The angiotensin converting enzyme inhibitor captopril protects nigrostriatal dopamine neurons in animal models of parkinsonism

Angiotensin-converting enzyme inhibition prevents l-dopa-induced dyskinesia in a 6-ohda-induced mouse model of Parkinson's disease

Parkinson's disease (PD) is characterised by severe movement defects and the degeneration of dopaminergic neurones in the midbrain. The symptoms of PD can be managed with dopamine replacement therapy using L-3, 4-dihydroxyphenylalanine (L-dopa), which is the gold standard therapy for PD. However, long-term treatment with L-dopa can lead to motor complications. The central renin-angiotensin system (RAS) is associated with the development of neurodegenerative diseases in the brain. However, the role of the RAS in dopamine replacement therapy for PD remains unclear. Here, we tested the co-treatment of the angiotensin-converting enzyme inhibitor (ACEI) with L-dopa altered L-dopa-induced dyskinesia (LID) in a 6-hydroxydopamine (6-OHDA)-lesioned mouse model of PD. Perindopril, captopril, and enalapril were used as ACEIs. The co-treatment of ACEI with L-dopa significantly decreased LID development in 6-OHDA-lesioned mice. In addition, the astrocyte and microglial transcripts involving Ccl2, C3, Cd44, and Iigp1 were reduced by co-treatment with ACEI and L-dopa in the 6-OHDA-lesioned striatum. In conclusion, co-treatment with ACEIs and L-dopa, such as perindopril, captopril, and enalapril, may mitigate the severity of L-DOPA-induced dyskinesia in a mouse model of PD.

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.

The classical and non-classical axes of renin-angiotensin system in Parkinson disease: The bright and dark side of the moon

Parkinson disease (PD) is a common brain neurodegenerative disease due to progressive degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc). Of note, the cardio-metabolic disorders such as hypertension are adversely affect PD neuropathology through exaggeration of renin-angiotensin system (RAS). The RAS affects the stability of dopaminergic neurons in the SNpc, and exaggeration of angiotensin II (AngII) is implicated in the development and progression of PD. RAS has two axes classical including angiotensin converting enzyme (ACE)/AngII/AT1R, and the non-classical axis which include ACE2/Ang1-7/Mas receptor, AngIII, AngIV, AT2R, and AT4R. It has been shown that brain RAS is differs from that of systemic RAS that produce specific neuronal effects. As well, there is an association between brain RAS and PD. Therefore, this review aims to revise from published articles the role of brain RAS in the pathogenesis of PD focusing on the non-classical pathway, and how targeting of this axis can modulate PD neuropathology.

Literature-Based Discovery Predicts Antihistamines Are a Promising Repurposed Adjuvant Therapy for Parkinson's Disease

Parkinson's disease (PD) is a movement disorder caused by a dopamine deficit in the brain. Current therapies primarily focus on dopamine modulators or replacements, such as levodopa. Although dopamine replacement can help alleviate PD symptoms, therapies targeting the underlying neurodegenerative process are limited. The study objective was to use artificial intelligence to rank the most promising repurposed drug candidates for PD. Natural language processing (NLP) techniques were used to extract text relationships from 33+ million biomedical journal articles from PubMed and map relationships between genes, proteins, drugs, diseases, etc., into a knowledge graph. Cross-domain text mining, hub network analysis, and unsupervised learning rank aggregation were performed in SemNet 2.0 to predict the most relevant drug candidates to levodopa and PD using relevance-based HeteSim scores. The top predicted adjuvant PD therapies included ebastine, an antihistamine for perennial allergic rhinitis; levocetirizine, another antihistamine; vancomycin, a powerful antibiotic; captopril, an angiotensin-converting enzyme (ACE) inhibitor; and neramexane, an N-methyl-D-aspartate (NMDA) receptor agonist. Cross-domain text mining predicted that antihistamines exhibit the capacity to synergistically alleviate Parkinsonian symptoms when used with dopamine modulators like levodopa or levodopa-carbidopa. The relationship patterns among the identified adjuvant candidates suggest that the likely therapeutic mechanism(s) of action of antihistamines for combatting the multi-factorial PD pathology include counteracting oxidative stress, amending the balance of neurotransmitters, and decreasing the proliferation of inflammatory mediators. Finally, cross-domain text mining interestingly predicted a strong relationship between PD and liver disease.

Exploration of multifaceted molecular mechanism of angiotensin-converting enzyme 2 (ACE2) in pathogenesis of various diseases

Angiotensin converting enzyme 2 (ACE2) is a homolog of ACE (a transmembrane bound dipeptidyl peptidase enzyme). ACE2 converts angiotensinogen to the heptapeptide angiotensin-(1-7). ACE2 and its product, angiotensin-(1-7), have counteracting effects against the adverse actions of other members of renin-angiotensin system (RAS). ACE2 and its principal product, angiotensin-(1-7), were considered an under recognized arm of the RAS. The COVID-19 pandemic brought to light this arm of RAS with special focus on ACE2. Membrane bound ACE2 serves as a receptor for SARS-CoV-2 viral entry through spike proteins. Apart from that, ACE2 is also involved in the pathogenesis of various other diseases like cardiovascular disease, cancer, respiratory diseases, neurodegenerative diseases and infertility. The present review focuses on the molecular mechanism of ACE2 in neurodegenerative diseases, cancer, cardiovascular disease, infertility and respiratory diseases, including SARS-CoV-2. This review summarizes unveiled roles of ACE2 in the pathogenesis of various diseases which further provides intriguing possibilities for the use of ACE2 activators and RAS modulating agents for various diseases.

Association of COVID-19 with Comorbidities: An Update

Coronavirus disease (COVID-19) is caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) which was identified in Wuhan, China in December 2019 and jeopardized human lives. It spreads at an unprecedented rate worldwide, with serious and still-unfolding health conditions and economic ramifications. Based on the clinical investigations, the severity of COVID-19 appears to be highly variable, ranging from mild to severe infections including the death of an infected individual. To add to this, patients with comorbid conditions such as age or concomitant illnesses are significant predictors of the disease's severity and progression. SARS-CoV-2 enters inside the host cells through ACE2 (angiotensin converting enzyme2) receptor expression; therefore, comorbidities associated with higher ACE2 expression may enhance the virus entry and the severity of COVID-19 infection. It has already been recognized that age-related comorbidities such as Parkinson's disease, cancer, diabetes, and cardiovascular diseases may lead to life-threatening illnesses in COVID-19-infected patients. COVID-19 infection results in the excessive release of cytokines, called "cytokine storm", which causes the worsening of comorbid disease conditions. Different mechanisms of COVID-19 infections leading to intensive care unit (ICU) admissions or deaths have been hypothesized. This review provides insights into the relationship between various comorbidities and COVID-19 infection. We further discuss the potential pathophysiological correlation between COVID-19 disease and comorbidities with the medical interventions for comorbid patients. Toward the end, different therapeutic options have been discussed for COVID-19-infected comorbid patients.

