The potential beneficial role of Ginkgetin in doxorubicin-induced hepatotoxicity: Elucidating the underlying claim

Doxorubicin (DOX) is a widely used chemotherapeutic agent for various tumors treatment; apart from its chemotherapeutic activity, the traditional usage of DOX has been limited by its adverse effects on multiple organs, mainly hepatotoxicity. The molecular mechanisms underlying DOX hepatotoxicity are mainly due to the production of reactive oxygen species (ROS) inducing oxidative stress, diminishing antioxidant enzymes, apoptosis, inflammation, and mitochondrial dysfunction. Thus, there is an urgent need to develop a therapy that minimizes DOX hepatotoxicity and widens its use in various types of cancers without fear of its serious hepatotoxicity. Ginkgetin (GINK), a natural biflavonoid, exhibits diverse actions, including promising free radical scavenging, antioxidant, and anti-inflammatory activities. So, this study's objectives were to determine whether GINK could mitigate DOX's hepatotoxic effects and look into a putative hepatoprotective molecular pathway. Mice were divided into five groups: Normal control, control GINK 100, Untreated DOX group, and DOX groups treated with GINK (50 and 100 mg/kg) intraperitoneally daily for four days before DOX administration and an additional three days afterward. GINK 100 pretreatment showed marked protection from DOX hepatotoxicity and also attenuation of histopathological structural alterations. These outcomes were corroborated biochemically by a considerable decrease in alanine aminotransferases, aspartate aminotransferase, and alkaline phosphatase levels. GINK significantly augmented silent information regulator 1 and nuclear translocation of NF-E2-related factor 2 and repressed the expression and protein levels of forkhead box protein O1, inducible nitric oxide synthase, and P53 relative to DOX group. GINK alleviated oxidative stress and induced significant anti-inflammatory effects via suppression of interleukin-6, nuclear factor Kabba B, and iNOS respectively. This study is the first to investigate GINK's potentially beneficial effects in acute DOX hepatotoxicity, possibly exhibiting antioxidant, anti-inflammatory, and anti-apoptotic effects by modulation of Sirt1/FOXO-1/NF-κB Signal.

Pharmacokinetic, Metabolism, and Metabolomic Strategies Provide Deep Insight Into the Underlying Mechanism of Ginkgo biloba Flavonoids in the Treatment of Cardiovascular Disease

Ginkgo biloba, known as the "living fossil," has a long history of being used as botanical drug for treating cardiovascular diseases and the content of flavonoids as high as 24%. More than 110 different kinds of flavonoids and their derivatives have been separated from G. biloba, including flavones, flavonols, biflavonoids, catechins, and their glycosides, etc., all of which display the ability to dilate blood vessels, regulate blood lipids, and antagonize platelet activating factor, and protect against ischemic damage. At present, many types of preparations based on G. biloba extract or the bioactive flavonoids of it have been developed, which are mostly used for the treatment of cardiovascular diseases. We herein review recent progress in understanding the metabolic regulatory processes and gene regulation of cellular metabolism in cardiovascular diseases of G. biloba flavonoids. First, we present the cardioprotective flavonoids of G. biloba and their possible pharmacological mechanism. Then, it is the pharmacokinetic and liver and gut microbial metabolism pathways that enable the flavonoids to reach the target organ to exert effect that is analyzed. In the end, we review the possible endogenous pathways toward restoring lipid metabolism and energy metabolism as well as detail novel metabolomic methods for probing the cardioprotective effect of flavonoids of G. biloba.

Simultaneous determination of two galangin metabolites from Alpinia Officinarum Hance in rat plasma by UF LC-MS/MS and its application in pharmacokinetics study

Galangin has multiple pharmacological efficacies, such as anti-cancer, anti-inflammation and anti-oxidation. Galangin can be rapidly converted into glucuronidated metabolites in vivo. This study aimed to establish an UFLC-MS/MS analytical method to simultaneously determine the concentrations of two glucuronidated metabolites of galangin, galangin-3-O-β-D-glucuronic acid (GG-1) and galangin-7-O-β-D-glucuronic acid (GG-2) in rat plasma. After oral administration of galangal extract (0.3 g/kg), blood samples were collected from the orbital sinus, then treated by methanol precipitation and further gradient-eluted with Phenomenex Kinetex 2.6 µm XB-C18 column. The mass spectrometer was manipulated in the negative electrospray ionization (ESI) and selected multiple reaction monitoring (MRM) mode for the analytes. The precursor-to-product ion pairs applied for GG-1, GG-2 and chrysin (as the internal standard, IS) were m/z 445.2→269.0, 445.2→268.9 and 253.0→142.9, respectively. The results showed that the linear ranges for both GG-1 and GG-2 were 2.0–2000.0 ng/mL (r² > 0.995). The inter- and intra-day precision were 89.3%–109.2%, RSD was less than 15%, and the repeatability was good. The recoveries of both metabolites and IS were over 89%, and matrix effect was within 15%. The validated analytical method was further applied to study the pharmacokinetic profiles of GG-1 and GG-2 in vivo. The pharmacokinetic parameters suggested that T_max of GG-1 was equivalent to that of GG-2, and MRT_0-t, t_1/2 of GG-2 were a little higher than those of GG-1. Importantly, AUC_0-t and C_max of GG-2 were almost twice as those of GG-1. In short, the validated UFLCMS/MS analytical method was feasible to simultaneously determine two galangin metabolites GG-1 and GG-2 in rat plasma and further analyze in vivo metabolism of galangin.

