquat, with increased expression of antioxidants, such as catalase, through forkhead box O (FoxO)-dependent mechanisms, whereas high levels of Sirt1 increased oxidative stress in the heart at baseline. Thus, mild to moderate expression of Sirt1 retards aging of the heart, whereas a high dose of Sirt1 induces cardiomyopathy. Furthermore, although high levels of Sirt1 increase oxidative stress, moderate expression of Sirt1 induces resistance to oxidative stress and apoptosis. These results suggest that Sirt1 could retard aging and confer stress resistance to the heart in vivo, but these beneficial effects can be observed only at low to moderate doses (up to 7.5-fold) of Sirt1.

Targeting antioxidants to mitochondria by conjugation to lipophilic cations

Mitochondrial oxidative damage contributes to a range of degenerative diseases. Consequently, the selective inhibition of mitochondrial oxidative damage is a promising therapeutic strategy. One way to do this is to invent antioxidants that are selectively accumulated into mitochondria within patients. Such mitochondria-targeted antioxidants have been developed by conjugating the lipophilic triphenylphosphonium cation to an antioxidant moiety, such as ubiquinol or alpha-tocopherol. These compounds pass easily through all biological membranes, including the blood-brain barrier, and into muscle cells and thus reach those tissues most affected by mitochondrial oxidative damage. Furthermore, because of their positive charge they are accumulated several-hundredfold within mitochondria driven by the membrane potential, enhancing the protection of mitochondria from oxidative damage. These compounds protect mitochondria from damage following oral delivery and may therefore form the basis for mitochondria-protective therapies. Here we review the background and work to date on this class of mitochondria-targeted antioxidants.

Stroke and Vascular Cognitive Impairment

Advances in stroke are occurring at an unprecedented pace, but often in disciplinary isolation and without optimal mechanisms for systematically translating, integrating and applying the findings.

Knowledge accrues in pieces, but is understood in patterns. To optimize knowledge acquisition and application, infrastructures and systems need to be set up along with appealing incentives. The approach needs to be transdisciplinary , going beyond the bounds of any given discipline, reciprocally translational , and transactional , meaning that the interchanges have to yield previously agreed benefits to the parties ( The Triple T Approach ). A new breed of leaders needs to be developed and nurtured to catalyze the process.

Opportunities abound. Stroke and most brain diseases share the same pathophysiological fundamental mechanisms. An integrated, systematic approach to these processes could yield not only greater understanding but new, common therapeutic targets for several diseases. Biphasic clinical trials could combine the best features of pragmatic and explanatory, randomized clinical trials. The greatest opportunity of all may be the largely under-explored and under-exploited borderlands between cerebrovascular and Alzheimer disease. One in three of us will have a stroke, become demented, or both. For each person who has a stroke or Alzheimer disease, two have some cognitive impairment short of dementia, often subclinical cerebrovascular disease on a substrate of Alzheimer changes. The fact that cerebrovascular and Alzheimer disease share the same risk factors, provide a great opportunity for prevention, if implemented at the “brain at risk” stage.

Systematically integrating what we know and evaluating what we do could spur progress. Research is not only an activity but an attitude. Making evaluation and incentives to excel part of the funding of all stroke activities would yield far ranging cumulative improvements in all aspects of stroke.

No system can replace the individual initiative, creativity and insights that lead to the great discoveries, but progress is not made by breakthroughs alone. No one’s work is so exalted that it cannot be improved, nor so humble that it has no value. We can all make a difference.

Mitochondrial targeting of quinones: therapeutic implications

Mitochondrial oxidative damage contributes to a range of degenerative diseases. Ubiquinones have been shown to protect mitochondria from oxidative damage, but only a small proportion of externally administered ubiquinone is taken up by mitochondria. Conjugation of the lipophilic triphenylphosphonium cation to a ubiquinone moiety has produced a compound, MitoQ, which accumulates selectively into mitochondria. MitoQ passes easily through all biological membranes and, because of its positive charge, is accumulated several hundred-fold within mitochondria driven by the mitochondrial membrane potential. MitoQ protects mitochondria against oxidative damage in vitro and following oral delivery, and may therefore form the basis for mitochondria-protective therapies.

Mitochondrial reactive oxygen species-mediated signaling in endothelial cells

Once thought of as toxic by-products of cellular metabolism, reactive oxygen species (ROS) have been implicated in a large variety of cell-signaling processes. Several enzymatic systems contribute to ROS production in vascular endothelial cells, including NA(D)PH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase, and the mitochondrial electron transport chain. The respiratory chain is the major source of ROS in most mammalian cells, but the role of mitochondria-derived ROS in vascular cell signaling has received little attention. A new paradigm has evolved in recent years postulating that, in addition to producing ATP, mitochondria also play a key role in cell signaling and regulate a variety of cellular functions. This review focuses on the emerging role of mitochondrial ROS as signaling molecules in vascular endothelial cells. Specifically, we discuss some recent findings that indicate that mitochondrial ROS regulate vascular endothelial function, focusing on major sites of ROS production in endothelial mitochondria, factors modulating mitochondrial ROS production, the physiological and clinical implications of endothelial mitochondrial ROS, and methodological considerations in the study of mitochondrial contribution to vascular ROS generation.

