4,4?-Diaminodiphenylmethan ? histologische, fermenthistochemische und autoradiographische Untersuchungen im akuten und subakuten Versuch an Ratten mit und ohne zus�tzliche Hitzebelastung

Role of the human N-acetyltransferase 2 genetic polymorphism in metabolism and genotoxicity of 4, 4'-methylenedianiline

4, 4'-Methylenedianiline (MDA) is used extensively as a curing agent in the production of elastomers and is classified as reasonably anticipated to be a human carcinogen based on sufficient evidence in animal experiments. Human N-acetyltransferase 1 (NAT1) and 2 (NAT2) catalyze the N-acetylation of aromatic amines and NAT2 is subjected to a common genetic polymorphism in human populations separating individuals into rapid, intermediate, and slow acetylator phenotypes. Although MDA is known to undergo N-acetylation to mono- and di-acetyl metabolites, very little is known regarding whether this metabolism is subject to the NAT2 genetic polymorphism. We investigated the N-acetylation of MDA by recombinant human NAT1, NAT2, genetic variants of NAT2, and cryoplateable human hepatocytes obtained from rapid, intermediate and slow acetylators. MDA N-acetylation was catalyzed by both recombinant human NAT1 and NAT2 exhibiting a fivefold higher affinity for human NAT2. N-acetylation of MDA was acetylator genotype dependent as evidenced via its N-acetylation by recombinant human NAT2 genetic variants or by cryoplateable human hepatocytes. MDA N-acetylation to the mono-acetyl or di-acetyl-MDA was highest in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytes. MDA-induced DNA damage in the human hepatocytes was dose-dependent and also acetylator genotype dependent with highest levels of DNA damage in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytes under the same MDA exposure level. In summary, the N-acetylation of MDA by recombinant human NAT2 and cryopreserved human hepatocytes support an important role for the NAT2 genetic polymorphism in modifying MDA metabolism and genotoxicity and potentially carcinogenic risk.

Formation and elution of toxic compounds from γ-ray-sterilized medical products and the Ames test of eluted components

No formation of N,N'-methylene dianiline (MDA) was observed in chain-extended thermoplastic polyurethane (PU) when sterilized by autoclaving or γ-ray irradiation. No formation of MDA was observed in nonchain-extended thermoplastic PU when sterilized by γ-ray irradiation. Less than 1 ppm of MDA was produced in nonchain-extended thermoplastic PU subjected to autoclave sterilization. Autoclave sterilization did not produce MDA in thermosetting PU potting material. MDA formation in potting material was promoted by γ-ray irradiation and increased with increasing irradiation doses at a quadratic equation of regression. MDA formation at 100 kGy irradiation amounted to a few ppm and less than one ppm at 25 kGy irradiation: therefore, the potential risk to human recipients was not significant. The elution of compounds other than MDA from potting material was more problematic. Solvent extracts from potting material showed mutagenicity in the absence of metabolic activity (S9Mix). MDA showed mutagenicity in the presence of metabolic activity, therefore MDA was not the major mutagenic candidate. The chemical and biological characteristics of the specific mutagens should be identified in a further study. The lack of MDA formation and a smaller presence of mutagens in autoclave-sterilized potting material indicated that autoclave sterilization was preferable if the material is able to tolerate heating.

Identification of metabolites of 4,4'-methylenedianiline in vascular smooth muscle cells by liquid chromatography-electrospray tandem mass spectrometry

A capillary liquid chromatography-electrospray tandem mass spectrometry (LC-ES-MS/MS) method was developed for the identification of metabolites of 4,4'-methylenedianiline (diaminodiphenyl methane, (DAPM)) derived from exposure of vascular smooth muscle cells (VSMC) to this compound. The use of precolumn concentration and column switching techniques prior to reversed-phase liquid chromatography coupled online to ES-MS enabled the separation and detection of low-level DAPM and its metabolites in the exposed cell samples. The employed LC-ES-MS method, and further LC-ES-MS/MS analysis enabled the structural assignments for two DAPM metabolites from vascular smooth muscle cells: N-acetyl methylenedianiline (N-acetyl-DAPM) and N,N'-diacetyl methylenedianiline (N,N'-diacetyl-DAPM).

