In Vivo Effects of Cyclosporin A and Ketoconazole on the Pharmacokinetics of Representative Substrates for P-Glycoprotein and Cytochrome P450 (CYP) 3A in Rats

Ketoconazole Reverses Imatinib Resistance in Human Chronic Myelogenous Leukemia K562 Cells

Chronic myeloid leukemia (CML) is a hematologic disorder characterized by the oncogene BCR-ABL1, which encodes an oncoprotein with tyrosine kinase activity. Imatinib, a BCR-ABL1 tyrosine kinase inhibitor, performs exceptionally well with minimal toxicity in CML chemotherapy. According to clinical trials, however, 20–30% of CML patients develop resistance to imatinib. Although the best studied resistance mechanisms are BCR-ABL1-dependent, P-glycoprotein (P-gp, a drug efflux transporter) may also contribute significantly. This study aimed to establish an imatinib-resistant human CML cell line, evaluate the role of P-gp in drug resistance, and assess the capacity of ketoconazole to reverse resistance by inhibiting P-gp. The following parameters were determined in both cell lines: cell viability (as the IC50) after exposure to imatinib and imatinib + ketoconazole, P-gp expression (by Western blot and immunofluorescence), the intracellular accumulation of a P-gp substrate (doxorubicin) by flow cytometry, and the percentage of apoptosis (by the Annexin method). In the highly resistant CML cell line obtained, P-gp was overexpressed, and the level of intracellular doxorubicin was low, representing high P-gp activity. Imatinib plus a non-toxic concentration of ketoconazole (10 μM) overcame drug resistance, inhibited P-gp overexpression and its efflux function, increased the intracellular accumulation of doxorubicin, and favored greater apoptosis of CML cells. P-gp contributes substantially to imatinib resistance in CML cells. Ketoconazole reversed CML cell resistance to imatinib by targeting P-gp-related pathways. The repurposing of ketoconazole for CML treatment will likely help patients resistant to imatinib.

Deproteinization of Chitin Extracted with the Help of Ionic Liquids

The isolation of chitin utilizing ionic liquid 1-ethyl-3-methylimidazolium acetate has been determined to result in polymer contaminated with proteins. For the first time, the proteins in chitin extracted with ionic liquid have been quantified; the protein content was found to vary from 1.3 to 1.9% of the total weight. These proteins were identified and include allergenic proteins such as tropomyosin. In order to avoid ‘traditional’ hydroxide-based deproteinization of chitin, which could reduce the molecular weight of the final product, alternative deproteinization strategies were attempted. Testing of the previously reported deproteinization method using aqueous K₃PO₄ resulted in protein reduction by factors varying from 2 to 10, but resulted in significant phosphate salt contamination of the final product. Contrarily, the incorporation of GRAS (Generally Recognized as Safe) compound Polysorbate 80 into the polymer washing step provided the polymer of comparable purity with no contaminants. This study presents new options for the deproteinization of chitin that can replace traditional approaches with methods that are environmentally friendly and can produce high purity polymer.

Polyoxypregnanes as safe, potent, and specific ABCB1-inhibitory pro-drugs to overcome multidrug resistance in cancer chemotherapy in vitro and in vivo

Multidrug resistance (MDR) mediated by ATP binding cassette subfamily B member 1 (ABCB1) is significantly hindering effective cancer chemotherapy. However, currently, no ABCB1-inhibitory drugs have been approved to treat MDR cancer clinically, mainly due to the inhibitor specificity, toxicity, and drug interactions. Here, we reported that three polyoxypregnanes (POPs) as the most abundant constituents of Marsdenia tenacissima (M. tenacissima) were novel ABCB1-modulatory pro-drugs, which underwent intestinal microbiota-mediated biotransformation in vivo to generate active metabolites. The metabolites at non-toxic concentrations restored chemosensitivity in ABCB1-overexpressing cancer cells via inhibiting ABCB1 efflux activity without changing ABCB1 protein expression, which were further identified as specific non-competitive inhibitors of ABCB1 showing multiple binding sites within ABCB1 drug cavity. These POPs did not exhibit ABCB1/drug metabolizing enzymes interplay, and their repeated administration generated predictable pharmacokinetic interaction with paclitaxel without obvious toxicity in vivo. We further showed that these POPs enhanced the accumulation of paclitaxel in tumors and overcame ABCB1-mediated chemoresistance. The results suggested that these POPs had the potential to be developed as safe, potent, and specific pro-drugs to reverse ABCB1-mediated MDR. Our work also provided scientific evidence for the use of M. tenacissima in combinational chemotherapy.

Recent Advances in Chemical Biology of Mitochondria Targeting

Mitochondria are vital subcellular organelles that generate most cellular chemical energy, regulate cell metabolism and maintain cell function. Mitochondrial dysfunction is directly linked to numerous diseases including neurodegenerative disorders, diabetes, thyroid squamous disease, cancer and septicemia. Thus, the design of specific mitochondria-targeting molecules and the realization of real-time acquisition of mitochondrial activity are powerful tools in the study and treatment of mitochondria dysfunction in related diseases. Recent advances in mitochondria-targeting agents have led to several important mitochondria chemical probes that offer the opportunity for selective targeting molecules, novel biological applications and therapeutic strategies. This review details the structural and physiological functional characteristics of mitochondria, and comprehensively summarizes and classifies mitochondria-targeting agents. In addition, their pros and cons and their related chemical biological applications are discussed. Finally, the potential biomedical applications of these agents are briefly prospected.

Differential Impacts of Azole Antifungal Drugs on the Pharmacokinetic Profiles of Dasatinib in Rats by LC-MS-MS

BACKGROUND

Dasatinib, as an oral multi-targeted inhibitor of BCR-ABL and SRC family kinases, has been widely used for the treatment of Philadelphia Chromosome Positive Leukemias in imatinib-acquired resistance and intolerance. The study aimed to develop and validate a simple and robust assay with a small volume of plasma based on liquid chromatography coupled with tandem mass spectrometry to determine the concentration of dasatinib and to investigate the impact of the cytochrome 3A4 inhibitors, including ketoconazole, voriconazole, itraconazole and posaconazole, on the pharmacokinetics of dasatinib in rats.

METHODS

Thirty rats were divided randomly into five groups, control group (0.5% carboxymethylcellulose sodium), ketoconazole (30 mg/kg) group, voriconazole group (30 mg/kg), itraconazole group (30 mg/kg) and posaconazole group (30 mg/kg). After 150 μL blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, and 48 h and precipitated with acetonitrile, the plasma concentration of dasatinib was determined through Fluoro- Phenyl column (150 mm×2.1 mm, 3 μm) in a positive ionization mode.

