Shaik Shavali

Ubiquinone (Coenzyme Q10) and Mitochondria in Oxidative Stress of Parkinson’s Disease

Parkinson’s disease is the second most common neurodegenerative disorder after Alzheimer’s disease affecting approximately1% of the population older than 50 years. There is a worldwide increase in disease prevalence due to the increasing age of human populations. A definitive neuropathological diagnosis of Parkinson’s disease requires loss of dopaminergic neurons in the substantia nigra and related brain stem nuclei, and the presence of Lewy bodies in remaining nerve cells. The contribution of genetic factors to the pathogenesis of Parkinson’s disease is increasingly being recognized. A point mutation which is sufficient to cause a rare autosomal dominant form of the disorder has been recently identified in the α-synuclein gene on chromosome 4 in the much more common sporadic, or ‘idiopathic’ form of Parkinson’s disease, and a defect of complex I of the mitochondrial respiratory chain was confirmed at the biochemical level. Disease specificity of this defect has been demonstrated for the parkinsonian substantia nigra. These findings and the observation that the neurotoxin 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), which causes a Parkinson-like syndrome in humans, acts via inhibition of complex I have triggered research interest in the mitochondrial genetics of Parkinson’s disease. Oxidative phosphorylation consists of five protein-lipid enzyme complexes located in the mitochondrial inner membrane that contain flavins (FMN, FAD), quinoid compounds (coenzyme Q10, CoQ10) and transition metal compounds (iron-sulfur clusters, hemes, protein-bound copper). These enzymes are designated complex I (NADH:ubiquinone oxidoreductase, EC 1.6. 5.3), complex II (succinate:ubiquinone oxidoreductase, EC 1.3.5.1), complex III (ubiquinol:ferrocytochrome c oxidoreductase, EC 1.10.2.2), complex IV (ferrocytochrome c:oxygen oxidoreductase or cytochrome c oxidase, EC 1.9.3.1), and complex V (ATP synthase, EC 3.6.1.34). A defect in mitochondrial oxidative phosphorylation, in terms of a reduction in the activity of NADH CoQ reductase (complex I) has been reported in the striatum of patients with Parkinson’s disease. The reduction in the activity of complex I is found in the substantia nigra, but not in other areas of the brain, such as globus pallidus or cerebral cortex. Therefore, the specificity of mitochondrial impairment may play a role in the degeneration of nigrostriatal dopaminergic neurons. This view is supported by the fact that MPTP generating 1-methyl-4-phenylpyridine (MPP+) destroys dopaminergic neurons in the substantia nigra. Although the serum levels of CoQ10 is normal in patients with Parkinson’s disease, CoQ10 is able to attenuate the MPTP-induced loss of striatal dopaminergic neurons.

Mitochondrial localization of alpha-synuclein protein in alpha-synuclein overexpressing cells.

Alpha-synuclein (alpha-syn) is implicated in the pathogenesis of Parkinsons disease (PD). Mutations in alpha-syn gene or alpha-syn locus (SNCA) triplication are associated with mitochondrial abnormalities and early onset of familial PD. The goals of the present study were to examine whether alpha-syn is localized in the mitochondria of alpha-syn overexpressing cells (HEK-syn cells); and whether alpha-syn overexpression causes cells to be more vulnerable to mitochondrial toxin, rotenone. Western blotting and confocal microscopy techniques were employed to assess localization of alpha-syn in the mitochondria of HEK-293 cells that were stably transfected with human wild-type alpha-syn. The results demonstrated that the mitochondrial fractions that were isolated from HEK-syn cells showed the presence of alpha-syn, whereas, no alpha-syn was detected in the mitochondrial fractions of control HEK cells. The mitochondria of HEK-syn cells were found to be more susceptible to rotenone-induced toxicity when compared to control HEK cells. The intracellular ATP levels were significantly decreased in HEK-syn cells in response to sub toxic concentrations of rotenone. These results suggest that under overexpression conditions, alpha-syn may translocate to mitochondria and cause enhanced toxicity in response to sub toxic concentrations of mitochondrial toxins. This study has implications to the pathogenesis of familial PD where alpha-syn overexpression is mainly involved.

Melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by increasing the release of β-endorphin an endogenous opioid

The occurrence of systematic diurnal variations in pain thresholds has been demonstrated in human. Salivary melatonin levels change following acute pain when other factors that could explain the change have been removed or controlled. Melatonin-induced analgesia is blocked by naloxone or pinealectomy. By using selective radioligands [3H]-DAMGO, [3H]-DPDPE, [3-U69593, and 3H]-nociceptin, we have shown that the bovine pinealocytes contain delta and mu, but not kappa or ORL1 opioid receptor subtypes. In the present study, by using melatonin receptor agonists (6-chloromelatonin or 2-iodo-N-butanoyl-5-methoxytryptamine) or melatonin receptor antagonist (2-phenylmelatonin), we have shown that these agents do not compete with opioid receptor subtypes. However, we observed a time-dependent release of beta-endorphin an endogenous opioid peptide, by melatonin from mouse pituitary cells in culture. Hence, it is suggested that melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by binding to its own receptors and increasing the release of beta-endorphin.

Reactive Macrophages Increase Oxidative Stress and Alpha-Synuclein Nitration During Death of Dopaminergic Neuronal Cells in Co-Culture: Relevance to Parkinson’s Disease

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons and a substantial decrease in the neurotransmitter dopamine in the nigro-striatal region of the brain. Increased markers of oxidative stress, activated microglias and elevated levels of pro-inflammatory cytokines have been identified in the brains of patients with PD. Although the precise mechanism of loss of neurons in PD remains unclear, these findings suggest that microglial activation may contribute directly to loss of dopaminergic neurons in PD patients. In the present study, we tested the hypothesis that activated microglia induces nitric oxide-dependent oxidative stress which subsequently causes death of dopaminergic neuronal cells in culture. We employed lipopolysaccharide (LPS) stimulated mouse macrophage cells (RAW 264.7) as a reactive microglial model and SH-SY5Y cells as a model for human dopaminergic neurons. LPS stimulation of macrophages led to increased production of nitric oxide in a time and dose dependent manner as well as subsequent generation of other reactive nitrogen species such as peroxynitrite anions. In co-culture conditions, reactive macrophages stimulated SH-SY5Y cell death characterized by increased peroxynitrite concentrations and nitration of alpha-synuclein within SH-SY5Y cells. Importantly 1400W, an inhibitor of the inducible nitric oxide synthase provided protection from cell death via decreasing the levels of nitrated alpha-synuclein. These results suggest that reactive microglias could induce oxidative stress in dopaminergic neurons and such oxidative stress may finally lead to nitration of alpha-synuclein and death of dopaminergic neurons in PD.

Salsolinol, a dopamine-derived tetrahydroisoquinoline, induces cell death by causing oxidative stress in dopaminergic SH-SY5Y cells, and the said effect is attenuated by metallothionein.

The endogenous neurotoxin, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), has been considered a potential neurotoxin in the etiology of Parkinsons disease (PD). Salsolinol and N-methyl(R)-salsolinol were identified in the brains and cerebrospinal fluid (CSF) of PD patients. Oxidative stress is known to be one of the major contributing factors in the cascade that may finally leads to the cell death in PD. The present study was undertaken to understand the role of salsolinol in oxidative-mediated neuronal toxicity in dopaminergic SH-SY5Y cells, and the neuroprotective effects of metallothionein (MT) against salsolinol toxicity in MT overexpressing (MT(trans)) fetal mesencephalic cells. Salsolinol increased the production of reactive oxygen species (ROS) and significantly decreased glutathione (GSH) levels and cell viability in SH-SY5Y cells. Salsolinol also decreased intracellular ATP levels and induced nuclear condensation in these cells. Salsolinol-induced depletion in cell viability was completely prevented by N-acetylcysteine in SH-SY5Y cells, and also prevented by MT in MT(trans) fetal mesencephalic cells compared to control(wt) cells. The extent of nuclear condensation and caspase activation was also less in MT(trans) cells than control(wt) cells. These results suggest that salsolinol causes oxidative stress by decreasing the levels of GSH and by increasing ROS production, and these events may lead to the death of dopaminergic cell. Furthermore, MT overexpression may protect dopaminergic neurons against salsolinol-induced neurotoxicity, most probably by the inhibition of oxidative stress and apoptotic pathways including caspase-3 activation.

