The role of toxicokinetics in xylene-induced ototoxicity in the rat and guinea pig.

In the rat, some aromatic solvents cause a high level of ototoxicity that is characterized by damage to outer hair cells in the cochlea, which results in irreversible hearing loss. However, there is a vast difference in their potency. Among the three isomers of xylene, only para-xylene has been shown to be ototoxic in the rat. Moreover, all the species do not show the same susceptibility to ototoxic solvents, the rat being the most susceptible and the guinea pig seeming resistant to this ototoxic effect. The objective of the study was to determine whether toxicokinetic factors could explain the differences in ototoxicity observed among the three isomers of xylene in the rat and the species-dependent ototoxicity in the rat and the guinea pig. Blood and brain concentrations of each isomer were monitored in Sprague-Dawley rats treated orally by gastric intubation with a single dose or a 10 day-repeated treatment of 8.47 mmol/kg (an ototoxic dosage for para-xylene) of each isomer. Moreover, histology of the cochlea was carried out and the toxicokinetics of meta-xylene was monitored in rats treated with a single dose or a 10 day-repeated treatment of 16.94 mmol/kg meta-xylene, a non-ototoxic isomer. Similarly, histology of the cochlea was carried out and the toxicokinetics of para-xylene was followed in guinea pigs treated by gavage with a single dose or a 10 day-repeated treatment of 8.47 mmol/kg para-xylene. Finally, the blood and brain concentrations of para-xylene were measured in both the rats and the guinea pigs after a 4-h exposure to 1800 ppm of para-xylene. Among the three isomers studied, para-xylene yielded the highest blood and brain concentrations in the acutely and repeatedly exposed rats. When given a high dosage of meta-xylene (16.94 mmol/kg), the rats showed blood and brain concentrations of meta-xylene in the same order as those obtained with 8.47 mmol/kg para-xylene, but no outer hair cell loss was observed. No outer hair cell loss was observed in the guinea pigs treated with para-xylene. Whatever the exposure pattern, the blood and brain concentrations of para-xylene in the rats were 3.1-9.5 times higher than those measured in the guinea pigs. These results indicate that toxicokinetic factors cannot explain the differences in ototoxicity observed with the three isomers in the rat. However, they suggest that the differences in susceptibility to para-xylene observed between the rats and the guinea pigs might be due to toxicokinetic factors.

Ototoxicity in rats exposed to ortho-, meta- and para-xylene vapours for 13 weeks.

Male Sprague-Dawley rats were exposed to ortho-, meta- or para-xylene by inhalation (450, 900 and 1,800 p.p.m., 6 hr/day, 6 days/week for 13 weeks) and sacrificed for morphological investigations 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Among the three isomers studied, only para-xylene produced moderate to severe ototoxicity in rats exposed at 900 and 1,800 p.p.m. Increased auditory thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 1800 p.p.m. para-xylene. The auditory threshold shifts (35 to 38 dB) did not reverse after 8 weeks of recovery Moderate and severe losses of outer hair cells of the organ of Corti occurred in animals exposed to 900 and 1800 p.p.m. para-xylene respectively. Thus, the no observed effect level of para-xylene was 450 p.p.m. based on the loss of outer hair cells observed by light and electron microscopy.

The ototoxic effects induced in rats by treatment for 12 weeks with 2-butenenitrile, 3-butenenitrile and cis-2-pentenenitrile.

Brainstem auditory and visual evoked-potentials were studied in male Sprague-Dawley rats during subchronic oral treatment with three unsaturated aliphatic nitriles. The rats were given, by gastric intubation, doses of 10, 20 and 40 mg x kg(-1) 3-butenenitrile (allyl cyanide) and 25, 50 and 100 mg x kg(-1) of either cis/trans-2-butenenitrile (crotononitrile) or cis-2-pentenenitrile once a day, 5 days per week for 12 weeks. Oral administration of the three unsaturated nitriles produced deafness and absence of reaction when the animals were subject to droptest. Rats in the high dosage groups exhibited a complete disappearance of the five waves of the auditory evoked-potentials. There was a decrease in the amplitudes of the 2nd component of the auditory evoked-potentials. Those changes were not reversible at the 8th week of the recovery period. A dose-dependent effect on inner and outer hair cells was observed in the organ of Corti. The basal part of the cochlea was the most affected. Though no measurements were made of systemic exposure, a tentative ranking of decreasing ototoxicity of these three unsaturated nitriles might be proposed based on the electrophysiological deficiencies and histological losses observed: 3-butenenitrile >cis-2-pentenenitrile >cis/trans-2-butenenitrile. Moreover, rats treated with those nitriles showed a corneal opacity as well as a decrease in the amplitude and lengthening of the peak latencies of the visual evoked-potentials. These latter changes were reversible by the end of the 8th week of the recovery period and appeared to be related to the opacity of the cornea.

