Inhibitory Effect of Dextran Derivatives on Multidrug Resistance-Related Efflux Transporters in Vitro.

Dextran is a promising candidate as a nanocarrier of chemotherapeutic drugs due to its biocompatibility, biodegradability, and ability to accumulate in tumors. Furthermore, dextran derivatives interact with P-glycoprotein (P-gp), so we hypothesized that they may be available as tumor-specific drug delivery systems with the ability to reverse multidrug resistance. Here, to test this idea, we investigated whether dextran and its derivatives inhibit breast cancer resistance protein (BCRP), multidrug resistance associated protein 1 (MRP1), and P-gp in vitro. First, we examined their effect on the uptake of specific fluorescent substrates by inside-out Sf-9 membrane vesicles overexpressing BCRP, MRP1, and P-gp. BCRP and MRP1 were significantly inhibited by 2-hydroxypropyl-trimethylammonium-dextran of 4 and 70 kDa (Q-D4 and Q-D70) at a concentration near the clinically used concentration of dextran; however, P-gp was not inhibited. A structure-activity study showed that Q-D4, Q-D70, and 40 kDa diethylaminoethyl-dextran (DEAE-D40) significantly inhibited BCRP, while 4, 40, and 70 kDa dextrans (D4, D40, and D70), dextran sulfate (Sul-D40), and the individual saccharide components of dextran did not. These results suggest that the cationic side chains, but not the saccharides, are important for BCRP inhibition. Finally, cell-based efflux assay was conducted. Q-D4, Q-D70, and DEAE-D40 did not specifically increase the retention of Hoechst33342 in BCRP-overexpressing KB cells. Similarly, Q-D4 and Q-D70 did not affect the intracellular retention of specific fluorescent substrates in MRP1- and P-gp-overexpressing KB cells. The ineffectiveness in cellular systems is presumably due to inability of the dextran derivatives to access transporters located on the cytoplasmic side of the cell membrane.

Intestinal Absorption of Alogliptin Is Mediated by a Fruit-Juice-Sensitive Transporter.

Alogliptin (ALG), an inhibitor of dipeptidylpeptidase-4, is used in the management of type 2 diabetes mellitus, and has a high absorption rate (>60-71%), despite its low lipophilicity (logP=-1.4). Here, we aimed to clarify the mechanism of its intestinal absorption. ALG uptake into Caco-2 cells was time-, temperature-, and concentration-dependent, but was not saturated at concentrations up to 10 mmol/L. The uptake was significantly inhibited by the organic anion transporting polypeptide (OATP) substrate fexofenadine and by the OATP inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), but was not inhibited by organic cation transporter (OCT)/organic cation/carnitine transporter (OCTN) or peptide transporter 1 (PEPT1) substrates. Grapefruit, orange, and apple juices and their constituents, which are known to strongly inhibit intestinal OATPs, significantly inhibited ALG uptake into Caco-2 cells. The pH dependence was bell-shaped, indicating the involvement of a pH-sensitive transporter. However, ALG uptake by HEK293 cells overexpressing OATP2B1, a key intestinal OATP transporter of amphiphilic drugs, was not different from that of mock cells. In a rat in vivo study, apple juice reduced systemic exposure to orally administered ALG without changing the terminal half-life. These observations suggest that intestinal absorption of ALG is carrier-mediated, and involves a fruit-juice-sensitive transporter other than OATP2B1.

Increased membrane permeation and blood concentration of 6-carboxyfluorescein associated with dysfunction of paracellular route barrier in the small intestine of ulcerative colitis model rats.

