Functional studies on the activity of efflux transporters in an ex vivo model with chicken splenocytes and evaluation of selected fluoroquinolones in this model

Multiple drug transporters contribute to the brain transfer of levofloxacin

AIMS

The aim of this study was to assess the influence of the major transporters at blood-brain barrier and blood-cerebrospinal fluid barrier on levofloxacin (LVFX) pharmacokinetics in rat. To explore the different effects of transporters on drug concentrations in cerebrospinal fluid (CSF) and brain extracellular fluid (ECF).

METHODS

High-performance liquid chromatography coupled with microdialysis was used to continuously and synchronously measure unbound concentrations of LVFX in rat blood, hippocampal ECF, and lateral ventricle CSF for comprehensive characterization of brain pharmacokinetics. The role of transporters in the brain efflux mechanism of LVFX was analyzed in the absence and presence of various transporter inhibitors.

RESULTS

Following LVFX (50 mg/kg) administration, the unbound partition coefficient of LVFX in brain ECF and CSF (K_p,uu,ECF and K_p,uu,CSF ) were 34.0 ± 1.7% and 41.2 ± 2.4%, respectively. When probenecid was coadministered with LVFX, the AUC and the mean residence time (MRT) in rat blood increased significantly (p < 0.05). After MK571 intervention, 1.35-fold and 1.16-fold increases in K_p,uu,ECF and K_p,uu,CSF were observed, respectively (p < 0.05). Treatment with Ko143 increased the levels of LVFX in brain ECF. The difference in LVFX concentration in brain ECF and CSF was <3-fold with or without treatment with transporter inhibitors.

CONCLUSION

Efflux of LVFX from the central nervous system (CNS) involves multidrug resistance-associated proteins (MRPs), breast cancer resistance protein (BCRP), and organic anion transporters (OATs). MRPs play an important role in mediating the brain/CSF-to-blood efflux of LVFX. LVFX concentrations in CSF can be used as a surrogate to predict the concentrations inside brain parenchyma.

The effects of cyclosporine A or activated charcoal co-administration on the pharmacokinetics of enrofloxacin in chickens

The study aimed to investigate the possible role of efflux transporter proteins in the pharmacokinetics of enrofloxacin (ENR) in broilers in the model of co-administration of activated charcoal (AC) or cyclosporine A (CsA). The concentrations of enrofloxacin and its metabolite ciprofloxacin were analyzed by liquid chromatography-mass spectrometry (LC-MS/MS) and population approach was used for pharmacokinetic analysis. It was found that body weight has a significant effect on the volume of distribution in the central compartment and on the systemic clearance. Oral AC increased the systemic clearance of intravenously administered ENR suggesting some role of enterohepatic recirculation. For orally administered ENR, CsA increased the area under the curve which can be explained by the inhibition of efflux transporters. Metabolism of the antibacterial drug was not affected by cyclosporine. The data suggest a role of efflux transporter proteins in the pharmacokinetics of drugs in chickens and drug-drug interactions have to be considered when substrates and modulators of these transporters are co-administered.

Age-related P-glycoprotein expression in the intestine and affecting the pharmacokinetics of orally administered enrofloxacin in broilers

