The joint neurotoxic action of inhaled methyl butyl ketone vapor and dermally applied O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens: potentiating effect

Sarin: health effects, metabolism, and methods of analysis

Sarin (O-isopropylmethylphosphonofluoridate) is a highly toxic nerve agent produced for chemical warfare. Sarin is an extremely potent acetylcholinesterase (AchE) inhibitor with high specificity and affinity for the enzyme. Death by sarin is due to anoxia resulting from airway obstruction, weakness of the muscles of respiration, convulsions and respiratory failure. The main clinical symptoms of acute toxicity of sarin are seizures, tremors and hypothermia. Exposure to sarin during incidents in Japan in 1994, 1995 and 1998, and possible exposure to low levels of sarin during the Gulf War, resulted in the deaths and injury of many people in Japan and caused possible long-term health effects on Gulf War veterans. Symptoms related to sarin poisoning in Japan still exist 1-3 years after the incident and include fatigue, asthenia, shoulder stiffness and blurred vision. Sarin produced seizures in rats and pigs. Recent studies showed that long-term exposure to low levels of sarin caused neurophysiological and behavioral alterations. Toxicity from sarin significantly increased following concurrent exposure to other chemicals such as pyridostigmine bromide. Further research to examine effects of sarin on the cellular and the molecular levels, gene transcription, endocrine system as well as its long-term impact is needed.

Spectrophotometric analysis of solubilized rat hair proteins following intraperitoneal injection of 2,5-hexanedione

The neurotoxic industrial solvents n-hexane and methyl n-butyl ketone are toxic by virtue of their common metabolite, 2,5-hexanedione (2,5-HD). Our previous work showed that pyrrole-like substances in solubilized rat hair proteins from rats injected (ip) daily with 2,5-HD demonstrated maximal absorbance in the 530-nm spectral region following reaction with Ehrlich's reagent (p-dimethylaminobenzaldehyde). Modification of the current analytical methods of achieving high specificity and lower detection limits with small sample quantities could have important implications for monitoring human populations. Adult male Sprague-Dawley rats were housed in individual metabolic cages with food and water provided ad libitum. Individual rats were injected (ip) daily with either 50 mg/kg 2,5-HD or physiologic-buffered saline (PBS). Plucked hair samples (dorsal, right flank, and left flank) were obtained from each rat before and at 7-day intervals after exposure to 2,5-HD or PBS for 28 days. Hair proteins solubilization and extraction procedures were adapted from earlier studies. We read 1 mL of dialyzed hair protein solution (2,5-HD or PBS control) against a reference cuvette containing water. Analyses utilized a Shimadzu UV 160 V recording spectrophotometer at an absorbency spectral range of 450 to 600 nm. In all spectral tracings, absorbance maxima (at 530 nm) characteristic of pyrrole-like substances were detected only in samples from 2,5-HD-treated rats. Absorbance at 530 nm was detected starting at Day 7 after exposure. The authors acknowledge Dr. Richard Whorton and Dr. Barbara Buckley for advice and for the use of their spectrophotometric equipment and Dr. Lowell A. Goldsmith for his help in our choice of the subject studied. This work was supported by the Walter P. Inman Memorial Fund in an award from Duke University to Dr. Leon Lack.

Effect of pesticide mixtures on in vitro nervous cells: comparison with single pesticides

The toxicity of dimethoate, azinphos-methyl, diazinon, pirimiphos methyl, organophosphorus insecticides, and benomyl (a benzimidazole fungicide) singly and in mixture was studied in a human neuroblastoma cell line, SH-SY5Y. The cells were incubated for 30 min and 4 h with pesticides at concentrations ranging from 0.4 to 100 micrograms/ml, or with the same compounds mixed as follows: (a) dimethoate-diazinon-azinphos; (b) benomyl-pirimiphos; (c) all together. Pesticides in the mixtures were at the same concentration used when tested singly. Diazinon, azinphos-methyl and pirimiphos, but not dimethoate and benomyl, inhibited acetylcholine esterase (AchE) activity, whereas all the compounds inhibited protein synthesis in the following order: benomyl > azinphos > diazinon >> pirimiphos = dimethoate. The mixtures showed a toxicity on AchE activity at a maximum equal to that of the most active compound in the mixture. On the contrary, the mixture were more toxic than the single compounds on protein synthesis, and in certain cases potentiation occurred. Therefore, we can conclude that it is not feasible to predict the toxicity of pesticide mixtures on the basis of the results of the toxicity of single components.

