Simultaneous use of sodium deoxycholate and dipotassium glycyrrhizinate enhances the cellular transport of poorly absorbed compounds across Caco-2 cell monolayers

Evaluation of nasal delivery systems of olanzapine by desorption electrospray ionization mass spectrometry imaging

Nose-to-brain delivery presents an attractive administration route for neuroactive drugs that suffer from compromised bioavailability or fail to pass the blood-brain barrier. However, the conventional gauge of effectiveness for intranasal delivery platforms primarily involves detecting the presence of the administered drug within the brain, with little insight into its precise localization within brain structures. This may undermine the therapeutic efficacy of drugs and hinder the design of systems that target specific brain regions. In this study, we designed two intranasal delivery systems for the antipsychotic drug, olanzapine, and evaluated its distribution in the rat brain following intranasal administration. The first evaluated system was an olanzapine-loaded microemulsion and the second one was nanoparticulate aqueous dispersion of olanzapine. Both systems exhibited characteristics that render them compatible for intranasal administration, and successfully delivered olanzapine to the brain. We further employed an ambient mass spectrometry imaging method, called desorption electrospray ionization mass spectrometry imaging, to visualize the signal intensity of olanzapine in different brain regions following the intranasal administration of these two systems. Substantial variations in the distribution patterns of olanzapine across various brain structures were revealed, potentially highlighting the importance of mass spectrometry imaging in designing and evaluating intranasal drug delivery platforms.

Application of Fucoidan in Caco-2 Model Establishment

The Caco-2 model is a common cell model for material intestinal absorption in vitro, which usually takes 21 days to establish. Although some studies have shown that adding puromycin (PM) can shorten the model establishment period to 7 days, this still requires a long modeling time. Therefore, exploring a shorter modeling method can reduce the experimental costs and promote the development and application of the model. Fucoidan is an acidic polysaccharide with various biological activities. Our study showed that the transepithelial electrical resistance (TEER) value could reach 600 Ω·cm2 on the fourth day after the addition of fucoidan and puromycin, which met the applicable standards of the model (>500 Ω). Moreover, the alkaline phosphatase (AKP) activity, fluorescein sodium transmittance, and cell morphology of this model all met the requirements of model establishment. Fucoidan did not affect the absorption of macromolecular proteins and drugs. The results indicate that fucoidan can be applied to establish the Caco-2 model and can shorten the model establishment period to 5 days.

Direct Inhibition of the First PDZ Domain of ZO-1 by Glycyrrhizin is a Possible Mechanism of Tight Junction Opening of Caco-2 Cells

Glycyrrhizin (GL) is known to exhibit a variety of useful pharmacological activities, including anti-inflammation, anti-hepatotoxicity, and enhancement of intestinal drug absorption. GL has been reported to modify the assembly of...

Bioavailability Enhancement of Poorly Soluble Drugs: The Holy Grail in Pharma Industry

Background:

Bioavailability, one of the prime pharmacokinetic properties of a drug, is defined as the fraction of an administered dose of unchanged drug that reaches the systemic circulation and is used to describe the systemic availability of a drug. Bioavailability assessment is imperative in order to demonstrate whether the drug attains the desirable systemic exposure for effective therapy. In recent years, bioavailability has become the subject of importance in drug discovery and development studies.

Methods:

A systematic literature review in the field of bioavailability and the approaches towards its enhancement have been comprehensively done, purely focusing upon recent papers. The data mining was performed using databases like PubMed, Science Direct and general Google searches and the collected data was exhaustively studied and summarized in a generalized manner.

Results:

The main prospect of this review was to generate a comprehensive one-stop summary of the numerous available approaches and their pharmaceutical applications in improving the stability concerns, physicochemical and mechanical properties of the poorly water-soluble drugs which directly or indirectly augment their bioavailability.

Conclusion:

The use of novel methods, including but not limited to, nano-based formulations, bio-enhancers, solid dispersions, lipid-and polymer-based formulations which provide a wide range of applications not only increases the solubility and permeability of the poorly bioavailable drugs but also improves their stability, and targeting efficacy. Although, these methods have drastically changed the pharmaceutical industry demand for the newer potential methods with better outcomes in the field of pharmaceutical science to formulate various dosage forms with adequate systemic availability and improved patient compliance, further research is required.

