Elevation of delta-aminolevulinic acid synthase and cytochrome PB1 P450 messenger RNA levels by dihydropyridines, dihydroquinolines, sydnones, and N-ethylprotoporphyrin IX.
A series of compounds that increase the activity of delta-aminolevulinic acid synthase (ALAS) in chick embryo hepatocyte cultures were studied for their effects on steady-state levels of mRNA for ALAS and phenobarbital-inducible cytochrome PB1 P450. N-Ethylprotoporphyrin IX (N-EtPP), which is believed to lower heme levels by inhibition of ferrochelatase (FC), had little effect on steady-state ALAS mRNA levels. 3,5-Diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4- isobutylpyridine (4-isobutyl DDC), which is believed to lower heme levels by repetitive destruction of the heme moiety of cytochrome P450, increased steady-state levels of ALAS mRNA levels approximately 2-fold. 3,5-Diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethyl DCC) which inhibits FC activity and destroys the heme moiety of cytochrome P450, increased ALAS mRNA levels approximately 4-fold. A combination of N-EtPP and 4-isobutyl DDC produced a synergistic increase in ALAS mRNA levels to approximately 6-fold over control levels. The synergistic increase in ALAS activity observed previously with this combination can be explained, at least in part, by a synergistic increase in ALAS mRNA levels. Other porphyrinogenic agents, which function as mechanism-based inactivators of cytochrome P450 and elevate ALAS activity, were found to elevate ALAS mRNA. These compounds included 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS), 2,4-diethyl-2-methyl-1,2-dihydroquinoline (DMDQ), and 2,2,4-trimethyl-1,2,dihydroquinoline (TMDQ). The elevation of ALAS mRNA by these porphyrinogenic agents is probably due to their lowering of cellular heme levels by a combination of ferrochelatase inhibition and repetitive destruction of the heme moiety of cytochrome P450. The lowering of heme levels should result in an enhancement of ALAS mRNA half-life as it has been demonstrated by others that heme shortens the half-life of ALAS mRNA. It was of interest that some of these drug treatments also caused an elevation in steady-state levels of cytochrome PB1 P450 mRNA; the exception was TTMS, which along with its analogue 3-(2-phenylethyl)-4-methylsydnone (PEMS), did not alter cytochrome PB1 P450 mRNA levels. Increases in steady-state levels of cytochrome PB1 P450 mRNA subsequent to increases in steady-state levels of ALAS mRNA were observed with 4-ethyl DDC, 4-isobutyl DDC, DMDQ, and TMDQ. The data obtained with N-EtPP and a combination of N-EtPP and 4-isobutyl DDC on cytochrome PB1 P450 mRNA levels do not support the contention that heme functions as a positive regulator of cytochrome P450 gene expression.
Mackie
J E
JE
Department of Pharmacology and Toxicology, Queen's University, Kingston, Ontario, Canada.
Back
D W
DW
Hamilton
J W
JW
Marks
G S
GS
D000624:5-Aminolevulinate Synthetase / Q000096:biosynthesis / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D002642:Chick Embryo; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics*; D004095:Dihydropyridines / Q000494:pharmacology*; D004790:Enzyme Induction / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006418:Heme / Q000096:biosynthesis; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008969:Molecular Sequence Data; D011524:Protoporphyrins / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis*; D013558:Sydnones / Q000494:pharmacology*; D013997:Time Factors; D015262:Xenobiotics / Q000494:pharmacology
D065607:Cytochrome P-450 Enzyme Inhibitors; D004095:Dihydropyridines; D011524:Protoporphyrins; D011804:Quinolines; D012333:RNA, Messenger; D013558:Sydnones; D015262:Xenobiotics; D006418:Heme; C030827:N-ethylprotoporphyrin IX; D003577:Cytochrome P-450 Enzyme System; D000624:5-Aminolevulinate Synthetase