In the colon of patients with ulcerative colitis (UC), decreased function of the paracellular barrier, especially hypofunction of the tight junction, is associated with pathological conditions. However, there has been no report to date on the function of tight junctions in the small intestine. Here, we focused on the barrier function of the small intestine, especially in tight junctions, and compared it with that of the colon. Dextran sulfate sodium (DSS) was used to induce ulcerative colitis in rats in order to evaluate the function of the paracellular barrier in the jejunum, ileum, and colon. An in vitro diffusion chamber method was used to evaluate membrane resistance, which is an index of tight junction function and mucosal permeability, using 6-carboxyfluorescein (6-CF), a paracellular marker. In the jejunum and colon, with decrease of membrane resistance in the DSS group, mucosal permeability increased, whereas no marked difference was observed in the ileum. In the in situ closed-loop method, absorption of 6-CF from the jejunum was higher than that from the ileum. Immunohistochemical staining of claudin-4 showed heterogeneous attenuation of claudin-4 in the jejunum. Pharmacokinetic parameters were calculated from the blood concentration after intravenous injection and oral administration of 6-CF. In the DSS group, there was a delay in the elimination phase, suggesting a decrease in renal function, and an increase in maximum blood concentration, associated with an increased absorption rate constant. The increased absorption and decreased renal function due to decreased paracellular barrier function in the small intestine and colon may cause fluctuations in drug efficacy and side effects.

Intestinal secretion of indoxyl sulfate as a possible compensatory excretion pathway in chronic kidney disease.

Indoxyl sulfate (IS) is a protein-bound uremic toxin that progressively accumulates in plasma during chronic kidney disease (CKD), and its accumulation is associated with the progression of CKD. This study examined the intestinal secretion of IS using in situ single-pass intestinal perfusion in a rat model of renal insufficiency, MRP2- and BCRP-overexpressing Sf9 membrane vesicles, and Caco-2 cell monolayers. An in situ single-pass perfusion study in CKD model rats demonstrated that a small amount of IS is secreted into intestinal lumen after iv administration of IS, and the clearance increased AUC-dependently. An excess amount of IS (3 mm) partially inhibited the MRP2- and BCRP-mediated uptake of specific fluorescent substrates, CDCF and Lucifer yellow, respectively, into the membrane vesicles, although IS was not taken up at a physiological concentration, 10 µm. In the Caco-2 cell monolayers, the IS transport was higher in the absorptive direction than in the secretory direction (p < 0.05). p-Aminohippuric acid (PAH) strongly inhibited IS transport in both directions (absorptive, p = 0.142; secretory, p < 0.01). Given that the blood IS levels are much higher than those in the intestinal lumen, it is possible that this unknown PAH-sensitive system contributes to the intestinal IS secretion. Although in situ inhibition study is needed to confirm that this unknown transporter mediates the in vivo intestinal secretion of IS, we speculate that this unknown active efflux system works as a compensatory excretion pathway for excess organic anions such as IS especially in end-stage renal disease.

Changes of Absorptive and Secretory Transporting System of (1 → 3) ß-D-glucan Based on Efflux Transporter in Indomethacin-induced Rat.

Infection and inflammation suppress the expression and activity of several drug transporters in liver. In the intestine, P-glycoprotein (P-gp/MDR1), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP) are important barriers to the absorption of many clinically important drugs. The expression and activity of these proteins were examined under inflammation. Drug transport was determined in jejunum and ileum segments isolated from 1.0 mg/kg, 5.0 mg/kg, and 7.5 mg/kg indomethacin-treated or control rats in diffusion chambers. Transport of laminaran, used as a model compound of (1-3) ß-D-glucan, was measured for 120 min in the presence or absence of inhibitors. Reverse transcription-polymerase chain reaction was used to measure mRNA levels. Compared with controls, levels of Mdr1a mRNA were significantly decreased in the jejunum and ileum of 7.5 mg/kg indomethacin-treated rats. Both reductions in the basolateral to apical efflux of laminaran and increases in the apical to basolateral influx of laminaran were observed, resulting in significant increases in the apical to basolateral absorption of laminaran in 7.5 mg/kg indomethacin-treated rats. The inhibitory effect of verapamil on laminaran transport was observed in control rats but not in indomethacin-treated rats. Fluorescein isothiocyanate dextran 40,000 permeability, membrane resistance, and claudin-4 mRNA level were not altered, indicating no change in the paracellular pathway. These results indicate that indomethacin-induced inflammation reduces the intestinal expression and activity of P-gp in rats, which elicits corresponding changes in the intestinal transport of laminaran. Hence, inflammatory diseases may impose variability in drug bioavailability through alterations in the intestinal expression and activity of drug transporters.

