Souheil Laham

Acidic metabolites of pseudocumene in rabbit urine.

In order to identify biological indicators of exposure to trimethylbenzenes, the metabolism of pseudocumene (1,2,4-trimethylbenzene) was investigated in rabbits. After oral administration of this compound, urine was collected for several days and analyzed for the presence of acidic metabolites. Isolation techniques included steam-distillation, direct extraction of urine by ethyl acetate, preparative thin-layer and column chromatography of the extract. The metabolites were identified by microanalysis, followed by TLC, gas chromatography-mass spectrometry, infrared and ultraviolet spectroscopy. Two major urinary metabolites were identified, namely 2,4-dimethylbenzoic acid and 3,4-dimethylhippuric acid. The presence of these acidic metabolites in urine is a good indication of exposure to pseudocumene.

Studies on inhalation toxicity of 2-propanol.

Biological effects of a single exposure to moderate or high concentrations of 2-propanol were investigated in Sprague-Dawley rats. Acute toxicity (LC50, t:8 hours) of this widely used solvent was determined and found to be 19000 ppm (17380-20760 ppm) for females and 22500 ppm (19200-26400 ppm) for males. Determination of blood levels of 2-propanol and its metabolite, acetone, was carried out during and after a single 4-hour exposure (Concentration range: 500 to 8000 ppm). The amount of acetone and 2-propanol was directly related to the various air concentrations of alcohol inhaled. Increase of exposure time to 8 hours enhanced considerably the amount of blood acetone which could be determined even 20 hours after exposure. These findings indicate a slow conversion of this alcohol to acetone which can be used as biochemical indicator to exposure. Histopathological examination of rats exposed to high levels of 2-propanol shows typical lesions of chemical pneumonitis and pulmonary edema accompanied by foamy vacuolization of liver cells and severe focal cytoplasmic degradation.

Induction of Urinary Bladder Hyperplasia in Sprague-Dawley Rats Orally Administered Tri-n-Butyl Phosphate

The effects of tri-n-butyl phosphate (TBP) were investigated in the Sprague-Dawley rat over an 18-wk period. Groups of randomized female (average weight [AW] = 206 +/- 10 g) and male (AW = 294 +/- 13 g) rats were divided into low-dose, high-dose, and control groups (12 rats/sex X group). Tri-n-butyl phosphate was administered by gavage once a day for 5 days/wk over an 18-wk period. Low-dose animals received 0.20 g/kg X day throughout the experiment and high-dose animals received 0.30 g/kg X day for the first 6 wk. For the remaining 12 wk, the high-dose level was increased to 0.35 g/kg X day. Histopathological examination of tissues revealed that all test rats examined developed diffuse hyperplasia of the urinary bladder epithelium. Similar changes were not found in the control animals.

Biological Conversion of Benzaldehyde to Benzylmercapturic Acid in the Sprague-Dawley Rat

The metabolism of benzaldehyde was investigated in Sprague-Dawley rats. After repeated oral administration of this compound (0.4-1.0 g/kg) for 13 consecutive days, urine was collected and analyzed for the presence of metabolites. The acidification of the pooled urine samples (pH:2.0) with 6 N H2SO4 was followed by ethyl acetate extraction, evaporation of the extract and methylation with diazomethane. Identification of the metabolite by comparison with a synthetic sample of benzylmercapturic acid (BENZM) was conducted by gas chromatography. Mass spectrometry examination of this metabolite revealed the following peaks characteristic of benzylmercapturic acid: m/z (%), 91(100), 176(27), 208(23), 43(20), 88(13), 117(10), 134(9), M+ 267(2). Monitoring of urines from both female and male rats showed a dose-related increase of benzylmercapturic acid which was found to be a reliable indicator of exposure to benzaldehyde.

Effects of Tri-n-butyl Phosphate on the Peripheral Nervous System of the Sprague-Dawley Rat

Tri-n-butyl phosphate, a widely used plasticizer and solvent, was orally administered to male and female Sprague-Dawley rats for 14 consecutive days (low dose: 0.28 mL/kg; high dose: 0.42 mL/kg). Effects of this industrial chemical were investigated on the peripheral nervous system of these animals. A significant (P less than 0.05) reduction in conduction velocity of caudal nerve was observed in high dose male rats. Electron microscopic examination of sciatic nerve showed morphological changes such as retraction of Schwann cell processes surrounding unmyelinated fibres in both sexes of high dose groups.

Microdetermination of mesitylenic acid in human urine.

