C. elegans Gonad Dissection and Freeze Crack for Immunofluorescence and DAPI Staining

The C. elegans germline makes an excellent model for studying meiosis, in part due to the ease of conducting cytological analyses on dissected animals. Whole mount preparations preserve the structure of meiotic nuclei, and importantly, each gonad arm contains all stages of meiosis, organized in a temporal-spatial progression that makes it easy to identify nuclei at different stages. Adult hermaphrodites have two gonad arms, each organized as a closed tube with proliferating germline stem cells at the distal closed end and cellularized oocytes at the proximal open end, which join in the center at the uterus. Dissection releases one or both gonad arms from the body cavity, allowing the entirety of meiosis to be visualized. Here, a common protocol for immunofluorescence against a protein of interest is presented, followed by DAPI staining to mark all chromosomes. Young adults are immobilized in levamisole and quickly dissected using two syringe needles. After germline extrusion, the sample is fixed before undergoing a freeze crack in liquid nitrogen, which helps permeabilize the cuticle and other tissues. The sample can then be dehydrated in ethanol, rehydrated, and incubated with primary and secondary antibodies. DAPI is added to the sample in the mounting medium, which allows reliable visualization of DNA and makes it easy to find animals to image under a fluorescent microscope. This technique is readily adopted by those familiar with handling C. elegans after a few hours spent practicing the dissection method itself. This protocol has been taught to high-schoolers and undergraduates working in a research lab and incorporated into a course-based undergraduate research experience at a liberal arts college.

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.

Loss of Acetylcholine Signaling Reduces Cell Clearance Deficiencies in Caenorhabditis elegans

The ability to eliminate undesired cells by apoptosis is a key mechanism to maintain organismal health and homeostasis. Failure to clear apoptotic cells efficiently can cause autoimmune diseases in mammals. Genetic studies in Caenorhabditis elegans have greatly helped to decipher the regulation of apoptotic cell clearance. In this study, we show that the loss of levamisole-sensitive acetylcholine receptor, but not of a typical neuronal acetylcholine receptor causes a reduction in the number of persistent cell corpses in worms suffering from an engulfment deficiency. This reduction is not caused by impaired or delayed cell death but rather by a partial restoration of the cell clearance capacity. Mutants in acetylcholine turn-over elicit a similar phenotype, implying that acetylcholine signaling is the process responsible for these observations. Surprisingly, tissue specific RNAi suggests that UNC-38, a major component of the levamisole-sensitive receptor, functions in the dying germ cell to influence engulfment efficiency. Animals with loss of acetylcholine receptor exhibit a higher fraction of cell corpses positive for the “eat-me” signal phosphatidylserine. Our results suggest that modulation by ion channels of ion flow across plasma membrane in dying cells can influence the dynamics of phosphatidylserine exposure and thus clearance efficiency.

Trichuris suis and Oesophagostomum dentatum show different sensitivity and accumulation of fenbendazole, albendazole and levamisole in vitro

Background

The single-dose benzimidazoles used against Trichuris trichiura infections in humans are not satisfactory. Likewise, the benzimidazole, fenbendazole, has varied efficacy against Trichuris suis whereas Oesophagostomum dentatum is highly sensitive to the drug. The reasons for low treatment efficacy of Trichuris spp. infections are not known.

Methodology

We studied the effect of fenbendazole, albendazole and levamisole on the motility of T. suis and O. dentatum and measured concentrations of the parent drug compounds and metabolites of the benzimidazoles within worms in vitro. The motility and concentrations of drug compounds within worms were compared between species and the maximum specific binding capacity (B_max) of T. suis and O. dentatum towards the benzimidazoles was estimated. Comparisons of drug uptake in living and killed worms were made for both species.

Principal findings

The motility of T. suis was generally less decreased than the motility of O. dentatum when incubated in benzimidazoles, but was more decreased when incubated in levamisole. The B_max were significantly lower for T. suis (106.6, and 612.7 pmol/mg dry worm tissue) than O. dentatum (395.2, 958.1 pmol/mg dry worm tissue) when incubated for 72 hours in fenbendazole and albendazole respectively. The total drug concentrations (pmol/mg dry worm tissue) were significantly lower within T. suis than O. dentatum whether killed or alive when incubated in all tested drugs (except in living worms exposed to fenbendazole). Relatively high proportions of the anthelmintic inactive metabolite fenbendazole sulphone was measured within T. suis (6–17.2%) as compared to O. dentatum (0.8–0.9%).

