Mitochondrial toxin 3-nitropropionic acid induces cardiac and neurotoxicity differentially in mice

Morin suppresses mTORc1/IRE-1α/JNK and IP3R-VDAC-1 pathways: Crucial mechanisms in apoptosis and mitophagy inhibition in experimental Huntington's disease, supported by in silico molecular docking simulations

AIMS

Endoplasmic reticulum stress (ERS) with aberrant mitochondrial-ER contact (MERC), mitophagy, and apoptosis are interconnected determinants in neurodegenerative diseases. Previously, we proved the potential of Morin hydrate (MH), a potent antioxidant flavonoid, to mitigate Huntington's disease (HD)-3-nitropropionic acid (3-NP) model by modulating glutamate/calpain/Kidins220/BDNF trajectory. Extending our work, we aimed to evaluate its impact on combating the ERS/MERC, mitophagy, and apoptosis.

METHODS

Rats were subjected to 3-NP for 14 days and post-treated with MH and/or the ERS inducer WAG-4S for 7 days. Disease progression was assessed by gross inspection and striatal biochemical, histopathological, immunohistochemical, and transmission electron microscopical (TEM) examinations. A molecular docking study was attained to explore MH binding to mTOR, JNK, the kinase domain of IRE1-α, and IP3R.

KEY FINDINGS

MH decreased weight loss and motor dysfunction using open field and rotarod tests. It halted HD degenerative striatal neurons and nucleus/mitochondria ultra-microscopic alterations reflecting neuroprotection. Mechanistically, MH deactivated striatal mTOR/IRE1-α/XBP1s&JNK/IP3R, PINK1/Ubiquitin/Mfn2, and cytochrome c/caspase-3 signaling pathways, besides enhancing p-PGC-1α and p-VDAC1. WAG-4S was able to ameliorate all effects initiated by MH to different extents. Molecular docking simulations revealed promising binding patterns of MH and hence its potential inhibition of the studied proteins, especially mTOR, IP3R, and JNK.

SIGNIFICANCE

MH alleviated HD-associated ERS, MERC, mitophagy, and apoptosis. This is mainly achieved by combating the mTOR/IRE1-α signaling, IP3R/VDAC hub, PINK1/Ubiquitin/Mfn2, and cytochrome c/caspase 3 axis to be worsened by WAG-4S. Molecular docking simulations showed the promising binding of MH to mTOR and JNK as novel identified targets.

RNA binding protein IGF2BP1 meditates oxidative stress-induced granulosa cell dysfunction by regulating MDM2 mRNA stability in an m6A-dependent manner

Both genetic and microenvironmental detrimental factors are involved in ovarian dysfunction, leading to the increasing rate of involuntary childlessness in recent years. Oxidative stress (OS), which is characterized by the imbalance of redox system with redundant reactive oxygen species (ROS) overwhelming the antioxidant defense, is regarded as one of the culprits of ovarian dysfunction. OS causes damage to various types of ovarian cells including granulosa cells (GCs), jeopardizing the ovarian microenvironment, disturbing follicular development and participating in various female reproductive disorders. However, the specific molecular pathological mechanisms underlying this process have not been fully elucidated. In this study, we found that 3-nitropropionic acid (3-NP) treatment led to significant IGF2BP1 downregulation via, at least partially, inducing ROS overproduction. IGF2BP1 regulates GCs viability, proliferation, cell cycle and cellular senescence by enhancing MDM2 mRNA stability in an m6A-dependant manner. IGF2BP1 overexpression partially rescued 3-NP induced GCs damages, while ectopically expressed MDM2 alleviated both 3-NP or IGF2BP1-knockdown induced GCs dysfunction. These results reveal an epigenetic molecular mechanism underlying OS-related GCs disorders, which may help to establish a novel potential clinical marker for predicting the GCs status as well as the follicular developmental potential.

The role of mycotoxins in neurodegenerative diseases: current state of the art and future perspectives of research

Mycotoxins are fungal metabolites that can cause various diseases in humans and animals. The adverse health effects of mycotoxins such as liver failure, immune deficiency, and cancer are well-described. However, growing evidence suggests an additional link between these fungal metabolites and neurodegenerative diseases. Despite the wealth of these initial reports, reliable conclusions are still constrained by limited access to human patients and availability of suitable cell or animal model systems. This review summarizes knowledge on mycotoxins associated with neurodegenerative diseases and the assumed underlying pathophysiological mechanisms. The limitations of the common in vivo and in vitro experiments to identify the role of mycotoxins in neurotoxicity and thereby in neurodegenerative diseases are elucidated and possible future perspectives to further evolve this research field are presented.

Using Rotenone to Model Parkinson's Disease in Mice: A Review of the Role of Pharmacokinetics

Rotenone is a naturally occurring toxin that inhibits complex I of the mitochondrial electron transport chain. Several epidemiological studies have shown an increased risk of Parkinson's disease (PD) in individuals exposed chronically to rotenone, and it has received great attention for its ability to reproduce many critical features of PD in animal models. Laboratory studies of rotenone have repeatedly shown that it induces in vivo substantia nigra dopaminergic cell loss, a hallmark of PD neuropathology. Additionally, rotenone induces in vivo aggregation of α-synuclein, the major component of Lewy bodies and Lewy neurites found in the brain of PD patients and another hallmark of PD neuropathology. Some in vivo rotenone models also reproduce peripheral signs of PD, such as reduced intestinal motility and peripheral α-synuclein aggregation, both of which are thought to precede classical signs of PD in humans, such as cogwheel rigidity, bradykinesia, and resting tremor. Nevertheless, variability has been noted in cohorts of animals exposed to the same rotenone exposure regimen and also between cohorts exposed to similar doses of rotenone. Low doses, administered chronically, may reproduce PD symptoms and neuropathology more faithfully than excessively high doses, but overlap between toxicity and parkinsonian motor phenotypes makes it difficult to separate if behavior is examined in isolation. Rotenone degrades when exposed to light or water, and choice of vehicle may affect outcome. Rotenone is metabolized extensively in vivo, and choice of route of exposure influences greatly the dose used. However, male rodents may be capable of greater metabolism of rotenone, which could therefore reduce their total body exposure when compared with female rodents. The pharmacokinetics of rotenone has been studied extensively, over many decades. Here, we review these pharmacokinetics and models of PD using this important piscicide.

