Structure-toxicity relationship of monoketones

Scientific Opinion on Flavouring Group Evaluation 7, Revision 5 (FGE.07Rev5): saturated and unsaturated aliphatic secondary alcohols, ketones and esters of secondary alcohols and saturated linear or branched-chain carboxylic acids from chemical group 5

The EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids was requested to evaluate 53 flavouring substances attributed to the Flavouring Group Evaluation 07, including four new substances but-3-en-2-ol, non-1-en-e-ol, hex-1-en-3-one and 1-nonene-3-one [FL-nos: 02.131, 02.187, 07.161 and 07.210] in this Revision 5, using the Procedure in Commission Regulation (EC) No 1565/2000. None of the 53 substances was considered to have genotoxic potential. The substances were evaluated through a stepwise approach that integrates information on the structure-activity relationships, intake from current uses, toxicological threshold of concern (TTC), and available data on metabolism and toxicity. The Panel concluded that all 53 substances do not give rise to safety concerns at their levels of dietary intake, estimated on the basis of the 'Maximised Survey-derived Daily Intake' (MSDI) approach. Besides the safety assessment of the flavouring substances, the specifications for the materials of commerce have also been considered and found adequate. For 50 substances, further information is required based on comparison of the 'modified Theoretical Added Maximum Daily Intakes' (mTAMDIs) with the TTCs. This would include more reliable intake data and then, if required, additional toxicological data.

A quantum chemical based toxicity study of estimated reduction potential and hydrophobicity in series of nitroaromatic compounds

Nitroaromatic compounds and the products of their degradation are toxic to bacteria, cells and animals. Various studies have been carried out to better understand the mechanism of toxicity of aromatic nitrocompounds and their relationship to humans and the environment. Recent data relate cytotoxicity of nitroaromatic compounds to their single- or two-electron enzymatic reduction. However, mechanisms of animal toxicity could be more complex. This work investigates the estimated reduction and oxidation potentials of 34 nitroaromatic compounds using quantum chemical approaches. All geometries were optimized with density functional theory (DFT) using the solvation model based on density (SMD) and polarizable continuum model (PCM) solvent model protocols. Quantitative structure-activity/property (QSAR/QSPR) models were developed using descriptors obtained from quantum chemical optimizations as well as the DRAGON software program. The QSAR/QSPR equations developed consist of two to four descriptors. Correlations have been identified between electron affinity (E_LUMO) and hydrophobicity (log P).

Molecularly Imprinted Dispersive Solid-Phase Extraction for the Determination of Triazine Herbicides in Grape Seeds by High-Performance Liquid Chromatography

Molecular imprinting technique, regarded as one of the current state-of-the-art researches, was incorporated with the simple dispersive solid-phase extraction (MI-DSPE) in this work for the extraction of triazine herbicides in grape seeds. The atrazine molecularly imprinted polymers (MIPs) were successfully prepared and characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The imprinting particles were used as the adsorbent in DSPE. Thus, a simple, rapid and selective method based on MIPs coupled with DSPE was established for the simultaneous cleaning-up and quantitative extraction of four triazine herbicides in grape seeds. The experiment parameters, including type of washing solvents, washing time and type of eluting solvents, were investigated and optimized. The performance of the present method was validated by high-performance liquid chromatography. Good linear responses were obtained in concentration range of 0.010-5.0 µg g(-1)with correlation coefficients (r(2)) higher than 0.9993. The recoveries at two spiked levels (1.0 and 2.0 µg g(-1)) were between 81.2 and 113.0% with relative deviations ranging from 1.2 to 10.7%. The limits of detection were ranged between 0.006 and 0.013 µg g(-1), which were lower than the values required by European regulations.

