Identification of oxidized protein hydrolase of human erythrocytes as acylpeptide hydrolase

HNF4A Regulated APEH Deficiency Promotes UPR Activation in Diabetic Kidney Disease

Diabetic kidney disease (DKD) constitutes a severe microvascular complication of diabetes and ranks among the leading causes of end-stage renal disease (ESRD). Endoplasmic reticulum stress (ERS) significantly contributes to the initiation and progression of DKD, as persistent ERS leads to excessive activation of the unfolded protein response (UPR), triggering cellular apoptosis. Protein carbonylation, a prominent oxidative modification caused by reactive oxygen species (ROS), is recognized as a critical initiator of ERS. Acyl peptide enzyme hydrolase (APEH) demonstrates cytoprotective properties by degrading carbonylated proteins and alleviating their abnormal aggregation. Nonetheless, the precise roles and mechanisms of APEH in DKD remain inadequately elucidated. This study employs 24-week db/db mice and a renal tubular epithelial cell model stimulated by high glucose and high fat conditions. By combining comprehensive multidatabase bioinformatics analysis, morphological characterization, and molecular biology techniques, we aim to elucidate the functional role and underlying regulatory mechanisms of APEH in DKD. Our findings indicate that DKD is associated with significantly reduced expression of both APEH and hepatocyte nuclear factor 4 alpha (HNF4A), leading to elevated protein carbonylation and subsequent activation of the UPR pathway, ultimately causing increased apoptosis in renal tubular epithelial cells. Further investigation through dual-luciferase reporter assays and ChIP-qPCR analysis confirmed that HNF4A directly regulates APEH expression by binding to its promoter region. Reduced APEH expression impairs the protective effects mediated by HNF4A, resulting in elevated protein carbonylation, enhanced UPR activation, and increased apoptosis, thereby exacerbating renal tubular epithelial cell injury in DKD. Collectively, these findings underscore the critical role of the HNF4A/APEH axis in regulating protein carbonylation and UPR signaling during DKD progression, highlighting a potential novel therapeutic target for DKD treatment.

Prodrug activation in malaria parasites mediated by an imported erythrocyte esterase, acylpeptide hydrolase (APEH)

The continued emergence of antimalarial drug resistance highlights the need to develop new antimalarial therapies. Unfortunately, new drug development is often hampered by undesirable drug-like properties of lead compounds. Prodrug approaches temporarily mask undesirable compound features, improving bioavailability and target penetration. We have found that lipophilic diester prodrugs of phosphonic acid antibiotics, such as fosmidomycin (Fsm), exhibit significantly higher antimalarial potency than their parent compounds [R.L. Edwards et al., Sci. Rep. 7, 8400 (2017)]. However, the activating enzymes for these prodrugs were unknown. Here, we show that an erythrocyte enzyme, acylpeptide hydrolase (APEH), is the major activating enzyme of multiple lipophilic ester prodrugs. Surprisingly, this enzyme is taken up by the malaria parasite, Plasmodium falciparum, where it localizes to the parasite cytoplasm and retains enzymatic activity. Using a fluorogenic ester library, we characterize the structure-activity relationship of APEH and compare it to that of P. falciparum esterases. We show that parasite-internalized APEH plays an important role in the activation of substrates with branching at the alpha carbon, in keeping with its exopeptidase activity. Our findings highlight a mechanism for antimicrobial prodrug activation, relying on a host-derived enzyme to yield activation at a microbial target. Mutations in prodrug-activating enzymes are a common mechanism for antimicrobial drug resistance [E. S. Istvan et al., Nat. Commun. 8, 14240 (2017); K. M. V. Sindhe et al., mBio 11, e02640-19 (2020); J. H. Butler et al., Acs Infect Dis. 6, 2994-3003 (2020)]. Leveraging an internalized host enzyme would circumvent this, enabling the design of prodrugs with higher barriers to drug resistance.

Discovery of an Enzyme-Activated Fluorogenic Probe for In Vivo Profiling of Acylaminoacyl-Peptide Hydrolase

Acylaminoacyl-peptide hydrolase (APEH), a serine peptidase that belongs to the prolyl oligopeptidase (POP) family, catalyzes removal of N-terminal acetylated amino acid residues from peptides. As a key regulator of protein N-terminal acetylation, APEH was involved in many important physiological processes while its aberrant expression was correlated with progression of various diseases such as inflammation, diabetics, Alzheimer's disease (AD), and cancers. However, while emerging attention has been attracted in APEH-related disease diagnosis and drug discovery, the mechanisms behind APEH and related disease progression are still unclear; thus, further investigating the physiological role and function of APEH is of great importance. To date, enzyme-activated fluorescent probes targeting POPs have been extensively reported and adopted in relevant medical research and applications. Nevertheless, as an important member of the POP family, APEH was rarely referred in the field of bioimaging while the fluorescent probe for in vivo sensing of APEH activity has not been reported yet. Thus, acquiring an efficient APEH-targeted probe is in urgent need. Herein, an enzyme-activated fluorogenic probe for in vivo profiling of APEH was first discovered via a substrate mimic-based strategy. By combination of stimulated molecular docking-based preliminary screening and experiment-based secondary screening, the optimal probe (named as TMN-AcA), which displayed high binding affinity, sensitivity, and specificity toward APEH, was screened out. Owing to the superior properties of TMN-AcA, endogenous APEH activity in various cell lines and transplanted tumor could be visualized while tissue distribution of APEH was revealed. Most importantly, APEH was first demonstrated to be a potential biomarker of multiple-organ injury via TMN-AcA-based bioimaging and immunohistochemistry (IHC) analysis while the newly developed probe could serve as a vital tool for APEH-related disease diagnosis and biological function study.

Prodrug activation in malaria parasites mediated by an imported erythrocyte esterase, acylpeptide hydrolase (APEH)

The continued emergence of antimalarial drug resistance highlights the need to develop new antimalarial therapies. Unfortunately, new drug development is often hampered by poor drug-like properties of lead compounds. Prodrugging temporarily masks undesirable compound features, improving bioavailability and target penetration. We have found that lipophilic diester prodrugs of phosphonic acid antibiotics, such as fosmidomycin, exhibit significantly higher antimalarial potency than their parent compounds (1). However, the activating enzymes for these prodrugs were unknown. Here, we show that an erythrocyte enzyme, acylpeptide hydrolase (APEH) is the major activating enzyme of multiple lipophilic ester prodrugs. Surprisingly, this enzyme is taken up by the malaria parasite, Plasmodium falciparum, where it localizes to the parasite cytoplasm and retains enzymatic activity. Using a novel fluorogenic ester library, we characterize the structure activity relationship of APEH, and compare it to that of P. falciparum esterases. We show that parasite-internalized APEH plays an important role in the activation of substrates with branching at the alpha carbon, in keeping with its exopeptidase activity. Our findings highlight a novel mechanism for antimicrobial prodrug activation, relying on a host-derived enzyme to yield activation at a microbial target. Mutations in prodrug activating enzymes are a common mechanism for antimicrobial drug resistance (2-4). Leveraging an internalized host enzyme would circumvent this, enabling the design of prodrugs with higher barriers to drug resistance.