RESULTS

The results suggested that ketoconazole, voriconazole, and posaconazole could increase the AUC0-t of dasatinib to varying degrees while significantly reducing its clearance. However, there was no significant impact on the pharmacokinetics of dasatinib, co-administered with itraconazole except for the CL and MRT0-t of dasatinib. Additionally, voriconazole could significantly increase Cmax of dasatinib by approximately 4.12 fold.

CONCLUSION

These data indicated that ketoconazole, posaconazole and voriconazole should be cautiously co-administered with dasatinib or close therapeutic drug monitoring of dasatinib concentration, which might cause the drug-drug interaction.

Robust combination of liver stereotactic body radiotherapy modulates pharmacokinetics of sorafenib toward preferable parameters

To evaluate the effect and mechanism of radiotherapy (RT)–sorafenib pharmacokinetics (PK) in different regimens with conventional or high dose irradiation. Between February 2012 and December 2018, 43 patients with portal vein tumor thrombosis treated with sorafenib plus conventional RT (58%) or stereotactic body radiation therapy (SBRT, 42%) were retrospectively reviewed. In vivo and in vitro studies of concurrent and sequential RT with sorafenib were designed. SBRT resulted in a 3-fold increase in complete recanalization compared to conventional RT group (28% vs. 8%, p = 0.014). Compared to the control group, the area under the concentration vs. time curve (AUC) of sorafenib was increased in the concurrent RT_2Gy and RT_9Gy groups and the sequential RT_9Gy group by 132% (p = 0.046), 163% (p = 0.038) and 102% (p = 0.018), respectively; and was decreased by 59% in the sequential RT_2Gy group (p = 0.036). Sequential RT_2Gy and RT_9Gy increased CYP3A4 activity by 82% (p = 0.028) and 203% (p = 0.0004), respectively, compared to that with the corresponding concurrent regimen. SBRT produced better recanalization than conventional RT with sorafenib. The AUC of sorafenib was modulated by RT. P-gp expression was not influenced by RT. The sequential RT regimen increased CYP3A4 activity that may increase the RT-sorafenib synergy effect and overall sorafenib activity. The biodistribution of sorafenib was modulated by local RT with the different regimens.

Species differences in the drug-drug interaction between atorvastatin and cyclosporine: In vivo study using a stable isotope-IV method in rats and dogs

In this study, drug-drug interaction (DDI) between atorvastatin (ATV) and cyclosporine (CsA) was kinetically analyzed using a stable isotope-IV method in rats and dogs. Obtained results were compared with the clinical data quoted from literatures to clarify the species difference in DDI both qualitatively and quantitatively. ATV only or ATV with CsA was orally administered to rats or dogs, and at 90 minutes after administration, a small amount of deuterium labeled ATV (ATV-d5) was intravenously injected. Assuming that ATV-d5 exhibits the same pharmacokinetic (PK) profile with ATV, PK parameters for absorption and elimination of ATV were calculated. Plasma levels of orally administered ATV were significantly enhanced by co-administration of CsA both in rats, dogs and humans, resulted in 9.8, 31, and 8.7-fold increase in systemic exposure calculated as AUC_po. High intensity of the DDI in dogs was mainly attributed to the marked decrease of the intrinsic hepatic clearance (to 1/10 of the control), which was induced by the inhibition of hepatic uptake of ATV via organic anion transporting polypeptide 1B1 (OATP1B1). CsA also affected the absorption of ATV form GI tract. Absorbed fraction of ATV into portal vein (calculated as F_a*F_g) was increased almost same extent in rats and dogs (around 3.0-fold) by co-administration of CsA. Inhibition of efflux transport via breast cancer resistance protein as well as the intestinal metabolism mediated by CYP enzymes contributed to the DDI occurred in the intestinal tract. In conclusion, PK analysis on the DDI between ATV and CsA in rats and dogs clearly demonstarted the factors to cause species differences in the extent of DDI. This type of quantitative analysis of DDIs in both small and large animals can be a great help to predict the extent of DDI in humans in the clinical study.

The Influence of Different Triazole Antifungal Agents on the Pharmacokinetics of Cyclophosphamide

Background: Cyclophosphamide is one of the most important chemotherapeutic drugs. Known as a widely accepted treatment strategy, chemotherapy may damage the immune function of cancer patients; as a result, invasive fungal infections (IFIs) occur. Triazole antifungal agents are the most acceptable drugs for IFI treatment, especially those infections caused by chemotherapy. Objective: We aimed to investigate the effects of different triazole antifungal drugs, including fluconazole, itraconazole, and ketoconazole, on the pharmacokinetics (PK) of cyclophosphamide. In addition, we also characterize the potential drug-drug interactions (DDIs) between cyclophosphamide and various triazole antifungal drugs. Methods: The necessary pharmacokinetic parameters and physicochemical data were obtained from published studies. Physiologically based pharmacokinetic (PBPK) models were developed and validated in virtual subjects using Simcyp software. The validated PBPK models were used to evaluate potential DDIs between cyclophosphamide and different triazole antifungal agents in cancer patients. Triazole antifungal agents were simulated by oral administration, whereas cyclophosphamide was simulated by intravenous administration. Results: Simulated plasma concentration-time curves of fluconazole, itraconazole, ketoconazole, and cyclophosphamide were in good consistency with the observed profiles. Our results suggested that the pharmacokinetic parameters of cyclophosphamide were increased by various extents when coadministered with different triazole antifungals. The area under the plasma concentration-time curve of cyclophosphamide was increased when combined with fluconazole, itraconazole, or ketoconazole. Conclusions and Relevance: Ketoconazole had the greatest effect on the PK of cyclophosphamide among the 3 triazole antifungals. Our study provides clues that the toxicity and adverse drug reactions that are associated with cyclophosphamide should be closely monitored when coadministered with ketoconazole.

