TY - JOUR
T1 - Natural chlorophyll inhibits aflatoxin B1-induced multi-organ carcinogenesis in the rat
AU - Simonich, Michael T.
AU - Egner, Patricia
AU - Roebuck, Bill D.
AU - Orner, Gayle A.
AU - Jubert, Carole
AU - Pereira, Cliff
AU - Groopman, John D.
AU - Kensler, Thomas W.
AU - Dashwood, Roderick H.
AU - Williams, David E.
AU - Bailey, George S.
N1 - Funding Information:
We especially thank Mandy Louderback for her excellence in rat husbandry and necropsy, and Adam Sinner for his diligent work on the enzyme assays as part of his training project. We thank Dr Michael Schimerlik of the Department of Biochemistry and Biophysics for help with modeling the fluorescence binding data. We also thank Yonghai Li and Cody Olsen of the Department of Statistics for their help with data analyses. Partly supported through National Institutes of Health grants CA90890, ES00210, ES03850, CA100608 and CA65525.
PY - 2007/6
Y1 - 2007/6
N2 - Chemoprevention by chlorophyll (Chl) was investigated in a rat multi-organ carcinogenesis model. Twenty-one male F344 rats in three gavage groups (N = 7 rats each) received five daily doses of 250 μg/kg [3H]-aflatoxin B1 ([3H]-AFB1) alone, or with 250 mg/kg chlorophyllin (CHL), or an equimolar amount (300 mg/kg) of Chl. CHL and Chl reduced hepatic DNA adduction by 42% (P = 0.031) and 55% (P < 0.008), respectively, AFB1-albumin adducts by 65% (P, 0.001) and 71% (P < 0.001), respectively, and the major AFB-N7-guanine urinary adduct by 90% (P = 0.0047) and 92% (P = 0.0029), respectively. To exploremechanisms, fluorescence quenching experiments established formation of a non-covalent complex in vitro between AFB1 and Chl (Kd = 1.22 ± 0.05 mM, stoichiometry = 1Chl:1AFB1) as well as CHL (Kd 5 3.05 ± 0.04 mM; stoichiometry 1CHL:1AFB1). The feces of CHL and Chl co-gavaged rats contained 137% (P = 0.0003) and 412% (P = 0.0048) more AFB1 equivalents, respectively, than control feces, indicating CHL and Chl inhibited AFB1 uptake. However, CHL or Chl treatment in vivo did not induce hepatic quinone reductase (NAD(P)H:quinone oxidoreductase) or glutathione S-transferase (GST) above control levels. These results are consistent with amechanism involving complex-mediated reduction of carcinogen uptake, and do not support a role for phase II enzyme induction in vivo under these conditions. In a second study, 30 rats in three experimental groups were dosed as in study 1, but for 10 days. At 18 weeks, CHL and Chl had reduced the volume percent of liver occupied by GST placental form-positive foci by 74% (P < 0.001) and 77% (P < 0.001), respectively compared with control livers. CHL and Chl reduced the mean number of aberrant crypt foci per colon by 63% (P = 0.0026) and 75% (P = 0.0004), respectively. These results show Chl and CHL provide potent chemoprotection against early biochemical and late pathophysiological biomarkers of AFB1 carcinogenesis in the rat liver and colon.
AB - Chemoprevention by chlorophyll (Chl) was investigated in a rat multi-organ carcinogenesis model. Twenty-one male F344 rats in three gavage groups (N = 7 rats each) received five daily doses of 250 μg/kg [3H]-aflatoxin B1 ([3H]-AFB1) alone, or with 250 mg/kg chlorophyllin (CHL), or an equimolar amount (300 mg/kg) of Chl. CHL and Chl reduced hepatic DNA adduction by 42% (P = 0.031) and 55% (P < 0.008), respectively, AFB1-albumin adducts by 65% (P, 0.001) and 71% (P < 0.001), respectively, and the major AFB-N7-guanine urinary adduct by 90% (P = 0.0047) and 92% (P = 0.0029), respectively. To exploremechanisms, fluorescence quenching experiments established formation of a non-covalent complex in vitro between AFB1 and Chl (Kd = 1.22 ± 0.05 mM, stoichiometry = 1Chl:1AFB1) as well as CHL (Kd 5 3.05 ± 0.04 mM; stoichiometry 1CHL:1AFB1). The feces of CHL and Chl co-gavaged rats contained 137% (P = 0.0003) and 412% (P = 0.0048) more AFB1 equivalents, respectively, than control feces, indicating CHL and Chl inhibited AFB1 uptake. However, CHL or Chl treatment in vivo did not induce hepatic quinone reductase (NAD(P)H:quinone oxidoreductase) or glutathione S-transferase (GST) above control levels. These results are consistent with amechanism involving complex-mediated reduction of carcinogen uptake, and do not support a role for phase II enzyme induction in vivo under these conditions. In a second study, 30 rats in three experimental groups were dosed as in study 1, but for 10 days. At 18 weeks, CHL and Chl had reduced the volume percent of liver occupied by GST placental form-positive foci by 74% (P < 0.001) and 77% (P < 0.001), respectively compared with control livers. CHL and Chl reduced the mean number of aberrant crypt foci per colon by 63% (P = 0.0026) and 75% (P = 0.0004), respectively. These results show Chl and CHL provide potent chemoprotection against early biochemical and late pathophysiological biomarkers of AFB1 carcinogenesis in the rat liver and colon.
UR - http://www.scopus.com/inward/record.url?scp=34447329571&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34447329571&partnerID=8YFLogxK
U2 - 10.1093/carcin/bgm027
DO - 10.1093/carcin/bgm027
M3 - Article
C2 - 17290047
AN - SCOPUS:34447329571
SN - 0143-3334
VL - 28
SP - 1294
EP - 1302
JO - Carcinogenesis
JF - Carcinogenesis
IS - 6
ER -