Selected Factors Affecting Oral Bioavailability of Nanoparticles Surface-Conjugated with Glycocholic Acid via Intestinal Lymphatic Pathway.

Here, we describe the absorption pathways of nanoparticles whose surface is modified with bile acid and present environmental factors that influence oral bioavailability (BA) from the gastrointestinal tract (GIT). The approach utilized 100 nm sized fluorescence-labeled, carboxylated polystyrene nanoparticles (CPN) conjugated with glycocholic acid (G/CPN) to exclude potential artifacts, if existing, and instability issues in evaluating the transit of G/CPN in the GIT and measuring BA. The in vitro study using SK-BR-3 that expresses the apical sodium bile acid transporter showed that once G/CPN is internalized, it stayed 2.9 times longer in the cells than CPN, indirectly suggesting that G/CPN takes intracellular trafficking pathways different from CPN in SK-BR-3 cells. In a Caco-2 cell monolayer, G/CPN passed through the monolayer without damaging the tight junction. G/CPN, when administered orally in rodents, showed sustained transit time in the GIT for at least 4 h and was absorbed into the intestinal lymphatic system and circulated into the blood. Ingestion of food before and after oral administration delays G/CPN absorption and decreases BA. A decrease in gastrointestinal motility by anesthetic condition increased the relative BA of G/CPN by up to 74%. Thus, the oral BA of G/CPN can be optimized by taking food ingestion and gastrointestinal motility into account.

Improved oral bioavailability of notoginsenoside R1 with sodium glycocholate-mediated liposomes: Preparation by supercritical fluid technology and evaluation in vitro and in vivo.

The chief objective of this research was to appraise liposomes embodying a bile salt, sodium glycocholate (SGC), as oral nanoscale drug delivery system to strengthen the bioavailability of a water-soluble and weakly penetrable pharmaceutical, notoginsenoside R1 (NGR1). NGR1-loaded liposomes were prepared with the improved supercritical reverse evaporation (ISCRPE) method and the preparation conditions were optimized with response surface methodology (RSM). The mean encapsulation efficiency (EE), particle size, and polydispersity index (PDI) of the optimized liposomal formulation (NGR1@Liposomes) were 49.49%, 308.3 nm, and 0.229, respectively. SGC-mediated liposomes (NGR1@SGC-Liposomes) were formulated based on the optimal preparation conditions and the mean EE, particle size, and PDI were 41.51%, 200.1 nm, and 0.130, respectively. The in vitro Caco-2 cellular uptake of fluorescent marker was increased by loading into NGR1@SGC-Liposomes as compared with the conventional liposomes. Furthermore, the intestinal permeability as well as the intestinal absorption of NGR1 were both significantly improved with NGR1@SGC-Liposomes as the nanovesicles. The in vivo pharmacokinetic study results showed that AUC0-t value of NGR1@SGC-Liposomes and NGR1@Liposomes was 2.68- and 2.03-fold higher than that of NGR1 aqueous solution, respectively. The AUC0-t of the NGR1@SGC-Liposomes group was significantly higher than that of NGR1@Liposomes. Thus, ISCRPE method is a feasible method for the preparation of water-soluble drug-loaded liposomes and bile salt-mediated liposomes may enhance the oral absorption of water-soluble and poorly permeable drugs.

Role of OATP1B3 in the transport of bile acids assessed using first-trimester trophoblasts.

AIMS: The aim of this study was to investigate the transport of two kinds of bile acids by organic anion transporting polypeptide 1B3 (OATP1B3) using first-trimester trophoblasts. The mechanisms of damage to fetuses with intrahepatic cholestasis of pregnancy were investigated, providing new potential strategies for targeted therapies aimed at reducing fetal risk. MATERIAL AND METHODS: The expression of OATP1B3 was knocked down by lentiviral vector-mediated RNA interference, and silencing efficiency was assessed using real-time polymerase chain reaction and Western blotting. The cytotoxicity of two bile acids (glycocholic acid [GCA] and glycochenodeoxycholic acid [GCDCA]) was assessed using the MTT method. Transport of bile acids was assessed by establishing an in vitro trophoblast monolayer model using polyester Transwell-clear inserts, and the concentration of bile acids in the upper compartment was assessed using high-pressure liquid chromatography. RESULTS: GCA and GCDCA (10 and 20 µM) were not cytotoxic to the SWAN cell line (P > 0.05). RNAi treatment decreased the mRNA and protein expressions of OATP1B3 by 94.42% and 49.51%, respectively (P < 0.05). The bile acid transport curves were similar in the control and negative RNAi groups, whereas those in the RNAi group differed significantly from those in the control and negative RNAi groups. The concentration of GCA and GCDCA in the upper compartment was significantly lower in the RNAi group than in the control and negative RNAi groups. CONCLUSIONS: OATP1B3 expression in trophoblasts was confirmed indirectly by its ability to transport the bile acids GCA and GCDCA.

