Effect of adrenergic stimulation on drug absorption via passive diffusion in Caco-2 cells

Possible Regulation of P-Glycoprotein Function by Adrenergic Agonists II: Study with Isolated Rat Jejunal Sheets and Caco-2 Cell monolayers

To clarify the regulation of drug absorption by the enteric nervous system, we investigated how adrenergic agonists (adrenaline (ADR), clonidine (CLO), dobutamine (DOB)) and dibutyryl cAMP (DBcAMP) affected P-glycoprotein (P-gp) function by utilizing isolated rat jejunal sheets and Caco-2 cell monolayers. ADR and CLO significantly decreased the secretory transport (Papptotal) of rhodamine-123 and tended to decrease the transport via P-gp (PappP-gp) and passive transport (Papppassive). In contrast, DBcAMP significantly increased and DOB tended to increase Papptotal and both tended to increase PappP-gpand Papppassive. Changes in P-gp expression on brush border membrane by adrenergic agonists and DBcAMP were significantly correlated with PappP-gp, while P-gp expression was not changed in whole cell homogenates, suggesting that the trafficking of P-gp would be responsible for its functional changes. Papppassive was inversely correlated with transmucosal or transepithelial electrical resistance, indicating that adrenergic agonists affected the paracellular permeability. Adrenergic agonists also changed cAMP levels, which were significantly correlated with PappP-gp. Furthermore, protein kinase A (PKA) or PKC inhibitor significantly decreased PappP-gp in Caco-2 cell monolayers, suggesting that they would partly contribute to the changes in P-gp activity. In conclusion, adrenergic agonists regulated P-gp function and paracellular permeability, which would be caused via adrenoceptor stimulation.

Establishment of a novel in vitro co-culture system of enteric neurons and Caco-2 cells for evaluating the effect of enteric nervous system on transepithelial transport of drugs

The gastrointestinal tract is innervated by extrinsic autonomic nerves and intrinsic enteric nervous system (ENS). However, the role of ENS in drug absorption has remained to be clarified. To investigate the effect of ENS on drug transport across the intestinal epithelial cells, we established a novel co-culture system of Caco-2 cells and enteric neurons differentiated from neural crest stem (NCS)-like cells isolated from mouse longitudinal muscle/myenteric plexus (LMMP). Immunostaining analysis revealed that the proportions of neuron, glia, and NCS-like cells were only <5 % at population in the primary culture of LMMP cells. Therefore, we proliferated NCS-like cells and differentiated them into neuronal cells and successfully increased the neuronal cell population upto about 40 %. Then, the differentiated neuronal cells were co-cultured with Caco-2 cell monolayers, and we found that the co-culture significantly decreased the transepithelial electrical resistance and enhanced the transport of fluorescein isothiocyanate-labeled dextran-4 across Caco-2 cell monolayers, suggesting that the enteric neurons would function to open the tight junction and facilitate the drug transport via the paracellular route. On the other hand, no changes in the permeability of antipyrine were observed, suggesting that the enteric neurons would not affect the passive transport via the transcellular pathway.

Effect of Excessive Serotonin on Pharmacokinetics of Cephalexin after Oral Administration: Studies with Serotonin-Excessive Model Rats

PURPOSE

Serotonin (5-HT) is important for gastrointestinal functions, but its role in drug absorption remains to be clarified. Therefore, the pharmacokinetics and oral absorption of cephalexin (CEX) were examined under 5-HT-excessive condition to understand the role of 5-HT.

METHODS

5-HT-excessive rats were prepared by multiple intraperitoneal dosing of 5-HT and clorgyline, an inhibitor for 5-HT metabolism, and utilized to examine the pharmacokinetics, absorption behavior and the intestinal permeability for CEX.

