Zur Chemie und Toxikologie der Ascariden

Elucidating the molecular and developmental biology of parasitic nematodes: Moving to a multiomics paradigm

In the past two decades, significant progress has been made in the sequencing, assembly, annotation and analyses of genomes and transcriptomes of parasitic worms of socioeconomic importance. This progress has somewhat improved our knowledge and understanding of these pathogens at the molecular level. However, compared with the free-living nematode Caenorhabditis elegans, the areas of functional genomics, transcriptomics, proteomics and metabolomics of parasitic nematodes are still in their infancy, and there are major gaps in our knowledge and understanding of the molecular biology of parasitic nematodes. The information on signalling molecules, molecular pathways and microRNAs (miRNAs) that are known to be involved in developmental processes in C. elegans and the availability of some molecular resources (draft genomes, transcriptomes and some proteomes) for selected parasitic nematodes provide a basis to start exploring the developmental biology of parasitic nematodes. Indeed, some studies have identified molecules and pathways that might associate with developmental processes in related, parasitic nematodes, such as Haemonchus contortus (barber's pole worm). However, detailed information is often scant and 'omics resources are limited, preventing a proper integration of 'omic data sets and comprehensive analyses. Moreover, little is known about the functional roles of pheromones, hormones, signalling pathways and post-transcriptional/post-translational regulations in the development of key parasitic nematodes throughout their entire life cycles. Although C. elegans is an excellent model to assist molecular studies of parasitic nematodes, its use is limited when it comes to explorations of processes that are specific to parasitism within host animals. A deep understanding of parasitic nematodes, such as H. contortus, requires substantially enhanced resources and the use of integrative 'omics approaches for analyses. The improved genome and well-established in vitro larval culture system for H. contortus provide unprecedented opportunities for comprehensive studies of the transcriptomes (mRNA and miRNA), proteomes (somatic, excretory/secretory and phosphorylated proteins) and lipidomes (e.g., polar and neutral lipids) of this nematode. Such resources should enable in-depth explorations of its developmental biology at a level, not previously possible. The main aims of this review are (i) to provide a background on the development of nematodes, with a particular emphasis on the molecular aspects involved in the dauer formation and exit in C. elegans; (ii) to critically appraise the current state of knowledge of the developmental biology of parasitic nematodes and identify key knowledge gaps; (iii) to cover salient aspects of H. contortus, with a focus on the recent advances in genomics, transcriptomics, proteomics and lipidomics as well as in vitro culturing systems; (iv) to review recent advances in our knowledge and understanding of the molecular and developmental biology of H. contortus using an integrative multiomics approach, and discuss the implications of this approach for detailed explorations of signalling molecules, molecular processes and pathways likely associated with nematode development, adaptation and parasitism, and for the identification of novel intervention targets against these pathogens. Clearly, the multiomics approach established recently is readily applicable to exploring a wide range of interesting and socioeconomically significant parasitic worms (including also trematodes and cestodes) at the molecular level, and to elucidate host-parasite interactions and disease processes.

Ascaroside Pheromones: Chemical Biology and Pleiotropic Neuronal Functions

Pheromones are neuronal signals that stimulate conspecific individuals to react to environmental stressors or stimuli. Research on the ascaroside (ascr) pheromones in Caenorhabditis elegans and other nematodes has made great progress since ascr#1 was first isolated and biochemically defined in 2005. In this review, we highlight the current research on the structural diversity, biosynthesis, and pleiotropic neuronal functions of ascr pheromones and their implications in animal physiology. Experimental evidence suggests that ascr biosynthesis starts with conjugation of ascarylose to very long-chain fatty acids that are then processed via peroxisomal β-oxidation to yield diverse ascr pheromones. We also discuss the concentration and stage-dependent pleiotropic neuronal functions of ascr pheromones. These functions include dauer induction, lifespan extension, repulsion, aggregation, mating, foraging and detoxification, among others. These roles are carried out in coordination with three G protein-coupled receptors that function as putative pheromone receptors: SRBC-64/66, SRG-36/37, and DAF-37/38. Pheromone sensing is transmitted in sensory neurons via DAF-16-regulated glutamatergic neurotransmitters. Neuronal peroxisomal fatty acid β-oxidation has important cell-autonomous functions in the regulation of neuroendocrine signaling, including neuroprotection. In the future, translation of our knowledge of nematode ascr pheromones to higher animals might be beneficial, as ascr#1 has some anti-inflammatory effects in mice. To this end, we propose the establishment of pheromics (pheromone omics) as a new subset of integrated disciplinary research area within chemical ecology for system-wide investigation of animal pheromones.