THERAPEUTIC EFFICACY OF SELEGILINE IN NEURODEGENERATIVE DISORDERS AND NEUROLOGICAL DISEASES

Selegiline inhibits the activity of monoamine oxidase B, enhances the release of dopamine, blocks the uptake of dopamine, acts as a calmodulin antagonist, and enhances the level of cyclic AMP, which in turn protects dopaminergic neurons. It possesses cognition-enhancing functions, rejuvenates serum insulin-like growth factor I in aged rats, and enhances life expectancy in rodents. Selegiline possesses neurotrophic-like actions, and rescues axotomized motorneurons independent of monoamine oxidase B inhibition. It enhances the synthesis of nerve growth factor, protects dopaminergic neurons from glutamate-mediated neurotoxicity, and protects dopaminergic neurons from toxic factors present in the spinal fluid of parkinsonian patients, and the said effect may be mediated via elaborating brain derived neurotrophic factor. Selegiline increases the striatal superoxide dismutase, protects against peroxynitrite- and nitric oxide-induced apoptosis, and guards dopaminergic neurons from toxicity induced by glutathione depletion. It stimulates the biosynthesis of interleukin 1-beta and interleukin-6, is an immunoenhancing substance, possesses antiapoptotic actions, and is neuroprotectant in nature. Selegiline has been shown to be efficacious in Parkinsons disease, global ischemia, Gille de la Tourette syndrome, and narcolepsy. Its therapeutic efficacy in Alzheimers disease remains uncertain. In Alzheimers disease, short term studies of selegiline suggest a beneficial effect; whereas long term studies are less convincing.

Neuroprotective actions of coenzyme Q10 in Parkinson's disease

Publisher Summary This chapter analyzes neuroprotective actions of coenzyme Q 10 in Parkinsons Disease (PD). PD is the second most common neurodegenerative disorder after Alzheimers disease. A definitive neuropathological diagnosis of PD requires loss of dopaminergic neurons in the substantia nigra and related brain stem nuclei and the presence of Lewy bodies in remaining nerve cells. The contribution of genetic factors to the pathogenesis of PD is increasingly being recognized. It has been found that 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) becomes oxidized to 1-methyl-4-phenyl-2,3-dihydropyridinium ion (MPDP + ) and finally to methyl-phenyl-tetrahydro-pyridinium ion (MPP + ), which generates free radicals and causes parkinsonism in human beings. A deficiency of NADH:ubiquinone oxidoreductase also causes striatal cell death. A deficiency of complex I may signify that an MPTP-like neurotoxin is generated endogenously, enhancing the vulnerability of striatum to oxidative stress reactions. Details of preparation of mitochondrial genome knock-out neurons are presented in the chapter. The chapter elaborates the neuroprotective potential of coenzyme Q10. Quantitative estimation results for coenzyme Q9 and Q10 are presented in the chapter. The chapter explores the molecular mechanism of neuroprotection provided by coenzyme Q10 in PD.

