Cyclosporin A and trifluoperazine, two resistance-modulating agents, increase ivermectin neurotoxicity in mice

Mitochondrial permeability transition pore (MPTP) desensitization increases sea urchin spermatozoa fertilization rate

Mitochondrial permeability transition pore (MPTP) is a protein complex whose opening promotes an abrupt increase in mitochondrial inner membrane permeability. Calcium signaling pathways are described in gametes and are involved in the fertilization process. Although mitochondria may act as Ca(2+) store and have a fast calcium-releasing mechanism through MPTP, its contribution to fertilization remains unclear. The work aimed to investigate the MPTP phenomenon in sea urchin spermatozoa and its role on the fertilization. Several pharmacological tools were used to evaluate the MPTP's physiology. Our results demonstrated that MPTP occurs in male gametes in a Ca(2+) - and voltage-dependent manner and it is sensitive to cyclosporine A. Additionally, our data show that MPTP opening does not alter ROS generation in sperm cells. Inhibition of MPTP in spermatozoa strongly improved the fertilization rate, which may involve mechanisms that increase the spermatozoa lifespan. The present work is the first report of the presence of a voltage- and Ca(2+) -dependent MPTP in gametes of invertebrates and indicates MPTP opening as another evolutionary feature shared by sea urchins and mammals. Studies about MPTP in sea urchin male gametes may contribute to the elucidation of several mechanisms involved in sperm infertility.

An association between systemic cyclosporine administration and development of acute bullous keratopathy in cats

OBJECTIVE

To determine whether any association exists between the onset of feline acute bullous keratopathy (ABK) and administration of systemic corticosteroid or immunosuppressive therapy.

ANIMALS STUDIED

Medical records of cats diagnosed with ABK between the years of 2000 and 2008 were retrospectively reviewed. Breed, age at diagnosis, weight, systemic disease status, eye affected, ophthalmic examination findings, systemic and topical therapy instituted, dosage and duration of therapy, visual outcome and histopathological analyses were recorded in cases meeting the inclusion criteria.

RESULTS

A total of 12 cats of a surveyed population of 70 167 met the inclusion criteria with 17/24 eyes affected by ABK. Medical and/or surgical therapy was utilized for management of ABK with 13/17 eyes remaining sighted at the time of last follow-up. In a subset of cases corneal cytology, aerobic bacterial culture, FHV-1 PCR, virus isolation and/or histopathology were performed; no infectious organisms were identified. A rupture in Descemet's membrane of the cornea was identified histologically in two globes. A total of 10 of 12 cats had been previously diagnosed with ongoing systemic disease. A total of 10 of 12 cats were receiving systemic therapy, and a significant association (P < 0.001) was noted between systemic administration of corticosteroids and/or cyclosporine A and the development of ABK. A total of 8 of 10 cats were administered oral prednisolone at doses between 1-2 mg/kg every 12-24 h. A total of 5 of 8 cats receiving oral prednisolone were concurrently administered oral cyclosporine at doses of 1.5-7 mg/kg every 12-24 h. Systemic cyclosporine therapy was found to be a significant risk factor (P < 0.001) for ABK development, while systemic prednisolone was not significant (P = 0.10).

CONCLUSIONS

Systemic cyclosporine administration appears to be a risk factor for development of ABK in the population of cats studied.

Inhibition of human MDR1 and BCRP transporter ATPase activity by organochlorine and pyrethroid insecticides

Despite the growing evidence suggesting that pesticides contribute to chronic diseases, there is a limited understanding of how these chemicals are removed from cells and whether pesticides can alter the disposition of drugs. The present study examined the effects of two classes of insecticides (organochlorine and pyrethroid) on the ATPase activity of the human multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) efflux transporters. Using plasma membranes from cells overexpressing MDR1 and BCRP, it was demonstrated that the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) (o,p'-DDT and p,p'-DDT isomers) as well as its metabolite (p,p'-dichlorodiphenyldichloroethane), inhibit both MDR1 and BCRP ATPase activity. In addition, p,p'-dichlorodiphenyldichloroethylene, and two pyrethroid pesticides inhibited BCRP ATPase activity between 4 and 7 μM. Additional research is necessary to further characterize the functional inhibition of MDR1 and BCRP activity and determine whether pesticides alter the transporter-mediated disposition of other chemicals.

