Registration Dossier

Administrative data

Link to relevant study record(s)

Referenceopen allclose all

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable, well-documented publication (review) which meets basic scientific principles
Objective of study:
absorption
distribution
excretion
metabolism
Qualifier:
no guideline followed
Principles of method if other than guideline:
- Principle of test: Comprehensive review of available results regarding ADME of the test substance DMF
- Short description of test conditions: Rats were administered DMF via oral, dermal and inhalation routes of exposure
GLP compliance:
not specified
Radiolabelling:
not specified
Species:
rat
Sex:
male/female
Details on test animals or test system and environmental conditions:
no details given
Route of administration:
other: oral, dermal, inhalation
Vehicle:
not specified
Details on exposure:
No information given
Type:
absorption
Results:
N,N-dimethylformamide is readily absorbed after oral intake, dermal exposure or inhalation.
Type:
distribution
Results:
N,N-dimethylformamide is rapidly and uniformly distributed in the organism.
Type:
metabolism
Results:
Metabolization takes place mainly in the liver by microsomal enzymes.
Details on excretion:
The cysteine adduct N-acetyl-S-(N-methylcarbamoyl)cysteine is also found in urine at levels of 1 % to 5 % of the dose in urine of laboratory animals (mice, rat, hamsters) treated parenterally and at 10 % to 23 % of the dose in persons who had inhaled the substance. Formation and excretion of the cysteine adduct (N-acetyl-S-(N-methylcarbamoyl)cysteine) in the urine of persons inhaling N,N-dimethylformamide takes place with a half-time of 23 hours.
Metabolites identified:
yes
Details on metabolites:
N-hydroxymethyl-N-methylformamide is the main metabolite of N,N-dimethylformamide in animals and human beings and it is excreted with the urine. Mono-N-methylformamide which was once considered to be the main metabolite of N,N-dimethylformamide is found only in low levels in the urine. It could be shown that mono-N-methylformamide was mainly an artefact formed on the gas chromatographic column.

Moreover it was shown, that intermediary metabolism produces to a lower extent via a second pathway glutathione adducts and its degradation products. As carbamoylating species, which reacts with glutathione methyl isocyanate was postulated but not proven. Moreover, investigations in animals had shown that at least after administration in single high doses, N,N-dimethylformamide can inhibit its own metabolism (saturated metabolism). Metabolic interaction occurs between N,N-dimethylformamide and ethanol. Ethanol and probably the ethanol metabolite, acetaldehyde inhibit the breakdown of N,N-dimethylformamide. Conversely, N,N-dimethylformamide inhibits the metabolism of ethanol and acetaldehyde. Thus, increased N,N-dimethylformamide levels in the blood were found after the administration of alcohol and increased alcohol or acetaldehyde levels for up to 24 hours were reported after exposure to N,N-dimethylformamide.

Conclusions:
Interpretation of results: no bioaccumulation potential based on study results
N,N-dimethylformamide is readily absorbed after oral intake, dermal exposure or inhalation. N,N-dimethylformamide is rapidly and uniformly distributed in the organism. Metabolization takes place mainly in the liver by microsomal enzymes. N-hydroxymethyl-N-methylformamide is the main metabolite of N,N-dimethylformamide in animals and human beings and it is excreted with the urine. Mono-N-methylformamide which was once considered to be the main metabolite of N,N-dimethylformamide is found only in low levels in the urine. It could be shown that mono-N-methylformamide was mainly an artefact formed on the gas chromatographic column. Another metabolite cysteine adduct (N-acetyl-S-(N-methylcarbamoyl)cysteine) is measured in the urine of persons inhaling N,N-dimethylformamide.
Executive summary:

Study design

This publication (review) provides an acceptable well-documented in vivo study (not according to OECD Test guideline) which meets basic scientific principles.

In this metabolism study, rats were administered N,N-dimethylformamide (DMF) via oral, dermal and inhalation routes of exposure.