Updated Perspectives on the Management of Drug-Induced Parkinsonism (DIP): Insights from the Clinic

Parkinsonism refers to the clinical combination of bradykinesia, rigidity, tremor, and postural instability. Parkinsonism is often neurodegenerative, but it can be secondary or iatrogenic, as in drug-induced parkinsonism (DIP), which is the topic of this review. We review the pathophysiology of DIP, differentiate DIP and idiopathic Parkinson's disease (PD), list culprit medications in the development of DIP, discuss the diagnosis of DIP as well as the motor and nonmotor signs and symptoms that can help with differentiation of DIP and PD, and detail the management of DIP.

Deciphering Intertwined Molecular Pathways Underlying Metabolic Syndrome Leading to Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that gradually develops over time in a progressive manner. The main culprit behind the disease pathology is dopaminergic deficiency in Substantia nigra Pars Compacta (SNpc) due to neuronal degeneration. However, there are other factors that are not only associated with it but also somehow responsible for inception of pathology. Metabolic syndrome is one such risk factor for PD. Metabolic syndrome is a cluster of diseases mainly including diabetes, hypertension, obesity, and hyperlipidemia which pose a risk for developing cardiovascular disorders. All of these disorders have their own pathological pathways that intertwine with PD pathology. This leads to alpha-synuclein aggregation, neuroinflammation, mitochondrial dysfunction, and oxidative stress which are facets in initiating PD pathology. Although few reports are available, this area is underexplored and has contradictory views. Hence, further studies are needed in order to establish a definite relationship between PD and metabolic syndrome. In this review, we aim to elucidate the molecular mechanisms to confirm the association between them and pave the way for potential repurposing of therapies.

Angiotensin converting enzyme inhibitor captopril prevents neuronal overexpression of amyloid-beta and alpha-synuclein in Drosophila melanogaster genetic models of neurodegenerative diseases

BACKGROUND

Parkinson disease (PD) and Alzheimer's disease (AD) are progressive neurodegenerative disorders characterized by loss of selective neurons in discreet part of the brain. The peptide angiotensin II (Ang II) plays significant role in hippocampal and striatal neurons degeneration through the generation of reactive oxygen species. Blockade of the angiotensin converting enzyme or ATI receptors provides protection in animal models of neurodegenerative diseases. In the present study, the neuroprotective effect of captopril was investigated in Drosophila melanogaster model using the UAS-GAL4 system to express the synuclein and Aβ42 peptide in the flies' neurons.

METHODS

The disease causing human Aβ42 peptide or α-syn was expressed pan-neuronally (elav-GAL4) or dopamine neuron (DDC-GAL4) using the UAS-GAL4 system. Flies were either grown in food media with or without captopril (1, 5, or 10µM). This was followed by fecundity, larva motility, negative geotaxis assay (climbing) and lifespan as a measure of neurodegeneration.

RESULTS

Elav-Gal4<Aβ or DDC-GAL4<α-syn flies displayed significant decrease in larva motility when compared with normal control (w1118) which was reversed by the supplementation of the media with captopril (5 or 10 mM) indicative of neuroprotection. Interestingly, supplementation of flies' media with captopril improved climbing activity in Elav-Gal4<Aβ or DDC-GAL4<α-syn flies when compared with vehicle treated only. Moreover, flies grown on captopril caused no significant change in lifespan.  Conclusion: Findings from this study confirmed the neuroprotective action of captopril in genetic or familial forms of neurodegeneration.

Angiotensin-(1-7) as a Potential Therapeutic Strategy for Delayed Cerebral Ischemia in Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a substantial cause of mortality and morbidity worldwide. Moreover, survivors after the initial bleeding are often subject to secondary brain injuries and delayed cerebral ischemia, further increasing the risk of a poor outcome. In recent years, the renin-angiotensin system (RAS) has been proposed as a target pathway for therapeutic interventions after brain injury. The RAS is a complex system of biochemical reactions critical for several systemic functions, namely, inflammation, vascular tone, endothelial activation, water balance, fibrosis, and apoptosis. The RAS system is classically divided into a pro-inflammatory axis, mediated by angiotensin (Ang)-II and its specific receptor AT₁R, and a counterbalancing system, presented in humans as Ang-(1-7) and its receptor, MasR. Experimental data suggest that upregulation of the Ang-(1-7)/MasR axis might be neuroprotective in numerous pathological conditions, namely, ischemic stroke, cognitive disorders, Parkinson's disease, and depression. In the presence of SAH, Ang-(1-7)/MasR neuroprotective and modulating properties could help reduce brain damage by acting on neuroinflammation, and through direct vascular and anti-thrombotic effects. Here we review the role of RAS in brain ischemia, with specific focus on SAH and the therapeutic potential of Ang-(1-7).

Multiple Aspects of Inappropriate Action of Renin-Angiotensin, Vasopressin, and Oxytocin Systems in Neuropsychiatric and Neurodegenerative Diseases

The cardiovascular system and the central nervous system (CNS) closely cooperate in the regulation of primary vital functions. The autonomic nervous system and several compounds known as cardiovascular factors, especially those targeting the renin–angiotensin system (RAS), the vasopressin system (VPS), and the oxytocin system (OTS), are also efficient modulators of several other processes in the CNS. The components of the RAS, VPS, and OTS, regulating pain, emotions, learning, memory, and other cognitive processes, are present in the neurons, glial cells, and blood vessels of the CNS. Increasing evidence shows that the combined function of the RAS, VPS, and OTS is altered in neuropsychiatric/neurodegenerative diseases, and in particular in patients with depression, Alzheimer’s disease, Parkinson’s disease, autism, and schizophrenia. The altered function of the RAS may also contribute to CNS disorders in COVID-19. In this review, we present evidence that there are multiple causes for altered combined function of the RAS, VPS, and OTS in psychiatric and neurodegenerative disorders, such as genetic predispositions and the engagement of the RAS, VAS, and OTS in the processes underlying emotions, memory, and cognition. The neuroactive pharmaceuticals interfering with the synthesis or the action of angiotensins, vasopressin, and oxytocin can improve or worsen the effectiveness of treatment for neuropsychiatric/neurodegenerative diseases. Better knowledge of the multiple actions of the RAS, VPS, and OTS may facilitate programming the most efficient treatment for patients suffering from the comorbidity of neuropsychiatric/neurodegenerative and cardiovascular diseases.

