Differences between rodents and humans in the metabolic toxification of N,N-dimethylformamide

The potential health risks of N,N-dimethylformamide: An updated review

N,N-dimethylformamide (DMF) is a universally used industrial material with exponential growth in production and consumption worldwide. The frequently reported occupational DMF poisoning cases in some countries and the gradually recognized unavoidable health risks to the general population highlight that DMF should still be a matter of concern. Previous studies have demonstrated that the liver is the primary target organ of DMF exposure and multiple mechanisms have been revealed. However, most of these studies investigate the detrimental effects of acute and subacute DMF exposure, while the effects of chronic DMF exposure are rarely studied. Furthermore, the key mechanism for the acute hepatotoxicity of DMF remains to be elucidated. Future research may focus on the identification of efficient preventive measures against the toxicity of DMF to occupational workers, the investigation of the detrimental effects of DMF at environmentally relevant doses, and the studies on the elimination and recycling of DMF in industrial wastes. Herein, we present an updated review of the metabolism of DMF, the biomarker of DMF exposure, underlying molecular mechanisms of DMF-induced hepatotoxicity, and the toxicity of DMF to both occupational workers and general populations and discuss the possible directions in future studies.

Human Biomonitoring Initiative (HBM4EU): Human Biomonitoring Guidance Values Derived for Dimethylformamide

Within the European Joint Program on Human Biomonitoring HBM4EU, human biomonitoring guidance values (HBM-GVs) for the general population (HBM-GV_GenPop) or for occupationally exposed adults (HBM-GV_Worker) are derived for prioritized substances including dimethylformamide (DMF). The methodology to derive these values that was agreed upon within the HBM4EU project was applied. A large database on DMF exposure from studies conducted at workplaces provided dose–response relationships between biomarker concentrations and health effects. The hepatotoxicity of DMF has been identified as having the most sensitive effect, with increased liver enzyme concentrations serving as biomarkers of the effect. Out of the available biomarkers of DMF exposure studied in this paper, the following were selected to derive HBM-GV_Worker: total N-methylformamide (tNMF) (sum of N-hydroxymethyl-N-methylformamide and NMF) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) in urine. The proposed HBM-GV_Worker is 10 mg·L⁻¹ or 10 mg·g⁻¹ creatinine for both biomarkers. Due to their different half-lives, tNMF (representative of the exposure of the day) and AMCC (representative of the preceding days’ exposure) are complementary for the biological monitoring of workers exposed to DMF. The levels of confidence for these HBM-GV_Worker are set to “high” for tNMF and “medium-low” for AMCC. Therefore, further investigations are required for the consolidation of the health-based HBM-GV for AMCC in urine.

Harmonization of acronyms for volatile organic compound metabolites using a standardized naming system

Increased interest in volatile organic compound (VOC) exposure has led to an increased need for consistent, systematic, and informative naming of VOC metabolites. As analytical methods have expanded to include many metabolites in a single assay, the number of acronyms in use for a single metabolite has expanded in an unplanned and inconsistent manner due to a lack of guidance or group consensus. Even though the measurement of VOC metabolites is a well-established means to investigate exposure to VOCs, a formal attempt to harmonize acronyms amongst investigators has not been published. The aim of this work is to establish a system of acronym naming that provides consistency in current acronym usage and a foundation for creating acronyms for future VOC metabolites.

Liver and heart toxicity due to 90-day oral exposure of ICR mice to N,N-dimethylformamide

N,N-dimethylformamide (DMF) is a colorless liquid with a faint amine odor, which is widely used in the world. DMF exposure may induce adverse effects on liver, but few studies showed damage to heart after exposure to DMF. In the present study, DMF was administered to ICR mice with the doses of 0.32, 0.63 and 1.26 g/kg of body weight by gavage for 90 days. The increase in the relative liver weight is accompanied with the presence of the centrilobular hepatocellular hypertrophy as well as increased serum levels of aspartate transaminase (AST) and alanine transaminase (ALT). An increase of malondialdehyde (MDA) level was shown in liver homogenate, while superoxide dismutase (SOD) and glutathione (GSH) activities decreased. Heart damage was also shown in mice exposed to DMF for 90 days, although pathological examination showed only slight inflammatory cell infiltration. Increased levels of serum lactate dehydrogenase (LDH), isoenzymes of creatine kinase (CK-MB) and cardiac troponin I (cTnI) were shown. Increased level of MDA was also shown in heart homogenate, in contrast with the decreased activity of SOD. These data suggested that the administration of DMF could induce liver and heart injuries and oxidative stress was involved in the toxic effects.

