Prolyl Oligopeptidase Activity Research Articles

5-Aminothiazoles Reveal a New Ligand-Binding Site on Prolyl Oligopeptidase Which is Important for Modulation of Its Protein-Protein Interaction-Derived Functions.

A series of novel 5-aminothiazole-based ligands for prolyl oligopeptidase (PREP) comprise selective, potent modulators of the protein-protein interaction (PPI)-mediated functions of PREP, although they are only weak inhibitors of the proteolytic activity of PREP. The disconnected structure-activity relationships are significantly more pronounced for the 5-aminothiazole-based ligands than for the earlier published 5-aminooxazole-based ligands. Furthermore, the stability of the 5-aminothiazole scaffold allowed exploration of wider substitution patterns than that was possible with the 5-aminooxazole scaffold. The intriguing structure-activity relationships for the modulation of the proteolytic activity and PPI-derived functions of PREP were elaborated by presenting a new binding site for PPI modulating PREP ligands, which was initially discovered using molecular modeling and later confirmed through point mutation studies. Our results suggest that this new binding site on PREP is clearly more important than the active site of PREP for the modulation of its PPI-mediated functions.

Abnormal Expression of Prolyl Oligopeptidase (POP) and Its Catalytic Products Ac-SDKP Contributes to the Ovarian Fibrosis Change in Polycystic Ovary Syndrome (PCOS) Mice.

Polycystic ovary syndrome (PCOS) is an endocrine disorder and metabolic syndrome. Ovarian fibrosis pathological change in PCOS has gradually attracted people's attention. In this study, we constructed a PCOS mouse model through the use of dehydroepiandrosterone. Sirius red staining showed that the ovarian tissues in PCOS mice had obvious fibrosis. Prolyl oligopeptidase (POP) is a serine protease and N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is its catalytic product. Studies show that abnormal expression and activity of POP and Ac-SDKP are closely related to tissue fibrosis. It was found that the expression of POP and Ac-SDKP was decreased in the ovaries of PCOS mice. Further studies showed that POP and Ac-SDKP promoted the expression of matrix metalloproteinases 2 (MMP-2) expression and decreased the expression of transforming growth factor beta 1 (TGF-β1) in granulosa cells. Hyperandrogenemia is a typical symptom of PCOS. We found that testosterone induced the low expression of POP and MMP2 and high expression of TGF-β1 in granulosa cells. POP overexpression and Ac-SDKP treatment inhibited the effect of testosterone on TGF-β1 and MMP2 in vitro and inhibited ovarian fibrosis in the PCOS mouse model. In conclusion, PCOS ovarian tissue showed obvious fibrosis. Low expression of POP and Ac-SDKP and changes in fibrotic factors contribute to the ovarian pathological fibrosis induced by androgen.

Prolyl oligopeptidase activity (POP) in early stage and medicated schizophrenia and in an animal model for schizophrenia study: In vivo effects of psychopharmacological substances on enzyme activity

Prolyl oligopeptidase (POP) is an enzyme highly expressed in the central nervous system, playing important roles in neurodevelopment, memory and learning. Moreover, changes in POP activity in peripheral blood have been associated with various neuropsychiatric disorders. Herein, the POP activity was measured by monitoring the hydrolysis of a specific MCA peptide substrate in plasma or homogenate of selected brain regions from a validated animal model for schizophrenia (SCZ) studies, namely spontaneously hypertensive rats (SHR), compared with control normotensive Wistar rats (NWR), before and after the treatment with antipsychotics. We also evaluated POP activity in plasma from patients with early stage or with chronic schizophrenia (SCZ) relative to paired healthy controls (HCs). No significant differences in POP activity were observed for patients in early stage or with chronic SCZ compared to HCs. POP activity was significantly lower in the plasma of SHR compared to NWR, with no changes in activity observed after a chronic treatment with typical or atypical antipsychotics. Interestingly, a significant decrease in POP activity was observed solely in prefrontal cortex of the SCZ animal model but not in any other brain region or plasma of NWR or SHR after the chronic treatment with antipsychotics. Despite the well-known cognitive impairments improvement in vivo demonstrated for the POP inhibitors, our data suggest the lack of correlation between the activity of this enzyme and early stage or chronic SCZ, as well as no significative pharmacological responses to psychoactive compounds were noticed for this enzyme here.

