Effects of angiotensin II on dopamine and serotonin turnover in the striatum of conscious rats

Angiotensin II involvement in the development and persistence of amphetamine-induced sensitization: Striatal dopamine reuptake implications

Amphetamine (AMPH) exposure induces behavioural and neurochemical sensitization observed in rodents as hyperlocomotion and increased dopamine release in response to a subsequent dose. Brain Angiotensin II modulates dopaminergic neurotransmission through its AT1 receptors (AT1-R), positively regulating striatal dopamine synthesis and release. This work aims to evaluate the AT1-R role in the development and maintenance of AMPH-induced sensitization. Also, the AT1-R involvement in striatal dopamine reuptake was analysed. The sensitization protocol consisted of daily AMPH administration for 5 days and tested 21 days after withdrawal. An AT1-R antagonist, candesartan, was administered before or after AMPH exposure to evaluate the participation of AT1-R in the development and maintenance of sensitization, respectively. Sensitization was evaluated by locomotor activity and c-Fos immunostaining. Changes in dopamine reuptake kinetics were evaluated 1 day after AT1-R blockade withdrawal treatment, with or without the addition of AMPH in vitro. The social interaction test was performed as another behavioural output. Repeated AMPH exposure induced behavioural and neurochemical sensitization, which was prevented and reversed by candesartan. The AT1-R blockade increased the dopamine reuptake kinetics. Neither the AMPH administration nor the AT1-R blockade altered the performance of social interaction. Our results highlight the AT1-R's crucial role in AMPH sensitization. The enhancement of dopamine reuptake kinetics induced by the AT1-R blockade might attenuate the neuroadaptive changes that lead to AMPH sensitization and its self-perpetuation. Therefore, AT1-R is a prominent candidate as a target for pharmacological treatment of pathologies related to dopamine imbalance, including drug addiction and schizophrenia.

The role of the brain renin-angiotensin system in Parkinson´s disease

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

GPR35 and mediators from platelets and mast cells in neutrophil migration and inflammation

Neutrophil recruitment from circulation to sites of inflammation is guided by multiple chemoattractant cues emanating from tissue cells, immune cells, and platelets. Here, we focus on the function of one G-protein coupled receptor, GPR35, in neutrophil recruitment. GPR35 has been challenging to study due the description of multiple ligands and G-protein couplings. Recently, we found that GPR35-expressing hematopoietic cells respond to the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA). We discuss distinct response profiles of GPR35 to 5-HIAA compared to other ligands. To place the functions of 5-HIAA in context, we summarize the actions of serotonin in vascular biology and leukocyte recruitment. Important sources of serotonin and 5-HIAA are platelets and mast cells. We discuss the dynamics of cell migration into inflamed tissues and how multiple platelet and mast cell-derived mediators, including 5-HIAA, cooperate to promote neutrophil recruitment. Additional actions of GPR35 in tissue physiology are reviewed. Finally, we discuss how clinically approved drugs that modulate serotonin uptake and metabolism may influence 5-HIAA-GPR35 function, and we speculate about broader influences of the GPR35 ligand-receptor system in immunity and disease.

The Angiotensin Antagonist Losartan Modulates Social Reward Motivation and Punishment Sensitivity via Modulating Midbrain-Striato-Frontal Circuits

Social deficits and dysregulations in dopaminergic midbrain-striato-frontal circuits represent transdiagnostic symptoms across psychiatric disorders. Animal models suggest that interactions between the dopamine (DA) and renin-angiotensin system (RAS) may modulate learning and reward-related processes. The present study therefore examined the behavioral and neural effects of the Angiotensin II type 1 receptor (AT1R) antagonist losartan on social reward and punishment processing in humans. A preregistered randomized double-blind placebo-controlled between-subject pharmacological design was combined with a social incentive delay (SID) functional MRI (fMRI) paradigm during which subjects could avoid social punishment or gain social reward. Healthy volunteers received a single-dose of losartan (50 mg, n = 43, female = 17) or placebo (n = 44, female = 20). We evaluated reaction times (RTs) and emotional ratings as behavioral and activation and functional connectivity as neural outcomes. Relative to placebo, losartan modulated the reaction time and arousal differences between social punishment and social reward. On the neural level the losartan-enhanced motivational salience of social rewards was accompanied by stronger ventral striatum-prefrontal connectivity during reward anticipation. Losartan increased the reward-neutral difference in the ventral tegmental area (VTA) and attenuated VTA associated connectivity with the bilateral insula in response to punishment during the outcome phase. Thus, losartan modulated approach-avoidance motivation and emotional salience during social punishment versus social reward via modulating distinct core nodes of the midbrain-striato-frontal circuits. The findings document a modulatory role of the renin-angiotensin system in these circuits and associated social processes, suggesting a promising treatment target to alleviate social dysregulations.SIGNIFICANCE STATEMENT Social deficits and anhedonia characterize several mental disorders and have been linked to the midbrain-striato-frontal circuits of the brain. Based on initial findings from animal models we here combine the pharmacological blockade of the Angiotensin II type 1 receptor (AT1R) via losartan with functional MRI (fMRI) to demonstrate that AT1R blockade enhances the motivational salience of social rewards and attenuates the negative impact of social punishment via modulating the communication in the midbrain-striato-frontal circuits in humans. The findings demonstrate for the first time an important role of the AT1R in social reward processing in humans and render the AT1R as promising novel treatment target for social and motivational deficits in mental disorders.

Targeting G Protein-Coupled Receptors in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized in part by the deterioration of dopaminergic neurons which leads to motor impairment. Although there is no cure for PD, the motor symptoms can be treated using dopamine replacement therapies including the dopamine precursor L-DOPA, which has been in use since the 1960s. However, neurodegeneration in PD is not limited to dopaminergic neurons, and many patients experience non-motor symptoms including cognitive impairment or neuropsychiatric disturbances, for which there are limited treatment options. Moreover, there are currently no treatments able to alter the progression of neurodegeneration. There are many therapeutic strategies being investigated for PD, including alternatives to L-DOPA for the treatment of motor impairment, symptomatic treatments for non-motor symptoms, and neuroprotective or disease-modifying agents. G protein-coupled receptors (GPCRs), which include the dopamine receptors, are highly druggable cell surface proteins which can regulate numerous intracellular signaling pathways and thereby modulate the function of neuronal circuits affected by PD. This review will describe the treatment strategies being investigated for PD that target GPCRs and their downstream signaling mechanisms. First, we discuss new developments in dopaminergic agents for alleviating PD motor impairment, the role of dopamine receptors in L-DOPA induced dyskinesia, as well as agents targeting non-dopamine GPCRs which could augment or replace traditional dopaminergic treatments. We then discuss GPCRs as prospective treatments for neuropsychiatric and cognitive symptoms in PD. Finally, we discuss the evidence pertaining to ghrelin receptors, β-adrenergic receptors, angiotensin receptors and glucagon-like peptide 1 receptors, which have been proposed as disease modifying targets with potential neuroprotective effects in PD.

Telotristat ethyl reverses myxomatous changes in mice mitral valves

Rationale

Myxomatous mitral valve degeneration is a common pathological manifestation of mitral valve regurgitation, with or without valvular prolapse. In addition to similarities between naturally occurring and serotonergic valve degeneration, an increasing body of evidence has recently suggested that serotonin signaling is a regulator of degenerative valvulopathies. Studies have found that serotonin can be synthesized locally by valvular cells and serotonin receptors in turn may be activated to promote signaling. Recently, telotristat ethyl (TE) has been introduced as a treatment for carcinoid disease, by selectively inhibiting tryptophan hydroxylase 1, the rate-limiting enzyme in peripheral serotonin synthesis. TE provides a unique tool to test inhibition of serotonin synthesis in vivo, without impacting brain serotonin, to further confirm the role of local serotonin synthesis on heart valves.

Objective

To confirm the link between serotonin and myxomatous valvular disease in vivo.

Methods and results

A hypertension-induced myxomatous mitral valve disease mouse model was employed to test the effect of TE on valvular degeneration. Circulating serotonin and local serotonin in valve tissues were tested by enzyme immunoassay and immunohistochemistry, respectively. TE was administrated in two modes: (1) parallel with angiotensin II (A2); (2) post A2 treatment. Myxomatous changes were successfully recapitulated in hypertensive mice, as determined by ECM remodeling, myofibroblast transformation, and serotonin signaling activation. These changes were at least partially reversed upon TE administration.

