Dermal absorption of N,N-dimethylacetamide in human volunteers

The Association Between Dimethylacetamide Exposure and Liver Toxicity: A Large Retrospective Analysis in Workers From Four European Factories

OBJECTIVE

This study examines the association between 8-h time weighted N, N-dimethylacetamide (DMAc) air exposure and potential hepatocellular injury in a retrospective study among fibre-production workers in four European factories.

METHODS AND RESULTS

Twenty-nine (1.5%) of 1844 alanine aminotransferase (ALT) observations had liver values two times above normal; 0.2% three times above normal and 0.05% five times above normal. Two (0.1%) observations were indicative of hepatocellular injury. Logistic regression analyses showed an odds ratio for elevated ALT of 0.88 per 1 ppm (P trend = 0.39). Linear random effects regression analyses showed a decrease of one international unit (IU/L) ALT per 1 ppm increase of DMAc exposure (P = 0.002).

CONCLUSIONS

This study found no association between DMAc exposure and hepatoxicity amongst European workers. The prevalence of elevated liver values was lower compared to the general population without occupational exposure.

Assessment of dermal exposure to N,N-dimethylacetamide in spray workers by combining personal exposure monitoring, biological monitoring, and glove permeation monitoring: A pilot study

OBJECTIVES

We assessed dermal exposure to N,N-dimethylacetamide (DMAC) in a spray worker by utilizing a combination of personal exposure monitoring, biological monitoring, and glove permeation monitoring. We also determined the protective effects of chemical protective gloves (CPGs).

METHODS

Surveys with and without CPG usage were performed on different days. In the survey with CPG usage, the worker had worn leather gloves over the CPG. Personal exposure monitoring and glove permeation monitoring were performed using 3M Organic Vapor Monitor 3500 and PERMEA-TEC Pads respectively. Urinary concentration of DMAC and its metabolites (N-methylacetamide [NMAC], N-hydroxymethyl-N-methylacetamide [DMAC-OH], S-(acetamidomethyl) mercapturic acid [AMMA]) were measured in the before-shift and end-of-shift samples collected from the worker.

RESULTS

Personal exposure DMAC concentration in the survey with CPG usage (0.32 ppm) was twice that in the survey without CPG usage (0.15 ppm). However, urinary concentrations of DMAC-OH and AMMA in the end-of-shift samples in the survey with CPG usage (DMAC-OH, 0.74 mg/g creatinine; AMMA, 0.10 mg/g creatinine) were lower than those in the survey without CPG usage (DMAC-OH, 1.27 mg/g creatinine; AMMA, 0.24 mg/g creatinine). Urinary concentrations of DMAC and NMAC were below the limit of detection in all samples. DMAC concentrations in PERMEA-TEC Pads that were used in the surveys with and without CPG usage were in the range of 0.3-2.1 µg/sample and 16.4-1985.2 µg/sample respectively.

CONCLUSIONS

The combination of CPG usage and leather gloves was effective in preventing dermal exposure to DMAC.

Concentration determination of urinary metabolites of N,N-dimethylacetamide by high-performance liquid chromatography-tandem mass spectrometry

OBJECTIVES

N,N-Dimethylacetamide (DMAC) is widely used in industry as a solvent. It can be absorbed through human skin. Therefore, it is necessary to determine exposure to DMAC via biological monitoring. However, the precision of traditional gas chromatography (GC) is low due to the thermal decomposition of metabolites in the high-temperature GC injection port. To overcome this problem, we have developed a new method for the simultaneous separation and quantification of urinary DMAC metabolites using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHODS

Urine samples were diluted 10-fold in formic acid, and 1-μl aliquots were injected into the LC-MS/MS equipment. A C18 reverse-phase Octa Decyl Silyl (ODS) column was used as the analytical column, and the mobile phase consisted of a mixture of methanol and aqueous formic acid solution.

RESULTS

Urinary concentrations of DMAC and its known metabolites (N-hydroxymethyl-N-methylacetamide (DMAC-OH), N-methylacetamide (NMAC), and S- (acetamidomethyl) mercapturic acid (AMMA) ) were determined in a single run. The dynamic ranges of the calibration curves were 0.05-5 mg/l (r≥0.999) for all four compounds. The limits of detection for DMAC, DMAC-OH, NMAC, and AMMA in urine were 0.04, 0.02, 0.05, and 0.02 mg/l, respectively. Within-run accuracies were 96.5%-109.6% with relative standard deviations of precision being 3.43%-10.31%.

CONCLUSIONS

The results demonstrated that the proposed method could successfully quantify low concentrations of DMAC and its metabolites with high precision. Hence, this method is useful for evaluating DMAC exposure. In addition, this method can be used to examine metabolite behaviors in human bodies after exposure and to select appropriate biomarkers.

