The brain RAS and Alzheimer's disease

Signaling pathways and genetics of brain Renin angiotensin system in psychiatric disorders: State of the art

Along the conventional pathways, Renin-angiotensin system (RAS) plays a key role in the physiology of the CNS and pathogenesis of psychiatric diseases. RAS is a complex regulatory pathway which is composed of several peptides and receptors and comprises two counter-regulatory axes. The classical (ACE1/AngII/AT1 receptor) axis and the contemporary (ACE2/Ang (1-7)/Mas receptor) axis. The genes coding for elements of both axes have been broadly studied. Numerous functional polymorphisms on components of RAS have been identified to serve as informative disease and treatment markers. This review summarizes the role of each peptide and receptor in the pathophysiology of psychiatric disorders (depression, bipolar disorders and schizophrenia), followed by a concise look at the role of genetic polymorphism of the RAS in the pathophysiology of these disorders.

Angiotensin Receptor Blockers and Cognition: a Scoping Review

PURPOSE OF REVIEW

To provide an overview of the association between angiotensin II receptor blocker (ARB) use and cognitive outcomes.

RECENT FINDINGS

ARBs have previously shown greater neuroprotection compared to other anti-hypertensive classes. The benefits are primarily attributed to the ARB's effect on modulating the renin-angiotensin system via inhibiting the Ang II/AT1R pathway and activating the Ang II/AT2R, Ang IV/AT4R, and Ang-(1-7)/MasR pathways. These interactions are associated with pleiotropic neurocognitive benefits, including reduced β-amyloid accumulation and abnormal hyperphosphorylation of tau, ameliorated brain hypo-fusion, reduced neuroinflammation and synaptic dysfunction, better neurotoxin clearing, and blood-brain barrier function restoration. While ACEis also inhibit AT1R, they simultaneously lower Ang II and block the Ang II/AT2R and Ang IV/AT4R pathways that counterbalance the potential benefits. ARBs may be considered an adjunctive approach for neuroprotection. This preliminary evidence, coupled with their underlying mechanistic pathways, emphasizes the need for future long-term randomized trials to yield more definitive results.

Therapeutic Implications of Renin-Angiotensin System Modulators in Alzheimer's Dementia

The Renin-Angiotensin System (RAS) has attracted considerable interest beyond its traditional cardiovascular role due to emerging data indicating its potential involvement in neurodegenerative diseases, including Alzheimer's dementia (AD). This review investigates the therapeutic implications of RAS modulators, specifically focusing on angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), and renin inhibitors in AD. ACEIs, commonly used for hypertension, show promise in AD by reducing angiotensin (Ang) II levels. This reduction is significant as Ang II contributes to neuroinflammation, oxidative stress, and β-amyloid (Aβ) accumulation, all implicated in AD pathogenesis. ARBs, known for vasodilation, exhibit neuroprotection by blocking Ang II receptors, improving cerebral blood flow and cognitive decline in AD models. Renin inhibitors offer a novel approach by targeting the initial RAS step, displaying anti-inflammatory and antioxidant effects that mitigate AD degeneration. Preclinical studies demonstrate RAS regulation's favorable impact on neuroinflammation, neuronal damage, cognitive function, and Aβ metabolism. Clinical trials on RAS modulators in AD are limited, but with promising results, ARBs being more effective that ACEIs in reducing cognitive decline. The varied roles of ACEIs, ARBs, and renin inhibitors in RAS modulation present a promising avenue for AD therapeutic intervention, requiring further research to potentially transform AD treatment strategies.

Brain Renin-Angiotensin System: From Physiology to Pathology in Neuronal Complications Induced by SARS-CoV-2

Angiotensin-converting enzyme 2 (ACE2), a key enzyme in the renin-angiotensin system (RAS), is expressed in various tissues and organs, including the central nervous system (CNS). The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease-2019 (COVID-19), binds to ACE2, which raises concerns about the potential for viral infection in the CNS. There are numerous reports suggesting a link between SARS-CoV-2 infection and neurological manifestations. This study aimed to present an updated review of the role of brain RAS components, especially ACE2, in neurological complications induced by SARS-CoV-2 infection. Several routes of SARS-CoV-2 entry into the brain have been proposed. Because an anosmia condition appeared broadly in COVID-19 patients, the olfactory nerve route was suggested as an early pathway for SARS-CoV-2 entry into the brain. In addition, a hematogenous route via disintegrations in the blood-brain barrier following an increase in systemic cytokine and chemokine levels and retrograde axonal transport, especially via the vagus nerve innervating lungs, have been described. Common nonspecific neurological symptoms in COVID-19 patients are myalgia, headache, anosmia, and dysgeusia. However, more severe outcomes include cerebrovascular diseases, cognitive impairment, anxiety, encephalopathy, and stroke. Alterations in brain RAS components such as angiotensin II (Ang II) and ACE2 mediate neurological manifestations of SARS-CoV-2 infection, at least in part. Downregulation of ACE2 due to SARS-CoV-2 infection, followed by an increase in Ang II levels, leads to hyperinflammation and oxidative stress, which in turn accelerates neurodegeneration in the brain. Furthermore, ACE2 downregulation in the hypothalamus induces stress and anxiety responses by increasing corticotropin-releasing hormone. SARS-CoV-2 infection may also dysregulate the CNS neurotransmission, leading to neurological complications observed in severe cases of COVID-19. It can be concluded that the neurological manifestations of COVID-19 may be partially associated with changes in brain RAS components.

Role of angiotensin receptor blockers in the context of Alzheimer's disease

As the world's population ages, the prevalence of age-related neurological disorders such as Alzheimer's disease (AD) is increasing. There is currently no treatment for Alzheimer's disease, and the few approved medications have a low success rate in lowering symptoms. As a result, several attempts are underway worldwide to identify new targets for the therapy of Alzheimer's disease. In preclinical studies of Alzheimer's disease, it was recently found that inhibition of angiotensin-converting enzyme (ACE) and blocking of the angiotensin II receptors reduce symptoms of neurodegeneration, Aβ plaque development, and tau hyperphosphorylation. Angiotensin II type I (AT1) blockers, such as telmisartan, candesartan, valsartan, and others, have a wide safety margin and are commonly used to treat hypertension. Renal and cardiovascular failures are reduced due to their vascular protective actions. Inhibition of AT1 receptors in the brain has a neuroprotective impact in humans, reducing the risk of stroke, increasing cognition, and slowing the progression of Alzheimer's disease. The review focuses on the mechanisms via which AT1 blockers may act beneficially in Alzheimer's disease. Although their effect is evident in preclinical studies, clinical trials, on the other hand, are in short supply to validate the strategy. More dose-response experiments with possible AT1 blockers and brain-targeted administration will be needed in the future.

Unraveling the links between neurodegeneration and Epstein-Barr virus-mediated cell cycle dysregulation

The Epstein-Barr virus is a well-known cell cycle modulator. To establish successful infection in the host, EBV alters the cell cycle at multiple steps via antigens such as EBNAs, LMPs, and certain other EBV-encoded transcripts. Interestingly, several recent studies have indicated the possibility of EBV's neurotrophic potential. However, the effects and outcomes of EBV infection in the CNS are under-explored. Additionally, more and more epidemiological evidence implicates the cell-cycle dysregulation in neurodegeneration. Numerous hypotheses which describe the triggers that force post-mitotic neurons to re-enter the cell cycle are prevalent. Apart from the known genetic and epigenetic factors responsible, several reports have shown the association of microbial infections with neurodegenerative pathology. Although, studies implicating the herpesvirus family members in neurodegeneration exist, the involvement of Epstein-Barr virus (EBV), in particular, is under-evaluated. Interestingly, a few clinical studies have reported patients of AD or PD to be seropositive for EBV. Based on the findings mentioned above, in this review, we propose that EBV infection in neurons could drive it towards neurodegeneration through dysregulation of cell-cycle events and induction of apoptosis.

