Potential sources of increased iron in the substantia nigra of parkinsonian patients

A novel role for glyceraldehyde-3-phosphate dehydrogenase and monoamine oxidase B cascade in ethanol-induced cellular damage

BACKGROUND

Alcoholism is a major psychiatric condition at least partly associated with ethanol (EtOH)-induced cell damage. Although brain cell loss has been reported in subjects with alcoholism, the molecular mechanism is unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction under stressful conditions and might contribute to EtOH-induced cell damage.

METHODS

Expression of GAPDH and MAO B protein was studied in human glioblastoma and neuroblastoma cell lines exposed to physiological concentrations of EtOH. Expression of these proteins was also examined in the prefrontal cortex from human subjects with alcohol dependence and in rats fed with an EtOH diet. Coimmunoprecipitation, subcellular fractionation, and luciferase assay were used to address nuclear GAPDH-mediated MAO B activation. To test the effects of inactivation, RNA interference and pharmacological intervention were used, and cell damage was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP Nick End Labeling (TUNEL) and hydrogen peroxide measurements.

RESULTS

Ethanol significantly increases levels of GAPDH, especially nuclear GAPDH, and MAO B in neuronal cells as well as in human and rat brains. Nuclear GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), and augments TIEG2-mediated MAO B transactivation, which results in cell damage in neuronal cells exposed to EtOH. Knockdown expression of GAPDH or treatment with MAO B inhibitors selegiline (deprenyl) and rasagiline (Azilect) can block this cascade.

CONCLUSIONS

Ethanol-elicited nuclear GAPDH augments TIEG2-mediated MAO B, which might play a role in brain damage in subjects with alcoholism. Compounds that block this cascade are potential candidates for therapeutic strategies.

Ethanol increases TIEG2-MAO B cell death cascade in the prefrontal cortex of ethanol-preferring rats

Brain cell loss has been reported in subjects with alcoholism. However, the molecular mechanisms are unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction with regards to ethanol exposure. We have recently reported that GAPDH protein expression was increased in the brains of rats fed with ethanol. Furthermore, GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), to augment TIEG2-mediated MAO B activation, resulting in neuronal cell damage due to ethanol exposure. The current study investigates whether the TIEG2-MAO B cascade is also active in the brains of rats fed with ethanol. Ten ethanol-preferring rats were fed with a liquid diet containing ethanol, with increasing amounts of ethanol up to a final concentration of 6.4% representing a final diet containing 36% of calories for 28 days. Ten control rats were fed the liquid diet without ethanol. The expression of TIEG2 protein, MAO B mRNA levels, MAO B catalytic activity, and the levels of anti-apoptotic protein Bcl 2 and apoptotic protein caspase 3 were determined in the prefrontal cortex of the rats. Ethanol significantly increased protein levels of TIEG2, active caspase 3, MAO B mRNA and enzyme activity, but significantly decreased Bcl 2 protein expression compared to control rats. In summary, ethanol increases the TIEG2-MAO B brain cell death cascade in rat brains, suggesting that the TIEG2-MAO B pathway is a novel pathway for brain cell damage resulting from ethanol exposure, and may contribute to chronic alcohol-induced brain damage.

Glyceraldehyde-3-phosphate dehydrogenase-monoamine oxidase B-mediated cell death-induced by ethanol is prevented by rasagiline and 1-R-aminoindan

The inhibitors of monoamine oxidase B (MAO B) are effectively used as therapeutic drugs for neuropsychiatric and neurodegenerative diseases. However, their mechanism of action is not clear, since the neuroprotective effect of MAO B inhibitors is associated with the blockage of glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-death cascade, rather than the inhibition of MAO B. Here, we provide evidence that GAPDH potentiates the ethanol-induced activity of MAO B and brain cell toxicity. The levels of nuclear GAPDH and MAO B activity are significantly increased in brain-derived cell lines upon 75 mM ethanol-induced cell death. Over-expression of GAPDH in cells enhances ethanol-induced cell death, and also increases the ethanol-induced activation of MAO B. In contrast, the MAO B inhibitors rasagiline and selegiline (0.25 nM) and the rasagiline metabolite, 1-R-aminoindan (1 muM) decreases the ethanol-induced MAO B, prevents nuclear translocation of GAPDH and reduces cell death. In addition, GAPDH interacts with transforming growth factor-beta-inducible early gene (TIEG2), a transcriptional activator for MAO B, and this interaction is increased in the nucleus by ethanol but reduced by MAO B inhibitors and 1-R-aminoindan. Furthermore, silencing TIEG2 using RNAi significantly reduces GAPDH-induced MAO B upregulation and neurotoxicity. In summary, ethanol-induced cell death, attenuated by MAO B inhibitors, may result from disrupting the movement of GAPDH with the transcriptional activator into the nucleus and secondly inhibit MAO B gene expression. Thus, the neuroprotective effects of rasagiline or 1-R-aminoindan on ethanol-induced cell death mediated by a novel GAPDH-MAO B pathway may provide a new insight in the treatment of neurobiological diseases including alcohol-use disorders.

