Rotenone model of Parkinson disease: multiple brain mitochondria dysfunctions after short term systemic rotenone intoxication

Protection of rat skeletal muscle fibers by either L-carnitine or coenzyme Q10 against statins toxicity mediated by mitochondrial reactive oxygen generation

Mitochondrial redox imbalance has been implicated in mechanisms of aging, various degenerative diseases and drug-induced toxicity. Statins are safe and well-tolerated therapeutic drugs that occasionally induce myotoxicity such as myopathy and rhabdomyolysis. Previous studies indicate that myotoxicity caused by statins may be linked to impairment of mitochondrial functions. Here, we report that 1-h incubation of permeabilized rat soleus muscle fiber biopsies with increasing concentrations of simvastatin (1–40 μM) slowed the rates of ADP-or FCCP-stimulated respiration supported by glutamate/malate in a dose-dependent manner, but caused no changes in resting respiration rates. Simvastatin (1 μM) also inhibited the ADP-stimulated mitochondrial respiration supported by succinate by 24% but not by TMPD/ascorbate. Compatible with inhibition of respiration, 1 μM simvastatin stimulated lactate release from soleus muscle samples by 26%. Co-incubation of muscle samples with 1 mM L-carnitine, 100 μM mevalonate or 10 μM coenzyme Q10 (Co-Q10) abolished simvastatin effects on both mitochondrial glutamate/malate-supported respiration and lactate release. Simvastatin (1 μM) also caused a 2-fold increase in the rate of hydrogen peroxide generation and a decrease in Co-Q10 content by 44%. Mevalonate, Co-Q10 or L-carnitine protected against stimulation of hydrogen peroxide generation but only mevalonate prevented the decrease in Co-Q10 content. Thus, independently of Co-Q10 levels, L-carnitine prevented the toxic effects of simvastatin. This suggests that mitochondrial respiratory dysfunction induced by simvastatin, is associated with increased generation of superoxide, at the levels of complexes-I and II of the respiratory chain. In all cases the damage to these complexes, presumably at the level of 4Fe-4S clusters, is prevented by L-carnitine.

Metal dyshomeostasis and inflammation in Alzheimer's and Parkinson's diseases: possible impact of environmental exposures

A dysregulated metal homeostasis is associated with both Alzheimer's (AD) and Parkinson's (PD) diseases; AD patients have decreased cortex and elevated serum copper levels along with extracellular amyloid-beta plaques containing copper, iron, and zinc. For AD, a putative hepcidin-mediated lowering of cortex copper mechanism is suggested. An age-related mild chronic inflammation and/or elevated intracellular iron can trigger hepcidin production followed by its binding to ferroportin which is the only neuronal iron exporter, thereby subjecting it to lysosomal degradation. Subsequently raised neuronal iron levels can induce translation of the ferroportin assisting and copper binding amyloid precursor protein (APP); constitutive APP transmembrane passage lowers the copper pool which is important for many enzymes. Using in silico gene expression analyses, we here show significantly decreased expression of copper-dependent enzymes in AD brain and metallothioneins were upregulated in both diseases. Although few AD exposure risk factors are known, AD-related tauopathies can result from cyanobacterial microcystin and β-methylamino-L-alanine (BMAA) intake. Several environmental exposures may represent risk factors for PD; for this disease neurodegeneration is likely to involve mitochondrial dysfunction, microglial activation, and neuroinflammation. Administration of metal chelators and anti-inflammatory agents could affect disease outcomes.

Protective effects of l-carnitine and piracetam against mitochondrial permeability transition and PC3 cell necrosis induced by simvastatin

Mitochondrial oxidative stress followed by membrane permeability transition (MPT) has been considered as a possible mechanism for statins cytotoxicity. Statins use has been associated with reduced risk of cancer incidence, especially prostate cancer. Here we investigated the pathways leading to simvastatin-induced prostate cancer cell death as well as the mechanisms of cell death protection by l-carnitine or piracetam. These compounds are known to prevent and/or protect against cell death mediated by oxidative mitochondrial damage induced by a variety of conditions, either in vivo or in vitro. The results provide evidence that simvastatin induced MPT and cell necrosis were sensitive to either l-carnitine or piracetam in a dose-dependent fashion and mediated by additive mechanisms. When combined, l-carnitine and piracetam acted at concentrations significantly lower than they act individually. These results shed new light into both the cytotoxic mechanisms of statins and the mechanisms underlying the protection against MPT and cell death by the compounds l-carnitine and piracetam.

AIF, reactive oxygen species, and neurodegeneration: a "complex" problem

Apoptosis-inducing factor (AIF) is a flavin-binding mitochondrial intermembrane space protein that is implicated in diverse but intertwined processes that include maintenance of electron transport chain function, reactive oxygen species regulation, cell death, and neurodegeneration. In acute brain injury, AIF acquires a pro-death role upon translocation from the mitochondria to the nucleus, where it initiates chromatin condensation and large-scale DNA fragmentation. Although harlequin mice exhibiting an 80-90% global reduction in AIF protein are resistant to numerous forms of acute brain injury, they paradoxically undergo slow, progressive neurodegeneration beginning at three months of age. Brain deterioration, accompanied by markers of oxidative stress, is most pronounced in the cerebellum and retina, although it also occurs in the cortex, striatum, and thalamus. Loss of an AIF pro-survival function linked to assembly or stabilization of electron transport chain complex I underlies chronic neurodegeneration. To date, most studies of neurodegeneration have failed to adequately separate the relative importance of the mitochondrial and nuclear functions of AIF in determining the extent of injury, or whether oxidative stress plays a causative role. This review explores the complicated relationship among AIF, complex I, and the regulation of mitochondrial reactive oxygen species levels. It also discusses the controversial role of complex I deficiency in Parkinson's disease, and what can be learned from the AIF- and complex I-depleted harlequin mouse.

[Manganese in atherogenesis: detection, origin, and role]

The role of transition metal ions in atherogenesis is controversial; they can participate in the hydroxyl radical generation and catalyze the reactive oxygen species neutralization reaction as cofactors of antioxidant enzymes. Using EPR spectroscopy, we revealed that 70% of the samples of aorta with atherosclerotic lesions possessed superoxide dismutase activity, 100% of the samples initiated Fenton reaction and demonstrated the presence of manganese paramagnetic centers. The sodA gene encoding manganese-dependent bacterial superoxide dismutase was not found in the samples of atherosclerotic plaques by PCR using degenerate primers. The data obtained indicates the perspectives of manganese analysis as a marker element in the express diagnostics of atherosclerosis.

