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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1986
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to test guidelines and in accordance with GLP
Cross-reference
Reason / purpose:
reference to same study

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1986
Report Date:
1986
Reference Type:
publication
Title:
Unnamed

Materials and methods

Objective of study:
toxicokinetics
Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Deviations:
yes
Remarks:
only 1 dose level examined
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Uniformly 14C-labeled DIPA with a specific activity of 75 uCi/mg was purchased from Amersham (Arlington Heights, IL). The radiotracer had a chemical purity of greater than 99.5% when measured by liquid chromatography. Unlabeled DIPA was reported with a purity >99% as obtained from the Michigan Division of The Dow Chemical Company, Midland, MI.
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
female
Details on test animals and environmental conditions:
Female CDF Fischer 344 rats were purchased from Charles River Breeding Laboratories, Kingston, NY, and weighed between 148 and 162 g when used. The rat is the preferred species for pharmacokinetic studies, and this strain was selected because it is available from a reliable commercial source. Female rats were used because Bronauah et al (1983) found their skin to be more permeable to polar chemicals than the skin of male rats.

Upon arrival at the laboratory, these animals were examined by a veterinarian and judged to be in good general health. The animals were given at least 7 days to acclimate to the laboratory prior to being placed on study, and were uniquely identified with numbered metal ear tags. While being acclimated to the laboratory, the rats were housed in pairs in stainless steel cages with wire-mesh floors. Deotized cage board was placed under the cages to minimize odor and aid in maintaining a clean environment. The cages were washed and the cage board changed in accordance with good laboratory practices. Throughout both the acclimation period and study, the animals were housed in rooms designed to control temperature (22 +/- 2°C) and relative humidity (40 to 60%), and to provide a 12 hour photoperiod and about 12 air changes per hour. Food (Purina Certified Rodent Chow #5002, Ralston Purina Co., St. Louis, MO) and municipal water were available ad libitum.

Three days prior to being dosed, the rats were transferred to all glass metabolism cages designed for the separate collection of urine, feces, and expired volatiles . Two days prior to being dosed, they were anesthetized with methoxyflurane and an indwelling cannula implanted in the right jugular vein using a modification of the procedure described by Harms and Ojeda (1974). Six animals were cannulated for both the intravenous (iv) and dermal segments of this study to insure that there would be at least 4 rats with patent cannulae when each dose was administered. Following surgery, these rats were returned to the metabolism cages for the final 36 hours of the acclimation period.