Paper-Based Resazurin Assay of Inhibitor-Treated Porcine Sperm

Porcine sperm motility was assessed via resazurin reduction color change in sperm cells using a novel paper-based assay of our own design. We applied mixtures of resazurin solution and porcine semen onto hydrophilic test circles on our paper-based device and investigated the resulting reduction reaction expressed as red and blue color intensity (RBCI). We quantified this reaction using a blue/pink color ratio from our 8 × 3 = 24 bit RGB color image. To examine enzymatic reactivity in sperm cells, we used two inhibitors: 3-Nitropropanoic acid (3-NPA) and 3-Bromopyruvic acid (3-BP). 3-NPA inhibits the citric acid cycle and electron transfer reaction in mitochondria, but did not strongly reduce sperm motility in our tests. 3-BP decreases reactivity of both mitochondrial electron transfer and glycolytic enzymes in cytosol, which significantly lowers porcine sperm motility. RBCIs of 3-NPA- and 3-BP-treated samples were significantly lower compared to our untreated control (p < 0.025). Based on these results, we feel that resazurin can be used to estimate the amount of reductants with and without inhibitor treatment. For continued research assessing the molecular mechanisms of resazurin reduction in porcine sperm, a combination assay using two or more redox indicators (e.g., resazurin and Thiazolyl Blue Tetrazolium Bromide (MTT)) embedded into our paper-based device could further our understanding of sperm cell bioenergetics.

Development of 2-Methoxyhuprine as Novel Lead for Alzheimer's Disease Therapy

Tacrine (THA), the first clinically effective acetylcholinesterase (AChE) inhibitor and the first approved drug for the treatment of Alzheimer’s disease (AD), was withdrawn from the market due to its side effects, particularly its hepatotoxicity. Nowadays, THA serves as a valuable scaffold for the design of novel agents potentially applicable for AD treatment. One such compound, namely 7-methoxytacrine (7-MEOTA), exhibits an intriguing profile, having suppressed hepatotoxicity and concomitantly retaining AChE inhibition properties. Another interesting class of AChE inhibitors represents Huprines, designed by merging two fragments of the known AChE inhibitors—THA and (−)-huperzine A. Several members of this compound family are more potent human AChE inhibitors than the parent compounds. The most promising are so-called huprines X and Y. Here, we report the design, synthesis, biological evaluation, and in silico studies of 2-methoxyhuprine that amalgamates structural features of 7-MEOTA and huprine Y in one molecule.

Construction of a Recyclable Genetic Marker and Serial Gene Deletions in the Human Pathogenic Mucorales Mucor circinelloides

Mucor circinelloides is a human pathogen, biofuel producer, and model system that belongs to a basal fungal lineage; however, the genetics of this fungus are limited. In contrast to ascomycetes and basidiomycetes, basal fungal lineages have been understudied. This may be caused by a lack of attention given to these fungi, as well as limited tools for genetic analysis. Nonetheless, the importance of these fungi as pathogens and model systems has increased. M. circinelloides is one of a few genetically tractable organisms in the basal fungi, but it is far from a robust genetic system when compared to model fungi in the subkingdom Dikarya. One problem is the organism is resistant to drugs utilized to select for dominant markers in other fungal transformation systems. Thus, we developed a blaster recyclable marker system by using the pyrG gene (encoding an orotidine-5'-phosphate decarboxylase, ortholog of URA3 in Saccharomyces cerevisiae). A 237-bp fragment downstream of the pyrG gene was tandemly incorporated into the upstream region of the gene, resulting in construction of a pyrG-dpl237 marker. To test the functionality of the pyrG-dpl237 marker, we disrupted the carRP gene that is involved in carotenoid synthesis in pyrG- mutant background. The resulting carRP::pyrG-dpl237 mutants exhibit a white colony phenotype due to lack of carotene, whereas wild type displays yellowish colonies. The pyrG marker was then successfully excised, generating carRP-dpl237 on 5-FOA medium. The mutants became auxotrophic and required uridine for growth. We then disrupted the calcineurin B regulatory subunit cnbR gene in the carRP::dpl237 strain, generating mutants with the alleles carRP::dpl237 and cnbR::pyrG These results demonstrate that the recyclable marker system is fully functional, and therefore the pyrG-dpl237 marker can be used for sequential gene deletions in M. circinelloides.

3-NP-induced Huntington's-like disease impairs Nrf2 activation without loss of cardiac function in aged rats

Cardiovascular diseases (CVDs) are one of the leading causes of death in patients over 60years with Huntington's disease (HD). Here, we investigated if age-related oxidative stress (OS) is a relevant factor to develop cardiac damage in an in vivo model of striatal neurodegeneration induced by 3-nitropropionic acid (3-NP). We also evaluated the potential effect of tert-butylhydroquinone (tBHQ) to increase the Nrf2-regulated antioxidant response in hearts from adult and aged rats intoxicated with 3-NP. Our results showed that 3-NP-treatment did not induce cardiac dysfunction, neither in adult nor in aged rats. However, at the cellular level, adult animals showed higher susceptibility to 3-NP-induced damage than aged rats, which suggest that chronic oxidative stress ongoing during aging might have induced an hormetic response that probably prevented from further 3-NP damage. We also found that the oxidative unbalance concurs with unresponsiveness of the Nrf2-mediated antioxidant response in old animals.

Tert-buthylhydroquinone pre-conditioning exerts dual effects in old female rats exposed to 3-nitropropionic acid

The brain is a very susceptible organ to structural and functional alterations caused by oxidative stress and its vulnerability increases with age. Understanding the antioxidant response activated by the transcription factor Nrf2 has become very important in the aging field in order to activate cellular protection. However, the role of Nrf2 inducers during old age has not been completely understood. Our aim was to activate the Nrf2 pathway by pre-treating old rats with a widely used Nrf2-inducer, tert-buthylhydroquinone (tBHQ), prior to 3-nitropropionic acid (3-NP) insult, in order to evaluate its effects at a behavioral, morphological and biochemical levels. 3-NP has been used to reproduce the biochemical and pathophysiological characteristics of Huntington's disease due to an oxidative effect. Our results suggest that tBHQ confers an important protective effect against 3-NP toxicity; nevertheless, Nrf2 seems not to be the main protective pathway associated to neuroprotection. Hormetic responses include the activation of more than one transcription factor. Nrf2 and NFκB are known to simultaneously initiate different cellular responses against stress by triggering parallel mechanisms, therefore NFκB nuclear accumulation was also evaluated.

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Old rats are able to activate an hormetic response against 3NP toxicity.

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tBHQ pre-conditioning exerts an antioxidant-prooxidant, dual role in old rats.