Design and strategies for bile acid mediated therapy and imaging

Bioinspired materials have received substantial attention across biomedical, biological, and drug delivery research because of their high biocompatibility and lower toxicity compared with synthetic materials.

An appraisal of the bioavailability enhancers in Ayurveda in the light of recent pharmacological advances

The concept of bioavailability enhancer is new to the modern system of medicine. Basically, this concept originated in Ayurveda and being used in this system of medicine since centuries. Bio-enhancers augment the bioavailability or biological activity of drugs when co-administered with principal drug at low doses. Ayurveda is using several drugs such as Piper longum Linn., Zingiber officinale Rosc., and Glycyrhhiza glabra Linn. as bio-enhancers and different methods for bio-enhancing since centuries. The bio-enhancement leads to reduction in therapeutic dose of principal drug, thus reducing the possibilities of toxicity and side effects of drug, potentiating the efficacy, reducing the resistance, decreasing the requirement of raw material for drug manufacture, and ultimately benefitting to the world economy by reducing the treatment cost. This review article attempts to consolidate different drugs as well as methods being used traditionally for enhancing bioavailability in Ayurvedic system of medicine and to discuss their possible mechanism of action. Authentic subject material has been reviewed from different Ayurvedic texts and from different related research and review articles. Thus, it is a humble effort to explore the different aspects of bio-enhancers including therapeutic techniques such as Shodhana, the drugs such as Pippali, and properties such as Yogavahi and Rasayana, which have been described in Ayurveda along with their mechanism of action and uses wherever available.

Bioavailability enhancers of herbal origin: an overview

Recently, the use of herbal medicines has been increased all over the world due to their therapeutic effects and fewer adverse effects as compared to the modern medicines. However, many herbal drugs and herbal extracts despite of their impressive in-vitro findings demonstrates less or negligible in-vivo activity due to their poor lipid solubility or improper molecular size, resulting in poor absorption and hence poor bioavailability. Nowadays with the advancement in the technology, novel drug delivery systems open the door towards the development of enhancing bioavailability of herbal drug delivery systems. For last one decade many novel carriers such as liposomes, microspheres, nanoparticles, transferosomes, ethosomes, lipid based systems etc. have been reported for successful modified delivery of various herbal drugs. Many herbal compounds including quercetin, genistein, naringin, sinomenine, piperine, glycyrrhizin and nitrile glycoside have demonstrated capability to enhance the bioavailability. The objective of this review is to summarize various available novel drug delivery technologies which have been developed for delivery of drugs (herbal), and to achieve better therapeutic response. An attempt has also been made to compile a profile on bioavailability enhancers of herbal origin with the mechanism of action (wherever reported) and studies on improvement in drug bioavailability, exhibited particularly by natural compounds.

Monoketocholate can decrease transcellular permeation of methotrexate across Caco-2 cell monolayers and reduce its intestinal absorption in rat

Objectives

Bile salts have been shown to decrease the absorption of methotrexate in the rat intestine by an unknown mechanism. We aimed to examine this effect.

Methods

We assessed apical-to-basolateral (AP-BL) permeation of methotrexate (5 μM) across Caco-2 cell monolayers pretreated with various concentrations (0, 0.25, 0.5, 1, 3 and 5 mm) of sodium cholate or its semisynthetic analogue, sodium 12-monoketocholate. We also determined the effect of orally administered 12-monoketocholate on the intestinal absorption of methotrexate in rats to evaluate a possible in-vitro–in-vivo correlation.

Key findings

It was found that sodium cholate and sodium 12-monoketocholate decreased the AP-BL permeation of methotrexate at low concentrations (maximal inhibition at 0.25 and 1 mm, respectively) and increased it at higher concentrations. Determination of [14C] mannitol permeation and electrical resistance of monolayers during experiments showed that membrane integrity was not compromised at low concentrations of bile salts but was disrupted at higher concentrations. Subsequently, we examined the effect of the simultaneous oral administration of sodium 12-monoketocholate (4, 20, 40 and 80 mg/kg) on the intestinal absorption of methotrexate in rats after an oral dose (5 mg/kg). The pharmacokinetic study showed that 12-monoketocholate at 4 and 20 mg/kg did not change the methotrexate area under the serum concentration–time curve whereas sodium 12-monoketocholate at 40 and 80 mg/kg significantly reduced it.