Administration / exposure

Route of administration:
other: intravenous or dermal
Vehicle:
other: intravenous dose vehicle was water; dermal dose vehicle was acetone
Details on exposure:
The iv dose solution was prepared by dissolving a weighed amount of unlabeled DIPA in distilled water and adjusting the pH to 7.3 with 12 N HCl. Sufficient 14C-DIPA was then added to produce a specific activity of 1.54 pCi/mg of DIPA. This solution was administered via the jugular cannula at a rate of 1 ml/kg of body weight and flushed into the rat with 0.5 ml of normal saline. Administration of these volumes resulted in each rat receiving about 5 pCi of radioactivity and a dose of 19.0 mg/kg of body weight. The dermal dose solution was prepared by dissolving sufficient unlabeled and 14C-labeled DIPA in acetone to provide a solution containing 18.9 mg DIPA/ml with a specific activity of 6.32 uCi/mg of DIPA. This dose solution was applied at a rate of 1 ml/kg to a shaved 1 cm2 area on the back (intrascapular region) of the rat with a Hamilton@ syringe. To apply this volume it was necessary to allow the acetone to evaporate and treat the same 1 cm2 of skin several times. A template cut from a Teflon sheet was used to define the 1 cm2 area to which the dose was applied. After the entire dose was applied this template was removed and analyzed for radioactivity. A 4 cm2 piece of Teflon was then used to cover the dose site and was fixed in place with adhesive tape. To further restrict access to the dose site the rats were placed in lycra-Spandex jackets for the duration of the study (i.e., 48 hr). Administration of these volumes resulted in each rat receiving about 19 uCi of radioactivity and a dermal dose of 19.5 mg/kg of body weight.
Duration and frequency of treatment / exposure:
single iv administration
dermal administration was 48 hours
Doses / concentrations
Remarks:
Doses / Concentrations:
19 mg/kg for iv administration
19.5 mg/kg for dermal administration
No. of animals per sex per dose:
Four
Control animals:
no
Positive control:
no data
Details on study design:
see details on exposure
Details on dosing and sampling:
Sample Collection and Analysis.
Blood specimens, of about 0.2 ml each, were collected via the jugular cannuala 10, 20, and 40 min, and 1, 2, 4, 6, 12, 18, and 24 hours following the iv dose, and at 0.5, 1, 2, 4, 6, 12, 24, 36, and 48 hr following the dermal dose. The blood specimens were collected in heparinized capillary tubes and spun to separate the plasma from the red blood cells (RBC). Urine was collected in traps immersed in dry ice. The urine traps were changed at 6, 12, 24, 36 (dermal dose only), and 48 hours post-dosing. To reduce carry over between samples, the cages and urine traps were rinsed with water when the urine was collected 6 and 12 hr after the iv dose and each time urine was collected following the dermal dose. Feces were collected at 12 hr intervals. To collect volatile organics and 14C02, air was drawn through the metabolism cage at a rate of about 500 ml/min. The air exiting the cage was then passed through a trap filled with charcoal (to trap volatile organics) and a trap filled with about 170 ml of a 3:7 (v/v) mixture of monoethanolamine and propylene glycol monomethyl ether to trap expired 14C02. The charcoal and 14C02 traps were changed at 12 hr intervals. The rats were anesthetized with C02 and killed by exsanguination 48 hr post dosing. The animals given the dermal dose were skinned, and the liver, kidney, and a sample of perirenal fat collected for analysis. Weighed aliquots of the plasma, urine, cage rinse, and 14C02 traps were mixed with ACS liquid scintillation fluid (Amersham, Arlington Heights, IL) and analyzed for radioactivity. The charcoal traps were divided into 10 fractions prior to being mixed with ACS liquid scintillation fluid and analyzed for radioactivity. Aqueous homogenates were prepared of the feces, carcass, liver, and kidneys from the dermally dosed rats. Weighed aliquots of these homogenates, and of the perirenal fat, skin (2 sites), and RBC samples from the dermally dosed rats were oxidized in a Biological Materials Oxidizer (R. J. Harvey Corp., Hillsdale, NJ). The 14C02 released on combustion of these samples was trapped in monoethanolamine and quantified in a liquid scintillation spectrometer. Radioactivity was quantified with either a LS9000 (Peckman Instrument Corporation, Irvine, CA) or a Mark 11 (Searle Analytical, Inc., Elk Grove Village, IL ) liquid scintillation counter. Counts per min were corrected for background and quench and converted to ug equivalents using the specific activity of 14C-DIPA in the dosing solution. The radiotracer, dose solutions, and selected urine specimens were analyzed by LC. The plasma did not contain sufficient radioactivity to justify LC analysis. The LC system consisted of a Water Associates Rodel M6000A pump, a Rheodyne Model 7125 injector, an Altex Model 156 refractive index detector (RI) and a Packard Model A7130 radioactivity monitor (RAM). The two detectors were connected in series with the RI detector immediately following the LC column. Two LC colurnn/eluent combinations were used. The radiotracer, dose solutions, and urine and plasma specimens from the iv segment were analyzed using a 5 mm (id) x 250 mm Partisil PXS 10125 SLX column (Whatman, Inc.) and a mobile phase of 70:30 (v/v) water/acetonitrile containing 0.005 M ammonium acetate and adjusted to a pH of 4.5 with acetic acid. The flow was maintained at 1 ml/min and the retention time measured at the RI detector was 13.8 min for MIPA and 15.2 min for DIPA. The high ionic strength of the urine specimens caused a reduction in the retention times which varied with the injection volume. To eliminate this problem, urines from the dermal dose segment were chromatographed using a 4.6 mm (id) x 300 mm Chromegabonds RP-SCX (10 um particles) column (E.S. Industries) and a mobile phase of 90: 10 (v/v) water:acetonitrile containing 0.05 M ammonium acetate and having a pH of 6.7. The flow was maintained at 1 ml/min and the retention times measured at the RI detector were 18.3 and 24.0 min for MIPA and DIPA, respectively. For all samples, a 4 mm ( i d ) x 26 mm precolumn packed with pellicular cation exchanger (Whatman, Inc.) was used to prolong column life. The urine samples were filtered through a 25 mm diameter, 0.45 um pore size nylon membrane syringe filter (MSI, Inc.) prior to being injected into the LC system (recovery of 14C from this filtration was 105 + 3.9%). The plasma was injected into the LC system without any sample cleanup. Recovery of radioactivity averaged 96.7% (SD = 6.3) for the Whatman Partisil column and 94.1% (SD +/- 4.4) for the E.S. Industries Chromegabond column.
Statistics:
Mean plasma concentrations and urinary excretion rates (i.e., mg DIPA in urine specimen/collection interval in hr) observed following intravenous and dermal administration of 14C-DIPA simultaneously to a two compartment open pharmacokinetic model in which the absorption, elimination and transfer between the rapid and slow exchange compartments were assumed to be first order processes. The differential equations which define this model are given below:

