Neuropeptides and Alzheimer's disease

Cerebrospinal Fluid and Brain Proteoforms of the Granin Neuropeptide Family in Alzheimer's Disease

The granin neuropeptide family is composed of acidic secretory signaling molecules that act throughout the nervous system to help modulate synaptic signaling and neural activity. Granin neuropeptides have been shown to be dysregulated in different forms of dementia, including Alzheimer's disease (AD). Recent studies have suggested that the granin neuropeptides and their protease-cleaved bioactive peptides (proteoforms) may act as both powerful drivers of gene expression and as a biomarker of synaptic health in AD. The complexity of granin proteoforms in human cerebrospinal fluid (CSF) and brain tissue has not been directly addressed. We developed a reliable nontryptic mass spectrometry assay to comprehensively map and quantify endogenous neuropeptide proteoforms in the brain and CSF of individuals diagnosed with mild cognitive impairment and dementia due to AD compared to healthy controls, individuals with preserved cognition despite AD pathology ("Resilient"), and those with impaired cognition but no AD or other discernible pathology ("Frail"). We drew associations between neuropeptide proteoforms, cognitive status, and AD pathology values. Decreased levels of VGF proteoforms were observed in CSF and brain tissue from individuals with AD compared to controls, while select proteoforms from chromogranin A showed the opposite effect. To address mechanisms of neuropeptide proteoform regulation, we showed that the proteases Calpain-1 and Cathepsin S can cleave chromogranin A, secretogranin-1, and VGF into proteoforms found in both the brain and CSF. We were unable to demonstrate differences in protease abundance in protein extracts from matched brains, suggesting that regulation may occur at the level of transcription.

Roles of β-Endorphin in Stress, Behavior, Neuroinflammation, and Brain Energy Metabolism

β-Endorphins are peptides that exert a wide variety of effects throughout the body. Produced through the cleavage pro-opiomelanocortin (POMC), β-endorphins are the primarily agonist of mu opioid receptors, which can be found throughout the body, brain, and cells of the immune system that regulate a diverse set of systems. As an agonist of the body's opioid receptors, β-endorphins are most noted for their potent analgesic effects, but they also have their involvement in reward-centric and homeostasis-restoring behaviors, among other effects. These effects have implicated the peptide in psychiatric and neurodegenerative disorders, making it a research target of interest. This review briefly summarizes the basics of endorphin function, goes over the behaviors and regulatory pathways it governs, and examines the variability of β-endorphin levels observed between normal and disease/disorder affected individuals.

Effect of memantine on the levels of glial cells, neuropeptides, and peptide-degrading enzymes in rat brain regions of ibotenic acid-treated alzheimer's disease model

It has been implicated that glia activation plays a critical role in the progression of Alzheimer's disease (AD). However, the precise mechanism of glia activation is not clearly understood yet. In our present studies, we confirmed our previous results where change the levels of neuropeptides and peptidases in ibotenic acid (IBO) infusion into the rat nucleus basalis magnocellularis, an animal model of AD. Furthermore, we extended our study to investigate a possible protection effect of co-administration on the changes of neuropeptides, and neuronal and glial cells in IBO-infused rat brain by memantine treatment. The levels of substance P and somatostatin were decreased in the striatum and frontal cortex 1 week after IBO infusion, and recovered to the control level by memantine treatment, indicating the involvement of neuropeptides in AD pathology. Furthermore, the immunohistochemical and enzymatic studies of GFAP and CD 11b, and peptidylarginine deiminase, markers of glia, in the striatum and frontal cortex showed the increase in IBO-treated rat brain as compared with controls, while co-administration of memantine and IBO no increase of astrocytes and microglia activation was observed. The present biochemical and immunohistochemical results suggest that glia activation might play an important role to the pathology of AD, and correlate with the changes of neuropeptide levels in AD brain that is recovered by memantine treatment.