Systemic inflammation elevates cytosolic prolyl oligopeptidase protein expression but not peptidase activity in the cerebral cortices of familial Alzheimer`s disease modeling mice

Changes in brain prolyl oligopeptidase (PREP) expression and activity have been associated with neuroinflammation and Alzheimer`s disease (AD). The role of PREP in AD, which onset can be contributed by peripheral infection-induced inflammation, is unknown. The aim of the study was to elucidate further the association of PREP with AD pathology and inflammation. Here, we quantitated PREP protein expression by liquid chromatography-tandem mass spectrometry-based quantitative targeted absolute proteomics and determined PREP peptidase activity in the cerebral cortices of familial AD (APdE9) and lipopolysaccharide (LPS)-induced inflammation mouse models. PREP activity was investigated using the fluorogenic substrate Suc-Gly-Pro-AMC. PREP expression was significantly increased (by 2-fold) in the brain cytosolic fraction of LPS treated APdE9 mice, while the peptidase activity remained unaltered. In the cortical crude membrane fraction, the PREP expression and activity were decreased by 35–40% in the LPS treated APdE9 mice. In conclusion, cortical cytosolic and membrane-bound PREP expression levels and enzyme activities were altered due to LPS-induced inflammation in the AD mouse model. Since the cytosolic protein expression increased without any concomitant increase in the peptidase activity, it is likely that PREP activity is affected by other factors than protein expression alone.

Proline-specific peptidase activities (DPP4, PRCP, FAP and PREP) in plasma of hospitalized COVID-19 patients

BackgroundCOVID-19 patients experience several features of dysregulated immune system observed in sepsis. We previously showed a dysregulation of several proline-selective peptidases such as dipeptidyl peptidase 4 (DPP4), fibroblast activation protein alpha (FAP), prolyl oligopeptidase (PREP) and prolylcarboxypeptidase (PRCP) in sepsis. In this study, we investigated whether these peptidases are similarly dysregulated in hospitalized COVID-19 patients. MethodsFifty-six hospitalized COVID-19 patients and 32 healthy controls were included. Enzymatic activities of DPP4, FAP, PREP and PRCP were measured in samples collected shortly after hospital admission and in longitudinal follow-up samples. ResultsCompared to healthy controls, both DPP4 and FAP activities were significantly lower in COVID-19 patients at hospital admission and FAP activity further decreased significantly in the first week of hospitalization. While PRCP activity remained unchanged, PREP activity was significantly increased in COVID-19 patients at hospitalization and further increased during hospital stay and stayed elevated until the day of discharge. ConclusionThe changes in activities of proline-selective peptidases in plasma are very similar in COVID-19 and septic shock patients. The pronounced decrease in FAP activity deserves further investigation, both from a pathophysiological viewpoint and as its utility as a part of a biomarker panel.

Cyclotides Isolated From Violet Plants of Cameroon Are Inhibitors of Human Prolyl Oligopeptidase.

