Metabolic transition in the development of Hymenolepis diminuta (Cestoda)

Tandem Mass Tagging (TMT) Reveals Tissue-Specific Proteome of L4 Larvae of Anisakis simplex s. s.: Enzymes of Energy and/or Carbohydrate Metabolism as Potential Drug Targets in Anisakiasis

Anisakis simplex s. s. is a parasitic nematode of marine mammals and causative agent of anisakiasis in humans. The cuticle and intestine of the larvae are the tissues most responsible for direct and indirect contact, respectively, of the parasite with the host. At the L4 larval stage, tissues, such as the cuticle and intestine, are fully developed and functional, in contrast to the L3 stage. As such, this work provides for the first time the tissue-specific proteome of A. simplex s. s. larvae in the L4 stage. Statistical analysis (FC ≥ 2; p-value ≤ 0.01) showed that 107 proteins were differentially regulated (DRPs) between the cuticle and the rest of the larval body. In the comparison between the intestine and the rest of the larval body at the L4 stage, 123 proteins were identified as DRPs. Comparison of the individual tissues examined revealed a total of 272 DRPs, with 133 proteins more abundant in the cuticle and 139 proteins more abundant in the intestine. Detailed functional analysis of the identified proteins was performed using bioinformatics tools. Glycolysis and the tricarboxylic acid cycle were the most enriched metabolic pathways by cuticular and intestinal proteins, respectively, in the L4 stage of A. simplex s. s. The presence of two proteins, folliculin (FLCN) and oxoglutarate dehydrogenase (OGDH), was confirmed by Western blot, and their tertiary structure was predicted and compared with other species. In addition, host–pathogen interactions were identified, and potential new allergens were predicted. The result of this manuscript shows the largest number of protein identifications to our knowledge using proteomics tools for different tissues of L4 larvae of A. simplex s. s. The identified tissue-specific proteins could serve as targets for new drugs against anisakiasis.

Stage-specific transcriptomic analysis of the model cestode Hymenolepis microstoma

Most parasitic flatworms go through different life stages with important physiological and morphological changes. In this work, we used a transcriptomic approach to analyze the main life-stages of the model tapeworm Hymenolepis microstoma (eggs, cysticercoids, and adults). Our results showed massive transcriptomic changes in this life cycle, including key gene families that contribute substantially to the expression load in each stage. In particular, different members of the cestode-specific hydrophobic ligand-binding protein (HLBP) family are among the most highly expressed genes in each life stage. We also found the transcriptomic signature of major metabolic changes during the transition from cysticercoids to adult worms. Thus, this work contributes to uncovering the gene expression changes that accompany the development of this important cestode model species, and to the best of our knowledge represents the first transcriptomic study with robust replicates spanning all of the main life stages of a tapeworm.

Complex I and II Subunit Gene Duplications Provide Increased Fitness to Worms

Helminths use an alternative mitochondrial electron transport chain (ETC) under hypoxic conditions, such as those found in the gastrointestinal tract. In this alternative ETC, fumarate is the final electron acceptor and rhodoquinone (RQ) serves as an electron carrier. RQ receives electrons from reduced nicotinamide adenine dinucleotide through complex I and donates electrons to fumarate through complex II. In this latter reaction, complex II functions in the opposite direction to the conventional ETC (i.e., as fumarate reductase instead of succinate dehydrogenase). Studies in Ascaris suum indicate that this is possible due to changes in complex II, involving alternative succinate dehydrogenase (SDH) subunits SDHA and SDHD, derived from duplicated genes. We analyzed helminth genomes and found that distinct lineages have different gene duplications of complex II subunits (SDHA, SDHB, SDHC, and SDHD). Similarly, we found lineage-specific duplications in genes encoding complex I subunits that interact with quinones (NDUF2 and NDUF7). The phylogenetic analysis of ETC subunits revealed a complex history with independent evolutionary events involving gene duplications and losses. Our results indicated that there is not a common evolutionary event related to ETC subunit genes linked to RQ. The free-living nematode Caenorhabditis elegans uses RQ and has two genes encoding SDHA (sdha-1 and sdha-2) and two genes encoding NDUF2 (nduf2-1 and nduf2-2). sdha-1 and nduf2-1 are essential genes and have a similar expression pattern during C. elegans lifecycle. Using knockout strains, we found that sdha-2 and nduf2-2 are not essential, even in hypoxia. Yet, sdha-2 and nduf2-2 expression is increased in the early embryo and in dauer larvae, stages where there is low oxygen tension. Strikingly, sdha-1 and sdha-2 as well as nduf2-1 and nduf2-2 showed inverted expression profiles during the C. elegans life cycle. Finally, we found that sdha-2 and nduf2-2 knockout mutant strain progeny is affected. Our results indicate that different complex I and II subunit gene duplications provide increased fitness to worms.