Mitochondria targeted therapeutic approaches in Parkinson's and Huntington's diseases

Substantial evidence from both genetic and toxin induced animal and cellular models and postmortem human brain tissue indicates that mitochondrial dysfunction plays a central role in pathophysiology of the neurodegenerative disorders including Parkinson's disease (PD), and Huntington's disease (HD). This review discusses the emerging understanding of the role of mitochondrial dysfunction including bioenergetics defects, mitochondrial DNA mutations, familial nuclear DNA mutations, altered mitochondrial fusion/fission and morphology, mitochondrial transport/trafficking, altered transcription and increased interaction of pathogenic proteins with mitochondria in the pathogenesis of PD and HD. This review recapitulates some of the key therapeutic strategies applied to surmount mitochondrial dysfunction in these debilitating disorders. We discuss the therapeutic role of mitochondrial bioenergetic agents such as creatine, Coenzyme-Q10, mitochondrial targeted antioxidants and peptides, the SIRT1 activator resveratrol, and the pan-PPAR agonist bezafibrate in toxin and genetic cellular and animal models of PD and HD. We also summarize the phase II-III clinical trials conducted using some of these agents. Lastly, we discuss PGC-1α, TORC and Sirtuins as potential therapeutic targets for mitochondrial dysfunction in neurodegenerative disorders. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Mitochondrial deficiency: a double-edged sword for aging and neurodegeneration

For decades, aging was considered the inevitable result of the accumulation of damaged macromolecules due to environmental factors and intrinsic processes. Our current knowledge clearly supports that aging is a complex biological process influenced by multiple evolutionary conserved molecular pathways. With the advanced age, loss of cellular homeostasis severely affects the structure and function of various tissues, especially those highly sensitive to stressful conditions like the central nervous system. In this regard, the age-related regression of neural circuits and the consequent poor neuronal plasticity have been associated with metabolic dysfunctions, in which the decline of mitochondrial activity significantly contributes. Interestingly, while mitochondrial lesions promote the onset of degenerative disorders, mild mitochondrial manipulations delay some of the age-related phenotypes and, more importantly, increase the lifespan of organisms ranging from invertebrates to mammals. Here, we survey the insulin/IGF-1 and the TOR signaling pathways and review how these two important longevity determinants regulate mitochondrial activity. Furthermore, we discuss the contribution of slight mitochondrial dysfunction in the engagement of pro-longevity processes and the opposite role of strong mitochondrial dysfunction in neurodegeneration.

Mitochondrial complex I inhibitors, acetogenins, induce HepG2 cell death through the induction of the complete apoptotic mitochondrial pathway

The development of new anti-neoplastic drugs is a key issue for cancer chemotherapy due to the reality that, most likely, certain cancer cells are resistant to current chemotherapy. The past two decades have witnessed tremendous advances in our understanding of the pathogenesis of cancer. These advances have allowed identification new targets as oncogenes, tumor supressor genes and the possible implication of the mitochondria (Fulda et al. Nat Rev Drug Discov 9:447-464, 2010). Annonaceous Acetogenins (ACGs) have been described as the most potent inhibitors of the respiratory chain because of their interaction with mitochondrial Complex I (Degli Esposti and Ghelli Biochim Biophys Acta 1187:116-120, 1994; Zafra-Polo et al. Phytochemistry 42:253-271, 1996; Miyoshi et al. Biochim Biophys Acta 1365:443-452, 1998; Tormo et al. Arch Biochem Biophys 369:119-126, 1999; Motoyama et al. Bioorg Med Chem Lett 12:2089-2092, 2002). To explore a possible application of natural products from Annonaceous plants to cancer treatment, we have selected four bis-tetrahydrofuranic ACGs, three from Annona cherimolia (cherimolin-1, motrilin and laherradurin) and one from Rollinia mucosa (rollinianstatin-1) in order to fully describe their mechanisms responsible within the cell (Fig. 1). In this study, using a hepato-carcinoma cell line (HepG2) as a model, we showed that the bis-THF ACGs caused cell death through the induction of the apoptotic mitochondrial pathway. Their potency and behavior were compared with the classical mitochondrial respiratory chain Complex I inhibitor rotenone in every apoptotic pathway step.

DJ-1 expression modulates astrocyte-mediated protection against neuronal oxidative stress

DJ-1 deficiency is a cause of genetic Parkinson's disease (PARK7 PD). In sporadic Parkinson's disease (PD), however, DJ-1 is abundantly expressed in reactive astrocytes. This may represent a compensatory protective response. In initial support of this hypothesis, we have shown in vitro that DJ-1-overexpressing astrocytes protect neurons against rotenone-induced death. Rotenone, a pesticide linked to increased PD risk, can stimulate oxidative stress. This process is implicated in PD pathogenesis. Since DJ-1 can enhance antioxidant systems, we hypothesized that augmenting its expression in astrocytes would protect cocultured neurons against oxidative stress. We report here that DJ-1-overexpressing astrocytes were significantly more protective against rotenone-induced neuronal thiol oxidation than wild-type astrocytes in neuron-astrocyte cocultures. DJ-1-knockdown astrocytes, on the other hand, were significantly impaired in their capacity to protect neurons against thiol oxidation. Each of these findings was replicated using astrocyte-conditioned media on neuron-enriched cultures. Thus, DJ-1-modulated, astrocyte-released soluble factors must be involved in the mechanism. This is the first demonstration that the manipulation of a PD-causing gene in astrocytes affects their ability to protect neurons against oxidative stress.

Interaction of TNF with angiotensin II contributes to mitochondrial oxidative stress and cardiac damage in rats

Recent evidence suggests that tumor necrosis factor alpha (TNF) and angiotensin II (ANGII) induce oxidative stress contribute to cardiovascular disease progression. Here, we examined whether an interaction between TNF and ANGII contributes to altered cardiac mitochondrial biogenesis and ATP production to cause cardiac damage in rats. Rats received intraperitoneal injections of TNF (30 µg/kg), TNF + losartan (LOS, 1 mg/kg), or vehicle for 5 days. Left ventricular (LV) function was measured using echocardiography. Rats were sacrificed and LV tissues removed for gene expression, electron paramagnetic resonance and mitochondrial assays. TNF administration significantly increased expression of the NADPH oxidase subunit, gp91phox, and the angiotensin type 1 receptor (AT-1R) and decreased eNOS in the LV of rats. Rats that received TNF only had increased production rates of superoxide, peroxynitrite and total reactive oxygen species (ROS) in the cytosol and increased production rates of superoxide and hydrogen peroxide in mitochondria. Decreased activities of mitochondrial complexes I, II, and III and mitochondrial genes were observed in rats given TNF. In addition, TNF administration also resulted in a decrease in fractional shortening and an increase in Tei index, suggesting diastolic dysfunction. TNF administration with concomitant LOS treatment attenuated mitochondrial damage, restored cardiac function, and decreased expression of AT1-R and NADPH oxidase subunits. Mitochondrial biogenesis and function is severely impaired by TNF as evidenced by downregulation of mitochondrial genes and increased free radical production, and may contribute to cardiac damage. These defects are independent of the downregulation of mitochondrial gene expression, suggesting novel mechanisms for mitochondrial dysfunction in rats given TNF.

Photooxidation of Amplex Red to resorufin: implications of exposing the Amplex Red assay to light

The Amplex Red assay, a fluorescent assay for the detection of H(2)O(2), relies on the reaction of H(2)O(2) and colorless, nonfluorescent Amplex Red with a 1:1 stoichiometry to form colored, fluorescent resorufin, catalyzed by horseradish peroxidase (HRP). We have found that resorufin is artifactually formed when Amplex Red is exposed to light. In the absence of H(2)O(2) and HRP, the absorption and fluorescence spectra of Amplex Red changed during exposure to ambient room light or instrumental excitation light, clearly indicating that the fluorescent product resorufin had formed. This photochemistry was initiated by trace amounts of resorufin that are present in Amplex Red stock solutions. ESR spin-trapping studies demonstrated that superoxide radical was an intermediate in this process. Oxygen consumption measurements further confirmed that superoxide and H(2)O(2) were artifactually produced by the photooxidation of Amplex Red. The artifactual formation of resorufin was also significantly increased by the presence of superoxide dismutase or HRP. This photooxidation process will result in a less sensitive assay for H(2)O(2) under ambient light exposure and potentially invalid measurements under high energy exposure such as UVA irradiation. In general, precautions should be taken to minimize exposure to light during measurement of oxidative stress with Amplex Red.

