Increase In P-450 Level Research Articles

Improvement of phase I drug metabolism with Schisandra chinensis against CCl4 hepatotoxicity in a rat model.

The seed extract of Schisandra chinensis was investigated in the rat for its restorative or therapeutic effect on Phase I hepatic drug metabolism following intoxication by carbon tetrachloride (CCl4). Male Sprague Dawley rats (220-250 g) were divided into two sets, one included rats with or without CCl4 intoxication, the other included CCl4 intoxicated rats with or without treatment of Schisandra extract. With the treatment regimen, rats received four oral doses of Schisandra (160 mg/kg) or the same volume of water at 8, 24, 32 and 48 h after CCl4 intoxication. A single oral dose (80 mg/kg) of antipyrine, a conventional probe for oxidative drug metabolism, was then administered. The levels of liver serum transaminases and cytochrome P450 were measured and the pharmacokinetics of antipyrine were assessed using a non-compartmental approach via WinNonlin. In comparison to the rats without CCl4 intoxication (t1/2: 2.2 +/- 0.9 h; Cl/F: 0.30 +/- 0.01 L/h/Kg; P450: 0.611 +/- 0.190 nmol/mg protein), CCl4 administration significantly decreased elimination (t1/2: 12.0 +/- 3.9 h) and oral clearance (Cl/F: 0.049 +/- 0.018 L/h/kg) of antipyrine, and markedly reduced the content of P450 (0.075 +/- 0.011 nmol/mg protein). Data obtained from intoxicated animals treated by Schisandra extract, compared to those without treatment, showed significant (p < 0.05) improvement in the t1/2 (4.45 +/- 1.7 h) and Cl/F (0.096 +/- 0.018 ml/h) estimates of antipyrine and a 2-3 fold increase in P450 level (0.190 +/- 0.072 nmol/mg protein). Findings in this study suggest that the seed extract of Schisandra appeared to be a promising agent for the improvement of Phase I oxidative metabolism in the liver damaged by CCl4.

Cell biology of cytochrome P-450 in the liver

Cytochromes P-450 (P-450) are members of a multigene superfamily of hemoproteins consisting the microsomal monooxygenase system with NADPH P-450 reductase (reductase) and/or reducing equivalents. Expression of many P-450 isoforms in hepatocytes is shown to be regulated at the level of transcription through interaction between cis-acting elements in the genes and DNA-binding (transacting) factors. Some isoforms of the CYP1A, 2B, 2E, and 3A subfamilies are regulated at the posttranscriptional level. For the topology of P-450 and reductase molecules in ER membrane of hepatocytes, models from stopped flow analysis and electron spin resonance are proposed. The densities of total P-450 and reductase molecules are revealed to be high enough to support the cluster model, suggesting that about ten P-450 molecules form an aggregate and surround one reductase molecule, and therefore the two enzymes form large micelles. ER proliferation after PB administration, which had been correlated with increase in P-450 level, is shown to be probably independent of the increase in P-450 level. There are considerable discrepancies among results reported on sublobular expression of various P-450 isoforms. Causes of the discrepancies are likely to be differences in experimental conditions of histochemical detection carried out and/or in species, strain, and/or sex.

Changes in extracellular matrix components and steroidogenic enzymes during growth and atresia of antral ovarian follicles in the sheep.

To investigate the involvement of extracellular matrix (ECM) in folliculogenesis in the sheep, parallel changes in ECM components and key steroidogenic enzymes were studied by quantitative immunohistochemistry and immunoblotting during follicular growth and atresia. Growth of ovarian follicles from 1 to 5 mm in diameter was characterized by a progressive increase in P450 cholesterol sidechain cleavage levels in both thecal (p < 0.001) and granulosa cells (p < 0.001), an increase in P450 aromatase levels in granulosa cells of follicles larger than 3.5 mm (p < 0.001), and an increase in levels of P450 17 alpha-hydroxylase C17,20 lyase (P450(17 alpha)) in the theca interna. In addition, during follicular growth, a change in localization of cells expressing P450(17 alpha) within the theca interna was observed, positive cells being sparse within the theca interna of small follicles and specifically located close to the basal laminae in large follicles. In parallel, follicular growth was associated with an increase in levels of type I collagen in granulosa cell layers (p < 0.01) and an increase in levels of fibronectin (p < 0.05), particularly the specific ED-A alternatively spliced variant of fibronectin, in the theca externa. Follicular atresia was characterized by a loss of P450 aromatase in granulosa cells (p < 0.001) and a decrease in levels of P450(17 alpha) in the theca interna (p < 0.05). Simultaneously, levels of fibronectin (p < 0.05), particularly the ED-A variant of fibronectin, decreased in the theca externa of atretic follicles. Within the wall of granulosa cells, levels of fibronectin (p < 0.05), laminin, type IV collagen, and heparan sulfate proteoglycans strongly increased during follicular atresia. Overall, these results show that follicular growth and atresia were associated with distinct changes in levels of ECM components, suggesting that ECM components may play a role in the regulation of proliferation, differentiation, and apoptosis of follicular cells.

Expression of a Ripening-Related Avocado (Persea americana) Cytochrome P450 in Yeast

One of the mRNAs that accumulates during the ripening of avocado (Persea americana Mill. cv Hass) has been previously identified as a cytochrome P450 (P450) monooxygenase and the corresponding gene designated CYP71A1. In this report we demonstrate that during ripening the accumulation of antigenically detected CYP71A1 gene product (CYP71A1) correlates with increases in total P450 and two P450-dependent enzyme activities: para-chloro-N-methylaniline demethylase, and trans-cinnamic acid hydroxylase (tCAH). To determine whether both of these activities are derived from CYP71A1, we have expressed this protein in yeast (Saccharomyces cerevisiae) using a galactose-inducible yeast promoter. Following induction, the microsomal fraction of transformed yeast cells undergoes a large increase in P450 level, attributable almost exclusively to the plant CYP71A1 protein. These membranes exhibit NADPH-dependent para-chloro-N-methylaniline demethylase activity at a rate comparable to that in avocado microsomes but have no detectable tCAH. These results demonstrate both that the CYP71A1 protein is not a tCAH and that a plant P450 is fully functional upon heterologous expression in yeast. These findings also indicate that the heterologous P450 protein can interact with the yeast NADPH:P450 reductase to produce a functional complex.