31P-NMR studies of the metabolisms of the parasitic helminths Ascaris suum and Fasciola hepatica

The evolution of metabolic profiling in parasitology

The uses of metabolic profiling technologies such as mass spectrometry and nuclear magnetic resonance spectroscopy in parasitology have been multi-faceted. Traditional uses of spectroscopic platforms focused on determining the chemical composition of drugs or natural products used for treatment of parasitic infection. A natural progression of the use of these tools led to the generation of chemical profiles of the parasite in in vitro systems, monitoring the response of the parasite to chemotherapeutics, profiling metabolic consequences in the host organism and to deriving host-parasite interactions. With the dawn of the post-genomic era the paradigm in many research areas shifted towards Systems Biology and the integration of biomolecular interactions at the level of the gene, protein and metabolite. Although these technologies have yet to deliver their full potential, metabolic profiling has a key role to play in defining diagnostic or even prognostic metabolic signatures of parasitic infection and in deciphering the molecular mechanisms underpinning the development of parasite-induced pathologies. The strengths and weaknesses of the various spectroscopic technologies and analytical strategies are summarized here with respect to achieving these goals.

Ultrastructural observations on oral ingestion and trans-tegumental uptake of clorsulon by the liver fluke, Fasciola hepatica

Three experiments have been carried out in vitro to determine the effect of oral and trans-tegumental uptake of clorsulon on the fine structure of the tegument and gut of Fasciola hepatica. Changes were assessed by transmission electron microscopy. In the first experiment, the flukes were ligatured to prevent the oral ingestion of drug and treated for 24 h in clorsulon (10 microg/ml). Limited swelling of the basal infolds was observed in the tegumental syncytium. Swollen mitochondria were present in the syncytium, the underlying tegumental cells and in the gastrodermal cells. Swelling and vesiculation of the cisternae of the granular endoplasmic reticulum (ger) was evident in the gastrodermal cells, together with a reduction in secretory activity. In the second experiment, flukes were fed for 24 h on red blood cells isolated from rats dosed with clorsulon at 12.5 mg/kg body weight; this experiment was designed to prevent the exposure of the tegumental surface to the drug. There was severe swelling of the basal infolds in the tegumental syncytium and swelling of mitochondria in the syncytium, tegumental cells and gastrodermal cells. In the tegumental cells there was a decrease in the number of Golgi complexes as well. A number of changes were evident in the gastrodermal cells: swelling of the ger cisternae, an increase in the number of autophagic vacuoles, a reduction in the number of secretory bodies and disruption of the lamellae projecting from the surface of the cells. In the third experiment, flukes were incubated for 24 h in clorsulon (10 microg/ml), with both absorptive surfaces being available for drug uptake. There was severe swelling of the basal infolds in the tegumental syncytium and large autophagic vacuoles were present. Swollen mitochondria were a feature of the tegument, tegumental cells and gastrodermal cells, as were swollen cisternae of ger in the tegumental and gastrodermal cells. Fewer Golgi complexes were observed in the tegumental cells and in the gastrodermal cells there were fewer secretory bodies and an increased number of autophagic vacuoles. Overall, the gastrodermal cells were more severely affected than the tegument. Greater disruption of the tegument occurred when the oral route of uptake was available. The results support those of previous studies which point to oral uptake of clorsulon being the major route of entry into the fluke.

Transmission electron microscope study of the ultrastructural changes induced in the tegument and gut of Fasciola hepatica following in vivo drug treatment with clorsulon