Conclusion/Significance

The general lower sensitivity of T. suis towards BZs in vitro seems to be related to a lower drug uptake. Furthermore, the relatively high occurrence of fenbendazole sulphone suggests a higher detoxifying capacity of T. suis as compared to O. dentatum.

The human whipworm Trichuris trichiura is together with the roundworm Ascaris lumbricoides and the hookworms Ancylostoma duodenale and Necator Americanus the most common intestinal worms worldwide. Together they place more than 5 billion people at risk of infection. The current global control strategy against these worms is regular administration of anthelmintic drugs, mostly albendazole and mebendazole, both belonging to the drug-class benzimidazoles. Both drugs have a low effect against T. trichiura infections, but the reasons for this are not known. We evaluated the in vitro effect of two benzimidazoles; i.e., albendazole, fenbendazole, and another type of anthelmintic, levamisole, on the whipworm (T. suis) and the nodular worm (Oesophagostomum dentatum) of the pig. Oesophagostomum dentatum is highly sensitive towards benzimidazoles in comparison to T. suis. We measured and compared the drug uptake in both species in both living and killed worms. Our results suggest that the reason for the difference in sensitivity is due to a lower drug uptake into T. suis as compared to O. dentatum. Furthermore, T. suis was able to metabolise fenbendazole into an inactive metabolite to a much larger extent than O. dentatum, suggesting a higher detoxifying capacity of T. suis as compared to O. dentatum.

Drug resistance and neurotransmitter receptors of nematodes: recent studies on the mode of action of levamisole

Here we review recent studies on the mode of action of the cholinergic anthelmintics (levamisole, pyrantel etc.). We also include material from studies on the free living nematode Caenorhabditis elegans. The initial notion that these drugs act on a single receptor population, while attractive, has proven to be an oversimplification. In both free living and parasitic nematodes there are multiple types of nicotinic acetylcholine receptor (nAChR) on the somatic musculature. Each type has different (sometimes subtly so) pharmacological properties. The implications of these findings are: (1) combinations of anthelmintic that preferentially activate a broad range of nAChR types would be predicted to be more effective; (2) in resistant isolates of parasite where a subtype has been lost, other cholinergic anthelmintics may remain effective. Not only are there multiple types of nAChR, but relatively recent research has shown these receptors can be modulated; it is possible to increase the response of a parasite to a fixed concentration of drug by altering the receptor properties (e.g. phosphorylation state). These findings offer a potential means of increasing efficacy of existing compounds as an alternative to the costly and time consuming development of new anthelmintic agents.

Identification and characterization of novel nicotinic receptor-associated proteins in Caenorhabditis elegans

Nicotinic acetylcholine receptors (nAChRs) mediate fast excitatory neurotransmission in neurons and muscles. To identify nAChR accessory proteins, which may regulate their expression or function, we performed tandem affinity purification of the levamisole-sensitive nAChR from Caenorhabditis elegans, mass spectrometry of associated components, and RNAi-based screening for effects on in vivo nicotine sensitivity. Among the proteins identified was the calcineurin A subunit TAX-6, which appeared to function as a negative regulator of nAChR activity. We also identified five proteins not previously linked to nAChR function, whose inactivation conferred nicotine resistance, implicating them as positive regulators of nAChR activity. Of these, the copine NRA-1 colocalized with the levamisole receptor at neuronal and muscle plasma membranes, and, when mutated, caused reduced synaptic nAChR expression. Loss of SOC-1, which acts in receptor tyrosine kinase (RTK) signaling, also reduced synaptic levamisole receptor levels, as did mutations in the fibroblast growth factor receptor EGL-15, and another RTK, CAM-1. Thus, tandem affinity purification is a viable approach to identify novel proteins regulating neurotransmitter receptor activity or expression in model systems like C. elegans.