Effects of Anticholinergic Drugs Used for the Therapy of Overactive Bladder on P-Glycoprotein Activity

We evaluated the effects of anticholinergic drugs principally used for the therapy of overactive bladder (OAB) on the activity of P-glycoprotein, an efflux transport protein, in Caco-2 cells. The time-dependent changes in the fluorescence of residual rhodamine 123, a P-glycoprotein activity marker, in the apical region of Caco-2 cells were measured in the presence of anticholinergic drugs using time-lapse confocal laser scanning microscopy. The effect of anticholinergic drugs on human P-glycoprotein ATPase activity was also measured. The fluorescence of residual rhodamine 123 in untreated Caco-2 cells decreased over time. The gradual decrease in the fluorescence was significantly inhibited by treatment with cyclosporine A, darifenacin, and trospium. In contrast, oxybutynin, N-desethyl-oxybutynin (DEOB), propiverine, and its active metabolites (M-1, M-2), imidafenacin, solifenacin, or tolterodine had little effect on the efflux of rhodamine 123. P-Glycoprotein ATPase activity was increased by darifenacin. Darifenacin and trospium reduced the rhodamine 123 transfer across the apical cell membrane. These data suggest that darifenacin and trospium interact with P-glycoprotein. Additionally, darifenacin influenced P-glycoprotein ATPase activity. These results suggest that darifenacin may be a substrate of P-glycoprotein. This study is the first paper to test simultaneously the effects of 10 anticholinergic drugs used currently for the therapy of OAB, on the P-glycoprotein.

P-glycoproteins play a role in ivermectin resistance in cyathostomins

Anthelmintic resistance is a global problem that threatens sustainable control of the equine gastrointestinal cyathostomins (Phylum Nematoda; Superfamily Strongyloidea). Of the three novel anthelmintic classes that have reached the veterinary market in the last decade, none are currently licenced in horses, hence current control regimens focus on prolonging the useful lifespan of licenced anthelmintics. This approach would be facilitated by knowledge of the resistance mechanisms to the most widely used anthelmintics, the macrocyclic lactones (ML). There are no data regarding resistance mechanisms to MLs in cyathostomins, although in other parasitic nematodes, the ABC transporters, P-glycoproteins (P-gps), have been implicated in playing an important role. Here, we tested the hypothesis that P-gps are, at least in part, responsible for reduced sensitivity to the ML ivermectin (IVM) in cyathostomins; first, by measuring transcript levels of pgp-9 in IVM resistant versus IVM sensitive third stage larvae (L3) pre-and post-IVM exposure in vitro. We then tested the effect of a range of P-gp inhibitors on the effect of IVM against the same populations of L3 using the in vitro larval development test (LDT) and larval migration inhibition test (LMIT). We demonstrated that, not only was pgp-9 transcription significantly increased in IVM resistant compared to IVM sensitive L3 after anthelmintic exposure (p < 0.001), but inhibition of P-gp activity significantly increased sensitivity of the larvae to IVM in vitro, an effect only observed in the IVM resistant larvae in the LMIT. These data strongly implicate a role for P-gps in IVM resistance in cyathostomins. Importantly, this raises the possibility that P-gp inhibitor-IVM combination treatments might be used in vivo to increase the effectiveness of IVM against cyathostomins in Equidae.

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Pgp-9 transcript levels were higher in ivermectin resistant versus susceptible cyathostomin populations.

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P-gp inhibitors increased ivermectin effect against cyathostomins in vitro.

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P-gp activity may play a role in ivermectin resistance in cyathostomins.

Carfilzomib resistance due to ABCB1/MDR1 overexpression is overcome by nelfinavir and lopinavir in multiple myeloma

Proteasome inhibitor (PI) carfilzomib (CFZ) has activity superior to bortezomib (BTZ) and is increasingly incorporated in multiple myeloma (MM) frontline therapy and relapsed settings. Most MM patients ultimately experience PI-refractory disease, an unmet medical need with poorly understood biology and dismal outcome. Pharmacologic targeting of ABCB1 improved patient outcomes, including MM, but suffered from adverse drug effects and insufficient plasma concentrations. Proteomics analysis identified ABCB1 overexpression as the most significant change in CFZ-resistant MM cells. We addressed the functional role of ABCB1 overexpression in MM and observed significantly upregulated ABCB1 in peripheral blood malignant plasma cells (PCs) vs untreated patients' bone marrow PC. ABCB1 overexpression reduces the proteasome-inhibiting activity of CFZ due to drug efflux, in contrast to BTZ. Likewise, the cytotoxicity of established anti-MM drugs was significantly reduced in ABCB1-expressing MM cells. In search for potential drugs targeting ABCB1 in clinical trials, we identified the HIV protease inhibitors nelfinavir (NFV) and lopinavir (LPV) as potent functional modulators of ABCB1-mediated drug export, most likely via modulation of mitochondria permeability transition pore. NFV and LPV restored CFZ activity at therapeutically relevant drug levels and thus represent ready-to-use drugs to be tested in clinical trials to target ABCB1 and to re-sensitize PC to established myeloma drugs, in particular CFZ.

A conceptually new treatment approach for relapsed glioblastoma: coordinated undermining of survival paths with nine repurposed drugs (CUSP9) by the International Initiative for Accelerated Improvement of Glioblastoma Care

To improve prognosis in recurrent glioblastoma we developed a treatment protocol based on a combination of drugs not traditionally thought of as cytotoxic chemotherapy agents but that have a robust history of being well-tolerated and are already marketed and used for other non-cancer indications. Focus was on adding drugs which met these criteria: a) were pharmacologically well characterized, b) had low likelihood of adding to patient side effect burden, c) had evidence for interfering with a recognized, well-characterized growth promoting element of glioblastoma, and d) were coordinated, as an ensemble had reasonable likelihood of concerted activity against key biological features of glioblastoma growth. We found nine drugs meeting these criteria and propose adding them to continuous low dose temozolomide, a currently accepted treatment for relapsed glioblastoma, in patients with recurrent disease after primary treatment with the Stupp Protocol. The nine adjuvant drug regimen, Coordinated Undermining of Survival Paths, CUSP9, then are aprepitant, artesunate, auranofin, captopril, copper gluconate, disulfiram, ketoconazole, nelfinavir, sertraline, to be added to continuous low dose temozolomide. We discuss each drug in turn and the specific rationale for use- how each drug is expected to retard glioblastoma growth and undermine glioblastoma's compensatory mechanisms engaged during temozolomide treatment. The risks of pharmacological interactions and why we believe this drug mix will increase both quality of life and overall survival are reviewed.

Preliminary study of effects of multiple oral dosing of clarithromycin on the pharmacokinetics of cyclosporine in dogs

Clarithromycin (CLM) has been known to increase the cyclosporine (CsA) trough level in human and feline organ transplant patients. However, the interaction of CLM with CsA has not been reported in dogs. In this study, the effects of multiple dosing of CLM on the pharmacokinetics of CsA in three healthy beagles were investigated. The treatments included CsA 10 mg/kg alone and CsA 10 mg/kg + multiple-dose of CLM 10 mg/kg. Co-administration of CLM with CsA resulted in significant increases of oral bioavailability of CsA. The results of our study suggest that administration of multiple therapeutic doses of CLM may decrease the required CsA dosage in CsA-based immunosuppressive therapy in renal transplanted dogs.

