Surviving in the fish gut: Comparative inhibitory capacities against the host proteinases in cestodes of the genus Proteocephalus

Currently, little is known about inhibitory substances enabling tapeworms to settle in fish intestines thereby avoiding proteolysis. Contrary to previous studies with certain host-parasite pairs, this research compares the inhibitory capacities in three tapeworm species of the same genus Proteocephalus from four different fishes (P. torulosus from dace and zope, P. sagittus from stone loach and P. cernuae from ruffe). The tapeworm extracts studied significantly reduced the activity of commercial trypsin (although to a lesser degree than the synthetic inhibitor of serine proteinases PMSF), displaying clear inter-specific variation in worms' inhibitory ability. We also measured the proteolytic activity of the host intestinal mucosa exposed to tapeworm extracts which served as inhibitors. Based on per cent inhibition values, all tapeworm extracts significantly suppressed the mucosal proteolytic activity, with marked differences between certain host-parasite pairs. SDS-PAGE electrophoresis of the incubation media and extracts detected in each tapeworm species 20-36 protein bands with apparent molecular weights from 10-12 to 312.5 kDa, mostly below 50 kDa. The incubation medium and extract of each parasite shared one to six bands ranging from 12 to 35 kDa, depending on its species, with only four bands common for two or more species. The band profiles suggest that in various Proteocephalus species inhibitory capacities against host proteinases can be ensured by different proteins.

Localization of the proteinase inhibitor activity in the fish cestode Eubothrium rugosum

The mechanisms enabling fish tapeworms to avoid proteolytic attacks by digestive enzymes of their fish host have been studied in less detail compared with mammalian cestodes. This study aimed to assess the inhibitory ability towards trypsin and chymotrypsin in Eubothrium rugosum, an intestinal parasite of burbot Lota lota, and establish its localization in the tapeworm. To this end, the worms were treated with Triton X-100 followed by differential centrifugation to isolate the tegumental brush border membrane. The protease inhibitory abilities of the worms were mostly determined by their excretory/secretory products released into the incubation medium. These inhibitory abilities proved to be linked mainly with the brush border fractions. Notably, the per cent inhibition of both studied digestive enzymes (trypsin and chymotrypsin) hardly depended on the duration of the parasite exposure in the incubation medium, probably due to intermittent glycocalyx renewal. Improved knowledge on functions of the excretory/secretory proteins produced by fish tapeworms may contribute to a better understanding of host-parasite relations and development of new approaches to the treatment and prevention of diseases caused by pathogenic helminths.

Experimental study of ultrastructural mechanisms and kinetics of tegumental secretion in cestodes parasitizing fish (Cestoda: Diphyllobothriidea)

The structural response and plasticity of the cestode tegument in response to the influence of the host organism is not yet well understood. The main aims of our in vitro study were to analyse the ultrastructural mechanisms and kinetics of tegumental secretion in two cestode species, Dibothriocephalus dendriticus and Ligula interrupta, in response to the influence of fish host blood serum. The incubation of plerocercoids in the culture medium, which contained fish host blood serum, resulted in an increased number of secretory products on the tegumental surface. Our study is the first to experimentally demonstrate the formation of plerocercoid protective layers influenced by the host's internal environment factors. The mechanism of the generation of the protective layer included the following: the intensive formation of organelles in the tegumental cytons and their transfer to the distal cytoplasm of the tegument; increases in extracellular vesicles and vacuoles released on the tegumental surface; arrangement of secretory products and fine-dispersed extracellular matrix in layers; and formation of the protective layer. The structural tegumental response included increases in the glycocalyx layer and structural changes. Our study revealed that the universal mechanism of protective layer formation was intrinsic to different tapeworms. We hypothesize that plerocercoids of cestodes parasitizing fish may use tegumental secretion in the formation of a protective layer and in the release of immunoregulator molecules to evade the host's immune response.

Cestode strobilation: prediction of developmental genes and pathways

BACKGROUND

Cestoda is a class of endoparasitic worms in the flatworm phylum (Platyhelminthes). During the course of their evolution cestodes have evolved some interesting aspects, such as their increased reproductive capacity. In this sense, they have serial repetition of their reproductive organs in the adult stage, which is often associated with external segmentation in a developmental process called strobilation. However, the molecular basis of strobilation is poorly understood. To assess this issue, an evolutionary comparative study among strobilated and non-strobilated flatworm species was conducted to identify genes and proteins related to the strobilation process.

RESULTS

We compared the genomic content of 10 parasitic platyhelminth species; five from cestode species, representing strobilated parasitic platyhelminths, and five from trematode species, representing non-strobilated parasitic platyhelminths. This dataset was used to identify 1813 genes with orthologues that are present in all cestode (strobilated) species, but absent from at least one trematode (non-strobilated) species. Development-related genes, along with genes of unknown function (UF), were then selected based on their transcriptional profiles, resulting in a total of 34 genes that were differentially expressed between the larval (pre-strobilation) and adult (strobilated) stages in at least one cestode species. These 34 genes were then assumed to be strobilation related; they included 12 encoding proteins of known function, with 6 related to the Wnt, TGF-β/BMP, or G-protein coupled receptor signaling pathways; and 22 encoding UF proteins. In order to assign function to at least some of the UF genes/proteins, a global gene co-expression analysis was performed for the cestode species Echinococcus multilocularis. This resulted in eight UF genes/proteins being predicted as related to developmental, reproductive, vesicle transport, or signaling processes.

CONCLUSIONS

Overall, the described in silico data provided evidence of the involvement of 34 genes/proteins and at least 3 developmental pathways in the cestode strobilation process. These results highlight on the molecular mechanisms and evolution of the cestode strobilation process, and point to several interesting proteins as potential developmental markers and/or targets for the development of novel antihelminthic drugs.

Heavy Metal Accumulation in the Intestinal Tapeworm Proteocephalus macrophallus Infecting the Butterfly Peacock Bass (Cichla ocellaris), from Southeastern Brazil

Here we evaluate the potential of heavy metal accumulation of Proteocephalus macrophallus parasitizing the Butterfly Peacock Bass (Cichla ocellaris). A total of 19 fish specimens were collected. From the hosts, samples of intestine, liver, muscle, and parasites were taken. Heavy metal concentrations (Al, As, Ba, Cd, Cr, Fe, Hg, Mg, Mn, Ni, Pb, Ti, and Zn) were obtained using Atomic Absorption Spectrometry. All analyzed elements was found in higher concentrations in the parasites comparing to its host tissues. The bioconcentration factors were higher in the intestine, varying between 5.91 (Ti) to 8.00 (Ba), followed by the muscle, 1.88 (Mg) to 6.39 (Zn), and liver, 1.67 (Al) to 2.02 (Ba). These results show that at the infection site heavy metal concentrations are reduced, since the elements are absorbed directly from the intestinal wall by the parasites. In general, P. macrophallus presents a reasonable capacity of metal accumulation comparing to its hosts.

Characterization of Tapeworm Metabolites and Their Reported Biological Activities

Parasitic helminths infect billions of people, livestock, and companion animals worldwide. Recently, they have been explored as a novel therapeutic modality to treat autoimmune diseases due to their potent immunoregulatory properties. While feeding in the gut/organs/tissues, the parasitic helminths actively release excretory-secretory products (ESP) to modify their environment and promote their survival. The ESP proteins of helminths have been widely studied. However, there are only limited studies characterizing the non-protein small molecule (SM) components of helminth ESP. In this study, using GC-MS and LC-MS, we have investigated the SM ESP of tapeworm Dipylidium caninum (isolated from dogs) which accidentally infects humans via ingestion of infected cat and dog fleas that harbor the larval stage of the parasite. From this D. caninum ESP, we have identified a total of 49 SM (35 polar metabolites and 14 fatty acids) belonging to 12 different chemotaxonomic groups including amino acids, amino sugars, amino acid lactams, organic acids, sugars, sugar alcohols, sugar phosphates, glycerophosphates, phosphate esters, disaccharides, fatty acids, and fatty acid derivatives. Succinic acid was the major small molecule present in the D. caninum ESP. Based on the literature and databases searches, we found that of 49 metabolites identified, only 12 possessed known bioactivities.