Effect of S 17092, a novel prolyl endopeptidase inhibitor, on substance P and alpha-melanocyte-stimulating hormone breakdown in the rat brain

In the present study, we have investigated the effects of a novel prolyl endopeptidase (EC 3.4.21.26, PEP) inhibitor, compound S 17092, on substance P (SP) and alpha-melanocyte-stimulating hormone (alpha-MSH) metabolism in the rat brain. In vitro experiments revealed that S 17092 inhibits in a dose-dependent manner PEP activity in rat cortical extracts (IC50 = 8.3 nm). In addition, S 17092 totally abolished the degradation of SP and alpha-MSH induced by bacterial PEP. In vivo, a significant decrease in PEP activity was observed in the medulla oblongata after a single oral administration of S 17092 at doses of 10 and 30 mg/kg (-78% and -82%, respectively) and after chronic oral treatment with S 17092 at doses of 10 and 30 mg/kg per day (-75% and -88%, respectively). Concurrently, a single administration of S 17092 (30 mg/kg) caused a significant increase in SP- and alpha-MSH-like immunoreactivity (LI) in the frontal cortex (+41% and +122%, respectively) and hypothalamus (+84% and +49%, respectively). In contrast, chronic treatment with S 17092 did not significantly modify SP- and alpha-MSH-LI in the frontal cortex and hypothalamus. Collectively, the present results show that S 17092 elevates SP and alpha-MSH concentrations in the rat brain by inhibiting PEP activity. These data suggest that the effect of S 17092 on memory impairment can be accounted for, at least in part, by inhibition of catabolism of promnesic neuropeptides such as SP and alpha-MSH.

Alzheimer's disease, neuropeptides, neuropeptidase, and amyloid-beta peptide metabolism

Amyloid-beta peptide (Abeta), the pathogenic agent of Alzheimer's disease (AD), is a physiological metabolite in the brain. We have focused our attention and effort on elucidating the unresolved aspect of Abeta metabolism: proteolytic degradation. Among a number of Abeta-degrading enzyme candidates, we used a novel in vivo paradigm to identify a member of the neutral endopeptidase family, neprilysin, as the major Abeta catabolic enzyme. Neprilysin deficiency results in defects in the metabolism of endogenous Abeta 40 and 42 in a gene dose-dependent manner. Our observations suggest that even partial down-regulation of neprilysin activity, which could be caused by aging, can contribute to AD development by promoting Abeta accumulation. Moreover, we discuss the fact that an aging-dependent decline of neprilysin activity, which leads to elevation of Abeta concentrations in the brain, is a natural process that precedes AD pathology. In this Perspective, we hypothesize that neprilysin down-regulation has a role in sporadic AD (SAD) pathogenesis, and we propose that this knowledge be used for developing preventive and therapeutic strategies through use of a G protein-coupled receptor (GPCR).

S 17092: a prolyl endopeptidase inhibitor as a potential therapeutic drug for memory impairment. Preclinical and clinical studies

Any treatment that could positively modulate central neuropeptides levels would provide a promising therapeutic approach to the treatment of cognitive deficits associated with aging and/or neurodegenerative diseases. Therefore, based on the activity in rodents, S 17092 (2S,3aS,7aS)-1][(R,R)-2-phenylcyclopropyl]carbonyl]-2-[(thiazolidin-3-yl)carbonyl]octahydro-1H-indole) has been selected as a potent inhibitor of cerebral prolyl-endopeptidase (PEP). By retarding the degradation of neuroactive peptides, S 17092 was successfully used in a variety of memory tasks. These tasks explored short-term, long-term, reference and working memory in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. S 17092 has also been safely administered to humans, and showed a clear peripheral expression of its mechanism of action through its inhibitory effect upon PEP activity in plasma. S 17092 exhibited central effects, as evidenced by EEG recording in healthy volunteers, and could improve a delayed verbal memory task. Collectively, the preclinical and clinical effects of S 17092 have suggested a promising role for this compound as an agent for the treatment of cognitive disorders associated with cerebral aging.

