The cynomolgus monkey (Macaca fascicularis) is the best animal model for the study of steroid glucuronidation

doi:10.1016/S0960-0760(03)00235-8

The Journal of Steroid Biochemistry and Molecular Biology

Volume 85, Issues 2–5, June 2003, Pages 235-245

https://doi.org/10.1016/S0960-0760(03)00235-8 Get rights and content

Abstract

Intense research efforts performed during the past decade clearly established the major role of glucuronidation and uridine-diphospho-glucuronosyltransferase (UGT) enzymes for steroid metabolism in humans. However, a clear understanding of the physiological importance of this metabolic process requires in vivo studies. Numerous evidences ascertain that simians are the most appropriate animal models for such studies. Indeed human and monkey have a similar pattern of steroidogenesis, unlike common laboratory mammals such as rat or mouse. Furthermore, human and monkey are unique in having high levels of circulating androsterone glucuronide and androstane-3α-diol glucuronide (3α-Diol-G). In addition, characterization of eight monkey UGT proteins demonstrated the similarity of their conjugation activity toward steroid hormones. Like human ones, monkey enzymes are expressed in steroid target tissues, where they preferentially glucuronidate androgen and estrogen metabolites. In monkey tissues, immunohistochemical studies demonstrated that UGT2B proteins are expressed in a cell-type specific manner in ovary and kidney, where they control androgens and aldosterone inactivation. These results identify the cynomolgus monkey as an appropriate animal model for the determination of cellular localization of UGT enzymes in steroid target tissues and for the identification of endogenous or exogenous stimuli affecting steroid glucuronidation.

Introduction

Conjugation of compounds by glucuronidation is a pathway found in all vertebrates [1]. This reaction is catalyzed by uridine-diphosphate-glucuronosyltransferase (UGT) enzymes and corresponds to the transfer of the glucuronosyl group from uridine-5′-diphosphoglucuronic acid (UDPGA) to acceptor molecules [1]. Substrates for UGT enzymes are generally hydrophobic compounds with oxygen, nitrogen and sulfur functional groups. The glucuronide products are more polar, generally water soluble and more easily excreted in bile or urine [1]. Glucuronidation is a major metabolic pathway for more than 40% of all the xenobiotics to which the human body is exposed, and for numerous endogenous molecules such as bilirubin, bile acids and steroids [2], [3].

Section snippets

UDP-glucuronosyltransferase (UGT) enzymes

To date, numerous UGT cDNAs have been isolated from several mammalian species. In humans, 16 proteins were characterized and categorized into two major families, UGT1 and UGT2, according to their primary amino acid sequence homology [4]. The entire UGT1 family is derived from a single gene locus (UGT1A), located on chromosome 2 (2q37), coding for nine functional proteins (UGT1A1, UGT1A3–1A10) and three pseudogenes [5], [6]. The physiological importance of UGT1 enzymes is demonstrated by

Glucuronidation of steroid hormones in humans

Numerous studies on steroid metabolism demonstrated that androsterone glucuronide (ADT-G) and 5α-androstane-3α, 17β-diol glucuronide (3α-Diol-G) are the major circulating C19-steroid metabolites in humans [29]. Furthermore, the plasma levels of these glucuronide derivatives reflect the peripheral tissue conversion of adrenal and gonadal precursor C19-steroids to active androgens in various pathophysiological conditions [30]. More recently, identification and characterization of human UGT2Bs

Human UGT enzymes are expressed in steroid target tissues

It is widely accepted that the liver is a major site of glucuronidation. However, there is accumulating evidences that extrahepatic tissues are also involved in the conjugation of steroids hormones. High levels of 5α-reduced C19-steroid glucuronides were measured in the human prostate, breast cyst fluid and ovarian follicular fluid, indicating that glucuronidation of these androgen metabolites occurs in these tissues [37], [38], [39]. In the skin, where local androgens synthesis occurs,

Characterization of the cynomolgus monkey as an animal model for studying steroid glucuronidation in extrahepatic tissues

Identification and characterization of human UGT enzymes during the 1990s evidenced the importance of these enzymes in the metabolism of steroid hormones. However, a clear understanding of the physiological role of UGTs in sex hormones inactivation and elimination required in vivo analyses. To obtain a relevant system in which to study the role of steroid glucuronidation, it was suggested that non-human primates may be the most appropriate animal model. Indeed, the crab-eating (or cynomolgus)