Report: An ex vivo up-take of levamisole molecules by cestode (Monezia expensa) of goat (Capra hirsa) and its detection through RP-HPLC

Detection of various molecules of drugs remained a prime issue especially in tissues of animals, humans and in their target parasites. The cestode/tapeworms pose a dilemma because of their weird body composition and uptake pattern of nutrients and medicines especially through absorption by tegument. We selected levamisole; thought to be potent antiparasitic/ani-cestodal drug. The uptake of levamisole (LEV) through cestodeal tissues is studied through HPCL in this paper. High performance liquid chromatography technique has been utilized to know the uptake of levamisole in tissues of cestodes of Goat (Monezia expensa) in small ruminants. The drug was exposed to M. expensa by in vitro till its death or a parasite ceases its movement. The tissue/ part of proglattids of the M. expensa were homogenized with some modifications and levamisole extraction was performed with liquid phase extraction method. The evaporation of solvent was done and the residual cestodal tissues were cleaned by solid phase. After the solid phase extraction method, the recovery of drug, detection and quantification of levamisole from cestodal tissues was determined through Reverse Phase Column High Performance Liquid Chromatography (RP-HPLC). Levamisole (LEV) molecules assay was obtained on a C18 reverse-phase (20um, 6mm x 150mm) column at flow rate of 1ml/min using acetonitrile and ammonium acetate as mobile phase and UV detection was done at 254nm. The development of method of Levamisole (LEV) detection from cestodal tissues by HPLC in vitro samples has been demonstrated first time in Pakistan, which can provide the solution of parasitic control and provide in sight in to the uptake of anti cestodal drugs either against human or livestock parasites.

PCBs in fish and their cestode parasites in Lake Victoria

Polychlorinated biphenyls (PCBs) are classified as persistent organic pollutants (POPs) regulated by the Stockholm Convention (2001). Although their production and use was stopped almost three decades ago, PCBs are environmental persistent, toxic, and bioaccumulate in biota. We assessed the levels of 7 PCB congeners (IUPAC nos. 28, 52, 101, 118, 138, 153, and 180) in sediment and fish (Oreochromis niloticus, Lates niloticus, and Rastrineobola argentea) and evaluated the potential of cestode fish endoparasite (Monobothrioides sp., Proteocephalaus sp., and Ligula intestinalis) as biomonitors of PCBs in Lake Victoria, Kenya. The median concentration of Σ7PCBs in sediments and fish were 2.2-96.3 μg/kg dw and 300-3,000 μg/kg lw, respectively. At all the sampling sites, CB138, CB153, and CB180 were the dominant PCB congeners in sediment and fish samples. Compared to the muscle of the piscine host, Proteocephalaus sp. (infecting L. niloticus) biomagnified PCBs ×6-14 while Monobothrioides sp. (infecting O. niloticus) biomagnified PCBs ×4-8. Meanwhile, L. intestinalis (infecting R. argentea) biomagnified PCBs ×8-16 compared to the muscle of unparasitized fish. We demonstrate the occurrence of moderate to high levels of PCB in sediments and fish in Lake Victoria. We also provide evidence that fish parasites bioaccumulate higher levels of PCBs than their piscine hosts and therefore provide a promising biomonitor of PCBs. We urge further a long-term study to validate the use of the above cestode fish parasites as biomonitoring tools for PCBs.

Host-parasite relationships as determinants of heavy metal concentrations in perch (Perca fluviatilis) and its intestinal parasite infection

The concentrations of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn and their bioconcentration factors (BCFs) were determined in two intestinal parasites, an acanthocephalan, Acanthocephalus lucii, a tapeworm, Proteocephalus percae, present in the same host, the European perch (Perca fluviatilis, L.), in the heavily polluted Ružín reservoir in eastern Slovakia. The bioaccumulation of heavy metals in the fish organs and parasites was studied for acanthocephalan and tapeworm monoinfections or mixed infections by the two parasites and for the size of their parasitic infrapopulations. Bioconcentration factors (c[parasite]/c[muscle tissue]) showed that the concentrations of As, Ni, Pb and Zn were higher in mixed infections than in monoinfections. Negative correlations between heavy metal concentrations in perch organs and the parasites were found. For example, higher concentrations of Ni and Zn in both parasite species corresponded with lower metal concentrations in perch and hard roe. Likewise, significant negative relationships between metal concentrations in fish organs and number of parasites were noticed with lower levels of Pb in fish harbouring higher numbers of tapeworms. Similarly, in both parasite species the concentrations of some essential elements (Cr, Mn) were lower at high infection intensities compared to low intensities. Our study revealed that the differential concentration of heavy metals in perch organs was affected by the type of infection (mono- or mixed-infection), and needs to be considered in field ecotoxicological and parasitological studies as a potentially important factor influencing the pollutant concentrations in fish.

Effect of Intestinal Tapeworm Clestobothrium crassiceps on Concentrations of Toxic Elements and Selenium in European Hake Merluccius merluccius from the Gulf of Lion (Northwestern Mediterranean Sea)

The capacity for heavy metal bioaccumulation by some fish parasites has been demonstrated, and their contribution to decreasing metal concentrations in tissues of parasitized fish has been hypothesized. The present study evaluated the effect of the cestode Clestobothrium crassiceps on the accumulation of trace elements in 30 European hake, Merluccius merluccius, in Spain (half of them infested by C. crassiceps). Tissue samples from all M. merluccius and specimens of C. crassiceps from the infected hakes were collected and stored until element analysis by inductively coupled plasma mass spectrometry (ICP-MS). Arsenic, mercury, and selenium were generally present in lower levels in the cestode than in all hake tissues. The mean value of the muscular Se:Hg molar ratio in the infested subsample was higher than that in hakes without cestodes. Values indicate that the edible part of infested hakes presents a lower amount of Cd and Pb in relation to noninfested hakes.

[COMPARATIVE ANALYSIS OF LIPID METABOLISM INDICES IN SOME PARASITES OF THE WHITE CHARR (SALVELINUS ALBUS) FROM THE LAKE KRINOTSKOE]

Comparative study of lipid metabolism indices (total lipids, separate lipid fractions, level of the lipid peroxidation processes, and antioxidant protection) was carried out in three parasite species collected from the white char in the Lake Kronotskoe: Diphyllobothrium ditremum Crepin, 1825 (Cestoda), Philonema oncorhynchi Kuitunen-Ekbaum, 1933 (Nematoda) H Neoechinorhynchus salmonis Ching, 1984 (Acanthocephala). Acanthocephalans possessed significantly greater levels of total lipids, triacylglycerol, and malondialdehyde; nematodes, of cholesterol and sterol esters; and cestodes, in phospholipids and constants of the substrate oxidation. Dependence between lipid metabolism of helminths and their taxonomic affiliation, morpho-functional features, the stage of the life cycle, and the site of infection in the host are discussed.