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 variations of endophilin A2-FoxO3a-autophagy signal in angiotensin II-induced dopaminergic neuron injury mouse model and by biochanin A

Biochanin A (Bioch A) is a natural plant estrogen, with various biological activities such as anti-apoptosis, anti-oxidation, and suppression of inflammation. In this study, we investigated the protective effects of Bioch A on angiotensin II (AngII) - induced dopaminergic (DA) neuron damage in vivo and on molecular mechanisms. Spontaneous activity and motor ability of mice among groups was detected by open-field test and swim-test. The expression of TH, microtubule-associated proteins light chain 3B II (LC3BII)/LC3BI, beclin-1, P62, forkhead box class O3 (FoxO3), phosphorylated (p) FoxO3a/FoxO3a, FoxO3, and endophilin A2 were determined by Western blot and immunohistochemistry or immunofluorescence staining. Our results showed that AngII treatment significantly increased the behavioral dysfunction of mice and DA neuron damage. Meanwhile, AngII treatment increased the expression of LC3BII/LC3BI, beclin-1, P62, and FoxO3a and decreased the expression of endophilin A2 and p-FoxO3a/FoxO3a, however, Bioch A treatment alleviate these changes. In summary, these results suggest that Bioch A exerts protective effects on AngII-induced mouse model may be related to regulating endophilin A2, FoxO3a, and autophagy-related proteins; however, the specific mechanism is not yet clear and needs further study.

Mitochondria-Endoplasmic Reticulum Crosstalk in Parkinson's Disease: The Role of Brain Renin Angiotensin System Components

The past few decades have seen an increased emphasis on the involvement of the mitochondrial-associated membrane (MAM) in various neurodegenerative diseases, particularly in Parkinson’s disease (PD) and Alzheimer’s disease (AD). In PD, alterations in mitochondria, endoplasmic reticulum (ER), and MAM functions affect the secretion and metabolism of proteins, causing an imbalance in calcium homeostasis and oxidative stress. These changes lead to alterations in the translocation of the MAM components, such as IP3R, VDAC, and MFN1 and 2, and consequently disrupt calcium homeostasis and cause misfolded proteins with impaired autophagy, distorted mitochondrial dynamics, and cell death. Various reports indicate the detrimental involvement of the brain renin–angiotensin system (RAS) in oxidative stress, neuroinflammation, and apoptosis in various neurodegenerative diseases. In this review, we attempted to update the reports (using various search engines, such as PubMed, SCOPUS, Elsevier, and Springer Nature) demonstrating the pathogenic interactions between the various proteins present in mitochondria, ER, and MAM with respect to Parkinson’s disease. We also made an attempt to speculate the possible involvement of RAS and its components, i.e., AT1 and AT2 receptors, angiotensinogen, in this crosstalk and PD pathology. The review also collates and provides updated information on the role of MAM in calcium signaling, oxidative stress, neuroinflammation, and apoptosis in PD.

Brain Renin-Angiotensin System as Novel and Potential Therapeutic Target for Alzheimer's Disease

The activation of the brain renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cognition. While the brain RAS has been studied before in the context of hypertension, little is known about its role and regulation in relation to neuronal function and its modulation. Adequate blood flow to the brain as well as proper clearing of metabolic byproducts become crucial in the presence of neurodegenerative disorders such as Alzheimer's disease (AD). RAS inhibition (RASi) drugs that can cross into the central nervous system have yielded unclear results in improving cognition in AD patients. Consequently, only one RASi therapy is under consideration in clinical trials to modify AD. Moreover, the role of non-genetic factors such as hypercholesterolemia in the pathophysiology of AD remains largely uncharacterized, even when evidence exists that it can lead to alteration of the RAS and cognition in animal models. Here we revise the evidence for the function of the brain RAS in cognition and AD pathogenesis and summarize the evidence that links it to hypercholesterolemia and other risk factors. We review existent medications for RASi therapy and show research on novel drugs, including small molecules and nanodelivery strategies that can target the brain RAS with potential high specificity. We hope that further research into the brain RAS function and modulation will lead to innovative therapies that can finally improve AD neurodegeneration.

Angiotensin-II Modulates GABAergic Neurotransmission in the Mouse Substantia Nigra

GABAergic projections neurons of the substantia nigra reticulata (SNr), through an extensive network of dendritic arbors and axon collaterals, provide robust inhibitory input to neighboring dopaminergic neurons in the substantia nigra compacta (SNc). Angiotensin-II (Ang-II) receptor signaling increases SNc dopaminergic neuronal sensitivity to insult, thus rendering these cells susceptible to dysfunction and destruction. However, the mechanisms by which Ang-II regulates SNc dopaminergic neuronal activity are unclear. Given the complex relationship between SN dopaminergic and GABAergic neurons, we hypothesized that Ang-II could regulate SNc dopaminergic neuronal activity directly and indirectly by modulating SNr GABAergic neurotransmission. Here, using transgenic mice, slice electrophysiology, and optogenetics, we provide evidence of an AT₁ receptor-mediated signaling mechanism in SNr GABAergic neurons where Ang-II suppresses electrically-evoked neuronal output by facilitating postsynaptic GABA_A receptors (GABA_ARs) and prolonging the action potential (AP) duration. Unexpectedly, Ang-II had no discernable effects on the electrical properties of SNc dopaminergic neurons. Also, and indicating a nonlinear relationship between electrical activity and neuronal output, following phasic photoactivation of SNr GABAergic neurons, Ang-II paradoxically enhanced the feedforward inhibitory input to SNc dopaminergic neurons. In sum, our observations describe an increasingly complex and heterogeneous response of the SN to Ang-II by revealing cell-specific responses and nonlinear effects on intranigral GABAergic neurotransmission. Our data further implicate the renin-angiotensin-system (RAS) as a functionally relevant neuromodulator in the substantia nigra, thus underscoring a need for additional inquiry.

Soluble (pro)renin receptor induces endothelial dysfunction and hypertension in mice with diet-induced obesity via activation of angiotensin II type 1 receptor

Until now, renin-angiotensin system (RAS) hyperactivity was largely thought to result from angiotensin II (Ang II)-dependent stimulation of the Ang II type 1 receptor (AT1R). Here we assessed the role of soluble (pro)renin receptor (sPRR), a product of site-1 protease-mediated cleavage of (pro)renin receptor (PRR), as a possible ligand of the AT1R in mediating: (i) endothelial cell dysfunction in vitro and (ii) arterial dysfunction in mice with diet-induced obesity. Primary human umbilical vein endothelial cells (HUVECs) treated with a recombinant histidine-tagged sPRR (sPRR-His) exhibited IκBα degradation concurrent with NF-κB p65 activation. These responses were secondary to sPRR-His evoked elevations in Nox4-derived H2O2 production that resulted in inflammation, apoptosis and reduced NO production. Each of these sPRR-His-evoked responses was attenuated by AT1R inhibition using Losartan (Los) but not ACE inhibition using captopril (Cap). Further mechanistic exploration revealed that sPRR-His activated AT1R downstream Gq signaling pathway. Immunoprecipitation coupled with autoradiography experiments and radioactive ligand competitive binding assays indicate sPRR directly interacts with AT1R via Lysine199 and Asparagine295. Important translational relevance was provided by findings from obese C57/BL6 mice that sPRR-His evoked endothelial dysfunction was sensitive to Los. Besides, sPRR-His elevated blood pressure in obese C57/BL6 mice, an effect that was reversed by concurrent treatment with Los but not Cap. Collectively, we provide solid evidence that the AT1R mediates the functions of sPRR during obesity-related hypertension. Inhibiting sPRR signaling should be considered further as a potential therapeutic intervention in the treatment and prevention of cardiovascular disorders involving elevated blood pressure.

