Regulation of CYP2A5 induction by porphyrinogenic agents in mouse primary hepatocytes

Abstract

All cytochrome P450 (CYP) enzymes contain heme as a prosthetic group. In contrast to other CYP enzymes, murine CYP 2 A 5 is upregulated in vivo by several agents that disturb cellular heme balance. To test the hypothesis that porphyrinogenic agents have the common feature of being able to increase CYP 2 A 5 expression, mouse liver primary hepatocytes were exposed to various porphyrinogenic chemicals and changes in CYP 2 A 5 catalytic activity and levels of mRNA were monitored. Phenobarbital increased hepatic CYP 2 A 5-mediated coumarin 7-hydroxylase (COH) activity (13.2-fold) and the amount of CYP 2 A 5 steady-state mRNA (10.6-fold). Hepatocyte COH activity was increased also by the ferrochelatase inhibitor griseofulvin and the protoporphyrinogen oxidase inhibitor acifluorfen (about 9-fold induction). Of these inducers, only phenobarbital affected CYP 1 A 12 and CYP 2 B 10 expression. In contrast, many other porphyrinogenic agents such as cobalt, 2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ), 1-[4-(3-acetyl-2,4,6-trimethylphenyl)-2,6-cyclohexanedionyl]-O-eth yl propionaldehyde oxime (ATMP), aminotriazole, and thioacetamide either decreased or had no effect on CYP 2 A 5. The increases in COH activity and CYP 2 A 5 mRNA were unaffected by combined treatment with the inducers and heme arginate, suggesting that heme is not a regulator of CYP 2 A 5 induction. Treatment with actinomycin D totally abolished both constitutive CYP 2 A 5 expression and its inducibility, suggesting that a transcriptional component is involved. These data suggest that, in mouse primary hepatocytes, CYP 2 A 5 induction is not a universal response to disturbed cellular heme biosynthesis.

cAMP Mediated Upregulation of CYP2A5 in Mouse Hepatocytes

“…Male DBA/2 mice, aged between 7 and 10 weeks, were used in this study. To isolate hepatocytes, mouse livers were perfused with collagenase solution as described previously (7,14). After filtration and centrifugation (50g, 2 min), isolated hepatocytes were dispersed in William's medium E containing dexamethasone (20 ng/ml), ITS (insulin 5 mg/l, transferrin 5 mg/l, sodium selenate 5 g/l), gentamicin (10 g/ml) and 10% FCS at a density of 5 ϫ 10 6 cells/90-mm uncoated (plasma-treated) plastic dish (Falcon 3003).…”

“…A number of structurally unrelated chemical hepatotoxins including heavy metals (12), porphyrinogenic agents (14,24), cocaine (25) and carbon tetrachloride (26) cause CYP2A5 induction. It is very interesting that many of these hepatotoxins elicit increased programmed cell death (apoptosis) in the liver (27,28).…”

CYP2A5 Induction and Hepatocellular Stress: An Adaptive Response to Perturbations of Heme Homeostasis

“…Pyrazole, contains two adjacent nitrogen atoms in a pyrrole ring and, as has already been noted, is a strong inducer of CYP2A5 as well as CYP2A6 [27,46,114]. Porphyrinogenic compounds such as griseofulvin and acifluorfen likely induce CYP2A5 by inhibiting enzymes in the heme biosynthetic pathway leading to the accumulation of protoporphyrins [22]. Several organic compounds containing indole (a benzene ring fused to pyrrole) are substrates or inhibitors of CYP2A5 and CYP2A6.…”

High Fat Diet-Induced Hepatic 18-Carbon Fatty Acids Accumulation Up-Regulates CYP2A5/CYP2A6 via NF-E2-Related Factor 2

“…The mechanism of CYP2A5/2A6 increased in different pathogenesis induced liver damage is still unclear. It has been proposed that the common mechanism in the CYP2A5-inducing conditions is a direct or indirect systemic effect elicited by toxicity or tissue damage, rather than the chemical itself (Camus-Randon et al, 1996; Salonpää et al, 1997). Lipid accumulation (hepatocytes steatosis) is generally the early stage of liver damages induced by various structurally unrelated chemicals.…”