The effect of premature and delayed birth on the development of UDP-glucuronosyltransferase activities towards bilirubin, morphine and testosterone in the rat

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

A unique bilirubin-UDP-glucuronosyltransferase deficiency related to neonatal jaundice in mice

This report describes biochemical and cellular characterization of a spontaneous mutation in ICR mice; the mutation has been phenotypically characterized as autosomal recessive jaundice in neonates and juveniles and given the gene symbol hub (J. Hered. 76:441-446, 1985; Mouse Newslett. 73:28, 1985). The results obtained demonstrate that (1) mice homozygous for the mutation are deficient in bilirubin-UDP-glucuronosyltransferase activity, and there is no deficiency in heterozygous mice, (2) the deficiency is lifelong, even though the clinical symptom of jaundice is transitory and restricted to neonates or juveniles, (3) bilirubin-UDP-glucuronosyltransferase activity in mutant and nonmutant mice is similarly induced by triiodothyronine, (4) glucuronidation and xylodation of bilirubin probably occur as the result of separate enzyme forms in mice, and (5) Western analysis using antibody to rat bilirubin-UDP-glucuronosyltransferase indicates that although there is no electrophoretic mobility difference, there is a diffuse band missing in mutant mice. Hepatic hyperplasia, cytomegaly, single-cell necrosis, and eosinophilic foci are also pleiotropic traits associated with homozygous but not heterozygous hub. The hub/hub mouse will be useful in the study of substrate specificity and regulation within a complex gene family and, perhaps, provide a new and useful animal model for the long-term health effects of deficiency in the metabolism of xenobiotics cleared via UDP-glucuronosyltransferase.

Expression of P450 isoenzymes during rat liver organogenesis

1. The expression of P450 isoenzymes in foetal and neonatal hepatic microsomes was determined by measuring the metabolism of marker substrates and by studying the expression of P450 isoenzymes at the protein and mRNA level. 2. Monooxygenase activities were not measurable at day 10 of gestation, but shortly before birth (day 20 of gestation) and thereafter a surge in monooxygenase activities was observed using ethoxyresorufin, aniline, nitroanisole, aminopyrine, dimethylnitrosamine and aldrin as substrates. 3. In contrast, as early as day 10 of gestation, post oxidative drug metabolism was measurable, when assessed for reactions catalysed by UDP-glucuronyltransferase, glutathione S-transferase and epoxide hydrolase. 4. Microsomal proteins isolated from foetal/perinatal rats did not crossreact with antibodies raised to CYP1A1, CYP1A2, CYP2A1, CYP2B1, CYP2E1, CYP3A1 and CYP4A1 at a protein loading of 3 micrograms total protein/well. 5. With the exception of CYP2E1 mRNA and CYP4A1 mRNA there was little evidence to suggest the expression of CYP1A1, CYP1A2 and CYP2A1 mRNA. 6. The mRNA of CYP2B1, CYP2C7 and CYP3A1 was not detectable in foetal/perinatal rat liver extracts at a loading rate of 10 micrograms total RNA. 7. Microsomal proteins isolated from neonatal rats crossreacted with antibodies raised to CYP2C6, CYP2E1, CYP3A1 and CYP4A1, albeit at varying intensities. 8. Concomitantly, CYP2A1, CYP2E1 and CYP4A1 mRNA transcripts were detectable in Northern blot hybridization experiments using neonatal rat liver RNA extracts.

Opiates, endorphins and the developing organism: a comprehensive bibliography

A comprehensive bibliography of the literature concerned with opiates, endorphins, and the developing organism is presented. A total of 1378 clinical and laboratory references, with citations beginning in 1875, are recorded. A series of indexed accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics. The clinical section is subdivided into: age of subject examined; maternal aspects; effects on the fetus; pharmacology, physiology, and the withdrawal syndrome; and "other" effects on the offspring. The laboratory section is subdivided into: type of opiate/endorphin studied; species utilized; and major subject areas explored.

Substrate specificity of human UDP-glucuronyltransferase in cultured lymphocytes

1. This study establishes the presence of UDP-glucuronyltransferase activity for non-steroidal as well as steroidal substrates, in cultured human B-lymphocytes. Glucuronidation of alpha-naphthol and testosterone was demonstrated in homogenates of two cell lines, SN1006 and RPMI-1788, and that of phenolphthalein, 4-methylumbelliferone, p-nitrophenol and estradiol in the cell line with the higher glucuronyltransferase activity, SN1006. 2. Kinetic studies of testosterone glucuronidation in homogenates of both cell lines revealed a similarity in the behaviour of glucuronyltransferase of these cells. Thus, comparable apparent Km values for UDPGA (0.63 mM) and for testosterone (14 microgram) were observed, although apparent maximal velocities, Vmax, differed several-fold (3.0 versus 0.55 pmol/10(6) cells per min, in SN1006 and RPMI-1788 cells, respectively). 3. Kinetic studies of glucuronidation of testosterone, estradiol, phenolphthalein, alpha-naphthol, 4-methylumbelliferone, and p-nitrophenol yielded comparable apparent Km values for UDPGA (0.56-0.67 mM), suggesting that the same, or similar, glucuronyltransferase(s) catalyse(s) glucuronidation of this wide range of substrates in lymphocytes. This was reinforced by the observation of competitive inhibition of testosterone glucuronidation by alpha-naphthol (Ki 0.25mM), 4-methylumbelliferone (Ki 0.8mM) and p-nitrophenol (Ki 0.8 mM). Thus, lymphocyte glucuronyltransferase activity with a broad substrate specificity, for steroidal and non-steroidal aglycones, is indicated.

The prenatal and postnatal development of UDP-glucuronyltransferase activity towards bilirubin and the effect of premature birth on this activity in the human liver

Liver UDP-glucuronyltransferase activity towards bilirubin was studied in a total of 88 human subjects, including foetuses, premature and full-term newborn babies, infants, children, and adults. Determination of very low enzyme activity was performed by high-pressure liquid chromatography. Prenatal and postnatal changes of the activity can be divided into four developmental phases, i.e. middle foetal, late foetal, neonatal and early infantile, and mature. The activities of the first three phases corresponded to about 0.1, 0.1-1 and 1-100%, respectively, of the mature-phase values (mean +/- S.D.: 1320 +/- 514 microgram/h per g of liver, n = 27).