The significance of azo-reduction in the mutagenesis and carcinogenesis of azo dyes

Azo dyes are widely used in textile, printing, cosmetic, drug and food-processing industries. They are also used extensively in laboratories as either biological stains or pH indicators. The extent of such use is related to the degree of industrialization. Since intestinal cancer is more common in highly industrialized countries, a possible connection may exist between the increase in the number of cancer cases and the use of azo dyes. Azo dyes can be reduced to aromatic amines by the intestinal microflora. The mutagenicity of a number of azo dyes is reviewed in this paper. They include Trypan Blue, Ponceau 3R, Pinceau 2R, Methyl Red, Methyl Yellow, Methyl Orange, Lithol Red, Orange I, Orange II, 4-Phenylazo-Naphthylamine, Sudan I, Sudan IV, Acid Alizarin Violet N, Fast Garnet GBC, Allura Red, Ponceau SX, Sunset Yellow, Tartrazine, Citrus Red No. 2, Orange B, Yellow AB, Carmoisine, Mercury Orange, Ponceau S, Versatint Blue, Phenylazophenol, Evan's Blue and their degraded aromatic amines. The significance of azo reduction in the mutagenesis and carcinogenesis of azo dyes is discussed.

An association of carcinogenesis and decrease of cellular NAD concentration

It is postulated that a decrease in nicotinamide adenine dinucleotide (NAD) concentration has a primary association with carcinogenesis. The following observations are presented as evidence: (1) NAD and adenosine triphosphate (ATP) concentrations are lower in cancer cells; (2) chemical carcinogens and radiation can cause a lowering of NAD concentration in precancerous cells: (3) biosynthesis of NAD in Ehrlich ascites tumor cells is altered; and (4) NAD is involved in regulating deoxyribonucleic acid (DNA) synthesis. The lowering of NAD concentration would lead to the expression of oncogene and/or virogene according to the protovirus hypothesis, and the cellular characteristics of cancer cells can also be explained through the lowering of cellular NAD concentration. Experimental approaches are also proposed.

Mutagenicity testing of some commonly used dyes

Seventeen commonly used dyes and 16 of their metabolites or derivatives were tested in the Salmonella-mammalian microsome mutagenicity test. Mutagens active with and without added Aroclor-induced rat liver microsome preparations (S9) were 3-aminopyrene, lithol red, methylene blue (USP), methyl yellow, neutral red, and phenol red. Those mutagenic only with S9 activation were 4-aminopyrazolone, 2,4-dimethylaniline, N,N-dimethyl-p-phenylenediamine, methyl red, and 4-phenyl-azo-1-naphthylamine. Orange II was mutagenic only without added S9. Nonmutagenic azo dyes were allura red, amaranth, ponceau R, ponceau SX, sunset yellow, and tartrazine. Miscellaneous dyes not mutagenic were methyl green, methyl violet 2B, and nigrosin. Metabolites of the azo dyes that were not mutagenic were 1-amino-2-naphthol hydrochloride, aniline, anthranilic acid, cresidine salt, pyrazolone T,R-amino salt (1-amino-2-naphthol-3,6-disulfonic disodium salt), R-salt, Schaeffer's salt (2-naphthol-6-sulfonic acid, sodium salt), sodium naphthionate, sulfanilamide, and sulfanilic acid. 4-Amino-1-naphthalenesulfonic acid sodium salt was also not mutagenic. Fusobacterium sp. 2 could reductively cleave methyl yellow to N,N-dimethyl-p-phenylenediamine which was then activated to a mutagen.

Production of a mutagen from ponceau 3R by a human intestinal anaerobe

Ponceau 3R was reduced in vitro by Fusobacterium sp. 2, a human intestinal anaerobe, to a product which is mutagenic when metabolically activated by liver S9 preparations in the Salmonella/mammalian-microsome mutagenicity test. This mutagenic metabolite has been identified as 2,4,5-trimethylaniline.

Reduction of azo dyes by intestinal anaerobes

Reduction of seven azo dyes (amaranth, Ponceau SX, Allura Red, Sunset Yellow, tartrazine, Orange II, and methyl orange) was carried out by cell suspensions of predominant intestinal anaerobes. It was optimal at pH 7.4 in 0.4 M phosphate buffer and inhibited by glucose. Flavin mononucleotide caused a marked enhancement of azo reduction by Bacteroides thetaiotaomicron. Other electron carriers, e.g., methyl viologen, benzyl viologen, phenosafranin, neutral red, crystal violet, flavin adenine dinucleotide, menadione, and Janus Green B can replace flavin mononucleotide. These data suggest that an extracellular shuttle is required for azo reduction.

Unaltered metabolism of taurolithocholic acid with changes in composition of rat intestinal microflora

Changes in composition of both total aerobes and anaerobes of rat intestinal microflora do not appear to affect the metabolism of taurolithocholic acid.

