Isopropyl acetate

Endpoint summary

Additional information

Male SD rats with jugular vein-implanted cannulas exteriorized through a gas uptake inhalation chamber, were individually exposed for 2 hr to a targeted initial concentration of 2000 ppm of isopropyl acetate while simultaneously monitoring respiratory rates with a body-only plethysmograph (head-only exposures). Blood samples were collected during each exposure for analysis of each parent chemical and its alcohol or acid metabolites. The tidal volume of respiration decreased at the start of each exposure then increased above the baseline rate before falling back towards the control value as the vapor was absorbed (although there was an unexplained increase again right at the end of the exposure. Similarly, the respiration rate initially fell before recovering to equilibrate at 84% of the baseline rate. Plethysmography in control rats not exposed to any chemical showed a similar increase in tidal and minute volumes over the 2 hr in the chamber. Decreases in chamber concentrations of isopropyl acetate was considerable over the 2 hr, indicating rapid respiratory absorption of this water-soluble chemical. Average isopropyl acetate concentrations dropped to 229 ppm at 2.06 hr. This compared to average isopropyl acetate concentrations in the control chamber (with dead rat) of 883 ppm at 1.93 hr. Blood levels of isopropyl acetate and its isopropanol metabolites indicated a rapid conversion of the former to the latter. In animals exposed to isopropyl acetate, blood levels of isopropyl acetate increased up to 54 μM at 10 minutes into the exposure, and declined over the remaining 80 minutes. Isopropyl alcohol blood levels increased up to 268 μM at 50 minutes, after which they declined to 245 μM at 90 minutes. Isopropyl alcohol blood levels exceeded isopropyl acetate blood levels at 5 minutes into the exposure, and at every time point thereafter.

An in vivo hydrolysis study was carried out in rats to determine the rate of hydrolysis of isopropyl acetate to isopropanol. Groups of four male rats were dosed iv with isopropyl acetate in physiological saline in two dose groups of 5 and 50mg/kgbw. Blood was sampled from the tail over a period of 60 minutes for analysis of isopropyl acetate, with sampling biased towards the initial part of the study period. The half life was determined to be in the range 2 -3 minutes with no difference between the two dose groups.

Another study reported the fate of isopropyl acetate following oral administration to rabbits at a dose of 1mL/kg. Stomach contents, urine and blood were analysed for a number of esters and parent alcohol including isopropyl acetate. Animals showed signs of drunkennes following exposure. The esters could not be detected in blood or urine although the parent alcohols were detected.  In the case of isopropyl acetate for up to 5 hours after dosing and longer in the urine.  There was evidence of acidosis, which would fit with the hydroysis of the ester.  The pH value of the blood at the start was 7.37 dropping to 7.06 after 30 mins before slowly recovering to 7.25 after 4 hours.  There was a consistent pattern with the other esters in that ethyl acetate caused a slightly more severe drop in pH and they butyl and amyl acetates a less severe drop, as would be expected following dosing based on weight rather than molecular weight.  The pH recovery of these other substances was similar too.  This was reflected too in changes to the CO2 and O2 partial pressures, which mirrored the changes to pH as would be expected following acidosis. The authors concluded that esters are metabolised to their parent alcohols when passing through the gastric mucosa.

Studies are also available on the closely related substance ethyl acetate. The rate of hydrolysis of ethyl acetate in male rats in vivo and in vitro has been studied. Ethyl acetate was rapidly hydrolyzed to ethanol following intravenous injection in rats, with an in vivo elimination half-life in blood of 33-37 seconds. Carboxyesterase capacity was not saturated at 100 mg/kg. There was no evidence that ethyl acetate or metabolites were preferentially sequestered in brain, based on total [14C] levels. The rapid in vivo hydrolysis of ethyl acetate to ethanol supports the use of systemic toxicity data on the alcohol in evaluating the potential effects of ester exposure.

Another study reported the rapid metabolism of ethyl acetate to ethanol in rats following intraperitoneal injection or inhalation exposure. Inhalation exposures at concentrations greater than 2000 ppm (approx. 7.32 mg/L) were required to show any accumulation of ethanol in the blood and levels of 10,000 ppm (approx. 36.6 mg/L) provided blood ethyl acetate levels of less than 10 mg/L, and blood ethanol levels of the order 150 mg/L. There is evidence in this study that ethyl acetate undergoes hydrolysis very rapidly in vivo and that esterases are not saturated at levels as high as 10,000 ppm (approx. 36.6 mg/L). Indeed, ester hydrolysis of ethyl acetate proceeds more rapidly than ethanol metabolism. At exposure below 2000 ppm (approx. 7.32 mg/L), ethanol metabolism removes the ethanol produced by ethyl acetate hydrolysis. The same authors performed an in vitro study using rat blood; in this experiment, a half-life of 65-70 min was determined following incubation of 0.2 g ethyl acetate/100 ml blood for 5h at 37^oC. This is significantly slower that results in vivo where the estimated hydrolysis of ethyl acetate in vivo was much faster (t_1/2= 5 min), suggesting that blood enzymes are not solely responsible for this reaction.

