Identification of membrane-bound variant of metalloendopeptidase neurolysin (EC 3.4.24.16) as the non-angiotensin type 1 (non-AT1), non-AT2 angiotensin binding site

Discovery of the Next Generation of Non-peptidomimetic Neurolysin Activators with High Blood-Brain Barrier Permeability: a Pharmacokinetics Study in Healthy and Stroke Animals

PURPOSE

There is growing interest in seeking pharmacological activation of neurolysin (Nln) for stroke treatment. Discovery of central nervous system drugs remains challenging due to the protection of the blood-brain barrier (BBB). The previously reported peptidomimetic Nln activators display unsatisfactory BBB penetration. Herein, we investigate the next generation of non-peptidomimetic Nln activators with high BBB permeability.

METHODS

A BBB-mimicking model was used to evaluate their in vitro BBB permeability. Protein binding, metabolic stability, and efflux assays were performed to determine their unbound fraction, half-lives in plasma and brains, and dependence of BBB transporter P-glycoprotein (P-gp). The in vivo pharmacokinetic profiles were elucidated in healthy and stroke mice.

RESULTS

Compounds KS52 and KS73 out of this generation exhibit improved peptidase activity and BBB permeability compared to the endogenous activator and previous peptidomimetic activators. They show reasonable plasma and brain protein binding, improved metabolic stability, and independence of P-gp-mediated efflux. In healthy animals, they rapidly distribute into brains and reach peak levels of 18.69% and 12.10% injected dose (ID)/ml at 10 min. After 4 h, their total brain concentrations remain 7.78 and 12.34 times higher than their A50(minimal concentration required for enhancing 50% peptidase activity). Moreover, the ipsilateral hemispheres of stroke animals show comparable uptake to the corresponding contralateral hemispheres and healthy brains.

CONCLUSIONS

This study provides essential details about the pharmacokinetic properties of a new generation of potent non-peptidomimetic Nln activators with high BBB permeability and warrants the future development of these agents as potential neuroprotective pharmaceutics for stroke treatment.

DNA methylation and 28-year cardiovascular disease risk in type 1 diabetes: the Epidemiology of Diabetes Complications (EDC) cohort study

BACKGROUND

The potential for DNA methylation (DNAm) as an early marker for cardiovascular disease (CVD) and how such an association might differ by glycemic exposure has not been examined in type 1 diabetes, a population at increased CVD risk. We thus performed a prospective epigenome-wide association study of blood leukocyte DNAm (EPIC array) and time to CVD incidence over 28 years in a childhood-onset (< 17 years) type 1 diabetes cohort, the Pittsburgh Epidemiology of Diabetes Complications (EDC) study (n = 368 with DNA and no CVD at baseline), both overall and separately by glycemic exposure, as measured by HbA1c at baseline (split at the median: < 8.9% and ≥ 8.9%). We also assessed whether DNAm-CVD associations were independent of established cardiometabolic risk factors, including body mass index, estimated glucose disposal rate, cholesterol, triglycerides, blood pressure, pulse rate, albumin excretion rate, and estimated glomerular filtration rate.

RESULTS

CVD (first instance of CVD death, myocardial infarction, coronary revascularization, ischemic ECG, angina, or stroke) developed in 172 participants (46.7%) over 28 years. Overall, in Cox regression models for time to CVD, none of the 683,597 CpGs examined reached significance at a false discovery rate (FDR) ≤ 0.05. In participants with HbA1c < 8.9% (n = 180), again none reached FDR ≤ 0.05, but three were associated at the a priori nominal significance level FDR ≤ 0.10: cg07147033 in MIB2, cg12324048 (intergenic, chromosome 3), and cg15883830 (intergenic, chromosome 1). In participants with HbA1c ≥ 8.9% (n = 188), two CpGs in loci involved in calcium channel activity were significantly associated with CVD (FDR ≤ 0.05): cg21823999 in GPM6A and cg23621817 in CHRNA9; four additional CpGs were nominally associated (FDR ≤ 0.10). In participants with HbA1c ≥ 8.9%, DNAm-CVD associations were only modestly attenuated after cardiometabolic risk factor adjustment, while attenuation was greater in those with HbA1c < 8.9%. No pathways were enriched in those with HbA1c < 8.9%, while pathways for calcium channel activity and integral component of synaptic membrane were significantly enriched in those with HbA1c ≥ 8.9%.

CONCLUSIONS

These results provide novel evidence that DNAm at loci involved in calcium channel activity and development may contribute to long-term CVD risk beyond known risk factors in type 1 diabetes, particularly in individuals with greater glycemic exposure, warranting further study.

Design, synthesis and biological evaluation of novel indole-3-carboxylic acid derivatives with antihypertensive activity

Molecular design, synthesis, in vitro and in vivo studies of novel derivatives of indole-3-carboxylic acid - new series of angiotensin II receptor 1 antagonists is presented. Radioligand binding studies using [¹²⁵I]-angiotensin II displayed that new derivatives of indole-3-carboxylic acid have a high nanomolar affinity for the angiotensin II receptor (AT₁ subtype) on a par with the known pharmaceuticals such as losartan. Biological studies of synthesized compounds in spontaneously hypertensive rats have demonstrated that compounds can lower blood pressure when administered orally. Maximum the decrease in blood pressure was 48 mm Hg with oral administration of 10 mg/kg and antihypertensive effect was observed for 24 hours, which is superior to losartan.