Age-dependent accumulation of mtDNA mutations in murine hematopoietic stem cells is modulated by the nuclear genetic background

Alterations in mitochondrial DNA (mtDNA) and consequent loss of mitochondrial function underlie the mitochondrial theory of aging. In this study, we systematically analyzed the mtDNA control region somatic mutation pattern in 2864 single hematopoietic stem cells (HSCs) and progenitors, isolated by flow cytometry sorting on Lin(-)Kit(+)CD34(-) parameters from young and old C57BL/6 (B6) and BALB/cBy (BALB) mice, to test the hypothesis that the accumulated mtDNA mutations in HSCs were strain-correlated and associated with HSC functional senescence during aging. An increased level of mtDNA mutations in single HSCs was observed in old B6 when compared with young B6 mice (P=0.003); in contrast, no significant age-dependent accumulation of mutations was observed in BALB mice (old versus young, P=0.202) and the level of mutations in both young and old BALB mice was close to that of old B6 mice (P>0.280). Cellular reactive oxygen species (ROS) in mouse HSCs could not be correlated with the level of mtDNA mutations in these cells, although B6 mice had a higher proportion of ROS(-) cells when compared with the BALB mice. Propagation assays of single HSCs showed B6 cells form larger colonies compared with cells from BALB mice, irrespective of age and mtDNA mutation load. We infer from our data that age-related mtDNA somatic mutation accumulation in mouse HSCs is influenced by the nuclear genetic background and that these mutations may not obviously correlate to either cellular ROS content or HSC senescence.

Mitochondrial ROS--radical detoxification, mediated by protein kinase D

The mitochondrial electron transport chain is the major source for the production of oxygen radicals. Mitochondria-generated reactive oxygen species (mROS) have been implicated in decreasing the life span and contributing to age-related diseases (known as the free radical theory of aging). Recently, the serine/threonine kinase protein kinase D1 (PKD1) was identified as a mitochondrial sensor for oxidative stress. mROS-activated PKD regulates a radical-sensing signaling pathway, which relays mROS production to the induction of nuclear genes that mediate cellular detoxification and survival. This PKD regulated signaling pathway is the first known mitochondria located and mitochondrially regulated antioxidant system that protects these organelles and cells from oxidative stress-mediated damage or cell death. The identification of this and further intracellular protective signaling pathways provides an opportunity to manipulate the effects of mROS, and might provide the key to targeting aging effects and age-related diseases that have been linked to mitochondrial dysfunctions.

Actin-induced hyperactivation of the Ras signaling pathway leads to apoptosis in Saccharomyces cerevisiae

Recent research has revealed a conserved role for the actin cytoskeleton in the regulation of aging and apoptosis among eukaryotes. Here we show that the stabilization of the actin cytoskeleton caused by deletion of Sla1p or End3p leads to hyperactivation of the Ras signaling pathway. The consequent rise in cyclic AMP (cAMP) levels leads to the loss of mitochondrial membrane potential, accumulation of reactive oxygen species (ROS), and cell death. We have established a mechanistic link between Ras signaling and actin by demonstrating that ROS production in actin-stabilized cells is dependent on the G-actin binding region of the cyclase-associated protein Srv2p/CAP. Furthermore, the artificial elevation of cAMP directly mimics the apoptotic phenotypes displayed by actin-stabilized cells. The effect of cAMP elevation in inducing actin-mediated apoptosis functions primarily through the Tpk3p subunit of protein kinase A. This pathway represents the first defined link between environmental sensing, actin remodeling, and apoptosis in Saccharomyces cerevisiae.

Multipotent antioxidants: from screening to design

Free-radicals play an important role in the pathogenesis of many diseases, accounting for continuing interest in the identification and development of novel antioxidants that prevent radical-induced damage. To develop more-powerful weapons that address complex diseases in which free-radicals might be significant, but not exclusive drivers, antioxidants that also have other pharmacological effects are desired. To obtain multipotent antioxidants, one can screen drug collections and/or natural-product libraries, or couple an antioxidant group with other pharmacophores. It is interesting to note that most rationally designed multifunctional antioxidants are structurally different from their naturally occurring counterparts. Therefore, nature's design strategy provides important clues as to how the design concept for multipotent antioxidants can be improved.

Reactive oxygen species-mediated mitochondria-to-nucleus signaling: a key to aging and radical-caused diseases

Mitochondria-generated reactive oxygen species have been implicated as a common feature that connects aging of organisms and age-related diseases. Efficient elimination of these radicals by antioxidants correlates with increased life span. Understanding how the mitochondrion signals to the nucleus to regulate antioxidant proteins might be a key to aging processes and treatment of human diseases.