Plasma pharmacokinetics of clorsulon following administration of a single subcutaneous or intravenous injection to cattle

The benzenedisulfonamide derivative clorsulon is a potent fasciolicide which is marketed in fixed combination injectables, typically combined with the macrocyclic lactone ivermectin. In the presented pharmacokinetic study, the plasma profile of clorsulon in 32 healthy, young Brown Swiss cattle was administered a single intravenous dose at 3 mg/kg body weight or subcutaneously at 3, 6 or 12 mg/kg body weight (4 intact male and 4 female animals per treatment) as a 30% w/v clorsulon injection formulation. Serial blood samples were collected up to 24 days after administration to establish the pharmacokinetics, bioavailability and dose proportionality of clorsulon. Following a single intravenous injection of clorsulon at 3 mg/kg body weight, the area under the concentration versus time curve from the start of dose administration to the time of the last quantifiable concentration (AUClast ) was 4830 ± 941 day*ng/mL, and half-live was 2.37 ± 0.98 days. The back extrapolated concentration at time 0 was 38,500 ± 6070 ng/mL. The volume of distribution at steady state and clearance were 685 ± 107 mL/kg and 664 ± 127 mL/day/kg, respectively. In the groups dosed at 3, 6 or 12 mg/kg body weight by subcutaneous injection, clorsulon plasma concentrations rose to maximum within 0.5 day and decreased to the last sample point. For these groups, the maximum plasma clorsulon concentrations were 3100 ± 838, 5250 ± 1220 and 10,800 ± 1730 ng/mL, respectively, and the AUClast was 5330 ± 925, 9630 ± 1300 and 21,500 ± 3320 day*ng/mL, respectively. Half-lives, 2.01 ± 0.62, 3.84 ± 1.42 and 5.36 ± 0.60 days, respectively, increased significantly with dose, likely related to increasing dose volume. Clorsulon was well absorbed and fully bioavailable (103%-114%) after subcutaneous injection. No gender-related difference in systemic exposure was observed. Assessment of Cmax and AUClast demonstrated a proportional increase in systemic exposure to the clorsulon subcutaneous doses over the range of 3-12 mg/kg body weight.

Coadministration of ivermectin and abamectin affects milk pharmacokinetics of the antiparasitic clorsulon in Assaf sheep

In veterinary field, drug exposure during milk production in dairy cattle is considered a major health problem which concerns dairy consumers. The induced expression of the ABC transporter G2 (ABCG2) in the mammary gland during lactation plays a significant role in the active secretion of many compounds into milk. The main objective of this study was to determine the involvement of ABCG2 in the secretion into milk of the antiparasitic clorsulon in sheep as well as the possible effect of the coadministration of model ABCG2 inhibitors such as macrocyclic lactones on this process. Cells transduced with the ovine variant of ABCG2 were used to carry out in vitro transepithelial transport assays in which we showed that clorsulon is a substrate of the ovine transporter. In addition, ivermectin and abamectin significantly inhibited clorsulon transport mediated by ovine ABCG2. In vivo interactions were studied in Assaf sheep after coadministration of clorsulon (in DMSO, 2 mg/kg, s.c.) with ivermectin (Ivomec®, 0.2 mg/kg, s.c.) or abamectin (in DMSO, 0.2 mg/kg, s.c.). After ivermectin and abamectin treatment, no relevant statistically significant differences in plasma levels of clorsulon were reported between the experimental groups since there were no differences in the area under the plasma concentration-curve (AUC) between clorsulon treatment alone and coadministration with macrocyclic lactones. With regard to milk, total amount of clorsulon, as percentage of dose excreted, did not show statistically significant differences when macrocyclic lactones were coadministered. However, the AUC for clorsulon significantly decreased (p < 0.05) after coadministration with ivermectin (15.15 ± 3.17 μg h/mL) and abamectin (15.30 ± 3.25 μg h/mL) compared to control group (20.73 ± 4.97 μg h/mL). Moreover, milk parameters such as half-life (T1/2) and mean residence time (MRT) were significantly lower (p < 0.05) after coadministration of macrocyclic lactones. This research shows that the milk pharmacokinetics of clorsulon is affected by the coadministration of ABCG2 inhibitors, reducing drug persistence in milk.