Crystal structure and solution scattering of Geobacillus stearothermophilus S9 peptidase reveal structural adaptations for carboxypeptidase activity

Acylaminoacyl peptidases (AAPs) play a pivotal role in various pathological conditions and are recognized as potential therapeutic targets. AAPs exhibit a wide range of activities, such as acylated amino acid-dependent aminopeptidase, endopeptidase, and less studied carboxypeptidase activity. We have determined the crystal structure of an AAP from Geobacillus stearothermophilus (S9gs) at 2.0 Å resolution. Despite being annotated as an aminopeptidase in the NCBI database, our enzymatic characterization proved S9gs to be a carboxypeptidase. Solution-scattering studies showed that S9gs exists as a tetramer in solution, and crystal structure analysis revealed adaptations responsible for the carboxypeptidase activity of S9gs. The findings present a hypothesis for substrate selection, substrate entry, and product exit from the active site, enriching our understanding of this rare carboxypeptidase.

Acarbose Mitigates Age-Dependent Alterations in Erythrocyte Membrane Transporters During Aging in Rats

Acarbose (ACA), a well-studied and effective inhibitor of α-amylase and α-glucosidase, is a postprandial-acting antidiabetic medicine. The membrane of the erythrocyte is an excellent tool for analyzing different physiological and biochemical activities since it experiences a range of metabolic alterations throughout aging. It is uncertain if ACA modulates erythrocyte membrane activities in an age-dependent manner. As a result, the current study was conducted to explore the influence of ACA on age-dependent deteriorated functions of transporters/exchangers, disrupted levels of various biomarkers such as lipid hydroperoxides (LHs), protein carbonyl (PCO), sialic acid (SA), total thiol (-SH), and erythrocyte membrane osmotic fragility. In addition to a concurrent increase in Na+/H+ exchanger activity and concentration of LH, PCO, and osmotic fragility, we also detected a considerable decrease in membrane-linked activities of Ca2+-ATPase (PMCA) and Na+/K+-ATPase (NKA), as well as concentrations of SA and -SH in old-aged rats. The aging-induced impairment of the activities of membrane-bound ATPases and the changed levels of redox biomarkers were shown to be effectively restored by ACA treatment.

A carbapenem antibiotic inhibiting a mammalian serine protease: structure of the acylaminoacyl peptidase-meropenem complex

The structure of porcine AAP (pAAP) in a covalently bound complex with meropenem was determined by cryo-EM to 2.1 Å resolution, showing the mammalian serine-protease inhibited by a carbapenem antibiotic. AAP is a modulator of the ubiquitin-proteasome degradation system and the site of a drug-drug interaction between the widely used antipsychotic, valproate and carbapenems. The active form of pAAP - a toroidal tetramer - binds four meropenem molecules covalently linked to the catalytic Ser587 of the serine-protease triad, in an acyl-enzyme state. AAP is hindered from fully processing the antibiotic by the displacement and protonation of His707 of the catalytic triad. We show that AAP is made susceptible to the association by its unusually sheltered active pockets and flexible catalytic triads, while the carbapenems possess sufficiently small substituents on their β-lactam rings to fit into the shallow substrate-specificity pocket of the enzyme.

Activity-Based Protein Profiling of Human and Plasmodium Serine Hydrolases and Interrogation of Potential Antimalarial Targets

Malaria remains a global health issue requiring the identification of novel therapeutic targets to combat drug resistance. Metabolic serine hydrolases are druggable enzymes playing essential roles in lipid metabolism. However, very few have been investigated in malaria-causing parasites. Here, we used fluorophosphonate broad-spectrum activity-based probes and quantitative chemical proteomics to annotate and profile the activity of more than half of predicted serine hydrolases in P. falciparum across the erythrocytic cycle. Using conditional genetics, we demonstrate that the activities of four serine hydrolases, previously annotated as essential (or important) in genetic screens, are actually dispensable for parasite replication. Of importance, we also identified eight human serine hydrolases that are specifically activated at different developmental stages. Chemical inhibition of two of them blocks parasite replication. This strongly suggests that parasites co-opt the activity of host enzymes and that this opens a new drug development strategy against which the parasites are less likely to develop resistance.

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P. falciparum has 48 predicted metabolic SHs. Many react with the ABP, FP-N₃

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The activity of 25 PfSHs and 8 HsSHs was profiled throughout the asexual life cycle

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Catalytic mutants of 4 PfSHs (formerly held essential) had no parasite growth effect

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Selective inhibitors for 2 HsSHs (APEH and LPLA2) affected parasite growth

Cryo-EM structure of acylpeptide hydrolase reveals substrate selection by multimerization and a multi-state serine-protease triad

The first structure of tetrameric mammalian acylaminoacyl peptidase, an enzyme that functions as an upstream regulator of the proteasome through the removal of terminal N-acetylated residues from its protein substrates, was determined by cryo-EM and further elucidated by MD simulations. Self-association results in a toroid-shaped quaternary structure, guided by an amyloidogenic β-edge and unique inserts. With a Pro introduced into its central β-sheet, sufficient conformational freedom is awarded to the segment containing the catalytic Ser587 that the serine protease catalytic triad alternates between active and latent states. Active site flexibility suggests that the dual function of catalysis and substrate selection are fulfilled by a novel mechanism: substrate entrance is regulated by flexible loops creating a double-gated channel system, while binding of the substrate to the active site is required for stabilization of the catalytic apparatus – as a second filter before hydrolysis. The structure not only underlines that within the family of S9 proteases homo-multimerization acts as a crucial tool for substrate selection, but it will also allow drug design targeting of the ubiquitin-proteasome system.

The structure of tetrameric mammalian acylaminoacyl peptidase – a key upstream regulator of the proteasome – was determined by cryo-EM (and elucidated by MD), showing a “shutters-and-channels” substrate selection apparatus created by oligomerization.

The Role of RBC Oxidative Stress in Sickle Cell Disease: From the Molecular Basis to Pathologic Implications

Sickle cell disease (SCD) is an inherited monogenic disorder and the most common severe hemoglobinopathy in the world. SCD is characterized by a point mutation in the β-globin gene, which results in hemoglobin (Hb) S production, leading to a variety of mechanistic and phenotypic changes within the sickle red blood cell (RBC). In SCD, the sickle RBCs are the root cause of the disease and they are a primary source of oxidative stress since sickle RBC redox state is compromised due to an imbalance between prooxidants and antioxidants. This imbalance in redox state is a result of a continuous production of reactive oxygen species (ROS) within the sickle RBC caused by the constant endogenous Hb autoxidation and NADPH oxidase activation, as well as by a deficiency in the antioxidant defense system. Accumulation of non-neutralized ROS within the sickle RBCs affects RBC membrane structure and function, leading to membrane integrity deficiency, low deformability, phosphatidylserine exposure, and release of micro-vesicles. These oxidative stress-associated RBC phenotypic modifications consequently evoke a myriad of physiological changes involved in multi-system manifestations. Thus, RBC oxidative stress in SCD can ultimately instigate major processes involved in organ damage. The critical role of the sickle RBC ROS production and its regulation in SCD pathophysiology are discussed here.