Results

Metabolization took place mainly in the liver by microsomal enzymes. N-hydroxymethyl-N-methylformamide (DMF-OH or HMMF) was the main metabolite of DMF in animals and human beings and it is excreted with the urine. Mono-N-methylformamide (MMF) which was once considered to be the main metabolite of DMF was found only in low levels in the urine. It could be shown that MMF was mainly an artefact formed on the gas chromatographic column. Moreover it was shown, that intermediary metabolism produces to a lower extent via a second pathway glutathione adducts and its degradation products. As carbamoylating species, which reacts with glutathione methyl isocyanate was postulated but not proven. Moreover, investigations in animals had shown that at least after administration in single high doses, DMF can inhibit its own metabolism (saturated metabolism). Metabolic interaction occurs between DMF and ethanol. Ethanol and probably the ethanol metabolite, acetaldehyde inhibit the breakdown of N,N-dimethylformamide. Conversely, N,N-dimethylformamide inhibits the metabolism of ethanol and acetaldehyde. Thus, increased DMF levels in the blood were found after the administration of alcohol and increased alcohol or acetaldehyde levels for up to 24 hours were reported after exposure to N,N-dimethylformamide.

Conclusion

DMF was readily absorbed via all exposure routes and uniformly distributed throughout the organism.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Only evaluated blood, urine, and limited tissues
Reason / purpose for cross-reference:
reference to other study
Reason / purpose for cross-reference:
reference to other study
Reason / purpose for cross-reference:
reference to other study
Objective of study:
distribution
excretion
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
yes
Radiolabelling:
no
Species:
rat
Strain:
other: Crl:CD BR
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc. (Kingston, NY)
- Age at study initiation: approximately 6 weeks of age
- Housing: stainless steel, wire-mesh cages suspended above Upjohn Deotized Animal Cage Boards or R2 Reemay-backed cage boards
- Individual metabolism cages: yes/no
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 +/- 2
- Humidity (%): 50 +/- 10
- Photoperiod (hrs dark / hrs light): 12 hour light/dark cycle
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
Test atmosphere of DMF was generated by vaporization of the DMF in an inert atmosphere. All animals received whole-body exposure.
Duration and frequency of treatment / exposure:
A total of ten 6 hr exposures were conducted 5 days a week for 2 weeks.
Dose / conc.:
0 ppm
Remarks:
control
Dose / conc.:
10 ppm
Dose / conc.:
250 ppm
Dose / conc.:
500 ppm
No. of animals per sex per dose / concentration:
There were 6 animals in the control group, and 32 animals in each exposure group.
Control animals:
yes
Details on study design:
no details given
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC / METABOLITE STUDY (Distribution, excretion)
- Tissues and body fluids sampled: urine, blood, plasma, tissue: liver, testes, kidney, nasal tissues, tracheas, lung, and prostate
- Time and frequency of sampling: Blood samples were collected at 0.5 hrs post exposure in the control group, and 0.5, 1, 2, 4, 6, 8, 12, and 24 hrs after exposure in DMF exposure groups. Urine samples were collected 12 and 24 hrs after exposure. Four animals from each group were anesthetized after 5 days of exposure and implanted subcutaneously with an osmotic mini pump, which provides a 7-day constant release of [3H]thymidine and then exposed for an additional 5 days. On the sixth day (24 hours post exposure), all animals designated for cell proliferation studies were sacrificed. Tissues were collected 24 hrs after exposure to assess cell proliferation and morphological changes.
- From how many animals: (samples pooled or not): There were generally four replicates for each analysis at each time point.
- Method type(s) for identification: Plasma and urine samples were analyzed for the presence of dimethylformamide (DMF), N-methylformamide (NMF), and N-(hydroxymethyl)-Nmethylformamide (DMF-OH) using GC.

