1,2,3,4-tetrahydroisoquinoline

Endpoint summary

Description of key information

In a repeated-dose (90-day) inhalation toxicity study (GLP-compliant, OECD TG 413) 5.2 mg/m³ (actual concentration; vapour) was a No-Observed-Adverse-Effect Concentration (NOAEC) in male and female rats. At higher concentrations (24.7 and 75.1 mg/m³) clinical signs indicative of irritation, slightly decreased growth rate and food consumption, some biochemical alterations and histopathological changes at the base of the epiglottis were observed.

Additional information

Repeated exposure by inhalation:

The toxicity of 1,2,3,4-Tetrahydroisoquinoline (THIQ) upon repeated inhalation exposure was examined in a GLP-compliant study performed according to OECD guideline 413 and the corresponding EU and EPA test guidelines (BASF SE, 2012). Groups of 10 male and 10 female Wistar rats were head-nose exposed to a dynamic inhalation atmosphere of THIQ for 6 hours on each workday (5 times every week) for 13 weeks (total of 65 exposure days). The target concentrations were 5 mg/m³, 25 mg/m³ and 75 mg/m³. A concurrent control group of 10 animals/sex was exposed to ethanol as solvent control. All animals were exposed to fresh air on the two days before the start of the exposure period to adapt them to the exposure conditions. The target concentrations for the 90-day study were based on the results of a 14-day range-finding study in which concentrations of 5.4, 31 and 150 mg/m³ were tested. Body weight gain and food consumption were reduced, concentration-dependently, and histopathology revealed strong irritation of the respiratory tract at 150 mg/m³ (level I nasal cavity: degeneration of squamous epithelium, in some animals with ulceration; level I larynx: epithelial alteration, mucous cell metaplasia and lympoid cell infiltration; large bronchi: mild mucous cell hyperplasia). Mucous cell hyperplasia was still observed in one animal at 31 mg/m³. No adverse effects were observed at 5.4 mg/m³ in the 14-day study.

The actual test atmosphere concentrations in the 90-day study, as measured by gas chromatography, were close to the target concentrations (5.2, 24.7 and 75.1 mg/m³ for the low-, mid- and high-concentration, respectively). At the low- and mid-concentration (below the saturation concentration of the test substance) the animals were exposed to vapour only. At the high-concentration (above the saturation concentration), the aerosol droplets evapourated partly and, consequently, the animals were exposed to a mixture of vapour and liquid aerosol (the aerosol fraction was 43.5% at 75.1 mg/m³). Measurement of the particle size distribution in one high-concentration sample showed that most of the particles were on the back-up filter (MMAD < 1.2 μm). However, as THIQ evapourated from the cascade impactor during sampling the measured aerodynamic diameters did not reflect the particle size in the test atmosphere. The measured mean concentrations of ethanol in the test atmospheres were 339.1 (control), 299.2 (low-concentration), 325.6 (mid-concentration) and 248.3 (high-concentration) ppm.

The following endpoints were evaluated to assess toxicity: daily clinical observations, weekly detailed clinical observations, neurobehavioural examination on study day 75 (functional observational battery including home cage and open field observations, sensory reactivity to different stimuli and grip strength; spontaneous motor activity), ophthalmoscopy, body weight, food consumption, routine haematology and clinical chemistry (in blood samples collected from fasted animals on the day after the last exposure), organ weights, macroscopic examination and histopathological examination of a wide range of tissues and organs (only control and high-concentration animals were subjected to full histopathology; examination of level I of the larynx was extended to the intermediate concentration groups).

At the low-concentration no treatment-related adverse effects were observed. At the higher concentrations animals of both sexes showed treatment-related, adverse clinical signs indicative of the irritating property of THIQ (salivation and reduced fur care at the mid- and high-concentration, escape attempts at the high-concentration). Body weight was slightly decreased (difference from controls did not exceed 10%) at the mid- and high-concentration from study day 21 (high-concentration) / 28 (mid-concentration) in males and transiently in females. Food consumption was slightly reduced in mid- and high-concentration males only. Treatment-related changes in clinical pathology parameters were limited to lower plasma levels of total protein and globulin at the mid- and high-concentration, lower glucose at the high-concentration, and higher inorganic phosphate at the high-concentrations. These biochemical changes occurred in both sexes. Histopathology revealed treatment-related changes in the larynx (level I). The changes occurred focally at the base of the epiglottis and comprised minimal to slight epithelial alteration (characterized by a focal flattening of epithelial cells) in 8/10 mid-concentration females and high-concentration males and females (7/10 and 9/10, respectively), minimal squamous metaplasia in 3/10 high-concentration males, and minimal to moderate submucosal lymphohistiocytic inflammation in high-concentration males and females (2/10 and 9/10, respectively). This inflammatory response was regarded to be an adverse effect of the test material. The squamous metaplasia was considered an adaptive, non-adverse effect because it was expected not to cause dysfunction of the larynx. The epithelial alteration was also considered to be adaptive and non-adverse. This epithelial alteration is considered to be the initial stage of a generally concentration-dependent transformation of normal epithelium into full laryngeal squamous metaplasia, which generally does not progress over time and regresses after termination of the exposure. Moreover, this epithelial alteration also occurs spontaneously without dysfunction of the larynx (it was seen in 4/10 male and 3/10 female concurrent controls).

