Acute intranigral homocysteine administration produces stereotypic behavioral changes and striatal dopamine depletion in Sprague–Dawley rats

Betaine-The dark knight of the brain

The role of betaine in the liver and kidney has been well documented, even from the cellular and molecular point of view. Despite literature reporting positive effects of betaine supplementation in Alzheimer's, Parkinson's and schizophrenia, the role and function of betaine in the brain are little studied and reviewed. Beneficial effects of betaine in neurodegeneration, excitatory and inhibitory imbalance and against oxidative stress in the central nervous system (CNS) have been collected and analysed to understand the main role of betaine in the brain. There are many 'dark' aspects needed to complete the picture. The understanding of how this osmolyte is transported across neuron and glial cells is also controversial, as the expression levels and functioning of the known protein capable to transport betaine expressed in the brain, betaine-GABA transporter 1 (BGT-1), is itself not well clarified. The reported actions of betaine beyond BGT-1 related to neuronal degeneration and memory impairment are the focus of this work. With this review, we underline the scarcity of detailed molecular and cellular information about betaine action. Consequently, the requirement of detailed focus on and study of the interaction of this molecule with CNS components to sustain the therapeutic use of betaine.

Metabolic phenotyping of opioid and psychostimulant addiction: A novel approach for biomarker discovery and biochemical understanding of the disorder

Despite the progress in characterising the pharmacological profile of drugs of abuse, their precise biochemical impact remains unclear. The metabolome reflects the multifaceted biochemical processes occurring within a biological system. This includes those encoded in the genome but also those arising from environmental/exogenous exposures and interactions between the two. Using metabolomics, the biochemical derangements associated with substance abuse can be determined as the individual transitions from recreational drug to chronic use (dependence). By understanding the biomolecular perturbations along this time course and how they vary across individuals, metabolomics can elucidate biochemical mechanisms of the addiction cycle (dependence/withdrawal/relapse) and predict prognosis (recovery/relapse). In this review, we summarise human and animal metabolomic studies in the field of opioid and psychostimulant addiction. We highlight the importance of metabolomics as a powerful approach for biomarker discovery and its potential to guide personalised pharmacotherapeutic strategies for addiction targeted towards the individual's metabolome.

Reinforcing mitochondrial functions in aging brain: An insight into Parkinson's disease therapeutics

Mitochondria, the powerhouse of the neural cells in the brain, are also the seat of certain essential gene signaling pathways that control neuronal functions. Deterioration of mitochondrial functions has been widely reported in normal aging as well as in a spectrum of age-associated neurological diseases, including Parkinson's disease (PD). Evidences accumulated in the recent past provide not only advanced information on the causes of mitochondrial bioenergetics defects and redox imbalance in PD brains, but also much insight into mitochondrial biogenesis, quality control of mitochondrial proteins, and genes, which regulate intra- and extra-mitochondrial signaling that control the general health of neural cells. The mitochondrial quality control machinery is affected in aging and especially in PD, thus affecting intraneuronal protein transport and degradation, which are primarily responsible for accumulation of misfolded proteins and mitochondrial damage in sporadic as well as familial PD. Essentially we considered in the first half of this review, mitochondria-based targets such as mitochondrial oxidative stress and mitochondrial quality control pathways in PD, relevance of mitochondrial DNA mutations, mitophagy, mitochondrial proteases, mitochondrial flux, and finally mitochondria-based therapies possible for PD. Therapeutic aspects are considered in the later half and mitochondria-targeted antioxidant therapy, mitophagy enhancers, mitochondrial biogenesis boasters, mitochondrial dynamics modulators, and gene-based therapeutic approaches are discussed. The present review is a critical assessment of this information to distinguish some exemplary mitochondrial therapeutic targets, and provides a utilitarian perception of some avenues for therapeutic designs on identified mitochondrial targets for PD, a very incapacitating disorder of the geriatric population, world over.

Melatonin protects against behavioral deficits, dopamine loss and oxidative stress in homocysteine model of Parkinson's disease

AIM

Hyperhomocysteinemia and homocysteine (Hcy) mediated dopaminergic neurotoxicity is a matter of concern in the pathophysiology of Parkinson's disease (PD). Our previous study established the involvement of oxidative stress in the substantia nigra (SN) of Hcy rat model of PD; however, the role of antioxidants, such as melatonin, was not tested in this model.