Exercise and Syzygium aromaticum reverse memory deficits, apoptosis and mitochondrial dysfunction of the hippocampus in Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD), the most common disease in the brain, is associated with cognitive and mitochondrial dysfunction. Emerging evidence suggests that endurance training and Syzygium aromaticum (L.) Merrill and Perry (Myrtaceae) (commonly referred to as clove) are effective interventions to maintain oxidative balance and improve cognitive function.

AIM OF THE STUDY

The present study aimed to investigate the effect of endurance training and clove oil affect spatial memory, apoptosis, mitochondrial homeostasis, and cognitive function in Alzheimer's rats.

MATERIALS AND METHODS

81 rats were randomly assigned to 9 groups: Healthy (H), sham (sh), Healthy-exercise (HE), Healthy-clove (HC), Healthy-exercise-clove (HEC), Alzheimer's (A), Alzheimer's-exercise (AE), Alzheimer's-clove (AC), and Alzheimer's-exercise-clove (AEC). Alzheimer's induction was induced by the injection of 1-42 amyloid into the CA1 region of the hippocampus. The exercise training protocol was performed for 3 weeks, every day for 30 min in swimming training, and clove oil supplementation (0.1 mg/kg) was gavaged daily for 3 weeks in the supplement rat. Shuttle box test was used to measure spatial memory after the last training session, and to determine the mRNAs and protein levels and apoptosis, Real-Time PCR, immunofluorescent, and tunnel methods were used, respectively.

RESULTS

Alzheimer's caused a significant decrease in the PRDX6 and GCN5L1 mRNAs and protein levels and a significant increase in apoptosis in the hippocampus of the Alzheimer's group compared to the control group (P = 0.001). Alzheimer's also reduced the time delay in entering the dark environment and increased the time spent in the dark environment (P = 0.001). Following endurance training and consumption of clove oil, spatial memory (P = 0.001), apoptosis (P = 0.001) and mRNAs and protein levels of PRDX6 (P = 0.001) and GCN5L1 (P = 0.017), were recovered in AE, AC and AEC groups, as compared with A group.

CONCLUSION

Swimming training and consumption of clove can possibly be considered as an effective intervention to maintain oxidative balance and improve mitochondrial homeostasis in Alzheimer's disease.

Ang(1-7) exerts Nrf2-mediated neuroprotection against amyloid beta-induced cognitive deficits in rodents

Alzheimer's disease (AD) is a neurodegenerative disorder with cognitive deficits in an individual. Ang(1-7) exhibits neuroprotection against amyloid beta (Aβ)-induced mitochondrial dysfunction and neurotoxicity in experimental conditions. Further, Ang(1-7) also exhibits nrf2-mediated antioxidant activity in experimental conditions. However, its therapeutic role on nrf2-mediated mitochondrial function is yet to be established in the Aβ-induced neurotoxicity. The experimental dementia was induced in the male rats by intracerebroventricular administration of Aβ_(1-42) on day-1 (D-1) of the experimental schedule of 14 days. Ang(1-7) was administered once daily from D-1 toD-14 to the Aβ-challenged rodents. Ang(1-7) attenuated Aβ-induced increase in escape latency and decrease in the time spent in the target quadrant during Morris water maze and percentage of spontaneous alteration behavior during Y-maze tests in the rats. Further, Ang(1-7) attenuated Aβ-induced cholinergic dysfunction in terms of decrease in the level of acetylcholine and activity of choline acetyltransferase, and increase in the activity of acetylcholinesterase, and increase in the level of Aβ in rat hippocampus, pre-frontal cortex and amygdala. Furthermore, Ang(1-7) reversed Aβ-induced decrease in the mitochondrial function, integrity and bioenergetics in all brain regions. Additionally, Ang(1-7) attenuated Aβ-induced increase in the extent of apoptosis and decrease in the level of heme oxygenase-1 in all selected brain regions. Trigonelline significantly abolished the therapeutic effectiveness of Ang(1-7) on Aβ-induced alterations in the behavioral, neurochemicals and molecular observations in the animals. Ang(1-7) may exhibit nrf2-mediated neuroprotection in these rodents. Hence, Ang(1-7) could be a potential therapeutic option in the pharmacotherapy of AD.

Angiotensin II Blood Levels Are Associated with Smaller Hippocampal and Cortical Volumes in Cognitively Normal Older Adults

BACKGROUND

There is emerging evidence about possible involvement of the renin-angiotensin system (RAS) in the pathogenesis of Alzheimer's disease (AD) and decline of cognitive function. However, little is known about associations with brain biomarkers.

OBJECTIVE

Our study aimed to examine associations between blood ACE-1 and ANG II levels and brain MRI based volumes in non-demented participants, and whether these associations were mediated by blood pressure.

METHODS

This cross-sectional study was conducted in 34 older participants from the Baltimore Experience Corps Trial (BECT) Brain Health Sub-study (BHS). Blood ANGII and ACE-1 levels were measured by ELISA and brain MRI volumes were generated using FreeSurfer 6.0. Multiple linear regression analysis, adjusting for intracranial volume and confounders, was used to determine associations between log transformed ANGII and ACE-1 levels and MRI volumes (mm3).

RESULTS

Participants were predominantly female (76%), African-American (94%), with mean age of 66.9 and education of 14.4 years. In the fully adjusted model we observed significant inverse associations between log ANGII levels and total grey matter (β=Angiotensin II associated with smaller hippocampus14,935.50, ±7,444.83, p = 0.05), total hippocampus (β=-129.97, ±105.27, p = 0.03), rostral middle frontal (β= -1580.40, ±584.74, p = 0.02), and supramarginal parietal (β= -978.90, ±365.54, p = 0.02) volumes. There were no associations between ANGII levels and total white matter or entorhinal cortex volumes, or ACE-1 levels and any brain volumes.

CONCLUSION

We observed that increased blood ANGII levels were associated with lower total grey matter, hippocampal, rostral middle frontal, and supramarginal parietal volumes, which are associated with cognitive domains that decline in preclinical AD.

Ang (1-7)/Mas receptor-axis activation promotes amyloid beta-induced altered mitochondrial bioenergetics in discrete brain regions of Alzheimer's disease-like rats

Renin Angiotensin System plays significant role in the memory acquisition and consolidation apart from its hemodynamic function in the pathophysiology of Alzheimer's disease (AD). It has been reported that Ang (1-7) ameliorates the cognitive impairment in experimental animals. However, the effect of Ang (1-7)/Mas receptor signaling is yet to be explored in Aβ42-induced memory impairment. Aβ42 was intracerebroventricularly injected into the male rats on day-1 (D-1) of the experimental schedule of 14 days. All the drugs were administered from D-1 to D-14 in the study design. Aβ42 significantly increased the escape latency during Morris water maze (MWM) test on D-10 to13 in the animals. Further, Aβ42 significantly decreased the time spent and percentage of total distance travelled in the target quadrant of the rats on D-14 in the MWM test. Aβ42 also significantly decreased the spontaneous alteration behavior on D-14 during Y-maze test. Moreover, there was a significant increase in the level of Aβ42, decrease in the cholinergic function (in terms of decreased acetylcholine and activity of cholinesterase, and increased activity of acetylcholinesterase), mitochondrial function, integrity and bioenergetics, and apoptosis in all the rat brain regions. Further, Aβ42 significantly decreased the level of expression of heme oxygenase-1 in all the rat brain regions. Ang (1-7) attenuated Aβ42-induced changes in the behavioral, biochemical and molecular observations in all the selected rat brain regions. However, A779, Mas receptor blocker, significantly abolished the beneficial effects of Ang (1-7) in Aβ42-induced cognitive deficit animals. These observations clearly indicate that the Ang (1-7)/Mas receptor activation could be a potential alternative option in the management of AD.

