Neurobehavioral effects of acute exposure to normal (n-) paraffins.

This article reports the results of neurobehavioral tests on C(5)-C(10) normal paraffinic constituents (n-paraffins). Shortly after exposure, effects were evaluated in several domains including clinical effects, motor activity, functional observations, and visual discrimination performance. The representative C(5) n-paraffin, n-pentane, did not produce any evidence of acute central nervous system (CNS) effects at levels up to 20 000 mg/m(3). Similarly, there was no compelling evidence that n-octane (C(8)) produced CNS effects at 14 000 mg/m(3), the highest concentration tested. n-decane (C(10)) produced minor, reversible acute CNS effects at 5000 mg/m(3), with 1500 mg/m(3) as the no-effect level. Consistent with literature data, there seemed to be a relationship between increasing molecular weight up to C(10) and acute CNS effects. However, the CNS effects were reversible. Repeated exposures did not provide evidence of metabolic induction.

The lactic acid stinging test predicts susceptibility to cumulative irritation caused by two lipophilic irritants.

BACKGROUND: Skin exposure to lipophilic irritants at workplaces is a risk factor for the development of occupational irritant hand dermatitis. Suitable lipophilic model irritants to be used in repeated irritation studies in volunteers are needed to gain a better understanding of the chemical-dependent mechanisms of skin irritation. OBJECTIVES: To investigate acute and cumulative irritation elicited by two new lipophilic model irritants, octane (CAS No. 111-65-9) and cumene (CAS No. 98-82-8), in stingers as compared with non-stingers. METHODS: Short-time occlusive and repetitive occlusive irritation patch tests were performed over 5 days with octane and cumene in two groups of healthy volunteers (n = 15 each) who were classified as stingers and non-stingers according to a preceding lactic acid stinging test. Acute and cumulative irritation was quantified using clinical assessments and bioengineering methods (laser Doppler flowmetry, transepidermal water loss, capacitance measurements, and skin colour reflectance). RESULTS: Significantly stronger cumulative irritation was observed in stingers than in non-stingers for both irritants (visual scoring, stratum corneum hydration, and skin colour reflectance). CONCLUSIONS: The preliminary results suggest the existence of a distinct sub-population with increased susceptibility to cumulative irritation induced by lipophilic irritants that can be identified by the lactic acid stinging test.

Development of an inhalation physiologically based pharmacokinetic (PBPK) model for 2,2, 4-trimethylpentane (TMP) in male Long-Evans rats using gas uptake experiments.

2,2,4-Trimethylpentane (TMP) is a volatile colorless liquid used primarily to increase the octane rating of combustible fuels. TMP is released in the environment through the manufacture, use, and disposal of products associated with the gasoline and petroleum industry. Short-term inhalation exposure to TMP (< 4 h; > 1000 ppm) caused sensory and motor irritations in rats and mice. Like many volatile hydrocarbons, acute exposure to TMP may also be expected to alter neurological functions. To estimate in vivo metabolic kinetics of TMP and to predict its target tissue dosimetry during inhalation exposures, a physiologically based pharmacokinetic (PBPK) model was developed for the chemical in Long-Evans male rats using closed-chamber gas-uptake experiments. Gas-uptake experiments were conducted in which rats (80-90 days old) were exposed to targeted initial TMP concentrations of 50, 100, 500, and 1000 ppm. The model consisted of compartments for the closed uptake chamber, lung, fat, kidney, liver, brain, and rapidly and slowly perfused tissues. Physiological parameters were obtained from literature. Partition coefficients for the model were experimentally determined for air/blood, fat, liver, kidney, muscle, and brain using vial equilibration methods. Common to other hydrocarbons, metabolism of TMP via oxidative reactions is assumed to mainly occur in the liver. The PBPK model simulations of the closed chamber data were used to estimate in vivo metabolic parameters for TMP in male Long-Evans rats.

Synthesis and structure-activity relationship of novel 1,4-diazabicyclo[2.2.2]octane derivatives as potent antimicrobial agents.

