p-cymene

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Data source

Reference

Reference Type:

publication

Title:

p-Cymene metabolism in rats and guinea-pigs

Author:

Walde A., Ve B., Scheline R. R. and Monge P.

Year:

2009

Bibliographic source:

Xenobiotica, 13:8, 503-512, DOI: 10.3109/00498258309052290

Materials and methods

Objective of study:

metabolism

Test guideline

Qualifier:

no guideline available

Principles of method if other than guideline:

- Principle of test:

The study on metabolic fate of p-cymene using GLC-mass spectrometric techniques employing high-resolution capillary columns for metabolite identification.

- Short description of test conditions:

Instrumental conditions
The GLC system used for quantitative measurements was that described by Klungseyr and Scheline (1981) except that the OV-1 capillary column used previously was replaced in most cases with one coated with SE-54. A Hewlett Packard model 5992A g.l.c.-mass spectrometry system, as described in the above report but with several instrumental improvements, was used for metabolite detection and identification. Improvements included the fitting of an S.G.E. on-column-injector model OCI-3 (Scientific Glass Engineering, Melbourne, Australia) and the replacement of the standard interface to the mass spectrometer with an open-split type of our own design.

Quantitative measurements
p-Toluic acid and p-methylbenzyl alcohol were used as internal standards for quantification of acidic and neutral metabolites, respectively. An exception to this procedure was made with p-isopropylbenzoylglycine (XVII) for which a correction factor was derived (Klungseyr and Scheline 1981, Sporstel and Scheline 1982) to compensate for differences in extraction characteristics and g.l.c. response between it and the internal standard.

- Parameters analysed / observed: metabolites extracted from urine

Urine Sample preparation:

Urine samples were treated according to methods similar to those described by Klungseyr and Scheline (1981). Following hydrolysis by a glucuronidase + sulphatase preparation and ether extraction, fractionation was carried out to give ‘acidic’ and ‘neutral’ fractions. The former were dissolved in ethyl acetate and converted to their methyl esters with diazomethane. Following evaporation of the ethyl acetate the samples were dissolved in dichloromethane. Neutral components consisting of alcohols and phenols
were converted to their trimethylsilyl (TMS) derivatives and these, following removal of excess reagent, were dissolved in hexane.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

p-cymene

EC Number:

202-796-7

EC Name:

p-cymene

Cas Number:

99-87-6

Molecular formula:

C10H14

IUPAC Name:

1-isopropyl-4-methylbenzene

Radiolabelling:

no

Test animals

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Dunkin Hartley strain, Olac 1976 Ltd.
- Weight at study initiation: 300-350 g
- Diet: switched from standard pellet diets to a purified diet two days before dosing (Klungseyr and Scheline 1981).

Administration / exposure

Route of administration:

other: oral and inhalation

Vehicle:

propylene glycol

Remarks:

1 ml

Details on exposure:

Exposure: intragastric administration of p-cymene by stomach tube or given by inhalation as described by Walde and Scheline (1983)

Duration and frequency of treatment / exposure:

48 hrs

Doses / concentrations

Dose / conc.:

100 mg/kg bw/day

No. of animals per sex per dose / concentration:

3 animals

Control animals:

not specified

Details on study design:

- Dose selection rationale: not specified

Details on dosing and sampling:

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: 48 hours
- From how many animals: (samples pooled or not) not speciifed
- Method type(s) for identification - GLC

Results and discussion

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

The following metabolites have been identified:

Any other information on results incl. tables

Table 1. Urinary metabolites of p-cymene in guinea pigs (n=3)
Metabolite	intragastric	Inhalation
2-p-Tolylpropan-2-ol	14 (12.7-17. 5)	3 (2 .4, 3 .5)
2-Hydroxy-4-isopropyl-1-methylbenzene (Carvacrol)	tr	tr
2-p-Tolylpropan-1-ol	8 (7.7-8.1)	9 (8.1,9.6)
p-lsopropylbenzyl alcohol (Cuminyl alcohol)	6 (3.7-8.8)	tr
2-p-Tolylpropan-1,2-diol	7 (5.3-9.0)	2 (1.2, 2.0)
(Hydroxycarvacrol)	1 (O.6-1.5)	tr
2-p-Tolylpropan-1,3-diol	tr	tr
2-p-(Hydroxymethyl)phenylpropan-2-ol	tr	tr
2-p-(Hydroxymethyl)phenylpropan-1-ol	tr	tr
2-p-Tolylpropionicacid	4 (4.1-4.8)	15 (10.6, 18.3)
p-Isopropylbenzoic acid (Cumic acid, cuminic acid)	tr	tr
p-lsopropenylbenzoic acid	-	-
2-p-Carboxyphenylpropionic acid	tr	tr
2-p-Carboxyphenylpropan-2-ol	tr	tr
2-p (Hydroxymethyl)phenylpropionic acid	tr	tr
2-p-Carboxyphenylpropan-1-ol	tr	tr
p- lsopropylbenzoylglycine (p-lsopropylhippuric acid, cuminuric acid)	31 (2 5.0-40 5)	31(24.9 -37.8)
p-lsopropenylbenzoylglycine	tr	tr
Total	71	60

Values are given % dose (with range or individual values in parentheses) for a 48-h period.

tr  - trace absent.