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.

Involvement of dopaminergic signaling in the cross talk between the renin-angiotensin system and inflammation

The renin-angiotensin system (RAS) is a fundamental regulator of blood pressure and has emerged as an important player in the control of inflammatory processes. Accordingly, imbalance on RAS components either systemically or locally might trigger the development of inflammatory disorders by affecting immune cells. At the same time, alterations in the dopaminergic system have been consistently involved in the physiopathology of inflammatory disorders. Accordingly, the interaction between the RAS and the dopaminergic system has been studied in the context of inflammation of the central nervous system (CNS), kidney, and intestine, where they exert antagonistic actions in the regulation of the immune system. In this review, we summarized, integrated, and discussed the cross talk of the dopaminergic system and the RAS in the regulation of inflammatory pathologies, including neurodegenerative disorders, such as Parkinson’s disease. We analyzed the molecular mechanisms underlying the interaction between both systems in the CNS and in systemic pathologies. Moreover, we also analyzed the impact of the commensal microbiota in the regulation of RAS and dopaminergic system and how it is involved in inflammatory disorders. Furthermore, we summarized the therapeutic approaches that have yielded positive results in preclinical or clinical studies regarding the use of drugs targeting the RAS and dopaminergic system for the treatment of inflammatory conditions. Further understanding of the molecular and cellular regulation of the RAS-dopaminergic cross talk should allow the formulation of new therapies consisting of novel drugs and/or repurposing already existing drugs, alone or in combination, for the treatment of inflammatory disorders.

Association of Antihypertensive Medication with Retinal Nerve Fiber Layer and Ganglion Cell-Inner Plexiform Layer Thickness

PURPOSE

To evaluate the association between different classes of antihypertensive medication with retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GC-IPL) thickness in a nonglaucomatous multiethnic Asian population.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

A total of 9144 eyes for RNFL analysis (2668 Malays, 3554 Indians, and 2922 Chinese) and 8549 eyes for GC-IPL analysis (2460 Malays, 3230 Indians, and 2859 Chinese) aged 44 to 86 years.

METHODS

Participants underwent standardized systemic and ocular examinations and interviewer-administered questionnaires for collection of data on medication and other variables. Intraocular pressure (IOP) readings were obtained by Goldmann applanation tonometry before pupil dilation for fundoscopy and OCT imaging. Blood pressure (BP) was measured with an automatic BP monitor. Mean arterial pressure (MAP) was defined as diastolic BP plus 1/3 (systolic BP - diastolic BP). Regression models were used to investigate the association of antihypertensive medication with OCT measurements of RNFL and GC-IPL.

MAIN OUTCOME MEASURES

Average and sectoral RNFL and GC-IPL thickness.

RESULTS

After adjusting for age, gender, ethnicity, MAP, IOP, body mass index (BMI), and presence of diabetes, we found that participants taking any type of antihypertensive medication (β = -0.83; 95% confidence interval [CI], -1.46 to -0.02; P = 0.01), specifically angiotensin-converting enzyme inhibitors (ACEIs) (β = -1.66; 95% CI, -2.57 to -0.75; P < 0.001) or diuretics (β = -1.38; 95% CI, -2.59 to -0.17; P < 0.05), had thinner average RNFL in comparison with participants who were not receiving antihypertensive treatment. Use of a greater number of antihypertensive medications was significantly associated with thinner average RNFL (P for trend = 0.001). This association was most evident in the inferior RNFL quadrant in participants using ACEIs (β = -2.44; 95% CI, -3.99 to -0.89; P = 0.002) or diuretics (β = -2.76; 95% CI, -4.76 to -0.76; P = 0.007). A similar trend was noted in our analysis of macular GC-IPL thickness.

CONCLUSIONS

Use of 2 or more antihypertensive medications, ACEI, and diuretics were associated with a loss of structural markers of retinal ganglion cell health in a multiethnic Asian population.

Effect of Captopril on Brain Oxidative Damage in Pentylenetetrazole-Induced Seizures in Mice

Background: Frequent seizure is followed by overproduction of free radicals and brain oxidative stress. Renin angiotensin system (RAS) has some effects on central nervous system. We designed this research to challenge the effect of captopril as an angiotensin converting enzyme (ACE) inhibitor against brain oxidative stress in pentylenetetrazole (PTZ) -induced seizures in mice. Methods: The groups were including (1) Control (saline); (2) PTZ (100 mg/kg, i.p.), (3-5) PTZ- captopril (Capto) that received three doses of Capto 10, 50 and 100 mg/kg 30 min before PTZ injection. Latency time in the onset minimal clonic seizures (MCS) and generalized tonic-clonic seizures (GTCS) were recorded. The level of malondialdehyde (MDA) and total thiol, as well as superoxide dismutase (SOD) and catalase (CAT) activity in the hippocampus and cortex were measured. Results: All doses of captopril postponed the onset of MCS and GTCS. Accumulation of MDA in the brain tissues of PTZ group was higher than control group, while total thiol content and CAT activity were lower. Pretreatment with captopril (100 mg/kg) diminished MDA concentration compared with PTZ group. Captopril (50 and 100 mg/kg) also increased the level of total thiol groups versus PTZ group. Captopril injection (50 and 100 mg/kg) elevated the activity of SOD and CAT in the brain tissues. In addition captopril administration diminished mortality rate caused by PTZ. Conclusion: Findings demonstrated that convulsions caused by PTZ were followed by oxidative stress status in the brain tissues. Pretreatment with captopril attenuated the effect of PTZ on brain tissue oxidative damage.<br />

Glial α-synuclein promotes neurodegeneration characterized by a distinct transcriptional program in vivo

α-Synucleinopathies are neurodegenerative diseases that are characterized pathologically by α-synuclein inclusions in neurons and glia. The pathologic contribution of glial α-synuclein in these diseases is not well understood. Glial α-synuclein may be of particular importance in multiple system atrophy (MSA), which is defined pathologically by glial cytoplasmic α-synuclein inclusions. We have previously described Drosophila models of neuronal α-synucleinopathy, which recapitulate key features of the human disorders. We have now expanded our model to express human α-synuclein in glia. We demonstrate that expression of α-synuclein in glia alone results in α-synuclein aggregation, death of dopaminergic neurons, impaired locomotor function, and autonomic dysfunction. Furthermore, co-expression of α-synuclein in both neurons and glia worsens these phenotypes as compared to expression of α-synuclein in neurons alone. We identify unique transcriptomic signatures induced by glial as opposed to neuronal α-synuclein. These results suggest that glial α-synuclein may contribute to the burden of pathology in the α-synucleinopathies through a cell type-specific transcriptional program. This new Drosophila model system enables further mechanistic studies dissecting the contribution of glial and neuronal α-synuclein in vivo, potentially shedding light on mechanisms of disease that are especially relevant in MSA but also the α-synucleinopathies more broadly.