A series of new quaternary 1,4-diazabicyclo[2.2.2]octane derivatives was synthesized and evaluated for activity against several strains of both Gram positive and Gram negative bacteria and one strain of fungus under different inoculum size. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against six species of microorganisms were tested. Results show a clear structure-activity relationship between alkyl chain length of substitutions of 1,4-diazabicyclo[2.2.2]octane tertiary amine sites and antimicrobial activity. In the case of compounds 4a-4k, MIC was found to decrease with the increase of the alkyl chain length from ethyl to dodecyl and then to increase at higher chain length (n > 14). The MIC values were found to be low for the compounds 4f and 4g with alkyl chains ranging from 10 to 12 carbons in length (1.6 µg/ml) and were comparable to the reference drug Ciprofloxacin. Also, time-kill assay was performed to examine the bactericidal kinetics. Results indicated that 4f and 4g had rapid killing effects against Staphylococcus aureus, and eliminated 100% of the initial inoculum of bacteria in 2.5 h at the concentration of 10 µg/ml. In addition, compound 4g eliminate more than 99.9% of the initial inoculum of Ps. aeruginosa after 2.5 h of interaction but the activity of compound 4f against this species seems to be weak. Thus, 4g had strong bactericidal activity and could rapidly kill Gram positive S. aureus, as well as Gram negative Ps. aeruginosa at low and high inoculum size.

Biotransformation and male rat-specific renal toxicity of diethyl ethyl- and dimethyl methylphosphonate.

Dimethyl methylphosphonate (DMMP) is a widely used chemical. Diethyl ethylphosphonate (DEEP) has been proposed as a replacement for DMMP in several applications. A long-term carcinogenesis study with DMMP in rats and mice showed a significant increase in the incidence of kidney tumors after 2 years of exposure in male but not in female rats and both sexes of mice. DMMP is not genotoxic. Due to these findings, a role of alpha(2u)-globulin accumulation in organ-specific tumorigenicity may be possible. alpha(2u)-Globulin is a low-molecular-weight protein synthesized in male rats under androgen control. Several male rat specific renal carcinogens have been shown to bind to alpha(2u)-globulin and to impair the renal degradation of this protein. This impairment results in alpha(2u)-globulin accumulation in the kidney, lysosomal overload, cell death, cell proliferation, and finally, renal tumor induction. To further characterize the toxicology of DMMP and DEEP, we investigated the biotransformation of these compounds and their ability to induce alpha(2u)-globulin accumulation in kidney. Biotransformation of both DMMP and DEEP were studied in male and female rats after single oral doses of 50 and 100 mg/kg. 31P-NMR and GC/MS showed that unchanged DMMP was excreted with urine; methyl phosphonate was identified as the only metabolite in urine. Unchanged DEEP was also excreted with urine; in addition, ethyl ethylphosphonate and ethylphosphonate were urinary metabolites. The majority of the applied dose of both compounds was recovered in urine within 24 h indicating rapid absorption and excretion. No sex-differences in rates of formation or excretion of metabolites were seen. To investigate alpha(2u)-globulin accumulation in the kidney after DMMP and DEEP, male and female Fischer-344 rats were administered DMMP or DEEP daily for five consecutive days by gavage. DMMP doses were 500- and 1,000-mg/kg body weight (bw); due to marked toxicity, daily DEEP dose of 50 and 100 mg/kg had to be used. Control rats received corn oil only and positive controls received five doses of 500-mg/kg bw trimethylpentane (TMP). Relative kidney weights were increased in male rats dosed with DMMP, DEEP, and TMP. alpha(2u)-Globulin in kidney cytosol was separated and quantified by capillary electrophoresis and by SDS-PAGE and Western blotting. In DMMP-, DEEP-, and TMP-treated rats, dose-dependent increases in the alpha(2u)-globulin content were observed by both methods in male, but not female rats. The increase of alpha(2u)-globulin accumulation was accompanied by the formation of protein droplets in the proximal tubules of male rats. These data demonstrate that the sex specific increase in kidney tumors by DMMP in male rats may be due to alpha(2u)-globulin accumulation and that similar toxic effects are to be expected from DEEP.

n-Octane and n-nonane induced alterations in xenobiotic metabolising enzyme activities and lipid peroxidation of rat liver.

After 2 and 7 days on n-octane and n-nonane administration (intraperitoneally) to female albino rats, alterations in the levels of hepatic xenobiotic metabolising enzyme activities and TBA reactants were observed. Fifty to eighty per cent reduction in the specific activities of benzo[a]pyrene hydroxylase, benzphetamine-N-demethylase, p-nitroanisole-O-demethylase and glutathione-S-transferase were observed. Cytochrome P-450 and free sulfhydryl contents of liver were also decreased significantly after 7 days treatment on n-octane and n-nonane. A 2- and 3- fold increase in liver lipid peroxidation estimated as TBA reactants was observed in the animals treated for 2 or 7 days with n-octane or n-nonane.

Alpha 2U-globulin: measurement in rat kidney following administration of 2,2,4-trimethylpentane.