Introduction of aromatic ring-containing substituents in cyclic nucleotides is associated with inhibition of toxin uptake by the hepatocyte transporters OATP 1B1 and 1B3.

Analogs of the cyclic nucleotides cAMP and cGMP have been extensively used to mimic or modulate cellular events mediated by protein kinase A (PKA), Exchange protein directly activated by cAMP (Epac), or protein kinase G (PKG). We report here that some of the most commonly used cyclic nucleotide analogs inhibit transmembrane transport mediated by the liver specific organic anion transporter peptides OATP1B1 and OATP1B3, unrelated to actions on Epac, PKA or PKG. Several cAMP analogs, particularly with 8-pCPT-substitution, inhibited nodularin (Nod) induced primary rat hepatocyte apoptosis. Inhibition was not mediated by PKA or Epac, since increased endogenous cAMP, and some strong PKA- or Epac-activating analogs failed to protect cells against Nod induced apoptosis. The cAMP analogs inhibiting Nod induced hepatocyte apoptosis also reduced accumulation of radiolabeled Nod or cholic acid in primary rat hepatocytes. They also inhibited Nod induced apoptosis in HEK293 cells with enforced expression of OATP1B1 or 1B3, responsible for Nod transport into cells. Similar results were found with adenosine analogs, disconnecting the inhibitory effect of certain cAMP analogs from PKA or Epac. The most potent inhibitors were 8-pCPT-6-Phe-cAMP and 8-pCPT-2'-O-Me-cAMP, whereas analogs like 6-MB-cAMP or 8-Br-cAMP did not inhibit Nod uptake. This suggests that the addition of aromatic ring-containing substituents like the chloro-phenyl-thio group to the purines of cyclic nucleotides increases their ability to inhibit the OATP-mediated transport. Taken together, our data show that aromatic ring substituents can add unwanted effects to cyclic nucleotides, and that such nucleotide analogs must be used with care, particularly when working with cells expressing OATP1B1/1B3, like hepatocytes, or intact animals where hepatic metabolism can be an issue, as well as certain cancer cells. On the other hand, cAMP analogs with substituents like bromo, monobutyryl were non-inhibitory, and could be considered an alternative when working with cells expressing OATP1 family members.

Nimodipine-loaded mixed micelles: formulation, compatibility, pharmacokinetics, and vascular irritability study.

BACKGROUND: The clinical application of nimodipine (NIM) is limited by several unfavorable properties, which are induced by its low aqueous solubility. In the present study, nimodipine-loaded egg phosphatidylcholine-sodium glycocholate mixed micelles (NIM-EPC-SGC-MMs) were prepared to improve the water solubility of NIM, thus allowing it to be more applicable for clinical use. METHODS: NIM-EPC-SGC-MMs were prepared using the coprecipitation method and the factors influencing formulation quality were optimized. After formulation, water solubility, solubilizing efficiency, drug loading, particle size, physical compatibility, pharmacokinetics, and vascular irritability were determined. RESULTS: The mean size of the NIM-EPC-SGC-MMs was 6.099 ± 0.048 nm under optimized conditions. The water solubility of NIM in EPC-SGC-MMs was enhanced 250-fold compared with free NIM. The physical compatibility, pharmacokinetic, and vascular irritability studies showed that, in comparison to the commercially available NIM injections, NIM-EPC-SGC-MMs presented better physical compatibility, the same pharmacokinetic profile, and less risk of local vascular irritation and phlebitis. CONCLUSION: EPC-SGC-MMs represent a promising new formulation suitable for the intravenous delivery of NIM.

A propofol microemulsion with low free propofol in the aqueous phase: formulation, physicochemical characterization, stability and pharmacokinetics.