The complex regulation of human glud1 and glud2 glutamate dehydrogenases and its implications in nerve tissue biology

Mammalian glutamate dehydrogenase (GDH) is a housekeeping mitochondrial enzyme (hGDH1 in the human) that catalyses the reversible inter-conversion of glutamate to α-ketoglutarate and ammonia, thus interconnecting amino acid and carbohydrate metabolism. It displays an energy sensing mechanism, which permits enzyme activation under low cellular energy states. As GDH is at the crossroads of important metabolic pathways, a tight control of its activity is essential. Indeed, to fulfill its role in metabolism and cellular energetics, mammalian GDH has evolved into a highly regulated enzyme subject to allosteric modulation by diverse compounds. The recent emergence (<23 million years ago) in apes and humans of a hGDH2 isoenzyme with distinct regulatory properties, as well as, the detection of gain-of-function variants in hGDH1 and hGDH2 that affect the nervous system, have introduced additional complexities. The properties of the two highly homologous human GDHs were studied using purified recombinant hGDH1 and hGDH2 obtained by expression of the corresponding cDNAs in Sf21 cells. Results showed that, in contrast to hGDH1 that maintains substantial basal activity (35-40% of its maximal capacity), hGDH2 displays low basal activity (3-8% of maximal) that is remarkably responsive to activation by rising levels of ADP and/or l-leucine. This is primarily due to the Arg443Ser evolutionary change, which also made hGDH2 markedly sensitive to estrogens and neuroleptic drugs. In contrast to hGDH1, which is subject to potent GTP inhibition, hGDH2 has dissociated its function from this energy switch, being able to metabolize glutamate even when the Krebs cycle generates GTP levels sufficient to inactivate the housekeeping hGDH1. Our data also show that spermidine, a polyamine thought to reduce oxidative stress and to prolong survival, and EGCG, a green tea polyphenol, inhibit hGDH2 at lower concentrations than hGDH1. The implications of these findings in nerve tissue biology are discussed.

Mitochondrial reactive oxygen species and calcium uptake regulate activation of phagocytic NADPH oxidase

Production of superoxide (O(2)(·-)) by NADPH oxidases contributes to the development of hypertension and atherosclerosis. Factors responsible for activation of NADPH oxidases are not well understood; interestingly, cardiovascular disease is associated with both altered NADPH oxidase activity and age-associated mitochondrial dysfunction. We hypothesized that mitochondrial dysfunction may contribute to activation of NADPH oxidase. The effect of mitochondrial inhibitors on phagocytic NADPH oxidase in human lymphoblasts and whole blood was measured at the basal state and upon PKC-dependent stimulation with PMA using extracellular 1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl-trimethylammonium or mitochondria-targeted 1-hydroxy-4-[2-triphenylphosphonio)-acetamido]-2,2,6,6-tetramethylpiperidine spin probes and electron spin resonance (ESR). Intracellular cytosolic calcium [Ca(2+)](i) was measured spectrofluorometrically using fura-2 AM. Incubation of lymphoblasts with the mitochondrial inhibitors rotenone, antimycin A, CCCP, or ruthenium red (an inhibitor of mitochondrial Ca(2+) uniporter) did not significantly change basal activity of NADPH oxidase. In contrast, preincubation with the mitochondrial inhibitors prior to PMA stimulation of lymphoblasts resulted in two- to three-fold increase of NADPH oxidase activity compared with stimulation with PMA alone. Most notably, the intracellular Ca(2+)-chelating agent BAPTA-AM abolished the effect of mitochondrial inhibitors on NADPH oxidase activity. Cytosolic Ca(2+) measurements with fura-2 AM showed that the mitochondrial inhibitors increased [Ca(2+)](i), while BAPTA-AM abolished the increase in [Ca(2+)](i). Furthermore, depletion of cellular Ca(2+) with thapsigargin attenuated CCCP- and antimycin A-mediated activation of NADPH oxidase in the presence of PMA by 42% and 31%, correspondingly. Our data suggest that mitochondria regulate PKC-dependent activation of phagocytic NADPH oxidase. In summary, increased mitochondrial O(2)(·-) and impaired buffering of cytosolic Ca(2+) by dysfunctional mitochondria result in enhanced NADPH oxidase activity, which may contribute to the development of cardiovascular diseases.

Prohibitin reduces mitochondrial free radical production and protects brain cells from different injury modalities

Prohibitin is an essential mitochondrial protein that has been implicated in a wide variety of functions in many cell types, but its role in neurons remains unclear. In a proteomic screen of rat brains in which ischemic tolerance was induced by electrical stimulation of the cerebellar fastigial nucleus, we found that prohibitin is upregulated in mitochondria. This observation prompted us to investigate the role of prohibitin in neuronal death and survival. We found that prohibitin is upregulated also in the ischemic tolerance induced by transient ischemia in vivo, or oxygen-glucose deprivation in neuronal cultures. Cell fractionation and electron-microscopic immunolabeling studies demonstrated that prohibitin is localized to neuronal mitochondria. Upregulation of prohibitin in neuronal cultures or hippocampal slices was markedly neuroprotective, whereas prohibitin gene silencing increased neuronal vulnerability, an effect associated with loss of mitochondrial membrane potential and increased mitochondrial production of reactive oxygen species. Prohibitin upregulation was associated with reduced production of reactive oxygen species in mitochondria exposed to the complex I inhibitor rotenone. In addition, prohibitin protected complex I activity from the inhibitory effects of rotenone. These observations, collectively, establish prohibitin as an endogenous neuroprotective protein involved in ischemic tolerance. Prohibitin exerts beneficial effects on neurons by reducing mitochondrial free radical production. The data with complex I activity suggest that prohibitin may stabilize the function of complex I. The protective effect of prohibitin has potential translational relevance in diseases of the nervous system associated with mitochondrial dysfunction and oxidative stress.

Forced swimming stress does not affect monoamine levels and neurodegeneration in rats

OBJECTIVE

The current study was aimed to investigate the correlations between immobility time in the forced swimming test (FST, a behavioral indicator of stress level) and hippocampal monoamine levels (markers of depression), plasma adrenalin level (a peripheral marker of stress) as well as fluoro-jade C staining (a marker of neurodegeneration).

METHODS

Male Sprague-Dawley rats were subjected to acute, sub-chronic (7 d) or chronic (14 d) FSTs and immobility time was recorded. Levels of noradrenalin, serotonin and dopamine in the hippocampus, and adrenalin level in the plasma were quantified by high-performance liquid chromatography with electrochemical detection. Brain sections from rats after chronic forced swimming or rotenone treatment (3 mg/kg subcutaneously for 4 d) were stained with fluoro-jade C.

RESULTS

The rats subjected to swimming stress (acute, sub-chronic and chronic) showed long immobility times [(214 +/- 5), (220 +/- 4) and (231 +/- 7) s, respectively], indicating that the animals were under stress. However, the rats did not exhibit significant declines in hippocampal monoamine levels, and the plasma adrenalin level was not significantly increased compared to that in unstressed rats. The rats that underwent chronic swimming stress did not manifest fluoro-jade C staining in brain sections, while degenerating neurons were evident after rotenone treatment.

CONCLUSION

The immobility time in the FST does not correlate with markers of depression (monoamine levels) and internal stress (adrenalin levels and neurodegeneration), hence this parameter may not be a true indicator of stress level.