[Ultrastructural characteristics of the vitellaria, uterus and vagina of Amphilina foliacea Rudolphi, 1819 (Cestoda: Amphilinidea)]

The ultrastructural features of the vitelline follicles, uterus and vagina of the amphilinid cestode Amphilina foliacea from the body cavity of Acipenser ruthenus of the Volga basin are described. Some new distinguishing characters are revealed, including the presence of a single type of the cellular component in the vitelline follicles with sarcoplasmic processes filling the space around and within vitellocytes. The,uterus of this species is recognized by the presence of the syncytial epithelial lining with underlying secretory perikaria and different kinds of luminal projections. The most distal part of the uterus, situated closely to the uterine pore, is characterized by nuclei occupying the syncytial uterine epithelium. Slightly further proximally, they are located basally and then transformed into sunken perikaria. The vaginal epithelium is characterized by the syncytial structure with underlying epithelial perikaria in its distal region, with intraepithelial location of the nuclei slightly further proximally and the absence of the nuclei in its proximal region (the seminal receptacle). The syncytial cytoplasm of the vagina contains numerous vesicles and possesses microvilli-like surface structures. The morphological aspects of the female reproductive system of A. foliacea are compared with those of other Cestoda and Neodermata.

Fish tapeworm Khawia sinensis: an indicator of environmental microcystins?

OBJECTIVES

Parasites have recently been recognized as accumulation indicators that take up and bio-concentrate substances from environmental pollution. Interestingly, helminths of fish are known to accumulate metals from the ambient environment and to contain several orders of magnitude higher concentrations than hosts. While the majority of reports mention inorganic toxin accumulation in parasites, studies concerning effects of organic pollution are infrequent and little is known about the potential of parasites to bio-accumulate microcystins.

METHODS

The parasite-host system of tapeworm Khawia sinensis and common carp (Cyprinus carpio) was used to address this issue. Both the tapeworms and livers were dissected from experimental carps orally exposed to cyanobacterial biomass for 20 days. The total dose of microcystins amounted to 27 mg/kg of feed, i.e., 0.4 mg/kg of fish mass a day. Microcystin concentrations in tapeworms and carp liver tissues were measured using the LC-MS/MS method.

RESULTS

Considering the three measured microcystin variants LR, YR and RR, only MC-RR was detected and its concentrations in tapeworms and carp liver tissue amounted to 5.78±3.78 ng/g and 2.11±0.74 ng/g fresh weight (p<0.05), respectively.

CONCLUSIONS

Here we show accumulation of microcystin MC-RR in the tapeworm Khawia sinensis, a parasite of common carp (Cyprinus carpio). As this is the first report addressing this issue, further studies will be necessary to examine this specific parasite-host system.

Effect of lead in water on the absorption of copper, iron, manganese and zinc by sheep (Ovis aries) infected with sheep tapeworm (Moniezia expansa)

The sheep tapeworm (Moniezia expansa) and its host Ovis aries were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) for their copper, iron, manganese, zinc and lead levels. Element concentrations in cestode parasites were compared to those in various organs (liver, kidney, and muscle) of sheep. Tapeworms in the small intestine of sheep that were administered 2g of Pb(CH(3)COO)(2) per os daily (7 days) had significantly higher lead concentrations than sheep tissues. Cu levels significantly increased after Pb administration in sheep muscle and sheep tapeworms. Contrarily, Zn content significantly decreased in sheep muscle, but significantly increased in sheep tapeworms. However, Mn content significantly decreased after Pb administration in sheep tapeworms. Furthermore, Fe content significantly decreased after Pb administration in sheep liver and kidneys.

A helminth cestode parasite express an estrogen-binding protein resembling a classic nuclear estrogen receptor

The role of an estrogen-binding protein similar to a known mammalian estrogen receptor (ER) is described in the estradiol-dependent reproduction of the helminth parasite Taenia crassiceps. Previous results have shown that 17-β-estradiol induces a concentration-dependent increase in bud number of in vitro cultured cysticerci. This effect is inhibited when parasites are also incubated in the presence of an ER binding-inhibitor (tamoxifen). RT-PCR assays using specific oligonucleotides of the most conserved ER sequences, showed expression by the parasite of a mRNA band of molecular weight and sequence corresponding to an ER. Western blot assays revealed reactivity with a 66 kDa protein corresponding to the parasite ER protein. Tamoxifen treatment strongly reduced the production of the T. crassiceps ER-like protein. Antibody specificity was demonstrated by immunoprecipitating the total parasite protein extract with anti-ER-antibodies. Cross-contamination by host cells was discarded by flow cytometry analysis. ER was specifically detected on cells expressing paramyosin, a specific helminth cell marker. Parasite cells expressing the ER-like protein were located by confocal microscopy in the subtegumental tissue exclusively. Analysis of the ER-like protein by bidimensional electrophoresis and immunoblot identified a specific protein of molecular weight and isoelectric point similar to a vertebrates ER. Sequencing of the spot produced a small fragment of protein similar to the mammalian nuclear ER. Together these results show that T. crassiceps expresses an ER-like protein which activates the budding of T. crassiceps cysticerci in vitro. To the best of our knowledge, this is the first report of an ER-like protein in parasites. This finding may have strong implications in the fields of host-parasite co-evolution as well as in sex-associated susceptibility to this infection, and could be an important target for the design of new drugs.

[Effect of Caryophyllaeus laticeps (Cestoda, Caryophyllidea) upon activity of digestive enzymes in bream]

The activities of the main digestive hydrolases were comparatively studied in bream infected and noninfected with cestodes Caryophyllaeus laticeps (Pallas, 1781). It was shown that enzyme activities are distributed in the fish intestine in an irregular manner; the gradient of protease and lipase activities along the gut is presented. Following the infection of bream by cestodes, the activities of the studied enzymes decreased and the percentages of activities of various proteinase subclasses changed. No relation between the distribution of worms along the intestine and the levels of activities of digestive hydrolases was revealed.

Metal specific partitioning in a parasite-host assemblage of the cestode Ligula intestinalis and the cyprinid fish Rastrineobola argentea

When evaluating metal accumulation patterns in parasite-host assemblages species specific metal requirements should be taken into account. The aim of the present study was therefore to determine the metal specific partitioning in a parasite-host assemblage of the cestode Ligula intestinalis and the cyprinid fish Rastrineobola argentea and to determine the effect of the parasites on the metal balance of the fish. To this purpose the host-parasite assemblage was analysed for several metals at sites in the coastal zone of Lake Victoria differing in metal contamination. Our results showed that some elements (Ca, Sr, and Mg) reflected the physiological differences of bone formation and ionic balance and pointed to physiological disturbances of infested R. argentea. Other essential metals including Cu and Co were subject of element competition between fish and parasite, while only a micro-element (Cr) and a non-essential metal (Cd) displayed a partitioning with high concentration in the parasite. The present study clearly demonstrated the impact of the large cestodes on their small fish hosts and it is concluded that the partitioning of metals in the assemblage of R. argentea and L. intestinalis is subject to metal specific mechanisms for essential and non-essential elements.