A review on the toxicity and non-target effects of macrocyclic lactones in terrestrial and aquatic environments

The avermectins, milbemycins and spinosyns are collectively referred to as macrocyclic lactones (MLs) which comprise several classes of chemicals derived from cultures of soil micro-organisms. These compounds are extensively and increasingly used in veterinary medicine and agriculture. Due to their potential effects on non-target organisms, large amounts of information on their impact in the environment has been compiled in recent years, mainly caused by legal requirements related to their marketing authorization or registration. The main objective of this paper is to critically review the present knowledge about the acute and chronic ecotoxicological effects of MLs on organisms, mainly invertebrates, in the terrestrial and aquatic environment. Detailed information is presented on the mode-of-action as well as the ecotoxicity of the most important compounds representing the three groups of MLs. This information, based on more than 360 references, is mainly provided in nine tables, presenting the effects of abamectin, ivermectin, eprinomectin, doramectin, emamectin, moxidectin, and spinosad on individual species of terrestrial and aquatic invertebrates as well as plants and algae. Since dung dwelling organisms are particularly important non-targets, as they are exposed via dung from treated animals over their whole life-cycle, the information on the effects of MLs on dung communities is compiled in an additional table. The results of this review clearly demonstrate that regarding environmental impacts many macrocyclic lactones are substances of high concern particularly with larval instars of invertebrates. Recent studies have also shown that susceptibility varies with life cycle stage and impacts can be mitigated by using MLs when these stages are not present. However information on the environmental impact of the MLs is scattered across a wide range of specialised scientific journals with research focusing mainly on ivermectin and to a lesser extent on abamectin doramectin and moxidectin. By comparison, information on compounds such as eprinomectin, emamectin and selamectin is still relatively scarce.

Macrocyclic Lactone Endectocides

The macrocyclic lactone endectocides such as ivermectin, abamectin, selamectin and moxidectin have revolutionized the treatment of parasitic diseases in animals, being active against internal and external parasites. Ivermectin was introduced into veterinary medicine in the 1980s and since that time a number of related compounds have been introduced. In the treatment of internal parasites they complement the use of levamisole and the benzimidazoles, but in recent years they have found utility in treating external insect parasites. These agents show very low levels of toxicity under most circumstances. However, they are neurotoxic particularly in subpopulations of animals with mutations in the MDR1 gene. Toxicity may be also seen during off-label use, possibly because the doses used have been extrapolated from use in other animals. Regardless of these considerations, the macrocyclic lactone endectocides are extremely effective and safe drugs in the treatment of parasitic diseases of animals.

Peptide-chlorambucil conjugates combat pgp-dependent drug efflux

Cancer drugs, such as the ovarian cancer drug adriamycin, are effective at slowing disease progression and improving remission rates in patients. However, drug resistance often arises, limiting the activity of these agents in some patients. In particular, efflux pumps, which export drugs out of cells, limit the efficacy of a variety of anticancer agents. While inhibitors to block these pumps currently exist, they are usually not used clinically because they alter other drug properties. Here, we report a novel inhibitor of drug efflux that only reduces pump activity temporarily. This decreases the risk that it will alter drug function and cause nonspecific toxicity. P-glycoprotein efflux pumps are commonly overexpressed by malignant cells and are a major contributing factor to the development of drug resistance. Many therapeutics containing basic nitrogens, hydrophobic character, or aromaticity are efficiently eliminated from cells, and Pgp inhibitors must often be coadministered to limit this process. However, currently available inhibitors often alter the pharmacokinetic profiles of therapeutics or increase off-target toxicity, limiting their clinical utility. Here, we report the development of a novel panel of peptide-chlorambucil conjugates capable of efficiently decreasing efflux of Pgp substrates. These conjugates selectively improve adriamycin toxicity and uptake for short, but not prolonged, periods reducing the risk of altered pharmacokinetics and off-target effects.

