N,N-dimethylformamide

Epidemiological data

Administrative data

Endpoint:

epidemiological data

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2016

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Cross‑sectional study on N,N‑dimethylformamide (DMF); effects on liver and alcohol intolerance

Author:

Kilo S

Year:

2016

Bibliographic source:

Int Arch Occup Environ Health (2016) 89:1309–1320; DOI 10.1007/s00420-016-1164-0

Materials and methods

Study type:

cross sectional study

Endpoint addressed:

repeated dose toxicity: inhalation

repeated dose toxicity: dermal

Test guideline

Qualifier:

no guideline available

Principles of method if other than guideline:

- Principle of test: This study was designed to evaluate possible liver damaging effects of DMF under current workplace conditions in synthetic fibres industries.
- Short description of test conditions: Among other laboratory parameters, liver function parameters of the workforce of two companies present at the days of study were investigated. Internal exposure to DMF was assessed via three different biomarkers [sum of N-methylformamide and N-hydroxymethyl-N-methylformamide, N-acetyl-S-(N-carbamoyl)cysteine (AMCC) and 3-methyl-5-isopropylhydantoin (MIH)]. Alcohol consumption was assessed by means of direct ethanol metabolites (ethylglucuronide and ethylsulfate).
- Parameters analysed / observed: Only parameters either indicative of potential liver effects or of alcohol-induced effects were included in this study. To assess hepatic effects of DMF, the activity of liver enzymes was assessed [alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT)]. Additionally, the main parameter of alcohol-induced strain on the liver, namely the formation of the glycoprotein carbohydratedeficient transferrin (CDT), and the liver independent strain parameter of alcohol consumption, the mean corpuscular erythrocyte volume (MCV), was included. The direct markers of alcohol consumption EtG and EtS have been analysed in urine.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

N,N-dimethylformamide

EC Number:

200-679-5

EC Name:

N,N-dimethylformamide

Cas Number:

68-12-2

Molecular formula:

C3H7NO

IUPAC Name:

N,N-dimethylformamide

Details on test material:

- Name of test material (as cited in study report): N,N-dimethylformamide

- Substance type: solvent
- Physical state: vapour
- Analytical purity: not applicable (exposure to DMF took place at the workplaces in a factory of polyacrylic fibre production)

Method

Type of population:

occupational

Ethical approval:

confirmed and informed consent free of coercion received

Remarks:

Subjects gave written informed consent, according to the Declaration of Helsinki. The study was approved by the Medical Ethics Committee of the University Erlangen-Nürnberg (study registration number: 19_12B).

Details on study design:

METHOD OF DATA COLLECTION
- Type: Questionnaire, Work history, Clinical tests
- Details: All workers were interviewed by means of a standardized questionnaire in a computer-processable format. The obtained data included personal information such as age, duration of employment at the same workplace and smoking habits, work-related data like the use of breathing protection or skin contact with DMF contaminated fibres and questions regarding signs of alcohol intolerance. Subsequently, a short clinical examination was performed and constitutional parameters (like weight and size) recorded. Blood samples were drawn during examination. Urine samples were taken at the end of the work day. Serum and urine samples were stored frozen until analysis. Whole blood samples were transferred to local routine laboratories the same day. The exposed workers were asked whether direct skin contact with DMF contaminated fibres occurred to obtain an indication of potential dermal exposure.

STUDY PERIOD: not specified

SETTING: two companies within chemical parks at two different geographic locations

STUDY POPULATION
- Selection criteria: The study was carried out as part of regular, legally required health examinations for workers (exposed and controls). Therefore, no preselection was made and all workers present at the days of investigation were examined. Thus, only employees on vacation or sick leave were not included.
- Total number of subjects participating in study: 395 workers (220 DMF exposed, 175 controls)
- Sex/age/race: male
- Smoker/nonsmoker: both
- Total number of subjects at end of study: 395 workers (220 DMF exposed, 175 controls)

OTHER DESCRIPTIVE INFORMATION ABOUT STUDY: The DMF-exposed workers and the controls have been similar in age (44 vs. 45 years, p = 0.333), weight (both 89 kg, p = 0.736) and waist-to-hip ratio (0.98 vs. 0.97, p = 0.231). The two sets of worker differed significantly in terms of duration of employment and smoking habits. On average, the duration of employment at the same work place was significantly shorter for DMF-exposed workers than for the controls (16 vs. 19 years, p < 0.001). Fifty percent more of the exposed workers did smoke, and if so, they did smoke on average more cigarettes per day than controls (17 vs. 16 cigarettes/day, p = 0.002).

Exposure assessment:

measured

Details on exposure:

TYPE OF EXPOSURE: dermal, inhalative at workplace

TYPE OF EXPOSURE MEASUREMENT: Biomonitoring blood
Internal exposure to DMF was assessed via three different biomarkers [sum of N-methylformamide and N-hydroxymethyl-N-methylformamide, N-acetyl-S-(N-carbamoyl)cysteine (AMCC) and 3-methyl-5-isopropylhydantoin (MIH)].

EXPOSURE LEVELS: exposed workers were divided into the groups low (<15 mg/m3 ambient DMF) and high (≥ 15 mg/m3 ambient DMF) exposure based on the current occupational exposure limit (OEL) of 15 mg/m3 as proposed by the Scientific Committee on Occupational Exposure Limits (SCOEL 2006).