Angiotensin (1-7) Expressing Probiotic as a Potential Treatment for Dementia

Increasing life expectancies are unfortunately accompanied by increased prevalence of Alzheimer's disease (AD). Regrettably, there are no current therapeutic options capable of preventing or treating AD. We review here data indicating that AD is accompanied by gut dysbiosis and impaired renin angiotensin system (RAS) function. Therefore, we propose the potential utility of an intervention targeting both the gut microbiome and RAS as both are heavily involved in proper CNS function. One potential approach which our group is currently exploring is the use of genetically-modified probiotics (GMPs) to deliver therapeutic compounds. In this review, we specifically highlight the potential utility of utilizing a GMP to deliver Angiotensin (1-7), a beneficial component of the renin-angiotensin system with relevant functions in circulation as well as locally in the gut and brain.

Naringin Exhibits Mas Receptor-Mediated Neuroprotection Against Amyloid Beta-Induced Cognitive Deficits and Mitochondrial Toxicity in Rat Brain

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with clinical manifestation of loss in cognitive functions in an individual. Though several drug candidates have been developed in the management of AD, an alternative option is still required due to serious adverse effects of the former. Recently, naringin exerts therapeutic benefits through rennin angiotensin system in experimental animals. However, its report  on Mas receptor-mediated action against amyloid beta (Aβ)-induced mitochondrial dysfunction in AD-like animals is lacking. The experimental dementia was induced in the male rats by intracerebroventricular administration of Aβ_(1-42) on day 1 (D-1) of the experimental schedule of 14 days. Naringin treatment for 14 days attenuated Aβ-induced cognitive impairments of the animals in Morris water maze (MWM) and Y-maze tests. Further, naringin ameliorated the Aβ-induced cholinergic dysfunction in terms of decrease in the activity of choline acetyl transferase (ChAT) and level of acetylcholine (ACh) and increase in the activity of acetylcholine esterase (AChE) in rat hippocampus, prefrontal cortex, and amygdala. Furthermore, naringin attenuated Aβ-induced decrease in mitochondrial function, integrity, and bioenergetics in all the brain regions. Naringin also attenuated Aβ-induced increase in mitochondrial and cytosolic calcium level in all the brain regions. Moreover, naringin reversed Aβ-induced increase in apoptosis and level of mitochondrial calcium uniporter and decrease in the level of hemeoxygenase-1 in all the brain regions. On the contrary, A779 significantly abolished the therapeutic potential of naringin on Aβ-induced alteration in behavioral, biochemical, and molecular observations in these experimental animals. Thus, these observations indicate that naringin could be potential alternative in the management of AD.

Dihydroartemisinin Ameliorates Decreased Neuroplasticity-Associated Proteins and Excessive Neuronal Apoptosis in APP/PS1 Mice

BACKGROUND

Alzheimer's disease (AD) is one of the worst neurodegenerative disorders worldwide, with extracellular senile plaques (SP), subsequent intracellular neurofibrillary tangles (NFTs) and final neuron loss and synaptic dysfunction as the main pathological characteristics. Excessive apoptosis is the main cause of irreversible neuron loss. Thus, therapeutic intervention for these pathological features has been considered a promising strategy to treat or prevent AD. Dihydroartemisin (DHA) is a widely used first-line drug for malaria. Our previous study showed that DHA treatment significantly accelerated Aβ clearance, improved memory and cognitive deficits in vivo and restored autophagic flux both in vivo and in vitro.

METHODS

The present study intended to explore the neuroprotective effect of DHA on neuron loss in APP/PS1 double-transgenic mice and the underlying mechanisms involved. Transmission electron microscope (TEM) analysis showed that DHA significantly reduced the swollen endoplasmic reticulum (ER) in APP/PS1 mice. Western blot analysis indicated that DHA upregulated the level of NeuN, NeuroD, MAP2, and synaptophysin and promoted neurite outgrowth. Meanwhile, DHA greatly corrected the abnormal levels of Brain-derived neurotrophic factor (BDNF) and rescued the neuronal loss in the hippocampal CA1 area. Western blot analysis revealed that DHA notably down-regulated the protein expression of full length caspase-3, cleaved caspase-3 and Bax. In parallel, the expression of the anti-apoptotic protein Bcl-2 increased after oral DHA treatment.

RESULTS

Altogether, these results indicate that DHA protected AD mice from neuron loss via promoting the expression of BDNF and other neuroplasticity-associated proteins and suppressing the inhibition of neuronal apoptosis.

Environmental Nanoparticles, SARS-CoV-2 Brain Involvement, and Potential Acceleration of Alzheimer's and Parkinson's Diseases in Young Urbanites Exposed to Air Pollution

Alzheimer's and Parkinson's diseases (AD, PD) have a pediatric and young adult onset in Metropolitan Mexico City (MMC). The SARS-CoV-2 neurotropic RNA virus is triggering neurological complications and deep concern regarding acceleration of neuroinflammatory and neurodegenerative processes already in progress. This review, based on our MMC experience, will discuss two major issues: 1) why residents chronically exposed to air pollution are likely to be more susceptible to SARS-CoV-2 systemic and brain effects and 2) why young people with AD and PD already in progress will accelerate neurodegenerative processes. Secondary mental consequences of social distancing and isolation, fear, financial insecurity, violence, poor health support, and lack of understanding of the complex crisis are expected in MMC residents infected or free of SARS-CoV-2. MMC residents with pre-SARS-CoV-2 accumulation of misfolded proteins diagnostic of AD and PD and metal-rich, magnetic nanoparticles damaging key neural organelles are an ideal host for neurotropic SARS-CoV-2 RNA virus invading the body through the same portals damaged by nanoparticles: nasal olfactory epithelium, the gastrointestinal tract, and the alveolar-capillary portal. We urgently need MMC multicenter retrospective-prospective neurological and psychiatric population follow-up and intervention strategies in place in case of acceleration of neurodegenerative processes, increased risk of suicide, and mental disease worsening. Identification of vulnerable populations and continuous effort to lower air pollution ought to be critical steps.

How Does SARS-CoV-2 Affect the Central Nervous System? A Working Hypothesis

Interstitial pneumonia was the first manifestation to be recognized as caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, in just a few weeks, it became clear that the coronavirus disease-2019 (COVID-19) overrun tissues and more body organs than just the lungs, so much so that it could be considered a systemic pathology. Several studies reported the involvement of the conjunctiva, the gut, the heart and its pace, and vascular injuries such as thromboembolic complications and Kawasaki disease in children and toddlers were also described. More recently, it was reported that in a sample of 214 SARS-CoV-2 positive patients, 36.4% complained of neurological symptoms ranging from non-specific manifestations (dizziness, headache, and seizures), to more specific symptoms such hyposmia or hypogeusia, and stroke. Older individuals, especially males with comorbidities, appear to be at the highest risk of developing such severe complications related to the Central Nervous System (CNS) involvement. Neuropsychiatric manifestations in COVID-19 appear to develop in patients with and without pre-existing neurological disorders. Growing evidence suggests that SARS-CoV-2 binds to the human Angiotensin-Converting Enzyme 2 (ACE2) for the attachment and entrance inside host cells. By describing ACE2 and the whole Renin Angiotensin Aldosterone System (RAAS) we may better understand whether specific cell types may be affected by SARS-CoV-2 and whether their functioning can be disrupted in case of an infection. Since clear evidences of neurological interest have already been shown, by clarifying the topographical distribution and density of ACE2, we will be able to speculate how SARS-CoV-2 may affect the CNS and what is the pathogenetic mechanism by which it contributes to the specific clinical manifestations of the disease. Based on such evidences, we finally hypothesize the process of SARS-CoV-2 invasion of the CNS and provide a possible explanation for the onset or the exacerbation of some common neuropsychiatric disorders in the elderly including cognitive impairment and Alzheimer disease.

