A novel anti-inflammatory oligopeptide produced by Entamoeba histolytica

Bioactive peptides and proteins for tissue repair: microenvironment modulation, rational delivery, and clinical potential

Bioactive peptides and proteins (BAPPs) are promising therapeutic agents for tissue repair with considerable advantages, including multifunctionality, specificity, biocompatibility, and biodegradability. However, the high complexity of tissue microenvironments and their inherent deficiencies such as short half-live and susceptibility to enzymatic degradation, adversely affect their therapeutic efficacy and clinical applications. Investigating the fundamental mechanisms by which BAPPs modulate the microenvironment and developing rational delivery strategies are essential for optimizing their administration in distinct tissue repairs and facilitating clinical translation. This review initially focuses on the mechanisms through which BAPPs influence the microenvironment for tissue repair via reactive oxygen species, blood and lymphatic vessels, immune cells, and repair cells. Then, a variety of delivery platforms, including scaffolds and hydrogels, electrospun fibers, surface coatings, assisted particles, nanotubes, two-dimensional nanomaterials, and nanoparticles engineered cells, are summarized to incorporate BAPPs for effective tissue repair, modification strategies aimed at enhancing loading efficiencies and release kinetics are also reviewed. Additionally, the delivery of BAPPs can be precisely regulated by endogenous stimuli (glucose, reactive oxygen species, enzymes, pH) or exogenous stimuli (ultrasound, heat, light, magnetic field, and electric field) to achieve on-demand release tailored for specific tissue repair needs. Furthermore, this review focuses on the clinical potential of BAPPs in facilitating tissue repair across various types, including bone, cartilage, intervertebral discs, muscle, tendons, periodontal tissues, skin, myocardium, nervous system (encompassing brain, spinal cord, and peripheral nerve), endometrium, as well as ear and ocular tissue. Finally, current challenges and prospects are discussed.

Anti-Inflammatory Dipeptide, a Metabolite from Ambioba Secretion, Protects Cerebral Ischemia Injury by Blocking Apoptosis Via p-JNK/Bax Pathway

MQ (l-methionyl-l-glutamic acid), anti-inflammatory dipeptide, is one of the metabolites of monocyte locomotion inhibitory factor, a thermostable pentapeptide secreted by Entamoeba histolytica. Monocyte locomotion inhibitory factor injection has been approved as an investigational drug for the potential neural protection in acute ischemic stroke. This study further investigated the neuroprotective effect of MQ in ischemic brain damage. Ischemia-reperfusion injury of the brain was induced in the rat model by middle cerebral artery occlusion. 2,3,5-triphenyltetrazolium chloride staining assay was used to measure cerebral infarction areas in rats. Laser Doppler measurement instrument was used to detect blood flow changes in the rat model. Nissl staining and NeuN staining were utilized to observe the numbers and structures of neuron cells, and the pathological changes in the brain tissues were examined by hematoxylin–eosin staining. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) staining was used to assess cell apoptosis. The changes in oxidative stress indexes, superoxide dismutase and malondialdehyde (MDA), were measured in serum. Methyl thiazolyl tetrazolium was used to measure the survival rates of PC12 cells. Flow cytometry assessed the apoptosis rates and the levels of reactive oxygen species. Real-time PCR was used to evaluate the mRNA expression levels, and Western blotting was used to analyze the changes in protein levels of p-JNK, Bax, cleaved Caspase3. We revealed that MQ improved neurobehavior, decreased cerebral infarction areas, altered blood flow volume, and the morphology of the cortex and hippocampus. On the other hand, it decreased the apoptosis of cortical neurons and the levels of MDA, and increased the levels of superoxide dismutase. In vitro studies demonstrated that MQ enhanced the cell survival rates and decreased the levels of reactive oxygen species. Compared to the oxygen-glucose deprivation/reperfusion group, the protein and mRNA expressions of p-JNK, Bax, cleaved Caspase3 was decreased significantly. These findings suggested that MQ exerts a neuroprotective effect in cerebral ischemia by blocking apoptosis via the p-JNK/Bax pathway.