The yeast complex I equivalent NADH dehydrogenase rescues pink1 mutants

Pink1 is a mitochondrial kinase involved in Parkinson's disease, and loss of Pink1 function affects mitochondrial morphology via a pathway involving Parkin and components of the mitochondrial remodeling machinery. Pink1 loss also affects the enzymatic activity of isolated Complex I of the electron transport chain (ETC); however, the primary defect in pink1 mutants is unclear. We tested the hypothesis that ETC deficiency is upstream of other pink1-associated phenotypes. We expressed Saccaromyces cerevisiae Ndi1p, an enzyme that bypasses ETC Complex I, or sea squirt Ciona intestinalis AOX, an enzyme that bypasses ETC Complex III and IV, in pink1 mutant Drosophila and find that expression of Ndi1p, but not of AOX, rescues pink1-associated defects. Likewise, loss of function of subunits that encode for Complex I–associated proteins displays many of the pink1-associated phenotypes, and these defects are rescued by Ndi1p expression. Conversely, expression of Ndi1p fails to rescue any of the parkin mutant phenotypes. Additionally, unlike pink1 mutants, fly parkin mutants do not show reduced enzymatic activity of Complex I, indicating that Ndi1p acts downstream or parallel to Pink1, but upstream or independent of Parkin. Furthermore, while increasing mitochondrial fission or decreasing mitochondrial fusion rescues mitochondrial morphological defects in pink1 mutants, these manipulations fail to significantly rescue the reduced enzymatic activity of Complex I, indicating that functional defects observed at the level of Complex I enzymatic activity in pink1 mutant mitochondria do not arise from morphological defects. Our data indicate a central role for Complex I dysfunction in pink1-associated defects, and our genetic analyses with heterologous ETC enzymes suggest that Ndi1p-dependent NADH dehydrogenase activity largely acts downstream of, or in parallel to, Pink1 but upstream of Parkin and mitochondrial remodeling.

Parkinson's disease is the most common neurodegenerative movement disorder, and mutations in several genes are known to cause the disorder. A common theme among several PD–associated genes is a link to mitochondria, organelles that use their electron transport chain to generate ATP. One of the PD–associated genes encodes a mitochondrial kinase Pink1, but it is not known what the primary role of Pink1 is within the mitochondria. Indeed, loss of Pink1 function in cells and model organisms results not only in mitochondrial morphological defects but also in an enzymatic deficit at the level of the first protein complex in the electron transport chain. Here, we express yeast Ndi1p (an enzyme that can bypass electron transport in Complex I) and sea squirt alternative oxidase (an enzyme that can bypass electron transport in Complex III/IV) in pink1 mutant fruit flies and find that supplementing the mutants with Ndi1p, but not with alternative oxidase, results in significant rescue of multiple phenotypes. Conversely, mitochondrial morphological defects in pink1 mutants are rescued by genetically improving mitochondrial fission, but this manipulation fails to improve the enzymatic deficiency at the level of Complex I. Our data thus pinpoint an important mode of action of Pink1 at the level of Complex I, and this action at least in part precedes defects at the level of mitochondrial remodeling.

Protective effects of baicalein against rotenone-induced neurotoxicity in PC12 cells and isolated rat brain mitochondria

Baicalein is one of the major flavonoids obtained from the Scutellaria root. Previous pharmacological studies found that baicalein had neuroprotective effects in animal models of Parkinson's disease. The purpose of this paper was to explore the molecular mechanism of the action of baicalein on PC12 cells and isolated rat brain mitochondria. Firstly, we investigated the effects of baicalein on rotenone-induced toxicity in PC12 cells. The results showed that baicalein suppressed rotenone-induced apoptosis, and inhibited the accumulation of reactive oxidant species, ATP deficiency, mitochondrial membrane potential dissipation, and caspase-3/7 activation in a concentration-dependent manner, indicating that baicalein likely improved mitochondrial function. Furthermore, we used isolated rat brain mitochondria to evaluate the effect of baicalein. Treatment with baicalein prevented rotenone-induced reactive oxidant species production, ATP deficiency and mitochondrial swelling in isolated brain mitochondria. Interestingly, exposure of isolated mitochondria to baicalein promoted mitochondrial active respiration. These results suggest that baicalein may be a mitochondria-targeted antioxidant and exerts neuroprotective effects on rotenone-induced neurotoxicity. This study supports our previous research that baicalein possesses neuroprotective activity in vivo and it is worthy of further study.

Cross talk between mitochondria and NADPH oxidases

Reactive oxygen species (ROS) play an important role in physiological and pathological processes. In recent years, a feed-forward regulation of the ROS sources has been reported. The interactions between the main cellular sources of ROS, such as mitochondria and NADPH oxidases, however, remain obscure. This work summarizes the latest findings on the role of cross talk between mitochondria and NADPH oxidases in pathophysiological processes. Mitochondria have the highest levels of antioxidants in the cell and play an important role in the maintenance of cellular redox status, thereby acting as an ROS and redox sink and limiting NADPH oxidase activity. Mitochondria, however, are not only a target for ROS produced by NADPH oxidase but also a significant source of ROS, which under certain conditions may stimulate NADPH oxidases. This cross talk between mitochondria and NADPH oxidases, therefore, may represent a feed-forward vicious cycle of ROS production, which can be pharmacologically targeted under conditions of oxidative stress. It has been demonstrated that mitochondria-targeted antioxidants break this vicious cycle, inhibiting ROS production by mitochondria and reducing NADPH oxidase activity. This may provide a novel strategy for treatment of many pathological conditions including aging, atherosclerosis, diabetes, hypertension, and degenerative neurological disorders in which mitochondrial oxidative stress seems to play a role. It is conceivable that the use of mitochondria-targeted treatments would be effective in these conditions.

DJ-1 knock-down impairs astrocyte mitochondrial function

Mitochondrial dysfunction has long been implicated in the pathogenesis of Parkinson's disease (PD). PD brain tissues show evidence for mitochondrial respiratory chain Complex I deficiency. Pharmacological inhibitors of Complex I, such as rotenone, cause experimental parkinsonism. The cytoprotective protein DJ-1, whose deletion is sufficient to cause genetic PD, is also known to have mitochondria-stabilizing properties. We have previously shown that DJ-1 is over-expressed in PD astrocytes, and that DJ-1 deficiency impairs the capacity of astrocytes to protect co-cultured neurons against rotenone. Since DJ-1 modulated, astrocyte-mediated neuroprotection against rotenone may depend upon proper astrocytic mitochondrial functioning, we hypothesized that DJ-1 deficiency would impair astrocyte mitochondrial motility, fission/fusion dynamics, membrane potential maintenance, and respiration, both at baseline and as an enhancement of rotenone-induced mitochondrial dysfunction. In astrocyte-enriched cultures, we observed that DJ-1 knock-down reduced mitochondrial motility primarily in the cellular processes of both untreated and rotenone treated cells. In these same cultures, DJ-1 knock-down did not appreciably affect mitochondrial fission, fusion, or respiration, but did enhance rotenone-induced reductions in the mitochondrial membrane potential. In neuron-astrocyte co-cultures, astrocytic DJ-1 knock-down reduced astrocyte process mitochondrial motility in untreated cells, but this effect was not maintained in the presence of rotenone. In the same co-cultures, astrocytic DJ-1 knock-down significantly reduced mitochondrial fusion in the astrocyte cell bodies, but not the processes, under the same conditions of rotenone treatment in which DJ-1 deficiency is known to impair astrocyte-mediated neuroprotection. Our studies therefore demonstrated the following new findings: (i) DJ-1 deficiency can impair astrocyte mitochondrial physiology at multiple levels, (ii) astrocyte mitochondrial dynamics vary with sub-cellular region, and (iii) the physical presence of neurons can affect astrocyte mitochondrial behavior.