Evaluation of Current Biological Exposure Index for Occupational N, N-dimethylformamide Exposure From Synthetic Leather Workers

The aim of this study was (1) to investigate the correlation between external exposure to N, N-dimethylformamide (DMF) and urinary excretion of DMF and N-methylformamide; (2) to assess whether the correspondence between the current occupational exposure limit setting and recommended urinary biological exposure index is substantial; and (3) to evaluate whether coexposure to toluene, methyl ethyl ketone, and ethyl acetate has an effect on urinary excretion of DMF and N-methylformamide (NMF). Urinary DMF and NMF were significantly correlated (P < 0.01) with one another and also significantly correlated with airborne DMF (P < 0.01) over the range of 1.55 to 152.8 mg/m. Urinary DMF can be considered a complementary marker for short-term exposure. Urinary concentration of NMF and DMF, corresponding to the 8-hour exposure to airborne DMF at 30 mg/m, was estimated to 38.4 mg/L or 39.4 mg/g creatinine for NMF and to 0.92 mg/L or 0.96 mg/g creatinine for DMF.

The effects of co-exposure to methyl ethyl ketone on the biological monitoring of occupational exposure to N,N-dimethylformamide

OBJECTIVES

(1) To assess whether urinary N,N-dimethylformamide (U-DMF) is suitable as a biomarker when co-exposure to methyl ethyl ketone (MEK) exists, and to evaluate whether it is suitable as an exposure biomarker of DMF. (2) To examine whether the co-exposure to MEK affects the characteristics of U-NMF and U-DMF. (3) To investigate if the difference in creatinine-adjusted and non-adjusted measurements of urinary biomarkers of DMF exposure is substantial.

METHODS

Personal exposure monitoring of N,N-dimethylformamide (DMF) and MEK on 11 synthetic-leather workers was performed for 5 consecutive days. Daily post-shift urine for each individual was collected and was analyzed for urinary N-methylformamide (U-NMF) and U-DMF levels on both non-adjusted and creatinine-adjusted bases.

RESULTS

Both U-NMF and U-DMF showed significant associations with airborne DMF. Positive and significant associations between U-NMF and U-DMF on either a non-adjusted basis or a creatinine-adjusted basis were found. Satisfactory linear associations ( P<0.01) between all kinds of urinary biomarkers and DMF exposure were found. The co-exposure to MEK exerted more effect on the relationship of airborne DMF to U-DMF than to U-NMF.

CONCLUSIONS

U-DMF is detectable when occupational DMF exposure is near or below the occupational exposure limit of 10 ppm. In view of the performance of sensitivity, specificity, and positive predictive value, U-NMF, in general, is superior to U-DMF. However, on a par with other findings in this and previous studies, U-DMF might be considered as a complimentary biomarker of exposure to DMF in addition to U-NMF. No distinction between creatinine-adjustment or non-adjustment for urine specimens was found in the biological monitoring of DMF exposure. Further exploration of the influence of co-exposure to MEK at higher exposure is warranted.

Inactivation of rat liver cytochrome P450 (P450) by N,N-dimethylformamide and N,N-dimethylacetamide

N,N-dimethylformamide (DMF), an organic solvent widely used in industry, is bioactivated by cytochrome P450 (P450) to reactive metabolites which are believed to be responsible for the hepatotoxicity observed in animals and humans. A decrease of the activating enzyme has been reported in rats treated with DMF, although the specific P450 isoform(s) involved and the nature of the reactive species responsible for this and the other toxic effects are still being investigated. In the present work, the effect of DMF and of the structurally related N,N-dimethylacetamide (DMAc) on the activating enzyme and the nature of the reactive species involved in the mechanism of P450 inactivation by the two chemicals were investigated in vitro. Incubation of liver microsomes from pyridine-induced rats with either substrate resulted in a dose-dependent (0-20 mM) loss of P450 (up to 28 and 24% for DMF and DMAc, respectively), microsomal haem (up to 24 and 20% for DMF and DMAc, respectively), but not protoporphyrin IX content. Moreover, bubbling of CO through the incubation mixture gave almost complete protection against substrate-dependent P450 inactivation, and the spin trapping agent N-tert-butyl-alpha-phenylnitrone, but neither glutathione nor vitamin C, provided a significant protection against DMF- or DMAc-dependent haem loss. Finally, electron spin resonance analysis of microsomal incubations in presence of DMF or DMAc showed spectral evidence for a carbon centered radical intermediate. The results indicate, overall, that both compounds are metabolized in vitro by P450, probably CYP2E1, to free radical metabolites which attack the haem prosthetic group, leading to suicidal enzyme inactivation.