Hyaline droplet formation was stimulated markedly in the kidneys of post-puberty male rats 24-48 h after a single oral dose of 12/24 mmol/kg 2,2,4-trimethylpentane [TMP]. Renal hyaline droplet formation could not be detected in female rats or in pre-puberty male rats following similar doses of TMP. A dose-dependent increase in the renal concentration of the androgen-dependent low molecular weight protein, alpha 2U-globulin was observed in post-puberty male rats 24 h after a single oral dose of TMP, over the range 0.3-12.0 mmol/kg. After administration of a single dose of 12 mmol/kg TMP to male rats, the renal concentration of alpha 2U-globulin rose steadily up to a peak after 48 h and then returned slowly to near normal after 7 days. Renal alpha 2U-globulin could not be detected in female rats and in pre-puberty male rats. An immunocytochemical assay was developed to examine the distribution of alpha 2U-globulin within the kidney. alpha 2U-Globulin was localised primarily in the S2 segment of renal proximal tubules in untreated male rats. Rats which received a single dose of 12 mmol TMP/kg showed not only a greater staining intensity, due to the presence of a higher concentration of alpha 2U-globulin, but also staining in adjacent segments of the renal cortex. Several urinary biochemical indicators of nephrotoxicity were measured daily in male rats for up to 72 h following a single dose of 12 mmol TMP/kg. Renal proximal tubular function was unimpaired by TMP treatment. On the basis of studies in untreated and TMP-treated rats, a strong association has been found between the presence of renal hyaline droplets and the occurrence of renal alpha 2U-globulin. The findings in the present study provide an explanation for the occurrence of renal hyaline droplets only in adult male rats, but do not, as yet, establish the toxicological significance of increases in renal hyaline droplet formation.

The metabolism of n-octane in Fischer 344 rats.

The urinary metabolites of n-octane in Fischer 344 rats given the hydrocarbon by gavage included 2-octanol, 3-octanol, 5-oxohexanoic acid, and 6-oxoheptanoic acid. The sex of the animals influenced the relative amounts of metabolites formed. Analyses were performed by gas-liquid chromatography (GC) and gas-liquid chromatography/mass spectrometry (GC/MS). This is the first reported finding of keto acids in hydrocarbon oxidative metabolism. No kidney damage was found as a result of n-octane dosing although the 2,2,4-trimethylpentane (iso-octane) isomer does cause kidney lesions in male rats.

Aviation gasoline: comparative subchronic nephrotoxicity study in the male rat.

Biochemical and histopathologic parameters of nephrotoxicity were measured in groups of male Fischer-344 rats after a 2-week, 5-days-a-week schedule of oral administration (0.5 ml/kg) of the following substances: aviation gasoline (grade 100) (AVG), automobile regular unleaded gasoline (ULG) and 2,2,4-trimethylpentane (TMP). Results of renal histopathologic examinations and biochemical parameters were compatible with the following order of increasing nephrotoxicity: ULG less than TMP less than AVG. The high nephrotoxic potential of aviation gasoline may be related to its elevated content in branched hydrocarbons.

A comparison of European High Test gasoline and PS-6 unleaded gasoline in their abilities to induce alpha 2u-globulin nephropathy and renal cell proliferation.

Male Fischer-344 rats were administered European High Test gasoline (EHT) (50-500 mg/kg), PS-6 unleaded gasoline (UG) (16-500 mg/kg) or 2,2,4-trimethylpentane (TMP) (0.95-30 mg/kg) by gavage for ten consecutive days. To measure cell replication, rats were exposed to [3H]thymidine continuously over the last 7 days of the exposure period. Twenty-four hours after the final dose, protein droplet (PD) accumulation, alpha 2u-globulin (alpha 2u) concentration and the nuclear labeling index (LI), as a measure of cell replication, were measured in the kidneys of control and treated rats. Dose-related increases in PD, alpha 2u and cell replication were detected in the kidneys of rats treated with either gasoline mixture or TMP. The accumulation of PD and the increase in alpha 2u was greater in the kidneys of UG- and TMP-treated rats than in the kidneys of rats treated with EHT. These differences were attributed to the higher composition of branched hydrocarbons in UG, which have been shown to be the biologically active components for these endpoints. The extent of renal cell proliferation was similar in both EHT-, UG- and TMP-treated rats. This suggests that other components besides the branched hydrocarbons are responsible for the increased renal cell replication in EHT-treated rats.

Rhodococcus rhodochrous ATCC12674 becomes alkane-tolerant upon GroEL2 overexpression and survives in the n-octane phase in two phase culture.