Single-cell redox imaging demonstrates a distinctive response of dopaminergic neurons to oxidative insults

AIMS

The study of the intracellular oxido-reductive (redox) state is of extreme relevance to the dopamine (DA) neurons of the substantia nigra pars compacta. These cells possess a distinct physiology intrinsically associated with elevated reactive oxygen species production, and they selectively degenerate in Parkinson's disease under oxidative stress conditions. To test the hypothesis that these cells display a unique redox response to mild, physiologically relevant oxidative insults when compared with other neuronal populations, we sought to develop a novel method for quantitatively assessing mild variations in intracellular redox state.

RESULTS

We have developed a new imaging strategy to study redox variations in single cells, which is sensitive enough to detect changes within the physiological range. We studied DA neurons' physiological redox response in biological systems of increasing complexity--from primary cultures to zebrafish larvae, to mammalian brains-and identified a redox response that is distinctive for substantia nigra pars compacta DA neurons. We studied simultaneously, and in the same cells, redox state and signaling activation and found that these phenomena are synchronized.

INNOVATION

The redox histochemistry method we have developed allows for sensitive quantification of intracellular redox state in situ. As this method is compatible with traditional immunohistochemical techniques, it can be applied to diverse settings to investigate, in theory, any cell type of interest.

CONCLUSION

Although the technique we have developed is of general interest, these findings provide insights into the biology of DA neurons in health and disease and may have implications for therapeutic intervention.

An effective novel delivery strategy of rasagiline for Parkinson's disease

This is the first report on the efficacy of a new controlled release system developed for rasagiline mesylate (RM) in a rotenone-induced rat model of Parkinson's disease (PD). PLGA microspheres in vitro released RM at a constant rate of 62.3 μg/day for two weeks. Intraperitoneal injection of rotenone (2 mg/kg/day) to Wistar rats produced typical PD symptoms. Catalepsy, akinesia and swim tests outcomes in animals receiving RM either in solution or within microspheres showed a reversal in descent latency when compared to rotenone-treated animals, being this reversal specially pronounced in animals receiving RM microspheres (dose equivalent to 1 mg/kg/day RM injected i.p. every 15 days). Nissl-staining of brain sections showed selective degeneration of the substantia nigra (SNc) dopaminergic neurons in rotenone-treated animals which was markedly reverted by RM microspheres. PET/CT with (18)F-DG resulted in mean increases of accumulation of radiotracer in striatum and SNc of around 40% in animals treated with RM microspheres which also had significant beneficial effects on Bcl-2, Bax, TNF-α mRNA and SOD2 levels as detected by real-time RT-PCR. Our results confirm the robust effect achieved by the new controlled release system developed for RM which exhibited better in vivo efficacy than RM given in solution.

Do mtDNA Mutations Participate in the Pathogenesis of Sporadic Parkinson's Disease?

The pathogenesis of sporadic Parkinson’s disease (PD) remains enigmatic. Mitochondrial complex-I defects are known to occur in the substantia nigra (SN) of PD patients and are also debated in some extracerebral tissues. Early sequencing efforts of the mitochondrial DNA (mtDNA) did not reveal specific mutations, but a long lasting discussion was devoted to the issue of randomly distributed low level point mutations, caused by oxidative stress. However, a potential functional impact remained a matter of speculation, since heteroplasmy (mutational load) at any base position analyzed, remained far below the relevant functional threshold. A clearly age-dependent increase of the ‘common mtDNA deletion’ had been demonstrated in most brain regions by several authors since 1992. However, heteroplasmy did hardly exceed 1% of total mtDNA. It became necessary to exploit PCR techniques, which were able to detect any deletion in a few microdissected dopaminergic neurons of the SN. In 2006, two groups published biochemically relevant loads of somatic mtDNA deletions in these neurons. They seem to accumulate to relevant levels in the SN dopaminergic neurons of aged individuals in general, but faster in those developing PD. It is reasonable to assume that this accumulation causes mitochondrial dysfunction of the SN, although it cannot be taken as a final proof for an early pathogenetic role of this dysfunction. Recent studies demonstrate a distribution of deletion breakpoints, which does not differ between PD, aging and classical mitochondrial disorders, suggesting a common, but yet unknown mechanism.

Effects of pioglitazone and retinoic acid in a rotenone model of Parkinson's disease

Parkinson's disease (PD) is a late-onset, progressive and neurodegenerative disorder of unknown etiology. Besides the other therapeutic approaches, new drug options in pharmacotherapy of PD are important. The aim of the present study was to investigate the effects of pioglitazone and retinoic acid, antioxidant and neuroprotective agents, on rotenone-induced model of PD in rats. Adult male Wistar rats (260-373 g) were subjects. Rotenone (2.5mg/kg, sc) was injected to rats for 70 days. At the end of rotenone administration, rats were treated with pioglitazone (10mg/kg, ip) and retinoic acid (1mg/kg, ip) or vehicles for 15 days. Then, rats were tested for evaluation of Parkinson signs by measurement of locomotor activity. In addition, dopamine levels were detected in striatum, hippocampus and hypothalamus in individual groups of control, rotenone and pioglitazone or retinoic acid-treated rats. Rotenone significantly reduced locomotor activity of the rats. It also significantly reduced dopamine levels in striatum and hippocampus, but not hypothalamus. Pioglitazone and retinoic acid reversed in reduction of locomotor activity significantly. Pioglitazone, but not retinoic acid, significantly reversed the reduced striatal dopamine level. Both drugs were ineffective on reduced levels of dopamine in hippocampus. Our results suggest that pioglitazone and retinoic acid have some beneficial effects on rotenone-induced model of PD in rats. Pioglitazone seems to be more effective than retinoic acid. These agents may be helpful for preventing or controlling of some signs of PD.

EPR detection of cellular and mitochondrial superoxide using cyclic hydroxylamines

Superoxide (O₂ⁱ⁻) has been implicated in the pathogenesis of many human diseases, but detection of the O(2)(•-) radicals in biological systems is limited due to inefficiency of O₂ⁱ⁻ spin trapping and lack of site-specific information. This work studied production of extracellular, intracellular and mitochondrial O₂ⁱ⁻ in neutrophils, cultured endothelial cells and isolated mitochondria using a new set of cationic, anionic and neutral hydroxylamine spin probes with various lipophilicity and cell permeability. Cyclic hydroxylamines rapidly react with O₂ⁱ⁻, producing stable nitroxides and allowing site-specific cO₂ⁱ⁻ detection in intracellular, extracellular and mitochondrial compartments. Negatively charged 1-hydroxy-4-phosphono-oxy-2,2,6,6-tetramethylpiperidine (PP-H) and positively charged 1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl-trimethylammonium (CAT1-H) detected only extramitochondrial O₂ⁱ⁻. Inhibition of EPR signal by SOD2 over-expression showed that mitochondria targeted mitoTEMPO-H detected intramitochondrial O₂ⁱ⁻ both in isolated mitochondria and intact cells. Both 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CP-H) and 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CM-H) detected an increase in cytoplasm O₂ⁱ⁻ stimulated by PMA, but only CM-H and mitoTEMPO-H showed an increase in rotenone-induced mitochondrial O₂ⁱ⁻. These data show that a new set of hydroxylamine spin probes provide unique information about site-specific production of the O₂ⁱ⁻ radical in extracellular or intracellular compartments, cytoplasm or mitochondria.