Dipeptidylamino-tripeptidylcarboxypeptidase NEMP3 and DPP3 (DPP III) are the same protein

Earlier it was shown that a group of extracellular low-specific metallopeptidases is present in the mammalian brain Kropotova and Mosevitsky (2016) [1]. These enzymes are weakly connected to the axonal ends of neurons. They were named Neuron bound Extracellular MetalloPeptidases (NEMP). The enzyme named NEMP3 turned out to be a unique exopeptidase that exhibits two activities: it removes the dipeptide from the N-end of the peptide, and it can also remove the tripeptide from the C-end of the peptide. Therefore, NEMP3 possesses the activities of dipeptidylaminopeptidase and of tripeptidylcarboxypeptidase. Mass spectrometry has revealed a homology of NEMP3 with DPP3 (DPP III, EC3.4.14.4), known as cytosolic dipeptidylaminopeptidase. We isolated DPP3 from rat and bovine liver and brain by the procedures used for this purpose by other authors. The effect of DPP3 on test peptides is the same as that of NEMP3. In particular, all DPP3 samples delete the tripeptide (AKF) from the C-end of the test peptide blocked at the N-end. The data obtained show that NEMP3 and DPP3 are the same protein (enzyme). Thus, DPP3 has two exopeptidase activities: the previously known activity of dipeptidylaminopeptidase and the activity of tripeptidylcarboxypeptidase discovered in this study. Another discovery is the extracellular activity of DPP 3 in the mammalian brain near synapses, which controls neuropeptides. DPP3 is involved in various processes, but in many cases its role remains to be clarified. The results obtained in this study will be useful for solving these questions.

In-Vivo and Ex-Vivo Brain Uptake Studies of Peptidomimetic Neurolysin Activators in Healthy and Stroke Animals

PURPOSE

Neurolysin (Nln) is a peptidase that functions to preserve the brain following ischemic stroke by hydrolyzing various neuropeptides. Nln activation has emerged as an attractive drug discovery target for treatment of ischemic stroke. Among first-in-class peptidomimetic Nln activators, we selected three lead compounds (9d, 10c, 11a) for quantitative pharmacokinetic analysis to provide valuable information for subsequent preclinical development.

METHODS

Pharmacokinetic profile of these compounds was studied in healthy and ischemic stroke-induced mice after bolus intravenous administration. Brain concentration and brain uptake clearance (K_in) was calculated from single time point analysis. The inter-relationship between LogP with in-vitro and in-vivo permeability was studied to determine CNS penetration. Brain slice uptake method was used to study tissue binding, whereas P-gp-mediated transport was evaluated to understand the potential brain efflux of these compounds.

RESULTS

According to calculated parameters, all three compounds showed a detectable amount in the brain after intravenous administration at 4 mg/kg; however, 11a had the highest brain concentration and brain uptake clearance. A strong correlation was documented between in-vitro and in-vivo permeability data. The efflux ratio of 10c was ~6-fold higher compared to 11a and correlated well with its lower K_in value. In experimental stroke animals, the K_in of 11a was significantly higher in ischemic vs. contralateral and intact hemispheres, though it remained below its A₅₀ value required to activate Nln.

CONCLUSIONS

Collectively, these preclinical pharmacokinetic studies reveal promising BBB permeability of 11a and indicate that it can serve as an excellent lead for developing improved drug-like Nln activators.

Identification and Characterization of Two Structurally Related Dipeptides that Enhance Catalytic Efficiency of Neurolysin

Neurolysin (Nln) is a recently recognized endogenous mechanism functioning to preserve the brain from ischemic injury. To further understand the pathophysiological function of this peptidase in stroke and other neurologic disorders, the present study was designed to identify small molecule activators of Nln. Using a computational approach, the structure of Nln was explored, which was followed by docking and in silico screening of ∼140,000 molecules from the National Cancer Institute Developmental Therapeutics Program database. Top ranking compounds were evaluated in an Nln enzymatic assay, and two hit histidine-dipeptides were further studied in detail. The identified dipeptides enhanced the rate of synthetic substrate hydrolysis by recombinant (human and rat) and mouse brain-purified Nln in a concentration-dependent manner (micromolar A50 and Amax ≥ 300%) but had negligible effect on activity of closely related peptidases. Both dipeptides also enhanced hydrolysis of Nln endogenous substrates neurotensin, angiotensin I, and bradykinin and increased efficiency of the synthetic substrate hydrolysis (Vmax/Km ratio) in a concentration-dependent manner. The dipeptides and competitive inhibitor dynorphin A (1-13) did not affect each other's affinity for Nln, suggesting differing nature of their respective binding sites. Lastly, drug affinity responsive target stability (DARTS) and differential scanning fluorimetry (DSF) assays confirmed concentration-dependent interaction of Nln with the activator molecule. This is the first study demonstrating that Nln activity can be enhanced by small molecules, although the peptidic nature and low potency of the activators limit their application. The identified dipeptides provide a chemical scaffold to develop high-potency, drug-like molecules as research tools and potential drug leads. SIGNIFICANCE STATEMENT: This study describes discovery of two molecules that selectively enhance activity of peptidase Nln-a newly recognized cerebroprotective mechanism in the poststroke brain. The identified molecules will serve as a chemical scaffold for development of drug-like molecules to further study Nln and may become lead structures for a new class of drugs. In addition, our conceptual and methodological framework and research findings might be used for other peptidases and enzymes, the activation of which bears therapeutic potential.