Conclusion

This study provides the first evidence of TE as a potential therapeutic for myxomatous mitral disease, either used to prevent or reverse myxomatous degeneration.

Antihypertensive drugs and brain function: mechanisms underlying therapeutically beneficial and harmful neuropsychiatric effects

A bidirectional relationship exists between hypertension and psychiatric disorders, including unipolar and bipolar depression, anxiety, post-traumatic stress disorder (PTSD), psychosis, schizophrenia, mania, and dementia/cognitive decline. Repurposing of antihypertensive drugs to treat mental disorders is thus being explored. A systematic knowledge of the mechanisms of action and clinical consequences of the use of antihypertensive agents on neuropsychiatric functions has not been achieved yet. In this article, we review the putative role of antihypertensive agents in psychiatric disorders, discuss the targets and mechanisms of action, and examine how and to what extent specific drug classes/molecules may trigger, worsen, or mitigate psychiatric symptoms. In addition, we review pharmacokinetics (brain penetration of drugs) and pharmacogenetics data that add important information to assess risks and benefits of antihypertensive drugs in neuropsychiatric settings. The scientific literature shows robust evidence of a positive effect of α1 blockers on PTSD symptoms, nightmares and sleep quality, α2 agonists on core symptoms, executive function and quality of life in Attention-Deficit/Hyperactivity Disorder, PTSD, Tourette's syndrome, and β blockers on anxiety, aggression, working memory, and social communication. Renin-angiotensin system modulators exert protective effects on cognition, depression, and anxiety, and the loop diuretic bumetanide reduced the core symptoms of autism in a subset of patients. There is no evidence of clear benefits of calcium channel blockers in mood disorders in the scientific literature. These findings are mainly from preclinical studies; clinical data are still insufficient or of anecdotal nature, and seldom systematic. The information herewith provided can support a better therapeutic approach to hypertension, tailored to patients with, or with high susceptibility to, psychiatric illness. It may prompt clinical studies exploring the potential benefit of antihypertensive drugs in selected patients with neuropsychiatric comorbidities that include outcomes of neuropsychiatric interest and specifically assess undesirable effects or interactions.

Losartan enhances cognitive and structural neuroplasticity impairments in spontaneously hypertensive rats

Hypertension is a risk factor for vascular dementia, which is the second most prevalent type of dementia, just behind Alzheimer's disease. This highlights the brain vulnerability due to hypertension, which may increase with aging. Thus, studying how hypertension affects neural cells and behavior, as well as the effects of antihypertensives on these alterations, it's important to understand the hypertension consequences in the brain. The spontaneously hypertensive rat (SHR) has been useful for the study of hypertension alterations in diverse organs, including the brain. Thus, we studied the losartan effects on cognitive and structural neuroplasticity impairments in SHR of 10 months of age. In the first instance, we evaluated the losartan effects on exploratory behavior and novel object recognition test (NORT) in the SHR. Then, we assessed the density and morphology of dendritic spines of pyramidal neurons from the prefrontal cortex (PFC) layers 3 and 5, and CA1 of the dorsal Hp (dHp). Our results indicate that in SHR, losartan treatment (2 months, 15 mg/Kg/day) reduces high blood pressure to age-matched vehicle-treated Wistar-Kyoto (WKY) rat levels. Moreover, losartan improved long-term memory in SHR compared with age-matched vehicle-treated WKY rats, without affecting the locomotor and anxiety behaviors. The behavioral improvement of the SHR can be associated with the increase in the number of dendritic spines and the mushroom spine population in the PFC and the dHp. In conclusion, losartan enhances cognitive impairments by controlling the high blood pressure and improving neuroplasticity in animals with chronic hypertension.

Recent Advances in the Endogenous Brain Renin-Angiotensin System and Drugs Acting on It

The RAS (renin-angiotensin system) is the part of the endocrine system that plays a prime role in the control of essential hypertension. Since the discovery of brain RAS in the seventies, continuous efforts have been put by the scientific committee to explore it more. The brain has shown the presence of various components of brain RAS such as angiotensinogen (AGT), converting enzymes, angiotensin (Ang), and specific receptors (ATR). AGT acts as the precursor molecule for Ang peptides—I, II, III, and IV—while the enzymes such as prorenin, ACE, and aminopeptidases A and N synthesize it. AT1, AT2, AT4, and mitochondrial assembly receptor (MasR) are found to be plentiful in the brain. The brain RAS system exhibits pleiotropic properties such as neuroprotection and cognition along with regulation of blood pressure, CVS homeostasis, thirst and salt appetite, stress, depression, alcohol addiction, and pain modulation. The molecules acting through RAS predominantly ARBs and ACEI are found to be effective in various ongoing and completed clinical trials related to cognition, memory, Alzheimer's disease (AD), and pain. The review summarizes the recent advances in the brain RAS system highlighting its significance in pathophysiology and treatment of the central nervous system-related disorders.

The effect of telmisartan, an angiotensin receptor blocker, on alcohol consumption and alcohol-induced dopamine release in the nucleus accumbens

Alcohol use disorder remains a major health problem. The mesocorticolimbic dopaminergic system, including the nucleus accumbens region and multiple neural circuits, is involved in its complex underlying mechanism. For instance, alcohol intake stimulates the central and peripheral renin-angiotensin system and increases angiotensin II levels, which predominantly affect angiotensin 1 receptors both in the periphery and in the brain. In this study, we aimed to investigate the effects of the intracerebroventricularly-administered angiotensin 1 receptor blocker telmisartan on the alcohol consumption of male Sardinian alcohol-preferring (sP) rats and on the alcohol-induced dopamine levels in the nucleus accumbens region in Wistar rats. Acute intracerebroventricular administration of telmisartan (100 nM) reduced the alcohol intake for 24 hours without affecting food and water consumption in sP rats. Acute intracerebroventricular injection of the opioid receptor antagonist naloxone (75 nM), tested as a reference compound, also reduced the alcohol consumption in sP rats; however, naloxone's effect lasted only for 30 minutes. In microdialysis experiments, telmisartan administered intracerebroventricularly did not change dopamine levels in the nucleus accumbens that had been induced by acute intraperitoneal alcohol administration in Wistar rats. According to these results, further studies are needed to elucidate the role of the renin-angiotensin system on alcohol use disorder pathophysiology.

Fluid intake, what's dopamine got to do with it?

Maintaining fluid balance is critical for life. The central components that control fluid intake are only partly understood. This contribution to the collection of papers highlighting work by members of the Society for the Study of Ingestive Behavior focuses on the role that dopamine has on fluid intake and describes the roles that various bioregulators can have on thirst and sodium appetite by influencing dopamine systems in the brain. The goal of the review is to highlight areas in need of more research and to propose a framework to guide that research. We hope that this framework will inspire researchers in the field to investigate these interesting questions in order to form a more complete understanding of how fluid intake is controlled.

The Renin-Angiotensin System Modulates Dopaminergic Neurotransmission: A New Player on the Scene

Parkinson’s disease (PD) is an extrapyramidal disorder characterized by neuronal degeneration in several regions of the peripheral and central nervous systems. It is the second most frequent neurodegenerative disease after Alzheimer’s. It has become a major health problem, affecting 1% of the world population over 60 years old and 3% of people beyond 80 years. The main histological findings are intracellular Lewy bodies composed of misfolded α-synuclein protein aggregates and loss of dopaminergic neurons in the central nervous system. Neuroinflammation, apoptosis, mitochondrial dysfunction, altered calcium homeostasis, abnormal protein degradation, and synaptic pathobiology have been put forward as mechanisms leading to cell death, α-synuclein deposition, or both. A progressive loss of dopaminergic neurons in the substantia nigra late in the neurodegeneration leads to developing motor symptoms like bradykinesia, tremor, and rigidity. The renin–angiotensin system (RAS), which is involved in regulating blood pressure and body fluid balance, also plays other important functions in the brain. The RAS is involved in the autocrine and paracrine regulation of the nigrostriatal dopaminergic synapses. Dopamine depletion, as in PD, increases angiotensin II expression, which stimulates or inhibits dopamine synthesis and is released via AT1 or AT2 receptors. Furthermore, angiotensin II AT1 receptors inhibit D1 receptor activation allosterically. Therefore, the RAS may have an important modulating role in the flow of information from the brain cortex to the basal ganglia. High angiotensin II levels might even aggravate neurodegeneration, activating the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex, which leads to increased reactive oxygen species production.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

Brain Renin-Angiotensin System at the Intersect of Physical and Cognitive Frailty