Formation and elution of toxic compounds from sterilized medical products: methylenedianiline formation in polyurethane

The formation of a toxic and carcinogenic compound, methylenedianiline (MDA), in sterilized medical use polyurethane (PU) is discussed. Due to good biocompatibility and biostability, PU is widely used for blood-containing devices. There are two types of PU currently available for medical use. One is chain-extended thermoplastic PU, the other is thermosetting PU used for potting material connecting fibers and modules in artificial dialyzers and plasma separators. Both gamma-ray irradiation and autoclave sterilization are predominantly used for the sterilization of these devices. MDA formation in sterilized PUs by gamma-ray irradiation and by autoclave treatment is compared. The Delany clause in the USA prohibits the manufacture of medical devices producing any toxic compound during fabrication and sterilization, therefore, the formation and elution of MDA and other toxic compounds should be seriously considered. Although MDA formation at a concentration of a few to a few hundred ppb in autoclaved chain-extended thermoplastic PU has been reported, there have been no papers describing MDA formation in autoclaved thermosetting PU potting material, or describing MDA formation in gamma-ray irradiated chain-extended thermoplastic PU and thermosetting PU. We elected to determine whether MDA was in fact produced in Pus sterilized by gamma-ray irradiation or by autoclave sterilization. Our objective was to estimate the risk factor to the human patients or recipient. Our conclusion is to confirm which sterilization of gamma-ray or autoclave is more appropriate. No formation of MDA was observed in autoclaved thermosetting PU potting material at 121 degrees C for 60 min. A few ppm of MDA was formed in irradiated potting material. MDA formation increased with increasing irradiation doses. MDA formed in irradiated potting material at 2.5 Mrad (less than one ppm) is not a significant risk to the recipient. The estimated cancer causing risk factor when absorbing one mg MDA/kg body weight/day is 0.29. Twenty-nine persons per 100 persons exhibit a cancer potential. More importantly, our experimental evidence indicated that serum extracts from irradiated potting material contained unknown compounds other than MDA. The presence of these compounds is considerably more significant and toxic. When tested, these compounds proved to be mutagenic in the absence of metabolic activity, thus promoting a need to identify and study further. Compounds indicating mutagenicity increased with increasing irradiation. Small amounts of mutagenic compounds were determined in extract from autoclaved potting material, smaller than that by gamma-ray irradiation. Therefore, autoclave sterilization is more appropriate, providing materials can withstand the process.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of metabolites of 4,4'-diaminodiphenylmethane (methylene dianiline) using liquid chromatographic and mass spectrometric techniques

The in vitro metabolism of 4,4'-diaminodiphenylmethane (methylene dianiline, MDA) was investigated using rabbit liver microsomes. Minimal clean-up of the microsomal incubations was carried out using zinc sulphate precipitation followed by solid-phase extraction on Sep-Pak C18 cartridges. Three metabolites were detected in hepatic microsomal incubations, namely the azodiphenylmethane (azo) azoxydiphenylmethane (azoxy) and 4-nitroso-4'-aminodiphenylmethane (nitroso) compounds. The azo and azoxy metabolites were produced enzymatically whereas the nitroso compound may have been formed via a non-enzymatic process. Reversed-phase high-performance liquid chromatography-plasma spray mass spectrometry was used to initially detect these metabolites. Fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry were utilized to further structurally characterise these compounds. Comparison of mass spectral data obtained from synthesised standards with data obtained on the putative metabolites substantiated the characterisation of these compounds.