Anthelmintic effects of Oroxylum indicum stem bark extract on juvenile and adult stages of Hymenolepis diminuta (Cestoda), an in vitro and in vivo study

Worldwide, traditional usage of herbal medicines is a common practice to treat various parasitic infections. In India, bark decoction of Oroxylum indicum (L.) Kurz. (Bignoniaceae) is used as a traditional medicine to cure intestinal-helminthic infections. This study investigated the anthelmintic efficacy of methanolic bark extract of O. indicum on Hymenolepis diminuta (Cestoda), using both in vitro and in vivo methods. Utilizing a mini-questionnaire, first, we collected information about the pattern of anthelmintic use of this plant. Later, in vitro efficacy of extract was tested at 10, 20 and 30 mg/ml on both the artificially excysted juveniles and adult H. diminuta worms. Herein, scanning electron microscopy (SEM) was also utilized to determine the possible effects of extract on tegumental surfaces of juvenile and adult cestode. In vivo, extract was tested at 250, 500 and 1000 mg/kg in H. diminuta albino rat model, against juvenile and adult cestode. Praziquantel (PZQ) served as reference drug in anthelmintic assays. The acute toxicity of extract was determined as per the OECD guidelines. The field questionnaire data revealed that 78 % of people in the area use O. indicum stem bark against intestinal helminths, and of these, 75 % of people also believed it highly efficacious anthelmintic remedy. In vitro testing of extract revealed significant effects on juvenile worms, and 30 mg/ml of extract caused mortality of juveniles at the initial period (0.25 ± 0.00 h). Conversely, PZQ (1 mg/ml) showed paralysis and mortality of juvenile cestodes in 0.44 ± 0.04 and 1.11 ± 0.06 h, respectively. As determined by SEM, in vitro exposure to extract showed substantial effects on both juveniles and adult worms in the form of wrinkled scolex, distorted tegument and eroded microtriches. In vivo study revealed better efficacy of extract against juveniles than adult stages of parasite. Treatment of rats with 1000 mg/kg of extract caused 79.3 % reduction in EPG counts and 70.8 % of reduction in worm counts, which compared well to PZQ efficacy. In acute toxicity study, administration of a single oral dose of 2000 mg/kg of extract to mice did not cause any signs of toxicity or mortality within 2-week observation. Hence, the LD50 of extract was estimated to be greater than 2000 mg/kg. In conclusion, the bark extract of O. indicum possesses concentration-dependent effects against the larval and adult H. diminuta worms, and thus the extract holds promise in the control of intestinal helminthiases. This also supports the common belief of people about the reputation of this plant as anthelmintic in traditional medicine. There is a need to standardize the formulations of this plant for their possible use as standardized herbal anthelmintic agents in the future.

