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Dimethylformamide (DMF) is an industrial solvent with hepatotoxic properties. The toxicity of DMF has been associated with its metabolism to S-(N-methylcarbamoyl)glutathione (SMG). The major urinary metabolite of DMF is N-(hydroxymethyl)-N-methylformamide (HMMF). HMMF undergoes oxidation in the formyl moiety, possibly via the intermediacy of its hydrolysis product N-methylformamide (NMF), and the reactive intermediate thus generated reacts with glutathione to yield SMG. Experiments were conducted to elucidate enzymatic details of the metabolism of DMF. Generation of HMMF from DMF in microsomes from rats which had received acetone, an inducer of cytochrome P450 2E1, was increased by 175% over that observed in control microsomes. In liver microsomes from 4 humans the metabolism of DMF to HMMF was inhibited by a monospecific antibody against rat liver P450 2E1, and the metabolic rates were correlated with those of NMF to SMG, a process known to be mediated via P450 2E1. DMF was also metabolized by purified rat liver P450 2E1. The kinetic parameters which characterize the metabolism of DMF or its deuterated isotopomers to the respective HMMF isotopomers, of HMMF to SMG and of NMF to SMG in liver microsomes, were computed from Eadie-Hofstee plots. The affinity of DMF for the metabolizing enzyme in rat liver microsomes is considerably higher (apparent Km = 0.20 mM) than that of NMF (Km = 4.28 mM) or of HMMF (Km = 2.52 mM). The respective values observed with human microsomes are very similar. The apparent Km values for the N-methyl oxidation of N,N-dimethyldeuterioformamide ([2H1]DMF) and N,N-bis(trideuteriomethyl)formamide ([2H6]DMF) in rat microsomes are 0.14 and 0.21 mM, respectively. The apparent Vmax for the oxidation of [2H1]DMF is similar to that computed for DMF, and the Vmax for [2H6]DMF is less than half of that computed for DMF. The kinetic deuterium isotope effect (KDIE) on DMF metabolism was determined in incubations with rat microsomes in three ways: (i) the noncompetitive intermolecular KDIE by the ratio of Vmax/Km for DMF to Vmax/Km for [2H6]DMF, (ii) the competitive intermolecular KDIE as the quotient of metabolic products HMMF to N-(hydroxydideuteriomethyl)-N-(trideuteriomethyl)formamide in incubations of DMF together with [2H6]DMF, and (iii) the intramolecular KDIE as the quotient of the ratio of N-(hydroxymethyl)-N-(trideuteriomethyl)formamide to N-(hydroxydideuteriomethyl)-N-methylformamide generated from N-(trideuteriomethyl)-N-methylformamide ([2H3]DMF). The respective values were found to be (i) 2.4, (ii) 5.0, and (iii) 5.2. DMF inhibited the oxidation of NMF or HMMF to SMG.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

We studied the plasma amino acid profiles in four models of hepatic injury in rats. In partially hepatectomized rats (65% of liver was removed) we observed significant increase of aromatic amino acids (AAA; i.e. tyrosine and phenylalanine), taurine, aspartate, threonine, serine, asparagine, methionine, ornithine and histidine. Branched-chain amino acids (BCAA; i.e. valine, leucine and isoleucine) concentrations were unchanged. In ischemic and carbon tetrachloride acute liver damage we observed extreme elevation of most of amino acids (BCAA included) and very low concentration of arginine. In carbon tetrachloride induced liver cirrhosis we observed increased levels of AAA, aspartate, asparagine, methionine, ornithine and histidine and decrease of BCAA, threonine and cystine. BCAA/AAA ratio decreased significantly in partially hepatectomized and cirrhotic rats and was unchanged in ischemic and acute carbon tetrachloride liver damage. We conclude that a high increase of most of amino acids is characteristic of fulminant hepatic necrosis; decreased BCAA/AAA ratio is characteristic of liver cirrhosis; and decrease of BCAA/AAA ratio may not be used as an indicator of the severity of hepatic parenchymal damage.

Skin penetration fo N,N-dimethylformamide (DMF) liquid or vapour was studied in volunteers. Exposure to liquid DMF was performed in two ways: in a "dipping experiment", one hand was dipped up to the wrist in DMF for 2-20 min, while in a "patch experiment", 2 mmol DMF was applied to the skin and allowed to be absorbed completely. The period of exposure to DMF vapour (50 mg.m-3) was 4 h. The DMF metabolites N-hydroxymethyl-N-methylformamide ("MF"), N-hydroxymethylformamide ("F"), and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) were monitored in the urine. Liquid DMF was absorbed through the skin at a rate of 9.4 mg.cm-2.h-1. Percutaneous absorption of DMF vapour depended strongly on ambient temperature and humidity and accounted for 13%-36% of totally excreted "MF". The results suggest that skin absorption of liquid DMF is likely to contribute to occupational exposure substantially more than penetration of DMF vapour. The yield of metabolites after transdermal DMF absorption was only half of that seen after pulmonary absorption. Elimination of "MF" and "F" but not that of AMCC was delayed, which supports the contention that AMCC should be used instead of "MF" as the most suitable biomarker of DMF in cases where percutaneous intake can occur.

The metabolism and toxicokinetics of cyclohexane (CH) and cyclohexanol (CH-ol), important solvents and chemical intermediates, were studied in volunteers after 8-h periods of inhalation exposure at concentrations of 1010 and 236 mg m(-3), respectively (occupational exposure limits: CH, 1050 mg m(-3); CH-ol, 200 mg m(-3)). Of the dose of absorbed parent compounds, the yields of urinary CH-ol and 1,2- and 1,4-cyclohexanediol (CH-diol) were 0.5%, 23.4%, and 11.3%, respectively, after exposure to CH and 1.1%, 19.1%, and 8.4%, respectively, after exposure to CH-ol as determined by a gas chromatography method involving hydrolysis of glucuronide conjugates. The metabolic patterns of CH and CH-ol were very similar to that of cyclohexanone (CH-one) studied in the laboratory previously. For all three compounds, peak excretion of CH-ol occurred at the end of the exposure period, after which it decayed rapidly. Excretion curves of 1,2- and 1,4-CH-diol reached maximal values within 0-6 h postexposure, with subsequent elimination half-lives being 14-18 h. The rate-limiting step in the elimination of CH compounds from the organism is renal clearance of CH-diols. Determination of CH-diols in end-of-shift urine samples is recommended as a useful new method of biomonitoring of CH, CH-ol, and CH-one at the workplace. However, due to accumulation of CH-diols in the body during repeated exposure, quantitative relationships between the exposure and the level of CH-diols have to be adjusted according to the day of sampling during the working week.

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