The renin–angiotensin system (RAS) was initially considered to be part of the endocrine system regulating water and electrolyte balance, systemic vascular resistance, blood pressure, and cardiovascular homeostasis. It was later discovered that intracrine and local forms of RAS exist in the brain apart from the endocrine RAS. This brain-specific RAS plays essential roles in brain homeostasis by acting mainly through four angiotensin receptor subtypes; AT₁R, AT₂R, MasR, and AT₄R. These receptors have opposing effects; AT₁R promotes vasoconstriction, proliferation, inflammation, and oxidative stress while AT₂R and MasR counteract the effects of AT₁R. AT₄R is critical for dopamine and acetylcholine release and mediates learning and memory consolidation. Consequently, aging-associated dysregulation of the angiotensin receptor subtypes may lead to adverse clinical outcomes such as Alzheimer’s disease and frailty via excessive oxidative stress, neuroinflammation, endothelial dysfunction, microglial polarization, and alterations in neurotransmitter secretion. In this article, we review the brain RAS from this standpoint. After discussing the functions of individual brain RAS components and their intracellular and intracranial locations, we focus on the relationships among brain RAS, aging, frailty, and specific neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and vascular cognitive impairment, through oxidative stress, neuroinflammation, and vascular dysfunction. Finally, we discuss the effects of RAS-modulating drugs on the brain RAS and their use in novel treatment approaches.

Dopamine D2 autoreceptor interactome: Targeting the receptor complex as a strategy for treatment of substance use disorder

Dopamine D2 autoreceptors (D2ARs), located in somatodendritic and axon terminal compartments of dopamine (DA) neurons, function to provide a negative feedback regulatory control on DA neuron firing, DA synthesis, reuptake and release. Dysregulation of D2AR-mediated DA signaling is implicated in vulnerability to substance use disorder (SUD). Due to the extreme low abundance of D2ARs compared to postsynaptic D2 receptors (D2PRs) and the lack of experimental tools to differentiate the signaling of D2ARs from D2PRs, the regulation of D2ARs by drugs of abuse is poorly understood. The recent availability of conditional D2AR knockout mice and newly developed virus-mediated gene delivery approaches have provided means to specifically study the function of D2ARs at the molecular, cellular and behavioral levels. There is a growing revelation of novel mechanisms and new proteins that mediate D2AR activity, suggesting that D2ARs act cooperatively with an array of membrane and intracellular proteins to tightly control DA transmission. This review highlights D2AR-interacting partners including transporters, G-protein-coupled receptors, ion channels, intracellular signaling modulators, and protein kinases. The complexity of the D2AR interaction network illustrates the functional divergence of D2ARs. Pharmacological targeting of multiple D2AR-interacting partners may be more effective to restore disrupted DA homeostasis by drugs of abuse.

Angiotensin type 2 receptors: Role in aging and neuroinflammation in the substantia nigra

Overactivity of the angiotensin-type-1 receptor (AT1)/NADPH-oxidase axis enhances aging processes, neuroinflammation and neurodegeneration. The role of AT2 receptors in the above-mentioned AT1-related effects in the aged brain, particularly substantia nigra, was investigated in this study. In the nigra, we observed a progressive decrease in AT2 mRNA expression with aging, and AT2 deletion led to changes in spontaneous motor behavior, dopamine receptors, renin-angiotensin system, and pro-oxidative and pro-inflammatory markers similar to those observed in aged wild type (WT) mice. Both aged WT mice and young AT2 KO mice showed an increased AT1, decreased MAS receptor and increased angiotensinogen mRNA and/or protein expression, as well as upregulation of pro-oxidative and pro-inflammatory markers. In cultures of microglial cells, activation of AT2 receptors inhibited the LPS-induced increase in AT1 mRNA and protein expression and neuroinflammatory markers. Both in AT2 KO microglial cultures and microglia obtained from adult AT2 KO mice, an increase in AT1 mRNA expression was observed. In cultured dopaminergic neurons, AT2 activation down-regulated AT1 mRNA and protein, and dopaminergic neurons from adult AT2 KO mice showed upregulation of AT1 mRNA expression. Both in microglia and dopaminergic neurons the pathway AT2/nitric oxide/cyclic guanosine monophosphate mediates the regulation of the AT1 mRNA and protein expression through downregulation of the Sp1 transcription factor. MAS receptors are also involved in the regulation of AT1 mRNA and protein expression by AT2. The results suggest that an aging-related decrease in AT2 expression plays a major role in the aging-related AT1 overexpression and AT1-related pro-inflammatory pro-oxidative effects.

Gut microbiota and neuroinflammation in pathogenesis of hypertension: A potential role for hydrogen sulfide

Inflammation and gut dysbiosis are hallmarks of hypertension (HTN). Hydrogen sulfide (H2S) is an important freely diffusing molecule that modulates the function of neural, cardiovascular and immune systems, and circulating levels of H2S are reduced in animals and humans with HTN. While most research to date has focused on H₂S produced endogenously by the host, H2S is also produced by the gut bacteria and may affect the host homeostasis. Here, we review an association between neuroinflammation and gut dysbiosis in HTN, with special emphasis on a potential role of H2S in this interplay.

The Potential Therapeutic Capacity of Inhibiting the Brain Renin-Angiotensin System in the Treatment of Co-Morbid Conditions in Epilepsy

Epilepsy is one of the most prevalent neurological diseases and although numerous novel anticonvulsants have been approved, the proportion of patients who are refractory to medical treatment of seizures and have progressive co-morbidities such as cognitive impairment and depression remains at about 20-30%. In the last decade, extensive research has identified a therapeutic capacity of the components of the brain renin-angiotensin system (RAS) in seizure- and epilepsy-related phenomena. Alleviating the activity of RAS in the central nervous system is considered to be a potential adjuvant strategy for the treatment of numerous detrimental consequences of epileptogenesis. One of the main advantages of RAS is associated with its modulatory influence on different neurotransmitter systems, thereby exerting a fine-tuning control mechanism for brain excitability. The most recent scientific findings regarding the involvement of the components of brain RAS show that angiotensin II (Ang II), angiotensin-converting enzyme (ACE), Ang II type 1 (AT₁) and type 2 (AT₂) receptors are involved in the control of epilepsy and its accompanying complications, and therefore they are currently of therapeutic interest in the treatment of this disease. However, data on the role of different components of brain RAS on co-morbid conditions in epilepsy, including hypertension, are insufficient. Experimental and clinical findings related to the involvement of Ang II, ACE, AT₁, and AT₂ receptors in the control of epilepsy and accompanying complications may point to new therapeutic opportunities and adjuvants for the treatment of common co-morbid conditions of epilepsy.

Angiotensin Type 1 Receptor Antagonists Protect Against Alpha-Synuclein-Induced Neuroinflammation and Dopaminergic Neuron Death

The loss of dopaminergic neurons and α-synuclein accumulation are major hallmarks of Parkinson's disease (PD), and it has been suggested that a major mechanism of α-synuclein toxicity is microglial activation. The lack of animal models that properly reproduce PD, and particularly the underlying synucleinopathy, has hampered the clarification of PD mechanisms and the development of effective therapies. Here, we used neurospecific adeno-associated viral vectors serotype 9 coding for either the wild-type or mutated forms of human alpha-synuclein (WT and SynA53T, respectively) under the control of a synapsin promoter to further induce a marked dopaminergic neuron loss together with an important microglial neuroinflammatory response. Overexpression of neuronal alpha-synuclein led to increased expression of angiotensin type 1 receptors and NADPH oxidase activity, together with a marked increase in the number of OX-6-positive microglial cells and expression of markers of phagocytic activity (CD68) and classical pro-inflammatory/M1 microglial phenotype markers such as inducible nitric oxide synthase, tumor necrosis factor alpha, interleukin-1β, and IL-6. Moreover, a significant decrease in the expression of markers of immunoregulatory/M2 microglial phenotype such as the enzyme arginase-1 was constantly observed. Interestingly, alpha-synuclein-induced changes in microglial phenotype markers and dopaminergic neuron death were inhibited by simultaneous treatment with the angiotensin type 1 blockers candesartan or telmisartan. Our results suggest the repurposing of candesartan and telmisartan as a neuroprotective strategy for PD.

