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James E Polli

Publications and source records attributed to James E Polli.

At least 19 recordsLinked to original sources
PubMed2006

Bias in estimation of transporter kinetic parameters from overexpression systems: Interplay of transporter expression level and substrate affinity.

The objective was to investigate the interplay between transporter expression levels and substrate affinity in controlling the influence of aqueous boundary layer (ABL) resistance on transporter kinetics in an over-expression system. Taurocholate flux was measured across human apical sodium-dependent bile acid transporter (hASBT)-Madin-Darby canine kidney monolayers on different occasions and kinetic parameters estimated with and without considering ABL. In error-free simulation/regression studies, flux values were generated across a range of J max, Kt, and substrate concentrations. Similar evaluation was performed for transport inhibition studies. Additionally, simulation/regression studies were performed, incorporating 15% random error to estimate the probability of successfully estimating Kt. Across different occasions, experimental J max and Kt estimates for taurocholate were strongly associated (p < 0.001; r2 = 0.82) when ABL was not considered. Simulation/regression results indicate that not considering ABL caused this association, such that Kt estimates were highly positively biased at high hASBT expression. In reanalyzing taurocholate flux data using the ABL-present model, Kt was relatively constant across occasions (approximately 5 microM) and not associated with J max (p = 0.24; r2 = 0.13). Simulations suggest that J max and Kt collectively determined ABL influence, which is most prominent under conditions of low monolayer resistance. Additionally, not considering ABL lead to negatively biased Ki estimates, especially at high J max. Error-inclusive simulation/regression studies indicated that the probability of successfully estimating Kt depended on the contribution of ABL resistance to flux; when flux became increasingly ABL-limited, probability of success decreased. Results indicate that ABL resistance can bias Kt and Ki estimates from overexpression systems, where the extent of bias is determined by transporter expression level and substrate affinity.

Animals↗
PubMed2006

Rapid identification of P-glycoprotein substrates and inhibitors.

Identifying molecules that interact with P-glycoprotein (P-gp) is important for drug discovery but is also generally reliant on time-consuming in vitro and in vivo studies. As an alternative approach, the current study applied pharmacophore models and database screening to rapidly retrieve molecules that bind as substrates or inhibitors for P-gp from commercial databases and then confirmed their affinity as inhibitors in vitro. Seven molecules (acitretin, cholecalciferol, misoprostol, nafcillin, repaglinide, salmeterol, and telmisartan) with no published details for P-gp affinity, one positive control inhibitor (miconazole), and two negative control molecules (phenelzine and zonisamide) were selected for testing. The MDCK-MDR1 in vitro cell model was used to confirm their inhibitory effect on [3H]digoxin transport, and the ATPase assay was used as an additional in vitro tool to indicate P-gp activation. All seven test drugs were confirmed to have P-gp affinity. Additionally, our experimental results provided plausible explanations for the published pharmacokinetic profiles of the tested drugs and their classification according to the biopharmaceutics and drug disposition classification system. In this study, we showed the successful application of pharmacophore models to accurately predict P-gp binding, which holds promise to anticipate drug-drug interactions from screening drug databases and a priori prediction of novel P-gp inhibitors or substrates.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Ion pair-mediated transport of metoprolol across a three lipid-component PAMPA system.