Using transmission electron microscopy (TEM), both the tegument and gut of Fasciola hepatica were examined in an effort to identify and characterise the ultrastructural changes induced following treatment with the flukicidal drug clorsulon. Male Sprague-Dawley rats infected with F. hepatica were dosed orally at 8-8.5 weeks post-infection with clorsulon at a concentration of 12.5 mg/kg body weight. After 24, 48 and 72 h, rats were sacrificed by cervical dislocation and mature flukes recovered from the bile ducts. After 24 h treatment in vivo, disruption of the tegumental syncytium was concentrated at the apex of the syncytium where a dark band consisting of numerous secretory bodies was present. Some blebbing of the apex had also occurred, "open" bodies were present in this region and the mitochondria were slightly swollen. In the cell bodies, swelling of the mitochondria and their cristae had also occurred and the Golgi complexes appeared to be smaller than normal. The disruption seen after 48 h treatment in vivo was similar but more severe: the frequency of blebbing had increased, as had the number of "open" bodies and the swelling of the mitochondria. Vacuoles had begun to appear in the syncytium-both autophagic and electron-lucent-and swelling of the mucopolysaccharide masses around the basal infolds had occurred. Lipid droplets were observed occasionally. In the cell bodies, autophagic vacuoles had begun to appear and swelling of the mitochondria had increased in severity. After 72 h treatment in vivo, more severe disruption was seen in the tegumental syncytium in which widespread swelling and blebbing of the apex was apparent. The basal infolds had become very badly swollen in a number of specimens and damage to the spines was evident. The mitochondria remained swollen, as did the mucopolysaccharide masses around the basal infolds. Lipid droplets were more frequently observed in the syncytium. In the tegumental cells, swelling of the mitochondria was greater and an increase in the number of autophagic vacuoles was apparent. The gut showed signs of disruption after 24 h treatment in vivo, in that the surface lamellae were disrupted and a build-up of autophagic vacuoles at the apex of the cells had taken place. Swelling of the mitochondria and the cisternae of granular endoplasmic reticulum (gER) was evident. There was a decrease in the number of secretory bodies. After 48 h treatment in vivo, the number of autophagic vacuoles in the gastrodermal cells had increased, the mitochondria and gER remained swollen and the disruption seen to the lamellae was still evident. In the 72 h-treated specimens, the disruption seen in the gastrodermal cells had increased significantly, with severe vacuolation of the apical cytoplasm. An increase in the number of autophagic vacuoles was evident, the mitochondria and the gER remained swollen and lipid droplets were present in the cells.

The biochemical basis of anthelmintic action and resistance

The most commonly used modern anthelmintics include the benzimidazoles, the nicotinic agonists. praziquantel, triclabendazole and the macrocyclic lactones. These drugs interfere with target sites that are either unique to the parasite or differ in their structural features from those of the homologous counterpart present in the vertebrate host. The benzimidazoles exert their effect by binding selectively and with high affinity to the beta-subunit of helminth microtubule protein. The target site of the nicotinic agonists (e.g. levamisole, tetrahydropyrimidines) is a pharmacologically distinct nicotinic acetylcholine receptor channel in nematodes. The macrocyclic lactones (e.g. ivermectin, moxidectin) act as agonists of a family of invertebrate-specific inhibitory chloride channels that are activated by glutamic acid. The primary mode of action of other important anthelmintics (e.g. praziquantel, triclabendazole) is unknown. Anthelmintic resistance is wide-spread and a serious threat to effective control of helminth infections, especially in the veterinary area. The biochemical and genetic mechanisms underlying anthelmintic resistance are not well understood, but appear to be complex and vary among different helminth species and even isolates. The major mechanisms helminths use to acquire drug resistance appear to be through receptor loss or decrease of the target site affinity for the drug. Knowledge on the mechanisms of drug action and resistance may be exploitable for the development of new drugs and may provide information on ways to overcome parasite resistance, respectively.

Metabolite mapping of human filarial parasite, Brugia malayi with nuclear magnetic resonance

