Human uridine diphosphate-glucuronosyltransferase UGT2B7 conjugates mineralocorticoid and glucocorticoid metabolites

Glucuronidation of orally administered drugs and the value of nanocarriers in strategies for its overcome

The gastrointestinal tract (GIT) plays a pivotal role in the absorption of orally administered drugs, with the small intestine serving as the primary site due to its extensive surface area and specialized cell types, including enterocytes and M cells. After oral administration, drugs are generally transported via the portal vein to the liver, where they undergo first-pass metabolism. This process involves various enzymatic reactions, including glucuronidation, facilitated by uridine diphosphate-glucuronosyltransferase (UGT), a major phase 2 reaction in mammalian metabolism. UGTs conjugate glucuronic acid to a wide array of endogenous and exogenous substrates, enhancing their solubility and excretion, but significantly affecting the bioavailability and therapeutic efficacy of drugs. UGT enzymes are ubiquitously distributed across tissues, prominently in the liver, but also in the GIT, kidneys, brain, and other organs where they play crucial roles in xenobiotic metabolism. Species-specific differences in UGT expression and activity impact the selection of animal models for pharmacological studies. Various experimental models - ranging from computational simulations (in silico) to laboratory experiments (in vitro) and animal studies (in vivo) - are employed throughout drug discovery and development to evaluate drug metabolism, including UGT activity. Effective strategies to counter pre-systemic metabolism are critical for improving drug bioavailability. This review explores several approaches including prodrugs, co-administration of specific molecules or use of inhibiting excipients in formulations. Strategies incorporating these excipients in nanoformulations demonstrate notable increases in drug absorption and bioavailability. This review highlights the importance of targeted delivery systems and excipient selection in overcoming metabolic barriers, aiming to optimize drug efficacy and patient outcomes.

In vitro inhibitory effects of selumetinib on activity of human UDP-glucuronosyltransferases and prediction of in vivo drug-drug interactions

Selumetinib is an oral, effective, and selective tyrosine kinase inhibitor targeting mitogen-activated protein kinase 1 and 2 (MEK1/2), which is clinically active in multiple tumor types, such as neurofibromatosis type 1 (NF1), melanoma, gliomas and non-small cell lung cancer (NSCLC). The purpose of this article was to assess the effects of selumetinib on the activities of twelve human UDP-glucosyltransferases (UGTs) including UGT1A1, 1A3, 1A4, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B15, and 2B17, and its potential for inducing clinical drug-drug interactions (DDIs). The results demonstrated that selumetinib potently inhibited the activity of UGT2B7 through the mechanism of mixed inhibition with the inhibition constant value of 5.79 ± 0.65 μM. Furthermore, the plasma concentration of UGT2B7 substrate as the co-administered drug was predicted to be increased by at least 84 % when patients took selumetinib 75 mg twice daily, suggesting a high potential to induce clinical DDIs. Selumetinib exhibited weak inhibitory effects on other human UGTs and was unlikely to trigger off UGTs-mediated DDIs except for UGT2B7. Therefore, the combination of selumetinib with the substrate drug of UGT2B7 requires additional attention to avoid adverse events in clinical treatment.

An Abbreviated History of Aldosterone Metabolism, Current and Future Challenges

The initial isolation of adrenal steroids from large quantities of animal adrenals resulted in an amorphous fraction resistant to crystallization and identification and had potent effects on electrolyte transport. Aldosterone was eventually isolated and identified in the fraction and was soon shown to cause hypertension when in excess. The autonomous and excessive production of aldosterone, primary aldosteronism, is the most common cause of secondary hypertension. Aldosterone is metabolized in the liver and kidney, and its metabolites are conjugated with glucuronic acid for excretion. The most common liver metabolite is 3α,5β-tetrahydroaldosterone-3-glucuronide, while that of the kidney is aldosterone-18-oxo-glucuronide. In terms of their value, especially the aldosterone-18-oxo-glucuronide, is commonly used for the diagnosis of primary aldosteronism because they provide an integrated value of the total daily production of aldosterone. Conversion of aldosterone to 18-oxo-glucuronide is impeded by drugs, like some common non-steroidal anti-inflammatory drugs that compete for UDP-glucuronosyltransferase-2B7, the most important glucuronosyltransferase for aldosterone metabolism. Tetrahydroaldosterone is the most abundant metabolite and the most reliable for the diagnosis of primary aldosteronism, but it is not commonly measured.