Inhibition of Autophagy by Captopril Attenuates Prion Peptide-Mediated Neuronal Apoptosis via AMPK Activation

Accumulation of prion protein (PrPc) into a protease-resistant form (PrPsc) in the brains of humans and animals affects the central nervous system. PrPsc occurs only in mammals with transmissible prion diseases. Prion protein refers to either the infectious pathogen itself or the main component of the pathogen. Recent studies suggest that autophagy is one of the major functions that keep cells alive and which has a protective effect against neurodegeneration. In this study, we investigated whether the anti-hypertensive drug, captopril, could attenuate prion peptide PrP (106-126)-induced calcium alteration-mediated neurotoxicity. Treatment with captopril increased both LC3-II (microtubule-associated protein 1A/1B-light chain 3-II) and p62 protein levels, indicating autophagy flux inhibition. Electron microscopy confirmed the occurrence of autophagic flux inhibition in neuronal cells treated with captopril. Captopril attenuated PrP (106-126)-induced neuronal cell death via AMPK activation and autophagy inhibition. Compound C suppressed AMPK activation as well as the neuroprotective effects of captopril. Thus, these data showed that an anti-hypertensive drug has a protective effect against prion-mediated neuronal cell death via autophagy inhibition and AMPK activation, and also suggest that anti-hypertensive drugs may be effective therapeutic agents against neurodegenerative disorders, including prion diseases.

Bradykinin-potentiating PEPTIDE-10C, an argininosuccinate synthetase activator, protects against H2O2-induced oxidative stress in SH-SY5Y neuroblastoma cells

Bradykinin-potentiating peptides (BPPs - 5a, 7a, 9a, 10c, 11e, and 12b) of Bothrops jararaca (Bj) were described as argininosuccinate synthase (AsS) activators, improving l-arginine availability. Agmatine and polyamines, which are l-arginine metabolism products, have neuroprotective properties. Here, we investigated the neuroprotective effects of low molecular mass fraction from Bj venom (LMMF) and two synthetic BPPs (BPP-10c, <ENWPHPQIPP; BPP-12b, <EWGRPPGPPIPP) in the SH-SY5Y cell line against H₂O₂-induced oxidative stress. The neuroprotective effects against H₂O₂-induced were analyzed by reactive oxygen species (ROS - DCFH) production; lipid peroxidation (TBARS); intracellular GSH; AsS, iNOS, and NF-kB expressions; nitrite levels (Griess); mitochondrial membrane potential (TMRM); and antioxidant activity (DPPH). Analysis of variance followed by Tukey's post hoc test were calculated for statistical comparisons. Pre-treatment with both BPPs significantly reduced cell death induced by H₂O₂, but BPP-10c showed higher protective capacity than BPP-12b. LMMF pretreatment was unable to prevent the reduction of cell viability caused by H₂O₂. The neuroprotective mechanism of BPP-10c against oxidative stress was investigated. BPP-10c reduced ROS generation and lipid peroxidation in relation to cells treated only with H₂O₂. BBP-10c increased AsS expression and was not neuroprotective in the presence of MDLA, a specific inhibitor of AsS. BPP-10c reduced iNOS expression and nitrate levels but decreased NF-kB expression. Furthermore, BPP-10c protected the mitochondrial membrane against oxidation. Overall, we demonstrated for the first time neuroprotective mechanisms of BPPs against oxidative stress, opening new perspectives to the study and application of these peptides for the treatment of neurodegenerative diseases.

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.

Azilsartan ameliorates apoptosis of dopaminergic neurons and rescues characteristic parkinsonian behaviors in a rat model of Parkinson's disease

Loss of dopaminergic neurons within the substantia nigra (SN) is a pathological hallmark of Parkinsons disease (PD), which leads to the onset of motor symptoms. Previously, our in vitro studies revealed that Angiotensin II (Ang II) induced apoptosis of dopaminergic neurons through its type 1 receptor (AT1R), but these findings needed to be confirmed via animal experiments. Here, using a rotenone-induced rat model of PD, we observed an overactivation of Ang II/AT1R axis in the SN, since Ang II level and AT1R expression were markedly increased. Furthermore, we provided in vivo evidence that Ang II directly elicited apoptosis of dopaminergic neurons via activation of AT1R in the SN of rats. More importantly, we showed for the first time that oral administration of azilsartan, a newly developed AT1R blocker approved by the U.S. Food and Drug Administration for hypertension treatment, rescued the apoptosis of dopaminergic neurons and relieved the characteristic parkinsonian symptoms in PD rats. These results support the application of AT1R blockers in PD therapy, and strengthen the notion that many therapeutic agents may possess pleiotropic action in addition to their main applications.

Paracrine and Intracrine Angiotensin 1-7/Mas Receptor Axis in the Substantia Nigra of Rodents, Monkeys, and Humans

In addition to the classical hormonal (tissue-to-tissue) renin-angiotensin system (RAS), there are a paracrine (cell-to-cell) and an intracrine (intracellular/nuclear) RAS. A local paracrine brain RAS has been associated with several brain disorders, including Parkinson’s disease (PD). Classically, angiotensin II (Ang II) is the main RAS effector peptide and acts through two major receptors: Ang II type 1 and 2 (AT1 and AT2) receptors. It has been shown that enhanced activation of the Ang II/AT1 axis exacerbates dopaminergic cell death. Several new components of the RAS have more recently been discovered. However, the role of new Ang 1-7/Mas receptor RAS component was not investigated in the brain and particularly in the dopaminergic system. In the present study, we observed Mas receptor labeling in dopaminergic neurons and glial cells in rat mesencephalic primary cultures; substantia nigra of rats, monkeys, and humans; and human induced pluripotent stem (iPS) cells derived from healthy controls and sporadic PD patients. The present data support a neuroprotective role of the Ang 1-7/Mas receptor axis in the dopaminergic system. We observed that this axis is downregulated with aging, which may contribute to the aging-related vulnerability to neurodegeneration. We have also identified an intracellular Ang 1-7/Mas axis that modulates mitochondrial and nuclear levels of superoxide. The present data suggest that nuclear RAS receptors regulate the adequate balance between the detrimental and the protective arms of the cell RAS. The results further support that the brain RAS should be taken into account for the design of new therapeutic strategies for PD.

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.

