Docosahexaenoic acid protects motor function and increases dopamine synthesis in a rat model of Parkinson's disease via mechanisms associated with increased protein kinase activity in the striatum.

Parkinson's disease (PD) is a devastating neurodegenerative disease that leads to motor deficits and selective destruction of nigrostriatal dopaminergic neurons. PD is typically treated by dopamine replacement agents; however, dopamine replacement loses effectiveness in the later stages of the disease. Here, we describe the neuroprotective effects of the omega-3 fatty acid docosahexaenoic acid (DHA) in the medial forebrain bundle 6-hydroxydopamine (6-OHDA) model of advanced-stage PD in rats. We show that daily administration of DHA protects against core symptoms of PD, including deficits in postural stability, gait integrity, and dopamine neurochemistry in motor areas of the striatum. Our results also demonstrate that DHA increases striatal dopamine synthesis via phosphorylation of the rate-limiting catecholamine synthesizing enzyme tyrosine hydroxylase, in a manner dependent on the second messenger-linked protein kinases PKA and PKC. We also show that DHA specifically reverses dopamine loss in the nigrostriatal pathway, with no effect in the mesolimbic or mesocortical pathways. This suggests that DHA is unlikely to produce pharmacotherapeutic or adverse effects that depend on dopamine pathways other than the nigrostriatal pathway. To our knowledge, previous reports have not examined the effects of DHA in such an advanced-stage model, documented that the dopamine synthesizing effects of DHA in vivo are mediated through the activation of protein kinases and regulation of TH activity, or demonstrated specificity to the nigrostriatal pathway. These novel findings corroborate the beneficial effects of omega-3 fatty acids seen in PD patients and suggest that DHA provides a novel means of protecting patients for dopamine neurodegeneration.

Alterations in neuronal control of body weight and anxiety behavior by glutathione peroxidase 4 deficiency.

Elevated levels of oxidative stress and neuronal inflammation in the hypothalamus or ventral midbrain, respectively, represent common denominators for obesity and Parkinson's Disease (PD). However, little is known about defense mechanisms that protect neurons in these regions from oxidative damage. Here, we aimed to assess whether murine Gpx4, a crucial antioxidant enzyme that protects neurons from membrane damage and ferroptosis, is critical for the protection from neuronal inflammation in two distinct pathophysiologic diseases, namely metabolic dysfunction in diet-induced obesity or PD. Gpx4 was deleted from either AgRP or POMC neurons in the hypothalamus, essential for metabolic homeostasis, or from dopaminergic neurons in the ventral midbrain, governing behaviors such as anxiety or voluntary movement. To induce a pro-inflammatory environment, AgRP and POMC neuron-specific Gpx4 knockout mice were subjected to high-fat high-sucrose (HFHS) diet. To exacerbate oxidative stress in dopaminergic neurons of the ventral midbrain, we systemically co-deleted the PD-related gene DJ-1. Gpx4 was dispensable for the maintenance of cellular health and function of POMC neurons, even in mice exposed to obesogenic conditions. In contrast, HFHS-fed mice with Gpx4 deletion from AgRP neurons displayed increased body adiposity. Gpx4 expression and activity were diminished in the hypothalamus of HFHS-fed mice compared to standard diet-fed controls. Gpx4 deletion from dopaminergic neurons induced anxiety behavior, and diminished spontaneous locomotor activity when DJ-1 was co-deleted. Overall, these data suggest a physiological role for Gpx4 in balancing metabolic control signals and inflammation in AgRP but not POMC neurons. Moreover, Gpx4 appears to constitute an important rheostat against neuronal dysfunction and PD-like symptoms in dopaminergic circuitry within the ventral midbrain.

Oral treatment with the NADPH oxidase antagonist apocynin mitigates clinical and pathological features of parkinsonism in the MPTP marmoset model.

This study evaluates the therapeutic efficacy of the NADPH oxidase inhibitor apocynin, isolated as principal bioactive component from the medicinal plant Picrorhiza kurroa, in a marmoset MPTP model of Parkinson's disease (PD). The methoxy-substituted catechol apocynin has a similar structure as homovanillic acid (HVA), a metabolite of dopamine (DA). Apocynin acquires its selective inhibitory capacity of the reactive oxygen species generating NADPH oxidase via metabolic activation by myeloperoxidase (MPO). As MPO is upregulated in activated brain microglia cells of PD patients and in MPTP animal models, the conditions for metabolic activation of apocynin and inhibition of microglia NADPH oxidase are in place. Marmoset monkeys received oral apocynin (100 mg/kg; p.o.) (n = 5) or Gum Arabica (controls; n = 5) three times daily until the end of the study, starting 1 week before PD induction with MPTP (1 mg/kg s.c. for 8 days). Parkinsonian symptoms, motor function, home-cage activity and body weight were monitored to assess the disease development and severity. Post-mortem numbers of the tyrosine hydroxylase expressing DA neurons in the substantia nigra were counted. During the MPTP injections, apocynin limited the body weight loss and relieved parkinsonian symptoms compared to controls (Linear regression, P < 0.05) indicating a reduction of disease progression. During the last test week, apocynin also improved the hand-eye coordination performance compared with vehicle treatment (resp. 39.3 ± 4.5 % and 17.7 ± 6.7 %; P = 0.048) and improved the home cage activity with 32 % (P = 0.029), indicating anti-Parkinson efficacy. Apocynin also increased the number of surviving DA neurons in MPTP-treated marmosets with 8.5 % (P = 0.059), indicating a tendency towards a neuroprotective efficacy. In conclusion, compensation for the loss of DA and its metabolite HVA by apocynin mitigates the PD progression and limits the parkinsonian signs and motor-function deterioration.