Role of the Abcg2 Transporter in Secretion into Milk of the Anthelmintic Clorsulon: Interaction with Ivermectin

Clorsulon is a benzenesulfonamide drug that is effective in treating helminthic zoonoses such as fascioliasis. When used in combination with the macrocyclic lactone ivermectin, it provides high broad-spectrum antiparasitic efficacy. The safety and efficacy of clorsulon should be studied by considering several factors such as drug-drug interactions mediated by ATP-binding cassette (ABC) transporters due to their potential effects on the pharmacokinetics and drug secretion into milk. The aim of this work was to determine the role of ABC transporter G2 (ABCG2) in clorsulon secretion into milk and the effect of ivermectin, a known ABCG2 inhibitor, on this process. Using in vitro transepithelial assays with cells transduced with murine Abcg2 and human ABCG2, we report that clorsulon was transported in vitro by both transporter variants and that ivermectin inhibited its transport mediated by murine Abcg2 and human ABCG2. Wild-type and Abcg2-/- lactating female mice were used to carry out in vivo assays. The milk concentration and the milk-to-plasma ratio were higher in wild-type mice than in Abcg2-/- mice after clorsulon administration, showing that clorsulon is actively secreted into milk by Abcg2. The interaction of ivermectin in this process was shown after the coadministration of clorsulon and ivermectin to wild-type and Abcg2-/- lactating female mice. Treatment with ivermectin had no effect on the plasma concentrations of clorsulon, but the milk concentrations and milk-to-plasma ratios of clorsulon decreased in comparison to those with treatment without ivermectin, only in wild-type animals. Consequently, the coadministration of clorsulon and ivermectin reduces clorsulon secretion into milk due to drug-drug interactions mediated by ABCG2.

A transmission electron microscope study on the route of entry of triclabendazole into the liver fluke, Fasciola hepatica

Uptake of triclabendazole by the liver fluke, Fasciola hepatica has been studied by experiments designed to block either oral uptake of drug, by use of ligatures, or trans-tegumental diffusion, by allowing the drug to bind to an excess of bovine serum albumin (BSA) in the medium. Changes to the tegumental system, musculature and gut were assessed using transmission electron microscopy. Flukes were incubated in vitro for 24 h in TCBZ.SO (15 microg/ml). Disruption to the tegument and muscle was similar in ligatured and non-ligatured flukes, suggesting that closing the oral route did not affect drug uptake. The ultrastructure of the gastrodermal cells remained unchanged. Non-ligatured flukes were also incubated for 24 h in vitro in TCBZ.SO (15 microg/ml) in the presence of red blood cells (RBCs). Oral uptake of blood was demonstrated, but gut ultrastructure remained normal, whereas the tegument was severely disrupted. In separate experiments, ligatured and non-ligatured flukes were incubated in TCBZ.SO (15 microg/ml) in the presence of BSA (30 mg/ml) for 24 h in vitro. There was a marked decrease in the degree of tegumental disruption observed compared with TCBZ.SO action alone; again, the gut remained normal. The findings support previous morphological and pharmacological studies indicating that trans-tegumental uptake of triclabendazole predominates in the liver fluke.

A scanning electron microscope study on the route of entry of triclabendazole into the liver fluke, Fasciola hepatica

