Piyarat Govitrapong

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.

Effect of Chronic Analgesic Exposure on the Central Serotonin System: A Possible Mechanism of Analgesic Abuse Headache

Objective.–To investigate the effects of chronic analgesic exposure on the central serotonin system and the relationship between the serotonin system and the analgesic efficacy of nonnarcotic analgesics.

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.

Pineal opioid receptors and analgesic action of melatonin

Abstract: Physicians have noted since antiquity that their patients complained of less pain and required fewer analgesics at night times. In most species, including the humans, the circulating levels of melatonin, a substance with analgesic and hypnotic properties, exhibit a pronounced circadian rhythm with serum levels being high at night and very low during day times. Moreover, melatonin exhibits maximal analgesic effects at night, pinealectomy abolishes the analgesic effects of melatonin, and mu opioid receptor antagonists disrupt the day‐night rhythm of nociception. It is believed that melatonin, with its sedative and analgesic effects, is capable of providing a pain free sleep so that the body may recuperate and restore itself to function again at its peak capacity. Moreover, in conditions when pain is associated with extensive tissue injury, melatonins ability to scavenge free radicals and abort oxidative stress is yet another beneficial effect to be realized. Since melatonin may behave as a mixed opioid receptor agonist‐antagonist, it is doubtful that a physician simply could potentiate the analgesic efficacy of narcotics such as morphine by coadministering melatonin. Therefore, future research may synthesize highly efficacious melatonin analogues capable of providing maximum analgesia and hopefully being devoid of addiction liability now associated with currently available narcotics.

Deferoxamine Attenuates Iron-Induced Oxidative Stress and Prevents Mitochondrial Aggregation and α-Synuclein Translocation in SK-N-SH Cells in Culture

One of the defining characteristics of neurodegenerative diseases, including Parkinson’s disease, is an abnormal accumulation of iron in the affected brain areas. By using SK-N-SH, a dopaminergic cell line, we have found that iron (100–250 µM FeSO4) decreased cell viability, increased lipid peroxidation, and the said effects were blocked by deferoxamine (DFO: 10 µM). Furthermore, DFO, in the absence of iron, enhanced the level of adenosine triphosphate (ATP), but caused chromatin condensation and cell death. Morphological studies revealed that iron (50–100 µM) altered mitochondrial morphology, disrupted nuclear membrane, and translocated α-synuclein from perinuclear region into the disrupted nucleus. The results of these studies suggest that DFO is able to block and attenuate iron-mediated oxidative stress. However, in the absence of excess iron, DFO itself may have deleterious effects on the morphology and hence integrity of dopaminergic neurons.

The mechanism for the neuroprotective effect of melatonin against methamphetamine-induced autophagy

Abstract:  Methamphetamine (METH) is a common drug of abuse that induces toxicity in the central nervous system and is connected to neurological disorders such as Parkinson’s disease. METH neurotoxicity is induced by reactive oxygen species (ROS) production and apoptosis. Moreover, autophagy is an alternative to cell death and a means for eliminating dysfunctional organelles. In other cases, autophagy can end up in cell death. Nonetheless, it is not clear whether autophagy is also correlated with apoptotic signaling in drug‐induced neurotoxicity. Therefore, we hypothesized that METH‐generated toxicity associated with initiating the apoptotic signaling cascade can also increase the autophagic phenotype in neuronal cells. Using the SK–N–SH dopaminergic cell line as our model system, we found that METH‐induced autophagy by inhibiting dissociation of Bcl‐2/Beclin 1 complex and its upstream pathway that thereby led to cell death. We uncovered a novel function for the anti‐apoptotic protein Bcl‐2, as it played a role in negatively regulating autophagy by blocking an essential protein in the signaling pathway, Beclin 1. Furthermore, Bcl‐2 was activated by c‐Jun N‐terminal kinase 1 (JNK 1), which is upstream of Bcl‐2 phosphorylation, to induce Bcl‐2/Beclin 1 dissociation. Furthermore, we demonstrated a novel role for melatonin in protecting cells from autophagic cell death triggered by the Bcl‐2/Beclin 1 pathway by inhibiting the activation of the JNK 1, Bcl‐2 upstream pathway. This study provides information regarding the link between apoptosis and autophagy signaling, which could lead to the development of therapeutic strategies that exploit the neurotoxicity of drugs of abuse.

Coenzyme Q(10) provides neuroprotection in iron-induced apoptosis in dopaminergic neurons.

The exact molecular mechanism of progressive loss of neuromelanin containing nigrostriatal dopaminergic neurons in Parkinsons disease (PD) remains unknown, yet evidence suggests that iron might play an important role in PD pathology. In this study we have determined the neuroprotective role of coenzyme Q10 (CoQ10) in iron-induced apoptosis in cultured human dopaminergic (SK-N-SH) neurons, in metallothionein gene-manipulated mice, and in α-synuclein knockout (α-synko) mice with a primary objective to assess a possible therapeutic and anti-inflammatory potential for CoQ10 in PD. Iron-induced mitochondrial damage and apoptosis were characterized by reactive oxygen species production, increased metallothionein and glutathione synthesis, caspase-3 activation, NF-κB induction, and decreased Bcl-2 expression, without any significant change in Bax expression. Lower concentrations of FeSO4 (1–10 μM) induced perinuclear aggregation of mitochondria, whereas higher concentrations (100–250 μM) induced CoQ10 depletion, plasma membrane perforations, mitochondrial damage, and nuclear DNA condensation and fragmentation. FeSO4-induced deleterious changes were attenuated by pretreatment with CoQ10 and by deferoxamine, a potent iron chelator, in SK-N-SH cells. 1-Methyl, 4-phenyl, 1,2,3,6-tetrahydropyridine (MPTP)-induced striatal release of free iron, and NF-κB expression were significantly increased; whereas ferritin and melanin synthesis were significnatly reduced in the substantia nigra pars compacta (SN pc) of MTdko mice as compared with controlwt mice, MTtrans mice, and α-synko mice. CoQ10 treatment inhibited MPTP-induced NF-κB induction in all of the genotypes. These data suggest that glutathione and metallothionein synthesis might be induced as an attempt to combat iron-induced oxidative stress, whereas exogenous administration of CoQ10 or of metallothionein induction might provide CoQ10-mediated neuroprotection in PD.

