Despite significant advances in contraceptive options for women over the last 50 yr, world population continues to grow rapidly. Scientists and activists alike point to the devastating environmental impacts that population pressures have caused, including global warming from the developed world and hunger and disease in less developed areas. Moreover, almost half of all pregnancies are still unwanted or unplanned. Clearly, there is a need for expanded, reversible, contraceptive options. Multicultural surveys demonstrate the willingness of men to participate in contraception and their female partners to trust them to do so. Notwithstanding their paucity of options, male methods including vasectomy and condoms account for almost one third of contraceptive use in the United States and other countries. Recent international clinical research efforts have demonstrated high efficacy rates (90-95%) for hormonally based male contraceptives. Current barriers to expanded use include limited delivery methods and perceived regulatory obstacles, which stymie introduction to the marketplace. However, advances in oral and injectable androgen delivery are cause for optimism that these hurdles may be overcome. Nonhormonal methods, such as compounds that target sperm motility, are attractive in their theoretical promise of specificity for the reproductive tract. Gene and protein array technologies continue to identify potential targets for this approach. Such nonhormonal agents will likely reach clinical trials in the near future. Great strides have been made in understanding male reproductive physiology; the combined efforts of scientists, clinicians, industry and governmental funding agencies could make an effective, reversible, male contraceptive an option for family planning over the next decade.

Advances in male contraception.

Irinotecan (CPT-11) is a promising antitumor agent, recently approved for use in patients with metastatic colorectal cancer. Its active metabolite, SN-38, is glucuronidated by hepatic uridine diphosphate glucuronosyltransferases (UGTs). The major dose-limiting toxicity of irinotecan therapy is diarrhea, which is believed to be secondary to the biliary excretion of SN-38, the extent of which is determined by SN-38 glucuronidation. The purpose of this study was to identify the specific isoform of UGT involved in SN-38 glucuronidation. In vitro glucuronidation of SN-38 was screened in hepatic microsomes from normal rats (n = 4), normal humans (n = 25), Gunn rats (n = 3), and patients (n = 4) with Crigler-Najjar type I (CN-I) syndrome. A wide intersubject variability in in vitro SN-38 glucuronide formation rates was found in humans. Gunn rats and CN-I patients lacked SN-38 glucuronidating activity, indicating the role of UGT1 isoform in SN-38 glucuronidation. A significant correlation was observed between SN-38 and bilirubin glucuronidation (r = 0.89; P = 0.001), whereas there was a poor relationship between para-nitrophenol and SN-38 glucuronidation (r = 0.08; P = 0.703). Intact SN-38 glucuronidation was observed only in HK293 cells transfected with the UGT1A1 isozyme. These results demonstrate that UGT1A1 is the isoform responsible for SN-38 glucuronidation. These findings indicate a genetic predisposition to the metabolism of irinotecan, suggesting that patients with low UGT1A1 activity, such as those with Gilbert's syndrome, may be at an increased risk for irinotecan toxicity.

/pdf/genetic-predisposition-to-the-metabolism-of-irinotecan-cpt-54sy16emdy.pdf

Genetic predisposition to the metabolism of irinotecan (CPT-11). Role of uridine diphosphate glucuronosyltransferase isoform 1A1 in the glucuronidation of its active metabolite (SN-38) in human liver microsomes.

Previous studies have identified the ATP-dependent export of glutathione conjugates as a physiological function of the multidrug resistance protein (MRP). The involvement of MRP in the transport of endogenous and xenobiotic conjugates was investigated further using membrane vesicles from MRP -transfected HeLa cells. The ATP-dependent transport of the glutathione conjugates [3H]leukotriene C4, S -(2,4-dinitrophenyl)-[3H]glutathione, and 3H-labeled oxidized glutathione was characterized by determination of the transport efficiency Vmax: K m amounting to 1031, 114, and 7.1 ml × mg protein-1 × min-1, respectively. Additional endogenous substrates for MRP-mediated transport included the steroid conjugate 17β-glucuronosyl [3H]estradiol and the bile salt conjugates [6α-14C]glucuronosylhyodeoxycholate and 3α-sulfatolithocholyl [3H]taurine. The K m value of MRP for 17β-glucuronosyl [3H]estradiol was 1.5 ± 0.3 µm, with a Vmax: K m ratio of 42 ml × mg protein-1 × min-1, and a K i value of 0.7 µm for the leukotriene receptor antagonist MK 571. MRP-mediated ATP-dependent transport was observed for the anticancer drug conjugates glucuronosyl [3H]etoposide and monochloro-mono[3H]glutathionyl melphalan, but not for unmodified [14C]doxorubicin, [3H]daunorubicin, or [3H]vinblastine. Our results establish that MRP functions as an ATP-dependent export pump not only for glutathione conjugates but also for glucuronidated and sulfated endogenous as well as exogenous compounds.

/pdf/transport-of-glutathione-glucuronate-and-sulfate-conjugates-4lah24d757.pdf

Transport of glutathione, glucuronate, and sulfate conjugates by the MRP gene-encoded conjugate export pump.