Hyperinfection strongyloidiasis in a liver transplant recipient treated with parenteral ivermectin

Severe strongyloidiasis, including hyperinfection and dissemination, is a recognized complication of solid organ transplantation. However, the development of strongyloidiasis in a liver transplant recipient has not been previously described. We present a case of severe strongyloidiasis occurring in a patient 4 months after liver transplantation and 1 month after receiving treatment for acute rejection. We assess the management challenges in this patient who remained symptomatic despite oral treatment with ivermectin and albendazole and eventual successful treatment with parenteral ivermectin. We review the published experience with alternative methods of ivermectin administration. We also investigate the possible source of infection, as the patient was not from an endemic area.

Independent Regulation of ABCB1 and ABCC Activities in Thymocytes and Bone Marrow Mononuclear Cells during Aging

Aging modifies a number of functional and phenotypic parameters of cells from the immune system. In this study, the activities of two members of the superfamily of ATP-binding cassette (ABC) transport proteins, ABCB1 and ABCC (measured by rhodamine 123 efflux and Fluo-3 efflux respectively), were compared in murine bone marrow cells and thymocytes of young (3-4 weeks old), adult (2-3 months old) and old (18 months old) mice. ABCB1 activity was shown to be age regulated in murine bone marrow mononuclear cells and thymocytes. In the bone marrow, the increased amount of cells with ABCB1 activity observed in old mice was restricted to the c-kit(-)Sca-1(+) and c-kit(+)Sca-1(+) subpopulations. Only a small percentage of c-kit(+) cells in the thymus had ABCB1 activity, and this subpopulation increased with age. In the thymus, old age augmented this activity in the CD4(-) CD8(-) double-negative cells and in the CD4(+) and CD8(+) single-positive populations. The activity of another ABC transporter, the ABCC-related activity, was also modified by age in the bone marrow. However, the age-related increase was observed in the subpopulations were ABCB1 was not modified, namely the non-progenitor population (c-kit(-)Sca-1(-)cells) and c-kit(+)Sca-1(-) cells. Nearly, all thymocytes expressed the ABCC1 molecule in an active form and aging did not affect this pattern. This study demonstrates an independent upregulation of ABCB1 and ABCC activities during the aging process. The increases were observed in different subsets of cells but followed a developmentally regulated pattern. The functions played by these transporters and alterations in aging are discussed.

Multidrug-resistance gene 1-type p-glycoprotein (MDR1 p-gp) inhibition by tariquidar impacts on neuroendocrine and behavioral processing of stress

The multidrug-resistance gene 1-type p-glycoprotein (MDR1 p-gp) is a major gate-keeper at the blood-brain barrier (BBB), protecting the central nervous system from accumulation of toxic xenobiotics and drugs. In addition, MDR1 p-gp has been found to control the intracerebral access of glucocorticoid hormones and thus to modulate the activity of the hypothalamic-pituitary-adrenocortical (HPA) system. In view of the implication of glucocorticoids in the control of behavior, we examined how acute pharmacological inhibition of MDR1 p-gp at the BBB by tariquidar (XR9576; 12 mg/kg, PO) impacts the neuroendocrine and behavioral processing of stress in C57BL/6JIcoHim inbred mice. Inhibition of MDR1 p-gp at the BBB did not alter emotional behavior at baseline. However, mice that were sensitized by water-avoidance stress, a mild psychological stressor, displayed significantly reduced anxiety-related behavior in the elevated plus-maze test when treated with tariquidar. Tariquidar, however, had no effect on stress-coping performance assessed in the forced swim test. Investigating the impact of acute MDR1 p-gp inhibition on the glucocorticoid system, we observed a significant attenuation of the mild stress-induced increase of plasma corticosterone after tariquidar administration. In order to examine whether the anti-anxiety effect of tariquidar in sensitized animals is mediated by glucocorticoids, the animals were treated with corticosterone (1mg/kg, SC) immediately after exposure to water-avoidance stress. Corticosterone caused a significant anxiolytic-like effect in this stress-related anxiety protocol, whereas tariquidar could not further enhance corticosterone's anti-anxiety effects. The current data show for the first time that pharmacological inhibition of MDR1 p-gp at the murine BBB by tariquidar alters emotional behavior and HPA axis activity. By facilitating the entry of corticosterone into the brain, tariquidar enhances feedback inhibition of the HPA system and in this way improves anxiety-related stress processing. These findings highlight a novel approach to the treatment of stress-related affective disorders in humans.