Alterations in Gene Expression of Renin-Angiotensin System Components and Related Proteins in Colorectal Cancer

MATERIALS AND METHODS

Quantitative expression of the RNA of these 17 genes in normal and cancerous tissues obtained using chip arrays from the public functional genomics data repository, Gene Expression Omnibus (GEO) application, was compared statistically.

RESULTS

Expression of four genes, AGT (angiotensinogen), ENPEP (aminopeptidase A) MME (neprilysin), and PREP (prolyl endopeptidase), was significantly upregulated in CRC specimens. Expression of REN (renin), THOP (thimet oligopeptidase), NLN (neurolysin), PRCP (prolyl carboxypeptidase), ANPEP (aminopeptidase N), and MAS1 (Mas receptor) was downregulated in CRC specimens.

CONCLUSIONS

Presuming gene expression parallel protein expression, these results suggest that increased production of the angiotensinogen precursor of angiotensin (ANG) peptides, with the reduction of the enzymes that metabolize it to ANG II, can lead to accumulation of angiotensinogen in CRC tissues. Downregulation of THOP, NLN, PRCP, and MAS1 gene expression, whose proteins contribute to the ACE2/ANG 1-7/Mas axis, suggests that reduced activity of this RAS branch could be permissive for oncogenicity. Components of the RAS may be potential therapeutic targets for treatment of CRC.

Delayed Exercise-induced Upregulation of Angiogenic Proteins and Recovery of Motor Function after Photothrombotic Stroke in Mice

Treatments promoting post-stroke functional recovery continue to be an unmet therapeutic problem with physical rehabilitation being the most reproduced intervention in preclinical and clinical studies. Unfortunately, physiotherapy is typically effective at high intensity and early after stroke - requirements that are hardly attainable by stroke survivors. The aim of this study was to directly evaluate and compare the dose-dependent effect of delayed physical rehabilitation (daily 5 h or overnight voluntary wheel running; initiated on post-stroke day 7 and continuing through day 21) on recovery of motor function in the mouse photothrombotic model of ischemic stroke and correlate it with angiogenic potential of the brain. Our observations indicate that overnight but not 5 h access to running wheels facilitates recovery of motor function in mice in grid-walking test. Western blotting and immunofluorescence microscopy experiments evaluating the expression of angiogenesis-associated proteins VEGFR2, doppel and PDGFRβ in the peri-infarct and corresponding contralateral motor cortices indicate substantial upregulation of these proteins (≥2-fold) in the infarct core and surrounding cerebral cortex in the overnight running mice on post-stroke day 21. These findings indicate that there is a dose-dependent relationship between the extent of voluntary exercise, motor recovery and expression of angiogenesis-associated proteins in this expert-recommended mouse ischemic stroke model. Notably, our observations also point out to enhanced angiogenesis and presence of pericytes within the infarct core region during the chronic phase of stroke, suggesting a potential contribution of this tissue area in the mechanisms governing post-stroke functional recovery.

Between two storms, vasoactive peptides or bradykinin underlie severity of COVID-19?

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to be a world-wide pandemic with overwhelming socioeconomic impact. Since inflammation is one of the major causes of COVID-19 complications, the associated molecular mechanisms have been the focus of many studies to better understand this disease and develop improved treatments for patients contracting SARS-CoV-2. Among these, strong emphasis has been placed on pro-inflammatory cytokines, associating severity of COVID-19 with so-called "cytokine storm." More recently, peptide bradykinin, its dysregulated signaling or "bradykinin storm," has emerged as a primary mechanism to explain COVID-19-related complications. Unfortunately, this important development may not fully capture the main molecular players that underlie the disease severity. To this end, in this focused review, several lines of evidence are provided to suggest that in addition to bradykinin, two closely related vasoactive peptides, substance P and neurotensin, are also likely to drive microvascular permeability and inflammation, and be responsible for development of COVID-19 pathology. Furthermore, based on published experimental observations, it is postulated that in addition to ACE and neprilysin, peptidase neurolysin (Nln) is also likely to contribute to accumulation of bradykinin, substance P and neurotensin, and progression of the disease. In conclusion, it is proposed that "vasoactive peptide storm" may underlie severity of COVID-19 and that simultaneous inhibition of all three peptidergic systems could be therapeutically more advantageous rather than modulation of any single mechanism alone.

The Effect of Histone Deacetylase Inhibitors Panobinostat or Entinostat on Motor Recovery in Mice After Ischemic Stroke

Using rigorous and clinically relevant experimental design and analysis standards, in this study, we investigated the potential of histone deacetylase (HDAC) inhibitors panobinostat and entinostat to enhance recovery of motor function after photothrombotic stroke in male mice. Panobinostat, a pan-HDAC inhibitor, is a FDA-approved drug for certain cancers, whereas entinostat is a class-I HDAC inhibitor in late stage of clinical investigation. The drugs were administered every other day (panobinostat-3 or 10 mg/kg; entinostat-1.7 or 5 mg/kg) starting from day 5 to 15 after stroke. To imitate the current standard of care in stroke survivors, i.e., physical rehabilitation, the animals run on wheels (2 h daily) from post-stroke day 9 to 41. The predetermined primary end point was motor recovery measured in two tasks of spontaneous motor behaviors in grid-walking and cylinder tests. In addition, we evaluated the running distance and speed throughout the study, and the number of parvalbumin-positive neurons in medial agranular cortex (AGm) and infarct volumes at the end of the study. Both sensorimotor tests revealed that combination of physical exercise with either drug did not substantially affect motor recovery in mice after stroke. This was accompanied by negligible changes of parvalbumin-positive neurons recorded in AGm and comparable infarct volumes among experimental groups, while dose-dependent increase in acetylated histone 3 was observed in peri-infarct cortex of drug-treated animals. Our observations suggest that add-on panobinostat or entinostat therapy coupled with limited physical rehabilitation is unlikely to offer therapeutic modality for stroke survivors who have motor dysfunction.