Combinatorial chemistry in nematodes: modular assembly of primary metabolism-derived building blocks

The nematode Caenorhabditis elegans was the first animal to have its genome fully sequenced and has become an important model organism for biomedical research. However, like many other animal model systems, its metabolome remained largely uncharacterized, until recent investigations demonstrated the importance of small molecule-based signalling cascades for virtually every aspect of nematode biology. These studies have revealed that nematodes are amazingly skilled chemists: using simple building blocks from conserved primary metabolism and a strategy of modular assembly, C. elegans and other nematode species create complex molecular architectures to regulate their development and behaviour. These nematode-derived modular metabolites (NDMMs) are based on the dideoxysugars ascarylose or paratose, which serve as scaffolds for attachment of moieties from lipid, amino acid, carbohydrate, citrate, and nucleoside metabolism. Mutant screens and comparative metabolomics based on NMR spectroscopy and MS have so-far revealed several 100 different ascarylose ("ascarosides") and a few paratose ("paratosides") derivatives, many of which represent potent signalling molecules that can be active at femtomolar levels, regulating development, behaviour, body shape, and many other life history traits. NDMM biosynthesis appears to be carefully regulated as assembly of different modules proceeds with very high specificity. Preliminary biosynthetic studies have confirmed the primary metabolism origin of some NDMM building blocks, whereas the mechanisms that underlie their highly specific assembly are not understood. Considering their functions and biosynthetic origin, NDMMs represent a new class of natural products that cannot easily be classified as "primary" or "secondary". We believe that the identification of new variants of primary metabolism-derived structures that serve important signalling functions in C. elegans and other nematodes provides a strong incentive for a comprehensive re-analysis of metabolism in higher animals, including humans.

Digestion in Parasitic Nematodes. II. The Digestion of Fats

Enzymes hydrolysing olive oil and ethyl butyrate (probably lipases and esterases) have been extracted from the intestines of Strongylus edentatus and Ascaris lumbricoides (pig strain).

Maximum enzyme activity was obtained at pH 8·0.

A. lumbricoides enzymes were assisted by sodium glycocholate. Sodium taurocholate had a retarding effect on the enzymes from both parasites.

Enzymes extracted from A. lumbricoides were activated by the presence of NaHCO3 solutions whereas S. edentatus enzymes were not activated by this salt.

Esterase action, relative to lipase action, was 2½ times greater in S. edentatus than in A. lumbricoides.

Protein Metabolism in Trematode Parasites

Paramphistomum explanation, Gastrothylax crumenifer, andFasciola giganticawere maintained for periods of twelve hours in a non-nutrient medium containing streptomycin and penicillin to prevent bacterial growth. They were kept under aerobic conditions at a suitable temperature of 37%C. The protein content in P.explanatumranged from 50·0% to 54·7% with an average of 52·96%±0·23 of the dry weight of the tissue. InG. crumeniferit ranged from 43·5% to 51·5% with an average of 48·8%±0·56 of d.w.t. InF. giganticait ranged from 63·8% to 68·3% with an average of 66·5%±0·26 of d.w.t. The nitrogen content of theP. explanationexcreted as ammonia after a starvation period of twelve hours was 3·95% and as uric acid it was 0·077%. InG. crumeniferthe ammonia was 2·91% and uric acid 0·033%. InF. giganticaammonia was 2·51% and uric acid 0·1%.

The distribution of lipids and glycogen in some female oxyuroids

1. The distribution of glycogen and lipids in three oxyuroids (Aspiculuris tetraptera, Enterobius vermicularis and Syphacia obvelata) is described and found to be similar to that in ascarids and other oxyuroids.

2. Evidence is presented for the presence of both polysaccharides (possibly glycogen) and lipids in the cuticle.

3. It is suggested that the chitinous layer of the egg-shell of A. tetraptera contains phospholipids in association with proteins.