Molecularly imprinted solid phase extraction in a syringe filter for determination of triazine herbicides in Radix Paeoniae Alba by ultra-fast liquid chromatography

A novel, cost-effective and simple solid phase extraction (SPE) method, by using a syringe connected with a nylon membrane filter as the adsorbent container, was developed for the extraction of triazine herbicides from Radix Paeoniae Alba (RPA) samples. The selective molecularly imprinted polymers (MIPs) synthesized with the template of atrazine were employed as the adsorbents for the enrichment and purification of analytes. The extraction parameters, including the volume and type of loading solvent, the type of washing solvent and eluting solvent, were investigated. Under the optimized conditions, the final extracts were analyzed by ultra-fast liquid chromatography (UFLC). Recoveries of the developed method range from 92.4% to 107.3% with intra- and inter-day relative standard deviations (RSDs) lower than 8.2%. The calibration curve is linear in the concentration range of 0.005-2.4 µg g(-1) for desmetryn, atrazine and terbumeton, and 0.005-1.5 µg g(-1) for dimethametryn and dipropetryn, with the correlation coefficient (R(2)) higher than 0.9995. The limits of detection (LODs) of five triazine herbicides are in the range of 0.09-0.39 ng g(-1), which are lower than the maximum residue levels (MRLs) established by various official organizations. Analytical results of three real Radix Paeoniae Alba samples indicate that the proposed method is cost-effective and easy-to-use than other routine pretreatment methods.

Estimating the toxicities of organic chemicals in activated sludge process

The experimental logEC50 toxicity values of 104 compounds causing bioluminescent repression of the bacterium strain Pseudomonas isolated from an industrial wastewater were studied. Using the Best Multilinear Regression method implemented in CODESSA PRO, models with up to 8 theoretical descriptors were obtained. Utilizing a rigorous descriptor selection and validation procedure a reliable QSAR model with four parameters was selected as best. The proposed model emphasizes the importance of the halogen atoms presented in each compound, the possibility of H-bond formation and the flexibility and degree of branching of the molecules. As pointed out by many researchers, the contribution of the octanol-water partition coefficient to the explanation of the toxicity effect was also found to be significant. In addition, the model currently proposed was compared to those reported earlier and its advantages were discussed in detail.

Prediction of acute mammalian toxicity from QSARs and interspecies correlations

With the ever-growing number of xenobiotics that can potentially contaminate the environment, the determination of their mammalian toxicity is of prime importance. In this context, LD50 tests on rats and mice have been used for a long time to express the relative hazard associated with the acute toxicity of inorganic and organic chemicals. However, these laboratory tests encounter important hurdles. They are costly, time consuming and actively opposed by animal rights activists. Moreover, new legislation policies, such as REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), aim at reducing the use of toxicity tests on vertebrates. Consequently, there is a need to find alternative methods for estimating the acute mammalian toxicity of chemicals. The quantitative structure-activity relationships (QSARs) and interspecies correlations appear particularly suited to reaching this goal. In this context, this paper reviews more than 150 models aiming at predicting rat and mouse LD50 values from molecular descriptors or (and) ecotoxicity data. The interest of these computational tools is discussed.

Comparison between the short-term and the long-term toxicity of six triazine herbicides on photobacteria Q67

The bioluminescence inhibition of six triazine herbicides including desmetryne (DES), simetryn (SIM), velpar (VEL), prometon (PRO), metribuzin (MET), and aminotriazine (AMI) on Vibrio qinghaiensis sp.-Q67 (Q67) was determined to investigate the effects of exposure duration on the ecotoxicological relevance of triazine herbicides. Based on the short-term microplate toxicity analysis (MTA), a long-term MTA was established to assess the impact of exposure time on the toxicities of the herbicides. The results show that the long-term toxicities of DES and SIM are similar to their short-term toxicities, and the long-term toxicities of VEL, PRO, and MET are higher than their short-term toxicities, while AMI without short-term toxicity has a high long-term toxicity. In addition, a parabolic relationship was found between the pEC(50) (the negative logarithm of the EC(50), log 1/EC(50)) and the logarithm of octanol-water partition coefficient (logK(ow)). To better understand their toxicity process, the time-dependent toxicities of the six herbicides on Q67 were determined over a period of 12 h during which measurements were taken every 30 min to generate an integral effect surface related to both concentration and duration.