Dermal uptake of organic vapors commonly found in indoor air

Transdermal uptake directly from air is a potentially important yet largely overlooked pathway for human exposure to organic vapors indoors. We recently reported (Indoor Air 2012, 22, 356) that transdermal uptake directly from air could be comparable to or larger than intake via inhalation for many semivolatile organic compounds (SVOCs). Here, we extend that analysis to approximately eighty organic compounds that (a) occur commonly indoors and (b) are primarily in the gas-phase rather than being associated with particles. For some compounds, the modeled ratio of dermal-to-inhalation uptake is large. In this group are common parabens, lower molecular weight phthalates, o-phenylphenol, Texanol, ethylene glycol, and α-terpineol. For other compounds, estimated dermal uptakes are small compared to inhalation. Examples include aliphatic hydrocarbons, single ring aromatics, terpenes, chlorinated solvents, formaldehyde, and acrolein. Analysis of published experimental data for human subjects for twenty different organic compounds substantiates these model predictions. However, transdermal uptake rates from air have not been measured for the indoor organics that have the largest modeled ratios of dermal-to-inhalation uptake; for such compounds, the estimates reported here require experimental verification. In accounting for total exposure to indoor organic pollutants and in assessing potential health consequences of such exposures, it is important to consider direct transdermal absorption from air.

Children's phthalate intakes and resultant cumulative exposures estimated from urine compared with estimates from dust ingestion, inhalation and dermal absorption in their homes and daycare centers

Total daily intakes of diethyl phthalate (DEP), di(n-butyl) phthalate (DnBP), di(isobutyl) phthalate (DiBP), butyl benzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) were calculated from phthalate metabolite levels measured in the urine of 431 Danish children between 3 and 6 years of age. For each child the intake attributable to exposures in the indoor environment via dust ingestion, inhalation and dermal absorption were estimated from the phthalate levels in the dust collected from the child's home and daycare center. Based on the urine samples, DEHP had the highest total daily intake (median: 4.42 µg/d/kg-bw) and BBzP the lowest (median: 0.49 µg/d/kg-bw). For DEP, DnBP and DiBP, exposures to air and dust in the indoor environment accounted for approximately 100%, 15% and 50% of the total intake, respectively, with dermal absorption from the gas-phase being the major exposure pathway. More than 90% of the total intake of BBzP and DEHP came from sources other than indoor air and dust. Daily intake of DnBP and DiBP from all exposure pathways, based on levels of metabolites in urine samples, exceeded the Tolerable Daily Intake (TDI) for 22 and 23 children, respectively. Indoor exposures resulted in an average daily DiBP intake that exceeded the TDI for 14 children. Using the concept of relative cumulative Tolerable Daily Intake (TDI(cum)), which is applicable for phthalates that have established TDIs based on the same health endpoint, we examined the cumulative total exposure to DnBP, DiBP and DEHP from all pathways; it exceeded the tolerable levels for 30% of the children. From the three indoor pathways alone, several children had a cumulative intake that exceeded TDI(cum). Exposures to phthalates present in the air and dust indoors meaningfully contribute to a child's total intake of certain phthalates. Such exposures, by themselves, may lead to intakes exceeding current limit values.

Predicting the absorption of chemical vapours

The focus of this review is on the systemic absorption of vapours via skin, including experimental data as well as regression and pharmacokinetic models. Dermal contribution ratios (DCR), i.e. amount absorbed through skin relative to total intake (skin and inhalation) at specified conditions, could be identified or calculated from published data for 33 chemical vapours. The ratios vary from ~0.0002 (vinyl chloride) to ~0.8 (2-butoxyethanol), with hydrophilic chemicals having a higher ratio than lipophilic ones. Multiple regression analysis of these data suggests that the DCR is largely explained by the octanol:water partition coefficient, vapour pressure and molecular weight (R(2)=0.69). Several physiologically-based pharmacokinetic models were identified; however, all describe the absorption of single substances. Regarding predictive models, only two models were found. In conclusion, dermal uptake of chemical vapours needs more attention, as such exposures are common, data are scarce and few predictive models exist.

