Registration Dossier

Administrative data

Link to relevant study record(s)

Description of key information

Short description of key information on bioaccumulation potential result: 
Smith, Wishnok, Deen, 1994, toxicology and applied pharmacology 125, 296-308, administration of DMA intraperitoneally to rats and investigation of the distribution, metabolism and excretion.
Mitchell et al. 1994, Xenobiotica, 1994, Vol. 24 No. 12, 1215-1221, administration of DMA orally to rats and mice and investigation of the distribution, metabolism and excretion via radiolabelling.
Ishiwata et al., 1984, IARC scientific publications / World Health Organisation, International Agency for Research on Cancer, administration of DMA orally via diet to rats and investigation of the distribution, metabolism and excretion.
Zeisel and DaCosta, 1986, Cancer Research 46, 6136-6138 December 1986, investigation of methylamine excretion after ingestion of fish containing methylamines in humans.
Asatoor et al., 1965, Biochimica et biophysica acta, 111 (1965) 384-392, administration of choline chloride (intraperitoneal) or [Me14C]choline chloride (orally) or egg lecithin or trimethylamine hydrochloride (orally) or trimethylamine hydrochloride (intraperitoneal) [14C]methylamine (intraperitoneal) or L[Me-14C]Methionine (intraperitoneal) or 14C-MMA to rats (orally or intraperitoneally) and analytical verification of DMA in Urine, to test whether these substances can be transformed in DMA and excreted that way.
Short description of key information on absorption rate:
Fluhr, 2005, Additive Impairment of the Barrier Function and Irritation by Biogenic Amines and Sodium Lauryl Sulphate: A Controlled in vivo Tandem Irritation Study, Skin Pharmacol Physiol 2005;18:88–97, 1 % DMA in distilled water on human skin (paravertebral mid back).
No significant irritation, but barrier disruption of the stratum corneum was observed.

Key value for chemical safety assessment

Bioaccumulation potential:
low bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
100
Absorption rate - inhalation (%):
100

Additional information

The metabolism, disposition and toxicokinetics of dimethylamine have been well characterized. First of all, it is important to take into account, that dimethylamine has three different sources: the diet (for example in fish), bacterial synthesis in the intestinal tract and endogenous synthesis. As TMAO is an end-product of nitrogen metabolism in fish, it can be metabolized to DMA and TMA by bacteria once fish have been killed. The endogenous concentration of DMA was found to be 2.5 +/- 0.2 nmol/mL.The much greater urinary excretion of DMA by normal rats than by germ-free rats is clear evidence for significant synthesis of DMA by gut bacteria. In particular, DMA can be build in the body during bacterial degradation of choline or lecithin inside the intestinal tract (DMA excretion was directly related to the dose of choline administered), but variations in choline intake that might occur as part of consumption of normal foods are not likely to significantly increase TMA and DMA production, and therefore change our exposure to precursors of nitrosamines only somewhat. Additionally monomethylamine can be methylated to DMA. In total the knowledge of the endogenous occurrence influences mainly the categorization and classification of dimethylamine.

In rats and in mice, dimethylamine and dimethylamine hydrochloride were rapidly absorbed, uniformly distributed (interestingly the volume of distribution exceeds the animal size, so it has to be stated, that DMA must accumulate in some tissues more than in others) and eliminated mainly unchanged (about 80 %) via urine in both sexes of rats (only negligible amount are excreted via feces or exhaled). The experiments conducted showed that DMA is avidly secreted by the renal tubules. About 20 % of the administered DMA appear in the urine as methylamine (3 -5 %) and non-methylamine metabolites. Nevertheless there exists also the possibility of DMA being metabolized to N-Nitrosodimethylamine, which is a potent carcinogen. It is not possible to exclude the possibility of nitrosamine formation, but it seems rather unlikely that a significant amount of nitrosamine can be built, since this reaction occurs mainly at low pH, like in the stomach and requires nitrite. For example; it was estimated that, if a man ate a 300-g meal containing 12 mg dimethylamine hydrochloride and 60 mg sodium nitrite, not more than about 3 µg DMN might be expected to be formed intragastrically. This dose ingested daily may be too low to be significantly carcinogenic, though it should be stressed that even tiny incidences may assume importance in a large population.

Interestingly, DMA secreted from the blood into the small intestine can be re-absorbed. So the intestinal DMA concentration is a balance between absorption, secretion and formation and the amount of intestinal moisture.

Based on the results obtained in these studies, dimethylamine may be considered to be a mostly in the intestine, rapidly absorbed, and well eliminated (mainly unchanged) substance in rats, mice and humans. It bears the possibility to be metabolized to the carcinogenic substance N-Nitrosodimethylamine.