Levamisole receptor phosphorylation: effects of kinase antagonists on membrane potential responses in Ascaris suum suggest that CaM kinase and tyrosine kinase regulate sensitivity to levamisole

A two-micropipette current-clamp technique was used to record electrophysiological responses from the somatic muscle of Ascaris suum. Levamisole and acetylcholine were applied to the bag region of the muscle using a microperfusion system. Depolarizations produced by 10 s applications of 10 μmol l-1 levamisole or 20 s applications of 10 μmol l-1 acetylcholine were recorded. The effect on the peak membrane potential change of the kinase antagonists H-7, staurosporine, KN-93 and genistein was observed. H-7 (30 μmol l-1), a non-selective antagonist of protein kinases A, C and G but which has little effect on Ca2+/calmodulin-dependent kinase II (CaM kinase II), did not produce a significant effect on the peak response to levamisole or acetylcholine. Staurosporine (1 μmol l-1), a non-selective kinase antagonist that has effects on protein kinases A, C and G, CaM kinase and tyrosine kinase, reduced the mean peak membrane potential response to levamisole from 6.8 mV to 3.9 mV (P<0.0001) and the mean response to acetylcholine from 5.5 mV to 2.8 mV (P=0.0016). The difference between the effects of H-7 and staurosporine suggested the involvement of CaM kinase II and/or tyrosine kinase. KN-93, a selective CaM kinase II antagonist,reduced the mean peak response to levamisole from 6.2 mV to 2.7 mV(P=0.035) and the mean peak response of acetylcholine from 4.7 mV to 2.0 mV (P=0.0004). The effects indicated the involvement of CaM kinase II in the phosphorylation of levamisole and acetylcholine receptors. The effect of extracellular Ca2+ on the response to levamisole was assessed by comparing responses to levamisole in normal and in low-Ca2+ bathing solutions. The response to levamisole was greater in the presence of Ca2+, an effect that may be explained by stimulation of CaM kinase II. Genistein (90 μmol l-1), a selective tyrosine kinase antagonist, reduced peak membrane potential responses to levamisole from a mean of 6.4 mV to 3.3 mV (P=0.001). This effect indicated the involvement of tyrosine kinase in maintaining the receptor.

Genes affecting the activity of nicotinic receptors involved in Caenorhabditis elegans egg-laying behavior

Egg-laying behavior in Caenorhabditis elegans is regulated by multiple neurotransmitters, including acetylcholine and serotonin. Agonists of nicotinic acetylcholine receptors such as nicotine and levamisole stimulate egg laying; however, the genetic and molecular basis for cholinergic neurotransmission in the egg-laying circuitry is not well understood. Here we describe the egg-laying phenotypes of eight levamisole resistance genes, which affect the activity of levamisole-sensitive nicotinic receptors in nematodes. Seven of these genes, including the nicotinic receptor subunit genes unc-29, unc-38, and lev-1, were essential for the stimulation of egg laying by levamisole, though they had only subtle effects on egg-laying behavior in the absence of drug. Thus, these genes appear to encode components of a nicotinic receptor that can promote egg laying but is not necessary for egg-laying muscle contraction. Since the levamisole-receptor mutants responded to other cholinergic drugs, other acetylcholine receptors are likely to function in parallel with the levamisole-sensitive receptors to mediate cholinergic neurotransmission in the egg-laying circuitry. In addition, since expression of functional unc-29 in muscle cells restored levamisole sensitivity under some but not all conditions, both neuronal and muscle cell UNC-29 receptors are likely to contribute to the regulation of egg-laying behavior. Mutations in one levamisole receptor gene, unc-38, also conferred both hypersensitivity and reduced peak response to serotonin; thus nicotinic receptors may play a role in regulating serotonin response pathways in the egg-laying neuromusculature.

Binding of [3H]m-aminolevamisole to receptors in levamisole-susceptible and -resistant Haemonchus contortus

M-aminolevamisole, a potent analogue of the commercial anthelmintic levamisole, was used to investigate ligand-binding properties of homogenates of larval and parasitic stages of the nematode parasite of sheep, Haemonchus contortus. Kinetics of the binding of [3H]m-aminolevamisole to homogenates was measured in a drug-susceptible isolate and compared with a levamisole-resistant isolate. Equilibrium binding studies and kinetic studies revealed a high affinity binding component with a KD of 3 nM. A low affinity component (KD = 2.4 microM) was also apparent in equilibrium studies. High affinity [3H]m-aminolevamisole binding was displaced in a concentration-dependent manner by levamisole analogues and cholinergic agonists. Compared with the susceptible isolate, binding in a levamisole-resistant isolate of the parasite, was quantitatively similar over a range of developmental stages and binding conditions. However, under the conditions of binding there was a reduced affinity (larger KD) and more binding sites (larger Bmax) at the low affinity site in the resistant compared with the susceptible isolate. It was concluded that the ligand was binding to acetylcholine receptor populations of the nematode and that resistance may be associated with alterations in the low affinity site of this receptor.

