M Wang

Publications (3)8.79 Total impact

• Article: Dipeptidyl peptidase IV is a target for covalent adduct formation with the acyl glucuronide metabolite of the anti-inflammatory drug zomepirac.

  M Wang, M D Gorrell, G W McGaughan, R G Dickinson
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  ABSTRACT: The nonsteroidal anti-inflammatory drug zomepirac (ZP) is metabolised to a chemically reactive acyl glucuronide conjugate (ZAG) which can form covalent adducts with proteins. In vivo, such adducts could initiate immune or toxic responses. In rats given ZP, the major band detected in liver homogenates by immunoblotting with a polyclonal ZP antiserum was at 110 kDa. This adduct was identified as ZP-modified dipeptidyl peptidase IV (DPP IV) by immunoblotting using the polyclonal ZP antiserum and monoclonal DPP IV antibodies OX-61 and 236.3. In vitro, ZAG, but not ZP itself, covalently modified recombinant human and rat DPP IV. Both monoclonal antibodies recognized DPP IV in livers from ZP- and vehicle-dosed rats. Confirmation that the 110 kDa bands which were immunoreactive with the ZP and DPP IV antibodies represented the same molecule was obtained from a rat liver extract reciprocally immunodepleted of antigens reactive with these two antibodies. Furthermore, immunoprecipitations with OX-61 antibody followed by immunolotting with ZP antiserum, and the reciprocal experiment, showed that both these antibodies recognised the same 110 kDa molecule in extracts of ZP-dosed rat liver. The results verify that DPP IV is one of the protein targets for covalent modification during hepatic transport and biliary excretion of ZAG in rats.
  Life Sciences 02/2001; 68(7):785-97. · 2.53 Impact Factor
• Article: Bile duct ligation promotes covalent drug-protein adduct formation in plasma but not in liver of rats given zomepirac.

  M Wang, R G Dickinson
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  ABSTRACT: Acyl glucuronides are reactive electrophilic metabolites of carboxylate drugs, capable of undergoing hydrolysis, rearrangement and covalent binding reactions with proteins in vivo. Such covalent drug-protein adducts may be prerequisites for certain idiosyncratic immune and toxic responses in susceptible individuals. The present study examined the effect of experimental cholestasis on the extent and pattern of formation of protein adducts in plasma and liver of rats given the non-steroidal antiinflammatory drug (NSAID) zomepirac (ZP). Groups of intact, bile-exteriorized and bile duct-ligated rats given a 50 mg/kg i.v. dose of ZP were studied for 24 hr. In intact rats, only 1.4% of the dose was recovered as the sum of ZP, ZP acyl glucuronide (ZAG) and its rearrangement isomers (iso-ZAG) in urine in 24 hr. In bile-exteriorized animals, 0.5% of the dose was recovered in urine in 24 hr, with 31.6% of the dose being recovered in bile (2.7% as ZP, 20.0% as ZAG and 8.9% as iso-ZAG). In the bile duct-ligated group, recovery of dose in 24 hr urine totalled 17.5% (1.7% as ZP, 6.7% as ZAG and 9.1% as iso-ZAG). ZAG and iso-ZAG were measurable in plasma only in the bile duct-ligated group, and covalent binding of ZP to plasma proteins was much higher (5-6 fold) than in intact or bile-exteriorized rats. Total adduct concentrations in liver were not significantly different among the three groups. Immunoblotting using a polyclonal ZP antiserum confirmed that serum albumin was a major target protein in plasma. The major ZP-modified bands in the livers of intact and bile-exteriorized rats were at about 110, 140 and 200 kDa. However, the bands at 110 and 140 kDa were much lower in the livers of bile duct-ligated rats. The results show that about 30% of ZP doses are normally excreted as ZAG and its isomers in bile, with only minor excretion in urine. Bile duct ligation shunts the glucuronide into blood (and urine), strongly promoting adduct formation with plasma proteins, and alters the pattern but not the total quantity of drug-modified proteins formed in the liver.
  Life Sciences 01/2001; 68(5):525-37. · 2.53 Impact Factor
• Article: Disposition and covalent binding of diflunisal and diflunisal acyl glucuronide in the isolated perfused rat liver.

  M Wang, R G Dickinson
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  ABSTRACT: Acyl glucuronides are intrinsically reactive metabolites of carboxylate drugs, capable of undergoing hydrolysis, intramolecular rearrangement (isomerization via acyl migration), and intermolecular transacylation reactions. Transacylation with nucleophilic groups located on protein molecules leads to covalent drug-protein adducts. Protein adducts can also form from the rearrangement isomers via a glycation mechanism. In this study, the isolated perfused rat liver preparation was used to separately trace the dispositions of the nonsteroidal anti-inflammatory drug diflunisal (DF), its reactive acyl glucuronide metabolite (DAG), and a mixture of DAG rearrangement isomers (iso-DAG), each administered at 30-microg DF equivalents/ml perfusate (four recirculating perfusions each group). After administration of DF, the drug was eliminated in a log linear manner over 3 hr, with apparent elimination half-life (t1/2) of 2.6 +/- 0.4 hr. The sulfate conjugate (DS), excreted almost exclusively into perfusate, accounted for 14.2% of the dose, with the phenolic glucuronide (DPG) and DAG (11.1 and 7.9% of dose, respectively) excreted primarily in bile. Only a small portion (2.3%) of the dose was recovered as novel "diglucuronides" (D-2G, arising from phenolic glucuronidation of iso-DAG), excreted exclusively in bile. Covalent DF-protein adducts were found in both perfusate (0.98%) and liver (0. 14%). After administration of DAG, rapid hydrolysis occurred (initial DAG t1/2 17.3 +/- 4.2 min). At 3 hr, recoveries (in comparison to DF-dosed perfusions) were similar for DF (51.7%) and DAG (8.3%), significantly decreased for DS (10.6%) and DPG (6.4%), and significantly increased for iso-DAG (0.8%), D-2G (9.1%), and covalent adducts in perfusate (1.49%) and liver (0.30%). After administration of iso-DAG, elimination from perfusate was slower (t1/2 55 +/- 15 min), and hydrolysis to DF was modest by comparison with DAG-dosed perfusions. Recoveries as iso-DAG and D-2G in bile were greatly enhanced (8.2 and 36.4%, respectively). Adduct formation was higher in liver (0.76% of dose) but not in perfusate (1.03%). Immunoblots of liver homogenates revealed drug-modified proteins at ca. 110 and 120 kDa. The results show that (a) DAG undergoes avid systemic deconjugation-conjugation cycling and isomerization to iso-DAG; (b) iso-DAG is more resistant to hydrolysis, is readily taken up by hepatocytes and undergoes novel metabolism (phenolic glucuronidation); and (c) the glycation pathway (i.e. using iso-DAG as substrate) plays a major role in formation of covalent DF-protein adducts in liver.
  Drug Metabolism and Disposition 03/1998; 26(2):98-104. · 3.73 Impact Factor