The purpose of this study was to develop a propofol microemulsion with a low concentration of free propofol in the aqueous phase. Propofol microemulsions were prepared based on single-factor experiments and orthogonal design. The optimal microemulsion was evaluated for pH, osmolarity, particle size, zeta potential, morphology, free propofol in the aqueous phase, stability, and pharmacokinetics in beagle dogs, and comparisons made with the commercial emulsion, Diprivan(®). The pH and osmolarity of the microemulsion were similar to those of Diprivan(®). The average particle size was 22.6±0.2 nm, and TEM imaging indicated that the microemulsion particles were spherical in appearance. The concentration of free propofol in the microemulsion was 21.3% lower than that of Diprivan(®). Storage stability tests suggested that the microemulsion was stable long-term under room temperature conditions. The pharmacokinetic profile for the microemulsion showed rapid distribution and elimination compared to Diprivan(®). We conclude that the prepared microemulsion may be clinically useful as a potential carrier for propofol delivery.

Long-term biokinetics and radiation exposure of patients undergoing 14C-glycocholic acid and 14C-xylose breath tests.

The (14)C-glycocholic acid and (14)C-xylose breath tests are clinically used for the diagnosis of intestinal diseases, such as bacterial overgrowth in the small intestine. The two tests have in earlier studies been thoroughly evaluated regarding their clinical value, but due to the long physical half-life of (14)C and the limited biokinetic and dosimetric data, which are available for humans, several hospitals have been restrictive in their use. The aim of this study was to investigate the long-term biokinetics and dosimetry of the two (14)C compounds in patients and volunteers, using the highly sensitive accelerator mass spectrometry (AMS) technique. Eighteen (18) subjects were included, 9 for each compound. The (14)C content in samples from exhaled air, urine, and, for some subjects, also feces were analyzed with both liquid scintillation counting (LSC) and AMS. The results from the glycocholic acid study showed that, up to 1 year after the administration, 67%+/-6% (mean+/-standard deviation) of the administered activity was recovered in exhaled air, 2.4%+/-0.4% was found in urine, and 7.6% (1 subject) in feces. In the xylose study, the major part was found in the urine (66%+/-2%). A significant part was exhaled (28%+/-5%), and the result from an initial 72-hour stool collection from 2 of the subjects showed that the excretion by feces was insignificant. The absorbed dose to various organs and tissues and the effective dose were calculated by using biokinetic models, based on a combination of experimental data from the present study and from earlier reports. In the glycocholic acid study, the highest absorbed dose was received by the colon (1.2 mGy/MBq). In the xylose study, the adipose tissue received 0.8 mGy/MBq. The effective dose was estimated to 0.5 (glycocholic acid) and 0.07 mSv/MBq (xylose). Thus, from a radiation protection point of view, we see no need for restrictions in using the two (14)C-labeled radiopharmaceuticals on adults with the activities normally administered (0.07-0.4 MBq).

Kinetic mechanism of ligand binding in human ileal bile acid binding protein as determined by stopped-flow fluorescence analysis.

Cooperative ligand binding to human ileal bile acid binding protein (I-BABP) was studied using the stopped-flow fluorescence technique. The kinetic data obtained for wild-type protein are in agreement with a four-step mechanism where after a fast conformational change on the millisecond time scale, the ligands bind in a sequential manner, followed by another, slow conformational change on the time scale of seconds. This last step is more pronounced in the case of glycocholate (GCA), the bile salt that binds with high positive cooperativity and is absent in mutant I-BABP proteins that lack positive cooperativity in their bile salt binding. These results suggest that positive cooperativity in human I-BABP is related to a slow conformational change of the protein, which occurs after the second binding step. Analogous to that in the intestinal fatty acid binding protein (I-FABP), we hypothesize that ligand binding in I-BABP is linked to a disorder-order transition between an open and a closed form of the protein.

Adsorption of bile acid by chitosan salts prepared with cinnamic acid and analogue compounds.

A chitosan (CS) powder treated with cinnamic acid and an analogue compound (CN) was prepared as CS-CN. Using it, bile acid adsorption by CS-CN and the release of CN were investigated in vitro. When CS-CN was soaked in a taurocholate solution, it released CN and simultaneously adsorbed the bile acid. For CS-CN prepared with cinnamic acid, the amount of CN released was 0.286 +/- 0.001 mmol/g CS-CN; the amount of taurocholate adsorbed was 0.284 +/- 0.003 mmol/g CS-CN. These two functions were recognized on alginate or pectin gel beads containing CS-CN. The amount of released CN was altered extensively by the species of CN used for gel-bead preparation. Results suggest that CS-CN is a candidate for complementary medicine to prevent lifestyle-related diseases.