Trace element concentrations in Raillietina micracantha in comparison to its definitive host, the feral pigeon Columba livia in Santa Cruz de Tenerife (Canary Archipelago, Spain)

The use of systems involving bird parasites as bioindicators of environmental pollution has been scarcely studied in comparison to other models involving fish and rodent parasites, which have been demonstrated as particularly adequate due to their bioaccumulation capacities. The present study evaluated the accumulation of nine trace elements in the cestode Raillietina micracantha and in its host Columba livia collected from the densely populated city of Santa Cruz de Tenerife (Canary Islands, Spain). Samples (kidney, liver, pectoral muscle, feathers, and R. micracantha) of 27 infected C. livia were selected for trace element analysis by inductively coupled plasma-mass spectrometry. Element levels in pigeon tissues revealed some degree of pollution in Santa Cruz de Tenerife, particularly by Pb and Zn. Pb and Mn mean concentrations were higher in R. micracantha than in the pigeon's soft tissues, with subsequent high bioaccumulation factors for Pb (kidney = 15.38, liver = 10.38, muscle = 79.83) and Mn (kidney = 6.81, liver = 7.52, muscle = 19.89, feathers = 6.11), among others. The negative relations detected for As concentrations between liver and R. micracantha emphasize a possible role of the cestode in As detoxification in host tissues. Considering the obtained bioaccumulation factors, the system R. micracantha/C. livia is proposed as another promising bioindicator system to evaluate environmental toxic element exposure, particularly Pb and Mn, in areas where pollution levels are still relatively low and where both common species are present.

Phytochemicals from Flemingia vestita (Fabaceae) and Stephania glabra (Menispermeaceae) alter cGMP concentration in the cestode Raillietina echinobothrida

Cyclic GMP (cGMP) mediates various physiological functions of nitric oxide (NO) synthesized by nitric oxide synthase (NOS). A crude peel extract and purified fraction of Flemingia vestita, as well as a crude rhizome extract of Stephania glabra and fractions were tested with respect to the activity of NOS, NO efflux and cGMP concentration in the cestode Raillietina echinobothrida in order to find out the possible mode of anthelmintic action of these plant-derived components. For comparison purposes, the parasites were also treated with pure genistein, sodium nitroprusside (SNP-a known NO donor), and the reference drug, praziquantel (PZQ). At the time of onset of paralysis in the parasites, a significant increase (32%-87%) in the NOS activity and a two to three fold increase of NO efflux into the incubation medium were observed in the treated parasites in comparison to their respective controls. The cGMP concentration in the treated parasites' tissue was also increased by 44%-103%. However, in the presence of NG-nitro-L-arginine methyl ester, a potent inhibitor of NOS, there was no increase in the cGMP concentration in the parasite tissue. This study indicates that the phytochemicals, in particular genistein and tetrahydropalmatine, from F. vestita and S. glabra, respectively, disturb the downstream signalling pathway of NO, as indicated by the change in cGMP concentration in the parasite tissue.

Trace element concentrations in Proteocephalus macrocephalus (Cestoda) and Anguillicola crassus (Nematoda) in comparison to their fish host, Anguilla anguilla in Ria de Aveiro, Portugal

The use of some fish parasites as bioindicators of heavy metal pollution has been demonstrated as particularly adequate due to their capacity of bioconcentration. This study evaluated the effect of Proteocephalus macrocephalus on the accumulation of trace elements in the edible fish, Anguilla anguilla, in a contaminated area in Portugal (Ria de Aveiro). Also, the model P. macrocephalus/A. anguilla was assessed as a bioindicator system in the presence of the highly prevalent nematode Anguillicola crassus. Samples (kidney, liver, muscle, A. crassus and P. macrocephalus) of 20 eels harbouring A. crassus and another 20 harbouring both A. crassus and P. macrocephalus were selected for element analysis by ICP-MS. The highest concentrations of Cr, Ni and Zn were detected in P. macrocephalus. However, there was a higher liver and muscle Cr concentration in eels not infected by P. macrocephalus. Also, the nematode A. crassus presented higher Cr concentrations in those eels harbouring P. macrocephalus. Results suggest that P. macrocephalus individuals accumulate Cr and Ni while levels of Cr in eel livers and Ni levels in eel kidney are reduced. The system P. macrocephalus/A. anguilla yielded bioaccumulation factors for Cr, Ni, Pb and Zn, whereas bioaccumulation of Cu, Cr and Pb in A. crassus varied according to eel co-infection with P. macrocephalus, thus emphasising the possible role of cestode infection in metal metabolization/storage processes in host tissues. Results suggest that heavy metal pollution in Ria de Aveiro has been decreasing although it is still higher than in other contaminated areas in Europe. Nevertheless, eel consumption in Ria de Aveiro represents no risk for humans although they may represent a real contamination risk for wildlife. The system P. macrocephalus/A. anguilla is proposed as another promising bioindicator system to evaluate environmental Cr, Ni, Pb and Zn exposure in estuarine areas where both species co-occur.

Heavy metals in the nase, Chondrostoma nasus (L. 1758), and its intestinal parasite Caryophyllaeus laticeps (Pallas 1781) from Austrian rivers: bioindicative aspects

Tissue samples from 121 adult specimens of the predominantly herbivorous fish species nase, Chondrostoma nasus (L. 1758), from five river sites in Austria were analyzed for their metal content. Sediments and water samples of the sites show different levels of metal load, with only one site considered being polluted with metals. The concentrations of cadmium, copper, lead, and zinc in the tissue of the gills, muscle, intestine, and liver of the fish were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). As in one of the unpolluted and the polluted river site, a well-established population of the tapeworm Caryophyllaeus laticeps (Pallas, 1781) occurred in the intestine of the fish; pooled samples of this worm were analysed as well. Both the nase and C. laticeps show bioindicative ability for metal pollution in rivers. The results allow a more differentiated characterization of the rivers than the sediment analyses. Cadmium is found mainly in the liver, with maximum concentrations of 1.57 microg/g dry weight from unpolluted sites and 5.58 microg/g from the polluted site. The highest concentrations of copper are also found in the liver, with values between 25 and 333 microg/g. A significantly elevated concentration of Cu in the intestine from an "unpolluted" site (mean: 24.06 microg/g) indicates an acute pollution in this area at the time of sampling. Lead was found mainly in the intestine and liver in concentrations between 0.09 and 4.05 microg/g and 0.26 and 1.94 microg/g, respectively. In the samples from the polluted site, it also could be detected in the gills (mean: 1.38 microg/g). The parasite C. laticeps shows different capacities for metal accumulation: Although the concentrations of Cu were significantly lower compared to the values of the fish liver, cadmium was detected in concentrations up to 5.1 times higher. Lead and zinc concentrations were found to be up to 9.7 and 3.0 times higher in the tapeworm compared to the fish liver, respectively.

Do glial cells exist in the nervous system of parasitic and free-living flatworms? An ultrastructural and immunocytochemical investigation

It is still unclear whether flatworms have specialized glial cells. At present there are no special methods available for the identification of glial cells in flatworms. The aim of this research was to carry out detailed investigations of the CNS in two species ofcestodes, and to get an idea whether these cells may fit into the concept of glia. Three types of glial cells have been found in Grillotia erinaceus: (1) fibroblast-like cells in the cerebral ganglion (CG); (2) glial cells in bulbar nerves with filaments and laminar cytoplasm; (3) a 3rd type of cells forms multilayer envelopes in the main cords (MC); also they make contacts with the excretory epithelium. To demonstrate the existence of glial cells, an immunocytochemical and ultrastructural investigation of Ligula intestinalis was undertaken. Intensive S100b-like immunoreaction (IR) was found in the GG and in the MC. IR-varicosities were mostly located asymmetrically on the MC, and no IR was found in neuropiles. Small glial cells were found on the surface of the MC; they have oval nuclei and dense cytoplasm with slim processes going around the neuropile and enclosing neurons. Long junctions are seen between cell processes but with neurons they usually possess juxtaposition contacts. Glial cells lack vesicles or synapse-like structures. Intensive S100b-like-IR has been shown in the CNS of cestodes for the first time. Results from ultrastructural research support the immunocytochemical date.

