Kinetic study of neuropeptide Y (NPY) proteolysis in blood and identification of NPY3-35: a new peptide generated by plasma kallikrein

Structural basis of neuropeptide Y signaling through Y1 and Y2 receptors

Neuropeptide Y (NPY), a 36-amino-acid peptide, functions as a neurotransmitter in both the central and peripheral nervous systems by activating the NPY receptor subfamily. Notably, NPY analogs display varying selectivity and exert diverse physiological effects through their interactions with this receptor family. [Pro34]-NPY and [Leu31, Pro34]-NPY, mainly acting on Y1R, reportedly increases blood pressure and postsynaptically potentiates the effect of other vasoactive substances above all, while N-terminal cleaved NPY variants in human body primary mediates angiogenesis and neurotransmitter release inhibition through Y2R. However, the recognition mechanisms of Y1R and Y2R with specific agonists remain elusive, thereby hindering subtype receptor-selective drug development. In this study, we report three cryo-electron microscopy (cryo-EM) structures of Gi2-coupled Y1R and Y2R in complexes with NPY, as well as Y1R bound to a selective agonist [Leu31, Pro34]-NPY. Combined with cell-based assays, our study not only reveals the conserved peptide-binding mode of NPY receptors but also identifies an additional sub-pocket that confers ligand selectivity. Moreover, our analysis of Y1R evolutionary dynamics suggests that this sub-pocket has undergone functional adaptive evolution across different species. Collectively, our findings shed light on the molecular underpinnings of neuropeptide recognition and receptor activation, and they present a promising avenue for the design of selective drugs targeting the NPY receptor family.

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

Detection of endogenous NPY release determined by novel GRAB sensor in cultured cortical neurons

Neuropeptide Y (NPY) is an abundantly expressed peptide in the nervous system. Its widespread distribution along with its receptors, both centrally and peripherally, indicates its broad functions in numerous biological processes. However, the low endogenous concentration and diffuse distribution of NPY make it challenging to study its actions and dynamics directly and comprehensively. Studies on the role of NPY have primarily been limited to exogenous application, transgene expression, or knock-out in biological systems, which are often combined with pharmacological probes to delineate the involvement of specific NPY receptors. Therefore, to better understand the function of NPY in time and space, direct visualization of the real-time dynamics of endogenous NPY is a valuable and desired tool. Using the first-generation and newly developed intensiometric green fluorescent G-protein-coupled NPY sensor (GRAB NPY1.0), we, for the first time, demonstrate and characterize the direct detection of endogenously released NPY in cultured cortical neurons. A dose-dependent fluorescent signal was observed upon exogenous NPY application in nearly all recorded neurons. Pharmacologically evoked neuronal activity induced a significant increase in fluorescent signal in 32% of neurons, reflecting the release of NPY, despite only 3% of all neurons containing NPY. The remaining pool of neurons expressing the sensor were either non-responsive or displayed a notable decline in the fluorescent signal. Such decline in fluorescent signal was not rescued in cortical cultures transduced with an NPY overexpression vector, where 88% of the neurons were NPY-positive. Overexpression of NPY did, however, result in sensor signals that were more readily distinguishable. This may suggest that biological factors, such as subtle changes in intracellular pH, could interfere with the fluorescent signal, and thereby underestimate the release of endogenous NPY when using this new sensor in its present configuration. However, the development of next-generation NPY GRAB sensor technology is expected soon, and will eventually enable much-wanted studies on endogenous NPY release dynamics in both cultured and intact biological systems.

The identification of two M20B family peptidases required for full virulence in Staphylococcus aureus

We have previously demonstrated that deletion of an intracellular leucine aminopeptidase results in attenuated virulence of S. aureus. Herein we explore the role of 10 other aminopeptidases in S. aureus pathogenesis. Using a human blood survival assay we identified mutations in two enzymes from the M20B family (PepT1 and PepT2) as having markedly decreased survival compared to the parent. We further reveal that pepT1, pepT2 and pepT1/2 mutant strains are impaired in their ability to resist phagocytosis by, and engender survival within, human macrophages. Using a co-infection model of murine sepsis, we demonstrate impairment of dissemination and survival for both single mutants that is even more pronounced in the double mutant. We show that these enzymes are localized to the cytosol and membrane but are not necessary for peptide-based nutrition, a hallmark of cell-associated aminopeptidases. Furthermore, none of the survival defects appear to be the result of altered virulence factor production. An exploration of their regulation reveals that both are controlled by known regulators of the S. aureus virulence process, including Agr, Rot and/or SarA, and that this cascade may be mediated by FarR. Structural modeling of PepT1 reveals it bears all the hallmarks of a tripeptidase, whilst PepT2 differs significantly in its catalytic pocket, suggesting a broader substrate preference. In sum, we have identified two M20B aminopeptidases that are integral to S. aureus pathogenesis. The future identification of protein and/or peptide targets for these proteases will be critical to understanding their important virulence impacting functions.

Neprilysin-dependent neuropeptide Y cleavage in the liver promotes fibrosis by blocking NPY-receptor 1

Development of liver fibrosis is paralleled by contraction of hepatic stellate cells (HSCs), the main profibrotic hepatic cells. Yet, little is known about the interplay of neprilysin (NEP) and its substrate neuropeptide Y (NPY), a potent enhancer of contraction, in liver fibrosis. We demonstrate that HSCs are the source of NEP. Importantly, NPY originates majorly from the splanchnic region and is cleaved by NEP in order to terminate contraction. Interestingly, NEP deficiency (Nep-/-) showed less fibrosis but portal hypertension upon liver injury in two different fibrosis models in mice. We demonstrate the incremental benefit of Nep-/- in addition to AT1R blocker (ARB) or ACE inhibitors for fibrosis and portal hypertension. Finally, oral administration of Entresto, a combination of ARB and NEP inhibitor, decreased hepatic fibrosis and portal pressure in mice. These results provide a mechanistic rationale for translation of NEP-AT1R-blockade in human liver fibrosis and portal hypertension.

Saxagliptin: A potential doping agent? A randomized, double-blinded, placebo-controlled, and crossover pilot study in young active men

Neuropeptide Ys (NPYs) contribute to sympathetic-adreno stimulation: NPY1-36 potentiates the effects of catecholamines (CATs), whereas NPY3-36 inhibits CAT release. We sought to investigate whether inhibiting dipeptidyl-peptidase-4 (DPP4), cleaving NPY1-36 into NPY3-36, leads to increased NPY1-36 potentiating effects and reduced NPY3-36 inhibitory effects on CATs, thereby improving endurance performance. Seven male participants (age 27 ± 3 years, BMI 23.1 ± 2.4 kg/m² ) performed time-to-exhaustion cycling exercise at 95% of peak power output with either placebo, or saxagliptin, a DPP4 inhibitor. Oxygen consumption (V̇O₂ ), heart rate variability, NPY1-36, NPY3-36, catecholamines, and lactate were measured at several time points before, during, and after exercise. With saxagliptin, DPP4 activity (12.7 ± 1.6 vs. 0.2 ± 0.3 U/L, p = 0.001; d = 10.7) was decreased at rest, while NPY3-36 (1.94 ± 0.88 vs. 0.73 ± 0.22 pm; p < 0.001; d = 2.04) decreased and NPY1-36 increased during exercise (2.64 ± 2.22 vs. 4.59 ± 2.98 pm; p < 0.01; d = 0.19). CATs were unchanged. Time-to-exhaustion was 32% higher with saxagliptin. The difference in time-to-exhaustion between placebo and saxagliptin was correlated with NPY1-36 differences (R = 0.78, p < 0.05). Peak V̇O₂ and other cardio-respiratory values were not different, whereas peak NPY concentrations were higher with saxagliptin. DPP4 blockade improved performance, increased NPY1-36, and decreased NPY3-36 concentrations which may have potentiating effects on the influences of CATs. However, DPP4 is involved in many different actions, thus NPYs are one group of factors that may underly its performance-enhancing effects; further studies are required to determine the exact mechanisms.