Role of drug efflux transporters in the brain for drug disposition and treatment of brain diseases

The blood-brain barrier (BBB) serves as a protective mechanism for the brain by preventing entry of potentially harmful substances from free access to the central nervous system (CNS). Tight junctions present between the brain microvessel endothelial cells form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the barrier properties of the brain capillary endothelial cells. Because of these properties, the BBB only allows entry of lipophilic compounds with low molecular weights by passive diffusion. However, many lipophilic drugs show negligible brain uptake. They are substrates for drug efflux transporters such as P-glycoprotein (Pgp), multidrug resistance proteins (MRPs) or organic anion transporting polypeptides (OATPs) that are expressed at brain capillary endothelial cells and/or astrocytic end-feet and are key elements of the molecular machinery that confers the special permeability properties to the BBB. The combined action of these carrier systems results in rapid efflux of xenobiotics from the CNS. The objective of this review is to summarize transporter characteristics (cellular localization, specificity, regulation, and potential inhibition) for drug efflux transport systems identified in the BBB and blood-cerebrospinal fluid (CSF) barrier. A variety of experimental approaches available to ascertain or predict the impact of efflux transport on brain access of therapeutic drugs also are described and critically discussed. The potential impact of efflux transport on the pharmacodynamics of agents acting in the CNS is illustrated. Furthermore, the current knowledge about drug efflux transporters as a major determinant of multidrug resistance of brain diseases such as epilepsy is reviewed. Finally, we summarize strategies for modulating or by-passing drug efflux transporters at the BBB as novel therapeutic approaches to drug-resistant brain diseases.

Veterinary pharmacovigilance. Part 6. Predictability of adverse reactions in animals from laboratory toxicology studies

Toxicological studies are conducted on constituents of veterinary medicinal products for a number of reasons. Aside from being a requirement of legislation, they are carried out for predictive purposes in the assessment of user safety or for the determination of consumer safety, for example, in the elaboration of maximum residue limits or tolerances. Alternatively, the results of toxicology studies may be available as they have been generated for registration of the drug for human medicinal purposes. This paper examines if the results of such studies have any predictive value for adverse reactions, which might occur during clinical use in animals. A number of adverse reactions, notably the Type A (toxicology or pharmacology dependent) should be predictable from these laboratory studies. However, as with human pharmaceutical products, they have less utility in predicting Type-B reactions (idiosyncratic in nature).

Effect of P-glycoprotein inhibitors erythromycin and cyclosporin A on brain pharmacokinetics of nimodipine in rats

Effect of P-glycoprotein (P-gp) inhibitors erythromycin (Ery) and cyclosporin A(CsA) on brain pharmacokinetics of nimodipine (NMD) in rats was studied. NMD concentrations in rat plasma and brain were determined after iv 2 mg/kg NMD alone, co-administration with Ery and CsA, respectively. It was found that concentrations of NMD in plasma of the three groups had a little difference, but brain concentrations of NMD in rats co-administrated with Ery and CsA were significantly higher than those in rats NMD alone. Significances of NMD in rat brain were found at 20, 40, 60 and 90 min after iv NMD. The brain T(1/2) in rat treated with ery(75.0 min) and CsA(79.0 min) were larger than that (44.2 min) in rats NMD alone. The results indicated that P-gp inhibitors Ery and CsA may increase concentration in rat brain by inhibiting elimination of NMD from brain.

Ivermectin: does P-glycoprotein play a role in neurotoxicity?