Molecular Basis of the Brain Renin Angiotensin System in Cardiovascular and Neurologic Disorders: Uncovering a Key Role for the Astroglial Angiotensin Type 1 Receptor AT1R

The central renin angiotensin system (RAS) is one of the most widely investigated cardiovascular systems in the brain. It is implicated in a myriad of cardiovascular diseases. However, studies from the last decade have identified its involvement in several neurologic abnormalities. Understanding the molecular functionality of the various RAS components can thus provide considerable insight into the phenotypic differences and mechanistic drivers of not just cardiovascular but also neurologic disorders. Since activation of one of its primary receptors, the angiotensin type 1 receptor (AT1R), results in an augmentation of oxidative stress and inflammatory cytokines, it becomes essential to investigate not just neuronal RAS but glial RAS as well. Glial cells are key homeostatic regulators in the brain and are critical players in the resolution of overt oxidative stress and neuroinflammation. Designing better and effective therapeutic strategies that target the brain RAS could well hinge on understanding the molecular basis of both neuronal and glial RAS. This review provides a comprehensive overview of the major studies that have investigated the mechanisms and regulation of the brain RAS, and it also provides insight into the potential role of glial AT1Rs in the pathophysiology of cardiovascular and neurologic disorders.

Brain Renin-Angiotensin System Blockade Attenuates Methamphetamine-Induced Hyperlocomotion and Neurotoxicity

Methamphetamine (METH) abuse has become a major public health concern worldwide without approved pharmacotherapies. The brain renin-angiotensin system (RAS) is involved in the regulation of neuronal function as well as neurological disorders. Angiotensin II (Ang II), which interacts with Ang II type 1 receptor (AT1-R) in the brain, plays an important role as a neuromodulator in dopaminergic transmission. However, the role of brain RAS in METH-induced behavior is largely unknown. Here, we revealed that repeated METH administration significantly upregulated the expression of AT1-R in the striatum of mice, but downregulated dopamine D3 receptor (D3R) expression. A specific AT1-R blocker telmisartan, which can penetrate the brain-blood barrier (BBB), or genetic deletion of AT1-R was sufficient to attenuate METH-triggered hyperlocomotion in mice. However, intraperitoneal injection of AT1-R blocker losartan, which cannot penetrate BBB, failed to attenuate METH-induced behavior. Moreover, intra-striatum re-expression of AT1 with lentiviral virus expressing AT1 reversed the weakened locomotor activity of AT1-/- mice treated with METH. Losartan alleviated METH-induced cytotoxicity in SH-SY5Y cells in vitro, which was accompanied by upregulated expressions of D3R and dopamine transporter. In addition, intraperitoneal injection of perindopril, which is a specific ACE inhibitor and can penetrate BBB, significantly attenuated METH-induced hyperlocomotor activity. Collectively, our results show that blockade of brain RAS attenuates METH-induced hyperlocomotion and neurotoxicity possibly through modulation of D3R expression. Our findings reveal a novel role of Ang II-AT1-R in METH-induced hyperlocomotion.

Bidirectional Neural Interaction Between Central Dopaminergic and Gut Lesions in Parkinson's Disease Models

The exact mechanism of gut dysfunction in Parkinson's disease and, conversely, the role of gut pathology in brain dopaminergic degeneration are controversial. We investigated the effects of nigral lesions on the colonic neurotransmission, the effect of gut inflammation on the nigrostriatal dopaminergic function, and the possible involvement of the vagus nerve and the local renin-angiotensin system (RAS). Nigrostriatal dopamine depletion was performed by bilateral injection 6-hydroxydopamine, and gut inflammation was induced by dextran sulfate sodium salt treatment in rats and mice, respectively, with or without vagal disruption. A decrease in central dopamine levels induced a decrease in colonic dopamine types 1 and 2 receptor expression together with an increase in the colonic levels of dopamine and a decrease in the levels of acetylcholine, which may explain a decrease in gut motility. Central dopaminergic depletion also induced an increase in the colonic levels of inflammatory and oxidative stress markers together with activation of the pro-inflammatory arm of the local RAS. Mice with acute (1 week) or subchronic (3 weeks) gut inflammation did not show a significant increase in colonic α-synuclein and phosphorylated α-synuclein expression during this relatively short survival period. Interestingly, we observed early changes in the nigrostriatal dopaminergic homeostasis, dopaminergic neuron death, and increased levels of nigral pro-inflammatory markers and RAS pro-inflammatory activity. The present results show that a dysregulation of the neural bidirectional gut-brain interaction may explain the early gut disturbances observed in parkinsonian patients, and also the increase in vulnerability of nigral dopaminergic neurons after gut inflammation.

Aging-related dysregulation in enteric dopamine and angiotensin system interactions: implications for gastrointestinal dysfunction in the elderly

Gastrointestinal dysfunction is a common problem in the elderly. Aging-related changes in interactions between local dopaminergic and renin-angiotensin systems (RAS) have been observed in the brain, renal and vascular tissues. However, it is not known if these interactions also occur in the gut, and are dysregulated with aging. We showed a mutual regulation between the colonic dopaminergic system and RAS using young and aged mice deficient for major angiotensin and dopamine receptors. Aged rats showed a marked decrease in colonic dopamine D2 receptor expression, together with an increase in angiotensin type 1 (AT1) receptor expression, a decrease in angiotensin type 2 (AT2) receptor expression (i.e. an increase in the RAS pro-inflammatory arm activity), and increased levels of inflammatory and oxidative markers. Aged rats also showed increased levels of colonic dopamine and noradrenalin, and a marked decrease in acetylcholine and serotonin levels. The present observations contribute to explain an aging-related pro-inflammatory state and dysregulation in gastrointestinal function, which may be counteracted by treatment of aged animals with the AT1 receptor blocker candesartan.

The intracellular angiotensin system buffers deleterious effects of the extracellular paracrine system

The 'classical' renin-angiotensin system (RAS) is a circulating system that controls blood pressure. Local/paracrine RAS, identified in a variety of tissues, including the brain, is involved in different functions and diseases, and RAS blockers are commonly used in clinical practice. A third type of RAS (intracellular/intracrine RAS) has been observed in some types of cells, including neurons. However, its role is still unknown. The present results indicate that in brain cells the intracellular RAS counteracts the intracellular superoxide/H₂O₂ and oxidative stress induced by the extracellular/paracrine angiotensin II acting on plasma membrane receptors. Activation of nuclear receptors by intracellular or internalized angiotensin triggers a number of mechanisms that protect the cell, such as an increase in the levels of protective angiotensin type 2 receptors, intracellular angiotensin, PGC-1α and IGF-1/SIRT1. Interestingly, this protective mechanism is altered in isolated nuclei from brains of aged animals. The present results indicate that at least in the brain, AT1 receptor blockers acting only on the extracellular or paracrine RAS may offer better protection of cells.

Renin-angiotensin system as a potential target for new therapeutic approaches in Parkinson's disease

INTRODUCTION

Currently, available therapies for Parkinson's disease (PD) are symptomatic. Therefore, the search for neuroprotective drugs remains a top priority. Areas covered: In this review, the potential symptomatic or disease-modifying effect of drugs targeting the Renin-Angiotensin System (RAS) in PD will be explored. Expert opinion: The importance of nigrostriatal local RAS has only begun to be unraveled in the last decades. On one hand, there is a complex feedback cycle between RAS and dopamine (DA). On the other hand, RAS affects dopaminergic neurons vulnerability. Neuroprotective effects in animal PD models have been shown for the angiotensin-converting enzyme (ACE) inhibitors captopril and perindopril, and the AT1 receptor antagonists losartan, candesartan and telmisartan. These effects appear to be mediated by a reduction in the overproduction of reactive oxygen species. In a proof-of-concept, randomized, double-blind, crossover study in PD patients, perindopril enhanced the effect of levodopa without inducing dyskinesias. There has not been any clinical trial exploring the neuroprotective effect of RAS drugs, but one cohort study in hypertensive patients suggested a protective effect of ACE inhibitors on PD risk. RAS is a promising target for symptomatic and neuroprotective therapies in PD. Further studies in PD animal models and patients are warranted.

