Acidic mammalian chitinase--a potential target for asthma therapy

Biochemical Properties of a Novel Cold-Adapted GH19 Chitinase with Three Chitin-Binding Domains from Chitinilyticum aquatile CSC-1 and Its Potential in Biocontrol of Plant Pathogenic Fungi

GH19 (glycoside hydrolase 19) chitinases play crucial roles in the enzymatic conversion of chitin and biocontrol of phytopathogenic fungi. Herein, a novel multifunctional chitinase of GH19 (CaChi19A), which contains three chitin-binding domains (ChBDs), was successfully cloned from Chitinilyticum aquatile CSC-1 and heterologously expressed in Escherichia coli. We also generated truncated mutants of CaChi19A_ΔI, CaChi19A_ΔIΔII, and CaChi19A_CatD consisting of two ChBDs and a catalytic domain, one ChBD and a catalytic domain, and only a catalytic domain, respectively. CaChi19A, CaChi19A_ΔI, CaChi19A_ΔIΔII, and CaChi19A_CatD exhibited cold adaptation, as their relative enzyme activities at 5 °C were 40.7, 51.6, 66.2, and 82.6%, respectively. Compared with CaChi19A and other variants, CaChi19A_ΔIΔII demonstrated a higher level of stability below 50 °C and retained relatively high activity over a wide pH range of 5-12. Analysis of the hydrolysis products revealed that CaChi19A and CaChi19A_ΔIΔII exhibit exoacting, endoacting, and N-acetyl-β-d-glucosaminidase activities toward colloidal chitin. Furthermore, CaChi19A and CaChi19A_ΔIΔII exhibited inhibitory effects on the hyphal growth of Fusarium oxysporum, Fusarium redolens, Fusarium fujikuroi, Fusarium solani, and Coniothyrium diplodiella, thereby illustrating effective biocontrol activity. These results indicated that CaChi19A and CaChi19A_ΔIΔII show advantages in some applications where low temperatures were demanded in industries as well as the biocontrol of fungal diseases in agriculture.

Serotonin-2 Receptor Agonists Produce Anti-inflammatory Effects through Functionally Selective Mechanisms That Involve the Suppression of Disease-Induced Arginase 1 Expression

Functional selectivity in the context of serotonin 2A (5-HT2A) receptor agonists is often described as differences psychedelic compounds have in the activation of Gq vs β-arrestin signaling in the brain and how that may relate to inducing psychoactive and hallucinatory properties with respect to each other. However, the presence of 5-HT2A receptors throughout the body in several cell types, including endothelial, endocrine, and immune-related tissues, suggests that functional selectivity may exist in the periphery as well. Here, we examine functional selectivity between two 5-HT2A receptor agonists of the phenylalkylamine class: (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] and (R)-2,5-dimethoxy-4-trifluoromethylamphetamine [(R)-DOTFM]. Despite comparable in vitro activity at the 5-HT2A receptor as well as similar behavioral potency, (R)-DOTFM does not exhibit an ability to prevent inflammation or elevated airway hyperresponsiveness (AHR) in an acute murine ovalbumin-induced asthma model as does (R)-DOI. Furthermore, there are distinct differences between protein expression and inflammatory-related gene expression in pulmonary tissues between the two compounds. Using (R)-DOI and (R)-DOTFM as tools, we further elucidated the anti-inflammatory mechanisms underlying the powerful anti-inflammatory effects of certain psychedelics and identified key mechanistic components of the anti-inflammatory effects of psychedelics, including suppression of arginase 1 expression.

A novel humanized Chi3l1 blocking antibody attenuates acetaminophen-induced liver injury in mice

Acetaminophen (APAP) overdose is a leading cause of acute liver injury in the USA. The chitinase 3-like-1 (Chi3l1) protein contributes to APAP-induced liver injury (AILI) by promoting hepatic platelet recruitment. Here, we report the development of a Chi3l1-targeting antibody as a potential therapy for AILI. By immunizing a rabbit successively with the human and mouse Chi3l1 proteins, we isolated cross-reactive monoclonal antibodies (mAbs) from single memory B cells. One of the human and mouse Chi3l1 cross-reactive mAbs was humanized and characterized in both in vitro and in vivo biophysical and biological assays. X-ray crystallographic analysis of the lead antibody C59 in complex with the human Chi3l1 protein revealed that the kappa light contributes to majority of the antibody-antigen interaction; and that C59 binds to the 4α-5β loop and 4α-helix of Chi3l1, which is a functional epitope and hotspot for the development of Chi3l1 blocking antibodies. We humanized the C59 antibody by complementarity-determining region grafting and kappa chain framework region reverse mutations. The humanized C59 antibody exhibited similar efficacy as the parental rabbit antibody C59 in attenuating AILI in vivo. Our findings validate Chi3l1 as a potential drug target for AILI and provide proof of concept of developing Chi3l1 blocking antibody as a therapy for the treatment of AILI.

Occupational exposure to gasoline in gasoline station male attendants promotes M1 polarization in macrophages

Several studies have reported the toxicological implications of exposure to petroleum hydrocarbon fumes in animal models. There is little documentation on the effect of such exposure on oxidative stress levels and immune response. To our knowledge, no documentation of M1 polarization in macrophages in gasoline station male attendants. Therefore, this study aimed to evaluate the harmful effects of gasoline vapors in 62 male attendants (16-70 years) compared to 29 age- and sex-matched-unexposed controls. The attendants were recruited from Damietta governorate gasoline stations. Gasoline exposure induced a significant increase in tumor necrosis factor-α (TNF-α) level (p < 0.05) as well as a slight but non-significant increase in the activity of acidic mammalian chitinase (AMCase) (p > 0.05). Further TNF-α/AMCase ratio was significantly increased (p < 0.01) in sera of the attendants when compared to those of the healthy controls. Also, the total leucocytic and lymphocytic counts were significantly increased (p < 0.01 and p < 0.001, respectively). On contrary, neutrophils to lymphocytes ratio (NLR) and platelets to lymphocytes ratio (PLR) were significantly decreased (p < 0.05 and p < 0.001, respectively). In addition, significant reduction in hemoglobin (Hb) concentration, plasma glutathione reduced form (GSH), and catalase, as well as superoxide dismutase (SOD) activities in red blood cells were observed in the exposed attendants. As a result, malondialdehyde (MDA), nitric oxide (NO) levels, and NO/AMCase ratio were significantly increased (p < 0.05). In conclusion, this study inferred that prolonged gasoline exposure can mediate immune activation, especially M1 macrophages polarization, possibly via oxidative stress-mediated mechanism.