Conclusions

Sodium 12-monoketocholate appears to decrease the intestinal absorption of methotrexate in rats by inhibition of transcellular active transport.

Pharmacology and toxicology of Bupleurum root-containing Kampo medicines in clinical use

Kampo (Japanese traditional herbal) medicines have been produced by combining multiple crude drugs, almost all of plant origin but with some of animal or mineral origin, and contain a great many substances. Their effect is a combination of the various interactions of the constituent substances, whether they are enhancing, synergistic or suppressive. Kampo medicine has an overall effect that is different from the combined effects of individual crude drugs, and several side effects such as anorexia, slight fever and nausea have been reported in the treatment of certain disorders and disease states with Kampo medicines. Among 210 medical formulations used in Japan, some relevant information on the clinical uses, pharmacology and toxicology of six manufactured Kampo medical formulations, Shosaikoto, Daisaikoto, Saikokeishito, Hochuekkito, Saibokuto and Saireito, containing Bupleurum root are reviewed. Studies of some potential interactions between Kampo medicine and western drugs are also considered.

ATP participates in the regulation of microvessel permeability

We demonstrated previously that stimulation of the P2Y receptor enhanced the macromolecular permeability of cultured endothelial cell monolayers via the paracellular pathway. To determine whether the P2Y receptor participates in the regulation of permeability in intact microvessels, we have examined the effects of exogenous and endogenous ATP on the permeation of the surface tissue of perfused rat tail caudal artery using a fluorescein isothiocyanate-dextran (FD-4; MW 4400; 1.0 mg mL(-1)). The permeation of FD-4 was assessed by a confocal fluorescence imaging system. We found that 2-methylthioadenosine 5'-triphosphate, a P2Y receptor agonist, enhanced the fluorescence intensity of FD-4 in the surface of the rat caudal artery tissue and that it was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, a P2 receptor antagonist. Also, noradrenaline, a sympathetic neurotransmitter, and bradykinin, an inflammatory autacoid, enhanced the fluorescence intensity of FD-4 in the surface tissue of the rat caudal artery. The enhancement by noradrenaline was significantly inhibited by the P2 receptor antagonist. In addition, noradrenaline and bradykinin caused the release of ATP, ADP, AMP and adenosine from the endothelium of the rat caudal artery. These results indicated that the exogenous and endogenous ATP increased the macromolecular permeability of blood capillaries via the P2Y receptor. Such purinergic regulation of endothelial permeability may function in physiological and pathophysiological conditions.

Absorption enhancement study of astragaloside IV based on its transport mechanism in caco-2 cells

The purpose of this study was to investigate the transport characteristics and mechanisms for discovering the possible causes of the low bioavailability of astragaloside IV and to develop an absorption enhancement strategy. Caco-2 cells used as the in vitro model. Results showed a low permeability coefficient (3.7 x 10(-8)cm/s for transport from the AP to BL direction), which remained unchanged throughout the concentration range studied, indicating that the transport of astragaloside IV was predominantly via a passive route. The AP to BL transport of astragaloside IV was found to be highly sensitive to the extracellular Ca2+ concentration, which suggested that its transport may be via a paracellular route. Both chitosan and sodium deoxycholate can increase the permeation efficiency of astragaloside IV. This study indicated that astragaloside IV having a low fraction dose absorbed in humans mainly due to its poor intestinal permeability, high molecular weight, low lipophilicity as well as its paracelluar transport may directly result in the low permeability through its passive transport. Meanwhile, chitosan and sodium deoxycholate can be used as absorption enhancers based on its transport mechanism.

