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.

Targeting Kinases in Fasciola hepatica: Anthelminthic Effects and Tissue Distribution of Selected Kinase Inhibitors

Protein kinases have been discussed as promising druggable targets in various parasitic helminths. New drugs are also needed for control of fascioliasis, a food-borne trematode infection and worldwide spread zoonosis, caused by the liver fluke Fasciola hepatica and related species. In this study, we intended to move protein kinases more into the spotlight of Fasciola drug research and characterized the fasciolicidal activity of two small-molecule inhibitors from human cancer research: the Abelson tyrosine kinase (ABL-TK) inhibitor imatinib and the polo-like 1 (PLK1) inhibitor BI2536. BI2536 reduced viability of 4-week-old immature flukes in vitro, while adult worms showed a blockade of egg production. Together with a significantly higher transcriptional expression of PLK1 in adult compared to immature worms, this argues for a role of PLK1 in fluke reproduction. Both fluke stages expressed ABL1-TK transcripts at similar high levels and were affected by imatinib. To study the uptake kinetic and tissue distribution of imatinib in F. hepatica, we applied matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) for the first time in this parasite. Drug imaging revealed the accumulation of imatinib in different fluke tissues from 20 min to 12 h of exposure. Furthermore, we show that imatinib is metabolized to N-desmethyl imatinib by F. hepatica, a bioactive metabolite also found in humans. Besides the vitellarium, gastrodermal tissue showed strong signal intensities. In situ hybridization demonstrated the gastrodermal presence of abl1 transcripts. Finally, we assessed transcriptional changes of physiologically important genes in imatinib-treated flukes. Moderately increased transcript levels of a gene encoding a multidrug resistance protein were detected, which may reflect an attempt to defend against imatinib. Increased expression levels of the cell cycle dependently expressed histone h2b and of two genes encoding superoxide dismutases (SODs) were also observed. In summary, our pilot study demonstrated cross-stage activity of imatinib but not BI2536 against immature and adult F. hepatica in vitro; a fast incorporation of imatinib within minutes, probably via the oral route; and imatinib-induced expression changes of physiologically relevant genes. We conclude that kinases are worth analyzing in more detail to evaluate the potential as therapeutic targets in F. hepatica.

Reference gene analysis and its use for kinase expression profiling in Fasciola hepatica

The liver fluke Fasciola hepatica causes fasciolosis, a foodborne zoonosis affecting humans and livestock worldwide. A reliable quantification of gene expression in all parasite life stages relevant for targeting by anthelmintics in the mammalian host is fundamental. The aim of this study was to define a set of stably expressed reference genes for qRT-PCR in Fasciola studies. We determined the expression stabilities of eight candidate reference genes by the algorithms NormFinder, geNorm, BestKeeper, and comparative ΔCT method. The most stably expressed reference genes for the comparison of intra-mammalian life stages were glutamyl-prolyl-tRNA synthetase (Fheprs) and tubulin-specific chaperone D (Fhtbcd). The two best reference genes for analysis of in vitro-cultured juveniles were Fhtbcd and proteasome subunit beta type-7 (Fhpsmb7). These genes should replace the housekeeping gene gapdh which is used in most Fasciola studies to date, but in fact was differentially expressed in our analysis. Based on the new reference genes, we quantified expression of five kinases (Abl1, Abl2, PKC, Akt1, Plk1) discussed as targets in other parasitic flatworms. Distinct expression patterns throughout development were revealed and point to interesting biological functions. We like to motivate using this set of validated reference genes for future F. hepatica research, such as studies on drug targets or parasite development.

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.

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.

Dose-dependent pharmacokinetics of valproate in guinea pigs of different ages

The dose-dependence of sodium valproate (VPA) pharmacokinetics in relation to age was studied using guinea pigs. Sodium valproate in doses of 20, 200, and 600 mg/kg was administered by rapid intravenous infusion to male guinea pigs 3, 21, and 42 days old. Serum levels of VPA were determined by gas chromatography. Pharmacokinetic parameters were calculated based upon a two-compartment model. The area under the plasma concentration-time curve (AUC) increased out of proportion at the 600 mg/kg dose level in all groups. Other pharmacokinetic changes were as follows: in 3-day-old guinea pigs, the slow disposition rate constant (beta), the elimination rate constant from central compartment (K10), and the total clearance (Clt) were significantly decreased and the beta phase half-life (t 1/2) and the volume of central compartment (V1) were significantly increased at the 600 mg/kg dose level. In 21-day-old guinea pigs, beta and K10 were significantly decreased and t1/2 and V1 were significantly increased at doses of both 200 mg/kg and 600 mg/kg. In 42-day-old guinea pigs, however, only V1 and the volume of distribution at steady-state (Vss) showed significant increase after increasing doses. The extraction ratio (E) and the clearance of unbound drug (Clu), which were calculated based on unbound plasma levels, indicate that the dose-dependent kinetics of VPA are probably due to saturation of metabolism and that the metabolic capacity for VPA in the newborn group is the smallest among all groups.

Model-independent procedure for area estimation and intergroup comparisons

A method is provided for estimating the area under a response-time curve for an experimental situation where independent observations are made at each time point. The procedure utilizes least-squares spline functions and the jackknife technique to provide area estimates, standard errors, and a statistical test for intergroup comparisons. The method is based on an empirical model and provides a means of analysis when no prior model can be specified or if the incorrect specification of a model will produce invalid results. The method is illustrated using data from a study comparing the pharmacokinetic behavior of a fasciolicide in rats having either a young or old parasitic infestation. The results obtained are comparable with those generated by a model-dependent approach.