Lack of bioavailability of dichlorobenzidine form diarylide azo pigments: molecular dosimetry for hemoglobin and DNA adducts

Applying Bayesian forecasting to predictive toxicology: the probability of innate carcinogenicity to humans of dyes synthesized from benzidine

The preclinical identification of health hazards relies on the performance (the historic agreement with the ultimate gold standard) of regulatorily recommended bioassays. However, any screening testing with less than 100% sensitivity, or 100% specificity, can deliver false results (outcomes discordant to the ultimate gold standard). Conversely, the predictive values approach (a.k.a. Bayesian forecasting) weighs (1) the performance of the predictive bioassay (battery, or framework) with (2) the prevalence of -positivity to the ultimate gold standard- in the most representative category to which the substance in evaluation can be allocated. Thus, the predictive values approach (PVA) provides the quantitative probability of toxicity to humans for substances that, circumstantially, are evaluable only through nonclinical data. Consequently, the PVA improves the predictivity of nonclinical toxicology, increasing the potential impact of hazard identifications based on preclinical data only. This article aimed to introduce the PVA through a worked example. Due to their toxicological homogeneity and public health relevance, the superfamily of colorants derived from benzidine (BZ) or some mutagenic congeners was selected (hereafter mentioned as BZ-related-colorants). For 259 BZ-related-colorants, the numeric probability of innate carcinogenicity to humans was estimated (from rodent carcinogenicity bioassays) or predicted (from alternative methods) through the PVA. A discussion was provided on (1) some limitations and implications of the PVA, and (2) the probable significance of the predictive values figured for up to 259 BZ-related-colorings.

The Need for, and the Role of the Toxicological Chemist in the Design of Safer Chemicals

During the past several decades, there has been an ever increasing emphasis for designers of new commercial (nonpharmaceutical) chemicals to include considerations of the potential impacts a planned chemical may have on human health and the environment as part of the design of the chemical, and to design chemicals such that they possess the desired use efficacy while minimizing threats to human health and the environment. Achievement of this goal would be facilitated by the availability of individuals specifically and formally trained to design such chemicals. Medicinal chemists are specifically trained to design and develop safe and clinically efficacious pharmaceutical substances. No such formally trained science hybrid exists for the design of safer commercial (nonpharmaceutical) chemicals. This article describes the need for and role of the "toxicological chemist," an individual who is formally trained in synthetic organic chemistry, biochemistry, physiology, toxicology, environmental science, and in the relationships between structure and commercial use efficacy, structure and toxicity, structure and environmental fate and effects, and global hazard, and trained to integrate this knowledge to design safer commercially efficacious chemicals. Using examples, this article illustrates the role of the toxicological chemist in designing commercially efficacious, safer chemical candidates.

A 3,3'-dichlorobenzidine-imprinted polymer gel surface plasmon resonance sensor based on template-responsive shrinkage

Molecularly imprinted polymer gel film on the gold substrate of a chip was prepared with minute amount of cross-linker for the fabrication of a surface plasmon resonance (SPR) sensor sensitive to 3,3'-dichlorobenzidine. The molecularly imprinted gel film was anchored on a gold chip by a surface-bound photo-radical initiator. The sensing of 3,3'-dichlorobenzidine is based on responsive shrinkage of the imprinted polymer gel film that is triggered by target binding. This change can improve the responsiveness of the imprinted SPR sensor to 3,3'-dichlorobenzidine. The molecularly imprinted polymer gel film was characterized with contact angle measurements, electrochemical impedance spectroscopy, cyclic voltammogram, swelling measurements and atomic force microscopy. The changes of SPR spectroscopy wavenumber shifts revealed that the imprinted gel sensing film can 'memorize' the binding of 3,3'-dichlorobenzidine compared to non-imprinted one. The imprinted gel-SPR sensor showed a linear response in the range of 9.0×10(-12) to 5.0×10(-10) mol L(-1) (R(2)=0.9998) for the detection of 3,3'-dichlorobenzidine, and it also exhibited high selectivity to 3,3'-dichlorobenzidine compared to its structurally related analogues. We calculated the detection limits to be 0.471 ng L(-1) for tap water and 0.772 ng kg(-1) for soil based on a signal to noise ratio of 3. The method showed good recoveries and precision for the samples spiked with 3,3'-dichlorobenzidine. This suggest that the imprinted gel-SPR sensing method can be used as a promising alternative for the detection of 3,3'-dichlorobenzidine.