A conserved loop structure of GH19 chitinases assists the enzyme function from behind the core-functional region

Plant GH19 chitinases have several loop structures, which may define their enzymatic properties. Among these loops, the longest loop, Loop-III, is most frequently conserved in GH19 enzymes. A GH19 chitinase from the moss Bryum coronatum (BcChi-A) has only one loop structure, Loop-III, which is connected to the catalytically important β-sheet region. Here, we produced and characterized a Loop-III-deleted mutant of BcChi-A (BcChi-A-ΔIII) and found that its stability and chitinase activity were strongly reduced. The deletion of Loop-III also moderately affected the chitooligosaccharide binding ability as well as the binding mode to the substrate-binding groove. The crystal structure of an inactive mutant of BcChi-A-ΔIII was successfully solved, revealing that the remaining polypeptide chain has an almost identical fold to that of the original protein. Loop-III is not necessarily essential for the folding of the enzyme protein. However, closer examination of the crystal structure revealed that the deletion of Loop-III altered the arrangement of the catalytic triad, Glu61, Glu70 and Ser102, and the orientation of the Trp103 side chain, which is important for sugar residue binding. We concluded that Loop-III is not directly involved in the enzymatic activity but assists the enzyme function by stabilizing the conformation of the β-sheet region and the adjacent substrate-binding platform from behind the core-functional regions.

Physiological and pathophysiological roles of acidic mammalian chitinase (CHIA) in multiple organs

Acidic mammalian chitinase (CHIA) belongs to the 18-glycosidase family and is expressed in epithelial cells and certain immune cells (such as neutrophils and macrophages) in various organs. Under physiological conditions, as a hydrolase, CHIA can degrade chitin-containing pathogens, participate in Type 2 helper T (Th2)-mediated inflammation, and enhance innate and adaptive immunity to pathogen invasion. Under pathological conditions, such as rhinitis, ocular conjunctivitis, asthma, chronic atrophic gastritis, type 2 diabetes, and pulmonary interstitial fibrosis, CHIA expression is significantly changed. In addition, studies have shown that CHIA has an anti-apoptotic effect, promotes epithelial cell proliferation and maintains organ integrity, and these effects are not related to chitinase degradation. CHIA can also be used as a biomolecular marker in diseases such as chronic atrophic gastritis, dry eye, and acute kidney damage caused by sepsis. Analysis of the authoritative TCGA database shows that CHIA expression in gastric adenocarcinoma, liver cancer, renal clear cell carcinoma and other tumors is significantly downregulated compared with that in normal tissues, but the specific mechanism is unclear. This review is based on all surveys conducted to date and summarizes the expression patterns and functional diversity of CHIA in various organs. Understanding the physiological and pathophysiological relevance of CHIA in multiple organs opens new possibilities for disease treatment.

Multi-functionality of a tryptophan residue conserved in substrate-binding groove of GH19 chitinases

GH19 and GH22 glycoside hydrolases belonging to the lysozyme superfamily have a related structure/function. A highly conserved tryptophan residue, Trp103, located in the binding groove of a GH19 chitinase from moss Bryum coronatum (BcChi-A) appears to have a function similar to that of well-known Trp62 in GH22 lysozymes. Here, we found that mutation of Trp103 to phenylalanine (W103F) or alanine (W103A) strongly reduced the enzymatic activity of BcChi-A. NMR experiments and the X-ray crystal structure suggested a hydrogen bond between the Trp103 side chain and the -2 sugar. Chitooligosaccharide binding experiments using NMR indicated that the W103F mutation reduced the sugar-binding abilities of nearby amino acid residues (Tyr105/Asn106) in addition to Trp103. This appeared to be derived from enhanced aromatic stacking of Phe103 with Tyr105 induced by disruption of the Trp103 hydrogen bond with the -2 sugar. Since the stacking with Tyr105 was unlikely in W103A, Tyr105/Asn106 of W103A was not so affected as in W103F. However, the W103A mutation appeared to reduce the catalytic potency, resulting in the lowest enzymatic activity in W103A. We concluded that Trp103 does not only interact with the sugar, but also controls other amino acids responsible for substrate binding and catalysis. Trp103 (GH19) and Trp62 (GH22) with such a multi-functionality may be advantageous for enzyme action and conserved in the divergent evolution in the lysozyme superfamily.

YKL-39 as a Potential New Target for Anti-Angiogenic Therapy in Cancer

YKL-39 belongs to the evolutionarily conserved family of Glyco_18-containing proteins composed of chitinases and chitinase-like proteins. Chitinase-like proteins (CLPs) are secreted lectins that lack hydrolytic activity due to the amino acid substitutions in their catalytic domain and combine the functions of cytokines and growth factors. One of the major cellular sources that produce CLPs in various pathologies, including cancer, are macrophages. Monocytes recruited to the tumor site and programmed by tumor cells differentiate into tumor-associated macrophages (TAMs), which are the primary source of pro-angiogenic factors. Tumor angiogenesis is a crucial process for supplying rapidly growing tumors with essential nutrients and oxygen. We recently determined that YKL-39 is produced by tumor-associated macrophages in breast cancer. YKL-39 acts as a strong chemotactic factor for monocytes and stimulates angiogenesis. Chemotherapy is a common strategy to reduce tumor size and aggressiveness before surgical intervention, but chemoresistance, resulting in the relapse of tumors, is a common clinical problem that is critical for survival in cancer patients. Accumulating evidence indicates that TAMs are essential regulators of chemoresistance. We have recently found that elevated levels of YKL-39 expression are indicative of the efficiency of the metastatic process in patients who undergo neoadjuvant chemotherapy. We suggest YKL-39 as a new target for anti-angiogenic therapy that can be combined with neoadjuvant chemotherapy to reduce chemoresistance and inhibit metastasis in breast cancer patients.

Targeted delivery of Chil3/Chil4 siRNA to alveolar macrophages using ternary complexes composed of HMG and oligoarginine micelles

Cell-type-specific genes involved in disease can be effective therapeutic targets; therefore, the development of a cell-type-specific gene delivery system is essential. In this study, targeted delivery of Chil3 and Chil4 siRNA to activated macrophages was developed using a ligand called high mobility group (HMG) and oligoarginine (OR) micelles. HMG binds to TLR4 and RAGE located on the surface of activated macrophages. Since HMG is positively charged, it binds to the negatively charged siRNA by charge interaction. However, the stable formation of the siRNA/HMG complex requires an additional molecule to act as a carrier. In this study, OR micelles were used as the carrier. Gel retardation assays showed that siRNA, HMG, and OR micelles formed stable siRNA/HMG/OR micelle ternary complexes. In vitro transfection showed that the ternary complexes selectively delivered siRNA to TLR4 expressing macrophages. In addition, intratracheal administration of siRNA/HMG/OR ternary complexes delivered Chil3 and Chil4 siRNA specifically to alveolar macrophages. Furthermore, the siRNA that was delivered using ternary complexes reduced Chil3 and Chil4 expression and suppressed the symptoms of asthma, such as airway inflammation and mucin secretion.