4. The distribution of phospholipids is described and it is suggested that their role is mainly structural.

I am grateful to Dr P. Tate for advice and encouragement and to Dr D. L. Lee for much useful discussion and advice.

Physiological studies on trematodes: calcium, magnesium and phosphorus content

1. Four trematodes,Gastrothylax crumenifer, Cotylophoron cotylophorum, Paramphistomum explanatumandFasciola giganticahave been used for quantitative analysis of their inorganic constituents.

2. Calcium, magnesium and phosphorus content have been determined.

3. All the four trematodes contain large amounts of phosphorus (0·61–1·05%); but the amounts of calcium (0·025–0·045%) and magnesium (0·029–0·065 %) are small.

Physiological studies on trematodes—lipid fractions inGastrothylax crumenifer

1. The different lipid fractions inGastrothylax crumeniferafter starvation for 8–10 hr. have been estimated.

2. The percentages of different fractions in the total ether extract were found to be: acetone-insoluble material 16, unsaponifiable matter 25, saturated fatty acids 5, unsaturated fatty acids 20, glycerol 2 and unidentified lipids 32.

3. The above percentages of lipid fractions have been compared with the corresponding data for different parasites obtained by other workers.

The uptake of radioactive phosphorus from host tissues and fluids by nematode parasites

1. Compared with the mammalian intestine, uterus and blood serum, the corresponding organs and perienteric fluid ofAscaris lumbricoideswere found to have a high phosphorus content. The muscle of the parasite, however, contained little more than half the phosphorus found in the mammalian muscle.

2.A. lumbricoidestook up inorganic ortho-phosphate largely or exclusively through the alimentary tract. Small amounts were taken up by the cuticle and the lateral line system, but did not appear to pass on to other tissues.

3.Nippostrongylus murisin the intestine of the rat took up radioactive phosphorus which had been injected into the host intramuscularly. When the host was dosedper osthe radioactivity appeared in the parasites at a lower concentration than in the host's small intestine.

4.Ascaridia gallifailed to show any radio-activity when host birds were injected intravenously with inorganic orthophosphate containing P32. A sudden rise and fall in the radioactivity of the parasites were found when host birds were dosedper os.

5. It is suggested that nematode parasites have a high demand for phosphate which they take up largelyper os. Ascaridia gallifeeds rapidly, but with poor phosphate absorption, on host gut contents.Nippostrongylus murisfeeds on host tissues. It is suggested that the different feeding habits ofN. murisandAscaridia gallimay have some relation to the efficacy of anthelmintics against these parasites.

The authors are indebted to Dr M. Kamen and Dr E. Reinhard of Washington University, St Louis, for a gift of radioactive phosphorus. Thanks are also due to Mr E. Parrish and Mr L. Turk of the McMaster Laboratory for their capable assistance.

Studies on the nature and properties of the perienteric fluid ofAscaris lumbricoides

1. The composition of the perienteric fluid ofAscaris lumbricoidesof the pig, immediately after removal from the host and after varying periods ofin vitrostarvation, is recorded.

2. Apart from the more frequently observed constituents of invertebrate tissue fluids, the body fluid ofAscariswas found to contain ascorbic acid, amino sugar and small amounts of uronic acid.

3. Large amounts of anion other than chloride, probably fatty acid, must have been present in the body fluid, though chloride was probably the predominant anion in fluids of parasites which had passed several days ofin vitrolife.

4. The chief factors (starvation, osmotic pressure and the nature of the medium, etc.) affecting the composition of the body fluid are briefly discussed.

The effects of acids on a soil nematode

1. The effects of the following acids were studied: hydrochloric, nitric, sulphuric, formic, acetic, propionic, butyric, isovaleric, glycollic, lactic, oxalic, malonic, succinic, malic, tartaric, and citric.

2. The general effects of immersion in acid media include an increased stickiness of the cuticle in certain solutions, and the development of lateral bulges in the cuticle at the anterior region of the body, not necessarily in the same solutions. Movement gradually decreases, and death eventually occurs, often followed by swelling.