Use of ACE-inhibitors and falls in patients with Parkinson's disease

Falls represent a major concern in patients with Parkinson's disease (PD); however, currently acknowledged treatments for PD are not effective in reducing the risk of falling. The aim was to assess the association of use of ACE-inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) with falls among patients with PD. We analysed data of 194 elderly with PD attending a geriatric Day Hospital. Self-reported history of falls that occurred over the last year, as well as use of drugs, including ACEIs and angiotensin II receptor blockers (ARBs) were recorded. The association of the occurrence of any falls with use of ACEIs, and ARBs was assessed by logistic regression analysis. The association between the number of falls and use of ACEIs, and ARBs was assessed according to Poisson regression. In logistic regression, after adjusting for potential confounders, use of ACEIs was associated with a reduced probability of falling over the last year (OR=0.15, 95% CI=0.03-0.81; P=0.028). This association did not vary with blood pressure levels (P for the interaction term=0.528). Also, using Poisson regression, use of ACEIs predicted a reduced number of falls among participants who fell (PR=0.31; 95% CI=0.10-0.94; P=0.039). No association was found between use of ARBs and falls. Our results indicate that use of ACEIs might be independently associated with reduced probability, and a reduced number of falls among patients with PD. Dedicated studies are needed to define the single agents and dosages that might most effectively reduce the risk of falling in clinical practice.

Water-Soluble Fullerene Derivatives as Brain Medicine: Surface Chemistry Determines If They Are Neuroprotective and Antitumor

Delivering drugs to the central nervous system (CNS) is a major challenge in treating CNS-related diseases. Nanoparticles that can cross blood-brain barrier (BBB) are potential tools. In this study, water-soluble C₆₀ fullerene derivatives with different types of linkages between the fullerene cage and the solubilizing addend were synthesized (compounds 1-3: C-C bonds, compounds 4-5: C-S bonds, compound 6: C-P bonds, and compounds 7-9: C-N bonds). Fullerene derivatives 1-6 were observed to induce neural stem cell (NSC) proliferation in vitro and rescue the function of injured CNS in zebrafish. Fullerene derivatives 7-9 were found to inhibit glioblastoma cell proliferation in vitro and reduce glioblastoma formation in zebrafish. These effects were correlated with the cell metabolic changes. Particularly, compound 3 bearing residues of phenylbutiryc acids significantly promoted NSC proliferation and neural repair without causing tumor growth. Meanwhile, compound 7 with phenylalanine appendages significantly inhibited glioblastoma growth without retarding the neural repair. We conclude that the surface functional group determines the properties as well as the interactions of C₆₀ with NSCs and glioma cells, producing either a neuroprotective or antitumor effect for possible treatment of CNS-related diseases.

Macrophages in neuroinflammation: role of the renin-angiotensin-system

Macrophages are essential players of the innate immune system which are involved in the initiation and progression of various inflammatory and autoimmune diseases including neuroinflammation. In the past few years, it has become increasingly clear that the regulation of macrophage responses by the local tissue milieu is also influenced by mediators which were first discovered as regulators in the nervous or also cardiovascular system. Here, the renin-angiotensin system (RAS) is a major focus of current research. Besides its classical role in blood pressure control, body fluid, and electrolyte homeostasis, the RAS may influence (auto)immune responses, modulate T cells, and particularly act on macrophages via different signaling pathways. Activation of classical RAS pathways including angiotensin (Ang) II and AngII type 1 (AT₁R) receptors may drive pro-inflammatory macrophage responses in neuroinflammation via regulation of chemokines. More recently, alternative RAS pathways were described, such as binding of Ang-(1-7) to its receptor Mas. Signaling via Mas pathways may counteract some of the AngII/AT₁R-mediated effects. In macrophages, the Ang-(1-7)/Mas exerts beneficial effects on neuroinflammation via modulating macrophage polarization, migration, and T cell activation in vitro and in vivo. These data delineate a pivotal role of the RAS in inflammation of the nervous system and identify RAS modulation as a potential new target for immunotherapy with a special focus on macrophages.

New and old roles of the peripheral and brain renin-angiotensin-aldosterone system (RAAS): Focus on cardiovascular and neurological diseases

It is commonly accepted that the renin-angiotensin-aldosterone system (RAAS) is a cardiovascular circulating hormonal system that plays also an important role in the modulation of several patterns in the brain. The pathway of the RAAS can be divided into two classes: the traditional pathway of RAAS, also named classic RAAS, and the non-classic RAAS. Both pathways play a role in both cardiovascular and neurological diseases through a peripheral or central control. In this regard, renewed interest is growing in the last years for the consideration that the brain RAAS could represent a new important therapeutic target to regulate not only the blood pressure via central nervous control, but also neurological diseases. However, the development of compounds able to cross the blood-brain barrier and to act on the brain RAAS is challenging, especially if the metabolic stability and the half-life are taken into consideration. To date, two drug classes (aminopeptidase type A inhibitors and angiotensin IV analogues) acting on the brain RAAS are in development in pre-clinical or clinical stages. In this article, we will present an overview of the biological functions played by peripheral and brain classic and non-classic pathways of the RAAS in several clinical conditions, focusing on the brain RAAS and on the new pharmacological targets of the RAAS.

Menopause and Parkinson's disease. Interaction between estrogens and brain renin-angiotensin system in dopaminergic degeneration

The neuroprotective effects of menopausal hormonal therapy in Parkinson's disease (PD) have not yet been clarified, and it is controversial whether there is a critical period for neuroprotection. Studies in animal models and clinical and epidemiological studies indicate that estrogens induce dopaminergic neuroprotection. Recent studies suggest that inhibition of the brain renin-angiotensin system (RAS) mediates the effects of estrogens in PD models. In the substantia nigra, ovariectomy induces a decrease in levels of estrogen receptor-α (ER-α) and increases angiotensin activity, NADPH-oxidase activity and expression of neuroinflammatory markers, which are regulated by estrogen replacement therapy. There is a critical period for the neuroprotective effect of estrogen replacement therapy, and local ER-α and RAS play a major role. Astrocytes play a major role in ER-α-induced regulation of local RAS, but neurons and microglia are also involved. Interestingly, treatment with angiotensin receptor antagonists after the critical period induced neuroprotection.