Aspergillus fumigatus corneal infection is regulated by chitin synthases and by neutrophil-derived acidic mammalian chitinase

Aspergillus fumigatus is an important cause of pulmonary and systemic infections in immune compromised individuals, and of corneal ulcers and blindness in immune competent patients. To examine the role of chitin synthases in Aspergillus corneal infection, we analyzed Aspergillus mutants of chitin synthase family 1 and family 2, and found that compared with the parent strain, the quadruple mutants from both families were more readily killed by neutrophils in vitro, and that both also exhibited impaired hyphal growth in the cornea. Further, inhibition of chitin synthases using Nikkomycin Z enhanced neutrophil killing in vitro and in vivo in a murine model of A. fumigatus corneal infection. Acidic mammalian chitinase (AMCase) is mostly produced by macrophages in asthmatic lungs; however, we now demonstrate that neutrophils are a major source of AMCase, which inhibits hyphal growth. In A. fumigatus corneal infection, neutrophils are the major source of AMCase, and addition of AMCase inhibitors or adoptive transfer of neutrophils from AMCase^-/- mice resulted in impaired hyphal killing. Together, these findings identify chitin synthases as important fungal virulence factors and neutrophil-derived AMCase as an essential mediator of host defense.

The Listeria innocua chitinase LinChi78 has a unique region that is necessary for hydrolytic activity

Chitinases are generally composed of multiple domains; a catalytic domain and one or more additional domains that are not absolutely required but may modify the chitinolytic activity. The LinChi78 chitinase from Listeria innocua has a catalytic domain (CatD), a fibronectin type III-like (FnIII) domain, a chitin-binding domain (ChBD), and an unknown-function region (UFR) located between the CatD and FnIII domains. The UFR is 146 amino acid residues in length and does not have a homologous domain in the Conserved Domain Database. We performed a functional analysis of these domains and the UFR using several C-terminally and internally deleted mutants of LinChi78. Hydrolysis of an artificial substrate was almost unaffected by deletion of the ChBD and/or the FnIII domain, although the ChBD-deleted enzymes were approximately 30% less active toward colloidal chitin than LinChi78. On the other hand, deletion of the UFR led to an extensive loss of chitinase activity toward an artificial substrate as well as polymeric substrates. Upon further analysis, we found that the GKQTI stretch, between the 567th (G) and 571th (I) amino acid residues, in the UFR is critical for LinChi78 activity and demonstrated that Gln569 and Ile571 play central roles in eliciting this activity. Taken together, these results indicated that LinChi78 has a unique catalytic region composed of a typical CatD and an additional region that is essential for activity. Characterization of the unique catalytic region of LinChi78 will improve our understanding of GH18 chitinases.

Structure-Based Virtual Screening, Compound Synthesis, and Bioassay for the Design of Chitinase Inhibitors

Chitinases play a vital part in the molting phase of insect pests. Inhibiting their activities by the use of drug-like small chemical molecules is thought to be an efficient strategy in pesticide design and development. On the basis of the crystal structure of OfChtI, a chitinase indispensable for the molting of the insect pest Ostrinia furnacalis (Asian corn borer), here we report a chemical fragment and five variant compounds as inhibitors of OfChtI obtained from a library of over 200 000 chemicals by a structure-based-virtual-screening approach. The compounds were synthesized with high atom economy and tested for their OfChtI-inhibitory activities in a bioassay. Compound 3 showed preferential inhibitory activity with a K_i value of 1.5 μΜ against OfChtI. Analysis of the structure-activity relationships of the compounds provided insight into their interactions with the enzyme active site, which may inform future work in improving the potencies of their inhibitory activities.

Transcriptome sequencing and differential gene expression analysis of the schistosome-transmitting snail Oncomelania hupensis inhabiting hilly and marshland regions

The freshwater snail Oncomelania hupensis is the unique intermediate host of the blood fluke Schistosoma japonicum, which is the major cause of schistosomiasis. The snail inhabits two contrasting environments: the hilly and marshland regions. The hilly snails are smaller in size and have the typical smooth shell, whereas the marshland snails are larger and possess the ribbed shell. To reveal the differences in gene expression between the hilly and marshland snails, a total of six snails, three per environment, were individually examined by RNA sequencing technology. All paired-end reads were assembled into contigs from which 34,760 unigenes were predicted. Based on single nucleotide polymorphisms, principal component analysis and neighbor-joining clustering revealed two distinct clusters of hilly and marshland snails. Analysis of expression changes between environments showed that upregulated genes relating to immunity and development were enriched in hilly snails, while those associated with reproduction were over-represented in marshland snails. Eight differentially expressed genes between the two types of snails were validated by qRT-PCR. Our study identified candidate genes that could be targets for future functional studies, and provided a link between expression profiling and ecological adaptation of the snail that may have implications for schistosomiasis control.

Crystal structure and thermodynamic dissection of chitin oligosaccharide binding to the LysM module of chitinase-A from Pteris ryukyuensis

We determined the crystal structure of a LysM module from Pteris ryukyuensis chitinase-A (PrLysM2) at a resolution of 1.8 Å. Structural and binding analysis of PrLysM2 indicated that this module recognizes chitin oligosaccharides in a shallow groove comprised of five sugar-binding subsites on one side of the molecule. The free energy changes (ΔG_r°) for binding of (GlcNAc)₆, (GlcNAc)₅, and (GlcNAc)₄ to PrLysM2 were determined to be -5.4, -5,4 and -4.6 kcal mol^-1, respectively, by ITC. Thermodynamic dissection of the binding energetics of (GlcNAc)₆ revealed that the driving force is the enthalpy change (ΔH_r° = -11.7 ± 0.2 kcal/mol) and the solvation entropy change (-TΔS_solv° = -5.9 ± 0.6 kcal/mol). This is the first description of thermodynamic signatures of a chitin oligosaccharide binding to a LysM module.

Genetic Variants in CHIA and CHI3L1 Are Associated with the IgE Response to the Ascaris Resistance Marker ABA-1 and the Birch Pollen Allergen Bet v 1

Helminth infections and allergic diseases are associated with IgE hyperresponsiveness but the genetics of this phenotype remain to be defined. Susceptibility to Ascaris lumbricoides infection and antibody levels to this helminth are associated with polymorphisms in locus 13q33-34. We aimed to explore this and other genomic regions to identify genetic variants associated with the IgE responsiveness in humans. Forty-eight subjects from Cartagena, Colombia, with extreme values of specific IgE to Ascaris and ABA-1, a resistance marker of this nematode, were selected for targeted resequencing. Burden analyses were done comparing extreme groups for IgE values. One-hundred one SNPs were genotyped in 1258 individuals of two well-characterized populations from Colombia and Sweden. Two low-frequency coding variants in the gene encoding the Acidic Mammalian Chitinase (CHIA rs79500525, rs139812869, tagged by rs10494133) were found enriched in high IgE responders to ABA-1 and confirmed by genetic association analyses. The SNP rs4950928 in the Chitinase 3 Like 1 gene (CHI3L1) was associated with high IgE to ABA-1 in Colombians and with high IgE to Bet v 1 in the Swedish population. CHIA rs10494133 and ABDH13 rs3783118 were associated with IgE responses to Ascaris. SNPs in the Tumor Necrosis Factor Superfamily Member 13b gene (TNFSF13B) encoding the cytokine B cell activating Factor were associated with high levels of total IgE in both populations. This is the first report on the association between low-frequency and common variants in the chitinases-related genes CHIA and CHI3L1 with the intensity of specific IgE to ABA-1 in a population naturally exposed to Ascaris and with Bet v 1 in a Swedish population. Our results add new information about the genetic influences of human IgE responsiveness; since the genes encode for enzymes involved in the immune response to parasitic infections, they could be helpful for understanding helminth immunity and allergic responses. We also confirmed that TNFSF13B has an important and conserved role in the regulation of total IgE levels, which supports potential evolutionary links between helminth immunity and allergic response.