TANAX(T-61): an overview

In this overview the authors describe the use of Tanax (T-61) for euthanasia. Tanax is a solution with three components (embutramide, mebenzonium iodide and tetracaine hydrochloride) used for painless death in pets and laboratory animals. It is also used for malicious intoxication in animals and for suicide attempts in humans. After a description of the modality and outcome of intoxication, the authors report the secondary toxic effects evoked by N, N -dimethyl-formamide, the solvent employed to dissolve the three components of Tanax. Finally, the analytical methods used to identify Tanax components in biological fluids and tissues are described.

Cloning and expression of rat CYP2E1 in Saccharomyces cerevisiae: detection of genotoxicity of N-alkylformamides

A cDNA coding for rat cytochrome P450 2E1 was cloned into the multicopy vector pYeDP60 and expressed in haploid RSY6 and diploid RS112 yeast strains of Saccharomyces cerevisiae under control of the GAL10-CYC1 promoter. Spectral and catalytic properties of the expressed 2E1 were examined in whole cells or microsomes of both strains. The level of CYP2E1 obtained in RS112 (200 pmol/mg microsomal protein) was the highest among CYP2E1 produced in the various expression systems. The monooxygenase activity in the microsomes of both strains, measured as aniline hydroxylase, was found comparable to that of control rat hepatic microsomes. In a reconstituted system in the presence of exogenous rat P450 reductase, their activity increased about 10-fold. When exposed to the carcinogen NDMA, a known 2E1 substrate, the recombination frequency determined in the 2E1-expressing RS112 cells was enhanced, in a dose-dependent manner, up to 20-fold. The exposure of the same cells to the hepatotoxic solvents, N-methyl- and N-ethylformamide, resulted in an induction of recombination frequency, which was not observed in the void plasmid containing RS112 cells in the presence of S9 hepatic fractions from pyrazole-induced rats, as a specific exogenous metabolic activation system. These results demonstrate that the 2E1-expressing cells metabolize the two N-alkylformamides to genotoxic intermediates and, therefore, they provide an useful tool to study the bioactivation mechanism of potential P450 2E1 substrates.

N,N-Dimethylformamide modulates acid extrusion from murine hepatoma cells

N,N-Dimethylformamide (DMF) affects cellular differentiation, causes hepatotoxicity and gastric irritation, and may be carcinogenic. Since these processes involve changes in cellular pH homeostasis, we investigated the effects of DMF on H+ extrusion and cytosolic pH (pHi) of mouse hepatoma cells (Hepa 1C1C7). Extracellular pH was monitored using a silicon-based sensor system (Cytosensor microphysiometer) and pHi was monitored by fluorescence spectrophotometry. Superfusion of cells with DMF (0.25 to 0.5 M) suppressed the extracellular acidification rate (ECAR) below baseline. Following washout of DMF there was a rapid, concentration-dependent, prolonged overshoot of ECAR above baseline rates. Removal of extracellular Na+ or superfusion with amiloride abolished the overshoot in acidification rate, indicating involvement of Na+/H+ exchange. The overshoot was dependent on extracellular glucose, suggesting that it arises from an increase in metabolic acid production. Fluorescence measurements showed that DMF did not change pHi. Furthermore, DMF did not alter the rate of pHi recovery of cells acid loaded using nigericin, indicating that DMF does not directly alter Na+/H+ exchange activity in these cells. In summary, these data suggest that suppression of acidification rate by DMF is likely due to decreased metabolic acid production. Washout of DMF is then accompanied by increased glucose metabolism and H+ efflux via Na+/H+ exchange. It is possible that alterations in H+ production and transport contribute to the hepatotoxicity of DMF and its effects on cellular differentiation.