Ultrasensitive and Cost-Effective Detection of Neuropeptide-Y by a Disposable Immunosensor: A New Functionalization Route for Indium-Tin Oxide Surface

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the human brain, and its levels in the blood change in neurodegenerative and neuroimmune disorders. This indicates that NPY may serve as a diagnostic and monitoring marker for associated disorders. In this paper, an electrochemical immunosensor was created to detect NPY biomarkers using a novel immobilization technique. The proposed biosensor system enables accurate, specific, cost-effective, and practical biomarker analysis. Indium tin oxide-coated polyethylene terephthalate (ITO-PET) sheets were treated with hexamethylene diisocyanate (HMDC) to covalently immobilize antibodies. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques were used to analyze each step of the biosensors. The proposed NPY biosensor has a broad linear detection range (0.01-100 pg mL-1), a low limit of detection (LOD) (0.02968 pg mL-1), and a low limit of quantification (LOQ) (0.0989 pg mL-1). Atomic force microscopy (AFM) was used to support in the optimization process, study the surface morphology, and visualize it. Studies of repeatability, reproducibility, storage, and Kramers-Kronig transformation were conducted during electrochemical characterization. After analytical experiments, the biosensor's responses to human serum samples were evaluated. According to the obtained data, the error margin is small, and the created biosensor offers a great deal of promise for the clinical measurement of NPY.

Proneuropeptide Y and neuropeptide Y metabolites in healthy volunteers and patients with a pheochromocytoma or paraganglioma

Neuropeptide Y (NPY1-36) is a vasoconstrictor peptide co-secreted with catecholamines by sympathetic nerves, the adrenal medulla, and neoplasms such as pheochromocytomas and paragangliomas (PPGLs). It is produced by the intracellular cleavage of proNPY and metabolized into multiple fragments with distinct biological activities. NPY immunoassays for PPGL have a diagnostic sensitivity ranging from 33 to 100%, depending on the antibody used. We have validated a multiplex micro-UHPLC-MS/MS assay for the specific and sensitive quantification of proNPY, NPY1-39, NPY1-37, NPY1-36, NPY2-36, NPY3-36, NPY1-35, NPY3-35, and the C-flanking peptide of NPY (CPON) (collectively termed NPYs), and determined the NPYs reference intervals and concentrations in 32 PPGL patients before, during, and after surgery. Depending on the peptide measured, NPYs were above the upper reference limit (URL) in 20% to 67% of patients, whereas plasma free metanephrine and normetanephrine, the gold standard for PPGL, were above the URL in 40% and 87% of patients, respectively. Age, sex, tachycardia, and tumor localization were not correlated with NPYs. Plasma free metanephrines performed better than NPYs in the detection of PPGL, but NPYs may be a substitute for an early diagnosis of PPGL for patients that suffer from severe kidney impairment or receiving treatments that interfere with catecholamine reuptake.

Kinetics of neuropeptide Y, catecholamines, and physiological responses during moderate and heavy intensity exercises

Neuropeptide Y 1-36 (NPY1-36) is a vasoconstrictor peptide co-secreted with norepinephrine (NE) by nerve endings during sympathetic activation. NPY1-36 potentiates NE action post-synaptically through the stimulation of the Y1 receptor, whereas its metabolite NPY3-36 resulting from DPP4 action activates Y2 presynaptic receptors, inhibiting NE and acetylcholine secretion. The secretions of NPY1-36 and NPY3-36 in response to sympathetic nervous system activation have not been studied due to the lack of analytical techniques available to distinguish them. We determined in healthy volunteers NPY1-36, NPY3-36 and catecholamine kinetics and how these neurotransmitters modulate the physiological stress response during and after moderate- and heavy-intensity exercises. Six healthy males participated in this randomized, double-blind, saxagliptin vs placebo crossover study. The volunteers performed an orthostatic test, a 30-min exercise at moderate intensity and a 15-min exercise at heavy intensity each followed by 50 min of recovery in two separate sessions with saxagliptin or placebo. Oxygen consumption (V̇O₂), ventilation and heart rate were continuously recorded. NE, epinephrine, NPY1-36 and NPY3-36 were quantified by tandem mass spectrometry. We found that exercise triggers NPY1-36 and NE secretion in an intensity-dependent manner and that NE returns faster to the baseline concentration than NPY1-36 after exercise. NPY3-36 rises during recovery parallel to the decline of NPY1-36. Saxagliptin reverses the NPY1-36/NPY3-36 ratio but does not affect hemodynamics, nor NPY1-36 and catecholamine concentrations. We found that NPY1-36 half-life is considerably shorter than previously established with immunoassays. NPY1-36 and NE secretions are finely regulated to prevent an excessive physiological Y1 stimulating response to submaximal exercise.

Biomarkers and Detection Platforms for Human Health and Performance Monitoring: A Review

Human health and performance monitoring (HHPM) is imperative to provide information necessary for protecting, sustaining, evaluating, and improving personnel in various occupational sectors, such as industry, academy, sports, recreation, and military. While various commercially wearable sensors are on the market with their capability of "quantitative assessments" on human health, physical, and psychological states, their sensing is mostly based on physical traits, and thus lacks precision in HHPM. Minimally or noninvasive biomarkers detectable from the human body, such as body fluid (e.g., sweat, tear, urine, and interstitial fluid), exhaled breath, and skin surface, can provide abundant additional information to the HHPM. Detecting these biomarkers with novel or existing sensor technologies is emerging as critical human monitoring research. This review provides a broad perspective on the state of the art biosensor technologies for HHPM, including the list of biomarkers and their physiochemical/physical characteristics, fundamental sensing principles, and high-performance sensing transducers. Further, this paper expands to the additional scope on the key technical challenges in applying the current HHPM system to the real field.

Impact of Intrinsic and Extrinsic Factors on the Pharmacokinetics of Peptides: When Is the Assessment of Certain Factors Warranted?

Peptides are short chains of 2 to 50 amino acids (molecular weight of less than 10 kDa) linked together by peptide bonds. As therapeutic agents, peptides are of interest because the body naturally produces many different peptides. Short-chain peptides have many advantages as compared with long-chain peptides (e.g., low toxicity). The first peptide corticotropin was approved in 1952 for multiple inflammatory diseases and West syndrome. Since then, more than 60 peptides have been approved by the FDA. Pharmacokinetics (PK) is widely used in modern-day drug development for designing a safe and efficacious dose to treat a wide variety of diseases. There are, however, several factors termed as “intrinsic” or “extrinsic” which can influence the PK of a drug, and as a result, one has to adjust the dose in a patient population. These intrinsic and extrinsic factors can be described as age, gender, disease states such as renal and hepatic impairment, drug–drug interaction, food, smoking, and alcohol consumption. It is well known that these intrinsic and extrinsic factors can have a substantial impact on the PK of small molecules, but for macromolecules, the impact of these factors is not well established. This review summarizes the impact of intrinsic and extrinsic factors on the PK of peptides.