Neurolysin substrates bradykinin, neurotensin and substance P enhance brain microvascular permeability in a human in vitro model

Increased brain microvascular permeability and disruption of blood-brain barrier (BBB) function are among hallmarks of several acute neurodegenerative disorders, including stroke. Numerous studies suggest the involvement of bradykinin (BK), neurotensin (NT) and substance P (SP) in BBB impairment and oedema formation after stroke; however, there is paucity of data in regard to the direct effects of these peptides on the brain microvascular endothelial cells (BMECs) and BBB. The present study aimed to evaluate the direct effects of BK, NT and SP on the permeability of BBB in an in vitro model based on human induced pluripotent stem cell (iPSC)-derived BMECs. Our data indicate that all three peptides increase BBB permeability in a concentration-dependent manner in an in vitro model formed from two different iPSC lines (CTR90F and CTR65M) and widely used hCMEC/D3 human BMECs. The combination of BK, NT and SP at a sub-effective concentration also resulted in increased BBB permeability in the iPSC-derived model indicating potentiation of their action. Furthermore, we observed abrogation of BK, NT and SP effects with pretreatment of pharmacological blockers targeting their specific receptors. Additional mechanistic studies indicate that the short-term effects of these peptides are not mediated through alteration of tight-junction proteins claudin-5 and occludin, but likely involve redistribution of F-actin and secretion of vascular endothelial growth factor. This is the first experimental study to document the increased permeability of the BBB in response to direct action of NT in an in vitro model. In addition, our study confirms the expected but not well-documented, direct effect of SP on BBB permeability and adds to the well-recognised actions of BK on BBB. Lastly, we demonstrate that peptidase neurolysin can neutralise the effects of these peptides on BBB, suggesting potential therapeutic implications.

Investigation of Receptor Heteromers Using NanoBRET Ligand Binding

Receptor heteromerization is the formation of a complex involving at least two different receptors with pharmacology that is distinct from that exhibited by its constituent receptor units. Detection of these complexes and monitoring their pharmacology is crucial for understanding how receptors function. The Receptor-Heteromer Investigation Technology (Receptor-HIT) utilizes ligand-dependent modulation of interactions between receptors and specific biomolecules for the detection and profiling of heteromer complexes. Previously, the interacting biomolecules used in Receptor-HIT assays have been intracellular proteins, however in this study we have for the first time used bioluminescence resonance energy transfer (BRET) with fluorescently-labeled ligands to investigate heteromerization of receptors on the cell surface. Using the Receptor-HIT ligand binding assay with NanoBRET, we have successfully investigated heteromers between the angiotensin II type 1 (AT1) receptor and the β2 adrenergic receptor (AT1-β2AR heteromer), as well as between the AT1 and angiotensin II type 2 receptor (AT1-AT2 heteromer).

The role of peptidase neurolysin in neuroprotection and neural repair after stroke

Current experimental stroke research has evolved to focus on detailed understanding of the brain’s self-protective and restorative mechanisms, and harness this knowledge for development of new therapies. In this context, the role of peptidases and neuropeptides is of growing interest. In this focused review, peptidase neurolysin (Nln) and its extracellular peptide substrates are briefly discussed in relation to pathophysiology of ischemic stroke. Upregulation of Nln following stroke is viewed as a compensatory cerebroprotective mechanism in the acute phase of stroke, because the main neuropeptides inactivated by Nln are neuro/cerebrotoxic (bradykinin, substance P, neurotensin, angiotensin II, hemopressin), whereas the peptides generated by Nln are neuro/cerebroprotective (angiotensin-(1–7), Leu-/Met-enkephalins). This notion is confirmed by experimental studies documenting aggravation of stroke outcomes in mice after inhibition of Nln following stroke, and dramatic improvement of stroke outcomes in mice overexpressing Nln in the brain. The role of Nln in the (sub)chronic phase of stroke is less clear and it is likely, that this peptidase does not have a major role in neural repair mechanisms. This is because, the substrates of Nln are less uniform in modulating neurorestorative mechanisms in one direction, some appearing to have neural repair enhancing/stimulating potential, whereas others doing the opposite. Future studies focusing on the role of Nln in pathophysiology of stroke should determine its potential as a cerebroprotective target for stroke therapy, because its unique ability to modulate multiple neuropeptide systems critically involved in brain injury mechanisms is likely advantageous over modulation of one pathogenic pathway for stroke pharmacotherapy.