A Novel Scaffold for Developing Specific or Broad-Spectrum Chitinase Inhibitors

Chitinases play important roles in pathogen invasion, arthropod molting, plant defense, and human inflammation. Inhibition of the activity of a typical chitinase by small molecules is of significance in drug development and biological research. On the basis of a recent reported crystal structure of OfChtI, the insect chitinase derived from the pest Ostrinia furnacalis, we computationally identified 17 compounds from a library of over 4 million chemicals by two rounds virtual screening. Among these, three compounds from one chemical class inhibited the activity of OfChtI with single-digit-micromolar IC₅₀ values, and one compound from another chemical class exhibited a broad inhibitory activity not only toward OfChtI but also toward bacterial, fungal, and human chitinases. A new scaffold was discovered, and a structure-inhibitory activity relationship was proposed. This work may provide a novel starting point for the development of specific or broad-spectrum chitinase inhibitors.

Characterization of two Listeria innocua chitinases of different sizes that were expressed in Escherichia coli

Two putative chitinase genes, lin0153 and lin1996, from the nonpathogenic bacterium Listeria innocua were expressed in Escherichia coli, and the gene products were characterized. The genes were close homologs of chitinases from the pathogenic bacterium Listeria monocytogenes, in which chitinases and chitin-binding proteins play important roles in pathogenesis in mice-infection models. The purified recombinant enzymes that are different in size, LinChi78 (lin0153 product) and LinChi35 (lin1996 product)-with molecular masses of 82 and 38 kDa, including vector-derived additional sequences, respectively-exhibited optimum catalytic activity under neutral and acidic conditions at 50 °C, respectively, and were stable over broad pH (4-11) and temperature (4-40 °C) ranges. LinChi35 displayed higher k cat and K M values for 4-nitrophenyl N,N-diacetyl-β-D-chitobioside [4NP-(GlcNAc)2] than LinChi78. Both enzymes produced primarily dimers from colloidal chitin as a substrate. However, LinChi78 and LinChi35 could hydrolyze oligomeric substrates in a processive exo- and nonprocessive endo-manner, respectively, and showed different reactivity toward oligomeric substrates. Both enzymes could bind chitin beads but were different in their binding ability toward crystalline α-chitin and cellulose. The structure-function relationships of these chitinases are discussed in reference to other bacterial chitinases.

Chitosan oligosaccharides in combination with Agaricus blazei Murill extract reduces hepatoma formation in mice with severe combined immunodeficiency

Chitosan and Agaricus blazei Murill (ABM) extracts possess antitumor activities. The aim of the present study was to investigate whether chitosan, ABM extract or the two in combination were effective against tumors in tumor‑bearing mice. The mice were subcutaneously injected with SK-Hep 1 cells and were then were divided into the following six groups: Group 1, control group; group 2, chitosan 5 mg/kg/day; group 3, chitosan 20 mg/kg/day; group 4, ABM (246 mg/kg/day) and chitosan (5 mg/kg/day) combined; group 5, ABM (984 mg/kg/day) and chitosan (20 mg/kg/day) combined; and group 6, ABM (984 mg/kg/day). The mice were treated with the different concentrations of chitosan, ABM or combinations of the two for 6 weeks. The levels of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and vascular endothelial growth factor (VEGF), and tissue histopathological features were examined in the surviving animals. Based on the results of the investigation, the treatments performed in groups 2, 3 and 4 were identified as being capable of reducing the weights of the tumors, however, group 4, which was treated with chitosan (5 mg/kg/day) in combination with ABM (246 mg/kg/day) was able to reduce the levels of GOT and VEGF. As a result, treatment with chitosan in combination with ABM may offer potential in cancer therapy and requires further investigation.

Interaction of di-N-acetylchitobiosyl moranoline with a family GH19 chitinase from moss, Bryum coronatum

Tri-N-acetylchitotriosyl moranoline, (GlcNAc)3-M, was previously shown to strongly inhibit lysozyme (Ogata M, Umemoto N, Ohnuma T, Numata T, Suzuki A, Usui T, Fukamizo T. 2013. A novel transition-state analogue for lysozyme, 4-O-β-tri-Nacetylchitotriosyl moranoline, provided evidence supporting the covalent glycosyl-enzyme intermediate. J Biol Chem. 288:6072-6082). The findings prompted us to examine the interaction of di-N-acetylchitobiosyl moranoline, (GlcNAc)2-M, with a family GH19 chitinase from moss, Bryum coronatum (BcChi19A). Thermal unfolding experiments using BcChi19A and the catalytic acid-deficient mutant (BcChi19A-E61A) revealed that the transition temperature (Tm) was elevated by 4.3 and 5.8°C, respectively, upon the addition of (GlcNAc)2-M, while the chitin dimer, (GlcNAc)2, elevated Tm only by 1.0 and 1.4°C, respectively. By means of isothermal titration calorimetry, binding free energy changes for the interactions of (GlcNAc)3 and (GlcNAc)2-M with BcChi19A-E61A were determined to be -5.2 and -6.6 kcal/mol, respectively, while (GlcNAc)2 was found to interact with BcChi19A-E61A with markedly lower affinity. nuclear magnetic resonance titration experiments using (15)N-labeled BcChi19A and BcChi19A-E61A revealed that both (GlcNAc)2 and (GlcNAc)2-M interact with the region surrounding the catalytic center of the enzyme and that the interaction of (GlcNAc)2-M is markedly stronger than that of (GlcNAc)2 for both enzymes. However, (GlcNAc)2-M was found to moderately inhibit the hydrolytic reaction of chitin oligosaccharides catalyzed by BcChi19A (IC50 = 130-620 μM). A molecular dynamics simulation of BcChi19A in complex with (GlcNAc)2-M revealed that the complex is quite stable and the binding mode does not significantly change during the simulation. The moranoline moiety of (GlcNAc)2-M did not fit into the catalytic cleft (subsite -1) but was rather in contact with subsite +1. This situation may result in the moderate inhibition toward the BcChi19A-catalyzed hydrolysis.