Comparative Effectiveness of Angiotensin II Receptor Blockers and Angiotensin-Converting Enzyme Inhibitors in Older Nursing Home Residents After Myocardial Infarction: A Retrospective Cohort Study

BACKGROUND

Evidence regarding differences in outcomes between angiotensin II receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEIs) among older nursing home (NH) residents after acute myocardial infarction (AMI) is limited.

OBJECTIVES

The purpose of our study was to estimate the post-AMI effects of ARBs versus ACEIs on mortality, rehospitalization, and functional decline outcomes in this important population.

METHODS

This retrospective cohort study used national Medicare claims linked to Minimum Data Set assessments. The study population included individuals aged ≥ 65 years who resided in a US NH ≥ 30 days, were hospitalized for AMI between May 2007 and March 2010, and returned to the NH. We compared 90-day mortality, rehospitalization, and functional decline outcomes between ARB and ACEI users with inverse-probability-of-treatment-weighted binomial and multinomial logistic regression models.

RESULTS

Of the 2765 NH residents, 270 (9.8%) used ARBs and 2495 (90.2%) used ACEIs. The mean age of ARB versus ACEI users was 82.3 versus 82.7 years, respectively. No marked differences existed between ARB and ACEI users for mortality [odds ratio (OR) 1.18; 95% confidence interval (CI) 0.78-1.79], rehospitalization (OR 1.22; 95% CI 0.90-1.65), or functional decline (OR 1.23; 95% CI 0.88-1.74). In subgroup analyses, ARBs were associated with increased mortality and rehospitalization in individuals with moderate to severe cognitive impairment and with increased rehospitalization in those aged < 85 years.

CONCLUSIONS

Our findings align with prior data and suggest that clinicians can prescribe either ARBs or ACEIs post-AMI for secondary prevention in NH residents, although the subgroup findings merit further scrutiny and replication. Providers should consider factors such as patient preferences, class-specific adverse events, and costs when prescribing.

Nerve growth factor in metabolic complications and Alzheimer's disease: Physiology and therapeutic potential

As the population ages, obesity and metabolic complications as well as neurological disorders are becoming more prevalent, with huge economic burdens on both societies and families. New therapeutics are urgently needed. Nerve growth factor (NGF), first discovered in 1950s, is a neurotrophic factor involved in regulating cell proliferation, growth, survival, and apoptosis in both central and peripheral nervous systems. NGF and its precursor, proNGF, bind to TrkA and p75 receptors and initiate protein phosphorylation cascades, resulting in changes of cellular functions, and are associated with obesity, diabetes and its complications, and Alzheimer's disease. In this article, we summarize changes in NGF levels in metabolic and neuronal disorders, the signal transduction initiated by NGF and proNGF, the physiological and pathophysiological relevance, and therapeutic potential in treating chronic metabolic diseases and cognitive decline.

Associations of Angiotensin Converting Enzyme-1 and Angiotensin II Blood Levels and Cognitive Function

BACKGROUND

Emerging evidence suggests a possible role of the renin angiotensin system in the pathophysiologic process of Alzheimer's disease, of which angiotensin converting enzyme-1 (ACE-1) and angiotensin II (ANGII) are important proteins. Few studies evaluated associations between blood ACE-1 and none between ANGII levels, and cognition.

OBJECTIVE

Our pilot study was aimed to examine associations between blood ACE-1 and ANG II levels and cognitive function in non-demented participants at baseline and over a 1-year period.

METHODS

56 participants were included from the Brain Health Substudy of the Baltimore Experience Corps Study. Linear regression analysis, adjusting for confounders, was used to determine associations between baseline ACE-1 and ANGII, and baseline and 1-year follow-up measures of psychomotor and processing speed, executive function, verbal learning memory and working memory, and whether these associations were mediated by blood pressure.

RESULTS

Participants were predominantly female (75%), African-American (93%), with mean age of 67.8 years and education of 14.3 years. There were no associations between baseline ACE-1 or ANGII levels and cognitive function; however, there were significant association between baseline ACE-1 levels and 1-year follow-up Trail Making Test, Part A (β= 0.003, p = 0.04) and Digit Span (β= -0.001, p = 0.02).

CONCLUSIONS

In this cognitively intact sample, elevated ACE-1 levels were associated with worse processing speed and working memory after 1 year. Findings from this pilot study suggest that changes in the RAS are associated with alterations in cognitive function warranting further assessment of the role of RAS in neurodegenerative disorders.

Neurofibrillary Tangles and Conversion to Mild Cognitive Impairment with Certain Antihypertensives

BACKGROUND

Individuals taking renin angiotensin system (RAS) acting antihypertensives exhibit slower cognitive decline and are less likely to progress from mild cognitive impairment (MCI) to Alzheimer's disease (AD), but the mechanism remains unclear.

OBJECTIVE

We tested the hypothesis that individuals taking RAS acting antihypertensives exhibit less AD-related neuropathology and slower disease progression than individuals taking non-RAS acting antihypertensives.

METHOD

Participants included 83 individuals with MCI who were taking an antihypertensive at baseline, had at least two follow-up visits, and had postmortem neuropathological data. Participants were old (M = 83.1 years), 32% male, well educated (M = 15.7 years), and 9.2% Black.

RESULTS

RAS medication users (N = 38) were less likely to progress to AD than non-RAS users (N = 45). RAS users exhibited fewer neurofibrillary tangles than non-RAS users in the hippocampal CA1 region (p < 0.01), entorhinal cortex (p = 0.03), and the angular gyrus, inferior temporal, mid-frontal cortex, and superior frontal (p = 0.01).

CONCLUSION

Prevention or clearance of neurofibrillary tangles represents a mechanism by which RAS medications may slow disease progression.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Connecting the brain cholesterol and renin-angiotensin systems: potential role of statins and RAS-modifying medications in dementia

Millions of people worldwide receive agents targeting the renin-angiotensin system (RAS) to treat hypertension or statins to lower cholesterol. The RAS and cholesterol metabolic pathways in the brain are autonomous from their systemic counterparts and are interrelated through the cholesterol metabolite 27-hydroxycholesterol (27-OHC). These systems contribute to memory and dementia pathogenesis through interference in the amyloid-beta cascade, vascular mechanisms, glucose metabolism, apoptosis, neuroinflammation and oxidative stress. Previous studies examining the relationship between these treatments and cognition and dementia risk have produced inconsistent results. Defining the blood-brain barrier penetration of these medications has been challenging, and the mechanisms of action on cognition are not clearly established. Potential biases are apparent in epidemiological and clinical studies, such as reverse epidemiology, indication bias, problems defining medication exposure, uncertain and changing doses, and inappropriate grouping of outcomes and medications. This review summarizes current knowledge of the brain cholesterol and RAS metabolism and the mechanisms by which these pathways affect neurodegeneration. The putative mechanisms of action of statins and medications inhibiting the RAS will be examined, together with prior clinical and animal studies on their effects on cognition. We review prior epidemiological studies, analysing their strengths and biases, and identify areas for future research. Understanding the pathophysiology of the brain cholesterol system and RAS and their links to neurodegeneration has enormous potential. In future, well-designed epidemiological studies could identify potential treatments for Alzheimer's disease (AD) amongst medications that are already in use for other indications.