Glucuronidation and its effect on the bioactivity of amentoflavone, a biflavonoid from Ginkgo biloba leaves

OBJECTIVES

Ginkgo biloba leaves contain amentoflavone (AMF), a dietary flavonoid that possesses antioxidant and anticancer activity. Flavonoids are extensively subjected to glucuronidation. This study aimed to determine the metabolic profile of AMF and the effect of glucuronidation on AMF bioactivity.

METHODS

A pharmacokinetic study was conducted to determine the plasma concentrations of AMF and its metabolites. The metabolic profile of AMF was elucidated using different species of microsomes. The antioxidant activity of AMF metabolites was determined using DPPH/ABTS radical and nitric oxide assays. The anticancer activity of AMF metabolites was evaluated in U87MG/U251 cells.

KEY FINDINGS

Pharmacokinetic studies indicated that the oral bioavailability of AMF was 0.06 ± 0.04%, and the area under the curve of the glucuronidated AMF metabolites (410.938 ± 62.219 ng/ml h) was significantly higher than that of AMF (194.509 ± 16.915 ng/ml h). UGT1A1 and UGT1A3 greatly metabolized AMF. No significant difference was observed in the antioxidant activity between AMF and its metabolites. The anticancer activity of AMF metabolites significantly decreased.

CONCLUSIONS

A low AMF bioavailability was due to extensive glucuronidation, which was mediated by UGT1A1 and UGT1A3. Glucuronidated AMF metabolites had the same antioxidant but had a lower anticancer activity than that of AMF.

Wogonin glucuronidation in liver and intestinal microsomes of humans, monkeys, dogs, rats, and mice

Wogonin, one of the flavonoids isolated from Scutellaria baicalensis, exhibits some beneficial bioactivities, including anti-inflammatory and anticancer effects, and is metabolized into glucuronide by UDP-glucuronosyltransferase (UGT) enzymes in humans. In the present study, wogonin glucuronidation was examined in the liver and intestinal microsomes of humans, monkeys, dogs, rats, and mice using a kinetic analysis.The kinetics of wogonin glucuronidation by liver microsomes followed the biphasic model in all species examined. CL_int values (x-intercept) based on v versus V/[S] plots were rats > humans ≈ monkeys > mice > dogs. The kinetics of intestinal microsomes fit the Michaelis-Menten model for humans, monkeys, rats, and mice and the substrate inhibition model for dogs. CL_int values were rats > monkeys > mice > dogs > humans. The tissue dependence of CL_int values was liver microsomes > intestinal microsomes for humans, dogs, and rats, and liver microsomes ≈ intestinal microsomes for monkeys and mice.These results demonstrated that the metabolic abilities of UGT enzymes toward wogonin in the liver and intestines markedly differ among humans, monkeys, dogs, rats, and mice, and suggest that species differences are closely associated with the biological effects of wogonin.

Pterostilbene supplements carry the risk of drug interaction via inhibition of UDP-glucuronosyltransferases (UGT) 1A9 enzymes

Pterostilbene (PT) is a natural stilbene common in small berries and food supplements, possessing numerous pharmacological activities. However, whether PT can affect the activities of UDP-glucuronosyltransferases (UGT) enzymes remains unclear. The aim of the present study was to investigate the effect of PT on UGT activities and to quantitatively evaluate the food-drug interaction potential due to UGT inhibition. Our data indicated that PT exhibited potent inhibition against HLM, UGT1A6, UGT1A9, UGT2B7, and UGT2B15, moderate inhibition against UGT1A1, UGT1A3, UGT1A8, and UGT2B4, negligible inhibition against UGT1A4, UGT1A7, UGT1A10, and UGT2B17. Further kinetic investigation demonstrated that PT exerted potent noncompetitive inhibition 4-MU glucuronidation by UGT1A9, with IC₅₀ and K_i values of 0.92 μM and 0.52 ± 0.04 μM, respectively. Quantitative prediction study suggested that coadministration of PT supplements at 100 mg/day or higher doses may result in at least a 50% increase in the AUC of drugs predominantly cleared by UGT1A9. Thus, the coadministration of PT supplements and drugs primarily cleared by UGT1A9 may result in potential drug interaction, and precautions should be taken when coadministration of PT supplements and drugs metabolized by UGT1A9.