MAIN METHODS

Melatonin (10, 20 and 30mg/kg, i.p.) was administered to rats injected with Hcy in right SN (1.0μmol in 2μl saline) to investigate its potency in attenuating the behavioral abnormalities, dopamine depletion and oxidative stress prompted by Hcy.

KEY FINDINGS

Treatment of melatonin protected against nigral dopamine loss and replenished the striatal dopamine loss that resulted in amelioration of rotational behavioral bias in Hcy denervated animals. Melatonin administration significantly improved mitochondrial complex-I activity and protected the SN neurons from the toxic insults of oxidative stress induced by Hcy. Amelioration of oxidative stress by melatonin in Hcy-infused SN was bought by dose-dependently scavenging of hydroxyl radicals, restoration of glutathione level and elevation in the activity of antioxidant enzymes.

SIGNIFICANCE

The observations bring into light the significant neuroprotective potentials of melatonin in Hcy model of PD which is attributed to the attenuation of oxidative stress in SN.

Oxidative stress and mitochondrial dysfunction are the underlying events of dopaminergic neurodegeneration in homocysteine rat model of Parkinson's disease

Homocysteine (Hcy) when injected intranigrally in rat caused parkinsonian behavioural phenotypes and loss of nigral dopaminergic neurons but the underlying mechanisms of neurotoxicity remains elusive. In the present study, we focused on oxidative stress as one of the mechanisms of neurotoxicity in Hcy-induced hemiparkinsonian rat model. Unilateral intranigral infusion of Hcy (1.0 μmol in 2 μl) caused inhibition of mitochondrial complex-I activity, decrease in the level of striatal dopamine, loss of midbrain dopaminergic neurons, and motor abnormalities. Hcy caused oxidative stress in the nigrostriatal pathway, with increase in generation of hydroxyl radicals, depletion in the level of reduced glutathione and enhanced activity of antioxidant enzymes (superoxide dismutase and catalase). Our results provided the evidence of critical involvement of oxidative stress as one of the mechanisms underlying Hcy-induced dopaminergic neurotoxicity in nigrostriatal pathway. As oxidative stress is one of the prime mechanisms of neurodegeneration in different animal models of Parkinson's disease, and since Hcy caused equivalent parkinsonian pathologies in rat model, the present study proclaims Hcy-induced rat model as a viable rodent model of Parkinson's disease.

Chronic exposure of homocysteine in mice contributes to dopamine loss by enhancing oxidative stress in nigrostriatum and produces behavioral phenotypes of Parkinson's disease

Increased homocysteine (Hcy) level has been implicated as an independent risk factor for various neurological disorders, including Parkinson’s disease (PD). Hcy has been reported to cause dopaminergic neuronal loss in rodents and causes the behavioral abnormalities. This study is an attempt to investigate molecular mechanisms underlying Hcy-induced dopaminergic neurotoxicity after its chronic systemic administration. Male Swiss albino mice were injected with different doses of Hcy (100 and 250 mg/kg; intraperitoneal) for 60 days. Animals subjected to higher doses of Hcy, but not the lower dose, produces motor behavioral abnormalities with significant dopamine depletion in the striatum. Significant inhibition of mitochondrial complex-I activity in nigra with enhanced activity of antioxidant enzymes in the nigrostriatum have highlighted the involvement of Hcy-induced oxidative stress. While, chronic exposure to Hcy neither significantly alters the nigrostriatal glutathione level nor it causes any visible change in tyrosine hydroxylase-immunoreactivity of dopaminergic neurons. The finding set us to hypothesize that the mild oxidative stress due to prolonged Hcy exposure to mice is conducive to striatal dopamine depletion leading to behavioral abnormalities similar to that observed in PD.

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Chronic intraperitoneal Hcy injection causes parkinsonian like motor abnormalities.

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Hcy injection caused complex-I inhibition in nigra and striatal dopamine depletion.

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Hcy injection caused enhanced activity of antioxidant enzymes in nigrostriatum.

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Hcy-induced mild oxidative stress is not sufficient to alter GSH and TH.

