Structural modeling and simulation studies of Brugia malayi glutathione-S-transferase with compounds exhibiting antifilarial activity: Implications in drug targeting and designing

Antifilarial efficacy of andrographolide: Ex vivo studies on bovine filarial parasite Setaria cervi

Lymphatic filariasis caused by filarial nematode is an important disease leading to considerable morbidity throughout tropical countries. Even after specific elimination programs, the disease continue to spread in endemic countries. Thus newer therapeutic interventions are urgently needed to control the spread. In the present study, we have seen the effect of andrographolide (andro), a diterpenoid lactone from the leaves of Andrographis paniculata on filarial parasite Setaria cervi. There was time and concentration dependent decrease in motility and viability leading to death of parasite after 6 h of the exposure of andro. Andro showed potential antifilarial activity with an IC₅₀ value of 24.80 μM assessed through MTT assay. There was concentration dependent decrease in the antioxidant enzymes activity and increase in proapoptotic markers after 5 h exposure of andro. Further, molecular docking analysis revealed that andro binds with filarial glutathione-S-transferase at glutathione (GSH) binding site and inhibiting enzyme activity competitively. Andro induced oxidative stress mediated apoptosis in parasites as evidenced by increase in the intracellular reactive oxygen species (ROS) and apoptotic markers.Therefore this study suggested that andro could be further explored as a new antifilarial drug.

Antibacterial, Anticandidal, and Antibiofilm Potential of Fenchone: In Vitro, Molecular Docking and In Silico/ADMET Study

The aim of the present study is to investigate the effective antimicrobial and antibiofilm properties of fenchone, a biologically active bicyclic monoterpene, against infections caused by bacteria and Candida spp. The interactions between fenchone and three distinct proteins from Escherichia coli (β-ketoacyl acyl carrier protein synthase), Candida albicans (1, 3-β−D-glucan synthase), and Pseudomonas aeruginosa (Anthranilate-CoA ligase) were predicted using molecular docking and in silico/ADMET methods. Further, to validate the in-silico prediction, the antibacterial and antifungal potential of fenchone was evaluated against E. coli, P. aeruginosa, and C. albicans by determining minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC), and minimum fungicidal concentration (MFC). The lowest MIC/MBC values of fenchone against E. coli and P. aeruginosa obtained was 8.3 ± 3.6/25 ± 0.0 and 266.6 ± 115.4/533.3 ± 230.9 mg/mL, respectively, whereas the MIC/MFC value for C. albicans was found to be 41.6 ± 14.4/83.3 ± 28.8 mg/mL. It was observed that fenchone has a significant effect on antimicrobial activity (p < 0.05). Our findings demonstrated that fenchone at 1 mg/mL significantly reduced the production of biofilm (p < 0.001) in E. coli, P. aeruginosa, and C. albicans by 70.03, 64.72, and 61.71%, respectively, in a dose-dependent manner when compared to control. Based on these results, it has been suggested that the essential oil from plants can be a great source of pharmaceutical ingredients for developing new antimicrobial drugs.

Polycyclic aromatic hydrocarbons in the cestode Oncomegas wageneri parasite of Mexican flounder Cyclopsetta chittendeni

The concentrations of polycyclic aromatic hydrocarbon metabolites (PAHm) and their bioconcentration factors (BCF) were determined in the larval stages of the cestode Oncomegas wageneri, recovered from the intestine of the Mexican flounder Cyclopsetta chittendeni, in the southern Gulf of Mexico. The PAHm concentrations in O. wageneri were measured using fixed-wavelength fluorescence spectrometry and compared with PAHm concentrations in host bile. Oncomegas wageneri PAHm concentrations were markedly higher than those in host tissues. The highest BCF values were obtained for 1-hydroxypyrene (OHP) and benzo(a)pyrene (BaP). Using a General Linear Model, a significant negative relationship was found between O. wageneri PAHm concentrations (as response variable) and the number of O. wageneri and oil well proximity. Low BCF values and PAHm concentrations in C. chittendeni correlated positively with O. wageneri PAHm concentrations. In contrast, high BCF values for PAHm concentrations in C. chittendeni had a negative association with O. wageneri PAHm concentrations. This study provides the first evidence of the presence of PAHm in intestinal larval cestodes of marine flatfishes, demonstrating levels of PAHm that were higher than levels in their hosts.

