The role of the dopamine transporter in dopamine-induced DNA damage

Insights into the circadian rhythm alterations of the novel PFOS substitutes F-53B and OBS on adult zebrafish

As alternatives to perfluorooctane sulfonate (PFOS), 6:2 Cl-PFESA (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are frequently detected in aquatic environments, but little is known about their neurotoxicity, especially in terms of circadian rhythms. In this study, adult zebrafish were chronically exposed to 1 μM PFOS, F-53B and OBS for 21 days taking circadian rhythm-dopamine (DA) regulatory network as an entry point to comparatively investigate their neurotoxicity and underlying mechanisms. The results showed that PFOS may affect the response to heat rather than circadian rhythms by reducing DA secretion due to disruption of calcium signaling pathway transduction caused by midbrain swelling. In contrast, F-53B and OBS altered the circadian rhythms of adult zebrafish, but their mechanisms of action were different. Specifically, F-53B might alter circadian rhythms by interfering with amino acid neurotransmitter metabolism and disrupting blood-brain barrier (BBB) formation, whereas OBS mainly inhibited canonical Wnt signaling transduction by reducing cilia formation in ependymal cells and induced midbrain ventriculomegaly, finally triggering imbalance in DA secretion and circadian rhythm changes. Our study highlights the need to focus on the environmental exposure risks of PFOS alternatives and the sequential and interactive mechanisms of their multiple toxicities.

Association between the LRP1B and APOE loci in the development of Parkinson's disease dementia

Parkinson's disease is one of the most common age-related neurodegenerative disorders. Although predominantly a motor disorder, cognitive impairment and dementia are important features of Parkinson's disease, particularly in the later stages of the disease. However, the rate of cognitive decline varies among Parkinson's disease patients, and the genetic basis for this heterogeneity is incompletely understood. To explore the genetic factors associated with rate of progression to Parkinson's disease dementia, we performed a genome-wide survival meta-analysis of 3,923 clinically diagnosed Parkinson's disease cases of European ancestry from four longitudinal cohorts. In total, 6.7% of individuals with Parkinson's disease developed dementia during study follow-up, on average 4.4 ± 2.4 years from disease diagnosis. We have identified the APOE ε4 allele as a major risk factor for the conversion to Parkinson's disease dementia [hazards ratio = 2.41 (1.94-3.00), P = 2.32 × 10-15], as well as a new locus within the ApoE and APP receptor LRP1B gene [hazards ratio = 3.23 (2.17-4.81), P = 7.07 × 10-09]. In a candidate gene analysis, GBA variants were also identified to be associated with higher risk of progression to dementia [hazards ratio = 2.02 (1.21-3.32), P = 0.007]. CSF biomarker analysis also implicated the amyloid pathway in Parkinson's disease dementia, with significantly reduced levels of amyloid β42 (P = 0.0012) in Parkinson's disease dementia compared to Parkinson's disease without dementia. These results identify a new candidate gene associated with faster conversion to dementia in Parkinson's disease and suggest that amyloid-targeting therapy may have a role in preventing Parkinson's disease dementia.

Bacopa Protects against Neurotoxicity Induced by MPP+ and Methamphetamine

The neurotoxins methamphetamine (METH) and 1-methyl-4-phenylpyridinium (MPP⁺) damage catecholamine neurons. Although sharing the same mechanism to enter within these neurons, METH neurotoxicity mostly depends on oxidative species, while MPP⁺ toxicity depends on the inhibition of mitochondrial activity. This explains why only a few compounds protect against both neurotoxins. Identifying a final common pathway that is shared by these neurotoxins is key to prompting novel remedies for spontaneous neurodegeneration. In the present study we assessed whether natural extracts from Bacopa monnieri (BM) may provide a dual protection against METH- and MPP⁺-induced cell damage as measured by light and electron microscopy. The protection induced by BM against catecholamine cell death and degeneration was dose-dependently related to the suppression of reactive oxygen species (ROS) formation and mitochondrial alterations. These were measured by light and electron microscopy with MitoTracker Red and Green as well as by the ultrastructural morphometry of specific mitochondrial structures. In fact, BM suppresses the damage of mitochondrial crests and matrix dilution and increases the amount of healthy and total mitochondria. The present data provide evidence for a natural compound, which protects catecholamine cells independently by the type of experimental toxicity. This may be useful to counteract spontaneous degenerations of catecholamine cells.