Monocyte Locomotion Inhibitory Factor confers neuroprotection and prevents the development of murine cerebral malaria

Cerebral malaria (CM) is a neurological complication derived from the Plasmodium falciparum infection in humans. The mechanisms involved in the disease progression are still not fully understood, but both the sequestration of infected red blood cells (iRBC) and leukocytes and an exacerbated host inflammatory immune response are significant factors. In this study, we investigated the effect of Monocyte Locomotion Inhibitory Factor (MLIF), an anti-inflammatory peptide, in a well-characterized murine model of CM. Our data showed that the administration of MLIF increased the survival and avoided the neurological signs of CM in Plasmodium berghei ANKA (PbA) infected C57BL/6 mice. MLIF administration down-regulated systemic inflammatory mediators such as IFN-γ, TNF-α, IL-6, CXCL2, and CCL2, as well as the in situ expression of TNF-α in the brain. In the same way, MLIF reduced the expression of CD31, CD36, CD54, and CD106 in the cerebral endothelium of infected animals and prevented the sequestration of iRBC and leucocytes in the brain microvasculature. Furthermore, MLIF inhibited the activation of astrocytes and microglia and preserved the integrity of the blood-brain barrier (BBB). In conclusion, our results demonstrated that the administration of MLIF increased survival and conferred neuroprotection by decreasing neuroinflammation in murine CM.

A validated UPLC-MS/MS method for the quantitation of an unstable peptide, monocyte locomotion inhibitory factor (MLIF) in human plasma and its application to a pharmacokinetic study

Monocyte locomotion inhibitory factor (MLIF, Met-Gln-Cys-Asn-Ser), a pentapeptide with anti-inflammatory activity, was developed for neural protection in acute ischemic stroke. Determination of MLIF in human plasma samples is of great importance for pharmacokinetic evaluation in clinical studies. A reliable and sensitive method based on ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) was established for the measurement of MLIF in human plasma. Instability of peptide in matrix was the primary challenge in method development, which was properly resolved by addition of acidification reagents like sulfuric acid. Samples were prepared by protein precipitation and then analyzed using a gradient chromatographic separation over an ACQUITY UPLC HSS T₃ column. The mobile phase consisted of acetonitrile containing 0.2% formic acid and water containing 0.2% formic acid and gradient elution was performed at a flow rate of 0.4 mL/min. Detection was carried out on a Xevo TQ-S tandem mass spectrometer and positive electrospray ionization was employed in the multiple reaction monitoring (MRM) mode. This method was fully validated over the concentration range of 0.5-40 ng/mL with a lower limit of quantification (LLOQ) of 0.5 ng/mL. The inter- and intra-batch precision was no more than 8.8% and the accuracy was between 88.7 and 104.2%. The mean extraction recovery was 43.3% and the detection was independent of matrix. Besides, the analyte proved to be stable under various handling processes and storage conditions after acidification. Finally, the method was applied to the first-in-human (FIH) study of MLIF in Chinese healthy subjects.

New monocyte locomotion inhibitory factor analogs protect against cerebral ischemia-reperfusion injury in rats

Monocyte locomotion inhibitory factor (MLIF) is an oligopeptide with anti-inflammatory properties. The carboxyl-terminal end group Cys-Asn-Ser serves as the pharmacophore of MLIF. The aim of this study was to investigate the neuroprotective effects of two new synthetic analogs, Arg-Cys-Asn-Ser and D-Cys-Asn-Ser, on focal cerebral ischemia, which were designed and synthesized to increase the penetrability and enzymatic stability of Cys-Asn-Ser. Ninety-one male Sprague-Dawley rats were randomly divided into six groups: I - Sham; II - Ischemia-reperfusion (I/R); III - Nimodipine; IV - Cys-Asn-Ser; V - D-Cys-Asn-Ser; and VI - Arg-Cys-Asn-Ser. The rats in groups II-VI were subjected to middle cerebral artery occlusion. After 24 hours of reperfusion, the neurological deficit, cerebral infarct volume, and levels of the pro-inflammatory factors interleukin-1β (IL-1β) and tumor necrosis factor-alpha in brain tissue homogenates were assessed. Compared with the sham group, the mean neurological deficit scores were significantly higher in groups II-VI (p ≤ 0.019 for all). The mean infarct volumes were significantly higher in I/R and Cys-Asn-Ser groups compared with the sham group (both p ≤ 0.046). The mean IL-1β level was significantly lower in D-Cys-Asn-Ser and Arg-Cys-Asn-Ser groups compared with I/R group (both p ≤ 0.046). In conclusion, the results showed that Arg-Cys-Asn-Ser and D-Cys-Asn-Ser have the potential for protective effects against focal cerebral ischemia injury.