Differential kinetics at PK/PEPCK branch point in the cestode, Raillietina echinobothrida

Pyruvate kinase (PK; EC 2.7.1.40) and phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) are essential regulatory enzymes of glucose oxidation in helminths, the PK/PEPCK branch point being the first divergent step between carbohydrate catabolism of the parasites and their hosts. Recently, PEPCK from the cestode parasite, Raillietina echinobothrida, has been purified and characterized. In order to find out the differential kinetics, if any, at PK/PEPCK branch point in the parasite, in this study, we purified and characterized the parasite PK and compared it with the parasite PEPCK. The purified PK displayed standard Michaelis-Menten kinetics with Kmapp of 77.8 µM for its substrate PEP, whereas the Kmapp was 46.9 µM for PEPCK. PEP exhibited differential kinetics at PK/PEPCK branch point of the parasite and behaved as a homotropic effector for PEPCK, but not for PK. The inhibitory constant (Ki) for genistein and daidzein (phytochemicals from Flemingia vestita) was determined and discussed. From these results, we hypothesize that PK/PEPCK branch point is a probable site for anthelmintic action.

Partial reverse of the TCA cycle is enhanced in Taenia crassiceps experimental neurocysticercosis after in vivo treatment with anthelminthic drugs

Neurocysticercosis (NCC) is the most common helminthic infection and neglected disease of the central nervous system. It is the leading cause of acquired epilepsy and seizures worldwide. Therefore, to study this important neglected disease, it is important to use experimental models. There is no report in the literature on how the parasite's metabolism reacts to antihelminthic treatment when it is still within the central nervous system of the host. Therefore, the aim of this study was to investigate the energetic metabolism of cysticerci experimentally inoculated in the encephala of BALB/c mice after treatment with low dosages (not sufficient to kill the parasite) of albendazole (ABDZ) and praziquantel (PZQ). BALB/c mice were intracranially inoculated with Taenia crassiceps cysticerci and, after 30 days, received treatment with low dosages of ABDZ and PZQ. After 24 h of treatment, the mice were euthanized, and the cysticerci were removed and analyzed through high-performance liquid chromatography (HPLC) to quantify the organic acids related to the energetic metabolism of the parasite. The partial reverse of the TCA cycle was enhanced by the ABDZ and PZQ treatments both with the higher dosage, as the organic acids of this pathway were significantly increased when compared to the control group and to the other dosages. In conclusion, it was possible to detect the increase of this pathway in the parasites that were exposed to low dosages of ABDZ and PZQ, as it is a mechanism that would amplify the energy production in a hostile environment.

Hymenolepis diminuta: mitochondrial transhydrogenase as an additional site for anaerobic phosphorylation

Employing adult Hymenolepis diminuta SMP and exogenous pyridine nucleotide-generating systems, reduced pyridine nucleotide-dependent net 32P incorporation into ATP was examined. NADH supported rotenone-sensitive 32P incorporation and this rate increased markedly with fumarate addition, in keeping with an active fumarate reductase. Interestingly, corresponding evaluations with NADPH did not result in detectable phosphorylation in the absence or presence of fumarate. However, with NAD addition, but without NAD generation, active NADPH-dependent phosphorylation occurred, thereby demonstrating mitochondrial transhydrogenase involvement, and 32P incorporation increased significantly with fumarate addition. More importantly, in the presence of rotenone and both NADPH and NAD generation, significant net 32P incorporation was noted, but was undetectable in the presence of DCCD or protonophores (e.g., niclosamide). Without NAD generation, minimal phosphorylation occurred. These data demonstrate that with ongoing NADPH and NAD generation, the H. diminuta, proton-translocating, mitochondrial transhydrogenase can serve as an additional anaerobic phosphorylation site. A model is presented.

Cyanide-resistant respiration in Taenia crassiceps metacestode (cysticerci) is explained by the H2O2-producing side-reaction of respiratory complex I with O2