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tBHQ activates a crosstalk mechanism between NFκB and Nrf2.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

Our aim was to elucidate whether osteopontin (OPN) is involved in the onset of mineralisation and progression of extracellular calcification in striatal lesions due to mitochondrial toxin 3-nitropropionic acid exposure. OPN expression had two different patterns when observed using light microscopy. It was either localised to the Golgi complex in brain macrophages or had a small granular pattern scattered in the affected striatum. OPN labelling tended to increase in number and size over a 2-week period following the lesion. Ultrastructural investigations revealed that OPN is initially localised to degenerating mitochondria within distal dendrites, which were then progressively surrounded by profuse OPN on days 7–14. Electron probe microanalysis of OPN-positive and calcium-fixated neurites indicated that OPN accumulates selectively on the surfaces of degenerating calcifying dendrites, possibly via interactions between OPN and calcium. In addition, 3-dimensional reconstruction of OPN-positive neurites revealed that they are in direct contact with larger OPN-negative degenerating dendrites rather than with fragmented cell debris. Our overall results indicate that OPN expression is likely to correlate with the spatiotemporal progression of calcification in the affected striatum, and raise the possibility that OPN may play an important role in the initiation and progression of microcalcification in response to brain insults.

Delayed Onset and Reduced Cognitive Deficits through Pre-Conditioning with 3-Nitropropionic Acid is Dependent on Sex and CAG Repeat Length in the R6/2 Mouse Model of Huntington's Disease

BACKGROUND

Impairments in energy metabolism are implicated in Huntington's disease (HD) pathogenesis. Reduced levels of the mitochondrial enzyme succinate dehydrogenase (SDH), the main element of complex II, are observed post mortem in the brains of HD patients, and energy metabolism defects have been identified in both presymptomatic and symptomatic HD patients.

OBJECTIVE

Chemical preconditioning with 3-nitropropionic acid (3-NP), an irreversible inhibitor of SDH, has been shown to increase tolerance against experimental hypoxia in both heart and brain. Here we studied the effect of chronic preconditioning in the R6/2 mouse model of HD using mice carrying CAG repeat lengths of either 250 or 400 repeats. Both are transgenic fragment models, with 250CAG mice having a more rapid disease progression than 400CAG mice.

METHODS

Low doses of 3-NP (24 mg/kg) were administered via the drinking water and the effect on phenotype progression and cognition function assessed.

RESULTS

After 3-NP treatment there were significant improvements in all aspects of the behavioural phenotype, apart from body weight, with timing and magnitude of improvements dependent on both CAG repeat length and sex. Specifically, a delay in the deterioration of general health (as shown by delayed onset of glycosuria and increased survival) was seen in both male and female 400CAG mice and in female 250CAG mice and was consistent with improved appearance of 3-NP treated R6/2 mice. Male 250CAG mice showed improvements but these were short term, and 3-NP treatment eventually had deleterious effects on their survival rate. When cognitive performance of 250CAG mice was assessed using a two-choice discrimination touchscreen task, we found that female mice showed significant improvements.

DISCUSSION

Together, our results support the idea that energy metabolism contributes to the pathogenesis of HD, and suggest that improving energy deficits might be a therapeutically useful target.

Lithium chloride could aggravate brain injury caused by 3-nitropropionic acid

Lithium, a well-known drug for the treatment of bipolar disorder, may also have the ability to reduce neurodegeneration and stimulate cell proliferation. Systemic injection of mitochondrial toxin 3-nitropropionic acid (3NPA) is known to induce a relatively selective, Huntington disease-like brain injury. The aim of this study was to determine the effect of lithium chloride (LiCl) on brain injury caused by 3NPA. Female adult Wistar rats were pre-treated with LiCl (127 mg/kg) 1 day before the first injection of 3NPA (28 mg/kg), and then for 8 days with the same treatment but receiving LiCl 1 hour before 3NPA. Control groups were pre-treated accordingly, with LiCl or with normal saline, but were not treated with 3NPA. Staining for cytochrome c oxidase activity and in situ hybridization autoradiography of synaptotagmin-4 and -7 mRNAs were used to evaluate brain injury caused by 3NPA. There was a significant reduction of body weight in the 3NPA+LiCl group (79%) compared to the 3NPA group (90%, p = 0.031) and both control groups (100%, p = 0.000). Densitometric evaluation of cytochrome c oxidase staining and in situ hybridization autoradiograms revealed that the pre-treatment with LiCl caused an increase in striatal lesion for about 40% (p = 0.049). Moreover, the lesion was observed also in the hippocampus of three animals from the 3NPA+LiCl group and in two animals from the 3NPA group. However, there were no differences between the LiCl and saline group in any of the measured parameters. We concluded that the pre-treatment with a relatively nontoxic dose of LiCl could aggravate brain injury caused by 3NPA.

ErbB2 overexpression upregulates antioxidant enzymes, reduces basal levels of reactive oxygen species, and protects against doxorubicin cardiotoxicity

Levels of the HER2/ErbB2 protein in the heart are upregulated in some women during breast cancer therapy, and these women are at high risk for developing heart dysfunction after sequential treatment with anti-ErbB2/trastuzumab or doxorubicin. Doxorubicin is known to increase oxidative stress in the heart, and thus we considered the possibility that ErbB2 protein influences the status of cardiac antioxidant defenses in cardiomyocytes. In this study, we measured reactive oxygen species (ROS) in cardiac mitochondria and whole hearts from mice with cardiac-specific overexpression of ErbB2 (ErbB2(tg)) and found that, compared with control mice, high levels of ErbB2 in myocardium result in lower levels of ROS in mitochondria (P = 0.0075) and whole hearts (P = 0.0381). Neonatal cardiomyocytes isolated from ErbB2(tg) hearts have lower ROS levels and less cellular death (P < 0.0001) following doxorubicin treatment. Analyzing antioxidant enzyme levels and activities, we found that ErbB2(tg) hearts have increased levels of glutathione peroxidase 1 (GPx1) protein (P < 0.0001) and GPx activity (P = 0.0031) in addition to increased levels of two known GPx activators, c-Abl (P = 0.0284) and Arg (P < 0.0001). Interestingly, although mitochondrial ROS emission is reduced in the ErbB2(tg) hearts, oxygen consumption rates and complex I activity are similar to control littermates. Compared with these in vivo studies, H9c2 cells transfected with ErbB2 showed less cellular toxicity and produced less ROS (P < 0.0001) after doxorubicin treatment but upregulated GR activity (P = 0.0237) instead of GPx. Our study shows that ErbB2-dependent signaling contributes to antioxidant defenses and suggests a novel mechanism by which anticancer therapies involving ErbB2 antagonists can harm myocardial structure and function.