Protective effects of MLIF analogs on cerebral ischemia-reperfusion injury in rats

The monocyte locomotion inhibitory factor (MLIF) is an anti-inflammatory oligopeptide produced by Entamoeba histolytica. Among its different effects, it inhibits locomotion of human monocytes, hence its original name. The carboxyl-terminal end group Cys-Asn-Ser is the pharmacophore of anti-inflammatory peptide Met-Gln-Cys-Asn-Ser. In this study, the N-terminal of Cys-Asn-Ser was modified. With the aim to enhance the antioxidant ability and penetrability of Cys-Asn-Ser, we designed and synthesized two tetrapeptides Tyr-Cys-Asn-Ser and His-Cys-Asn-Ser. The neuroprotective effects of Tyr-Cys-Asn-Ser and His-Cys-Asn-Ser on focal ischemia reperfusion were investigated, and their pharmacological activities compared with Cys-Asn-Ser were studied. In order to study the mechanism of neuroprotective effect of these peptides, the level of oxidative stress markers malondialdehyde (MDA) and superoxide dismutase (SOD) and pro-inflammatory factors interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and myeloperoxidase (MPO) were detected in brain tissue homogenate.

Anti-inflammatory defense mechanisms of Entamoeba histolytica

The monocyte locomotion inhibitory factor (MLIF), a heat-stable oligopeptide found in the supernatant fluid of Entamoeba histolytica axenic cultures, may contribute to the delayed inflammation observed in amoebic hepatic abscess. This factor was isolated by ultra-filtration and high powered liquid chromatography, obtaining a primary Met-Gln-Cys-Asn-Ser structure, identified afterwards as the carboxyl-terminal (…Cys-Asn-Ser) active site. The selective anti-inflammatory effects of the pentapeptide have been observed in both in vitro and in vivo models, using a synthetic pentapeptide to maintain the same anti-inflammatory conditions during the experimental assays. Anti-inflammatory effects observed include inhibition of human monocyte locomotion and the respiratory burst in monocytes and neutrophils, increasing expression of anti-inflammatory cytokines and inhibiting expression of the adhesion molecules VLA-4 and VCAM, among others. In this review, we will describe the effects of MLIF detected so far and how it might be used as a therapeutical agent against inflammatory diseases.

The role of lipopeptidophosphoglycan in the immune response to Entamoeba histolytica

The sensing of Pathogen Associated Molecular Patterns (PAMPs) by innate immune receptors, such as Toll-like receptors (TLRs), is the first step in the inflammatory response to pathogens. Entamoeba histolytica, the etiological agent of amebiasis, has a surface molecule with the characteristics of a PAMP. This molecule, which was termed lipopeptidophosphoglycan (LPPG), is recognized through TLR2 and TLR4 and leads to the release of cytokines from human monocytes, macrophages, and dendritic cells; LPPG-activated dendritic cells have increased expression of costimulatory molecules. LPPG activates NKT cells in a CD1d-dependent manner, and this interaction limits amebic liver abscess development. LPPG also induces antibody production, and anti-LPPG antibodies prevent disease development in animal models of amebiasis. Because LPPG is recognized by both the innate and the adaptive immune system (it is a “Pamptigen”), it may be a good candidate to develop a vaccine against E. histolytica infection and an effective adjuvant.

Recent discoveries in the pathogenesis and immune response toward Entamoeba histolytica

Entamoeba histolytica is an enteric dwelling human protozoan parasite that causes the disease amoebiasis, which is endemic in the developing world. Over the past four decades, considerable effort has been made to understand the parasite and the disease. Improved diagnostics can now differentiate pathogenic E. histolytica from that of the related but nonpathogenic Entamoeba dispar, thus minimizing screening errors. Classically, the triad of Gal-lectin, cysteine proteinases and amoebapores of the parasite were thought to be the major proteins involved in the pathogenesis of amoebiasis. However, other amoebic molecules such as lipophosphopeptidoglycan, perioxiredoxin, arginase, and lysine and glutamic acid-rich proteins are also implicated. Recently, the genome of E. histolytica has been sequenced, which has widened our scope to study additional virulence factors. E. histolytica genome-based approaches have now confirmed the presence of Golgi apparatus-like vesicles and the machinery for glycosylation, thus improving the chances of identifying potential drug targets for chemotherapeutic intervention. Apart from Gal-lectin-based vaccines, promising vaccine targets such as serine-rich E. histolytica protein have yielded encouraging results. Considerable efforts have also been made to skew vaccination responses towards appropriate T-helper cell immunity that could augment the efficacy of vaccine candidates under study. Thus, ongoing efforts mining the information made available with the sequencing of the E. histolytica genome will no doubt identify and characterize other important potential vaccine/drug targets and lead to effective immunologic strategies for the control of amoebiasis.

