Evidence that ligand formation is a mechanism underlying the maintenance of cytochrome P-450 in rat liver cell culture. Potent maintenance by metyrapone

The loss of cytochrome P-450 in cultured rat hepatocytes can be prevented by substituted pyridines, especially isonicotinamide, 3-hydroxypyridine and metyrapone. The effect of these compounds is independent of protein synthesis, suggesting that they maintain pre-existing cytochrome P-450. The efficiency of pyridines at maintaining cytochrome P-450 in hepatocyte culture is highly correlated with their ability to bind to this cytochrome, suggesting that ligand formation with cytochrome P-450 prevents its accelerated turnover in liver cell culture.

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Relationship between the ability of nicotinamide to maintain nicotinamide-adenine dinucleotide in rat liver cell culture and its effect on cytochrome P-450

Biochemical Journal ◽

10.1042/bj1840461 ◽

1979 ◽

Vol 184 (2) ◽

pp. 461-463 ◽

Cited By ~ 45

Author(s):

A J Paine ◽

L J Hockin ◽

R F Legg

Keyword(s):

Cell Culture ◽

Causal Relationship ◽

Rat Liver ◽

Liver Cell ◽

Nicotinamide Adenine Dinucleotide ◽

Rat Hepatocytes ◽

Nicotinamide Adenine ◽

Cultured Hepatocytes ◽

Liver Cell Culture ◽

Cytochrome P 450

Rat hepatocytes cultured for 24 h lose 60% of their NAD content. Treatment with nicotinamide prevents the loss of NAD as well as the previously reported loss of cytochrome P-450, suggesting a possible causal relationship. However, isonicotinamide also prevents the loss of cytochrome P-450, but does not increase the concentration of NAD, demonstrating that the ability of nicotinamide to maintain cytochrome P-450 is not apparently related to its effect on the NAD content of cultured hepatocytes.

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Porphyrinogenic effects in chick embryo liver cell culture of chloramphenicol analogues that are mechanism-based inactivators of cytochrome P-450

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y91-079 ◽

1991 ◽

Vol 69 (4) ◽

pp. 526-530 ◽

Cited By ~ 2

Author(s):

R. P. Green-Thompson ◽

D. S. Riddick ◽

J. E. Mackie ◽

G. S. Marks ◽

J. R. Halpert

Keyword(s):

Cell Culture ◽

Chick Embryo ◽

Rat Liver ◽

Liver Cell ◽

Prosthetic Group ◽

Uroporphyrinogen Decarboxylase ◽

Compound A ◽

Liver Cell Culture ◽

Embryo Liver ◽

Cytochrome P 450

Structural analogues of chloramphenicol (CAP) cause mechanism-based inactivation of rat liver cytochrome P-450 (P450) either via protein acylation or destruction of the heme prosthetic group. The goal of the present work was to determine whether CAP analogues that cause loss of the P450 heme moiety also cause porphyrin accumulation in chick embryo liver cell culture. The porphyrin profiles produced by exposure of cells to CAP analogues (160 μM) were determined by high-performance liquid chromatography with fluorescence detection. Of three CAP analogues that do not cause loss of the heme moiety of rat liver P450IIB1, two dichloroacetamides were not porphyrinogenic. The third compound, a chlorofluoroacetamide, caused porphyrin accumulation. This result may be due to the presence of P450 isozymes in chick embryo hepatocytes, distinct from rat liver P450IIB1, that are susceptible to destruction by this analogue. Of four CAP analogues that inactivate rat liver P450IIB1 with concomitant heme loss, a dichloroacetamide and two chlorofluoroacetamides caused porphyrin accumulation. The remaining compound, a monochloroacetamide, was not porphyrinogenic, perhaps because the P450 apoprotein cannot be reconstituted with fresh heme drawn from the regulatory "free heme pool" following inactivation by this analogue. Alternatively, there may be no P450 isozyme in chick embryo liver cell culture that is susceptible to inactivation by this compound.Key words: cytochrome P-450, chloramphenicol, chick embryo hepatocyte, mechanism-based inactivation, uroporphyrinogen decarboxylase.

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