Parallel Artificial Membrane Permeability Assay (PAMPA) is a method to screen drug candidates for membrane permeability. The objective was to characterize the transport of a model weak base, metoprolol, across a three lipid-component PAMPA system (denoted A-PAMPA, for anionic-PAMPA) and challenge ion pairing as a mechanism for metoprolol transport. A-PAMPA was designed to mimic the lipid composition of the enterocyte's plasma membrane and included 1,2-dioleoyl-sn-glycero-3-[phospho-l-serine] (PS18:1) as an anionic lipid-component. Metoprolol flux was measured across A-PAMPA, as well as across three other PAMPA systems. Permeability studies were conducted under various conditions, with varying pH, ionic strength, and presence/absence of competing cations. Permeabilities of mannitol and benzoic acid, as model neutral and anionic solutes, were also measured. PAMPA membrane fluidity was inferred from anisotropy measurements in liposomes. Ion pairing between metoprolol and PS18:1 was assessed via NMR. Metoprolol transport across A-PAMPA was dominated by an ion pair-mediated mechanism (i.e. metoprolol-PS18:1 complex), rather than a membrane fluidity-mediated mechanism. Compared to other PAMPA systems, metoprolol permeability across A-PAMPA and PS18:1 was high. Permeability and anisotropy values suggested PS18:1 selectively facilitated metoprolol transport, while neutral lipid did not. Additional studies supporting ion pairing of metoprolol across A-PAMPA showed that a) metoprolol transport was self-inhibited across A-PAMPA but not across neutral lipid PAMPA; b) competing cations reduced metoprolol permeability across A-PAMPA but not across neutral lipid PAMPA; and c) NMR spectrum of a mixture of metoprolol and PS18:1 showed a broadening of some metoprolol peaks, presumably due to metoprolol interaction with anionic lipid. Metoprolol transport across a three lipid-component PAMPA system that contained anionic lipid was facilitated by apparent ion pairing.

Adrenergic beta-Antagonists↗
PubMed2006

Interaction of native bile acids with human apical sodium-dependent bile acid transporter (hASBT): influence of steroidal hydroxylation pattern and C-24 conjugation.

PURPOSE: The human apical sodium-dependent bile acid transporter (hASBT) is a potential target for drug delivery, but an understanding of hASBT substrate requirements is lacking. The objective of this study was to characterize hASBT interaction with its native substrates, bile acids, and to evaluate C-24 conjugation and steroidal hydroxylation on transport affinity and inhibition potency. METHODS: Transport and inhibition kinetics of 15 bile acids were evaluated (cholate, chenodeoxycholate, deoxycholate, ursodeoxycholate, and lithocholate, including their glycine and taurine conjugates) with an hASBT-Madin-Darby canine kidney (MDCK) monolayer assay. Samples were analyzed via liquid chromatography-mass spectrometry (LC-MS) or chromatography-mass spectrometry-mass spectrometry (LC-MS-MS). RESULTS: C-24 conjugation improved the inhibitory potency of all native bile acids. There was an inverse association between number of steroidal hydroxyl groups and inhibitory potency. Glycolithocholate and taurolithocholate were the most potent inhibitors. Results from transport studies followed trends from inhibition studies. Conjugated dihydroxy and monohydroxy bile acids exhibited the highest hASBT-mediated transport (i.e., lower Kt and higher Jmax). Across the 15 bile acids, Kt generally followed Ki. Additionally, Jmax correlated with Ki, where greater inhibition potency was associated with higher transport capacity. CONCLUSION: C-24 conjugation and steroidal hydroxylation pattern modulated native bile acid interaction with hASBT, with C-24 effect dominating steroidal hydroxylation effect. Results indicate that bile acid binding to hASBT may be the rate-limiting step in the apical transport of bile acids.

Amination↗
PubMed2006

Lipid composition effect on permeability across PAMPA.