Angiotensin II type 1/adenosine A 2A receptor oligomers: a novel target for tardive dyskinesia

Tardive dyskinesia (TD) is a serious motor side effect that may appear after long-term treatment with neuroleptics and mostly mediated by dopamine D₂ receptors (D₂Rs). Striatal D₂R functioning may be finely regulated by either adenosine A_2A receptor (A_2AR) or angiotensin receptor type 1 (AT₁R) through putative receptor heteromers. Here, we examined whether A_2AR and AT₁R may oligomerize in the striatum to synergistically modulate dopaminergic transmission. First, by using bioluminescence resonance energy transfer, we demonstrated a physical AT₁R-A_2AR interaction in cultured cells. Interestingly, by protein-protein docking and molecular dynamics simulations, we described that a stable heterotetrameric interaction may exist between AT₁R and A_2AR bound to antagonists (i.e. losartan and istradefylline, respectively). Accordingly, we subsequently ascertained the existence of AT₁R/A_2AR heteromers in the striatum by proximity ligation in situ assay. Finally, we took advantage of a TD animal model, namely the reserpine-induced vacuous chewing movement (VCM), to evaluate a novel multimodal pharmacological TD treatment approach based on targeting the AT₁R/A_2AR complex. Thus, reserpinized mice were co-treated with sub-effective losartan and istradefylline doses, which prompted a synergistic reduction in VCM. Overall, our results demonstrated the existence of striatal AT₁R/A_2AR oligomers with potential usefulness for the therapeutic management of TD.

Brain Renin-Angiotensin System and Microglial Polarization: Implications for Aging and Neurodegeneration

Microglia can transform into proinflammatory/classically activated (M1) or anti-inflammatory/alternatively activated (M2) phenotypes following environmental signals related to physiological conditions or brain lesions. An adequate transition from the M1 (proinflammatory) to M2 (immunoregulatory) phenotype is necessary to counteract brain damage. Several factors involved in microglial polarization have already been identified. However, the effects of the brain renin-angiotensin system (RAS) on microglial polarization are less known. It is well known that there is a “classical” circulating RAS; however, a second RAS (local or tissue RAS) has been observed in many tissues, including brain. The locally formed angiotensin is involved in local pathological changes of these tissues and modulates immune cells, which are equipped with all the components of the RAS. There are also recent data showing that brain RAS plays a major role in microglial polarization. Level of microglial NADPH-oxidase (Nox) activation is a major regulator of the shift between M1/proinflammatory and M2/immunoregulatory microglial phenotypes so that Nox activation promotes the proinflammatory and inhibits the immunoregulatory phenotype. Angiotensin II (Ang II), via its type 1 receptor (AT1), is a major activator of the NADPH-oxidase complex, leading to pro-oxidative and pro-inflammatory effects. However, these effects are counteracted by a RAS opposite arm constituted by Angiotensin II/AT2 receptor signaling and Angiotensin 1–7/Mas receptor (MasR) signaling. In addition, activation of prorenin-renin receptors may contribute to activation of the proinflammatory phenotype. Aged brains showed upregulation of AT1 and downregulation of AT2 receptor expression, which may contribute to a pro-oxidative pro-inflammatory state and the increase in neuron vulnerability. Several recent studies have shown interactions between the brain RAS and different factors involved in microglial polarization, such as estrogens, Rho kinase (ROCK), insulin-like growth factor-1 (IGF-1), tumor necrosis factor α (TNF)-α, iron, peroxisome proliferator-activated receptor gamma, and toll-like receptors (TLRs). Metabolic reprogramming has recently been involved in the regulation of the neuroinflammatory response. Interestingly, we have recently observed a mitochondrial RAS, which is altered in aged brains. In conclusion, dysregulation of brain RAS plays a major role in aging-related changes and neurodegeneration by exacerbation of oxidative stress (OS) and neuroinflammation, which may be attenuated by pharmacological manipulation of RAS components.

Dopamine modulates astroglial and microglial activity via glial renin-angiotensin system in cultures

Dopamine is an immunomodulatory molecule that acts on immune effector cells both in the CNS and peripheral tissues. However, the role of changes in dopamine levels in the neuroinflammatory response is controversial. The local/paracrine renin-angiotensin system (RAS) plays a major role in inflammatory processes in peripheral tissues and brain. In the present study, we investigated the possible role of the brain RAS in the effects of dopamine on the glial inflammatory responses. Astrocytes are the major source of the precursor protein angiotensinogen and angiotensin II (AII) in the brain. Neurotoxins such as MPP⁺ (1-methyl-4-phenylpyridinium) can act directly on astrocytes to increase levels of angiotensinogen and AII. Conversely, dopamine, via type-2 (D2) receptors, inhibited production of angiotensinogen, decreased expression of angiotensin type-1 (AT1) receptors and increased expression of AT2 receptors. In microglia, dopamine and dopamine agonists also regulated RAS activity. First, indirectly, via downregulation of the astrocyte-derived AII. Second, via dopamine-induced regulation of microglial angiotensin receptors. Dopamine decreased the microglial AT1/AT2 ratio leading to inhibition of the pro-inflammatory AT1/NADPH-oxidase/superoxide axis. D2 receptors were particularly responsible for microglial RAS inhibition in basal culture conditions. However, both D1 and D2 agonists inhibited the AT1/NADPH-oxidase axis in lipopolysaccharide-treated (LPS; i.e. activated) microglia. The results indicate that the decrease in dopamine levels observed in early stages of Parkinson's disease and aging may promote neuroinflammation and disease progression via glial RAS exacerbation.

Expression of angiotensinogen and receptors for angiotensin and prorenin in the rat and monkey striatal neurons and glial cells

The renin-angiotensin system (RAS) was initially considered as a circulating humoral system, which function is the regulation of blood pressure. However, it is now known that there exists local RAS in many tissues, including brain. In recent studies, we have demonstrated the presence of a local RAS in the substantia nigra of rodents and primates that modulates dopamine release and dopamine receptor expression. However, overactivation of local RAS exacerbates neuroinflammation, oxidative stress and dopaminergic cell death. In the striatum, it is not clear whether angiotensin receptors are located in dopaminergic terminals, glial cells and/or the projection neurons. The present study shows the location of major components of the RAS in striatal projection neurons of rats and monkeys (both in neurons of the direct and the indirect pathways). Striatal astrocytes and microglial cells also express major RAS components, which increase after induction of neuroinflammation by intrastriatal injection of lipopolysaccharide. Angiotensin receptors were located at the cell surface and also at cytoplasmic and nuclear levels. The results obtained by immunolabeling and confocal microscopy were confirmed with laser microdissection of striatal neurons and glial cells and detection of mRNA expression by PCR. The sequence of the resulting PCR products was verified by DNA sequencing. In addition to the interaction between angiotensin and dopamine receptors in dopaminergic neurons to regulate dopamine release, interaction between angiotensin and dopamine receptors in projection striatal neurons may further modulate the effects of dopamine on the direct and indirect pathways by fine-tuning striatal dopaminergic neurotransmission.

Peripheral levels of angiotensins are associated with depressive symptoms in Parkinson's disease

BACKGROUND

The pathogenesis of PD remains elusive. The renin-angiotensin-system (RAS) has recently been implicated in the degeneration of dopaminergic neurons. This study aimed to compare plasma levels of components of the RAS of individuals with PD with controls. We also investigated the association between these circulating markers and motor, depressive and cognitive parameters.

METHODS

Thirty PD patients and twenty controls were subjected to clinical evaluation, including cognitive and depressive symptoms assessment. Plasma levels of Angiotensin (Ang) I, Ang II, Ang- (1-7), angiotensin-converting enzyme (ACE) and ACE2 were measured by Enzyme-Linked Immunosorbent Assay (ELISA).

RESULTS

PD patients presented lower plasma levels of Ang I, Ang II and Ang- (1-7) than control individuals. Among PD patients, lower circulating levels of angiotensins were associated with increased severity of depressive symptoms.

CONCLUSIONS

This is the first study showing that peripheral levels of RAS components are changed in PD and associated with depressive symptoms.

Influence of ACE gene on differential response to sertraline versus fluoxetine in patients with major depression: a randomized controlled trial

BACKGROUND

Extensive distribution of the different components of renin angiotensin system (RAS) in the brain, along with their roles in promoting anxiety, depression and brain inflammation, opposes RAS as a potential therapeutic target in major depression. Actions of angiotensin II, the main product of RAS, are reduced by antidepressants and this signifies the complex interplay of different mechanisms involved in response to therapy. Here, we hypothesized that genetic polymorphisms of RAS may affect the outcome of therapy in depressed patients.

METHODS

The frequencies of variants of genes encoding for angiotensin-converting enzyme (ACE) insertion/deletion (I/D), rs4291 and rs4343 polymorphisms were determined in extracted DNAs of 200 newly diagnosed depressed patients. Patients were randomly divided into two groups, one treated with fluoxetine and the other treated with sertraline for 12 weeks. Responsive patients were determined by psychiatrist using Hamilton questionnaire and were compared with regard to their genetic variants.