In conclusion, under the conditions of this study, inhalation exposure to 24.7 and 75.1 mg/m³ 1,2,3,4-Tetrahydroisoquinoline for 90 days (65 exposures) caused clinical signs of toxicity (indicative of the irritation property of the test material), slightly reduced growth rate and food consumption, and microscopic changes in the larynx at the base of the epiglottis (focal epithelial alteration and squamous metaplasia which were considered adaptive and non-adverse, and, at the high-concentration only, focal submucosal lymphohistiocytic inflammation which was regarded to be adverse). No signs of a neurotoxic effect were observed at any concentration. Based on these findings, the low-concentration of 5.2 mg/m³ (actual concentration) was a No-Observed-Adverse-Effect Concentration (NOAEC) in male and female rats.

Repeated exposure by other routes (intraperitoneal):

Two mechanistic studies (non-GLP, non-guideline), one in rats and one in mice, were conducted to investigate whether 1,2,3,4-Tetrahydroisoquinoline influences the levels of Tyrosinhydroxylase and Dopamine in the corpus striatum (BASF SE, 2011a,b). In these studies male Wistar rats and male C57BL/6 J Rj mice were treated intraperitoneally with 1,2,3,4-Tetrahydroisoquinoline on 4 consecutive days at 3, 50 and 200 mg/kg bw/day (10 rats and 10 mice per dose; each dose was divided in two applications, one early morning, one afternoon). The highest dose was reduced to 100 mg/kg bw/day after the first application because of severe clinical signs of toxicity. Concurrent control groups of the same size were treated similarly with the vehicle (physiological saline) only. Hereafter, the animals were kept for a 9-day treatment-free observation period. Endpoints to assess toxicity included clinical observations, body weight, food consumption, motor activity, brain weight, necropsy and microscopic examination of the brain (HE stained slides; neuronal cell count on slides stained immunohistochemically for tyrosine hydroxylase, a specific marker to reveal dopaminergic neurons and their synaptic end terminals). Analysis of dopamine in the corpus striatum was not conducted because no suitable analytical method could be developed.

At 200/100 mg/kg bw, 2 rats and 3 mice were found dead during the treatment period. At this dose level severe clinical signs of general toxicity as well as neurobehavioural changes of were observed. During the treatment period, most high-dose rats showed poor general condition, hypothermia, piloerection, abdominal respiration, reduced attention, unsteady gait, and hindlimp paresis. Poor condition, hypothermia, reduced attention and unsteady gait persisted until a few days after cessation of treatment. In one animal hindlimb paresis persisted until the end of the study. Salivation occurred in half of the animals after the first dose. Most or all high-dose mice showed reduced attention, high-stepping gait and unsteady gait until the end of the treatment period. Four mice had tremors after the first dose on day 1, and three mice showed moderate tonic-clonic convulsions after the first dose on day 0. During the post-treatment period, one mouse showed poor condition and piloerection. Additionally, high-dose rats and mice lost weight and consumed markedly less food during the treatment period. Their growth rate normalized after cessation of treatment.

At 50 mg/kg bw, clinical signs occurred in both species, though to a lesser extent than at 200/100 mg/kg bw. All mid-dose rats showed reduced attention on days 1-3 and a few rats occasionally showed salivation or piloerection. The only finding in mid-dose mice was reduced attention (in five animals), mainly after dosing on days 0-1. Rats given 50 mg/kg bw, but not mice, also showed growth retardation and reduced food consumption during the treatment period (less severe than at 200/100 mg/kg bw).

At 3 mg/kg bw, one rat showed unsteady gait on day 3 (before and after the first application) while mice showed no signs of toxicity. Growth and food consumption were not affected at 3 mg/kg bw. The other examinations (motor activity, necropsy, weight and microscopic examination of the brain) showed no treatment-related changes.

Justification for classification or non-classification

Based on the available data, the test substance is not classified with regard to repeated dose toxicity according to Directive 67/548/EEC (DSD) and Regulation (EC) No 1272/2008 (CLP), respectively.