Virtual screening and docking of lead like molecules against Glutathione-S-Transferase protein from Brugia malayi

Glutathione-S-transferase(s) (GST) is an important chemotherapeutic target in lymphatic filarasis caused by Brugia malayi and Wuchereria bancrofti. It has been playing an important role as major detoxification enzyme and help in intracellular transportation of hydrophobic substrates. Therefore, it is of interest to screen GST from Brugia malayi with millions of known ligands at the ZINC database using AUTODOCK for the identification of potential inhibitors with improved binding characteristics. We report two potent inhibitors ZINC00179016 and ZINC08385519 which are the molecules of pyrrolidinedione and benzimidazole families respectively as potential inhibitors of GST from Brugia malayi with suitable binding properties.

The effect of β-glucan and its potential analog on the structure of Dectin-1 receptor

Dectin-1 is a recently discovered pattern-recognition receptor that plays an important role in antifungal innate immunity, which acts a specific receptor for β-glucan (BG). The present study, aimed at clarifying effect of BG and a new analog, maltotriose (MT) on Dectin-1 receptor. We implemented molecular docking of MT on Dectin-1 along with model-independent all-atom-molecular dynamics simulations. Simulations were carried out at three levels of complexity: (1) Apo-Dectin-1; (2) BG:Dectin-1; (3) MT:Dectin-1. All three system complexes were undergone stability check before showing a comparative analysis. A characteristic feature, noted for the MT:Dectin-1, is a shifting of loops (loop1 and loop2) orientation towards atoms of MT, a broad interaction suggested a robust and tight binding on comparison with BG:Dectin-1. Free energy estimation corroborated the observation, which furthermore, made a close agreement by revealing contribution of energy components of interacting residues. In addition, cluster analysis of complexes exhibit a smooth continuous transition to a new confirmation, represented by a series of clusters each having a longer lifetime. Principal component analysis revealed a broken pipe at binding site of BG:Dectin-1 during movement of atoms whereas in MT:Dectin-1 exhibited wide band and high amplitude motion of atoms in trajectory, was due to loop orientation toward MT. Observation was further shown by measuring distances and hydrogen binding calculation. Simulations of the BG:Dectin-1 and MT:Dectin-1 complex revealed first time the influence of BG and MT ligands. This study might extend the knowledge of the BG and MT interaction on Dectin-1 and proposed further potential bioassay of MT.

Two decades of antifilarial drug discovery: a review

Filariasis is one of the oldest, most debilitating, disabling, and disfiguring neglected tropical diseases with various clinical manifestations and a low rate of mortality, but has a high morbidity rate, which results in social stigma.

The Role of Xenobiotic-Metabolizing Enzymes in Anthelmintic Deactivation and Resistance in Helminths

Xenobiotic-metabolizing enzymes (XMEs) modulate the biological activity and behavior of many drugs, including anthelmintics. The effects of anthelmintics can often be abolished by XMEs when the drugs are metabolized to an inefficient compound. XMEs therefore play a significant role in anthelmintic efficacy. Moreover, differences in XMEs between helminths are reflected by differences in anthelmintic metabolism between target species. Taking advantage of the newly sequenced genomes of many helminth species, progress in this field has been remarkable. The present review collects up to date information regarding the most important XMEs (phase I and phase II biotransformation enzymes; efflux transporters) in helminths. The participation of these XMEs in anthelmintic metabolism and their possible roles in drug resistance are evaluated.

Copper(II) oxide nanoparticles augment antifilarial activity of Albendazole: In vitro synergistic apoptotic impact against filarial parasite Setaria cervi

Mass treatment of lymphatic filariasis with Albendazole (ABZ), a therapeutic benzimidazole, is fraught with serious limitations such as possible drug resistance and poor macrofilaricidal activity. Therefore, we need to develop new ABZ-based formulations to improve its antifilarial effectiveness. CuO nanoparticles were used as an adjuvant with ABZ to form ABZ-CuO nanocomposite, which was characterized by UV-vis spectroscopy, FT-IR, AFM and SEM. Antifilarial activity of nanocomposite was evaluated using relative motility assay and dye exclusion test in dark and under UV light. ROS generation, antioxidant levels, lipid peroxidation and DNA fragmentation in nanocomposite treated parasites were estimated. Biophysical techniques were employed to ascertain the mode of binding of nanocomposite to parasitic DNA. Nanocomposite increases parasite mortality as compared to ABZ in dark, and its antifilarial effect was increased further under UV light. Elevated ROS production and decline of parasitic-GST and GSH levels were observed in nanocomposite treated worms in dark, and these effects were pronounced further under UV light. Nanocomposite leads to higher DNA fragmentation as compared to ABZ alone. Further, we found that nanocomposite binds parasitic DNA in an intercalative manner where it generates ROS to induce DNA damage. Thus, oxidative stress production due to ROS generation and consequent DNA fragmentation leads to apoptosis in worms. This is the first report supporting CuO nanoparticles as a potential adjuvant with ABZ against filariasis along with enhanced antifilarial activity of nanocomposite under UV light. These findings, thus, indicate that development of ABZ-loaded nanoparticle compounds may serve as promising leads for filariasis treatment.