Traditional medicine and the use of herbal remedies are well established in the African health care system. For instance, Violaceae plants are used for antimicrobial or anti-inflammatory applications in folk medicine. This study describes the phytochemical analysis and bioactivity screening of four species of the violet tribe Allexis found in Cameroon. Allexis cauliflora, Allexis obanensis, Allexis batangae and Allexis zygomorpha were evaluated for the expression of circular peptides (cyclotides) by mass spectrometry. The unique cyclic cystine-rich motif was identified in several peptides of all four species. Knowing that members of this peptide family are protease inhibitors, the plant extracts were evaluated for the inhibition of human prolyl oligopeptidase (POP). Since all four species inhibited POP activity, a bioactivity-guided fractionation approach was performed to isolate peptide inhibitors. These novel cyclotides, alca 1 and alca 2 exhibited IC50 values of 8.5 and 4.4 µM, respectively. To obtain their amino acid sequence information, combinatorial enzymatic proteolysis was performed. The proteolytic fragments were evaluated in MS/MS fragmentation experiments and the full-length amino acid sequences were obtained by de novo annotation of fragment ions. In summary, this study identified inhibitors of the human protease POP, which is a drug target for inflammatory or neurodegenerative disorders.

Prolyl oligopeptidase inhibition by KYP-2407 increases alpha-synuclein fibril degradation in neuron-like cells

Growing evidence emphasizes insufficient clearance of pathological alpha-synuclein (αSYN) aggregates in the progression of Parkinson’s disease (PD). Consequently, cellular degradation pathways represent a potential therapeutic target. Prolyl oligopeptidase (PREP) is highly expressed in the brain and has been suggested to increase αSYN aggregation and negatively regulate the autophagy pathway. Inhibition of PREP with a small molecule inhibitor, KYP-2407, stimulates autophagy and reduces the oligomeric species of αSYN aggregates in PD mouse models. However, whether PREP inhibition has any effects on intracellular αSYN fibrils has not been studied before. In this study, the effect of KYP2407 on αSYN preformed fibrils (PFFs) was tested in SH-SY5Y cells and human astrocytes. Immunostaining analysis revealed that both cell types accumulated αSYN PFFs intracellularly but KYP-2047 decreased intracellular αSYN deposits only in SH-SY5Y cells, as astrocytes did not show any PREP activity. Western blot analysis confirmed the reduction of high molecular weight αSYN species in SH-SY5Y cell lysates, and secretion of αSYN from SH-SY5Y cells also decreased in the presence of KYP-2407. Accumulation of αSYN inside the SH-SY5Y cells resulted in an increase of the auto-lysosomal proteins p62 and LC3BII, as well as calpain 1 and 2, which have been shown to be associated with PD pathology. Notably, treatment with KYP-2407 significantly reduced p62 and LC3BII levels, indicating an increased autophagic flux, and calpain 1 and 2 levels returned to normal in the presence of KYP-2407. Our findings indicate that PREP inhibition can potentially be used as therapy to reduce the insoluble intracellular αSYN aggregates.

The effect of prolyl oligopeptidase inhibitors on alpha-synuclein aggregation and autophagy cannot be predicted by their inhibitory efficacy

Previous studies have shown that prolyl oligopeptidase (PREP) negatively regulates autophagy and increases the aggregation of alpha-synuclein (αSyn), linking it to the pathophysiology of Parkinson’s disease. Our earlier results have revealed that the potent small molecular PREP inhibitor KYP-2047 is able to increase autophagy and decrease dimerization of αSyn but other PREP inhibitors have not been systematically studied for these two protein-protein interaction mediated biological functions of PREP. In this study, we characterized these effects for 12 known PREP inhibitors with IC50-values ranging from 0.2 nM to 1010 nM. We used protein-fragment complementation assay (PCA) to assess αSyn dimerization and Western Blot of microtubule-associated protein light chain 3B II (LC3B-II) and a GFP-LC3-RFP expressing cell line to study autophagy. In addition, we tested selected compounds in a cell-free αSyn aggregation assay, native gel electrophoresis, and determined the compound concentration inside the cell by LC-MS. We found that inhibition of the proteolytic activity of PREP did not predict decreased αSyn dimerization or increased autophagy, and we also confirmed that this result did not simply reflect concentration differences of the compounds inside the cell. Thus, PREP ligands regulate the effect of PREP on autophagy and αSyn aggregation through a conformational stabilization of the enzyme that is not equivalent to inhibiting its proteolytic activity.