scRNA-Seq of Cultured Human Amniotic Fluid from Fetuses with Spina Bifida Reveals the Origin and Heterogeneity of the Cellular Content

Amniotic fluid has been proposed as an easily available source of cells for numerous applications in regenerative medicine and tissue engineering. The use of amniotic fluid cells in biomedical applications necessitates their unequivocal characterization; however, the exact cellular composition of amniotic fluid and the precise tissue origins of these cells remain largely unclear. Using cells cultured from the human amniotic fluid of fetuses with spina bifida aperta and of a healthy fetus, we performed single-cell RNA sequencing to characterize the tissue origin and marker expression of cultured amniotic fluid cells at the single-cell level. Our analysis revealed nine different cell types of stromal, epithelial and immune cell phenotypes, and from various fetal tissue origins, demonstrating the heterogeneity of the cultured amniotic fluid cell population at a single-cell resolution. It also identified cell types of neural origin in amniotic fluid from fetuses with spina bifida aperta. Our data provide a comprehensive list of markers for the characterization of the various progenitor and terminally differentiated cell types in cultured amniotic fluid. This study highlights the relevance of single-cell analysis approaches for the characterization of amniotic fluid cells in order to harness their full potential in biomedical research and clinical applications.

Nervonic acid improves liver inflammation in a mouse model of Parkinson's disease by inhibiting proinflammatory signaling pathways and regulating metabolic pathways

BACKGROUND

Nervonic acid (NA) - a type of bioactive fatty acid that is found in natural sources - can inhibit inflammatory reactions and regulate immune system balance. Therefore, the use of NA for the treatment of neurodegenerative diseases has received considerable attention. Our previous study found that NA inhibited inflammatory responses in the brain of Parkinson's disease (PD) mouse models. In addition to the brain, PD is also associated with visceral organ dysfunction, especially impaired liver function. Thus, studying the role of NA in PD-mediated inflammation of the liver is particularly important.

METHODS

A combined transcriptome and metabolomic approach was utilized to investigate the anti-inflammatory effects of NA on the liver of PD mice. Inflammatory signaling molecules and metabolic pathway-related genes were examined in the liver using real-time PCR and western blotting.

RESULTS

Liver transcriptome analysis revealed that NA exerted anti-inflammatory effects by controlling several pro-inflammatory signaling pathways, such as the down-regulation of the tumor necrosis factor and nuclear factor kappa B signaling pathways, both of which were essential in the development of inflammatory disease. In addition, liver metabolomic results revealed that metabolites related to steroid hormone biosynthesis, arachidonic acid metabolism, and linoleic acid metabolism were up-regulated and those related to valine, leucine, and isoleucine degradation pathways were down-regulated in NA treatment groups compared with the PD model. The integration of metabolomic and transcriptomic results showed NA significantly exerted its anti-inflammatory function by regulating the transcription and metabolic pathways of multiple genes. Particularly, linoleic acid metabolism, arachidonic acid metabolism, and steroid hormone biosynthesis were the crucial pathways of the anti-inflammatory action of NA. Key genes in these metabolic pathways and key molecules in inflammatory signaling pathways were also verified, which were consistent with transcriptomic results.

CONCLUSION

These findings provide novel insights into the liver protective effects of NA against PD mice. This study also showed that NA could be a useful dietary element for improving and treating PD-induced liver inflammation.

Effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on sublingual buprenorphine metabolism in heroin addicts: An improved PCR-RFLP assay for the detection of rs7662029 polymorphism

This study aimed to determine the effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on plasma buprenorphine (BUP) concentration and different treatment responses in a sample of 109 patients with opioid use disorder (OUD) treated with sublingual BUP/naloxone. Polymorphisms were analysed by PCR-RFLP. Plasma concentrations of BUP and its metabolite norbuprenorphine were detected by LC-MS/MS. Craving, withdrawal, depression and anxiety were measured by appropriate scales. OUD patients with rs7439366 CC or rs7662029 GG genotypes had significantly lower dose-normalized (BUP/D) and dose/kg-normalized BUP (BUP/D.kg^-1) levels than those who were CT or AA carriers. Significant associations between UGT2B7 rs7662029 and increased craving (p = 0.037) and withdrawal symptoms (p = 0.029) were detected. Our findings were pointing to an important role of UGT2B7 in the metabolism of sublingual BUP/naloxone in the heroin addicts for the first time. A novel PCR-RFLP assay was developed for the determination of UGT2B7 rs7662029 polymorphism, based on utilizing novel restriction enzyme.