Activation of P2Y receptor enhances high-molecular compound absorption from rat ileum

While there are no reports concerning the effects of extracellular nucleotides on the intestinal absorption of drugs, it is well known that extracellular nucleotides are important regulators of intestinal epithelial ion transport. This report using fluorescein isothiocyanate dextran 4000 (FD-4) as the model compound is the first to investigate the effects of purine nucleotides on absorption of poorly absorbed drugs from intestine. ATP enhanced the absorption of FD-4 from rat ileum in a concentration-dependent manner. ADP also enhanced the absorption of FD-4. Other purine nucleotides (adenosine, AMP, UTP and UDP) did not show an absorption-enhancing effect. The absorption-enhancing effect by ATP was inhibited by suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonate (PPADS), which are known P2 receptor antagonists. Additionally, 2-methylthio ATP (a P2Y receptor agonist) enhanced the absorption of FD-4, but alpha,beta-methylene ATP (a P2X receptor agonist) did not. These findings suggest that activation of the P2Y receptor may improve the absorption of water-soluble and high-molecular compounds from the ileum.

Quantitative estimation of the effects of bile salt surfactant systems on insulin stability and permeability in the rat intestine using a mass balance model

The oral delivery of peptides and proteins is compromised by chemical and proteolytic instability as well as by permeability limitations. The aim of this study was to delineate the relative contributions of simple bile salt and bile salt:fatty acid mixed micellar systems to protein stability vs permeability enhancement in the rat intestine. Insulin disappearance from the rat intestine was evaluated when administered in simple micellar systems of sodium cholate (NaC), sodium taurocholate (NaTC) and sodium glycocholate (NaGC), and in mixed micellar systems of these bile salts and linoleic acid (LA). In-vitro stability studies were used to evaluate the extent of insulin degradation in the different micellar systems. After correction for insulin degradation in all systems a mass balance model was used to estimate the fractions of insulin absorbed for all systems. Mass balance estimates for the extent of insulin absorption in control perfusion systems were consistent with previously reported predictions of the model for ileal insulin absorption. Mass balance estimates for NaGC suggested no significant effects on the fraction of insulin absorbed relative to control. However, insulin absorption was estimated to occur to a significantly greater extent for NaTC simple micellar systems and was coincident with increased permeability of the hydrophilic marker molecule PEG 4000. The mass balance model estimated higher fractions of insulin absorbed for all mixed micellar systems in line with enhanced plasma insulin levels and higher PEG 4000 permeabilities for these systems.

Myosin light chain kinase and Rho-kinase participate in P2Y receptor-mediated acceleration of permeability through the endothelial cell layer

We have shown that P2Y receptor stimulation accelerates macromolecular permeation through the endothelial cell layer. To elucidate the mechanism of this acceleration, we examined the effects of ML-9, a myosin light chain kinase inhibitor, and Y-27632, a Rho-kinase inhibitor, on fluorescein isothiocyanate dextran (FD-4) permeation across the human umbilical vein endothelial cell monolayer. FD-4 permeation was analysed by high-performance liquid chromatography fluorescence detection. A P2Y receptor agonist, 2meS-ATP, enhanced the permeability of FD-4, which was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a P2Y-receptor antagonist. The 2meS-ATP-induced increase in the permeability of FD-4 was significantly inhibited by ML-9. Also, Y-27632 prevented the 2meS-ATP-induced increase in the permeability of FD-4. Neither ML-9 nor Y-27632 influenced the spontaneous permeation of FD-4. These results suggest that phosphorylation of the myosin light chain may play an important role in the purinergic regulation of macromolecular permeation through the vascular endothelium.

Absorption-enhancing effect of glycyrrhizin induced in the presence of capric acid

The absorption-enhancing effect of the simultaneous administration of sodium caprate (Cap-Na) and dipotassium glycyrrhizinate (Grz-K) was investigated to clarify an effect of Grz-K. A combination of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K had a rapid and long-lasting absorption-enhancing activity in Caco-2 cell monolayers under conditions where Cap-Na and Grz-K showed a weak and no activity, respectively. The simultaneous treatment of a Caco-2 cell monolayer with Cap-Na and Grz-K showed no change in intracellular calcium ion level, although a major mechanism of absorption-enhancing effect for Cap-Na was elevation of intracellular calcium ion level. On the other hand, the simultaneous enhancing effect of Cap-Na and Grz-K was inhibited by H7, a PKC inhibitor. Possibly, Grz-K showed an absorption-enhancing effect via PKC cellular signaling pathway after penetration into cell according to increasing membrane permeability by Cap-Na. The absorption of sCT by the rat colon was enhanced by a combination of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K, and its effect continued even 9h after the onset of the experiment. Furthermore, the simultaneous treatment of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K showed a negligible histological changes to the colon mucosal membrane and a negligible toxicity on Caco-2 cell monolayer. A combination of Cap-Na and Grz-K shows a synergistic absorption-enhancing effect with little mucosal injury, which is applicable to colon-specific delivery.

