Organophosphorus-induced neurotoxicity in the absence of neuropathy target esterase inhibition: the effects of triphenyl phosphine in the European ferret

Organophosphate neurotoxicity to the voluntary motor system on the trail of environment-caused amyotrophic lateral sclerosis: the known, the misknown, and the unknown

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset paralytic disorder. It is characterized by progressive degeneration of the motor neurons controlling voluntary movement. The underlying mechanisms remain elusive, a fact that has precluded development of effective treatments. ALS presents as a sporadic condition 90-95% of the time, i.e., without familial history or obvious genetic mutation. This suggests that ALS has a strong environmental component. Organophosphates (OPs) are prime candidate neurotoxicants in the etiology of ALS, as exposure to OPs was linked to higher ALS incidence among farmers, soccer players, and Gulf War veterans. In addition, polymorphisms in paraoxonase 1, an enzyme that detoxifies OPs, may increase individual vulnerability both to OP poisoning and to the risk of developing ALS. Furthermore, exposure to high doses of OPs can give rise to OP-induced delayed neuropathy (OPIDN), a debilitating condition akin to ALS characterized by similar motor impairment and paralysis. The question we pose in this review is: "what can we learn from acute exposure to high doses of neurotoxicants (OPIDN) that could help our understanding of chronic diseases resulting from potentially decades of silent exposure (ALS)?" The resemblances between OPIDN and ALS are striking at the clinical, etiological, neuropathological, cellular, and potentially molecular levels. Here, we critically present available evidence, discuss current limitations, and posit future research. In the search for the environmental origin of ALS, OPIDN offers an exciting trail to follow, which can hopefully lead to the development of novel strategies to prevent and cure these dreadful disorders.

Rat NTE-related esterase is a membrane-associated protein, hydrolyzes phenyl valerate, and interacts with diisopropylfluorophosphate through a serine catalytic machinery

The serine hydrolases constitute multi-families of proteins that include lipases, esterases, and proteases. These enzymes contain a signature motif GXSXG, in which the serine residue acts as the nucleophile and initiates catalysis. This report describes the characterization of a novel serine hydrolase from rat. This enzyme exhibits a moderate sequence identity with the neuropathy target esterase (NTE), thus is designated NTE-related esterase (NRE). Transfection with the NRE cDNA resulted in marked increases in the hydrolysis of phenyl valerate and reactivity with diisopropylfluorophosphate. Such increases, however, were markedly or completely abolished in mutants that had a substitution (Ala, Cys, Asp, or His) on the serine residue in the GXSXG motif, providing direct evidence that NRE is a serine hydrolase. By Northern blot analyses, three NRE transcripts were detected and they differed markedly in length (approximately 2.6, 4.2, and 5.0 kb). The 4.2-kb transcript was present in all organs analyzed except the testis, in which both 2.6- and 5.0-kb transcripts were detected. The testicular transcripts were completely depleted in rats treated with clofibrate, whereas the levels of NRE mRNA in the liver were markedly increased in rats treated with perfluorodecanoic acid. Both clofibrate and perfluorodecanoic acid are efficacious activators of the peroxisome proliferator activated receptor-alpha (PPAR-alpha). The differential effects on the levels of NRE mRNA suggest that these chemicals regulate the expression of NRE through mechanism(s) rather than the activation of PPAR-alpha.

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.