Synergistic effect of α-dihydroergocryptine and L-dopa or dopamine on dopaminergic neurons in primary culture

From the tyrosine hydroxylase hypothesis of Parkinson's disease to modern strategies: a short historical overview

A time span of 60 years covers the detection of catecholamines in the brain, their function in movement and correlation to Parkinson’s disease (PD). The clinical findings that orally given l-DOPA can alleviate or even prevent akinesia gave great hope for the treatment of PD. Attention focused on the role of tyrosine hydroxylase (TH) as the rate-limiting enzyme in the formation of catecholamines. It became evident that the enzyme driven formation is lowered in PD. Such results could only be obtained from studying human brain samples demonstrating the necessity for human brain banks. Originally, a TH enzyme deficiency was suspected in PD. Studies were conducted on the enzyme properties: its induction and turnover, the complex regulation starting with cofactor requirements as tetrahydrobiopterin and ferrous iron, and the necessity for phosphorylation for activity as well as inhibition by toxins or regulatory feedback inhibition by catecholamines. In the course of time, it became evident that neurodegeneration and cell death of dopaminergic neurons is the actual pathological process and the decrease of TH a cophenomenon. Nevertheless, TH immunochemistry has ever since been a valuable tool to study neuronal pathways, neurodegeneration in various animal models of neurotoxicity and cell cultures, which have been used as well to test potential neuroprotective strategies.

MicroRNA-326 Inhibits Apoptosis and Promotes Proliferation of Dopaminergic Neurons in Parkinson's Disease Through Suppression of KLK7-Mediated MAPK Signaling Pathway

Parkinson's disease (PD), one of the motor system disorders, is characterized by the loss of dopamine-producing brain cells. Accumulating evidence has highlighted the involvement of microRNAs (miRs) in the development and progression of PD. Hence, we aimed at exploring possible effects of miR-326 on the progression of PD in mice in an attempt to elucidate the underlying mechanism associated with the kallikrein-related peptidase 7 (KLK7)-mediated mitogen-activated protein kinase (MAPK) signaling pathway. In order to identify the regulatory relationship between miR-326 and KLK7 and its biological significance in PD, PD mouse models were established and subsequently treated with mimics or inhibitors of miR-326 or siRNA-KLK7. The content of striatal dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyrosine (3-MT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA); positive expression of tyrosine hydroxylase (TH) and inducible nitric oxide synthase (iNOS); and the levels of IL-1, IL-6, TNF-α, INF-γ, and MAPK signaling pathway-related genes were determined accordingly. The results obtained indicated that KLK7 was negatively targeted by miR-326, with lower miR-326 and higher KLK7 detected among PD mice. The overexpression of miR-326 or silencing of KLK7 was demonstrated to increase the content of DA, DOPAC, HVA, 3-MT, SOD, GSH-Px, and TH positive expression, while reducing iNOS positive expression, MDA content and cell apoptosis, as well as inhibited levels of IL-1, IL-6, TNF-α, INF-γ, and mRNA and protein levels of p38, ERK, JNK, and caspase-3. Taken together, these results provided evidence suggesting that miR-326 could inhibit iNOS activation and apoptosis of dopaminergic neurons through inhibiting the MAPK signaling pathway and negatively regulating KLK7 in mice with PD. These findings highlight the potential of miR-326 as a novel target for future PD treatment.

Hormetic approaches to the treatment of Parkinson's disease: Perspectives and possibilities

Age-related changes in the brain reflect a dynamic interaction of genetic, epigenetic, phenotypic, and environmental factors that can be temporally restricted or more longitudinally present throughout the lifespan. Fundamental to these mechanisms is the capacity for physiological adaptation through modulation of diverse molecular and biochemical signaling occurring from the intracellular to the network-systemic level throughout the brain. A number of agents that affect the onset and progression of Parkinson's disease (PD)-like effects in experimental models exhibit temporal features, and mechanisms of hormetic dose responses. These findings have particular significance since the hormetic dose response describes the amplitude and range of potential therapeutic effects, thereby affecting the design and conduct of studies of interventions against PD (and other neurodegenerative diseases), and may also be important to a broader consideration of hormetic processes in resilient adaptive responses that might afford protection against the onset and/or progression of PD and related disorders.