Metabolite mapping of human filarial parasite, Brugia malayi was carried out in vitro as well as in situ in host Mastomys coucha by 31P nuclear magnetic resonance (NMR) spectroscopy. Detection of parasites by visualizing contrast spots due to pathologic changes was observed by 1H magnetic resonance imaging (MRI). Major metabolites of adult B. malayi observed by 31P-NMR spectroscopy were of sugar phosphates (SP), phosphomonoesters (PME), glycerophosphoryl-ethanolamine (GPE), -choline (GPC), phosphoenolpyruvate (PEP), inorganic phosphate (Pi), nucleoside diphosphosugar and nucleotides-mono, -di and -tri phosphates. PEP and GPC were present in high concentration; PEP being the major energy reservoir and GPC the major phospholipid in this species of filaria. The 31P NMR spectra of testis of mastomys, showed seven major peaks of SP, PME, phosphocreatine (PCr), phosphodiesters (PDE), Pi, and nucleotides di- and tri-phosphates. The 31P-NMR spectra of testis of B. malayi infected animal also consisted of seven major peaks with significant decrease in the SP and PME peak showing changes in the carbohydrate and lipid metabolism of filaria infected testis. Thus, in vivo 31P MRS provided a non-invasive assessment of tissue bioenergetics and phospholipid metabolism.

Fasciolicides: efficacy, actions, resistance and its management

The modes of action of fasciolicides are described. Closantel and other salicylanilides interfere with energy metabolism by uncoupling oxidative phosphorylation in the fluke. Other fasciolicides are believed to have a metabolic action-halogenated phenols (via uncoupling) and clorsulon (via inhibition of glycolysis)-but direct evidence is lacking. Benzimidazoles (in particular, triclabendazole) bind to fluke tubulin and disrupt microtubule-based processes. Diamphenethide inhibits protein synthesis in the fluke. Other potential drug actions may contribute to overall drug efficacy. In particular, a number of fasciolicides-salicylanilides, phenols, diamphenethide-induce a rapid paralysis of the fluke, so their action may have a neuromuscular basis, although the actions remain ill-defined. Resistance to salicylanilides and triclabendazole has been detected in the field, although drug resistance does not appear to be a major problem yet. Strategies to minimize the development of resistance include the use of synergistic drug combinations, together with the design of integrated management programmes and the search for alternatives to drugs, in particular, vaccines.

Comparative in vitro effects of closantel and selected beta-ketoamide anthelmintics on a gastrointestinal nematode and vertebrate liver cells

PNU-87407 and PNU-88509, beta-ketoamide anthelmintics that are structurally related to each other and to the salicylanilide anthelmintic closantel, exhibit different anthelmintic spectra and apparent toxicity in mammals. The basis for this differential pharmacology was examined in experiments that measured motility and adenosine triphosphate (ATP) levels in larval and adult stages of the gastrointestinal nematode, Haemonchus contortus, and in a vertebrate liver cell line and mitochondria. PNU-87407 and PNU-88509 both exhibited functional cross-resistance with closantel in larval migration assays using closantel-resistant and -sensitive isolates of H. contortus. Each compound reduced motility and ATP levels in cultured adult H. contortus in a concentration- and time-dependent manner; however, motility was reduced more rapidly by PNU-88509, and ATP levels were reduced by lower concentrations of closantel than the beta-ketoamides. Tension recordings from segments of adult H. contortus showed that PNU-88509 induces spastic paralysis, while PNU-87407 and closantel induce flaccid paralysis of the somatic musculature. Marked differences in the actions of these compounds were also observed in the mammalian preparations. In Chang liver cells, ATP levels were reduced after 3 h exposures to > or = 0.25 microM PNU-87407, > or = 1 microM closantel or > or = 10 microM PNU-88509. Reductions in ATP caused by PNU-88509 were completely reversible, while the effects of closantel and PNU-87407 were irreversible. PNU-87407, closantel and PNU-88509 uncoupled oxidative phosphorylation in isolated rat liver mitochondria, inhibiting the respiratory control index (with glutamate or succinate as substrate) by 50% at concentrations of 0.14, 0.9 and 7.6 microM, respectively.

The effects of closantel treatment on the ultrastructure of Haemonchus contortus

H. contortus were recovered from sheep 0-14 h after intramuscular treatment with closantel. Ultrastructural examination revealed that mitochondria were more electron dense and contained swollen cristae compared with untreated controls. Following treatment, the basal channels in the intestine became prominent and there was vesicle formation in all organs examined. In contrast, closantel-resistant H. contortus appeared normal after drug treatment. It is likely that closantel affects membrane associated processes responsible for fluid and ion homeostasis as well as mitochondrial function. Untreated H. contortus were maintained in balanced salt solution for 12 h which caused lesions indicative of fluid imbalance, but at 23 h there were serious structural abnormalities.