The development and validation of a combined kinetic fluorometric activity assay for fibroblast activation protein alpha and prolyl oligopeptidase in plasma

BackgroundFibroblast activiation protein alpha (FAP) is considered a diagnostic and prognostic biomarker for various types of cancer. FAP shares substrate specificity with prolyl oligopeptidase (PREP), studied in (neuro)inflammation and neurodegeneration as well as cancer. Current assays inadequately discriminate between FAP and PREP and there is need for an assay that reliably quantitates the FAP/PREP activity ratio in plasma. MethodsFAP and PREP activities were measured in human EDTA-plasma in presence of well characterized PREP and FAP inhibitors. ResultsA combined kinetic assay was developed in conditions to optimally measure FAP as well as PREP activity with Z-Gly-Pro-AMC as substrate. Limit of detection was 0.009 U/L and limit of quantitation was 0.027 U/L for the combined FAP-PREP assay. Within-run coefficient of variation was 3% and 4% and between-run precision was 7% and 12% for PREP and FAP, respectively. Accuracy was demonstrated by comparison with established end-point assays. Hemolysis interferes with the assay with 1.5 g/L hemoglobin as cut-off value. PREP (but not FAP) activity can increase upon lysis of platelets and red blood cells during sample preparation. ConclusionWith this new assay, on average 67% of the Z-Gly-Pro-AMC converting activity in plasma can be attributed to FAP.

Chemical constituents from Valeriana polystachya Smith and evaluation of their effects on the acetylcholinesterase and prolyl oligopeptidase activities

Two new iridoids (1–2) and a new decomposition product of valepotriates (3), together with fifteen known compounds (4–18) were isolated from the roots and rhizomes of Valeriana polystachya Smith, a native species from the Pampa Biome. Their structures were elucidated by means of NMR spectroscopy, mass spectrometry and optical rotation. The structures of 3 and 18 were further confirmed by single crystal X-ray diffraction analysis. In the group of the isolated compounds, 6β-hydroxysitostenone, hydroxymaltol and isovillosol were isolated from the Valeriana genus for the first time. The extracts and isolated compounds were evaluated for their in vitro activities against acetylcholinesterase (AChE) and prolyloligopeptidase (POP). Compounds 7, 9 and 11 showed weak inhibitory activity against AChE, while 3 and 5 displayed exceptional POP inhibitory activity, with IC50 values of 5.3 ± 0.07 and 7.9 ± 0.4 μM, respectively.

Extracellular prolyl oligopeptidase derived from activated microglia is a potential neuroprotection target.

Prolyl oligopeptidase (PREP) is an abundant peptidase in the brain and periphery, but its physiological functions are still largely unknown. Recent findings point to a role for PREP in inflammatory processes. This study assessed the cellular and extracellular PREP activities in cultures of mouse primary cortical neurons, microglial cells and astrocytes, and immortalized microglial BV-2 cells under neuroinflammatory conditions induced by lipopolysaccharide (LPS) and interferon gamma (IFNγ). Furthermore, we evaluated the neuroprotective effect of a specific PREP inhibitor, KYP-2047, in a neuroinflammation model based on a coculture of primary cortical neurons and activated BV-2 cells. The inflammatory insult reduced intracellular and increased extracellular PREP activity specifically in microglial cells, suggesting that activated microglia excretes active PREP. A targeted proteomics approach revealed up-regulation in PREP protein levels in BV-2 cell growth medium but down-regulation in crude membrane-bound PREP after LPS+IFNγ. In the coculture of BV-2 cells and primary neurons, an increase in extracellular PREP activity was also detected after inflammation. KYP-2047 (10 μmol/L) significantly protected neurons against microglial toxicity and reduced the levels of the pro-inflammatory cytokine tumour necrosis factor alpha. In conclusion, these data point to an extracellular role for microglial PREP in the inflammatory process. Inhibition of PREP during neuroinflammation is a potential target for neuroprotection. Thus, PREP inhibitors may offer a novel therapeutic approach for the treatment of neurodegenerative disorders with an inflammatory component including Parkinson's and Alzheimer's diseases.