Delayed atomoxetine or fluoxetine treatment coupled with limited voluntary running promotes motor recovery in mice after ischemic stroke

Currently, there is an unmet need for treatments promoting post-stroke functional recovery. The aim of this study was to evaluate and compare the dose-dependent effect of delayed atomoxetine or fluoxetine therapy (starting on post-stroke day 5), coupled with limited physical exercise (2 hours daily voluntary wheel running; post-stroke days 9 to 42), on motor recovery of adult male mice after photothrombotic stroke. These drugs are selective norepinephrine or serotonin reuptake inhibitors indicated for disorders unrelated to stroke. The predetermined primary end-point for this study was motor function measured in two tasks of spontaneous motor behaviors in grid-walking and cylinder tests. Additionally, we quantified the running distance and speed throughout the study, the number of parvalbumin-positive neurons in the medial agranular cortex and infarct volumes. Both sensorimotor tests revealed that neither limited physical exercise nor a drug treatment alone significantly facilitated motor recovery in mice after stroke. However, combination of physical exercise with either of the drugs promoted restoration of motor function by day 42 post-stroke, with atomoxetine being a more potent drug. This was accompanied by a significant decrease in parvalbumin-positive inhibitory interneurons in the ipsilateral medial agranular cortex of mice with recovering motor function, while infarct volumes were comparable among experimental groups. If further validated in larger studies, our observations suggest that add-on atomoxetine or fluoxetine therapy coupled with limited, structured physical rehabilitation could offer therapeutic modality for stroke survivors who have difficulty to engage in early, high-intensity physiotherapy. Furthermore, in light of the recently completed Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) and Efficacy oF Fluoxetine-a randomisEd Controlled Trial in Stroke (EFFECTS) trials, our observations call for newly designed studies where fluoxetine or atomoxetine pharmacotherapy is evaluated in combination with structured physical rehabilitation rather than alone. This study was approved by the Texas Tech University Health Sciences Center Institutional Animal Care and Use Committee (protocol # 16019).

Peptidase neurolysin functions to preserve the brain after ischemic stroke in male mice

Previous studies documented up-regulation of peptidase neurolysin (Nln) after brain ischemia, however, the significance of Nln function in the post-stroke brain remained unknown. The aim of this study was to assess the functional role of Nln in the brain after ischemic stroke. Administration of a specific Nln inhibitor Agaricoglyceride A (AgaA) to mice after stroke in a middle cerebral artery occlusion model, dose-dependently aggravated injury measured by increased infarct and edema volumes, blood-brain barrier disruption, increased levels of interleukin 6 and monocyte chemoattractant protein-1, neurological and motor deficit 24 h after stroke. In this setting, AgaA resulted in inhibition of Nln in the ischemic hemisphere leading to increased levels of Nln substrates bradykinin, neurotensin, and substance P. AgaA lacked effects on several physiological parameters and appeared non-toxic to mice. In a reverse approach, we developed an adeno-associated viral vector (AAV2/5-CAG-Nln) to overexpress Nln in the mouse brain. Applicability of AAV2/5-CAG-Nln to transduce catalytically active Nln was confirmed in primary neurons and in vivo. Over-expression of Nln in the mouse brain was also accompanied by decreased levels of its substrates. Two weeks after in vivo transduction of Nln using the AAV vector, mice were subjected to middle cerebral artery occlusion and the same outcome measures were evaluated 72 h later. These experiments revealed that abundance of Nln in the brain protects animals from stroke. This study is the first to document functional significance of Nln in pathophysiology of stroke and provide evidence that Nln is an endogenous mechanism functioning to preserve the brain from ischemic injury.

Peptidase neurolysin is an endogenous cerebroprotective mechanism in acute neurodegenerative disorders

Stroke and traumatic brain injury (TBI) are significant clinical problems characterized by high rate of mortality and long-lasting disabilities, and an unmet need for new treatments. Current experimental stroke and TBI research are evolving to focus more on understanding the brain's self-protective mechanisms to meet the critical need of developing new therapies for these disorders. In this hypothesis-based manuscript, I provide several lines of evidence that peptidase neurolysin (Nln) is one of the brain's potent, self-protective mechanisms promoting preservation and recovery of the brain after acute injury. Based on published experimental observations and ongoing studies in our laboratory, I posit that Nln is a compensatory and cerebroprotective mechanism in the post-stroke/TBI brain that functions to process a diverse group of extracellular neuropeptides and by that to reduce excitotoxicity, oxidative stress, edema formation, blood brain barrier hyper-permeability, and neuroinflammation. If this hypothesis is correct, Nln could potentially serve as a single therapeutic target to modulate the function of multiple targets, the involved neuropeptide systems, critically involved in various mechanisms of brain injury and cerebroprotection/restoration. Such multi-pathway target would be highly desired for pharmacotherapy of stroke and TBI, because targeting one pathophysiological pathway has proven to be ineffective for such complex disorders.

Preparation and preliminary characterization of recombinant neurolysin for in vivo studies

The goal of this study was to produce milligram quantities of pure, catalytically active, endotoxin-free recombinant neurolysin (rNln) in standard laboratory conditions for use as a research tool. To this end, we transformed E. coli cells with a plasmid construct for polyhistidine-tagged rNln, selected a high-expressing clone and determined the optimal time-point for translation of rNln. rNln was purified to homogeneity from the soluble pool of the cell lysate using Ni-NTA affinity and size-exclusion chromatography, followed by removal of endotoxins. Using this protocol ∼3mg pure, catalytically active and nearly endotoxin-free (≈0.003EU/μg protein) rNln was reproducibly obtained from 1l of culture. Lack of cytotoxicity of rNln preparation was documented in cultured mouse cells, whereas stability in whole mouse blood. Intraperitonealy administered rNln in mice reached the systemic circulation in intact and enzymatically active form with Tmax of 1h and T1/2 of ∼30min. Administration of rNln (2 and 10mg/kg) did not alter arterial blood pressure, heart rate, body temperature and blood glucose levels in mice. These studies demonstrate that the rNln preparation is suitable for cell culture and in vivo studies and can serve as a research tool to investigate the (patho)physiological function of this peptidase.