Angiotensin-(1-7) protects from brain damage induced by shiga toxin 2-producing enterohemorrhagic Escherichia coli

Shiga toxin 2 (Stx2)-producing enterohemorrhagic induced brain damage. Since a cerebroprotective action was reported for angiotensin (Ang)-(1-7), our aim was to investigate whether Ang-(1-7) protects from brain damage induced by Stx2-producing enterohemorrhagic Escherichia coli The anterior hypothalamic area of adult male Wistar rats was injected with saline solution or Stx2 or Stx2 plus Ang-(1-7) or Stx2 plus Ang-(1-7) plus A779. Rats received a single injection of Stx2 at the beginning of the experiment, and Ang-(1-7), A779, or saline was administered daily in a single injection for 8 days. Cellular ultrastructural changes were analyzed by transmission electron microscopy. Stx2 induced neurodegeneration, axonal demyelination, alterations in synapse, and oligodendrocyte and astrocyte damage, accompanied by edema. Ang-(1-7) prevented neuronal damage triggered by the toxin in 55.6 ± 9.5% of the neurons and the Stx2-induced synapse dysfunction was reversed. In addition, Ang-(1-7) blocked Stx2-induced demyelination in 92 ± 4% of the axons. Oligodendrocyte damage caused by Stx2 was prevented by Ang-(1-7) but astrocytes were only partially protected by the peptide (38 ± 5% of astrocytes were preserved). Ang-(1-7) treatment resulted in 50% reduction in the number of activated microglial cells induced by Stx2, suggesting an anti-inflammatory action. All these beneficial effects elicited by Ang-(1-7) were blocked by the Mas receptor antagonist and thus it was concluded that Ang-(1-7) protects mainly neurons and oligodendrocytes, and partially astrocytes, in the central nervous system through Mas receptor stimulation.

Delayed protective effect of telmisartan on lung ischemia/reperfusion injury in valve replacement operations

The present study aimed to investigate the delayed protective effect of telmisartan on lung ischemic/reperfusion injury in patients undergoing heart valve replacement operations. In total, 180 patients diagnosed with rheumatic valve diseases were randomly divided into the telmisartan (T), captopril (C) and placebo (P) groups. In the telmisartan group, the patients were pretreated with telmisartan (1 mg/kg/day), at the time period 96-48 h before the operation, whereas in the C group, the patients were treated with captopril (1 mg/kg/day) at the time period 96-48 h prior to the operation control group. Each drug treatment group included a corresponding placebo treatment. The variables pulmonary vascular resistance (PVR) and A-aDO₂ were measured prior to CPB and at 1, 3, 6 and 12 h after CPB. Pulmonary neutrophil (PMN) count in the left and right atrium blood as well as SOD malondialdehyde (MDA), NO, angiotensin II (AngII) value in the left atrium blood, were measured 30 min prior to and after CPB. The PVR parameters of the telmisartan and captopril groups were significantly lower than those of the placebo group (P<0.05). The A-aDO₂ values in the telmisartan and captopril groups were significantly lower than those in the placebo group at 1, 3 and 6 h following CPB treatment. The difference between the right and left atrium blood PMN was significantly lower in the telmisartan and captopril intervention groups compared to that in the placebo group 30 min following CPB treatment. The left atrium blood SOD and NO values were significantly higher, whereas the MDA value was significantly lower in the telmisartan group compared to the control group 30 min following CPB treatment. As for AngII, there was no difference between the C and T groups, compared with the P group. In the two groups 30 min after treatment with CPB, 24 patients experienced varying degrees of cough, with the telmisartan group showing a significant difference (P<0.05). The hospitalization time was compared in the three groups of patients and it was found to be significantly shorter in the telmisartan group than the captopril and placebo groups (P<0.05). In conclusion, it was found that for the time period 96-48 h before heart valve replacement operations telmisartan (1 mg/kg/day) delayed the protective effect on lung ischemia/reperfusion injury in patients with rheumatic valve diseases. The results of the present study indicated that the protective effect may be associated with the increment of endogenetic NO and the enhanced ability against lipid peroxidation.

Future prospects of antibacterial metal nanoparticles as enzyme inhibitor

Nanoparticles are being widely used as antibacterial agents with metal nanoparticles emerging as the most efficient antibacterial agents. There have been many studies which have reported the mechanism of antibacterial activity of nanoparticles on bacteria. In this review we aim to emphasize on all the possible mechanisms which are involved in the antibacterial activity of nanoparticles and also to understand their mode of action and role as bacterial enzyme inhibitor by comparing their antibacterial mechanism to that of antibiotics with enzyme inhibition as a major mechanism. With the emergence of widespread antibiotic resistance, nanoparticles offer a better alternative to our conventional arsenal of antibiotics. Once the biological safety of these nanoparticles is addressed, these nanoparticles can be of great medical importance in our fight against bacterial infections.

Subjective and Cardiovascular Effects of Intravenous Methamphetamine during Perindopril Maintenance: A Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study

BACKGROUND

Our pilot study suggested that the angiotensin-converting enzyme inhibitor perindopril might reduce some subjective effects produced by i.v. methamphetamine. We characterized the impact of a wider range of perindopril doses on methamphetamine-induced effects in a larger group of non-treatment-seeking, methamphetamine-using volunteers.

METHODS

Before treatment, participants received 30mg methamphetamine. After 5 to 7 days of perindopril treatment (0, 4, 8, or 16mg/d), participants received 15 and 30mg of methamphetamine on alternate days. Before and after treatment, participants rated subjective effects and cardiovascular measures were collected.

RESULTS

Prior to treatment with perindopril, there were no significant differences between treatment groups on maximum or peak subjective ratings or on peak cardiovascular effects. Following perindopril treatment, there were significant main effects of treatment on peak subjective ratings of "anxious" and "stimulated"; compared to placebo treatment, treatment with 8mg perindopril significantly reduced peak ratings of both anxious (P=.0009) and stimulated (P=.0070). There were no significant posttreatment differences between groups on peak cardiovascular effects.

CONCLUSIONS

Moderate doses of perindopril (8mg) significantly reduced peak subjective ratings of anxious and stimulated as well as attenuated many other subjective effects produced by methamphetamine, likely by inhibiting angiotensin II synthesis. Angiotensin II is known to facilitate the effects of norepinephrine, which contributes to methamphetamine's subjective effects. The lack of a classic dose-response function likely results from either nonspecific effects of perindopril or from between-group differences that were not accounted for in the current study (i.e., genetic variations and/or caffeine use). The current findings suggest that while angiotensin-converting enzyme inhibitors can reduce some effects produced by methamphetamine, more consistent treatment effects might be achieved by targeting components of the renin-angiotensin system that are downstream of angiotensin-converting enzyme.

Aging of perennial cells and organ parts according to the programmed aging paradigm

If aging is a physiological phenomenon-as maintained by the programmed aging paradigm-it must be caused by specific genetically determined and regulated mechanisms, which must be confirmed by evidence. Within the programmed aging paradigm, a complete proposal starts from the observation that cells, tissues, and organs show continuous turnover: As telomere shortening determines both limits to cell replication and a progressive impairment of cellular functions, a progressive decline in age-related fitness decline (i.e., aging) is a clear consequence. Against this hypothesis, a critic might argue that there are cells (most types of neurons) and organ parts (crystalline core and tooth enamel) that have no turnover and are subject to wear or manifest alterations similar to those of cells with turnover. In this review, it is shown how cell types without turnover appear to be strictly dependent on cells subjected to turnover. The loss or weakening of the functions fulfilled by these cells with turnover, due to telomere shortening and turnover slowing, compromises the vitality of the served cells without turnover. This determines well-known clinical manifestations, which in their early forms are described as distinct diseases (e.g., Alzheimer's disease, Parkinson's disease, age-related macular degeneration, etc.). Moreover, for the two organ parts (crystalline core and tooth enamel) without viable cells or any cell turnover, it is discussed how this is entirely compatible with the programmed aging paradigm.