Relative Expression of Mouse Udp-glucuronosyl Transferase 2b1 Gene in the Livers, Kidneys, and Hearts: The Influence of Nonsteroidal Anti-inflammatory Drug Treatment

BACKGROUND

Mouse Udp-glucuronosyl Transferase (UGT) 2b1 is equivalent to the human UGT2B7 enzyme, which is a phase II drug-metabolising enzyme and plays a major role in the metabolism of xenobiotic and endogenous compounds. This study aimed to find the relative expression of the mouse ugt2b1 gene in the liver, kidney, and heart organs and the influence of Nonsteroidal Anti-inflammatory Drug (NSAID) administration.

METHODS

Thirty-five Blab/c mice were divided into 5 groups and treated with different commonly-used NSAIDs; diclofenac, ibuprofen, meloxicam, and mefenamic acid for 14 days. The livers, kidneys, and hearts were isolated, while the expression of ugt2b1 gene was analysed with a quantitative real-time polymerase chain reaction technique.

RESULTS

It was found that the ugt2b1 gene is highly expressed in the liver, and then in the heart and the kidneys. NSAIDs significantly upregulated (ANOVA, p < 0.05) the expression of ugt2b1 in the heart, while they downregulated its expression (ANOVA, p < 0.05) in the liver and kidneys. The level of NSAIDs' effect on ugt2b1 gene expression was strongly correlated (Spearman's Rho correlation, p < 0.05) with NSAID's lipophilicity in the liver and its elimination half-life in the heart.

CONCLUSION

This study concluded that the mouse ugt2b1 gene was mainly expressed in the liver, as 14-day administration of different NSAIDs caused alterations in the expression of this gene, which may influence the metabolism of xenobiotic and endogenous compounds.

The 11β-hydroxyandrostenedione pathway and C11-oxy C21 backdoor pathway are active in benign prostatic hyperplasia yielding 11keto-testosterone and 11keto-progesterone

In clinical approaches to benign prostatic hyperplasia (BPH) and prostate cancer (PCa), steroidogenesis or the disruption thereof is the main thrust in treatments restricting active androgen production. Extensive studies have been undertaken focusing on testosterone and dihydrotestosterone (DHT). However, the adrenal C11-oxy C₁₉ steroid, 11β-hydroxyandrostenedione (11OHA4), also contributes to the active androgen pool in the prostate microenvironment, and while it has been shown to impact castration resistant prostate cancer, the C11-oxy C₁₉ steroids together with the C11-oxy C₂₁ steroids have not been studied in BPH. The study firstly investigated the metabolism of these adrenal steroids in the BPH-1 model. Comprehensive profiles identified 11keto-testosterone as the predominant active androgen in the metabolism of the C11-oxy C₁₉ steroids, and we identified, for the first time, 11β-hydroxy-5α-androstane-3α,17β-diol, a novel steroid in the 11OHA4-pathway. Analysis of the inactivation and reactivation of the metabolites showed that DHT is more readily inactivated than 11keto-dihydrotestosterone (11KDHT). The conversion of 11β-hydroxyprogesterone (11βOHPROG) yielded 11keto-progesterone (11KPROG), while the latter yielded 11keto-dihydroprogesterone (11KDHPROG). BPH tissue analysis identified high levels of 11β-hydroxyandrosterone (4-14 ng/g) and 11keto-androsterone (9-160 ng/g), together with androstenedione (A4; ∼7.5 ng/g). The major C11-oxy C₂₁ steroids detected were 11βOHPROG (∼46 ng/g), 11KPROG (∼130 ng/g) as well as 11KDHPROG (∼282 ng/g). While circulatory 11βOHPROG was detected below the limit of quantification, 11KPROG and 11KDHPROG were detected at 6 and 8.5 nmol/L, respectively. Glucuronide derivatives of both 11KPROG and pregnanetriol were also detected. 11OHA4 was the major free androgen in circulation at 85.9 nmol/L, ±12-fold higher than A4, together with 5α-androstane-3α,17β-diol quantified at 69.3 nmol/L. Circulatory C11-oxy C₁₉ steroids levels were also significantly higher (8-fold) than the C11-oxy C₂₁ steroid levels, while the former were similar to the C₁₉ steroid levels, in contrast to levels in PCa. The study highlights the contribution of adrenal C11-oxy steroids to the androgen pool in BPH underscoring their limited reactivation and elimination, and significant inter-individual variations regarding steroid levels and conjugation. Targeted steroid metabolome analysis is critical to understanding prostate steroidogenesis and disease progression, and analysis of circulatory C11-oxy C₁₉ and C11-oxy C₂₁ steroids, together with intraprostatic levels, add to our current understanding of BPH.