Hepatotoxicity of N, N-dimethylformamide (DMF) in acute poisoning with the veterinary euthanasia drug T-61

1. We report on a patient who was resuscitated after a suicide attempt with the veterinary euthanasia product T-61 and treated with N-acetylcysteine (NAC) to prevent hepatotoxicity from N,N-dimethylformamide (DMF), the solvent of T-61. 2. Serum concentrations of DMF were high as compared with values published on occupational exposure. 3. The patient showed only a transient increase in liver enzymes with eventually a full recovery. 4. The hepatoprotective effect of NAC was studied in a rat model using the rise in serum sorbitol dehydrogenase (SDH) as a marker for DMF-induced hepatotoxicity. 5. Four series of randomized, controlled and double-blind experiments were carried out and consistently showed a lower increase in SDH in NAC-treated animals in each series. The difference was statistically significant only when the data of the 4 series were pooled. This is probably due to the large interindividual variations in the effect of DMF. 6. We hypothesize that in the rat NAC may have a protective effect. Whether NAC is also protective in patients, in which it is administered after exposure to DMF, cannot be concluded from the present experiments.

Effects of dimethylformamide on in vivo fatigue and metabolism in rat skeletal muscle measured by 31P-NMR

Dimethylformamide (DMF) is widely used as an industrial solvent in spite of well-established hepatotoxicity and adverse effects on in vitro muscle contractility. The doses used in the studies describing these effects were higher than the doses required to solubilize drugs to be injected at very low levels and the potential effects of DMF at very low levels has not yet been explored. The goal of this work was to study the effects of an acute, low dose of DMF (3 mu/100 g body weight, administered i.p.) on mechanical parameters and energy metabolism of contracting rat skeletal muscle. Metabolic changes were followed by 31P nuclear magnetic resonance spectroscopy. Tension was significantly lower during the fatigue test in DMF-treated rats than in controls. Phosphomonoesters and inorganic phosphorus level were lower, and intracellular pH was higher in DMF-treated rats than in controls, showing that energy metabolism was activated to a lesser degree, in relation with the lower mechanical performance, after DMF. Skeletal muscle is a target organ for dimethylformamide which has a major effect on muscle contractility by decreasing the tension developed. The effects of DMF suggest that it is unsuitable for use as a drug vehicle for in vivo injections, even at a very low nonhepatotoxic doses.

Biological monitoring of workers exposed to N, N-dimethylfomamide. I. Methods of analysis

Some methods for analysing N,N-dimethylformamide and its metabolites [hydroxymethyl-N-methylformamide, hydroxymethylformamide and N-acetyl-S-(N-methylcarbamoyl)cysteine] in the urine of exposed workers are described. Unchanged dimethylformamide was measured after pretreatment of urine (2 ml) with silica gel cartridges and elution with methanol. The gas chromatographic analysis using a nitrogen phosphor detector made it possible to detect N,N-dimethylformamide in urine even when workers were exposed to low concentrations of the solvent (about 1 mg/m3). N-Hydroxymethyl-N-methylformamide and N-hydroxymethylformamide were analysed as N-methylformamide and formamide respectively after direct injection of urine into the gas chromatograph. The injection port temperature played an important role in the gas chromatographic determination of these products. Reliable results were obtained when direct or split injections were performed at 250 degrees C. The splitless injection gave the same reliable results at 150 degrees C. In urine samples from occupationally non-exposed persons, N-methylformamide could not be detected. In contrast, formamide (or its precursor, hydroxymethylformamide) was present in every urine sample. Our results in respect of 19 urine samples analysed with the injection port of the gas chromatograph at 250 degrees C gave a mean of 8.6 mg/l of formamide. N-Acetyl-S-(N-methylcarbamoyl)cysteine was determined using a modified method for analysing organic acid in urine samples. The metabolite was extracted with ethyl ether in an acid environment, treated with a silylating reagent and measured by gas chromatography/mass spectrometry.