Geranylgeranylacetone blocks doxorubicin-induced cardiac toxicity and reduces cancer cell growth and invasion through RHO pathway inhibition

Doxorubicin is a widely used chemotherapy for solid tumors and hematologic malignancies, but its use is limited due to cardiotoxicity. Geranylgeranylacetone (GGA), an antiulcer agent used in Japan for 30 years, has no significant adverse effects, and unexpectedly reduces ovarian cancer progression in mice. Because GGA reduces oxidative stress in brain and heart, we hypothesized that GGA would prevent oxidative stress of doxorubicin cardiac toxicity and improve doxorubicin's chemotherapeutic effects. Nude mice implanted with MDA-MB-231 breast cancer cells were studied after chronic treatment with doxorubicin, doxorubicin/GGA, GGA, or saline. Transthoracic echocardiography was used to monitor systolic heart function and xenografts evaluated. Mice were euthanized and cardiac tissue evaluated for reactive oxygen species generation, TUNEL assay, and RHO/ROCK pathway analysis. Tumor metastases were evaluated in lung sections. In vitro studies using Boyden chambers were performed to evaluate GGA effects on RHO pathway activator lysophosphatidic acid (LPA)-induced motility and invasion. We found that GGA reduced doxorubicin cardiac toxicity, preserved cardiac function, prevented TUNEL-positive cardiac cell death, and reduced doxorubicin-induced oxidant production in a nitric oxide synthase-dependent and independent manner. GGA also reduced heart doxorubicin-induced ROCK1 cleavage. Remarkably, in xenograft-implanted mice, combined GGA/doxorubicin treatment decreased tumor growth more effectively than doxorubicin treatment alone. As evidence of antitumor effect, GGA inhibited LPA-induced motility and invasion by MDA-MB-231 cells. These anti-invasive effects of GGA were suppressed by geranylgeraniol suggesting GGA inhibits RHO pathway through blocking geranylation. Thus, GGA protects the heart from doxorubicin chemotherapy-induced injury and improves anticancer efficacy of doxorubicin in breast cancer.

Nitric oxide inhibits succinate dehydrogenase-driven oxygen consumption in potato tuber mitochondria in an oxygen tension-independent manner

NO (nitric oxide) is described as an inhibitor of plant and mammalian respiratory chains owing to its high affinity for COX (cytochrome c oxidase), which hinders the reduction of oxygen to water. In the present study we show that in plant mitochondria NO may interfere with other respiratory complexes as well. We analysed oxygen consumption supported by complex I and/or complex II and/or external NADH dehydrogenase in Percoll-isolated potato tuber (Solanum tuberosum) mitochondria. When mitochondrial respiration was stimulated by succinate, adding the NO donors SNAP (S-nitroso-N-acetyl-DL-penicillamine) or DETA-NONOate caused a 70% reduction in oxygen consumption rate in state 3 (stimulated with 1 mM of ADP). This inhibition was followed by a significant increase in the Km value of SDH (succinate dehydrogenase) for succinate (Km of 0.77±0.19 to 34.3±5.9 mM, in the presence of NO). When mitochondrial respiration was stimulated by external NADH dehydrogenase or complex I, NO had no effect on respiration. NO itself and DETA-NONOate had similar effects to SNAP. No significant inhibition of respiration was observed in the absence of ADP. More importantly, SNAP inhibited PTM (potato tuber mitochondria) respiration independently of oxygen tensions, indicating a different kinetic mechanism from that observed in mammalian mitochondria. We also observed, in an FAD reduction assay, that SNAP blocked the intrinsic SDH electron flow in much the same way as TTFA (thenoyltrifluoroacetone), a non-competitive SDH inhibitor. We suggest that NO inhibits SDH in its ubiquinone site or its Fe–S centres. These data indicate that SDH has an alternative site of NO action in plant mitochondria.

hMTH1 expression protects mitochondria from Huntington's disease-like impairment

Huntington disease (HD) is a neurodegenerative disease caused by expansion of CAG repeats in the huntingtin (Htt) gene. The expression of hMTH1, the human hydrolase that degrades oxidized purine nucleoside triphosphates, grants protection in a chemical HD mouse model in which HD-like features are induced by the mitochondrial toxin 3-nitropropionic acid (3-NP). To further examine the relationship between oxidized dNTPs and HD-like neurodegeneration, we studied the effects of hMTH1 expression in a genetic cellular model for HD, such as striatal cells expressing mutant htt (Hdh^Q111). hMTH1 expression protected these cells from 3-NP and H₂O₂-induced killing, by counteracting the mutant htt-dependent increased vulnerability and accumulation of nuclear and mitochondrial DNA 8-hydroxyguanine levels. hMTH1 expression reverted the decreased mitochondrial membrane potential characteristic of Hdh^Q111 cells and delayed the increase in mitochondrial reactive oxygen species associated with 3-NP treatment. Further indications of hMTH1-mediated mitochondrial protection are the partial reversion of 3-NP-induced alterations in mitochondrial morphology and the modulation of DRP1 and MFN1 proteins, which control fusion/fission rates of mitochondria. Finally, in line with the in vitro findings, upon 3-NP in vivo treatment, 8-hydroxyguanine levels in mitochondrial DNA from heart, muscle and brain are significantly lower in transgenic hMTH1-expressing mice than in wild-type animals.

DYT1 knock-in mice are not sensitized against mitochondrial complex-II inhibition

DYT1 is caused by a partly penetrant dominant mutation in TOR1A that leads to a glutamic acid deletion (ΔE) in torsinA. Identifying environmental factors that modulate disease pathogenesis and penetrance could help design therapeutic strategies for dystonia. Several cell-based studies suggest that expression of torsinA(ΔE) increases the susceptibility of neuronal cells to challenges to their oxidative/energy metabolism. Based on those reports, we hypothesized that mice expressing torsinA(ΔE) would be more susceptible than control littermates to the effects of oxidative stress and ATP deficits caused by disruption of the mitochondrial respiratory chain in neurons. To test this hypothesis, we administered 20 or 50 mg/kg/day of the irreversible complex-II inhibitor 3-nitropropionic acid (3-NP) intraperitoneally for 15 consecutive days to young heterozygote DYT1 knock-in (KI) mice and wild type littermates. Repeated phenotypic assessments were performed at baseline, during and after the injections. Animals were then sacrificed and their brains processed for protein analysis. The administration of 20 mg/kg 3-NP led to increased levels of torsinA in the striatum, the main target of 3-NP, but did not cause motor dysfunction in DYT1 KI or control mice. The administration of 50 mg/kg/day of 3-NP caused the death of ∼40% of wild type animals. Interestingly, DYT1 KI animals showed significantly reduced mortality. Surviving animals exhibited abnormal motor behavior during and right after the injection period, but recovered by 4 weeks postinjection independent of genotype. In contrast to the findings reported in cultured cells, these studies suggest the DYT1 mutation does not sensitize central neurons against the toxic effects of oxidative stress and energy deficits.