Rational drug design and synthesis of molecules targeting the angiotensin II type 1 and type 2 receptors

The angiotensin II (Ang II) type 1 and type 2 receptors (AT1R and AT2R) orchestrate an array of biological processes that regulate human health. Aberrant function of these receptors triggers pathophysiological responses that can ultimately lead to death. Therefore, it is important to design and synthesize compounds that affect beneficially these two receptors. Cardiovascular disease, which is attributed to the overactivation of the vasoactive peptide hormone Αng II, can now be treated with commercial AT1R antagonists. Herein, recent achievements in rational drug design and synthesis of molecules acting on the two AT receptors are reviewed. Quantitative structure activity relationships (QSAR) and molecular modeling on the two receptors aim to assist the search for new active compounds. As AT1R and AT2R are GPCRs and drug action is localized in the transmembrane region the role of membrane bilayers is exploited. The future perspectives in this field are outlined. Tremendous progress in the field is expected if the two receptors are crystallized, as this will assist the structure based screening of the chemical space and lead to new potent therapeutic agents in cardiovascular and other diseases.

The impact of age-related dysregulation of the angiotensin system on mitochondrial redox balance

Aging is associated with the accumulation of various deleterious changes in cells. According to the free radical and mitochondrial theory of aging, mitochondria initiate most of the deleterious changes in aging and govern life span. The failure of mitochondrial reduction-oxidation (redox) homeostasis and the formation of excessive free radicals are tightly linked to dysregulation in the Renin Angiotensin System (RAS). A main rate-controlling step in RAS is renin, an enzyme that hydrolyzes angiotensinogen to generate angiotensin I. Angiotensin I is further converted to Angiotensin II (Ang II) by angiotensin-converting enzyme (ACE). Ang II binds with equal affinity to two main angiotensin receptors—type 1 (AT₁R) and type 2 (AT₂R). The binding of Ang II to AT₁R activates NADPH oxidase, which leads to increased generation of cytoplasmic reactive oxygen species (ROS). This Ang II-AT₁R–NADPH-ROS signal triggers the opening of mitochondrial K_ATP channels and mitochondrial ROS production in a positive feedback loop. Furthermore, RAS has been implicated in the decrease of many of ROS scavenging enzymes, thereby leading to detrimental levels of free radicals in the cell. AT₂R is less understood, but evidence supports an anti-oxidative and mitochondria-protective function for AT₂R. The overlap between age related changes in RAS and mitochondria, and the consequences of this overlap on age-related diseases are quite complex. RAS dysregulation has been implicated in many pathological conditions due to its contribution to mitochondrial dysfunction. Decreased age-related, renal and cardiac mitochondrial dysfunction was seen in patients treated with angiotensin receptor blockers. The aim of this review is to: (a) report the most recent information elucidating the role of RAS in mitochondrial redox hemostasis and (b) discuss the effect of age-related activation of RAS on generation of free radicals.

Recent insights and therapeutic perspectives of angiotensin-(1-9) in the cardiovascular system

Chronic RAS (renin-angiotensin system) activation by both AngII (angiotensin II) and aldosterone leads to hypertension and perpetuates a cascade of pro-hypertrophic, pro-inflammatory, pro-thrombotic and atherogenic effects associated with cardiovascular damage. In 2000, a new pathway consisting of ACE2 (angiotensin-converting enzyme2), Ang-(1-9) [angiotensin-(1-9)], Ang-(1-7) [angiotensin-(1-7)] and the Mas receptor was discovered. Activation of this novel pathway stimulates vasodilation, anti-hypertrophy and anti-hyperplasia. For some time, studies have focused mainly on ACE2, Ang-(1-7) and the Mas receptor, and their biological properties that counterbalance the ACE/AngII/AT1R (angiotensin type 1 receptor) axis. No previous information about Ang-(1-9) suggested that this peptide had biological properties. However, recent data suggest that Ang-(1-9) protects the heart and blood vessels (and possibly the kidney) from adverse cardiovascular remodelling in patients with hypertension and/or heart failure. These beneficial effects are not modified by the Mas receptor antagonist A779 [an Ang-(1-7) receptor blocker], but they are abolished by the AT2R (angiotensin type 2 receptor) antagonist PD123319. Current information suggests that the beneficial effects of Ang-(1-9) are mediated via the AT2R. In the present review, we summarize the biological effects of the novel vasoactive peptide Ang-(1-9), providing new evidence of its cardiovascular-protective activity. We also discuss the potential mechanism by which this peptide prevents and ameliorates the cardiovascular damage induced by RAS activation.

Electroosmotic perfusion of tissue: sampling the extracellular space and quantitative assessment of membrane-bound enzyme activity in organotypic hippocampal slice cultures

This review covers recent advances in sampling fluid from the extracellular space of brain tissue by electroosmosis (EO). Two techniques, EO sampling with a single fused-silica capillary and EO push-pull perfusion, have been developed. These tools were used to investigate the function of membrane-bound enzymes with outward-facing active sites, or ectoenzymes, in modulating the activity of the neuropeptides leu-enkephalin and galanin in organotypic-hippocampal-slice cultures (OHSCs). In addition, the approach was used to determine the endogenous concentration of a thiol, cysteamine, in OHSCs. We have also investigated the degradation of coenzyme A in the extracellular space. The approach provides information on ectoenzyme activity, including Michaelis constants, in tissue, which, as far as we are aware, has not been done before. On the basis of computational evidence, EO push-pull perfusion can distinguish ectoenzyme activity with a ~100 μm spatial resolution, which is important for studies of enzyme kinetics in adjacent regions of the rat hippocampus.