SUMMARY

Studies have been carried out to establish the relative importance of oral and trans-tegumental uptake of triclabendazole by the liver fluke, Fasciola hepatica. Experiments were designed to block either oral uptake of drug, by use of ligatures, or trans-tegumental diffusion, by allowing the drug to bind to bovine serum albumin (BSA) in the medium. Changes to the surface morphology of the tegument and gut were assessed by scanning electron microscopy. Flukes were incubated in vitro for 24 h in TCBZ.SO at a concentration of 15 microg/ml. Tegumental disruption in ligatured and non-ligatured flukes was similar, suggesting that closing the oral route did not affect drug uptake. The gut remained unaffected by drug treatment. When BSA (30 mg/ml) was present in the medium, there was a marked decline in the level of tegumental disruption. Again, the gut retained a normal morphology. Non-ligatured flukes were also incubated for 24 h in vitro in TCBZ.SO (15 microg/ml) in the presence of red blood cells. Oral ingestion of blood was demonstrated, although the gut surface retained a normal morphology. In contrast, the tegumental surface was severely affected by the drug. The findings support previous pharmacological studies which suggest that trans-tegumental uptake of triclabendazole predominates in the liver fluke.

Fasciola hepatica: ultrastructural effects of a combination of triclabendazole and clorsulon against mature fluke

A study has been carried out to investigate the ultrastructural effects of triclabendazole (TCBZ) at half-normal concentration, clorsulon at half-normal concentration, and a combination of these two drugs against mature Fasciola hepatica. The Cullompton TCBZ-susceptible isolate was used for these experiments. Flukes were incubated for 24 h in vitro in TCBZ sulphoxide (7.5 microg/ml), clorsulon (5 microg/ml), or a combination of the two drugs. For the in vivo experiment, rats were dosed with TCBZ (5 mg/kg body weight), clorsulon (5 mg/kg body weight), or a combination of the two drugs, and flukes recovered after 48 h. Fine structural changes within the tegumental syncytium and tegumental cells were assessed by transmission electron microscopy. Treatment with the combination of drugs produced greater disruption to the flukes than the individual drugs at half-normal concentrations, both in vivo and in vitro; also than TCBZ.SO at normal concentration in vitro. The changes observed aid in the understanding of the gross changes to the tegumental surface described previously (Meaney M, Allister J, McKinstry B, McLaughlin K, Brennan GP, Forbes AB, Fairweather I. Parasitol Res 99:609-621, 2006). The results indicate that there are additive effects between TCBZ and clorsulon and suggest that the use of drug combinations would be of value in the treatment of TCBZ-resistant fluke.

Fasciola hepatica: morphological effects of a combination of triclabendazole and clorsulon against mature fluke

A study has been carried out to investigate the morphological effects of half-strength triclabendazole (TCBZ), half-strength clorsulon, and a combination of these two drugs against mature Fasciola hepatica. The Cullompton TCBZ-susceptible isolate was used for these experiments. Flukes were incubated for 24 h in vitro in TCBZ sulphoxide (7.5 microg/ml), clorsulon (5 microg/ml), or a combination of the two drugs. For the in vivo experiment, rats were dosed with TCBZ (6.25 mg/kg body weight), clorsulon (5 mg/kg body weight), or a combination of the two drugs and flukes recovered after 48 h. Surface changes to the flukes were assessed by scanning electron microscopy. Treatment with the combination of drugs produced greater disruption to the flukes than the individual drugs at half-strength, both in vivo and in vitro. Disruption to the tegument of the flukes induced by the individual drugs at half-strength was relatively minor and less than that caused by the drugs at full-strength. The results suggest that there are additive effects between TCBZ and clorsulon, which may be indicative of synergy: the use of drug combinations would be of value in the treatment of triclabendazole-resistant fluke.

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.

A scanning electron microscope study on the route of entry of clorsulon into the liver fluke, Fasciola hepatica

Three experiments were carried out in vitro to determine the roles of the tegument and gut of Fasciola hepatica in the uptake of the flukicidal drug, clorsulon. Changes to the two surfaces were assessed by scanning 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). The gastrodermal surface remained normal and few changes to the tegumental surface were observed. 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. The gastrodermal surface was severely disrupted and the gut lamellae were disorganised and necrotic. Swelling of the tegument and blebbing on the tegumental surface were evident, but the changes were not severe. More severe swelling of the tegument was observed in the third experiment, in which flukes were incubated for 24 h in clorsulon (10 microg/ml), with both absorptive surfaces being available for drug uptake. The gastrodermal surface was badly disrupted and the gut lamellae were disorganised and necrotic. Taking the results of the three experiments together, the gastrodermal surface was more affected than the tegument and the greatest disruption to the two surfaces was seen when both routes of entry were available to the fluke. The data support a previous study which indicated that entry of clorsulon into the fluke in vivo is principally by the oral ingestion of drug bound to the red blood cells.