For the cell proliferation tests tissues were collected and processed to slides. [3H]thymidine incorporated into the DNA of replicating cells was visualized. Approximately 2000 cells were counted per slide. Labeling index was calculated as the percentage of replicating cells.
Statistics:
Plasma half lives were estimated by linear regression of log transformed plasma concentration vs. sampling time. Area under the plasma concentration-time curves (AUC) were determined by the trapezoidal method.
Details on distribution in tissues:
DMF levels in plasma decreased to non-detect levels earlier in the post-exposure period compared to the six hour single exposure study. In rats, the AUC value for DMF following multiple exposures to 500 ppm was 3-fold lower than the AUC values after a single 500 ppm exposure. The peak plasma DMF concentration was substantially higher after multiple exposure compared to single exposure at the 500 ppm exposure level. The peak plasma "NMF" (the sum of DMF-OH and N-methylformamide (NMF) decreased rapidly between 8 and 24 hrs after 500 ppm exposure following multiple exposure. Multiple exposure at the 500 ppm level in the rat had enhanced DMF metabolism compared to single exposure. The DMF AUC following multiple 500 ppm exposure was 19-fold higher than that of multiple 250 ppm exposure. The estimated DMF plasma half lives in rats were 2.4 and 1.6 hrs following 250 and 500 ppm exposures, respectively.
Details on excretion:
DMF was poorly eliminated in the urine. For the 500 ppm exposure, DMF levels in the urine were low due to its persistence in the plasma.
Test no.:
#1
Toxicokinetic parameters:
AUC: DMF, rat, 250 ppm multiple exposure = 670 µg. hr/mL
Test no.:
#2
Toxicokinetic parameters:
AUC: DMF, rat, 500 ppm multiple exposure = 2100 µg. hr/mL
Test no.:
#3
Toxicokinetic parameters:
AUC: "NMF", rat, 250 ppm multiple exposure = 674 mg. hr/mL
Test no.:
#4
Toxicokinetic parameters:
AUC: "NMF", rat, 500 ppm multiple exposure = 1581 µg. hr/mL
Test no.:
#5
Toxicokinetic parameters:
half-life 1st: "NMF", rat, 250 ppm multiple exposure = 1.3 hr
Test no.:
#6
Toxicokinetic parameters:
half-life 1st: "NMF", rat, 500 ppm multiple exposure = 2.4 hr
Test no.:
#7
Toxicokinetic parameters:
half-life 1st: DMF, rat, 250 ppm multiple exposure = 2.4 hr
Test no.:
#8
Toxicokinetic parameters:
half-life 1st: DMF, rat, 250 ppm multiple exposure = 1.6 hr
Metabolites identified:
yes
Details on metabolites:
- Poor elimination via urine.
- For exposures of 500 ppm, low urine DMF levels, due to persistence in the plasma.
- Following multiple 250 ppm exposure: more DMF-OH in plasma than NMF.
- Following multiple 500 ppm exposure to DMF, DMF-OH:NMF ratio equal to 1. DMF-OH is the most abundant compound detected in the urine.
- Following 10 ppm exposure, DMF-OH levels disproportionally lower than those following 250 ppm, possibly due to more rapid metabolism and elimination in the 10 ppm exposure.
- DMF-OH urine levels after multiple exposure to 250 and 500 ppm DMF were lower compared to single exposure.
- DMF-OH is found in plasma to a greater extend than NMF.
- The estimated "NMF" plasma half lives in rats were 1.3 and 2.4 hrs following 250 and 500 ppm exposures, respectively, and the values were 1.4 and 1.8 hrs following 250 and 500 ppm exposures, respectively.
- The lung might be a potential target organ of DMF exposure.

DMF-OH and NMF

There was more DMF-OH in plasma than NMF following multiple 250 ppm exposure. However, the DMF-OH:NMF ratio was equal to 1, following multiple 500 ppm exposure to DMF.

The most abundant compound detected in the urine was DMF-OH. Metabolism of NMF to excretion products not analysed in this study might account for the low levels of NMF in the urine. DMF-OH levels following 10 ppm exposure were disproportionally lower than those following 250 ppm exposure in most cases, possibly due to the more rapid metabolism and elimination of DMF-OH in the 10 ppm exposure. The DMF-OH urine levels after multiple exposure to 250 and 500 ppm DMF were lower compared to single exposure.

The estimated "NMF" plasma half lives in rats were 1.3 and 2.4 hrs following 250 and 500 ppm exposures, respectively, and the values were 1.4 and 1.8 hrs following 250 and 500 ppm exposures, respectively.