Host-parasite interactions from an ecotoxicological perspective

In recent years there has been an increasing number of papers showing how parasitism and pollution can interact with each other in aquatic organisms. Apart from parasitological aspects these interactions are also important in terms of ecotoxicological research. The current presentation aims at identifying three promising directions for future research in the interdisciplinary field of parasitology and ecotoxicology. 1. Parasites as sinks for pollutants within their hosts: Some parasites are able to reduce pollutant levels in the tissues of their host. The reduction of pollutants is an interesting implication since parasites are beneficial to their hosts from this perspective. In other cases free-living accumulation indicators may erroneously indicate low levels of pollution if they are infected with parasites. 2. Parasites as a diagnostic tool to test bioavailability of substances. In order to take up and accumulate pollutants the substances have to be metabolized by the host first. Accordingly, the detection of substances within endoparasites is a sign for the biological availability of pollutants. 3. Changes of biomarker responses of the host against pollutants. Parasites can alter physiological reactions of their hosts against pollutants in different ways. Therefore, in ecotoxicological studies, examining the question whether exposure to certain chemicals affects the physiological homeostasis of a test organism, it is important to use organisms that are known to be uninfected.

In vitro testing of anthelmintic efficacy of Flemingia vestita (Fabaceae) on carbohydrate metabolism in Rallietina echinobothrida

The root tuber peel of Flemingia vestita has been in use in local traditional medicine against intestinal worm infections in Meghalaya (North-East India). In order to evaluate and authenticate the anthelminitc efficacy of the isoflavones of F. vestita, the root peel extract of this putative plant was tested against several helminth parasites, extensively on Rallietina echinobothrida, with respect to different parameters of these parasites. In this paper, we describe various methods to evaluate the anthelmintic efficacy of this medicinal plant with respect to carbohydrate metabolism in R. echinobothrida at paralytic time caused by the isoflavones of F. vestita. To meet the high energy demand by the parasite due to the anthelmintic stress, glucose breakdown follows the PEPCK-malate pathway in the parasite.

Genistein from Flemingia vestita (Fabaceae) enhances NO and its mediator (cGMP) production in a cestode parasite, Raillietina echinobothrida

Cyclic GMP (cGMP) is responsible for various cellular functions including signal pathways and it acts as a mediator for nitric oxide (NO). In order to evaluate the anthelmintic efficacy of the plant-derived isoflavones, the crude peel extract of Flemingia vestita and pure genistein were tested with respect to the activity of nitric oxide synthase (NOS), NO efflux and the cGMP concentration in Rallietina echinobothrida, the cestode parasite of domestic fowl. For comparison, the parasites were also treated with genistein (the major isoflavone present in the crude peel extract), sodium nitroprusside (SNP), a known NO donor, and praziquantel (PZQ), the reference drug. At the time of onset of paralysis in the parasite, the activity of NOS showed a significant increase (35-46%) and a 2-fold increase of NO efflux into the incubation medium in the treated worms in comparison to the respective controls. The cGMP concentration in the parasite tissue increased by 46-84% in the treated test worms in comparison to the controls. The results show that the isoflavones, genistein in particular, from the crude peel extract of F. vestita influence the cGMP concentration in the parasite tissue, which plays a major role in the downstream signal pathways.

Lactic acid, pyruvic acid and lactate/pyruvate ratio in the Anoplocephalid tapeworm Stilesia globipunctata infecting sheep (Ovis aries)

Lactic acid content was found to vary among the different proglottid types of the parasite. This higher amount of lactic acid might be considered as the end product of anaerobic metabolism. The pyruvic acid level of the parasitic proglottides remained lower than lactate level. The intermediary carbohydrate metabolites, viz. lactate, pyruvate and the lactate/pyruvate ratio being indicators of high rate metabolism, their levels may notably infer the metabolic status of the parasite and also the interaction between the parasite species Stilesia globipunctata and the sheep host.

Ascorbic acid levels in the proglottides of cestode parasite Avitellina lahorea (Woodland, 1972) and host serum (sheep) in relation to their sexual maturity

The ascorbic acid level was highest in immature proglottides and lowest in gravid proglottides of Avitellina lahorea, the gut parasite of sheep. The ascorbic acid content in all the regions of the parasite viz., immature, mature and gravid taken together remained higher to the value of the host serum. The above gradient between the parasite and the host serum interface suggested its active uptake on the part of the parasite.

Drug transport mechanisms in helminth parasites: Passive diffusion of benzimidazole anthelmintics

Anthelmintic molecules must reach their receptors inside target parasites to exert the pharmacological effect. Available data suggest that the main route of entry of antiparasitic drugs into helminth parasites would be through their external surface. However, it is unclear if trans-tegumental/cuticular penetration is the most important way of entry of benzimidazole (BZD) anthelmintics into their target parasites compared to oral ingestion. The relative involvement of active and passive transport mechanisms has not been defined. The goal of the work reported here was to determine the main processes involved in the entry of BZD anthelmintic molecules into the three main classes of helminth parasites. Adult specimens of Moniezia benedeni (cestode), Fasciola hepatica (trematode) and Ascaris suum (nematode) were incubated in Kreb's Ringer Tris buffer (pH 7.4, 37 degrees C) (1g parasite/10 ml incubation medium) for 15, 45, and 90 min, respectively, in the presence of a concentration gradient of either fenbendazole (FBZ), oxfendazole or triclabendazole sulphoxide (TCBZSO) (1-30 mol/ml, n=4). Dead helminth specimens were also incubated with the same drug concentration gradient. Specimens of F. hepatica with the oral route closed off by ligation were incubated with TCBZSO in the presence or absence of bovine serum albumin. After the incubation time elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography analysis to measure drug/metabolite concentrations. Equivalent drug concentrations were measured within ligated and non-ligated liver flukes, demonstrating that BZD do mainly penetrate by trans-tegumental diffusion. The higher the concentration of BZD molecules in the incubation medium, the greater their concentration recovered within the helminth parasites. High correlation coefficients (>0.98) were obtained between initial drug concentration in the incubation medium and those measured inside the nematode, cestode, and trematode parasites. FBZ concentrations recovered from tissues of dead cestodes/nematodes over time were significantly greater compared to those measured in living parasites. These differences in drug diffusion may be related to the morphological/functional properties of the parasite's external surfaces. The outcome of the work reported here indicates that passive drug transfer through the external helminth surface is the main transport mechanism accounting for BZD accumulation into target parasites.

Effect of isoflavone from Flemingia vestita (Fabaceae) on the Ca2+ homeostasis in Raillietina echinobothrida, the cestode of domestic fowl

The alcoholic crude root-peel extract of Flemingia vestita and its major isoflavone, genistein, have been shown to have a vermifugal/vermicidal effect by causing a flaccid paralysis accompanied by alterations in the structural architecture of the tegumental interface and metabolic activity in Raillietina echinobothrida, the cestode of domestic fowl. In the present study, the crude root-peel extract and pure genistein were tested in vitro with respect to Ca2+ homeostasis and the occurrence of some metal ions was detected in the parasite. Live cestodes were incubated in pre-defined concentrations of the crude root-peel extract, genistein and praziquantel (as reference drug), till the paralysis time with simultaneous maintenance of respective controls. In the parasite tissue, a significant amount of Ca2+ (approximately 400 microg/g dry tissue wt) was found to be present besides magnesium, iron, zinc, lead and chromium, whilst manganese, cadmium and nickel were below the level of detection. The Ca2+ concentration was decreased significantly by 39%-49%, in the parasite tissue exposed to the test materials in comparison to the respective controls. There was also an increase in Ca2+ efflux by 91%-160% into the culture medium under similar treatments. The changes in Ca2+ homeostasis may be related to the rapid muscular contraction and consequent paralysis in the parasite due to the anthelmintic stress caused by the phytochemicals of F. vestita.