Alteration in Brain Functional and Effective Connectivity in Subjects With Hypertension

To reveal the physiological mechanism of the cognitive decline in subjects with hypertension, the functional connectivity (FC) was assessed by using the wavelet phase coherence (WPCO), and effective connectivity (EC) was assessed by using the coupling strength (CS) of near-infrared spectroscopy (NIRS) signals. NIRS signals were continuously recorded from the prefrontal cortex, sensorimotor cortex, and occipital lobes of 13 hypertensive patients (hypertension group, 70 ± 6.5 years old) and 16 elderly healthy subjects (control group, 71 ± 5.5 years old) in resting and standing periods. WPCO and CS were calculated in four frequency intervals: I, 0.6–2; II, 0.145–0.6; III, 0.052–0.145; and IV, 0.021–0.052 Hz. CS quantifies coupling amplitude. In comparison with the control group, the hypertension group showed significantly decreased (p < 0.05) WPCO and CS in intervals III and IV and in the resting and standing states. WPCO and CS were significantly decreased in the resting state compared with those in the standing state in the hypertension group (p < 0.05). Decreased WPCO and CS indicated a reduced network interaction, suggesting disturbed neurovascular coupling in subjects with hypertension. Compared with the control group, the hypertension group showed significantly lower Mini-Mental State Examination (MMSE) (p = 0.028) and Montreal Cognitive Assessment (MoCA) scores (p = 0.011). In the hypertension group, correlation analysis showed that WPCO and CS were significantly positively correlated with MMSE and MoCA scores, respectively. These findings may provide evidence of impaired cognitive function in hypertension and can enhance the understanding on neurovascular coupling.

Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies

OBJECTIVES

To explore effects of the brain renin-angiotensin system (RAS) on cognition.

DESIGN

Systematic review of experimental (non-human) studies assessing cognitive effects of RAS peptides angiotensin-(3-8) [Ang IV] and angiotensin-(1-7) [Ang-(1-7)] and their receptors, the Ang IV receptor (AT4R) and the Mas receptor.

RESULTS

Of 450 articles identified, 32 met inclusion criteria. Seven of 11 studies of normal animals found Ang IV had beneficial effects on tests of passive or conditioned avoidance and object recognition. In models of cognitive deficit, eight of nine studies found Ang IV and its analogs (Nle¹-Ang IV, dihexa, LVV-hemorphin-7) improved performance on spatial working memory and passive avoidance tasks. Two of three studies examining Ang-(1-7) found it benefited memory. Mas receptor removal was associated with reduced fear memory in one study.

CONCLUSION

Studies of cognitive impairment show salutary effects of acute administration of Ang IV and its analogs, as well as AT4R activation. Brain RAS peptides appear most effective administered intracerebroventricularly, close to the time of learning acquisition or retention testing. Ang-(1-7) shows anti-dementia qualities.

Moringa oleifera supplemented diet modulates nootropic-related biomolecules in the brain of STZ-induced diabetic rats treated with acarbose

There are strong correlations between diabetes mellitus and cognitive dysfunction. This study sought to investigate the modulatory effects of Moringa oleifera leaf (ML) and seed (MS) inclusive diets on biomolecules [acetylcholinesterase (AChE), butyrylcholinesterase (BChE)] angiotensin-I converting enzyme (ACE), arginase, catalase, glutathione transferase (GST) and glutathione peroxidase (GSH-Px) activities, glutathione (GSH) and nitric oxide (NO) levels] associated with cognitive function in the brain of streptozotocin (STZ)-induced diabetic rats treated with acarbose (ACA). The rats were made diabetic by intraperitoneal administration of 0.1 M sodium-citrate buffer (pH 4.5) containing STZ [60 mg/kg b.w (BW)] and fed with diets containing 2 and 4% ML/MS. Acarbose (25 mg/kg BW) was administered by gavage daily for 14 days. The animals were distributed in eleven groups of eight animals as follows: control, STZ-induced, STZ + ACA, STZ + 2% ML, STZ + ACA + 2% ML, STZ + 4% ML, STZ + ACA + 4% ML, STZ + 2% MS, STZ + ACA + 2% MS, STZ + 4% MS, STZ + ACA + 4% MS. There were marked increase in AChE, BChE, arginase, ACE and concomitant decrease in catalase, GST, GSH-Px, activities and NO levels in STZ-diabetic group compared with the control. However, there was a decrease in AChE, BChE and ACE activities and concomitant increase in the antioxidant molecules in the groups fed with supplemented diets treated with/without ACA compared with the STZ-diabetic group. These findings suggest that ML/MS supplemented diet could prevent cognitive dysfunction-induced by chronic hyperglycemia.

Relationship Between Antihypertensive Medications and Cognitive Impairment: Part II. Review of Physiology and Animal Studies

PURPOSE OF REVIEW

There is an established association between hypertension and increased risk of poor cognitive performance and dementia including Alzheimer's disease; however, associations between antihypertensive medications (AHM) and dementia risk are less clear. An increased interest in AHM has resulted in expanding publications; however, none of the recent reviews provide comprehensive review. Our extensive review includes 24 mechanistic animal and human studies published over the last 5 years assessing relationship between AHM and cognitive function.

RECENT FINDINGS

All classes of AHM showed similar result patterns in animal studies. The mechanism by which AHM exert their effect was extensively studied by evaluating well-established pathways of AD disease process, including amyloid beta (Aβ), vascular, oxidative stress and inflammation pathways, but only few studies evaluated the blood pressure lowering effect on the AD disease process. Methodological limitations of the studies prevent comprehensive conclusions prior to further work evaluating AHM in animals and larger human observational studies, and selecting those with promising results for future RCTs.

Losartan improves cerebrovascular function in a mouse model of Alzheimer's disease with combined overproduction of amyloid-β and transforming growth factor-β1

Alterations of the renin-angiotensin system have been implicated in the pathogenesis of Alzheimer's disease. We tested the efficacy of losartan (10 mg/kg/day for three months), a selective angiotensin II type 1 receptor antagonist, in alleviating cerebrovascular and cognitive deficits in double-transgenic mice (six months at endpoint) that overexpress a mutated form of the human amyloid precursor protein (APP_Swe,Ind) and a constitutively active form of the transforming growth factor-β1, thereafter named A/T mice. Losartan rescued cerebrovascular reactivity, particularly the dilatory responses, but failed to attenuate astroglial activation and to normalize the neurovascular uncoupling response to sensory stimulation. The cognitive deficits of A/T mice were not restored by losartan nor were the increased brain levels of soluble and insoluble Aβ_1-40 and Aβ_1-42 peptides normalized. Our results are the first to demonstrate the capacity of losartan to improve cerebrovascular reactivity in an Alzheimer's disease mouse model of combined Aβ-induced vascular oxidative stress and transforming growth factor-β1-mediated vascular fibrosis. These data suggest that losartan may be promising for restoring cerebrovascular function in patients with vascular diseases at risk for vascular dementia or Alzheimer's disease. However, a combined therapy may be warranted for rescuing both vascular and cognitive deficits in a multifaceted pathology like Alzheimer's disease.

Transient Mild Cerebral Ischemia Significantly Deteriorated Cognitive Impairment in a Mouse Model of Alzheimer's Disease via Angiotensin AT1 Receptor

BACKGROUND

Ischemic stroke is suggested to be potentially associated with cognitive impairment in Alzheimer's disease (AD). We hypothesized that cerebral ischemia deteriorates cognitive impairment in AD, through angiotensin II.