The macrocyclic lactone ivermectin (Mectizan(R)) is widely used for the control of human filarial infections, particularly as a donated product for onchocerciasis and lymphatic filariasis. In the case of control of lymphatic filariasis in Africa, it is used in combination with donated albendazole. In areas co-endemic for Onchocerciasis and Loa loa, serious adverse reactions have been observed in patients with apparently high microfilaria counts of Loa loa. Recent findings suggest that the severe central nervous system side effects seen in various vertebrates following ivermectin treatment may be due to an absence of, or functional deficiency in P-glycoprotein. P-glycoprotein is expressed in the apical membrane of brain capillary epithelial cells and is responsible for limiting the brain penetration of a range of compounds. Toxicity of ivermectin in some collie dogs may be explained by a 4-bp deletion mutation of the mdr1 gene resulting in a frame shift, generating stop codons that prematurely terminate synthesis of P-glycoprotein. Additionally, sub-populations of CF-1 identified as expressing reduced levels of P-glycoprotein exhibit increased toxicity to substrates of this transporter. Furthermore, while the traditional view of drug-drug interactions is alteration in drug clearance mediated through a change in hepatic drug metabolism, some of these changes may arise through competition for binding sites on P-glycoprotein in the blood-brain barrier, resulting in reduced extracellular efflux and enhanced CNS toxicity. In conclusion, P-glycoprotein is an integral component of the human blood brain barrier and plays a central role in limiting drug uptake into the brain. Altered expression or function of p-glycoprotein could conceivably allow elevation of brain concentrations of ivermectin and produce severe neurotoxicity. This might arise through a genetic polymorphism in p-glycoprotein or co-administration of ivermectin with a drug or foodstuff that might inhibit this efflux transporter.

Administration of drugs known to inhibit P-glycoprotein increases brain bilirubin and alters the regional distribution of bilirubin in rat brain

P-glycoprotein (P-gp) is an ATP-dependent integral plasma membrane efflux pump, expressed in abundance in brain capillary endothelial cells and astrocytes. P-gp contributes to the blood-brain barrier in limiting the influx and retention of a variety of lipophilic compounds, including unconjugated bilirubin. Several drugs block P-gp function and thereby enhance intracellular accumulation of P-gp substrates. In this study we proposed that pretreatment with drugs known to inhibit P-gp function in clinically relevant doses would alter the uptake of bilirubin in the brain of 32- to 36-d-old rats. In the first arm of the study, the animals received pretreatment with an i.v. infusion of either propanolol, erythromycin, verapamil, ceftriaxone, rifampin, or saline, 10 min before an i.v. bolus of 50 mg/kg bilirubin was given. Except for the erythromycin-treated rats, all treatment groups had significantly higher brain-to-serum bilirubin ratios than control animals (p < 0.05, Welch's t test). In the second arm of the study, treatment with either ceftriaxone or rifampin or saline i.v. preceded a 50 mg/kg i.v. bolus of radioactive bilirubin. Analysis of seven different brain regions by scintillation counting showed that the distribution patterns differed significantly between the study groups (p < 0.001, ANOVA), however, not in accordance with a kernicteric staining pattern. Because of limited knowledge of expression and function of P-gp and other membrane transport proteins in the newborn, the implications of this study remain to be seen. We speculate that drugs known to inhibit P-gp function may increase the risk of bilirubin encephalopathy in the hyperbilirubinemic infant.

Review of the pharmacokinetics, interactions and adverse reactions of cyclosporine in people, dogs and cats

Cyclosporine is being increasingly used in veterinary medicine. Oral formulations of the drug have found many therapeutic uses, but topical formulations have met with only limited success, probably owing to their poor penetration through the stratum corneum. The concurrent use of ketoconazole to inhibit cyclosporine metabolism has been shown to reduce the required dose and hence the cost of cyclosporine therapy. In human medicine, adverse reactions to the drug, especially nephrotoxicity, are common but in dogs given the commonly used oral dose of 5 mg/kg per day there have been few adverse reactions. However, no toxicity studies lasting longer than 12 months have been carried out in this species. This paper reviews the pharmacokinetics, drug and procedural interactions, contraindications and the adverse reactions to cyclosporine, with particular reference to its use in the treatment of dermatological conditions in dogs, cats and people.