The Human UGT2B7 Nanodisc

The 20 uridine diphosphate glycosyl-transferases (UGTs) encoded in the human genome form an essential homeostatic network of overlapping catalytic functions that surveil and regulate the activity and clearance of scores of small molecule metabolites. Biochemical and biophysical UGT studies have been hampered by the inability to purify these membrane-bound proteins. Here, using cell-free expression and nanodisc technology, we assemble and purify to homogeneity the first UGT nanodisc-the human UGT2B7•nanodisc. The complex is readily isolated in milligram quantities. It is stable and its initial-rate parameters are identical within error to those associated with UGT2B7 in microsomal preparations (i.e., Supersomes). The high purity of the nanodisc preparation simplifies UGT assays, which allows complexities traditionally associated with microsomal assays (latency and the albumin effect) to be circumvented. Each nanodisc is shown to harbor a single UGT2B7 monomer. The methods described herein should be widely applicable to UGTs, and these findings are expected to set the stage for experimentalists to more freely explore the structure, function, and biology of this important area of phase II metabolism. SIGNIFICANCE STATEMENT: Lack of access to pure, catalytically competent human uridine diphosphate glucuronosyl-transferases (UGTs) has long been an impediment to biochemical and biophysical studies of this disease-relevant enzyme family. Here, we demonstrate this barrier can be removed using nanodisc technology-a human UGT2B7•nanodisc is assembled, purified to homogeneity, and shown to have activity comparable to microsomal UGT2B7.

Human steroid biosynthesis, metabolism and excretion are differentially reflected by serum and urine steroid metabolomes: A comprehensive review

Advances in technology have allowed for the sensitive, specific, and simultaneous quantitative profiling of steroid precursors, bioactive steroids and inactive metabolites, facilitating comprehensive characterization of the serum and urine steroid metabolomes. The quantification of steroid panels is therefore gaining favor over quantification of single marker metabolites in the clinical and research laboratories. However, although the biochemical pathways for the biosynthesis and metabolism of steroid hormones are now well defined, a gulf still exists between this knowledge and its application to the measured steroid profiles. In this review, we present an overview of steroid hormone biosynthesis and metabolism by the liver and peripheral tissues, specifically highlighting the pathways linking and differentiating the serum and urine steroid metabolomes. A brief overview of the methodology used in steroid profiling is also provided.

Liver and Steroid Hormones-Can a Touch of p53 Make a Difference?

The liver is the main metabolic organ in the body, serving as a significant hormonal secretory gland and functioning to maintain hormone balance and homeostasis. Steroid hormones regulate various biological pathways, mainly in the reproductive system and in many metabolic processes. The liver, as well as steroid hormones, contribute significantly, through functional intertwine, to homeostasis maintenance, and proper responses during stress. Malfunction of either has a significant impact on the other and may lead to severe liver diseases as well as to several endocrine syndromes. Thus, the regulation on liver functions as on steroid hormones levels and activities is well-controlled. p53, the well-known tumor suppressor gene, was recently found to regulate metabolism and general homeostasis processes, particularly within the liver. Moreover, p53 was shown to be involved in steroid hormones regulation. In this review, we discuss the bi-directional regulation of the liver and the steroid hormones pointing to p53 as a novel regulator in this axis. A comprehensive understanding of the molecular mechanisms of this axis may help to prevent and treat related disease, especially with the increasing exposure of the population to environmental steroid hormones and steroid hormone-based medication.

