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Stereoselective Oxidation Kinetics of Deoxycholate in Recombinant and Microsomal CYP3A Enzymes: Deoxycholate 19-Hydroxylation Is an In Vitro Marker of CYP3A7 Activity

The primary bile acids (BAs) synthesized from cholesterol in the liver are converted to secondary BAs by gut microbiota. It was recently disclosed that the major secondary BA, deoxycholate (DCA) species, is stereoselectively oxidized to tertiary BAs exclusively by CYP3A enzymes. This work subsequently investigated the in vitro oxidation kinetics of DCA at C-1β, C-3β, C-4β, C-5β, C-6α, C-6β, and C-19 in recombinant CYP3A enzymes and naive enzymes in human liver microsomes (HLMs). The stereoselective oxidation of DCA fit well with Hill kinetics at 1-300 μM in both recombinant CYP3A enzymes and pooled HLMs. With no contributions or trace contributions from CYP3A5, CYP3A7 favors oxidation at C-19, C-4β, C-6α, C-3β, and C-1β, whereas CYP3A4 favors the oxidation at C-5β and C-6β compared with each other. Correlation between DCA oxidation and testosterone 6β-hydroxylation in 14 adult single-donor HLMs provided proof-of-concept evidence that DCA 19-hydroxylation is an in vitro marker reaction for CYP3A7 activity, whereas oxidation at other sites represents mixed indicators for CYP3A4 and CYP3A7 activities. Deactivation caused by DCA-induced cytochrome P450-cytochrome P420 conversion, as shown by the spectral titrations of isolated CYP3A proteins, was observed when DCA levels were near or higher than the critical micelle concentration (about 1500 μM). Unlike CYP3A4, CYP3A7 showed abnormally elevated activities at 500 and 750 μM, which might be associated with an altered affinity for DCA multimers. The disclosed kinetic and functional roles of CYP3A isoforms in disposing of the gut bacteria-derived DCA may help in understanding the structural and functional mechanisms of CYP3A.

Spectroscopic Investigation of the Interaction of the Anticancer Drug Mitoxantrone with Sodium Taurodeoxycholate (NaTDC) and Sodium Taurocholate (NaTC) Bile Salts

The focus of the present work was to investigate the interaction of the anticancer drug mitoxantrone with two bile salts, sodium taurodeoxycholate (NaTDC) and sodium taurocholate (NaTC). Ultraviolet-visible (UV-Vis) absorption and electron paramagnetic resonance (EPR) spectroscopy were used to quantify the interaction and to obtain information on the location of mitoxantrone in bile salt micelles. The presence of submicellar concentrations of both bile salts induces mitoxantrone aggregation and the extent of drug aggregation in NaTDC is higher than in NaTC. For micellar bile salts concentrations, mitoxantrone monomers are entrapped in the micellar core. Binding constants, micelle/water partition coefficients and the corresponding thermodynamic parameters for binding and partitioning processes were estimated using the changes in monomer absorbance in the presence of bile salts. Binding interaction of mitoxantrone is stronger for NaTDC than NaTC micelles, whereas partitioning efficiency is higher for NaTC micelles for all investigated temperatures. Thermodynamic parameters indicate that both binding and partitioning processes are spontaneous and entropy controlled. The spectral behavior and thermodynamic parameters indicate distinct types of mitoxantrone interaction with NaTDC and NaTC micelles supported by the differences in nature and structure of bile salts micelles.

Beta-blockers and benzodiazepines location in SDS and bile salt micellar systems. An ESR study

The work here described aimed to find out the location of the different species of two families of pharmaceutical substances, namely two beta-blockers (atenolol and nadolol) and two benzodiazepines (midazolam and nitrazepam) in synthetic (sodium dodecyl sulphate, SDS) and natural (bile salts-sodium cholate and sodium deoxycholate) micellar aggregate solutions. Electronic spin resonance spectroscopy studies were carried out, at 25 degrees C and at an ionic strength of 0.10 M in NaCl, using 5-, 12- and 16-doxylstearic acid probes (AS). The immobilization degree of solubilized stearic acid spin probes was found to vary with the position of the nitroxide group in the sequence 5-doxylstearic acid>12-doxylstearic acid>16-doxylstearic acid for SDS and 12-doxylstearic acid>5-doxylstearic acid>16-doxylstearic acid for both bile salts investigated. Therefore, from the rotational correlational time values obtained, it can be inferred that the structure of bile salt micelles is markedly different from that of SDS micelles and the results suggest that the bile salt micelles studied have similar structure independently of differences in the molecular structure of the respective bile salts. Drug location studies were performed at pH 4.0 (SDS solutions) or 7.0 (bile salt solutions) and 10.8 in order to study the effect of the drug ionisation on its relative position on micelles. The results have shown that drug location is controlled by the (i) drug hydrophilicity and acid/base properties, with the more soluble compound in water (atenolol) exhibiting smaller variation of rotational correlational time (in SDS and bile salts solutions), and with both beta-blockers exhibiting smaller deviations in the protonated forms and (ii) the bile salt monomers, with the dihydroxylic bile salt (deoxycholate) producing larger differences. The work described herein allow us to conclude that the (protonated) beta-blockers are probably located on the surface of the detergent micelles, and linked to them by means of essentially electrostatic forces, while the (neutral) benzodiazepines are probably located deeper in the interior of the micelles.

Micelle formation of bile salts and zwitterionic derivative as studied by two-dimensional NMR spectroscopy

The self-association of sodium taurodeoxycholate (NaTDC) and a zwitterionic derivative of cholic acid (CHAPS) in deuterium oxide was investigated by one- and two-dimensional nuclear magnetic resonance spectroscopy (NMR) spectroscopy. Analysis of the concentration dependence of the chemical shifts of several protons suggested that NaTDC and CHAPS form nonamers and heptamers, respectively, as well as dimer. The equilibrium constants of dimerization and the micellar aggregation numbers are close to the literature values. From the intensities of intermolecular cross-peaks in the nuclear Overhauser effect spectroscopy (NOESY) and rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectra of NaTDC and CHAPS micellar solutions, partial structures of their micelles were estimated. The CHAPS micelle consists mainly of the back-to-back association, similarly to taurocholate (NaTC). However, the NaTDC micelle consists of the back-to-face association, because the face of NaTDC is rather hydrophobic. Furthermore, the back of bile molecules forms a convex plane and the face forms a concave plane. The back-to-face structure of NaTDC will be stabilized by a close contact between these planes. The chemical shift changes of several protons of CHAPS and NaTC in the micellar state are close to each other, but are different from those of NaTDC. This finding is consistent with the difference in their micellar structures.