Characterization of glutathione conjugates derived from reactive metabolites of bakuchiol

Bakuchiol, a natural constituent and its pharmacological benefits

Background and aims

Natural compounds extracted from medicinal plants have recently gained attention in therapeutics as they are considered to have lower Toxicity and higher tolerability relative to chemically synthesized compounds. Bakuchiol from Psoralea corylifolia L. is one such compound; it is a type of meroterpene derived from the leaves and seeds of Psoralea corylifolia plants. Natural sources of bakuchiol have been used in traditional Chinese and Indian medicine for centuries due to its preventive benefits against tumors and inflammation. It plays a strong potential role as an antioxidant with impressive abilities to remove Reactive Oxygen Species (ROS). This review has focused on bakuchiol's extraction, therapeutic applications, and pharmacological benefits.

Methods

A search strategy has been followed to retrieve the relevant newly published literature on the pharmacological benefits of bakuchiol. After an extensive study of the retrieved articles and maintaining the inclusion and exclusion criteria, 110 articles were finally selected for this review.

Results

Strong support of primary research on the protective effects via antitumorigenic, anti-inflammatory, antioxidative, antimicrobial, and antiviral activities are delineated.

Conclusions

From ancient to modern life, medicinal plants have always been drawing the attention of human beings to alleviate ailments for a healthy and balanced lifestyle. This review is a comprehensive approach to highlighting bona fide essential pharmacological benefits and mechanisms underlying their therapeutic applications.

Elucidation of the relationship between evodiamine-induced liver injury and CYP3A4-mediated metabolic activation by UPLC-MS/MS analysis

Evodiamine (EVD), which has been reported to cause liver damage, is the main constituent of Evodia rutaecarpa (Juss.) Benth and may be bioactivated into reactive metabolites mediated by cytochrome P450. However, the relationships between bioactivation and EVD-induced hepatotoxicity remain unknown. In this study, comprehensive hepatotoxicity evaluation was explored, which demonstrated that EVD caused hepatotoxicity in both time- and dose-dependent manners in mice. By application of UPLC-Q/TOF-MS/MS, two GSH conjugates (GM1 and GM2) derived from reactive metabolites of EVD were identified, in microsomal incubation systems exposed to EVD with glutathione (GSH) as trapping agents. CYP3A4 was proved to be the main metabolic enzyme. Correspondingly, the N-acetyl-L-cysteine conjugate derived from the degradation of GM2 was detected in the urine of mice after exposure to EVD. For the first time, the iminoquinone intermediate was found in EVD-pretreated rat bile by the high-resolution MS platform. Pretreatment with ketoconazole protected the animals from hepatotoxicity, decreased the protein expression of cleaved caspase-1 and -3, but increased the area under the serum-concentration-time curve of EVD in blood determined by UPLC-QQQ-MS/MS. Depletion of GSH by buthionine sulfoximine exacerbated EVD-induced hepatotoxicity. These results implicated that the CYP3A4-mediated metabolic activation was responsible for the observed hepatotoxicity induced by EVD.

In Vitro and In Vivo Metabolic Activation of Tolterodine Mediated by CYP3A

Tolterodine (TOL) is an antimuscarinic drug used for the treatment of patients with overactive bladder presenting urinary frequency, urgency, and urge incontinence. During the clinical use of TOL, adverse events such as liver injury took place. The present study aimed at the investigation of the metabolic activation of TOL possibly associated with its hepatotoxicity. One GSH conjugate, two NAC conjugates, and two cysteine conjugates were found in both mouse and human liver microsomal incubations supplemented with TOL, GSH/NAC/cysteine, and NADPH. The detected conjugates suggest the production of a quinone methide intermediate. The same GSH conjugate was also observed in mouse primary hepatocytes and in the bile of rats receiving TOL. One of the urinary NAC conjugates was observed in rats administered TOL. One of the cysteine conjugates was found in a digestion mixture containing hepatic proteins from animals administered TOL. The observed protein modification was dose-dependent. CYP3A primarily catalyzes the metabolic activation of TOL. Ketoconazole (KTC) pretreatment reduced the generation of the GSH conjugate in mouse liver and cultured primary hepatocytes after TOL treatment. In addition, KTC reduced the susceptibility of primary hepatocytes to TOL cytotoxicity. The quinone methide metabolite may be involved in TOL-induced hepatotoxicity and cytotoxicity.