Fully deacetylated chitooligosaccharides act as efficient glycoside hydrolase family 18 chitinase inhibitors

Small molecule inhibitors against chitinases have potential applications as pesticides, fungicides, and antiasthmatics. Here, we report that a series of fully deacetylated chitooligosaccharides (GlcN)2-7 can act as inhibitors against the insect chitinase OfChtI, the human chitinase HsCht, and the bacterial chitinases SmChiA and SmChiB with IC50 values at micromolar to millimolar levels. The injection of mixed (GlcN)2-7 into the fifth instar larvae of the insect Ostrinia furnacalis resulted in 85% of the larvae being arrested at the larval stage and death after 10 days, also suggesting that (GlcN)2-7 might inhibit OfChtI in vivo. Crystal structures of the catalytic domain of OfChtI (OfChtI-CAD) complexed with (GlcN)5,6 were obtained at resolutions of 2.0 Å. These structures, together with mutagenesis and thermodynamic analysis, suggested that the inhibition was strongly related to the interaction between the -1 GlcN residue of the inhibitor and the catalytic Glu(148) of the enzyme. Structure-based comparison showed that the fully deacetylated chitooligosaccharides mimic the substrate chitooligosaccharides by binding to the active cleft. This work first reports the inhibitory activity and proposed inhibitory mechanism of fully deacetylated chitooligosaccharides. Because the fully deacetylated chitooligosaccharides can be easily derived from chitin, one of the most abundant materials in nature, this work also provides a platform for developing eco-friendly inhibitors against chitinases.

Crystal structure of a "loopless" GH19 chitinase in complex with chitin tetrasaccharide spanning the catalytic center

DESCRIPTIONS

The structure of a GH19 chitinase from the moss Bryum coronatum (BcChi-A) in complex with the substrate was examined by X-ray crystallography and NMR spectroscopy in solution. The X-ray crystal structure of the inactive mutant of BcChi-A (BcChi-A-E61A) liganded with chitin tetramer (GlcNAc)4 revealed a clear electron density of the tetramer bound to subsites -2, -1, +1, and +2. Individual sugar residues were recognized by several amino acids at these subsites through a number of hydrogen bonds. This is the first crystal structure of GH19 chitinase liganded with oligosaccharide spanning the catalytic center. NMR titration experiments of chitin oligosaccharides into the BcChi-A-E61A solution showed that the binding mode observed in the crystal structure is similar to that in solution. The C-1 carbon of -1 GlcNAc, the Oε1 atom of the catalytic base (Glu70), and the Oγ atom of Ser102 form a "triangle" surrounding the catalytic water, and the arrangement structurally validated the proposed catalytic mechanism of GH19 chitinases. The glycosidic linkage between -1 and +1 sugars was found to be twisted and under strain. This situation may contribute to the reduction of activation energy for hydrolysis. The complex structure revealed a more refined mechanism of the chitinase catalysis.

Crystallization and preliminary X-ray diffraction analysis of an active-site mutant of `loopless' family GH19 chitinase from Bryum coronatum in a complex with chitotetraose

The catalytic mechanism of family GH19 chitinases is not well understood owing to insufficient information regarding the three-dimensional structures of enzyme-substrate complexes. Here, the crystallization and preliminary X-ray diffraction analysis of a selenomethionine-labelled active-site mutant of `loopless' family GH19 chitinase from the moss Bryum coronatum in complex with chitotetraose, (GlcNAc)4, are reported. The crystals were grown using the vapour-diffusion method. They diffracted to 1.58 Å resolution using synchrotron radiation at the Photon Factory. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 74.5, b = 58.4, c = 48.1 Å, β = 115.6°. The asymmetric unit of the crystals is expected to contain one protein molecule, with a Matthews coefficient of 2.08 Å(3) Da(-1) and a solvent content of 41%.

Phospholipase A2 in experimental allergic bronchitis: a lesson from mouse and rat models

Background

Phospholipases A₂ (PLA₂) hydrolyzes phospholipids, initiating the production of inflammatory lipid mediators. We have previously shown that in rats, sPLA₂ and cPLA₂ play opposing roles in the pathophysiology of ovalbumin (OVA)-induced experimental allergic bronchitis (OVA-EAB), an asthma model: Upon disease induction sPLA₂ expression and production of the broncho-constricting CysLTs are elevated, whereas cPLA₂ expression and the broncho-dilating PGE₂ production are suppressed. These were reversed upon disease amelioration by treatment with an sPLA₂ inhibitor. However, studies in mice reported the involvement of both sPLA₂ and cPLA₂ in EAB induction.

Objectives

To examine the relevance of mouse and rat models to understanding asthma pathophysiology.

Methods

OVA-EAB was induced in mice using the same methodology applied in rats. Disease and biochemical markers in mice were compared with those in rats.

Results

As in rats, EAB in mice was associated with increased mRNA of sPLA₂, specifically sPLA₂gX, in the lungs, and production of the broncho-constricting eicosanoids CysLTs, PGD₂ and TBX₂ in bronchoalveolar lavage (BAL). In contrast, EAB in mice was associated also with elevated cPLA₂ mRNA and PGE₂ production. Yet, treatment with an sPLA₂ inhibitor ameliorated the EAB concomitantly with reverting the expression of both cPLA₂ and sPLA₂, and eicosanoid production.

Conclusions

In both mice and rats sPLA₂ is pivotal in OVA-induced EAB. Yet, amelioration of asthma markers in mouse models, and human tissues, was observed also upon cPLA₂ inhibition. It is plausible that airway conditions, involving multiple cell types and organs, require the combined action of more than one, essential, PLA₂s.

Attenuation of allergic airway inflammation in a murine model of asthma by Licochalcone A

CONTEXT

Licochalcone A (Lico A) is a major and biogenetically characteristic chalcone isolated from the root of Xinjiang liquorice, Glycyrrhiza inflata.

OBJECTIVE

We focused on investigating whether Lico A possesses distinct anti-inflammatory activity on a non-infectious mouse model of asthma, and we aimed to elucidate its involvement with the mitogen-activated protein kinases pathway.

METHODS

BALB/c mice that were sensitized and challenged to ovalbumin (OVA) were treated with Lico A (50 mg/kg) 1 h before they were challenged with OVA.

RESULTS

Our study demonstrated that Lico A may effectively inhibit the increase in T-helper type 2 cytokines, such as interleukin (IL)-4, IL-5 and IL-13 in bronchoalveolar lavage fluid, and reduced serum levels of OVA-specific IgE and IgG. Furthermore, Lico A substantially inhibited OVA-induced eosinophilia in lung tissue and mucus hyper-secretion by goblet cells in the airway. Meanwhile, pretreatment with Lico A resulted in a significant reduction in mRNA expression of acidic mammalian chitinase, chitinase 3-like protein 4 (Ym2), E-selectin, Muc5ac, CCL11 and CCR3 in lung tissues and airway hyper-responsiveness to methacholine.

CONCLUSIONS

These findings suggest that Lico A may effectively delay the progression of airway inflammation and could be used as a therapy for patients with allergic airway inflammation.