Predictions of the EC50 for action potential block for aliphatic solutes

Experiments were conducted to test the hypothesis that aliphatic hydrocarbons bind to pockets/crevices of sodium (Na(+)) channels to cause action potential (AP) block. Aliphatic solutes exhibiting successively greater octanol/water partitition coefficients (K (ow)) were studied. Each solute blocked Na(+) channels. The 50% effective concentration (EC(50)) to block APs could be mathematically predicted as a function of the solute's properties. The solutes studied were methyl ethyl ketone (MEK), cyclohexanone, dichloromethane, chloroform and triethylamine (TriEA); the K (ow) increased from MEK to TriEA. APs were recorded from frog nerves, and test solutes were added to Ringer's solution bathing the nerve. When combined with EC(50)s for solutes with log K (ow)s < 0.29 obtained previously, the solute EC(50)s could be predicted as a function of the fractional molar volume (dV/dm = [dV/dn]/100), polarity (P) and the hydrogen bond acceptor basicity (beta) by the following equation: EC(50) = 2.612({-2.117[dv/dm]+0.6424P+2.628 beta}) Fluidity changes cannot explain the EC(50)s. Each of the solutes blocks Na(+) channels with little or no change in kinetics. Na(+) channel block explains much of the EC(50) data. EC(50)s are produced by a combination of effects including ion channel block, fluidity changes and osmotically induced structural changes. As the solute log K (ow) increases to values near 1 or greater, Na(+) channel block dominates in determining the EC(50). The results are consistent with the hypothesis that the solutes bind to channel crevices to cause Na(+) channel and AP block.

Safety assessment of MIBK (methyl isobutyl ketone)

MIBK (Methyl Isobutyl Ketone) is an aliphatic ketone that functions as both a denaturant and solvent in cosmetic products. Current use in cosmetic products is very limited, but MIBK is reported to be used in one nail correction pen (volume = 3 ml) at a concentration of 21%. The maximum percutaneous absorption rate in guinea pigs is 1.1 micromol/min/cm2 at 10 to 45 min. Metabolites include 4-hydroxy-4-methyl-2-pentanone (oxidation product) and 4-methyl-2-pentanol (4-MPOL) (reduction product). Values for the serum half-life and total clearance time of MIBK in animals were 66 min and 6 h, respectively. In clinical tests, most of the absorbed MIBK had been eliminated from the body 90 min post exposure. MIBK was not toxic via the oral or dermal route of exposure in acute, short-term, or subchronic animal studies, except that nephrotoxicity was observed in rats dosed with 1 g/kg in a short-term study. MIBK was an ocular and skin irritant in animal tests. Ocular irritation was noted in 12 volunteers exposed to 200 ppm MIBK for 15 min in a clinical test. A depression of the vestibulo-oculomotor reflex was seen with intravenous infusion of MIBK (in an emulsion) at 30 microM/kg/min in female rats. The no-observed-effect level in rats exposed orally to MIBK was 50 mg/kg. Both gross and microscopic evidence of lung damage were reported in acute inhalation toxicity studies in animals. Short-term and subchronic inhalation exposures (as low as 100 ppm) produced effects in the kidney and liver that were species and sex dependent. Dermal doses of 300 or 600 mg/kg for 4 months in rats produced reduced mitotic activity in hair follicles, increased thickness of horny and granular cell layers of the epidermis, a decrease in the number of reactive centers in follicles (spleen), an increase in the number of iron-containing pigments in the area of the red pulp (spleen), and a reduction in the lipid content of the cortical layer of the adrenal glands. Neuropathological changes in the most distal portions of the tibial and ulnar nerves were observed in young adult rats which inhaled 1500 ppm MIBK for up to 5 months. No adverse effects were seen in any other neurological end point by any route of exposure in other studies using rats or other animal species. Clinical tests demonstrated a threshold for MIBK-induced irritation of the lungs at 0.03 to 0.1 mg/L after 1 min of respiration. MIBK was not mutagenic in the Ames test or in a mitotic gene-conversion assay in bacteria. Mammalian mutagenicity test results were also negative in the following assays: mouse lymphoma, unscheduled DNA synthesis, micronucleus, cell transformation, and chromosome damage. MIBK did not induce any treatment-related increases in embryotoxicity or fetal malformations in pregnant Fischer 344 rats or CD-1 mice that inhaled MIBK at concentrations of 300, 1000, or 3000 ppm. There was evidence of treatment-related maternal toxicity only at the highest concentration tested. MIBK applied to the tail of rats daily at doses of 300 or 600 mg/kg for 4 months produced changes in the testes, including a reduction in the number of spermatocytes, spermatids, and spermatozoa. An ongoing carcinogenicity study of MIBK being conducted by the National Toxicology Program will be considered when the results are available. On the basis of the information that is currently available, MIBK is considered safe as used in nail polish removers and as an alcohol denaturant in cosmetic products.