In rats, statistically significant increases in the labelling index of lung were observed in the 10 ppm and 500 ppm groups. However, there was no dose-response between 10 ppm and 500 ppm groups. No effects were observed in rat liver, prostate, and nasal tissues. Results suggested that the lung might be a potential target organ of DMF exposure.

Conclusions:
Interpretation of results: no bioaccumulation potential based on study results
- The AUCs for DMF exposed to 250 and 500 ppm were 670 and 2100 ug.hr/mL, respectively.
- The DMF plasma half lives for 250 and 500 ppm were 2.4 and 1.6 hours, respectively.
- DMF-OH represented 90 % of the summed DMF, DMF-OH, and NMF excreted in the urine.
- Cellular proliferation indexes were statistically significantly elevated in the lungs after multiple exposures, but not in the liver.
Executive summary:

This in vivo GLP-study, comparable to OECD Test Guideline 417 was performed to assess distribution and excretion of N,N-dimethylformamide (DMF) after inhalation in rats.

The AUCs for DMF for 250 and 500 ppm were 670 and 2100 µg. hr/mL, respectively. The DMF plasma half lives for 250 and 500 ppm were 2.4 and 1.6 hours, respectively. DMF-OH represented 90 % of the summed DMF, DMF-OH, and NMF excreted in the urine. Cellular proliferation indexes were statistically significantly elevated in the lungs after multiple exposure, but not in the liver. Regarding the cellular proliferation indices, the study design is similar to that by Hundley et al. (1993). It seems that the same results are presented but there is additional information about investigations in organs of rats. In details, four animals from each group (exposure regimes were the same as by Hundley et al., 1993) were anesthetized after 5 days of exposure and implanted subcutaneously with an osmotic minipump, which provides a 7-day constant release of [3H]thymidine and then exposed for an additional 5 days. On the sixth day (24 hours post exposure), all animals designated for cell proliferation studies were sacrificed. The liver, testes, kidney, nasal tissues, tracheas, lung, and prostate were collected 24 hrs after exposure to assess cell proliferation and morphological changes. There were generally four replicates for each analysis at each time point. For the cell proliferation tests tissues were collected and processed to slides. [3H]thymidine incorporated into the DNA of replicating cells was visualized. Approximately 2000 cells were counted per slide. Labelling index was calculated as the percentage of replicating cells. Statistically significant increases in the labelling index of lung were observed in the 10 ppm and 500 ppm groups. However, there was no dose-response between 10 ppm and 500 ppm groups. No effects were observed in rat liver, prostate, and nasal tissues. Results suggested that the lung might be a potential target organ of DMF exposure.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented publication which meets basic scientific principles
Reason / purpose for cross-reference:
reference to other study
Objective of study:
metabolism
Qualifier:
no guideline followed
Principles of method if other than guideline:
- Principle of test: Investigation of metabolism of DMF in cynomolgus monkeys.
- Short description of test conditions: Whole-body inhalation experiment with monkeys at concentrations of 30, 100, and 500 ppm for 6 hours a day, 5 days a week over a 13-week period.
- Parameters analysed / observed: AUC values were determined for DMF and "NMF" (NMF plus DMF-OH) in blood plasma and in urine samples.
GLP compliance:
not specified
Radiolabelling:
not specified
Species:
monkey
Strain:
other: cynomolgus
Sex:
male/female
Details on test animals or test system and environmental conditions:
No details given
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body
Duration and frequency of treatment / exposure:
6 h/d, 5d/w over 13 weeks
Dose / conc.:
30 ppm
Remarks:
about 0.091mg/L
Dose / conc.:
100 ppm
Remarks:
about 0.30 mg/L
Dose / conc.:
500 ppm
Remarks:
about 1.5 mg/L
No. of animals per sex per dose / concentration:
2 monkeys/sex/group
Control animals:
yes
Details on study design:
- Dose selection rationale: based on findings of 12-week inhalation study in rats in mice (Craig, 1989).
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY and METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, blood plasma
- Time and frequency of sampling: Serial blood samples (from 2 monkeys/sex/group) were taken at the end of the first day of exposure and following 15, 29, 57 and 85 days of testing. Blood samples for pharmacokinetic analysis were collected at 0.5 and 1, 2, 3, 4, 6, 8, 12 and 24 hours following exposure. Beginning with the Day 29 collection, control animals' collection times were reduced to 2 collections at 0.5 and 24 hours and the final collection times for control animals were 0.5, 24 and 48 hours. The purpose of this change was to minimize manipulations on the monkeys since DMF was not detected in plasma samples from control animals from Day 1 and Day 15. Also, 36 and 48 hour time points were added to the Day 57 and 85 blood collections for all test monkeys to check for DMF in the plasma for longer time points. Urine samples were collected from the same monkeys that provided blood samples. Freely-voided urine was collected for a 6-hour period following the termination of exposure at the end of the first exposure day and following Day 15, 29, 57, and 85.
Type:
metabolism
Results:
DMF was rapidly converted to "NMF"
Test no.:
#1
Toxicokinetic parameters:
AUC: DMF AUC values increased 19- to 37-fold in male and 35- to 54-fold in female monkeys as the inhalation concentrations increased 5-fold (100 to 500 ppm). So saturation of DMF metabolism as concentrations increased from 100 to 500 ppm.
Metabolites identified:
yes
Details on metabolites:
DMF was rapidly converted to "NMF" following 30 ppm exposure.