Biological monitoring of workers exposed to N-N-dimethylformamide. II. Dimethylformamide and its metabolites in urine of exposed workers

N,N-Dimethylformamide (DMF) exposure was monitored in a synthetic leather factory; at the same time, urinary dimethylformamide and its metabolites were measured in urine samples collected before and at the end of workshifts. The study was run during two different periods. During the first phase ten workers were observed for 3 days (Monday, Tuesday and Wednesday) in the same week. In the second phase 16 workers were involved in the study on a Friday and on the following Monday. Urinary DMF, as well as hydroxymethyl-N-methylformamide and hydroxymethylformamide [measured as N-methylformamide (NMF) and formamide, respectively], were measured as a "physiological" product in subjects not exposed to dimethylformamide. Environmental exposure to DMF ranged between 10 and 25 mg/m3. The unmodified solvent found in urine collected at the end of the exposure was significantly related to the environmental concentrations of DMF; its urinary concentrations were found to range between 0.1 and 1 mg/l. Higher concentrations of NMF (mean 23.3 mg/l) and formamide (24.7 mg/l) were measured in urine samples collected at the end of workshifts. The same concentrations were related to individual exposures to DMF. N-Acetyl-S-(N-methylcarbamoyl)cysteine in the urine of workers exposed to DMF showed a mean concentration of 40.4 mg/l on Friday (before and after the workshift) and a mean concentration of 10.3 mg/l on Monday. Its slow kinetic profile favours its body accumulation during the working week.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatotoxicity and P-4502E1-dependent metabolic oxidation of N,N-dimethylformamide in rats and mice

A comparative biochemical and histological study on the hepatotoxicity of a single dose of N,N-dimethylformamide (DMF) and N-methylformamide (NMF) in control and acetone-treated SD male rats and CD-1 male mice was performed. In control and acetone-pretreated rats, neither DMF nor NMF caused hepatic damage or elevation of plasma transaminases. In contrast, in acetonized but not in control mice, DMF administration yielded some evidence of liver necrosis and elevation of ALAT (alanine-amino transferase) activity. After a DMF dose of 1000 mg/kg, ALAT activity was found 1215 +/- 832 mU/ml and 47 +/- 18 mU/ml in acetonized and control mice, respectively. NMF treatment was hepatotoxic in control mice and lethal in acetonized mice. In control mice, an NMF dose of 600 mg/kg increased ALAT activity from a basal value of 35 +/- 5 to 2210 +/- 1898 mU/ml. When the oxidative metabolism of DMF was investigated, microsomes from both rats and mice preinduced by acetone increased the demethylation rate of DMF 7 to 10-fold compared to that (about 0.25 nmol/min per mg protein) of the corresponding control microsomes. The enzymatic affinities for DMF oxidation, however, were different: in mice the Km (0.05 mM) was one order of magnitude lower than that (0.56 mM) found in rats. The experiments performed with purified rat and mouse P-450 2E1 in a reconstituted system confirmed that the P-450 2E1 isoforms are very active catalysts towards DMF oxidation (the turnover was about 10 nmol/min per nmol P-450 for both enzymes) but with a strikingly different affinity. Whereas the Km for mouse P-450 2E1 was 0.08 +/- 0.03 mM, that for rat P-450 2E1 was 1.1 +/- 0.2 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological monitoring of workers exposed to N,N-dimethylformamide by determination of the urinary metabolites, N-methylformamide and N-acetyl-S-(N-methylcarbamoyl) cysteine

Biological monitoring of workers exposed to N,N-dimethylformamide (DMF) was carried out by determination of the urinary metabolites, N-methylformamide (MF, mainly from N-hydroxymethylformamide) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), which were derived from two different routes of metabolism of the solvent. The urinary levels of MF increased rapidly at the start of the work shift, and decreased almost to zero within 24 h after the beginning of the last exposure. The highest level was found between the end of the afternoon shift and bedtime. AMCC levels remained constant over the consecutive work days and increased after the cessation of exposure, with the peak concentration being observed at 16-40 h after the cessation of exposure. AMCC levels at the beginning of the next morning shift were closely correlated with personal exposure levels of DMF in air, although the correlation of MF and DMF in air was highest in the urine at the end of the shift. Hence urinary AMCC represents an index of the average exposure during several preceding work days and may indicate the internal dose. By contrast, MF represents an index of daily exposure.