Glycogen accumulation in cardiomyocytes and cardiotoxic effects after 3NPA treatment

Mitochondrial toxin 3-nitropropionic acid (3NPA) is a neurotoxin that inhibits the activity of succinate dehydrogenase, a key enzyme of oxidative energy production, and characteristically provokes neurodegeneration in the striatum, resembling Huntington's disease. 3NPA also affects the activity of glycogen-sinthase-kinase-3b (GSK-3b), an enzyme implicated in glycogen synthesis and in signal transduction. The aim of this study was to evaluate cardiac glycogen content and histopathological changes in the hearts of rats after subchronic treatment with 3NPA.Female adult Wistar rats were treated daily with 30mg/kg of 3NPA subcutaneously 8 days. The control group was treated with normal saline for 8 days. For the comparison of measured parameters between groups we used the Student's t-test (p<0.05). The stereological evaluation of glycogen content in histological sections of the heart was processed with periodic acid-Schiff (PAS). Histochemical procedure showed a significant accumulation of glycogen granules in the 3NPA group (0.028mm(3)/mm(3)±0.022), whereas the hearts of control animals were nearly devoid of glycogen granules (0.002mm(3)/mm(3)±0.001). Haematoxylin-eosin histological staining showed diffuse swelling of cardiomyocytes (3NPA=15.989μm ±1.649; saline=13.456μm ± 0.786), loss of cell cross-striations, lower myofibril volume fraction (3NPA=0.3922mm(3)/mm3 ± 0.0230, saline=0.4550mm(3)/mm3 ± 0.0083), and mononuclear infiltration in the interstitial tissue, mostly along the blood vessels. Sirius red staining showed fibrosis of the heart (3NPA=0.0531mm93)/mm(3)±0.0090, saline=0.0135mm(3)/mm3 ± 0.0051). TUNEL staining showed TUNEL-positive cells in the 3NPA group (2.04cells/mm2 ± 0.92) and almost no TUNEL-positive cells in the saline group (0.27cells/mm2 ± 0.14). This experiment shows that 3NPA-induced histopathological changes in the heart are accompanied by a significant accumulation of glycogen granules in cardiomyocytes.

Low doses of 3-nitropropionic acid in vivo induce damage in mouse skeletal muscle

Mitochondrial alterations are believed to play a critical role in the pathophysiology of neurodegenerative diseases and in some well-described myopathies. In the present study, we evaluated muscle changes in vivo after blocking the mitochondrial complex II of the respiratory chain by using 3-nitropropionic acid (3-NP). This neurotoxin has been used as a pharmacological tool in animal models to address some of the metabolic modifications that might underlie central neurodegeneration; however, changes in peripheral musculature have not been documented. We believe that skeletal muscles must be affected because their integrity highly depends on oxidative metabolism. Therefore, histochemical, ultrastructural, and biochemical changes were studied in the muscles of mice treated with low doses of 3-NP (15 mg/kg, i.p., for 5 days). 3-NP-treated mice displayed changes in alkaline phosphatase (APase), succinic dehydrogenase (SDH), and cytochrome c oxidase (COX) levels in the gracilis and gastrocnemius muscles. These changes were statistically significant for APase and SDH in both muscles and for COX only in the gastrocnemius. No significant alterations in acetylcholinesterase (AChE) expression were observed in either muscle. Analysis of the muscle ultrastructure revealed mitochondrial atrophy as well as sarcomere and nuclei disorganization. At the biochemical level, nitric oxide (NO) and lipid peroxidation (LPO) changed in the muscles of 3-NP-treated mice, suggesting metabolic alterations due to oxidative stress. Early damage in the striatal tissue and behavioral modifications are also documented.

Cystamine protects from 3-nitropropionic acid lesioning via induction of nf-e2 related factor 2 mediated transcription

Systemic administration of cystamine is known to protect from both chemical and genetic models of neurotoxicity. Despite positive effects in laboratory models, cystamine has not been successfully translated to clinical application for neurodegenerative disease. Furthermore, the long held assumption that cystamine protects through tissue transglutaminase inhibition has recently been challenged. The studies described here examine other potential mechanisms of cystamine-mediated protection in an attempt to reveal molecular targets for neurodegenerative therapy. Based on previously described effects of cystamine, we examined the potential for activation of NF-E2 related factor 2 (Nrf2) mediated signaling through the antioxidant response element (ARE). We found that cystamine activates Nrf2/ARE both in cell culture and in brain tissue and then probed the mechanism of activation in cell culture. In live animals, we show that neuroprotection from 3-nitropropionic acid (3NP) toxicity is Nrf2-dependent. Therefore, these findings provide strong evidence that Nrf2 signaling may be an effective target for prevention of neurodegeneration.

3-nitropropionic acid-induced mitochondrial permeability transition: comparative study of mitochondria from different tissues and brain regions

The adult rat striatum is particularly vulnerable to systemic administration of the succinate dehydrogenase inhibitor 3-nitropropionic acid (3NP), which is known to induce degeneration of the caudate-putamen, as occurs in Huntington's disease. The aim of the present study was to compare the susceptibility of isolated mitochondria from different rat brain regions (striatum, cortex, and cerebellum) as well as from the liver, kidney, and heart to mitochondrial permeability transition (MPT) induced by 3NP and Ca(2+). In the presence of micromolar Ca(2+) concentrations, 3NP induces MPT in a dose-dependent manner, as estimated by mitochondrial swelling and a decrease in the transmembrane electrical potential. A 3NP concentration capable of promoting a 10% inhibition of ADP-stimulated, succinate-supported respiration was sufficient to stimulate Ca(2+)-induced MPT. Brain and heart mitochondria were generally more sensitive to 3NP and Ca(2+)-induced MPT than mitochondria from liver and kidney. In addition, a partial inhibition of mitochondrial respiration by 3NP resulted in more pronounced MPT in striatal mitochondria than in cortical or cerebellar organelles. A similar inhibition of succinate dehydrogenase activity was observed in rat tissue homogenates obtained from various brain regions as well as from liver, kidney, and heart 24 hr after a single i.p. 3NP dose. Mitochondria isolated from forebrains of 3NP-treated rats were also more susceptible to Ca(2+)-induced MPT than those of control rats. We propose that the increased susceptibility of the striatum to 3NP-induced neurodegeneration may be partially explained by its susceptibility to MPT, together with the greater vulnerability of this brain region to glutamate receptor-mediated Ca(2+) influx.