A role for P-glycoprotein in environmental toxicology

P-Glycoprotein (P-gp) is a transmembrane protein, playing significant roles in the process of drug discovery and development and in pest resistance to pesticides. P-gp affects absorption, disposition, and elimination of different compounds and is mainly expressed in intestines, liver, kidneys, heart, colon, and placenta. The expression of P-gp in the blood-brain barrier (BBB) has been associated with the restricted access of many compounds to the central nervous system. Generated knockout mice by disruption of mdr 1a gene, encoding for P-gp, showed that this protein was expressed in the BBB. The absence or the low levels of P-gp elevated drug concentrations in tissues and decreased drug elimination. P-gp is responsible for resistance of cells to agents, particularly the anticancer drugs, by removing these drugs from cells. Increased expression of P-gp is implicated in decreased HIV drug availability at certain intracellular sites. The role of P-gp in affecting efficacy and toxicity of environmental toxicants such as pesticides and heavy metals has not been adequately investigated. Studies showed that P-gp contributes to resistance to pesticides in certain pest species, and to decrease toxicity by removing compounds from cells in mammals. Placental drug-transporting P-gp plays a significant role in limiting the transport of toxicants such as potential teratogens to the fetus. Several in vitro or in vivo assays, including using P-gp knockout or naturally deficient mice, were described for testing P-gp modulators. The role of P-gp following concurrent exposure to more multiple compounds needs further research. P-gp modulators should be carefully used, since some modulators that reverse P-gp efflux action in vitro may lead to alterations of tissue function and increase toxicity of xenobiotics in normal tissues. Recent reports from the pharmaceutical studies on the significance of P-gp as transporters in altering the efficacy and toxicity clearly highlight the need for further research in interaction with environmental toxicants.

Current treatments for scabies

Scabies is a frequent interhuman ectoparasitic infection. Several treatments are available worldwide. There are local treatments: synthetic pyrethrins, benzyl benzoate, lindane, crotamiton. Recently a few studies were published concerning ivermectin, systemic antiparasitic agent use in onchocercosis treatment. We reviewed the literature with an evidence-based medicine method. We attempt to answer two questions in particular: what is the treatment of choice for common scabies in a patient otherwise in good health? What is the role of systemic ivermectin? We also report specific situations. Among local treatments, studies are heterogeneous according to products, countries, group of treated patients, with or without contact subjects, and the method of treatment application. There are very few high proof-level controlled studies. In France, a combination of benzyl benzoate 10% and sulfiram 2% is used most, according to professional consensus. The most studied product is the cream permethrin 5%, available in the USA and UK. Its efficacy seems slightly superior to lindane and less toxic. It is more efficient than crotamiton. There is no study comparing benzyl benzoate and permethrin. Concerning systemic ivermectin, five controlled studies showed its efficiency in common scabies. But its relative efficiency over local treatment has not been established. A few open studies showed its efficacy in institutional epidemic, profuse scabies and in HIV-positive patients. Local treatment of choice in common scabies remains to be determined among the four principal molecules. There is no study comparing permethrin or esdepallethrin to benzyl benzoate. In what cases should we prescribe crotamiton or lindane? Indication of ivermectin seems proved in common scabies and probably for HIV-positive patients. It remains to be determined if it should be prescribed in the first instance, be double or triple, be associated or not with local treatment. In case of keratotic scabies, ivermectin seems interesting with two applications within 1 week, and should be associated with local treatment (duration remains to be defined). Ivermectin is probably useful in institutional epidemic, and therapeutic attitude remains to be defined. Ivermectin seems to have little or no risk. Treatment must be adapted case-by-case, according to feasibility. It is still important to treat contacts, and modality of this treatment remains to be specified.