Levamisole binding sites in Haemonchus contortus

Larval and adult extracts from isolates of Haemonchus contortus were assayed for specific [3H]levamisole binding activity. All of the tissue preparations displayed [3H]levamisole binding sites. The sensitive isolate SE and resistant isolate RJ showed no differences in larval and adult binding data. Larval SE extracts had higher receptor density (Bmax = 648 fmol mg-1) and dissociation constant (Kd = 1.28 microM) for [3H]levamisole than larval extracts of the American isolate RUSA (Bmax = 87 fmol mg-1 and Kd = 0.15 microM). Extracts of adult SE and RUSA isolates contain as much as 327 fmol mg-1 of protein and 205 fmol mg-1 of protein, respectively, and similar dissociation constants (Kd = 0.77 microM and Kd = 0.81 microM, respectively). There was a good correlation between specific binding activity of larval and adult extracts in both SE and RUSA isolates. The nicotinic cholinergic antagonist alpha-bungarotoxin had no effects in either isolate on [3H]levamisole binding activity. The results confirm that levamisole acts at a cholinergic receptor in H. contortus, and suggest that target site modification could be involved in the development of levamisole resistance.

Heterogeneous levamisole receptors: a single-channel study of nicotinic acetylcholine receptors from Oesophagostomum dentatum

A muscle vesicle preparation from Oesophagostomum dentatum, a 5 mm parasitic nematode, was developed for single-channel recording. Properties of nicotinic acetylcholine receptors activated by the anthelmintic levamisole (10 microM) were investigated using cell-attached and isolated inside-out patches. The current-voltage relationships of the single-channel currents were linear with conductances in the range 24.6-57.7 pS (mean 39.5 pS). The distributions of open times were fitted with a single exponential and mean open times were in the range 0.98-4.43 ms (mean 2.2 ms). The distributions of conductances and open times of the channels showed that the receptors could not be described as a single homogeneous population. There were two main channel subtypes: one subtype, designated G35, had a mean conductance of 35.2 pS and mean open time of 1.6 ms: another subtype designated G45, had a mean conductance of 44.6 pS and mean open time of 2.7 ms. A channel with a conductance near 25 pS. designated G25, and a channel with a conductance near 55 pS. designated G55, were also observed. The designations were based on the mean conductances. G. of the channel subtypes. A model for the heterogeneous population of nicotinic acetylcholine channels predicting four subtypes of receptor separated by their conductance is discussed and related to the development of levamisole resistance.

Characterization of an acetylcholine receptor gene of Haemonchus contortus in relation to levamisole resistance

The anthelminitic drug levamisole is thought to bind to nicotinic acetylcholine receptors of nematodes. It is possible that resistance to this drug is associated with either a change in binding characteristics or a reduction in the number of nicotinic acetylcholine receptors. Therefore, the molecular mechanism of levamisole resistance in the parasitic nematode Haemonchus contortus was studied by isolating and characterising cDNA clones encoding a putative ligand binding nicotinic acetylcholine receptor subunit, HCAl, of two susceptible and one levamisole resistant population. Hcal is related to unc-38, a nicotinic acetylcholine receptor subunit gene associated with levamisole resistance in Caenorhabditis elegans. Although extensive sequence analyses of hcal sequences revealed polymorphism at amino acid level, no association with levamisole resistance could be detected. Restriction fragment length polymorphism analyses confirmed that, although polymorphism was detected, no selection of a specific allele of hcal has taken place during selection for levamisole resistance in various levamisole resistant populations.

