Abstract
Since sulfation is the main metabolic pathway of troglitazone, accounting for about 70% of the metabolites detected in human plasma, we have aimed to identify human cytosolic sulfotransferases catalyzing the sulfation of troglitazone and to examine a possible role of the sulfation in the cytotoxicity observed in cell lines of human origin (HepG2 and Hep3B). Experiments using the recombinant sulfotransferases and human liver cytosols indicated that phenol sulfotransferase (ST1A3) and estrogen sulfotransferase (ST1E4) were the sulfotransferases most active toward troglitazone. Immunoblot analyses indicated that hepatic content of ST1A3 is about 13 times higher than that of ST1E4, suggesting that ST1A3 is mainly responsible for the sulfation of troglitazone in the liver. Lactate dehydrogenase (LDH) leakage was elicited by troglitazone in a concentration-dependent manner in the hepatoma cells. The troglitazone metabolites (the sulfate, glucuronide, and quinone forms) caused negligible LDH leakage. These findings suggest that accumulation of unmetabolized troglitazone causes the cytotoxicity in the hepatoma cells and may be responsible for toxicity in human liver.
Footnotes
-
This study was supported in part by grant-in-aids from the Ministry of Education, Science and Culture and the Ministry of Health and Welfare, Japan; the Japan Health Sciences Foundation, Smoking Research Foundation, Japan; and Human & Animal Bridge Discussion Group, Japan.
-
↵2 STs or SULTs are as follows: ST1A3, ST1A5, ST1B2, ST1C2, ST1E4, and ST2A3 correspond to SULT1A1, SULT1A3, SULT1B1, SULT1C2, SULT1E1 and SULT2A1, respectively.
- Abbreviations used are::
- ST or SULT
- cytosolic sulfotransferase
- PAPS
- 3′-phosphoadenosine-5′-phosphosulfate
- His-ST
- recombinant ST protein that has additional amino acid residues at theN-terminal
- ΔHis-ST
- fused portion removed from His-ST by digestion with enterokinase
- DMEM
- Dulbecco's modified Eagle's medium
- DMSO
- dimethyl sulfoxide
- HPLC
- high-performance liquid chromatography
- LDH
- lactate dehydrogenase
- Received November 2, 2001.
- Accepted May 15, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
