Nicotine regulates the expression of UDP-glucuronosyltransferase (UGT) in humanized UGT1 mouse brain

Regulation of phase I and phase II neurosteroid enzymes in the hippocampus of an Alzheimer's disease rat model: A focus on sulphotransferases and UDP-glucuronosyltransferases

Neurosteroids have been associated with neurodegenerative diseases because they are involved in the modulation of neurotransmitter, neurotropic and neuroprotective actions. Emerging evidence suggests that the enzymes responsible for the synthesis of neurosteroids change during the progression of Alzheimer's disease (AD). The present study aimed to assess the changes in phase I and II enzymes involved in the metabolism of neurosteroids of the progestogen, androgenic and estrogenic steroidogenic pathways and the possibility that the neurosteroids are actively converted into the most abundant metabolites (i.e. glucuronides and sulphates). The gene expression for the phase I and II neurosteroid biosynthetic enzymes were studied in the hippocampus of streptozotocin AD rat model. Male Sprague-Dawley rats were randomly divided into control, sham (saline injected into the hippocampus) and 3 and 12 weeks post-STZ administration (STZ-G3w and STZ-G12w, respectively) groups. Behavioral assessments showed memory impairment in both STZ-injected groups, whereas the formation of amyloid-beta was more pronounced in the STZ-12w group. Gene expression of the hippocampus revealed that glucuronidation and sulphation enzymes transcript of the phase I metabolites were upregulated at the late stage of the disease progression (Hsd17b10, Hsd3b1, Akr1c3 and Cyp19a1) except for Sts. The phase II Sult and Ugt enzymes were mostly upregulated in the STZ-G12w rats (Sult1a1, Sult1e1, Ugt1a1, Ugt1a7c, Ugt1a6, Ugt2b35 and Ugt2b17) and normally expressed in the STZ-G3w group (Sult2a2, Sult2a6, Sult2b1, Ugt2b7, Sult4a1 and Ugt1a7c). In conclusion, changes occur in the phase I and II enzymes transcript of the progestogen, androgenic and estrogenic steroidogenic pathways during the progression of AD.

Alterations of Cytochrome P450s and UDP-Glucuronosyltransferases in Brain Under Diseases and Their Clinical Significances

Cytochrome P450s (CYPs) and UDP-glucuronosyltransferases (UGTs) are both greatly important metabolic enzymes in various tissues, including brain. Although expressions of brain CYPs and UGTs and their contributions to drug disposition are much less than liver, both CYPs and UGTs also mediate metabolism of endogenous substances including dopamine and serotonin as well as some drugs such as morphine in brain, demonstrating their important roles in maintenance of brain homeostasis or pharmacological activity of drugs. Some diseases such as epilepsy, Parkinson's disease and Alzheimer's disease are often associated with the alterations of CYPs and UGTs in brain, which may be involved in processes of these diseases via disturbing metabolism of endogenous substances or resisting drugs. This article reviewed the alterations of CYPs and UGTs in brain, the effects on endogenous substances and drugs and their clinical significances. Understanding the roles of CYPs and UGTs in brain provides some new strategies for the treatment of central nervous system diseases.

Enzymatic analysis of glucuronidation of synthetic cannabinoid 1-naphthyl 1-(4-fluorobenzyl)-1H-indole-3-carboxylate (FDU-PB-22)

Recently, there has been a rise in abuse of synthetic cannabinoids (SCBs). The consumption of SCBs results in various effects and can induce toxic reactions, including paranoia, seizures, tachycardia and even death. 1-Naphthyl 1-(4-fluorobenzyl)-1H-indole-3-carboxylate (FDU-PB-22) is a third generation SCB whose metabolic pathway has not been fully characterized. In this study, we conducted in vitro pharmacokinetic analysis of FDU-PB-22 metabolism. Metabolic reactions containing FDU-PB-22 and human liver microsomes (HLMs) were independent of NADPH but not UDP-glucuronic acid (UDPGA), suggesting that UDP-glucuronosyltransferases (UGTs) are the primary enzymes involved in this metabolism. It was further determined that the metabolite extensively formed after incubating FDU-PB-22 with UDPGA in HLMs was the glucuronide of FDU-PB-22 3-carboxyindole (FBI-COOH). Various hepatic UGTs showed enzymatic activity for FBI-COOH. A series of UGT inhibitors showed moderate to strong inhibition of FBI-COOH-glucuronidation in HLMs, suggesting that multiple UGT isoforms are involved in FBI-COOH-glucuronidation in the liver. Interestingly, an extra-hepatic isoform, UGT1A10, exhibited the highest activity with a K_m value of 38 µM and a V_max value of 5.90 nmol/min/mg. Collectively, these results suggest that both genetic mutations of and the co-administration of inhibitors for FDU-PB-22-metabolizing UGTs will likely increase the risk of FDU-PB-22-induced toxicity.