BmDJ-1 is a key regulator of oxidative modification in the development of the silkworm, Bombyx mori

We cloned cDNA for the Bombyx mori DJ-1 protein (BmDJ-1) from the brains of larvae. BmDJ-1 is composed of 190 amino acids and encoded by 672 nucleotides. Northern blot analysis showed that BmDJ-1 is transcribed as a 756-bp mRNA and has one isoform. Reverse transcriptase (RT)-PCR experiments revealed that the BmDJ-1 was present in the brain, fatbody, Malpighian tubule, ovary and testis but present in only low amounts in the silkgland and hemocyte of day 4 fifth instar larvae. Immunological analysis demonstrated the presence of BmDJ-1 in the brain, midgut, fatbody, Malpighian tubule, testis and ovary from the larvae to the adult. We found that BmDJ-1 has a unique expression pattern through the fifth instar larval to adult developmental stage. We assessed the anti-oxidative function of BmDJ-1 using rotenone (ROT) in day 3 fifth instar larvae. Administration of ROT to day 3 fifth instar larvae, together with exogenous (BmNPV-BmDJ-1 infection for 4 days in advance) BmDJ-1, produced significantly lower 24-h mortality in BmDJ-1 groups than in the control. 2D-PAGE revealed an isoelectric point (pI) shift to an acidic form for BmDJ-1 in BmN4 cells upon ROT stimulus. Among the factors examined for their effects on expression level of BmDJ-1 in the hemolymph, nitric oxide (NO) concentration was identified based on dramatic developmental stage-dependent changes. Administration of isosorbide dinitrate (ISDN), which is an NO donor, to BmN4 cells produced increased expression of BmDJ-1 compared to the control. These results suggest that BmDJ-1 might control oxidative stress in the cell due to NO and serves as a development modulation factor in B. mori.

Effect of bovine serum albumin on mitochondrial respiration in the brain and liver of mice and rats

We studied the effect of BSA (in the isolation medium) on the oxidation rate of succinate, glutamate, pyruvate, and α-ketoglutarate by mitochondria of the brain and liver from C57Bl/6g mice and Taconic Sprague Dawley rats. BSA had no effect on liver mitochondrial respiration, but increased oxidation of substrates (particularly of succinate) in brain mitochondria. Therefore, the major effect of BSA on brain mitochondria is manifested in activation of SDH. The improvement of mitochondrial properties in the brain after treatment with BSA is associated with antioxidant activity of this agent. Our results confirm the hypothesis that inhibition of SDH in brain mitochondria is not the artifact. This process serves as a mechanism protecting neurons from free oxygen radicals during succinate oxidation.

DJ-1 deficiency in astrocytes selectively enhances mitochondrial Complex I inhibitor-induced neurotoxicity

Parkinson's disease (PD) brains show evidence of mitochondrial respiratory Complex I deficiency, oxidative stress, and neuronal death. Complex I-inhibiting neurotoxins, such as the pesticide rotenone, cause neuronal death and parkinsonism in animal models. We have previously shown that DJ-1 over-expression in astrocytes augments their capacity to protect neurons against rotenone, that DJ-1 knock-down impairs astrocyte-mediated neuroprotection against rotenone, and that each process involves astrocyte-released factors. To further investigate the mechanism behind these findings, we developed a high-throughput, plate-based bioassay that can be used to assess how genetic manipulations in astrocytes affect their ability to protect co-cultured neurons. We used this bioassay to show that DJ-1 deficiency-induced impairments in astrocyte-mediated neuroprotection occur solely in the presence of pesticides that inhibit Complex I (rotenone, pyridaben, fenazaquin, and fenpyroximate); not with agents that inhibit Complexes II-V, that primarily induce oxidative stress, or that inhibit the proteasome. This is a potentially PD-relevant finding because pesticide exposure is epidemiologically-linked with an increased risk for PD. Further investigations into our model suggested that astrocytic GSH and heme oxygenase-1 antioxidant systems are not central to the neuroprotective mechanism.

Metabolic and functional differences between brain and spinal cord mitochondria underlie different predisposition to pathology

Mitochondrial dysfunctions contribute to neurodegeneration, the locations of which vary among neurodegenerative diseases. To begin to understand what mechanisms may underlie higher vulnerability of the spinal cord motor neurons in amyotrophic lateral sclerosis, compared with brain mitochondria, we studied three major functions of rat brain mitochondria (BM) and spinal cord mitochondria (SCM) mitochondria: oxidative phosphorylation, Ca(2+) sequestration, and production of reactive oxygen species (ROS), using a new metabolic paradigm (Panov et al., J. Biol. Chem. 284: 14448-14456, 2009). We present data that SCM share some unique metabolic properties of the BM. However, SCM also have several distinctions from the BM: 1) With the exception of succinate, SCM show significantly lower rates of respiration with all substrates studied; 2) immunoblotting analysis showed that this may be due to 30-40% lower contents of respiratory enzymes and porin; 3) compared with BM, SCM sequestered 40-50% less Ca(2+), and the total tissue calcium content was 8 times higher in the spinal cord; 4) normalization for mitochondria from 1 g of tissue showed that BM can sequester several times more Ca(2+) than was available in the brain tissue, whereas SCM had the capacity to sequester only 10-20% of the total tissue Ca(2+); and 5) with succinate and succinate-containing substrate mixtures, SCM showed significantly higher state 4 respiration than BM and generated more ROS associated with the reverse electron transport. We conclude that SCM have an intrinsically higher risk of oxidative damage and overload with calcium than BM, and thus spinal cord may be more vulnerable under some pathologic conditions. (250).

Therapeutic potential of targeting group III metabotropic glutamate receptors in the treatment of Parkinson's disease

Current drugs used in the treatment of Parkinson's disease (PD), for example, L-DOPA and dopamine agonists, are very effective at reversing the motor symptoms of the disease. However, they do little to combat the underlying degeneration of dopaminergic neurones in the substantia nigra pars compacta (SNc) and their long-term use is associated with the appearance of adverse effects such as L-DOPA-induced dyskinesia. Much emphasis has therefore been placed on finding alternative non-dopaminergic drugs that may circumvent some or all of these problems. Group III metabotropic glutamate (mGlu) receptors were first identified in the basal ganglia a decade ago. One or more of these receptors (mGlu4, mGlu7 or mGlu8) is found on pre-synaptic terminals of basal ganglia pathways whose overactivity is implicated not only in the generation of motor symptoms in PD, but also in driving the progressive SNc degeneration. The finding that drugs which activate group III mGlu receptors can inhibit transmission across these overactive synapses has lead to the proposal that group III mGlu receptors are promising targets for drug discovery in PD. This paper provides a comprehensive review of the role and target potential of group III mGlu receptors in the basal ganglia. Overwhelming evidence obtained from in vitro studies and animal models of PD supports group III mGlu receptors as potentially important drug targets for providing both symptom relief and neuroprotection in PD.