Characterization of combined linagliptin and Y2R agonist treatment in diet-induced obese mice

Dipeptidyl peptidase IV (DPP-IV) inhibitors improve glycemic control by prolonging the action of glucagon-like peptide-1 (GLP-1). In contrast to GLP-1 analogues, DPP-IV inhibitors are weight-neutral. DPP-IV cleavage of PYY and NPY gives rise to PYY3-36 and NPY3-36 which exert potent anorectic action by stimulating Y2 receptor (Y2R) function. This invites the possibility that DPP-IV inhibitors could be weight-neutral by preventing conversion of PYY/NPY to Y2R-selective peptide agonists. We therefore investigated whether co-administration of an Y2R-selective agonist could unmask potential weight lowering effects of the DDP-IV inhibitor linagliptin. Male diet-induced obese (DIO) mice received once daily subcutaneous treatment with linagliptin (3 mg/kg), a Y2R-selective PYY3-36 analogue (3 or 30 nmol/kg) or combination therapy for 14 days. While linagliptin promoted marginal weight loss without influencing food intake, the PYY3-36 analogue induced significant weight loss and transient suppression of food intake. Both compounds significantly improved oral glucose tolerance. Because combination treatment did not further improve weight loss and glucose tolerance in DIO mice, this suggests that potential negative modulatory effects of DPP-IV inhibitors on endogenous Y2R peptide agonist activity is likely insufficient to influence weight homeostasis. Weight-neutrality of DPP-IV inhibitors may therefore not be explained by counter-regulatory effects on PYY/NPY responses.

NPY and Gene Therapy for Epilepsy: How, When,... and Y

Neuropeptide Y (NPY) is a neuropeptide abundantly expressed in the mammalian central and peripheral nervous system. NPY is a pleiotropic molecule, which influences cell proliferation, cardiovascular and metabolic function, pain and neuronal excitability. In the central nervous system, NPY acts as a neuromodulator, affecting pathways that range from cellular (excitability, neurogenesis) to circuit level (food intake, stress response, pain perception). NPY has a broad repertoire of receptor subtypes, each activating specific signaling pathways in different tissues and cellular sub-regions. In the context of epilepsy, NPY is thought to act as an endogenous anticonvulsant that performs its action through Y2 and Y5 receptors. In fact, its overexpression in the brain with the aid of viral vectors can suppress seizures in animal models of epilepsy. Therefore, NPY-based gene therapy may represent a novel approach for the treatment of epilepsy patients, particularly for pharmaco-resistant and genetic forms of the disease. Nonetheless, considering all the aforementioned aspects of NPY signaling, the study of possible NPY applications as a therapeutic molecule is not devoid of critical aspects. The present review will summarize data related to NPY biology, focusing on its anti-epileptic effects, with a critical appraisal of key elements that could be exploited to improve the already existing NPY-based gene therapy approaches for epilepsy.

Angiotensin-Converting Enzyme Inhibitor Protects Against Cisplatin Nephrotoxicity by Modulating Kinin B1 Receptor Expression and Aminopeptidase P Activity in Mice

Cisplatin is a highly effective chemotherapeutic agent. However, its use is limited by nephrotoxicity. Enalapril is an angiotensin I-converting enzyme inhibitor used for the treatment of hypertension, mainly through the reduction of angiotensin II formation, but also through the increase of kinins half-life. Kinin B1 receptor is associated with inflammation and migration of immune cells into the injured tissue. We have previously shown that the deletion or blockage of kinin B1 and B2 receptors can attenuate cisplatin nephrotoxicity. In this study, we tested enalapril treatment as a tool to prevent cisplatin nephrotoxicity. Male C57Bl/6 mice were divided into 3 groups: control group; cisplatin (20 mg/kg i.p) group; and enalapril (1.5 mg;kg i.p) + cisplatin group. The animals were treated with a single dose of cisplatin and euthanized after 96 h. Enalapril was able to attenuate cisplatin-induced increase in creatinine and urea, and to reduce tubular injury and upregulation of apoptosis-related genes, as well as inflammatory cytokines in circulation and kidney. The upregulation of B1 receptor was blocked in enalapril + cisplatin group. Carboxypeptidase M expression, which generates B1 receptor agonists, is blunted by cisplatin + enalapril treatment. The activity of aminopeptidase P, a secondary key enzyme able to degrade kinins, is restored by enalapril treatment. These findings were confirmed in mouse renal epithelial tubular cells, in which enalaprilat (5 μM) was capable of decreasing tubular injury and inflammatory markers. We treated mouse renal epithelial tubular cells with cisplatin (100 μM), cisplatin+enalaprilat and cisplatin+enalaprilat+apstatin (10 μM). The results showed that cisplatin alone decreases cell viability, cisplatin plus enalaprilat is able to restore cell viability, and cisplatin plus enalaprilat and apstatin decreases cell viability. In the present study, we demonstrated that enalapril prevents cisplatin nephrotoxicity mainly by preventing the upregulation of B1 receptor and carboxypeptidase M and the increased concentrations of kinin peptides through aminopeptidase activity restoration.

Quantification of Neuropeptide Y and Four of Its Metabolites in Human Plasma by Micro-UHPLC-MS/MS

Neuropeptide Y (NPY) is a 36-amino acid peptide circulating at a subpicomolar concentration participating in multiple physiological and pathological processes. NPY is prone to peptidolysis, generating metabolites with modified affinity for the five known receptors of NPY that mediate distinct effects. It is, therefore, crucial to distinguish each metabolite to understand the multiple functions of NPY. Since immunoassays are not able to distinguish NPY from its metabolites, we have validated a microliquid chromatography tandem mass spectrometry (micro-LC-MS/MS) assay for the quantification of endogenous NPY, NPY2-36, NPY3-36, NPY1-35, and NPY3-35 in human plasma. Sample preparation relies on immunoextraction in 96-well plates, followed by solid-phase extraction prior to micro-LC-MS/MS. The LLOQ ranged from 0.03 to 0.16 pM, intra- and inter-assay precision were <27% and trueness <22%. We determined reference intervals in 155 healthy volunteers and 40 hypertensive patients. We found that NPY3-36 is the main circulating peptide in resting conditions and that NPY and catecholamines are simultaneously increased during orthostasis. We also showed that the concentrations of NPY and its metabolites are similar in healthy volunteers and hypertensive patients. NPY is the prototype peptide that circulates in concentrations expected to be beyond instrumental capacities. We have been successful in developing a high-throughput specific and sensitive assay by including a deep knowledge of the physicochemical properties of these peptides to an efficient multistep sample preparation, and a micro-LC chromatography. We believe that our methodological approach opens the possibility to selectively quantify other endogenous peptides cleaved by peptidases whose concentrations are below 1 pM.

Neuropeptide Y system mRNA expression changes in the hippocampus of a type I diabetes rat model

BACKGROUND

Neuropeptide Y (NPY) plays a crucial role in many neurobiological functions, such as cognition and memory. Cognitive and memory impairment have been described in diabetic patients. The metabolism of NPY is determined by the activity of proteases, primarily dipeptidyl-peptidase-IV (DPP-IV). Therefore, DPP-IV inhibitors, such as sitagliptin, may modulate the function of NPY. In this study, we investigated the effect of type 1 diabetes and sitagliptin treatment on the regulation of the mRNA encoding for NPY and its receptors (Y1, Y2, and Y5 receptors) in the hippocampus.

