Substrate Report for: VPA-glucuronide

Serum concentrations of valproic acid (VPA) are markedly decreased by coadministration of carbapenem antibiotics (CBPMs). Although inhibition of deconjugation of VPA-glucuronide (VPA-G) to VPA by CBPMs has been proposed as one of the mechanisms to account for this drug-drug interaction, little information is available on the mode of inhibition. In the present study, we characterized the enzyme involved in the deconjugation of VPA-G by using human and rat liver cytosol. It is suggested that 1) deconjugation activity inhibited by CBPMs may be selective for VPA-G, 2) deconjugation of VPA-G may be mediated by enzyme(s) other than beta-glucuronidase, and 3) the irreversible inactivation may be responsible for the inhibition of deconjugation of VPA-G by CBPMs. Finally, the kinetic parameters for inactivation (K'(app) and k(inact)) were determined for four CBPMs of diverse structure from in vitro experiments. Based on the results of simulation analyses with these parameters and the degradation rate constant of the putative VPA-G deconjugation enzyme obtained from experiments using rats, it is probable that the deconjugation enzyme for VPA-G in the liver is rapidly and mostly inactivated by these CBPMs under clinical situations.

Plasma levels of valproic acid (VPA) are decreased by concomitant use with carbapenem antibiotics, such as panipenem (PAPM). One of the plausible mechanisms of this interaction is the inhibition of VPA glucuronide (VPA-G) hydrolysis by carbapenems in the liver. To elucidate this interaction mechanism, we purified VPA-G hydrolase from human liver cytosol, in which the hydrolytic activity was mainly located. After chromatographic purification, the VPA-G hydrolase was identified as acylpeptide hydrolase (APEH). APEH-depleted cytosol, prepared by an immunodepletion method, completely lacked the hydrolytic activity. These results demonstrate that APEH is a single enzyme involved in PAPM-sensitive VPA-G hydrolysis in cytosol. In addition, the hydrolytic activity of recombinant human APEH was inhibited by PAPM and the inhibition profile by typical esterase inhibitors (diisopropyl fluorophosphate, 5,5'-dithiobis(2-nitrobenzoic acid), p-chloromercuribenzoic acid, and d-saccharic acid 1,4-lactone) was similar to that of human liver cytosol. Cytosolic VPA-G hydrolase activity was slightly inhibited by cholinesterase and carboxylesterase inhibitors. beta-Glucuronidase activity remained in APEH-depleted cytosol, whereas VPA-G hydrolase activity was completely abolished. Thus, either cholinesterase, carboxylesterase, or beta-glucuronidase in cytosol would not be involved in VPA-G hydrolysis. Taken together, APEH plays a major role in the PAPM-sensitive VPA-G hydrolysis in the liver. These findings suggest that APEH could be a key enzyme for the drug interaction of VPA with carbapenems via VPA-G hydrolysis.

The serum concentration of valproic acid (VPA) in epilepsy patients decreased in the administration of carbapenem antibiotics (CP), such as meropenem, panipenem, biapenem or imipenem, to a sub-therapeutic level. The liver is the key organ for the decrease of VPA concentration by CP, because it has been reported that no decrease of the VPA level by CP was found in hepatectomized rats. This effect was also shown with monkey and rat liver slices. In this report, we show the results of in vitro inhibition of VPA-glucuronidase in human liver microsomes and cytosol by CP. We found the highest metabolic activity of VPA-glucuronide in human liver cytosol. The level in liver cytosol was 149 pmol/min/mg protein. The level in human liver microsomes (HLM) was one-fifth of that in cytosol and the level in serum was negligible. We found that this hydrolysis depends on VPA-glucuronidase in cytosol, because digestion was inhibited by D-saccharic acid 1,4-lactonemonohydrate of a specific inhibitor of beta-glucuronidase, but not by phenylmethylsulfonylfluoride of an esterase inhibitor. We also found the inhibition of VPA-glucuronidase in cytosol by CP, and the maximum inhibition was found with panipenem (IC(50) = 3 microM). We also found inhibition of VPA-glucuronidase in HLM by meropenem. These results showed that the inhibition in liver slices depended on the inhibition of VPA-glucuronidase by CP. We considered that the inhibition of VPA-glucuronidase by CP in cytosol is a key factor to decrease the plasma VPA level.

Serum concentrations of valproic acid (VPA) are markedly decreased by coadministration of carbapenem antibiotics (CBPMs). Although inhibition of deconjugation of VPA-glucuronide (VPA-G) to VPA by CBPMs has been proposed as one of the mechanisms to account for this drug-drug interaction, little information is available on the mode of inhibition. In the present study, we characterized the enzyme involved in the deconjugation of VPA-G by using human and rat liver cytosol. It is suggested that 1) deconjugation activity inhibited by CBPMs may be selective for VPA-G, 2) deconjugation of VPA-G may be mediated by enzyme(s) other than beta-glucuronidase, and 3) the irreversible inactivation may be responsible for the inhibition of deconjugation of VPA-G by CBPMs. Finally, the kinetic parameters for inactivation (K'(app) and k(inact)) were determined for four CBPMs of diverse structure from in vitro experiments. Based on the results of simulation analyses with these parameters and the degradation rate constant of the putative VPA-G deconjugation enzyme obtained from experiments using rats, it is probable that the deconjugation enzyme for VPA-G in the liver is rapidly and mostly inactivated by these CBPMs under clinical situations.