Identification and characterization of a novel prolyl oligopeptidase in filarial parasite Setaria cervi

A 75 kDa serine protease having prolyl oligopeptidase activity has been purified from Setaria cervi, a bovine filarial parasite. The MALDI-MS/MS analysis of the purified protein revealed 6 peptides showing nearest match S9A (prolyl oligopeptidase) family protein from Plesiocystis pacifica. The ScPOP was found to be unique compared to mammalian POP with respect to its kinetic properties. To elucidate its role, filarial parasites were exposed to specific inhibitor of POP, Z-Pro-prolinal (ZPP) for 8 h. The inhibition of POP induced calcium signaling via phospholipase c stimulation which further triggered mitochondrial mediated apoptosis in filarial parasites.

New compounds identified through in silico approaches reduce the \u03b1-synuclein expression by inhibiting prolyl oligopeptidase in vitro

Prolyl oligopeptidase (POP) is a serine protease that is responsible for the maturation and degradation of short neuropeptides and peptide hormones. The inhibition of POP has been demonstrated in the treatment of α-synucleinopathies and several neurological conditions. Therefore, ligand-based and structure-based pharmacophore models were generated and validated in order to identify potent POP inhibitors. Pharmacophore-based and docking-based virtual screening of a drug-like database resulted in 20 compounds. The in vitro POP assays indicated that the top scoring compounds obtained from virtual screening, Hit 1 and Hit 2 inhibit POP activity at a wide range of concentrations from 0.1 to 10 µM. Moreover, treatment of the hit compounds significantly reduced the α-synuclein expression in SH-SY5Y human neuroblastoma cells, that is implicated in Parkinson’s disease. Binding modes of Hit 1 and Hit 2 compounds were explored through molecular dynamics simulations. A detailed investigation of the binding interactions revealed that the hit compounds exhibited hydrogen bond interactions with important active site residues and greater electrostatic and hydrophobic interactions compared to those of the reference inhibitors. Finally, our findings indicated the potential of the identified compounds for the treatment of synucleinopathies and CNS related disorders.

Prolyl oligopeptidase attenuates hepatic stellate cell activation through induction of Smad7 and PPAR-γ.

Prolyl oligopeptidase (POP) is a serine endopeptidase widely distributed in vivo with high activity in the liver. However, its biological functions in the liver have remained largely elusive. A previous study by our group has shown that POP produced N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) and thereby exerted an anti-fibrogenic effect on hepatic stellate cells (HSCs) in vitro. It was therefore hypothesized that POP may affect the activation state of HSCs and has an important role in liver fibrosis. The HSC-T6 immortalized rat liver stellate cell line was treated with the POP inhibitor S17092 or transfected with recombinant lentivirus to overexpress POP. Cell proliferation and apoptosis were determined using a Cell Counting Kit-8 and flow cytometry, respectively. The activation status of HSCs was determined by examination of the expression of α-smooth muscle actin (α-SMA), collagen I, monocyte chemoattractant protein-1 (MCP-1), transforming growth factor (TGF)-β-Smad signaling and peroxisome proliferator activated receptor-γ (PPAR-γ). Inhibition by S17092 decreased, whereas lentiviral expression increased the activity of POP and cell proliferation, while neither of the treatments affected cell apoptosis. Of note, S17092 significantly increased, whereas POP overexpression decreased the expression of α-SMA and MCP-1 without affecting the expression of collagen I and TGF-β1. Furthermore, S17092 caused a reduction, whereas POP overexpression caused an upregulation of Smad7 protein and PPAR-γ, but not phosphorylated-Smad2/3 expression. In conclusion, POP attenuated the activation of HSCs through inhibition of TGF-β signaling and induction of PPAR-γ, which may have therapeutic potential in liver fibrosis.

