Characterization of the Binding of Drugs to Human Intestinal Fatty Acid Binding Protein (IFABP): Potential Role of IFABP as an Alternative to Albumin for in Vitro-in Vivo Extrapolation of Drug Kinetic Parameters

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

“…Inclusion of BSA in HLM incubations increased CL int, u, UGT up to 7-fold, which is within the range of previously reported data (Kilford et al, 2009;Rowland et al, 2009;Manevski et al, 2011). In addition, the presence of BSA in the incubations led to increases in HKM and HIM CL int, u, UGT values, supporting reports that linoleic and arachidonic acids (the most potent UGT inhibitors of FFAs) (Tsoutsikos et al, 2004) are abundant in all three tissues investigated (Soydan et al, 1996;Hoffmann et al, 2005;Rowland et al, 2007).…”

“…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 preliminary experiments, minimal depletion was observed for the acidic drugs when 2% BSA was used, and, therefore, CL int, UGT could not be determined. This is most likely because acids bind strongly to BSA (Rowland et al, 2009), and the remaining free drug for depletion is minimal. Nonspecific binding of gemfibrozil and diclofenac at BSA concentrations ranging from 0.5 to 2% were determined (data not shown); nonspecific binding was reduced at lower BSA concentrations, but the resultant fraction unbound from protein in the incubation (f u, inc ) values remained Ͻ0.1.…”

“…Nonspecific binding of gemfibrozil and diclofenac at BSA concentrations ranging from 0.5 to 2% were determined (data not shown); nonspecific binding was reduced at lower BSA concentrations, but the resultant fraction unbound from protein in the incubation (f u, inc ) values remained Ͻ0.1. Previous research showed a plateau in the increase of CL int, u, UGT results at 1% BSA (Rowland et al, 2007(Rowland et al, , 2009. Therefore, to allow quantifiable depletion and adequate sequestration of free fatty acids, a concentration of 1% BSA was used for the acidic drugs (diclofenac, gemfibrozil, MPA, and telmisartan), and 2% BSA was found to be suitable for bases/neutral drugs (ezetimibe, naloxone, and propofol).…”

“…Bovine serum albumin (BSA) has been used to sequester FFAs in microsomal assays and prevent inhibition of glucuronidation (Rowland et al, 2007(Rowland et al, , 2008. Addition of BSA has resulted in up to 16-fold increases in glucuronidation intrinsic clearance (CL int, UGT ) obtained either by depletion or metabolite formation in human liver microsomes (HLM), resulting in improved prediction accuracy when in vitro-in vivo extrapolation (IVIVE) of such data was performed (Rowland et al, 2008(Rowland et al, , 2009Kilford et al, 2009;Manevski et al, 2011). Analogous to liver, arachidonic and linoleic acids represent two of the most abundant FFAs in renal and intestinal tissue (Soydan et al, 1996;Hoffmann et al, 2005;Rowland et al, 2007).…”