Downregulation of Selected Cytokines in Amebiasis

A 220-kDa E. histolytica lectin is capable of downregulating some inflammatory cytokines (IL-5, IL-6, INF-gamma and TNF-alpha) and thus of inducing an overall anti-inflammatory Th-phenotype in leucocytes of selected, perhaps constitutionally predisposed, individuals irrespective of their HLA-DR3 profile (i.e., in this study patients long recovered from amebic abscess of the liver). This probably inhibited cytokine response pattern could increase the risk for developing amebic abscess of the liver in the course of invasive intestinal amebiasis.

Could the homologous sequence of anti-inflammatory pentapeptide (MLIF) produced by Entamoeba histolytica in the N protein of rabies virus affect the inflammatory process?

Amebiasis and rabies are public health problems, and they have in common a poor inflammatory effect in the target organs that they affect. In the GenBank, it was found that the anti-inflammatory peptide monocyte locomotion inhibitory factor (MLIF) produced by Entamoeba histolytica homologates 80%, with a fragment of the N protein of the rabies virus. We speculated if the N protein could contribute to the scant inflammatory reaction produced by rabies virus in central nervous system. The N protein was obtained and studied in vitro and in vivo. The N protein, as MLIF, inhibited the respiratory burst in human mononuclear phagocytes (43%, p<0.05), but in contrast to MLIF, it increased chemotaxis and it did not significantly inhibit delayed hypersensitivity skin reaction to 1-chloro-2-4-dinitrobenzene in guinea pigs. Therefore, the full peptide sequence has to be present or it has to be cleaved-free from the large recombinant N protein molecule (55 kDa) to become active.

Genomic and proteomic approaches highlight phagocytosis of living and apoptotic human cells by the parasite Entamoeba histolytica

Phagocytosis plays a major role during the invasive process of the human intestine by the pathogenic amoeba E. histolytica. This parasite is the etiologic agent causing amoebic dysentery, a worldwide disease causing 50 million of clinical cases leading to about 100,000 deaths annually. The invasive process is characterized by a local acute inflammation and the destruction of the intestinal tissue at the invasion site. The recent sequencing of the E. histolytica genome has opened the way to large-scale approaches to study parasite virulence such as processes involved in human cell phagocytosis. In particular, two different studies have recently described the phagosome proteome, providing new insights into the process of phagocytosis by this pathogenic protozoan. It has been previously described that E. histolytica induces apoptosis and phagocytosis of the human target cells. Induction of apoptosis by the trophozoites is thought to be involved in the close regulation of the inflammatory response occurring during infection. Little is known about the molecular mechanisms responsible for induction of apoptosis or in the recognition of apoptotic cells by E. histolytica. In this review, we comment on the recent data we obtained after isolation of the early phagosomes and the identification of its associated proteins. We focus on the surface molecules potentially involved in human cell recognition. In particular, we propose several parasite molecules, potentially involved in the induction of apoptosis and/or the phagocytosis of human apoptotic cells.

A novel protease from Entamoeba histolytica homologous to members of the family S28 of serine proteases

Serine proteases are one of the biologically most important and widely distributed enzyme families. A protease capable of degrading the substrate Suc-AAF-AMC was isolated from axenically grown trophozoites of Entamoeba histolytica. The enzyme was purified by ion-exchange chromatography and electroelution, and appeared on 2D-PAGE as a spot of 60 kDa and pI of 4.65. Data obtained from zymogram suggest the active protease is present either as homodimer (130 kDa) or homotetramer (250 kDa). The optimal temperature of the enzyme was 37 degrees C, and it exhibited activity over a broad pH range. The protease was strongly inhibited by TPCK and chelating agents. The enzymatic activity was restored upon addition of calcium. BLAST analysis with the sequence of internal peptides of the protein revealed two open reading frames within the genome of E. histolytica, homologous to members of the family S28, clan SC of serine proteases.