Estimating the toxicities of organic chemicals to bioluminescent bacteria and activated sludge

Toxicity assays based on bioluminescent bacteria have several advantages including a quick response and an easily measured signal. The Shk1 assay is a procedure for wastewater toxicity testing based on the bioluminescent bacterium Shk1. Using the Shk1 assay, the toxicity of 98 organic chemicals were measured and EC50 values were obtained. Quantitative structure-activity relationship (QSAR) models based on the logarithm of the octanol-water partition coefficient (log(Kow)) were developed for individual groups of organic chemicals with different functional groups. The correlation coefficients for different groups of organic compounds varied between 0.69 and 0.99. An overall QSAR model without discriminating the functional groups, which can be used for a quick estimate of the toxicities of organic chemicals, was also developed and model predictions were compared to experimental data. The model accuracy was found to be one order of magnitude from the observed values.

Anesthetic activity of monoketones in mice: relationship to hydrophobicity and in vivo effects on Na+/K+ -ATPase activity and membrane fluidity

The in vivo anesthetic activity of monoketones in mice was examined in relation to their hydrophobicity and to the in vivo effects on Na+/K+ -adenosine triphosphatase (Na+/K+ -ATPase) activity and membrane fluidity. Anesthetic potency (AD50) of monoketones was determined; AD50 implys the dose required to anesthetize 50% of the animals from the treated group. The n-octanol/water partition coefficient (P) was used as an index of hydrophobicity. Membrane fluidity was determined by using 1,6-diphenyl-1,3,5-hexatriene (DPH) or 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH as fluorescence probes. Log (1/AD50) was the parabolic function of log P, log ((1/AD50) = -0.167(log P)2 + 0.698 log P - 1.365, and the log P that corresponds to the minimum AD50 was estimated to be 2.09. Brain synaptosomes were prepared from mice that were considered anesthetized with each of the 4 monoketones (1.5-fold AD50), methyl n-propyl, methyl n-amyl, methyl 3-methylhexyl and methyl n-octyl ketone. The Na+/K+ -ATPase activity was inhibited by methyl n-propyl ketone alone, membrane DPH fluidity was decreased by each of the 4 monoketones, and membrane TMA-DPH fluidity was decreased by methyl n-propylketone alone. These results suggest an involvement of the decreased DPH fluidity in monoketone-induced anesthesia.