UDP-Glucuronosyltransferases (UGTs) are glycoproteins localized in the endoplasmic reticulum (ER) which catalyze the conjugation of a broad variety of lipophilic aglycon substrates with glucuronic acid using UDP-glucuronic acid (UDP-GIcUA) as the sugar donor. Glucuronidation is a major factor in the elimination of lipophilic compounds from the body. In this review, current information on the substrate specificities of UGT1A and 2B family isoforms is discussed. Recent findings with regard to UGT structure and topology are presented, including a dynamic topological model of UGTs in the ER. Evidence from experiments on UGT interactions with inhibitors directed at specific amino acids, photoaffinity labeling, and analysis of amino acid alignments suggest that UDP-GIcUA interacts with residues in both the N- and C-terminal domains, whereas aglycon binding sites are localized in the N-terminal domain. The amino acids identified so far as crucial for substrate binding and catalysis are arginine, lysine, histidine, proline, and residues containing carboxylic acid. Site-directed mutagenesis experiments are critical for unambiguous identification of the active-site architecture.

Structural and functional studies of udp-glucuronosyltransferases*

Intrahepatic cholestasis of pregnancy: molecular pathogenesis, diagnosis and management.

beta-Glucosidase 2 (GBA2) is a resident enzyme of the endoplasmic reticulum thought to play a role in the metabolism of bile acid-glucose conjugates. To gain insight into the biological function of this enzyme and its substrates, we generated mice deficient in GBA2 and found that these animals had normal bile acid metabolism. Knockout males exhibited impaired fertility. Microscopic examination of sperm revealed large round heads (globozoospermia), abnormal acrosomes, and defective mobility. Glycolipids, identified as glucosylceramides by mass spectrometry, accumulated in the testes, brains, and livers of the knockout mice but did not cause obvious neurological symptoms, organomegaly, or a reduction in lifespan. Recombinant GBA2 hydrolyzed glucosylceramide to glucose and ceramide; the same reaction catalyzed by the beta-glucosidase acid 1 (GBA1) defective in subjects with the Gaucher's form of lysosomal storage disease. We conclude that GBA2 is a glucosylceramidase whose loss causes accumulation of glycolipids and an endoplasmic reticulum storage disease.

/pdf/mutation-of-b-glucosidase-2-causes-glycolipid-storage-4v2r1gk80k.pdf

Mutation of β-glucosidase 2 causes glycolipid storage disease and impaired male fertility

The aim of this study was to define whether N-acetylglucosaminidation is a selective conjugation pathway of structurally related bile acids in humans. The following bile acids released enzymatically from N-acetylglucosaminides were identified: 3 alpha,7 beta-dihydroxy-5 beta-cholanoic (ursodeoxycholic), 3 beta, 7 beta-dihydroxy-5 beta-cholanoic (isoursodeoxycholic), 3 beta,7 beta-dihydroxy-5 alpha-cholanoic (alloisoursodeoxycholic), 3 beta,7 beta-dihydroxy-5-cholenoic, 3 alpha,7 beta,12 alpha-trihydroxy-5 beta-cholanoic, and 3 alpha,6 alpha,7 beta-trihydroxy-5 beta-cholanoic acids. The selectivity of conjugation was studied by administration of 0.5 g ursodeoxycholic (UDCA) or hyodeoxycholic (HDCA) acids, labeled with 13C, to patients with extrahepatic cholestasis, and of 0.5 g of 13C-labeled chenodeoxycholic acid (CDCA) to patients with extra- or intrahepatic cholestasis. After administration of [24-13C]-CDCA, labeled glucosides, and the glucuronide of CDCA were excreted in similar amounts. Labeled N-acetylglucosaminides of UDCA and isoUDCA were also formed. When [24-13C]-UDCA was given, 13C-label was detected in the N-acetylglucosaminide, the glucosides, and the glucuronide of UDCA, and in the N-acetylglucosaminide of isoUDCA. In the patient studied, 32% of the total UDCA excreted in urine was conjugated with N-acetylglucosamine. In contrast, 96% of the excreted amount of [24-13C]HDCA was glucuronidated, and 13C-labeled glucosides but no N-acetylglucosaminide were detected. The selectivity of N-acetylglucosaminidation towards bile acids containing a 7 beta-hydroxyl group was confirmed in vitro using human liver and kidney microsomes and uridine diphosphate glucose (UDP)-N-acetylglucosamine. These studies show that N-acetylglucosaminidation is a selective conjugation pathway for 7 beta-hydroxylated bile acids.

/pdf/bile-acid-n-acetylglucosaminidation-in-vivo-and-in-vitro-4ju1z2oniq.pdf

Bile acid N-acetylglucosaminidation. In vivo and in vitro evidence for a selective conjugation reaction of 7 beta-hydroxylated bile acids in humans.

Purification and Characterization of a Microsomal Bile Acid β-Glucosidase from Human Liver

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2887%2981532-6

H. Matern

Papers

Mutation of β-glucosidase 2 causes glycolipid storage disease and impaired male fertility

Bile acid N-acetylglucosaminidation. In vivo and in vitro evidence for a selective conjugation reaction of 7 beta-hydroxylated bile acids in humans.

Purification and Characterization of a Microsomal Bile Acid β-Glucosidase from Human Liver

Evidence for bile acid glucosides as normal constituents in human urine.

Molecular Cloning and Expression of Human Bile Acid β-Glucosidase