Phosphorus metabolites of liver from mice infected with Hymenolepis microstoma

31P NMR in vivo spectra of mouse livers infected with Hymenolepis microstoma for 130 or 265 days showed modifications in phosphorus-containing metabolite ratios when compared to those of normal liver. After 130 days of infection the metabolite ratio of inorganic phosphate (Pi)/beta ATP significantly increased whereas that of phosphocreatine (PCr)/beta ATP significantly decreased. In older, 265 day infections, the increase in Pi/beta ATP and decrease in PCr/beta ATP persisted. Changes in the group infected for 130 days were accompanied by lowered pH. Analysis of liver extracts from mice with 130-day-old. H. microstoma revealed significantly lower concentrations of Pi, ATP and ADP compounds. In those from mice infected for 265 days the concentration of Pi remained low whereas concentrations of ATP and ADP increased to levels in between those of controls and the 130-day-old infection. In addition, levels of phosphorylethanolamine (PE) and of an unknown metabolite significantly increased in this latter group. Worm extracts contained high levels of glycerophosphorylcholine (GPC), Pi, fructose 1,6-diphosphate (FDP), PE, diphosphodiesters (DPDE), phosphorylcholine (PC) and glycerolphosphorylethanolamine (GPE) in order of declining concentrations, respectively.

Metabolites of alveolar Echinococcus as determined by [31P]- and [1H]-nuclear magnetic resonance spectroscopy

[31P]-Nuclear magnetic resonance (NMR) in vivo spectra of Echinococcus multilocularis cysts growing subcutaneously in Meriones unguiculatus showed prominent signals due to phosphomonoesters (PME), phosphodiesters (PDE), inorganic phosphate (Pi) and the alpha, beta and gamma phosphate groups of adenosine triphosphate (ATP). The internal pH of the parasite cysts was 6.7-6.8. The 31P spectra of extracts of these subcutaneous cysts showed peaks identified as glucose-6-phosphate (Glu-6-P), glycerol-3-phosphate (Gly-3-P), phosphorylethanolamine (PE), adenosine-5'-monophosphate (5'-AMP), nicotinamide adenine dinucleotide phosphate (NADP), phosphorylcholine (PC), Pi, glycerolphosphorylethanolamine (GPE), glycerolphosphorylcholine (GPC), phosphoenolpyruvate (PEP), adenosine diphosphate (ADP), ATP and diphosphodiesters (DPDE). These metabolites were also detected at comparable concentrations in the extracts of intraperitoneally grown cysts. In addition, significantly more phosphocreatine (PCr), probably of host origin, was detected in the subcutaneous cysts than in the intraperitoneal cysts. [1H]-NMR spectra of cyst extracts revealed that parasites grown in the abdominal cavity contained significantly less glucose but significantly more succinate, acetate, alanine and beta-hydroxybutyrate. Glycogen, creatine, glycine, taurine, betaine, cholines and lactate were present at similar concentrations in cyst material from both locations.

Phospholipids and protein kinase C in acetylcholine-dependent signal transduction in Ascaris suum

Quantitatively, the major phospholipid in the muscle of the nematode Ascaris suum was found to be phosphatidylcholine (lecithin). Stimulation of Ascaris muscle with acetylcholine or the agonists carbachol and levamisole increased the level of phosphorylcholine, 1,2-diacylglycerides and phosphatidic acid. Increased levels of these compounds, together with the demonstration of phospholipase C activity, suggest that phospholipid hydrolysis may be associated with the ACh response of the muscle via second messenger pathways. In other tissues, diacylglycerides and phosphatidic acid have been reported to regulate protein kinase C activity. Protein kinase C activity also was demonstrated in the muscle of Ascaris. For optimal activity the kinase was dependent upon Ca2+, unsaturated 1,2-diacylglyceride and phospholipid. All of the data are in accord with the possible involvement of a second messenger system being operative in the ACh-stimulated contraction of Ascaris muscle.