Species differences in drug glucuronidation: Humanized UDP-glucuronosyltransferase 1 mice and their application for predicting drug glucuronidation and drug-induced toxicity in humans

More than 20% of clinically used drugs are glucuronidated by a microsomal enzyme UDP-glucuronosyltransferase (UGT). Inhibition or induction of UGT can result in an increase or decrease in blood drug concentration. To avoid drug-drug interactions and adverse drug reactions in individuals, therefore, it is important to understand whether UGTs are involved in metabolism of drugs and drug candidates. While most of glucuronides are inactive metabolites, acyl-glucuronides that are formed from compounds with a carboxylic acid group can be highly toxic. Animals such as mice and rats are widely used to predict drug metabolism and drug-induced toxicity in humans. However, there are marked species differences in the expression and function of drug-metabolizing enzymes including UGTs. To overcome the species differences, mice in which certain drug-metabolizing enzymes are humanized have been recently developed. Humanized UGT1 (hUGT1) mice were created in 2010 by crossing Ugt1-null mice with human UGT1 transgenic mice in a C57BL/6 background. hUGT1 mice can be promising tools to predict human drug glucuronidation and acyl-glucuronide-associated toxicity. In this review article, studies of drug metabolism and toxicity in the hUGT1 mice are summarized. We further discuss research and strategic directions to advance the understanding of drug glucuronidation in humans.

UDP-glucuronosyltransferases (UGTs) and their related metabolic cross-talk with internal homeostasis: A systematic review of UGT isoforms for precision medicine

UDP-glucuronosyltransferases (UGTs) are the primary phase II enzymes catalyzing the conjugation of glucuronic acid to the xenobiotics with polar groups for facilitating their clearance. The UGTs belong to a superfamily that consists of diverse isoforms possessing distinct but overlapping metabolic activity. The abnormality or deficiency of UGTs in vivo is highly associated with some diseases, efficacy and toxicity of drugs, and precisely therapeutic personality. Despite the great effects and fruitful results achieved, to date, the expression and functions of individual UGTs have not been well clarified, the inconsistency of UGTs is often observed in human and experimental animals, and the complex regulation factors affecting UGTs have not been systematically summarized. This article gives an overview of updated reports on UGTs involving the various regulatory factors in terms of the genetic, environmental, pathological, and physiological effects on the functioning of individual UGTs, in turn, the dysfunction of UGTs induced disease risk and endo- or xenobiotic metabolism-related toxicity. The complex cross-talk effect of UGTs with internal homeostasis is systematically summarized and discussed in detail, which would be of great importance for personalized precision medicine.

Expression of UDP-Glucuronosyltransferase 1 (UGT1) and Glucuronidation Activity toward Endogenous Substances in Humanized UGT1 Mouse Brain

Although UDP-glucuronosyltransferases (UGTs) are important phase II drug-metabolizing enzymes, they are also involved in the metabolism of endogenous compounds. Certain substrates of UGTs, such as serotonin and estradiol, play important roles in the brain. However, the expression of UGTs in the human brain has not been fully clarified. Recently, humanized UGT1 mice (hUGT1 mice) in which the original Ugt1 locus was disrupted and replaced with the human UGT1 locus have been developed. In the present study, the expression pattern of UGT1As in brains from humans and hUGT1 mice was examined. We found that UGT1A1, 1A3, 1A6, and 1A10 were expressed in human brains. The expression pattern of UGT1As in hUGT1 mouse brains was similar to that in human brains. In addition, we examined the expression of UGT1A1 and 1A6 in the cerebellum, olfactory bulbs, midbrain, hippocampus, and cerebral cortex of hUGT1 mice. UGT1A1 in all brain regions and UGT1A6 in the cerebellum and cerebral cortex of 6-month-old hUGT1 mice were expressed at a significantly higher rate than those of 2-week-old hUGT1 mice. A difference in expression levels between brain regions was also observed. Brain microsomes exhibited glucuronidation activities toward estradiol and serotonin, with mean values of 0.13 and 5.17 pmol/min/mg, respectively. In conclusion, UGT1A1 and UGT1A6 might play an important role in function regulation of endogenous compounds in a region- and age-dependent manner. Humanized UGT1 mice might be useful to study the importance of brain UGTs in vivo.