Chemico-Biological Interactions 156 (2005) 151–153

Letter to the Editor

Re: Xue et al. Effects of analogs of indole-3-carbinolcyclic trimerization, etc. Chem. Biol. Interact. 152(2005) 119

Dear Dr. Bond,

Xue et al. state that 5,6,11,12,17,18-hexahydro-cyclononal[1,2-b;4,5-b:7,8-b]triindole (CTr, also ref-erred to as CTI and CT) is a “major digestive productof indole-3-carbinol (I3C).” Published data does notsupport this.

Studies on the acid condensation products of I3Chave been published since the 1960s. They are of inter-est given the potential health benefits of the indole.However, a review clearly shows that there is no con-sensus about what the acid condensation productsof I3C are, including major digestive products. Forexample, a recent report, based on data from the first

major acid condensation products from a simple reac-tion with hydrochloric acid and water. This conflictswith Bjeldanes et al.[6] who reported that CT was alsoa major product of this reaction, but confirms Amat-Guerri et al.[7].

The disposition of I3C in rodents has been reported.In male Fischer 344 rats, I3C dissolved in DMSOadministered in corn oil by gavage for 7 days yieldedDIM, LT, HI-IM and three unidentified major metabo-lites in liver by ethyl acetate extraction[5]. It wasreported that CT was a minor product in liver whenstomach pH was∼4.3.

In accordance with the reported impact of pH ondigestive products, De Kruif et al.[8] reported that CTformed in approximately equal amounts to DIM and2,3-bis[3-indolylmethyl]indole (BII) in solution onlyat pH below 3 and not at all above pH 4.5. A differenttype of rat (male Wistar) was used in this study, and I3C

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study to use standards and a fully-validated analyti-cal assay indicates that the major digestive productsof I3C are I3C, and an oxidized metabolite of I3C[1].

The acid condensation products of I3C elicited bya simple solution of HCL and water are mutable,depending on experimental conditions including sol-vent, temperature, dilution, presence or absence of freeradical-scavenging agents, and duration. The potential

was dissolved in DMSO and administered in water bgavage. Under these conditions, DIM and BII were thmajor digestive products identified in tissues, with nCT being detected in any tissue with dichloromethaextraction. CT was not detected in the gastric contenand lowering the pH of the rats’ diet to 1.5 did not causCT to form.

In female CD1 mice administered I3C in corn oil bgavage, the major digestive products were I3C, DIM

of beginning with one indole and ending with two dif-ferent results was elucidated as far back as 1970, andthere is no indication that multiple experimental factorsi incet

g toa as

LT, HI-IM and an oxidative I3C product that exceededI3C by three times when extracted bytert-butylmethylether[1].

oilb od-u tate[ ctsw I3C

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mpacting laboratory results have been resolved shat time.

Using the method of Grose[2], Stresser et al.[5]enerated 3,3′-diindolylmethane (I33, also referreds DIM) and 2-(indol-3-ylindol-3-ylmethane) (LT)

009-2797/$ – see front matter © 2005 Elsevier Ireland Ltd. Aldoi:10.1016/j.cbi.2005.07.006

In rainbow trout administered I3C in salmony gavage and in food, the major digestive prcts were I3C and DIM, extracted with ethyl ace

9]. It is notable that levels of digestive produere significantly different depending on whether

reserved.

152 Letter to the Editor / Chemico-Biological Interactions 156 (2005) 151–153

was consumed in the diet or delivered in oil bygavage.

Clearly, there is no consensus on I3C condensationproducts, either in simple solution or in animals, andit is not accurate to state that CT is a major digestiveproduct of I3C. In a single study, in a single animal,major digestive products change within minutes, somedisappearing entirely (such as CT in De Kruif et al.[8]).The variables are so confounding that some researchershave reported four times that I3C inhibits aflatoxin tox-icity [10–13], two times that it increases it[14–16], andonce that it has no effect[17].

Laboratory conditions determine what the diges-tive products of I3C are; they are different fromone study to the next, as reflected in the data. Invitro precipitation of I3C oligomers with HCL donot accurately depict in vivo products[3,4]. Differ-ences in interspecies metabolism where (as a singleexample of many) trout and rabbits readily convertaflatoxin to its toxic form, coho salmon and guineapigs do not[17,18], preclude extrapolation of phar-macokinetic data from one species to another. Thein vitro and in vivo digestive products of I3C haveyet to be determined, and extrapolation of existingdata beyond the present experiment is invalidatedby multiple confounding factors as reflected in theliterature.

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[6] L.F. Bjeldanes, J.Y. Kim, K.R. Grose, J.C. Bartholomew,C.A. Bradfield, Aromatic hydrocarbon responsiveness-receptoragnoists generated from indole-3-carbinol in vitro andin vivo—comparisons with 2,3,7,8-tetrachlorodibenzo-para-dioxin, Proc. Natl. Acad. Sci. U.S.A. 88 (1991) 9543–9547.

[7] F. Amat-Guerri, R. Martinez-Utrilla, C. Pascual, Condensationof 3-hydromethylindoles with 3-substituted indoles, Formationof 2,3-methylenediindole derivatives, J. Chem. Res. Miniprint1578–1586.

