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 language | English |
|---|---|
| Pages (from-to) | 191-203 |
| Number of pages | 13 |
| Journal | Mutation Research Regular Papers |
| Volume | 308 |
| Issue number | 2 |
| DOIs | |
| State | Published - 16 Jul 1994 |
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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 journal › Article
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
Y1 - 1994/7/16
N2 - 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.
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
KW - Chlorophyllin antimutagenicity
UR - http://www.scopus.com/inward/record.url?scp=0028050207&partnerID=8YFLogxK
U2 - 10.1016/0027-5107(94)90154-6
DO - 10.1016/0027-5107(94)90154-6
M3 - Article
C2 - 7518046
AN - SCOPUS:0028050207
VL - 308
SP - 191
EP - 203
JO - Mutation Research Regular Papers
JF - Mutation Research Regular Papers
SN - 0027-5107
IS - 2
ER -