[Examination of involuntary admissions in relations of CRPD].

When we examine the problems of involuntary admissions, CRPD (the convention on the rights of persons with disabilities-2006) must be considered within the context of the problems. The principle of the convention is based on enjoyment of legal capacity of persons with disabilities. So, it is necessary to recognize the relation and the contradiction between disease-disorder-disability spectrum and capacity-ability spectrum. The two spectrums have been developed after the Second World War with development of societies of the world. Author presents the recognition of involuntary admissions of Japan. So, Japanese psychiatry must select the road to community psychiatry to solve the problems.

Changes in the localization of ileal P-glycoprotein induced by intestinal ischemia/reperfusion.

P-glycoprotein is one of the most important transporters in the ATP binding cassette transporter. Moreover, it is well known that the efficacy of immunosuppressants, which are used after organ transplantation, is controlled by P-glycoprotein (P-gp). We investigated how ischemia/reperfusion (I/R), which occurs after transplantation, influences the expression level and function of P-gp. To clarify the influence of intestinal I/R on the localization of P-gp, an intestinal ischemia model was produced using a spring scale and surgical sutures for 1 h, followed by reperfusion for 24 h. The expression levels of mRNA and protein of P-gp were examined. The protein expression levels of P-gp in ileal homogenate and the brush border membrane (BBM) were significantly decreased until 3 h after reperfusion. While the protein expression level of P-gp in homogenate showed a tendency to increase, that in the BBM continued to significantly decrease until 24 h after reperfusion. In contrast, the protein expression level of P-gp in the basolateral membrane (BLM) increased significantly until 24 h after reperfusion. While no significant change in multidrug resistance (mdr)-1a mRNA was found, the levels of mdr-1b and mdr-2 significantly increased during intestinal I/R. In addition, the levels of inflammatory cytokines mRNA and nitric oxide (NO) also significantly increased. It was shown that mdr-1b and mdr-2 mRNA strongly participate in the recovery of P-gp protein level after intestinal I/R. We detected the abnormal localization of P-gp in the ileal membrane during intestinal I/R, suggesting NO and/or inflammatory cytokines participate in the abnormal localization of P-gp.

Effect of aminoguanidine on ischemia/reperfusion injury in rat small intestine.

Ischemia/reperfusion (I/R) injury is induced by reactive oxygen species (ROS). During intestinal I/R, the amount of nitric oxide (NO), which is a ROS, is increased. In this study, we examined the protection against I/R injury by inhibition of NO generation. Wistar/ST rats were exposed to 1 h of ischemia, followed by reperfusion for 4 h. The rats were intravenously injected with 100 mg/kg aminoguanidine (AG), which is a selective inducible NO synthase (iNOS) inhibitor, for 5 min before ischemia. The increase in NO(2)(-) by intestinal I/R was significantly inhibited by AG 1 h after reperfusion. Moreover, the increase in area under curve of 0 to 1 h after reperfusion (AUC(0-1)) of paracellular marker was inhibited. However, 3 h after reperfusion, the survival ratio of rats was significantly decreased in the intestinal I/R condition with AG. The amount of NO(2)(-) and AUC of 3 to 4 h after reperfusion (AUC(3-4)) of paracellular marker in intestinal I/R groups were increased by AG compared with those in the I/R condition without AG 3 h after reperfusion. These data indicated that AG, which was given by single pre-administration, can clearly inhibit intestinal I/R injury 1 h after reperfusion. However, the injury occurs again 3 h after reperfusion and grows worse.

Effects of antioxidants on drug absorption in in vivo intestinal ischemia/reperfusion.