Development of a strategy for biological monitoring in a chemical plant producing 3,3'-dichlorobenzidine dihydrochloride

In a chemical plant in Germany producing 3,3'-dichlorobenzidine dihydrochloride for the manufacture of colorants, blood and urine samples were taken for biological monitoring. 3,3'-Dichlorobenzidine (DBZ) was analyzed in urine by thin-layer chromatography and subsequently further combined with analysis of adducts of 3,3'-DBZ in hemoglobin. Data highlight current ranges of industrial exposure to 3,3'-DBZ in Germany and demonstrate the applicability of biological monitoring to minimize this exposure. Effective biological monitoring was achieved by a combination of monitoring hemoglobin adducts with spot samplings of urinary 3,3'-DBZ excretion in cases of reported exposure periods. Data presented might help to identify biological guidance values (BGV/BAR) for 3,3'-DBZ-exposed individuals.

Carcinogenicity of azo colorants: influence of solubility and bioavailability

In the past, azo colorants based on benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine (o-tolidine), and 3,3'-dimethoxybenzidine (o-dianisidine) have been synthesized in large amounts and numbers. Studies in exposed workers have demonstrated that the azoreduction of benzidine-based dyes occurs in man. The metabolic conversion of benzidine-, 3,3'-dimethylbenzidine- and 3,3'-dimethoxybenzidine-based dyes to their (carcinogenic) amine precursors in vivo is a general phenomenon that must be considered for each member of this class of chemicals. Several epidemiological studies have demonstrated that the use of the benzidine-based dyes has caused bladder cancer in humans. However, in contrast to water-soluble dyes, the question of biological azoreduction of (practically insoluble) pigments has been a matter of discussion. As a majority of azo pigments are based on 3,3'-dichlorobenzidine, much of the available experimental data are focused on this group. Long-term animal carcinogenicity studies performed with pigments based on 3,3'-dichlorobenzidine did not show a carcinogenic effect. The absence of a genotoxic effect has been supported by mutagenicity studies with the 3,3'-dichlorobenzidine-based Pigment Yellow 12. Studies in which azo pigments based on 3,3'-dichlorobenzidine had been orally administered to rats, hamsters, rabbits and monkeys could generally not detect significant amounts of 3,3'-dichlorobenzidine in the urine. It, therefore, appears well established that the aromatic amine components from azo pigments based on 3,3'-dichlorobenzidine are practically not bioavailable. Hence, it is very unlikely that occupational exposure to insoluble azo pigments would be associated with a substantial risk of (bladder) cancer in man. According to current EU regulations, azo dyes based on benzidine, 3,3'-dimethoxybenzidine and 3,3'-dimethylbenzidine have been classified as carcinogens of category 2 as "substances which should be regarded as if they are carcinogenic to man". This is not the case for 3,3'-dichlorobenzidine-based azo pigments.

Biomonitoring of arylamines and nitroarenes

Arylamines and nitroarenes are very important intermediates in the industrial manufacture of dyes, pesticides and plastics, and are significant environmental pollutants. The metabolic steps of N-oxidation and nitroreduction to yield N-hydroxyarylamines are crucial for the toxic properties of arylamines and nitroarenes. Nitroarenes are reduced by microorganisms in the gut or by nitroreductases and aldehyde dehydrogenase in hepatocytes to nitrosoarenes and N-hydroxyarylamines. N-Hydroxyarylamines can be further metabolized to N-sulphonyloxyarylamines, N-acetoxyarylamines or N-hydroxyarylamine N-glucuronide. These highly reactive intermediates are responsible for the genotoxic and cytotoxic effects of this class of compounds. N-Hydroxyarylamines can form adducts with DNA, tissue proteins, and the blood proteins albumin and haemoglobin in a dose-dependent manner. DNA and protein adducts have been used to biomonitor humans exposed to such compounds. All these steps are dependent on enzymes, which are present in polymorphic forms. This article reviews the metabolism of arylamines and nitroarenes and the biomonitoring studies performed in animals and humans exposed to these substances.