Assessment of CYP3A-mediated drug-drug interaction potential for victim drugs using an in vivo rat model

The present study aims to determine if an in vivo rat model of drug-drug interaction (DDI) could be useful to discriminate a sensitive (buspirone) from a 'non-sensitive' (verapamil) CYP3A substrate, using ketoconazole and ritonavir as perpetrator drugs. Prior to in vivo studies, ketoconazole and ritonavir were shown to inhibit midazolam hydroxylation with IC50 values of 350 ± 60 nm and 11 ± 3 nm, respectively, in rat liver microsomes (RLM). Buspirone and verapamil were also shown to be substrates of recombinant rat CYP3A1/3A2. In the rat model, the mean plasma AUC0-inf of buspirone (10 mg/kg, p.o.) was increased by 7.4-fold and 12.8-fold after co-administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. The mean plasma AUC0-inf of verapamil (10 mg/kg, p.o.) was increased by 3.0-fold and 4.8-fold after co-administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. Thus, the rat DDI model correctly identified buspirone as a sensitive CYP3A substrate (>5-fold AUC change) in contrast to verapamil. In addition, for both victim drugs, the extent of DDI when co-administered was greater with ritonavir compared with ketoconazole, in line with their in vitro CYP3A inhibition potency in RLM. In conclusion, our study extended the rat DDI model applicability to two additional victim/perpetrator pairs. In addition, we suggest that use of this model would increase our confidence in estimation of the DDI potential for victim drugs in early discovery.

Increased susceptibility of a triclabendazole (TCBZ)-resistant isolate of Fasciola hepatica to TCBZ following co-incubation in vitro with the P-glycoprotein inhibitor, R(+)-verapamil

A study was carried out to investigate whether the action of triclabendazole sulphoxide (TCBZ.SO) against the liver fluke, Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for this in vitro study and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. For experiments with the Oberon isolate, flukes were incubated for 24 h with either R(+)-VPL (1×10-4 m) on its own, TCBZ.SO (15 μg mL-1) alone, a combination of R(+)-VPL (1×10-4 m) plus TCBZ.SO (15 μg mL-1), TCBZ.SO (50 μg mL-1) on its own, or a combination of TCBZ.SO (50 μg mL-1) plus R(+)-VPL (1×10-4 m). They were also incubated in TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive; and in TCBZ.SO (50 μg mL-1) alone for a time to match that of the combination inactivity time. Flukes from the Cullompton isolate were treated with either TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive, or with TCBZ.SO (50 μg mL-1) alone time-matched to the combination inactivity time. Morphological changes resulting from drug treatment and following Pgp inhibition were assessed by means of scanning electron microscopy. Incubation in R(+)-VPL alone had a minimal effect on either isolate. TCBZ.SO treatment had a relatively greater impact on the TCBZ-susceptible Cullompton isolate. When R(+)-VPL was combined with TCBZ.SO in the incubation medium, however, the surface disruption to both isolates was more severe than that seen after TCBZ.SO treatment alone; also, the time taken to reach inactivity was shorter. More significantly, though, the potentiation of drug activity was greater in the Oberon isolate; also, it was more distinct at the higher concentration of TCBZ.SO. So, the Oberon isolate appears to be particularly sensitive to efflux pump inhibition. The results of this study suggest that enhanced drug efflux in the Oberon isolate may be involved in the mechanism of resistance to TCBZ.

Effect of ketoconazole, a cytochrome P450 inhibitor, on the efficacy of quinine and halofantrine against Schistosoma mansoni in mice

The fear that schistosomes will become resistant to praziquantel (PZQ) motivates the search for alternatives to treat schistosomiasis. The antimalarials quinine (QN) and halofantrine (HF) possess moderate antischistosomal properties. The major metabolic pathway of QN and HF is through cytochrome P450 (CYP) 3A4. Accordingly, this study investigates the effects of CYP3A4 inhibitor, ketoconazole (KTZ), on the antischistosomal potential of these quinolines against Schistosoma mansoni infection by evaluating parasitological, histopathological, and biochemical parameters. Mice were classified into 7 groups: uninfected untreated (I), infected untreated (II), infected treated orally with PZQ (1,000 mg/kg) (III), QN (400 mg/kg) (IV), KTZ (10 mg/kg)+QN as group IV (V), HF (400 mg/kg) (VI), and KTZ (as group V)+HF (as group VI) (VII). KTZ plus QN or HF produced more inhibition (P<0.05) in hepatic CYP450 (85.7% and 83.8%) and CYT b5 (75.5% and 73.5%) activities, respectively, than in groups treated with QN or HF alone. This was accompanied with more reduction in female (89.0% and 79.3%), total worms (81.4% and 70.3%), and eggs burden (hepatic; 83.8%, 66.0% and intestinal; 68%, 64.5%), respectively, and encountering the granulomatous reaction to parasite eggs trapped in the liver. QN and HF significantly (P<0.05) elevated malondialdehyde levels when used alone or with KTZ. Meanwhile, KTZ plus QN or HF restored serum levels of ALT, albumin, and reduced hepatic glutathione (KTZ+HF) to their control values. KTZ enhanced the therapeutic antischistosomal potential of QN and HF over each drug alone. Moreover, the effect of KTZ+QN was more evident than KTZ+HF.

Erratum to: inhibition of triclabendazole metabolism in vitro by ketoconazole increases disruption to the tegument of a triclabendazole-resistant isolate of Fasciola hepatica

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP 450) enzyme pathway was inhibited using ketoconazole (KTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 system was inhibited by a 2-h pre-incubation in ketoconazole (40 μM), then incubated for a further 22 h in NCTC medium containing either KTZ, KTZ + nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM), KTZ + NADPH + TCBZ (15 μg/ml), or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO; 15 μg/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with KTZ + TCBZ, but more particularly KTZ + TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own: for example, there was severe swelling of the basal infolds and their associated mucopolysaccharide masses, accompanied by an accumulation of secretory bodies just below the apex. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis, production, and transport of secretory bodies were badly disrupted. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

A novel method using confocal laser scanning microscopy for sensitive measurement of P-glycoprotein-mediated transport activity in Caco-2 cells

OBJECTIVES

The aim of this study was to use time-lapse confocal laser scanning microscopy to establish a more sensitive and specific method for evaluating P-glycoprotein activity in Caco-2 cells.