Effects of Chinese Herbal Medicines on Intestinal Drug Absorption

Sho-saiko-to (Xiao-Chai-Hu-Tang), one of the major traditional Chinese medicines, has been frequently prescribed with other synthetic or biotechnological drugs for the treatment of various acute or chronic diseases in Japan, and thus it is important to understand the interactions between Sho-saiko-to and coadministered drugs. This paper reviews the effects of Sho-saiko-to on the pharmacokinetics and pharmacodynamics of concomitant drugs in the gastrointestinal tract. Sho-saiko-to slightly hastens the gastrointestinal absorption of the sulfonylurea compound tolbutamide. Furthermore, it is considered that the increase in the gastrointestinal absorption rate by Sho-saiko-to may potentiate the hypoglycemic effects of tolbutamide in the early period after oral administration. Sho-saiko-to can facilitate the epithelial membrane permeability of tolbutamide at an early phase across the rat jejunum in situ and Caco-2 cell monolayers. It is also suggested that Sho-saiko-to enhances the energy-dependent transport of tolbutamide and has an inhibitory effect on the passive paracellular transport of tolbutamide in Caco-2 cells. This result might be related to the accelerated in vivo absorption rate of tolbutamide by concomitant dosing with Sho-saiko-to in rats. In addition, Sho-saiko-to has inhibitory effects on the efflux pump mediated by MDR1, and it appears that the crude constituents in Glycyrrhizae radix, glycyrrhizic acid and liquiritin, contribute to MDR1 suppression.

Toxicological considerations of Kampo medicines in clinical use

Kampo (Japanese herbal) medicines, produced by combining multiple crude drugs, almost all of plant origin but with some of animal or mineral origin, contain great many substances. Since Kampo medicine results from the combination of many substances, their effect is a combination of the various interactions of the constituent substances. It has been demonstrated that several potential side effects such as allergic reactions, diarrhea and vomiting may be experienced when administering Kampo medicine. In addition, it has been reported that Kampo medicine may have antagonistic or synergistic interactions with western drugs or with some foods such as grapefruit juice. Among the 210 medicinal prescriptions used in present-day Japan, the clinical uses and the acute, chronic and mutagenic toxicity of some Kampo medicines are described. Studies of some potential interaction between Kampo medicines and western drugs are also considered.

Excipient effects on in vitro cytotoxicity of a novel paclitaxel self‐emulsifying drug delivery system

Paclitaxel is a potent chemotherapeutic agent currently administered intravenously in polyoxyethylated castor oil (Cremophor EL) and dehydrated ethanol (1:1) for the treatment of solid tumors. The objective of this work was to develop a novel self-emulsifying drug delivery system (SEDDS) devoid of cremophor for the i.v./oral delivery of paclitaxel and to investigate the in vitro cytotoxicity of the combined excipients. The SEDDS formulations were characterized in terms of droplet size using a ternary phase diagram. The Caco-2 cell line was used to monitor the cytotoxicity of the excipients. Cell viability was determined colorimetrically at 570 nm utilizing the MTT assay. The distribution of the formulations on the phase diagram indicated the presence of macroemulsions ( approximately 1 microm), submicron emulsions (50-200 nm), and microemulsions (below 10 nm). An increase in the sodium deoxycholate excipient content led to an increase in physical stability but caused more chemical degradation of the drug and more cytotoxicity. The drug in the novel SEDDS was chemically stable for at least 1 year when kept as a two-part formulation. The drug loading was increased by approximately fivefold compared to the marketed i.v. formulation; the excipients presented a significantly reduced cytotoxicity and led to a stable microemulsion.