Metabolism and hepatotoxicity of N,N-dimethylformamide, N-hydroxymethyl-N-methylformamide, and N-methylformamide in the rat

The metabolism and hepatotoxicity of N,N-dimethylformamide (DMF) and two of its metabolites, N-hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) were evaluated over a 4-day period in rats. DMF toxicity was dose dependent and delayed toxicity after the administration of a high DMF dose (13.7 mmol/kg) in comparison to a lower dose (4.1 mmol/kg) was observed. Treatment of rats with 13.7 mmol/kg DMF, HMMF, or NMF showed i) that DMF is more toxic than HMMF or NMF, and ii) that hepatotoxicity occurs later for DMF than for HMMF or NMF. Analysis of serum and urine samples demonstrated that DMF is first metabolized to HMMF, which is then partially converted to NMF. After HMMF administration, NMF was found both in serum and in urine. The time course of DMF and HMMF toxicity in relation to NMF formation fitted the hypothesis that the hepatotoxicity of DMF and HMMF is mediated via NMF. The degree of hepatotoxicity after HMMF and NMF treatment is similar. However, the degree of DMF hepatotoxicity is much higher than in the case of NMF or HMMF. The role of NMF as an obligatory intermediate in DMF and HMMF hepatotoxicity is discussed.

Dimethylformamide pharmacokinetics following inhalation exposures to rats and mice

Whole-body inhalation exposures to N,N-dimethylformamide (DMF) were conducted with rats and mice. The exposure concentrations were 10, 250, and 500 ppm DMF. The exposure routines consisted of single 1-, 3-, or 6-hour exposures and ten 6-hour exposures (ten exposure days in 2 weeks). Area under the plasma concentration curve (AUC) values were determined following exposure for DMF and "N-methylformamide" ["NMF" represented N-methylformamide plus N-(hydroxymethyl)-N-methylformamide (DMF-OH)]. The DMF AUC values increased 8- and 29-fold for rats and mice, respectively, following single six-hour exposures to 250 and 500 ppm DMF. These data are indicative of saturation of DMF metabolism. Peak "NMF" plasma concentrations for rats and mice, following single 6-hour exposures, did not increase as DMF exposure concentrations increased from 250 to 500 ppm. In addition, the "NMF" plasma levels in rats following a single 6-hour 500 ppm DMF exposure did not decay by 24 hours post exposure. These "NMF" plasma data also indicate saturation of DMF metabolism. Multiple exposures to 500 ppm DMF resulted in a 3- and 4-fold reduction in DMF AUC values for rats and mice, respectively, compared to AUC values following a single six-hour 500 ppm DMF exposure. This indicates enhanced metabolism of DMF resulting from multiple 500 ppm DMF exposures and together with saturation of DMF metabolism suggest using exposure levels below 500 ppm in a chronic bioassay. Selected plasma samples were simultaneously assayed for NMF and DMF-OH. The "NMF" values consisted of between 30 to 60 percent DMF-OH depending upon the exposure group (conversely NMF represented 30 to 60 percent of the "NMF" levels). Urinary analysis of all samples revealed DMF-OH represented over 90 percent of the summed DMF, DMF-OH and NMF quantities.

The microsomal demethylation of N,N-dimethylbenzamides. Substituent and kinetic deuterium isotope effects

The metabolism of N,N-dimethylbenzamides by phenobarbital-induced rat liver microsomes results in the formation of N-methylbenzamides and formaldehyde. The reaction proceeds via the formation of an intermediate N-hydroxymethyl-N-methylbenzamide, which, for the microsomal oxidation of N,N-dimethylbenzamide, was isolated and characterized. Confirmation of the N-hydroxymethyl-N-methylbenzamide was obtained by its independent synthesis from N-methylbenzamide and formaldehyde. The intermolecular kinetic deuterium isotope effects for the reaction are 0.9 (+/- 0.1) for Vmax and 1.4 (+/- 0.1) for Vmax/Km. The intramolecular kinetic deuterium isotope effect, determined from the relative amounts of N-methylbenzamide and N-trideuteriomethylbenzamide formed in the microsomal demethylation of N-trideuteriomethyl-N-methylbenzamide, is 6.0 +/- 0.3. There is no correlation of Vmax or Vmax/Km with the substituent in the aromatic ring, nor with the calculated ionization potentials of the benzamides. The results are interpreted in terms of a mechanism in which the benzamide undergoes direct hydrogen atom abstraction to form a carbon centred radical. This carbon centred radical subsequently forms an N-hydroxymethyl-N-methylbenzamide that decomposes to formaldehyde and an N-methylbenzamide. Semi-empirical AM1 self consistent field molecular orbital calculations identify that loss of a hydrogen atom from the E-methyl group is thermodynamically more favourable than from the Z-methyl group by ca. 5 kJ/mol.