3. The survival times in various solutions were noted. Preliminary experiments showed that the logarithm of the survival time was approximately proportional to the logarithm of the normality of the acid. Later results showed great variability, and it was necessary to restrict the work to a single normality of each acid.

4. The toxicities of 0·206 N solutions of the sixteen acids were measured. These results showed that the mineral acids had markedly greater effects than the organic acids, and the importance of the former was further illustrated by using mixtures of HCl containing varying amounts of organic acids. The differences between the mineral acids may be explained by the lyotropic effects of the anions.

5. Equal normalities of organic acids were made up in a solution of HCl sufficiently strong to render the organic acids almost entirely undissociated. The relative toxicities of the mixtures were essentially the same as those of the dissociated acids.

6. The differences between the acids are thus partly due to the pH differences, and partly due to the dissimilar effects of the undissociated acids. The latter are believed to be due to a variety of causes, including molecular size, polarity of the molecule, and other factors as yet undecided.

The distribution of glycogen and fat in Thelastoma bulhõesi (Magalhães, 1900), a nematode parasitic in cockroaches

1. The distribution of glycogen and fat in Thelastoma bulhõesi has been shown to be essentially the same as in Ascaris lumbricoides.

2. The chief storage areas of glycogen are the muscle cells and the lateral lines, with smaller amounts in the dorsal and ventral lines, the intestine and the oesophagus.

3. The chief storage areas of fat are the dorsal, ventral and lateral lines, the intestine, the oocytes, oogonia and ova.

4. Fat has been found in the lumen of the intestine of several nematodes, especially in the males of Hammerschmidtiella diesingi after 24 hr. starvation.

5. Both glycogen and fat in females of T. bulhõesi were considerably reduced, except in the gonads, after 12 days starvation.

6. Staining whole mounts with oil red O was found to be the most convenient method of determining if the food reserves were being used or not.

The physiology and cultivation in artificial media of nematodes parasitic in the alimentary tract of animals

It is intended that this review shall give an account of what is known of the physiology of the parasitic stages of nematodes parasitic in animals, with particular reference to those species which are found in the alimentary tract of their hosts. An account will also be given of attempts which have been made to keep the adult and larval phases of parasitic nematodes alive in vitro and of the bearing of the available physiological data upon this problem.

The distribution of esterase enzymes in Ascaris lumbricoides

1. The distribution of non-specific esterase and of cholinesterase in Ascaris lumbricoides has been determined using histochemical methods.

2. Non-specific esterase has been shown to be present in the cuticle, in the walls of the excretory canals, in the innervation processes of the muscles, in the coelomocytes, in the oesophageal glands, in the intestine, in the rectal glands, in the male and female reproductive systems, in parts of the nervous system and as 'caps' of enzyme on fat globules in the hypodermis and muscles.

3. Cholinesterase has been detected in the innervation processes and sheath of the muscles, in the sphincter muscles, in the intestine, in the sensory papillae and amphids, and in parts of the nervous system, including a nerve in the spicules.

4. Parts of the nervous system and the innervation processes of the muscles contain an esterase which is not inhibited by cholinesterase inhibitors and it is suggested that there may be esterase, distinct from cholinesterase, involved in nerve transmission.

5. Merocrine secretion of esterase has been observed in the intestine.

Metabolism of haemoglobin and haematin compounds in Ascaris lumbricoides

Variations in the colour of individual Ascciris lumbricoides from the pig are shown to depend on changes in the concentration of the perienteric fluid haemoglobin. Whilst the concentra­tion of the haemoglobin remains constant for several days when the worms are kept in a saline solution, it is rapidly increased when suitable substrates are added to the medium. These must always include a porphyrin or metalloporphyrin containing a vinyl group. Horse haemoglobin was found to be the most suitable substrate under the experimental conditions. Simpler substances cannot be utilized for haemoglobin synthesis. This is only the second example of inability to synthesize protohaematin which is known in the Metazoa. The distribution of haematin has been studied in whole worms and in histological sections by means of peroxidatic reactions. Only the cuticle and the excretory canal appear to be haematin-free. The amount of haemoglobin in the body wall does not seem to fluctuate like that in the perienteric fluid. More is present in the hypodermal layers and the nerve ring than in the actual musculature. Haematin compounds occur in relatively large amounts in the reproductive system, and have been studied spectroscopically in suspensions of uterine eggs. Consideration of the known reactions of the perienteric fluid haemoglobin with oxygen lead to the conclusion that it cannot be effective as a storer or carrier of oxygen in the metabolism of the worm itself. It is suggested that it represents a metabolic pool of haematin from which other haemoproteins are elaborated, and that the variation in concentration is the result of a mechanism for allowing the worm to store haematin at times when it is present in excess in the gut of the host. It is further suggested that the primary function of this mechanism is to enable a maximal rate of egg laying to be maintained. The haematin content of the eggs and the numbers laid would readily account for the quantity of haemoglobin involved. Although the data are insufficient to enable any generalization to be made at present, there are indications that similar phenomena occur in other ascarids and more distantly related nematodes.