METHODS

Type 1 diabetes was induced in male Wistar rats by i.p. injection of streptozotocin. Starting two weeks after diabetes onset, animals were treated orally with sitagliptin (5mg/kg, daily) for two weeks. The mRNA expression of Npy and its receptors (Npy1r, Npy2r, and Npy5r) in the hippocampus was evaluated using in situ hybridization with ³³P-labeled oligonucleotides.

RESULTS

The mRNA expression of Npy, Npy1r and Npy5r was higher in the dentate gyrus, whereas Npy2r highest level was observed in the CA3 subregion. The mRNA expression of Npy, Npy1r and Npy5r in dentate gyrus, CA1 and CA3 was not affected by diabetes and/or by sitagliptin treatment. Type 1 diabetes increased the mRNA expression of Npy2r in the CA3 subregion, which was prevented by sitagliptin treatment.

CONCLUSIONS

Our results show that type 1 diabetes, at early stages, induces mild changes in the NPY system in the hippocampus that were counteracted by sitagliptin treatment.

Expression of neuropeptide Y is increased in an activated human HSC cell line

Neuropeptide Y (NPY) is an abundant neuropeptide in the mammalian central and peripheral nervous systems. Transgenic mice overexpressing NPY in noradrenergic neurons have increased level of hepatic triglycerides, fatty acids and cholesterol, which contributed to the development of hepatosteatosis. However, the roles of NPY in the activation of hepatic stellate cells (HSCs) and the underlying mechanisms remain unclear. This study aimed to investigate the expression and secretion of NPY in human immortalized HSC LX-2 cells and the regulatory function of NPY on the fibrogenic response in LX-2 cells, to explore the potential association between NPY and LX-2 activation. The results showed an increase in the expression and secretion of NPY(1–36) in activated LX-2 cells. Both endogenous and exogenous NPY(1–36) induced the phosphorylation of mTOR, p70S6K, and 4EBP1 and promoted the fibrogenic response via NPY Y1 receptor subtype (NPY1R), as these responses were blocked by either an NPY1R antagonist (BIBP3226) or NPY1R knockdown. Moreover, NPY(1–36) serum levels were increased in patients with liver cirrhosis (LC) and hepatocellular carcinoma (HCC) and presented a positive relationship with MELD scores in LC patients. These findings suggest that immortalized HSCs LX-2 have the potential to produce NPY(1–36). High serum levels of NPY(1–36) is correlated with hepatic dysfunction in cirrhotic patients.

Placental Neuropeptide Y ( NPY) and NPY receptors expressions and serum NPY levels in preeclampsia

IMPACT STATEMENT

Neuropeptide Y (NPY) has been reported as a vasoconstrictive substance which might be associated with preeclampsia. The novel findings of this study were that Y1R, Y2R, and Y5R expressions were significantly lower in the PE than the NP group. Moreover, the NPY receptor expression ratio between the PE/NP groups was lowest for Y2R (0.27) compared to Y1R (0.42) and Y5R (0.40) suggestive of a reduction of this receptor in the preeclampsia group. Our results suggested that decreased Y2R mRNA in the PE group might be associated with abnormalities of placental angiogenesis which probably contributes to the pathophysiology of preeclampsia.

Plasma kallikrein cleaves and inactivates apelin-17: Palmitoyl- and PEG-extended apelin-17 analogs as metabolically stable blood pressure-lowering agents

Apelins are human peptide hormones with various physiological activities, including the moderation of cardiovascular, renal, metabolic and neurological function. Their potency is dependent on and limited by proteolytic degradation in the circulatory system. Here we identify human plasma kallikrein (KLKB1) as a protease that cleaves the first three N-terminal amino acids (KFR) of apelin-17. The cleavage kinetics are similar to neprilysin (NEP), which cleaves within the critical 'RPRL'-motif thereby inactivating apelin. The resulting C-terminal 14-mer after KLKB1 cleavage has much lower biological activity, and the presence of its N-terminal basic arginine seems to negate the blood pressure lowering effect. Based on C-terminally engineered apelin analogs (A2), resistant to angiotensin converting enzyme 2 (ACE2), attachment of an N-terminal C16 fatty acid chain (PALMitoylation) or polyethylene glycol chain (PEGylation) minimizes KLKB1 cleavage of the 17-mers, thereby extending plasma half-life while fully retaining biological activity. The N-terminally PEGylated apelin-17(A2) is a highly protease resistant analog, with excellent apelin receptor activation and pronounced blood pressure lowering effect.

The C-terminal flanking peptide of neuropeptide Y (NPY) is not essential for seizure-suppressant actions of prepro-NPY overexpression in male rats

The full coding sequence of neuropeptide Y (NPY), prepro-NPY, is sequentially metabolized into three peptides; an N-terminus 28-amino acid signaling peptide, the NPY peptide itself (NPY1-36), and a 30-amino acid C-terminus peptide, known as the C-terminal flanking peptide of neuropeptide-Y (CPON). While the signaling peptide directs intracellular trafficking and NPY1-36 is well characterized, the biological function of CPON is unknown. This is noteworthy because CPON is co-stored and co-released along with NPY1-36 and could thus potentially serve important functions. To assess the role of CPON, we adapted a viral genetic approach using two different vector designs encoding NPY, but where the CPON coding sequence was excluded from one of the vectors. Thus, the effect of CPON was indirectly assessed. Male rats received intrahippocampal injections of either a vector encoding NPY1-39 whose metabolism yields NPY1-36 and not CPON, or a prepro-NPY vector encoding both NPY1-36 and CPON. A third vector encoding EGFP served as control. We subsequently studied to what extent CPON might affect seizure susceptibility and memory performance, respectively, to address two important questions to evaluate the potential of NPY gene therapy in epilepsy. Both NPY vectors, as compared to EGFP control, were found to be equally effective at suppressing acute kainate-induced seizures, and both did not influence learning and memory performance in the Morris water maze. Thus CPON itself does not appear to aid actions governed by vector-mediated overexpression of NPY1-36 within the hippocampus. Whether CPON serves other important functions remains to be determined.

C-terminal degradation of PYY peptides in plasma abolishes effects on satiety and beta-cell function

The importance of dipeptidyl peptidase-4 mediated N-terminal metabolism of the enteroendocrine-derived hormone, peptide YY (PYY), for receptor binding and subsequent biological action profile is well established. However, an intact C-terminus may be fundamental also for bioactivity of PYY peptides. The current study has demonstrated C-terminal degradation of the major recognised circulating forms of PYY, PYY(1-36) and PYY(3-36), in plasma, resulting in production of PYY(1-34) and PYY(3-34). Interestingly, the angiotensin-converting-enzyme (ACE) inhibitor, captopril, blocked formation of PYY(3-34) from PYY(3-36) in plasma, but did result in the appearance of PYY(3-35). In addition, we were able to evidence C-terminal truncation of PYY(1-35) and PYY(3-35) to PYY(1-34) and PYY(3-34), respectively. As expected, PYY(1-36) and PYY(3-36) inhibited (P < 0.05-P < 0.001) glucose- and alanine-stimulated insulin secretion from BRIN-BD11 beta-cells. In contrast, PYY(1-34), PYY(3-34), PYY(1-35) and PYY(3-35) were devoid of insulinostatic actions. Both PYY(1-36) and PYY(3-36), but not related PYY metabolites, significantly (P < 0.05-P < 0.001) enhanced proliferation of BRIN BD11 and 1.1B4 beta-cell lines, and protected (P < 0.01-P < 0.001) these cell lines against cytokine-induced apoptosis. As expected, PYY(3-36) induced clear (P < 0.05-P < 0.01) appetite suppressive effects in mice, but this action was eliminated by mono- or di-peptide C-terminal truncation. Interestingly, captopril significantly (P < 0.05) augmented the anorexigenic effects of PYY(3-36) in mice. PYY(1-36), PYY(3-36), PYY(1-34) and PYY(3-34) lacked effects on in vivo glucose tolerance or glucose-induced insulin release. Taken together, these data highlight the unrecognised importance of C-terminal integrity of PYY peptides for biological activity and therapeutic usefulness in obesity-diabetes.