Toxicological aspects of Kampo medicines in clinical use

Among 210 medicinal prescriptions used in present-day Japan, the clinical uses and the acute, chronic and mutagenic toxicity study of 16 Kampo (Japanese herbal) medicines are summarized. These Kampo medicines are classified into two categories; eight prescriptions containing Bupleurum root (Bupleurum falcatum L.) such as Sho-saiko-to and Saiko-keishi-to, and eight prescriptions not containing Bupleurum root such as Juzen-taiho-to and Ninjin-yoei-to. Studies of some potential interaction between herbal medicine and western drugs are also described.

Possibility of a patch system as a new oral delivery system

A new oral patch system has been designed to increase the residence time of model drugs within the gastrointestinal tract. The system consisted of three layers (1) water-insoluble backing layer (2) drug-carrying adhesive layer composed of a model drug, fluorescein (FL) or fluorescein isothiocyanate-dextran (FD), and gel-forming polymer and (3) pH-sensitive enteric polymer. These three layers system was prepared as 3.0 mm diameter patches. As references, tablet containing FL or FD was prepared. In vitro dissolution studies showed that the mean dissolution time (MDT) of model drugs from patch preparation was 0.739+/-0.021 h for FL and 0.407+/-0.021 h for FD, which were longer than from tablet, 0.327+/-0.008 h for FL and 0.270+/-0.019 h for FD. The two test preparations were orally administered to beagle dogs in a crossover manner at a FL dose of 30 mg/dog and the measured plasma FL concentrations were used for pharmacokinetic analysis. With FL patch preparation, area under the plasma drug concentration vs. time curve (AUC) was 2.12+/-0.24 microgh/ml and mean residence time (MRT) was 4.60+/-0.18 h, which were greater than those of tablet, AUC was 1.52+/-0.16 microgh/ml and MRT was 3.18+/-0.09 h, respectively. Oral patch preparation also increased both AUC and MRT of FD, a model macromolecular drug, which was formulated into both patches and tablets and administered to dogs (30 mg/dog). The AUC and MRT of FD from the patch preparation were 1.11+/-0.13 microgh/ml and 5.58+/-0.55 h and from tablets were 0.53+/-0.08 microg h/ml and 4.09+/-0.29 h, respectively. These results suggest that oral patch preparation has as a potential a new oral delivery system to obtain a long residence time of drug in the gastrointestinal tract.

Enhanced permeability of molecular weight markers and poorly bioavailable compounds across Caco-2 cell monolayers using the absorption enhancer, zonula occludens toxin

PURPOSE

Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions. The objective of this work was to determine the stability of Zot and to examine the permeability of a series of molecular weight hydrophilic markers and therapeutic agents in the presence of Zot.

METHOD

The transport of molecular weight markers (i.e., PEG 4000, FITC-dextran 10.000 and inulin) and therapeutic agents (i.e., acyclcovir, cyclopsorin, paclitaxel. doxorubicin) was evaluated with Zot (0, 2, and 4 microg/mL) using Caco-2 cell monolayers.

RESULTS

Zot was found to be stable over a 10-day period. Significantly higher (p < 0.05) permeability of the molecular weight markers, in lin, and PEG4000 were observed with Zot (4 microg/mL). The transport of each therapeutic marker was significantly increased with paclitaxel displaying a >3-fold enhancement in Papp values with Zot (4 microg/mL). A 30% decrease in transepithelial electrical resistance values wa observed, which returned to baseline 30 min after Zot was removed.

CONCLUSIONS

Considering the problems of poor oral bioavailability, it is concluded that Zot is a promising drug delivery technology to be used to enhance drug transport across the intestinal mucosa. Future applications are targeted at assessing its usefulness in oral drug delivery using in vivo systems.