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.

The evolution of methods for urinary steroid metabolomics in clinical investigations particularly in childhood

The metabolites of cortisol, and the intermediates in the pathways from cholesterol to cortisol and the adrenal sex steroids can be analysed in a single separation of steroids by gas chromatography (GC) coupled to MS to give a urinary steroid profile (USP). Steroids individually and in profile are now commonly measured in plasma by liquid chromatography (LC) coupled with MS/MS. The steroid conjugates in urine can be determined after hydrolysis and derivative formation and for the first time without hydrolysis using GC-MS, GC-MS/MS and liquid chromatography with mass spectrometry (LC-MS/MS). The evolution of the technology, practicalities and clinical applications are examined in this review. The patterns and quantities of steroids changes through childhood. Information can be obtained on production rates, from which children with steroid excess and deficiency states can be recognised when presenting with obesity, adrenarche, adrenal suppression, hypertension, adrenal tumours, intersex condition and early puberty, as examples. Genetic defects in steroid production and action can be detected by abnormalities from the GC-MS of steroids in urine. New mechanisms of steroid synthesis and metabolism have been recognised through steroid profiling. GC with tandem mass spectrometry (GC-MS/MS) has been used for the tentative identification of unknown steroids in urine from newborn infants with congenital adrenal hyperplasia. Suggestions are made as to areas for future research and for future applications of steroid profiling. As routine hospital laboratories become more familiar with the problems of chromatographic and MS analysis they can consider steroid profiling in their test repertoire although with LC-MS/MS of urinary steroids this is unlikely to become a routine test because of the availability, cost and purity of the internal standards and the complexity of data interpretation. Steroid profiling with quantitative analysis by mass spectrometry (MS) after chromatography now provides the most versatile of tests of adrenal function in childhood.

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.

Farnesoid X receptor alpha: a molecular link between bile acids and steroid signaling?

Bile acids are cholesterol metabolites that have been extensively studied in recent decades. In addition to having ancestral roles in digestion and fat solubilization, bile acids have recently been described as signaling molecules involved in many physiological functions, such as glucose and energy metabolisms. These signaling pathways involve the activation of the nuclear receptor farnesoid X receptor (FXRα) or of the G protein-coupled receptor TGR5. In this review, we will focus on the emerging role of FXRα, suggesting important functions for the receptor in steroid metabolism. It has been described that FXRα is expressed in the adrenal glands and testes, where it seems to control steroid production. FXRα also participates in steroid catabolism in the liver and interferes with the steroid signaling pathways in target tissues via crosstalk with steroid receptors. In this review, we discuss the potential impacts of bile acid (BA), through its interactions with steroid metabolism, on glucose metabolism, sexual function, and prostate and breast cancers. Although several of the published reports rely on in vitro studies, they highlight the need to understand the interactions that may affect health. This effect is important because BA levels are increased in several pathophysiological conditions related to liver injuries. Additionally, BA receptors are targeted clinically using therapeutics to treat liver diseases, diabetes, and cancers.

CYP2C19 genotype has a major influence on labetalol pharmacokinetics in healthy male Chinese subjects

PURPOSE

The pharmacokinetics (PK) of labetalol show wide inter-subject variability, but the genetic causes for this are largely undetermined. This study was performed to examine whether common polymorphisms in UGT1A1, UGT2B7, CYP2C19 and ABCB1 affect the PK of labetalol.

METHODS

The PK of labetalol were determined in 37 Chinese healthy male subjects who took a single oral dose of 200 mg labetalol. Plasma concentrations of labetalol were determined by a high-performance liquid chromatographic method. Subjects were genotyped for the CYP2C19 2 and 3, UGT1A1 6, 28 and 60, UGT2B7 2 and ABCB1 1236C>T, 2677G>T/A and 3435C>T polymorphisms.

RESULTS

Subjects with the CYP2C19 2/ 2 genotype had a higher peak concentration (255.5 ± 80.1 vs. 156.0  ±  66.3 ng/mL; P < 0.05) and area under the concentration-time curve (AUC0-∞; 1,473.7 ± 493.6 vs. 502.8 ± 176.1 ng[Symbol: see text]h/mL; P < 0.001) than subjects with 60 or 28, and UGT2B7 2 did not result in a significant effect. Subjects with ABCB1 2677TA or TT or ABCB1 3435TT genotypes had higher AUC0-∞ and lower total clearance than the wild-types (P < 0.05), but this appeared to be related to the distribution of CYP2C19 genotypes. The CYP2C19 genotype appeared to be the only predictor of labetalol concentrations, accounting for approximately 60 % of the total variance in the AUC0-∞.