Essential proteins and possible therapeutic targets of Wolbachia endosymbiont and development of FiloBase--a comprehensive drug target database for Lymphatic filariasis

Lymphatic filariasis (Lf) is one of the oldest and most debilitating tropical diseases. Millions of people are suffering from this prevalent disease. It is estimated to infect over 120 million people in at least 80 nations of the world through the tropical and subtropical regions. More than one billion people are in danger of getting affected with this life-threatening disease. Several studies were suggested its emerging limitations and resistance towards the available drugs and therapeutic targets for Lf. Therefore, better medicine and drug targets are in demand. We took an initiative to identify the essential proteins of Wolbachia endosymbiont of Brugia malayi, which are indispensable for their survival and non-homologous to human host proteins. In this current study, we have used proteome subtractive approach to screen the possible therapeutic targets for wBm. In addition, numerous literatures were mined in the hunt for potential drug targets, drugs, epitopes, crystal structures, and expressed sequence tag (EST) sequences for filarial causing nematodes. Data obtained from our study were presented in a user friendly database named FiloBase. We hope that information stored in this database may be used for further research and drug development process against filariasis. URL: http://filobase.bicpu.edu.in.

Nematicidal activity of acetophenones and chalcones against Meloidogyne incognita and structure-activity considerations

BACKGROUND

With the ultimate goal of identifying new compounds active against root-knot nematodes, a set of 14 substituted chalcones were synthesised, starting from acetophenones. These chalcones and various acetophenones were tested in vitro against Meloidogyne incognita.

RESULTS

The most potent acetophenones were 4-nitroacetophenone and 4-iodoacetophenone, with EC(50/24 h) values of 12 ± 5 and 15 ± 4 mg L(-1) respectively, somewhat weaker than that of the chemical control fosthiazate in our previous experiments (EC(50/24 h) 0.4 ± 0.3 mg L(-1)). When we converted the acetophenones to chalcones, the nematicidal activity differed, based on their substitution pattern. The condensation of 4-nitroacetophenone with 2,4,6-trihydroxybenzaldehyde to give the corresponding chalcone (E)-1-(4-nitrophenyl)-3-(2,4,6-trihydroxyphenyl)prop-2-en-1-one led to a slight reduction in activity (EC(50/24 h) value 25 ± 17 mg L(-1)). Moreover, (E)-3-(2-hydroxy-5-iodophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one showed better activity (EC(50/24) h value 26 ± 15 mg L(-1)) than 4-methoxyacetophenone (EC(50/24 h) value 43 ± 10 mg L(-1)).

CONCLUSIONS

Acetophenones and chalcones may represent good leads in the discovery of new nematicidal compounds and may have potential use in crop management as active ingredients.

The cytochrome P450 family in the parasitic nematode Haemonchus contortus

Haemonchus contortus, a highly pathogenic and economically important parasitic nematode of sheep, is particularly adept at developing resistance to the anthelmintic drugs used in its treatment and control. The basis of anthelmintic resistance is poorly understood for many commonly used drugs with most research being focused on mechanisms involving drug targets or drug efflux. Altered or increased drug metabolism is a possible mechanism that has yet to receive much attention despite the clear role of xenobiotic metabolism in pesticide resistance in insects. The cytochrome P450s (CYPs) are a large family of drug-metabolising enzymes present in almost all living organisms, but for many years thought to be absent from parasitic nematodes. In this paper, we describe the CYP sequences encoded in the H. contortus genome and compare their expression in different parasite life-stages, sexes and tissues. We developed a novel real-time PCR approach based on partially assembled CYP sequences "tags" and confirmed findings in the subsequent draft genome with RNA-seq. Constitutive expression was highest in larval stages for the majority of CYPs, although higher expression was detected in the adult male or female for a small subset of genes. Many CYPs were expressed in the worm intestine. A number of H. contortus genes share high identity with Caenorhabditis elegans CYPs and the similarity in their expression profiles supports their classification as putative orthologues. Notably, H. contortus appears to lack the dramatic CYP subfamily expansions seen in C. elegans and other species, which are typical of CYPs with exogenous roles. However, a small group of H. contortus genes cluster with the C. elegans CYP34 and CYP35 subfamilies and may represent candidate xenobiotic metabolising genes in the parasite.