1-Benzyl-1,2,3,4-tetrahydroisoquinoline, a Parkinsonism-inducing endogenous toxin, increases α-synuclein expression and causes nuclear damage in human dopaminergic cells

1‐Benzyl‐1,2,3,4‐tetrahydroisoquinoline (1BnTIQ), an endogenous neurotoxin, is known to cause parkinsonism in rodents and nonhuman primates. The levels of 1BnTIQ in cerebrospinal fluid of patients with Parkinsons disease (PD) were reported to be three times higher than those in control subjects. In the present study, we have evaluated the effects of 1BnTIQ on α‐synuclein (α‐syn) expression together with biochemical and morphological changes in human dopaminergic SH‐SY5Y cells in culture. 1BnTIQ at lower concentrations (1–50 μM) increased α‐syn protein expression in a time‐ and dose‐dependent manner in these cells. There was also up‐regulation of α‐syn mRNA by 1BnTIQ. Inhibition of complex I by rotenone and depletion of glutathione by L‐buthionine sulfoxamine also correlated with an increase in α‐syn expression, suggesting that oxidative stress may cause an increase in α‐syn levels in dopaminergic cells. Furthermore, 1BnTIQ significantly depleted glutathione levels. 1BnTIQ at higher concentrations (500 μM) increased reactive oxygen species levels, decreased ATP levels, and caused nuclear damage in the cells. The 1BnTIQ‐induced α‐syn up‐regulation was inhibited by cotreatment with the antioxidants selegiline, coenzyme Q10, and N‐acetylcystein and the caspase inhibitor DEVD‐CHO. Taken together, these results suggest that α‐syn up‐regulation and oxidative stress are contributing factors in 1BnTIQ‐induced neurotoxicity in dopaminergic neurons in PD.

Metallothionein provides zinc-mediated protective effects against methamphetamine toxicity in SK-N-SH cells

Methamphetamine (METH) is a drug of abuse and neurotoxin that induces Parkinsons-like pathology after chronic usage by targeting dopaminergic neurons. Elucidation of the intracellular mechanisms that underlie METH-induced dopaminergic neuron toxicity may help in understanding the mechanism by which neurons die in Parkinsons disease. In the present study, we examined the role of reactive oxygen species (ROS) in the METH-induced death of human dopaminergic SK-N-SH cells and further assessed the neuroprotective effects of zinc and metallothionein (MT) against METH-induced toxicity in culture. METH significantly increased the production of reactive oxygen species, decreased intracellular ATP levels and reduced the cell viability. Pre-treatment with zinc markedly prevented the loss of cell viability caused by METH treatment. Zinc pre-treatment mainly increased the expression of metallothionein and prevented the generation of reactive oxygen species and ATP depletion caused by METH. Chelation of zinc by CaEDTA caused a significant decrease in MT expression and loss of protective effects of MT against METH toxicity. These results suggest that zinc-induced MT expression protects dopaminergic neurons via preventing the accumulation of toxic reactive oxygen species and halting the decrease in ATP levels. Furthermore, MT may prevent the loss of mitochondrial functions caused by neurotoxins. In conclusion, our study suggests that MT, a potent scavenger of free radicals is neuroprotective against dopaminergic toxicity in conditions such as drug of abuse and in Parkinsons disease.

Insulin-like growth factor-1 protects human dopaminergic SH-SY5Y cells from salsolinol-induced toxicity.

Parkinsons disease (PD) is characterized by an extensive loss of dopaminergic neurons in the substantia nigra pars compacta. Salsolinol (SAL), a dopamine-derived tetrahydroisoquinoline, has been suspected to be involved in the etiology of PD. In the present study, the neuroprotective effect of insulin-like growth factor-1 (IGF-1) was studied against SAL-induced toxicity in human dopaminergic SH-SY5Y cells. SAL (100 microM) decreased cell viability in SH-SY5Y cells significantly after 24 h exposure. Both exogenous IGF-1 and IGF-1 gene transfer significantly prevented the SAL-induced cell death and increased cell viability. Wortmannin, a specific phosphatidylinositol-3-kinase (PI-3 kinase) inhibitor, completely blunted the IGF-1-induced neuroprotection, suggesting that PI-3 kinase pathway is critical in mediating the neuroprotective effects of IGF-1. These results suggest that IGF-1 may be a useful growth factor in the treatment of PD.