Distribution of non-AT1, non-AT2 binding of 125I-sarcosine1, isoleucine8 angiotensin II in neurolysin knockout mouse brains

The recent identification of a novel binding site for angiotensin (Ang) II as the peptidase neurolysin (E.C. 3.4.24.16) has implications for the renin-angiotensin system (RAS). This report describes the distribution of specific binding of ¹²⁵I-Sarcosine¹, Isoleucine⁸ Ang II (¹²⁵I-SI Ang II) in neurolysin knockout mouse brains compared to wild-type mouse brains using quantitative receptor autoradiography. In the presence of p-chloromercuribenzoic acid (PCMB), which unmasks the novel binding site, widespread distribution of specific (3 µM Ang II displaceable) ¹²⁵I-SI Ang II binding in 32 mouse brain regions was observed. Highest levels of binding >700 fmol/g initial wet weight were seen in hypothalamic, thalamic and septal regions, while the lowest level of binding <300 fmol/g initial wet weight was in the mediolateral medulla. ¹²⁵I-SI Ang II binding was substantially higher by an average of 85% in wild-type mouse brains compared to neurolysin knockout brains, suggesting the presence of an additional non-AT₁, non-AT₂, non-neurolysin Ang II binding site in the mouse brain. Binding of ¹²⁵I-SI Ang II to neurolysin in the presence of PCMB was highest in hypothalamic and ventral cortical brain regions, but broadly distributed across all regions surveyed. Non-AT₁, non-AT₂, non-neurolysin binding was also highest in the hypothalamus but had a different distribution than neurolysin. There was a significant reduction in AT₂ receptor binding in the neurolysin knockout brain and a trend towards decreased AT₁ receptor binding. In the neurolysin knockout brains, the size of the lateral ventricles was increased by 56% and the size of the mid forebrain (−2.72 to +1.48 relative to Bregma) was increased by 12%. These results confirm the identity of neurolysin as a novel Ang II binding site, suggesting that neurolysin may play a significant role in opposing the pathophysiological actions of the brain RAS and influencing brain morphology.

Peptidomic analysis of the neurolysin-knockout mouse brain

A large number of intracellular peptides are constantly produced following protein degradation by the proteasome. A few of these peptides function in cell signaling and regulate protein-protein interactions. Neurolysin (Nln) is a structurally defined and biochemically well-characterized endooligopeptidase, and its subcellular distribution and biological activity in the vertebrate brain have been previously investigated. However, the contribution of Nln to peptide metabolism in vivo is poorly understood. In this study, we used quantitative mass spectrometry to investigate the brain peptidome of Nln-knockout mice. An additional in vitro digestion assay with recombinant Nln was also performed to confirm the identification of the substrates and/or products of Nln. Altogether, the data presented suggest that Nln is a key enzyme in the in vivo degradation of only a few peptides derived from proenkephalin, such as Met-enkephalin and octapeptide. Nln was found to have only a minor contribution to the intracellular peptide metabolism in the entire mouse brain. However, further studies appear necessary to investigate the contribution of Nln to the peptide metabolism in specific areas of the murine brain.

BIOLOGICAL SIGNIFICANCE

Neurolysin was first identified in the synaptic membranes of the rat brain in the middle 80's by Frederic Checler and colleagues. Neurolysin was well characterized biochemically, and its brain distribution has been confirmed by immunohistochemical methods. The neurolysin contribution to the central and peripheral neurotensin-mediated functions in vivo has been delineated through inhibitor-based pharmacological approaches, but its genuine contribution to the physiological inactivation of neuropeptides remains to be firmly established. As a result, the main significance of this work is the first characterization of the brain peptidome of the neurolysin-knockout mouse. This article is part of a Special Issue entitled: Proteomics, mass spectrometry and peptidomics, Cancun 2013. Guest Editors: César López-Camarillo, Victoria Pando-Robles and Bronwyn Jane Barkla.

Functional up-regulation of endopeptidase neurolysin during post-acute and early recovery phases of experimental stroke in mouse brain

In this study, we provide evidence for the first time that membrane-bound endopeptidase neurolysin is up-regulated in different parts of mouse brain affected by focal ischemia-reperfusion in a middle cerebral artery occlusion model of stroke. Radioligand binding, enzymatic and immunoblotting experiments in membrane preparations of frontoparietal cortex, striatum, and hippocampus isolated from the ischemic hemisphere of mouse brain 24 h after reperfusion revealed statistically significant increase (≥ twofold) in quantity and activity of neurolysin compared with sham-operated controls. Cerebellar membranes isolated from the ischemic hemisphere served as negative control supporting the observations that up-regulation of neurolysin occurs in post-ischemic brain regions. This study also documents sustained functional up-regulation of neurolysin in frontoparietal cortical membranes for at least 7 days after stroke, which appears not to be transcriptionally or translationally regulated, but rather depends on translocation of cytosolic neurolysin to the membranes and mitochondria. Considering diversity of endogenous neurolysin substrates (neurotensin, bradykinin, angiotensins I/II, substance P, hemopressin, dynorphin A(1-8), metorphamide, somatostatin) and the well-documented role of these peptidergic systems in pathogenesis of stroke, resistance to ischemic injury and/or post-stroke brain recovery, our findings suggest that neurolysin may play a role in processes modulating the brain's response to stroke and its recovery after stroke.

