Benzidine metabolism

It is of more than a little interest to note that the sites of tumor formation do not always match across species. Benzidine, a substance once widely used in dye manufacture, was shown many years ago to be a carcinogenic risk for the bladder in workers exposed to excessive levels. The rat bladder is not responsive to this substance, but its liver is. It wasn t until Wilhelm Hueper turned to the dog that bladder cancer could be reproduced in a laboratory animal. It is now understood that benzidine metabolism is similar in dogs and people, and that metabolism in the rat takes a different course. It is also understood that certain benzidine metabolites, and not benzidine itself, are the proximate causes of tumors. Knowledge of metabolic differences helps explain the species similarities and differences in tumor response. If we had available the rat data and no human data, we would be in error to conclude that benzidine was a cause of human liver cancer. 

A number of arylamines are potent bladder carcinogens such as 4-aminobiphenyl, 1-naphthylamine, and benzidine. Metabolic activation of these carcinogens requires the action of UDP-glucuronosyl transferase on N-hydroxyarylamines to form N-glucuronides. 

Zenser, T.V., Lakshmi, V.M. and Davis, B.B. (1999) Human and Escherichia coli /3-glucuronidase hydrolysis of glucuronide conjugates of benzidine and 4-aminobiphenyl, and their hydroxy metabolites. Drug Metabolism and Disposition The Biological Fate of Chemicals, 27, 1064—1067. 

The metabolic formation of N-sulfonyloxy-N-acetyl-2-aminofluorene (N-sulfonyloxy-AAF) and its observed electrophilic reactivity, provided the first evidence for the importance of enzymatic conjugation reactions in chemical carcinogenesis (23,24). This reaction was shown to be catalyzed by PAPS-dependent sulfotrans-ferases that are located predominantly in liver cytosol and has been subsequently demonstrated for N-hydroxy arylamide metabolites of several other carcinogens, including N-acetyl-4-aminobiphenyl (AABP), benzidine, N-acetyl-2-aminophenanthrene and phenacetin. 

That the aromatic amine benzidine is mutagenic only at the TK locus in L5178Y TK+,/ cells. The most disturbing finding was that benzidine (detectable without metabolism by S9 mix) did not produce detectable DNA adducts (as shown by 32P-post-labeling) in L5178Y cells. Thus, the mechanism... 

Soil Benzidine was added to different soils and incubated in the dark at 23 °C under a carbon dioxide-free atmosphere. After 1 yr, 8.3 to 11.6% of the added benzidine degraded to carbon dioxide primarily by microbial metabolism and partially by hydrolysis (Graveel et al, 1986). Tentatively identified biooxidation compounds using GC/MS include hydroxybenzidine, 3-hydroxybenzidine, 4-amino-4 -nitrobiphenyl, A(A -dihydroxybenzidine, 3,3 -dihydroxybenzidine and 4,4 -dinitrobiphenyl (Baird et al, 1977). Under aerobic conditions, the half-life was estimated to be 2 to 8 d (Lu et ah, 1977). 

There is no information on the metabolism of 3,3 -dichlorobenzidine in children. Limited data in humans suggest that N-acetylation is an important metabolic pathway (Belman et al. 1968), and a detoxification mechanism. N-Acetylation in humans is likely done by one of two families of N-acetyltransferases. One of these families, NAT2, is developmentally regulated (Leeder and Kearns 1997). Some enzyme activity can be detected in the fetus by the end of the first trimester. Almost all infants exhibit the slow acetylator phenotype between birth and 2 months of age. The adult phenotype distribution is reached by the age of 4-6 months, whereas adult activity is found by approximately 1-3 years of age. Also, UDP-glucurono-syltransferase, responsible for the formation of glucuronide conjugates, seems to achieve adult activity by 618 months of age (Leeder and Kearns 1997). These data suggest that metabolism of 3,3 -dichloro-benzidine by infants will differ from that in adults in extent, rate, or both. 

In metabolism studies of azo dyes and pigments in the hamster, in vivo cleavage of the benzidine-based dye, Direet Black 38, to benzidine was shown by analysis of the urine. However, studies of the 3,3 -diehlorobenzidine-based pigment. Pigment Yellow 12, showed no evidenee for in vivo cleavage to release 3,3 -diehlorobenzidine (Nony et al. 1980). 