Mouse models of Huntington's disease and methodological considerations for therapeutic trials

Huntington's disease (HD) is an autosomal dominant, progressive, and fatal neurodegenerative disorder caused by an expanded polyglutamine cytosine-adenine-guanine repeat in the gene coding for the protein huntingtin. Despite great progress, a direct causative pathway from the HD gene mutation to neuronal dysfunction and death has not yet been established. One important advance in understanding the pathogenic mechanisms of this disease has been the development of multiple murine models that replicate many of the clinical, neuropathological, and molecular events in HD patients. These models have played an important role in providing accurate and experimentally accessible systems to study multiple aspects of disease pathogenesis and to test potential therapeutic treatment strategies. Understanding how disease processes interrelate has become important in identifying a pharmacotherapy in HD and in the design of clinical trials. A review of the current state of HD mouse models and their successes in elucidating disease pathogenesis are discussed. There is no clinically proven treatment for HD that can halt or ameliorate the inexorable disease progression. As such, a guide to assessing studies in mouse models and salient issues related to translation from mice to humans are included.

Cardiac dysfunction in the R6/2 mouse model of Huntington's disease

Recent evidence suggests that mutant huntingtin protein-induced energetic perturbations contribute to neuronal dysfunction in Huntington's disease (HD). Given the ubiquitous expression of huntingtin, other cell types with high energetic burden may be at risk for HD-related dysfunction. Early-onset cardiovascular disease is the second leading cause of death in HD patients; a direct role for mutant huntingtin in this phenomenon remains unevaluated. Here we tested the hypothesis that expression of mutant huntingtin is sufficient to induce cardiac dysfunction, using a well-described transgenic model of HD (line R6/2). R6/2 mice developed cardiac dysfunction by 8 weeks of age, progressing to severe failure at 12 weeks, assessed by echocardiography. Limited evidence of cardiac remodeling (e.g. hypertrophy, fibrosis, apoptosis, beta(1) adrenergic receptor downregulation) was observed. Immunogold electron microscopy demonstrated significant elevations in nuclear and mitochondrial polyglutamine presence in the R6/2 myocyte. Significant alterations in mitochondrial ultrastructure were seen, consistent with metabolic stress. Increased cardiac lysine acetylation and protein nitration were observed and were each significantly associated with impairments in cardiac performance. These data demonstrate that mutant huntingtin expression has potent cardiotoxic effects; cardiac failure may be a significant complication of this important experimental model of HD. Investigation of the potential cardiotropic effects of mutant huntingtin in humans may be warranted.

Adenosine A2A receptors in bone marrow-derived cells but not in forebrain neurons are important contributors to 3-nitropropionic acid-induced striatal damage as revealed by cell-type-selective inactivation

Endogenous adenosine acting at the adenosine A2A receptor (A2AR) can modify brain injury in a variety of neurological disorder models. However, both A2AR activation and inactivation have been shown to be neuroprotective in different situations, raising the intriguing possibility that A2ARs in distinct cellular elements may have different and even opposing effects. In this study, we developed three novel transgenic models to dissect out cell-type-specific actions of A2ARs on striatal damage by the mitochondrial toxin 3-nitropropionic acid (3-NP). Whereas global inactivation of A2ARs exacerbated 3-NP-induced neurological deficit behaviors and striatal damage, selective inactivation of A2ARs in forebrain neurons (using the Cre/loxP strategy) did not affect neurological deficit or striatal damage after the acute systemic treatment of 3-NP and intrastriatal injection of malonate. However, selective inactivation of A2ARs in bone marrow-derived cells (BMDCs) by transplanting bone marrow cells from global A2AR knock-out (KO) mice into wild-type C57BL/6 mice produced a similar phenotype of global A2AR KO mice, i.e., exacerbation of 3-NP-induced striatal damage. Thus, cell-type-selective inactivation of A2ARs reveals that A2ARs in BMDCs but not in forebrain neurons are an important contributor to striatal damage induced by mitochondrial dysfunction.

Localization of superoxide anion production to mitochondrial electron transport chain in 3-NPA-treated cells

3-Nitropropionic acid (3-NPA), an inhibitor of succinate dehydrogenase (SDH) at complex II of the mitochondrial electron transport chain induces cellular energy deficit and oxidative stress-related neurotoxicity. In the present study, we identified the site of reactive oxygen species production in mitochondria. 3-NPA increased O2- generation in mitochondria respiring on the complex I substrates pyruvate+malate, an effect fully inhibited by rotenone. Antimycin A increased O2- production in the presence of complex I and/or II substrates. Addition of 3-NPA markedly increased antimycin A-induced O2- production by mitochondria incubated with complex I substrates, but 3-NPA inhibited O2- formation driven with the complex II substrate succinate. At 0.6 microM, myxothiazol inhibits complex III, but only partially decreases complex I activity, and allowed 3-NPA-induced O2- formation; however, at 40 microM myxothiazol (which completely inhibits both complexes I and III) eliminated O2- production from mitochondria respiring via complex I substrates. These results indicate that in the presence of 3-NPA, mitochondria generate O2- from a site between the ubiquinol pool and the 3-NPA block in the respiratory complex II.

Chemical-induced atrial thrombosis in NTP rodent studies

Cardiac thrombosis, one of the causes of sudden death throughout the world, plays a principal role in several cardiovascular diseases, such as myocardial infarction and stroke in humans. Data from studies of induction of chemical thrombosis in rodents help to identify substances in our environment that may contribute to cardiac thrombosis. Results for more than 500 chemicals tested in rodents in 2-year bioassays have been published as Technical Reports of the National Toxicology Program (NTP) http://ntp-server.niehs.nih.gov/index. We evaluated atrial thrombosis induced by these chemical exposures and compared it to similarly induced lesions reported in the literature. Spontaneous rates of cardiac thrombosis were determined for control Fischer 344 rats and B6C3F1 mice: 0% in rats and mice in 90-day studies and, in 2-year studies, 0.7% in both genders of mice, 4% in male rats, and 1% in female rats. Incidences of atrial thrombosis were increased in high-dosed groups involving 13 compounds (incidence rate: 20-100%): 2-butoxyethanol, C.I. Direct Blue 15, bis(2-chloroethoxy)methane, diazoaminobenzene, diethanolamine, 3,3'-dimethoxybenzidine dihydrochloride, hexachloroethane, isobutene, methyleugenol, oxazepam, C.I. Pigment Red 23, C.I. Acid Red 114, and 4,4'-thiobis(6-t-butyl-m-cresol). The main localization of spontaneously occurring and chemically induced thromboses occurred in the left atrium. The literature survey suggested that chemical-induced atrial thrombosis might be closely related to myocardial injury, endothelial injury, circulatory stasis, hypercoagulability, and impaired atrial mechanical activity, such as atrial fibrillation, which could cause stasis of blood within the left atrial appendage, contributing to left atrial thrombosis. Supplementary data referenced in this paper are not printed in this issue of Toxicologic Pathology. They are available as downloadable files at http://taylorandfrancis.metapress.com/openurl.asp?genre=journal&issn=0192-6233. To access them, click on the issue link for 33(5), then select this article. A download option appears at the bottom of this abstract. In order to access the full article online, you must either have an individual subscription or a member subscription accessed through www.toxpath.org.

