The glucuronidation of mycophenolic acid by human liver, kidney and jejunum microsomes

Abstract

Aims To estimate the relative contribution of liver, kidney and jejunum to MPA elimination via glucuronidation from in vitro kinetic data. Methods The kinetics of MPA glucuronidation by human liver, kidney and jejunum microsomes were characterized. Mycophenolic acid glucuronide (MPAG) concentrations in microsomal incubations were determined using a speci®c h.p.l.c. procedure. Non-speci®c microsomal binding of MPA was excluded using an equilibrium dialysis approach. Results Microsomes from all three tissues catalysed the conversion of MPA to MPAG. Mean microsomal intrinsic clearances for MPAG formation by liver, kidney and jejunum microsomes were 46.6, 73.5 and 24.5 ml (min mg) x1 , respectively. When extrapolated to the whole organ, however, hepatic intrinsic clearance was 21-and 38-fold higher than the respective intrinsic clearances for kidney and small intestine. Conclusions The data suggest that the liver is the organ primarily responsible for the systemic clearance of MPA, with little contribution from the kidney, and that the small intestine would be expected to contribute to ®rst-pass extraction to a minor extent only.

Characterization of In Vitro Glucuronidation Clearance of a Range of Drugs in Human Kidney Microsomes: Comparison with Liver and Intestinal Glucuronidation and Impact of Albumin

“…Although recovery of propofol was low (Ͻ30%), f u, inc values determined both in the presence and absence of BSA were comparable to values reported by Rowland et al (2008), and so the experimental data have been used. The f u, inc values for the other drugs investigated (both in the presence and absence of BSA) were comparable to values reported in the literature (where available) (Bowalgaha and Miners, 2001;Al-Jahdari et al, 2006;Gertz et al, 2008;Cubitt et al, 2009;Kilford et al, 2009). From preliminary experiments, the volume shift between the donor and acceptor side of the membrane was generally less than 5%, and therefore correction for volume shift had minimal impact on the experimental f u, inc .…”

“…For non-BSA data, the kidney/liver scaled CL int, u, UGT ratios were generally lower than those calculated from previously published data, with the exception of MPA (Bowalgaha and Miners, 2001;Shipkova et al, 2001;Bernard and Guillemette, 2004). Intestine/liver scaled CL int, u, UGT ratios for diclofenac, gemfibrozil, and naloxone were also lower than those calculated from data in Cubitt et al (2009), with the exception of propofol (Raoof et al, 1996).…”

“…At the low substrate concentrations used herein, nonspecific binding is expected to be below the saturation limit and therefore independent of substrate concentration. This assumption is supported by previous data showing that nonspecific binding of propofol (in the presence and absence of BSA) and MPA (in the absence of BSA) is independent of substrate concentration when determined over a range of concentrations exceeding those used in the current study (Bowalgaha and Miners, 2001;Rowland et al, 2008Rowland et al, , 2009. Dialysis membranes (12-14 kDa molecular mass cutoff) were purchased from HTDialysis, LLC (Gales Ferry, CT).…”

“…In vitro characterization of renal glucuronidation and its importance relative to liver and intestinal glucuronidation has been relatively limited (Raoof et al, 1996;Bowalgaha and Miners, 2001;Soars et al, 2001).…”

Inhibition of Intestinal and Hepatic Glucuronidation of Mycophenolic Acid by Ginkgo biloba Extract and Flavonoids

“…In this study, microsomal intrinsic clearance (V max /K m ) for MPAG formation was 4-fold higher by HLM compared with HIM (25.12 versus 6.08 l/ min/mg protein). This result is in accordance with previously reported values (Bowalgaha and Miners, 2001;Shipkova et al, 2001;Picard et al, 2005). In the intestine, UGT1A7, 1A8, 1A9, and 1A10 conjugate MPA to MPAG with different affinities, whereas in the liver, MPAG is selectively formed by UGT1A9 (Picard et al, 2005).…”