Ivermectin sensitivity in collies is associated with a deletion mutation of the mdr1 gene

A subpopulation of collie dogs is extremely sensitive to neurotoxicity induced by ivermectin. The aim of this study was to determine the mechanistic basis for this phenomenon. The multi-drug-resistance gene (mdr1) encodes a large transmembrane protein, P-glycoprotein (P-gp), that is an integral part of the blood-brain barrier. P-gp functions as a drug-transport pump at the blood-brain barrier, transporting a variety of drugs from the brain back into the blood. Since ivermectin is a substrate for P-gp, we hypothesized that ivermectin-sensitive collies had altered mdr1 expression compared with unaffected collies. We report a deletion mutation of the mdr1 gene that is associated with ivermectin sensitivity. The 4-bp deletion results in a frame shift, generating several stop codons that prematurely terminate P-gp synthesis. Dogs that are homozygous for the deletion mutation display the ivermectin-sensitive phenotype, while those that are homozygous normal or heterozygous do not display increased sensitivity to ivermectin.

Prochloraz and nonylphenol diethoxylate inhibit an mdr1-like activity in vitro, but do not alter hepatic levels of P-glycoprotein in trout exposed in vivo

P-glycoproteins (P-gps) encoded by multidrug resistance 1 (mdr1) genes are ATP-dependent transporters located in the cytoplasmic membrane which mediate the efflux of a broad spectrum of hydrophobic compounds from the cell. The tissue distribution of P-gps suggests their role in the organismal defense against xenobiotics by effecting xenobiotic excretion and reducing xenobiotic uptake. In the present work, the interaction of P-gp(s) in the liver and in primary cultured hepatocytes of rainbow trout with two model pollutants was studied - the imidazole fungicide prochloraz and the alkylphenolic surfactant nonylphenol diethoxylate (NP2EO). Using a monoclonal antibody (mAB C219) directed against a conserved P-gp epitope, an immunoreactive protein of 160 kDa was detected in immunoblots of liver extracts from control trout. In sections of control trout livers, immunohistochemistry with the mAB C219 resulted in specific staining of bile canaliculi. In juvenile trout exposed for 7 days to sublethal concentrations of prochloraz (0.027 microM; 0.27 microM) or NP2EO (0.32 microM; 1.30 microM), no changes in levels of hepatic P-gp(s) were found in immunoblot and immunochemical investigations. The efflux of the fluorescent mdr 1 substrate rhodamine 123 (Rh123) from cultured isolated trout hepatocytes was partly inhibited by verapamil and vinblastine, compounds known to interfere with mdr 1-dependent transport. This demonstrates the presence of a mdr1-like mechanism in trout liver which is probably involved in the biliary excretion of hydrophobic xenobiotics. Non-cytotoxic concentrations of prochloraz and NP2EO were tested for effects on the efflux of Rh123 from trout hepatocytes. Prochloraz was a potent inhibitor of the mdr1-like mechanism, being effective at 0.3 microM and above. NP2EO inhibited Rh123 efflux only at the highest concentration tested (31.6 microM). The accumulation and elimination of 14C-prochloraz by cultured trout hepatocytes was not affected by mdr 1-type substrates (Rh123, vinblastine) and a mdr 1 inhibitor (verapamil). This shows that prochloraz is, despite its inhibitory potency, not a substrate of the mdr1-like mechanism in trout liver. The inhibition by prochloraz and NP2EO of the md r1-like mechanism in trout hepatocytes suggests that water pollutants can interfere with P-gp-function in fish and thus may impair the organismal defense against xenobiotics.

Ivermectin excretion by isolated functionally intact brain endothelial capillaries