3-Nitropropionic acid: a mitochondrial toxin to uncover physiopathological mechanisms underlying striatal degeneration in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding Huntingtin. The mechanisms underlying the preferential degeneration of the striatum, the most striking neuropathological change in HD, are unknown. Of those probably involved, mitochondrial defects might play an important role. The behavioural and anatomical similarities found between HD and models using the mitochondrial toxin 3-nitropropionic acid (3NP) in rats and primates support this hypothesis. Here, we discuss the recently identified mechanisms of 3NP-induced striatal degeneration. Two types of important factor have been identified. The first are the 'executioner' components that have direct roles in cell death, such as c-Jun N-terminal kinase and Ca2+-activated protease calpains. The second are 'environmental' factors, such as glutamate, dopamine and adenosine, which modulate the striatal degeneration induced by 3NP. Interestingly, these recent studies support the hypothesis that 3NP and mutated Huntingtin have certain mechanisms of toxicity in common, suggesting that the use of 3NP might give new insights into the pathogenesis of HD. Research on 3NP provides additional proof that the neurochemical environment of a given neurone can determine its preferential vulnerability in neurodegenerative diseases.

Gait dynamics in mouse models of Parkinson's disease and Huntington's disease

BACKGROUND

Gait is impaired in patients with Parkinson's disease (PD) and Huntington's disease (HD), but gait dynamics in mouse models of PD and HD have not been described. Here we quantified temporal and spatial indices of gait dynamics in a mouse model of PD and a mouse model of HD.

METHODS

Gait indices were obtained in C57BL/6J mice treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg/day for 3 days) for PD, the mitochondrial toxin 3-nitropropionic acid (3NP, 75 mg/kg cumulative dose) for HD, or saline. We applied ventral plane videography to generate digital paw prints from which indices of gait and gait variability were determined. Mice walked on a transparent treadmill belt at a speed of 34 cm/s after treatments.

RESULTS

Stride length was significantly shorter in MPTP-treated mice (6.6 +/- 0.1 cm vs. 7.1 +/- 0.1 cm, P < 0.05) and stride frequency was significantly increased (5.4 +/- 0.1 Hz vs. 5.0 +/- 0.1 Hz, P < 0.05) after 3 administrations of MPTP, compared to saline-treated mice. The inability of some mice treated with 3NP to exhibit coordinated gait was due to hind limb failure while forelimb gait dynamics remained intact. Stride-to-stride variability was significantly increased in MPTP-treated and 3NP-treated mice compared to saline-treated mice. To determine if gait disturbances due to MPTP and 3NP, drugs affecting the basal ganglia, were comparable to gait disturbances associated with motor neuron diseases, we also studied gait dynamics in a mouse model of amyotrophic lateral sclerosis (ALS). Gait variability was not increased in the SOD1 G93A transgenic model of ALS compared to wild-type control mice.

CONCLUSION

The distinct characteristics of gait and gait variability in the MPTP model of Parkinson's disease and the 3NP model of Huntington's disease may reflect impairment of specific neural pathways involved.

Protection from mitochondrial complex II inhibition in vitro and in vivo by Nrf2-mediated transcription

Complex II inhibitors 3-nitropropionic acid (3NP) and malonate cause striatal damage reminiscent of Huntington's disease and have been shown to involve oxidative stress in their pathogenesis. Because nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent transcriptional activation by means of the antioxidant response element is known to coordinate the up-regulation of cytoprotective genes involved in combating oxidative stress, we investigated the significance of Nrf2 in complex II-induced toxicity. We found that Nrf2-deficient cells and Nrf2 knockout mice are significantly more vulnerable to malonate and 3NP and demonstrate increased antioxidant response element (ARE)-regulated transcription mediated by astrocytes. Furthermore, ARE preactivation by means of intrastriatal transplantation of Nrf2-overexpressing astrocytes before lesioning conferred dramatic protection against complex II inhibition. These observations implicate Nrf2 as an essential inducible factor in the protection against complex II inhibitor-mediated neurotoxicity. These data also introduce Nrf2-mediated ARE transcription as a potential target of preventative therapy in neurodegenerative disorders such as Huntington's disease.

Experimental basis for the putative role of GluR6/kainate glutamate receptor subunit in Huntington's disease natural history

Age of onset of Huntington's disease (HD) statistically correlates with the length of expanded CAG repeats in the IT15 gene. However, other factors such as polymorphism in the 3' untranslated region of the GluR6 kainate receptor gene subunit may contribute to variability in the age at onset. To investigate this issue, we studied the motor disorder and related striatal damage induced by 3-nitropropionic acid (3-NP) subacute administration in GluR6 knockout mice (GluR6(-/-)) as compared to wild-type mice. In two different age groups (6 months and 1 year), we observed that GluR6(-/-) mice did not display more motor impairment nor more striatal histopathological damage than GluR6(+/+) mice, although 1-year-old GluR6(-/-) mice displayed reduced activity parameters either at baseline or after 3-NP administration compared to GluR6(+/+). In both age groups, GluR6(-/-) mice died earlier and displayed earlier motor symptoms during 3-NP-induced metabolic compromise, suggesting that GluR6-containing kainate receptors may be implicated during neurodegeneration, such as in HD, rather than in the final outcome.

