RESUMEN
Loperamide is a µ-opioid agonist with poor gastrointestinal absorption, mainly because of its modest aqueous solubility and being a P-glycoprotein (Pgp) efflux substrate. Nevertheless, studies associated with therapeutic effects strongly suggest that loperamide holds potential pharmacological advantages over traditional µ-opioid agonists commonly used for analgesia. Thus, in this Communication, we assessed in MDCK-hMDR1 cell lines the effects over loperamide uptake and efflux ratio, when loaded into Eudragit RS (ERS) nanocarriers coated with poloxamer 188 (P188). ERS was chosen for enhancing loperamide aqueous dispersibility and P188 as a potential negative Pgp modulator. In uptake assays, it was observed that Pgp limited the accumulation of loperamide into cells and that preincubation with P188, but not coincubation, led to increasing loperamide uptake at a similar extent of Pgp pharmacological inhibition. On the other hand, the efflux ratio displayed no alterations when Pgp was pharmacologically inhibited, whereas ERS/P188 nanocarriers effectively enhanced loperamide uptake and absorptive transepithelial transport. The latter suggests that loperamide transport across cells is significantly influenced by the presence of the unstirred water layer (UWL), which could hinder the visualization of Pgp-efflux effects during transport assays. Thus, results in this work highlight that formulating loperamide into this nanocarrier enhances its uptake and transport permeability.
Asunto(s)
Antidiarreicos/administración & dosificación , Portadores de Fármacos/química , Loperamida/administración & dosificación , Subfamilia B de Transportador de Casetes de Unión a ATP/genética , Subfamilia B de Transportador de Casetes de Unión a ATP/metabolismo , Resinas Acrílicas/química , Administración Oral , Animales , Antidiarreicos/farmacocinética , Disponibilidad Biológica , Perros , Humanos , Absorción Intestinal , Mucosa Intestinal/metabolismo , Loperamida/farmacocinética , Células de Riñón Canino Madin Darby , Metacrilatos/química , Nanopartículas/química , Permeabilidad , Poloxámero/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , SolubilidadRESUMEN
Bile acids (BAs) are the end products of cholesterol metabolism. One of the critical steps in their biosynthesis involves the isomerization of the 3ß-hydroxyl (-OH) group on the cholestane ring to the common 3α-configuration on BAs. BAs are actively recaptured from the small intestine by the human Apical Sodium-dependent Bile Acid Transporter (hASBT) with high affinity and capacity. Previous studies have suggested that no particular hydroxyl group on BAs is critical for binding or transport by hASBT, even though 3ß-hydroxylated BAs were not examined. The aim of this study was to elucidate the role of the 3α-OH group on BAs binding and translocation by hASBT. Ten 3ß-hydroxylated BAs (Iso-bile acids, iBAs) were synthesized, characterized, and subjected to hASBT inhibition and uptake studies. hASBT inhibition and uptake kinetics of iBAs were compared to that of native 3α-OH BAs. Glycine conjugates of native and isomeric BAs were subjected to molecular dynamics simulations to identify topological descriptors related to binding and translocation by hASBT. Iso-BAs bound to hASBT with lower affinity and exhibited reduced translocation than their respective 3α-epimers. Kinetic data suggests that, in contrast to native BAs where hASBT binding is the rate-limiting step, iBAs transport was rate-limited by translocation and not binding. Remarkably, 7-dehydroxylated iBAs were not hASBT substrates, highlighting the critical role of 7-OH group on BA translocation by hASBT, especially for iBAs. Conformational analysis of gly-iBAs and native BAs identified topological features for optimal binding as: concave steroidal nucleus, 3-OH "on-" or below-steroidal plane, 7-OH below-plane, and 12-OH moiety toward-plane. Our results emphasize the relevance of the 3α-OH group on BAs for proper hASBT binding and transport and revealed the critical role of 7-OH group on BA translocation, particularly in the absence of a 3α-OH group. Results have implications for BA prodrug design.
Asunto(s)
Ácidos y Sales Biliares/química , Ácidos y Sales Biliares/metabolismo , Transportadores de Anión Orgánico Sodio-Dependiente/química , Transportadores de Anión Orgánico Sodio-Dependiente/metabolismo , Simportadores/química , Simportadores/metabolismo , Ácidos y Sales Biliares/síntesis química , Transporte Biológico , Humanos , Hidroxilación , Conformación Molecular , Transportadores de Anión Orgánico Sodio-Dependiente/antagonistas & inhibidores , Unión Proteica , Simportadores/antagonistas & inhibidoresRESUMEN
PURPOSE: To explore the involvement of transmembrane domain (TM) 7 of the human apical sodium-dependent bile acid transporter (hASBT) on bile acid (BA) binding/translocation, using two electrophilic BA derivatives as molecular probes. METHODS: Two electrophilic derivatives of chenodeoxycholic acid (CDCA) were designed, synthesized and evaluated for their ability to inactivate hASBT, and the human organic cation/carnitine transporter (hOCTN2) as a control (i.e. a non-BA transporting model). The ability of electrophilic derivatives to interact with hASBT was evaluated by 2-aminoethyl-methanethiosulfonate (MTSEA)-biotin labeling of thiol groups in TM7 cysteine mutants. RESULTS: Unlike native BAs, the electrophilic CDCA derivatives specifically inactivated hASBT, but not hOCTN2, and inhibited hASBT in a time- and concentration-dependent fashion. Preincubation of hASBT Cys-mutants in the exofacial half of TM7 with reactive electrophilic probes blocked transporter biotinylation by MTSEA-biotin, similar to 2-(trimethylammonium)ethyl-methanethiosulfonate (MTSET) blocking. This blocking pattern differed from that produced by native BAs, which exposed exofacial TM7 residues, thereby increasing staining. CONCLUSION: Kinetic and biochemical data indicate these novel electrophilic BAs are potent and specific irreversible inhibitors of hASBT and offer new evidence about the role of TM7 in binding/translocation of bile acids.