The disposition of 14C-levamisole in the lactating cow

1. 14C-Levamisole 1(-)-2,3,5,6-tetrahydro-6-phenyl[U-14C]imidazo[2,1-b]-thiazole was administered orally and subcutaneously to lactating cows (8 mg/kg body weight). Urine, faeces, milk and blood samples were collected from 0-48 h after dosing and tissues were collected 48 h after dosing. 2. 14C-Labelled residues (ppm 14C-levamisole equivalents) in blood were highest at 3 h (2.2 ppm, oral dose) or 6 h (2.1 ppm, subcutaneous dose) and then declined to less than 0.5 ppm 48 h after dosing. 3. 14C-Labelled residues in milk were highest in samples collected from 0-12 h after dosing (1.55 ppm and 1.86 ppm of levamisole equivalents from oral and subcutaneously dosed animals, respectively) and declined to 0.06 ppm in milk collected from 36-48 h after dosing. Milk collected from 0-48 h after dosing accounted for 0.2% (oral dose) and 0.6% (subcutaneous dose) of the total 14C-activity administered as 14C-levamisole. The parent compound, 14C-levamisole, accounted for 12% or less (declined with time after dosing) of the total 14C-activity in the milk. Three 14C-labelled metabolites (formed by oxidation of imidazoline ring and/or opening of thiazolidine ring) in the milk were isolated and identified. 4. Urinary excretion accounted for 83% and 84% and faecal excretion accounted for 11% and 9% of the total 14C-activity given orally and subcutaneously, respectively, as 14C-levamisole. No 14C-levamisole was detected in the urine; the major urinary metabolite (formed by opening of thiazolidine ring) was isolated and identified. 5. The 14C-activity remaining in the animals 48 h after dosing was widely distributed in body tissues; however, the concentration in the liver was substantially higher than in all other tissues examined. Less than 5% of the 14C-activity in the liver was present as 14C-levamisole.

Metabolism of levamisole, an anti-colon cancer drug, by human intestinal bacteria

1. Anaerobic incubation of levamisole with human intestinal flora resulted in the formation of three thiazole ring-opened metabolites, namely, levametabol-I, II and III. These new hydroxamic lactam-type metabolites were isolated and characterized by various spectroscopic methods. 2. Various pure cultures of human intestinal bacterial strains were shown, by quantitative h.p.l.c. analysis, to have ring-opening ability. Strong metabolizers include Bacteroides and Clostridium spp. Bacterial mixtures prepared from human faeces showed much greater ability to transform levamisole (74% in 48 h) than any pure strain culture. 3. Greatly decreased levamisole-transforming activity was observed with autoclaved bacterial cultures, and no activity was found with broth medium alone. This indicates that metabolism requires the presence of anaerobic bacteria and involves, at least in part, a non-enzymic process.

Histochemical visualization of lymphatic capillaries in the rat: a comparison of methods demonstrated at the posterior pharyngeal surface

A sufficient differentiation of lymphatic capillaries from blood capillaries in conventional light microscopy still eludes researches. The endothelium and media of lymphatic capillaries are characterized by a strong 5'-nucleotidase activity, whereas blood capillaries reveal no or significantly lower activity. Alkaline phosphatase activity, on the other hand, missing in the lymphatic capillaries is positive in most of the blood capillaries. For the histochemical visualization of the entire blood capillary bed, dipeptidyl peptidase IV-activity has to be used together with alkaline phosphatase. Various fixation and detection methods of 5'-nucleotidase are compared. In order to demonstrate 5'-nucleotidase activity, a method modified after Heusermann (1979) is considered to be most suitable. The results obtained are discussed with regard to their significance concerning the visualization of lymphatic capillaries. They are compared with a series of investigations in which alkaline phosphatase and dipeptidyl peptidase IV-activity are visualized in blood capillaries additional to the 5'-nucleotidase reaction. Various color reactions reveal a differentiation between blood capillaries and small lymphatics. The isolated visualization of 5'-nucleotidase activity with a simultaneous inhibition of alkaline phosphatase with L-tetramisole is considered to be the best way to histochemically demonstrate lymphatic capillaries. It was shown for the first time that only in the presence of L-tetramisole can small lymphatics be adequately visualized. A satisfactory differentiation between blood and lymphatic capillaries succeeded by means of a different color intensity of the reaction product.