Redox Signaling in Neurotransmission and Cognition During Aging

SIGNIFICANCE

Oxidative stress increases in the brain with aging and neurodegenerative diseases. Previous work emphasized irreversible oxidative damage in relation to cognitive impairment. This research has evolved to consider a continuum of alterations, from redox signaling to oxidative damage, which provides a basis for understanding the onset and progression of cognitive impairment. This review provides an update on research linking redox signaling to altered function of neural circuits involved in information processing and memory. Recent Advances: Starting in middle age, redox signaling triggers changes in nervous system physiology described as senescent physiology. Hippocampal senescent physiology involves decreased cell excitability, altered synaptic plasticity, and decreased synaptic transmission. Recent studies indicate N-methyl-d-aspartate and ryanodine receptors and Ca²⁺ signaling molecules as molecular substrates of redox-mediated senescent physiology.

CRITICAL ISSUES

We review redox homeostasis mechanisms and consider the chemical character of reactive oxygen and nitrogen species and their role in regulating different transmitter systems. In this regard, senescent physiology may represent the co-opting of pathways normally responsible for feedback regulation of synaptic transmission. Furthermore, differences across transmitter systems may underlie differential vulnerability of brain regions and neuronal circuits to aging and disease.

FUTURE DIRECTIONS

It will be important to identify the intrinsic mechanisms for the shift in oxidative/reductive processes. Intrinsic mechanism will depend on the transmitter system, oxidative stressors, and expression/activity of antioxidant enzymes. In addition, it will be important to identify how intrinsic processes interact with other aging factors, including changes in inflammatory or hormonal signals. Antioxid. Redox Signal. 28, 1724-1745.

Rats overexpressing the dopamine transporter display behavioral and neurobiological abnormalities with relevance to repetitive disorders

The dopamine transporter (DAT) plays a pivotal role in maintaining optimal dopamine signaling. DAT-overactivity has been linked to various neuropsychiatric disorders yet so far the direct pathological consequences of it has not been fully assessed. We here generated a transgenic rat model that via pronuclear microinjection overexpresses the DAT gene. Our results demonstrate that DAT-overexpression induces multiple neurobiological effects that exceeded the expected alterations in the corticostriatal dopamine system. Furthermore, transgenic rats specifically exhibited behavioral and pharmaco-therapeutic profiles phenotypic of repetitive disorders. Together our findings suggest that the DAT rat model will constitute a valuable tool for further investigations into the pathological influence of DAT overexpression on neural systems relevant to neuropsychiatric disorders.

Water Extract of Fructus Hordei Germinatus Shows Antihyperprolactinemia Activity via Dopamine D2 Receptor

Objective. Fructus Hordei Germinatus is widely used in treating hyperprolactinemia (hyperPRL) as a kind of Chinese traditional herb in China. In this study, we investigated the anti-hyperPRL activity of water extract of Fructus Hordei Germinatus (WEFHG) and mechanism of action. Methods. Effect of WEFHG on serum prolactin (PRL), estradiol (E2), progesterone (P), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and hypothalamus protein kinase A (PKA) and cyclic adenosine monophosphate (cAMP) levels of hyperPRL rats were investigated. And effect of WEFHG on PRL secretion, D2 receptors, and dopamine transporters (DAT) was studied in MMQ, GH3, and PC12 cells, respectively. Results. WEFHG reduced the secretion of PRL in hyperPRL rats effectively. In MMQ cell, treatment with WEFHG at 1–5 mg/mL significantly suppressed PRL secretion and synthesis. Consistent with a D2-action, WEFHG did not affect PRL in rat pituitary lactotropic tumor-derived GH3 cells that lack the D2 receptor expression but significantly increased the expression of D2 receptors and DAT in PC12 cells. In addition, WEFHG reduced the cAMP and PKA levels of hypothalamus in hyperPRL rats significantly. Conclusions. WEFHG showed anti-hyperPRL activity via dopamine D2 receptor, which was related to the second messenger cAMP and PKA.

SLC6A3 is a risk factor for Parkinson's disease: a meta-analysis of sixteen years' studies

The human dopamine transporter gene (gene symbol: SLC6A3) is considered as a candidate risk factor for Parkinson's disease because dopamine transporter accumulates cytotoxic dopamine or other toxins in the dopamine neurons. However, findings from numerous association studies in different populations have been inconsistent with each other. In this study, we performed a combined analysis of published case-control genetic association data between SLC6A3 and Parkinson's disease. The results indicate that SLC6A3 confers a modest but significant risk for Parkinson's disease in various populations. Allele 10-repeat of the 40-base pair variable number tandem repeat, a well studied polymorphism in the 3' untranslated region of SLC6A3, confers neuroprotection in East Asian (OR: 0.78, 95% CI: 0.65, 0.94 and p=0.009) but not in Caucasian populations. Genotype GG and allele G of the promoter single nucleotide polymorphism rs2652510 is associated with a risk in Caucasians (allelic G, OR: 1.26, 95% CI: 1.04-1.54, and p=0.018; genotypic GG OR: 1.37, 95% CI: 1.03-1.84 and p=0.032). Such information implies a population-dependent involvement of SLC6A3 in the etiology of Parkinson's disease.