RESULTS

Carriers of the D allele and patients with DD genotype responded significantly better to sertraline than to fluoxetine (P = 0.0006, odds ratio (OR) = 3.0, 95 % confidence interval (CI) = 1.80-5.08; P = 0.006, OR = 3.7, 95 % CI = 1.66-8.29, respectively). Mutant genotypes (GG and TT) of rs4343 and rs4291 polymorphisms were also more frequent in patients responding to sertraline, though not achieving the significance level (P = 0.162 and P = 0.256, respectively).

CONCLUSION

These findings suggest that special genetic variants of RAS may influence or be an indicator for better response to sertraline.

Genetic Variants of Angiotensin-Converting Enzyme Are Linked to Autism: A Case-Control Study

Background

Autism is a disease of complex nature with a significant genetic component. The importance of renin-angiotensin system (RAS) elements in cognition and behavior besides the interaction of angiotensin II (Ang II), the main product of angiotensin-converting enzyme (ACE), with neurotransmitters in CNS, especially dopamine, proposes the involvement of RAS in autism. Since the genetic architecture of autism has remained elusive, here we postulated that genetic variations in RAS are associated with autism.

Methods

Considering the relation between the three polymorphisms of ACE (I/D, rs4343 and rs4291) with the level of ACE activity, we have investigated this association with autism, in a case-control study. Genotype and allele frequencies of polymorphisms were determined in DNAs extracted from venous blood of 120 autistic patients and their age and sex-matched healthy controls, using polymerase chain reaction (PCR) and PCR–restriction fragment length polymorphism (PCR–RFLP) methods.

Results

There were strong associations between both DD genotype of ACE I/D and the D allele, with autism (P = 0.006, OR = 2.9, 95% CI = 1.64–5.13 and P = 0.006, OR = 2.18, 95% CI = 1.37–3.48 respectively). Furthermore, a significant association between the G allele of rs4343 and autism was observed (P = 0.006, OR = 1.84, 95%CI = 1.26–2.67). Moreover, haplotype analysis revealed an association between DTG haplotype and autism (P = 0.008).

Conclusion

Our data suggests the involvement of RAS genetic diversity in increasing the risk of autism.

The novel nonapeptide acein targets angiotensin converting enzyme in the brain and induces dopamine release

BACKGROUND AND PURPOSE

Using an in-house bioinformatics programme, we identified and synthesized a novel nonapeptide, H-Pro-Pro-Thr-Thr-Thr-Lys-Phe-Ala-Ala-OH. Here, we have studied its biological activity, in vitro and in vivo, and have identified its target in the brain.

EXPERIMENTAL APPROACH

The affinity of the peptide was characterized using purified whole brain and striatal membranes from guinea pigs and rats . Its effect on behaviour in rats following intra-striatal injection of the peptide was investigated. A photoaffinity UV cross-linking approach combined with subsequent affinity purification of the ligand covalently bound to its receptor allowed identification of its target.

KEY RESULTS

The peptide bound with high affinity to a single class of binding sites, specifically localized in the striatum and substantia nigra of brains from guinea pigs and rats. When injected within the striatum of rats, the peptide stimulated in vitro and in vivo dopamine release and induced dopamine-like motor effects. We purified the target of the peptide, a ~151 kDa protein that was identified by MS/MS as angiotensin converting enzyme (ACE I). Therefore, we decided to name the peptide acein.

CONCLUSION AND IMPLICATIONS

The synthetic nonapeptide acein interacted with high affinity with brain membrane-bound ACE. This interaction occurs at a different site from the active site involved in the well-known peptidase activity, without modifying the peptidase activity. Acein, in vitro and in vivo, significantly increased stimulated release of dopamine from the brain. These results suggest a more important role for brain ACE than initially suspected.

Brain Angiotensin II AT1 receptors are involved in the acute and long-term amphetamine-induced neurocognitive alterations

RATIONALE

Angiotensin II, by activation of its brain AT1-receptors, plays an active role as neuromodulator in dopaminergic transmission. These receptors participate in the development of amphetamine-induced behavioral and dopamine release sensitization. Dopamine is involved in cognitive processes and provides connectivity between brain areas related to these processes. Amphetamine by its mimetic activity over dopamine neurotransmission elicits differential responses after acute administration or after re-exposure following long-term withdrawal periods in different cognitive processes.

OBJECTIVE

The purpose of this study is to evaluate the AT1-receptor involvement in the acute and long-term amphetamine-induced alterations in long-term memory and in cellular-related events.

METHODS

Male Wistar rats (250-300 g) were used in this study. Acute effects: Amphetamine (0.5/2.5 mg/kg i.p.) was administered after post-training in the inhibitory avoidance (IA) response. The AT1-receptor blocker Losartan was administered i.c.v. before a single dose of amphetamine (0.5 mg/kg i.p.). Long-term effects: The AT1-receptors blocker Candesartan (3 mg/kg p.o.) was administered for 5 days followed by 5 consecutive days of amphetamine (2.5 mg/kg/day, i.p.). The neuroadaptive changes were evidenced after 1 week of withdrawal by an amphetamine challenge (0.5 mg/kg i.p.). The IA response, the neuronal activation pattern, and the hippocampal synaptic transmission were evaluated.

RESULTS

The impairing effect in the IA response of post-training acute amphetamine was partially prevented by Losartan. The long-term changes induced by repeated amphetamine (resistance to acute amphetamine interference in the IA response, neurochemical altered response, and increased hippocampal synaptic transmission) were prevented by AT1-receptors blockade.

CONCLUSIONS

AT1-receptors are involved in the acute alterations and in the neuroadaptations induced by repeated amphetamine associated with neurocognitive processes.

Inhibition of endoplasmic reticulum stress-activated IRE1α-TRAF2-caspase-12 apoptotic pathway is involved in the neuroprotective effects of telmisartan in the rotenone rat model of Parkinson's disease

Telmisartan, one unique angiotensin II type 1 receptor blocker, has been attracting attention due to its putative peroxisome proliferator-activated receptor (PPAR)-γ or β/δ actions. Recently, telmisartan has been reported to exert neuroprotective effects in animal models of Parkinson's disease (PD). However, the underlying mechanisms have not been fully clarified. Recently, accumulating evidence has shown that endoplasmic reticulum (ER) stress plays a crucial role in rotenone-induced neuronal apoptosis. Additionally, studies have revealed that inositol-requiring enzyme/endonuclease 1α (IRE1α) is necessary and sufficient to trigger ER stress. In the present study, we aimed to determine whether ER stress-activated IRE1α-mediated apoptotic pathway is involved in the neuroprotection of telmisartan in the rotenone rats of PD and explore the possible involvement of PPAR-β/δ activation. The catalepsy tests were performed to test the catalepsy symptom. The dopamine content and α-synuclein expression were ascertained through high-performance liquid chromatography and immunohistochemistry, respectively. The expression of IRE1α, TNF receptor associated factor 2 (TRAF2), caspase-12 and PPAR-β/δ was detected by western blot. Neuronal apoptosis was assessed by TUNEL and immunohistochemistry. Our results show that telmisartan ameliorated the catalepsy symptom and attenuated dopamine depletion as well as α-synuclein accumulation. Moreover, telmisartan decreased ER stress-mediated neuronal apoptosis. Furthermore, telmisartan inhibited IRE1α-TRAF2-caspase-12 apoptotic signaling pathway. Additionally, telmisartan activated PPAR β/δ, implying that PPAR-β/δ activation properties of telmisartan are possibly or partially involved in the neuroprotective effects. In conclusion, our findings suggest that suppressing ER stress-activated IRE1α-TRAF2-caspase-12 apoptotic pathway is involved in the neuroprotective effects of telmisartan in the rotenone rats of PD.

Dopamine Receptors and Neurodegeneration

Dopamine (DA) is one of the major neurotransmitters and participates in a number of functions such as motor coordination, emotions, memory, reward mechanism, neuroendocrine regulation etc. DA exerts its effects through five DA receptors that are subdivided in 2 families: D1-like DA receptors (D1 and D5) and the D2-like (D2, D3 and D4). All DA receptors are widely expressed in the central nervous system (CNS) and play an important role in not only in physiological conditions but also pathological scenarios. Abnormalities in the DAergic system and its receptors in the basal ganglia structures are the basis Parkinson's disease (PD), however DA also participates in other neurodegenerative disorders such as Huntington disease (HD) and multiple sclerosis (MS). Under pathological conditions reorganization of DAergic system has been observed and most of the times, those changes occur as a mechanism of compensation, but in some cases contributes to worsening the alterations. Here we review the changes that occur on DA transmission and DA receptors (DARs) at both levels expression and signals transduction pathways as a result of neurotoxicity, inflammation and in neurodegenerative processes. The better understanding of the role of DA receptors in neuropathological conditions is crucial for development of novel therapeutic approaches to treat alterations related to neurodegenerative diseases.

