Mechanisms of the in vitro antimutagenic action of chlorophyllin against benzo[a]pyrene: Studies of enzyme inhibition, molecular complex formation and degradation of the ultimate carcinogen

Nicholas Tachino, Dexin Guo, Wan Mohaiza Dashwood, Shane Yamane, Randy Larsen, Roderick Dashwood

Research output: Contribution to journalArticle

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Abstract

Mechanisms of the antimutagenic action of chlorophyllin (CHL) towards benzo[a]pyrene (BP) were studied in vitro. In the Salmonella assay, CHL inhibited the mutagenic activity of BP in the presence of an S9 activation system and was particularly effective against the direct-acting ultimate carcinogen, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). Spectral studies indicated that the time-dependent hydrolysis of BPDE to tetrols was augmented in the presence of CHL concentrations on the order of 5 μM. Dose-related inhibition of several cytochrome P450-dependent enzyme activities was observed upon addition of CHL to in vitro incubations. Spectral changes for the interaction between CHL and cytochrome P450 indicated that CHL does not bind to the active site of the enzyme, but exerts its inhibitory effect indirectly. This was achieved by inhibiting NADPH-cytochrome P450 reductase (Ki ∼ 120 μM with cytochrome c as substrate), and did not involve lowering of the effective substrate concentration by complex formation with the procarcinogen. It is concluded that the in vitro antimutagenic activity of CHL towards BP involves accelerated degradation of the ultimate carcinogen, with inhibition of carcinogen activation occurring only at high CHL concentrations. The latter mechanism is unlikely to occur in vivo following p.o. administration due to the limited uptake of CHL from the gut, but tissue concentrations may be sufficiently high to cause degradation of BPDE.

Original languageEnglish
Pages (from-to)191-203
Number of pages13
JournalMutation Research Regular Papers
Volume308
Issue number2
DOIs
StatePublished - 16 Jul 1994

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Benzo(a)pyrene
Carcinogens
7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide
Enzymes
Cytochrome P-450 Enzyme System
In Vitro Techniques
chlorophyllin
NADPH-Ferrihemoprotein Reductase
Cytochromes c
Salmonella
Catalytic Domain
Hydrolysis

Keywords

  • Benzo[a]pyrene
  • Chlorophyllin antimutagenicity

Cite this

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title = "Mechanisms of the in vitro antimutagenic action of chlorophyllin against benzo[a]pyrene: Studies of enzyme inhibition, molecular complex formation and degradation of the ultimate carcinogen",
abstract = "Mechanisms of the antimutagenic action of chlorophyllin (CHL) towards benzo[a]pyrene (BP) were studied in vitro. In the Salmonella assay, CHL inhibited the mutagenic activity of BP in the presence of an S9 activation system and was particularly effective against the direct-acting ultimate carcinogen, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). Spectral studies indicated that the time-dependent hydrolysis of BPDE to tetrols was augmented in the presence of CHL concentrations on the order of 5 μM. Dose-related inhibition of several cytochrome P450-dependent enzyme activities was observed upon addition of CHL to in vitro incubations. Spectral changes for the interaction between CHL and cytochrome P450 indicated that CHL does not bind to the active site of the enzyme, but exerts its inhibitory effect indirectly. This was achieved by inhibiting NADPH-cytochrome P450 reductase (Ki ∼ 120 μM with cytochrome c as substrate), and did not involve lowering of the effective substrate concentration by complex formation with the procarcinogen. It is concluded that the in vitro antimutagenic activity of CHL towards BP involves accelerated degradation of the ultimate carcinogen, with inhibition of carcinogen activation occurring only at high CHL concentrations. The latter mechanism is unlikely to occur in vivo following p.o. administration due to the limited uptake of CHL from the gut, but tissue concentrations may be sufficiently high to cause degradation of BPDE.",
keywords = "Benzo[a]pyrene, Chlorophyllin antimutagenicity",
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Mechanisms of the in vitro antimutagenic action of chlorophyllin against benzo[a]pyrene : Studies of enzyme inhibition, molecular complex formation and degradation of the ultimate carcinogen. / Tachino, Nicholas; Guo, Dexin; Dashwood, Wan Mohaiza; Yamane, Shane; Larsen, Randy; Dashwood, Roderick.

In: Mutation Research Regular Papers, Vol. 308, No. 2, 16.07.1994, p. 191-203.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Mechanisms of the in vitro antimutagenic action of chlorophyllin against benzo[a]pyrene

T2 - Studies of enzyme inhibition, molecular complex formation and degradation of the ultimate carcinogen

AU - Tachino, Nicholas

AU - Guo, Dexin

AU - Dashwood, Wan Mohaiza

AU - Yamane, Shane

AU - Larsen, Randy

AU - Dashwood, Roderick

PY - 1994/7/16

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AB - Mechanisms of the antimutagenic action of chlorophyllin (CHL) towards benzo[a]pyrene (BP) were studied in vitro. In the Salmonella assay, CHL inhibited the mutagenic activity of BP in the presence of an S9 activation system and was particularly effective against the direct-acting ultimate carcinogen, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). Spectral studies indicated that the time-dependent hydrolysis of BPDE to tetrols was augmented in the presence of CHL concentrations on the order of 5 μM. Dose-related inhibition of several cytochrome P450-dependent enzyme activities was observed upon addition of CHL to in vitro incubations. Spectral changes for the interaction between CHL and cytochrome P450 indicated that CHL does not bind to the active site of the enzyme, but exerts its inhibitory effect indirectly. This was achieved by inhibiting NADPH-cytochrome P450 reductase (Ki ∼ 120 μM with cytochrome c as substrate), and did not involve lowering of the effective substrate concentration by complex formation with the procarcinogen. It is concluded that the in vitro antimutagenic activity of CHL towards BP involves accelerated degradation of the ultimate carcinogen, with inhibition of carcinogen activation occurring only at high CHL concentrations. The latter mechanism is unlikely to occur in vivo following p.o. administration due to the limited uptake of CHL from the gut, but tissue concentrations may be sufficiently high to cause degradation of BPDE.

KW - Benzo[a]pyrene

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