Further evidence for a dissociation between different forms of mnemonic expressions in a mouse model of age-related cognitive decline: effects of tacrine and S 17092, a novel prolyl endopeptidase inhibitor

It has been demonstrated previously on the radial maze that the emergence of an age-related mnemonic impairment is critically dependent on the form which the discrimination problems took. Hence, when the arms were presented one by one (i.e., successive go-no-go discrimination), both adult and aged mice learned to distinguish between positive (baited) and negative (unbaited) arms readily, as evidenced by their increased readiness to enter positive relative to negative arms (i.e., by a differential in arm-entry latencies). A selective impairment in the aged mice was seen when these arms were presented subsequently as pairs, such that the mice were confronted with an explicit choice (i.e., simultaneous 2-choice discrimination). When discriminative performance was measured by the differential run speed between positive and negative arms, aged mice were also impaired. This was particularly pronounced in the 2-choice discrimination condition. We examined the effects of tacrine (3mg/kg, subcutaneously) or S 17092 (10mg/kg, orally) in aged mice on the three behavioral indices of this 2-stage spatial discrimination paradigm. The results indicated that: (1) Tacrine, but not S 17092, enhanced the acquisition of go-no-go discrimination as reflected in arm-entry latencies; (2) both drugs improved choice accuracy in simultaneous discrimination, although the effect of tacrine was less striking and, in particular, far from statistical significance in the very first 2-choice responses; and (3) neither drugs significantly affected run-speed performance. We conclude further that the specific patterns of drug effects on the three indices of discriminative performance might suggest that each index is associated with a distinct form of mnemonic expression relying on separate neural systems.

S 17092-1, a highly potent, specific and cell permeant inhibitor of human proline endopeptidase

Several lines of evidence indicate that proline endopeptidase (PE) could participate to the symptomatology and/or etiology of Alzheimer's disease. Thus, proline endopeptidase appears to contribute to the degradation of neuropeptides involved in learning and memory and could also control the production of the amyloidogenic peptide Abeta. Therefore the design of potent, selective and permeant inhibitors of human PE should lead to potential probes to assess the genuine contribution of this enzyme in Alzheimer's pathology. A novel perhydroindol carboxylic derivative, S17092-1 inhibits the hydrolysis of Z-Gly-Pro-7AMC-hydrolysing activity present in human brain nuclei with a high affinity (Ki = 1 nM) and behaves as a highly potent (Ki = 1.5 nM) inhibitor of partially purified human PE. By contrast, S17092-1 is unable to affect a series of other peptidases including aminopeptidases B and M, dipeptidylaminopeptidase IV, endopeptidases 3.4.24.11, 3.4.24.15, 3.4.24.16, calpains and angiotensin-converting enzyme. Furthermore, we show that the embryonic human kidney 293 cell line displays an intracellular PE-like activity that is blocked after preincubating cells with S17092-1, indicating that this inhibitor penetrates in HEK293 cells and could affect intracellular human PE. Altogether, we establish that S17092-1 behaves as a highly potent, specific and cell permeant inhibitor of human proline endopeptidase and can be seen as a probe to examine PE contribution in Alzheimer's disease.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and on cholinergic and peptidergic neurons in rats with ibotenate-induced lesions of the nucleus basalis magnocellularis