In the course of studies on comparative metabolism of 1,3,5-trimethylbenzene (mesitylene), it was found necessary to determine one of the metabolites, 3,5-dimethylbenzoic acid (mesitylenic acid), which is present in the urine of humans and various animal species exposed to this chemical.This metabolite is first removed from acidified urine by steam distillation followed by several ether extractions of the distillate. The extract is then chromatographed on thin-layer plates (SiO2, 250 microns) and, after development in a suitable solvent, is viewed under ultraviolet light. The spot of mesitylenic acid is marked, eluted with EtOH and finally read against a blank in a spectrophotometer. This method has been applied successfully to human urine and is specific for 3,5-dimethylbenzoic acid (3,5-DMBA).ZusammenfassungBei vergleichenden Untersuchungen zum Metabolismus von 1,3,5-Dimethylbenzol (Mesitylen) ergab sich die Notwendigkeit, eine Bestimmungsmethode für den Metaboliten 3,5-Dimethylbenzoesäure (Mesitylensäure), der im Harn des Menschen und verschiedener Tierarten nach Exponierung gegenüber diesem Stoff auftritt, auszuarbeiten. — Dieser Metabolit wird nach Ansäuerung des Harnes durch Wasserdampfdestillation abgetrennt, gefolgt von mehreren Ätherextraktionen des Destillata. Der Extrakt wird auf Dünnschichtplatten (SiO2, 250 micron) chromatographiert und nach Entwicklung in einem geeigneten Lösungsmittel unter UV-Licht lokalisiert. Der Weg der Mesitylensäure wird markiert, mit Äthanol eluiert und schlie×lich gegen eine Leerprobe spektrophotometrisch ausgemessen. Diese Methode ist spezifisch für 3,5-Dimethylbenzoesäure (3,5-DMBA) und erfolgreich bei Harnuntersuchungen des Menschen angewendet worden.

SUBACUTE INHALATION TOXICITY OF BENZALDEHYDE IN THE SPRAGUE-DAWLEY RAT

Benzaldehyde was administered by inhalation to female and male Sprague-Dawley rats for 14 consecutive days (low level: 500 ppm; medium level: 750 ppm; high level: 1000 ppm). Effects of this chemical were investigated during and at the end of the exposure period. Throughout the experiment, significant hypothermia and a reduction of motor activity were observed in all rats exposed to benzaldehyde and were accompanied in high-level rats by a severe impairment of the central nervous system, as evidenced by abnormal gait, tremors, and a positive Straub sign. Histopathologic examination of tissues from exposed rats showed a goblet cell metaplasia that was largely confined to the respiratory epithelium lining the nasal septum in male rats. No other abnormal microscopic changes were observed. A no effect level was not observed in these studies.

Metabolism of benzaldehyde in New Zealand White rabbits

The quantitative metabolism of benzaldehyde (BENZ) has been investigated in male New Zealand White rabbits (3 rabbits/group). A single oral dose of this material was administered to two test groups (low-dose group: 0.35 g/kg/rabbit; high-dose group: 0.75 g/kg/rabbit) whereas water (0.75 g/Kg/rabbit) was given orally to the third group. Urine of all groups was collected daily for 15 consecutive days. Daily monitoring indicated the urinary excretion of the following metabolites: hippuric acid (HA), free (FBA) and conjugated benzoic acid (benzoylglucuronic acid: BGA), benzyl glucuronide (BG) and benzyl mercapturic acid (BMA). Although the total amount of urinary metabolites excreted by the low-dose group (83.2% of the total dose) was not significantly different from that excreted by the high-dose group (82.3% of the total dose), some metabolites showed differences in their urinary output: HA, 69.9% in the low-dose group vs. 66.7% in the high-dose group; BGA, 8.8% in the low-dose group vs. 11.2% in the high-dose group; BG, 2.9% in the low-dose group vs. 3.0% in the high-dose group; FBA, 1.6% in the low-dose group vs. 1.4% in the high-dose group. In both treated groups, BMA was present in trace amounts (< 0.01% of the total dose).

Subchronic oral toxicity of tributoxyethyl phosphate in the Sprague-Dawley rat

The effects of the widely used alkyl phosphate, tributoxyethyl phosphate (TBOP), were investigated in male and female Sprague-Dawley rats. This chemical was administered (low dose: 0.25 ml/kg X day; high dose: 0.50 ml/kg X day) by gavage once a day for 5 days/wk, over a period of 18 wk. Histopathological examination of tissues in treated male rats showed the presence of cardiac lesions, including myocardial necrosis with inflammatory cell infiltration. This study indicated that oral administration of TBOP may have caused or contributed to the early onset of a common background finding in this rat strain.

Biological Conversion of N-Phenyl-2-Naphthylamine to 2-Naphthylamine in the Sprague-Dawley Rat

The metabolism of a widely used plastic and rubber antioxidant, N-Phenyl-2-Naphthylamine, was investigated in Sprague-Dawley rats. After repeated oral administration of this compound, urine and feces were collected for several days and analyzed for the presence of metabolites. Identification techniques included a preliminary clean-up followed by thin-layer chromatography of amines and gas chromatography-mass spectrometry of their hexafluoroacyl derivatives (HFBA). The compounds identified in both urine and feces were characterized as N-Phenyl-2-Naphthylamine (PBNA) and 2-Naphthylamine (BNA). Data obtained on urinary excretion of BNA seem to indicate that repeated administration of PBNA enhances its own metabolism.