CONCLUSION

Our results suggest that the PK of labetalol are significantly affected by the common CYP2C19 polymorphisms in individuals of Chinese ethnicity. Future larger studies are needed to evaluate the effect of CYP2C19 and UGT1A1 polymorphisms on the PK of labetalol stereoisomers and the pharmacodynamic effects.

Functions and transcriptional regulation of adult human hepatic UDP-glucuronosyl-transferases (UGTs): mechanisms responsible for interindividual variation of UGT levels

Ten out of 19 UDP-glucuronosyltransferases (UGTs) are substantially expressed in adult human liver (>1% of total UGTs); 5 UGT1 isoforms (UGT1A1, 1A3, 1A4, 1A6 and 1A9) and 5 UGT2 family members (UGT2B4, 2B7, 2B10, 2B15 and 2B17) (Izukawa et al. [11]). Surprisingly, UGT2B4 and UGT2B10 mRNA were found to be abundant in human liver suggesting an underestimated role of the liver in detoxification of their major substrates, bile acids and eicosanoids. Among factors responsible for high interindividual variation of hepatic UGT levels (genetic diversity including polymorphisms and splice variants, regulation by liver-enriched transcription factors such as HNF1 and HNF4, and ligand-activated transcription factors) nuclear receptors (PXR, CAR, PPARalpha, etc.), and the Ah receptor are discussed. Unraveling the mechanisms responsible for interindividual variation of UGT expression will be beneficial for drug therapy but still remains a major challenge.

Aldosterone glucuronidation by human liver and kidney microsomes and recombinant UDP-glucuronosyltransferases: inhibition by NSAIDs

AIMS

To characterize: i) the kinetics of aldosterone (ALDO) 18beta-glucuronidation using human liver and human kidney microsomes and identify the human UGT enzyme(s) responsible for ALDO 18beta-glucuronidation and ii) the inhibition of ALDO 18beta-glucuronidation by non-selective NSAIDs.

METHODS

Using HPLC and LC-MS methods, ALDO 18beta-glucuronidation was characterized using human liver (n= 6), human kidney microsomes (n= 5) and recombinant human UGT 1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B10, 2B15, 2B17 and 2B28 as the enzyme sources. Inhibition of ALDO 18beta-glucuronidation was investigated using alclofenac, cicloprofen, diclofenac, diflunisal, fenoprofen, R- and S-ibuprofen, indomethacin, ketoprofen, ketorolac, meclofenamic acid, mefenamic acid, S-naproxen, pirprofen and tiaprofenic acid. A rank order of inhibition (IC(50)) was established and the mechanism of inhibition investigated using diclofenac, S-ibuprofen, indomethacin, mefenamic acid and S-naproxen.

RESULTS

ALDO 18beta-glucuronidation by hepatic and renal microsomes exhibited Michaelis-Menten kinetics. Mean (+/-SD) K(m), V(max) and CL(int) values for HLM and HKCM were 509 +/- 137 and 367 +/- 170 microm, 1075 +/- 429 and 1110 +/- 522 pmol min(-1) mg(-1), and 2.36 +/- 1.12 and 3.91 +/- 2.35 microl min(-1) mg(-1), respectively. Of the UGT proteins, only UGT1A10 and UGT2B7 converted ALDO to its 18beta-glucuronide. All NSAIDs investigated inhibited ALDO 18beta-G formation by HLM, HKCM and UGT2B7. The rank order of inhibition (IC(50)) of renal and hepatic ALDO 18beta-glucuronidation followed the general trend: fenamates > diclofenac > arylpropionates.

CONCLUSION

A NSAID-ALDO interaction in vivo may result in elevated intra-renal concentrations of ALDO that may contribute to the adverse renal effects of NSAIDs and their effects on antihypertensive drug response.