Prolyl Oligopeptidase Inhibition Attenuates Steatosis in the L02 Human Liver Cell Line.

BackgroundProlyl oligopeptidase (POP) is a serine endopeptidase that is widely distributed in vivo, particularly in the liver. Significant changes in functional mitochondrial proteins involved with mitochondrial oxidoreductases/transporters and nucleic acid binding proteins were observed after POP inhibition in the liver, which suggested a role of POP in regulating liver energy metabolism. Steatosis in nonalcoholic fatty liver disease (NAFLD) is associated with disturbances in lipid and energy metabolism in hepatocytes. Here, we aimed to study the effect of POP on hepatocyte steatosis.MethodsThe human liver cell line L02 was used to investigate the biological effects of POP. An in vitro cell model of steatosis was successfully induced with oleic acid and palmitic acid. L02 cells were also subjected to S17092 (a POP inhibitor) at different concentrations for 24 or 48 h. Ac-SDKP levels and POP activity were measured to assess the rate of inhibition of POP by S17092. The POP gene and protein expression levels were detected using real-time PCR and Western blots, respectively. Oil red O staining was performed and the triglyceride levels in the L02 cells were also measured. Cell proliferation and apoptosis were detected using CCK-8 and flow cytometry, respectively. The expression of genes involved in lipid metabolism was detected using real-time PCR. The effects of POP inhibition on LC3B II were detected by Western blot.ResultsCompared with the control, the POP mRNA levels increased by approximately 30%, and the POP protein levels increased by almost 60% in the steatotic L02 cells. After S17092 (0.026~130 μM) incubation for 24 or 48 h, cell proliferation was significantly decreased in the free fatty acid (FFA)-treated cells at 26–130 μM; however, S17092 did not affect the proliferation of L02 cells after 24 h of incubation with S17092 at 0.026–65 μM without FFA treatment. S17092 treatment (13 and 26 μM) also elicited no significant effect on apoptosis in normal L02 cells, but FFA treatment increased cell apoptosis, which was attenuated by S17092 incubation. S17092 treatment inhibited intracellular POP activity and decreased the AcSDKP level at the concentration of 0.026–26 μM. After treatment with FFA for 24 h, oil red O staining revealed significant lipid accumulation in the cells in the model group compared with the controls; however, lipid accumulation was suppressed after the administration of S17092 (13 and 26 μM). Accordingly, the triglyceride levels in the FFA-treated cells were approximately 5-fold greater than those of the controls and were decreased by approximately 25% and 45% after the administration of S17092 at 13 and 26 μM, respectively. The mRNA levels of FASN, PPAR-γ, and SREBP-1c were higher in the FFA-treated cells than in the normal controls, and all of these levels were significantly inhibited in the presence of S17092 at both 13 and 26 μM. S17092 treatment did not affect LC3B II in the FFA-treated cells compared with FFA treatment alone.ConclusionThe expression of POP increases with hepatocyte steatosis, and POP inhibitors can significantly reduce intracellular lipid accumulation, which might be related to the inhibition of genes involved in lipid synthesis.

Dysregulation of the renin-angiotensin system during lung ischemia-reperfusion injury