METHODS

The change in the fluorescence of residual rhodamine 123 at the apical and central regions of Caco-2 cells was measured in the presence of digoxin or St John's wort by using time-lapse confocal laser scanning microscopy. The data were compared with measurements made using conventional techniques, a fluorescence microplate reader and a fluorescence microscope.

KEY FINDINGS

The percentage decrease of rhodamine 123 caused by 10 µm digoxin or 0.1 µg/ml St John's wort was significantly larger in the apical region of the Caco-2 cell than in the central region or in the whole cell. The digoxin-induced inhibition in the apical region as measured by time-lapse confocal laser scanning microscopy was greater than that measured in the whole cell by a microplate reader or a fluorescence microscope.

CONCLUSIONS

The assay of residual rhodamine 123 in the apical region of Caco-2 cells by confocal laser scanning microscopy was more sensitive than the conventional methods using a microplate reader or fluorescence microscopy. It will be a valuable screening tool for studying both the inhibition and induction of P-glycoprotein activity.

The use of 13C-erythromycin as an in vivo probe to evaluate CYP3A-mediated drug interactions in rats

(14)C-erythromycin breath test has been utilized to evaluate the extent of CYP3A activity in vivo. However, its radioactivity sometimes impedes its clinical application. In this study, we employed erythromycin labeled with (13)C ((13)C-EM), a nonradioactive stable isotope, as an in vivo probe of breath test to evaluate CYP3A-mediated drug interactions in rats. A physiologically based pharmacokinetic (PBPK) model to describe (13)CO(2) exhalation altered by drug interactions was newly constructed. Rats received an intravenous or oral administration of (13)C-EM with or without a CYP3A inhibitor or inducer, that is, ketoconazole (KCZ) or dexamethasone (DEX), respectively. Breath samples were taken at designated times, measured with an infrared spectrophotometer, and the Δ(13) CO(2) value (‰) in each sample was obtained. The C(max) and AUC(0-t) of Δ(13) CO(2) were significantly decreased with KCZ and increased with DEX. The PBPK model in this study successfully described the (13)CO(2) exhalation after (13)C-EM administration in the absence and presence of drug interactions. In conclusion, this study proposed a simple and rapid in vivo methodology to utilize (13)C-EM for the quantitative analysis of CYP3A inhibition and induction. This method using small animals may be useful in early drug development processes.

Inhibition of triclabendazole metabolism in vitro by ketoconazole increases disruption to the tegument of a triclabendazole-resistant isolate of Fasciola hepatica

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP 450) enzyme pathway was inhibited using ketoconazole (KTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 system was inhibited by a 2-h pre-incubation in ketoconazole (40 μM), then incubated for a further 22 h in NCTC medium containing either KTZ, KTZ + nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM), KTZ + NADPH + TCBZ (15 μg/ml), or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO; 15 μg/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with KTZ + TCBZ, but more particularly KTZ + TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own: in the syncytium, for example, there was severe swelling of the basal infolds and their associated mucopolysaccharide masses, accompanied by an accumulation of secretory bodies just below the apex. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis, production, and transport of secretory bodies were badly disrupted. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

Fluconazole decreases cyclosporine dosage in renal transplanted dogs

The effect of fluconazole (Fcz) on the cyclosporine (CsA) dosage was investigated in renal transplanted dogs receiving CsA-based immunosuppressive therapy. Initially, CsA was administered orally twice daily to raise the blood trough level between 400 and 600 ng/ml. After the addition of Fcz, the CsA dosage was adjusted to maintain its therapeutic blood concentration. Fcz significantly decreased CsA dosage in both normal and renal transplanted dogs, but a higher dosage of CsA was needed in renal transplanted dogs. In conclusion, Fcz decreases required CsA dosage and thereby reduces the cost of immunosuppressive therapy in canine renal transplantation.

Furanocoumarin derivatives in Kampo extract medicines inhibit cytochrome P450 3A4 and P-glycoprotein

Furanocoumarins in grapefruit are known to show inhibitory effects against P-glycoprotein (P-gp) and CYP3A4 in intestinal epithelial cells; however, furanocoumarin derivatives are widely contained in the plants of Rutaceae and Umbelliferae families, which are used as components of Kampo extract medicines. In this study, we investigated the inhibitory effects of 12 furanocoumarins extracted from plants in the Umbelliferae family against P-gp and CYP3A4 activity. Furthermore, we studied their inhibitory effect on P-gp when furanocoumarins are used as Kampo extract medicine rather than as an isolated single compound. From screening of the CYP3A4 inhibitory effect, notopterol and rivulobirin A, the only dimer types of furanocoumarin, were found to be potent inhibitors of CYP3A4. On the other hand, byakangelicol and rivulobirin A showed strong P-gp inhibition from the screening of P-gp inhibitor evaluated by quinidine permeation through the Caco-2 monolayer; however, the chemical structural relationship of furanocoumarins between P-gp and CYP3A4 inhibitory effects could not be obtained. We also investigated the effect of these furanocoumarins on the transport of digoxin through the Caco-2 monolayer. The inhibitory effect of rivulobirin A was more potent than that of byakangelicol. Application of either Senkyu-cha-cho-san or Sokei-kakketsu-to, which are composed of herbal remedies in the Umbelliferae group, significantly decreased the efflux ratio of digoxin. In conclusion, it was found that some furanocoumarins extracted from the plants in the Umbelliferae family strongly inhibited P-gp and CYP3A4. Kampo extract medicines containing herbal remedies belonging to the Umbelliferae family may cause a drug-drug interaction with P-gp or a CYP3A4 substrate drug.

Interplay of drug metabolism and transport: a real phenomenon or an artifact of the site of measurement?

The interdependence of both transport and metabolism on the disposition of drugs has recently gained heightened attention in the literature, and has been termed the "interplay of transport and metabolism". Such "interplay" is observed when inhibition of biliary clearance of a drug results in an "apparent" increase in the metabolic clearance of the drug or vice versa. In this manuscript, we derived and explored through simulations a physiological-based pharmacokinetic model that integrates both transport and metabolism and explains the "apparent" dependence of hepatic clearance on both these processes. In addition, we show that the phenomenon of hepatic "transport-metabolism interplay" is a result of using the plasma concentration as a point of reference when calculating metabolic or biliary clearance, and this interplay is maximal when the drug is actively transported into the hepatocytes (i.e., hepatocyte sinusoidal influx clearance is greater than the sinusoidal efflux clearance). When the hepatic drug concentration is used as a reference point to calculate metabolic or biliary clearance, this interplay ceases to exist. A mechanistic understanding of this interplay phenomenon can be used to explain the somewhat paradoxical results that may be observed in drug-drug interaction studies when a drug is cleared by both metabolism and biliary excretion. That is, when one of these two pathways is inhibited, the other pathway appears to be induced or activated. This interplay results in an increase in hepatic drug concentrations and therefore has implications for the hepatic efficacy and toxicity of a drug.

