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Phenylmethylsulfonyl fluoride protects rats from Mipafox-induced delayed neuropathy
Abstract:
Initiation of organophosphorus-induced delayed neuropathy (OPIDN) is thought to consist of two molecular events involving the phosphorylation of the target enzyme, neurotoxic esterase, or neuropathy target enzyme (NTE), and a subsequent "aging" reaction which transforms the inhibited NTE into a charged moiety critical to the neuropathic process. Compounds that inhibit NTE but cannot age because of their chemical structure abort this two-stage initiation process, and when administered before a neurotoxic organophosphorus compound (OP), protect against the neuropathy by blocking NTE's active site (Johnson, 1970). In support of this, we report that prior exposure to a nonaging NTE inhibitor, phenylmethylsulfonyl fluoride (PMSF), protects rats from neurological damage after subsequent exposure to a neurotoxic OP, Mipafox. Adult, male, Long Evans rats were exposed to either PMSF (250 mg/kg, sc) or to Mipafox (15 mg/kg, ip) and a time course of brain NTE inhibition and recovery was defined. A separate group of PMSF-treated rats was exposed to Mipafox when brain NTE inhibition was 87.7 +/- 2.3%. Conversely, another group of rats, pretreated with Mipafox, was dosed with PMSF when NTE inhibition was 90.2 +/- 0.8%. A third group of animals, treated with PMSF, was exposed to Mipafox 14 days later, when NTE activity had recovered to within 10 +/- 4.2% of control amounts. Histopathological survey (14 to 21 days post-exposure) indicated severe cervical cord damage (damage score greater than or equal to 3) in the following frequencies: PMSF, 0%; Mipafox, 85%; PMSF-4 hr-Mipafox, 0%; Mipafox-4 hr-PMSF, 100%; PMSF-14 days-Mipafox, 75%; controls, 0%. These data indicate that PMSF pretreatment protects rats against Mipafox-induced neurological damage and that the timing of administration and order of presentation are critical to this protection. These results support the hypothesis that the initiation of OPIDN is a multistage event involving inhibition and aging, and these stages are experimentally separable.
Insights
Phenylmethylsulfonyl fluoride (PMSF) prevents organophosphorus-induced delayed neuropathy (OPIDN) by blocking neurotoxic esterase (NTE) inhibition. This study demonstrates that the timing of inhibitor administration is critical for protection against nerve damage.
Area of Science:
- Neuroscience
- Toxicology
- Biochemistry
Background:
- Organophosphorus-induced delayed neuropathy (OPIDN) is a neurotoxic process initiated by specific organophosphorus compounds.
- OPIDN is believed to involve two key molecular events: phosphorylation of neurotoxic esterase (NTE) and a subsequent "aging" reaction.
- Compounds that inhibit NTE but do not undergo aging can act as protective agents by blocking NTE's active site.
Purpose of the Study:
- To investigate the protective effect of phenylmethylsulfonyl fluoride (PMSF), a non-aging NTE inhibitor, against Mipafox-induced OPIDN in rats.
- To determine the critical role of the timing and order of administration of NTE inhibitors in preventing OPIDN.
Main Methods:
- Adult male Long Evans rats were exposed to PMSF or Mipafox, with varying time intervals and sequences between treatments.
- Neurotoxic esterase (NTE) inhibition levels were monitored over time.
- Histopathological examination of the cervical cord was performed 14 to 21 days post-exposure to assess neurological damage.
Main Results:
- Prior administration of PMSF significantly protected rats from Mipafox-induced neurological damage.
- Protection was observed when PMSF was given before Mipafox, but not when Mipafox was administered first.
- The timing of PMSF administration relative to Mipafox exposure was crucial for preventing OPIDN, with protection diminishing as NTE activity recovered.
Conclusions:
- Phenylmethylsulfonyl fluoride (PMSF) pretreatment effectively protects against Mipafox-induced organophosphorus-induced delayed neuropathy (OPIDN).
- The findings support a two-stage model for OPIDN initiation, involving distinct inhibition and aging phases.
- The experimental separability of these stages highlights the importance of timing in the development and prevention of OPIDN.