Oral uridine pro-drug PN401 decreases neurodegeneration, behavioral impairment, weight loss and mortality in the 3-nitropropionic acid mitochondrial toxin model of Huntington's disease

Huntington's disease (HD) is associated with decreased activity of mitochondrial succinate dehydrogenase (complex II). De novo biosynthesis of uridine nucleotides is directly coupled to the respiratory chain. Cells with impaired mitochondrial function become uridine auxotrophs and can be maintained with high micromolar concentration of uridine and pyruvate. The therapeutic role of pyrimidines and possible changes in uridine content has not been assessed in neurological diseases involving mitochondrial dysfunction in vivo. Oral administration of PN401 delivers much higher levels of uridine to the circulation than oral administration of uridine itself. Administration of complex II inhibitor 3-nitropropionic acid (3NP) induced neuronal damage in the striatum, substantia nigra and/or thalamus in 80% of the mice and led to 38% mortality. Treatment with PN401 almost completely prevented the neuronal damage due to 3NP and completely prevented mortality. In two subsequent experiments, 3NP-induced weight loss, mortality and behavioral impairment in rotarod performance and spontaneous motor activity were attenuated by treatment with oral PN401. 3NP did not reduce forebrain total uridine nucleotides (TUN), though higher doses of PN401 associated with optimal neuroprotection did elevate TUN to supranormal levels. Thus, oral PN401 treatment has neuroprotective effects in a HD model of mitochondrial dysfunction and the mechanism is more complex than correction of a pyrimidine deficit.

Rotenone induces non‐specific central nervous system and systemic toxicity

We investigated the dopaminergic (DA) neuronal degeneration in animals subjected to systemic treatment of rotenone via subcutaneous delivery. Behavioral observations revealed a hypokinetic period in rats sacrificed at 3 and 5 days, and dystonic episodes in animals sacrificed at 8 days. Less than 20% of the total number of animals given rotenone depicted brain lesions after 8 days of treatment, as demonstrated by a significant loss of DA fibers in the striatum, but not of DA nigral neurons. Tyrosine hydroxylase-negative striatal territories were characterized by post-synaptic toxicity as demonstrated by a decreased number of interneurons labeled for choline acetyltransferase, NADPH-diaphorase, parvalbumin, and projection neurons labeled for calbindin and nerve growth factor inducible-B (NGFI-B). Post-synaptic neurodegeneration was demonstrated further by abundant striatal staining for Fluoro-Jade. Decrease in the nuclear orphan receptor Nurr1 expression was the only significant change observed at the level of the substantia nigra. Autopsy reports confirmed that animals suffered from severe digestion problems. These data suggest that hypokinesia observed between 3 and 5 days is the result of general health problems rather than a specific motor deficit associated to Parkinson's disease (PD) symptoms. Overall, the effects of rotenone toxicity are widespread, and subcutaneous administration of this toxin does not provide the neuropathological and behavioral basis for a relevant and reliable PD model.

Magnetic resonance imaging and spectroscopy in assessing 3-nitropropionic acid-induced brain lesions: an animal model of Huntington’s disease

Huntington's disease (HD) is an inherited neurodegenerative disease, in which there is progressive motor and cognitive deterioration, and for which the pathogenesis of neuronal death remains controversial. Mitochondrial toxins like 3-nitropropionic acid (3-NP) and malonate, functioning as the inhibitors of the complex II of mitochondrial respiratory chain, have been found to effectively induce specific behavioral changes and selective striatal lesions in rats and non-human primates mimicking those in HD. Furthermore, several kinds of transgenic mouse models of HD have been recently developed, and used in the development and assessment of novel treatments for HD. In the past, most studies evaluating the animal models for HD were based on histological changes or in vitro neuronal cultures. With the emergence of advanced magnetic resonance technologies, non-invasive magnetic resonance imaging (MRI) and spectroscopy provide more detail of cerebral alterations, including the changes of cerebral structure, function and metabolites. These studies support the hypothesis that mitochondrial dysfunction with increased excitation of N-methyl-D-aspartate (NMDA) receptors can replicate the neurobehavioral changes, selective brain injury and neurochemical alterations in HD. The present review focuses on our work as well as that of others regarding 3-NP-induced neurotoxicity and other animal models of HD. Using both conventional and advanced MRI and spectroscopy, we summarize the pathogenesis and possible therapeutic strategies in chemical and transgenic models of HD. The results show magnetic resonance techniques to be powerful techniques in the evaluation of pathogenesis and therapeutic intervention for both chemical and transgenic models of HD.

Neuroprotective effects of (+/-)-huprine Y on in vitro and in vivo models of excitoxicity damage

We have investigated the neuroprotective effects of (+/-)-huprine Y on excitotoxic lesions in rat cerebellar granule cells (CGCs). (+/-)-Huprine Y prevented cell death induced by 100 microM glutamate, as well as, 10 microM MK-801, a NMDA receptor antagonist, in a significant manner. On the other hand, intracellular calcium increase induced by NMDA (200 microM), measured by fura-2 fluorescence, was prevented by (+/-)-huprine Y with an EC(50) of 12.44 microM, which evidences the modulatory action of this compound on NMDA-induced calcium currents. In vivo, we have studied (+/-)-huprine Y neuroprotective effects on striatal lesions induced by the subacute administration of the mitochondrial toxin 3-nitropropionic acid (3-NP, 30 mg/kg, ip, for 10 days). We have assessed that both the behavioral and the morphological consequences of the lesion were prevented by pretreatment with (+/-)-huprine Y (2.5 mg/kg/twice a day, ip). Striatal gliosis induced by 3-NP treatment was prevented by (+/-)-huprine Y pretreatment, as demonstrated by the attenuation of both the increase in [(3)H]PK 11195 specific binding indicative of microgliosis and the expression of hsp27 kDa, a chaperone expressed mainly in astrocytes. In conclusion, (+/-)-huprine Y attenuated excitotoxic-induced lesions, both in vitro and in vivo, and further evidence is provided for the potential use of this compound in the prevention of neurodegenerative disorders.

Dopamine transporter knock-out mice are hypersensitive to 3-nitropropionic acid-induced striatal damage

Evidence suggests that dopamine is involved in the modulation of striatal excitotoxic processes. To further investigate this issue, we studied the effects of systemic 'low-dose' (total dose, 340 mg/kg in 7 days) 3-nitropropionic acid (3-NP) intoxication in dopamine transporter knock-out mice (DAT-/-) compared to wildtype (DAT+/+) mice. Systemic 'low-dose' 3-NP induced a significant impairment in a rotarod task only in DAT-/- mice. Histopathology also demonstrated a significant reduction of the striatal volume (-7%, P < 0.05), neuronal density (-12.5%, P < 0.001) and absolute number estimates of striatal neurons (-11.5%, P < 0.001) in DAT-/- compared to DAT+/+ mice, with increased glial activation, independent of the degree of succinate dehydrogenase inhibition. These findings strengthen the hypothesis for dopamine modulation of excitotoxicity within the nigrostriatal system.