Ketone potentiation of haloalkane-induced hepato- and nephrotoxicity. I. Dose-response relationships

Carbon tetrachloride (CCl4) induced hepatotoxicity and chloroform (CHCl3) induced nephrotoxicity were evaluated in male Sprague-Dawley rats pretreated with acetone (A), methyl ethyl ketone (MEK), and methyl isobutyl ketone (MiBK). Dose-response relationships for A, MEK, and MiBK potentiation of CCl4-induced hepatotoxicity and CHCl3-induced nephrotoxicity were compared. A, MEK, and MiBK pretreatment at a dosage of 6.8 mmol/kg, given daily for 3 d, markedly potentiated CCl4-induced liver toxicity as indicated by a decrease in the CCl4 ED50 to 3.4, 4.6, and 1.8 mmol/kg, respectively, compared to vehicle-pretreated rats (17.1 mmol/kg). Similarly, pretreatment with these ketones (13.6 mmol/kg) potentiated CHCl3 kidney toxicity but to a lesser degree; CHCl3 ED50 values for vehicle-, A-, MEK-, and MiBK-pretreated rats were 3.4, 1.6, 2.1, and 2.2 mmol/kg, respectively. Our results indicate a potency ranking profile for the potentiation of CCl4 hepatotoxicity of MiBK > A > MEK and of A > MEK > or = MiBK for CHCl3 nephrotoxicity. These dissimilar ranking profiles could be due to differences in mechanisms of action for the two target sites.

Structure-acute toxicity relationship of aromatic hydrocarbons in mice

The structure-acute toxicity relationship of aromatic hydrocarbons was examined in mice. In all test compounds, the acute toxicity was determined under 2 conditions: control LD50 (LD50-cont) and carbon tetrachloride (CCl4)-pretreated LD50 (LD50-CCl4). The CCl4-pretreatment was done in order to evaluate the toxic potency of compound itself without the influence of metabolism. Both log (1/LD50-cont) and log (1/LD50-CCl4) were functions of the log P, n-octanol/water partition coefficient, i.e., log (1/LD50-cont) = 0.080 log P - 1.532 and log (1/LD50-CCl4) = -0.040(logP)2 + 0.157 log P - 1.373. Both equations were statistically significant (P < 0.01). The ratio of LD50-cont/LD50-CCl4 indicated that metabolic activation is more evident in hydrophobic compounds than in hydrophilic compounds. The results suggest that hydrophobicity of the aromatic hydrocarbons plays an important role in determining their acute toxicity.

Structure-toxicity relationship of monoketones: in vitro effects on beta-adrenergic receptor binding and Na(+)-K(+)-ATPase activity in mouse synaptosomes

The structure-toxicity relationship of monoketones, a class of organic solvents widely used in industry, was investigated with respect to their in vitro effects on synaptosomal membrane proteins. The toxic parameters used were Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase), a well-known marker enzyme often used as a membrane toxicity model, and 3H-dihydroalprenolol (3H-DHA)-labeled beta-adrenergic receptor binding that has been shown to be vulnerable to solvent-induced changes in membrane fluidity. In vitro treatments with 12 kinds of monoketones (carbon chain length from 3-10) dose-dependently inhibited both 3H-DHA binding to mouse synaptosomes and Na(+)-K(+)-ATPase activity. The potency of inhibition (IC50) for both the two parameters was linearly related to n-octanol/water partition coefficient and synaptosome/buffer partition coefficient of the test compounds. Additions of monoketones did not significantly alter the number of 3H-DHA binding sites but markedly decreased their affinity. In each monoketone, the IC50 values for 3H-DHA binding and Na(+)-K(+)-ATPase activity were generally within the same range. The anisotropy of fluorescence probe 1,6-diphenyl-1,3,5-hexatriene-labeled synaptosomal membranes was dose-dependently decreased by the monoketones, implying increased membrane fluidity. These results indicate that increasing lipophilicity of monoketones results in increased solvent penetration of synaptic membrane preparations, leading to conformational changes in membrane structure and increased ability to inhibit both neuroreceptor binding and enzyme activity. The present data confirm the importance of the lipid micro-environment of membranes in maintaining the normal functions of membrane-bound proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-toxicity relationship of ethylene glycol ethers