ABSTRACTAim/Purpose of the Study: Activation of the renin-angiotensin system leading to increased angiotensin-(1–7) (Ang-(1–7)) and decreased angiotensin 2 (Ang 2) levels may be a new therapeutic approach to reduce acute lung injury. Prolylcarboxypeptidase (PRCP) and prolyloligopeptidase (PREP) are capable of hydrolyzing Ang 2 into Ang-(1–7). However, their relation with circulating Ang 2 levels after lung ischemia–reperfusion injury (LIRI) has never been explored. This study determines whether the activity and expression of PRCP and PREP in plasma and lung tissue is related to circulating Ang 2 levels in a murine model of LIRI. Materials and Methods: LIRI in Swiss mice (6 animals per group) was induced by temporary left lung hilar clamping (1 h) followed by 0, 1 or 24 h of reperfusion. Animals in the sham group received thoracotomy only. PRCP activity was measured via RP-HPLC, PREP activity using a fluorogenic substrate and plasma Ang 2 levels via ELISA. Western blotting was used to determine the PRCP and PREP protein expression profiles in left lung tissue. Results: Plasma Ang 2 levels significantly rise after lung ischemia and remain increased after 1 h and 24 h of reperfusion compared to the sham group. While a significant decrease in plasma PREP activity was found after 24 h of reperfusion, a transient increase in plasma PRCP activity was observed after ischemia. However, no correlation with plasma Ang 2 levels could be demonstrated. The activity profiles of PRCP and PREP and the protein expression of PRCP in the lung tissues remained unchanged after LIRI. Conclusions: LIRI causes a dysregulation of circulating Ang 2 levels and plasma PREP activity, although no direct link between both phenomena could be shown. The activity profile of pulmonary PRCP and PREP was not significantly changed after LIRI, which implies a minor role for local PRCP and PREP in the ischemic lung itself.

Chemical Composition and Inhibitory Effects of Hypericum brasiliense and H. connatum on Prolyl Oligopeptidase and Acetylcholinesterase Activities.

The genus Hypericum (family Clusiaceae) comprises various species that are used in traditional medicine, such as wound healing, antidepressant, and anticancer agents. The aim of this study was to evaluate the inhibitory capacity of extracts and fractions from two Hypericum species used in the Brazilian folk medicine (H. brasiliense and H. connatum) against the enzymes prolyl oligopeptidase (POP), dipeptidyl peptidase-IV (DPP-IV), and acetylcholinesterase (AChE), as well as to identify their main active constituents. Dried aerial parts of H. connatum and H. brasiliense were subjected to extraction with 8:2 methanol-H2O. Each hydroalcoholic extract was fractioned resulting in ethyl acetate and aqueous fractions. The activity of POP, DPP-IV and AChE was determined in vitro in 96-well microplates. The main components identified in the plant extracts were chlorogenic acid (1), quercitrin (2), rutin (3), quercetin (4), and isoquercitrin (5). Hydroalcoholic extracts, ethyl acetate and aqueous fractions showed high POP inhibitory activity with IC50 values of 2.6 to 3.7 µg/mL. AChE and DPP-IV inhibitory effects were very low for all extracts and substances. Chlorogenic acid (1) and quercetin (4) were the main constituent responsible for the activity observed against POP. Parallel artificial membrane permeability assay of ethyl acetate fractions of both species showed that the metabolite that can effectively pass through the lipid membrane is 4, the aglycone form of 2, 3 and 5.

Clinical Implications of Plasma N-acetyl-seryl-aspartyl-lysyl-proline Level in Stable Kidney Transplant Recipients.

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is a natural inhibitor of pluripotent hematopoietic stem cell proliferation and is normally found in human plasma. Because AcSDKP is partially eliminated in urine, accumulation of AcSDKP due to chronic renal failure may cause anemia. However, the status of plasma AcSDKP level in stable kidney transplant recipients is unknown although some recipients develop anemia after kidney transplantation. In this study, we investigated the relationship between plasma AcSDKP-like immunoreactive substance (IS) level and clinical characteristics associated with renal anemia in stable kidney transplant recipients. Forty Japanese kidney transplant recipients who underwent transplantation more than 90 days prior to the study were included. Morning blood samples were collected and plasma AcSDKP-IS levels were measured using an enzyme immunoassay. A significant correlation was observed between plasma AcSDKP-IS level and creatinine clearance. On the other hand, no significant correlation was observed between plasma AcSDKP-IS level and prolyl oligopeptidase activity, angiotensin II, or erythropoietin level. A significant difference in plasma AcSDKP-IS level was observed between recipients with no renal anemia and those with renal anemia. These results suggest that plasma AcSDKP level may depend largely on renal function and suggest a possibility that accumulation of AcSDKP may be partially involved in the pathogenesis of renal anemia in stable kidney transplant recipients.

