Androgen glucuronyl transferase activity in rat liver, evidence for the importance of hepatic tissue in 5 alpha-reduced androgen metabolism

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Enzyme-assisted synthesis and structure characterization of glucuronide conjugates of eleven anabolic steroid metabolites

Enzyme-assisted in vitro synthesis of eleven glucuronide-conjugated anabolic androgenic steroid (AAS) metabolites was performed using biphenyl-induced rat liver microsomal enzymes. The substrates within the study were the main compounds and metabolites detected in human urine after dosing of, e.g. metandienone, metenolone, methyltestosterone, nandrolone, and testosterone. Yields of glucuronidation reactions were 13-28% for most compounds, but significantly higher (77-78%) for the substrates with 4-ene-3-one double bond system of the steroid A-ring. Characterization of glucuronide-conjugated AAS structures was based on nuclear magnetic resonance spectroscopy ((1)H NMR) and on liquid chromatographic-mass spectrometric (LC-MS) and tandem mass spectrometric (LC-MS/MS) analyses in positive and negative ion mode electrospray ionization (ESI). Only minor differences were observed in optimal synthesis conditions between various substrates, which offer a potential to apply this in vitro assay as a default method for glucuronidation of new AAS substrates. The method allowed for a rapid production pathway of stereochemically pure AAS glucuronides in milligram amount, such as needed, e.g. in the development of analytical methods in forensic or pharmaceutical sciences, as well as in doping control.

Activity and expression of various isoforms of uridine diphosphate glucuronosyltransferase are differentially regulated during hepatic regeneration in rats

PURPOSE

Glucuronidation pathway is very important in the detoxification of endogenous and exogenous compounds. The objective of this study was to evaluate the activity and expression of various hepatic uridine diphosphate glucuronosyltransferases (UGTs) in rats at various time points after initiation of hepatic regeneration by partial hepatectomy (PHx).

METHODS

The mRNA expression of various UGTs was evaluated using real-time polymerase chain reaction (real-time PCR) with specific primers. The in vitro activity of UGTs was evaluated using different substrates such as estradiol (UGT1A1), acetaminophen (UGT1A6/7), morphine (UGT2B1), testosterone (UGT2B1/3/6), androsterone (UGT2B2), and (-)-borneol (UGT2B12).

RESULTS

Whereas the activity and mRNA expression of UGT1A1, UGT2B1, UGT2B1/3/6, UGT2B2, and UGT2B12 were lower, the activity and mRNA expression of UGT1A6/7 were preserved during hepatic regeneration. The mRNA expression of UGT2B8 was down-regulated, whereas the mRNA expression of UGT1A5 and UGT1A8 was not altered by PHx. The mRNA expression of UGT1A2 and UGT1A3 was increased during hepatic regeneration.

CONCLUSION

UGT-mediated drug-metabolizing ability of the liver was altered differentially in the regenerating rat liver. Individualized dosing regimen for different UGT substrates may be needed when using such substrates of these enzymes in patients with a regenerating liver, especially during the early postoperative period. However, the glucuronide conjugating capacity of the liver in the donor of a living donor liver transplantation is expected to completely return to normal with time after surgery.

Anticonvulsant activity of androsterone and etiocholanolone

PURPOSE

Men with epilepsy often have sexual or reproductive abnormalities that are attributed to alterations in androgen levels, including subnormal free testosterone. Levels of the major metabolites of testosterone-androsterone (5alpha-androstan-3alpha-ol-17-one; 5alpha,3alpha-A), a neurosteroid that acts as a positive allosteric modulator of GABA(A) receptors, and its 5beta-epimer etiocholanolone (5beta-androstan-3alpha-ol-17-one; 5beta,3alpha-A)-also may be reduced in epilepsy. 5alpha,3alpha-A has been found in adult brain, and both metabolites, which also can be derived from androstenedione, are present in substantial quantities in serum along with their glucuronide and sulfate conjugates. This study sought to determine whether these endogenous steroid metabolites can protect against seizures.

METHODS

The anticonvulsant activity of 5alpha,3alpha-A and 5beta,3alpha-A was investigated in electrical and chemoconvulsant seizure models in mice. The steroids also were examined for activity against extracellularly recorded epileptiform discharges in the CA3 region of the rat hippocampal slice induced by perfusion with 55 microM 4-aminopyridine (4-AP).

RESULTS

Intraperitoneal injection of 5alpha,3alpha-A-protected mice in a dose-dependent fashion from seizures in the following models (ED50, dose in mg/kg protecting 50% of animals): 6-Hz electrical stimulation (29.1), pentylenetetrazol (43.5), pilocarpine (105), 4-AP (215), and maximal electroshock (224). 5beta,3alpha-A also was active in the 6-Hz and pentylenetetrazol models, but was less potent (ED50 values, 76.9 and 139 mg/kg, respectively), whereas epiandrosterone (5alpha,3beta-A) was inactive (ED50, <or=300 mg/kg). 5alpha,3alpha-A (10-100 microM) also inhibited epileptiform discharges in a concentration-dependent fashion in the in vitro slice model, whereas 5beta,3alpha-A was active but of lower potency, and 5alpha,3beta-A was inactive.