Comparative study on the accumulation of heavy metals in different organs of tench (Tinca tinca L. 1758) and plerocercoids of its endoparasite Ligula intestinalis

Concentrations of heavy metals (Cu, Fe, Zn, Mn, Cr, Pb and Cd) in some organs of tench and tissues of its parasite found in Kovada Lake (Turkey) were analyzed using atomic absorption spectrophotometry and subsequently compared with the data from sediments and water. Only Cu, Fe, Zn and Mn were detected in water, sediment, plerocercoids of Ligula intestinalis and fish samples, while levels of Cr, Pb and Cd were below the detection limits. Four elements were found at higher concentrations in the plerocercoid than in different fish tissues (muscle, liver and gill), being 1.6-37.4 times higher than that measured in muscle, liver and gill. Significant positive (for Cu) and negative (for Fe, Zn and Mn) correlations were found between the quantity of heavy metals in water and tissues of L. intestinalis plerocercoids while there were significant positive (for Cu and Zn) and negative (for Fe and Mn) correlations between the quantity of heavy metals in bottom sediment and tissues of L. intestinalis plerocercoids. Cestodes were found suitable to reflect the amount heavy metals in sediments, providing more reliable information about the actual pollution of the reservoirs.

[Peculiarities of lipid peroxidation indices in Ligula intestinalis (Cestoda: Pseudophyllidea) and its host--Abramis brama (L.)]

A comparative analysis of indices of peroxidation lipids in tissues of Ligula inteslinalis plerocercoids and in the intermediate fish host, the bream Abramis brama, was performed for the content of common lipids (CL), malonate di-aldehyde (MDA), which is a product of lipid peroxidation (POL), and common antioxidate activity (CAA). The dependence of indices upon size of parasites is recovered. The long-sized parasites had higher rate of MDA and intense CAA. The higher rate of MDA and low one of CAA was observed in the infected fishers comparing to the healthy ones.

Echinococcus granulosus antigen B hydrophobic ligand binding properties

Antigen B (AgB), an immunodominant component of the cestode parasite Echinococcus granulosus, presents homology to and shares apparent structural similarities with helix-rich hydrophobic ligand binding proteins (HLBPs) from other cestodes. In order to investigate the fatty acid binding properties of AgB, two of its subunit components (rAgB8/1 and rAgB8/2) were expressed in Escherichia coli and purified, and the native antigen was purified from the hydatid cyst fluid by affinity chromatography using a monoclonal antibody raised against rAgB8/1. The interaction of the purified native and recombinant proteins with the fluorescent ligands DAUDA, ANS, DACA and 16-AP was investigated. The palmitic acid derived fluorescent ligand, 16-AP, showed the greatest enhancement in fluorescence when bound to native AgB or to its recombinant subunits, and the dissociation constants for 16-AP binding were determined. Surprisingly, in contrast to HLBPs from other cestodes, interactions with other fatty acids, including palmitic acid, caused an increase in fluorescence instead of competing with 16-AP. Our results suggest that AgB might have evolved different functions in the binding of hydrophobic compounds, dependent on cestode environment.

Anthelmintic efficacy of Flemingia vestita (Fabaceae): alterations in glucose metabolism of the cestode, Raillietina echinobothrida

The root-tuber peel of Flemingia vestita and its active component, genistein, were tested in respect of glucose metabolism in the cestode, Raillietina echinobothrida. Live R. echinobothrida, collected from the intestine of freshly slaughtered domestic fowl, were incubated at 39+/-1 degrees C in defined concentrations of the root-peel crude extract (5 mg/ml), genistein (0.2 mg/ml) and praziquantel (1 microg/ml) in phosphate buffered saline with 1% of dimethyl sulphoxide with simultaneous maintenance of controls. In the treated worms, there was a significant decrease in the glycogen concentration accompanied with the decrease of glucose by 14-32%, whereas the malate concentration increased by 49-134% as compared to controls. Both in controls and treated parasites, however, the pyruvate content was not measurable. While alanine and lactate contents showed a decline by 7-25% in the parasites exposed to all test materials, the lactate efflux into the incubation medium showed 37-71% increase in treatments indicating an overall increase of lactate production in comparison to controls. The results showing a decline in the glycogen and glucose contents and a significant rise in the malate content and lactate efflux under treatment conditions suggest that the energy demand in the parasites possibly got enhanced under stress, though it did not influence a switch over towards aerobic degradation of glucose in the parasites.

Accumulation of heavy metals by intestinal helminths in fish: an overview and perspective

Intestinal helminths of fish are of increasing interest as potential bioindicators for heavy metal contamination in aquatic habitats. Among these parasites cestodes and acanthocephalans in particular have an enormous heavy metal accumulation capacity exceeding that of established free living sentinels. Metal concentrations several thousand times higher in acanthocephalans than in host tissues were described from field and laboratory studies. Whereas larval stages inside their intermediate hosts are not able to take up high quantities of metals, young worms begin to take up metals immediately after infection of the final host. After four to five weeks of exposure, the parasites reach a steady-state concentration orders of magnitude higher than the ambient water level. Thus, acanthocephalans are not only very effective in taking up metals, but they can also respond very rapidly to changes in environmental exposure. The mechanism which enable acanthocephalans to take up metals from the intestinal lumen of the host appears to be based on the presence of bile acids, which form organo-metallic complexes that are easily absorbed by the worms due to their lipophilicity. Investigations of the environmental conditions affecting metal uptake have shown that the parasites are more consistent and reliable indicators for metal pollution than the host tissues as metal levels of the latter are much more dependent on the water chemistry. Thus, after some years of research on the uptake of metals by acanthocephalans and on the factors affecting metal accumulation in intestinal parasites it should be asked if acanthocephalans meet the criteria commonly accepted for sentinels. If parasites can be considered as promising sentinels, we need reasons for the establishment of ‘new’ indicators. Therefore, this review summarises the present knowledge about parasites as bioindicators and compares the accumulation properties of parasites and established free living indicators. Finally, this review presents possible answers to the question why it could be advantageous to have new and even more sensitive indicators for environmental monitoring purposes.

[Final stages of carbohydrate metabolism in a cestode Eubothrium rugosum (Cestoda: Pseudophyllidea)]

Characteristics of final stages of carbohydrate metabolism in a cestode Eubothrium rugosum from the burbot intestine have been studied. It is found out that in the course of in vitro incubation the worms produce lactic acid to the environment with a concomitant acidification of the medium. The rate of pH changes and lactate production eventually fell during the incubation. The medium pH being the result of helminth's metabolism varies within the normal physiological limits of the host intestine pH and pH optima for its basic digestive enzymes.

[Carbohydrate metabolism of Bothriocephalus scorpii (Cestoda: Bothriocephalidae)]

The cestodes Bothriocephalus scorpii during the incubation in vitro assimilated glucose from the incubation medium and synthesized of glycogen. End products of carbohydrate metabolism in B. scorpii were lactic, succinic and volatile fatty acids. Mitochondria isolated from B. scorpii intensively oxidized succinate, alpha-ketoglutarate, isocitrate and less intensevely oxidized citrate, oxalacetate, pyruvate, cis-aconitate and malate.