Analysis of copy number variation in the rhesus macaque genome identifies candidate loci for evolutionary and human disease studies

Copy number variants (CNVs) are heritable gains and losses of genomic DNA in normal individuals. While copy number variation is widely studied in humans, our knowledge of CNVs in other mammalian species is more limited. We have designed a custom array-based comparative genomic hybridization (aCGH) platform with 385 000 oligonucleotide probes based on the reference genome sequence of the rhesus macaque (Macaca mulatta), the most widely studied non-human primate in biomedical research. We used this platform to identify 123 CNVs among 10 unrelated macaque individuals, with 24% of the CNVs observed in multiple individuals. We found that segmental duplications were significantly enriched at macaque CNV loci. We also observed significant overlap between rhesus macaque and human CNVs, suggesting that certain genomic regions are prone to recurrent CNV formation and instability, even across a total of approximately 50 million years of primate evolution ( approximately 25 million years in each lineage). Furthermore, for eight of the CNVs that were observed in both humans and macaques, previous human studies have reported a relationship between copy number and gene expression or disease susceptibility. Therefore, the rhesus macaque offers an intriguing, non-human primate outbred model organism with which hypotheses concerning the specific functions of phenotypically relevant human CNVs can be tested.

Human Renal Cortical and Medullary UDP-Glucuronosyltransferases (UGTs): Immunohistochemical Localization of UGT2B7 and UGT1A Enzymes and Kinetic Characterization ofS-Naproxen Glucuronidation

There is currently little information regarding the localization of UDP-glucuronosyltransferases (UGTs) in human renal cortex and medulla, and the functional contribution of renal UGTs to drug glucuronidation remains poorly defined. Using human kidney sections and human kidney cortical microsomes (HKCM) and human kidney medullary microsomes (HKMM), we combined immunohistochemistry to investigate UGT1A and UGT2B7 expression with in vitro microsomal studies to determine the kinetics of S-naproxen acyl glucuronidation. With the exception of the glomerulus, Bowman's capsule, and renal vasculature, UGT1A proteins and UGT2B7 were expressed throughout the proximal and distal convoluted tubules, the loops of Henle, and the collecting ducts. Additionally, UGT1A and UGT2B7 expression was demonstrated in the macula densa, supporting a potential role of UGTs in regulating aldosterone. Consistent with the immunohistochemical data, S-naproxen acyl glucuronidation was catalyzed by HKCM and HKMM. Kinetic data were well described by the two-enzyme Michaelis-Menten equation. K(m) values for the high-affinity components were 34 +/- 14 microM (HKCM) and 45 +/- 14 microM (HKMM). Fluconazole inhibited the high-affinity component establishing UGT2B7 as the enzyme responsible for S-naproxen glucuronidation in cortex and medulla. The low-affinity component was relatively unaffected by fluconazole (<15% inhibition), supporting the presence of other UGTs with S-naproxen glucuronidation capacity (e.g., UGT1A6 and UGT1A9) in cortex and medulla. We postulate that the ubiquitous distribution of UGTs in mammalian kidney may buffer physiological responses to endogenous mediators, but at the same time competitive xenobiotic-endobiotic interactions may provide an explanation for the adverse renal effects of drugs, including nonsteroidal anti-inflammatory drugs.

Klotho--a common link in physiological and rheumatoid arthritis-related aging of human CD4+ lymphocytes

Human CD4(+) T lymphocytes undergo aging-related changes leading to decreased immunity to infections and neoplasms, and to increased frequency of autoimmune diseases including rheumatoid arthritis (RA). Certain changes, observed in the CD4(+) cells of RA patients, resemble those observed during physiological aging, but occur at earlier age. Underlying cellular mechanism(s) of these similarities are so far largely unknown. Here we show that KLOTHO, a beta-glucuronidase gene whose activity changes are associated with aging phenotype, is down-regulated at the mRNA, protein, and enzymatic (beta-glucuronidase) activity levels both in the healthy elderly and especially in RA CD4(+) lymphocytes. Although the exact role of Klotho activity for CD4(+) cell function is unknown, we propose here that it might be involved in anti-inflammatory processes occurring in the young and healthy individuals, but reduced in both healthy elderly and RA patients. To support this hypothesis, we show here that the reduction of Klotho expression and activity in both elderly and patients' lymphocytes occurs in concert with the down-regulation of T cell costimulatory molecule CD28, the latter known to be dependent on increased levels of TNF-alpha. Thus, a common mechanism of KLOTHO down-regulation, but executed at various times in life, may underlie both physiological and disease-related T cell aging. Klotho activity might become a target of anti-RA drug development as well as a tool to help increase the immune system efficiency in the elderly.