We conducted behavioral and neurochemical studies of a novel prolyl endopeptidase inhibitor, (S)2-[[(S)-2-(hydroxyacetyl)-1pyrrolidinyl]carbonyl]-N-(phenylmeth yl)-1-pyrrolidine-carboxamide (JTP-4819), in rats with lesions of the nucleus basalis magnocellularis (NBM-lesioned rats) induced by ibotenate. Administration of JTP-4819 (1 and 3 mg/kg, p.o.), on and after the 8th day, significantly shortened the escape latency in the Morris water maze as compared to the vehicle-treated group. JTP-4819 also significantly increased the path length in the quadrant with the platform removed in the spatial probe trial. Neurochemical studies of brains removed after the Morris water maze task showed that choline acetyltransferase activity in the cerebral cortex, but not the hippocampus, was significantly reduced by NBM lesioning, while there were no changes of muscarinic M1 receptor binding activity detected using [3H]pirenzepine. JTP-4819 had almost no effect on these cholinergic parameters in NBM-lesioned rats. Substance P-like immunoreactivity (LI), thyrotropin-releasing hormone (TRH)-LI, and arginine-vasopressin-LI were not significantly changed in the cerebral cortex and hippocampus of NBM-lesioned rats as compared to sham-operated rats. However, these neuropeptide levels were significantly increased in both brain regions by repeated administration of JTP-4819 (1, 3 and/or 10 mg/kg, p.o.). These results suggest that JTP-4819 ameliorated memory impairment due to NBM lesioning by potentiating SP, TRH and AVPergic neurons secondary to PEP inhibition.

Present imperfect: a critical review of animal models of the mnemonic impairments in Alzheimer's disease

This paper reviews the current literature on animal models of the memory impairments of Alzheimer's disease (AD). The authors suggest that modeling of the mnemonic deficits in AD be limited to the amnesia observed early in the course of the disease, to eliminate the influence of impairments in non-mnemonic processes. Tasks should be chosen for their specificity and selectivity to the behavioral phenomena observed in early-stage AD and not for their relevance to hypothetical mnemonic processes. Tasks that manipulate the delay between learning and remembering are better able to differentiate Alzheimer patients from persons with other disorders, and better able to differentiate effects of manipulations in animals. The most commonly used manipulations that attempt to model the amnesia of AD are reviewed within these constraints. The authors conclude that of the models examined, lesions of the medial septal nucleus produce behavioral deficits that are most similar to the mnemonic impairments in the earliest stage of AD. However, the parallel is not definitive and more work is needed to clarify the relationship between neurobiology and behavior in AD.

Alterations of peptide metabolism and neuropeptidase activity in senile dementia of the Alzheimer's type

Work in our laboratory has shown that in addition to previously characterized changes in the level of neuropeptides in SDAT brain, the activity of degradative enzymes responsible for peptide metabolism is also affected. In addition to other reported alterations in peptide metabolism, we have observed that SS-28 degradation is increased in Brodmann area 22 whereas substance P degradation is increased in temporal cortex. Changes in the degradation of these neuropeptides known to be affected in SDAT correlate well with alterations in the activity of specific neuropeptidases. Trypsin-like serine protease activity is increased in SDAT Brodmann area 22 which parallels the increased degradation of SS-28. The activity of MEP 24.15 is decreased in temporal cortex which corresponds to the decreased degradation of substance P. Changes in the activity of these degradative enzymes in SDAT brain can potentially affect the action of other neuropeptide substrates because the neuropeptidases discussed here terminate the action of several neuropeptides. As more neuropeptide and degradative peptidase alterations are discovered in SDAT, greater emphasis may be placed on the role that peptides and neuropeptidases play in the progression of SDAT.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and central cholinergic neurons in aged rats

The effects of a novel prolyl endopeptidase inhibitor (PEP), (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)- 1-pyrrolidinecar-boxamide (JTP-4819), on performance of the Morris water maze task and on central cholinergic function were investigated in aged rats. Spatial memory (escape latency, path length, and swimming speed to the platform) was impaired in aged rats performing the Morris water maze task when compared to young rats. Administration of JTP-4819 (1 mg/kg, p.o.) for 14 days improved this memory deficit in aged rats, as shown by the decrease in escape latency and path length. In addition, when JTP-4819 (at doses of 1 and 3 mg/kg, p.o.) was administered for 3 wk, it reversed the age-related increase of ChAT activity in the cerebral cortex and the decrease of 3H-choline uptake in the hippocampus. These data suggest that JTP-4819 ameliorates age-related impairment of spatial memory and partly reverses central cholinergic dysfunction, possibly due to the enhancement of neuropeptide function by inhibition of PEP mediated degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone.