Protein-bound pyrroles in rat hair following subchronic intraperitoneal injections of 2,5-hexanedione

Studies were initiated to ascertain whether body hair could be used to develop a biological marker for chronic exposure to industrial neurotoxicants that yield the metabolite 2,5-hexanedione (2,5-HD), that is, n-hexane and methyl n-butyl ketone. Rats were injected daily with a 50 mg/kg ip dose of 2,5-HD for 45 d. At intervals, body hair and individual vibrissae were removed (under general anesthesia) and tested for the presence of pyrrole substances with p-N,N-dimethylaminobenzaldehyde (DMAB, Ehrlich's reagent). Vibrissae and body hair were stained a reddish color that was distinctly different from that observed with the hair taken from control animals. Solubilized body hair protein from the treated animals gave a positive Ehrlich's test, while that from control animals was negative. Spectral analysis of the DMAB-treated hair from experimental animals disclosed a maximum absorbance at 530 nm, which indicated the presence of pyrrole substituents. Serial analysis of individual nose hairs taken during 2,5-HD administration showed a progression with time of the region staining positively for pyrroles, thus indicating that the process can proceed in growing hair. These findings suggest the potential utility of hair as an indicator for chronic exposure to this class of industrial chemicals possessing neurotoxicity potential. This could complement urinary analysis, which is now used to confirm recent exposure.

Assessment of the neurotoxic potential of chlorpyrifos relative to other organophosphorus compounds: a critical review of the literature

Chlorpyrifos (diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate) is a broad-spectrum organophosphorus (OP) insecticide. Anticipated increases in the already extensive use of this compound have prompted this reassessment of its neurotoxicity. Because chlorpyrifos and other OP insecticides are designed to produce acute cholinergic effects through inhibition of acetylcholinesterase (AChE) and some OP compounds can cause OP compound-induced delayed neurotoxicity (OPIDN) via chemical modification of neurotoxic esterase (neuropathy target esterase, NTE), this review focuses on the capacity of chlorpyrifos to precipitate these and other adverse neurological consequences. Chlorpyrifos exhibits only moderate acute toxicity in many mammalian species, due largely to detoxification of the active metabolite, chlorpyrifos oxon, by A-esterases. Rats given large doses of chlorpyrifos (sc in oil) have prolonged inhibition of brain AChE, possibly due to slow release of the parent compound from a depot. Associated cognitive and motor deficits return to normal well before recovery of AChE activity and muscarinic receptor down-regulation, as expected from classic tolerance. Controlled studies of OP compound exposures in humans also indicate that cognitive dysfunction requires substantial AChE inhibition. Information is relatively sparse on neurological dysfunction that is secondary to theoretical reproductive, developmental, or immunological effects, but the best available data indicate that such effects are unlikely to result from exposures to chlorpyrifos. In accord with the much greater inhibitory potency of chlorpyrifos oxon for AChE than for NTE, clinical reports and experimental studies indicate that OPIDN from acute exposures to chlorpyrifos requires doses well in excess of the LD50, even when followed by repeated doses of the OPIDN potentiator phenylmethanesulfonyl fluoride (PMSF). Likewise, studies in hens show that subchronic exposures at the maximum tolerated daily dose do not result in OPIDN. Although exposure to chlorpyrifos as a result of normal use is unlikely to produce classical OPIDN, a recent report stated that mild reversible sensory neuropathy had occurred in eight patients who had been exposed subchronically to unknown amounts of chlorpyrifos. It is not clear whether these cases represent an incorrect linkage of cause and effect, a newly disclosed reversible sensory component of OPIDN, or an entirely new phenomenon. The question of the potential for chlorpyrifos to cause this mild sensory neuropathy could be resolved by the use of quantitative tests of sensory function in animal experiments and/or prospective studies of humans with known exposures to chlorpyrifos.