N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine (CP-100,356) as a "chemical knock-out equivalent" to assess the impact of efflux transporters on oral drug absorption in the rat

The utility of the diaminoquinazoline derivative CP-100,356 as an in vivo probe to selectively assess MDR1/BCRP-mediated drug efflux was examined in the rat. CP-100,356 was devoid of inhibition (IC(50) >50 microM) against major human P450 enzymes including P4503A4. In human MDR1-transfected MDCKII cells, CP-100,356 inhibited acetoxymethyl calcein (calcein-AM) uptake (IC(50) approximately 0.5 +/- 0.07 microM) and digoxin transport (IC(50) approximately 1.2 +/- 0.1 microM). Inhibition of prazosin transport (IC(50) approximately 1.5 +/- 0.3 microM) in human BCRP-transfected MDCKII cells by CP-100,356 confirmed the dual MDR1/BCRP inhibitory properties. CP-100,356 was a weak inhibitor of OATP1B1 (IC(50) approximately 66 +/- 1.1 microM) and was devoid of MRP2 inhibition (IC(50) >15 microM). In vivo inhibitory effects of CP-100,356 in rats were examined after coadministration with MDR1 substrate fexofenadine and dual MDR1/BCRP substrate prazosin. Coadministration with increasing doses of CP-100,356 resulted in dramatic increases in systemic exposure of fexofenadine (36- and 80-fold increase in C(max) and AUC at a CP-100,356 dose of 24 mg/kg). Significant differences in prazosin pharmacokinetics were also discernible in CP-100,356-pretreated rats as reflected from a 2.6-fold increase in AUC. Coadministration of CP-100,356 and P4503A substrate midazolam did not result in elevations in systemic exposure of midazolam in the rat. The in vivo methodology should have utility in drug discovery in selective and facile assessment of the role of MDR1 and BCRP efflux transporters in oral absorption of new drug candidates.

Effect of cyclosporine on drug transport and pharmacokinetics of nifedipine

Nifedipine (NFP) is an anti-hypersensitive drug and a well-known substrate of cytochrome P450 3A4 (CYP3A4), while cyclosporine (CSP) is a potent p-glycoprotein (P-gp) inhibitor. P-gp is a drug transporter, which determines the absorption and bioavailability of many drugs that are substrates for P-gp. Drugs that induce or inhibit P-gp may have a profound effect on the absorption and pharmacokinetics (PK) of drugs transported by P-gp within the body, possibly compromising their bioavailability. But the role of P-gp in the NFP efflux and its impact on PK profile is not known. Hence in our present study we attempted to investigate the effect of CSP on oral absorption and PK of NFP. Rhodamine 123 (Rho 123), a known P-gp substrate was used as a positive control. Male Wistar rats (350-400 g) were used for the study. Rats were divided into 4 groups (n=6 each); one group was treated with vehicle (cremophor) followed by NFP (0.2 mg/kg; i.v. bolus) and the other group with CSP (10 mg/kg; i.v.) followed by NFP. Group 3 and 4 were treated with vehicle (cremophor) followed by Rho 123 (0.2 mg/kg, i.v.) and CSP (10 mg/kg; i.v.) followed by Rho 123 (0.2 mg/kg, i.v.) respectively. The blood samples were collected at 0, 5, 10, 15, 30, 60, 90, 120, 180 and 240 min after NFP administration. NFP concentrations in plasma were analyzed by LC-MS-MS and Rho 123 was analyzed by fluorimetric detector. NFP efflux was significantly decreased in CSP treated rats (49.1% decrease, P<0.05), while NFP concentration in plasma were not changed. However the decrease in NFP efflux did not show any significant changes in NFP PK parameters (T(max); 2.0 vs. 2.5 min, C(max); 0.084 vs. 0.076 microg/ml, T(1/2); 84.0 vs. 91.4 min, AUC(0-t); 4.183 vs. 3.467 microg h/ml, AUC(infinity); 5.915 vs. 4.769 microg h/ml, AUMC(0-t); 224.073 vs. 173.063 microg h/ml, AUMC(infinity); 776.871 vs. 575.038 microg h/ml, MRT(0-t); 53.608 vs. 49.538 microg h/ml, MRT(infinity); 118.194 vs. 115.246 microg h/ml, CL(tot); 0.0375 vs. 0.0433 l/h, Vd(ss); 3.999 vs. 4.641 l in NFP alone vs. CSP+NFP groups respectively). Thus the results indicate that NFP would belong to a group of P-gp substrate. The decrease in efflux of NFP by CSP, through inhibition of P-gp, into the intestinal lumen did not show any impact on PK. This could be due to the activity of other transporters and/or CYP3A4 may have more limiting role than P-gp on NFP metabolism and disposition that is why inhibiting P-gp did not lead to increase the bioavailability and PK alterations.

Influence of quinidine, fluvoxamine, and ketoconazole on the enantioselective pharmacokinetics of citalopram in rats

Citalopram (CITA) is available as a racemic mixture or as (+)-(S)-CITA. In humans, CITA is metabolized to demethylcitalopram (DCITA) by CYP2C19, CYP2D6, and CYP3A and to didemethylcitalopram by CYP2D6. There are no data regarding the enzymes involved in CITA and DCITA metabolism in rats. The present study investigated the influence of CYP inhibitors on the enantioselective metabolism of CITA in rats. Male Wistar rats (n = 6) received a single dose of 20 mg·kg–1 CITA after pretreatment with 80 mg·kg–1 quinidine, 10 mg·kg–1 fluvoxamine, 50 mg·kg–1 ketoconazole, or vehicle (control). Blood samples were collected up to 20 h after CITA administration. The CITA and DCITA enantiomers were analyzed by LC-MS/MS using a Chiralcel OD-R column. The kinetic disposition of CITA was enantioselective in rats (AUCS/R ratio = 0.4). Coadministration with quinidine resulted in non-enantioselective inhibition of the metabolism of CITA. Coadministration with fluvoxamine or ketoconazole, however, inhibited only the metabolism of (+)-(S)-CITA, but not of (–)-(R)-CITA when the racemic drug was administered to rats.