[8] C.A. De Kruif, J.W. Marsman, J.C. Venekamp, H.E. Falke, J.Noordhoek, B.J. Blaauboer, H.M. Wortelboer, Structure eluci-dation of acid reaction products of indole-3-carbinol: detectionin vivo and enzyme induction in vitro, Chem-Biol. Interact. 80(1991) 303–315.

[9] R.H. Dashwood, L. Uyetake, A.T. Fong, J.D. Hendricks, G.S.Bailey, In vivo disposition of the natural anti-carcinogen indole-3-carbinol after po administration to rainbow trout, Food Chem.Toxicol. 27 (1989) 385–392.

[10] G. Bailey, M. Taylor, D. Selivonchick, T. Eisele, J. Hendricks,J. Nixon, N. Pawlowski, R. Sinnhuber, Mechanisms of dietarymodification of aflatoxin B1 carcinogenesis, Basic Life Sci. 21(1982) 149–165.

[11] A.T. Fong, H.I. Swanson, R.H. Dashwood, D.E. Williams, J.D.Hendricks, G.S. Bailey, Mechanisms of anti-carcinogenesis byindole-3-carbinol. Studies of enzyme induction, electrophile-scavenging, and inhibition of aflatoxin B1 activation, Biochem.Pharmacol. 39 (1990) 19–26.

[12] R.H. Dashwood, D.N. Arbogast, A.T. Fong, C. Pereira,J.D. Hendricks, G.S. Bailey, Quantitative inter-relationshipsbetween aflatoxin B1 carcinogen dose, indole-3-carbinoland anti-carcinogen dose, target organ DNA adductionand final tumor response, Carcinogenesis 10 (1989) 175–181.

[13] J.E. Nixon, J.D. Hendricks, N.E. Pawlowski, C.B. Pereira, R.O.en-arc-

[ ks,by

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eferences

[1] M.J. Anderton, M.M. Manson, R.D. Verschoyle, A. GeschJ.H. Lamb, P.B. Farmer, W.P. Steward, M.L. Williams, Phmacokinetics and tissue disposition of indole-3-carbinol anacid condensation products after oral administration to mClin. Cancer Res. 10 (2004) 5233–5241.

[2] K.R. Grose, L.F. Bjeldanes, Oligomerization of indolecarbinol in aqueous acid, Chem. Res. Toxicol. 5 (19188–193.

[3] N. Takahashi, R.H. Dashwood, L.F. Bjeldanes, D.E. WilliaG.S. Bailey, Mechanisms of indole-3-carbinol (I3C) anticcinogenesis: inhibition of aflaoxin B1-DNA adduction andmutagenesis by I3C acid condensation products, Food CToxicol. 33 (1995) 851–857.

[4] J. Bergman, S. Hogberg, J.O. Lindstrom, Macrocyclic condensation products of indole and simple aldehydes, Tetrahedr(1970) 3347–3352.

[5] D.M. Stresser, D.E. Williams, D.A. Griffin, G.S. Bailey, Mecanisms of tumor modulation by indole-3-carbinol—disposiand excretion in male Fischer-344 rats, Drug Metab. Dispo(1995) 965–975.

Sinnhuber, G.S. Bailey, Inhibition of aflatoxin B1 carcinogesis in rainbow trout by flavone and indole compounds, Cniogenesis 5 (1984) 615–619.

14] R.H. Dashwood, A.T. Fong, D.E. Williams, J.D. HendricG.S. Bailey, Promotion of aflatoxin B1 carcinogenesisthe natural tumor modulator indole-3-carbinol: influeof dose, duration and intermittent exposure on indolcarbinol promotional potency, Cancer Res. 51 (1991) 232365.

15] A. Oganesian, J.D. Hendricks, C.B. Pereira, G.A. Orner,Bailey, D.E. Williams, Potency of dietary indole-3-carbinol apromoter of aflatoxin B1-initiated hepatocarcinogenesis: refrom a 9000 animal tumor study, Carcinogenesis 20 (1453–458.

16] T.A. Eisele, G.S. Bailey, J.E. Nixon, The effect of indo3-carbinol, an aflatoxin B1 hepatocarcinoma inhibitor,other indole analogs on the rainbow trout hepatic mfunction oxidase system, Toxicol. Lett. 19 (1983) 1138.

17] A.S. Salhab, G.S. Edwards, Comparative in vitro metaboof aflatoxicol by liver preparations from animals and humCancer Res. 37 (1977) 1016–1021.

Letter to the Editor / Chemico-Biological Interactions 156 (2005) 151–153 153

[18] G.S. Bailey, D.E. Williams, J.S. Wilcox, P.M. Loveland, R.A.Coulombe, J.D. Hendricks, Aflatoxin B1 carcinogenesis andits relation to DNA adduct formation and adduct persistence insensitive and resistant salmonid fish, Carcinogenesis 9 (1988)1919–1926.

Terri Mitchell∗1707 Pass Road, Biloxi, MS 39531, USA

∗ Tel.: +1 228 875 0057; fax: +1 228 875 0571.E-mail address: grakus@i-55.com

29 July 2005