Insectivorous bats digest chitin in the stomach using acidic mammalian chitinase

The gastrointestinal tract of animals is adapted to their primary source of food to optimize resource use and energy intake. Temperate bat species mainly feed on arthropods. These contain the energy-rich carbohydrate chitin, which is indigestible for the endogenous enzymes of a typical mammalian gastrointestinal tract. However, the gastrointestinal tract of bat species should be adapted to their diet and be able to digest chitin. We hypothesized that (i) European vespertilionid bat species have the digestive enzyme chitinase and that (ii) the chitinolytic activity is located in the intestine, as has been found for North American bat species. The gastrointestinal tracts of seven bat species (Pipistrellus pipistrellus, Plecotus auritus, Myotis bechsteinii, Myotis nattereri, Myotis daubentonii, Myotis myotis, and Nyctalus leisleri) were tested for chitinolytic activity by diffusion assay. Gastrointestinal tracts of P. pipistrellus, P. auritus, M. nattereri, M. myotis, and N. leisleri were examined for acidic mammalian chitinase by western blot analysis. Tissue sections of the gastrointestinal tract of P. pipistrellus were immunohistochemically analyzed to locate the acidic mammalian chitinase. Chitinolytic activity was detected in the stomachs of all bat species. Western blot analysis confirmed the acidic mammalian chitinase in stomach samples. Immunohistochemistry of the P. pipistrellus gastrointestinal tract indicated that acidic mammalian chitinase is located in the stomach chief cells at the base of the gastric glands. In conclusion, European vespertilionid bat species have acidic mammalian chitinase that is produced in the gastric glands of the stomach. Therefore, the gastrointestinal tracts of insectivorous bat species evolved an enzymatic adaptation to their diet.

Chitinases: in agriculture and human healthcare

Biological control of phytopathogenic fungi and insects continues to inspire the research and development of environmentally friendly bioactive alternatives. Potentially lytic enzymes, chitinases can act as a biocontrol agent against agriculturally important fungi and insects. The cell wall in fungi and protective covers, i.e. cuticle in insects shares a key structural polymer, chitin, a β-1,4-linked N-acetylglucosamine polymer. Therefore, it is advantageous to develop a common biocontrol agent against both of these groups. As chitin is absent in plants and mammals, targeting its metabolism will signify an eco-friendly strategy for the control of agriculturally important fungi and insects but is innocuous to mammals, plants, beneficial insects and other organisms. In addition, development of chitinase transgenic plant varieties probably holds the most promising method for augmenting agricultural crop protection and productivity, when properly integrated into traditional systems. Recently, human proteins with chitinase activity and chitinase-like proteins were identified and established as biomarkers for human diseases. This review covers the recent advances of chitinases as a biocontrol agent and its various applications including preparation of medically important chitooligosaccharides, bioconversion of chitin as well as in implementing chitinases as diagnostic and prognostic markers for numerous diseases and the prospect of their future utilization.

Backbone chemical shifts assignments, secondary structure, and ligand binding of a family GH-19 chitinase from moss, Bryum coronatum

Family GH19 chitinases have been recognized as important in the plant defense against fungal pathogens. However, their substrate-recognition mechanism is still unknown. We report here the first resonance assignment of NMR spectrum of a GH19 chitinase from moss, Bryum coronatum (BcChi-A). The backbone signals were nearly completely assigned, and the secondary structure was estimated based on the chemical shift values. The addition of the chitin dimer to the enzyme solution perturbed the chemical shifts of HSQC resonances of the amino acid residues forming the putative substrate-binding cleft. Further NMR analysis of the ligand binding to BcChi-A will improve understanding of the substrate-recognition mechanism of GH-19 enzymes.

Chitin oligosaccharide binding to a family GH19 chitinase from the moss Bryum coronatum

Substrate binding of a family GH19 chitinase from a moss species, Bryum coronatum (BcChi-A, 22 kDa), which is smaller than the 26 kDa family GH19 barley chitinase due to the lack of several loop regions ('loopless'), was investigated by oligosaccharide digestion, thermal unfolding experiments and isothermal titration calorimetry (ITC). Chitin oligosaccharides [β-1,4-linked oligosaccharides of N-acetylglucosamine with a polymerization degree of n, (GlcNAc)(n), n = 3-6] were hydrolyzed by BcChi-A at rates in the order (GlcNAc)(6) > (GlcNAc)(5) > (GlcNAc)(4) >> (GlcNAc)(3). From thermal unfolding experiments using the inactive BcChi-A mutant (BcChi-A-E61A), in which the catalytic residue Glu61 is mutated to Ala, we found that the transition temperature (T(m) ) was elevated upon addition of (GlcNAc)(n) (n = 2-6) and that the elevation (ΔT(m)) was almost proportional to the degree of polymerization of (GlcNAc)(n). ITC experiments provided the thermodynamic parameters for binding of (GlcNAc)(n) (n = 3-6) to BcChi-A-E61A, and revealed that the binding was driven by favorable enthalpy changes with unfavorable entropy changes. The change in heat capacity (ΔC(p)°) for (GlcNAc)(6) binding was found to be relatively small (-105 ± 8 cal·K(-1) ·mol(-1)). The binding free energy changes for (GlcNAc)(6), (GlcNAc)(5), (GlcNAc)(4) and (GlcNAc)(3) were determined to be -8.5, -7.9, -6.6 and -5.0 kcal·mol(-1), respectively. Taken together, the substrate binding cleft of BcChi-A consists of at least six subsites, in contrast to the four-subsites binding cleft of the 'loopless' family 19 chitinase from Streptomyces coelicolor.

DATABASE

Chitinase, EC 3.2.1.14.

Acidic Mammalian chitinase and the eye: implications for ocular inflammatory diseases

Chitinases have an important role in the defense of organisms against chitin-containing parasites. An acidic mammalian chitinase (AMCase) has been detected in epithelial cells in lung tissue samples taken from patients with asthma as well as in conjunctival epithelium of patients with inflammatory ocular diseases. Particularly, elevated AMCase activity has been observed in ocular tissues of patients with vernal keratoconjunctivitis, seasonal allergic conjunctivitis, and in patients affected by dry eye syndrome. This enzyme is induced via a T_H2-specific, IL-13-dependent pathway. AMCase may thus be a key mediator of IL-13-induced responses in T_H2-driven inflammatory ocular diseases.

Potent family-18 chitinase inhibitors: x-ray structures, affinities, and binding mechanisms

Six novel inhibitors of Vibrio harveyi chitinase A (VhChiA), a family-18 chitinase homolog, were identified by in vitro screening of a library of pharmacologically active compounds. Unlike the previously identified inhibitors that mimicked the reaction intermediates, crystallographic evidence from 14 VhChiA-inhibitor complexes showed that all of the inhibitor molecules occupied the outer part of the substrate-binding cleft at two hydrophobic areas. The interactions at the aglycone location are well defined and tightly associated with Trp-397 and Trp-275, whereas the interactions at the glycone location are patchy, indicating lower affinity and a loose interaction with two consensus residues, Trp-168 and Val-205. When Trp-275 was substituted with glycine (W275G), the binding affinity toward all of the inhibitors dramatically decreased, and in most structures two inhibitor molecules were found to stack against Trp-397 at the aglycone site. Such results indicate that hydrophobic interactions are important for binding of the newly identified inhibitors by the chitinase. X-ray data and isothermal microcalorimetry showed that the inhibitors occupied the active site of VhChiA in three different binding modes, including single-site binding, independent two-site binding, and sequential two-site binding. The inhibitory effect of dequalinium in the low nanomolar range makes this compound an extremely attractive lead compound for plausible development of therapeutics against human diseases involving chitinase-mediated pathologies.