Dietary Effects on the Composition of Fecal Flora of Rats

A long-term animal feeding experiment was conducted to compare the effect of meat and Wayne laboratory chow diets on the composition of rat fecal flora. Fecal bacteria were enumerated on selective media under both aerobic and anaerobic conditions. Intrarectal administration of N -methyl- N′ -nitro- N -nitro-soguanidine (MNNG) affected the count only on the phenylethylalcohol and veillonella-neomycin agars, whereas a slightly higher number of anaerobes appeared in the feces of rats that were treated with MNNG as compared with those obtained in the feces of untreated rats on the meat diet. In the absence of MNNG, feces of meat-fed rats yielded higher bacterial counts on aerobically incubated MacConkey agar, deoxycholate agar, and Pfizer selective enterococcus agar as well as higher numbers of clostridia on anaerobic egg yolk agar than did feces of rats on the Wayne diet. Feces of the group fed the Wayne diet produced more colonies on aerobic mitis-salivarius agar and lactobacillus agar as well as on anaerobically incubated phenylethylalcohol agar, veillonellaneomycin agar, bifidobacteria agar, fusobacterium (Nissui) agar, and kanamycin-vancomycin blood agar. These differences were consistent throughout the 1-year feeding period.

Mutagenic activity of tryptophan metabolites produced by rat intestinal microflora

The catabolism of tryptophan by rat intestinal microflora was studied for the production of mutagenic metabolites that might be involved in the etiology of colon cancer. Various tryptophan metabolites were assayed for mutagenic and comutagenic activity in the Ames bacterial test system. These included metabolites that were identified by thin-layer chromatography in cultures of rat fecal bacteria, other compounds structurally related to tryptophan, whole unfractionated mixed fecal bacteria culture filtrates, and concentrated solvent extracts. A total of 27 materials were tested with 5 Salmonella strains in the mutagenesis assay. Most substances were inactive, and only one compound, o-aminoacetophenone, which was unlikely to be produced in the intestine, showed weak comutagenic activity. Our results did not support the hypothesis that tryptophan metabolites produced by intestinal microflora are major etiologic factors in cancer of the colon.

Effect of alfalfa fiber substrate on culture counts of rumen bacteria

A medium has been developed using alfalfa fiber as the sole substrate. It gave high culture counts (3 X 10(9) to 8 X 10(9)/ml) of rumen bacteria. When this medium was combined with the medium 98-5 of Bryant and Robinson, modified to contain 33% rumen fluid instead of 40% clarified rumen fluid, a higher count was obtained than with either medium alone.

Inhibitory effects of H2 on growth of Clostridium cellobioparum

Hydrogen inhibits the growth of hydrogen-producing Clostridium cellobioparum, but not of Escherichia coli or Bacteroides ruminicola. The inhibition is reversible. When hydrogen was removed either by palladium black or by gassing out the tube, glucose utilization increased as did optical density and hydrogen production of C. cellobioparum. Removal of the H2 by methanogenic bacteria favors the growth of C. cellobioparum. Grown with Methanobacterium ruminantium in various concentrations of glucose, the Clostridium reaches a higher optical density and produces more H2 and a higher viable cell count. The cell yield is also higher than in pure culture. In mixed culture, C. cellobioparum produces more acetic acid and less lactic acid, ethanol, and butyric acid than in pure culture. The significance of this metabolic shift and hydrogen utilization in methanogenesis is discussed.

Formation of indoleacetic acid by intestinal anaerobes

Indoleacetic acid was produced from tryptophan by only three of 23 intestinal anaerobes studied. Evidence is presented to show that the formation of indoleacetic acid proceeds through the intermediate, indolepyruvic acid, via transamination with alpha-ketoglutarate rather than by tryptamine pathway.

Tryptophanase of fecal flora as a possible factor in the etiology of colon cancer

Twenty-three strains of intestinal anaerobes obtained from two laboratories were examined for indole production from tryptophan. Among the 23 isolates tested, three of Bacteroides fragilis thetaiotaomicron and one Citrobacter sp. were indole positive. The tryptophanase of the indole-positive strains of intestinal anaerobes was inducible by tryptophan and was susceptible to glucose repression. The products of tryptophanase activity were formed in stoichiometric amounts by dialyzed, freshly prepared extracts. The tryptophan concentration and tryptophanase activity in feces from rats on an all-meat diet were significantly higher than those in feces from rats on a normal diet. The results indicated that the higher tryptophanase activity in the feces of rats fed an all-meat diet is due to the inducibility of this enzyme by tryptophan and is not due to any inhibitor in the feces of rats on a normal diet. The results also suggested that a population with a diet rich in meat has a greater chance for exposure to possible carcinogens such as indole and other tryptophan metabolites. This agrees with the hypothesis, based on epidemiologic data, that a high intake of meat may be related to the development of colon cancer in man.

Estimation of growth rate from the mitotic index

The growth rate of a eukaryotic population dividing at a constant rate can be estimated from the equation, t(m)/g ln 2 = ln (1 + R), in which t(m) is the time required for mitosis, g is the generation time, and R is the fraction of cells undergoing mitosis. Values for t(m) and R can be determined by direct microscope examination of the population. The validity of the derived equation has been checked with an exponentially growing culture of a prokaryote, Escherichia coli, in which chloramphenicol was administered to inhibit protein synthesis. Cells having enough protein completed the division process whereas the rest of the population was inhibited. From the plot of the growth curve before and after administration of chloramphenicol, t(m) and R were estimated. The calculated and actual growth rates were almost identical.