Dose-related accumulation of organophosphate phosphamidon in discrete regions of the CNS: correlation with its neurotoxicity

Effect of piracetam and vitamin E on phosphamidon-induced impairment of memory and oxidative stress in rats

Organophosphate pesticides, such as phosphamidon (PHOS), have been shown to adversely affect memory and induce oxidative stress after both acute and chronic exposure. The present study was therefore designed to investigate the effects of piracetam (PIR) and vitamin E on PHOS-induced modulation of cognitive function and oxidative stress in rats. Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on an elevated plus maze. Oxidative stress was assessed by examining the levels of malondialdehyde (MDA) and nonprotein thiols (NP-SH) in isolated homogenized whole brain samples. The results showed a significant reduction in SDL and a prolongation of TL in the PHOS (1.74 mg/kg/day per oral; p.o.)-treated group at weeks 6 and 8, as compared to the control group. Administration of PIR (600 mg/kg/day p.o.) or vitamin E (125 mg/kg/day p.o.) for 2 weeks antagonized the effect of PHOS on SDL as well as TL. PHOS per se produced a significant increase in brain MDA levels and a decrease in brain NP-SH levels, whereas administration of PIR (600 mg/kg/day p.o.) or vitamin E (125 mg/kg/day p.o.) attenuated these effects. Thus, the results of the study showed that both PIR and vitamin E attenuated the cognitive dysfunction and oxidative stress induced by PHOS in the rat brain.

Brain involvement in organophosphate poisoning

Organophosphate poisonings cause substantial morbidity and mortality worldwide; however, the neurological effects have not been clearly established. We have studied cerebral perfusion to investigate neurotoxic effects. Clinical effects, plasma cholinesterase activity, and brain single photon emission computerization tomography (SPECT) data were investigated in 16 patients with organophosphate poisonings. The subjects were from an adult intensive care unit in a university hospital. Cholinesterase activity in plasma was determined upon admission and then every day in the morning. Brain SPECT studies were performed during the first week, at the end of therapy, and 3 months after discharge. Patients were classified into 3 groups using a modified Namba classification: latent poisoning (Group A); mild and moderate poisoning (Group B); or severe poisoning (Group C). None of the 6 patients in Group A showed any symptoms; 3 patients in Group B had muscarinic and nicotinic effects; 5 patients in Group C had muscarinic, nicotinic, and central nervous system symptoms. The average plasma cholinesterase for Groups A, B, and C were 54.16 +/- 9.10, 42.2 +/- 12.02, and 13 +/- 4.84 U/ml, respectively (normal range of plasma cholinesterase is 40-80 U/ml). Only 1 patient from Group A required treatment with oxime; 2 patients from Group B and all patients in Group C were given oxime, atropine sulfate, and mechanical ventilation. In the brain SPECT studies, the patients in Group A showed fewer perfusion defect areas than did Group B and C patients. All cases showed perfusion defects especially in the parietal lobe. In addition, perfusion improvement took more time for Group C than for the other groups. The intensive care unit stays of Group C were statistically longer than for Groups A and B. We concluded that brain SPECT is a highly sensitive diagnostic method, together with clinical symptoms and plasma cholinesterase activity, for monitoring the clinical prognosis of organophosphate poisonings.