An NH(2)-terminal truncated cytochrome P450 CYP3A4 showing catalytic activity is present in the cytoplasm of human liver cells

Cytochrome P450 3A4 (CYP3A4), is the dominant human liver hemoprotein enzyme localized in the endoplasmic reticulum (ER), and is responsible for the metabolism of more than 50% of clinically relevant drugs. While we were studying CYP3A4 expression and activity in human liver, we found that anti-CYP3A4 antibody cross-reacted with a lower band in liver cytoplasmic fraction. We assessed the activities of CYP3A4 and its truncated form in the microsomal and cytoplasmic fraction, respectively. In the cytoplasmic fraction, truncated CYP3A4 showed catalytic activity when reconstituted with NADPH-cytochrome P-450 reductase and cytochrome b5. In order to determine which site was deleted in the truncated form in vitro, we transfected cells with N-terminal tagged or C-terminal tagged human CYP3A4 cDNA. The truncated CYP3A4 is the N-terminal deleted form and was present in the soluble cytoplasmic fraction. Our result shows, for the first time, that N-terminal truncated, catalytically active CYP3A4 is present principally in the cytoplasm of human liver cells.

Clinical usefulness of serum isocitrate dehydrognase as a marker of centrilobular hepatic necrosis in patients with hyperthyroidism / 대한내과학회지

BACKGROUND: The zonal differentiation of hepatic necrosis is important in the aspect of treatment, follow-up and prognosis of patients. The purpose of this study was evaluating the clinical usefulness of serum isocitrate dehydrogenase (ICDH) as a marker of centrilobular hepatic necrosis in patients with hyperthyroidism. METHODS: We determined the serum ICDH and alanine aminotransferase (ALT) activities in 56 patients with hyperthyroidism, 16 patients with chronic viral hepatitis, and 17 normal controls. RESULTS: The activities of serum ICDH were significantly higher in patients with hyperthyroidism than those of patients with chronic viral hepatitis or normal control (p< 0.01), even though those of serum ALT were higher in patients with chronic viral hepatitis (p< 0.01). The ratio of serum ICDH and ALT activities were markedly different between the patients with hyperthyroidism and chronic viral hepatitis (p< 0.001). There was a significant correlation between the serum ICDH and ALT activities in patients with hyperthyroidism as well as in those with chronic viral hepatitis (p< 0.05). In patients with hyperthyroidism, the serum ICDH levels were more significantly correlated with serum triiodothyronine (T3) than thyroxine (T4) levels. In a patients with hyperthyroidism and elevated ALT levels, the serum ICDH activity decreased progressively and was normalized ultimately, as serum ALT level and thyroid function were normalized with antithyroid medication. CONCLUSION: The serum ICDH or ratio of serum ICDH and ALT activities might be useful clinically in differentiating the centrilobular from periportal hepatic necrosis, and following up the degree of hepatic necrosis in patients with hyperthyroidism.