Ischemia/reperfusion (I/R) injury must be overcome in order to succeed in small intestinal transplantation. Reactive oxygen species (ROS) are generated by I/R, and they induce lipid peroxidation which is one of the causes of mucosal lesion. We previously reported the protection effects of antioxidants to I/R injury in the in vitro study. In the present study, we examined the inhibitive effect of antioxidants on intestinal I/R injury in the in vivo study. Intestinal ischemia was induced in Wistar/ST rats using the spring scale and the surgical suture for 1 h, followed by reperfusion for 1 h. We used 4,5-dihydroxy-1,3-benzene-disulfonic acid (Tiron), astaxanthin (ATX) and epigallocatechin gallate (EGCG) as antioxidants. The inhibitive effects on mucosal lesion, opening of TJ and decrease in protein expression level of P-gp by in vivo intestinal I/R were admitted by three kinds of antioxidant. Tiron and EGCG inhibited P-gp function but ATX did not. Therefore, for the use of P-gp substrate like immunosuppressants after the intestinal transplantation, ATX, which does not inhibit P-gp is considered to be effective for intestinal I/R injury.

Effects of acylcarnitines on efflux transporting system in Caco-2 cell monolayers.

This study examined the effects of the absorption enhancers, acylcarnitines, on efflux transporting systems, including P-glycoprotein (P-gp) and other efflux transporters, and elucidated the importance of acyl chain length and the concentration of acylcarnitine on the activity of efflux transport. The effects of two acyl (lauroyl and palmitoyl) carnitines on the influx and efflux of lucifer yellow and fluorescein isothiocyanate dextran 4,000, which have characteristic vectorial transport, were examined in Caco-2 cell monolayers. Lauroylcarnitine and palmitoylcarnitine increased influx and decreased efflux of these substrates, in a manner dependent on their concentration and acyl chain lengths by increasing influx and inhibiting efflux of the substrates. The results indicated that both the acyl moiety and long acyl chains play important roles in the modification of influx and efflux transport. Because no marked changes in the levels of P-gp protein or the leakage of LDH were observed at 1 h after the application of acylcarnitines, it was concluded that these acylcarnitines had an effect on modulation of the function of P-gp or other efflux transporters without cytotoxicity.

Retraction Note to: Changes of Absorptive and Secretory Transporting System of (1 → 3) ß-D-glucan Based on Efflux Transporter in Indomethacin-induced Rat.

The Editor-in-Chief has retracted this article [1] based on an investigation by the Ministry of Education, Culture, Sports, Science and Technology, Japan, which found that the article contained overlap with a previously published article by Kalitsky-Szirtes J, et al. [2].

Mechanistic analysis for drug permeation through intestinal membrane.

For drug absorption, intestinal drug permeability's through both the paracellular and transcellular routes were analyzed. Absorption enhancers, such as sodium caprate (C10), decanoylcarnitine (DC) and tartaric acid (TA), increased the paracellular permeability of water-soluble, low lipophilic and poorly absorbable drugs by enlargement of tight junction (TJ) adhering to the intercellular portion; that is, expansion of the paracellular routes. C10 increased the intracellular calcium level to induce contraction of calmodulin-dependent actin filaments. Although DC also increased the intracellular calcium level, the action was independent of calmodulin, and thus the action mechanism of DC was considered to differ from that of C10. DC and TA decreased the intracellular ATP level and the intracellular pH, suggesting that intracellular acidosis increases the calcium level through decrease in ATP level followed by opening TJ. TA had no effect on Western blot analysis, but TA significantly inhibited excretion of rhodamine 123, one of the P-glycoprotein (P-gp) substrates, from the serosal to mucosal side, suggesting that TA increases the intestinal absorption of P-gp substrates, possibly by inhibiting the P-gp function without changing the expression of P-gp. During ischemia/reperfusion (I/R) injury during small intestine grafting, TJ opening and decrease in P-gp function simultaneously occurred. The in vitro model of I/R showed that lipid peroxidation is a trigger of the injury, and superoxide and iron ion participate in TJ opening and decrease in P-gp function. Colonic epithelial cells have the specific transcellular transport systems for lipopolysaccharide (LPS), one of which shows substrate specificity in the interaction with CD14 and/or that of TLR4. In the infective disease induced by LPS, the mucosal LPS sensitive transport capability was decreased and in the secretory direction, the receptor-mediated uptake mechanism disappeared. LPS taken up into the cells can be excreted by P-gp or mrp. The expression levels and function of the secretory transporters were considered to be increased in the infective condition. In conclusion, changes in TJ as the membrane structure and P-gp as the membrane function are important factors controlling intestinal membrane transport.