Efficacy, safety, and residue evaluation of levamisole gel formulation in sows

Anthelmintic efficacy, safety, and residue studies were conducted in sows and gilts with a levamisole gel containing 11.5% levamisole HCl. In 12 sows and 12 gilts, 8 mg of levamisole HCl equivalent/kg of body weight orally was 100% (resinate) and 91.1% (gel) effective against 55-day-old Ascaris suum and 100% (gel) and 96.1% (resinate) effective against Oesophagostomum dentatum. In 20 sows given levamisole gel (8 mg of levamisole HCl/kg) orally just before breeding, 4 to 6 weeks after breeding, 4 to 6 weeks before farrowing, and just before farrowing, there were no adverse effects. Transient salivation was noticed in five sows after treatment. In 4 groups of 4 sows each given levamisole gel orally to provide 8, 24, 40, or 80 mg of levamisole HCl/kg, adverse clinical signs were not observed in sows treated with 8 mg/kg. Transient salivation was noticed in one sow given 24 mg/kg, two sows given 40 mg/kg, and four sows given 80 mg/kg. Multiple emesis and chomping occurred in one sow given 80 mg/kg. Levamisole residues in edible tissues from sows given 8 mg of levamisole gel/kg orally were less than 0.1 mg/kg of muscle and fat in sows killed on posttreatment day (PTD) 3 and less than 0.1 mg/kg of kidney in sows killed on PTD 5. Liver residues averaged 0.78 mg/kg in sows killed on PTD 3 and were reduced to 0.31 mg/kg in sows killed on PTD 5. The 99% upper tolerance limit with 95% confidence on the withdrawal time to assure levamisole residues of less than 0.10 mg/kg in liver tissue was 11 days.

The levamisole receptor, a cholinergic receptor of the nematode Caenorhabditis elegans

We describe a glass fiber filter binding assay for the levamisole receptor, a putative acetylcholine receptor of the nematode Caenorhabditis elegans, and we show that receptor detected in vitro binds both levamisole derivatives and cholinergic agonists with the pharmacological specificity expected of the physiologically functional nematode receptor. The receptor is detected by the binding of tritiated meta-aminolevamisole ([3H]MAL, 27 Ci/mmol). In extracts of the wild-type nematode, there is a saturable, high affinity binding activity for [3H]MAL (Kd approximately 5-10 nM). Well fed wild-type worms contain as much as 3 fmol of high affinity binding activity per mg of extract protein (0.14 pmol/g of wet weight of worms) and dauer larvae, a special juvenile stage, contain as much as 15 fmol of activity per mg of protein. Specific binding activity per mg of protein is highest in larval stages and decreases severalfold in the adult worm. The rates of formation and dissociation of the [3H]MAL-receptor complex are relatively slow (dissociation half-life, 17 min), in agreement with physiological studies of levamisole on Ascaris muscle strips. Levamisole derivatives and cholinergic agonists have the same relative potencies in inhibiting [3H]MAL binding as they do in causing nematode muscle contraction. Vertebrate cholinergic antagonists do not inhibit [3H]MAL binding, but several antagonists (mecamylamine, alpha-bungarotoxin, and cobra venom) potentiate the binding of [3H]MAL and can be used to demonstrate more clearly the presence of a second, lower affinity binding activity whose ligand-binding affinity is also potentiated by these agents. Both high and low affinity wild-type binding components are missing in the extremely levamisole-resistant mutant unc-74(x19).

Effects of levamisole on primary cultures of adult rat hepatocytes

Levamisole represents one of several new compounds that exhibit immunomodulating activity. Pharmacological data have documented a relationship between liver drug metabolism of levamisole and its subsequent immunomodulating activity. To directly investigate this relationship in a controlled manner, primary cultures of adult rat hepatocytes were treated with levamisole, and ultrastructural and biochemical effects were analyzed. Ultrastructurally, levamisole did not disrupt the cellular architecture of the hepatocytes. Biochemically, levamisole stimulated alkaline phosphatase activity and elevated microsomal cytochrome P-450 content after a 48-hr incubation. High pressure liquid chromatographic analysis of levamisole metabolites produced by cultured hepatocytes suggested the formation of a hepatocyte-specific metabolite(s) that may be associated with its immunological mode of action.