Distinguishing Parkinson's disease and essential tremor with transcranial sonography

OBJECTIVES

Until today there is no reliable test that can clearly distinguish Parkinson's disease (PD) from the essential tremor (ET). Our aim was to determine the usefulness of the transcranial sonography (TCS) in the differential diagnosis of the PD and ET as well as the interobserver reliability for this method.

METHODS

Transcranial sonography of substantia nigra and clinical examination were performed on 80 PD patients, 30 ET patients, and 80 matched controls by two independent physicians.

RESULTS

Bilateral SN hyperechogenicity over the margin of 0.20 cm(2) was found in 91% of PD patients, 10% of healthy subjects, and in 13% patients with ET. Interobserver agreement for this method was significant (Student's t-test, P = 1.000).

CONCLUSIONS

Substantia nigra hyperechogenicity on TCS is a highly specific finding of PD, where in healthy individuals or in ET patients, it might correspond to an increased risk of developing PD later in life or might also be because of the impairment of nearby area of nucleus ruber in ET patients, as suggested by positron emission tomography studies. TCS may serve as a practical and sufficiently sensitive neuroimaging tool in PD diagnoses and in distinguishing it from ET; its repeatability and accuracy might add to its practical value.

Contribution of disturbed iron metabolism to the pathogenesis of Parkinson’s disease

Extensive research has revealed a complex pathophysiology in Parkinson’s disease, with different factors contributing to the progressive neurodegeneration. Within this complex pathophysiology, a central role of iron and iron-induced oxidative stress has been discussed for many years, as elevated tissue iron levels, especially within the substantia nigra, have been detected by different techniques in a number of postmortem studies. These findings could be verified intra vitam by advancing MRI techniques, and more recently transcranial ultrasound. Different causes, such as disruption of the BBB, local changes in the normal iron-regulatory system, release of iron from intracellular storages or intraneuronal transportation from iron-rich areas, as well as genetic variations leading to changes in brain iron metabolism, are being discussed to be responsible for the increased tissue iron levels. Although it is still not clear whether increased iron levels constitute a primary or secondary phenomenon in the etiology of Parkinson’s disease, its interaction with many pathophysiologcial cascades and contribution to all forms of Parkinson’s disease, idiopathic as well as monogenetic, stresses the importance of further elucidating the mechanism of brain iron homeostasis and its possible alterations to finally develop pharmacological interventions that may disrupt the chain of pathological events leading to neurodegeneration.

The MPTP mouse model: cues on DA release and neural stem cell restorative role

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to cause parkinsonism in humans and this fact is a major incentive for using this toxin as an animal model to study the pathogenesis of Parkinson's disease (PD). Although the monkey MPTP model remains the best, most studies have been performed in mice. The so-called acute and sub-acute regimens are commonly used. Both induce tissue striatal dopamine (DA) depletion and nigral neuron death. Tissue striatal DA depletion does not necessarily correlate with impairment of striatal dopaminergic functioning. In freely moving mice, systemic acute or sub-acute MPTP directly induces prolonged release of striatal DA. Such DA release may be considered the first step in MPTP-induced striatal DA depletion. Reportedly, neural stem cells improve symptoms in the MPTP model of PD by interacting with the MPTP-induced pathological nigrostriatal milieu.

T2* and FSE MRI distinguishes four subtypes of neurodegeneration with brain iron accumulation

BACKGROUND

Neurodegeneration with brain iron accumulation (NBIA) defines a group of genetic disorders characterized by brain iron deposition and associated with neuronal death. The known causes of NBIA include pantothenate kinase-associated neurodegeneration (PKAN), neuroferritinopathy, infantile neuroaxonal dystrophy (INAD), and aceruloplasminemia.

OBJECTIVE

To define the radiologic features of each NBIA subtype.

METHODS

Brain MRIs from patients with molecularly confirmed PKAN (26 cases), neuroferritinopathy (21 cases), INAD (four cases), and aceruloplasminemia (10 cases) were analyzed blindly to delineate patterns of iron deposition and neurodegeneration.

RESULTS

In most cases of PKAN, abnormalities were restricted to globus pallidus and substantia nigra, with 100% having an eye of the tiger sign. In a minority of PKAN cases there was hypointensity of the dentate nuclei (1/5 on T2* sequences, 2/26 on fast spin echo [FSE]). In INAD, globus pallidus and substantia nigra were involved on T2* and FSE scans, with dentate involvement only seen on T2*. By contrast, neuroferritinopathy had consistent involvement of the dentate nuclei, globus pallidus, and putamen, with confluent areas of hyperintensity due to probable cavitation, involving the pallida and putamen in 52%, and a subset having lesions in caudate nuclei and thalami. More uniform involvement of all basal ganglia and the thalami was typical in aceruloplasminemia, but without cavitation.

CONCLUSIONS

In the majority of cases, different subtypes of neurodegeneration associated with brain iron accumulation can be reliably distinguished with T2* and T2 fast spin echo brain MRI, leading to accurate clinical and subsequent molecular diagnosis.