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.

Clorsulon pharmacokinetics in sheep and goats following oral and intravenous administration

Clorsulon was measured in plasma and urine of sheep and goats after administration of a single intravenous (i.v.) and after a single oral dose of 7 mg/kg. A three-compartment model with elimination occurring from the central compartment was determined to best describe the i.v. data, whereas a one-compartment model with a single exponential absorption phase best described the oral plasma data. The bioavailability of orally administered clorsulon was approximately 55% in goats and 60% in sheep. Peak plasma concentrations occurred at 14 h and 15 h after oral administration in goats and sheep, respectively. Absorption from the gastro-intestinal tract effectively prolonged the elimination of clorsulon by increasing the elimination half-life from 17 to 28 h in sheep and from 12 to 23 h in goats for the i.v. and oral routes, respectively. In both goats and sheep, approximately 50% of the i.v. dose was recovered in urine as parent drug at 48 h after administration, whereas 41% and 30% of the dose was recovered after oral administration for goats and sheep, respectively. The elimination rate constant (kel) in goats was nearly twice as large as the value determined in sheep, and the urea under the i.v. plasma curve in goats was only 63% of the value in sheep indicating that goats are more effective in their capacity to eliminate clorsulon than are sheep. These differences in drug disposition between sheep and goats may account for the reduced efficacy of clorsulon reported in goats.

The interactions between drugs and the parasite surface

The interrelationships between drugs and parasite surfaces are considered under the headings of (a) effects on membrane transport, (b) drug uptake mechanisms and (c) effects on surface morphology and function: praziquantel is discussed under a separate heading. The range of chemotherapeutic compounds that cause permeability changes and concomitant morphological disruption is discussed in terms of mode of drug action. Interpretation of the available data renders it difficult to identify the primary mode of action in the drugs considered. Drug uptake mechanisms are known for relatively few compounds; drug resistance as a function of drug acquisition is discussed. The role of the parasite surface as a specific drug target is argued.

Fasciola hepatica: motility response to metabolic inhibitors in vitro

The effects of metabolic inhibitors on the in vitro motility of Fasciola hepatica have been determined by means of an isometric transducer system. Sodium fluoride, an inhibitor of glycolysis, causes a long-term suppression of motility; this is also the effect of sodium iodoacetate (another glycolysis inhibitor) at low concentrations (1 X 10(-5) M and below). However, higher concentrations of iodoacetate induce a rapid inhibition of activity leading to a spastic paralysis. Both rotenone and oligomycin, which act as inhibitors of oxidative phosphorylation, produce a long-term suppression of movement. Carbonylcyanide-p-trifluoromethoxyphenylhydrazone and carbonylcyanide-m-chlorophenylhydrazone, which are uncouplers of oxidative phosphorylation, induce a spastic paralysis of the fluke; this is rapid at high concentrations (1 X 10(-4) and 1 X 10(-5) M). A brief stimulation of activity is evident at 1 X 10(-5) M and lasts longer at 1 X 10(-6) and 1 X 10(-7) M, before inhibition sets in. There is no stimulation at low concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (1 X 10(-8) and 1 X 10(-9) M), only inhibition leading to a medium-term spastic paralysis. In contrast, a third uncoupler, 2,4-dinitrophenol, causes a flaccid paralysis and the effect is rapid only at high concentrations, being accompanied by an initial increase in muscle tone at 1 X 10(-2) M and a brief stimulation of motility at 1 X 10(-3) M. Stimulation lasts longer at 1 X 10(-4) and 1 X 10(-5) M, but is not evident at concentrations below this. The effects on motility at these lower concentrations are essentially long term in nature. That the rapid effects of the uncouplers on muscle tone and motility are not due primarily to uncoupling is shown by 2,4,6-trinitrophenol and hydroquinone, compounds structurally related to 2,4-dinitrophenol. 2,4,6-Trinitrophenol is a membrane-impermeable compound devoid of uncoupling activity; at 1 X 10(-3) M, it causes an immediate inhibition of activity and increase in muscle tone. The antioxidant hydroquinone produces an initial stimulation of motility with some increase in tone, but this is followed by a sharp decline and a short-term flaccid paralysis. The results are discussed in relation to the postulated effects of certain fasciolicides on the energy metabolism of the liver fluke.