Acyl Peptide Enzyme Hydrolase (APEH) activity is inhibited by lipid metabolites and peroxidation products

Acyl Peptide Enzyme Hydrolase (APEH) activity is decreased in certain diseases but the mechanism and impact behind this loss in activity is not well understood. We hypothesized that lipid metabolites and lipid peroxidation products produced in inflammatory diseases may bind to and inhibit APEH activity. In vitro studies carried out in mammalian cell lysates, as well as with purified APEH protein, support our hypothesis that cellular lipid metabolites and lipid peroxidation products significantly decrease APEH activity. Enzymatic assays and molecular docking in silico analysis suggest that larger lipid metabolites are the best APEH inhibitors. APEH activity was measured in vivo in mice exposed to chronic e-cigarette vapor, as e-cigarettes are known to increase reactive oxygen species and lipid peroxidation products. In support of our in vitro findings, APEH activity in our mouse model demonstrates decreased APEH activity in the brains of mice exposed to e-cigarette vapor. These results provide a novel mechanism by which APEH activity may be inhibited in disease states. Furthermore, APEH inhibition may contribute to disease development and progression in pathologies associated with redox imbalances and can potentially act as biomarker for oxidative stress in disease.

Metformin protects red blood cells against rotenone induced oxidative stress and cytotoxicity

CONTEXT

The anti-diabetic medicine metformin has been reported as an anti-ageing drug candidate as it mimics the benefits of caloric restriction and reduces ageing-related oxidative stress in various experimental organisms.

OBJECTIVE

We investigated the possible anti-oxidative role of metformin against rotenone-induced oxidative stress and cytotoxicity in erythrocytes of Wistar rats. Rotenone is a well-known inducer of oxidative stress which leads to a cellular redox imbalance.

MATERIALS AND METHODS

We have co-exposed the experimental rats with rotenone (2.5 mg/kg, i.p.) and metformin (300 mg/kg, orally) for 30 days to investigate the protective effects of metformin on various rotenone-induced impaired oxidative stress biomarkers in rat erythrocytes.

RESULTS

We found that a significant alleviation in the levels of rotenone-induced pro-oxidant and anti-oxidant markers following exposure of metformin.

DISCUSSION AND CONCLUSIONS

Our findings suggest that metformin supplementation shows a protective role in against rotenone-induced redox imbalance and cytotoxicity in rat erythrocytes.

Selective inhibition of acylpeptide hydrolase in SAOS-2 osteosarcoma cells: is this enzyme a viable anticancer target?

Serine hydrolases play crucial roles in many physiological and pathophysiological processes and a panel of these enzymes are targets of approved drugs. Despite this, most of the human serine hydrolases remain poorly characterized with respect to their biological functions and substrates and only a limited number of in vivo active inhibitors have been so far identified. Acylpeptide hydrolase (APEH) is a member of the prolyl-oligopeptidase class, with a unique substrate specificity, that has been suggested to have a potential oncogenic role. In this study, a set of peptides was rationally designed from the lead compound SsCEI 4 and in vitro screened for APEH inhibition. Out of these molecules, a dodecapeptide named Ala 3 showed the best inhibitory effects and it was chosen as a candidate for investigating the anti-cancer effects induced by inhibition of APEH in SAOS-2 cell lines. The results clearly demonstrated that Ala 3 markedly reduced cell viability via deregulation of the APEH-proteasome system. Furthermore, flow cytometric analysis revealed that Ala 3 anti-proliferative effects were closely related to the activation of a caspase-dependent apoptotic pathway. Our findings provide further evidence that APEH can play a crucial role in the pathogenesis of cancer, shedding new light on the great potential of this enzyme as an attractive target for the diagnosis and the quest for selective cancer therapies.

Phosphonic Analogs of Alanine as Acylpeptide Hydrolase Inhibitors

Acylpeptide hydrolase is a serine protease, which, together with prolyl oligopeptidase, dipeptidyl peptidase IV and oligopeptidase B, belongs to the prolyl oligopeptidase family. Its primary function is associated with the removal of N-acetylated amino acid residues from proteins and peptides. Although the N-acylation occurs in 50-90 % of eukaryotic proteins, the precise functions of this modification remains unclear. Recent findings have indicated that acylpeptide hydrolase participates in various events including oxidized proteins degradation, amyloid β-peptide cleavage, and response to DNA damage. Considering the protein degradation cycle cross-talk between acylpeptide hydrolase and proteasome, inhibition of the first enzyme resulted in down-regulation of the ubiquitin-proteasome system and induction of cancer cell apoptosis. Acylpeptide hydrolase has been proposed as an interesting target for the development of new potential anticancer agents. Here, we present the synthesis of simple derivatives of (1-aminoethyl)phosphonic acid diaryl esters, phosphonic analogs of alanine diversified at the N-terminus and ester rings, as inhibitors of acylpeptide hydrolase and discuss the ability of the title compounds to induce apoptosis of U937 and MV-4-11 tumor cell lines.

Identification of potential oxidative stress biomarkers for spinal cord injury in erythrocytes using mass spectrometry

Oxidative stress is a hallmark of secondary injury associated with spinal cord injury. Identifying stable and specific oxidative biomarkers is of important significance for studying spinal cord injury-associated secondary injury. Mature erythrocytes do not contain nuclei and mitochondria and cannot be transcribed and translated. Therefore, mature erythrocytes are highly sensitive to oxidative stress and may become a valuable biomarker. In the present study, we revealed the proteome dynamics of protein expression in erythrocytes of beagle dogs in the acute and subacute phases of spinal cord injury using mass spectrometry-based approaches. We found 26 proteins that were differentially expressed in the acute (0-3 days) and subacute (7-21 days) phases of spinal cord injury. Bioinformatics analysis revealed that these differentially expressed proteins were involved in glutathione metabolism, lipid metabolism, and pentose phosphate and other oxidative stress pathways. Western blot assays validated the differential expression of glutathione synthetase, transaldolase, and myeloperoxidase. This result was consistent with mass spectrometry results, suggesting that erythrocytes can be used as a novel sample source of biological markers of oxidative stress in spinal cord injury. Glutathione synthetase, transaldolase, and myeloperoxidase sourced from erythrocytes are potential biomarkers of oxidative stress after spinal cord injury. This study was approved by the Experimental Animal Centre of Ningxia Medical University, China (approval No. 2017-073) on February 13, 2017.

RAS Function in cancer cells: translating membrane biology and biochemistry into new therapeutics

The three human RAS proteins are mutated and constitutively activated in ∼20% of cancers leading to cell growth and proliferation. For the past three decades, many attempts have been made to inhibit these proteins with little success. Recently; however, multiple methods have emerged to inhibit KRAS, the most prevalently mutated isoform. These methods and the underlying biology will be discussed in this review with a special focus on KRAS-plasma membrane interactions.

Reduced neurobehavioral functioning in agricultural workers and rural inhabitants exposed to pesticides in northern Chile and its association with blood biomarkers inhibition

BACKGROUND

Previous biomonitoring studies have shown that people in the rural population of Coquimbo, the major agricultural area in northern Chile are being occupationally and environmentally exposed to organophosphate/carbamate (OP/CB) pesticides. Given their harmful effects, this study had two aims; first, to evaluate the effect of cumulative or chronic exposure to OP/CB pesticides on the neurobehavioral performance of agricultural workers and rural inhabitants; second, to determine if changes in the neurobehavioral performance are associated to changes in blood biomarkers of OP/CB pesticides during the spray season, when exposure is higher.