Neurotoxicity of endocrine disruptors: possible involvement in brain development and neurodegeneration

Environmental chemicals that act as endocrine disruptors do not appear to pose a risk to human reproduction; however, their effects on the central nervous systems are less well understood. Animal studies suggested that maternal exposure to endocrine-disrupting chemicals (EDC) produced changes in rearing behavior, locomotion, anxiety, and learning/memory in offspring, as well as neuronal abnormalities. Some investigations suggested that EDC exert effects on central monoaminergic neurons, especially dopaminergic neurons. Our data demonstrated that EDC attenuate the development of dopaminergic neurons, which might be involved in developmental disorders. Perinatal exposure to EDC might affect neuronal plasticity in the hippocampus, thereby potentially modulating neuronal development, leading to impaired cognitive and memory functions. Endocrine disruptors also attenuate gender differences in brain development. For example, the locus ceruleus is larger in female rats than in males, but treatments with bisphenol-A (BPA) enlarge this region in males. Some reports indicated that EDC induce hypothyroidism, which might be evidenced as abnormal brain development. Endocrine disruptors might also affect mature neurons, resulting in neurodegenerative disorders such as Parkinson's disease. The current review focused on alterations in the brain induced by EDC, specifically on the possible involvement of EDC in brain development and neurodegeneration.

Neuroprotection by a mitochondria-targeted drug in a Parkinson's disease model

The objective of this study was to assess the neuroprotective effects of a mitochondria-targeted antioxidant, Mito-Q(10), the coenzyme-Q analog attached to a triphenylphosphonium cation that targets the antioxidant to mitochondria, in experimental models of Parkinson's disease (PD). Primary mesencephalic neuronal cells and cultured dopaminergic cells were treated with 1-methyl-4-phenylpyridinium (MPP(+)), an active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and mice were used for testing the efficacy of Mito-Q(10). MPP(+) treatment caused a dose-dependent loss of tyrosine hydroxylase and membrane potential and an increase in caspase-3 activation in dopaminergic cells, which were reversed by Mito-Q(10). MPTP treatment induced a loss of striatal dopamine and its metabolites, inactivation of mitochondrial aconitase in the substantia nigra, and a loss of locomotor activity in mice. Treatment with Mito-Q(10) significantly inhibited both MPP(+)- and MPTP-induced neurotoxicity in cell culture and mouse models. Collectively, these results indicate that mitochondrial targeting of antioxidants is a promising neuroprotective strategy in this preclinical mouse model of PD.

Synaptic mitochondria in synaptic transmission and organization of vesicle pools in health and disease

Cell types rich in mitochondria, including neurons, display a high energy demand and a need for calcium buffering. The importance of mitochondria for proper neuronal function is stressed by the occurrence of neurological defects in patients suffering from a great variety of diseases caused by mutations in mitochondrial genes. Genetic and pharmacological evidence also reveal a role of these organelles in various aspects of neuronal physiology and in the pathogenesis of neurodegenerative disorders. Yet the mechanisms by which mitochondria can affect neurotransmission largely remain to be elucidated. In this review we focus on experimental data that suggest a critical function of synaptic mitochondria in the function and organization of synaptic vesicle pools, and in neurotransmitter release during intense neuronal activity. We discuss how calcium handling, ATP production and other mitochondrial mechanisms may influence synaptic vesicle pool organization and synaptic function. Given the link between synaptic mitochondrial function and neuronal communication, efforts toward better understanding mitochondrial biology may lead to novel therapeutic approaches of neurological disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and psychiatric disorders that are at least in part caused by mitochondrial deficits.

Mitochondrial dysfunction and loss of Parkinson's disease-linked proteins contribute to neurotoxicity of manganese-containing welding fumes

Welding generates complex metal aerosols, inhalation of which is linked to adverse health effects among welders. An important health concern of welding fume (WF) exposure is neurological dysfunction akin to Parkinson's disease (PD), thought to be mediated by manganese (Mn) in the fumes. Also, there is a proposition that welding might accelerate the onset of PD. Our recent findings link the presence of Mn in the WF with dopaminergic neurotoxicity seen in rats exposed to manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) fumes. To elucidate the molecular mechanisms further, we investigated the association of PD-linked (Park) genes and mitochondrial function in causing dopaminergic abnormality. Repeated instillations of the two fumes at doses that mimic ∼1 to 5 yr of worker exposure resulted in selective brain accumulation of Mn. This accumulation caused impairment of mitochondrial function and loss of tyrosine hydroxylase (TH) protein, indicative of dopaminergic injury. A fascinating finding was the altered expression of Parkin (Park2), Uchl1 (Park5), and Dj1 (Park7) proteins in dopaminergic brain areas. A similar regimen of manganese chloride (MnCl(2)) also caused extensive loss of striatal TH, mitochondrial electron transport components, and Park proteins. As mutations in PARK genes have been linked to early-onset PD in humans, and because welding is implicated as a risk factor for parkinsonism, PARK genes might play a critical role in WF-mediated dopaminergic dysfunction. Whether these molecular alterations culminate in neurobehavioral and neuropathological deficits reminiscent of PD remains to be ascertained.

Estrogen modification of human glutamate dehydrogenases is linked to enzyme activation state

Mammalian glutamate dehydrogenase (GDH) is a housekeeping enzyme central to the metabolism of glutamate. Its activity is potently inhibited by GTP (IC(50) = 0.1-0.3 μM) and thought to be controlled by the need of the cell in ATP. Estrogens are also known to inhibit mammalian GDH, but at relatively high concentrations. Because, in addition to this housekeeping human (h) GDH1, humans have acquired via a duplication event an hGDH2 isoform expressed in human cortical astrocytes, we tested here the interaction of estrogens with the two human isoenzymes. The results showed that, under base-line conditions, diethylstilbestrol potently inhibited hGDH2 (IC(50) = 0.08 ± 0.01 μM) and with ∼18-fold lower affinity hGDH1 (IC(50) = 1.67 ± 0.06 μM; p < 0.001). Similarly, 17β-estradiol showed a ∼18-fold higher affinity for hGDH2 (IC(50) = 1.53 ± 0.24 μM) than for hGDH1 (IC(50) = 26.94 ± 1.07 μM; p < 0.001). Also, estriol and progesterone were more potent inhibitors of hGDH2 than hGDH1. Structure/function analyses revealed that the evolutionary R443S substitution, which confers low basal activity, was largely responsible for sensitivity of hGDH2 to estrogens. Inhibition of both human GDHs by estrogens was inversely related to their state of activation induced by ADP, with the slope of this correlation being steeper for hGDH2 than for hGDH1. Also, the study of hGDH1 and hGDH2 mutants displaying different states of activation revealed that the affinity of estrogen for these enzymes correlated inversely (R = 0.99; p = 0.0001) with basal catalytic activity. Because astrocytes are known to synthesize estrogens, these hormones, by interacting potently with hGDH2 in its closed state, may contribute to regulation of glutamate metabolism in brain.

Parkinson's disease mutations in PINK1 result in decreased Complex I activity and deficient synaptic function

Mutations of the mitochondrial PTEN (phosphatase and tensin homologue)-induced kinase1 (PINK1) are important causes of recessive Parkinson disease (PD). Studies on loss of function and overexpression implicate PINK1 in apoptosis, abnormal mitochondrial morphology, impaired dopamine release and motor deficits. However, the fundamental mechanism underlying these various phenotypes remains to be clarified. Using fruit fly and mouse models we show that PINK1 deficiency or clinical mutations impact on the function of Complex I of the mitochondrial respiratory chain, resulting in mitochondrial depolarization and increased sensitivity to apoptotic stress in mammalian cells and tissues. In Drosophila neurons, PINK1 deficiency affects synaptic function, as the reserve pool of synaptic vesicles is not mobilized during rapid stimulation. The fundamental importance of PINK1 for energy maintenance under increased demand is further corroborated as this deficit can be rescued by adding ATP to the synapse. The clinical relevance of our observations is demonstrated by the fact that human wild type PINK1, but not PINK1 containing clinical mutations, can rescue Complex 1 deficiency. Our work suggests that Complex I deficiency underlies, at least partially, the pathogenesis of this hereditary form of PD. As Complex I dysfunction is also implicated in sporadic PD, a convergence of genetic and environmental causes of PD on a similar mitochondrial molecular mechanism appears to emerge.