Discussion on bioaccumulation potential result:

The study performed by Smith et al. in 1994, dealt with the metabolic fate of DMA or TMA after injection to rats. There are three sources of dimethylamine (DMA): diet, bacterial synthesis, and endogenous synthesis. Fish contains significant quantities of DMA and TMA, and is probably a major dietary source of methylamines. As TMAO is an end-product of nitrogen metabolism in fish, it can be metabolized to DMA and TMA by bacteria once fish have been killed. The endogenous concentration of DMA, was found to be 2.5 +/- 0.2 nmol/mL. So DMA enters the body from intestinal absorption of both dietary DMA and DMA formed by bacterial action in the lower gut or after endogenous synthesis after conversion of choline to DMA (see also Asatoor et al. 1965) and leaves by urinary excretion. The much greater urinary excretion of DMA by normal rats than by germ-free rats is clear evidence for significant synthesis of DMA by gut bacteria. Urine analysis following doses of stable isotopes showed also that DMA was not converted to TMA or TMAO. There is also some endogenous synthesis of DMA, possibly from monomethylamine (MMA). So the results of these metabolic balance studies indicate that there is net synthesis of DMA by gut bacteria and net consumption of TMAO by endogenous processes. When dimethylamine hydrochloride (DMA-HCl) is administered in vivo intravenously or intraperitoneally it is readily absorbed (Smith, 1994). After the uptake it is uniformly distributed in the body, interestingly with the volume of distribution exceeding the animal size, suggesting that it is highly concentrated at one or more locations in the body (Smith, 1994). The tissue-to-blood concentration ratio of 8 found for DMA in kidney greatly exceeds values for other body compartments, including gastric fluid (Smith et al., 1994).The apparent volume of distribution and clearance were dose-dependent. About 20 % of the administered DMA appear in the urine as non-methylamine metabolites.The experiments revealed, that the only important pathway for elimination of the three methylamines (and their metabolites) tested is urinary excretion. Fecal excretion, exhalation in breath, and retention in tissues are all negligible in normal rats. The experiments conducted showed that DMA is avidly secreted by the renal tubules, or there might exist as an alternative explanation for the dose dependence of the volume of distribution an active transport of DMA or TMA from extracellular to intracellular fluid. The results strongly suggest that there are various regions outside the gastrointestinal contents which contain high concentrations relative to the blood of these methylamines.

Another Study by Mitchell et al, 1994, confirmed the results achieved by Smith et al, 1994. In both rodents DMA was rapidly absorbed in the small intestine, caecum and large intestine and is distributed rapidly through the blood and then disappeared rapidly into the urine, which was the major route of excretion with the majority of radioactivity (91%) being voided during the first day (Mitchell et al, 1994). Only a small proportion was secreted in the intestine and bile. Interestingly DMA secreted from the blood into the small intestine can be re-absorbed. So the intestinal DMA concentration is a balance between absorption, secretion and formation and the amount of intestinal moisture.

The majority of [14C]-dimethylamine administered was excreted unchanged in the urine with only small amounts being demethylated to [14C]-methylamine. In all 0 -24 h urine samples examined two radioactive areas were found, which corresponded to authentic methylamine and dimethylamine (little variation between the species with 96 -6 +/- 2 -5 and 95 5 +/- 1 -3 % of the radioactivity being present as dimethylamine in rat and mouse respectively. The demethylation product, methylamine, only accounted for 3-4 ± 1-5 (rat) and 4-5 ± 1-3% (mouse) of the 0-24 h urinary radioactivity output.(Mitchell et al., 1994). Additional small amounts of radioactivity were observed in the 24-72 h urine (2%), in feces (2%) and in exhaled air (1%), with a further quantity (1%) being detected within the carcass after 3 days. Good overall recoveries were achieved; suggesting that only trace amounts of volatile compounds had been exhaled and escaped detection.

Ischiwata et al. examined 1994 the absorption, distribution and excretion of DMA in wistar rats. The fate of DMA in rats is very little or no absorption in the stomach but rapid absorption in the intestine - especially in the upper part of the small intestine - secretion of some of the compounds from the blood into the saliva or the digestive tract, and excretion of most of an ingested or otherwise administered dose of either compound in the urine (Ishiwata et al., 1984).