Methylene dianiline: acute toxicity and effects on biliary function

4,4'-Methylene dianiline (4,4'-diaminodiphenylmethane, DAPM), which is used in the polymer industry, causes hepatobiliary damage in exposed humans. Our objectives were to characterize the acute toxicity of DAPM in liver, particularly on secretion of biliary constituents and on biliary epithelial cell gamma-glutamyl transpeptidase (GGT) activity. Biliary cannulas were positioned in Sprague-Dawley male rats under pentobarbital anesthesia. After 1 hr of control bile collection, each rat was given 250 mg DAPM/kg (50 mg/ml) po in 35% ethanol or 35% ethanol only; bile was collected for a further 4 hr. Groups of rats were also examined for liver injury and biliary function at 8 and 24 hr after DAPM. Four hours after DAPM administration, main bile duct cells were severely damaged with minimal damage to peripheral bile ductule cells. Focal periportal hepatocellular necrosis and extensive cytolysis of cortical thymocytes occurred by 24 hr. Serum indicators of liver injury were elevated by 4 hr and continued to rise through 24 hr. By 4 hr, biliary protein concentration was increased 4-fold while concentrations of biliary bile salt, bilirubin, and glutathione were decreased by approximately 80, 50, and 200%, respectively. DAPM also induced a striking effect on biliary glucose with an approximately 20-fold increase. Histochemical staining of main bile duct GGT was absent by 8 hr after DAPM. Bile flow was diminished by 40% at 4 hr; three of five rats had no bile flow by 8 hr and none had any bile flow by 24 hr. These results indicate that DAPM rapidly diminishes bile flow and alters the secretion of biliary constituents and is highly injurious to biliary epithelial cells.

Formation of 4,4'-methylenedianiline in polyurethane potting materials by either gamma-ray or autoclave sterilization

In this experiment, we found that a potential carcinogen, 4,4'-methylenedianiline (MDA), was produced from gamma-ray irradiated potting materials, medical thermosetting polyurethane (PU). gamma-Ray irradiated PUs were immersed in either methanol or in equine serum. The time course of MDA leached from the potting materials and other variables were compared. A significant relationship was noted between the amount extracted and the rigidity of the potting material. The accumulated amount of extracted MDA (a few ppm in the original sample) increased with increasing irradiation dose by a second-order equation. One sample indicated reduced MDA elution after irradiation in the early stage. MDA extraction with serum was 82-87% that with methanol. In one case, MDA leaching into serum in the early stage was higher than that into methanol. Autoclave sterilization did not promote MDA formation, thus indicating that autoclaving would be preferable.

Monitoring exposure to 4,4'-methylenedianiline by the gas chromatography-mass spectrometry determination of adducts to hemoglobin

The determination of the covalently bound reaction products of 4,4'-methylenedianiline (MDA) to hemoglobin was investigated as a possible method for biological dosimetry in humans. The extent of binding to rat hemoglobin of MDA was determined by dosing animals with the 14C-ring-labeled compound. Two adducts were released from the hemoglobin on hydrolysis under mildly basic conditions which were identified as MDA and N-acetyl-MDA and accounted for between 36 and 45% of the total radioactivity bound to the protein. A quantitative assay procedure was subsequently developed for measuring both of the base released adducts in rat hemoglobin. The method utilized solvent extraction followed by derivatization with pentafluoropropionic anhydride and subsequent separation and quantitation by capillary gas chromatography with selective ion monitoring mass spectrometry using deuterium-labeled analogues of MDA and N-acetyl-MDA as internal standards. A dose-response relationship was established in orally dosed rats between production of each of the hemoglobin released adducts and dose of MDA (1-12 mg/kg). The possible use of such adduct determinations as dosimeters for industrial workers exposed to MDA is discussed.

Determination of the N-acetyl metabolites of 4,4'-methylene dianiline and 4,4'-methylene-bis(2-chloroaniline) in urine

A sensitive and specific gas chromatographic/mass spectrometric assay is described for the determination of N-acetyl 4,4'-methylene dianiline (N-acetyl MDA) and N-acetyl 4,4'-methylene-bis(2-chloroaniline) (N-acetyl MbOCA) in urine. The method is based on the solvent extraction of the compounds together with deuterium-labelled internal standards, the compounds being separated and detected by capillary gas chromatography/mass spectrometry as their pentafluoropropyl derivatives. The method has been applied to the detection of N-acetyl MbOCA and N-acetyl MDA in the urine of workers occupationally exposed to MbOCA and MDA. The results show that whilst N-acetyl MbOCA is a relatively minor urinary metabolite a significant proportion of MDA is excreted as the N-acetylated compound.