METHODS

For the first aim, a cross sectional study of neurobehavioral performance in adult volunteers (men and women, 18-50 years-old, right-handed) was carried out in the pre-spray season. Sampling was done by convenience and a questionnaire was used to categorize participants depending on their level of chronic exposure, as either: occupationally exposed (OE, n = 87), environmentally exposed (EE, n = 81), or non-exposed controls or reference group (RG, n = 100). A neurobehavioral test battery consisting of 21 tests to measure cognitive, motor and emotional state was applied. For the second aim, neurobehavioral measures were taken a second time from EE and OE groups during the spray season, and their exposure corroborated by blood-based biomarker inhibition.

RESULTS

Lower neurobehavioral performance was observed in the pre-spray evaluation of EE and OE groups compared to the non-exposed, OE being the worst performing group. Seasonal exposure impaired performance in both exposure groups on all tests except those on attention and mood. Data modeling of the basal (pre-spray) measurements showed that the level of exposure was the best predictor of performance. During spraying, inhibition of BChE activity in the EE group was the best predictor of low performance in tests measuring logical, auditory and visual memory, inhibitory control of cognitive interference, constructional and planning abilities, executive functions, and motor speed and coordination.

CONCLUSION

Long-term occupational or environmental exposure to pesticides caused impairment in neurobehavioral functioning, which worsened during the spraying season, mainly in EE. BChE inhibition was the best predictor for seasonal neurobehavioral changes in EE.

Oxidative Stress and Thrombosis during Aging: The Roles of Oxidative Stress in RBCs in Venous Thrombosis

Mid-life stage adults are at higher risk of developing venous thrombosis (VT)/thromboembolism (VT/E). Aging is characterized by an overproduction of reactive oxygen species (ROS), which could evoke a series of physiological changes involved in thrombosis. Here, we focus on the critical role of ROS within the red blood cell (RBC) in initiating venous thrombosis during aging. Growing evidence has shifted our interest in the role of unjustifiably unvalued RBCs in blood coagulation. RBCs can be a major source of oxidative stress during aging, since RBC redox homeostasis is generally compromised due to the discrepancy between prooxidants and antioxidants. As a result, ROS accumulate within the RBC due to the constant endogenous hemoglobin (Hb) autoxidation and NADPH oxidase activation, and the uptake of extracellular ROS released by other cells in the circulation. The elevated RBC ROS level affects the RBC membrane structure and function, causing loss of membrane integrity, and decreased deformability. These changes impair RBC function in hemostasis and thrombosis, favoring a hypercoagulable state through enhanced RBC aggregation, RBC binding to endothelial cells affecting nitric oxide availability, RBC-induced platelet activation consequently modulating their activity, RBC interaction with and activation of coagulation factors, increased RBC phosphatidylserine exposure and release of microvesicles, accelerated aging and hemolysis. Thus, RBC oxidative stress during aging typifies an ultimate mechanism in system failure, which can affect major processes involved in the development of venous thrombosis in a variety of ways. The reevaluated concept of the critical role of RBC ROS in the activation of thrombotic events during aging will help identify potential targets for novel strategies to prevent/reduce the risk for VT/E or VT/E recurrences in mid-life stage adults.

Acylpeptide hydrolase (APEH) sequence variants with potential impact on the metabolism of the antiepileptic drug valproic acid

Acylpeptide hydrolase (APEH) is a serine protease involved in the recycling of amino acids from acylated peptides. Beyond that, APEH participates in the metabolism of the antiepileptic drug valproic acid (2-propylpentanoic acid; VPA) by catalyzing the hydrolysis of the VPA metabolite valproylglucuronide (VPA-G) to its aglycon. It has been shown that the inhibition of APEH by carbapenem antibiotics decreases therapeutic VPA levels by enhancing the urinary elimination of VPA in form of VPA-G. As various sequence variants of the APEH gene (which encodes the APEH protein) are listed in databases, but have not been functionally characterized yet, we assume, that some APEH sequence variants may have pharmacogenetic relevance due to their impaired cleavage of VPA-G. APEH sequence variants predicted to affect enzyme activity were selected from databases, and overexpressed in HEK293 cells (stable transfection), a cell line derived from human embryonic kidney cells. APEH activity in cell homogenates was determined spectrophotometrically by monitoring the hydrolysis of the synthetic substrate N-acetyl-L-alanine-nitroanilide. APEH enzyme activity and protein expression of the sequence variants were compared with those of APEH with the reference sequence. Three out of five tested missense sequence variants resulted in a considerable decrease of enzyme activity assessed with the standard substrate N-acetyl-L-alanine-nitroanilide, suggesting an effect on pharmacokinetics of VPA. Our work underlines the need to consider the APEH genotype in investigations of altered VPA metabolism.

Achieving Functionality Through Modular Build-up: Structure and Size Selection of Serine Oligopeptidases

Enzymes of the prolyl oligopeptidase family (S9 family) recognize their substrates not only by the specificity motif to be cleaved but also by size - they hydrolyze oligopeptides smaller than 30 amino acids. They belong to the serine-protease family, but differ from classical serine-proteases in size (80 kDa), structure (two domains) and regulation system (size selection of substrates). This group of enzymes is an important target for drug design as they are linked to amnesia, schizophrenia, type 2 diabetes, trypanosomiasis, periodontitis and cell growth. By comparing the structure of various members of the family we show that the most important features contributing to selectivity and efficiency are: (i) whether the interactions weaving the two domains together play a role in stabilizing the catalytic triad and thus their absence may provide for its deactivation: these oligopeptidases can screen their substrates by opening up, and (ii) whether the interaction-prone β-edge of the hydrolase domain is accessible and thus can guide a multimerization process that creates shielded entrance or intricate inner channels for the size-based selection of substrates. These cornerstones can be used to estimate the multimeric state and selection strategy of yet undetermined structures.

Acylpeptide hydrolase is a novel regulator of KRAS plasma membrane localization and function

The primary site for KRAS signaling is the inner leaflet of the plasma membrane (PM). We previously reported that oxanthroquinone G01 (G01) inhibited KRAS PM localization and blocked KRAS signaling. In this study, we identified acylpeptide hydrolase (APEH) as a molecular target of G01. APEH formed a stable complex with biotinylated G01, and the enzymatic activity of APEH was inhibited by G01. APEH knockdown caused profound mislocalization of KRAS and reduced clustering of KRAS that remained PM localized. APEH knockdown also disrupted the PM localization of phosphatidylserine (PtdSer), a lipid critical for KRAS PM binding and clustering. The mislocalization of KRAS was fully rescued by ectopic expression of APEH in knockdown cells. APEH knockdown disrupted the endocytic recycling of epidermal growth factor receptor and transferrin receptor, suggesting that abrogation of recycling endosome function was mechanistically linked to the loss of KRAS and PtdSer from the PM. APEH knockdown abrogated RAS-RAF-MAPK signaling in cells expressing the constitutively active (oncogenic) mutant of KRAS (KRASG12V), and selectively inhibited the proliferation of KRAS-transformed pancreatic cancer cells. Taken together, these results identify APEH as a novel drug target for a potential anti-KRAS therapeutic.

Polymorphism of regulatory region of APEH gene (c.-521G>C, rs4855883) as a relevant predictive factor for radiotherapy induced oral mucositis and overall survival in head neck cancer patients

Background

The study purpose was to examine the correlation between SNP in the regulatory region (c.-521G>C, rs4855883) of APEH gene as well as the incidence and severity of radiotherapy (RTH) induced oral mucositis (OM) and overall survival (OS) in head and neck cancer (HNC) patients.