Applicant's summary and conclusion

Conclusions:

The following metabolites have been identified: 2-p-tolylpropan-2-ol (14% and 3% of the dose after oral and inhalation exposure, respectively), 2-p-tolylpropan-1-ol (8% and 9% after oral and inhalation exposure, respectively), cuminyl alcohol (6% after oral exposure, traces - inhalation ), 2-p-tolylpropan-1,2-diol (7% and 2% after oral and inhalation exposure, respectively), Hydroxycarvacrol (1% after oral administration), 2-p-tolylpropan-1,3-diol (traces after oral and inhalation exposure), 2-p-(hydroxymethyl)phenylpropan-2-ol (traces after oral and inhalation exposure), 2-p(hydroxymethyl)phenylpropan-1-ol (traces after oral and inhalation exposure), 2-p-tolylpropionic acid (4% and 15% after oral and inhalation exposure, respectively), cumic acid (traces after oral and inhalation exposure), p-isopropenylbenzoic acid (not detected), 2-p carboxylphenylpropionic acid (traces after oral and inhalation exposure), 2-p-carboxyphenylpropan-2-ol (traces after oral and inhalation exposure), 2-p(hydroxymethyl)phenylpropionic acid (traces after oral and inhalation exposure), 2-p-carboxyphenylpropan-1-ol (traces after oral and inhalation exposure), p-isopropylbenzoylglycine (31% after oral and inhalation exposure ) and p-isopropenylbenzoylglycine (traces after oral and inhalation exposure).

Executive summary:

In the study of Walde (1983), urinary metabolites were identified using GLC. method after a single oral and inhalation dose (100 mg/kg) of p-cymene dissolved in propylene glycol to male guinea-pigs, Dunkin Hartley strain, Olac 1976 Ltd.

Urine was collected after 48 hrs. The total recovery (tr) values indicate that the identified urinary metabolites account for 71 -60% of the administered p-cymene after intragastric and inhalation exposure, respectively. The remaining material probably consists of metabolites excreted in the faeces and unextractable urinary material.

The following metabolites have been identified: 2-p-tolylpropan-2-ol (14% and 3% of the dose after oral and inhalation exposure, respectively), 2-p-tolylpropan-1-ol (8% and 9% after oral and inhalation exposure, respectively), cuminyl alcohol (6% after oral exposure, traces - inhalation ), 2-p-tolylpropan-1,2-diol (7% and 2% after oral and inhalation exposure, respectively),Hydroxycarvacrol(1% after oral administration), 2-p-tolylpropan-1,3-diol (traces after oral and inhalation exposure), 2-p-(hydroxymethyl)phenylpropan-2-ol (traces after oral and inhalation exposure), 2-p(hydroxymethyl)phenylpropan-1-ol (traces after oral and inhalation exposure), 2-p-tolylpropionic acid (4% and 15% after oral and inhalation exposure, respectively), cumic acid (traces after oral and inhalation exposure), p-isopropenylbenzoic acid (not detected), 2-p carboxylphenylpropionic acid (traces after oral and inhalation exposure), 2-p-carboxyphenylpropan-2-ol (traces after oral and inhalation exposure), 2-p(hydroxymethyl)phenylpropionic acid (traces after oral and inhalation exposure), 2-p-carboxyphenylpropan-1-ol (traces after oral and inhalation exposure), p-isopropylbenzoylglycine (31% after oral and inhalation exposure ) and p-isopropenylbenzoylglycine (traces after oral and inhalation exposure).

The   formation of phenolic metabolites from p-cymene was previously claimed not to occur. The sensitive and   far more specific methods used   in the present investigation guinea-pigs are able to carry out the ring-hydroxylation. The results shown in table 3  indicate that small amounts of carvacrol and  a hydroxycarvacrol are formed  in  this  species.  Ring-hydroxylation occurs only at the site adjacent to the methyl group, i.e.  thymol formation was not detected.

The metabolism of p-cymene has long been regarded to proceed preferentially via oxidation of the methyl group to give cumic acid (p-isopropylbenzoic  acid) which may then be conjugated with glycine, forming cuminuric acid  (p-isopropylhippuric acid).  

The results of this study showed that all three of the possible monohydric alcohols (one from methyl group oxidation, two from isopropyl group oxidation) as well as several monohydroxylated carboxylic acids and a dicarboxylic acid derivative were excreted by rats dosed with p-cymene. Thus, the metabolism of p-cymene have revealed that the metabolic picture is more complex than previously reported and especially that the isopropyl group is a site of considerable metabolic activity.