Psoraleae Fructus Ethanol Extract Induced Hepatotoxicity via Impaired Lipid Metabolism Caused by Disruption of Fatty Acid β-Oxidation

Herb-induced liver injury (HILI) is gradually increasing, and Psoraleae Fructus (PF) has been reported to induce hepatotoxicity. However, its underlying toxicity mechanism has been only poorly revealed. In this paper, we attempted to explore the liver injury and mechanism caused by Psoraleae Fructus ethanol extract (PFE). First, we administered PFE to mice for 4 weeks and evaluated their serum liver function indices. H&E staining was performed to observe the pathological changes of the livers. Oil red O staining was used to visualize hepatic lipids. Serum-untargeted metabolomics and liver proteomics were used to explore the mechanism of PF hepatotoxicity, and transmission electron microscopy was determined to assess mitochondria and western blot to determine potential target proteins expression. The results showed that PFE caused abnormal liver biochemical indicators and liver tissue injury in mice, and there was substantial fat accumulation in liver tissue in this group. Furthermore, metabolomic analysis showed that PFE changed bile acid synthesis, lipid metabolism, etc., and eight metabolites, including linoleic acid, which could be used as potential biomarkers of PFE hepatotoxicity. Proteomic analysis revealed that differential proteins were clustered in the mitochondrial transmembrane transport, the long-chain fatty acid metabolic process and purine ribonucleotide metabolic process. Multiomics analysis showed that eight pathways were enriched in both metabolomics and proteomics, such as bile secretion, unsaturated fatty acid biosynthesis, and linoleic acid metabolism. The downregulation of SLC27A5, CPT1A, NDUFB5, and COX6A1 and upregulation of cytochrome C and ABCC3 expressions also confirmed the impaired fatty acid oxidative catabolism. Altogether, this study revealed that PFE induced hepatotoxicity by damaging mitochondria, reducing fatty acid β-oxidation levels, and inhibiting fatty acids ingested by bile acids.

Metabolic Activation and Cytotoxicity of Fungicide Carbendazim Mediated by CYP1A2

Carbendazim (CBZ) is a broad-spectrum fungicide widely used in many nations for foliar spray as well as seed and soil treatment. The resulting contamination and environmental pollution have been drawing public attention. In particular, CBZ was reported to cause liver damage in rats and zebrafish, and the mechanisms of its toxicity have not been clarified. The purposes of this study were to investigate the metabolic activation of CBZ and to determine a possible role of the reactive metabolites in CBZ-induced liver injury reported. One oxidative metabolite (M1), one glutathione conjugate (M2), and one N-acetyl cysteine conjugate (M3) were detected in human and rat liver microsomal incubations fortified with glutathione or N-acetyl cysteine after exposure to CBZ. CYP1A2 was the major enzyme responsible for the metabolic activation of CBZ. Biliary M2 and urinary M3 were detected in rats treated with CBZ. CBZ-derived protein adduction was found in cultured rat primary hepatocytes treated with CBZ. The increase of administration concentration intensified not only the cytotoxicity but also protein adduction induced by CBZ, suggesting a correlation of the cytotoxicity with the observed protein modification. The findings facilitate the understanding of the mechanisms of toxic action of CBZ.

Metabolic activation of deferiprone mediated by CYP2A6

Deferiprone (DFP) is a metal chelating agent generally used to treat patients with thalassaemia, due to iron overload in clinical settings.Studies have revealed that long-term use of DFP can induce hepatotoxicity, however, mechanisms of its toxic action remain unclear. The present studies are aimed to characterize the reactive metabolite of DFP, to define the metabolic pathway, and to determine the P450 enzymes participating in the bioactivation.A demethylation metabolite (M1) was observed in rat liver microsomal incubations. Additionally, a glutathione (GSH) conjugate (M2) and an N-acetylcysteine (NAC) conjugate (M3) were detected in microsomal incubations fortified with DFP and GSH/NAC.Biliary M2 and urinary M3 were respectively found in animals administered DFP.CYP2A6 enzyme dominated the catalysis to bioactivate DFP.

Glutathione conjugation and protein modification resulting from metabolic activation of venlafaxine in vitro and in vivo

Venlafaxine (VLF), an antidepressant agent, is widely used to combat major depressive disorders, particularly for the treatment of selective serotonin reuptake inhibitor-resistant depression. VLF has been shown to cause liver injury. The present study aimed to investigate the metabolic activation of VLF and explore the mechanisms of hepatotoxicity induced by VLF.One glutathione (GSH) conjugate and one cysteine conjugate were both detected in mouse and human liver microsomal incubations containing VLF and GSH or cysteine. The two conjugates were also detected in cultured mouse primary hepatocytes and bile of rats after exposure to VLF. The in vitro and in vivo studies demonstrated that VLF was metabolized to a quinone methide intermediate reactive to GSH and cysteine residues of hepatic protein. The observed protein covalent binding revealed dose-dependency. The metabolic activation of VLF was P450-dependent, and CYP3A4 was found as the predominant enzyme involved in the bioactivation process.These findings facilitate better understanding of the metabolic activation-hepatotoxicity relationship of VLF and provide chemists with information about new potential structural alerts during drug design process.