The ultimate purpose of the present study was to evaluate correlations between acute in vivo and in vitro toxicity and log P (P is n-octanol-water partition coefficient). The in vitro toxicity to cloned cells (neuroblastoma N18TG-2 and glioma C6) in culture (ED50) and the in vivo toxicity to mice (LD50) of ethylene glycol ethers were studied in terms of the structure-activity relationship. The test ethers showed a wide range of ED50 values in both cells. LD50 was determined under two conditions: LD50-cont. was estimated in mice pretreated with olive oil and LD50-CCl4 in CCl4-pretreated mice. Multiple regression analyses revealed a significant correlation between log 1/LD50 and log P as follows: log (1/LD50-cont.) = -0.120 (log P)2+0.487log P-1.182, and log (1/LD50-CCl4) = -0.128 (log P)2+0.566log P-1.157. There was no significant correlation either between ED50 and LD50 or between ED50 for N18TG-2 and ED50 for C6. The results suggest that metabolic activation might not occur during acute toxicity from the ethers, and that hydrophobicity, expressed as log P, plays an important role in acute toxicity.

Critical review of the toxicity of methyl n-butyl ketone: risk from occupational exposure

Methyl n-butyl ketone (MBK) was considered rather harmless until an outbreak of peripheral neuropathy occurred in 1973 among workers exposed to MBK. MBK easily penetrates the skin; pulmonary retention is approximately 80-85% in man. Distribution is widespread with highest levels in blood and liver; MBK also reaches the fetal tissues. MBK metabolism probably depends on the route of exposure, and is very similar to that of n-hexane. The critical organ is the nervous system. These effects find expression as peripheral neuropathy, with potential for serious effects of the central nervous system. From the viewpoint of neurotoxicity, 2,5-hexanedione is the most important metabolite. The neurotoxicity is potentiated by several compounds, while MBK itself potentiates the toxicity of other chemicals. From animal experiments, a no-adverse-effect level (NAEL) could not be established. Peripheral neuropathy may develop in workers exposed to only a few ppm of MBK. The difference in the Occupational Exposure Limits for MBK and n-hexane, as established by several organizations, is questioned in view of the neurotoxic effects of these substances.

Survey of the QSAR and in vitro approaches for developing non-animal methods to supersede the in vivo LD50 test

Quantitative structure-activity relationship (QSAR) studies and in vitro studies in which correlations with LD50 have been sought are reviewed. QSAR methods have shown some success in relating LD50 to certain physicochemical properties of the compound, particularly lipophilicity, but have been less successful in correlating LD50 with electronic properties of molecules (related to reactivity) or structural variables. It is concluded that insufficient evidence is available to determine whether QSAR methods can be of general use in predicting the acute toxicity (LD50) of chemicals, and that until further work is undertaken to develop QSARs for a much wider range of homologous series of compounds, this situation is unlikely to be resolved. New chemical descriptors that are more directly relevant to the mechanism of toxic action of the chemical should be identified. Cytotoxicity in vitro is poorly correlated with LD50, but good correlations have been obtained between toxicity in vivo and in vitro, using systems in which the toxic endpoint reflects the probable mechanism(s) of acute toxicity of the test chemical (e.g. the assessment of neurotoxins using neural cell systems). Therefore, it seems that the successful application of in vitro methods requires a better understanding of the mechanisms of acute toxicity in vivo and the development of mammalian cell culture systems that can model more closely the metabolic fate of the chemicals in vivo.

Toward a quantitative comparative toxicology of organic compounds

Correlation equations between logP (P = octanol water partition coefficient) and the biological activity of alcohols has been derived for 101 examples on all sorts of systems, from simple proteins to whole animals. This provides an overview of the toxic nature of hydrophobic compounds which can be used as a basis for comparison of more complex chemicals. About 100 examples of the hydrophobic effects of chemicals, other than alcohols, to various living systems or their parts are presented for comparison. It is clear that hydrophobic xenobiotics are toxic to almost every form of life, including humans (or parts there of).