Pharmacological characterization of a novel non-AT1, non-AT2 angiotensin binding site identified as neurolysin

The discovery of a novel non-AT1, non-AT2 binding site for angiotensins in the rodent brain and testis that is unmasked by the organomercurial compound para-chloromercuribenzoic acid (PCMB) has catalyzed efforts to purify and characterize this protein. We recently reported that this protein is neurolysin and now report upon the specificity of this binding site for various neuropeptides. Competition binding assays in rat brain and testis used (125)I-Sar(1), Ile(8) angiotensin II (Ang II) as the radioligand in the presence of saturating concentrations of AT1 and AT2 receptor antagonists and 100 μM parachloromercuribenzoate. Primary screening of 36 peptides and other compounds at 10 μM concentration revealed seven peptides that inhibited specific binding >50 %: ghrelin, Tyr(1) S36057 (a melanin-concentrating hormone receptor ligand), orphanin FQ and its congeners (Tyr(1) and Tyr(14)), Dynorphin A (1-8), and Ang (1-9). The selective neurolysin inhibitor Proline-Isoleucine dipeptide was inactive at 1 mM. These results suggest that the ability of PCMB to unmask high affinity binding of Ang II to neurolysin is a pharmacological effect and that neurolysin may significantly affect the activity of the renin-angiotensin system.

The effects of para-chloromercuribenzoic acid and different oxidative and sulfhydryl agents on a novel, non-AT1, non-AT2 angiotensin binding site identified as neurolysin

A novel, non-AT1, non-AT2 brain binding site for angiotensin peptides that is unmasked by p-chloromercuribenzoate (PCMB) has been identified as a membrane associated variant of neurolysin. The ability of different organic and inorganic oxidative and sulfhydryl reactive agents to unmask or inhibit 125I-Sar1Ile8 angiotensin II (SI-Ang II) binding to this site was presently examined. In tissue membranes from homogenates of rat brain and testis incubated in assay buffer containing losartan (10 μM) and PD123319 (10 μM) plus 100 μM PCMB, 5 of the 39 compounds tested inhibited 125I-SI Ang II binding in brain and testis. Mersalyl acid, mercuric chloride (HgCl2) and silver nitrate (AgNO3) most potently inhibited 125I-SI Ang II binding with IC50s ~1-20 μM. This HgCl2 inhibition was independent of any interaction of HgCl2 with angiotensin II (Ang II) based on the lack of effect of HgCl2 on the dipsogenic effects of intracerebroventricularly administered Ang II and 125I-SI Ang II binding to AT1 receptors in the liver. Among sulfhydryl reagents, cysteamine and reduced glutathione (GSH), but not oxidized glutathione (GSSG) up to 1mM, inhibited PCMB-unmasked 125I-SI Ang II binding in brain and testis. Thimerosal and 4-hydroxymercuribenzoate moderately inhibited PCMB-unmasked 125I-SI Ang II binding in brain and testis at 100 μM; however, they also unmasked non-AT1, non-AT2 binding independent of PCMB. 4-Hydroxybenzoic acid did not promote 125 I-SI Ang II binding to this binding site indicating that only specific organomercurial compounds can unmask the binding site. The common denominator for all of these interacting substances is the ability to bind to protein cysteine sulfur. Comparison of cysteines between neurolysin and the closely related enzyme thimet oligopeptidase revealed an unconserved cysteine (cys650, based on the full length variant) in the proposed ligand binding channel (Brown et al., 2001) [45] near the active site of neurolysin. It is proposed that the mercuric ion in PCMB and closely related organomercurial compounds binds to cys650, while the acidic anion forms an ionic bond with a nearby arginine or lysine along the channel to effect a conformational change in neurolysin that promotes Ang II binding.

The intracrine renin-angiotensin system

The RAS (renin-angiotensin system) is one of the earliest and most extensively studied hormonal systems. The RAS is an atypical hormonal system in several ways. The major bioactive peptide of the system, AngII (angiotensin II), is neither synthesized in nor targets one specific organ. New research has identified additional peptides with important physiological and pathological roles. More peptides also mean newer enzymatic cascades that generate these peptides and more receptors that mediate their function. In addition, completely different roles of components that constitute the RAS have been uncovered, such as that for prorenin via the prorenin receptor. Complexity of the RAS is enhanced further by the presence of sub-systems in tissues, which act in an autocrine/paracrine manner independent of the endocrine system. The RAS seems relevant at the cellular level, wherein individual cells have a complete system, termed the intracellular RAS. Thus, from cells to tissues to the entire organism, the RAS exhibits continuity while maintaining independent control at different levels. The intracellular RAS is a relatively new concept for the RAS. The present review provides a synopsis of the literature on this system in different tissues.

Intracardiac intracellular angiotensin system in diabetes

The renin-angiotensin system (RAS) has mainly been categorized as a circulating and a local tissue RAS. A new component of the local system, known as the intracellular RAS, has recently been described. The intracellular RAS is defined as synthesis and action of ANG II intracellularly. This RAS appears to differ from the circulating and the local RAS, in terms of components and the mechanism of action. These differences may alter treatment strategies that target the RAS in several pathological conditions. Recent work from our laboratory has demonstrated significant upregulation of the cardiac, intracellular RAS in diabetes, which is associated with cardiac dysfunction. Here, we have reviewed evidence supporting an intracellular RAS in different cell types, ANG II's actions in cardiac cells, and its mechanism of action, focusing on the intracellular cardiac RAS in diabetes. We have discussed the significance of an intracellular RAS in cardiac pathophysiology and implications for potential therapies.