Anthelmintic efficacy of Flemingia vestita (Fabaceae): Effect of genistein on glycogen metabolism in the cestode, Raillietina echinobothrida

The edible root-tuber peel of Flemingia vestita and its major active component, genistein, have been earlier shown to have a vermifugal/vermicidal effect on cestodes in vitro by causing a flaccid paralysis and alterations in the tegumental architecture and activity of several enzymes associated with the tegumental interface of the parasite. Pursuing further investigation on the mode of action of this putative anthelmintic, the crude peel extract and pure genistein were further tested in respect of glycogen metabolism in the fowl tapeworm, Raillietina echinobothrida. On exposure to the plant root peel crude extract (5 mg/ml) and genistein (0.2 mg/ml), the glycogen concentration was found to decrease by 15-44%, accompanied by an increase of activity of the active form of glycogen phosphorylase (GPase a) by 29-39% and decrease of activity of the active form of glycogen synthase (GSase a) by 36-59% in treated parasites as compared to untreated controls, but without affecting the total activity (a+b) of both the enzymes. Praziquantel (1 microg/ml), the reference drug, also caused quantitative reduction in glycogen level and alterations in enzyme activities somewhat at par with the genistein treatment. These results suggest that this plant-derived component may influence the glycogen metabolism of the parasite by directing it towards utilization of glycogen.

[Effect of Ligula intestinalis on lipid metabolism in blood of the host Abramis brama]

The results of analysis in the blood of healthy and ones infected with the plerocercoides Ligula intestinalis Bream Abramis brama L. over index common lipids (CL) and them quality content, peroxidation (POL), peroxide gemoliz erythrocytes (PGE), common antioxidant activity (CAA) are displayed. It is plerocercoids L. intestinalis effects points character lipids exchanges. At ones infected individual comparatively with healthy increase of CL, alteration correlation lipids fraction, intensification POI and PGE as well as a decrease of CAA, that negative effects on vital function of the blood.

Transtegumental diffusion of benzimidazole anthelmintics into Moniezia benedeni: correlation with their octanol-water partition coefficients

The experiments described here report on the correlation between the ex vivo diffusion of different benzimidazole (BZD) anthelmintics into the cestode parasite Moniezia benedeni, and their octanol-water partition coefficients (P.C.). The characterisation of the drug diffusion process into target parasites is relevant to understand the mechanism of drug penetration and the pharmacological activity of anthelmintic drugs. Specimens of the tapeworm M. benedeni, used as a helminth parasite model, were obtained from untreated cattle killed at the local abattoir. The collected parasites were incubated (5-210 min) with either fenbendazole (FBZ), albendazole (ABZ), ricobendazole (RBZ), oxfendazole (OFZ), mebendazole (MBZ), oxibendazole (OBZ), or thiabendazole (TBZ), in a Kreb's Ringer Tris buffer medium at a final concentration of 5 nmol/ml. After the incubation time elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography (HPLC) analysis to measure drug/metabolite concentrations. Additionally, the octanol-water P.C. for each molecule was estimated as an indicator of drug lipophilicity, using reversed phase HPLC analysis. All the incubated drugs were recovered from the tapeworms as early as 5 min post incubation. There was a high correlation (r=0.87) between drug lipophilicity, expressed as octanol-water P.C. (Log P), and drug availability within the parasite. The most lipophilic BZD compounds (FBZ, ABZ, and MBZ), with P.C. values higher than 3.7, were measured at significative higher concentrations within the tapeworm compared to those drugs with the lowest P.C. values. Considering the results from the current and previous studies, it is clear that passive diffusion is a major mechanism of BZD penetration into cestode parasites, where lipid solubility is a determinant factor influencing the diffusion of these anthelmintic molecules through the parasite tegument.

Enantioselective binding of albendazole sulphoxide to cytosolic proteins from helminth parasites

The pharmacological effect of the active albendazole metabolite, albendazole sulphoxide (ABZSO), depends on its sustained presence at the site of parasite location and its binding to helmith beta-tubulin. ABZSO is found in the plasma and tissues of albendazole-treated animals in two enantiomeric forms: (+)ABZSO and (-)ABZSO. Knowledge of enantioselectivity in drug action is necessary, since any difference in target proteins affinity between enantiomers may have implications on the pharmacological effect of this anthelmintic molecule. The binding of ABZSO to mammalian and helminth parasites cytosolic proteins, as well as the differential binding of both enantiomers, were studied. Cytosolic proteins from Moniezia expansa (cestode), Ascaris suum (nematode), Fasciola hepatica (trematode), rat liver and brain as well as purified porcine brain tubulin were used. Drug analysis was performed by HPLC using both C18 and chiral columns. ABZSO protein binding was quantitatively different between parasite species (4.17, 2.5 and 1.07 ng/mg for cestode, nematode and trematode, respectively); this binding to helminth cytosolic proteins was enantioselective. Enantiomeric ratios of (-)ABZSO/(+)ABZSO as a percentage were: 43/57 (Ascaris), 36/64 (Moniezia) and 91/9 (Fasciola). Conversely, the binding of ABZSO to mammalian cytosolic proteins showed no enantioselectivity. The overall binding affinity of ABZSO for mammalian cytosolic proteins was lower than that observed in helminth proteins. The characterization of the comparative binding pattern of ABZSO enantiomers to cytosolic proteins from helminth parasites and mammalian tissues may contribute to understanding the pharmacological properties of this chiral anthelmintic molecule.

Comparative metabolism of albendazole and albendazole sulphoxide by different helminth parasites

Albendazole (ABZ) is a broad-spectrum benzimidazole anthelmintic widely used in human and veterinary medicine. The aim of the current work was to characterise the sulphoxidative metabolism of ABZ, and the sulphoreduction of ABZ sulphoxide (ABZSO), by microsomal (Ms) and cytosolic (Cyt) fractions of three different helminth species: Fasciola hepatica, Moniezia expansa and Ascaris suum. After the incubation assays, parasite material was analysed by HPLC to characterise the metabolic product formed. Both the Ms and Cyt fractions of the three parasites studied were able to oxidise ABZ into ABZSO in a non-enantioselective fashion. Oxidation of ABZ was greater in the Ms fraction of the trematode (50%) than in both cestode (19%) and nematode (14%) parasites. Only the incubation of ABZSO with both subcellular fractions of M. expansa generated ABZ as a metabolic product. The results obtained here indicate that helminths have the capacity to biotransform benzimidazole compounds; however, this metabolic activity differs qualitatively and quantitatively among helminth species.

In vivo and ex vivo uptake of albendazole and its sulphoxide metabolite by cestode parasites: relationship with their kinetic behaviour in sheep

The current experiments correlate the disposition kinetics of albendazole (ABZ) following its intravenous (i.v.) and intraruminal (i.r.) administrations to Moniezia spp.-infected sheep, with the pattern of drug/metabolite uptake by tapeworms collected from treated animals. The ex vivo uptake pattern of ABZ and albendazole sulphoxide (ABZSO) by the same cestode parasite was also investigated. Naturally infected (Moniezia spp.) Corriedale lambs were treated with ABZ by either i.v. (Group A, n = 15) or i.r. (Group B, n = 15) administration at 7.5 mg/kg. Plasma and abomasal fluid samples were obtained over a 120-h period. Two animals per group were killed at 0.5, 1, 2, 4 and 6 h post-treatment; parasite material (tapeworms), bile and intestinal fluid samples were recovered. Furthermore, Moniezia spp. tapeworms obtained from sheep killed at the local abattoir were incubated with either ABZ or ABZSO for different time periods in a Kreb's Ringer Tris buffer (ex vivo experiments). Samples were analysed by high performance liquid chromatography for ABZ, ABZSO and albendazole sulphone (ABZSO2). ABZ plasma concentrations decreased rapidly and were not detectable beyond 10 h following i.v. administration. ABZSO and ABZSO2 were the metabolites recovered in plasma after both treatments. ABZ and its metabolites were extensively distributed to the digestive tract, mainly into the abomasal fluid, after the i.v. and i.r. administrations. The parent drug and its active ABZSO metabolite were recovered in tapeworms collected from both i.v. and i.r. treated lambs. However, the availability of both ABZ and ABZSO was higher in parasite material recovered from i.v. treated animals. The uptake of ABZ by the cestode parasite, both in vivo and ex vivo, was significantly greater than that of its sulphoxide metabolite, which agrees with the higher lipophilicity of the parent drug.