Statistical methods:

Please refer to 'Any other information on materials and methods'

Results and discussion

Results:

Liver function
Regarding the liver enzymes, exposed workers had a significantly reduced ALP activity. Other enzyme activity did not differ between exposed workers and controls, but a slightly lower AST activity was observed in exposed workers compared to controls. CDT levels were not different between control and DMF-exposed workers, and MCV was mildly elevated in the group of exposed workers. Between-group comparisons were performed based on exposure to DMF and within-group comparisons based on the separation of the exposed workers by the OEL for DMF (15 mg/m3) proposed by SCOEL (2006) into high and low-exposure subgroups. No significant increase was observed between groups or within group neither for any of the liver function tests nor for CDT and MCV. The ALP activity was significantly lower in workers exposed to DMF compared to controls, but did not differ within the exposed group. Likewise, slightly lower levels of the expression of AST were seen in DMF-exposed workers compared to the control cohort. Between-group comparisons revealed a small increase in MCV and within group comparison a small drop in CDT for high exposed worker. Also for workers who consume alcoholic beverages neither the liver enzyme activity nor, CDT or MCV increased comparing between the groups of exposed workers and controls or within the DMF-exposed worker. Again, lower activity levels were seen for ALP and ALT in exposed workers compared to controls. Between-group comparisons showed higher MCV levels in the exposed group. Within the group of DMF-exposed workers, no changes in liver enzyme activity, CDT or MCV were found.

Alcohol intolerance
Nearly 43 % of the workers reported experiencing some form of alcohol intolerance. Almost half of the workers stated to have an alcohol flush reaction when consuming alcohol after shift. Concerning the questions as to gastrointestinal disturbances, only the loss of appetite was more pronounced in DMF-exposed worker than in controls. Headache as one possible symptom of DMF-induced alcohol intolerance was reported by distinctly more workers of the control cohort. Workers who stated having alcohol flush reaction in connection with alcohol consumption after work had on average higher levels of biomarkers than those without facial flushing. No dependency was seen from the regularity of alcohol intake. As a counterpoint to the distribution of the biomarkers in relation to the facial flush, CDT levels had no influence on the reported development of the flush after consuming alcohol after work (data not shown). No modification of the amount of consumed alcohol on facial flushing was seen. CDT levels were elevated together with an increased consumption of alcohol in both, the exposed workers and the controls.

Confounding factors:

Smoking was positive and highly significant association with MCV in all four linear regression analyses. Additionally, smoking was significantly associated with CDT in the analysis together with NMF as exposure parameter and by trend with AMCC (p = 0.067) and MIH (p = 0.056). A significant negative association between smoking and ALT was only observed with exposition as independent parameter and by trend with AMCC and MIH as further parameters (p = 0.096, both).
A significant positive association of age with CDT and MCV and significant negative with GGT and ALT were found. The duration of employment was not associated with liver enzyme activity, CDT or MCV. The use of drugs known to interact with liver function was significantly and positive associated in all three linear regression analyses with the DMF biomarker with GGT. Finally, the WHR showed in all linear regression analyses a significant negative interaction with MCV and CDT and a significant, positive association with the activity of the two liver enzymes GGT and ALT.

Any other information on results incl. tables

Multiple linear regression analyses basically led to the same results in connection with all three tested biomarkers, namely NMF and AMCC in urine and MIH in blood. None of the DMF biomarker showed a positive (directly proportional) relation to the liver enzyme activity (AP, GGT, AST, ALT) or CDT and MCV. In linear regression analysis using DMF exposure as binary parameter (i.e. comparing exposed worker and controls), CDT was elevated by trend. All three biomarkers showed a significant, but negative association with the expression of AP. In addition, a significant but also negative association was seen between AMCC and CDT. A highly significant association was found within all linear regression analyses for alcohol consumption (lnEtS + lnEtG) with AP, GGT, CDT and MVC. By trend, a negative (p = 0.057) association of ethanol consumption with ALT was found in multiple linear regression analysis with DMF exposition as independent parameter.

Applicant's summary and conclusion

Conclusions:

The present study indicates that long-term exposure to DMF, which was specified by median urinary AMCC levels of 4.84 mg/g creatinine and DMF haemoglobin adduct levels of 60.5 nmol/MIH/g globin, respectively, does not result in any adverse liver effects. In contrast, these DMF exposure levels still elicit certain alcohol intolerance reactions.

Executive summary:

Study design

There are still concerns regarding occupational exposure to hepatotoxic DMF. This study was designed to evaluate possible liver damaging effects of DMF under current workplace conditions in synthetic fibres industries. Methods Among other laboratory parameters, liver function parameters (alkaline phosphatase (ALP), aspartate aminotransferase, alanine aminotransferase and gammaglutamyltransferase), the mean corpuscular erythrocyte volume (MCV) and carbohydrate-deficient transferrin (CDT) of the workforce of two companies present at the days of study were investigated. Internal exposure to DMF was assessed via three different biomarkers [sum of N-methylformamide and N-hydroxymethyl-N-methylformamide, N-acetyl-S-(N-carbamoyl)cysteine (AMCC) and 3-methyl-5-isopropylhydantoin (MIH)]. Alcohol consumption was assessed by means of direct ethanol metabolites (ethylglucuronide and ethylsulfate).

Results

None of the tested liver enzyme activities showed a positive association with any of the three exposure markers, nor did CDT and MCV. CDT was negatively associated with AMCC and the ALP activity negatively with all three exposure markers. Changes in liver function are seen mainly in conjunction with ethanol consumption but also with increasing body weight and age. MCV was associated with smoking. Almost half of the workers stated to experience alcohol flush reaction.

Conclusion

The present study indicates that long-term exposure to DMF, which was specified by median urinary AMCC levels of 4.84 mg/g creatinine and DMF haemoglobin adduct levels of 60.5 nmol/MIH/g globin, respectively, does not result in any adverse liver effects. In contrast, these DMF exposure levels still elicit certain alcohol intolerance reactions.