Bioavailability is the most important factor for the efficacy of any drug and it is determined by P- glycoprotein (P-gp) expression. Confirmation of P-gp expression during ontogeny is needed for understanding the differences in therapeutic efficacy of any drug in juvenile and adult animals. In this study, Abcb1 mRNA levels in the liver and intestine of broilers during ontogeny were analysed by RT qPCR. Cellular distribution of P-gp was detected by immunohistochemstry. Age-related differences of enrofloxacin pharmacokinetics were also studied. It was found that broilers aged 4 week-old expressed significantly (P<0.01) higher levels of P-gp mRNA in the liver, jejunum and ileum, than at other ages. However, there was no significant (P>0.05) age-related difference in the duodenum. Furthermore, the highest and lowest levels of Abcb1 mRNA expression were observed in the jejunum, and duodenum, respectively. P-gp immunoreactivity was detected on the apical surface of the enterocytes and in the bile canalicular membranes of the hepatocytes. Pharmacokinetic analysis revealed that the 8 week-old broilers, when orally administrated enrofloxacin, exhibited significantly higher C_max (1.97 vs. 0.98 μg•ml^-1, P=0.009), AUC(14.54 vs. 9.35 μg•ml^-1•h, P=0.005) and Ka (1.38 vs. 0.43 h^-1, P=0.032), as well as lower T_peak (1.78 vs. 3.28 h, P=0.048) and T_1/2ka (0.6 vs. 1.64 h, P=0.012) than the 4 week-old broilers. The bioavailability of enrofloxacin in 8 week-old broilers was increased by 15.9%, compared with that in 4 week-old birds. Interestingly, combining verapamil, a P-gp modulator, significantly improved pharmacokinetic behaviour of enrofloxacin in all birds. The results indicate juvenile broilers had a higher expression of P-gp in the intestine, affecting the pharmacokinetics and reducing the bioavailability of oral enrofloxacin in broilers. On the basis of our results, it is recommended that alternative dose regimes are necessary for different ages of broilers for effective therapy.

Nootropic activity of lipid-based extract of Bacopa monniera Linn. compared with traditional preparation and extracts

Objectives

The aim was to design an alternative solvent-free extraction method using the hydrophilic lipid Gelucire (polyethylene glycol glycerides) for herbal extraction and to confirm the efficacy of extraction using biological screening.

Methods

Bacopa monniera Linn. (BM) was selected for the study. Conventional methanolic extract (MEBM), Ayurvedic ghrita (AGBM) and lipid extracts (LEBM) were prepared and standardised by high-performance thin-layer chromatography (HPTLC). Nootropic activity in rats was evaluated using the two-trial Y-maze test and the anterograde amnesia induced by scopolamine (1 mg/kg i.p.) determined by the conditioned avoidance response. The extracts were administered daily at doses of 100, 200 and 400 mg/kg orally. At the end of the conditioned avoidance response test, brain monoamine levels were estimated by HPLC.

Key findings

The LEBM, MEBM and AGBM contained 3.56%, 4.10% and 0.005% bacoside A, respectively. Significantly greater spatial recognition was observed with LEBM (P &lt; 0.001 at 400 and 200 mg/kg) and MEBM (P &lt; 0.001 at 400 mg/kg, P &lt; 0.01 at 200 mg/kg) than AGBM. The conditioned avoidance response was significantly higher in the groups treated with high doses of LEBM and MEBM than AGBM. There were significant decreases in brain noradrenaline (P &lt; 0.001) and 5-hydroxytryptamine (P &lt; 0.01) levels and an increase in dopamine levels (P &lt; 0.05) in the LEBM-treated groups compared with the stress control group.

Conclusions

The proposed LEBM is solvent free, does not have the shortcomings associated with conventional extraction, and had comparable nootropic activity to the MEBM.

Fluoroquinolone efflux mediated by ABC transporters

Quinolones and fluoroquinolones are broad spectrum bactericidal drugs, which are widely used in both human and veterinary medicine. These drugs can quite easily enter cells and are often used to treat intracellular pathogens. Some fluoroquinolones have been reported to undergo efflux, which could explain their low bioavailability. There is a growing need to understand resistance mechanisms to quinolones, involving for instance mutations or the action of efflux pumps. Several members of the ATP-binding cassette (ABC) drug efflux transporter family (MDR, MRP, ABCG2) significantly affect the pharmacokinetic disposition of quinolones. Active secretory mechanisms common to all fluoroquinolones have been suggested, as well as competition between fluoroquinolones at transporter sites. For grepafloxacin and its metabolites, MRP2 has been demonstrated to mediate biliary excretion. However, MDR1 is responsible for grepafloxacin intestinal secretion. Recently it has been shown that ciprofloxacin and enrofloxacin are efficiently transported ABCG2 substrates which are actively secreted into milk. It appears that multiple ABC transporters contribute to the overall secretion of fluoroquinolones. The objective of this work is to review the recent advances in insights into ABC transporters and their effects on fluoroquinolone disposition and resistance including data on drug secretion into milk.