A 31P nuclear magnetic resonance study of Crithidia luciliae

31P NMR has been used to observe phosphorus-containing compounds in both perchloric acid and KOH extracts and in whole cell suspensions of Crithidia luciliae. Cells were grown in Bone and Steinert medium, or in a modified RPMI culture medium and harvested after about 72 h in mid- to late log phase. 31P NMR spectra of the perchloric acid extracts indicated that 3-phosphoglycerate, which is normally at low concentrations in most cells, was the dominant phosphorus-containing compound in the sugar phosphate region. 3-Phosphoglycerate is the end product of glycosomal glycolysis and our finding is consistent with previous observations of the failure to detect prior glycolytic intermediates. Other metabolites observed were ATP, ADP, NAD(P)+, phosphoenolpyruvate and low molecular weight polyphosphates (PPn, n less than 20). The presence of high-molecular-weight polyphosphates was established by spectra recorded on extracts obtained through subsequent treatment of the insoluble fraction with KOH. 31P NMR experiments on whole cells indicated that the average main internal pH of cells in late-log growth phase was approx. pH 7.2 +/- 0.1, using the orthophosphate resonance as an indicator. The cells responded to the addition of glucose (final concentration approx. 35 mM) with a decrease in pH, both internal (delta pH = -0.9 (55 min)-1) and external (delta pH = -1.3 (15 min)-1). Polyphosphates and ATP could not be observed in whole cell experiments, although perchloric acid extracts of identically treated cells showed no significant depletion of these compounds.

Developmental regulation of energy metabolism in Caenorhabditis elegans

Changes in energy metabolism during larval development in Caenorhabditis elegans have been investigated using phosphorus nuclear magnetic resonance (31P NMR). The relative concentrations of ATP, ADP, AMP, sugar phosphates, and other metabolites were observed to change during larval development, producing stage-specific spectra. These spectra are consistent with enzyme assays for isocitrate dehydrogenase and isocitrate lyase, indicating that high activity of the glyoxylate pathway during embryonic development decreases during the first larval (L1) stage, and respiration during the L2, L3, and L4 stages occurs preferentially through the TCA cycle. Metabolic strategies were further studied using mutants that are predisposed to enter the dauer stage, a developmentally arrested third-stage larva formed under conditions of overcrowding and limited food. After the L1 molt, energy metabolism in animals destined to become dauer larvae diverges from that of animals committed to growth. Relative to the L1, the L2 larvae committed to growth exhibit increased isocitrate dehydrogenase activity as well as increases in ATP and other high-energy phosphates, but predauer (L2d) larvae exhibit declining enzyme activities and declining levels of high-energy phosphates. The predominant phosphorus NMR signal in dauer larva extracts corresponds to inorganic phosphate. We conclude that metabolism is regulated during C. elegans larval development, with a major transition apparent after the L1 stage. This transition does not occur in larvae destined to form dauer larvae.

Acidic intracellular pH shift during Caenorhabditis elegans larval development

During recovery from the developmentally arrested, nonfeeding dauer stage of the nematode Caenorhabditis elegans, metabolic activation is accompanied by a decrease in intracellular pH (pHi). Phosphorus-31 nuclear magnetic resonance (31P NMR) analyses of perchloric acid extracts show that inorganic phosphate predominates in dauer larvae, whereas ATP and other high-energy metabolites are abundant within 6 hr after dauer larvae have been placed in food to initiate development. Although metabolic activation has been associated with an alkaline pHi shift in other organisms, in vivo 31P NMR analysis of recovering dauer larvae shows a pHi decrease from approximately 7.3 to approximately 6.3 within 3 hr after the animals encounter food. This shift occurs before feeding begins, and it coincides with, or soon follows, the developmental commitment to recover from the dauer stage, suggesting that control of pHi may be important in the regulation of larval development in nematodes.