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.

Development of a 13C-glycocholic acid blood test to assess bacterial metabolic activity of the small intestine in canines.

The objectives of this study were to establish optimal doses of 13C-glycocolic acid (GCA) for use in a GCA blood test as a marker for canine small intestinal bacterial metabolic activity. Four doses of GCA were administered orally to 8 healthy dogs. Blood samples were collected at various time points up to 480 min. The percent dose/min of 13C administered as GCA (PCD) and cumulative PCD (CUMPCD) were determined by fractional mass spectrometry. No dog showed any clinically obvious side effects. Doses of 1 and 2 mg/kg of bodyweight (BW) led to a significant increase in PCD and CUMPCD (P < 0.001). The mean CUMPCD was significantly higher for the 1 mg/kg BW dose compared with the 2 and 4 mg/kg BW doses (P < 0.05). Administration of 1 mg/kg BW of 13C-glycocholic acid led to an increase in CUMPCD over baseline in gas extracted from blood samples and appears to be the best parameter to evaluate for future clinical studies.

Sodium glycocholate transport across Caco-2 cell monolayers, and the enhancement of mannitol transport relative to transepithelial electrical resistance.

Ideally, the amount of enhancer remaining at the donor side during an in vitro transport study should be known, in order to know the true enhancer concentration during a permeability study. The purpose of the present study is to estimate the flux of the enhancer, sodium glycocholate (GC), through Caco-2 cell monolayers, and to study the effect of various enhancer concentrations on the permeability of GC itself, the permeability of mannitol and the transepithelial electrical resistance (TEER). Apical to basolateral permeability was measured with various concentrations 0.50% (10.2mM), 0.75% (15.5mM) and 1.00% (20.5mM) of GC. The GC permeabilities (Papp) were 4.7+/-1.1, 12.8+/-2.8 and 25.8+/-4.3 (x10(-7)cms(-1)), respectively. Mannitol transport changed accordingly with the Papp; 8.5+/-0.8, 9.9+/-2.7, 20.4+/-2.8 and 31.0+/-4.9 (x10(-7)cms(-1)) for GR, 0.50, 0.75 and 1.00% GC, respectively, with a TEER after 120min, relative to initial, of 86+/-6, 77+/-10, 61+/-11 and 49+/-7%. In conclusion a low and concentration-dependent permeability was found for GC across the Caco-2 cells. Mannitol transport increased and TEER decreased accordingly with increasing GC concentrations. TEER decreased in less than 10min to a certain level, without further reduction in a 120min period, indicating that the enhancer effect is momentarily, rather than time-dependent. The apical GC concentration and enhancer effect may be considered well defined during the experiment, due to the observed low permeability of GC.

Permeability of antisense oligonucleotide through porcine buccal mucosa.

Antisense oligonucleotides (AONs) that can modulate malfunctioning genes have a great potential to become future therapeutic agents. In this study, we investigated the feasibility of buccal delivery of AONs using ISIS 3082 as a model compound. An isocratic HPLC method was developed to quantify ISIS 3082. The permeability coefficient of this AON at 37 degrees C, determined by using side-by-side diffusion cells, was 1.05x10(-9) (cm/s). The flux of ISIS 3082 across buccal mucosa was dependent upon its concentration in the donor chamber. The permeation of ISIS 3082 was increased when 100 mM of sodium glycocholate was used as a permeation enhancer. The potential of delivering AONs via buccal route with the aid of permeation enhancers is explored in this study.

Transport of amphipathic anions by human multidrug resistance protein 3.