NaPi-mediated transcellular permeation is the dominant route in intestinal inorganic phosphate absorption in rats.

Inorganic phosphate in food is absorbed two ways, the transcellular route via the brush border membrane and the paracellular route via tight junctions. NaPi, a sodium-dependent inorganic phosphate transporter, is expressed in rat and human intestine. However, the relative contribution of NaPi to total carrier-mediated transport of physiological concentrations of inorganic phosphate in rat intestine is not clear. Here, we characterized inorganic phosphate transport across the rat small intestine using a voltage-clamp analysis which allowed the diffrentiation of inorganic phosphate permeation through these two (transcellular and paracellular) routes. Results showed that, under a physiologically normal transmucosal electrical potential difference (about 2 mV), permeation of inorganic phosphate by the transcellular route was greater than that by the paracellular route. Further, transport was significantly decreased by the addition to the incubation medium of phosphonoformic acid, a sodium-dependent phosphate transporter inhibitor, and severely inhibited under sodium-free conditions. Similar results were obtained without the voltage-clamp. Together, these results suggest that NaPi-mediated transcellular permeation is the dominant route in the absorption of inorganic phosphate across the small intestine.

The novel formulation design of self-emulsifying drug delivery systems (SEDDS) type O/W microemulsion III: the permeation mechanism of a poorly water soluble drug entrapped O/W microemulsion in rat isolated intestinal membrane by the Ussing chamber method.

We used ibuprofen as a poorly water soluble model drug, to examine the influence of bile salts and mucin layers on the permeability of that entrapped in an O/W microemulsion, in a rat isolated intestinal membrane by the Ussing chamber method. Under the presence of 3 kinds of the primary bile salts such a sodium taurocholate, etc., or a secondary bile salt such a sodium taurochenodeoxycholate at 0.01 mmol/L concentration, a significant difference was not demonstrated in the permeation clearance of the ibuprofen entrapped O/W microemulsion, as compared with the case without the bile salts. Thus, the bile salts did not have a remarkable influence on the permeability of the drug entrapped in the O/W microemulsion, and it was verified that this O/W microemulsion was hardly influenced by the flow of the bile secretion. On the other hand, when N-acetyl-L-cysteine (NAC) with the removal ability of a mucin layer was combined with the ibuprofen entrapped O/W microemulsion at the concentration of 3 and 10 mmol/L, it was shown that the permeation clearance of free ibuprofen did not decrease, but that of ibuprofen entrapped in the O/W microemulsion decreased with the increase of the NAC concentration. Therefore, it is confirmed that the mucin layer participates in the permeability of the drug entrapped in the O/W microemulsion. From these results, the mechanism in which the drug entrapped in the O/W microemulsion is released in a mucin layer, without passing through the route of the mixed micelle formation by bile, thereafter the drug permeates an intestinal membrane, is supposed.

Improvement of intestinal absorption of P-glycoprotein substrate by D-tartaric acid.