The Drosophila vesicular monoamine transporter reduces pesticide-induced loss of dopaminergic neurons

Dopamine is cytotoxic and may play a role in the development of Parkinson's disease. However, its interaction with environmental risk factors such as pesticides remains poorly understood. The vesicular monoamine transporter (VMAT) regulates intracellular dopamine content, and we have tested the neuroprotective effects of VMAT in vivo using the model organism Drosophila melanogaster. We find that Drosophila VMAT (dVMAT) mutants contain fewer dopaminergic neurons than wild type, consistent with a developmental effect, and that dopaminergic cell loss in the mutant is exacerbated by the pesticides rotenone and paraquat. Overexpression of DVMAT protein does not increase the survival of animals exposed to rotenone, but blocks the loss of dopaminergic neurons caused by this pesticide. These results are the first to demonstrate an interaction between a VMAT and pesticides in vivo, and provide an important model to investigate the mechanisms by which pesticides and cellular DA may interact to kill dopaminergic cells.

Structure and organization of mitochondrial respiratory complexes: a new understanding of an old subject

The enzymatic complexes of the mitochondrial respiratory chain have been extensively investigated in their structural and functional properties. A clear distinction is possible today between three complexes in which the difference in redox potential allows proton translocation (complexes I, III, and IV) and those having the mere function to convey electrons to the respiratory chain. We also have a clearer understanding of the structure and function of most respiratory complexes, of their biogenesis and regulation, and of their capacity to generate reactive oxygen species. Past investigations led to the conclusion that the complexes are randomly dispersed and functionally connected by diffusion of smaller redox components, coenzyme Q and cytochrome c. More-recent investigations by native gel electrophoresis and single-particle image processing showed the existence of supramolecular associations. Flux-control analysis demonstrated that complexes I and III in mammals and I, III, and IV in plants kinetically behave as single units, suggesting the existence of substrate channeling. This review discusses conditions affecting the formation of supercomplexes that, besides kinetic advantage, have a role in the stability and assembly of the individual complexes and in preventing excess oxygen radical formation. Disruption of supercomplex organization may lead to functional derangements responsible for pathologic changes.

Ketones prevent synaptic dysfunction induced by mitochondrial respiratory complex inhibitors

Ketones have previously shown beneficial effects in models of neurodegenerative disorders, particularly against associated mitochondrial dysfunction and cognitive impairment. However, evidence of a synaptic protective effect of ketones remains lacking. We tested the effects of ketones on synaptic impairment induced by mitochondrial respiratory complex (MRC) inhibitors using electrophysiological, reactive oxygen species (ROS) imaging and biochemical techniques. MRC inhibitors dose-dependently suppressed both population spike (PS) and field potential amplitudes in the CA1 hippocampus. Pre-treatment with ketones strongly prevented changes in the PS, whereas partial protection was seen in the field potential. Rotenone (Rot; 100 nmol/L), a MRC I inhibitor, suppressed synaptic function without altering ROS levels and PS depression by Rot was unaffected by antioxidants. In contrast, antioxidant-induced PS recovery against the MRC II inhibitor 3-nitropropionic acid (3-NP; 1 mmol/L) was similar to the synaptic protective effects of ketones. Ketones also suppressed ROS generation induced by 3-NP. Finally, ketones reversed the decreases in ATP levels caused by Rot and 3-NP. In summary, our data demonstrate that ketones can preserve synaptic function in CA1 hippocampus induced by MRC dysfunction, likely through an antioxidant action and enhanced ATP generation.

trans-Resveratrol as a neuroprotectant

Epidemiological evidence indicates that nutritionally-derived polyphenols such as resveratrol (RES) have neuroprotective properties. Administration of RES to culture media protects a wide variety of neuronal cell types from stress-induced death. Dietary supplementation of RES can ameliorate neuronal damage and death resulting from both acute and chronic stresses in rodents. The specific molecular mechanisms by which RES acts at the cellular level remain incompletely understood. However, many experimental data indicate that RES reduces or prevents the occurrence of oxidative damage. Here we discuss possible mechanisms by which RES might exert protection against oxidative damage and cell death. Evidence suggesting that RES’s chemical antioxidant potential is not sufficient explanation for its effects is discussed. Putative biological activities, including interactions with estrogen receptors and sirtuins are critically discussed. We provide a synthesis of how RES’s phytoestrogenic properties might mediate the neuronal stress resistance underlying its observed neuroprotective properties.

Environmental toxins and Parkinson's disease: putative roles of impaired electron transport chain and oxidative stress

Despite recent advancements in the biomedical fields, the etiology and pathogenesis of Parkinson's disease (PD) is still poorly understood, though the crucial roles of oxidative stress and impaired mitochondrial respiration have been suggested in the development of PD. The oxidative modification of the proteins of mitochondrial electron transport chain alters their normal function leading to the state of energy crisis in neurons. Exposure of environmental chemicals such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and rotenone in mouse produces the symptoms akin to PD and therefore these neurotoxins are commonly used in experimental studies on PD. Another environmental toxin, paraquat (a commonly used herbicide) has also been implicated with the onset of PD. The neurotoxicity of these chemicals is accompanied by the blockade of electron flow from NADH dehydrogenase to coenzyme Q. The agents with the ability to improve mitochondrial respiration and ATP production have been shown to exert beneficial effects in PD patients as well as in the animal models of PD. This review summarizes the current research implicating the impairment of mitochondrial respiratory chain and the role of environmental toxins in the pathogenesis of PD.

Losartan improved respiratory function and coenzyme Q content in brain mitochondria of young spontaneously hypertensive rats

Increased production of free radicals and impairment of mitochondrial function are important factors in the pathogenesis of hypertension. This study examined the impact of hypertension on mitochondrial respiratory chain function, coenzyme Q(9) (CoQ(9)), coenzyme Q(10) (CoQ(10)), and alpha-tocopherol content in brain mitochondria, and the effect of blockade of angiotensin II type 1 receptors (AT1R) in the prehypertensive period on these parameters. In addition, blood pressure, heart and brain weight to body weight ratios, and the geometry of the basilar artery supplying the brain were evaluated. In the 9th week blood pressure and heart weight/body weight ratio were significantly increased and brain weight/body weight ratio was significantly decreased in spontaneously hypertensive rats (SHR) when compared to Wistar rats (WR). The cross-sectional area of the basilar artery was increased in SHR. Glutamate-supported respiration, the rate of ATP production, and concentrations of CoQ(9), CoQ(10), and alpha-tocopherol were decreased in SHR. The succinate-supported function and cytochrome oxidase activity were not changed. The treatment of SHR with losartan (20 mg/kg/day) from 4th to 9th week of age exerted preventive effect against hypertension, heart and arterial wall hypertrophy, and brain weight/body weight decline. After the therapy, the rate of ATP production and the concentration of CoQ increased in comparison to untreated SHR. The impairment of energy production and decreased level of lipid-soluble antioxidants in brain mitochondria as well as structural alterations in the basilar artery may contribute to increased vulnerability of brain tissue in hypertension. Long-term treatment with AT1R blockers may prevent brain dysfunction in hypertension.