Rinde E, Troll W. 1975. Metabolic reduction of benzidine azo dyes to benzidine in rhesus monkey. JNatl Cancer Inst 55(1) 181-182. 

Limited information is available on the metabolism of 1,2-diphenylhydrazine. Two of the known metabolites, aniline and benzidine, may contribute to the toxicity and/or carcinogenicity of the substance. 

M. Boeniger, The Carcinogenicity and Metabolism of Azo Dyes, Especially those derived from Benzidine, DHHS (NIOSH) Publication No. 80 119, US Department of Health and Human Services, Ohio 1980. 

Since workers can be exposed to these compounds during their manufacture and use, it is important to have reliable analytical methods for determining the degree of exposure through body fluid analysis. Additionally, since these compounds can be present at significant levels in commercial products (derived from them) it is desirable to monitor their level in such products (e.g. dyestuffs) as well. Furthermore, many of the commercial products can be metabolized to the original chemical (e.g. benzidine based dyes can be metabolized to benzidine) making it desirable to monitor the body fluids of workers exposed to the commercial products. 

H.B. (1980) Metabolism ofhisazohiphenyl dyes derived from benzidine, 3, 3 -methylbenzidine and 3, 3 -dimethoxylbenzidine to carcinogenic aromatic amines in the dog and rat. Toxicol. Appl. Pharmacol. 56, 248—258. 

Figure 4.69 Metabolism of the carcinogen benzidine showing oxidation and acetylation. Both routes of acetylation can give rise to a reactive nitrenium ion and DNA adducts. Abbreviation. NAT, N-acetyltransferase.

The metabolism of the benzidine-based dyes C.I. Direct Red 28, C.I. Direct Blue 6, C.I. Direct Brown 95, and C.I. Direct Black 38 was studied in Rhesus monkeys. After ingestion of the dyes, benzidine and monoacetylbenzidine could be detected as metabolites in the urine. This indicated that the dyes had been converted to benzidine [29], Recent in vitro studies on C. I. DirectBlue 14 show that bacteria isolated from healthy human skin have reductase activity and are able to cleave the dye into the corresponding arylamine, in this case 3,3 -dimethylbenzi-dine [30],... 

Dyes metabolized to benzidine Environmental tobacco smoke Erionite... 

Benzidine is metabolized to highly toxic, reactive metabolites, such as N-hydroxyarylamides and N-hydroxyarylamines, which act as procarcinogens and are more mutagenic than parent compounds. The metabolites act as DNA adducts and bind to cell receptors. The metabolites on conjugation with sulfuric, acetic, and glucuronic acids form ultimate carcinogens. Acetylated benzidine metabolites such as N-acetoxyarylamines are known to cause bladder cancer in dye industry workers. 

For humans, there are no data regarding the absorption of diphenylhydrazines by any exposure route. Gastrointestinal absorption of 1,2-diphenylhydrazine in rats can be inferred by the presence of the parent compound and its metabolites in the urine and by systemic toxic effects following oral administration. No data are available regarding inhalation or dermal absorption in animals. Data are unavailable regarding the metabolism of 1,1-diphenylhydra-zine. Limited data regarding the metabolism of 1,2-diphenylhydrazine by rats suggest benzidine and aniline to be major metabolites with minor... 

Azo Compounds Azo dyes are widely used in the food, pharmaceutical, cosmetic, textile, and leather industry. They are synthetic compounds characterized by one (monoazo) or several intramolecular N = N bonds. Azo dyes, if they are systemically absorbed, can be metabolized by the way of azoreductases of intestinal microflora by liver cells and skin surface bacteria. This metabolism leads to aromatic amines that can be hazardous. In the 1930s, some azo derivatives like 4-dimethyl aminoazoben-zene (Butter Yellow, Cl Solvent Yellow 2, Cl 11020) and o-aminoazotoluene were experimentally found to be directly carcinogenic to liver and bladder after feeding. Other complex azo dyes like Direct Black 38 or Direct Blue 6 (Figure 28) release the aromatic amine benzidine. Some examples of azo dyes metabolized in benzidine and benzidine-congeners are listed in Table 3. 

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