Plasma levels of valproic acid (VPA) are decreased by concomitant use with carbapenem antibiotics, such as panipenem (PAPM). One of the plausible mechanisms of this interaction is the inhibition of VPA glucuronide (VPA-G) hydrolysis by carbapenems in the liver. To elucidate this interaction mechanism, we purified VPA-G hydrolase from human liver cytosol, in which the hydrolytic activity was mainly located. After chromatographic purification, the VPA-G hydrolase was identified as acylpeptide hydrolase (APEH). APEH-depleted cytosol, prepared by an immunodepletion method, completely lacked the hydrolytic activity. These results demonstrate that APEH is a single enzyme involved in PAPM-sensitive VPA-G hydrolysis in cytosol. In addition, the hydrolytic activity of recombinant human APEH was inhibited by PAPM and the inhibition profile by typical esterase inhibitors (diisopropyl fluorophosphate, 5,5'-dithiobis(2-nitrobenzoic acid), p-chloromercuribenzoic acid, and d-saccharic acid 1,4-lactone) was similar to that of human liver cytosol. Cytosolic VPA-G hydrolase activity was slightly inhibited by cholinesterase and carboxylesterase inhibitors. beta-Glucuronidase activity remained in APEH-depleted cytosol, whereas VPA-G hydrolase activity was completely abolished. Thus, either cholinesterase, carboxylesterase, or beta-glucuronidase in cytosol would not be involved in VPA-G hydrolysis. Taken together, APEH plays a major role in the PAPM-sensitive VPA-G hydrolysis in the liver. These findings suggest that APEH could be a key enzyme for the drug interaction of VPA with carbapenems via VPA-G hydrolysis.

The serum concentration of valproic acid (VPA) in epilepsy patients decreased in the administration of carbapenem antibiotics (CP), such as meropenem, panipenem, biapenem or imipenem, to a sub-therapeutic level. The liver is the key organ for the decrease of VPA concentration by CP, because it has been reported that no decrease of the VPA level by CP was found in hepatectomized rats. This effect was also shown with monkey and rat liver slices. In this report, we show the results of in vitro inhibition of VPA-glucuronidase in human liver microsomes and cytosol by CP. We found the highest metabolic activity of VPA-glucuronide in human liver cytosol. The level in liver cytosol was 149 pmol/min/mg protein. The level in human liver microsomes (HLM) was one-fifth of that in cytosol and the level in serum was negligible. We found that this hydrolysis depends on VPA-glucuronidase in cytosol, because digestion was inhibited by D-saccharic acid 1,4-lactonemonohydrate of a specific inhibitor of beta-glucuronidase, but not by phenylmethylsulfonylfluoride of an esterase inhibitor. We also found the inhibition of VPA-glucuronidase in cytosol by CP, and the maximum inhibition was found with panipenem (IC(50) = 3 microM). We also found inhibition of VPA-glucuronidase in HLM by meropenem. These results showed that the inhibition in liver slices depended on the inhibition of VPA-glucuronidase by CP. We considered that the inhibition of VPA-glucuronidase by CP in cytosol is a key factor to decrease the plasma VPA level.

The serum concentration of valproic acid (VPA) in epilepsy patients decreased by the administration of carbapenem antibiotics, such as meropenem, panipenem or imipenem, to a sub-therapeutic level. This review summarized several case reports of this interaction between VPA (1-4 g dose) and carbapenem antibiotics to elucidate the possible mechanisms decreasing VPA concentration by carbapenem antibiotics. Studies to explain the decrease were carried out using rats by the following sites: absorption of VPA in the intestine, glucuronidation in the liver, disposition in blood and renal excretion. In the intestinal absorption site, there are two possible mechanisms: inhibition of the intestinal transporter for VPA absorption by carbapenem antibiotics, and the decrease of beta-glucuronidase supplied from enteric bacteria, which were killed by antibiotics. This is consistent with a view that the decrease of VPA originated from VPA-Glu, relating to entero-hepatic circulation. The second key site is in the liver, because of no decreased in VPA level by carbapenem antibiotics in hepatectomized rats. There are three possible mechanisms in the liver to explain the decreased phenomenon: first, decrease of the UDPGA level by carbapenem antibiotics. UDPGA is a co-factor for UDP-glucuronosyltransferase (UGT)-mediated glucuronidation of VPA. Second, the direct activation of UGT by carbapenem antibiotics. This activation was observed after pre-incubation of human liver microsomes with carbapenem antibiotics. Third, the inhibition of beta-glucuronidase in liver by carbapenem antibiotics and the decreased VPA amount liberated from VPA-Glu. The third site is the distribution of VPA in blood (erythrocytes and plasma). Plasma VPA distributed to erythrocytes by the inhibition of transporters (Mrp4), which efflux VPA from erythrocytes to plasma, by carbapenem antibiotics. The increase of renal excretion of VPA as VPA-Glu depends on the increase of VPA-Glu level by UGT. One or a combination of some factors in these mechanisms might relate to the carbapenem-mediated decrease of the plasma VPA level.