Fasciola hepatica: motility response to fasciolicides in vitro

The effects of a wide range of fasciolicides on the in vitro motility of Fasciola hepatica have been determined by means of an isometric transducer system. Carbon tetrachloride and diamphenethide do not affect movement at concentrations up to 500 and 100 micrograms/ml, respectively; at 1000 micrograms/ml, however, carbon tetrachloride induces a rapid tonic paralysis. Brotianide and the deacetylated metabolite of diamphenethide cause a rapid flaccid paralysis of the fluke at concentrations of 1.0 micrograms/ml and above. In contrast, the effect of MK-401 is a long-term one, a flaccid paralysis occurring after 20 hr only at 200 micrograms/ml. Praziquantel also produces a flaccid paralysis of the fluke, but this follows an initial increase, then decrease in muscle tone. The effect is rapid at 500 micrograms/ml, but long-term at 100 and 200 micrograms/ml; at these lower concentrations there is also a stimulation of activity. Oxyclozanide , rafoxanide, niclofolan , bithionol, and hexacholorophene induce a rapid spastic paralysis of the fluke at concentrations of 1.0 micrograms/ml and above. Both phasic and tonic components are evident in the response at concentrations of 1.0 micrograms/ml and below; the phasic component disappears at higher concentrations. Nitroxynil produces a similar effect, evident at higher concentrations. Among the benzimidazoles, mebendazole, oxfendazole, and albendazole sulphoxide cause a suppression of motility, whilst thiabendazole and albendazole produce a stimulation of movement. The effects are not rapid, however, for only mebendazole at 500 micrograms/ml causes total inactivity of the fluke within a 12-hr period. Possible explanations for these effects on fluke motility are discussed.

Mechanism of action of MK-401 against Fasciola hepatica: inhibition of phosphoglycerate kinase

The effect of MK-401 (4-amino-6-trichloroethenyl 1,3-benzenedisulfonamide) on Fasciola hepatica phosphoglycerate kinase (EC 2.7.2.3) was investigated. MK-401 was a competitive inhibitor of both 3-phosphoglycerate and ATP and had a Ki of 0.29 mM. ATP, 1,3-diphosphoglycerate and MK-401 protected the Fasciola enzyme from inhibition by N-ethylmaleimide. Analogues of MK-401 with different substituents at the 6 position (R = Cl, CF3, C2 F3, C3 F7) were competitive inhibitors of both 3-phosphoglycerate and ATP and a good correlation between the Ki and in vivo activity of these analogues was observed.

Purification and characterization of phosphoglycerate kinase from Fasciola hepatica

Phosphoglycerate kinase (EC 2.7.2.3) of Fasciola hepatica was purified 375-fold to homogeneity. The enzyme was monomeric, and had a molecular weight of 47 900 and a sedimentation coefficient of 3.0-3.5 S. The enzyme was composed of 397 amino acids and was relatively rich in sulfur amino acids containing 13 methionine and 2 cysteine residues per mole. The enzyme possessed a highly reactive essential sulfhydryl group and was inhibited irreversibly by iodoacetamide and N-ethylmaleimide and reversibly by p-chloromercuribenzoate and 5,5'-dithio-bis(2-nitrobenzoic acid). Initial velocity studies suggested that reaction occurred via a sequential mechanism. The Km values for 3-phosphoglycerate and ATP were 1.26 and 0.90 mM, respectively. ADP was a noncompetitive inhibitor with respect to both ATP and 3-phosphoglycerate.