Homocysteine Level and Mechanisms of Injury in Parkinson's Disease as Related to MTHFR, MTR, and MTHFD1 Genes Polymorphisms and L-Dopa Treatment

An elevated concentration of total homocysteine (tHcy) in plasma and cerebrospinal fluid is considered to be a risk factor for Alzheimer's disease (AD) and Parkinson's disease (PD). Homocysteine (Hcy) levels are influenced by folate concentrations and numerous genetic factors through the folate cycle, however, their role in the pathogenesis of PD remains controversial. Hcy exerts a neurotoxic action and may participate in the mechanisms of neurodegeneration, such as excitotoxicity, oxidative stress, calcium accumulation, and apoptosis. Elevated Hcy levels can lead to prooxidative activity, most probably through direct interaction with N-methyl-D-aspartate (NMDA) receptors and sensitization of dopaminergic neurons to age-related dysfunction and death. Several studies have shown that higher concentration of Hcy in PD is related to long-term administration of levodopa (L-dopa). An elevation of plasma tHcy levels can also reflect deficiencies of cofactors in remethylation of Hcy to methionine (Met) (folates and vitamin B12) and in its transsulfuration to cysteine (Cys) (vitamin B6). It is believed that the increase in the concentration of Hcy in PD can affect genetic polymorphisms of the folate metabolic pathway genes, such as MTHFR (C677T, A1298C and G1793A), MTR (A2756G), and MTHFD1 (G1958A), whose frequencies tend to increase in PD patients, as well as the reduced concentration of B vitamins. In PD, increased levels of Hcy may lead to dementia, depression and progression of the disease.

Association of MTHFR, MTR, and MTRR polymorphisms with Parkinson's disease among ethnic Chinese in Taiwan

BACKGROUND

Influence of folate/homocysteine conversion is considered to be important in the pathogenesis of Parkinson's disease (PD). However, association of the folate metabolic pathway gene polymorphisms with PD susceptibility remains unclear.

METHODS

To test this possibility in PD, we conducted a hospital-based case-control study constituting 211 patients and 218 age- and sex-matched controls of ethnic Chinese in Taiwan. Genotyping assay was performed to screen for polymorphisms of the methylenetetrahydrofolate reductase (MTHFR C677T), methyltetrahydrofolate-homocysteine methyltransferase (MTR A2756G), and 5-methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR A1049G and C1783T) genes and assess the association between these genotype polymorphisms and PD risk using logistic regression analysis.

RESULTS

Of these four non-synonymous polymorphisms, the MTRR 1049GG variant was significantly associated with PD susceptibility (OR=3.17, 95%CI=1.08-9.35). Furthermore, we stratified our patients based on the MTHFR 677TT genotype in different strata, a significant association between the joint effect of polymorphisms and PD risk was observed in those patients whose genotypes were MTRR A1049G/MTR A2756G or MTRR C1783T/MTR A2756G (P<0.05).

CONCLUSION

Our findings provide support for the synergistic effects of polymorphisms in the folate metabolic pathway genes in PD susceptibility; the increased PD risk would be more significant in carriers with the polymorphisms of MTHFR, MTR, and MTRR genes.

Melatonin inhibits 6-hydroxydopamine production in the brain to protect against experimental parkinsonism in rodents

We tested the hypothesis that melatonin regulates formation of 6-hydroxydopamine (6-OHDA) in the brain and thereby protects animals from dopaminergic neurotoxicity and the development of parkinsonism in animals. Employing a ferrous-ascorbate-dopamine (FAD) hydroxyl radical ((*)OH) generating system, in the present study we demonstrate a dose-dependent attenuation of 6-OHDA generation by melatonin in vitro. Intra-median forebrain bundle infusion of FAD caused significant depletion of striatal dopamine (DA), which was blocked by melatonin. Per-oral administration of l-3,4-dihydroxyphenylalanine (L-DOPA) for 7 days caused a dose-dependent increase in the formation of 6-OHDA in the mouse striatum, which was increased synergistically by the systemic administration of the parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the 7th day of L-DOPA treatment. Melatonin treatment significantly attenuated both the L-DOPA and MPTP-induced increases in the levels of striatal 6-OHDA, and protected against striatal DA depletion caused by the neurotoxin. These observations suggest a novel mode of melatonin-induced dopaminergic neuroprotection in two models of Parkinson's disease, and suggest the possible therapeutic use of this well-known antioxidant indoleamine neurohormone in parkinsonism.