A novel prolyl endopeptidase inhibitor, JTP-4819, with potential for treating Alzheimer's disease

The pharmacological actions of JTP-4819, a new prolyl endopeptidase (PEP) inhibitor targeted for the treatment of Alzheimer's disease, are reviewed with respect to its effects on PEP activity, brain neurotransmitters, and memory-related behaviour in rats. JTP-4819 was shown to be a very potent and specific inhibitor of PEP. At nanomolar concentration, JTP-4819 inhibited the degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone by PEP in supernatants of the rat cerebral cortex and hippocampus. Repeated administration of JTP-4819 reversed the aging-induced decrease in brain substance P-like and thyrotropin-releasing hormone-like immunoreactivity, suggesting that this drug may be able to improve the imbalance of peptidergic neuronal systems that develops with senescense by inhibiting PEP activity. JTP-4819 increased acetylcholine release from the frontal cortex and hippocampus, regions closely associated with memory, in both young and aged rats. In addition, it improved performance in several memory and learning-related tests (e.g., the Morris water maze task in aged or MCA-occluded rats and the passive avoidance test). This memory-enhancing effect of JTP-4819 may result from prevention of the metabolic degradation of brain neuropeptides by PEP as well as from the enhancement of acetylcholine release. Taken together, these unique and potent pharmacological actions of JTP-4819 suggest that it may have the potential to be used for treating Alzheimer's disease.

Pharmacological studies of a novel prolyl endopeptidase inhibitor, JTP-4819, in rats with middle cerebral artery occlusion

We studied behavioral and pharmacological effects of a novel prolyl endopeptidase inhibitor, (S)-2-[[(S)-2-(hydroxyacetyl)- 1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)-1-pyrrolidine-car boxamide (JTP-4819), in rats with middle cerebral artery occlusion. Administration of JTP-4819 (0.1 and 1 mg/kg p.o for 7 days) significantly prolonged passive avoidance latency, while the latency of rats with middle cerebral artery occlusion receiving the vehicle was significantly shorter than that of sham-operated rats. The prolonged escape latency in the Morris water maze task in rats with middle cerebral artery occlusion was also significantly reduced by administration of JTP-4819 (0.3 and 1 mg/kg p.o.). Interestingly, administration of JTP-4819 (0.3-3 mg/kg p.o. for 15 days) restored the decreased cortical thyrotropin-releasing hormone (TRH)-like immunoreactivity content of rats with middle cerebral artery occlusion but did not affect the cortical and hippocampal substance P- or arginine vasopressin-like immunoreactivity content. These results suggest that JTP-4819 ameliorates memory impairment due to middle cerebral artery occlusion by restoring the cortical TRH content.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on neuropeptide metabolism in the rat brain

The effect of a novel prolyl endopeptidase (PEP) inhibitor, (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl] carbonyl]-N-(phenylmethyl)-1-pyrrolidine-carboxamide (JTP-4819), on neuropeptide metabolism was investigated in the rat brain. JTP-4819 exhibited a strong in vitro inhibitory effect on cortical and hippocampal PEP activity, with the IC50 values being approximately 0.58 +/- 0.02 and 0.61 +/- 0.06 nM, respectively. JTP-4819 also inhibited the in vitro degradation of substance P (SP), arginine-vasopressin (AVP), and thyrotropin-releasing hormone (TRH) by rat brain supernatants, with the IC50 values being respectively 3.4, 2.1, and 1.4 nM in the cerebral cortex and 3.3, 2.8, and 1.9 nM in the hippocampus. Oral administration of JTP-4819 at doses of 1 and 3 mg/kg increased SP-like immunoreactivity (LI) and AVP-LI in the cerebral cortex. JTP-4819 also increased hippocampal SP-LI and AVP-LI at doses of 1 and 3 mg/kg, as well as hippocampal TRH-LI at a dose of 3 mg/kg. These findings suggest that JTP-4819 inhibited the degradation of SP, AVP, and TRH in the rat brain secondary to the inhibition of PEP, and thus increased cortical and hippocampal SP-LI and AVP-LI as well as hippocampal TRH-LI.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on thyrotropin-releasing hormone-like immunoreactivity in the cerebral cortex and hippocampus of aged rats