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.

Efficient and biologically relevant consensus strategy for Parkinson's disease gene prioritization

BACKGROUND

The systemic information enclosed in microarray data encodes relevant clues to overcome the poorly understood combination of genetic and environmental factors in Parkinson's disease (PD), which represents the major obstacle to understand its pathogenesis and to develop disease-modifying therapeutics. While several gene prioritization approaches have been proposed, none dominate over the rest. Instead, hybrid approaches seem to outperform individual approaches.

METHODS

A consensus strategy is proposed for PD related gene prioritization from mRNA microarray data based on the combination of three independent prioritization approaches: Limma, machine learning, and weighted gene co-expression networks.

RESULTS

The consensus strategy outperformed the individual approaches in terms of statistical significance, overall enrichment and early recognition ability. In addition to a significant biological relevance, the set of 50 genes prioritized exhibited an excellent early recognition ability (6 of the top 10 genes are directly associated with PD). 40 % of the prioritized genes were previously associated with PD including well-known PD related genes such as SLC18A2, TH or DRD2. Eight genes (CCNH, DLK1, PCDH8, SLIT1, DLD, PBX1, INSM1, and BMI1) were found to be significantly associated to biological process affected in PD, representing potentially novel PD biomarkers or therapeutic targets. Additionally, several metrics of standard use in chemoinformatics are proposed to evaluate the early recognition ability of gene prioritization tools.

CONCLUSIONS

The proposed consensus strategy represents an efficient and biologically relevant approach for gene prioritization tasks providing a valuable decision-making tool for the study of PD pathogenesis and the development of disease-modifying PD therapeutics.

Peganum Harmala L. Extract Reduces Oxidative Stress and Improves Symptoms in 6-Hydroxydopamine-Induced Parkinson's Disease in Rats

Parkinson's disease is one of the most common neurodegenerative disorders. There are many documents about the effects of oxidative stress in Parkinson's disease etiology. Angiotensin II activates NADPH dependent oxidases and causes superoxides formation. Peganum harmala L. extract, which has angiotensin converting enzyme (ACE) inhibitory effect, is considered to evaluate oxidative stress inhibition and Parkinson's disease improvement. Male rats weighting 200-250 g were divided into 5 groups: Control, Neurotoxin (injection of 6-hydroxydopamine into left hemisphere substantia nigra), Peganum harmala's seeds aqueous extract (10 mg/kg) and captopril (5 mg/kg). Peganum harmala and captopril were injected intraperitonealy -144, -120, -96, -72, -48, -24, -2, 4 and 24 h relative to 6-hydroxydopamine injection time. Muscle stiffness, apomorphine induced unilateral rotation, amount of brain's protein oxidation and lipid peroxidation, ACE activity and histology of substantia nigra were assayed in all groups. Peganum harmala improved Muscle stiffness and one-direction rotation behavior significantly. It also reduced brain's lipid and protein oxidation levels in neurotoxin-injected rats significantly. In Peganum harmala group compared to control group, brain's ACE activity was significantly inhibited. In histological study, Peganum harmala prevented degeneration of dopaminergic neurons, too. In conclusion, aqueous extract of Peganum harmala could prevent symptoms and reduced oxidative stress markers in rats with Parkinson's disease induced by 6-hydroxydopamine.

Exercise and Nutritional Benefits in PD: Rodent Models and Clinical Settings

Physical exercise offers a highly effective health-endowering activity as has been evidence using rodent models of Parkinson's disease (PD). It is a particularly useful intervention in individuals employed in sedentary occupations or afflicted by a neurodegenerative disorder, such as PD. The several links between exercise and quality-of-life, disorder progression and staging, risk factors and symptoms-biomarkers in PD all endower a promise for improved prognosis. Nutrition provides a strong determinant for disorder vulnerability and prognosis with fish oils and vegetables with a mediterranean diet offering both protection and resistance. Three factors determining the effects of exercise on disorder severity of patients may be presented: (i) Exercise effects upon motor impairment, gait, posture and balance, (ii) Exercise reduction of oxidative stress, stimulation of mitochondrial biogenesis and up-regulation of autophagy, and (iii) Exercise stimulation of dopamine (DA) neurochemistry and trophic factors. Running-wheel performance, as measured by distance run by individual mice from different treatment groups, was related to DA-integrity, indexed by striatal DA levels. Finally, both nutrition and exercise may facilitate positive epigenetic outcomes, such as lowering the dosage of L-Dopa required for a therapeutic effect.

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.

Viral transduction of renin rapidly establishes persistent hypertension in diverse murine strains

Mice provide a unique platform to dissect disease pathogenesis, with the availability of recombinant inbred strains and diverse genetically modified strains. Leveraging these reagents to elucidate the mechanisms of hypertensive tissue injury has been hindered by difficulty establishing persistent hypertension in these inbred lines. ANG II infusion provides relatively short-term activation of the renin-angiotensinogen system (RAS) with concomitant elevated arterial pressure. Longer-duration studies using renin transgenic mice are powerful models of chronic hypertension, yet are limited by the genetic background on which the transgene exists and the exposure throughout development. The present studies characterized hypertension produced by transduction with a renin-coding adeno-associated virus (ReninAAV). ReninAAV mice experienced elevated circulating renin with concurrent elevations in arterial pressure. Following a single injection of ReninAAV, arterial pressure increased on average +56 mmHg, an increase that persisted for at least 12 wk in three distinct and widely used strains of adult mice: 129/S6, C56BL/6, and DBA/2J. This was accomplished without surgical implantation of pumps or complex breeding and backcrossing. In addition, ReninAAV mice developed pathophysiological changes associated with chronic hypertension, including increased heart weight and albuminuria. Thus ReninAAV provides a unique tool to study the onset of and effects of persistent hypertension in diverse murine models. This model should facilitate our understanding of the pathogenesis of hypertensive injury.

Angiotensin-(1-7): beyond its central effects on blood pressure

Angiotensin (Ang) (1-7) is the main component of the depressor and protective arm of the renin-angiotensin system. Ang-(1-7) induces vasodilation, natriuresis and diuresis, cardioprotection, inhibits angiogenesis and cell growth and opposes the pressor, proliferative, profibrotic, and prothrombotic actions mediated by Ang II. Centrally, Ang-(1-7) induces changes in mean arterial pressure and this effect may be linked with its inhibitory neuromodulatory action on norepinephrine neurotransmission. The present review is focused on the role of Ang-(1-7) as a protective agent in the brain.