Dopamine receptors and Parkinson's disease

Parkinson's disease (PD) is a progressive extrapyramidal motor disorder. Pathologically, this disease is characterized by the selective dopaminergic (DAergic) neuronal degeneration in the substantia nigra. Correcting the DA deficiency in PD with levodopa (L-dopa) significantly attenuates the motor symptoms; however, its effectiveness often declines, and L-dopa-related adverse effects emerge after long-term treatment. Nowadays, DA receptor agonists are useful medication even regarded as first choice to delay the starting of L-dopa therapy. In advanced stage of PD, they are also used as adjunct therapy together with L-dopa. DA receptor agonists act by stimulation of presynaptic and postsynaptic DA receptors. Despite the usefulness, they could be causative drugs for valvulopathy and nonmotor complication such as DA dysregulation syndrome (DDS). In this paper, physiological characteristics of DA receptor familyare discussed. We also discuss the validity, benefits, and specific adverse effects of pharmaceutical DA receptor agonist.

9-Methyl-beta-carboline up-regulates the appearance of differentiated dopaminergic neurones in primary mesencephalic culture

beta-Carbolines (BCs) derive from tryptophan and its derivatives. They are formed endogenously in humans and mammals and occur inter alia in cooked meat and tobacco smoke. They have been detected in human brain, cerebrospinal fluid, and plasma. Up to now they were predominantly identified as compounds exhibiting neurotoxic actions. Since significantly higher amounts are present in parkinsonian patients, they are regarded as potential pathogenetic factors in Parkinson's disease. We identified for the first time a BC (9-methyl-BC; 9-me-BC) exerting neuroprotective and neuron-differentiating effects. Treatment of primary mesencephalic dopaminergic cultures with 9-me-BC inhibited the basal release of lactate dehydrogenase and reduced the number of cells stained with propidium iodide. Caspase-3 activity was decreased, the total protein content was unchanged and ATP content was increased. Furthermore, the expression of inflammation-related genes was reduced. The number of differentiated dopaminergic neurones was significantly increased and a wide array of neurotrophic/transcription factors (Shh, Wnt1, Wnt5a, En1, En2, Nurr1, Pitx3) and marker genes (Th, Dat, Aldh1a1) decisive for dopaminergic differentiation was stimulated. Consistently, the dopamine content was slightly, although non-significantly, increased and the dopamine uptake capacity was elevated. An anti-proliferative effect was observed in human neuroblastoma SH-SY5Y cells which is consistent with a reduced incorporation of bromodesoxyuridine into the DNA of primary mesencephalic cells. Whether the additional dopaminergic neurones in primary culture derive from dopaminergic precursor cells, previously tyrosine hydroxylase negative dopaminergic neurones or are the result of a transdifferentiation process remains to be established.

CDP-choline reduces dopaminergic cell loss induced by MPP(+) and glutamate in primary mesencephalic cell culture

Cytidine-5'-diphosphocholine (citicoline or CDP-choline) is an essential endogenous intermediate in the biosynthesis of phosphatidylcholine. In the present study, primary dopaminergic cultures from mouse mesencephala were treated with citicoline to investigate its neuroprotective potential on the survival of dopaminergic neurons exposed to MPP(+) and glutamate. Treatment with citicoline alone significantly increased the survival of dopaminergic neurons compared to controls. MPP(+) or glutamate decreased the total number of dopaminergic neurons whereas citicoline afforded significant protection against either toxicity. Moreover, citicoline significantly decreased propidium iodide uptake by cultured cells. The study concludes that citicoline exerts stimulant and neuroprotective actions on cultured dopaminergic neurons.