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36 results on '"Little, Joanna M."'

13. Glucuronidation of Fatty Acids and Prostaglandins by Human UDP-Glucuronosyltransferases.

Author

Kang, Y. James, Las, Lawrence H., Radominska-Pandya, Anna, Little, Joanna M., and Bull, Arthur

Abstract

This chapter summarizes methods and experimental approaches involved in the study of glucuronidation of several naturally occurring metabolites of the free fatty acids (FFAs), linoleic acid (LA), and arachidonic acid (AA). Data on FA glucuronidation from both human liver micro-somes and human recombinant UDP-glucuronosyltransferase 2B7 (UGT2B7) are presented. Several unique methods for synthesis of FAs that are not commercially available are also described. Moreover, comprehensive methods for measurements of FA glucuronidation, isolation of biosynthesized glucuronides, and analysis by HPLC, HPLC-MS, and GC-MS are discussed in detail. The enzymatic assays presented in this chapter can also be used for studying glucuronidation of other hydrophobic endogenous compounds, including many drugs and environmental pollutants. The potential value of these methods is highlighted by the growing appreciation of the roles of FFA and FA-glucuronides in human health and disease. [ABSTRACT FROM AUTHOR]

Published
2005
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27. Application of photoaffinity labeling with [3H] all trans- and 9-cis-retinoic acids for characterization of cellular retinoic acid-binding proteins I and II.

Author

Radominska-Pandya, Anna, Chen, Guangping, Samokyszyn, Victor M., Little, Joanna M., Gall, Walter E., Zawada, Gregory, Terrier, Nadege, Magdalou, Jacques, and Czernik, Piotr

Abstract

Cellular retinoic acid-binding proteins (CRABPs) are carrier proteins thought to play a crucial role in the transport and metabolism of all- trans-retinoic acid (atRA) and its derivatives within the cell. This report describes a novel photoaffinity-based binding assay involving competition between potential ligands of CRABP and [3H]atRA or [3H]-9- cis-RA for binding to the atRA-binding sites of CRABP I and II. Photoaffinity labeling of purified CRABPs with [3H]atRA was light- and concentration-dependent, saturable, and protected by several retinoids in a concentration-dependent manner, indicating that binding occurred in the CRABP atRA-binding site. Structure-function relationship studies demonstrated that oxidative changes to the atRA β-ionone ring did not affect ligand potency. However, derivatives lacking a terminal carboxyl group and some cis isomers did not bind to CRABPs. These studies also identified two novel ligands for CRABPs: 5,6-epoxy-RA and retinoyl-β-D-glucuronide (RAG). The labeling of both CRABPs with 9- cis-RA occurred with much lower affinity. Experimental evidence excluded nonspecific binding of RAG to CRABPs and UDP-glucuronosyltransferases, the enzymes responsible for RAG synthesis. These results established that RAG is an effective ligand of CRABPs. Therefore, photoaffinity labeling with [3H]atRA can be used to identify new ligands for CRABP and retinoid nuclear receptors and also provide information concerning the identity of amino acid(s) localized in the atRA-binding site of these proteins. [ABSTRACT FROM AUTHOR]

Published
2001
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31. A Historical Overview of the Heterologous Expression of Mammalian UDP-Glucuronosyltransferase Isoforms Over the Past Twenty Years

Author

Radominska-Pandya, Anna, Bratton, Stacie, and Little, Joanna M.

Abstract

UDP-Glucuronosyltransferases (UGTs) are actively involved in detoxification of xenobiotics and endogenous compounds and are a major source of drug inactivation and drug-drug interactions. UGTs are membrane-bound enzymes mostly localized in the endoplasmic reticulum (ER) and inner and outer nuclear membranes. UGT activities are totally dependent on the phospholipid content of the membrane and, as a result, are usually inactive when isolated from the ER in the presence of detergent. Several UGT expression systems have been described by different laboratories. They include expression in mammalian cells such as COS, V79 and HEK293. Also, baculovirus-infected insect cells systems have been developed and allow the expression of UGT isoforms with or without histidine molecule tags (His-tags). Moreover, as for CYP450, UGT isoforms have been expressed in E.coli. This review concentrates on a detailed description of all these expression systems in terms of their use for substrate specificity studies and the preparation of pure UGT proteins for active site identification and other structural studies. The effect of detergents and alamethicin on UGT catalytic activity in different expression systems will be discussed. Moreover, extensive comparative studies on the characterization of recombinant UGTs in terms of substrate specificity, evaluation of kinetic parameters, and the effect of inhibitors will be presented in this review. An overall picture of the use of different UGT expression systems will help in selecting the best one for identification of the individual UGT isoforms involved in the glucuronidation of drugs, environmental pollutants and physiologically important endogenous compounds. Especially important is an expression system where UGTs are biosynthesized with His-tags. UGTs expressed in this system can be easily purified to homogeneity, which will result in significant development of structure-function relationship studies, including the identification of substrate active sites and eventual crystallization. These are underdeveloped areas of UGT research and the availability of these recombinant UGTs will allow these gaps to be filled.

Published
2005

32. Foetal bile pigment handling after administration of [14C] haemin

Author

Jackson, Benjamin T., Lester, Roger, Little, Joanna M., Piasecki, George J., Rauschecker, Helmut F. J., and Smith, Paul M.

Abstract

1. Advanced techniques for intra‐uterine surgery were used to study haem degradation in foetal sheep prepared in uterowith indwelling jugular, carotid and biliary cannulas. [14C]haemin was administered I.V. to the foetus, and plasma disappearance, biliary excretion, placental transfer and tissue distribution of radioactivity were measured over a 5–8 hr period.

Published
1973
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33. Ethanol—Its Nephrotoxic Effect in the Rat

Author

Van Thiel, David H., Williams, William D., Gavaler, Judith S., Little, Joanna M., Estes, Larry W., and Rabin, Bruce S.

Subjects
Kidney Concentrating Ability, Male, Ethanol, Creatinine, Osmolar Concentration, Animals, Proteins, Articles, Acute Kidney Injury, Kidney Tubular Necrosis, Acute, Kidney, Lipid Metabolism, Rats
Abstract

The nephrotoxic effect of ethanol feeding on renal structure and function was evaluated in rats and compared to that in dextrose-fed isocaloric control animals. Alcohol-fed animals had larger kidneys than their controls. Despite this increase in renal mass, the alcohol-fed animals had a 50% reduction in creatinine clearance and a 67% reduction in osmolar clearance compared to their controls. When specific renal constituents were compared, the alcohol-fed animals were found to have twice the renal protein and a 50% increase in renal lipid. Despite these marked structural and functional differences, the light microscopic appearance of the kidneys of the two groups did not appear significantly different. In contrast, the electron microscopic differences were substantial. The renal epithelial cells, particularly of the distal tubules and Henle's loops, were found to show varying degrees of cellular injury and were observed to be sloughing into the lumens. These electron microscopic observations are similar to those obtained in tubular necrosis due to a variety of nephrotoxic agents. We propose, therefore, that chronic alcohol feeding of rats produces significant renal dysfunction and abnormalities of structure such that ethanol should be considered a true nephrotoxin.

Published
1977

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