METHODS

We used 5XFAD mouse, a model of AD with vascular and cerebral amyloid-β deposition. Transient cerebral ischemia of mice was induced by bilateral common carotid artery occlusion (BCCAO) for 17 minutes. The posttreatment with olmesartan, an ARB, or vehicle was started at 24 hours after BCCAO and was performed for 5 weeks. Experimental mice consisted of 5 groups: (i) wild-type mice, (ii) wild-type mice with BCCAO, (iii) 5XFAD mice, (iv) 5XFAD mice with BCCAO, (v) 5XFAD mice with BCCAO and olmesartan postadministration.

RESULTS

BCCAO in 5XFAD caused greater escape latency (P < 0.01) on water maze test than that in wild type, indicating that transient brief cerebral ischemia enhanced cognitive decline in 5XFAD mice. Posttreatment with olmesartan significantly reduced escape latency (P < 0.01) on water maze test, retention trial latency (P < 0.05) on passive avoidance test, and retention time of outer zone (P < 0.01) on open-field test in 5XFAD subjected to BCCAO. This protective effect of olmesartan against cognitive impairment in 5XFAD with BCCAO was associated with the protection of neuron and attenuation of oxidative stress in hippocampus and the suppression of blood-brain barrier disruption.

CONCLUSIONS

We obtained the evidence that transient brief cerebral ischemia deteriorated cognitive impairment in AD model through AT1 receptor.

Enalapril Alone or Co-Administered with Losartan Rescues Cerebrovascular Dysfunction, but not Mnemonic Deficits or Amyloidosis in a Mouse Model of Alzheimer's Disease

The co-administration of angiotensin converting enzyme inhibitors (ACEi) and angiotensin II (AngII) receptor blockers (ARB) that bind angiotensin type 1 receptors (AT1R) may protect from Alzheimer's disease (AD) better than each treatment taken alone. We tested the curative potential of the non brain-penetrant ACEi enalapril (3 mg/kg/day) administered for 3 months either alone or in combination with the brain penetrant ARB losartan (10 mg/kg/day) in aged (∼15 months) transgenic mice overexpressing a mutated form of the human amyloid-β protein precursor (AβPP, thereafter APP mice). We studied cerebrovascular function, protein levels of oxidative stress markers (superoxide dismutases SOD1, SOD2 and the NADPH oxidase subunit p67phox), amyloid-β (Aβ) pathology, astrogliosis, cholinergic innervation, AT1R and angiotensin IV receptor (AT4R) levels, together with cognitive performance. Both treatments normalized cerebrovascular reactivity and p67phox protein levels, but they did not reduce the cerebrovascular levels of SOD1. Combined treatment normalized cerebrovascular SOD2 levels, significantly attenuated astrogliosis, but did not reduce the increased levels of cerebrovascular AT1R. Yet, combined therapy enhanced thioflavin-S labeled Aβ plaque burden, a tendency not significant when Aβ1 - 42 plaque load was considered. None of the treatments rescued cognitive deficits, cortical AT4R or cholinergic innervation. We conclude that both treatments normalized cerebrovascular function by inhibiting the AngII-induced oxidative stress cascade, and that the positive effects of the combined therapy on astrogliosis were likely due to the ability of losartan to enter brain parenchyma. However, enalapril did not potentiate, and may even dampen, the reported cognitive benefits of losartan, raising caution when selecting the most appropriate antihypertensive therapy in AD patients.

Captopril and Valsartan May Improve Cognitive Function Through Potentiation of the Brain Antioxidant Defense System and Attenuation of Oxidative/Nitrosative Damage in STZ-Induced Dementia in Rat

Purpose: Previous findings have shown the crucial roles of brain renin-angiotensin system (RAS) in pathogenesis of Alzheimer's disease (AD). Since RAS inhibitors may have beneficial effects on dementia and cognitive function in elderly people, the aim of present study was to examine the neuroprotective actions of captopril and valsartan on memory function and neuronal damage in experimental model of AD. Methods: Adult forty male Wistar rats (220-280g) were randomly divided into 5 groups; Control, Vehicle, Alzheimer and treatment groups. AD was induced by the injections of streptozotocin (3mg/kg, bilateral intracerebroventricular) at days 1&3. Treated rats received orally captopril (50mg/kg/day) and valsartan (30mg/kg/day). Memory function and histological assessments were done at termination of experiment. Finally, superoxide dismutase (SOD) and catalase (CAT) activities as well as malondialdehyde (MDA) and NOx contents were determined. Results: There was a significant increase in the mean value of latency in Alzheimer group (66%). Captopril and valsartan considerably decreased this value in both treatment groups (45% and 72%, respectively). In Alzheimer group the activities of brain's SOD and CAT reduced (40% and 47%, respectively) in accompany with an increase in MDA and NOx contents (49% and 50%, respectively). Captopril and valsartan significantly increased the activities of brain's SOD and CAT concomitant reduction in MDA and NOx contents. Also, histopathological damages noticeably decreased in both treatment groups. Conclusion: Our findings indicate that RAS inhibition by using captopril and valsartan potentiates the antioxidant defense system of brain and reduces oxidative/nitrosative stress in accompany with neuronal damage during AD.

Older Adults Taking AT1-Receptor Blockers Exhibit Reduced Cerebral Amyloid Retention

BACKGROUND

Evidence suggests that angiotensin II AT1-receptor blockers (ARBs) may be protective against dementia, and studies in transgenic animals indicate that this may be due to improved amyloid-β (Aβ) clearance.

OBJECTIVE

We investigated whether taking ARBs was associated with an attenuation of age-related increases in cerebral Aβ retention, and reduced progression to dementia.

METHODS

Eight hundred seventy-one stroke-free and dementia-free older adults from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study underwent baseline lumbar puncture, and a subgroup (n = 124) underwent 12 and 24 month follow-up lumbar puncture. Participants were followed at variable intervals for clinical progression to dementia. Linear mixed models and ANCOVA compared ARBs users with those taking other antihypertensives (O-antiHTN) or no antihypertensives (No-antiHTN) on cerebrospinal fluid (CSF) Aβ and phosphorylated tau (P-tau) levels. Cox regression and chi-square analyses compared groups on progression to dementia.

RESULTS

ARBs users exhibited greater vascular risk and lower educational attainment than the No-antiHTN group. Longitudinal analyses indicated higher CSF Aβ and lower P-tau in ARBs users versus other groups. Cross-sectional analyses revealed age-related decreases in CSF Aβ in other groups but not ARBs users. ARBs users were less likely to progress to dementia and showed reduced rate of progression relative to the No-antiHTN group.

DISCUSSION

Patients taking ARBs showed an attenuation of age-related decreases in CSF Aβ, a finding that is consistent with studies done in transgenic animals. These findings may partly explain why ARBs users show reduced progression to dementia despite their lower educational attainment and greater vascular risk burden.

Targeting AGEs Signaling Ameliorates Central Nervous System Diabetic Complications in Rats

Diabetes is a chronic endocrine disorder associated with several complications as hypertension, advanced brain aging, and cognitive decline. Accumulation of advanced glycation end products (AGEs) is an important mechanism that mediates diabetic complications. Upon binding to their receptor (RAGE), AGEs mediate oxidative stress and/or cause cross-linking with proteins in blood vessels and brain tissues. The current investigation was designed to investigate the effect of agents that decrease AGEs signaling, perindopril which increases soluble RAGE (sRAGE) and alagebrium which cleaves AGEs cross-links, compared to the standard antidiabetic drug, gliclazide, on the vascular and central nervous system (CNS) complications in STZ-induced (50 mg/kg, IP) diabetes in rats. Perindopril ameliorated the elevation in blood pressure seen in diabetic animals. In addition, both perindopril and alagebrium significantly inhibited memory decline (performance in the Y-maze), neuronal degeneration (Fluoro-Jade staining), AGEs accumulation in serum and brain, and brain oxidative stress (level of reduced glutathione and activities of catalase and malondialdehyde). These results suggest that blockade of AGEs signaling after diabetes induction in rats is effective in reducing diabetic CNS complications.