Analysis of noncovalent chitinase-chito-oligosaccharide complexes by infrared-matrix assisted laser desorption ionization and nanoelectrospray ionization mass spectrometry

Transferring noncovalently bound complexes from the condensed phase into the gas phase represents a challenging task due to weak intermolecular bonds that have to be maintained during the phase transition. Currently, electrospray ionization (ESI) is the standard mass spectrometric (MS) technique to analyze noncovalent complexes. Although infrared matrix-assisted laser desorption ionization (IR-MALDI)-MS also provides particular soft desorption/ionization conditions, this method has so far hardly been applied for the analysis of noncovalent complexes. In this study, we employed IR-MALDI orthogonal time-of-flight (o-TOF)-MS in combination with the liquid matrix glycerol to characterize the specific complex formation of chito-oligosaccharide (CHOS) ligands with two variants of Chitinase A (ChiA) from Serratia marcescens, the inactive E315Q mutant and the active W167A mutant, respectively. The IR-MALDI-o-TOF-MS results were compared to those obtained using nano-ESI-quadrupole (q)-TOF-MS and ultraviolet (UV)-MALDI-o-TOF-MS. Using IR-MALDI-o-TOF-MS, specific noncovalent complexes between ChiA and CHOS were detected with distributions between enzymes with bound oligosaccharides vs free enzymes that were essentially identical to those obtained by nano-ESI-q-TOF-MS. Chitinase-CHOS complexes were not detected when UV-MALDI was employed for desorption/ionization. The results show that IR-MALDI-MS can be a valuable tool for fast and simple screening of noncovalent enzyme-ligand interactions.

Determination of substrate binding energies in individual subsites of a family 18 chitinase

Thermodynamic parameters for binding of N-acetylglucosamine (GlcNAc) oligomers to a family 18 chitinase, ChiB of Serratia marcescens, have been determined using isothermal titration calorimetry. Binding studies with oligomers of different lengths showed that binding to subsites -2 and +1 is driven by a favorable enthalpy change, while binding to the two other most important subsites, +2 and +3, is driven by entropy with unfavorable enthalpy. These remarkable unfavorable enthalpy changes are most likely due to favorable enzyme-substrate interactions being offset by unfavorable enthalpic effects of the conformational changes that accompany substrate-binding.

Functional comparison of recombinant acidic mammalian chitinase with enzyme from murine bronchoalveolar lavage

Acidic mammalian chitinase (AMCase) is an enzyme that selectively degrades the biopolymer chitin. Several chitinase enzymes are utilized by mammals to hydrolyze chitin encountered by inhalation and ingestion. AMCase is distinct from other mammalian chitinases as its activity is retained in strongly acidic conditions (pH <2.0). AMCase expression is induced by antigen-induced mouse models of allergic lung inflammation. This protein has also been implicated in the pathogenesis of asthma although its precise role is poorly defined. We describe a novel way to express and purify active murine AMCase. This material retains properties observed in mouse bronchoalveolar lavage (BAL) fluid with regard to pH preference of activity and its inhibition by cyclic peptide inhibitors argifin and argadin. We found that chitinase in BAL from both antigen-challenged and control animals have similar properties in this regard. This strongly supports the notion the same enzyme (AMCase) gives rise to chitinase activity in both challenged and unchallenged animals. We also describe expression of active human AMCase. The methods described in this paper provide a reliable source of recombinant AMCase that can be utilized to expand understanding of AMCase's role in regulating allergic inflammation.

Fungal exposure modulates the effect of polymorphisms of chitinases on emergency department visits and hospitalizations

RATIONALE

Chitinases are enzymes that cleave chitin, which is present in fungal cells. Two types of human chitinases, chitotriosidase and acidic mammalian chitinase, and the chitinase-like protein, YKL-40, seem to play an important role in asthma. We hypothesized that exposure to environmental fungi may modulate the effect of chitinases in individuals with asthma.

OBJECTIVES

To explore whether interactions between high fungal exposure and common genetic variants in the two chitinases in humans, CHIT1 and CHIA, and the chitinase 3-like 1 gene, CHI3L1, are associated with severe asthma exacerbations and other asthma-related outcomes.

METHODS

Forty-eight single nucleotide polymorphisms (SNPs) in CHIT1, CHIA, and CHI3L1 and one CHIT1 duplication were genotyped in 395 subjects and their parents as part of the Childhood Asthma Management Program. Household levels of mold (an index of fungal exposure) were determined on house dust samples. We conducted family-based association tests with gene-environment interactions. Our outcome was severe exacerbation, defined as emergency department visits and hospitalizations from asthma over a 4-year period, and our secondary outcomes included indices of lung function and allergy-related phenotypes.

MEASUREMENTS AND MAIN RESULTS

Of the 395 subjects who had mold levels at randomization, 24% (95 subjects) had levels that were greater than 25,000 units per gram of house dust (high mold exposure). High mold exposure significantly modified the relation between three SNPs in CHIT1 (rs2486953, rs4950936, and rs1417149) and severe exacerbations (P for interaction 0.0010 for rs2486953, 0.0008 for rs4950936, and 0.0005 for rs1417149). High mold exposure did not significantly modify the relationship between any of the other variants and outcomes.

CONCLUSIONS

Environmental exposure to fungi, modifies the effect of CHIT1 SNPs on severe asthma exacerbations.

Production of chitooligosaccharides and their potential applications in medicine

Chitooligosaccharides (CHOS) are homo- or heterooligomers of N-acetylglucosamine and D-glucosamine. CHOS can be produced using chitin or chitosan as a starting material, using enzymatic conversions, chemical methods or combinations thereof. Production of well-defined CHOS-mixtures, or even pure CHOS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities. Understanding the mechanisms underlying these bioactivities is of major importance. However, so far in-depth knowledge on the mode-of-action of CHOS is scarce, one major reason being that most published studies are done with badly characterized heterogeneous mixtures of CHOS. Production of CHOS that are well-defined in terms of length, degree of N-acetylation, and sequence is not straightforward. Here we provide an overview of techniques that may be used to produce and characterize reasonably well-defined CHOS fractions. We also present possible medical applications of CHOS, including tumor growth inhibition and inhibition of T(H)2-induced inflammation in asthma, as well as use as a bone-strengthener in osteoporosis, a vector for gene delivery, an antibacterial agent, an antifungal agent, an anti-malaria agent, or a hemostatic agent in wound-dressings. By using well-defined CHOS-mixtures it will become possible to obtain a better understanding of the mechanisms underlying these bioactivities.