Functional analysis of genetic polymorphism in Wuchereria bancrofti glutathione S-transferase antioxidant gene: impact on protein structure and enzyme catalysis

Wuchereria bancrofti glutathione S-transferase (Wb-GST) is referred as a promising chemotherapeutic target for lymphatic filariasis. GST represents the major class of detoxifying enzymes of the tissue dwelling parasitic helminths. Though many inhibition studies were carried out for Wb-GST, understanding its genetic distribution in parasite population is necessary to develop ideal inhibitor. Our genetic polymorphic studies exposed the existence of three variant Wb-GST alleles in the four endemic regions of India. Moreover, it also revealed the variability in the distribution of Wb-GST alleles in the studied population. Therefore we cloned, expressed and purified the recombinant variant Wb-GST proteins to study the mutation impact on its structure and hence on its catalysis. Among the studied mutations, the I60F/G78S substitutions in the N-terminal domain and loop region connecting the two domains of Wb-GST lowered the affinity for glutathione and its analog, S-hexyl glutathione. Moreover, molecular modeling and docking studies revealed that the I60F/G78S mutations affected the proximity of Trp38 and Arg95 in glutathione binding site resulting in weaker interaction with S-hexyl glutathione. Besides, the variants also had lower affinity (Ki) and higher IC50 values for well-known GST inhibitors. Interestingly, the Wb-GST variant proteins showed enhanced catalytic efficiency for lipid peroxidation products which are produced due to oxidative stress. Thus, our study provides evidence for the functional impact of mutations on Wb-GST protein and also spotlights the mechanisms of parasite survival against the host oxidative stress environment.

Current drug targets for helminthic diseases

More than 2 billion people are infected with helminth parasites across the globe. The burgeoning drug resistance against current anthelmintics in parasitic worms of humans and livestock requires urgent attention to tackle these recalcitrant worms. This review focuses on the advancements made in the area of helminth drug target discovery especially from the last few couple of decades. It highlights various approaches made in this field and enlists the potential drug targets currently being pursued to target economically important helminth species both from human as well as livestock to combat disease pathology of schistosomiasis, onchocerciasis, lymphatic filariasis, and other important macroparasitic diseases. Research in the helminths study is trending to identify potential and druggable targets through genomic, proteomic, biochemical, biophysical, in vitro experiments, and in vivo experiments in animal models. The availability of major helminths genome sequences and the subsequent availability of genome-scale functional datasets through in silico search and prioritization are expected to guide the experimental work necessary for target-based drug discovery. Organized and documented list of drug targets from various helminths of economic importance have been systematically covered in this review for further exploring their use and applications, which can give physicians and veterinarians effective drugs in hand to enable them control worm infections.

Structural and catalytic role of two conserved tyrosines in Delta-class glutathione S-transferase from Locusta migratoria

Glutathione S-transferases (GSTs) are an important family of detoxifying enzymes and play a key role in pesticide resistance in the insect. Tyrosine is essential for its detoxification function. In the present study, two conserved tyrosine residues are located at positions 108 and 116 in H-site of LmGSTD1. To elucidate how the two residues participate in the catalytic process and keeping structural stability, four mutants, Y108A, Y108E, Y116A, and Y116E, were generated. It was found that the four mutants affected the specific activity of LmGSTD1 in various degrees, depending on the types of substrate and reaction mechanism. Steady-state kinetics assay revealed that Y108E and Y116E had a significant influence on GSH-binding ability, which indicates the two tyrosine residues of H-site contribute to topology rearrangement of G-site. Both Y116A and Y116E exhibited lower CDNB-binding affinity, suggesting that Y116 takes part in hydrophobic substrate binding. The thermostability assay, intrinsic, and 8-anilino-1-naphthalenesulfonic acid (ANS) florescence results showed that the two tyrosine residues were involved in regulation of active-site conformation. Finally, homology modeling provided evidence that the two tyrosines in H-site participate in hydrophobic substrate binding. Furthermore, Y108 is closer to the S atom of S-hexylglutathione. In conclusion, the two tyrosines in LmGSTD1 are important residues in both the catalytic process and protein stability.