DMF and NMF Plasma Profiles

DMF and I'NMF" profiles are depicted in Figure 1 (a through h). The shapes of the plasma profiles were similar for both sexes and plasma profiles did not change with duration of exposure (Day 1 through Week 12). Plasma profiles exhibited quantitative changes consistent with saturation of DMF metabolism, between the 100 and 500 ppm DMF inhalation exposures. DMF plasma concentrations entered the decay phase much sooner following 100 ppm exposures compared to 500 ppm exposures (Figure 1: a, b, e, and f, please see attached). Similar relationships were also observed for "NMF" plasma levels (Figure 1: c, d, g, and h).

 

DMF and" NMF" AUC Values

The AUC values for DMF and "NMF" listed in Table 1 were generated from the data used to create the plasma profiles. The DMF AUC values increased disproportionally between the 100 and 500 ppm exposures. The increase in AUC values for the appropriate day of exposure comparison ranged from 19- to 37-fold for males and 35- to 54-fold for females compared to the 5-fold increase in exposure levels. To a lesser degree the increases in DMF AUC values between the 30 and 100 ppm exposures were also disproportionate.

The "NMF" AUC values increased for both sexes between Day 1 and Day 15 of exposure to 500 ppm DMF (Table 1). Duration of exposure from Day 15 through Day 85 had no apparent effect upon DMF and "NMF" AUC values. 'INMF" AUC values were 5- to 10-fold greater than their companion DMF AUC values following the 30 and 100 ppm exposures. Following 500 ppm DMF exposures, the "NMF" AUC values were approximately 2-fold greater than their companion DMF AUC values. The 'INMF" AUC values increased with increased DMF exposure levels.

 

DMF and "NMF" Plasma Concentrations

Peak DMF and "NMF" plasma concentrations are presented in Table 2. Peak 'INMF" plasma concentrations increased in relative proportion to the increase in DMF exposure concentrations. Peak DMF plasma concentrations exhibited disproportionally larger increases relative to the increase in DMF exposure concentrations. Between Day 1 and Day 15 the peak "NMF" plasma levels increased substantially for the 500 ppm exposure group; no distinct pattern was observed between Day 15 and Day 85.

Peak I'NMF" plasma concentrations following 30 ppm DMF exposures were substantially higher than their companion peak DMF plasma concentrations. DMF and "NMF" peak plasma levels were equivalent following 100 ppm exposures; DMF plasma levels were greater than companion "NMF" plasma levels following 500 ppm exposures.