Impact of type 1 diabetes mellitus and sitagliptin treatment on the neuropeptide Y system of rat retina

BACKGROUND

Neuropeptide Y (NPY) is a neuromodulator that is expressed in the retina. Increasing evidence suggests that NPY has pronounced anti-inflammatory effects, which might depend on the inhibition of dipeptidyl-peptidase-IV (DPP-IV). The aim of this study was to investigate the impact of type 1 diabetes mellitus (DM) and sitagliptin, a DPP-IV inhibitor, on the NPY system in the retina using an animal model.

METHODS

Type 1 DM was induced in male Wistar rats by an intraperitoneal injection of streptozotocin. Starting 2 weeks after DM onset, animals were treated orally with sitagliptin (5 mg/kg.day) for 2 weeks. The expression of NPY and NPY receptors (Y1 , Y2 and Y5 receptors) was measured by quantitative polymerase chain reaction, Western blot and/or enzyme-linked immunosorbent assay. The immunoreactivity of NPY and NPY receptors was evaluated by immunohistochemistry, and the [35 S]GTPγS binding assay was used to assess the functional binding of NPY receptors.

RESULTS

DM decreased the mRNA levels of NPY in the retina, as well as the protein levels of NPY and Y5 receptor. No changes were detected in the localization of NPY and NPY receptors in the retina and in the functional binding of NPY to all receptors. Sitagliptin alone reduced retinal NPY mRNA levels. The effects of DM on the NPY system were not affected by sitagliptin.

CONCLUSION

DM modestly affects the NPY system in the retina and these effects are not prevented by sitagliptin treatment. These observations suggest that DPP-IV enzyme is not underlying the NPY changes detected in the retina induced by type 1 DM.

Copper Binding Induces Nitration of NPY under Nitrative Stress: Complicating the Role of NPY in Alzheimer's Disease

Neuropeptide Y (NPY) is a 36 amino acid peptide that regulates a multitude of physiological functions in the central nervous system and has been shown to be involved in Alzheimer's disease (AD). A change in copper homeostasis is a remarkable feature of AD, and the dysregulation may contribute to toxicity in neural cells. Moreover, it has been shown that copper could interact with many neuropeptides and result in catalyzing the production of reactive oxygen species, which may lead to peptide oxidation. Besides, copper could also catalyze protein tyrosine nitration under oxidative stress, and there are two tyrosine residues playing an important role in NPY. Therefore, it is also likely that copper has an action on NPY and potentially influences its functions through tyrosine nitration. In this paper, the studies of the interaction of copper with NPY and the copper-catalyzed NPY nitration were performed. The electrochemical techniques, UV-vis spectroscopy, mass spectrometry, and fluorescence titration, have been applied to show that copper can interact with NPY to form a Cu-NPY complex with a conditional dissociation constant of 0.021 μmol/L, and the binding promotes the generation of •OH. Dot blotting results reveal that NPY can be nitrated upon binding with copper under nitrative stress. Furthermore, liquid chromatography-mass spectrometry (LC-MS) identify that the tyrosine residues in NPY are all nitrated during the nitration process, which will cause the inactivation of NPY shown by our previous study. This study supports the hypothesis that copper has a close correlation with NPY and implicates the peptide in AD. These data may provide a new insight into understanding the pathology and pathogenesis of AD.

Evaluating prodrug characteristics of a novel anticoagulant fusion protein neorudin, a prodrug targeting release of hirudin variant 2-Lys47 at the thrombosis site, by means of in vitro pharmacokinetics

Recombinant neorudin (EPR-hirudin, EH), a low-bleeding anticoagulant fusion protein, is an inactive prodrug designed to be converted to the active metabolite, hirudin variant 2-Lys47 (HV2), locally at the thrombus site by FXa and/or FXIa, following activation of the coagulation system. Our aim was to evaluate the prodrug characteristics of EH by comparing the biotransformation of EH and HV2 in biological matrices, including rat blood, liver, and kidney homogenates, demonstrating the cleavage of EH to HV2 by FXa and FXIa, and comparing the conversion of EH to HV2 between fresh whole blood and whole-blood clot homogenate, using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Both EH and HV2 were stable in blood and unstable in the liver and kidney homogenates. Eight EH metabolites and eight HV2 metabolites identified as N-terminal fragments were found in the liver and kidney. C-terminal proteolysis is therefore the major metabolic pathway, with serine/cysteine carboxypeptidases and metallocarboxypeptidases being responsible for the degradation of EH and HV2 in the liver and kidney, respectively. EH was cleaved to release HV2 by FXIa. Higher levels of HV2 were produced from EH in the whole-blood clot homogenate, in which the coagulation system was activated compared with those in fresh whole blood. In conclusion, the metabolism of EH and HV2 shares the same cleavage pattern, and EH is transformed into HV2 when the coagulation system is activated, where FXIa is a specific enzyme. Our in vitro study revealed the anticipated prodrug characteristics of EH newly designed as an inactive prodrug of hirudin.

Identification of novel loci affecting circulating chromogranins and related peptides

Chromogranins are pro-hormone secretory proteins released from neuroendocrine cells, with effects on control of blood pressure. We conducted a genome-wide association study for plasma catestatin, the catecholamine release inhibitory peptide derived from chromogranin A (CHGA), and other CHGA- or chromogranin B (CHGB)-related peptides, in 545 US and 1252 Australian subjects. This identified loci on chromosomes 4q35 and 5q34 affecting catestatin concentration (P = 3.40 × 10-30 for rs4253311 and 1.85 × 10-19 for rs2731672, respectively). Genes in these regions include the proteolytic enzymes kallikrein (KLKB1) and Factor XII (F12). In chromaffin cells, CHGA and KLKB1 proteins co-localized in catecholamine storage granules. In vitro, kallikrein cleaved recombinant human CHGA to catestatin, verified by mass spectrometry. The peptide identified from this digestion (CHGA360-373) selectively inhibited nicotinic cholinergic stimulated catecholamine release from chromaffin cells. A proteolytic cascade involving kallikrein and Factor XII cleaves chromogranins to active compounds both in vivo and in vitro.

