Zonation of cytochrome P450 isozyme expression and induction in rat liver

Abstract

The regional expression of six different cytochrome P450 (CYP) forms in rat liver under constitutive and induced conditions was compared using immunological techniques. Immunostaining of consecutive thin sections from control liver revealed that the same hepatocytes, forming a 6 -8 cells thick layer surrounding the terminal hepatic venules, were stained for CYP2B1/2, CYP2E1 and CYP3A3. Staining of CYP2A1 extended further into the midzonal region, whereas all cells of the acinus stained for CYPEtOH2. These results were supported by Western blot analysis of cell lysates from the periportal or perivenous region obtained by zone-restricted digitonin treatment during in situ perfusion. The data suggest three distinct patterns of constitutive P450 expression : perivenousrestricted (CYP2B1/2, CYP2E1 and CYP3A1); perivenous-dominated (CYP2A1) and panacinar (CYPEtOH2).Chronic exposure to ethanol caused induction of CYP2E3 in the same cells already being constitutively expressed, whereas CYPEtOH2 was more induced in the periportal area. The relative induction of CYP2B1/2, CYP3A1 and CYPEtOH2 after treatment with phenobarbital was stronger inperiportal hepatocytes, resulting in levelling out of the initial perivenous dominance of CYP2B1/2 and CYP3A1, whereas CYPEtOH2 became periportal-dominated. Acetone induced CYP2E3, CYP2C11 and CYP3A1 selectively in the perivenous area. These studies indicate that a particular P450 isozyme is generally induced in the same cells where it is constitutively expressed, and that this regional selectivity is independent of the kind of inducer. The data suggest that, during maturation, the hepatocytes acquire various phenotypes in the periportal and perivenous region, to respond differently to endogenous and exogenous signals in the control of P450 expression.The microsomal monooxygenase system is responsible for the oxidative metabolism of structurally unrelated endogeneous and exogeneous compounds. The diversity of the functions of this system is due to the existence of multiple forms of the terminal enzyme component, cytochrome P450 (CUP) exhibiting different, but overlapping, substrate specificites. Characteristic of the P450 system is its inducibility by thousands of structurally different chemicals, making it adaptable to the environment. At present 10 gene families, with 3 9 subfamilies in total have been identified in mammals [I]. Cytochrome P450 is found in many organs, but the concentration is highest in the liver. Many proteins are unevenly distributed in the liver acinus [2, 31. This is also true for cytochrome P450, which is more abundant in the perivenous (centrilobular) regions [4, 51. Previous immunohistochemical studies indicate a heterogeneous acinar distribution of some P450 isozymes, both in human and rodent liver [6 -111. It is also becoming increasingly evident that induction of these proteins by various xenobiotics does not occur throughoutCenter, Box 350, SF-00101 Hclsinki, Finland the acinus, but usually is restricted to some parts [h, 7,10, 12, 131. The factors gover...

Regulation of the Major Detoxication Functions by Phenobarbital and 3‐Methylcholanthrene in Co‐Cultures of Rat Hepatocytes and Liver Epithelial Cells

“…It is known that phenobarbital responsiveness of CYP genes is regionally determined in the liver, and that this heterogeneity is at least partly preserved in isolated hepatocytes (Bars et al, 1992;Buhler et al, 1992). Together with the relatively low transfection efficiency, of the order of lo%, as estimated by in situ staining of hepatocytes following electroporation with pgalactosidase-encoding plasmids (data not shown), the restriction of the response to phenobarbital to only a subset of cells could account for the small induction of the 163-bp fragment.…”

Liver‐specific loss of β‐catenin blocks glutamine synthesis pathway activity and cytochrome p450 expression in mice†‡

“…The following primary antibodies were used: mouse anti-␤-catenin (1:500 dilution) (Becton and Dickinson, Franklin Lakes, NJ) 16,17 ; mouse anti-GS (1: 500 dilution, Becton and Dickinson) 16,17 ; rabbit anti-GLT-1 (1:500 dilution) (gift from Masahiko Watanabe) 21,22 ; sheep anti-CYP1A2 (1:1,000 dilution) (Chemicon, Temecula, CA) 23 ; rabbit anti-CYP2E1 (1: 1,000 dilution) (gift from Magnus Ingelman-Sundberg). 16,24 Biotinylated anti-rabbit (Vector Laboratories) and anti-sheep (Jackson Immunoresearch, West Grove, PA) antibodies were used as secondary antibodies at a 1:200 dilution. Mouse monoclonal primary antibodies were detected with an M.O.M.…”

Localization and Age-Related Changes in Cytochrome P450 Expression in APA Hamster Livers.

“…In rats, Rich et al revealed that the expression of CYP2B1/2 is Values are the means ± SD for five animals. restricted to within a few cells scattered around the central vein [9], whereas others reported that CYP2B1/ 2 is expressed throughout the acinus with no evidence of zonal localization [11,14]. These differences might be mainly due to the strain differences in the rats examined and/or antibodies used [9].…”

“…This phenomenon is thought to explain the decrease in detoxication activities observed frequently in aged individuals [8]. Another characteristic is heterogenous expression of some P450 isozymes in the liver [9][10][11][12][13]. This specific localization of P450 isozymes is very important, since many potentially toxic factors such as drugs and carcinogens are activated to toxic intermediates by each P450 isozyme and damage the liver, especially the perivenous region where most P450 isozymes exist abundantly.…”

“…This specific localization of P450 isozymes is very important, since many potentially toxic factors such as drugs and carcinogens are activated to toxic intermediates by each P450 isozyme and damage the liver, especially the perivenous region where most P450 isozymes exist abundantly. Previous investigations revealed that many foreign compounds induced P450 isozymes in restricted parts of the hepatic acinus [9,11,[14][15][16][17].…”