Methods

OM in 62 HNC patients subjected to irradiation was assessed using RTOG/EORTC scale. DNA was isolated from whole blood of HNC patients. Mini-sequencing method (SNaPshot PCR) was used to determine the genotype.

Results

The following frequency of occurrence of APEH gene was observed: CC: 37.1%, CG: 43.6% and GG: 19.3%. It was established that the presence of CC genotype reduced the risk of occurrence of grade 2 and 3 OM symptoms: 3-fold in RTH week 2 (in case of CC vs GC or GG it was: 26.8% vs 73.2% patients, respectively, OR = 0.27, 95 CI: 0.09–0.83; p = 0.0222), 6-fold in RTH week 3 (in case of CC vs GC or GG it was: 29.4% vs 70.6% patients, respectively, OR = 0.16, 95 CI: 0.04–0.67; p = 0.0125) and grade 3 OM symptoms 4-fold in RTH week 6 (in case of CC vs GC or GG it was: 19.2% vs 80.8% patients, respectively, OR = 0.23, 95 CI: 0.07–0.77; p = 0.0166). CC genotype was associated with lower OS (CC vs GG or GC: 29 months vs 38 months; HR = 2.48, 95% CI: 0.90–6.85; p = 0.0266).

Conclusion

CC genotype of APEH gene was correlated with the risk of more severe radiotherapy-induced OM in HNC patients and lower rates of survival.

Biomonitoring of blood cholinesterases and acylpeptide hydrolase activities in rural inhabitants exposed to pesticides in the Coquimbo Region of Chile

In Chile, agriculture is a relevant economic activity and is concomitant with the use of pesticides to improve the yields. Acute intoxications of agricultural workers occur with some frequency and they must be reported to the surveillance system of the Ministry of Health. However the impacts of chronic and environmental pesticide exposure have been less studied. Among pesticides frequently used in Chile for insects control are organophosphates (OP) and carbamates (CB). They are inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). In this study we determined the pattern of both biomarkers activity in three populations with different type of chronic exposure to OP/CB: environmentally exposed (EE), occupationally exposed (OE) and a reference group (RG) without exposure. Besides this, we also measured the activity of acylpeptide hydrolase (APEH), an enzyme involved in relevant functions in the central synapses that is also expressed in erythrocytes and previously reported to be highly inhibited by some OP. A baseline measurement was done in both exposure groups and then a second measurement was done during the spraying season. The RG was measured only once at any time of the year. Our results indicate that people under chronic OP/CB exposure showed an adaptive response through an increase of basal BChE activity. During the spray season only BChE activity was decreased in the EE and OE groups (p<0.05 and p<0.01, respectively) and the higher magnitude of BChE inhibition was observed in the EE group. The analysis of the frequencies of inhibition above 30% (biological tolerance limit declared by Chilean legislation) indicated that BChE was most frequently inhibited in the EE group (53% of the individuals displayed inhibition) and AChE in the OE group (55% of the individuals displayed AChE inhibition). APEH activity showed the highest frequency of inhibition in the EE group independent of its magnitude (64%). Our results demonstrate that the rural population living nearby agricultural settings displays high levels of environmental exposure. APEH activity seems to be a sensitive biomarker for acute low-level exposure and its usefulness as a routine biomarker must to be explored in future studies. Systematic biomonitoring and health outcomes studies are necessary as well as obtaining the baseline for BChE and AChE activity levels with the aim to improve environmental and occupational health policies in Chile.

Identification of novel prognostic indicators for triple-negative breast cancer patients through integrative analysis of cancer genomics data and protein interactome data

Triple negative breast cancers (TNBCs) are highly heterogeneous and aggressive without targeted treatment. Here, we aim to systematically dissect TNBCs from a prognosis point of view by building a subnetwork atlas for TNBC prognosis through integrating multi-dimensional cancer genomics data from The Cancer Genome Atlas (TCGA) project and the interactome data from three different interaction networks. The subnetworks are represented as the protein-protein interaction modules perturbed by multiple genetic and epigenetic interacting mechanisms contributing to patient survival. Predictive power of these subnetwork-derived prognostic models is evaluated using Monte Carlo cross-validation and the concordance index (C-index). We uncover subnetwork biomarkers of low oncogenic GTPase activity, low ubiquitin/proteasome degradation, effective protection from oxidative damage, and tightly immune response are linked to better prognosis. Such a systematic approach to integrate massive amount of cancer genomics data into clinical practice for TNBC prognosis can effectively dissect the molecular mechanisms underlying TNBC patient outcomes and provide potential opportunities to optimize treatment and develop therapeutics.

In Vivo Sub-chronic Treatment with Dichlorvos in Young Rats Promotes Synaptic Plasticity and Learning by a Mechanism that Involves Acylpeptide Hydrolase Instead of Acetylcholinesterase Inhibition. Correlation with Endogenous β-Amyloid Levels

Acylpeptide hydrolase (APEH) is a serine hydrolase that displays two catalytic activities, acting both as an exopeptidase toward short N-acylated peptides and as an endopeptidase toward oxidized peptides or proteins. It has been demonstrated that this enzyme can degrade monomers, dimers, and trimers of the Aβ_1-40 peptide in the conditioned media of neuroblastoma cells. In a previous report, we showed that the specific inhibition of this enzyme by the organophosphate molecule dichlorvos (DDVP) triggers an enhancement of long-term potentiation in rat hippocampal slices. In this study, we demonstrate that the same effect can be accomplished in vivo by sub-chronic treatment of young rats with a low dose of DDVP (0.1 mg/kg). Besides exhibiting a significant enhancement of LTP, the treated animals also showed improvements in parameters of spatial learning and memory. Interestingly, higher doses of DDVP such as 2 mg/kg did not prove to be beneficial for synaptic plasticity or behavior. Due to the fact that at 2 mg/kg we observed inhibition of both APEH and acetylcholinesterase, we interpret that in order to achieve positive effects on the measured parameters only APEH inhibition should be obtained. The treatment with both DDVP doses produced an increase in the endogenous concentration of Aβ_1-40, although this was statistically significant only at the dose of 0.1 mg/kg. We propose that APEH represents an interesting pharmacological target for cognitive enhancement, acting through the modulation of the endogenous concentration of Aβ_1-40.

Rapamycin alleviates oxidative stress-induced damage in rat erythrocytes

An imbalanced cellular redox system promotes the production of reactive oxygen species (ROS) that may lead to oxidative stress-mediated cell death. Erythrocytes are the best-studied model of antioxidant defense mechanism. The present study was undertaken to investigate the effect of the immunosuppressant drug rapamycin, an inducer of autophagy, on redox balance of erythrocytes and blood plasma of oxidatively challenged rats. Male Wistar rats were oxidatively challenged with HgCl2 (5 mg/kg body mass (b.m.)). A significant (p < 0.05) induction in ROS production, plasma membrane redox system (PMRS), intracellular Ca2+ influx, lipid peroxidation (LPO), osmotic fragility, plasma protein carbonyl (PCO) content, and plasma advanced oxidation protein products (AOPP) and simultaneously significant reduction in glutathione (GSH) level and ferric reducing ability of plasma (FRAP) were observed in rats exposed to HgCl2. Furthermore, rapamycin (0.5 mg/kg b.m.) provided significant protection against HgCl2-induced alterations in rat erythrocytes and plasma by reducing ROS production, PMRS activity, intracellular Ca2+ influx, LPO, osmotic fragility, PCO content, and AOPP and also restored the level of antioxidant GSH and FRAP. Our observations provide evidence that rapamycin improves redox status and attenuates oxidative stress in oxidatively challenged rats. Our data also demonstrate that rapamycin is a comparatively safe immunosuppressant drug.