Cellular localization of UGT2B enzymes in monkey tissues

The physiological importance of UGT enzymes depends not only on their ability to conjugate steroid hormones, but also on their tissue- and cell-specific expression. As example, in human prostate the expression of UGT2B15 and UGT2B17, two major androgen-conjugating enzymes is cell-type specific in the two cell layers epithelium. Indeed, UGT2B17 is expressed only in androgen producing basal cells, whereas UGT2B15 expression is detected only in androgen responsive luminal cells [60]. These

Conclusion

The present data identify the cynomolgus monkey as a relevant animal model for studying steroid glucuronidation. This model constitutes a unique tool for determining whether UGT enzymes conjugate active steroids or their reduced metabolites inside target cells. Emerging evidences from in vitro systems indicate that UGT enzymes expression is regulated by a wide variety of endogenous or exogenous stimuli [23], [26], [69], [70], [71], [72], [73]. However, complexities of glucuronidation renders

Acknowledgements

The authors thank Dr. V. Bocher for critical reading of the manuscript.

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^☆: Presented at the 11th International Congress on Hormonal Steroids and Hormones and Cancer, ICHS & ICHC, Fukuoka, Japan, 21–25 October 2002.

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The cynomolgus monkey (Macaca fascicularis) is the best animal model for the study of steroid glucuronidation☆

Abstract

Introduction

Section snippets

UDP-glucuronosyltransferase (UGT) enzymes

Glucuronidation of steroid hormones in humans

Human UGT enzymes are expressed in steroid target tissues

Characterization of the cynomolgus monkey as an animal model for studying steroid glucuronidation in extrahepatic tissues

Cellular localization of UGT2B enzymes in monkey tissues

Conclusion

Acknowledgements

J. Steroid Biochem. Mol. Biol.

Prog. Nucleic Acid. Res. Mol. Biol.

J. Biol. Chem.

Arch. Biochem. Biophys.

Brain. Res. Mol. Brain Res.

Brain Res. Mol. Brain Res.

J. Biol. Chem.

Biochem. Biophys. Res. Commun.

Biochem. Biophys. Res. Commun.

J. Mol. Biol.

Biochem. Biophys. Res. Commun.

J. Biol. Chem.

Fertil. Steril.

J. Steroid Biochem. Mol. Biol.

Eur. J. Cancer

J. Invest. Dermatol.

J. Steroid Biochem. Mol. Biol.

Reprod. Toxicol.

J. Steroid Biochem. Mol. Biol.

Gastroenterology

J. Mol. Biol.

Biochem. Biophys. Res. Commun.

Arch. Biochem. Biophys.

Mol. Cell. Endocrinol.

Pharmacogenomics: translating functional genomics into rational therapeutics

Science

The UDP glycosyltransferase gene superfamily: recommended nomenclature update based on evolutionary divergence

Pharmacogenetics

The novel UGT1 gene complex links bilirubin, xenobiotics, and therapeutic drug metabolism by encoding UDP-glucuronosyltransferase isozymes with a common carboxyl terminus

J. Pharmacokinet. Biopharm.

The novel bilirubin/phenol UDP-glucuronosyltransferase UGT1 gene locus: implications for multiple nonhemolytic familial hyperbilirubinemia phenotypes

Pharmacogenetics

Identification of a genetic alteration in the code for bilirubin UDP-glucuronosyltransferase in the UGT1 gene complex of a Crigler–Najjar type I patient

J. Clin. Invest.

Investigation of the substrate specificity of a cloned expressed human bilirubin UDP-glucuronosyltransferase: UDP-sugar specificity and involvement in steroid and xenobiotic glucuronidation

Biochem. J.

Substrate specificities of two stably expressed human liver UDP-glucuronosyltransferases of the UGT1 gene family

Drug Metab. Dispos.

Odorant signal termination by olfactory UDP glucuronosyl transferase

Nature

The glucuronidation of opioids, other xenobiotics, and androgens by human UGT2B7Y (268) and UGT2B7H (268)

Drug Metab. Dispos.

Isolation and characterization of UGT2B15(Y85): a UDP-glucuronosyltransferase encoded by a polymorphic gene

Pharmacogenetics

Characterization and substrate specificity of UGT2B4 (E458): a UDP-glucuronosyltransferase encoded by a polymorphic gene

Pharmacogenetics