Enhanced transport of P-glycoprotein substrate saquinavir in presence of thiolated chitosan

It was the aim of this study to investigate the effect of chitosan-4-thiobutylamidine (Ch-TBA) and reduced glutathione (GSH) on the absorption of P-glycoprotein (P-gp) and multidrug resistance protein (MRP) substrate saquinavir in vitro and in vivo. Bidirectional transport studies were performed with Caco-2 cell monolayers and additionally with freshly excised rat small intestinal mucosa mounted in Ussing type chambers. Furthermore, a delivery system based on Ch-TBA and GSH was evaluated in vivo in rats. The functional activity of the efflux pumps in Caco-2 cells and rat intestinal mucosa during the experiment was proven by the efflux ratio of saquinavir, which was 6.4 for Caco-2 cells and 2.1 for rat intestinal mucosa, respectively. Ch-TBA and particularly the combination of Ch-TBA with GSH enhanced apical (AP) absorption and decreased the secretory transport of saquinavir. In presence of 0.5% Ch-TBA and 0.5% GSH, the uptake of saquinavir was 1.6-fold improved in Caco-2 monolayer and 2.1-fold improved in rat intestinal mucosa. In vivo, the area under the plasma concentration time curve (AUC) of saquinavir was 1.4-fold and Cmax 1.6-fold increased, in comparison with control. Results of this study showed that Ch-TBA in combination with GSH can be an interesting tool for increasing the oral bioavailability of actively secreted compounds.

Effects of cyclosporin A and itraconazole on the pharmacokinetics of atorvastatin in rats

AIM

To evaluate the effects of cyclosporin A and itraconazole, which were used as inhibitors of P-glycoprotein (P-gp) and/or cytochrome P450 (CYP) 3A4 on the pharmacokinetics of atorvastatin in rats.

METHODS

The pharmacokinetic parameters of atorvastatin were measured after intravenous (2 mg/kg) and intragastric (10 mg/kg) administration of atorvastatin in rats, which were pretreated with cyclosporin A (5, 10, and 20 mg/kg) or itraconazole (5, 10, and 20 mg/kg).

RESULTS

Compared with the control rats, cyclosporin A and itraconazole altered the pharmacokinetics of atorvastatin significantly. The AUC0-t values of atorvastatin after intragastric administration, pretreated with cyclosporin A (5-20 mg/kg), increased by 32.3%, 61.8%, and 187.2%, respectively, but the CLbile values decreased (P<0.01, 5-20 mg/kg). With pretreatment of itraconazole (5-20 mg/kg), the AUC(0-t) values of atorvastatin increased by 88.2%, 102%, and 123%, respectively, but the CL(bile) values decreased (P<0.01, 5-20 mg/kg).

CONCLUSION

These data indicated that cyclosporin A could be effective in inhibiting the efflux of atorvastatin, and itraconazole could be effective in inhibiting both the metabolism and biliary excretion of atorvastatin.

Development of anin vivorat screen model to predict pharmacokinetic interactions of CYP3A4 substrates

With the advent of polytherapy, drug interactions have become a common clinical problem. Although in vitro data are routinely used for the prediction of drug interactions, in vitro systems are not dynamic and sometimes fail to predict drug interactions. We sought to use the rat as an in vivo screening model to predict pharmacokinetic interactions with ketoconazole. The pharmacokinetic studies were conducted following an oral dose of CYP3A substrates and an optimized oral regimen of ketoconazole. In vitro reaction phenotyping was conducted using individual human and rat cDNA-expressed CYP enzymes and human or rat liver microsomes in the presence of ketoconazole. The in vitro experiments indicated that the test compounds were largely metabolized by CYP3A in both human and rat. The compounds could be rank-ordered with respect to the increase in C(max) and area under the curve (AUC) values relative to midazolam in the presence of ketoconazole. The degree of pharmacokinetic interaction with ketoconazole was dependent, in part, upon their in vitro metabolism in the presence of rat CYP3A1/3A2 and in rat and human microsomes, co-incubated with ketoconazole, and on their fraction metabolized (f(m)) in the rat relative to other disposition pathways. Based on the rank-order of interaction, the compounds could be prioritized for further preclinical development.

Ketoconazole increases the plasma levels of ivermectin in sheep

The parasiticide ivermectin and the antifungal drug ketoconazole are drugs that interact with P-glycoprotein. We have tested the ability of ketoconazole at a clinical dose to modify the pharmacokinetics of ivermectin in sheep. Lacaune lambs were administered with a single oral dose of ivermectin alone at 0.2 mg/kg (n=5) or in combination with a daily oral dose of ketoconazole (10 mg/kg) given for 3 days before and 2 days after the ivermectin (n=5). The plasma kinetics of ivermectin and its metabolite were followed over 15 days by HPLC analysis. Co-administration of ketoconazole induced higher plasma concentrations of ivermectin, leading to a substantial increase in the overall exposure of the animals to the drug. Ketoconazole did not reduce the production of the main ivermectin metabolite but it may rather act by inhibiting P-glycoprotein, and thus increasing the absorption of ivermectin. The use of a P-gp reversing agent such as ketoconazole could be useful tool to optimize antiparasitic therapy in the face of the worldwide development of anthelmintic resistance.

Concentrations of Mycophenolic Acid and Glucuronide Metabolites Under Concomitant Therapy With Cyclosporine or Tacrolimus

Mycophenolate mofetil [MMF, the prodrug of mycophenolic acid (MPA)] is usually administered at double doses with cyclosporine than with tacrolimus because it is believed that MPA exposure is lower during cyclosporine therapy. This study aimed to compare 12 hour, steady-state concentration-time profiles of MPA and its phenol- and acyl-glucuronide metabolites (MPAG and AcMPAG, respectively) in stable kidney transplant recipients maintained either on cyclosporine (n = 12) or tacrolimus (n = 12). During the absorption phase in the cyclosporine group, dose-normalized concentrations of total and free MPA were significantly higher but the overall area under the concentration-time curve (AUC0-12) was not significantly different. Additionally, exposure to AcMPAG was higher in the cyclosporine group (P < 0.05). Ten of 12 patients in the cyclosporine group were on ketoconazole therapy; however, the exposure to MPA or MPAG was not different when MMF was given orally to Sprague-Dawley rats with or without ketoconazole. In conclusion, cyclosporine modulates the disposition of MPA and metabolites differently from tacrolimus; however, patients on cyclosporine may not require double doses of MMF to achieve the same exposure.

