| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
Formation of covalently bound protein adducts with lithocholic acid (LCA) has been proposed as a possible explanation for hypersensitivity and toxic responses of this bile acid. We therefore carried out to capture of LCA-modified cellular proteins in the bile duct-ligated rat liver by immunoprecipitation using an antibody with high affinity to the 3α-hydroxy-5β-steroid moiety of LCA. Results of the structural analysis of the captured proteins by the basic proteomic technique of 2-DE combined with the use of MALDI-TOFMS and computer assisted programs indicated the presence of LCA bound Rab proteins, which may be the course of LCA-induced liver toxicity.
Further studies on the formation of the glutathione (GSH) conjugates via trans-acylation reactions between GSH and reactive acyl-linked metabolites of bile acids have been carried out to demonstrate the presence of detoxification mechanism. For this purpose, the authentic GSH conjugates of five major bile acids were chemically synthesized
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and their structures were characterized by ESI-tandem mass spectrometry in negative and positive ion modes. Incubation of cholyl-adenylate and cholyl-CoA, reactive metabolites of cholic acid (CA), with GSH in a phosphate buffer (pH 7.5) solution demonstrated that both compounds are able to acylate GSH in vitro. In addition, we cloned and expressed rat and human liver bile acid CoA-ligase to better understand the mechanism for the formation of acyl-adenylate and bile acid bound proteins.
Finally, our efforts were directed to explore the proteins having affinity with LCA in rat liver by using affinity adsorbents, in which LCA was covalently bound to an activated agarose through the bridges introduced at the C-3 and C-24 positions of LCA. Results of LC/ESI-MS^n analysis of the captured proteins after separation by SDS-PAGE revealed the presence of functional proteins, i.e., carbamoyl phosphate synthase I, glutamate dehydrogenase, acyl-CoA acyltransferase, glutathione-S-transferase, and catalase, indicating the hypothesis involved in the appearance of the liver toxicity by inhibition of these enzymes by LCA. Less
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