Neuropeptide Y3-36 incorporated into PVAX nanoparticle improves functional blood flow in a murine model of hind limb ischemia

We generated a novel nanoparticle called PVAX, which has intrinsic antiapoptotic and anti-inflammatory properties. This nanoparticle was loaded with neuropeptide Y_3-36 (NPY_3-36), an angiogenic neurohormone that plays a central role in angiogenesis. Subsequently, we investigated whether PVAX-NPY_3-36 could act as a therapeutic agent and induce angiogenesis and vascular remodeling in a murine model of hind limb ischemia. Adult C57BL/J6 mice (n = 40) were assigned to treatment groups: control, ischemia PBS, ischemia PVAX, ischemia NPY_3-36, and Ischemia PVAX-NPY_3-36 Ischemia was induced by ligation of the femoral artery in all groups except control and given relevant treatments (PBS, PVAX, NPY_3-36, and PVAX-NPY_3-36). Blood flow was quantified using laser Doppler imaging. On days 3 and 14 posttreatment, mice were euthanized to harvest gastrocnemius muscle for immunohistochemistry and immunoblotting. Blood flow was significantly improved in the PVAX-NPY_3-36 group after 14 days. Western blot showed an increase in angiogenic factors VEGF-R2 and PDGF-β (P = 0.0035 and P = 0.031, respectively) and antiapoptotic marker Bcl-2 in the PVAX-NPY_3-36 group compared with ischemia PBS group (P = 0.023). Proapoptotic marker Smad5 was significantly decreased in the PVAX-NPY_3-36 group as compared with the ischemia PBS group (P = 0.028). Furthermore, Y₂ receptors were visualized in endothelial cells of newly formed arteries in the PVAX-NPY_3-36 group. In conclusion, we were able to show that PVAX-NPY_3-36 can induce angiogenesis and arteriogenesis as well as improve functional blood flow in a murine model of hind limb ischemia.NEW & NOTEWORTHY Our research project proposes a novel method for drug delivery. Our patented PVAX nanoparticle can detect areas of ischemia and oxidative stress. Although there have been studies about delivering angiogenic molecules to areas of ischemic injury, there are drawbacks of nonspecific delivery as well as short half-lives. Our study is unique because it can specifically deliver NPY_3-36 to ischemic tissue and appears to extend the amount of time therapy is available, despite NPY_3-36's short half-life.

NPY binds with heme to form a NPY–heme complex: enhancing peroxidase activity in free heme and promoting NPY nitration and inactivation

NPY binding with heme enhances the peroxidase activity of free heme, resulting in the important tyrosine nitration, which will attenuate its bioactivity.

Identifying neuropeptide Y (NPY) as the main stress-related substrate of dipeptidyl peptidase 4 (DPP4) in blood circulation

BACKGROUND

Dipeptidyl peptidase 4 (DPP4; EC 3.4.14.5; CD26) is a membrane-bound or shedded serine protease that hydrolyzes dipeptides from the N-terminus of peptides with either proline or alanine at the penultimate position. Substrates of DPP4 include several stress-related neuropeptides implicated in anxiety, depression and schizophrenia. A decline of DPP4-like activity has been reported in sera from depressed patient, but not fully characterized regarding DPP4-like enzymes, therapeutic interventions and protein.

METHODS

Sera from 16 melancholic- and 16 non-melancholic-depressed patients were evaluated for DPP4-like activities and the concentration of soluble DPP4 protein before and after treatment by anti-depressive therapies. Post-translational modification of DPP4-isoforms and degradation of NPY, Peptide YY (PYY), Galanin-like peptide (GALP), Orexin B (OrxB), OrxA, pituitary adenylate cyclase-activating polypeptide (PACAP) and substance P (SP) were studied in serum and in ex vivo human blood. N-terminal truncation of biotinylated NPY by endothelial membrane-bound DPP4 versus soluble DPP4 was determined in rat brain perfusates and spiked sera.

RESULTS

Lower DPP4 activities in depressed patients were reversed by anti-depressive treatment. In sera, DPP4 contributed to more than 90% of the overall DPP4-like activity and correlated with its protein concentration. NPY displayed equal degradation in serum and blood, and was equally truncated by serum and endothelial DPP4. In addition, GALP and rat OrxB were identified as novel substrates of DPP4.

CONCLUSION

NPY is the best DPP4-substrate in blood, being truncated by soluble and membrane DPP4, respectively. The decline of soluble DPP4 in acute depression could be reversed upon anti-depressive treatment. Peptidases from three functional compartments regulate the bioactivity of NPY in blood.

Metabolism of peptide YY 3-36 in Göttingen mini-pig and rhesus monkey

Peptide YY 3-36-amide (PYY3-36) is a peptide hormone, which is known to decrease appetite and food-intake by activation of the Y2 receptor. The current studies were designed to identify the metabolites of PYY3-36 in mini-pig and rhesus monkey. Plasma samples were analyzed by high resolution LC-MS (and MS/MS) in order to unambiguously identify the metabolites of PYY3-36. In summary, the metabolism of PYY3-36 was similar in mini-pig and rhesus monkey. Several metabolites were identified and PYY3-34 was identified at the highest levels in plasma. In addition, mini-pigs were also dosed with PYY1-36-amide, PYY3-35, PYY3-34 and [N-methyl 34Q]-PYY3-36-amide in order to investigate the mechanisms by which PYY was metabolized. PYY3-35 was rapidly converted to PYY3-34 whereas dosing of PYY3-34 to mini-pigs only showed circulating degradation products at low levels, i.e., PYY3-34 was metabolically more stable than PYY3-36 and PYY3-35. [N-methyl 34Q]-PYY3-36-amide was hypothesized to be stable toward cleavage between 34Q and 35R and after i.v. administration to mini-pigs, one major cleavage product was identified as [N-methyl 34Q]-PYY3-35. Overall, this showed that cleavage between 35R and 36Y was possible as well as between 34Q and 35R (as shown for PYY3-35), which indicated that metabolism of PYY3-36 to PYY3-34 may be a two-step process. PYY1-36 was also dosed to mini-pigs, which showed that PYY1-36 was metabolized in the C-terminal as PYY3-36. The overall degradation pattern of PYY1-36 was more complex due to the simultaneous enzymatic degradation in the N-terminal to form PYY2-34/36 and PYY3-34/36. In vitro incubations with heparin stabilized plasma showed that PYY3-36 was degraded with a half-life of 175 min, whereas incubations with PYY3-35 (half-life of 6 min) showed a rapid formation of PYY3-34. In conclusion, the present studies showed that PYY3-36 underwent enzymatic degradation in the C-terminal part and that the major circulating metabolite was PYY3-34. Furthermore, it may be a sequential two-step process leading to the formation of PYY3-35 and subsequently the metabolically more stable PYY3-34.

In vivo and in vitro degradation of peptide YY3-36 to inactive peptide YY3-34 in humans

Peptide YY (PYY) is a 36-amino-acid peptide released from enteroendocrine cells upon food intake. The NH2 terminally truncated metabolite, PYY3-36, exerts anorexic effects and has received considerable attention as a possible antiobesity drug target. The kinetics and degradation products of PYY metabolism are not well described. A related peptide, neuropeptide Y, may be degraded from the COOH terminus, and in vivo studies in pigs revealed significant COOH-terminal degradation of PYY. We therefore investigated PYY metabolism in vitro after incubation in human blood and plasma and in vivo after infusion of PYY1-36 and PYY3-36 in eight young, healthy men. A metabolite, corresponding to PYY3-34, was formed after incubation in plasma and blood and during the infusion of PYY. PYY3-34 exhibited no agonistic or antagonistic effects on the Y2 receptor. PYY1-36 infused with and without coadministration of sitagliptin was eliminated with half-lives of 10.1 ± 0.5 and 9.4 ± 0.8 min (means ± SE) and metabolic clearance rates of 15.7 ± 1.5 and 14.1 ± 1.1 ml·kg(-1)·min(-1) after infusion, whereas PYY3-36 was eliminated with a significantly longer half-life of 14.9 ± 1.3 min and a metabolic clearance rate of 9.4 ± 0.6 ml·kg(-1)·min(-1) We conclude that, upon intravenous infusion in healthy men, PYY is inactivated by cleavage of the two COOH-terminal amino acids. In healthy men, PYY3-36 has a longer half-life than PYY1-36.

Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma

Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.

Proteolytic degradation of neuropeptide Y (NPY) from head to toe: Identification of novel NPY-cleaving peptidases and potential drug interactions in CNS and Periphery

The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application. The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application.

The anorexic hormone Peptide YY3-36 is rapidly metabolized to inactive Peptide YY3-34 in vivo

Peptide YY (PYY) is a 36 amino acid peptide hormone released from enteroendocrine cells. An N-terminally degraded metabolite, PYY3-36, has anorexigenic effects, which makes the PYY system a target for obesity treatment. However, little is known about the kinetics and degradation products of PYY. A related peptide, Neuropeptide Y (NPY), may be degraded from the C-terminus. We therefore investigated PYY degradation after in vitro incubations in porcine plasma and blood and in vivo by infusing PYY3-36 into multicatheterized pigs (n = 7) (2 pmol/kg/min). Plasma samples were analyzed by region-specific radioimmunoassays (RIA) and HPLC analysis. A metabolite, corresponding to PYY3-34 was formed after incubation in plasma and blood and during the infusion study. When taking the C-terminal degradation into account, the half-life (T½) of PYY in blood and plasma amounted to 3.4 ± 0.2 and 6.2 ± 0.2 h, respectively. After PYY3-36 infusion in pigs, the peptide was degraded with a T½ of 3.6 ± 0.5 min. Significant extraction (20.5 ± 8.0%) compatible with glomerular filtration was observed across the kidneys and significant C-terminal degradation (26.5 ± 4.8%) was observed across the liver. Net balances across the hind limb, splanchnic bed, and lungs were not significantly different from zero. PYY3-34 was unable to activate the Y2 receptor in a transfected cell line. In conclusion, PYY3-36 is extensively degraded to PYY3-34 in the pig, a degradation that renders the peptide inactive on the Y2 receptor. Currently used assays are unlikely to be able to detect this degradation and therefore measure falsely elevated levels of PYY3-36, leading to underestimation of its physiological effects.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Synthesis and in vitro and in vivo evaluation of an (18)F-labeled neuropeptide Y analogue for imaging of breast cancer by PET

Imaging of Y1R expression in breast cancer is still a challenging task. Herein, we report a suitable (18)F-labeled high-molecular-weight glycopeptide for imaging of peripheral neuropeptide Y (NPY) Y1 receptor (Y1R)-positive tumors by preclinical small-animal positron emission tomography (PET). The Y1R-preferring NPY [F(7),P(34)]NPY analogue was functionalized with an alkyne-bearing propargylglycine (Pra) in position 4. The corresponding fluoroglycosylated (FGlc) peptide analogue [Pra(4)(FGlc),F(7),P(34)]NPY and its (18)F-labeled analogue were synthesized by click chemistry-based fluoroglycosylation. The radiosynthesis was performed by (18)F-fluoroglycosylation starting from the 2-triflate of the β-mannosylazide and the alkyne peptide [Pra(4),F(7),P(34)]NPY. The radiosynthesis of the(18)F-labeled analogue was optimized using a minimum amount of peptide precursor (40 nmol), proceeding with an overall radiochemical yield of 20-25% (nondecay corrected) in a total synthesis time of 75 min with specific activities of 40-70 GBq/μmol. In comparison to NPY and [F(7),P(34)]NPY, in vitro Y1R and Y2R activation studies with the cold [Pra(4)(FGlc),F(7),P(34)]NPY on stably transfected COS-7 cells displayed a high potency for the induction of Y1R-specific inositol accumulation (pEC50 = 8.5 ± 0.1), whereas the potency at Y2R was significantly decreased. Internalization studies on stably transfected HEK293 cells confirmed a strong glycopeptide-mediated Y1R internalization and a substantial Y1R subtype selectivity over Y2R. In vitro autoradiography with Y1R-positive MCF-7 tumor tissue slices indicated high specific binding of the (18)F-labeled glycopeptide, when binding was reduced by 95% ([Pra(4),F(7),P(34)]NPY) and by 86% (BIBP3226 Y1R antagonist) in competition studies. Biodistribution and small-animal PET studies on MCF-7 breast tumor-bearing nude mice revealed radiotracer uptake in the MCF-7 tumor of 1.8%ID/g at 20 min p.i. and 0.7%ID/g at 120 min p.i. (n = 3-4), increasing tumor-to-blood ratios from 1.2 to 2.4, and a tumor retention of 76 ± 4% (n = 4; 45-90 min p.i.). PET imaging studies with MCF-7 tumor-bearing nude mice demonstrated uptake of the (18)F-labeled glycopeptide in the tumor region at 60 min p.i., whereas only negligible tumor uptake was observed in animals injected with a nonbinding (18)F-labeled glycopeptide pendant as a measure of nonspecific binding. In conclusion, PET imaging experiments with the (18)F-labeled NPY glycopeptide revealed Y1R-specific binding uptake in MCF-7 tumors in vivo together with decreased kidney uptake compared to DOTA-derivatives of this peptide. We consider this glycopeptide to be a potent lead peptide for the design of improved (18)F-glycopeptides with shorter amino acid sequences that would further facilitate PET imaging studies of Y1R-positive breast tumors.

The homeostatic role of neuropeptide Y in immune function and its impact on mood and behaviour

Neuropeptide Y (NPY), one of the most abundant peptides in the nervous system, exerts its effects via five receptor types, termed Y1, Y2, Y4, Y5 and Y6. NPY's pleiotropic functions comprise the regulation of brain activity, mood, stress coping, ingestion, digestion, metabolism, vascular and immune function. Nerve-derived NPY directly affects immune cells while NPY also acts as a paracrine and autocrine immune mediator, because immune cells themselves are capable of producing and releasing NPY. NPY is able to induce immune activation or suppression, depending on a myriad of factors such as the Y receptors activated and cell types involved. There is an intricate relationship between psychological stress, mood disorders and the immune system. While stress represents a risk factor for the development of mood disorders, it exhibits diverse actions on the immune system as well. Conversely, inflammation is regarded as an internal stressor and is increasingly recognized to contribute to the pathogenesis of mood and metabolic disorders. Intriguingly, the cerebral NPY system has been found to protect against distinct disturbances in response to immune challenge, attenuating the sickness response and preventing the development of depression. Thus, NPY plays an important homeostatic role in balancing disturbances of physiological systems caused by peripheral immune challenge. This implication is particularly evident in the brain in which NPY counteracts the negative impact of immune challenge on mood, emotional processing and stress resilience. NPY thus acts as a unique signalling molecule in the interaction of the immune system with the brain in health and disease.