APEH Inhibition Affects Osteosarcoma Cell Viability via Downregulation of the Proteasome

The proteasome is a multienzymatic complex that controls the half-life of the majority of intracellular proteins, including those involved in apoptosis and cell-cycle progression. Recently, proteasome inhibition has been shown to be an effective anticancer strategy, although its downregulation is often accompanied by severe undesired side effects. We previously reported that the inhibition of acylpeptide hydrolase (APEH) by the peptide SsCEI 4 can significantly affect the proteasome activity in A375 melanoma or Caco-2 adenocarcinoma cell lines, thus shedding new light on therapeutic strategies based on downstream regulation of proteasome functions. In this work, we investigated the functional correlation between APEH and proteasome in a panel of cancer cell lines, and evaluated the cell proliferation upon SsCEI 4-treatments. Results revealed that SsCEI 4 triggered a proliferative arrest specifically in osteosarcoma U2OS cells via downregulation of the APEH–proteasome system, with the accumulation of the typical hallmarks of proteasome: NF-κB, p21^Waf1, and polyubiquitinylated proteins. We found that the SsCEI 4 anti-proliferative effect involved a senescence-like growth arrest without noticeable cytotoxicity. These findings represent an important step toward understanding the mechanism(s) underlying the APEH-mediated downregulation of proteasome in order to design new molecules able to efficiently regulate the proteasome system for alternative therapeutic strategies.

Molecular cloning, expression and characterization of acylpeptide hydrolase in the silkworm, Bombyx mori

Acylpeptide hydrolase (APH) can catalyze the release of the N-terminal amino acid from acetylated peptides. There were many documented examples of this enzyme in various prokaryotic and eukaryotic organisms. However, knowledge about APH in insects still remains unknown. In this study, we cloned and sequenced a putative silkworm Bombyx mori APH (BmAPH) gene. The BmAPH gene encodes a protein of 710 amino acids with a predicted molecular mass of 78.5kDa. The putative BmAPH and mammal APHs share about 36% amino acid sequence identity, yet key catalytic residues are conserved (Ser566, Asp654, and His686). Expression and purification of the recombinant BmAPH in Escherichia coli showed that it has acylpeptide hydrolase activity toward the traditional substrate, Ac-Ala-pNA. Furthermore, organophosphorus (OP) insecticides, chlorpyrifos, phoxim, and malathion, significantly inhibited the activity of the APH both in vitro and in vivo. In addition, BmAPH was expressed in all tested tissues and developmental stages of the silkworm. Finally, immunohistochemistry analysis showed that BmAPH protein was localized in the basement membranes. These results suggested that BmAPH may be involved in enhancing silkworm tolerance to the OP insecticides. In a word, our results provide evidence for understanding of the biological function of APH in insects.

Catalytically distinct states captured in a crystal lattice: the substrate-bound and scavenger states of acylaminoacyl peptidase and their implications for functionality

Acylaminoacyl peptidase (AAP) is an oligopeptidase that only cleaves short peptides or protein segments. In the case of AAP from Aeropyrum pernix (ApAAP), previous studies have led to a model in which the clamshell-like opening and closing of the enzyme provides the means of substrate-size selection. The closed form of the enzyme is catalytically active, while opening deactivates the catalytic triad. The crystallographic results presented here show that the open form of ApAAP is indeed functionally disabled. The obtained crystal structures also reveal that the closed form is penetrable to small ligands: inhibitor added to the pre-formed crystal was able to reach the active site of the rigidified protein, which is only possible through the narrow channel of the propeller domain. Molecular-dynamics simulations investigating the structure of the complexes formed with longer peptide substrates showed that their binding within the large crevice of the closed form of ApAAP leaves the enzyme structure unperturbed; however, their accessing the binding site seems more probable when assisted by opening of the enzyme. Thus, the open form of ApAAP corresponds to a scavenger of possible substrates, the actual cleavage of which only takes place if the enzyme is able to re-close.

Role of αA-crystallin-derived αA66-80 peptide in guinea pig lens crystallin aggregation and insolubilization

Earlier we reported that low molecular weight (LMW) peptides accumulate in aging human lens tissue and that among the LMW peptides, the chaperone inhibitor peptide αA66-80, derived from α-crystallin protein, is one of the predominant peptides. We showed that in vitro αA66-80 induces protein aggregation. The current study was undertaken to determine whether LMW peptides are also present in guinea pig lens tissue subjected to hyperbaric oxygen (HBO) in vivo. The nuclear opacity induced by HBO in guinea pig lens is the closest animal model for studying age-related cataract formation in humans. A LMW peptide profile by mass spectrometry showed the presence of an increased amount of LMW peptides in HBO-treated guinea pig lenses compared to age-matched controls. Interestingly, the mass spectrometric data also showed that the chaperone inhibitor peptide αA66-80 accumulates in HBO-treated guinea pig lens. Following incubation of synthetic chaperone inhibitor peptide αA66-80 with α-crystallin from guinea pig lens extracts, we observed a decreased ability of α-crystallin to inhibit the amorphous aggregation of the target protein alcohol dehydrogenase and the formation of large light scattering aggregates, similar to those we have observed with human α-crystallin and αA66-80 peptide. Further, time-lapse recordings showed that a preformed complex of α-crystallin and αA66-80 attracted additional crystallin molecules to form even larger aggregates. These results demonstrate that LMW peptide-mediated cataract development in aged human lens and in HBO-induced lens opacity in the guinea pig may have common molecular pathways.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of acylpeptide hydrolase from Deinococcus radiodurans

Acylpeptide hydrolase (APH; EC 3.4.19.1), which belongs to the S9 family of serine peptidases (MEROPS), catalyzes the removal of an N-acylated amino acid from a blocked peptide. The role of this enzyme in mammalian cells has been suggested to be in the clearance of oxidatively damaged proteins as well as in the degradation of the β-amyloid peptides implicated in Alzheimer's disease. Detailed structural information for the enzyme has been reported from two thermophilic archaea; both of the archaeal APHs share a similar monomeric structure. However, the mechanisms of substrate selectivity and active-site accessibility are totally different and are determined by inter-domain flexibility or the oligomeric structure. An APH homologue from a bacterium, Deinococcus radiodurans (APHdr), has been crystallized using microbatch-under-oil employing the random microseed matrix screening method. The protein crystallized in space group P21, with unit-cell parameters a = 77.6, b = 189.6, c = 120.4 Å, β = 108.4°. A Matthews coefficient of 2.89 Å(3) Da(-1) corresponds to four monomers, each with a molecular mass of ∼73 kDa, in the asymmetric unit. The APHdr structure will reveal the mechanisms of substrate selectivity and active-site accessibility in the bacterial enzyme. It will also be helpful in elucidating the functional role of this enzyme in D. radiodurans.