Molecular evidence and functional expression of multidrug resistance associated protein (MRP) in rabbit corneal epithelial cells

Multidrug resistance associated protein (MRP) is a major family of efflux transporters involved in drug efflux leading to drug resistance. The objective of this study was to explore physical barriers for ocular drug absorption and to verify if the role of efflux transporters. MRP-2 is a major homologue of MRP family and found to express on the apical side of cell membrane. Cultured Rabbit Corneal Epithelial Cells (rCEC) were selected as an in vitro model for corneal epithelium. [14C]-erythromycin which is a proven substrate for MRP-2 was selected as a model drug for functional expression studies. MK-571, a known specific and potent inhibitor for MRP-2 was added to inhibit MRP mediated efflux. Membrane fraction of rCEC was used for western blot analysis. Polarized transport of [14C]-erythromycin was observed in rCEC and transport from B-->A was significantly high than from A-->B. Permeability's increased significantly from A-->B in the presence of MK-571 and ketoconozole. Uptake of [14C]-erythromycin in the presence of MK-571 was significantly higher than control in rCEC. RT-PCR analysis indicated a unique and distinct band at approximately 498 bp corresponding to MRP-2 in rCEC and MDCK11-MRP-2 cells. Immunoprecipitation followed by Western Blot analysis indicated a specific band at approximately 190 kDa in membrane fraction of rCEC and MDCK11-MRP-2 cells. For the first time we have demonstrated high expression of MRP-2 in rabbit corneal epithelium and its functional activity causing drug efflux. RT-PCR, immunoprecipitation followed by Western blot analysis further confirms the result.

Evaluation of antipsychotic drugs as inhibitors of multidrug resistance transporter P-glycoprotein

RATIONALE

The multidrug resistance transporter, P-glycoprotein (P-gp), is involved in efflux transport of several antipsychotics in the blood-brain barrier (BBB).

OBJECTIVES

In the present study, we evaluated the inhibitory effect of the antipsychotics, i.e., risperidone, olanzapine, quetiapine, clozapine, haloperidol, chlorpromazine, a major metabolite of risperidone, 9-OH-risperidone, and a positive control inhibitor, PSC833, on the cellular uptake of a prototypic substrate of P-gp, rhodamine (Rhd) 123, in LLC-PK1 and L-MDR1 cells.

MATERIALS AND METHODS

After incubation of the antipsychotics (1-100 microM) and the positive (10 microM PSC833) or negative (1% dimethyl sulfoxide) controls with 5 microM Rhd 123 for 1 h, the effects of the antipsychotics on the intracellular accumulation of Rhd 123 were examined using a flow cytometric method.

RESULTS

All the antipsychotics showed various degrees of inhibitory effects on P-gp activity. The rank order of the concentration of inhibitor to cause 50% of the maximal increment of intracellular Rhd 123 fluorescence (EC(50)) was: PSC833 (0.5 microM) < olanzapine (3.9 microM) < chlorpromazine (5.8 microM) < risperidone (6.6 microM) < haloperidol (9.1 microM) < quetiapine (9.8 microM) < 9-OH-risperidone (12.5 microM) < clozapine (30 microM). Considering that the antipsychotics' plasma concentrations are generally lower than 1 microM, the present results suggest that olanzapine and risperidone are the only agents that may inhibit P-gp activity in the BBB. However, most of the antipsychotics are extensively accumulated in tissues. In addition, when given orally, the drug concentrations in the gastrointestinal tract are likely to be high.

CONCLUSIONS

Pharmacokinetic interactions due to inhibition of P-gp activity by the antipsychotics appear possible and warrant further investigation.

In vivo evaluation of an oral delivery system for P-gp substrates based on thiolated chitosan

Recently, thiolated polymers, so called thiomers, have been reported to modulate drug absorption by inhibition of intestinal P-glycoprotein (P-gp). The aim of the present study was to provide a proof-of-principle for a delivery system based on thiolated chitosan in vivo in rats, using rhodamine-123 (Rho-123) as representative P-gp substrate. In vitro, the permeation enhancing effect of unmodified chitosan, chitosan-4 thiobutylamidine (Ch-TBA) and the combination of Ch-TBA with reduced glutathione (GSH) was evaluated by using freshly excised rat intestinal mucosa mounted in Ussing-type chambers. In comparison to buffer only, Rho-123 transport in presence of 0.5% (w/v) chitosan, 0.5% (w/v) Ch-TBA and the combination of 0.5% (w/v) Ch-TBA/0.5% (w/v) GSH, was 1.8-fold, 2.6-fold, 3.8-fold improved, respectively. Furthermore, enteric-coated tablets based on unmodified chitosan or Ch-TBA/GSH, were investigated in vivo. In rats, the Ch-TBA/GSH tablets increased the area under the plasma concentration time curve (AUC0-12) of Rho-123 by 217% in comparison to buffer control and by 58% in comparison to unmodified chitosan. This in vivo study showed that a delivery system based on thiolated chitosan significantly increased the oral bioavailability of P-gp substrate Rho-123.

Modulation of intestinal barrier properties by miltefosine

Miltefosine (hexadecylphosphocholine, HePC) is the first effective oral agent for the treatment of visceral leishmaniasis. This study aimed to determine whether this oral administration alters the integrity and transport capacities of the intestinal barrier. The objectives of this study were: (i) to evaluate the cytotoxicity of HePC, (ii) to investigate the effects of HePC on paracellular and transcellular transport and (iii) to investigate the influence of HePC on three major transporters of the intestinal barrier, namely, P-glycoprotein, the human intestinal peptide transporter (PepT-1) and the monocarboxylic acid transporter (MCT-1) in Caco-2 cell monolayers, used as an in vitro model of the human intestinal barrier. We show that HePC reduced the transepithelial electrical resistance and increased D-[14C]mannitol permeability in a dose-dependent manner but had no effect on [3H]testosterone permeability, demonstrating that HePC treatment enhances paracellular permeability via an opening of the tight junction complex without affecting the transcellular route. Morphological studies using confocal fluorescence microscopy showed no perturbation of the normal distribution of ZO-1, occludin or E-cadherin but revealed a redistribution of the tight junction-associated protein claudin-1 and the perijunctional actin after incubation with HePC. Finally, HePC was found to inhibit the intestinal P-glycoprotein in the Caco-2 cell model after a single short exposure. These results suggest that HePC could modify the oral bioavailability of other therapeutic compounds absorbed via the paracellular route or which are substrates of the intestinal P-glycoprotein.