An investigation has been conducted on the foreign compound-metabolizing activity of human liover collected fresh from surgery or at autopsy from cadavers 3 to 18 hr old, and the effects of low temperature storage on the foreign compound-metabolizing activity of fresh human liver. The enzyme activities studied were microsomal cytochrome P-450 content, biphenyl 4-hdyroxylation, benzo(a)pyrene metabolism, halothane reduction, and 4-hydroxybiphenyl UDP-glucuronosyl transferase, as well as cytosolic tiopurine methyltransferase, thermostable (TS) phenosulfotransferase, thermolabile (TL) phenolsulfotransferase, and 5-fluorouracil dehydrogenase. Cadaver liver was a poor source of material for metabolism studies with the majority of the enzymes investigated. There was an 84% decrease in the yield of microsomal protein, a 64% decrease in cytochrome P-450 content per mg of microsomal protein, and a 36% decrease in the biphenyl 4-hdyroxylase specific activity in human cadaver liver that was a few hours old. UDP-glucuronosyl transferase showed a 70% decrease, TS phenolsulfotransferase a 84% decrease, TL phenolsulfotransferase a 97% decrease, and thiopurine methyltransferase no significant change in specific activity. The loss of activity for many of these enzymes could be simulated by keeping fresh human liver at the temperature of the body after death. Surgical waste provided a good source of fresh, histologically normal, human liver for metabolism studies. Microsomal cytochrome P-450 content showed a significant increase with the age of the liver donor. Metabolism of benzo(a)pyrene to 3-hydroxybenzo(a)pyrene and benzo(a)pyrene-7,8- and -9,10-diols showed up to 136% higher rates in fresh liver microsomes from female donors. Benzo(a)pyrene-7,8-diol formation was decreased 48% in patients with a history of alcohol use. When liver was stored as microsomes, homogenate, or pieces for up to 1 year at -80°C there was no change in the microsomal cytochrome P-450 content. Halothane metabolism showed a 44% decrease when stored 1 year as microsomes but no change when stored as homogenate or pieces. Biphenyl 4-hydroxylase activity showed up to a 63% increase during storage for 1 year as microsome, pieces, or homogenate. Microsomal benzo(a)pyrene metabolism was decreased in liver stored in any form for 1 month, with 3-hydroxybenzo(a)pyrene formation showing the greatest loss. Microsomal UDP-glucuronosyl transferase with 4-hydroxybiphenyl as a substrate was not affected by storage of the liver in any form up to 1 year. Cytosolic TS and TL phenosulfotransferase, and thiopurine methyltransferase were stable in liver stored up to 6 months as either cytosol or as liver pieces. Retrospective studies showed that TS and TL phenolsulfotransferase activities were stable for up to 3 years and that thiopurine methyltransferase activity was stable up to 4 years in liver pieces stored at -80°C. Thus, although conjugating enzyme activities in human liver appear to be stable during extended storage at low temperatures, cytochrome P-450-dependent activities can show selective increases, decreases, or no change. There appears to be no way to predict how a cytochrome P-450 activity will change. To avoid these difficulties, studies on the quantitative metabolism of foreign compounds by human liver cytochrome P-450 should be conducted using fresh liver but studies with selected conjugating activities may be conducted with frozen hepatic tissue or supernatant.
|Original language||English (US)|
|Number of pages||8|
|Journal||Drug Metabolism and Disposition|
|State||Published - 1988|
ASJC Scopus subject areas
- Pharmaceutical Science