Angiotensin receptor blockers and risk of dementia: cohort study in UK Clinical Practice Research Datalink

Aims

This was a cohort study to evaluate whether individuals exposed to angiotensin receptor blockers have a reduced risk of dementia compared with those exposed to angiotensin-converting enzyme inhibitors.

Methods

The study included new users of angiotensin receptor blockers or angiotensin-converting enzyme inhibitors (from 1995 to 2010) from UK primary care practices contributing to the Clinical Research Practice Datalink. The association between exposure to angiotensin receptor blockers and the risk of incident dementia was analysed using a Cox model, adjusting for age, sex, body mass index, diabetes, hypertension, heart failure, statin use, socioeconomic status, alcohol, smoking, number of consultations and calendar year.

Results

A total of 426 089 persons were included in the primary analysis, with 45 541 persons exposed to angiotensin receptor blockers and the remainder to angiotensin-converting enzyme inhibitors. The total number of new diagnoses of dementia was 6517. There was weak evidence of a decreased risk of dementia with exposure to angiotensin receptor blockers, with follow-up beginning at 1 year after the start of treatment (adjusted hazard ratio 0.92, 95% confidence interval 0.85–1.00). An analysis restricted to the first 12 months after the index date showed a larger effect on dementia risk (adjusted hazard ratio 0.60, 95% confidence interval 0.50–0.72).

Conclusions

A small reduction in dementia risk was seen with angiotensin receptor blockers in comparison to angiotensin-converting enzyme inhibitors. However, the strongest association was seen in early follow-up, suggesting that the inverse association is unlikely to be causal, but instead reflects other important but unmeasured differences between angiotensin receptor blocker and angiotensin-converting enzyme inhibitor users.

Potential cognitive decline linked to angiotensin-converting enzyme gene but not hypertension: Evidence from cognitive event-related potentials

OBJECTIVES

The aims of the present study were to investigate the effect of hypertension and angiotensin-converting enzyme (ACE) genotypes on cognitive event-related potentials (ERPs), and whether the impact of ACE genotypes on P300 is related to the influence of hypertension.

METHODS

Using the Cognitive Abilities Screening Instrument (CASI), we recruited 97 mentally healthy middle-aged and older adults. Medical histories were collected, and blood pressure, ACE insertion/deletion polymorphisms and ERPs in an auditory oddball task were measured for all participants.

RESULTS

When the participants were stratified according to the presence or absence of hypertension, there were no differences in CASI score, percentage of ACE genotypes and ERPs. The subjects with the D/D homozygote displayed lower amplitude and longer latency of P300, although there were no differences in CASI score and the percentage of hypertension.

CONCLUSIONS

The subjects with the D/D genotype tended to have decreased amplitude and prolonged latency of P300 ERPs which reflected subtle cognitive impairment. There were no associations between hypertension, CASI score and P300 measurements.

SIGNIFICANCE

Using ERPs, potential cognitive decline was linked to ACE genotypes, independently of the effect of hypertension.

Hypertension Accelerates the Progression of Alzheimer-Like Pathology in a Mouse Model of the Disease

Cerebrovascular impairment is frequent in patients with Alzheimer disease and is believed to influence clinical manifestation and severity of the disease. Cardiovascular risk factors, especially hypertension, have been associated with higher risk of developing Alzheimer disease. To investigate the mechanisms underlying the hypertension, Alzheimer disease cross talk, we established a mouse model of dual pathology by infusing hypertensive doses of angiotensin II into transgenic APPPS1 mice overexpressing mutated human amyloid precursor and presenilin 1 proteins. At 4.5 months, at the early stage of disease progression, only hypertensive APPPS1 mice presented impairment of temporal order memory performance in the episodic-like memory task. This cognitive deficit was associated with an increased number of cortical amyloid deposits (223±5 versus 207±5 plaques/mm 2 ; P <0.05) and a 2-fold increase in soluble amyloid levels in the brain and in plasma. Hypertensive APPPS1 mice presented several cerebrovascular alterations, including a 25% reduction in cerebral microvessel density and a 30% to 40% increase in cerebral vascular amyloid deposits, as well as a decrease in vascular endothelial growth factor A expression in the brain, compared with normotensive APPPS1 mice. Moreover, the brain levels of nitric oxide synthase 1 and 3 and the nitrite/nitrate levels were reduced in hypertensive APPPS1 mice (by 49%, 34%, and 33%, respectively, compared with wild-type mice; P <0.05). Our results indicate that hypertension accelerates the development of Alzheimer disease–related structural and functional alterations, partially through cerebral vasculature impairment and reduced nitric oxide production.

Association of gene variants of the renin-angiotensin system with accelerated hippocampal volume loss and cognitive decline in old age

OBJECTIVE

Genetic factors confer risk for neuropsychiatric phenotypes, but the polygenic etiology of these phenotypes makes identification of genetic culprits challenging. An approach to this challenge is to examine the effects of genetic variation on relevant endophenotypes, such as hippocampal volume loss. A smaller hippocampus is associated with gene variants of the renin-angiotensin system (RAS), a system implicated in vascular disease. However, no studies to date have investigated longitudinally the effects of genetic variation of RAS on the hippocampus.

METHOD

The authors examined the effects of polymorphisms of AGTR1, the gene encoding angiotensin-II type 1 receptor of RAS, on longitudinal hippocampal volumes of older adults. In all, 138 older adults (age ≥60 years) were followed for an average of about 4 years. The participants underwent repeated structural MRI and comprehensive neurocognitive testing, and they were genotyped for four AGTR1 single-nucleotide polymorphisms (SNPs) with low pairwise linkage disequilibrium values and apolipoprotein E (APOE) genotype.

RESULTS

Genetic variants at three AGTR1 SNPs (rs2638363, rs1492103, and rs2675511) were independently associated with accelerated hippocampal volume loss over the 4-year follow-up period in the right but not left hemisphere. Intriguingly, these AGTR1 risk alleles also predicted worse episodic memory performance but were not related to other cognitive measures. Two risk variants (rs2638363 and rs12721331) interacted with the APOE4 allele to accelerate right hippocampal volume loss.

CONCLUSIONS

Risk genetic variants of the RAS may accelerate memory decline in older adults, an effect that may be conferred by accelerated hippocampal volume loss. Molecules involved in this system may hold promise as early therapeutic targets for late-life neuropsychiatric disorders.

The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-met system

A subset of angiotensin IV (AngIV)-related molecules are known to possess procognitive/antidementia properties and have been considered as templates for potential therapeutics. However, this potential has not been realized because of two factors: 1) a lack of blood-brain barrier-penetrant analogs, and 2) the absence of a validated mechanism of action. The pharmacokinetic barrier has recently been overcome with the synthesis of the orally active, blood-brain barrier-permeable analog N-hexanoic-tyrosine-isoleucine-(6) aminohexanoic amide (dihexa). Therefore, the goal of this study was to elucidate the mechanism that underlies dihexa's procognitive activity. Here, we demonstrate that dihexa binds with high affinity to hepatocyte growth factor (HGF) and both dihexa and its parent compound Norleucine 1-AngIV (Nle(1)-AngIV) induce c-Met phosphorylation in the presence of subthreshold concentrations of HGF and augment HGF-dependent cell scattering. Further, dihexa and Nle(1)-AngIV induce hippocampal spinogenesis and synaptogenesis similar to HGF itself. These actions were inhibited by an HGF antagonist and a short hairpin RNA directed at c-Met. Most importantly, the procognitive/antidementia capacity of orally delivered dihexa was blocked by an HGF antagonist delivered intracerebroventricularly as measured using the Morris water maze task of spatial learning.