 

Plasma DMF-OH concentrations

Plasma samples were selected for simultaneous DMF-OH and NMF analysis based upon having substantial 'INMF" plasma concentrations. The DMF-OH and NMF concentrations presented in Table 3 demonstrate that for any given time point DMF-OH and NMF represented a substantial circulating plasma concentration. The DMF-OH to NMF ratios in plasma tend to decrease between Day 1 and Day 15 following either 100 or 500 ppm exposures for both sexes.

 

DMF and "NMF" Plasma Half-Life

Estimated plasma half-lives for DMF and "NMF" are presented in Table 4. The estimated half-lives appeared unaffected by exposure levels, exposure duration, and sex. Plasma half-lives ranged from 1.0 to 2.3 hours and 3.9 to 15 hours for DMF and "NMF", respectively. "NMF" half-lives were approximately 3- to 12-fold greater than their companion DMF half –lives.

 

Urinary Excretion Of DMF, NMF, and DMF-OH

Relative percent urinary excretion values for DMF, NMF and DMF-OH are presented in Table 5.

With a few exceptions, DMF-OH represented over 60 percent of the sum of DMF, NMF and DMF-OH excreted in the collected urine samples. DMF was excreted unchanged and, depending upon the urine sample, represented as little as 2.1 and as much as 33 percent of the urinary excretion. NMF was excreted in levels similar to those observed for DMF.

Conclusions:
Interpretation of results: no bioaccumulation potential based on study results
These data are consistent with saturation of DMF metabolism as inhaled DMF concentrations increased from 100 to 500 ppm. Estimated plasma half-lives ranged from 1 - 2 hours to 4 - 15 hours for DMF and "NMF", respectively. DMF was rapidly converted to "NMF" following 30 ppm exposures, with "NMF" plasma concentrations higher than DMF plasma concentrations at the 0.5 h timepoint. DMF-OH was always the main urinary metabolite (56 - 95 %) regardless of exposure levels or time on study.
Executive summary:

Study design

This publication provides an acceptable, well-documented study which meets basic scientific principles. It is a non-GLP, non-OECD Test Guideline study.

Male and female cynomolgus monkeys received whole-body inhalation exposures to dimethylformamide (DMF) at concentrations of 30, 100, and 500 ppm for 6 hours a day, 5 days a week over a 13-week period. Serial blood samples were drawn at the conclusion of the first day of exposure and following 15, 29, 57, and 85 days of testing. Area under the plasma concentration curve (AUC) values were determined for DMF and ''NMF" [N-methylformamide (NMF) plus N-(hydroxymethy1)-N-methyleormamide (DMF-OH)]. Urine samples were also collected and assayed for DMF, NMF and DMF-OH.

Results

The systemic exposure to DMF increased disproportionately as the airborne DMF concentrations increased. DMF AUC values increased 19- to 37-fold in male and 35- to 54-fold in female monkeys as the inhalation concentrations increased 5-fold (100 to 500 ppm). These data are consistent with saturation of DMF metabolism as inhaled DMF concentrations increased from 100 to 500 ppm. AUC values, peak plasma concentrations, and plasma half-lives were essentially unaltered over the duration of the study - within each exposure concentration tested. Estimated plasma half-lives ranged from 1 to 2 hours and 4 to 15 hours for DMF and "NMF" respectively. DMF was rapidly converted to "NMF" following 30 ppm exposures, with "NMF" plasma concentrations higher than DMF plasma concentrations at the 0.5 hour time point. In plasma samples simultaneously assayed for DMF-OH and NMF, the concentration of DMF-OH exceeded, was equal to, or was less than NMF concentrations depending upon the plasma sample. DMF-OH was always the main urinary metabolite (56 to 95 percent) regardless of exposure level or time on study".

Conclusion

DMF-OH was always the main urinary metabolite (56 - 95 %) regardless of exposure levels or time on study.

Description of key information

There are numerous human and animal studies available using the dermal, inhalation, oral i.p. or i.v. routes;

DMF is readily absorbed via all exposure routes in human beings and animals. Dermal absorption from the vapour phase may even exceed pulmonary absorption;

DMF and its metabolites are rapidly and uniformly distributed throughout the organism, predominantly in the blood and kidneys;

The liver is the major organ of DMF metabolisation. DMF is metabolised by hydroxylation to its major metabolite N-hydroxymethyl- N-methylformamide which can further be oxidised to mono-N-methylformamide (MMF).