The multidrug resistance-associated protein 1 (MRP1) and the canalicular multispecific organic anion transporter (cMOAT or MRP2) are ATP-binding cassette transporters that confer resistance to some anticancer drugs and efflux glutathione and glucuronate conjugates from the cell. The MRP subfamily of ABC transporters, however, contains at least four other members of which MRP3 (MOAT-D) bears the closest structural resemblance to MRP1. Although transfection studies have established that human MRP3 confers increased resistance to several anticancer agents, neither the substrate selectivity nor physiological functions of this transporter have been determined. Here we report the results of investigations of the in vitro transport properties of cloned human MRP3 using membrane vesicles prepared from MRP3-transfected HEK293 cells. It is shown that the expression of MRP3 is specifically associated with enhancement of the MgATP-dependent transport into membrane vesicles of the glucuronide estradiol 17-beta-D-glucuronide (E(2)17betaG), the glutathione conjugates 2,4-dinitrophenyl S-glutathione (DNP-SG) and leukotriene C4 (LTC4), the antimetabolite methotrexate, and the bile acid glycocholate. DNP-SG, LTC4, and E(2)17betaG are transported at moderate affinity and low capacity with Km and Vmax values of 5.7 +/- 1.7 microM and 3.8 +/- 0.1 pmol/mg/min, 5.3 +/- 2.6 microM and 20.2 +/- 5.9 pmol/mg/min, and 25.6 +/- 5.4 microM and 75.6 +/- 5.9 pmol/mg/min, respectively. Methotrexate and glycocholate are transported at low affinity and high capacity with Km and Vmax values of 776 +/- 319 microM and 288 +/- 54 pmol/mg/min and 248 +/- 113 microM and 183 +/- 34 pmol/mg/min, respectively. On the basis of these findings, the osmotic dependence of the transport measured and its inability to transport taurocholate, MRP3, like MRP1 and cMOAT, is concluded to be competent in the transport of glutathione S-conjugates, glucuronides, and methotrexate, albeit at low to moderate affinity. In contrast to MRP1, cMOAT, and all other characterized mammalian ABC transporters, however, MRP3 is active in the transport of the monoanionic human bile constituent glycocholate.

Cytostar-T scintillating microplate assay for measurement of sodium-dependent bile acid uptake in transfected HEK-293 cells.

Real-time measurements of bile acid uptake into HEK-293 cell monolayers expressing the human sodium/bile acid cotransporters have been demonstrated using Cytostar-T microplates with an integral scintillating base. In these 96-well microplates, which permits culturing and observation of adherent cell monolayers, uptake of (14)C-labeled glycocholate and taurocholate into transfected HEK-293 cells was time-dependent, sodium-stimulated, and saturable. The sodium-activated uptake of 30 microM [(14)C]glycocholate (GC) via the ileal (IBAT) and liver (LBAT) transporters was 30-40 times higher than GC uptake in a sodium-free background. In addition, ouabain inhibition of the plasma membrane Na(+), K(+)-ATPase, causing the sodium gradient to collapse, resulted in total loss of glycocholate transport. Induction of gene expression by sodium butyrate showed that the amount of labeled bile acid accumulated in the cell monolayers at steady state was a function of the total amount of transporter expressed. Uptake of labeled bile acids was inhibited both by the specific IBAT inhibitor, 2164U90, and by various bile acids. No major difference was observed between IBAT and LBAT in their specificity for the bile acids tested while the dihydroxy bile acids had the highest affinity for both the transporters studied. The Cytostar-T proximity assay has been demonstrated to be an accurate and reproducible method for monitoring specific bile acid transport in transfected mammalian cells and the results are similar to those obtained by traditional methods. We conclude that the technique is an attractive approach to the cellular study of membrane transport of radiolabeled solutes in general and suggest a role in screening and characterization of novel transport inhibitors.

Further evidence of the usefulness of bile acids as molecules for shuttling cytostatic drugs toward liver tumors.

BACKGROUND/AIMS: To use bile acids as shuttles for directing cytostatic drugs toward liver tumors, the ability of the tumor to take up these compounds must be maintained. Thus, we investigated whether glycocholate (GC) derivatives such as the fluorescent FITC-GC and the cytostatic Bamet-R2 are taken up by neoplastic tissue at different stages of chemically-induced rat liver carcinogenesis. METHODS: Placental glutathione-S-transferase (GST-P) was immunohistochemically detected. Uptake studies were carried out on pure GST-P-positive cell cultures, obtained by treatment with ethacrinic acid. FITC-GC, Bamet-R2 or cisplatin was administered (i.v.) to anaesthetized rats. Platinum in culture cells, liver and kidney was measured by flameless atomic absorption. RESULTS: Co-localization after FITC-GC i.v. administration revealed that only 15% (20 weeks) and 30% (32 weeks) of GST-P-positive tissue was not able to take up FITC-GC. GC uptake was lower in GST-P-positive cells than in normal hepatocytes. Bamet-R2, uptake was lower than that for GC, but similar in both cell types. The amount of Bamet-R2 or cisplatin retained by GST-P-positive tissue after in vivo administration was progressively increased during carcinogenesis. Moreover, this amount was higher for Bamet-R2 than for cisplatin. By contrast, in the kidney, it was higher for cisplatin than for Bamet-R2. CONCLUSION: These results indicate that at the different stages of rat hepatocarcinogenesis most GST-P-positive tissue is able to take up bile acid derivatives, such as Bamet-R2.