Angiotensin II type 1 receptor blocker losartan prevents and rescues cerebrovascular, neuropathological and cognitive deficits in an Alzheimer's disease model

Angiotensin II (AngII) receptor blockers that bind selectively AngII type 1 (AT1) receptors may protect from Alzheimer's disease (AD). We studied the ability of the AT1 receptor antagonist losartan to cure or prevent AD hallmarks in aged (~18months at endpoint, 3months treatment) or adult (~12months at endpoint, 10months treatment) human amyloid precursor protein (APP) transgenic mice. We tested learning and memory with the Morris water maze, and evaluated neurometabolic and neurovascular coupling using [(18)F]fluoro-2-deoxy-D-glucose-PET and laser Doppler flowmetry responses to whisker stimulation. Cerebrovascular reactivity was assessed with on-line videomicroscopy. We measured protein levels of oxidative stress enzymes (superoxide dismutases SOD1, SOD2 and NADPH oxidase subunit p67phox), and quantified soluble and deposited amyloid-β (Aβ) peptide, glial fibrillary acidic protein (GFAP), AngII receptors AT1 and AT2, angiotensin IV receptor AT4, and cortical cholinergic innervation. In aged APP mice, losartan did not improve learning but it consolidated memory acquisition and recall, and rescued neurovascular and neurometabolic coupling and cerebrovascular dilatory capacity. Losartan normalized cerebrovascular p67phox and SOD2 protein levels and up-regulated those of SOD1. Losartan attenuated astrogliosis, normalized AT1 and AT4 receptor levels, but failed to rescue the cholinergic deficit and the Aβ pathology. Given preventively, losartan protected cognitive function, cerebrovascular reactivity, and AT4 receptor levels. Like in aged APP mice, these benefits occurred without a decrease in soluble Aβ species or plaque load. We conclude that losartan exerts potent preventive and restorative effects on AD hallmarks, possibly by mitigating AT1-initiated oxidative stress and normalizing memory-related AT4 receptors.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

Beneficial effect of candesartan and lisinopril against haloperidol-induced tardive dyskinesia in rat

INTRODUCTION

Tardive dyskinesia is a serious motor disorder of the orofacial region, resulting from chronic neuroleptic treatment of schizophrenia. Candesartan (AT1 antagonist) and lisinopril (ACE inhibitor) has been reported to possess antioxidant and neuroprotective effects. The present study is designed to investigate the effect of candesartan and lisinopril on haloperidol-induced orofacial dyskinesia and oxidative damage in rats.

MATERIALS AND METHODS

Tardive dyskinesia was induced by administering haloperidol (1 mg/kg i.p.) and concomitantly treated with candesartan (3 and 5 mg/kg p.o.) and lisinopril (10 and 15 mg/kg p.o.) for 3 weeks in male Wistar rats. Various behavioral parameters were assessed on days 0, 7, 14 and 21 and biochemical parameters were estimated at day 22.

RESULTS

Chronic administration of haloperidol significantly increased stereotypic behaviors in rats, which were significantly improved by administration of candesartan and lisinopril. Chronic administration of haloperidol significantly increased oxidative stress and neuro-inflammation in the striatum region of the rat's brain. Co-administration of candesartan and lisinopril significantly attenuated the oxidative damage and neuro-inflammation in the haloperidol-treated rat.

CONCLUSIONS

The present study supports the therapeutic use of candesartan and lisinopril in the treatment of typical antipsychotic-induced orofacial dyskinesia and possible antioxidant and neuro-inflammatory mechanisms.

A Role for the Brain RAS in Alzheimer's and Parkinson's Diseases

The brain renin-angiotensin system (RAS) has available the necessary functional components to produce the active ligands angiotensins II (AngII), angiotensin III, angiotensins (IV), angiotensin (1-7), and angiotensin (3-7). These ligands interact with several receptor proteins including AT1, AT2, AT4, and Mas distributed within the central and peripheral nervous systems as well as local RASs in several organs. This review first describes the enzymatic pathways in place to synthesize these ligands and the binding characteristics of these angiotensin receptor subtypes. We next discuss current hypotheses to explain the disorders of Alzheimer's disease (AD) and Parkinson's disease (PD), as well as research efforts focused on the use of angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), in their treatment. ACE inhibitors and ARBs are showing promise in the treatment of several neurodegenerative pathologies; however, there is a need for the development of analogs capable of penetrating the blood-brain barrier and acting as agonists or antagonists at these receptor sites. AngII and AngIV have been shown to play opposing roles regarding memory acquisition and consolidation in animal models. We discuss the development of efficacious AngIV analogs in the treatment of animal models of AD and PD. These AngIV analogs act via the AT4 receptor subtype which may coincide with the hepatocyte growth factor/c-Met receptor system. Finally, future research directions are described concerning new approaches to the treatment of these two neurological diseases.

Effects of angiotensin (5-8) microinfusions into the ventrolateral periaqueductal gray on defensive behaviors in rats

Peptides of the renin-angiotensin system modulate blood pressure and hydro-electrolyte composition. Angiotensin (Ang) receptors are localized in brain areas related to the regulation of autonomic and endocrine control and involved in sensory perception, memory process and behavioral responses. Among these areas, the ventrolateral periaqueductal gray (vlPAG) is one of the most important structures of the neuronal circuitry controlling the autonomic and behavioral components of emotional states. Although Ang II metabolism in the vlPAG forms several Ang-peptides including Ang (5-8), the role of this tetrapeptide in the organization of defensive responses has not yet been described. To address this issue, the purpose of the present study was to determine the effects of intra-vlPAG injections of Ang (5-8) (0.2, 0.4 and 0.8 nmol/0.25 μL) in rats submitted to the elevated plus-maze (EPM) test. Additionally, it was evaluated the effects of intra-vlPAG Ang (5-8) on the expression of conditioned fear, assessed by the fear-potentiated startle and contextual conditioned freezing tests. The results showed that Ang (5-8) produced an intense, dose-related reduction in the entries into and time spent in the open arms of the EPM, decreased direct exploration and increased risk assessment behaviors. Moreover, intra-vlPAG injections of Ang (5-8) before the test session promoted pro-aversive effects in the FPS and enhanced contextual freezing. Taken together, these results point out to an important anxiogenic-like action for Ang (5-8) in the mediation of defensive behaviors organized in the vlPAG.

Renin Angiotensin System in Cognitive Function and Dementia

Angiotensin II represents a key molecule in hypertension and cerebrovascular pathology. By promoting inflammation and oxidative stress, enhanced Ang II levels accelerate the onset and progression of cell senescence. Sustained activation of RAS promotes end-stage organ injury associated with aging and results in cognitive impairment and dementia. The discovery of the angiotensin-converting enzyme ACE2-angiotensin (1–7)-Mas receptor axis that exerts vasodilator, antiproliferative, and antifibrotic actions opposed to those of the ACE-Ang II-AT1 receptor axis has led to the hypothesis that a decrease in the expression or activity of angiotensin (1–7) renders the systems more susceptible to the pathological actions of Ang II. Given the successful demonstration of beneficial effects of increased expression of ACE2/formation of Ang1–7/Mas receptor binding and modulation of Mas expression in animal models in containing cerebrovascular pathology in hypertensive conditions and aging, one could reasonably hope for analogous effects regarding the prevention of cognitive decline by protecting against hypertension and cerebral microvascular damage. Upregulation of ACE2 and increased balance of Ang 1–7/Ang II, along with positive modulation of Ang II signaling through AT2 receptors and Ang 1–7 signaling through Mas receptors, may be an appropriate strategy for improving cognitive function and treating dementia.