Novel assay and pharmacokinetics of levamisole and p-hydroxylevamisole in human plasma and urine

A new gas chromatographic method was developed for the quantification of levamisole in human plasma and urine, using a nitrogen-phosphorus flame ionization detector. The adsorption of the drug onto glass was prevented by treating the glassware with a siliconizing agent. The sensitivity of the assay was 10 ng ml-1 and as low as 2 ng ml-1 can be detected in plasma. The urinary metabolite p-hydroxylevamisole was analysed by high performance liquid chromatography with ultraviolet detection. The sensitivity of this assay was 0.50 micrograms ml-1. Plasma and urinary concentrations of levamisole were determined in 10 healthy volunteers including seven men and three women following the administration of a single 150 mg dose of levamisole. Levamisole was rapidly absorbed (tmax 1.5 h), giving a peak plasma concentration of 716.7 +/- 217.5 ng ml-1. The plasma elimination half-life of levamisole was 5.6 +/- 2.5 h. Only 3.2 +/- 2.9 per cent of the oral dose was recovered as unchanged drug in the urine, suggesting the importance of clearance of levamisole by routes other than the kidney, and most probably by hepatic metabolism. The urinary concentrations of p-hydroxylevamisole were determined before and after hydrolysis of the urine samples with beta-glucuronidase, and the level of conjugation of the metabolite with glucuronic acid was then estimated. Cumulative recovery of the metabolite accounted for 1.6 +/- 1.1 per cent and 12.4 +/- 5.5 per cent of the oral dose of levamisole before and after hydrolysis, respectively, indicating that p-hydroxylation is a relatively important route of metabolism of levamisole, and that the p-hydroxylated metabolite is excreted mainly in conjugation with glucuronic acid. Except for the absorption rate of levamisole which is approximately twice as rapid in women as in men, there is no marked difference in the pharmacokinetics of levamisole between healthy men and women.

Levamisole and bovine mastitis

Levamisole is an anthelmintic drug which also has immunomodulatory properties. The application of these immunomodulatory properties in the prevention and, or, treatment of bovine mastitis is considered. In the light of the available evidence on the use of levamisole against mastitis and of our understanding of the pathogenesis of mastitis it is thought that the prospect of using levamisole beneficially is limited. However, drying-off and parturition are two times at which levamisole may have rational application in mastitis prevention.

Tissue distribution and elimination of [3H]levamisole in the rat after oral and intramuscular administration

Total radioactivity and drug concentrations were determined in plasma, organs and excreta of male rats given a single oral or intramuscular dose (7.5 mg/kg) of [3H]levamisole. The anthelmintic drug was distributed mostly within the digestive contents after oral administration and in kidneys and liver after intramuscular injection. The parent drug accounted only for 32 to 45% of total radioactivity in plasma and it appeared metabolized in both urine and bile. The urine (0-72 h) contained 68-78% of the radioactive dose, as parent drug and other tritiated materials. The 4-hydroxylation of levamisole did not represent a major metabolic pathway of the drug in the rat.

Pharmacokinetics of [3H]levamisole in pigs after oral and intramuscular administration

A single oral (10 mg/kg of body weight) or IM (7.5 mg/kg) dose of [3H]levamisole was administered to pigs. Liquid scintillation counting and high performance liquid chromatography were used to determine total radioactivity and drug levels in plasma, duodenal and cecal contents, bile, and urine for 24 and 72 hours after dosing. Pharmacokinetic analysis indicated a 1-compartment open model with higher plasma bioavailability of levamisole after IM injection. Biological half-lives for elimination of the drug were 9.3 and 6.9 hours after oral and IM administration, respectively. Anthelmintic concentrations were higher in intestinal contents after oral gavage than after IM injection. The drug appeared extensively metabolized in all body fluids and particularly in bile, regardless of the route of administration. Biliary excretion of radioactivity and unchanged levamisole represented only slight percentages of the administered dose (approx 0.4% and 4.2%, respectively, in 72 hours). In contrast, about 60% and 20% of the dose were eliminated via urine as tritiated materials and unchanged drug. The choice of the most efficacious route of administration is discussed in regard to localization of helminthic disease.

Effects of breed, season, temperature, and solvents on the permeability of frozen and reconstituted cattle skin to levamisole

In vitro measurements have been made of the permeability of frozen and reconstituted cattle skins to levamisole. Breeds used were Red Poll cross, Hereford/Shorthorn cross, Hereford/Santa Gatrudis cross (or Brahman), Friesian (or Friesian/Jersey cross), and Hereford cattle killed in early fall, early summer, or winter. Inter- and intrabreed differences in skin permeability were small, but skin permeability in summer and fall was appreciably greater than in winter. Increases in skin temperature also increased skin permeability. The solvent properties of the skin toward neutral molecules appeared to be similar to those of water, suggesting that skin is a relatively polar barrier.