RESULTS

Higher levels of 5-HT in brain, plasma and small intestines were recognized in 5-HT-excessive rats, where the oral bioavailability of CEX was significantly enhanced. The intestinal mucosal transport via passive diffusion of CEX was significantly increased, while its transport via PEPT1 was markedly decreased specifically in the jejunal segment, which was supported by the decrease in PEPT1 expression on brush border membrane (BBM) of intestinal epithelial cells. Since no change in antipyrine permeability and significant increase in FITC dextran-4 permeability were observed in 5-HT-excessive rats, the enhanced permeability for CEX would be attributed to the opening of tight junction, which was supported by the significant decrease in transmucosal electrical resistance. In 5-HT-excessive rats, furthermore, total body clearance of CEX tended to be larger and the decrease in PEPT2 expression on BBM in kidneys was suggested to be one of the reasons for it.

CONCLUSIONS

5-HT-excessive condition enhanced the oral bioavailability of CEX in rats, which would be attributed to the enhanced permeability across the intestinal mucosa via passive diffusion through the paracellular route even though the transport via PEPT1 was decreased.

Possible Regulation of P-glycoprotein Function by Adrenergic Agonists in a Vascular-luminal Perfused Preparation of Small Intestine

Although the functions of small intestine are largely regulated by enteric nervous system (ENS), an independent intrinsic innervation, as well as central nervous system (CNS), the neural regulation of drug absorption from the small intestine still remains to be clarified. To obtain some information on it, the effect of adrenergic agonists on P-glycoprotein (P-gp) function was investigated by utilizing a vascular-luminal perfused rat small intestine. Adrenaline significantly decreased the secretion of rhodamine-123 (R-123) into the intestinal lumen, but dibutyryl cAMP (DBcAMP) significantly enhanced R-123 secretion. The inhibition study with quinidine clearly indicated that the decrease in secretory clearance of R-123 by adrenaline or the increase by DBcAMP would be attributed to the decrease or increase in P-gp activity, respectively. Expression levels of P-gp in whole mucosal homogenates were not changed at all by any chemicals examined, but those on brush border membrane (BBM) of intestinal epithelial cells were significantly decreased or increased by adrenaline or DBcAMP, respectively. Furthermore, changes in P-gp activity caused by adrenergic agonists and DBcAMP were significantly correlated with changes in expression level of P-gp in BBM, suggesting that the trafficking of P-gp from cytosolic pool to BBM would be regulated by adrenergic agonists and DBcAMP.

Hydrophobic Amino Acid Tryptophan Shows Promise as a Potential Absorption Enhancer for Oral Delivery of Biopharmaceuticals

Cell-penetrating peptides (CPPs) have great potential to efficiently deliver drug cargos across cell membranes without cytotoxicity. Cationic arginine and hydrophobic tryptophan have been reported to be key component amino acids for cellular internalization of CPPs. We recently found that l-arginine could increase the oral delivery of insulin in its single amino acid form. Therefore, in the present study, we evaluated the ability of another key amino acid, tryptophan, to enhance the intestinal absorption of biopharmaceuticals. We demonstrated that co-administration with l-tryptophan significantly facilitated the oral and intestinal absorption of the peptide drug insulin administered to rats. Furthermore, l-tryptophan exhibited the ability to greatly enhance the intestinal absorption of other peptide drugs such as glucagon-like peptide-1 (GLP-1), its analog Exendin-4 and macromolecular hydrophilic dextrans with molecular weights ranging from 4000 to 70,000 g/mol. However, no intermolecular interaction between insulin and l-tryptophan was observed and no toxic alterations to epithelial cellular integrity-such as changes to cell membranes, cell viability, or paracellular tight junctions-were found. This suggests that yet to be discovered inherent biological mechanisms are involved in the stimulation of insulin absorption by co-administration with l-tryptophan. These results are the first to demonstrate the significant potential of using the single amino acid l-tryptophan as an effective and versatile bioavailability enhancer for the oral delivery of biopharmaceuticals.