Role of plasma kallikrein in diabetes and metabolism

Plasma kallikrein (PK) is a serine protease generated from plasma prekallikrein, an abundant circulating zymogen expressed by the Klkb1 gene. The physiological actions of PK have been primarily attributed to its production of bradykinin and activation of coagulation factor XII, which promotes inflammation and the intrinsic coagulation pathway. Recent genetic, molecular, and pharmacological studies of PK have provided further insight into its role in physiology and disease. Genetic analyses have revealed common Klkb1 variants that are association with blood metabolite levels, hypertension, and coagulation. Characterisation of animal models with Klkb1 deficiency and PK inhibition have demonstrated effects on inflammation, vascular function, blood pressure regulation, thrombosis, haemostasis, and metabolism. These reports have also identified a host of PK substrates and interactions, which suggest an expanded physiological role for this protease beyond the bradykinin system and coagulation. The review summarises the mechanisms that contribute to PK activation and its emerging role in diabetes and metabolism.

Systemic treatment with neuropeptide Y receptor Y1-antagonist enhances atherosclerosis and stimulates IL-12 expression in ApoE deficient mice

AIMS

Neuropeptide Y (NPY) and Y1 receptors are involved in the mechanisms related to the development of atherosclerosis. We investigated the effects of systemically given NPY and its receptor Y1-antagonist on the development of atherosclerosis and associated inflammatory molecules in ApoE(-/-) mice during high-fat diet.

METHODS

Five weeks old ApoE(-/-) were fed atherogenic high cholesterol diet for 8weeks. The mice were injected with two doses of NPY (50 or 100μg/kg) or Y1 receptor antagonist BIBP3226 (100μg/kg) or vehicle intraperitoneally for 8weeks. Atherosclerosis lesion areas in aortic arch and descending aortas were determined, inflammatory molecules and NPY were determined in aortic wall, spleen, liver or in serum.

RESULTS

Neuropeptide Y1 receptor antagonist, BIBP3226 (100μg/kg) increased atherosclerotic lesion areas compared to vehicle in descending aortas in ApoE(-/-) mice (p=0.021). The expression levels of macrophage-derived cytokine, interleukin-12 (IL-12) in spleens and livers were 8-fold increased with BIBP3226 (p=0.006 and p=0.003, respectively) as determined by RT-qPCR. Cholesterol levels in serum correlated positively with VCAM-1 expression (p=0.003) and negatively with NPY expression (p=0.044) in aortic wall in mice treated with BIBP 3226.

CONCLUSIONS

The results indicate that systemic treatment with Y1-antagonist enhances atherosclerosis development in ApoE deficient mice by triggering an overwhelming IL-12 production. The findings are highly valuable for evaluation of the development potential of Y1 ligands for therapeutics to treat or prevent atherosclerosis.

Neuropeptide Y is produced by adipose tissue macrophages and regulates obesity-induced inflammation

Neuropeptide Y (NPY) is induced in peripheral tissues such as adipose tissue with obesity. The mechanism and function of NPY induction in fat are unclear. Given the evidence that NPY can modulate inflammation, we examined the hypothesis that NPY regulates the function of adipose tissue macrophages (ATMs) in response to dietary obesity in mice. NPY was induced by dietary obesity in the stromal vascular cells of visceral fat depots from mice. Surprisingly, the induction of Npy was limited to purified ATMs from obese mice. Significant basal production of NPY was observed in cultured bone marrow derived macrophage and dendritic cells (DCs) and was increased with LPS stimulation. In vitro, addition of NPY to myeloid cells had minimal effects on their activation profiles. NPY receptor inhibition promoted DC maturation and the production of IL-6 and TNFα suggesting an anti-inflammatory function for NPY signaling in DCs. Consistent with this, NPY injection into lean mice decreased the quantity of M1-like CD11c⁺ ATMs and suppressed Ly6c^hi monocytes. BM chimeras generated from Npy^−/− donors demonstrated that hematopoietic NPY contributes to the obesity-induced induction of Npy in fat. In addition, loss of Npy expression from hematopoietic cells led to an increase in CD11c⁺ ATMs in visceral fat with high fat diet feeding. Overall, our studies suggest that NPY is produced by a range of myeloid cells and that obesity activates the production of NPY in adipose tissue macrophages with autocrine and paracrine effects.

Challenges in mass spectrometry-based quantification of bioactive peptides: a case study exploring the neuropeptide Y family

The study of biologically active peptides is critical to the understanding of physiological pathways, especially those involved in the development of disease. Historically, the measurement of biologically active endogenous peptides has been undertaken by radioimmunoassay, a highly sensitive and robust technique that permits the detection of physiological concentrations in different biofluid and tissue extracts. Over recent years, a range of mass spectrometric approaches have been applied to peptide quantification with limited degrees of success. Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) belong to the NPY family exhibiting regulatory effects on appetite and feeding behavior. The physiological significance of these peptides depends on their molecular forms and in vivo concentrations systemically and at local sites within tissues. In this report, we describe an approach for quantification of individual peptides within mixtures using high-performance liquid chromatography electrospray ionization tandem mass spectrometry analysis of the NPY family peptides. Aspects of quantification including sample preparation, the use of matrix-matched calibration curves, and internal standards will be discussed. This method for the simultaneous determination of NPY, PYY, and PP was accurate and reproducible but lacks the sensitivity required for measurement of their endogenous concentration in plasma. The advantages of mass spectrometric quantification will be discussed alongside the current obstacles and challenges.

Identification of an intracellular M17 family leucine aminopeptidase that is required for virulence in Staphylococcus aureus

Staphylococcus aureus is a highly virulent bacterial pathogen capable of causing a variety of ailments throughout the human body. It is a major public health concern due to the continued emergence of highly pathogenic methicillin resistant strains (MRSA) both within hospitals and in the community. Virulence in S. aureus is mediated by an array of secreted and cell wall associated virulence factors, including toxins, hemolysins and proteases. In this work we identify a leucine aminopeptidase (LAP, pepZ) that strongly impacts the pathogenic abilities of S. aureus. Disruption of the pepZ gene in either Newman or USA300 resulted in a dramatic attenuation of virulence in both localized and systemic models of infection. LAP is required for survival inside human macrophages and gene expression analysis shows that pepZ expression is highest in the intracellular environment. We examine the cellular location of LAP and demonstrate that it is localized to the bacterial cytosol. These results identify for the first time an intracellular leucine aminopeptidase that influences disease causation in a Gram-positive bacterium.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.

Mass spectrometry of peptides and proteins from human blood

It is difficult to convey the accelerating rate and growing importance of mass spectrometry applications to human blood proteins and peptides. Mass spectrometry can rapidly detect and identify the ionizable peptides from the proteins in a simple mixture and reveal many of their post-translational modifications. However, blood is a complex mixture that may contain many proteins first expressed in cells and tissues. The complete analysis of blood proteins is a daunting task that will rely on a wide range of disciplines from physics, chemistry, biochemistry, genetics, electromagnetic instrumentation, mathematics and computation. Therefore the comprehensive discovery and analysis of blood proteins will rank among the great technical challenges and require the cumulative sum of many of mankind's scientific achievements together. A variety of methods have been used to fractionate, analyze and identify proteins from blood, each yielding a small piece of the whole and throwing the great size of the task into sharp relief. The approaches attempted to date clearly indicate that enumerating the proteins and peptides of blood can be accomplished. There is no doubt that the mass spectrometry of blood will be crucial to the discovery and analysis of proteins, enzyme activities, and post-translational processes that underlay the mechanisms of disease. At present both discovery and quantification of proteins from blood are commonly reaching sensitivities of ∼1 ng/mL.