Antimutagenic potency of chlorophyllin in the salmonella assay and its correlation with binding constants of mutagen‐inhibitor complexes

Abstract

Chlorophyllin (CHL) is a water-soluble salt of chlorophyll that exhibits antimutagenic activity in short-term genotoxicity assays and inhibits carcinogen-DNA binding in vivo. The antimutagenic potency of CHL was studied against several structurally related heterocyclic amines using the Salmonella assay. The mutagens included 2-amino-3-methylimidazo[4,5,-f]-quinoline (IQ) and seven related IQ-type compounds, and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and three additional non-IQ-type compounds. No relationship was observed between mutagenic potency (revertants/ng mutagen) and antimutagenic potency when expressed in terms of the CHL dose/plate-inhibiting mutagenicity by 50 percent (I50). However, a correlation was observed between mutagenic potency and the mole ratio of CHL to mutagen giving 50% inhibition (MR50), with most mutagens requiring several hundredfold to several thousandfold molar excess of CHL for inhibition. In spectrophotometric studies, CHL formed noncovalent molecular complexes with the heterocyclic amines, with binding constants in the range 3-13 x 10(3) M-1. Binding constants were inversely correlated with I50 and MR50 values, i.e., with increasing strength of complex formation less CHL/plate and a lower mole ratio of CHL to mutagen was required to inhibit mutagenicity. The results support an inhibitory mechanism in which chlorophylls operate as "interceptor molecules," interacting with carcinogens and mutagens directly and limiting their bioavailability.

Chemopreventive properties of chlorophylls towards aflatoxin B1: a review of the antimutagenicity and anticarcinogenicity data in rainbow trout

“…By reducing the bioavailability of many genotoxins, these putative 'interceptor molecules' might represent an important first line of defense, perhaps rivaling such mechanisms as induction of detoxification enzymes or inhibition of carcinogen activating enzymes. In the period since the review by Hartman and Shankel was published, a number of papers has described the ability of CHL, chlorophylls, and other porphyrins to form molecular complexes with various carcinogens and mutagens in a manner consistent with the interceptor molecule hypothesis [8][9][10][11][12][13][14]. We will briefly review the evidence supporting the formation of a molecular complex between CHL and AFB 1 .…”

“…We will briefly review the evidence supporting the formation of a molecular complex between CHL and AFB 1 . However, the reader is referred to other work that describes the interactions formed between heterocyclic amines, polycyclic aromatic hydrocarbons, or a number of miscellaneous polycyclic planar mutagens and CHL, chlorophylls, or related porphyrins [8][9][10][11][12][13][14].…”

The “interceptor” properties of chlorophyllin measured within the three-component system: Intercalator–DNA–chlorophyllin

“…Anti-mutagenic activity of CHL was demonstrated with respect to heterocyclic amines [1][2][3], benzo[a]pyrene [4,5], aflatoxin [6][7][8][9][10], heavy metals [11], and ionizing radiation [12]. Diversity of the agents whose antimutagenic activity was neutralized by CHL points out that different protective mechanisms may be involved.…”

Interactions of chlorophyllin with acridine orange, quinacrine mustard and doxorubicin analyzed by light absorption and fluorescence spectroscopy

“…It has frequently been reported during the past decade that CHL has strong anti-oxidative, antimutagenic and anti-carcinogenic properties [1]. Thus, the mutagenicity of such diverse agents as heterocyclic amines [2][3][4][5], aflatoxin B 1 [6,7], benzo[a]pyrene [8][9][10][11], dibenzo[a, 1]pyrene [12], doxorubicin [13], cyclophosphamide [14], reactive oxygen intermediates (ROIs) [15] or heavy metal ions [16][17][18], was shown to be reduced in the presence of CHL.…”

“…Another mechanism that has been advanced was based on the observation that CHL reacts directly with active groups of mutagens, resulting in their neutralization [19,22,23]. Still another mechanism to account for the antimutagenic property of CHL was explained by the formation of heterologous complexes with mutagens [3,4,9]. The latter mechanism was postulated based on the observation that CHL was most effective in reducing mutagenicity in the case of polycyclic compounds with flat aromatic structures [5,11,24].…”