Pharmacokinetic profiles contribute to the differences in behavioral pharmacology of 071031B enantiomers as novel serotonin and norepinephrine reuptake inhibitors

Our previous study indicated that a chiral compound 071031B was a novel serotonin and noradrenaline reuptake inhibitor with superior antidepressant activity compared to duloxetine. The present study aimed to investigate chiral pharmacology differences of 071031B enantiomers, S-071031B and R-071031B, and disclose mechanisms underlying the behavioral differences based on target profiles and pharmacokinetic profiles. In vivo behavioral tests indicated that S-071031B was more potent than R-071031B in two depression models (the forced swimming test in mice and rats) and two pain models (the acetic acid-induced writhing and formalin tests in mice). In vitro assays revealed that both S-071031B and R-071031B showed high affinity for human serotonin transporters and norepinephrine transporters with equal potency, and showed consistently equipotent inhibitory effects on serotonin and norepinephrine uptake. Pharmacokinetic studies demonstrated that oral availability and hepatic metabolism, rather than pH stability, intestinal transport, and plasma binding, contributed to enantiomers' behavioral differences. Based on these findings, it is suggested that S-071031B is a more active enantiomer, and the differential pharmacokinetic profiles, but not target affinity, contribute to differences of S-071031B and R-071031B in behavioral pharmacology. Moreover, current PK-PD study may provide positive exploration for chiral antidepressants development.

In Vitro Evaluation of Absorption Characteristics of Peramivir for Oral Delivery

BACKGROUND AND OBJECTIVE

Peramivir is a novel antiviral agent approved for the treatment of severe influenza. However, the development of oral formulation of peramivir has been severely hurdled by poor bioavailability (human, ≤3%). The present work aims to evaluate oral permeability characteristics of peramivir.

METHODS

In vitro gastrointestinal stability, metabolic stability in human intestinal S9 fraction and Caco-2 permeability were performed. The liquid chromatography with tandem mass spectrometric (LC-MS/MS) was used to quantify peramivir in buffer and biological sample. Using GastroPlus™ software, intestinal effective permeability coefficient (P _eff) of peramivir was estimated.

RESULTS

Our results indicated that peramivir maintained stability in pH 5.5 and 7.4 buffers, fasted state simulated gastric fluid and fasted state simulated intestinal fluid, and human intestinal S9 fractions. The apparent permeability coefficient (P _app) values of peramivir (10 μM) were 3.29 ± 0.73 × 10^-7 cm/s in a Caco-2 cell model. In vivo intestinal effective permeability coefficient (P _eff) was estimated to be 0.06 × 10^-4 cm/s. Furthermore, co-incubating with cyclosporine, mitoxantrone, rifampicin, or paroxetine, the apical (AP) to basolateral (BL) flux of peramivir decreased (p < 0.05). The efflux and influx of peramivir was not significantly affected with co-incubation with verapamil, MK-571, or diclofenac (p > 0.05).

CONCLUSIONS

These results revealed that carrier-mediated transports, including OATP1B (organic anion transport 1B) and OCT1 (organic cation transport 1), might be involved in the absorption of peramivir. In conclusion, our results provide insight into the poor oral bioavailability of peramivir. Peramivir can be classified as a BCS-III (high solubility/low permeability) and BDDCS-III high solubility/poor metabolism) drug. The oral bioavailability of peramivir primarily depends on its permeability across cell membranes. Both of passive and active transports are involved in the permeability of peramivir.

Subdiffusion-reaction processes with A→B reactions versus subdiffusion-reaction processes with A+B→B reactions