Melatonin protects against hydrogen peroxide-induced cell death signaling in SH-SY5Y cultured cells: involvement of nuclear factor kappa B, Bax and Bcl-2

Abstract:  Oxidative stress is defined as a disturbance in the prooxidant–antioxidant balance, leading to potential cell damage. Reactive oxygen species such as superoxide radicals, hydroxyl radicals and hydrogen peroxide may act also as secondary intermediaries in intracellular signaling leading to cell death. The neuroprotective effect of melatonin has been observed both in vivo and in vitro. The objective of this research, therefore, was to better understand the cellular mechanisms of neuronal cell degeneration induced via oxidative stress and the protective roles of melatonin on this cell death. In the present study, the effects of melatonin on H2O2‐induced neuronal cell degeneration in human dopaminergic neuroblastoma SH‐SY5Y cultured cells were investigated. The results showed that H2O2 significantly decreased cell viability and melatonin reversed the toxic effects of H2O2. An inhibition of caspase enzyme activity by Ac‐DEVD‐CHO, a caspase‐3 inhibitor, significantly increased cell viability in H2O2‐treated cells. The phosphorylation of transcription factors, nuclear factor kappa B (NF‐κB) was increased in H2O2‐treated cells and this effect was abolished by melatonin. Translocation of phosphorylated NF‐κB to perinuclear and nuclear sites, estimated using immunofluorescence, occurred to a greater extent in H2O2‐treated cells than in untreated control cells and again this effect was abolished by melatonin. In addition, induction of Bcl‐2 and Bax proteins was demonstrated in SH‐SY5Y cultured cells treated with H2O2, whereas the induction of Bax but not Bcl‐2 was diminished by melatonin. In light of these finding, it is possible that the antioxidative stress effect of melatonin associated with inhibition of Bax expression, may offer a means of treating neuronal degeneration and disease.

Melatonin attenuates methamphetamine‐induced overexpression of pro‐inflammatory cytokines in microglial cell lines

Abstract:  Methamphetamine (METH), the most commonly abused drug, has long been known to induce neurotoxicity. METH causes oxidative stress and inflammation, as well as the overproduction of both reactive oxygen species (ROS) and reactive nitrogen species (RNS). The role of METH‐induced brain inflammation remains unclear. Imbroglio activation contributes to the neuronal damage that accompanies injury, disease and inflammation. METH may activate microglia to produce neuroinflammatory molecules. In highly aggressively proliferating immortalized (HAPI) cells, a rat microglial cell line, METH reduced cell viability in a concentration‐ and time‐dependent manner and initiated the expression of interleukin 1β (IL‐1β), interleukin 6 (IL‐6) and tumor necrosis factor α. METH also induced the production of both ROS and RNS in microglial cells. Pretreatment with melatonin, a major secretory product of the pineal gland, abolished METH‐induced toxicity, suppressed ROS and RNS formation and also had an inhibitory effect on cytotoxic factor gene expression. The expression of cytotoxic factors produced by microglia may contribute to central nervous system degeneration in amphetamine abusers. Melatonin attenuates METH toxicity and inhibits the expression of cytotoxic factor genes associated with ROS and RNS neutralization in HAPI microglia. Thus, melatonin might be one of the neuroprotective agents induced by METH toxicity and/or other immunogens.

Melatonin increases proliferation of cultured neural stem cells obtained from adult mouse subventricular zone

Abstract:  Melatonin, a circadian rhythm–promoting molecule secreted mainly by the pineal gland, has a variety of biological functions and neuroprotective effects including control of sleep–wake cycle, seasonal reproduction, and body temperature as well as preventing neuronal cell death induced by neurotoxic substances. Melatonin also modulates neural stem cell (NSC) function including proliferation and differentiation in embryonic brain tissue. However, the involvement of melatonin in adult neurogenesis is still not clear. Here, we report that precursor cells from adult mouse subventricular zone (SVZ) of the lateral ventricle, the main neurogenic area of the adult brain, express melatonin receptors. In addition, precursor cells derived from this area treated with melatonin exhibited increased proliferative activity. However, when cells were treated with luzindole, a competitive inhibitor of melatonin receptors, or pertussis toxin, an uncoupler of Gi from adenylate cyclase, melatonin‐induced proliferation was reduced. Under these conditions, melatonin induced the differentiation of precursor cells to neuronal cells without an upregulation of the number of glia cells. Because stem cell replacement is thought to play an important therapeutic role in neurodegenerative diseases, melatonin might be beneficial for stimulating endogenous neural stem cells.