MMF has a greater toxicological relevance because of conjugation to glutathione forming S-methylcarbamoylglutathione. The last seems to be responsible for hepatotoxic and developmental toxic effects;

DMF and it metabolites are excreted primarily via the urine and to a lesser extent via faeces and expired air;

At higher doses, delayed biotransformation rates were observed (DMF inhibits its own metabolism);
Ethanol and probably the metabolite acetaldehyde inhibit the breakdown of DMF and conversely, DMF inhibits the metabolism of ethanol and acetaldehyde.

Therefore, exposure to DMF can cause severe alcohol intolerance in humans.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
100
Absorption rate - inhalation (%):
100

Additional information

Absorption

When N-N-dimethylformamide (DMF) is administered in vivo orally, via inhalation or via skin, it is readily absorbed in animals and in humans (Käfferlein et al., 2005; Wrbitzky and Angerer, 1998; Filser et al., 1994; Hundley et al., 1993a, Greim et al., 1992, Mráz and Nohova, 1992a,b). In humans, inhalation is the most relevant exposure route for DMF (Chang et al., 2004). A linear correlation was observed between the concentration of DMF vapour and concentrations of DMF in blood plasma of rats treated by inhalation and in humans after 8-hour working shift (Filser et al., 1994; Wrbitzky and Angerer, 1998; Chang et al., 2004). Besides this, dermal exposure provides a substantial contribution to the total body burden of DMF in exposed workers (Chang et al., 2004, Wang et al., 2009). DMF can be well absorbed via direct contact with the skin and via vapour whereby skin absorption of the liquid DMF contributes to occupational exposure more than penetration of the DMF vapour (Mráz and Nohova, 1992b). In humans, percutaneous absorption of DMF vapour correlates positively with the increase of temperature and humidity and amounted to 13 % - 36 % (Mráz and Nohova, 1992b) and 40.4 % (Nomiyama et al., 2001) of totally excreted NMF.

Distribution

DMF concentrations as well as its biotransformation product monomethylformamide (MMF) were measured in blood and other tissues of rats exposed to vapours of DMF (Lundberg et al., 1983). Both DMF and MMF were distributed fairly uniformly over the different tissues, though blood and kidneys usually had the highest concentrations. In a study with rats exposed by inhalation to DMF (labelled) vapours, statistically significant increases in the labeling index of lung were observed. Therefore, an assumption was made that the lungs might also be a potential target organ of DMF exposure (DuPont Co., 1990). No effects were observed in rat liver, prostate, and nasal tissues (DuPont Co., 1990).

Metabolism

The metabolism of DMF occurs in the liver (Greim et al., 1992) via two main pathways, with one leading to the formation of N-(hydroxymethyl)-N-methylformamide (DMF-OH or HMMF), the major metabolite of DMF (DuPont Co., 1990; Greim et al., 1992; Mráz and Nohova, 1992a, Mráz et al., 1993; Hundley et al., 1993a,b). Long time, HMMF was considered as N-methylformamide (NMF) (DuPont, 1966, 1971). However, more recent investigations demonstrated that NMF was mainly an artifact formed on the gas chromatographic column (Brindley et al., 1983; Scailteur and Lauwerys, 1984a,b; Scailteur et al., 1984) due to instability of HMMF to GLC conditions. HMMF can hydrolyse to N-methylformamide (NMF) although the latter was detected only at small amounts in the urine of animals which had received DMF (Kestell et al., 1986a; Hundley et al., 1993a,b). Enzymatic N-methyl oxidation of NMF can produce N-(hydroxymethyl)formamide (HMF), which further hydrolyses to formamide (Mráz and Nohova, 1992a). The other main pathway of DMF metabolism involves oxidation of the formyl group of NMF, leading to the formation of a reactive metabolic intermediate, probably methylisocyanate, which can react with glutathione to S-(N-methylcarbamoyl) glutathione (SMG) (Mráz et al., 1993; Filser et al., 1994). SMG is transformed to N-acetyl-S-(N-methylcarbamoyl) cysteine (AMCC) (Mráz et al., 1993; Filser et al., 1994). AMCC was more prominent in humans than in animals (Mráz et al., 1993) and is thought to be associated with hepatotoxicity (Kestell et al., 1987; Greim et al. 1992). It seems that hepatic P 450 2E1 is an important catalyst of the metabolism of DMF in both steps: the generation of SMG from NMF and in the metabolic activation of DMF to HMMF (Mráz et al., 1993).

