Human Intestinal Raf Kinase Inhibitor Protein (RKIP) Catalyzes Prasugrel as a Bioactivation Hydrolase

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Vicagrel is hydrolyzed by Raf kinase inhibitor protein in human intestine

As an analog of clopidogrel and prasugrel, vicagrel is completely hydrolyzed to intermediate thiolactone metabolite 2-oxo-clopidogrel (also the precursor of active thiol metabolite H4) in human intestine, predominantly by AADAC and CES2; however, other unknown vicagrel hydrolases remain to be identified. In this study, recombinant human Raf kinase inhibitor protein (rhRKIP) and pooled human intestinal S9 (HIS9) fractions and microsome (HIM) preparations were used as the different enzyme sources; prasugrel as a probe drug for RKIP (a positive control), vicagrel as a substrate drug of interest, and the rate of the formation of thiolactone metabolites 2-oxo-clopidogrel and R95913 as metrics of hydrolase activity examined, respectively. In addition, an IC₅₀ value of inhibition of rhRKIP-catalyzed vicagrel hydrolysis by locostatin was measured, and five classical esterase inhibitors with distinct esterase selectivity were used to dissect the involvement of multiple hydrolases in vicagrel hydrolysis. The results showed that rhRKIP hydrolyzed vicagrel in vitro, with the values of K_m , V_max , and CL_int measured as 20.04 ± 1.99 μM, 434.60 ± 12.46 nM/min/mg protein, and 21.69 ± 0.28 ml/min/mg protein, respectively, and that an IC₅₀ value of locostatin was estimated as 1.24 ± 0.04 mM for rhRKIP. In addition to locostatin, eserine and vinblastine strongly suppressed vicagrel hydrolysis in HIM. It is concluded that RKIP can catalyze the hydrolysis of vicagrel in the human intestine, and that vicagrel can be hydrolyzed by multiple hydrolases, such as RKIP, AADAC, and CES2, concomitantly.

Fluorine impairs carboxylesterase 1-mediated hydrolysis of T-2 toxin and increases its chondrocyte toxicity

Background

T-2 toxin is recognized as one of the high-risk environmental factors for etiology and pathogenesis of Kashin-Beck disease (KBD). Previous evidence indicates decreased serum fluorine level in KBD patients. However, whether fluoride could regulate carboxylesterase 1 (CES1)-mediated T-2 toxin hydrolysis and alter its chondrocyte toxicity remains largely unknown.

Methods

In this study, in vitro hydrolytic kinetics were explored using recombinant human CES1. HPLC-MS/MS was used to quantitative determination of hydrolytic metabolites of T-2 toxin. HepG2 cells were treated with different concentration of sodium fluoride (NaF). qRT-PCR and western blot analysis were used to compare the mRNA and protein expression levels of CES1. C28/I2 cells were treated with T-2 toxin, HT-2 toxin, and neosolaniol (NEO), and then cell viability was determined by MTT assay, cell apoptosis was determined by Annexin V-FITC/PI, Hoechst 33258 staining, and cleaved caspase-3, and cell cycle was monitored by flow cytometry assay, CKD4 and CDK6.

Results

We identified that recombinant human CES1 was involved in T-2 toxin hydrolysis to generate HT-2 toxin, but not NEO, and NaF repressed the formation of HT-2 toxin. Both mRNA and protein expression of CES1 were significantly down-regulated in a dose-dependent manner after NaF treatment in HepG2 cells. Moreover, we evaluated the chondrocyte toxicity of T-2 toxin and its hydrolytic metabolites. Results showed that T-2 toxin induced strongest cell apoptosis, followed by HT-2 toxin and NEO. The decreased the proportion of cells in G0/G1 phase was observed with the descending order of T-2 toxin, HT-2 toxin, and NEO.

Conclusions

This study reveals that CES1 is responsible for the hydrolysis of T-2 toxin, and that fluoride impairs CES1-mediated T-2 toxin detoxification to increase its chondrocyte toxicity. This study provides novel insight into understanding the relationship between fluoride and T-2 toxin in the etiology of KBD.

Metabolic Activation of Militarine In Vitro and In Vivo

Bletilla striata is consumed as food and herbal medicine. Militarine (MLT) is a major ingredient in B. striata. Previous studies demonstrated that MLT showed teratogenic toxicity to zebrafish embryos. The present study aimed to identify reactive metabolites possibly involved in the cytotoxicity of MLT and determine the metabolic pathways involved. MLT was found to be hydrolyzed to p-hydroxybenzyl alcohol (HBA) by β-glucosidase and esterases. The resulting HBA further underwent spontaneous dehydration to form quinone methide. HBA was also metabolized to the corresponding sulfate, followed by departure of the sulfate to generate a quinone methide. The resultant quinone methide reacted with hepatic glutathione (GSH) and protein to form the corresponding GSH conjugate and protein adduction. Additionally, inhibition of sulfotransferases (SULTs) attenuated the susceptibility of hepatocytes to the toxicity of MLT. This study provides that the hydrolytic enzymes β-glucosidase, esterases, and SULTs participate in the metabolic activation of MLT.