The relationship between oxidative stress and post-translational modification of the dopamine transporter in bipolar disorder

Bipolar disorder (BD) has been consistently associated with altered levels of oxidative stress markers, although the cause and consequences of these alterations remain to be elucidated. One of the main hypotheses regarding the pathogenesis of mania involves increased dopaminergic transmission. In this review, the authors aim to discuss a potential mechanism by which increased oxidative stress inhibits the uptake of dopamine through the post-translational modification of the dopamine transporter and its implications for BD. Within the next 5 years, the authors believe that the mechanisms of dopamine transporter oxidation and its impact on the pathophysiology of BD will be elucidated, which may open avenues for the development of more specific interventions for the treatment of this debilitating illness.

Not only dopamine D2 receptors involved in Peony-Glycyrrhiza Decoction, an herbal preparation against antipsychotic-associated hyperprolactinemia

Clinical studies have demonstrated the effectiveness of an herbal preparation called Peony-Glycyrrhiza Decoction (PGD) in alleviating antipsychotic-induced hyperprolactinemia (hyperPRL). In the present study, we further examined the pharmacological action of PGD on prolactin (PRL) secretion using in vitro and in vivo models, with specific attention to the role of dopaminergic mediators and other sex hormones. Treatment with PGD at 1-5mg/ml significantly suppressed PRL secretion and synthesis in MMQ cells, a model of hyperPRL derived from pituitary adenoma cells. The suppressive effects were completely abolished by pretreatment with 10μM haloperidol, a dopamine D(2) receptor antagonist. Consistent with a D(2)-action, PGD did not affect PRL in rat pituitary lactotropic tumor-derived GH3 cells that lack the D(2) receptor expression but significantly increased the expression of D(2) receptors and dopamine transporters (DAT) in PC12 cells. In a rat model of hyperPRL, produced by repeated injection of the dopamine blocker metoclopramide (MCP), chronic PGD (2.5-10g/kg daily) significantly reduced elevated serum PRL. The reduction in magnitude was similar to that elicited by bromocriptine (BMT), a dopamine D(2) receptor agonist currently used for treatment of hyperPRL. Neither PGD nor BMT altered serum estradiol, but PGD reversed decreased serum progesterone to control level, whereas BMT did not. These results indicate that the anti-hyperPRL effects of PGD are associated not only with D(2) receptor and DAT modulation, but also with a normalization of other sex hormone dysfunction. This experimental evidence supports clinical use of PGD as an effective treatment of antipsychotic-induced hyperPRL.

Angiotensin II induces DNA damage via AT1 receptor and NADPH oxidase isoform Nox4

Epidemiological studies revealed increased renal cancer incidences and higher cancer mortalities in hypertensive individuals. Activation of the renin-angiotensin-aldosterone system leads to the formation of reactive oxygen species (ROS). In vitro, in renal cells, and ex vivo, in the isolated perfused mouse kidney, we could show DNA-damaging potential of angiotensin II (Ang II). Here, the pathway involved in the genotoxicity of Ang II was investigated. In kidney cell lines with properties of proximal tubulus cells, an activation of NADPH oxidase and the production of ROS, resulting in the formation of DNA strand breaks and micronuclei induction, was observed. This DNA damage was mediated by the Ang II type 1 receptor (AT1R), together with the G protein G ( α-q/11 ) . Subsequently, phospholipase C (PLC) was activated and intracellular calcium increased. Both calcium stores of the endoplasmic reticulum and extracellular calcium were involved in the genotoxicity of Ang II. Downstream, a role for protein kinase C (PKC) could be detected, because its inhibition hindered Ang II from damaging the cells. Although PKC was activated, no involvement of its known target, the NADPH oxidase isoform containing the Nox2 subunit, could be found, as tested by small-interfering RNA down-regulation. Responsible for the DNA-damaging activity of Ang II was the NADPH oxidase isoform containing the Nox4 subunit. In summary, in kidney cells the DNA-damaging activity of Ang II depends on an AT1R-mediated activation of NADPH oxidase via PLC, PKC and calcium signalling, with the NADPH subunit Nox4 playing a crucial role.