Zeisel and DaCosta reported that DMA excretion in humans was more than 4 times greater on the day that methylamine-containing fish was eaten than on the control day. (Zeisel and DaCosta, 1986). Human subjects (n = 5) ingested a diet of known methylamine content for 2 days. On Day 3, they ate fish at the luncheon and dinner meals. On Day 4, they again ate the control diet. A single portion of fish contained as many methylamines as were normally excreted by the human in 2 days. Dimethylamine excretion increased more than 4-fold (from 5.6 to 24.1 µmol/24h/kg of body weight).

In humans, DMA is absorbed after eating fish with an increased level of methylamines (DMA and TMA). With respect to the metabolism of DMA the following conclusion can be drawn: DMA is readily absorbed via oral route (Zeisel, 1986). After ingestion of fish with elevated levels of methylamines the DMA excretion via urine is elevated (2.8-fold). Most of the increase in urine methylamine excretion was in the form of DMA.

The study performed by Asatoor et al, in 1965, already gives important data concerning the DMA. They investigated whether DMA is generated in the mammalian body by feeding rats (in cases also administered via injection) with either choline chloride, lecithin, [14C]methylamine, or [Me14C]choline chloride (orally) or egg lecithin or trimethylamine hydrochloride (orally) or trimethylamine hydrochloride (intraperitoneal) and then analytical verification of DMA in Urine, to test whether these substances can be transformed in DMA and excreted that way. They could prove that DMA is endogenously built out of choline and lecithin. Furthermore TMA is in part metabolized to DMA, which is then excreted mainly via urine. Additionally MMA is partly methylated to form DMA. So these results are in accordance with the results obtained by Ischiwata et al. in 1984.

Zeisel an Coworkers investigated in 1989 the fate of via orogastric intubation administered choline in the rat intestine (Spraque-Dawley). With the help of radiolabeled choline its uptake and its metabolism were investigated in the intestines. Additionally the metabolites excreted via urine were determined. They found that choline increased the excretion of TMA and TMAO and increased DMA excretion. The absorption mechanisms for choline has a high capacity (most of the choline was absorbed). At the low dose, choline-derived radiolabel was absorbed from the intestinal lumen before it reached the areas of gut colonized with bacteria. At the high dose of choline, much more label reached the colon, and they suggest that an appreciable portion of the choline-derived radiolabel that was absorbed did so via diffusion across the colon. In terms of absolute amounts, much more choline-derived radiolabel was present in the colon after the high dose. They believe that the disproportionate rise in TMA and TMAO excretion observed at the higher choline dose occurred because choline reached the bacterially colonized large intestine in appreciable quantities. The capacity for TMA oxidation must be very large, since TMAO excretion could increase over a thirtyfold range. Despite this capacity, significant amounts of TMA (approximately 10% of the TMA that must have been formed prior to conversion to TMAO) escaped this fate and was excreted intact. It has been suggested that the major precursor of DMA is the TMA formed by gut bacteria. The rate of increase in DMA excretion with increasing choline dose was different from the rate of increase in TMA excretion at the lower doses of choline. The amount of TMAO that was formed suggests that increasing amounts of TMA could have been transiently available for DMA synthesis as choline doses were increased. At the higher choline dose there was no jump in DMA excretion, but there was a large increase in TMA and TMAO excretion. This suggests that formation of DMA was not tightly linked to the availability of TMA. The data show that DMA excretion was directly related to the dose of choline administered, suggesting that choline, or a metabolite of choline, is likely to be a precursor of DMA. Previously, they found that the presence of gut bacteria was not essential for the formation and excretion of DMA in rats, while gut bacteria made a significant contribution to TMA excretion.

In summary, they have found that there is a critical concentration of choline which must be achieved within gut lumen before choline absorption processes in the small intestine are overloaded, thus allowing sufficient choline to reach the large intestine. Since it is the large intestine which is colonized with bacteria, large doses of choline are, therefore, much more likely to be converted by bacteria to TMA. The data suggest that variations in choline intake that might occur as part of consumption of normal foods are not likely to significantly increase TMA and DMA production, and therefore are not likely to greatly change our exposure to precursors of nitrosamines. Dietary intake of preformed DMA and TMA and endogenous production of these amines are likely to be far more significant sources.

In 1998, Zhang et al. investigated the excretion of DMA after administration of various related amine precursors. They found trimethylamine N-oxide (at a dose rate of 1 mmol/kg body weight) to be 20 times more efficient at providing dimethylamine than an equivalent dose of choline. Additionally less than 1 % of the choline dose was converted to dimethylamine. Slightly more of an equivalent trimethylamine dose (1.6%) was converted to dimethylamine. So trimethylamine N-oxide is undoubtedly a significant dietary source of dimethylamine and its carries the potential of being converted to carcinogenic nitrosodimethylamine. However, other dietary sources of dimethylamine probably lie undetected amidst the myriad of anutrient chemicals within foodstuffs, and the continued excretion of small amounts of dimethylamine from antibiotic treated and germfree rats (Asatoor et al., 1967; Zeisel et al., 1985) implies that dietary components, although probably the major source, are not the only originator of dimethylamine.