Polyspecific substrate uptake by the hepatic organic anion transporter Oatp1 in stably transfected CHO cells.

The rat liver organic anion transporting polypeptide (Oatp1) has been extensively characterized mainly in the Xenopus laevis expression system as a polyspecific carrier transporting organic anions (bile salts), neutral compounds, and even organic cations. In this study, we extended this characterization using a mammalian expression system and confirm the basolateral hepatic expression of Oatp1 with a new antibody. Besides sulfobromophthalein [Michaelis-Menten constant (Km) of approximately 3 microM], taurocholate (Km of approximately 32 microM), and estradiol- 17beta-glucuronide (Km of approximately 4 microM), substrates previously shown to be transported by Oatp1 in transfected HeLa cells, we determined the kinetic parameters for cholate (Km of approximately 54 microM), glycocholate (Km of approximately 54 microM), estrone-3-sulfate (Km of approximately 11 microM), CRC-220 (Km of approximately 57 microM), ouabain (Km of approximately 3,000 microM), and ochratoxin A (Km of approximately 29 microM) in stably transfected Chinese hamster ovary (CHO) cells. In addition, three new substrates, taurochenodeoxycholate (Km of approximately 7 microM), tauroursodeoxycholate (Km of approximately 13 microM), and dehydroepiandrosterone sulfate (Km of approximately 5 microM), were also investigated. The results establish the polyspecific nature of Oatp1 in a mammalian expression system and definitely identify conjugated dihydroxy bile salts and steroid conjugates as high-affinity endogenous substrates of Oatp1.

Cholephilic characteristics of a new cytostatic complex of cisplatin with glycocholate (Bamet-R2).

The aim of this work was to investigate both the existence of enterohepatic circulation of cisplatin-cholylglycinate complex, Bamet-R2, and the relevance of biliary versus urinary excretion of this compound. Two experimental models were used: (i) intraluminal perfusion of 'in situ' ileum in anaesthetized rats bearing a biliary catheter that permitted bile sample collection and (ii) conscious rats in which a permanent intraarterial catheter had been implanted to carry out sequential blood sampling after intravenous (i.v.) or intragastric (i.g.) drug administration. Total platinum in serum, bile, ileum, liver, urine and feces was measured by flameless atomic absorption spectroscopy. Serum concentration versus time curves obtained after i.v. administration of 1 micromol Bamet-R2 or cisplatin revealed that the area under the curve was significantly higher for Bamet-R2 than for cisplatin (+48%). Non-ultrafiltrable platinum accounted for 54.8 and 48.4% of serum platinum 168 h after cisplatin and Bamet-R2 i.v. administration, respectively. When the animals received i.g. 1 micromol cisplatin or Bamet-R2, serum concentrations of total platinum were markedly higher (three-fold) after Bamet-R2 than after cisplatin administration. The area under the curve was, also in this case, significantly higher for Bamet-R2 than for cisplatin (+28%). This was in part due to the enhanced intestinal absorption of Bamet-R2, as confirmed in experiments on perfused rat ileum, where a markedly higher amount of the drug was found in ileum tissue and bile after perfusion with media containing Bamet-R2 as compared with experiments where cisplatin instead of Bamet-R2 was added to perfusion media. Moreover, after i.v. administration to conscious rats, excretion of Bamet-R2 by the kidney was three-fold lower than that of cisplatin, while elimination of the former compound into feces was four-fold higher than that of the latter. In summary, these results indicate that in addition to the previously reported cytostatic activity of Bamet-R2, this complex has interesting cholephilic characteristics typical of bile acids, such as low urinary excretion together with enhanced intestinal absorption and biliary secretion, probably endowed by the cholylglycyl moiety included in the Bamet-R2 molecule.