Nontargeted Metabolomics by High-Resolution Mass Spectrometry to Study the In Vitro Metabolism of a Dual Inverse Agonist of Estrogen-Related Receptors β and γ, DN203368

DN203368 ((E)-3-[1-(4-[4-isopropylpiperazine-1-yl]phenyl) 3-methyl-2-phenylbut-1-en-1-yl] phenol) is a 4-hydroxy tamoxifen analog that is a dual inverse agonist of estrogen-related receptor β/γ (ERRβ/γ). ERRγ is an orphan nuclear receptor that plays an important role in development and homeostasis and holds potential as a novel therapeutic target in metabolic diseases such as diabetes mellitus, obesity, and cancer. ERRβ is also one of the orphan nuclear receptors critical for many biological processes, such as development. We investigated the in vitro metabolism of DN203368 by conventional and metabolomic approaches using high-resolution mass spectrometry. The compound (100 μM) was incubated with rat and human liver microsomes in the presence of NADPH. In the metabolomic approach, the m/z value and retention time information obtained from the sample and heat-inactivated control group were statistically evaluated using principal component analysis and orthogonal partial least-squares discriminant analysis. Significant features responsible for group separation were then identified using tandem mass spectra. Seven metabolites of DN203368 were identified in rat liver microsomes and the metabolic pathways include hydroxylation (M1-3), N-oxidation (M4), N-deisopropylation (M5), N,N-dealkylation (M6), and oxidation and dehydrogenation (M7). Only five metabolites (M2, M3, and M5-M7) were detected in human liver microsomes. In the conventional approach using extracted ion monitoring for values of mass increase or decrease by known metabolic reactions, only five metabolites (M1-M5) were found in rat liver microsomes, whereas three metabolites (M2, M3, and M5) were found in human liver microsomes. This study revealed that nontargeted metabolomics combined with high-resolution mass spectrometry and multivariate analysis could be a more efficient tool for drug metabolite identification than the conventional approach. These results might also be useful for understanding the pharmacokinetics and metabolism of DN203368 in animals and humans.

Identification of Quinone Methide Intermediate Resulting from Metabolic Activation of Icaritin in Vitro and in Vivo

Many herbal medicines such as epimedium have been reported to cause adverse effects, and icaritin is the common aglycone of many glucosides in epimedium. Our present work aimed at the clarification of the metabolic activation of icaritin possibly responsible for the adverse effects of epimedium. A quinone methide metabolite (M1) was detected in icaritin-fortified microsomal incubations. A glutathione (GSH) conjugate (M2) and N-acetyl-l-cysteine (NAC) conjugate (M3) derived from icaritin were observed in GSH/NAC-supplemented rat/human liver microsomal incubations. CYP3A family was the predominant enzyme catalyzing the bioactivation of icaritin. In conclusion, sufficient evidence indicates the metabolic activation of icaritin to quinone methide metabolite.

Metabolic detoxification of bakuchiol is mediated by oxidation of CYP 450s in liver microsomes

Bakuchiol, one of bioactive compounds isolated from the dried ripe fruits of Psoralea corylifolia L., possesses a variety of pharmacological activities. In this study, the metabolites of bakuchiol in rat liver microsomes as well as their cytotoxicities were studied. A total of eight metabolites were isolated and identified as 14-carboxylbakuchiol (M1), 14,15-dihydroxybakuchiol (M2), 12,13-dihydroxybakuchiol (M3), 15-hydroxybakuchiol (M4), 14-hydroxybakuchiol (M5), bakuchiol hydrate (M6), 15-hydroxybakuchiol acetate (M7), and 14-hydroxybakuchiol acetate (M8). All the metabolites are new compounds except for M3. The main type of biotransformation is oxidation reaction, including hydroxylation, epoxidation and carboxylation. Cytotoxicities of bakuchiol and its metabolites against human kidney-2 (HK-2) cell line were evaluated. The median inhibition concentration (IC₅₀) values of bakuchiol, M4, M6 and M8 were (29.48 ± 0.22) μM, (67.51 ± 6.80) μM, (90.23 ± 3.89) μM, and (86.62 ± 6.08) μM, respectively, and the IC₅₀ values of M1, M2, M3, M5, and M7 were all in excess of 100 μM. To further verify the metabolic reliability, the metabolits of bakuchiol in vivo and the metabolic species variations in human and rat liver microsomes were studied using UPLC-MS/MS method. This study provides valuable information for further investigation of metabolism and toxicity of bakuchiol in vivo.