Incidence of experimental cirrhosis on hepatic disposition of [3H] levamisole in rats

Levamisole [phenyl-2 3H] was injected intravenously (4.7 mg kg-1) into anaesthetized controls and rats in which cirrhosis had been induced by a combination of carbon tetrachloride and phenobarbitone. The biliary excretion (6 h) of the parent drug and its metabolites formed a significant part of the administered dose. Although bile flow did not vary, biliary excretion of levamisole and metabolites were respectively increased and decreased in cirrhotic compared with control animals. These differences could be the result of cirrhosis-induced decrease in the hepatic biotransformation of levamisole and also to limited active carrier transport for the output of metabolites into bile canaliculi.

A comparison of frozen and reconstituted cattle and human skin as barriers to drug penetration

An in vitro study of the permeabilities of frozen and reconstituted cattle skin and human skin to levamisole was done. Cattle skin was 400 times more permeable to levamisole from an organic solvent (largely 2-ethoxyethanol) than was human skin. The diffusion coefficient value of levamisole in cattle skin and the partition coefficient value of levamisole from the organic solvent into the skin suggested that a relatively large amount of drug passed through skin appendages such as hair follicles or sweat/sebaceous ducts. Transcellular transport across the stratum corneum was rate-determining in human skin penetration.

Pharmacokinetics of levamisole in sheep

Levamisole, at a dose rate of 7.5 mg/kg, produced mean peak plasma concentrations of 3.1, 0.7 and 0.8 microgram/ml in four sheep after administrations by the subcutaneous, oral and intraruminal routes respectively. The mean peak concentrations in abomasal fluid were 33, 164 and 21 micrograms/ml respectively. The bioavailability of levamisole to the systemic compartment was less after oral and intraruminal administration than after subcutaneous administration. In six sheep there were no significant differences in the plasma concentrations obtained after subcutaneous administration in the thoracic, neck or gluteal regions. Dividing the dose between five sites in the gluteal region produced higher peak plasma concentrations than when injected into a single site.

The general immunopharmacology of levamisole

The need for treatments to correct an immunological defect, or to restore an impaired immune response asociated with disease or ageing, has led to the development of nonspecific immunoactive agents. Levamisole, a synthetic low molecular weight compound, is the first member of a new class of drugs which can increase the functions of cellular immunity in normal, healthy laboratory animals. The properties of levamisole have contributed to improved understanding of the molecular events which mediate or trigger immune responses. Levamisole can act either as an immunostimulant agent or an immunosuppressive agent. These apparently paradoxical effects depend upon the dose administered, the timing of its administration, the experimental assay used to measure effects, and the host genetic background. Levamisole's potential for opposite effects explains certain apparent inconsistencies observed in experimental or clinical assays. The drug's actions are modulated by the interaction between the T-cell recruiting efficacy of the sulphur moiety and the cholinergic effects of the imidazole ring. The clinical implications resulting from the immunopharmacological properties of levamisole are obvious: one should avoid its use in diseases without known association with an immune defect, and always attempt to correlate clinical data with modifications of immune parameters, since the therapeutic usefulness of correctly administered levamisole parallels improvement in tests of cellular immunity. Immunomodulators act by modifying the functions of the host cells involved in defences against invaders, and the effectiveness of an immunotherapeutic drug is dependent upon characteristics of the individual host. Thus, therapy with such drugs must be individualised; the appropriate agent and dosage should be chosen according to the immune capabilities of individual patients.

Excretion of levamisole in milk from cows treated with various formulations

The rate of disappearance of levamisole in milk from cows given levamisole hydrochloride drench, levamisole resinate in feed pellets, levamisole hydrochloride boluses, or levamisole phosphate injectable was determined. Each formulation was given as a single treatment to each of five cows at a rate equivalent to 8 mg of levamisole hydrochloride/kg of body weight. Levamisole hydrochloride residues in milk averaged .50, .55, .58, and .32 ppm at 12 hr after the administration of levamisole drench, feed, bolus, and injectable formulations. Levamisole hydrochloride residues were below .01 ppm in milk at 48 h after drench treatment and at 60 h after treatment with other three formulations. Toxicity symptoms were not observed in any cows following treatment.