Differential regulation of liver P-450III cytochromes in choline-deficient rats: Implications for the erythromycin breath test as a parameter of liver function
✍ Scribed by Joseph C. Kolars; Scott A. Murray; Ken M. Peters; Paul B. Watkins
- Publisher
- John Wiley and Sons
- Year
- 1990
- Tongue
- English
- Weight
- 930 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0270-9139
No coin nor oath required. For personal study only.
✦ Synopsis
Progressive liver fibrosis in rats develops when they are fed a diet deficient in choline. This diet also results in a pronounced and selective decrease in the liver microsomal content of a phase I drug-metabolizing enzyme belonging to the cytochrome P-450111 gene family. Because P-450111 cytochromes characteristically catalyze the N-demethylation of erythromycin, we believed that the production of breath CO, from erythromycin would be dramatically reduced in choline-deficient rats. However, when 12 cholinedeficient rats were compared with 9 control rats, the reduction in CO, production from erythromycin (mean decrease 71%) was essentially identical to that from aminopyrine (mean decrease 69%). a substrate believed to be metabolized normally by the hepatocyte in fibrotic liver disease. Furthermore, we found that the relative erythromycin and aminopyrine demethylase activities were comparable when measured in uitro in liver microsomes prepared from the choline-deficient rats. To determine the molecular basis for the erythromycin demethylase activity in the choline-deficient rats, the liver microsomes were subjected to immunoblot analysis using a variety of polyclonal and monoclonal antibodies capable of distinguishing individual P-450111-related proteins. Our studies confirm that a mdor erythromycin demethylase belonging to the P-45OIII family, termed P-450p, was greatly reduced in the choline-deficient rat liver. However, the specific concentration of a second P-45Oprelated protein was essentially normal and that of a third P-45Oprelated protein was actually increased in the choline-deficient rat liver. These changes occurred over weeks and months on the choline-deficient diet and are not consistent with "feminization" of the liver.
The P-45Oprelated proteins appeared to catalyze erythromycin demethylase activity because antibodies recognizing them inhibited the mqjority (62%) of this activity in choline-deficient rat microsomes. Finally,