The expression levels of prolyl oligopeptidase responds not only to neuroinflammation but also to systemic inflammation upon liver failure in rat models and cirrhotic patients.

BackgroundLiver failure in experimental animals or in human cirrhosis elicits neuroinflammation. Prolyl oligopeptidase (PREP) has been implicated in neuroinflammatory events in neurodegenerative diseases: PREP protein levels are increased in brain glial cells upon neuroinflammatory insults, but the circulating PREP activity levels are decreased in multiple sclerosis patients in a process probably mediated by bioactive peptides. In this work, we studied the variation of PREP levels upon liver failure and correlated it with several inflammatory markers to conclude on the relation of PREP with systemic and/or neuroinflammation.MethodsPREP enzymatic activity and protein levels measured with immunological techniques were determined in the brain and plasma of rats with portacaval shunt (PCS) and after treatment with ibuprofen. Those results were compared with the levels of PREP measured in plasma from cirrhotic patients with or without minimal hepatic encephalopathy (MHE). Levels of several pro-inflammatory cytokines and those of NO/cGMP homeostasis metabolites were measured in PCS rats and cirrhotic patients to conclude on the role of PREP in inflammation.ResultsIn PCA rats, we found that PREP levels are significantly increased in the hippocampus, striatum and cerebellum, that in the cerebellum the PREP increase was significantly found in the extracellular space and that the levels were restored to those measured in control rats after administration of an anti-inflammatory agent, ibuprofen. In cirrhotic patients, circulatory PREP activity was found to correlate to systemic and neuroinflammatory markers and had a negative correlation with the severity of the disease, although no clear relation to MHE.ConclusionsThese results support the idea that PREP levels could be used as indicators of cirrhosis severity in humans, and using other markers, it might contribute to assessing the level of neuroinflammation in those patients. This work reports, for the first time, that PREP is secreted to the extracellular space in the cerebellum most probably due to glial activation and supports the role of the peptidase in the inflammatory response.

Inhibition of Human Prolyl Oligopeptidase Activity by the Cyclotide Psysol 2 Isolated from Psychotria solitudinum.

Cyclotides are head-to-tail cyclized peptides comprising a stabilizing cystine-knot motif. To date, they are well known for their diverse bioactivities such as anti-HIV and immunosuppressive properties. Yet little is known about specific molecular mechanisms, in particular the interaction of cyclotides with cellular protein targets. Native and synthetic cyclotide-like peptides from Momordica plants are potent and selective inhibitors of different serine-type proteinases such as trypsin, chymotrypsin, matriptase, and tryptase-beta. This study describes the bioactivity-guided isolation of a cyclotide from Psychotria solitudinum as an inhibitor of another serine-type protease, namely, the human prolyl oligopeptidase (POP). Analysis of the inhibitory potency of Psychotria extracts and subsequent fractionation by liquid chromatography yielded the isolated peptide psysol 2 (1), which exhibited an IC50 of 25 μM. In addition the prototypical cyclotide kalata B1 inhibited POP activity with an IC50 of 5.6 μM. The inhibitory activity appeared to be selective for POP, since neither psysol 2 nor kalata B1 were able to inhibit the proteolytic activity of trypsin or chymotrypsin. The enzyme POP is well known for its role in memory and learning processes, and it is currently being considered as a promising therapeutic target for the cognitive deficits associated with several psychiatric and neurodegenerative diseases, such as schizophrenia and Parkinson’s disease. In the context of discovery and development of POP inhibitors with beneficial ADME properties, cyclotides may be suitable starting points considering their stability in biological fluids and possible oral bioavailability.