The parallel artificial membrane permeability assay (PAMPA) system has promise to rapidly screen drug candidate passive permeability, but has been poorly described in terms of its lipid membrane structure and function. The objective was to investigate the role of PAMPA lipid composition on the permeability of five model compounds. PAMPA was used and employed individual phospholipids that varied in phosphate head group and acyl chain unsaturation. Transport of benzoic acid, taurocholic acid, metoprolol, sucrose, and mannitol was measured. Membrane fluidity was assessed by 1,3-diphenylhexatriene fluorescence anisotropy. Results indicate that compound permeability across PAMPA differed in their sensitivity to membrane lipid composition, where compounds with appreciable permeability (i.e. at least 0.2 x 10(-6)cm/s) were possibly sensitive to membrane fluidity and apparent ion pair effects. Benzoic acid permeability ranged 51-fold across membrane types, suggesting acyl chain effect on membrane fluidity. Mannitol, sucrose, and taurocholic acid permeabilities were low and independent of lipid composition. Metoprolol permeability ranged 17-fold and exhibited a markedly high permeability across 1,2-dioleoyl-sn-glycero-3-[phospho-L-serine] due to apparent ion pair-facilitated transport. Compound permeability was lowest across the phosphatidylcholines, which is consistent with phosphatidylcholine exhibiting relatively high membrane rigidity. In contrast to results from phosphatidylethanolamines and phosphatidylserines, acyl chain unsaturation had no effect on permeability across phosphatidylcholines. In conclusion, while much remains unknown about PAMPA structure and subsequent PAMPA permeability, results here from five solutes suggest that, for solutes with appreciable permeability, lipid composition modulated drug permeability through possible membrane fluidity and apparent ion pair influences.

Anisotropy↗
PubMed2005

Development of stably transfected monolayer overexpressing the human apical sodium-dependent bile acid transporter (hASBT).

PURPOSE: The human apical sodium-dependent bile acid transporter (hASBT) represents a potential target for prodrug design to increase oral drug absorption. Unfortunately, available monolayer cell culture models do not reliably express hASBT, and nonpolarized cells only allow for uptake assessment, which limits prodrug development efforts. The objective of this study was to develop and characterize a stably transfected hASBT-MDCK cell line. METHODS: cDNA encoding hASBT was cloned into pcDNA3.1-V5-polyHis-B to generate an expression plasmid that was then transfected into MDCK-II cells. Clonal populations were chosen based on high hASBT activity and monolayer integrity. Western blot confirmed the expression of the recombinant hASBT; functionality was characterized using taurocholic acid. RESULTS: In the selected clone, hASBT-mediated taurocholate permeability across hASBT-MDCK monolayers was almost 25-fold higher with sodium, than without sodium where hASBT is not functional. In the presence of sodium, taurocholate and mannitol permeabilities were 23.0x10(-6) cm/sec and 2.60x10(-6) cm/s, respectively, indicating high hASBT functionality and monolayer integrity. hASBT-MDCK monolayer properties were stable over 6 months and demonstrated low within-day variability. Taurocholate uptake and inhibition kinetic parameters from hASBT-MDCK were similar to those obtained from hASBT-COS7 model, confirming hASBT functionality in hASBT-MDCK. CONCLUSIONS: Results indicate that the developed hASBT-MDCK system is a competent, high-expression, stable assay for hASBT transport and inhibition studies.

Animals↗
PubMed2004

Increased acyclovir oral bioavailability via a bile acid conjugate.

The objective of this work was to design an acyclovir prodrug that would utilize the human apical sodium-dependent bile acid transporter (hASBT) and enhance acyclovir oral bioavailability. Using each chenodeoxycholate, deoxycholate, cholate, and ursodeoxycholate, four bile acid prodrugs of acyclovir were synthesized, where acyclovir was conjugated to a bile acid via a valine linker. The affinity of the prodrug for hASBT was determined through inhibition of taurocholate uptake by COS-7 cells transfected with hASBT (hASBT-COS). The prodrug with the highest inhibitory affinity was further evaluated in vitro and in vivo. The prodrug acyclovir valylchenodeoxycholate yielded the highest affinity for hASBT (Ki = 35 microM), showing that chenodeoxycholate is the free bile acid with the greatest affinity for hASBT. Acyclovir valylchenodeoxycholate's affinity was similar to that of cholic acid (Ki = 25 microM). Further characterization showed that acyclovir was catalytically liberated from acyclovir valylchenode-oxycholate by esterase. Relative to cellular uptake studies of acyclovir alone, the cellular uptake from the prodrug resulted in a 16-fold greater acyclovir accumulation within hASBT-COS cells, indicating enhanced permeation properties of the prodrug. Enhanced permeability was due to hASBT-mediated uptake and increased passive permeability. The extent of acyclovir uptake in the presence of sodium was 1.4-fold greater than the extent of passive prodrug uptake in the absence of sodium (p = 0.02), indicating translocation of the prodrug by hASBT. The prodrug also exhibited an almost 12-fold enhanced passive permeability, relative to acyclovir's passive permeability. Oral administration of acyclovir valylchenodeoxycholate to rats resulted in a 2-fold increase in the bioavailability of acyclovir, compared to the bioavailability after administration of acyclovir alone. Results indicate that a bile acid prodrug strategy may be useful in improving the oral bioavailability of intestinal permeability-limited compounds.

