Small intestinal UDP-glucuronosyltransferase sheUGT1A07: partial purification and cDNA cloning from sheep small intestine

High glucuronidation activity of environmental estrogens in the carp (Cyprinus carpino) intestine

Many adverse effects on carp reproductive organs have been reported to be caused by exposure to environmental estrogens, such as nonylphenol and bisphenol A, which contaminate the aquatic environment. The glucuronidation activities of xenoestrogens (bisphenol A and diethylstilbestrol) and phytoestrogens (coumestrol, genistein and biochanin A), but not nonylphenol and octylphenol, were observed in microsomes prepared from carp organs. The highest levels of glucuronidation of environmental estrogens, for which the optimum temperature was 25-30 degrees C, were observed in the intestinal microsomes of 2-year-old carp. These activities in carp intestine increased developmentally, and the maximum levels corresponded to 5-10 % of that in rat liver microsomes. However, the glucuronidation of phytoestrogen by carp intestinal microsomes corresponded to that of rat liver microsomes. Only bisphenol A-glucuronide was excreted from the everted intestine, indicating that bisphenol A is metabolized in the carp intestine mainly as glucuronide. These results suggest that glucuronidation by carp intestine plays an important role for the detoxification of xenoestrogens and phytoestrogens, except for nonylphenol and octylphenol.

Cloning of UGT1A9 cDNA from liver tissues and its expression in CHL cells

AIM: To clone the cDNA of UGT1A9 from a Chinese human liver and establish the Chinese hamster lung (CHL) cell line expressing human UGT1A9.

METHODS: cDNA of UGT1A9 was transcripted from mRNA by reverse transcriptase-ploymerase chain reaction, and was cloned into the pGEM-T vector which was amplified in the host bacteric E. coli DH5α. The inserted fragment, verified by DNA sequencing, was subcloned into the Hind III/Not I site of a mammalian expression vector pREP9 to construct the plasmid termed pREP9-UGT1A9. CHL cells were transfected with the resultant recombinants, pREP9-UGT1A9, and selected by G418 (400 mg•L¯¹) for one month. The surviving clone (CHL-UGT1A9) was harvested as a pool and sub-cultured in medium containing G418 to obtain samples for UGT1A9 assays. The enzyme activity of CHL-UGT1A9 towards propranolol in S9 protein of the cell was determined by HPL C.

RESULTS: The sequence of the cDNA segment cloned, which was 1666 bp in length, was id entical to that released by GeneBank (GenBank accession number: AF056188) in co ding region. The recombinant constructed, pREP9-UGT1A9, contains the entire coding region, along with 18 bp of the 5’ and 55 bp of the 3’ untranslated region of the UGT1A9 cDNA, respectively. The cell lines established expressed the protein of UGT1A9, and the enzyme activity towards propranolol in S9 protein was found to be 101 ± 24 pmol•min^-1•mg^-1 protein (n = 3), but was not detectable in parental CHL cells.

CONCLUSION: The cDNA of UGT1A9 was successfully cloned from a Chinese human liver and transfected into CHL cells. The CHL-UGT1A9 cell lines established efficiently expressed the protein of UGT1A9 for the further enzyme study of drug glucuronidation.

Conjugation of para-nitrophenol by the isolated perfused neonatal sheep liver

We examined the metabolism of para-nitrophenol (PNP) in the isolated perfused neonatal sheep liver (n = 8, 0.25-11 days) and compared the findings with our previous data from the perfused near-term fetal sheep liver (Ring, J. A., et al. Drug Metab Dispos 1996, 24, 1378). A three-step dosage regimen was used (72, 144, and 288 micromol of PNP). At the end of each dosage phase, PNP had fallen below detectable levels, and 101 +/- 16% of the dose was accounted for as PNP conjugates. Elimination of PNP from perfusate varied with dose. Elimination was first order with the 72-micromol dose; with the 144-micromol dose, elimination was first order in four livers but Michaelis-Menten kinetics in the remaining four. With all the 288-micromol doses, elimination was Michaelis-Menten and gave the following biochemical parameters: K(m) = 255 +/- 138 microM (fetal = 14.7 microM, P < 0.01), V(max) = 515 +/- 285 nmol/min/g liver (fetal = 34.3 nmol/min/g liver, P < 0.01), and intrinsic hepatic clearance = 2.36 +/- 1.21 mL/min/g liver (fetal = 4.74 mL/min/g liver, P > 0. 05). The mean shunt-corrected hepatic extraction ratio of PNP was 0. 82 (range, 0.40-1.0) and strongly correlated with neonatal age (r = 0.90, P < 0.05). We conclude that PNP is highly extracted by the isolated perfused neonatal sheep liver at much higher efficiency than in the near-term fetal sheep, reflecting a maturation of conjugation that progresses further in the early neonatal period.