Electrophysiological deficiency in peripheral nerve induced by treatment for 12 weeks with 2-butenenitrile, 3-butenenitrile, cis-2-pentenenitrile and 3,3-iminodipropionitrile in rats.

Motor and sensory conduction velocities and amplitudes of the sensory and motor action potentials of the tail nerve were studied in male Sprague-Dawley rats during subchronic oral treatment with three unsaturated aliphatic nitriles. The rats were given, by gastric intubation, doses of 10, 20 and 40 mg x kg(-1) 3-butenenitrile (allyl cyanide) and 25, 50 and 100 mg x kg(-1) of either cis/trans-2-butenenitrile (crotononitrile) or cis-2-pentenenitrile once a day, 5 days per week for 12 weeks. Moreover, 3,3'-iminodipropionitrile was administered likewise at doses of 25, 50 and 100 mg x kg(-1) as reference neurotoxicant. Oral administration of the three unsaturated nitriles produced deafness and absence of reaction when the animals were subject to droptest. Moreover, rats exhibited both time- and concentration-dependent decreases in motor and sensory conduction velocities and amplitudes of the sensory action potentials. Nerve conduction velocities were partially reversible after 8 weeks of recovery. Rats receiving 3,3'-iminodipropionitrile developed deafness, head weaving and significant irreversive deficiencies in all the electrophysiological parameters studied. Further toxicological studies with related unsaturated nitriles should be carried out to determine the potential importance of the cis/trans isomerism in the observed neurotoxicity.

Relative neurotoxicological properties of five unsaturated aliphatic nitriles in rats.

Motor and sensory conduction velocities (MCV and SCV) and amplitudes of the sensory and motor action potentials (ASAP and AMAP) of the tail nerve were studied in male Sprague-Dawley rats during chronic oral treatment with five unsaturated aliphatic nitriles. Rats were given doses of 12.5, 25 and 50 mg kg(-1) of acrylonitrile, 50, 70 and 90 mg kg(-1) of methacrylonitrile, 25, 50 and 100 mg kg(-1) of trans-3-pentenenitrile and 50, 100 and 200 mg kg(-1) of either 3-methyl-2-butenenitrile or 4-pentenenitrile once a day, 5 days per week for 12 weeks. Moreover, due the the early results obtained after oral treatment, neurophysiological examinations were also carried out in rats exposed by inhalation to 25, 50 and 100 ppm of acrylonitrile for 6 h a day, 5 days per week for 24 weeks. Rats given acrylonitrile orally developed behavioural sensitization characterized by salivation, locomotor hyperactivity and moderately intense stereotypies. Moreover, rats in the high dose group developed weakness in hindlimbs associated with decreases in SCV and ASAP. Rats exposed to acrylonitrile vapours exhibited time- and concentration-dependent decreases in MCV, SCV and ASAP, which were partially reversible after 8 weeks of recovery. None of the other four nitriles caused any abnormal behaviour or any changes in the electrophysiological parameters in spite of an obvious general toxicity. Based upon these results, it can be concluded that the nervous system of the rat appears to be a target following either oral or inhalation exposures of acrylonitrile.

Triethylbenzene-induced sensorimotor neuropathy in rats.

1,2,4-Triethylbenzene (1,2,4-TEB) and 1,3,5-triethylbenzene (1,3,5-TEB) were administered orally to male Sprague-Dawley rats. Experimental and appropriate control rats were examined electrophysiologically for motor and sensory conduction velocities (MCV and SCV), and the amplitudes of the sensory (ASAP) and muscular action potentials (AMAP), at bi-weekly intervals. Oral administration of 1,2,4-TEB (200 or 400 mg kg-1, once daily, 4 days per week for 8 weeks) produced a time- and dose-dependent decrease in MCV, SCV, AMAP and ASAP. Rats treated with 1,2,4-TEB exhibited a bluish discoloration of the skin and the urine was greyish-greenish. No changes in MCV, SCV, AMAP and ASAP developed in rats given 1,3,5-TEB orally (200 or 400 mg kg-1, daily, 4 days per week for 8 weeks). The results indicate that 1,2,4-TEB is a neurotoxic isomer of TEB and that the presence of two ethyl radicals in the ortho-position on an aromatic ring could be a critical molecular arrangement resulting in chromogenic and neurotoxic properties.

Diethylbenzene inhalation-induced electrophysiological deficits in peripheral nerves and changes in brainstem auditory evoked potentials in rats.