Absorption, metabolism and elimination of N,N-dimethylformamide in humans

Excretion of N,N-dimethylformamide (DMF) and DMF metabolites N-hydroxymethyl-N-methylformamide ("MF"), N-hydroxymethyl-formamide ("F") and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) has been monitored in the urine of volunteers during and after their 8-h exposure to DMF vapour at a concentration of 10, 30 and 60 mg.m-3. The pulmonary ventilation in these experiments was typically about 10 l.min-1 and the retention in the respiratory tract was 90%. After exposure to 30mg DMF.m-3, the yield of compound determined in the urine represented 0.3% (DMF), 22.3% ("MF"), 13.2% ("F") and 13.4% (AMCC) of the dose absorbed via the respiratory tract. The excretion curves of the particular compounds attained their maximum 6-8h (DMF), 6-8h ("MF"), 8-14h ("F") and 24-34h (AMCC) after the start of the exposure. The half-times of excretion were approximately 2, 4, 7 and 23 h respectively. In contrast to slow elimination of AMCC after exposure to DMF, AMCC was eliminated rapidly after AMCC intake. This discrepancy could be explained by rate-limiting reversible protein binding of a reactive metabolic intermediate of DMF, possibly methylisocyanate.

Effects of dimethylformamide on hepatic microsomal monooxygenase system and glutathione metabolism in rats

The effects of repeated exposure to N,N-dimethylformamide (DMF) on hepatic microsomal monooxygenase system and glutathione metabolism were investigated. DMF was administered to Wistar male rats by subcutaneous (s.c.) injection at 0.5 ml/kg body weight daily for 1 week. Macroscopically, mild liver swelling was observed and liver weights significantly increased after 1 week of exposure to DMF. Hematological changes were not detected. In exposed rats, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, cholinesterase and total cholesterol significantly increased. Hepatic microsomal cytochrome P-450 and protoheme decreased by 34% and 24%, respectively, while microsomal protein and cytochrome b5 were not affected. NADH-ferricyanide reductase activity decreased by 24% while NADPH-cytochrome c reductase activity showed no change. Glutathione reductase (GR) activity showed a significant decrease after the first injection and remained depressed throughout the study, with no change in glutathione peroxidase (GPx) activity. Glutathione S-transferase (GST) activity showed a significant increase at 3 days after DMF treatment and gradually increased by 66% at 1 week. In a subsequent experiment with a single administration of DMF (4 ml/kg), reduced glutathione (GSH) in the liver was decreased by 28% at 8 h, but recovered to control levels by 24 h. These results indicate that DMF alters the hepatic microsomal monooxygenase system and glutathione metabolism. These findings may greatly contribute to the elucidation of the pathogenesis of DMF hepatotoxicity.

Occupational dimethylformamide exposure. 3. Health effects of dimethylformamide after occupational exposure at low concentrations

A factory survey was conducted in a plant where N,N-dimethylformamide (DMF) was in use during the production of polyurethane plastics and related materials. In all, 318 DMF-exposed workers (195 men and 123 women) and 143 non-exposed controls (67 men and 76 women) were examined for time-weighted average exposure (to DMF and other solvents by diffusive sampling), hematology, serum biochemistry, subjective symptoms, and clinical signs. Most of the exposed workers were exposed only to DMF, whereas others were exposed to a combination of DMF and toluene. DMF exposure in the former group was up to 7.0 ppm (geometric mean on a workshop basis), whereas it was up to 2.1 ppm in combination with 4.2 ppm toluene. Both hematology and serum biochemistry, results (including aspartate and alanine aminotransferases, gamma-glutamyl transpeptidase and amylase) were essentially comparable among the 3 groups. There was, however, a dose-dependent increase in subjective symptoms, especially during work, and in digestive system-related symptoms such as nausea and abdominal pain in the past 3-month period. The prevalence rate of alcohol intolerance complaints among male (assumedly) social drinkers was also elevated in relation to DMF dose.