A previous history of repeated amphetamine exposure modifies brain angiotensin II AT1 receptor functionality

Previous results from our laboratory showed that angiotensin II AT1 receptors (AT1-R) are involved in the neuroadaptative changes induced by amphetamine. The aim of the present work was to study functional and neurochemical responses to angiotensin II (ANG II) mediated by AT1-R activation in animals previously exposed to amphetamine. For this purpose male Wistar rats (250-320 g) were treated with amphetamine (2.5mg/kg/day intraperitoneal) or saline for 5 days and implanted with intracerebroventricular (i.c.v.) cannulae. Seven days after the last amphetamine administration the animals received ANG II (400 pmol) i.c.v. One group was tested in a free choice paradigm for sodium (2% NaCl) and water intake and sacrificed for Fos immunoreactivity (Fos-IR) determinations. In a second group of rats, urine and plasma samples were collected for electrolytes and plasma renin activity determination and then they were sacrificed for Fos-IR determination in Oxytocinergic neurons (Fos-OT-IR).

RESULTS

Repeated amphetamine exposure (a) prevented the increase in sodium intake and Fos-IR cells in caudate-putamen and accumbens nucleus induced by ANG II i.c.v. (b) potentiated urinary sodium excretion and Fos-OT-IR in hypothalamus and (c) increased the inhibitory response in plasma renin activity, in response to ANG II i.c.v. Our results indicate a possible functional desensitisation of AT1-R in response to ANG II, induced by repeated amphetamine exposure. This functional AT1-R desensitisation allows to unmask the effects of ANG II i.c.v. mediated by oxytocin. We conclude that the long lasting changes in brain AT1-R functionality should be considered among the psychostimulant-induced neuroadaptations.

Dopamine D2 and angiotensin II type 1 receptors form functional heteromers in rat striatum

Identification of G protein-coupled receptors and their specific function in a given neuron becomes essential to better understand the variety of signal transduction mechanisms associated with neurotransmission. We hypothesized that angiotensin II type 1 (AT1) and dopamine D2 receptors form heteromers in the central nervous system, specifically in striatum. Using bioluminescence resonance energy transfer, a direct interaction was demonstrated in cells transfected with the cDNA for the human version of the receptors. Heteromerization did not affect cAMP signaling via D2 receptors but attenuated the coupling of AT1 receptors to Gq. A common feature of heteromers, namely cross-antagonism, i.e. the blockade of the signaling of one receptor by the blockade of the partner receptor, was tested in co-transfected cells. Candesartan, the selective AT1 receptor antagonist, was able to block D2-receptor mediated effects on cAMP levels, MAP kinase activation and β-arrestin recruitment. This effect of candesartan, which constitutes a property for the dopamine-angiotensin receptor heteromer, was similarly occurring in primary cultures of neurons and rat striatal slices. The expression of heteromers in striatum was confirmed by robust labeling using in situ proximity ligation assays. The results indicate that AT1 receptors are expressed in striatum and form heteromers with dopamine D2 receptors that enable drugs selective for the AT1 receptor to alter the functional response of D2 receptors.

Effects of AT1 receptor antagonism on kainate-induced seizures and concomitant changes in hippocampal extracellular noradrenaline, serotonin, and dopamine levels in Wistar-Kyoto and spontaneously hypertensive rats

In the management of epilepsy, AT1 receptor antagonists have been suggested as an additional treatment strategy. A hyperactive brain angiotensin (Ang) II system and upregulated AT1 receptors are implicated in the cerebrovascular alterations in a genetic form of hypertension. Uncontrolled hypertension could also, in turn, be a risk factor for a seizure threshold decrease and development of epileptogenesis. The present study aimed to assess the effects of the selective AT1 receptor antagonist ZD7155 on kainic acid (KA)-induced status epilepticus (SE) development and accompanying changes in the hippocampal extracellular (EC) neurotransmitter levels of noradrenaline (NAD), serotonin (5-HT), and dopamine (DA) in spontaneously hypertensive rats (SHRs) and their parent strain Wistar-Kyoto (WKY) rats, since monoamines are well-known neurotransmitters involved in mechanisms of both epilepsy and hypertension. Status epilepticus was evoked in freely moving rats by a repetitive intraperitoneal (i.p.) administration of KA in subconvulsant doses. In the treatment group, ZD7155 (5mg/kg i.p.) was coadministered with the first KA injection. Spontaneously hypertensive rats exhibited higher susceptibility to SE than WKY rats, but the AT1 receptor antagonist did not alter the development of SE in SHRs or in WKY rats. In vivo microdialysis demonstrated significant KA-induced increases of the hippocampal NAD and DA levels in SHRs and of NAD, 5-HT, and DA in WKY rats. Although SHRs developed more severe seizures while receiving a lower dose of KA compared to WKY rats, AT1 receptor antagonism completely prevented all KA-induced increases of hippocampal monoamine levels in both rat strains without affecting seizure development per se. These results suggest a lack of direct relationship between KA-induced seizure susceptibility and adaptive changes of hippocampal NAD, 5-HT, and DA levels in the effects of ZD7155 in WKY rats and SHRs.

Angiotensin II type 2 receptor signaling affects dopamine levels in the brain and prevents binge eating disorder

INTRODUCTION

Binge eating disorder (BED) is associated with dopaminergic activation as food reward, resulting in metabolism-related disorders. Stimulation of angiotensin type 2 (AT2) receptor is reported to inhibit dopamine synthesis. We investigated the possible roles of AT2 receptor-mediated dopamine regulation in the pathogenesis of BED.

MATERIALS AND METHODS

Male C57BL/6 mice, type 2 diabetic (KKAy) mice and AT2 receptor-null (AT2KO) mice at eight weeks old were treated with AT2 receptor agonist, compound 21 (C21) or saline for two weeks. Mice were subjected to fasting for two days followed by re-feeding for seven days.

RESULTS

Treatment with C21 attenuated the rebound proportion of body weight, food intake and water intake in KKAy mice, but not in C57BL/6 and AT2KO mice. Dopamine concentration in the striatum was further increased by fasting in KKAy and AT2KO mice. Administration of C21 significantly attenuated this fasting-induced increase in dopamine level only in KKAy mice. Dopamine receptor D1, D2 expression in the substantia nigra were markedly lower in KKAy mice compared with C57BL/6 mice, while administration of C21 increased their expression in KKAy mice.

CONCLUSIONS

Our study suggests that AT2 receptor stimulation may be a new therapeutic approach to improve eating disorder associated with dopamine resistance.

Association of angiotensin-converting enzyme gene polymorphism with schizophrenia and depressive symptom severity in a Chinese population

BACKGROUND

Depressive symptoms are frequently observed in schizophrenia patients. Angiotensin-converting enzyme (ACE), a key enzyme of renin-angiotensin system, can catalyze the degradation of neuropeptides and modulate dopaminergic and serotonergic neurotransmission. Previous studies have revealed the association of the ACE gene insertion/deletion polymorphism with depressive disorder and its treatment response but not with the depressive symptoms in schizophrenia.

OBJECTIVE

The aim of this study is to examine whether this polymorphism was associated with susceptibility to schizophrenia and with its psychopathological symptoms, especially depressive symptoms in a Han Chinese population.

METHODS

This polymorphism was genotyped in 382 chronic patients and 538 healthy controls. Psychopathology was characterised using the positive and negative syndrome scale.

RESULTS

The allelic and genotypic frequencies of this polymorphism significantly differed between patients and controls (both p < 0.001). A significant difference in the positive and negative syndrome scale depressive symptom score was observed among the three genotypes (p < 0.03), with higher score in patients with insertion/insertion (I/I) than with deletion/deletion (D/D) genotypes (p < 0.05). Furthermore, there was a significant linear correlation between the number of I alleles and the depressive symptom score (p < 0.05).

CONCLUSIONS

The ACE gene insertion/deletion polymorphism may play a role in susceptibility to schizophrenia and also in its depressive symptom severity in a Han Chinese population.