Cigarette smoking and hyperglycemia increase renal response to low levels of cadmium in welders: cystatin C as a sensitive marker

The present study was undertaken to investigate the utility of cystatin C (CysC) as an early biomarker of cadmium (Cd)-induced renal injury. The study was carried out on 50 adult male individuals divided into five groups of 10 individuals as follows: control, welders, smoker welders, diabetic welders, and smoker diabetic welders. The results indicated that plasma levels of CysC, creatinine, urea, and uric acid were significantly higher in welders compared to control individuals. In addition, the levels of whole blood Cd, lipid peroxidation, and protein oxidation products as well as erythrocyte osmotic fragility were significantly higher in welders compared to control individuals. In contrast, the levels of plasma albumin and whole blood glutathione were significantly decreased in welders compared to control individuals. The alterations of the measured parameters were enhanced in the presence of smoking and hyperglycemia besides exposure to welding fumes. These results suggest that CysC can be used as a sensitive biomarker of the early stages of Cd-induced renal injury.

Protein adducts as biomarkers of exposure to organophosphorus compounds

Exposure to organophosphorus (OP) compounds can lead to serious neurological damage or death. Following bioactivation by the liver cytochromes P450, the OP metabolites produced are potent inhibitors of serine active-site enzymes including esterases, proteases and lipases. OPs may form adducts on other cellular proteins. Blood cholinesterases (ChEs) have long served as biomarkers of OP exposure in humans. However, the enzymatic assays used for biomonitoring OP exposures have several drawbacks. A more useful approach will focus on multiple biomarkers and avoid problems with the enzymatic activity assays. OP inhibitory effects result from a covalent bond with the active-site serine of the target enzymes. The serine OP adducts become irreversible following a process referred to as aging where one alkyl group dissociates over variable lengths of time depending on the OP adduct. The OP-adducted enzyme then remains in circulation until it is degraded, allowing for a longer window of detection compared with direct analysis of OPs or their metabolites. Mass spectrometry (MS) provides a very sensitive method for identification of post-translational protein modifications. MS analyses of the percentage adduction of the active-site serine of biomarker proteins such as ChEs will eliminate the need for basal activity levels of the individual and will provide for a more accurate determination of OP exposure. MS analysis of biomarker proteins also provides information about the OP that has caused inhibition. Other useful biomarker proteins include other serine hydrolases, albumin, tubulin and transferrin.

Role of acylamino acid-releasing enzyme/oxidized protein hydrolase in sustaining homeostasis of the cytoplasmic antioxidative system

Acylamino acid-releasing enzyme/oxidized protein hydrolase (AARE/OPH) has been biochemically demonstrated to be a bifunctional protease that has exopeptidase activity against Nα-acylated peptides and endopeptidase activity against oxidized and glycated proteins; however, its physiological role remains unknown. In this study, to determine its physiological significance, we produced AARE/OPH-overexpressing and -suppressed plants and assessed the biological impacts of AARE/OPH. The subcellular localization of Arabidopsis AARE/OPH was found to be cytoplasmic and nuclear by transient expression analysis of tdTomato-fused Arabidopsis AARE/OPH. Overexpression of AARE/OPH exhibited no apparent effect on the level of oxidized proteins because wild types probably have inherently high AARE/OPH activity. Through RNAi gene suppressing, we successfully produced AARE/OPH-suppressed Arabidopsis plants (aare) that exhibited almost no AARE activity. In the aare plant, electrolyte leakage by methyl viologen treatment was enhanced compared to that of non-transformant plants, suggesting that the plasma membranes of aare easily suffered oxidative damage, probably as a result of deterioration of the cytoplasmic antioxidative system. Correspondingly, proteomic analysis revealed that the aare plant accumulated a number of oxidized proteins including cytoplasmic antioxidant enzymes. On the basis of these results, we concluded that AARE/OPH plays a homeostatic role in sustaining the cytoplasmic antioxidative system.

Identification and characterisation of a novel acylpeptide hydrolase from Sulfolobus solfataricus: structural and functional insights

A novel acylpeptide hydrolase, named APEH-3_Ss, was isolated from the hypertermophilic archaeon Sulfolobus solfataricus. APEH is a member of the prolyl oligopeptidase family which catalyzes the removal of acetylated amino acid residues from the N terminus of oligopeptides. The purified enzyme shows a homotrimeric structure, unique among the associate partners of the APEH cluster and, in contrast to the archaeal APEHs which show both exo/endo peptidase activities, it appears to be a “true” aminopeptidase as exemplified by its mammalian counterparts, with which it shares a similar substrate specificity. Furthermore, a comparative study on the regulation of apeh gene expression, revealed a significant but divergent alteration in the expression pattern of apeh-3_Ss and apeh_Ss (the gene encoding the previously identified APEH_Ss from S. solfataricus), which is induced in response to various stressful growth conditions. Hence, both APEH enzymes can be defined as stress-regulated proteins which play a complementary role in enabling the survival of S. solfataricus cells under different conditions. These results provide new structural and functional insights into S. solfataricus APEH, offering a possible explanation for the multiplicity of this enzyme in Archaea.

Synaptic localization of acylpeptide hydrolase in adult rat telencephalon

Acylpeptide hydrolase (ACPH), a serine protease present in the central nervous system (CNS), is believed to have a function in modulating synaptic plasticity, cleavage of beta amyloid peptide and degradation of aggregated oxidized proteins. In this report, we demonstrate for the first time the presence of ACPH in the synapse and its preferential localization at the pre-synaptic side. We isolated subcellular fractions from the rat telencephalon enriched in pre- versus post-synaptic components by using differential centrifugation steps to evaluate ACPH catalytic activity and expression level. Relative ACPH levels were determined by Western blot techniques while antibodies against synaptophysin and PSD-95 were used as positive pre- and post-synaptic markers, respectively. Our results show that ACPH protein levels are significantly increased at the synapse, which correlates with a 56% increase in ACPH activity. Furthermore, Western blot experiments show that ACPH is preferentially located at the pre-synaptic side and this is consistent with the increase of its enzymatic activity in fractions enriched in pre-synaptic components. These results give new insights regarding the localization and a putative role of ACPH in the CNS.

Identification and characterization of biomarkers of organophosphorus exposures in humans

Over 1 billion pounds of organophosphorus (OP) chemicals are manufactured worldwide each year, including 70 million pounds of pesticides sprayed in the US. Current methods to monitor environmental and occupational exposures to OPs such as chlorpyrifos (CPS) have limitations, including low specificity and sensitivity, and short time windows for detection. Biomarkers for the OP tricresyl phosphate (TCP), which can contaminate bleed air from jet engines and cause an occupational exposure of commercial airline pilots, crewmembers and passengers, have not been identified. The aim of our work has been to identify, purify, and characterize new biomarkers of OP exposure. Butyrylcholinesterase (BChE) inhibition has been a standard for monitoring OP exposure. By identifying and characterizing molecular biomarkers with longer half-lives, we should be able to clinically detect TCP and OP insecticide exposure after longer durations of time than are currently possible. Acylpeptide hydrolase (APH) is a red blood cell (RBC) cytosolic serine proteinase that removes N-acetylated amino acids from peptides and cleaves oxidized proteins. Due to its properties, it is an excellent candidate for a biomarker of exposure. We have been able to purify APH and detect inhibition by both CPS and metabolites of TCP. The 120-day lifetime of the RBC offers a much longer window for detecting exposure. The OP-modified serine conjugate in the active site tryptic peptide has been characterized by mass spectrometry. This research uses functional proteomics and enzyme activities to identify and characterize useful biomarkers of neurotoxic environmental and occupational OP exposures.