Inhibition of acidic mammalian chitinase by RNA interference suppresses ovalbumin-sensitized allergic asthma

Asthma, a chronic helper T cell type 2-mediated inflammatory disease, is characterized by airway hyperresponsiveness and inflammation. Growing evidence suggests that increased expression of acidic mammalian chitinase (AMCase) may play a role in the pathogenesis of asthma. In the present study, we sought to develop an RNA interference approach to suppress allergic asthma in mice through silencing of AMCase expression. Mice sensitized with ovalbumin (OVA) were intratracheally administered a recombinant adeno-associated virus expressing short hairpin RNA (rAAV-shRNA) against AMCase. In OVA-sensitized mice, the development of allergic symptoms was significantly associated with elevated AMCase expression. After administration of rAAV-shRNA, there was a significant reduction of AMCase expression in the lung and in bronchoalveolar lavage fluid (BALF) cells of sensitized mice. Sensitized mice receiving rAAV-shRNA showed a significant improvement in allergic symptoms, including airway hyperresponsiveness (AHR), eosinophil infiltration, eotaxin, interleukin-13 secretion in BALF, and serum OVA-specific IgE level. Our data suggest the hyperexpression of AMCase in asthma can be suppressed by rAAV-mediated shRNA. Silencing AMCase expression by shRNA may be a promising therapeutic strategy in asthma.

Potential role of chitinase 3-like-1 in inflammation-associated carcinogenic changes of epithelial cells

The family of mammalian chitinases includes members both with and without glycohydrolase enzymatic activity against chitin, a polymer of N-acetylglucosamine. Chitin is the structural component of fungi, crustaceans, insects and parasitic nematodes, but is completely absent in mammals. Exposure to antigens containing chitin- or chitin-like structures sometimes induces strong T helper type-I responses in mammals, which may be associated with the induction of mammalian chitinases. Chitinase 3-like-1 (CHI3L1), a member of the mammalian chitinase family, is induced specifically during the course of inflammation in such disorders as inflammatory bowel disease, hepatitis and asthma. In addition, CHI3L1 is expressed and secreted by several types of solid tumors including glioblastoma, colon cancer, breast cancer and malignant melanoma. Although the exact function of CHI3L1 in inflammation and cancer is still largely unknown, CHI3L1 plays a pivotal role in exacerbating the inflammatory processes and in promoting angiogenesis and remodeling of the extracellular matrix. CHI3L1 may be highly involved in the chronic engagement of inflammation which potentiates development of epithelial tumorigenesis presumably by activating the mitogen-activated protein kinase and the protein kinase B signaling pathways. Anti-CHI3L1 antibodies or pan-chitinase inhibitors may have the potential to suppress CHI3L1-mediated chronic inflammation and the subsequent carcinogenic change in epithelial cells.

Acidic mammalian chitinase in dry eye conditions

PURPOSE

An acidic mammalian chitinase (AMCase) seems to be implicated in allergic asthma and allergic ocular pathologies. The aim of this work was to investigate the role of AMCase during Sjögren's Syndrome (SS) and Meibomian Gland Dysfunction (MGD) dry eye diseases.

METHODS

Six patients with MGD dry eye (20-58 years, median 40) and six patients with dry eye associated to SS (32-60 years, median 47) were enrolled in this study. AMCase activity was measured in tears and AMCase mRNA expression was evaluated by real-time polymerase chain reaction from RNA extracted from epithelial cells of the conjunctiva. Six healthy adult subjects of the same age (34-44 years, median 39) were also studied as the control group.

RESULTS

AMCase activity was significantly increased in patients affected by MGD dry eye (18.54 +/- 1.5 nmol/ml/h) and SS dry eye (8.94 +/- 1.0 nmol/ml/h) respectively, compared to healthy controls (1.6 +/- 0.2 nmol/ml/h). AMCase activity was higher in the tears of subjects with MGD dry eye (P < 0.001). AMCase mRNA was detected in conjunctival epithelial cells and the expression was significantly higher in MGD dry eye than SS dry eye. A significant correlation between AMCase activity in the tears and mRNA in conjunctival epithelial cells was found.

CONCLUSION

AMCase may be an important marker in the pathogenesis of dry eye, suggesting the potential role of AMCase as a therapeutic target in these frequent pathologies.

Chitinases and chitinase-like proteins: potential therapeutic targets for the treatment of T-helper type 2 allergies

Mammalian chitinase and chitinase-like proteins (CLPs) are a family of mediators increasingly associated with infection, T cell-mediated inflammation, wound healing, allergy and asthma. Although our current knowledge of the function of mammalian chitinases and CLPs is very limited, important information can be deduced from research carried out in lower organisms, and in different immunopathological conditions. Enzymatically active mammalian chitinase proteins may have evolved to degrade the copious amounts of chitin mammals are exposed to on a daily basis, and to form an innate barrier to chitin-containing organisms. CLPs are homologous to chitinases but lack the ability to degrade chitin. It is most striking that both chitinases and CLPs are up-regulated in T-helper type 2 (Th2)-driven conditions, and the first evidence is now emerging that these proteins may accentuate Th2 reactivity, and possibly contribute to the repair process that follows inflammation. Following studies demonstrating that chitinase inhibition leads to an attenuated allergic response, several strategies are being used to develop enzyme inhibitors for therapeutic use in human diseases. In this review, we will summarize recent insights into the effects of chitinases and CLPs in the context of Th2-dominated pathology with particular focus on allergy and asthma, discussing whether chitinase enzyme inhibitors may be of therapeutic value.

Chitin, chitinases and chitinase-like proteins in allergic inflammation and tissue remodeling

Chitin, the second most abundant polysaccharide in nature after cellulose, consist exoskeleton of lower organisms such as fungi, crustaceans and insects except mammals. Recently, several studies evaluated immunologic effects of chitin in vivo and in vitro and revealed new aspects of chitin regulation of innate and adaptive immune responses. It has been shown that exogenous chitin activates macrophages and other innate immune cells and also modulates adaptive type 2 allergic inflammation. These studies further demonstrate that chitin stimulate macrophages by interacting with different cell surface receptors such as macrophage mannose receptor, toll-like receptor 2 (TLR-2), C-type lectin receptor Dectin-1, and leukotriene B4 receptor (BLT1). On the other hand, a number of chitinase or chitinase-like proteins (C/CLP) are ubiquitously expressed in the airways and intestinal tracts from insects to mammals. In general, these chitinase family proteins confer protective functions to the host against exogenous chitin-containing pathogens. However, substantial body of recent studies also set light on new roles of C/CLP in the development and progression of allergic inflammation and tissue remodeling. In this review, recent findings on the role of chitin and C/CLP in allergic inflammation and tissue remodeling will be highlighted and controversial and unsolved issues in this field of studies will be discussed.