Comparative structural modeling and docking studies of oxalate oxidase: Possible implication in enzyme supplementation therapy for urolithiasis

In humans oxalate is end product of protein metabolism, with no enzyme present to act on it. In conditions of its enhanced endogenous synthesis or increased absorption from the diet, oxalate accumulation leads to hyperoxaluria which can further lead to a number of pathological conditions including urolithiasis. Urolithiasis has been a perplexing problem due to its high incidence and rate of recurrence after treatment like Extracorporeal-shock wave lithotripsy (ESWL). Hence other prophylactic treatment becomes necessary. One of the newer approaches of curing such metabolic disorders is the enzyme supplementation therapy. Oxalate oxidase (OxOx) is a commonly occurring enzyme in plants, bacteria and fungi that catalyses oxidative cleavage of oxalate to CO(2) with reduction of dioxygen to H(2)O(2). Present study, used Hordeum vulgare OxOx crystal structure (PDB ID 2ET1A) as a template for constructing 3D models of OxOx from Triticum aestivum, Arabidopsis thaliana, Sclerotiana sclerotiarum. Similarly Homology models for isoforms Ceriporiopsis subvermispora 336, C. subvermispora 422 were constructed by using template Bacillus subtilis oxalate decarboxylase (Oxdc) (PDB ID 2UY8A) by comparative modeling approach in SWISS MODEL, MODELLER, 3D JIGSAW and GENO 3D program server. Based on overall stereochemical quality (PROCHECK, PROSA, VARIFY 3D), best models were selected, energy minimized, refined and characterized for active site in BioMed CaChe V 6.1 workspace. Selected models were further studied for structure function relationship with substrate (oxalate) and its analogue (glycolate) by using docking approach. Calculated interaction energy between the oxalate and constructed enzyme indicated that homology models for OxOx of T. aestivum, A. thaliana and S. sclerotiarum, can account for better regio-specificity of this enzyme towards oxalate. That supports the interested metabolism and thus may further implement in enzyme supplementation therapy for urolithiasis.

The role of a Brugia malayi p38 MAP kinase ortholog (Bm-MPK1) in parasite anti-oxidative stress responses

Filariasis, caused by thread-like nematode worms, affects millions of individuals throughout the tropics and is a major cause of acute and chronic morbidity. Filarial nematodes effectively evade host immunological responses and are long lived within their hosts. Recently an emphasis has been placed on enzymatic and non-enzymatic anti-oxidant systems which counteract the generation of reactive oxygen species (ROS) by macrophages and granulocytes, a first line of defense against parasites. We have characterized an anti-oxidant pathway in the filarial parasite Brugia malayi related to the evolutionarily conserved human mitogen-activated p38 protein kinase and the Caenorhabditis elegans PMK-1 protein kinase stress pathways. We have expressed a recombinant p38/PMK-1 ortholog from B. malayi (Bm-MPK1) and have successfully activated the kinase with mammalian upstream kinases. In addition, we have demonstrated inhibition of Bm-MPK1 activity using a panel of known p38 inhibitors. Using the potent and highly selective allosteric p38 inhibitor, BIRB796, we have implicated Bm-MPK1 in a pathway which offers B. malayi protection from the effects of ROS. Our results, for the first time, describe a stress-activated protein kinase pathway within the filarial parasite B. malayi which plays a role in protecting the parasite from ROS. Inhibition of this pathway may have therapeutic benefit in treating filariasis by increasing the sensitivity of filarial parasites to ROS and other reactive intermediates.

Identification of major antigenic peptide of filarial glutathione-S-transferase

In our earlier report, a 26kDa Setaria cervi glutathione-S-transferase showed significant protection (82%) in jirds infected with L3 larvae of Brugia malayi. In the present study we have identified the major antigenic epitopes in ScGST. Carboxypeptidase B has been used to digest the ScGST in to smaller fragments. The digested products were separated as four protein bands on SDS-PAGE. The smallest fragment of 6kDa (P4) from ScGST was identified as major antigenic epitope because of its significant reactivity with jird anti ScGST sera and human filarial sera in immunoblotting. The MALDI-LC/MS sequencing of ScGST P4 peptide ((5)KLTYFSIRGRGLAEPIRL(20), (22)KVPDDQQFLDDLISR(36) and (47)VFHFGQGPHHGPPR(62)) suggested that this protein band has a fragment of 5-62 residues long that matched with the N-terminal end of filarial GST. The antigenicity plot of ScGST was compared with BmGST model and both exhibited three immunogenic peaks within the first 60 residues towards N-terminal. In BmGST the N-terminal region was also detected with N-glycosylation signal peptide NAS adding to its high immunogenic property. Further, P4 showed strong reactivity with IgG1 and IL-4 response in endemic normal sera suggested its role in Th2 response which in turn is correlated with antibody dependent cell mediated cytotoxicity. Thus taking these results into account we propose 5-62 residues long N-terminal peptide of GST as a potential target for further vaccination studies against filarial infection.