Motor and sensory conduction velocities (MCV and SCV), amplitude of the sensory action potential (ASAP) of the tail nerve and parameters of brainstem auditory evoked potentials (BAEP) were studied in male Sprague-Dawley rats after prolonged inhalation exposure to a commercial isomer mixture of diethylbenzene (DEB mixture) containing 6% 1,2-DEB. The MCV, SCV and ASAP were studied in one control group (10 rats) and three groups of 12 rats exposed to 500, 700 or 900 ppm DEB mixture for 6 h daily, 5 days per week, for 18 weeks. Rats used for recording BAEP (one control group and two other groups of 15 rats) were exposed to 600 and 800 ppm DEB mixture. The exposure time was the same. Rats exposed to DEB mixture exhibited a time- and concentration-dependent decrease in MCV, SCV and ASAP and a time- and concentration-dependent increase of both the peak latencies of all BAEP components and the interpeak (I-V) differences.

Possible involvement of 1,2-diacetylbenzene in diethylbenzene-induced neuropathy in rats.

The role of 1,2-diacetylbenzene (1,2-DAB) in the peripheral nerve toxicity of 1,2-diethylbenzene (1,2-DEB) was investigated in rats. Gas chromatography-mass spectrometry identified 1,2-DAB in the urine samples of rats given 165 mg kg-1 1,2-DEB orally on four consecutive days. 1,2-DAB shared not only the ability of 1,2-DEB to cause bluish discoloration of skin, internal organs and urine, but unlike 1,2-DEB it turned hair blue at the site of intraperitoneal injection. Intraperitoneal administration of 10 mg kg-1 and 20 mg kg-1 1,2-DAB to groups of 12 rats, 4 days a week for 11 and 6 weeks, caused a dose- and time-dependent decrease in mean sensory and motor conduction velocities. Recovery in a 5-week post-exposure period was gradual but consistent. The effect of 1,2-DAB on the amplitude of the sensory action potential was ambiguous. The findings support the hypothesis that the formation of 1,2-diacetylbenzene derivatives contributes to the neurotoxicity of 1,2-DEB.

Diethylbenzene-induced sensorimotor neuropathy in rats.

The commercial isomer mixture of diethylbenzene (DEB mixture), 1,2-diethylbenzene (1,2-DEB), 1,3-diethylbenzene (1,3-DEB) and 1,4-diethylbenzene (1,4-DEB) were administered orally to male Sprague-Dawley rats. The experimental rats and the appropriate controls were examined electrophysiologically for motor and sensory conduction velocities (MCV and SCV), and for the amplitude of the sensory action potential (ASAP) of the tail nerve, at weekly or bi-weekly intervals. Oral administration of DEB mixture (750 or 500 mg kg-1, once daily, 5 days per week for 10 weeks) and 1,2-DEB (100 mg kg-1, once daily, 4 days per week for 8 weeks) produced a time-dependent decrease in MCV, SCV and ASAP. Rats treated with DEB mixture and 1,2-DEB exhibited a blue discoloration of tissues and urine. No changes in MCV, SCV and ASAP developed in rats administered orally with 1,3-DEP and 1,4-DEB (500 mg kg-1, once daily, 5 days per week for 8 weeks). The results indicate that 1,2-DEB is the isomer responsible for neurotoxicity and suggest that a metabolic pathway giving rise to coloured compounds is involved in the neurotoxicity of DEB.

Quantitative evaluation of sensory irritating and neurobehavioural properties of aliphatic ketones in mice.

A decrease in respiratory rate resulting from irritation of upper airways and a decrease in duration of immobility in a 'behavioural despair' swimming test occurred in mice during and following short-term inhalation exposures to some commonly used aliphatic ketones. Linear concentration-effect relationships were obtained that allowed two different median active levels (MALs) to be calculated. MALs that produced a 50% decrease in respiratory rate (RD50) were calculated as indicators of the sensory irritation potency of diisobutyl ketone, mesityl oxide, methyl amyl ketone, methyl isoamyl ketone and methyl propyl ketone. MALs that produced a 50% decrease in immobility (ID50) were determined for acetone, isophorone, mesityl oxide, methyl amyl ketone, methyl isoamyl ketone, methyl isobutyl ketone and methyl propyl ketone. The systematic determination of MALs permits classification of ketones in terms of their relative potencies for eliciting a given effect. The lowest MAL indicates the primary manifestation of toxicity, against which protection should be taken. MALs associated with such critical responses may be useful in the establishment of safe levels of occupational exposure to ketones, a conclusion supported by the linear relationship that was found to exist between MALs and occupational standards.