Homocysteine is toxic for dopaminergic neurons in primary mesencephalic culture

Hyperhomocysteinemia associated with L-3,4-dihydroxyphenylalanine (L-dopa) treatment has been observed in patients with Parkinson's disease. We investigated the toxicity of homocysteine (Hcy) on E14-rat-primary mesencephalic culture. Exposure to 0-5 mM Hcy decreased number of tyrosine hydroxylase (TH)-positive dopaminergic neurons and microtubule associated protein 2 (MAP2)-positive neurons in a dose-dependent manner. TH-positive neurons had vulnerability to the insult of Hcy compared with the other MAP2-positive neurons. In dopaminergic neurons, 5 microM reserpine enhanced the Hcy toxicity, whereas 50 microM alpha-methyltyrosine attenuated the toxic effect, showing that the intracellular dopamine increased the cytotoxicity of Hcy. Hcy enhanced the toxicity of 1-methyl-4-phenylpyridinium (MPP+) for dopaminergic neurons. It was suggested that the Hcy toxicity was associated with the oxidative stress. Hcy is toxic for dopaminergic neurons, and hyperhomocysteinemia may modify the clinical course of Parkinson's disease.

Long-term L-DOPA treatment causes indiscriminate increase in dopamine levels at the cost of serotonin synthesis in discrete brain regions of rats

(1) The treatment of choice for Parkinson's disease (PD) is 3,4-dihydroxyphenylalanine (L-DOPA) with peripheral decarboxylase inhibitor, but long-term therapy leads to motor and psychiatric complications. In the present study we investigated 5-hydroxytryptamine (5-HT) and dopamine concentrations in serotonergic and dopaminergic nuclei following chronic administration of L-DOPA to find whether the neurotransmitter synthesis in these brain areas are compensated. (2) Rats were administered L-DOPA (250 mg/kg) and carbidopa (25 mg/kg) daily for 59 and 60 days, and killed on the 60th day, respectively at 24 h and 30 min after the last dose. L-DOPA, norepinephrine, 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), dopamine, homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in striatum, nucleus raphe dorsalis (NRD), nucleus accumbens (NAc), substantia nigra, cerebellum, and cortex employing HPLC-electrochemical procedure. (3) Prolonged treatment of L-DOPA caused depression in the animals as revealed in a forced swim test. Serotonin content was significantly decreased in all brain regions studied 30 min after long-term L-DOPA, except in NAc. The cortex and striatum showed lowered levels of this indoleamine 24 h after 59 doses of L-DOPA. Dopamine, HVA, and DOPAC concentrations were significantly higher in all the regions studied after 30 min, and in the cerebellum after 24 h of L-DOPA. The levels of DOPAC were elevated in all the brain areas studied 24 h after prolonged L-DOPA treatment. (4) The present results suggest that long-term L-DOPA treatment results in significant loss of 5-HT in serotonergic and dopaminergic regions of the brain. Furthermore, while L-DOPA metabolism per se was uninfluenced, dopamine synthesis was severely impaired in all the regions. The imbalance of serotonin and dopamine formation may be the cause of overt cognitive, motor, and psychological functional aberrations seen in parkinsonian patients following prolonged L-DOPA treatment.

Melatonin protects against rotenone-induced oxidative stress in a hemiparkinsonian rat model

In the present study, we evaluated the effect of melatonin, a well-known free radical scavenger and neuroprotector, against rotenone-induced oxidative stress in a hemiparkinsonian rat model. The effect of melatonin on glutathione (GSH) depletion caused by unilateral, intranigral infusion of rotenone was investigated employing a spectrofluorimetric procedure. We also studied the effect of melatonin on rotenone-induced changes in the antioxidant enzymes superoxide dismutase (SOD) and catalase in the cytosolic fractions of substantia nigra (SN), employing spectrophotometric procedures. Rotenone-induced hydroxyl radicals (*OH) in the isolated mitochondria, as measured employing a sensitive HPLC-electrochemical method, were significantly scavenged by melatonin. Melatonin treatment restored the rotenone-induced decrease in GSH level and changes in antioxidant enzyme (SOD and catalase) activities in the SN. Our results strongly indicate melatonin's beneficial use in Parkinson's disease therapy as an antioxidant.