Glyceraldehyde-3-phosphate dehydrogenase: activity inhibition and protein overexpression in rotenone models for Parkinson's disease.

Rotenone, a widely used pesticide and an environmental risk factor for Parkinson's disease (PD), induces nigrostriatal injury, Lewy body-like inclusions, and Parkinsonian symptoms in rat models for PD. Our previous data indicated that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) overexpression and glycolytic inhibition were co-current in rotenone-induced PC12 (rat adrenal pheochromocytoma cells) cell death. However, whether GAPDH overexpression plays any role in dopaminergic neurodegeneration in vivo remains unknown. In this study, we have found that GAPDH overexpression and GAPDH-positive Lewy body-like aggregates in nigral dopaminergic neurons while nigral GAPDH glycolytic activity decreases in rotenone-based PD animal models. Furthermore, GAPDH knockdown reduces rotenone toxicity significantly in PC12. These in vitro and in vivo data suggest that GAPDH contributes to the pathogenesis of Parkinson's disease, possibly representing a new molecular target for neuroprotective strategies and alternative therapies for PD.

Inhibition of inducible nitric oxide synthase expression and cell death by (-)-epigallocatechin-3-gallate, a green tea catechin, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease.

The aim of this study was to investigate the involvement of inducible nitric oxide synthase (iNOS) in the action of (-)-epigallocatechin-3-gallate (EGCG), a potential neuroprotective agent against Parkinson's disease (PD), and to test for toxicity resulting from high doses of EGCG. EGCG was administered to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice at two different doses (10mg/kg and 50mg/kg). EGCG treatment reduced the neuronal death rate to less than 50%. The level of iNOS expression in the MPTP group was 20% higher than that seen in the control group, but in the EGCG groups, iNOS expression was reduced to the level observed in the negative control group. The two doses of EGCG were equally beneficial for cell rescue, and no toxicity was observed with the higher dose. Inhibition of iNOS may be an important mechanism underlying the prevention of MPTP toxicity, and EGCG may potentially be a neuroprotective agent against PD.

Ablation of the inflammatory enzyme myeloperoxidase mitigates features of Parkinson's disease in mice.

Parkinson's disease (PD) is characterized by a loss of ventral midbrain dopaminergic neurons, which can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Inflammatory oxidants have emerged as key contributors to PD- and MPTP-related neurodegeneration. Here, we show that myeloperoxidase (MPO), a key oxidant-producing enzyme during inflammation, is upregulated in the ventral midbrain of human PD and MPTP mice. We also show that ventral midbrain dopaminergic neurons of mutant mice deficient in MPO are more resistant to MPTP-induced cytotoxicity than their wild-type littermates. Supporting the oxidative damaging role of MPO in this PD model are the demonstrations that MPO-specific biomarkers 3-chlorotyrosine and hypochlorous acid-modified proteins increase in the brains of MPTP-injected mice. This study demonstrates that MPO participates in the MPTP neurotoxic process and suggests that inhibitors of MPO may provide a protective benefit in PD.

Cultured human foetal cerebral cortex, transfected with tyrosine hydroxylase cDNA, as a source of neural transplant material.

Obtaining an adequate supply of foetal dopaminergic tissue to treat Parkinson's disease by neural transplantation can be difficult. In this study primary cultures of human foetal cerebral cortex cells were transfected, using cationic lipids, with a eukaryotic expression vector (pCIneo-THI) containing the cDNA for human tyrosine hydroxylase isoform I (TH). Cortical cells from human (10-14 week) foetuses were cultured for 11 days in vitro and transfected twice with pCIneo-THI during this time. The double transfection process resulted in 3-4% of the cells becoming TH positive. When grafted into the striatum of 6-OHDA lesioned rats the transfected foetal cerebral cortex cells reduced amphetamine-induced circling behaviour by 75%, while grafts of untransfected cells had no significant effect on turning. TH transfected foetal cerebral cortex cells may therefore be a useful alternative supply of tissue for use in neural transplants to treat Parkinson's disease.