Enhancement of paracellular transport of heparin disaccharide across Caco-2 cell monolayers

The enhancement of paracellular transport of heparin disaccharide using several absorption enhancers across Caco-2 cell monolayers was tested. The cytotoxicity of these enhancers was also examined. The enhancing effects by Quillaja saponin, dipotassium glycyrrhizinate, 18beta-glycyrrhetinic acid, sodium caprate and taurine were determined by changes in transepithelial electrical resistance (TEER) and the amount of heparin disaccharide transported across Caco-2 cell monolayers. Among the absorption enhancers, 18beta-glycyrrhetinic acid and taurine decreased TEER and increased the permeability of heparin disaccharide in a dose-dependent and time-dependent manner with little or negligible cytotoxicity. Our results indicate that these absorption enhancers can widen the tight junction, which is a dominant paracellular absorption route of hydrophilic compounds. It is highly possible that these absorption enhancers can be applied as pharmaceutical excipients to improve the transport of macromolecules and hydrophilic drugs having difficulty in permeability across the intestinal epithelium.

The effect of absorption enhancers on the initial degradation kinetics of insulin by alpha-chymotrypsin

The goal of this investigation was to establish a fast method to screen various insulin absorption enhancers by following their effect on the initial kinetics of insulin incubated with alpha-chymotrypsin at 37 degrees C. A simple, sensitive and reproducible reversed phase high performance liquid chromatography (HPLC) method has been developed to carry out this goal. Linear responses (r > 0.999) were observed over the range of 0.4-4 U/ml for insulin. There was no significant difference (P < 0.05) between inter- and intra-day studies for insulin. The mean relative standard deviations (RSD%) of the results of within-day precision and accuracy of insulin were 12%. The assay was sensitive to detect the existence of any metabolite due to the addition of any absorption enhancers, even if it was not seen with insulin alone. Three metabolites (A-C) were detected only when insulin was incubated with alpha-chymotrypsin at 37 degrees C. Metabolite D was observed when either glycocholic acid (0.5, 1%) or taurochenodeoxycholate (0.5, 1%) was incubated with insulin in the absence of alpha-chymotrypsin at 37 degrees C. The compounds that significantly increased insulin T50% were glycyrrhizic acid (0.5%) > deoxycholic acid (1%) > deoxycholic acid (0.5%) > glycyrrhizic acid (1%) > cholic acid (0.5, 1%). Capric acid (0.5%), hydroxypropyl-alpha-cyclodextrin (0.5, 1%) and dimethyl-alpha-cyclodextrin (0.5, 1, 5%) did not significantly affect insulin T50%. The bile salts increased insulin T50% in this order: deoxycholate > cholate > glycocholate > taurocholate > taurodeoxycholate > taurochenodeoxycholate > glycodeoxycholate. The results obtained would support the feasibility of utilizing such method for screening any compound incorporated in insulin formulation. These compounds should be used in the minimum possible concentration to avoid or minimize insulin degradation.

Effects of sho-saiko-to (xiao chai hu tang), a Chinese traditional medicine, on the gastric function and absorption of tolbutamide in rats

This study was carried out to investigate the effects of Sho-saiko-to (Xiao Chai Hu Tang), a Chinese traditional medicine, on the gastric function including the gastric emptying rate (GER) and intragastric pH in rats. Additionally, the effects of the GER and intragastric pH on tolbutamide absorption after oral administration were examined. The GER measured at 40 min after dosing was reduced to about 70% by the pretreatment of Sho-saiko-to (500 mg/kg). The plasma tolbutamide concentration in the rats treated with a 250 mg/kg dose of Sho-saiko-to was significantly lower than that in the control group. Plasma tolbutamide concentrations increased along with the GER in the group co-administered Sho-saiko-to, and there were significant correlations between the GERs and plasma levels in both time points at 20 and 40 min after administration. In the study using pylorus-ligated rats, Sho-saiko-to significantly elevated the intragastric pH, but induced no change in the concentrations of tolbutamide dissolved in the gastric content. Additionally, Sho-saiko-to did not change the area under the plasma concentration-time curve (AUC) of tolbutamide up to 60 min after administration into the stomach loop, and gastric absorption has been considered to minimally contribute to whole absorption of tolbutamide in the gastrointestinal tract. These results indicate that Sho-saiko-to has an inhibitory effect on the function of gastric emptying in rats. The reduced gastric emptying could affect gastrointestinal absorption, resulting in the lower plasma concentration of tolbutamide after oral administration. Furthermore, it is suggested that Sho-saiko-to can raise the intragastric pH but affect neither the intragastric dissolution nor the gastric absorption of tolbutamide.