The influence of iron stores on cadmium body burden in a Thai population

Cadmium is a toxin of increasing public health concern due to its presence in most human foodstuffs and in cigarette smoke. Exposure to cadmium leads to tissue bioaccumulation and, in particular, has nephrotoxic effects. The aim of the present study was to investigate the association between cadmium body burden and iron stores in a Thai population. A total of 182 healthy adult Thai subjects of both genders (89 males, 93 females) aged between 18 and 57 years and weighing 40-95 kg were included in this study. The total amounts of cadmium excreted in urine over 2 h (microg/g creatinine) were used as an index of long-term cadmium exposure. Quantitation of cadmium was performed using electrothermal (graphite furnace) atomic absorption spectrometry. The urinary cadmium excreted displayed a normal frequency distribution. The average urinary cadmium level did not exceed the WHO maximum tolerable internal dose for the non-exposed population (2 microg/g creatinine). Body iron stores reflected by serum ferritin levels did not show any correlation with cadmium burden in both males and females, although a relatively stronger influence of body iron store status on cadmium burden was shown in females. When the levels of serum ferritin were stratified into five levels (<20, 20-100, 101-200, 201-300, and >300 microg/l), a significant difference in total cadmium body burden was observed between females and males only in the group with a low level of serum ferritin of <20 microg/l. The cadmium body burden in females was about twice that in males in this group.

S-(acetamidomethyl)mercapturic acid (AMMA): a new biomarker for occupational exposure to N,N-dimethylacetamide

N,N-dimethylacetamide (DMA) is used in the textile and plastics industry as a solvent alternative to more toxic N,N-dimethylformamide. Here we studied toxicokinetics of two major urinary metabolites of DMA, namely, S-(acetamidomethyl)mercapturic acid (AMMA) and N-methylacetamide (NMA). Urine samples were collected from workers exposed to DMA in a factory manufacturing acrylic fibers. AMMA and NMA were determined by HPLC/MS and GC/MS, respectively. The working scheme in the factory consisted of periods of three consecutive working shifts alternated regularly with two days off work. In the first stage of the study, NMA and AMMA were determined in urine samples collected before, in the middle, and at the end of one working shift. In the second stage, urine was collected five times during three consecutive days after a two-day rest: before and at the end of the first and second working shifts and before the third shift. It was found that the end-of-shift NMA levels were several folds higher than the pre-shift levels of the same day and dropped significantly until the next shift. On the other hand, there were no significant differences in AMMA levels before and at the end of the same shift but a continuous rise during the three-day working period was observed. Median values of NMA concentrations at the end of working shifts were between 10.1 and 17.3 mg/g creatinine, median AMMA concentrations in the second or third day of the working period varied between 12.4 and 38.1 mg/g creatinine. The approximate half-lives of NMA and AMMA (means) in the exposed workers were about 9 and 29 h, respectively. Thus, while NMA in the end-of-shift urine samples remains a preferential biomarker of DMA exposure during that shift, AMMA determined at the end of a work-week reflects cumulative exposure over the last few days. Further studies are needed to determine AMMA concentrations corresponding to the threshold limit value of DMA.

A cross-sectional observation of effect of exposure to N-methyl-2-pyrrolidone (NMP) on workers' health

This study was aimed at clarifying the effect of exposure to N-methyl-2-pyrrolidone (NMP) on workers' health. Fifteen male NMP-exposed workers and 15 referent male workers were recruited for this study. Exposure concentrations were assessed by determining NMP in the breathing zones and urinary NMP. Clinical examinations, motor and sensory nerve conduction velocities in the dominant arm, and neurobehavioral tests were carried out. The subjects were asked to complete self-administered questionnaires for subjective symptoms and psychological assessment. The mean NMP exposure concentrations ranged from 0.14 to 0.26 ppm, and urinary NMP levels at the end of each workday ranged from 0.17 to 0.22 mg/l, throughout the work week. In terms of clinical data, motor and sensory nerve conduction velocities, neurobehavioral tests, and subjective symptom assessments, there were no differences and no dose-dependent changes in either the means or the prevalence of abnormal findings between NMP-exposed and referent workers.

Dimethylacetamide-induced hepatic injuries among spandex fibre workers

OBJECTIVES

To investigate clinical features of dimethylacetamide-induced hepatic injuries (DIHIs).

METHODS

Workers exposed to dimethylacetamide (DMAc) in two spandex factories were monitored for DIHI. We identified 38 DIHI cases as study subjects between 2001 and 2004. DMAc exposure was estimated with urinary N-methylacetamide (NMAc) results from 2003 to 2004.

RESULTS

All 38 cases showed hepatocellular-type liver injury. The interval between first exposure and identification of hepatic injury (latent period) was mostly less than two months and never exceeded six months. In addition, three repeat DIHI cases showed much shorter latent periods for recurrence than their initial latent periods of hepatic injury. A 50% decline of serum alanine aminotransferase (ALT) levels after the cessation of DMAc exposure took less than 14 days and a 90% decline less than 31 days. The median urinary NMAc level of DIHI group (samples from the department of DIHI cases) was 25.1 mg/g Cr; higher than that of all other urinary NMAc results (11.8 mg/g Cr).

