Stereoselective binding properties of naproxen glucuronide diastereomers to proteins

Abstract

The stability of naproxen glucuronide (NAP-G) diastereomers was investigated in buffer, 0.3% and 3% human serum albumin (HSA) solutions, and human plasma. R-NAP-G was found to be less stable in phosphate buffer than its S-diastereomer, whereas incubation media containing protein in general increased the degradation rate of NAP-G but also caused a change of the stereoselective stability where the R-NAP-G was more stable than S-NAP-G. Reversible binding of NAP-Gs to HSA (0.3%) was investigated and compared with the corresponding properties of naproxen (NAP) enantiomers. NAP-G diastereomers exhibited a considerable and stereoselective affinity to HSA, although less than that observed for the NAP enantiomers. In vitro irreversible binding of NAP-Gs to HSA, human and rat plasma proteins was also investigated. Irreversible binding was higher for R-NAP-G (50 microM) than for S-NAP-G (50 microM) in all incubation media. This stereoselective difference was observed with HSA containing medium as well as in rat and human plasma. Incubation with unconjugated NAP did not lead to irreversible binding. Preincubation of HSA with acetylsalicylic acid (approximately 11 mM) and glucuronic acid (50 mM) decreased the extent of irreversible binding suggesting involvement of lysine residues for covalent binding. Preincubation with S-NAP also decreased the irreversible binding yield.

Extrapolation of Diclofenac Clearance from in Vitro Microsomal Metabolism Data: Role of Acyl Glucuronidation and Sequential Oxidative Metabolism of the Acyl Glucuronide

“…First, a significant amount of diclofenac AG may be oxidized to 4Ј-hydroxy diclofenac AG via the so-called "metabolite firstpass effect" before its egress from the hepatocytes into the bloodstream (Pang and Gillette, 1979). Second, acyl glucuronides, in general, exhibit a significantly reduced degree of plasma protein binding relative to the parent drug because of their greater hydrophilicity (Ojingwa et al, 1994;Bischer et al, 1995). Third, it is possible that because of rapid metabolism of diclofenac via this pathway, high local concentrations of diclofenac AG are achieved in the liver, which may saturate any binding to blood components.…”

Practical Aspects of the Ligand-Binding and Enzymatic Properties of Human Serum Albumin.

“…81) Among the drugs that become glucuronidated and interact covalently with HSA are furosemide, 77) salicylic acid, 82) gemfibrozil, 83) clofibric acid, 84) fenofibric acid, 84) and NSAIDs like tolmetin, 77,85) benoxaprofen, 80) zomepirac, 77) beclobric acid, 77) ibuprofen, 86) ibufenac, 86) suprofen, 81) ketoprofen, 87) and diflunisal. 88) Stereoselectivity was observed for, e.g., carprofen, 77) fenoprofen, 77) and naproxen 89) ; in all cases the R-forms exhibited the highest covalent binding. Photoactivated naproxen and frusemide, as well as photoactivated frusemide glucuronide, also bind covalently to HSA.…”

Inhibition of Methotrexate Uptake <i>via</i> Organic Anion Transporters OAT1 and OAT3 by Glucuronides of Nonsteroidal Anti-inflammatory Drugs

“…Moreover, our previous studies suggested that the ratio of reversible binding to human serum albumin (HSA) of NSAIDs-Glu, such as naproxen glucuronide and fenoprofen glucuronide, tends to be weaker than that of their parent NSAIDs. 37,38) Assuming that diclofenac glucuronide has a similar tendency, it is unsurprising that inhibition of OAT3-mediated MTX uptake by diclof- -and S-naproxen (g, h) at various concentrations at 37°C. Results are the mean of duplicate experiments.…”