We recently reported that the overexpression of GroEL2 played an important role in increasing the alkane tolerance of Rhodococcus erythropolis PR4. In the present study, we examined the effects of the introduction of groEL2 on the alkane tolerance of other Rhodococcus strains. The introduction of groEL2 into Rhodococcus strains led to increased alkane tolerance. The translocation of R. rhodochrous ATCC12674 cells to and survival in the n-octane (C8) phase in two phase culture were significantly enhanced by the introduction of groEL2 derived from strain PR4, suggesting that engineering cells to overexpress GroEL2 represents an effective strategy for enhancing organic solvent tolerance in Rhodococcus.

Study of the potential oxidative stress induced by six solvents in the rat brain.

The mechanisms of action involved in the neurotoxicity of solvents are poorly understood. In vitro studies have suggested that the effects of some solvents might be due to the formation of reactive oxygen species (ROS). This study assesses hydroxyl radical (OH) generation and measures malondialdehyde (MDA) levels in the cerebral tissue of rats exposed to six solvents (n-hexane, n-octane, toluene, n-butylbenzene, cyclohexane and 1,2,4-trimethylcyclohexane). Three of these solvents have been shown to generate ROS in studies carried out in vitro on granular cell cultures from rat cerebellum. We assessed OH production by quantifying the rate of formation of 3,4-dihydroxybenzoic acid using a trapping agent, 4-hydroxybenzoic acid, infused via the microdialysis probe, into the prefrontal cortex of rats exposed intraperitoneally to the solvents. Extracellular MDA was quantified in microdialysates collected from the prefrontal cortex of rats exposed, 6h/day for ten days, to 1000ppm of the solvents (except for n-butylbenzene, generated at 830ppm) in inhalation chambers. Tissue levels of free and total MDA were measured in different brain structures for rats acutely (intraperitoneal route) and sub-acutely (inhalation) exposed to solvents. None of the six solvents studied increased the production of hydroxyl radicals in the prefrontal cortex after acute administration. Nor did they increase extracellular or tissue levels of MDA after 10 days' inhalation exposure. On the other hand, a decrease in the concentrations of free MDA in brain structures was observed after acute administration of n-hexane, 1,2,4-trimethylcyclohexane, toluene and n-butylbenzene. Therefore, data of this study carried out in vivo did not confirm observations made in vitro on cell cultures.

Mutagenicity of octane and tetrasodium pyrophosphate in bacterial reverse mutation (Ames) test.

We investigated the genotoxicities or mutagenicities of 2 chemicals (octane and tetrasodium pyrophosphate) with limited toxicological data in spite of their common usage based on Ames reverse mutation test. In this test, treatment of 2 chemicals at each five dose did not induce mutagenicity in Salmonella typhimurium TA98, TA100, TA1535, TA1537, and in Escherichia coli WP2uvrA with and without metabolic activation. These results indicate that 2 chemicals do not have mutagenic potentials under the conditions examined in each study. Despite these results, it can affect by inducing inhalation, skin or eye contact, ingestion, and have affected central nervous system as a target organ. It is thus necessary to prepare the local exhaust system and personal protective equipments. Based on this study, we suggest that future studies should be directed toward chronic inhalation, carcinogenic test and so on.

The fate of inhaled octane and the nephrotoxicant, isooctane, in rats.

To determine if inhaled nephrotoxic branched and nonnephrotoxic straight chain alkanes differ substantially in their biological fate, male F344 rats were exposed to 14C-labeled isooctane and octane vapors at approximately 1 and 350 ppm by the nose-only mode for 2 hr. Radioactivity in exhalant, urine, and feces was determined for 70 hr post exposure, after which residual radioactivity in the rat carcasses was determined. Absorbed [14C]isooctane equivalents were eliminated almost exclusively via the kidneys, while absorbed [14C]octane equivalents were excreted about equally via the kidneys and as 14CO2. Kidney excretion of isooctane-introduced 14C was protracted over the entire 70 hr postexposure observation period whereas for octane-introduced 14C, kidney excretion was essentially complete after 10-20 hr. About 5% of the [14C]octane equivalents inhaled at 1 ppm remained in the carcass 70 hr after inhalation exposure. Two percent of the [14C]octane equivalents inhaled at 350 ppm and 1-2% of the [14C]isooctane equivalents inhaled at either 1 or 350 ppm remained in the carcass 70 hr after inhalation exposure. The different patterns of excretion of metabolites of isooctane compared to octane may be a factor affecting the differences in nephrotoxicity between these two compounds.