Wild rabbit host and some parasites show trophic-level relationships for delta 13C and delta 15N: a first report

We report the first isotopic study of an animal host-parasite system. Parasitic, intestinal nematodes, Graphidium strigosum and Passalurus ambiguus, were 15N-enriched relative to their host, the European rabbit Oryctolagus cuniculus, while parasitic cestodes, Cittataenia denticulata and Mosgovoyia pectinata, were 15N-depleted, suggesting different trophic relationships. Host embryos were more similar in their delta 13C and delta 15N values to maternal muscle than were any of the parasites. Coprophagy, the direct recycling of food by the rabbit eating its own faeces, did not lead to isotopic differences between stomach contents and faeces, suggesting that the major point for isotopic discrimination in lagomorph nitrogen metabolism is in the animal rather than in the gut. We conclude that bulk delta 13C and delta 15N can reveal valuable new information about host-parasite relationships, and these could be explored further at the biochemical level using compound-specific isotopic analyses.

Digestion and digestive-transport surfaces in cestodes and their fish hosts

The structural and functional organization of digestive-transport surfaces in some lower cestodes and their fish hosts was studied. It has been shown that the ultrastructure of cestode microtriches and fish enterocyte microvilli being the basis of membrane-linked digestion is quite similar. These organelles increase the digestive-transport surfaces both in helminths and fishes. However, the hydrolytic enzyme activity in helminths is usually 2-4 times lower than that of the fishes. Desorption (adsorption) characteristics of various hydrolases in helminths and fishes are also different. In helminths the easily desorbed fraction of each enzyme is always more abundant than in fishes. In contrast, the intensity of transport processes in helminths is higher when compared with fishes. The adaptation of digestive-transport surfaces and enzyme systems to feeding conditions is discussed.

Heavy metal concentrations in adult acanthocephalans and cestodes compared to their fish hosts and to established free-living bioindicators

Intestinal helminths of fish caught from freshwater and brackish water biotopes throughout Europe were analysed by electrothermal atomic absorption spectrometry for their heavy metal (Pb and Cd) levels. The metal concentrations of the parasites were compared to those of different organs (muscle, liver, intestine) of the fish hosts and to those detected in the whole bodies of the respective intermediate hosts. The three acanthocephalan species analysed contained very high amounts of Pb and Cd. The lead level of Pomphorhynchus laevis was up to 2700 times higher and the cadmium concentration was approximately 500 times higher than the muscle of chub, its host. Concurrent analysis of larval acanthocephalans in the crustacean intermediate host indicated that the bioconcentration of heavy metals by these parasites occurs only in the final host. In two species of cestodes accumulation of metals was also recorded although the degree of bioconcentration was somewhat lower. Nevertheless, Monobothrium wageneri contained 75 times more Pb and 43 times more Cd than the muscle of its host, the tench. In contrast, no bioconcentration of heavy metals was detected in the swimbladder nematode Anguillicola crassus. It contained less lead than the muscle of its final host, the eel. In one biotope the concentration of 18 elements was compared between the whole soft tissues of the zebra mussel, Dreissena polymorpha, the parasite Acanthocephalus lucii and its final host, perch. The acanthocephalan accumulated most of the elements to considerably higher concentrations than the zebra mussel, which has been considered an effective bioindicator of heavy metals. The sessile nature of the zebra mussel may allow a better identification of small-scale local differences in environmental heavy metal contamination. However, acanthocephalan parasites will provide an ecologically-important index of average exposure of their mobile fish host to biologically-available metals within its natural range.

Lead and cadmium content of two cestodes, Monobothrium wageneri and Bothriocephalus scorpii, and their fish hosts

The adult cestodes Monobothrium wageneri and Bothriocephalus scorpii from the intestines of their respective final hosts, tench (Tinca tinca) caught in the river Ruhr, Germany, and turbot (Scophthalmus maximus) collected from two sampling sites on the coast of Gdansk, Poland, were analyzed for lead and cadmium by atomic absorption spectrometry. Both cestode species contained significantly higher cadmium contents than did the muscle, liver, and intestine of their fish hosts. Whereas M. wageneri also contained several times more lead than did the organs of tench, B. scorpii showed nearly the same lead burden as did the liver and intestine of turbot. Posterior sections of B. scorpii comprising gravid proglottids contained significantly higher concentrations of lead and cadmium than did the anterior proglottids.

Immunocytochemical evidence for the presence of prolactin in the plerocercoid of Ligula intestinalis (Cestoda: Pseudophyllidea)

Immunoreactivity to prolactin in the nervous system of the plerocercoid of Ligula intestinalis was demonstrated by immunocytochemical method. Numerous PRL immunoreactive perikarya with long varicose fibres were observed in the peripheral nervous system in the worm, mainly in the transversal muscle layer and medullary parenchyma of the midbody. A few fibres were found in the main nerve cords of the central nervous system. PRL positive neurons sent their processes to associate with the main nerve cords. The immunostaining terminals appeared in the subtegument region in the lateral border of the plerocercoid. The result indicates that PRL immunoreactivity is well-developed in the plerocercoid of the cestode. The significance of the localization of prolactin in the worm is discussed.

Immunocytochemical distribution of neuropeptide F (NPF) in the gastropod mollusc, Helix aspersa, and in several other invertebrates

The distribution of neuropeptide F (NPF) immunoreactivity in the snail, Helix aspersa, has been demonstrated by immunocytochemistry using 2 region-specific antisera. One, designated NPF3, was raised against a synthetic N-terminal fragment of Helix aspersa NPF; the other, designated PP221, was raised against the C-terminal hexapeptide amide of mammalian pancreatic polypeptide (PP) but cross-reacts fully with the analogous C-terminal region of Helix aspersa NPF. The distribution of NPF immunoreactivity has also been compared with that of FMRFamide using alternate serial sections of Helix aspersa ganglia. Results showed that NPF immunoreactivity was abundant and widespread in the central and peripheral nervous systems and the pattern of immunostaining obtained using both region-specific antisera was similar. Likewise, immunocytochemistry of neural tissues of a congeneric species, Helix pomatia, and 2 prosobranch gastropods, Buccinum undatum and Littorina littorea, produced similar staining patterns with both antisera. However, in the cephalopod mollusc, Loligo vulgaris, and the cestode, Moniezia expansa, positive immunostaining was only obtained with the C-terminal PP antiserum. Immunostaining of alternate serial sections of Helix aspersa ganglia with NPF3, and an antiserum raised to FMRFamide, showed that while a few neurones were immunoreactive with one antiserum only, in the majority, both immunoreactivities were co-localised. NPF thus appears to be an important neuropeptide of widespread distribution in Helix aspersa and the differential immunocytochemical staining obtained using the 2 region-specific antisera would suggest a high degree of primary structural conservation within the gastropod molluscs, but lack of conservation of the N-terminal region of the peptide in other invertebrate groups.