We consider the subdiffusion-reaction process with reactions of a type A+B→B (in which particles A are assumed to be mobile, whereas B are assumed to be static) in comparison to the subdiffusion-reaction process with A→B reactions which was studied by Sokolov, Schmidt, and Sagués [Phys. Rev. E 73, 031102 (2006)]. In both processes a rule that reactions can only occur between particles which continue to exist is taken into account. Although in both processes a probability of the vanishing of particle A due to a reaction is independent of both time and space variables (assuming that in the system with the A+B→B reactions, particles B are distributed homogeneously), we show that subdiffusion-reaction equations describing these processes as well as their Green's functions are qualitatively different. The reason for this difference is as follows. In the case of the former reaction, particles A and B have to meet with some probability before the reaction occurs in contradiction with the case of the latter reaction. For the subdiffusion process with the A+B→B reactions we consider three models which differ in some details concerning a description of the reactions. We base the method considered in this paper on a random walk model in a system with both discrete time and discrete space variables. Then the system with discrete variables is transformed into a system with both continuous time and continuous space variables. Such a method seems to be convenient in analyzing subdiffusion-reaction processes with partially absorbing or partially reflecting walls. The reason is that within this method we can determine Green's functions without a necessity of solving a fractional differential subdiffusion-reaction equation with boundary conditions at the walls. As an example, we use the model to find the Green's functions for a subdiffusive reaction system (with the reactions mentioned above), which is bounded by a partially absorbing wall. This example shows how the model can be used to analyze the subdiffusion-reaction process in a system with partially absorbing or reflecting thin membranes. Employing a simple phenomenological model, we also derive equations related to the reaction parameters used in the considered models.

Prevention of neutrophil extravasation by α2-adrenoceptor-mediated endothelial stabilization

Adrenergic receptors are expressed on the surface of inflammation-mediating cells, but their potential role in the regulation of the inflammatory response is still poorly understood. The objectives of this work were to study the effects of α2-adrenergic agonists on the inflammatory response in vivo and to determine their mechanism of action. In two mouse models of inflammation, zymosan air pouch and thioglycolate-induced peritonitis models, the i.m. treatment with xylazine or UK14304, two α2-adrenergic agonists, reduced neutrophil migration by 60%. The α2-adrenergic antagonist RX821002 abrogated this effect. In flow cytometry experiments, the basal surface expression of L-selectin and CD11b was modified neither in murine nor in human neutrophils upon α2-agonist treatment. Similar experiments in HUVEC showed that UK14304 prevented the activation-dependent upregulation of ICAM-1. In contrast, UK14304 augmented electrical resistance and reduced macromolecular transport through a confluent HUVEC monolayer. In flow chamber experiments, under postcapillary venule-like flow conditions, the pretreatment of HUVECs, but not neutrophils, with α2-agonists decreased transendothelial migration, without affecting neutrophil rolling. Interestingly, α2-agonists prevented the TNF-α-mediated decrease in expression of the adherens junctional molecules, VE-cadherin, β-catenin, and plakoglobin, and reduced the ICAM-1-mediated phosphorylation of VE-cadherin by immunofluorescence and confocal analysis and Western blot analysis, respectively. These findings indicate that α2-adrenoceptors trigger signals that protect the integrity of endothelial adherens junctions during the inflammatory response, thus pointing at the vascular endothelium as a therapeutic target for the management of inflammatory processes in humans.

The characterization of arachnoid cell transport II: paracellular transport and blood-cerebrospinal fluid barrier formation

We used an immortalized arachnoid cell line to test the arachnoid barrier properties and paracellular transport. The permeabilities of urea, mannitol, and inulin through monolayers were 2.9 ± 1.1 × 10(-6), 0.8 ± .18 × 10(-6), 1.0 ± .29 × 10(-6)cm/s. Size differential permeability testing with dextran clarified the arachnoidal blood-cerebrospinal fluid (CSF) barrier limit and established a rate of transcellular transport to be about two orders of magnitude slower than paracellular transport in a polyester membrane diffusion chamber. The theoretical pore size for paracellular space is 11Å and the occupancy to length ratio is 0.8 and 0.72 cm(-1) for urea and mannitol respectively. The permeability of the monolayer was not significantly different from apical to basal and vice versa. Gap junctions may have a role in contributing to barrier formation. Although the upregulation of claudin by dexamethasone did not significantly alter paracellular transport, increasing intracellular cAMP decreased mannitol permeability. Calcium modulated paracellular transport, but only selectively with the ion chelator, EDTA, and with disruption of intracellular stores. The blood-CSF barrier at the arachnoid is anatomically and physiologically different from the vascular-based blood-brain barrier, but is similarly subject to modulation. We describe the basic paracellular transport characteristics of this CSF "sink" of the brain which will allow for a better description of mass and constitutive balance within the intracranial compartment.