We investigated the effects of a novel prolyl endopeptidase inhibitor, JTP-4819 ((S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl]carbonyl]-N- (phenylmethyl)-1-pyrrolidinecarboxamide), on thyrotropin-releasing hormone (TRH)-like immunoreactivity (TRH-LI) in the cerebral cortex and hippocampus of aged rats. The TRH-LI content of both brain regions in aged rats was significantly lower than that in young rats. A single oral dose of JTP-4819 (3 mg/kg) restored the cortical TRH-LI content in aged rats, while doses of 0.3-3 mg/kg restored it in the hippocampus. Repeated oral administration of JTP-4819 at a dose of 1 mg/kg for 21 days produced a significant increase of TRH-LI in the cerebral cortex, while it did so in the hippocampus at doses of 0.3 and 1 mg/kg. Our findings suggest that JTP-4819 may improve the functioning of TRHergic neurons, which deteriorate with senescence.

Effects of chronic intraventricular nerve growth factor treatment on vasoactive intestinal peptide and neuropeptide Y levels in the hippocampal formation and cerebral cortex following fimbrial transections

The present study determined whether chronic intracerebroventricular (i.c.v.) nerve growth factor (NGF) treatment alters the hippocampal content of vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) in rats with unilateral fimbrial transections. In addition, effects of chronic NGF treatment on cortical VIP and NPY levels were determined. Following partial and full fimbrial transections, hippocampal choline acetyltransferase (ChAT) activity was reduced by 41% and 60% ipsilateral to the lesioned side, respectively. Chronic NGF treatment partially attenuated (by 48%) the reduction of ChAT following partial lesions, but not full lesions. Neither the hippocampal contents of VIP or NPY were altered by partial or full fimbrial transections nor by chronic NGF treatment. However, in the NGF-treated rats, significant increases not only in cortical ChAT activity (by 28%), but also cortical VIP levels (by 68%) were observed. Cortical NPY levels remained unchanged following chronic NGF administration. In summary, the results suggest that the increases in cortical VIP levels observed in chronic NGF-treated rats may be specific to this tissue and consequent to the enhanced cholinergic tone exerted by this neurotrophin in the basalocortical pathway. Additionally, it appears that NGF when administered in pharmacological doses is not involved in the regulation of NPY synthesis in the hippocampus or cortex despite the presence of an NGF-responsive element associated with the rat NPY gene.

Insulin-like growth factors and insulin-like growth factor binding proteins in cerebrospinal fluid and serum of patients with dementia of the Alzheimer type

After acid gel-chromatography cerebrospinal fluid and serum levels of immunoreactive insulin-like growth factor 1 and 2 (IGF-1 and IGF-2) were determined in patients with dementia of the Alzheimer type (AD) and in healthy subjects. The AD CSF levels of immunoreactive IGF-1 did not differ from the subjects but the levels of immunoreactive IGF-2 was significantly elevated in both serum and CSF in the AD patient group. Additionally immunoreactive IGF-1 in AD serum was found to be significantly elevated. To characterize the CSF IGF binding protein activity (IGFBP), ligand blotting was performed on whole CSF from AD patients and subjects. The results demonstrate two major forms of IGFBP in CSF with approximate molecular weights of 33 KDa and 30 KDa. The two IGFBP forms are suggested to represent IGFBP-2 and IGFBP-6. A highly significant increase in both the IGFBPs was observed in the CSF of the AD patients compared to the healthy subjects.