In 1993, Gut et al, investigated the in vitro oxidation of trimethylamine (TMA) to TMA N-oxide (TMAO) and dimethylamine (DMA) in rat liver microsomes. In details the role of flavin-containing monooxygenase and cytochrome P450 in the N-oxidation and N-demethylation of TMA was studied. Pretreatment of rats with phenobarbital, 3-methylcholanthrene, ethanol or pregnenolone 16 alpha-carbonitrile had little or no effect on the liver microsomal metabolism of TMA to TMAO or DMA. Changing the atmosphere in the incubation vessel from 20% oxygen/80% nitrogen (air) to 100% oxygen had a selective stimulatory effect on the N-oxygenation of TMA but did not affect TMA N-demethylation. In addition, the Km for TMA N-demethylation was 5-fold higher than for the N-oxygenation reaction. The results of these studies suggest that the enzyme systems responsible for N-demethylation and N-oxygenation are different and that they are under different regulatory control. Carbon monoxide (CO/O2 = 80/20) had little or no inhibitory effect on either the N-demethylation or N-oxygenation of TMA by liver microsomes from control or pregnenolone 16 alpha-carbonitrile- treated rats. Additional studies indicated that methimazole, an inhibitor of FAD-containing monooxygenase (FMO), was a potent inhibitor of TMA oxidation. Evidence was presented that FMOs are the major enzymes responsible for N-demethylation and N-oxygenation of TMA in rat liver microsomes and that cytochrome P450 enzymes do not play a major role in the metabolism of TMA to TMAO or DMA. But since N-demethylation of tertiary amines is an unusual reaction for FMO, a possibility of another thermolabile enzyme catalyzing N-demethylation of TMA cannot be excluded entirely.

Mirvish et al. reinvestigated in 1970 the dimethylamine nitrosation, with the aid of tritiated dimethylamine labeled in the methyl groups, and they give estimates of DMN formation in the stomach and during food storage. Since nitrosation occurs most readily under acidic conditions, DMN and other nitrosamines could also be produced in the gastric contents during digestion. At pH 3.4, the rate of dimethylnitrosamine (DMN) formation was proportional to the dimethylamine concentration and to the square of nitrite concentration and the rate of reaction was maximal. The rate constants were used to estimate the amount of DMN expected to be formed in the gastric contents after ingestion of food containing various concentrations of dimethylamine and nitrite and during storage of such food. If the amine and nitrite concentrations are raised while remaining equal to each other, DMN formation should increase with the cube of reactant concentration.

For example; it was estimated that, if a man ate a 300-g meal containing 12 mg dimethylamine hydrochloride and 60 mg sodium nitrite, not more than about 3 µg DMN might be expected to be formed intragastrically. This dose ingested daily may be too low to be significantly carcinogenic, though it should be stressed that even tiny incidences may assume importance in a large population.

In conclusion, it should be possible theoretically to induce liver tumors in rats by feeding high doses of dimethylamine and nitrite, despite the negative results obtained by earlier workers. Nitrosamine formation should be suspected particularly in foods stored under mildly acidic conditions. The formation of nitrosamines other than DMN could be a more serious problem than that of DMN itself, since the rate of nitrosation increases 1000-fold as the basicity of the amine decreases on proceeding from dimethylamine to aromatic amines such as N-methylaniline.

Discussion on absorption rate:

In the study performed by Fluhr et al, 2005, it was shown that biogenic amines cause disruption of the permeability barrier. However, the application of each of the three biogenic amines did not reveal a significant irritation or increase in SC pH. Sequential application of SLS further enhanced the barrier disruption induced by the biogenic amines. The only exception was the irritation parameter Chroma a*, where no significant increase of redness could be observed. The TMA/SLS irritation and barrier disruption was slightly more prominent than those induced by AM/SLS and DMA/SLS, which can be explained by the higher concentration (1.5 vs. 1.0%). Since these results are detectable in all analyzed parameters, we assume that the described features may be consistent properties of biogenic amines. They assume that the mechanism by which the biogenic amines induce a barrier disruption and inflammatory reaction are different from that of SLS. The contact with both classes of irritants however did not show over additive effects.