Acyclovir↗
PubMed2004

Surfactant-mediated dissolution: contributions of solubility enhancement and relatively low micelle diffusivity.

The objective of this study was to assess the contributions of surfactant-mediated solubility and micellar diffusivity on the ability of surfactant to enhance drug dissolution. The following model was derived to predict the degree to which surfactants enhance griseofulvin dissolution: phi = 1 + (fm/ff).((D(D-M)2/3)/(DD2/3)) where phi is the degree of surfactant-mediated dissolution enhancement, fm is the fraction of the drug in micelle, and ff is the fraction of free drug, and DD and D(D-M) are the diffusivities of free drug and drug-loaded micelles, respectively. The Wood apparatus was used to measure the dissolution of griseofluvin in the presence of the anionic surfactant sodium dodecyl sulfate (SDS), the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), and the neutral surfactants Tween 80 and Cremophor EL. DD was estimated using the Levich equation. D(D-M) was measured using dynamic light scattering. Griseofulvin solubility was evaluated in SDS, CTAB, Tween 80, and Cremophor EL at the surfactant concentrations used in the dissolution studies. DD was 11.0 x 10(-6) cm2/s. D(D-M) was 1.29 x 10(-6) cm2/s, 0.956 x 10(-6) cm2/s, 0.569 x 10(-6) cm2/s, and 0.404 x 10(-6) cm2/s for griseofulvin-loaded micelles of SDS, CTAB, Tween 80, and Cremophor EL, respectively. At the highest surfactant concentrations studied, griseofulvin solubility increased 107-fold, 31-fold, fourfold, and threefold for SDS, CTAB, Tween 80, and Cremophor EL. Dissolution into SDS and CTAB were markedly enhanced, but only about one-third as much as solubility enhancement. Dissolution enhancement in the presence of SDS and CTAB were in excellent agreement with model predicted values, with prediction error less than 12%. The model predicted dissolution into Tween 80 and Cremophor EL to be minimally enhanced, as was observed, although the model underpredicted dissolution into these two neutral surfactants. The derived model predicted surfactant-mediated dissolution and reflects dissolution enhancement to be promoted by surfactant-enhanced solubility, but limited by the relatively slow diffusion of drug-loaded surfactant micelles.

Diffusion↗
PubMed2003

Characterization of dexloxiglumide in vitro biopharmaceutical properties and active transport.