The purpose of the present experiment was to examine the effects of D-tartaric acid (TA) on intestinal drug absorption under both in situ and in vitro experimental conditions. In the in vitro diffusion chamber experiments, TA (10 mM) added to the mucosal side of rat colon significantly decreased rhodamine123 (Rho 123) transport from the serosal to mucosal side. Since TA has been shown to change the integrity of the epithelial tight junctions in rat colon at low pH conditions, resulting in improved paracellular drug transport, the effect of TA on membrane resistance was examined at pH 7.4 in the present study. It was found that membrane resistance, an indicator of paracellular integrity, did not change at pH 7.4. In the in situ loop method, TA (20 mM) increased the absorption of Rho123 in both ileum and colon but not in jejunum. TA (20 mM) also increased the absorption of daunorubicin in the ileum, but TA (20 mM) did not change the expression level of P-glycoprotein (P-gp). TA (20 mM) significantly inhibited excretion of i.v.-administered Rho123 and daunorubicin into the ileal lumen. In conclusion, for the first time we demonstrated that TA increases the intestinal absorption of P-gp substrates Rho123 and daunorubicin, possibly by modulating the P-gp function without changing the expression level of P-gp in the rat intestine.

Ischemia/reperfusion injury in the monolayers of human intestinal epithelial cell line caco-2 and its recovery by antioxidants.

We previously established a in vitro system for assessing early ischemia/reperfusion injury using monolayers of human intestinal epithelial cell line Caco-2, in which lipid peroxidation caused by tertiary-butylhydroperoxide (t-BuOOH), a lipid peroxidation inducer, acts as a trigger of the injury. By now, we have shown that superoxide anion participates in the opening of tight junctions (TJ) induced by reoxygenation following the induction of lipid peroxidation by t-BuOOH at a low concentration. The present objectives are to elucidate the dysfunction of P-glycoprotein (P-gp) in addition to the opening of TJ by t-BuOOH at a high concentration condition using rhodamine123 (Rho123) as a P-gp substrate and cyclosporine A (CyA) as a P-gp inhibitor. Also, we compared the inhibition effect of lutein and other compounds such as biliverdin as a radical scavenger on the opening of TJ and the dysfunction of P-gp. t-BuOOH at a high concentration increased the permeability of Rho123 in the apical to basal direction and decreased basal to apical direction when compared with control conditions. t-BuOOH at a high concentration showed no significant difference between directional transport of Rho123 and no inhibition was observed in the permeability of both directions by CyA. The staining intensity of Western blot was decreased by t-BuOOH at a high concentration. Although lutein and the other compounds had recovery effects on the opening of TJ and P-gp dysfunction induced by t-BuOOH, lutein is more advantageous than other compounds since it has effective effects at the lower concentration. In conclusion, the barrier dysfunction such as the inhibition of P-gp in addition to the opening of TJ was induced by t-BuOOH at a high concentration condition. The above two barrier dysfunctions was ameliorated by antioxidant such as lutein and biliverdin.

The novel formulation design of self-emulsifying drug delivery systems (SEDDS) type O/W microemulsion II: stable gastrointestinal absorption of a poorly water soluble new compound, ER-1258 in bile-fistula rats.

The stabilization effect of the novel self-emulsifying drug delivery systems (SEDDS) type O/W microemulsion on the gastrointestinal absorption of a poorly water soluble new compound, ER-1258 was examined by bile-fistula model rats. In the components of this formulation, medium chain fatty acid triglyceride (MCT), diglyceryl monooleate (DGMO-C), polyoxyethylene hydrogenated castor oil 40 (HCO-40) and ethanol were used as an oil, a lipophilic surfactant, a hydrophilic surfactant and a solubilizer at the mixture ratio of 25/5/45/25 w/w%, respectively. The ratios of AUC in the non-treated rats to that in the bile-fistula rats were 5.1, 12.1 and 3.0 for the suspension, the oily solution and the SEDDS type O/W microemulsion, respectively. The risk from which the difference between individuals of the compound absorption amounts resulting from the flow of the bile secretion serves as the maximum was high in order of oily solution>suspension>SEDDS type O/W microemulsion. Therefore, it was verified that the SEDDS type O/W microemulsion was able to reduce this risk, compared with the other formulations. When short chain fatty acid triglyceride (Triacetin) was used as an oil, the similar effect was demonstrated in the formulation composed of sorbitan sesquioleate (SO-15) as a lipophilic surfactant and polyoxyethylene hydrogenated castor oil 60 (HCO-60) or polyoxyethylene 20 sorbitan monooleate (TO-10M) as a hydrophilic surfactant.

