Computational study of the competitive binding of valproic acid glucuronide and carbapenem antibiotics to acylpeptide hydrolase

Effect of a Declined Plasma Concentration of Valproic Acid Induced by Meropenem on the Antiepileptic Efficacy of Valproic Acid

OBJECTIVE

This study aimed to indicate whether a declined plasma concentration of valproic acid (VPA) induced by co-administration of meropenem (MEPM) could affect the antiepileptic efficacy of VPA.

METHODS

We retrospectively reviewed data of hospitalized patients who were diagnosed with status epilepticus or epilepsy between 2010 and 2019. Patients co-administered VPA and MEPM during hospitalization were screened and assigned to the exposure group, while those co-administerd VPA and other broad-spectrum antibiotics were allocated to the control group.

RESULTS

The exposure group and control group included 50 and 11 patients, respectively. With a similar dosage of VPA, the plasma concentration of VPA significantly decreased during co-administration (24.6 ± 4.3 μg/mL) compared with that before co-administration (88.8 ± 13.6 μg/mL, p < 0.0001), and it was partly recovered with the termination of co-administration (39.8 ± 13.2 μg/mL, p = 0.163) in the exposure group. The inverse probability of treatment weighting estimated the treatment efficacy via changes in seizure frequency, seizure duration, and concomitant use of antiepileptic drugs, which were not significantly different between the exposure and control groups. In the exposure group, there was no significant differences in seizure frequency between the periods of before-during and before-after (p = 0.074 and 0.153, respectively). Seizure duration during VPA-MEPM co-administration was not significantly different from that before co-administration (p = 0.291).

CONCLUSIONS

In this study, the reduced plasma concentration of VPA induced by the co-administration of MEPM did not affect the antiepileptic efficacy of VPA. This conclusion should be interpreted with caution, and more research is warranted.

TRIAL REGISTRATION

Chinese Clinical Trial Registry: ChiCTR2000034567. Registered on 10 July 2020.

A carbapenem antibiotic inhibiting a mammalian serine protease: structure of the acylaminoacyl peptidase-meropenem complex

The structure of porcine AAP (pAAP) in a covalently bound complex with meropenem was determined by cryo-EM to 2.1 Å resolution, showing the mammalian serine-protease inhibited by a carbapenem antibiotic. AAP is a modulator of the ubiquitin-proteasome degradation system and the site of a drug-drug interaction between the widely used antipsychotic, valproate and carbapenems. The active form of pAAP - a toroidal tetramer - binds four meropenem molecules covalently linked to the catalytic Ser587 of the serine-protease triad, in an acyl-enzyme state. AAP is hindered from fully processing the antibiotic by the displacement and protonation of His707 of the catalytic triad. We show that AAP is made susceptible to the association by its unusually sheltered active pockets and flexible catalytic triads, while the carbapenems possess sufficiently small substituents on their β-lactam rings to fit into the shallow substrate-specificity pocket of the enzyme.

Acylpeptide hydrolase (APEH) sequence variants with potential impact on the metabolism of the antiepileptic drug valproic acid

Acylpeptide hydrolase (APEH) is a serine protease involved in the recycling of amino acids from acylated peptides. Beyond that, APEH participates in the metabolism of the antiepileptic drug valproic acid (2-propylpentanoic acid; VPA) by catalyzing the hydrolysis of the VPA metabolite valproylglucuronide (VPA-G) to its aglycon. It has been shown that the inhibition of APEH by carbapenem antibiotics decreases therapeutic VPA levels by enhancing the urinary elimination of VPA in form of VPA-G. As various sequence variants of the APEH gene (which encodes the APEH protein) are listed in databases, but have not been functionally characterized yet, we assume, that some APEH sequence variants may have pharmacogenetic relevance due to their impaired cleavage of VPA-G. APEH sequence variants predicted to affect enzyme activity were selected from databases, and overexpressed in HEK293 cells (stable transfection), a cell line derived from human embryonic kidney cells. APEH activity in cell homogenates was determined spectrophotometrically by monitoring the hydrolysis of the synthetic substrate N-acetyl-L-alanine-nitroanilide. APEH enzyme activity and protein expression of the sequence variants were compared with those of APEH with the reference sequence. Three out of five tested missense sequence variants resulted in a considerable decrease of enzyme activity assessed with the standard substrate N-acetyl-L-alanine-nitroanilide, suggesting an effect on pharmacokinetics of VPA. Our work underlines the need to consider the APEH genotype in investigations of altered VPA metabolism.