Immunization with a tetramer derivative of an anti-inflammatory pentapeptide produced by Entamoeba histolytica protects gerbils (Meriones unguiculatus) against experimental amoebic abscess of the liver

Axenically grown Entamoeba histolytica produces a pentapeptide (Met-Gln-Cys-Asn-Ser) with several anti-inflammatory properties, including the inhibition of human monocyte locomotion (Monocyte Locomotion Inhibitory Factor (MLIF)). A construct displays the same effects as the native material. It remains to be seen if MLIF is used, or even produced in vivo by the tissue-invading parasite. If MLIF were to be relevant in invasive amoebiasis, immunizing against it could diminish this parasite advantage and prevent lesions. KLH-linked MLIF mixed with Freund's adjuvant was too aggressive an immunizing material to answer this question. However, immunization with a tetramer of MLIF (but not a scrambled version of MLIF) around a lysine core (MLIF-MAPS), that displays increased antigenicity, yet lacks excessive innate immunity activation, completely protects gerbils against amoebic abscess of the liver caused by the intraportal injection of virulent E. histolytica. Liver abscesses caused by Listeria monocytogenes were not prevented. Invasive E. histolytica may produce the parent protein of MLIF in vivo, and if appropriately cleaved, it may play a role in invasive amoebiasis. MLIF may join new vaccination strategies against amoebiasis.

An anti-inflammatory oligopeptide produced by Entamoeba histolytica down-regulates the expression of pro-inflammatory chemokines

Axenically grown Entamoeba histolytica produces a pentapeptide (Met-Gln-Cys-Asn-Ser) with anti-inflammatory properties that, among others, inhibits the in vitro and in vivo locomotion of human monocytes, sparing polymorphonuclear leucocytes from this effect [hence the name originally given. Monocyte Locomotion Inhibitory Factor (MLIF)]. A synthetic construct of this peptide displays the same effects as the native material. We now added MLIF to resting and PMA-stimulated cells of a human monocyte cell line and measured the effect upon mRNA and protein expression of pro-inflammatory chemokines (RANTES, IP-10, MIP-1alpha, MIP-1beta, MCP-1, IL-8, I-309 and lymphotactin) and the shared CC receptor repertoire. The constitutive expression of these chemokines and the CC receptors was unaffected, whereas induced expression of MIP-1alpha, MIP-1beta, and I-309, and that of the CCR1 receptor--all involved in monocyte chemotaxis--was significantly inhibited by MLIF. This suggests that the inhibition of monocyte functions by MLIF may not only be exerted directly on these cells, but also--and perhaps foremost--through a conglomerate down-regulation of endogenous pro-inflammatory chemokines.

Consumption of L-arginine mediated by Entamoeba histolytica L-arginase (EhArg) inhibits amoebicidal activity and nitric oxide production by activated macrophages

In this study we discuss the cloning and expression of Entamoeba histolytica arginase (EhArg), an enzyme that catalyses the hydrolysis of L-arginine to L-ornithine and urea. L-norvaline, a competitive inhibitor of E. histolytica L-arginase, inhibits the growth of the parasite, which suggests that the catabolism of L-arginine mediated by EhArg is essential. Nitric oxide (NO) is an antimicrobial agent that inhibits some key enzymes in the metabolism of Entamoeba histolytica. NO is synthesized by activated macrophages from L-arginine, the substrate of NO synthase (NOS-II). We show that E. histolytica inhibits NO mediated amoebicidal activity of activated macrophages by consuming L-arginine present in the medium.

The monocyte locomotion inhibitory factor produced by Entamoeba histolytica inhibits induced nitric oxide production in human leukocytes

The monocyte locomotion inhibitory factor, an anti-inflammatory pentapeptide produced by Entamoeba histolytica, inhibits the in vitro production of nitric oxide induced by cytokines (INF-gamma, TNF-alpha) or PMA in human leukocytes. This can be added to the other previously reported functional effects of this factor, such as the inhibition of monocyte locomotion and the synthesis of reactive oxygen intermediates in both monocytes and neutrophils. The decreased nitric oxide production may interfere with the killing of amebas by neutrophils in the early invasive stages of amebiasis, when oxidative mechanisms are used [reactive oxygen and nitrogen intermediates either individually or synergistically via peroxynitrite (ONOO(-))], and in the advanced stages, when both non-oxidative and oxidative (including nitric oxide) mechanisms are employed by macrophages. Diminished nitric oxide production by leukocytes may also contribute to the paucity of late inflammatory components in amebic abscess of the liver and other amebic lesions.