Nemoglobins: Divergent nematode globins

Globins are proteins commonly associated with oxygen transport in vertebrate blood, but the invertebrate phyla display a wide variety of globin types that reflect their disparate life styles and evolutionary history. It has been known for over 100 years that parasitic nematodes contain globins, but recent molecular investigations are only now beginning to shed some light on their curious properties. Mark Blaxter here describes the diversity of the different globins found in nematodes, and reviews emerging data on their evolution and function.

Amino acid metabolism in helminths

Amino acids are major constituents of biological material. Chemically they are extremely stable and combine a relatively simple molecular structure with a wide range of properties and functions. In general, amino acid metabolism in helminths has been relatively neglected and the information available is often uneven and of uncertain quality. However, the search for new target sites for anthelmintic development has led to a renewed interest in this area. The amino acid composition of helminths is similar to that of other invertebrates and no unique amino acids have been reported. With the possible addition of tyrosine, helminths seem to require the same 10 essential amino acids as mammals and, where studied in detail, the pathways of amino acid synthesis in helminths are similar to those of mammals. Although amino acids are not a significant energy source in parasites, helminths are able to catabolize amino acids by pathways which, again, appear identical to those found in mammals. Helminths have also been shown to carry out a number of oxidative reactions associated with amino acid metabolism, including cysteine dioxygenase, proline hydroxylase and tryptophan hydroxylase. There are, however, differences in detail between the pathways of amino acid metabolism in helminths and mammals, particularly in the metabolism of the sulphur amino acids and arginine and proline. These differences may be exploitable in anthelmintic design and proline analogues and proline biosynthesis inhibitors show some potential as fasciolicides (Sheers et al., 1982). Differences in metabolism between parasites and their hosts may be the result of parasitic adaptation or they may merely reflect general features of the invertebrate phyla as a whole. Thus a comparison of amino acid metabolism in parasitic helminths with that of their free-living relatives may give some insight into the biochemical basis of parasitism.

[Effects of a latent Toxoplasma infection on the learning ability in white laboratory rats and mice (author's transl)]

1. Both white laboratory rats and white laboratory mice had a diminished learning capacity in connection with a latent Toxoplasma infection. 2. Five infected couples of rats out of 12 pairs were not able to learn their task by the double-training program in a given period of time. A second group of five rats was able to learn this program but later than the noninfected control-group of brothers and sisters did. 3. Mice seem to be more damaged by Toxoplasma infections than rats in their learning capacity. All infected mice did not reach the same ability than their control brothers and sisters. The reason for this differences could reflect the higher infection rate of the brain of mice than rats during the latent phase of infection.

Protein metabolism in Isoparorchis hypselobagri

Isoparorchis hypselobagri was maintained in a non-nutrient medium containing streptomycin and penicillin to prevent bacterial growth for a period of 12 hours. The parasites were kept under aerobic conditions at a suitable temperature of 30 degrees C. The protein content in Isoparorchis hypselobagri ranged from 56.25% to 67.5% with an average of 63.5%+/-4.6 of dry seight of the tissue. The nitrogen of Isoparorchis hypselobagri excreted as ammonia, after 12 hours of starvation was 3.04% of the total body nitrogen and as uric acid 1.6% of total body nitrogen.

Trace elements in Isoparorchis hypselobagri

The trace elements contents of the tissue of Isoparorchis hypselobagri were ascertained by quantitative analyses. The iron content was found to be particularly high in comparison of copper and zinc.