The objective of this work was to characterize dexloxiglumide biopharmaceutical properties in vitro and relate these characteristics to its in vivo absorption performance, and to assess dexloxiglumide interaction with P-glycoprotein (P-gp) and MRP1 to anticipate its drug interaction potential. Dexloxiglumide aqueous solubility was moderate and pH dependent. Dexloxiglumide exhibited moderate Caco-2 permeability that was polarized, concentration dependent, and pH dependent. The apical-to-basolateral (AP-BL) permeability at pH 5 [14.5 (+/-1.8) x 10(-6) cm/s] was 2-fold higher than at pH 7.5 [7.24 (+/-0.27) x 10(-6) cm/s]. Neutral and ionized dexloxiglumide species displayed permeabilities of 30.8 (+/-8.4) x 10(-6) cm/s and 9.03 (+/-1.31) x 10(-6) cm/s, respectively. The transport of dexloxiglumide across MDR1-MDCK (P-gp overexpressing Madine Darby canine kidney cells) monolayers was polarized, with a BL-AP/AP-BL permeability ratio of 9.35 (+/-0.73), which was reduced to 1.03 (+/-0.03) by P-gp inhibition. Rhodamine 123 efflux was reduced by dexloxiglumide from 4.06 (+/-0.34) to 2.84 (+/-0.15) across Caco-2 monolayers, and from 17.3 (+/-0.9) to 8.26 (+/-1.38) across MDR1-MDCK monolayers, further indicating dexloxiglumide interaction with P-gp. Additionally, P-gp ATPase activity increased with dexloxiglumide concentration. Dexloxiglumide was effluxed from MRP1-NIH3T3 cells (NIH-3T3 cells expressing the multidrug resistance-associated protein 1). Dexloxiglumide increased MRP1-substrate fluorescein uptake 4-fold, and fluorescein increased dexloxiglumide uptake 1.8-fold. Overall, in vitro transport studies indicate dexloxiglumide to be moderately soluble and moderately permeable, which is in agreement with the incomplete oral absorption of dexloxiglumide. In vitro, dexloxiglumide was moderately modulated by P-gp and MRP1, which provides a rationale for the design of drug interaction studies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Midazolam exhibits characteristics of a highly permeable P-glycoprotein substrate.

PURPOSE: The purpose of this study was to investigate whether midazolam exhibits characteristics of a highly permeable P-glycoprotein (P-gp) substrate and to evaluate the potential influence of P-gp inhibition on 1-OH midazolam formation during midazolam transport. METHODS: P-gp interaction was investigated by P-gp ATPase assay, efflux inhibition studies, and transport studies of midazolam across MDR1-MDCK and 1-alpha,25-dihydroxy vitamin D3-induced Caco-2 monolayers with and without the P-gp inhibitor GF120918. RESULTS: Midazolam was highly permeable and transport appeared essentially unpolarized. In MDR1-MDCK, the basolateral-to-apical (B-to-A) permeability was slightly higher (16%) than apical-to-basolateral (A-to-B) permeability (p = 0.04); GF120918 increased A-to-B permeability by 27% (p = 0.01), and increased cellular midazolam accumulation during A-to-B transport by 45% (p = 0.01). Midazolam (200 microM) decreased rhodamine123 and vinblastine B/A ratios 3-fold (p < 0.006), while increasing their cellular accumulation (p < 0.003). P-gp ATPase activation by midazolam was dose-dependent and saturable [Km = 11.5(+/- 4.0) microM; Vmax = 41.1(+/- 7.4) nmol/mg/min]. P-gp inhibition increased 1-OH midazolam formation in A-to-B studies 1.3-fold when midazolam donor > or = 10 microM (p < 0.03). In B-to-A studies, P-gp inhibition did not significantly increase metabolite formation (p = 0.06). Midazolam's extraction ratio was not influenced by P-gp (p = 0.2). CONCLUSION: The results indicate that midazolam exhibited characteristics of a highly permeable P-gp substrate. 1-OH midazolam formation during A-to-B midazolam transport increased slightly when P-gp was inhibited.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Effects of nonionic surfactants on membrane transporters in Caco-2 cell monolayers.