Over-expressed human divalent metal transporter 1 is involved in iron accumulation in MES23.5 cells

Elevated iron accumulation has been reported in brain regions in some neurodegenerative disorders. However, the mechanism for this is largely unknown. Divalent metal transporter 1 (DMT1) is an important divalent cation transporter. The aim of the present study is to construct recombinant adenovirus encoding human DMT1 with iron responsive element (DMT1+IRE) and infect MES23.5 dopaminergic cells in order to investigate the relationship between increased DMT1+IRE expression and iron accumulation. The human DMT1 gene was obtained by RT-PCR from tissues of human duodenum. AdDMT1+IRE was successfully constructed and identified by PCR, restriction endonuclease analyses and DNA sequencing, respectively. It was able to efficiently infect MES23.5 cells, which was confirmed by RT-PCR and Western blots. When incubated with 100 microM ferrous iron for 6h, the intracellular iron levels dramatically increased in AdDMT1+IRE infected MES23.5 cells compared to the solely adenovirus infected cells. Meanwhile, the levels of hydroxyl free radicals and malondialdehyde (MDA) in these cells increased. This led to the activation of caspase-3. The apoptosis in AdDMT1+IRE infected cells was shown with hypercondensed nuclei using Hoechst staining. Analysis of DNA extracted from these cells showed the typical "ladder pattern", indicating the formation of mono- and oligonucleosomes. These results suggested that increased DMT1+IRE expression in MES23.5 cells caused the increased intracellular iron accumulation. This resulted in the increased oxidative stress leading to ultimate cell apoptosis.

Prevention and restoration of lactacystin-induced nigrostriatal dopamine neuron degeneration by novel brain-permeable iron chelators

Dysfunction of the ubiquitin-proteasome system (UPS) and accumulation of iron in substantia nigra (SN) are implicated in the pathogenesis of Parkinson's disease (PD). UPS dysfunction and iron misregulation may reinforce each other's contribution to the degeneration of dopamine (DA) neurons. In the present study, we use a new brain-permeable iron chelator, VK-28 [5-(4-(2-hydroxyethyl) piperazin-1-yl (methyl)-8-hydroxyquinoline], and its derivative M30 [5-(N-methyl-N-propargyaminomethyl)-8-hydroxyquinoline] in vivo to test their neuroprotective and neurorestorative properties against proteasome inhibitor (lactacystin) -induced nigrostriatal degeneration. Bilateral microinjections of lactacystin (1.25 microg/side) into the mouse medial forebrain bundle were performed. Administration of VK-28 (5 mg/kg, once a day) or M30 (5 mg/kg, once a day) was applied intraperitoneally 7 days before or after the lactacystin microinjection until the mice were sacrificed 28 days after microinjection. We found that VK-28 and M30 both significantly improved behavioral performances and attenuated lactacystin-induced DA neuron loss, proteasomal inhibition, iron accumulation, and microglial activation in SN. In addition, M30 restored the Bcl-2 level, which was suppressed after lactacystin injection. These findings suggest that brain-permeable iron chelators can improve DA neuron survival under UPS impairment. Furthermore, M30, a derivative of VK-28 and neuroprotective agent rasagiline, may serve as a better neuroprotective therapy for PD.

Iron in chronic brain disorders: imaging and neurotherapeutic implications

Iron is important for brain oxygen transport, electron transfer, neurotransmitter synthesis, and myelin production. Though iron deposition has been observed in the brain with normal aging, increased iron has also been shown in many chronic neurological disorders including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. In vitro studies have demonstrated that excessive iron can lead to free radical production, which can promote neurotoxicity. However, the link between observed iron deposition and pathological processes underlying various diseases of the brain is not well understood. It is not known whether excessive in vivo iron directly contributes to tissue damage or is solely an epiphenomenon. In this article, we focus on the imaging of brain iron and the underlying physiology and metabolism relating to iron deposition. We conclude with a discussion of the potential implications of iron-related toxicity to neurotherapeutic development.

Mitochondrial mechanisms of estrogen neuroprotection

Oxidative stress, bioenergetic failure and mitochondrial dysfunction are all implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease (AD). The mitochondrial involvement in neurodegenerative diseases reflects the regulatory role mitochondrial failure plays in both necrotic cell death and apoptosis. The potent feminizing hormone, 17 beta-estradiol (E2), is neuroprotective in a host of cell and animal models of stroke and neurodegenerative diseases. The discovery that 17alpha-estradiol, an isomer of E2, is equally as neuroprotective as E2 yet is >200-fold less active as a hormone, has permitted development of novel, more potent analogs where neuroprotection is independent of hormonal potency. Studies of structure-activity relationships and mitochondrial function have led to a mechanistic model in which these steroidal phenols intercalate into cell membranes where they block lipid peroxidation reactions, and are in turn recycled. Indeed, the parental estrogens and novel analogs stabilize mitochondria under Ca(2+) loading otherwise sufficient to collapse membrane potential. The neuroprotective and mitoprotective potencies for a series of estrogen analogs are significantly correlated, suggesting that these compounds prevent cell death in large measure by maintaining functionally intact mitochondria. This therapeutic strategy is germane not only to sudden mitochondrial failure in acute circumstances, such as during a stroke or myocardial infarction, but also to gradual mitochondrial dysfunction associated with chronic degenerative disorders such as AD.