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.

Subclinical effects of groundwater contaminants. IV. Effects of repeated oral exposure to combinations of benzene and toluene on regional brain monoamine metabolism in mice

Benzene and toluene are known neurotoxicants that may interact in vivo. The effect of combined treatment with benzene and toluene on the endogenous concentrations of the catecholamines norepinephrine (NE) and dopamine (DA), the catecholamine metabolites vanillylmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the indoleamine serotonin (5-HT) and its metabolite 5-hydroxy-indoleacetic acid (5-HIAA), were investigated in six discrete brain regions of CD-1 mice. Groups of male, adult mice were continuously exposed to benzene (166 mg/l), toluene (80 and 325 mg/l), and combinations of benzene + toluene (80 or 325 mg/l) in drinking water for 4 weeks. Benzene produced increases of NE in the hypothalamus, cortex, midbrain and medulla oblongata, DA in the hypothalamus and corpus striatum, and 5-HT in all dissected brain regions except cerebellum. Elevated levels of various monoamine metabolites were also observed in these brain areas. Toluene ingestion alone also significantly increased the concentrations of NE, DA, 5-HT, and their metabolites in several brain regions. Mice given the combined treatments exhibited raised regional neurochemical levels when compared to the untreated controls. Increased concentrations of biogenic amine metabolites in several brain regions were greater in the combined exposures of benzene and toluene than when either chemical was used alone. The findings were different from those observed on immune parameters using similar treatment protocols, where simultaneous exposure to toluene prevented the immunotoxic effects of benzene.

Low non-neuropathic tri-o-cresyl phosphate (TOCP) doses inhibit neuropathy target esterase near the neuropathic threshold in n-hexane pretreated hens

Simultaneous intoxication with hexacarbon solvents and organophosphorus compounds has been considered a possible critical factor in some occupational neuropathies and their interactions proved to cause potentiation effects in hens [1-3]. A high degree of inhibition of neuropathy target esterase (NTE) is needed to develop organophosphorus induced polyneuropathy (OPIDP). In this work, the inhibition of NTE, BuChE and AChE by TOCP on control and n-hexane pretreated (7-15 days, 300 mg/kg per day) hens is studied. Using a single TOCP dose of 200 mg/kg, n-hexane pretreated hens showed synergistic effects, but no significant differences were observed in the inhibition of cholinesterases and NTE in brain or spinal cord. With lower TOCP dose (20 mg/kg) statistically significant differences were observed, which were not drastic but could be important because they involved an increase of inhibition up to critical threshold values (from 40-50% to 60-70% inhibition). However, no clinical effects were observed in these animals. Possible mechanisms of neurotoxic interaction are discussed.

Neurotoxic effects of combined treatment of 2,5-hexanedione and triethyllead chloride

Triethyllead chloride and 2,5-hexanedione are known neurotoxicants that apparently work through separate mechanisms. The effect of combined treatment of triethyllead chloride and 2,5-hexanedione for 6 weeks on Fischer 344 rats was investigated. Ten rats were given 0.7 mg/kg triethyllead chloride in a volume of 2 ml/kg by gavage while another group was given 0.5% 2,5-hexanedione in drinking water and vehicle by gavage (2 ml/kg). A third group was given a combination of the two treatments. A fourth group served as controls and was given vehicle by gavage. 2,5-Hexanedione produced a reversible loss of body weight, decreased grip strength, and decreased horizontal motor activity. Triethyllead chloride alone increased hot-plate latencies. Triethyllead chloride and 2,5-hexanedione treated animals recovered 4 weeks after cessation of treatment. Neither treatment alone produced fatalities. In combination (2,5-hexanedione + triethyllead chloride) decreases in body weight appeared additive and there was a 40% mortality by 6 weeks of dosing. Rats given the combined treatment had significant loss of both grip strength and increased hot-plate latencies. Neurobehavioral deficits and neuropathological changes were greater in the combined treatment with 2,5-HD and TEL than when either chemical was used alone; there was little indication of a synergistic interaction between these two types of neurotoxicants.