The objectives of this study were (1) to investigate the transporter inhibition activity of three nonionic surfactants on P-glycoprotein, the human intestinal peptide transporter, and the monocarboxylic acid transporter in Caco-2 cell monolayers, and (2) to evaluate the role of membrane fluidity and protein kinase C in surfactant-induced transporter inhibition. All three surfactants inhibited P-glycoprotein (P-gp). Over a range from 0 to 1 mM, Tween 80 and Cremophor EL increased apical-to-basolateral permeability (AP-BL) and decreased basolateral-to-apical (BL-AP) permeability of the P-gp substrate rhodamine 123. Vitamin E TPGS's effect was equally large, but essentially only reduced the BL-AP permeability of rhodamine 123, and did so at a vitamin E TPGS concentration of only 0.025 mM. These P-gp inhibition effects would appear to be related to these excipients' modulation of membrane fluidity, where Tween 80 and Cremophor EL fluidized cell lipid bilayers, while vitamin E TPGS rigidized lipid bilayers. However, among the three surfactants, only Tween 80 inhibited the peptide transporter, as measured by glycyl sarcosine permeability. Likewise, only Cremophor EL inhibited the monocarboxylic acid transporter, as measured by benzoic acid permeability. Nevertheless, at least one of these three surfactants inhibited each P-gp, the human intestinal peptide transporter, and the monocarboxylic acid transporter. A common functional feature of these three surfactants was their ability to modulate fluidity, although results indicate that even strong membrane fluidity modulation alone was not sufficient to reduce transporter activity. N-octyl glucoside, a nonionic surfactant that did not modulate membrane fluidity, did not affect transporter functioning. Protein kinase C inhibitors failed to affect rhodamine 123 and glycyl sarcosine permeability, suggesting protein kinase C inhibition was not the mechanism of transporter inhibition. These results suggest that surfactants can inhibit multiple transporters but that changes in membrane fluidity may not be a generalized mechanism to reduce transporter activity.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Biopharmaceutics classification system: the scientific basis for biowaiver extensions.

The current BSC guidance issued by the FDA allows for biowaivers based on conservative criteria. Possible new criteria and class boundaries are proposed for additional biowaivers based on the underlying physiology of the gastrointestinal tract. The proposed changes in new class boundaries for solubility and permeability are as follows: 1. Narrow the required solubility pH range from 1.0-7.5 to 1.0-6.8. 2. Reduce the high permeability requirement from 90% to 85%. The following new criterion and potential biowaiver extension require more research: 1. Define a new intermediate permeability class boundary. 2. Allow biowaivers for highly soluble and intermediately permeable drugs in IR solid oral dosage forms with no less than 85% dissolved in 15 min in all physiologically relevant dissolution media, provided these IR products contain only known excipients that do not affect the oral drug absorption. The following areas require more extensive research: 1. Increase the dose volume for solubility classification to 500 mL. 2. Include bile salt in the solubility measurement. 3. Use the intrinsic dissolution method for solubility classification. 4. Define an intermediate solubility class for BCS Class II drugs. 5. Include surfactants in in vitro dissolution testing.

Biopharmaceutics↗
PubMed2002

Novel metrics to compare dissolution profiles.

PURPOSE: To evaluate four novel metrics that compare dissolution profiles and assess their performance characteristics by comparing dissolution profiles of FAST and SLOW immediate release metoprolol tartrate tablets. METHODS: The four novel metrics (rho, rho m, delta a, and delta s), along with f2, were applied to dissolution data from FAST and SLOW metoprolol tartrate tablets. For example, rho m is defined as: [formula: see text] where Rt is the percent dissolved of the reference product at time t, Tt the percent dissolved of the test product at time t, and RATIOt the larger of either Rt/Tt or Tt/Rt. The mean metric values, upper (or lower) confidence limits, and skewness values were calculated, in order to characterize the performance of each metric. RESULTS: The mean values of rho, rho m, delta a, delta s, and f2 were 1.80, 0.80, 0.47, 0.36, and 19.6, respectively. The novel metrics indicate that greater than a 50% relative difference exists between the FAST and SLOW profiles. The upper 95% confidence limits for rho, rho m, delta a, and delta s were 1.84, 0.83, 0.48, and 0.38, respectively, with f2 having a lower limit of 19.1. Skewness values for ln-transformed rho, rho m, delta a, delta s, and f2 were 0.81, 0.71, 0.86, 0.47, and -0.94, respectively, suggesting favorable metric distribution properties. CONCLUSIONS: The direct curve comparison metrics rho, rho m, delta a, and delta s appear to be viable methods to compare dissolution profiles, particularly rho m.

Mathematics↗
PubMedDate not supplied

Chemical substituent effect on pyridine permeability and mechanistic insight from computational molecular descriptors.