Metabolism of inspired ethyl acetate in the upper respiratory tract (URT) of rats has been studied. Deposition efficiencies averaged between 10 and 35% in the rat URT. 40 -65% of the deposited ethyl acetate was metabolized in the URT of the rat. This first-pass metabolism increased URT deposition efficiencies, led to high metabolite levels in URT tissues, and decreased the amount of parent ethyl acetate available for absorption into the bloodstream. Metabolic parameters were as follows: Rat: Maximum velocity (Vmax) of hydrolization = 470 +/- 57 ug/min; Michaelis-Menten constant (Km) = 722 ug/ml.

A PBPK model for predicting the localised concentration of the metabolites of ethyl acetate in the olefactory tissues in rats and mice concluded that an interspecies factor of 0.33 would be appropriate if the critical mode of action is due to acetaldehyde tissue concentrations and <0.15 if the critical metabolite is acetic acid.

The hydrolysis rates of several acetic acid esters were determined in vitro using S-9 homogenate preparations from various tissues. For each assay 50 µL of a 0.5M solution of ester in ethanol were incubated at 37°C for 30 min with 2 - 5 mL S-9 homogenate in 0.01M tris buffer at pH 7.4 containing 0.7 to 2.5 mg protein. The amount of acetic acid/acetate resulting from hydrolysis was analyzed by ion chromatography. The hydrolysis rate of iso-butyl acetate in rat ethmoturbinate S-9 homogenate was determined to be 67 ± 2.03 nmol/mg S-9 protein /min (n = 3 to 5). Hydrolysis rates for other tissues are not reported. For n-butyl acetate a slightly higher hydrolysis rate of 77 ± 2.13 nmol/mg S-9 protein/min was evaluated. As demonstrated with pentyl acetate and phenyl acetate, liver S-9 homogenate had the highest catalytic activity of all rat tissues tested (nasal, trachea, lung tissues). For linear alkyl acetates (C1 to C6 and C8), hydrolysis rates with rat ethmoturbinate preparations increased with chain length up to a maximum for pentyl acetate (94 nmol/mg S-9 protein/min). Longer chain acetates (hexyl and octyl) showed again decreasing hydrolysis rates.

The rate of hydrolysis of n-butyl acetate(nBA) in male rats in vivo at the highest intravenous dose level possible was investigated.^[14C]n-Butyl acetate was administered via a tail vein to 32 male Sprague Dawley rats at a mean of 30.2 mg/kg bodyweight (16.8 µCi/rat). Liquid scintillation analysis of the whole blood and brain tissue for total radioactivity following this dose revealed rapid systemic distribution of the dose and very rapid elimination from both whole blood and brain tissue. High performance liquid chromatography with radiochemical detection was used to separate and quantitate n-butyl acetate, its hydrolysis product n-butanol, and products of the subsequent oxidative and conjugative metabolism of n-butanol. These analyses indicated that n-butyl acetate was very rapidly eliminated from the blood (biphasic elimination; elimination t1/2 = 0.41 min), and was detected in brain tissue only at low concentrations (mean maximum of 3.8 µg equivalents/g at 1.9 min) in the first 2.5 min following dosing. n-butanol was found at higher concentrations in both blood (C_max= 52 µg equivalents/g at T_max2.6 min) and brain (C_max= 79 µg equivalents/g at T_max2.5 min), but this was also rapidly eliminated in both tissues (biphasic elimination; t1/2, of 1.0 - 1.2 min) and was undetectable beyond 20 min post dosing. n-Butyric acid was present at low concentrations in blood (mean maximum of 5.7 µg equivalents/g at 7.4 min) and declined slowly following dosing; it was largely undetected in brain tissue. Early eluting, polar metabolites, presumably Krebs cycle intermediates of [14C]n-butanol and glucuronide and sulfate conjugates of [14C]n-butanol, were detected in the whole blood (mean maximum of 12.2 µg equivalents/g at 4.2 min), but were seen only in trace amounts in brain tissue. The hydrolysis of n-butyl acetate in blood and brain is estimated to be 99% complete by 2.7 min at this dose level.