Loss of angiotensin II receptor expression in dopamine neurons in Parkinson's disease correlates with pathological progression and is accompanied by increases in Nox4- and 8-OH guanosine-related nucleic acid oxidation and caspase-3 activation

Background

In rodent models of Parkinson’s disease (PD), dopamine neuron loss is accompanied by increased expression of angiotensin II (AngII), its type 1 receptor (AT1), and NADPH oxidase (Nox) in the nigral dopamine neurons and microglia. AT1 blockers (ARBs) stymie such oxidative damage and neuron loss. Whether changes in the AngII/AT1/Nox4 axis contribute to Parkinson neuropathogenesis is unknown. Here, we studied the distribution of AT1 and Nox4 in dopamine neurons in two nigral subregions: the less affected calbindin-rich matrix and the first-affected calbindin-poor nigrosome 1 of three patients, who were clinically asymptomatic, but had nigral dopamine cell loss and Braak stages consistent with a neuropathological diagnosis of PD (prePD). For comparison, five clinically- and neuropathologically-confirmed PD patients and seven age-matched control patients (AMC) were examined.

Results

AT1 and Nox4 immunoreactivity was noted in dopamine neurons in both the matrix and the nigrosome 1. The total cellular levels of AT1 in surviving dopamine neurons in the matrix and nigrosome 1 declined from AMC>prePD>PD, suggesting that an AngII/AT1/Nox4 axis orders neurodegenerative progression. In this vein, the loss of dopamine neurons was paralleled by a decline in total AT1 per surviving dopamine neuron. Similarly, AT1 in the nuclei of surviving neurons in the nigral matrix declined with disease progression, i.e., AMC>prePD>PD. In contrast, in nigrosome 1, the expression of nuclear AT1 was unaffected and similar in all groups. The ratio of nuclear AT1 to total AT1 (nuclear + cytoplasmic + membrane) in dopamine neurons increased stepwise from AMC to prePD to PD. The proportional increase in nuclear AT1 in dopamine neurons in nigrosome 1 of prePD and PD patients was accompanied by elevated nuclear expression of Nox4, oxidative damage to DNA, and caspase-3-mediated cell loss.

Conclusions

Our observations are consistent with the idea that AngII/AT1/Nox4 axis-mediated oxidative stress gives rise to the dopamine neuron dysfunction and loss characteristic of the neuropathological and clinical manifestations of PD and suggest that the chance for a neuron to survive increases in association with lower total as well as nuclear AT1 expression. Our results support the need for further evaluation of ARBs as disease-modifying agents in PD.

Brain renin-angiotensin system and dopaminergic cell vulnerability

Although the renin-angiotensin system (RAS) was classically considered as a circulating system that regulates blood pressure, many tissues are now known to have a local RAS. Angiotensin, via type 1 receptors, is a major activator of the NADPH-oxidase complex, which mediates several key events in oxidative stress (OS) and inflammatory processes involved in the pathogenesis of major aging-related diseases. Several studies have demonstrated the presence of RAS components in the basal ganglia, and particularly in the nigrostriatal system. In the nigrostriatal system, RAS hyperactivation, via NADPH-oxidase complex activation, exacerbates OS and the microglial inflammatory response and contributes to progression of dopaminergic degeneration, which is inhibited by angiotensin receptor blockers and angiotensin converting enzyme (ACE) inhibitors. Several factors may induce an increase in RAS activity in the dopaminergic system. A decrease in dopaminergic activity induces compensatory upregulation of local RAS function in both dopaminergic neurons and glia. In addition to its role as an essential neurotransmitter, dopamine may also modulate microglial inflammatory responses and neuronal OS via RAS. Important counterregulatory interactions between angiotensin and dopamine have also been observed in several peripheral tissues. Neurotoxins and proinflammatory factors may also act on astrocytes to induce an increase in RAS activity, either independently of or before the loss of dopamine. Consistent with a major role of RAS in dopaminergic vulnerability, increased RAS activity has been observed in the nigra of animal models of aging, menopause and chronic cerebral hypoperfusion, which also showed higher dopaminergic vulnerability. Manipulation of the brain RAS may constitute an effective neuroprotective strategy against dopaminergic vulnerability and progression of Parkinson's disease.

Effect of chronic treatment with angiotensin type 1 receptor antagonists on striatal dopamine levels in normal rats and in a rat model of Parkinson's disease treated with L-DOPA

Beneficial effects of angiotensin type-1 receptor (AT1) inhibition have been observed in a number of brain processes mediated by oxidative stress and neuroinflammation, including Parkinson's disease. However, important counterregulatory interactions between dopamine and angiotensin systems have recently been demonstrated in several peripheral tissues, and it is possible that a decrease in dopamine levels due to AT1 inhibition may interfere with neuroprotective strategies. The present experiments involving rats with normal dopaminergic innervation indicate that chronic treatment with the AT1 antagonist candesartan does not significantly affect striatal levels of dopamine, serotonin or metabolites, as does not significantly affect motor behavior, as evaluated by the rotarod test. Interestingly, chronic administration of candesartan to normal rats induced a marked increase in dopamine D1 and a decrease in dopamine D2 receptor expression. In a rat model of Parkinson's disease treated with L-DOPA, no differences in striatal dopamine and serotonin levels were observed between candesartan-treated rats and untreated, which suggests that chronic treatment with candesartan does not significantly affect the process of L-DOPA decarboxylation and dopamine release in Parkinson's disease patients. Candesartan did not induce any differences in the striatal expression of dopamine D1 and D2 and serotonin 5-HT1B receptors in 6ydroxydopamine-lesioned rats treated with L-DOPA. The results suggest that chronic treatment with AT1 antagonists as a neuroprotective strategy does not significantly affect striatal dopamine release or motor behavior. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Renin-Angiotensin system and sympathetic neurotransmitter release in the central nervous system of hypertension

Many Studies suggest that changes in sympathetic nerve activity in the central nervous system might have a crucial role in blood pressure control. The present paper discusses evidence in support of the concept that the brain renin-angiotensin system (RAS) might be linked to sympathetic nerve activity in hypertension. The amount of neurotransmitter release from sympathetic nerve endings can be regulated by presynaptic receptors located on nerve terminals. It has been proposed that alterations in sympathetic nervous activity in the central nervous system of hypertension might be partially due to abnormalities in presynaptic modulation of neurotransmitter release. Recent evidence indicates that all components of the RAS have been identified in the brain. It has been proposed that the brain RAS may actively participate in the modulation of neurotransmitter release and influence the central sympathetic outflow to the periphery. This paper summarizes the results of studies to evaluate the possible relationship between the brain RAS and sympathetic neurotransmitter release in the central nervous system of hypertension.

Cocaine administration increases angiotensin I-converting enzyme (ACE) expression and activity in the rat striatum and frontal cortex

Some central effects of cocaine administration seem to be related to angiotensin II (Ang II) or its metabolites. Nonetheless, it is still an open question whether or not the levels of angiotensin I-converting enzyme (ACE), the main Ang II generating enzyme, are modified by cocaine administration. To evaluate the effect of acute and subchronic cocaine administration on ACE activity and mRNA expression, male rats were randomly assigned to saline or cocaine group. Acute and subchronic cocaine administration induced a significant increase in ACE activity and mRNA expression in the frontal cortex and striatum but not in the hippocampus. These results suggest that some of the Ang II related effects of cocaine upon the central nervous system can be mediated by changes on the expression and activity of ACE in the striatum and frontal cortex.

Location of prorenin receptors in primate substantia nigra: effects on dopaminergic cell death

Angiotensin II acts via angiotensin type 1 receptors and is a major inducer of inflammation and oxidative stress. Local renin-angiotensin systems play a major role in the development of age-related disorders in several tissues. These processes are delayed, but not totally abolished, by blockade of angiotensin signaling. A specific receptor for renin and its precursor prorenin has recently been identified. We previously showed that neurotoxin-induced dopaminergic (DA) cell loss is decreased by inhibition of angiotensin receptors, but the location and functional effects of prorenin receptor (PRR) in the brain, including the DA system, are unknown. In the substantia nigra of Macaca fascicularis and in rat primary mesencephalic cultures, double immunofluorescence analysis revealed PRR immunoreactivity in neurons (including DA neurons) and microglia, but not in astrocytes. Administration of the PRR blocker, handle region peptide, led to a significant decrease in 6-hydroxydopamine-induced DA cell death in the cultures,whereas administration of renin with simultaneous blockade of angiotensin receptors led to an increase in 6-hydroxydopamine-induced cell death. These results suggest that active agent angiotensin II-independent PRR intracellular signaling may contribute to exacerbation of DA cell death in vivo. Therefore, potential neuroprotective strategies for DA neurons in Parkinson disease should address both angiotensin and PRR signaling.