Concentration-dependent behavioral changes in mice following short-term inhalation exposure to various industrial solvents.

Mice were exposed during a 4-hr period to various concentrations of 13 aliphatic or aromatic solvents which affect primarily the central nervous system (CNS). The test compounds were benzyl chloride, butyl alcohol, chlorobenzene, cyclohexanone, 1,2-dichloroethylene, diisobutyl ketone, isopropyl acetate, methyl ethyl ketone, styrene, tetrachloroethylene, 1,1,1-trichloroethane, toluene, and ortho-xylene. After exposure, measurements were made to see whether these neurotoxicants would decrease the immobility developed in a "behavioral despair" swimming test. Each chemical was shown to reduce the total duration of immobility measured over a 3-min period in a concentration-related manner. The systematic determination of the atmospheric concentrations responsible for a 50% decrease in immobility (ID50) permitted classification of the solvents in terms of their relative potencies. The possibility of using such experimental data as tentative guidelines for setting safe levels of work exposure to the neurotoxicants was suggested, considering the existence of quantitative relationships between the ID50 values and the current occupational standards.

[Allergenic properties of a series of N-phenyl N'alcoyl paraphenylenediamines]. / Etude allergologique concernant une série de N-phényl-N'-alcoyl paraphénylène diamines.

The well known high allergenic potential of N-phenyl N'-isopropyl paraphenylenediamine (I.P.P.D.), as well as that of N-phenyl N'-1,3 dimethylbutyl paraphenylenediamine, though allegedly milder, prompted us to investigate the allergenicity of a series of N-phenyl N'-alcoyl paraphenylenediamines. We chose an existing technical grade series with substituents ranging from methyl to dodecyl. The results, on laboratory animals (Kligman and Magnusson's maximalization test), and on I.P.P.D.-sensitized humans (ROC Neodermotest, 48th hour) indicate a group sensitization with nearly systematic cross-reactions.

Occupational eczema from N-isopropyl -N'-phenylparaphenylenediamine (IPPD) and N-dimethy-1,3 butyl-N'-phenylparaphenylenediamine (DMPPD) in tyres.

Forty-two cases of contact sensitivity to N-isopropyl-N'-phenylparaphenylenediamine (IPPD), an amine antiozonant used in rubber manufacture, were collated from several firms and plants dealing with tyres. Ten motor car tyres manufactured by eight different firms all induce sensitivity reactions in seven subjects allergic to IPPD. Clinical cross-reaction tests show that 100% of the subjects sensitive to IPPD are also sensitive to N-phenyl-N'-cyclohexy-paraphenylenediamine (CPPD), another amine antiozonant, and 37% to paraphenylenediamine (PPD). The various types of tyres were analyzed by gas chromatography and then by infra-red and thin-layer chromatography where necessary. None of the 12 tyres examined was found to be free from aromatic amines. Test reactions carried out with various automobile accessories on subjects allergic to IPPD in tyres gave positive results precisely in those cases where the articles contained IPPD. The authors then studied occupational sensitivity to N-dimethyl-1,3 butyl-N'-phenylparaphenylenediamine (DMPPD), a rubber antiozonant purported to be non-sensitizing and marketed in the United States. The The DMPPD tests were positive for all the IPPD-allergic patients tested; there is no doubt as to the allergenic nature of DMPPD. The irritant and sensitizing potentials of the four amines in question were tested in laboratory animals: PPD proved to be the most allergenic product, IPPD the least allergenic, and DMPPD and CPPD seem to give identical results. All these products produce positive cross-reactions in varying degrees of severity.

[The irritant and allergenic action of two isocyanates: toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI)]. / Pouvior irritant et allergisant de deux isocyanates: toluène diisocyanate (T. D. I.), diphénylméthane diisocyante (M. D. I.)

This is a study on the irritant capacity of two isocyanates (T. D. I. Toluene diisocyanate and M. D. I. diphenyl methane diisocyanate). The experiment was carried out on the hide and ocular mucous membrane of albino rabbits, using Draize method as well as the method for appraising cosmetics. An histopathological examination of the evolution of the lesions was then achieved together with a study on the delayed allergenic capacity. This study was carried out on albino guinea-pig hides using Kligman and Magnusson technique. In these experimental conditions, the conclusions were the following:--on rabbit hide, T. D. I. is a medium irritant, more caustic than M. D. I.,--on ocular mucous membrane, M. D. I. is a mild irritant; T. D. I. a strong one,--on guinea-pig hide, T. D. I. and M. D. I. may induce cutaneous sensitivity similar to contact allergy. Their allergenic capacity is long lasting but varies according to the allergen concentration.