The nature of the cyanide-resistant respiration of Taenia crassiceps metacestode was studied. Mitochondrial respiration with NADH as substrate was partially inhibited by rotenone, cyanide and antimycin in decreasing order of effectiveness. In contrast, respiration with succinate or ascorbate plus N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was more sensitive to antimycin and cyanide. The saturation kinetics for O2 with NADH as substrate showed two components, which exhibited different oxygen affinities. The high-O2-affinity system (Km app=1.5 microM) was abolished by low cyanide concentration; it corresponded to cytochrome aa3. The low-O2-affinity system (Km app=120 microM) was resistant to cyanide. Similar O2 saturation kinetics, using succinate or ascorbate-TMPD as electron donor, showed only the high-O2-affinity cyanide-sensitive component. Horse cytochrome c increased 2-3 times the rate of electron flow across the cyanide-sensitive pathway and the contribution of the cyanide-resistant route became negligible. Mitochondrial NADH respiration produced significant amounts of H2O2 (at least 10% of the total O2 uptake). Bovine catalase and horse heart cytochrome c prevented the production and/or accumulation of H2O2. Production of H2O2 by endogenous respiration was detected in whole cysticerci using rhodamine as fluorescent sensor. Thus, the CN-resistant and low-O2-affinity respiration results mainly from a spurious reaction of the respiratory complex I with O2, producing H2O2. The meaning of this reaction in the microaerobic habitat of the parasite is discussed.

Rhodoquinone reaction site of mitochondrial complex I, in parasitic helminth, Ascaris suum

The components and organization of the respiratory chain in helminth mitochondria vary remarkably depending upon the stage of the life cycle. Mitochondrial complex I in the parasitic helminth Ascaris suum uses ubiquinone-9 (UQ(9)) and rhodoquinone-9 (RQ(9)) under aerobic and anaerobic conditions, respectively. In this study, we investigated structural features of the quinone reduction site of A. suum complex I using a series of quinazoline-type inhibitors and also by the kinetic analysis of rhodoquinone-2 (RQ(2)) and ubiquinone-2 (UQ(2)) reduction. Structure-activity profiles of the inhibition by quinazolines were comparable, but not completely identical, between NADH-RQ(2) and NADH-UQ(2) oxidoreductase activities. However, the inhibitory mechanism of quinazolines was competitive and partially competitive against RQ(2) and UQ(2), respectively. The pH profiles of both activities differed remarkably; NADH-RQ(2) oxidoreductase activity showed an optimum pH at 7.6, whereas NADH-UQ(2) oxidoreductase activity showed two optima pH at 6.4 and 7.2. Our results indicate that although A. suum complex I uses both RQ(2) and UQ(2) as an electron acceptor, the manner of reaction (or binding) of the two quinones differs.

An anthelmintic compound, nafuredin, shows selective inhibition of complex I in helminth mitochondria

Infections with parasitic helminths are important causes of morbidity and mortality worldwide. New drugs that are parasite specific and minimally toxic to the host are needed to counter these infections effectively. Here we report the finding of a previously unidentified compound, nafuredin, from Aspergillus niger. Nafuredin inhibits NADH-fumarate reductase (complexes I + II) activity, a unique anaerobic electron transport system in helminth mitochondria, at nM order. It competes for the quinone-binding site in complex I and shows high selective toxicity to the helminth enzyme. Moreover, nafuredin exerts anthelmintic activity against Haemonchus contortus in in vivo trials with sheep. Thus, our study indicates that mitochondrial complex I is a promising target for chemotherapy, and nafuredin is a potential lead compound as an anthelmintic isolated from microorganisms.

An anthelmintic compound, nafuredin, shows selective inhibition of complex I in helminth mitochondria

Infections with parasitic helminths are important causes of morbidity and mortality worldwide. New drugs that are parasite specific and minimally toxic to the host are needed to counter these infections effectively. Here we report the finding of a previously unidentified compound, nafuredin, from Aspergillus niger. Nafuredin inhibits NADH-fumarate reductase (complexes I + II) activity, a unique anaerobic electron transport system in helminth mitochondria, at nM order. It competes for the quinone-binding site in complex I and shows high selective toxicity to the helminth enzyme. Moreover, nafuredin exerts anthelmintic activity against Haemonchus contortus in in vivo trials with sheep. Thus, our study indicates that mitochondrial complex I is a promising target for chemotherapy, and nafuredin is a potential lead compound as an anthelmintic isolated from microorganisms.