Cellular specific expression of the androgen-conjugating enzymes UGT2B15 and UGT2B17 in the human prostate epithelium

In humans, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-HSD, and 5alpha-reductase enzymes convert dehydroepiandrosterone (DHEA), androstenedione, and testosterone into the most potent natural androgen dihydrotestosterone (DHT) in the prostate. This androgen is transformed mainly in situ to two Phase I metabolites, androsterone (ADT) and androstane-3alpha,17beta-diol (3alpha-DIOL), which can, however, be back-converted to DHT. Here, we report recent findings on the characterization of specific anti-UDP-glucuronosyltransferases (UGT) 2B15 and 2B17 antibodies and their use to identify UGT2B expressing-cells in the human prostate epithelium. We found that UGT2B17 is expressed in basal cells where DHEA is converted into 3alpha-DIOL and ADT. By contrast, the expression of UGT2B 15 was observed only in luminal cells, where DHT is formed from testosterone. These results demonstrate that, in the human prostate, UGT2B15 and UGT2B17 genes have complementary roles, and are expressed in cells where their specific substrates are synthesized. This reinforces the hypothesis that UGT enzymes catalyze an important mechanism for modulating the action of steroids and protecting the steroid-sensitive tissues from deleteriously high steroid concentrations.

Steroid hormone biotransformation and xenobiotic induction of hepatic steroid metabolizing enzymes

Normal reproductive development depends on the interplay of steroid hormones with their receptors at specific tissue sites. The concentrations of hormone ligands in the circulation and at target sites are maintained through coordinated regulation on steroid biosynthesis and degradation. Changed bioavailability of steroids, through alteration of steroidogenesis or biotransformation rates, leads to changes in endocrine function. Steroid hormones lose their receptor reactivity in most cases when they are bound to binding proteins, while metabolic conversion can result in either active or inactive metabolites. Hydroxylation by cytochrome P450 (CYP) enzymes and conjugation with glucuronide and sulfate are among the major hepatic pathways of steroid inactivation. The expression of these biotransformation enzymes can be induced by many xenobiotics. The barbiturate phenobarbital and the environmental toxicant 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) are among the well characterized inducers for the CYP 2B and 3A enzymes and selected conjugation enzymes. The induction of the steroid biotransformation enzymes is partly mediated through the activation of a group of nuclear receptors including the glucocorticoid receptor, the constitutive androstane receptor (CAR), the pregnane X receptor (PXR), and the peroxisome proliferator activated receptors (PPAR). Drug or chemical-induced increases in hepatic enzyme activities are often a basis for drug-drug interactions that lead to enhanced elimination and reduced therapeutic efficacy of steroidal drugs. The effects of enzyme induction on endogenous steroid clearance, along with its possible consequence, are less well understood. While enzyme induction by xenobiotics may increase clearance of the endogenous steroid, regulatory mechanisms for steroid homeostasis may adapt and compensate for altered clearance.

Inactivation of androgens by UDP-glucuronosyltransferase enzymes in humans

In humans, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-HSD and 5alpha-reductase activities in androgen target tissues, such as the prostate and skin, convert dehydroepiandrosterone, androstenedione and testosterone into the most potent natural androgen dihydrotestosterone (DHT). This androgen is converted mainly in situ into two phase I metabolites, androsterone (ADT) and androstane-3alpha,17beta-diol (3alpha-DIOL), which might be back converted to DHT. Here, we discuss the recent findings regarding the characterization of specific UDP-glucuronosyltransferases (UGTs), UGT2B7, B15 and B17, responsible for the glucuronidation of these metabolites. The tissue distribution and cellular localization of the UGT2B transcripts and proteins in humans clearly indicate that these enzymes are synthesized in androgen-sensitive tissues. It is postulated that the conjugating activity of UGT enzymes is the main mechanism for modulating the action of steroids and protecting the androgen-sensitive tissues from deleteriously high concentrations of DHT, ADT and 3alpha-DIOL.