CONCLUSIONS

Our data suggest that DMAc can induce hepatocellular-type liver injury and the mechanism of DIHI may be idiosyncratic. Although our exposure estimation was incomplete, the workers with DIHIs might be exposed to higher levels of environmental DMAc than the workers who did not develop DIHIs. All workers exposed to DMAc need to be closely observed for occurrence of hepatic injury for at least six months.

Incidence of dimethylacetamide induced hepatic injury among new employees in a cohort of elastane fibre workers

OBJECTIVE

To investigate the incidence of N,N-dimethylacetamide (DMA) induced hepatic injury among new elastane fibre workers and to explore factors relating to DMA induced hepatic injury.

METHODS

Elastane fibre workers exposed to DMA were monitored for hepatic injury. Four hundred and forty new workers employed from 1 January 2002 to 31 July 2004 were included as study subjects. DMA exposure estimates were based on urinary N-methylacetamide (NMA) concentrations.

RESULTS

There were 28 cases of DMA induced hepatic injury. The overall incidence of DMA induced hepatic injury among new elastane fibre workers was 0.089/person-year. Incidence rates were 7-10 times higher in high exposure groups than in low exposure groups. Fewer DMA induced hepatic injuries occurred among workers employed for a longer period. Workers whose exposure duration was more than seven months showed no hepatic injury in either the high or low exposure groups. Exposure category and duration of employment were significant variables in the multiple logistic regression analysis.

CONCLUSIONS

Results suggest the existence of dose dependent DMA induced hepatic injury. The inverse relation between the incidence of DMA induced hepatic injury and duration of employment may reflect a type of healthy survivor effect or tolerance to DMA induced hepatic injury.

Monitoring of N,N-dimethylacetamide in children during i.v.-busulfan therapy by liquid chromatography-mass spectrometry

Recently, an intravenous (i.v.) formulation of busulfan using the potentially hepatotoxic and neurotoxic N,N-dimethylacetamide (DMA) as a solvent was introduced. There is a need to assess the exposure of DMA in patients during the intravenous high dose therapy. A rapid and selective LC-MS method was developed to quantify relevant DMA concentration in plasma. After protein precipitation with trichloroacetic acid, the isocratic separation was achieved using a 150 mm x 2 mm C18 column and elution with a mobile phase containing 0.1% formic acid in water/acetonitrile (97:3). Detection of DMA was carried out with a ThermoFinnigan single-quadrupole mass spectrometer in selected-ion monitoring mode as H+ -adduct at m/z 88.2. Deuterium-labelled DMA was used as the internal standard. The LC-MS method was accurate, precise and reproducible in the range from 0.25 to 150 mg/l and met the generally accepted criteria for bioanalytical methods. Two calibration ranges from 0.25 to 7.5 mg/l and 7.5 to 150 mg/l were used. The intra- (n = 7) and interassay (n = 7) accuracy and precision were both < 7.7% and the limit of quantification is 0.25 mg/l. The method was successfully applied to investigate 203 plasma samples in children during the i.v.-busulfan therapy.

Biological monitoring of occupational exposure to N,N-dimethylacetamide with identification of a new metabolite

AIMS

To study the concentration of N,N-dimethylacetamide (DMA) and its metabolite, N-methylacetamide (NMA), in urine of workers occupationally exposed to DMA in a factory producing synthetic acrylic fibres.

METHODS

During the first phase, 223 workers exposed to low environmental concentrations of DMA provided urine samples at the end of a work shift. High concentrations of the unmodified solvent and its metabolite were found in a group of workers whose job was to start up machinery. The second and third phases focused on conditions favouring high uptake of DMA.

RESULTS

The highest concentrations of unmodified solvent and NMA were found in the urine of workers recently engaged in starting up machinery. NMA in urine was 1.5-173.6 mg/g creatinine (median 20.5). In spite of the low environmental concentration, about 20% of the urine concentration of NMA was higher than 30 mg/g creatinine. Dermal absorption of DMA was high. A shower and a change of clothing at the end of the work shift, and washing away any solvent left on the skin, ensured that dermal absorption of DMA did not continue. This significantly reduced the NMA urinary concentration at values lower than 30 mg/g creatinine. In some urine samples, S-acetamidomethyl-mercapturic acid was identified by NMR analysis; this is probably a metabolite of N,N-dimethylacetamide--it has never before been identified in humans or animals.

CONCLUSIONS

Even at low environmental concentrations of DMA, dermal absorption can be considerable. Unmodified DMA and NMA concentrations in urine are good biomarkers for monitoring occupational exposure to the solvent.

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.