The objective was (1) to evaluate the chemical substituent effect on Caco-2 permeability, using a congeneric series of pyridines, and (2) compare molecular descriptors from a computational chemistry approach against molecular descriptors from the Hansch approach for their abilities to explain the chemical substituent effect on pyridine permeability. The passive permeability of parent pyridine and 14 monosubstituted pyridines were measured across Caco-2 monolayers. Computational chemistry analysis was used to obtain the following molecular descriptions: solvation free energies, solvent accessible surface area, polar surface area, and cavitation energy. Results indicate that the parent pyridine was highly permeable and that chemical substitution was able to reduce pyridine permeability almost 20-fold. The substituent effect on permeability provided the following rank order: 3-COO- < 4-NH2 < 3-CONH2 < 3-Cl < 3-CHO < 3-OH < 3-CH2OH < 3-C6H5 < 3-NH2 < 3-CH2C6H5 < 3-C2H5 < 3-H < 3-CH3 < 3-F < 4-C6H5. This substituent effect was better explained via molecule descriptors from the computational chemistry approach than explained by classic descriptors from Hansch. Computational descriptors indicate that aqueous desolvation, but not membrane partitioning per se, dictated substituent effect on permeability.

Caco-2 Cells↗
PubMedDate not supplied

Influence of charge and steric bulk in the C-24 region on the interaction of bile acids with human apical sodium-dependent bile acid transporter.

The human apical sodium-dependent bile acid transporter (hASBT) is a potential target for drug delivery, but an understanding of hASBT substrate requirements is limited. The objective of this study was to evaluate the influence of ionic character and steric bulk in the C-24 region of bile acid conjugates in governing interaction with hASBT. Ionic character was studied using chenodeoxycholate (CDCA) conjugates of glutamic acid and lysine, which varied in charge (monoanionic, dianionic, cationic, neutral, and zwitterionic) and location of charge (proximal or distal to C-24). Steric effects were evaluated using ester conjugates that varied in ester substituent size (methyl, benzyl, and tert-butyl) and location (proximal and/or distal). Conjugate interaction with hASBT was assessed via transport and inhibition studies, using a hASBT-MDCK monolayer. Monoanionic, cationic, and neutral conjugates of CDCA exhibited high inhibitory potency (Ki<10 microM). High inhibition potency of neutral and cationic conjugates indicated that a negative charge is not essential for hASBT binding. Dianionic conjugates exhibited low inhibition potency (Ki>100 microM). Conjugates with a single bulky ester substituent proximal or distal to the C-24 region exhibited high inhibition potency. However, two bulky substituents practically abolished interaction. In transport studies, monoanionic conjugates were high affinity hASBT substrates. Meanwhile, cationic and zwitterionic conjugates were not substrates for hASBT. Overall, C-24 ionic character influenced interaction with hASBT. Although the presence of a single negative charge was not essential for interaction with hASBT, monoanionic conjugates were favored for hASBT-mediated transport compared to cationic and zwitterionic conjugates.

Bile Acids and Salts↗
PubMedDate not supplied

Apical sodium dependent bile acid transporter (ASBT, SLC10A2): a potential prodrug target.

A major hurdle impeding the successful clinical development of drug candidates can be poor intestinal permeability. Low intestinal permeability may be enhanced by a prodrug approach targeting membrane transporters in the small intestine. Transporter specificity, affinity, and capacity are three factors in targeted prodrug design. The human apical sodium dependent bile acid transporter (SLC10A2) belongs to the solute carrier family (SLC) of transporters and is an important carrier protein expressed in the small intestine. In spite of its appearing to be an excellent target for prodrug design, few studies have targeted human apical sodium dependent bile acid transporter (hASBT) to improve oral bioavailability. This review discusses bile acids including their chemistry and their absorptive disposition. Additionally, hASBT-mediated prodrug targeting is discussed, including QSAR, in vitro models for hASBT assay, and the current progress in utilizing hASBT as a drug delivery target.

Administration, Oral↗