Analysis of n-hexane, 2-hexanone, 2,5-hexanedione, and related chemicals by capillary gas chromatography and high-performance liquid chromatography

Analytical methods, using capillary gas chromatography and normal-phase high-performance liquid chromatography, were developed for the analysis of the neurotoxic chemicals n-hexane, 2-hexanone, and 2,5-hexanedione and their suspected metabolites. Two gas chromatographic methods, using a 50-m glass capillary OV 101 column and cyclohexane as an internal standard, were employed. In both methods, the injector and detector temperatures were 220 and 280 degrees C, respectively. In method I the following temperature program was used: isothermic at 50 degrees C for 30 min, followed by a temperature increase of 10 degrees C/min to a final temperature of 180 degrees C, which was then maintained for 7 min. This method was used to analyze the following compounds: n-hexane, 2,5-dimethylfuran, 2-hexanone, 3-hexanone, hexanal, 1-hexanol, 2-hexanol, 3-hexanol, 5-hydroxy-2-hexanone, gamma-valerolactone, 2,5-hexanedione, and 2,5-hexanediol. Method II, which was developed for n-hexane and eight of its more common metabolites, used the following temperature program: isothermic at 70 degrees C for 15 min, followed by a temperature increase of 40 degrees C/min to a final temperature of 220 degrees C, which was maintained for 5 min. A linear relationship between peak area and amount injected was observed over a 100-fold range. The minimum detectable amounts ranged from 0.05 to 1 microgram, depending on the compound. Normal-phase HPLC, using a 5-micron silica cartridge fitted into an RCM-100 radial-compression separation system, was utilized to analyze 2-hexanone and its metabolites 2,5-dimethylfuran, gamma-valerolactone, 5-hydroxy-2-hexanone, and 2,5-hexanedione.(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern of neurotoxicity of n-hexane, methyl n-butyl ketone, 2,5-hexanediol, and 2,5-hexanedione alone and in combination with O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens

This investigation was designed to study the neurotoxicity produced in hens by the aliphatic hexacarbons n-hexane, methyl n-butyl ketone (MnBK), 2,5-hexanediol (2,5-HDOH), and 2,5-hexanedione (2,5-HD) following daily dermal application of each chemical alone and in combination with O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN). Dermal application was carried out on the unprotected back of the neck. To assess whether the joint neurotoxic action of various chemicals is caused by the enhancement of absorption through the skin or by interaction at the molecular level, two additional experiments were performed. In the first experiment, EPN was dissolved in each of the aliphatic hydrocarbons prior to their topical application. In the second experiment, EPN was dissolved in acetone and applied at a different location from that of the aliphatic hexacarbons. Dermal application was carried out for 90 d followed by a 30-d observation period. The results show that hens treated with EPN developed severe ataxia followed by improvement during the observation period; n-hexane produced leg weakness with subsequent recovery, whereas the same dose of MnBK, 2,5-HDOH, or 2,5-HD produced clinical signs of neurotoxicity characterized by gross ataxia; concurrent dermal application of EPN with n-hexane or 2,5-HDOH at the same site or at different sites produced an additive neurotoxic action; simultaneous dermal application of EPN and MnBK at different sites resulted in an additive effect, whereas it caused potentiation when applied at the same site; and concurrent topical application of EPN and 2,5-HD produced a potentiating neurotoxic effect. While no histopathologic lesion was produced at the end of the observation period when any test chemical was applied alone, binary treatments of EPN and aliphatic hexacarbons resulted in histopathologic changes in some hens, with morphology and distribution characteristic of EPN neurotoxicity. The joint potentiating or additive action of aliphatic hexacarbons on EPN neurotoxicity was: 2,5-HD greater than MnBK greater than 2,5-HDOH greater than n-hexane. The mechanism of this joint action seems to be related both to enhancing skin absorption of EPN and/or its metabolic activation by n-hexane and its related chemicals.