dAO/dt = -AO * Ka
dA1/dt = AO * ka - A1 *( ke + k12) + A2 * k21
dA2/dt = A1 * k12 -A2 * k21
dA3/dt = A1 * ke
A, Al, A2, and A3 represent the amounts of 14C-DIPA on the skin, in the rapid and slow exchange compartments, and excreted in the urine, respect
ively. ka and ke represent first order rate constants describing the dermal absorption and urinary excretion o f 14C-DIPA, and k12 and, k21 are first-order rate constants describing the transfer between the rapid and slow exchange compartments. Concentrations of 14C-DIPA in the plasma (Cp), the renal clearance of I4C-DIPA (Clr), and the dispositional rate constants a and B were calculated as follows:

Cp = A1/(V1)
Clr = k * V1 * BWT * 60 min/hr
a,B = 0.5 * ((k12 + k21 +ke) +/-((k12 +k21 +k2)2 -4 * k21 *ke)1/2
VI represents the apparent volume of the rapid exchange compartment, and BWT the average body weight of the rats. Optimum estimates for the
model parameters were obtained using DACSL (Agin and Blau, 1982).

Results and discussion

Preliminary studies:
Intravenous Dose
During the first 12 hr after iv administration, the concentration of radioactivity in the plasma decreased rapidly in a biexponential manner that was well described by a two compartment pharmacokinetic model. The half-life for the rapid initial a phase was 0.7 hr and that of the slower terminal B phase was 6.3 hr. Concentrations of radioactivity in the plasma specimens collected more than 12-hr post-dosing were at or below the limit of quantitation (i.e., 0.5 to 1.5 times background), and were not used when the model parameters were estimated. An average of 96.8% (range 93.2 to 102.8%) of the intravenously administered radioactivity was excreted in the urine.

Most (71.3%) of the dose was eliminated during the first 6 hr and by 12 hr 93.1% of the dose had been excreted in the urine. Analysis of the urine by LC indicated that over 99% of the radioactivity in the urine was unchanged 14C-DIPA.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
An average of 69.2% (SD = 17.0%) of the dermal dose was recovered. Most of the administered radioactivity was recovered from the bandage (25.7%) and the skin (27.3%). The low recovery from one of the four dermally dosed rats (i.e., 47.8% for rat 85A-9094) was due to the small amount of radioactivity recovered from its Teflon patch; 7.6% of the dose was recovered from this rat's patch versus 26-32% from the patch from each of the other animals. Of the radioactivity recovered from the skin, most (87%) was at or adjacent to the site where the dose was applied.