1. Functionally intact brain endothelial capillaries were isolated from porcine brain. p-Glycoprotein was localized at the lumenal membrane of intact capillaries by immunohistochemistry using a murine monoclonal antibody and a secondary FITC fluorescent labelled anti-mouse IgG. Western blot staining of p-glycoprotein in isolated endothelial cells confirmed the immunohistochemistry. 2. Excretion of the fluorescent labelled anthelmintic drug Ivermectin (BODIPY-Ivermectin) was studied in the isolated brain endothelial capillaries. Drug accumulation in the capillary lumen was visualized by fluorescence confocal laser scanning microscopy and was measured by image analysis. Secretion of BODIPY-Ivermectin into the capillary lumen exhibited characteristics of specific and energy-dependent transport. Steady state lumenal fluorescence intensity averaged 1.6 times cellular fluorescence and was reduced 3--4 times below cellular levels when metabolism was inhibited by NaCN. 3. BODIPY-Ivermectin secretion was inhibited in a concentration-dependent manner by unlabeled Ivermectin. In addition, lumenal but not cellular fluorescence intensity was significantly decreased when capillaries were incubated with PSC-833, Cyclosporin A or Verapamil, all inhibitors of p-glycoprotein. Conversely, unlabelled Ivermectin reduced the p-glycoprotein (Pgp)-mediated secretion of a fluorescent derivative of Verapamil, (BODIPY-Verapamil). 4. BODIPY-Ivermectin secretion was not affected in the presence of Leucotriene C(4) (LTC(4)), a potent inhibitor of multidrug resistance related protein (mrp)-mediated transport processes. In addition, excretion of Fluorescein-Methotrexate, an mrp-substrate, was not inhibited by Ivermectin. 5. Uptake experiments with isolated porcine brain capillary cells showing increased cellular uptake of BODIPY-Ivermectin in the presence of unlabelled drug or PSC-833 supported the findings of a Pgp interaction in intact capillaries. 6. The data are consistent with BODIPY-Ivermectin and Ivermectin being transported across the lumenal membrane of brain capillaries. For the first time Pgp-interaction of Ivermectin at the blood brain barrier is demonstrated on a cellular level in an intact vascular tissue.

The blood-brain barrier and oncology: new insights into function and modulation

The efficacy of chemotherapy for malignant primary or metastatic brain tumours is still poor. This is at least partly due to the presence of the blood-brain barrier (BBB). The functionality of the BBB can be explained by physicochemical features and efflux pump mechanisms. An overview of the literature is presented with emphasis on oncology. The BBB consists of capillary endothelial cells that lack fenestrations and are connected together with continuous tight junctions, with a high electrical resistance. Permeability of tight junctions can be increased in vitro by contraction of the cytoskeleton, caused by bradykinin agonists. Different efflux pumps are present in the BBB. Examples are P-glycoprotein (P-gp), organic anion transporters, (OAT) and multidrug-resistance-associated proteins (MRP)(1 and 3). These pumps act as a multi-specific efflux pump for various chemotherapeutic drugs. Experiments have shown that P-gp can be inhibited by different non-chemotherapeutic substrates such as cyclosporin A. The functionality in vivo of P-gp can be measured with positron emission tomography and [(11)C]-verapamil or with single photon emission computer tomography and(99m)Tc-sestamibi. MRP(1)and MRP(3)act as organic anion transporters that in vitro act as efflux pumps for substances that are conjugated or co-transported with glutathione and glucuronide, respectively. Methotrexate has been recently demonstrated to be transported by MRP(1)and MRP(3). Results of studies which demonstrate the clinical relevance and applicability of BBB modulators are eagerly awaited.

The in vivo effect of the administration of resistance-modulating agents on rhodamine 123 distribution in mice thymus and lymph nodes

P-glycoprotein (Pgp) has been widely associated with the multidrug resistance phenotype. Nevertheless, this protein has been detected in many normal tissues and cells, including liver, kidney, endothelial cells that constitute the hematological barrier of the brain and testes, and cells from the immune system. Many in vitro models have been used to study drugs that modulate Pgp activity and the multidrug resistance phenomenon. In the present work, we investigate the in vivo effects of resistance-modulating agents on lymphoid organs. Rhodamine 123 (Rho123), a well-known Pgp substrate, was administered to mice, and the fluorescence level in thymus and lymph node cells measured. The fluorescence level on these organs showed a dose-dependent response. Cyclosporin A (CSA), Verapamil (VP) and Trifluoperazine (TFP), three resistance-modulating agents, were administered to mice 1 h prior to 1 mg/kg Rho123 administration. Surprisingly, VP (10 mg/kg) and TFP (750 microg/kg) did not modulate Rho123 retention by thymus and lymph node cells. CSA (50 mg/kg) was the only drug that increased the fluorescence level in both organs. These results point out to the need of a wider study on the in vivo effects of resistance-modulating agents in different organs and systems.