CONCLUSIONS

5alpha,3alpha-A and 5beta,3alpha-A have anticonvulsant properties. Although of low potency, the steroids are present in high abundance and could represent endogenous modulators of seizure susceptibility.

Enzyme-assisted synthesis and structure characterization of glucuronide conjugates of methyltestosterone (17 alpha-methylandrost-4-en-17 beta-ol-3-one) and nandrolone (estr-4-en-17 beta-ol-3-one) metabolites

A new and useful method based on enzyme-assisted synthesis was developed for producing 3 alpha-O-beta-D-glucuronide conjugates from synthetic phase I metabolites of methyltestosterone and nandrolone. The formed glucuronide conjugates of 17 alpha-methyl-5 alpha-androstane-3 alpha,17 beta-diol (I), 17 alpha-methyl-5 beta-androstane-3 alpha,17 beta-diol (II), 5 alpha-estran-3 alpha-ol-17-one (III), and 5 beta-estran-3 alpha-ol-17-one (IV) are urinary metabolites, indicating the human misuse of the above-mentioned anabolic androgenic steroids (AAS). The common lack of reference material precludes the use and validation of these biomarkers in human doping control. Liver microsomes from Aroclor 1254-induced rats were used as a highly active source of mammalian UDP-glucuronosyltransferases (UGT, EC 2.4.1.17). After purification by protein precipitation, liquid-liquid extraction (dichloromethane), C-18 solid-phase extraction, and lyophilization, the steroid glucuronide structures were characterized by (1)H and (13)C NMR spectroscopy and tandem mass spectrometry. The enzymatic method was highly stereoselective, producing a single major conjugate from the parent steroids I-IV. The stereochemically pure steroid glucuronide conjugates were recovered in milligram amounts (1.0-2.8 mg, yield 12-29%), which is sufficient for veterinary and human doping control analyses; for pharmaco-, toxico-, and enzyme kinetic studies in the pharmaceutical industry; for clinical laboratories; and for forensic medicine. A new sensitive LC-MS method was developed for controlling the product purity in syntheses, as well as for enzyme kinetic characterization of AAS-metabolizing UGT activities in rat liver toward the aglycones I-IV. In this study, the UGT enzymes responsible for the formation of 3 alpha-O-linked glucuronides from the substrates I, II, III, and IV exhibited the specific enzyme activity values: 25, 124, 48, and 212 nmol/mg microsomal protein in a 2-h incubation, respectively.

Levels of plasma C19 steroids and 5 alpha-reduced C19 steroid glucuronides in primates, rodents, and domestic animals

In this study, a comparison of circulating levels of androsterone glucuronide and androstane-3 alpha, 17 beta-diol glucuronide in the male and female of several mammalian species was performed. Glucuronidated steroids were not detected in the circulation of the dog, bovine, swine, and rodent. High levels of circulating glucuronidated steroids were measured in the cynomolgus monkey and found to be 10-fold higher than in humans. The determination of tissue levels of unconjugated and conjugated C19 steroids was then performed in intact and castrated rats treated with androgens. Steroid glucuronides were not detected in the plasma, skin, prostate, or liver of either intact or treated rats, although the levels of unconjugated steroids in the plasma and tissues were increased after steroid treatments. Significant levels were detected in the bile, thus suggesting hepatic formation of steroid glucuronides in the rat. It is suggested that the monkey represents the best animal model to date to study the contribution of diphosphoglucuronosyltransferases present in steroid target peripheral tissues to circulating levels of steroid glucuronides.

Androgen metabolism by hepatic and renal tissues of the fetal rhesus monkey

Liver and kidney from fetal monkeys (day 125 of gestation) were fractionated into low speed pellets, microsomal and cytosolic fractions. Liver cytosols converted as much testosterone (T) to 5 beta-androstane-3 alpha,17 beta-diol (5 beta-diol) at 0 degrees C as at 4 degrees-45 degrees C without exogenous cofactors. The principal product formed from 5 alpha-dihydrotestosterone (5 alpha-DHT) was 5 alpha-diol. A 1000-fold molar excess of radioinert 5 beta- or 5 alpha-DHT inhibited 5 beta-diol formation from [3H]T by cytosols and increased 5 beta-DHT formation. Similarly, using 5 alpha-DHT as substrate, 5 alpha-diol formation was inhibited. Microsomal and low speed pellets with added cofactors formed products which recrystallized with either etiocholanolone or androsterone from [3H]T or [3H]DHT, respectively. Little product was formed without cofactor. Whole liver homogenates produced 5 beta-reduced products from [3H]T in the presence of an NADPH generating system whereas kidney homogenates produced 5 alpha-reduced products. These data provide new information on the capacity of fetal monkey liver and kidney to metabolize androgens. The 3 alpha-reductases are cytosolic. The 5 alpha- and 5 beta-reductases are mostly in the low speed pellet but are sufficiently represented in cytosols to mediate diol formation. The 17-hydroxysteroid dehydrogenases are in the microsomal fraction. Our results suggest that 5 alpha-DHT is the active androgen in fetal liver since testosterone is metabolized to 5 beta-DHT and 5 beta-diol which are inactive androgens.