Following the dermal dose, the highest concentration of radioactivity in the plasma (1.1 ug/g) was observed 0.5 hr after the dose was applied to the skin. The pharmacokinetic model as developed could not predict the spike in plasma 14C-concentrations observed 0.5 hr postdosing, and underpredicted the concentration of radioactivity in the plasma 24, 36, and 48 hr post-dosing. Concentrations of radioactivity in the red blood cells were similar to those found in the plasma
Details on distribution in tissues:
1.4% of the dose was found in the liver, kidneys and carcass.
Details on excretion:
14.8% was found in the excreta.

Consistent with the intravenous data, urine was the only major route for the excretion of 14C-DIPA. Based on the urinary excretion of 14C-DIPA between 6 and 48 hr post-dosing, little radioactivity appeared to have been eliminated during the first 3 to 4 hr after the dermal dose was administered. After this 3 to 4-hr delay, radioactivity was excreted into the urine at a constant rate which was well described by the pharmacokinetic model. Analysis of the urine by LC indicated that over 99% of the radioactivity in the urine was unchanged 14C-DIPA.
Toxicokinetic parametersopen allclose all
Test no.:
#1
Toxicokinetic parameters:
half-life 1st: 0.39 h
Test no.:
#2
Toxicokinetic parameters:
Cmax: 11 µg/ml
Test no.:
#3
Toxicokinetic parameters:
AUC: 13.52 µg h ml-1

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
There were no metabolites identified in urine samples

Any other information on results incl. tables

Following intravenous administration, 14C-DIPA was rapidly cleared from the plasma and excreted in the urine in a biexponential manner. The half-life for the rapid initial phase was 0.7 hr and that of the slower terminal phase was 6.3 hr. Within 48 hr, 96.8% if the intravenous dose was excreted unchanged in the urine. When the dermal animals were sacrificed at 48 hr post-dosing, 22.5% of the dose was found on the skin at the dose site, and another 25.7% was recovered from the bandage. In addition, 1.4% of the dose was found in the liver, kidney, and carcass, and 14.8% was found in the excreta. These data indicate that in 48 hr only 16.2% of the 14C-DIPA applied to the back of rats was absorbed and represents an absorption rate of less than 0.3% of the dose per hour. Because DIPA was slowly absorbed through the skin and rapidly eliminated via the urine, these data suggest that toxicologically significant concentrations of DIPA are unlikely to occur as a result of dermal exposure to this chemical in cosmetics.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): no bioaccumulation potential based on study results
Because DIPA was slowly absorbed through the skin and rapidly eliminated via the urine, these data suggest that toxicologically significant concentrations of DIPA are unlikely to occur as a result of dermal exposure to this chemical in cosmetics.
Executive summary:

Diisopropanolamine (DIPA) is a component of many cosmetic formulations. The purpose of this study was to obtain data on the percutaneous absorption and subsequent elimination of DIPA which could be used in support of the continued use of DIPA in cosmetics. In this study, groups of 4 female Fischer 341 rats were given a single intravenous (iv) or dermal dose o f 19 mg of 14C-labeled DIPA/kg of body weight. Following i v administration, 14C-DIPA was rapidly cleared from the plasma and excreted into the urine in a biexponential manner. The half-life for the rapid initial phase was 0.7 hr and that of the slower terminal phase was 6.3 hr. Within 48 hr, 96.8% of the iv dose was excreted unchanged in the urine. The dermal dose was applied to the back of the rat and covered with an occulsive bandage for 48 hr. When these animals were sacrificed 48 hr post-dosing, 22.5% of the dose was found on the skin at the dose site, and another 25.7% was recovered from the bandage. In addition, 1.4% of the dose was found in the liver, kidney, and carcass, and 14.8% was found in the excreta. These data indicate that in 48 hr only 16.2% of the 14C-DIPA applied t o the back of these rats was absorbed, and this represents an absorption rate of less than 0.3% of the dose per hour. Because DIPA was slowly absorbed through skin and rapidly eliminated via the urine, these data suggest that toxicologically significant concentrations of DIPA are unlikely to occur as a result of dermal exposure to this chemical in cosmetics.