Regional difference in P-glycoprotein function in rat intestine.

It has been reported that inhibition of the P-glycoprotein (P-gp) results in the improved absorption of P-gp substrate in the intestinal tract. In fact, the increased permeability of P-gp substrate across the intestinal epithelium was observed following inhibition of P-gp in in vitro experiments. To develop the formulation containing P-gp inhibitor and P-gp substrate for practical use, it is necessary to know whether the results obtained in the in vitro experiments are reproducible at whole body level. It is also important to find out the regional difference of the P-gp activity in the intestinal tract. In this study, we examined whether verapamil, a specific inhibitor of P-gp, improves the absorption of rhodamine123 (Rho123), a substrate of P-gp, from the jejunum, ileum, and colon of rats using the in situ loop method. The water content in the loop decreased during the experiment, resulting in a significant change of the Rho123 concentration in the loop. Thus, to accurately determine the absorption rate of Rho123, it was necessary to measure the water movement. It was found that there was a regional difference in the water movement, i.e., greatest in colon, followed by ileum. Verapamil did not change the water movement in any intestinal regions. When the concentration of Rho123 in the loop was corrected by water movement, the Rho123 clearance was in the order of ileum (1.15 microL/min/cm), colon (0.83 microL/min/cm) and jejunum (0.47 microL/min/cm). In the presence of verapamil, the Rho123 clearance was significantly increased at jejunum and ileum but not in colon (ileum: 2.08 microL/min/cm, colon: 1.14 microL/min/cm, jejunum: 1.28 microL/min/cm). These results suggest that P-gp inhibits the drug absorption in jejunum and ileum. From these results, it is possible to evaluate the role of P-gp and its regional difference in the in situ experiments. In particular, the inhibition of P-gp results in an increase in absorption of the P-gp substrate limited to jejunum and ileum.

The novel formulation design of self-emulsifying drug delivery systems (SEDDS) type O/W microemulsion I: enhancing effects on oral bioavailability of poorly water soluble compounds in rats and beagle dogs.

We examined the design of the versatile novel self-emulsifying drug delivery systems (SEDDS) type O/W microemulsion formulation which enhances the oral bioavailability by raising the solubility of poorly water soluble compounds. Namely, seven kinds of poorly water soluble compounds such as disopyramide, ibuprofen, ketoprofen, tolbutamide, and other new compounds, as the model compounds were used to compare the plasma concentration profile of the compound following single oral administration of each compound to rats and beagle dogs as a solution, an oily solution, a suspension (or a powder), an O/W microemulsion, and a SEDDS type O/W microemulsion. And the enhancing effect of the SEDDS type O/W microemulsion on the gastrointestinal absorption of these compounds was evaluated. In the components of the SEDDS type O/W microemulsion, medium chain fatty acid triglyceride (MCT), diglyceryl monooleate (DGMO-C), polyoxyethylene hydrogenated castor oil 40 (HCO-40), and ethanol were used as an oil, a lipophilic surfactant, a hydrophilic surfactant, and a solubilizer, at the mixture ratio of 25/5/45/25 (w/w%), respectively. Thereby, to six kinds of the model compounds except disopyramide, the solubility was from 340 to 98,000 times that in water, and the AUCs in plasma concentration of the compound were equivalent to that of solution or O/W microemulsion administration, or was increased by 1.5 to 78 times that of suspension administration. Accordingly, this novel SEDDS type O/W microemulsion is the versatile, useful formulation which enhances the oral bioavailability by raising the solubility of poorly water soluble compounds.