At high exposures, biotransformation of DMF was delayed in rats and monkeys (Mráz et al., 1993a,b; Hundley et al., 1993). A quantitative difference between the metabolic pathway of DMF to AMCC in humans and rodents was also observed (Mráz et al., 1989). A relatively higher proportion of AMCC was determined in humans comparing to animals supposing that the hepatotoxic potential of DMF in humans may be linked to this metabolite. Further, they supposed that rodents are less sensitive to DMF-induced hepatotoxicity due to their poor ability to metabolize DMF via this route. The glutathione- and its sequel adducts (S-methylcarbamoylcystein and the corresponding mercapturic acid S-methylcarbamoyl-N-acetyl-cysteine) appeared to be responsible for developmental toxic effects in an in vitro assay (Klug et al., 1998, cited in OECD SIDS, 2004).

Alcohol intolerance symptoms were reported by workers exposed to DMF (Angerer and Drexler, 2005; Cai et al., 1992; Yonemoto et al., 1980; Lyle et al., 1979). Ethanol and probably the metabolite acetaldehyde inhibit the breakdown of DMF and conversely, DMF inhibits the metabolism of ethanol and acetaldehyde. Furthermore, ethanol induces cytochrome P450 2E1 which facilitates the initial hydroxylation of DMF. Thus, exposure to DMF can cause severe alcohol intolerance (Yonemoto and Suzuki, 1980; Eben and Kimmerle, 1983, cited in OECD SIDS Report for SIAM 13, 2004). Additionally, DMF can be bioactivated to methyl isocyanate, a reactive species associated with hepatoxicity.

Excretion

DMF-OH represented 90 % of the summed DMF, DMF-OH, and MMF excreted in the urine (DuPont Co., 1990). DMF-OH was always the main urinary metabolite (56 - 95 %) regardless of exposure levels or time on study with monkeys (Hundley et al., 1993b), rats (Mráz et al., 1993) and humans (Mráz and Nohova, 1992, Käfferlein et al., 2005). In humans, the elimination of DMF metabolites after exposure via the skin to DMF vapour is slower compared to inhalation exposure (Mráz and Nohova, 1992, Nomiyama et al., 2001). The same applies to the dermal exposure of liquid DMF. Thus, for DMF skin represents a compartment characterized by rapid absorption, extensive accumulation and slow elimination.

Concerning accumulation potential, the biological half-life of DMF is about 4 hours (Kimmerle and Eben, 1975 (cited in Wrbitzky and Angerer, 1998), Mráz and Nohova, 1992a). The majority of substance was eliminated within 24 hours (Lauwerys et al., 1980). NMF was detectable in the urine 4 hours after beginning of the exposure. DMF concentration in blood decreased rapidly and was no longer detectable 4 hours after exposure. Urine analysis also showed that during repeated exposure to DMF, no accumulation of NMF occurred in the body. No accumulation was detected in humans during the 4 days of the investigation of the concentrations of NMF if concentrations of DMF were between 0.1 and 37.9 ppm (median 1.2 ppm) (Wrbitzky and Angerer, 1998). For AMCC, however, accumulation is described (Mráz and Nohova, 1992 a). After repeated inhalative exposure to 30 mg/m³ DMF, persons excreted the mercapturic acid at levels of ~13 % of the dose absorbed via respiratory tract with a total half-life (i.e. DMF biotransformation and excretion) of 23 hours (Mráz and Nohova, 1992).