Acyl peptide hydrolase degrades monomeric and oligomeric amyloid-beta peptide

Background

The abnormal accumulation of amyloid-beta peptide is believed to cause malfunctioning of neurons in the Alzheimer's disease brain. Amyloid-beta exists in different assembly forms in the aging mammalian brain including monomers, oligomers, and aggregates, and in senile plaques, fibrils. Recent findings suggest that soluble amyloid-beta oligomers may represent the primary pathological species in Alzheimer's disease and the most toxic form that impairs synaptic and thus neuronal function. We previously reported the isolation of a novel amyloid-beta-degrading enzyme, acyl peptide hydrolase, a serine protease that degrades amyloid-beta, and is different in structure and activity from other amyloid-beta-degrading enzymes.

Results

Here we report the further characterization of acyl peptide hydrolase activity using mass spectrometry. Acyl peptide hydrolase cleaves the amyloid-beta peptide at amino acids 13, 14 and 19. In addition, by real-time PCR we found elevated acyl peptide hydrolase expression in brain areas rich in amyloid plaques suggesting that this enzyme's levels are responsive to increases in amyloid-beta levels. Lastly, tissue culture experiments using transfected CHO cells expressing APP751 bearing the V717F mutation indicate that acyl peptide hydrolase preferentially degrades dimeric and trimeric forms of amyloid-beta.

Conclusion

These data suggest that acyl peptide hydrolase is involved in the degradation of oligomeric amyloid-beta, an activity that, if induced, might present a new tool for therapy aimed at reducing neurodegeneration in the Alzheimer's brain.

Peroxyl-oxidized Erythrocyte Membrane Band 3 Protein with Anion Transport Capacity is Degraded by Membrane-bound Proteinase

Human red blood cells anion exchange protein (band 3) exposed to peroxyl radicals produced by thermolysis of 2,2'-azo-bis(2-amidinopropane) (AAPH) is degraded by proteinases that prevent accumulation of oxidatively damaged proteins. To assess whether this degradation affects anion transport capacity we used the anionic fluorescent probe 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-y) amino] ethanosulfonate (NBD-taurine). A decrease of band 3 function was observed after exposure to peroxyl radicals. In the presence of proteinase inhibitors the decrement of anion transport through band 3 was smaller indicating that removal achieved by proteinases includes oxidized band 3 which still retain transport ability. Proteinases recognize band 3 aggregates produced by peroxyl radicals as was evaluated by immunoblotting. It is concluded that decrease of band 3 transport capacity may result from a direct protein oxidation and from its degradation by proteinases and that band 3 aggregates removal may prevent macrophage recognition of the senescent condition which would lead to cell disposal.

In vitro models of oxidative stress in rat erythrocytes: Effect of antioxidant supplements

The present study was designed to induce oxidative stress in lipid and aqueous phases through azo bis(2-amidinopropane)dihydrochloride (AAPH), 2,2'-azobis 2,4-dimethylvaleronitrile (ADVN) and hydrogen peroxide (H(2)O(2)) either alone or in combination with vitamin C or vitamin El and to assess the vulnerability of rat erythrocytes to oxidative stress. While AAPH acted equally on cell membrane and cytosol, ADVN increased OS in the membrane. The extent of hemolysis and increased membrane fragility caused was more in the case of azo compounds than of H(2)O(2). While vitamin E (2mM) reduced oxidative stress in the membrane, vitamin C (60mM) was more effective in the lysates. The concentration of malondialdehyde and advanced oxidation protein products was lowered by antioxidants. The level of lipofuscin, a product of lipid peroxidation was also increased by ADVN and H(2)O(2). Antioxidants, did, however, reduce the accumulation of protein carbonyl content in cells exposed to azo compounds although they were ineffective in inhibiting oxidation of membrane band 3 protein and sulphydryl content. Taken together, our study demonstrated the antioxidative property of vitamin E and vitamin C in reducing oxidative stress in aqueous as well as lipid phases of erythrocytes and further suggested the feasibility of in vitro models in evaluating the mechanisms of oxidative injury.

Acyl peptide hydrolase, a serine proteinase isolated from conditioned medium of neuroblastoma cells, degrades the amyloid-? peptide

Considerable evidence indicates that the amyloid-beta (Abeta) peptide, a proteolytic fragment of the amyloid precursor protein, is the pathogenic agent in Alzheimer's disease (AD). A number of proteases have been reported as capable of degrading Abeta, among them: neprilysin, insulin-degrading enzyme, endothelin-converting enzyme-1 and -2, angiotensin-converting enzyme and plasmin. These proteases, originating from a variety of cell types, degrade Abeta of various conformational states and in different cellular locations. We report here the isolation of a serine protease from serum-free conditioned medium of human neuroblastoma cells. Tandem mass spectrometry (MS/MS)-based sequencing of the isolated protein identified acyl peptide hydrolase (APH; EC3.4.19.1) as the active peptidase. APH is one of four members of the prolyl oligopeptidase family of serine proteases expressed in a variety of cells and tissues, including erythrocytes, liver and brain, but its precise biological activity is unknown. Here, we describe the identification of APH as an Abeta-degrading enzyme, and we show that the degradation of Abeta by APH isolated from transfected cells is inhibited by APH-specific inhibitors, as well as by synthetic Abeta peptide. In addition, we cloned APH from human brain and from neuroblastoma cells. Most importantly, our results indicate that APH expression in AD brain is lower than in age-matched controls.

Blood acylpeptide hydrolase activity is a sensitive marker for exposure to some organophosphate toxicants

Acylpeptide hydrolase (APH) unblocks N-acetyl peptides. It is a major serine hydrolase in rat blood, brain, and liver detected by derivatization with (3)H-diisopropyl fluorophosphate (DFP) or a biotinylated fluorophosphonate. Although APH does not appear to be a primary target of acute poisoning by organophosphorus (OP) compounds, the inhibitor specificity of this secondary target is largely unknown. This study fills the gap and emphasizes blood APH as a potential marker of OP exposure. The most potent in vitro inhibitors for human erythrocyte and mouse brain APH are DFP (IC(50) 11-17 nM), chlorpyrifos oxon (IC(50) 21-71 nM), dichlorvos (IC(50) 230-560 nM), naled (IC(50) 370-870 nM), and their analogs with modified alkyl substituents. (3)H-diisopropyl fluorophosphate is a potent inhibitor of mouse blood and brain APH in vivo (ED(50) 0.09-0.2 mg/kg and 0.02-0.03 mg/l for ip and vapor exposure, respectively). Mouse blood and brain APH and blood butyrylcholinesterase (BChE) are of similar sensitivity to DFP in vitro and in vivo (ip and vapor exposure), but APH inhibition is much more persistent in vivo (still >80% inhibition after 4 days). The inhibitory potency of OP pesticides in vivo in mice varies from APH selective (dichlorvos, naled, and trichlorfon), to APH and BChE selective (profenofos and tribufos), to ChE selective or nonselective (many commercial insecticides). Sarin administered ip at a lethal dose to guinea pigs inhibits blood acetylcholinesterase and BChE completely but erythrocyte APH only partially. Blood APH activity is therefore a sensitive marker for exposure to some but not all OP pesticides and chemical warfare agents.