Pharmacokinetics of B-Ring Unsubstituted Flavones

B-ring unsubstituted flavones (of which the most widely known are chrysin, baicalein, wogonin, and oroxylin A) are 2-phenylchromen-4-one molecules of which the B-ring is devoid of any hydroxy, methoxy, or other substituent. They may be found naturally in a number of herbal products used for therapeutic purposes, and several have been designed by researchers and obtained in the laboratory. They have generated interest in the scientific community for their potential use in a variety of pathologies, and understanding their pharmacokinetics is important for a grasp of their optimal use. Based on a comprehensive survey of the relevant literature, this paper examines their absorption (with deglycosylation as a preliminary step) and their fate in the body, from metabolism to excretion. Differences among species (inter-individual) and within the same species (intra-individual) variability have been examined based on the available data, and finally, knowledge gaps and directions of future research are discussed.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

UGT1A polymorphisms as genetic biomarkers for hepatocellular carcinoma risk in Caucasian population

BACKGROUND & AIMS

The definition of new biomarkers of hepatocellular carcinoma (HCC) risk, especially in high-risk HBV/HCV-positive population, is urgently needed to improve HCC clinical management. This study focused on variants of UDP-glucuronosyltransferase 1A (UGT1A) enzymes that catalyse the reaction of glucuronidation, one of the most important chemical defence pathway of the body. The aim of this study was to elucidate the contribution of UGT1A polymorphisms in predicting HCC susceptibility in Caucasians.

METHODS

In this retrospective case-control analysis, 192 HCC liver transplanted patients represent the study group. Two age/sex-matched groups were used as control, one composed of 167 HBV- and/or HCV-infected individuals, and the other of 192 healthy subjects. All the cases were characterized for a panel of UGT1A1, UGT1A7 and UGT1A9 variants. The study end-point was the association between UGT1A markers and HCC onset.

RESULTS

UGT1A7*3 allele emerged as a protective marker for HCC development among both high-risk HBV/HCV-positive patients (OR=0.64, P=.0026), and healthy subjects (OR=0.47, P=.0051). UGT1A1*28 (OR=0.61, P=.0013) and UGT1A9*22 (OR=2.18, P=.0003) alleles were also associated to HCC occurrence, especially among healthy subjects. UGT1A haplotype, summarizing the UGT1A genetic alterations, confirmed the protective role against HCC development emerged for low-activity alleles. The observed associations could probably be linked to an increase of serum levels of health-beneficial molecules including free bilirubin.

CONCLUSION

A predictive effect of UGT1A polymorphisms on HCC risk was identified. If confirmed, these findings could contribute to improve the HCC surveillance, treatment tailoring and patients care.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

Identification of flavone glucuronide isomers by metal complexation and tandem mass spectrometry: regioselectivity of uridine 5'-diphosphate-glucuronosyltransferase isozymes in the biotransformation of flavones

Flavone glucuronide isomers of five flavones (chrysin, apigenin, luteolin, baicalein, and scutellarein) were differentiated by collision-induced dissociation of [Co(II) (flavone-H) (4,7-diphenyl-1,10-phenanthroline)(2)](+) complexes. The complexes were generated via postcolumn addition of a metal-ligand solution after separation of the glucuronide products generated upon incubation of each flavone with an array of uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) isozymes. Elucidation of the glucuronide isomers allowed a systematic investigation of the regioselectivity of 12 human UGT isozymes, including 8 UGT1A and 4 UGT2B isozymes. Glucuronidation of the 7-OH position was the preferred site for all the flavones except for luteolin, which possessed adjacent hydroxyl groups on the B ring. For all flavones and UGT isozymes, glucuronidation of the 5-OH position was never observed. As confirmed by the metal complexation/MS/MS strategy, glucuronidation of the 6-OH position only occurred for baicalein and scutellarein when incubated with three of the UGT isozymes.

Understanding substrate selectivity of human UDP-glucuronosyltransferases through QSAR modeling and analysis of homologous enzymes

The UDP-glucuronosyltransferase (UGT) enzyme catalyzes the glucuronidation reaction which is a major metabolic and detoxification pathway in humans. Understanding the mechanisms for substrate recognition by UGT assumes great importance in an attempt to predict its contribution to xenobiotic/drug disposition in vivo. Spurred on by this interest, 2D/3D-quantitative structure activity relationships and pharmacophore models have been established in the absence of a complete mammalian UGT crystal structure. This review discusses the recent progress in modeling human UGT substrates including those with multiple sites of glucuronidation. A better understanding of UGT active site contributing to substrate selectivity (and regioselectivity) from the homologous enzymes (i.e. plant and bacterial UGTs, all belong to family 1 of glycosyltransferase (GT1)) is also highlighted, as these enzymes share a common catalytic mechanism and/or overlapping substrate selectivity.

Regioselectivity of human UDP-glucuronosyltransferase isozymes in flavonoid biotransformation by metal complexation and tandem mass spectrometry

Based on reactions with five flavonoids, the regioselectivities of twelve human UDP-glucuronosyltransferase (UGT) isozymes were elucidated. The various flavonoid glucuronides were differentiated based on LC-MS/MS fragmentation patterns of [Co(II)(flavonoid-H)(4,7-diphenyl-1,10-phenanthroline)(2)](+) complexes generated upon post-column complexation. Glucuronide distributions were evaluated to allow a systematic assessment of the regioselectivity of each isozyme. The various UGT enzymes, including eight UGT1A and four UGT2B, displayed a remarkable range of selectivities, both in terms of the positions of glucuronidation and relative reactivity with flavanones versus flavonols.