Transport and biotransformation of the new cytostatic complex cis-diammineplatinum(II)-chlorocholylglycinate (Bamet-R2) by the rat liver.

Rat liver uptake and bile output of the cytostatic complex cis-diammineplatinum(II)-chlorocholylglycinate (Bamet-R2) were studied. Up to 100 microM, Bamet-R2 uptake by rat hepatocytes in primary culture followed saturation kinetics (Vmax = 0.65 +/- 0.12 nmol/5 min per mg protein; K(M) = 45.2 +/- 10.7 microM). Bamet-R2 uptake was lower than that of cholylglycinate (CG) but higher than that of cisplatin. Replacement of 116 mM NaCl by 116 mM choline chloride did not significantly reduce Bamet-R2 uptake. Addition of 500 microM CG, cholic acid, estrone sulfate, or ouabain to 50 microM Bamet-R2-containing incubation media inhibited Bamet-R2 uptake. No liver biotransformation of Bamet-R2 occurred, as indicated by HPLC analysis of bile collected from anesthetized rats after intravenous administration of the drug. Bamet-R2 uptake and secretion into bile by isolated rat livers exceeded those of cisplatin but were lower than those of CG. Differences between Bamet-R2 and CG were more marked for bile output than for liver uptake. Thus, higher Bamet-R2 than CG or cisplatin liver content was found. Co-administration of Bamet-R2 and CG revealed that CG induced a slight reduction in Bamet-R2 uptake and a marked inhibition in Bamet-R2 bile output. By contrast, Bamet-R2 had no effect on CG on either liver uptake or bile output. In sum, the present data indicate that Bamet-R2 is efficiently taken up and secreted into bile by the rat liver by mechanisms shared in part by natural bile acids.

Rat liver transport and biotransformation of a cytostatic complex of bis-cholylglycinate and platinum (II).

BACKGROUND/AIMS: Bile acids have previously been used as shuttles for directing organic drugs to the liver. The aim of this study was to investigate liver transport and biotransformation of a new cytostatic bioinorganic complex (Bamet-H2), that was obtained by binding platinum(II) to two cholylglycinate moieties. METHODS: Using rat hepatocytes in primary culture, the kinetics of cholylglycinate, cisplatin and Bamet-H2 uptake were studied. Sodium-dependency of Bamet-H2 uptake was investigated by replacement of 116 mM NaCl by 116 mM choline chloride. Liver biotransformation was investigated by HPLC analysis of bile samples collected from anesthetized rats following intravenous Bamet-H2 administration. Using isolated rat liver preparations, which were perfused with erythrocyte- and albumin-free Krebs-Henseleit solutions for 40 min, measurement of cholylglycinate, cisplatin and Bamet-H2 uptake and bile output was carried out. Interaction between Bamet-H2 and cholylglycinate for liver transport was studied by co-administration of 1 microM Bamet-H2 plus 500 microM cholylglycinate and 1 microM [14C]-cholylglycinate plus 500 microM Bamet-H2. RESULTS: Both cholylglycinate and Bamet-H2 uptake by rat hepatocytes followed saturation kinetics. Comparison between the two compounds indicated that the Vmax (22.2 versus 8.5 nmol.5 min(-1).mg protein(-1)), and Kt (365 versus 171 microM) were higher for Bamet-H2 uptake. The efficiency of Bamet-H2 uptake (Vmax/Kt) was significantly reduced (-35%) in the absence of sodium. Cisplatin uptake by rat hepatocytes was approximately 10-fold lower than that for Bamet-H2 at any dose used. Moreover, this was not saturable up to 400 microM cisplatin. Bamet-H2 was not biotransformed during its intrahepatic residence in anesthetized rats. Bamet-H2 uptake and secretion into bile by isolated rat livers exceeded cisplatin but were less than cholylglycinate. Differences between Bamet-H2 and cholylglycinate were more marked for bile output than for liver uptake. Thus, higher drug liver content was found after perfusion with Bamet-H2 than with cholylglycinate or cisplatin. Co-administration of Bamet-H2 and cholylglycinate revealed the existence of partial cross-inhibition in both liver uptake and bile output. Bamet-H2 induced a more profound alteration on cholylglycinate uptake and bile secretion than cholylglycinate on both process for Bamet-H2. CONCLUSION: These results suggest that in the transfer of Bamet-H2 from the sinusoids to the canaliculi both bile acid and non-bile acid transport systems are involved.