Positive and inverse correlation of blood lead level with erythrocyte acetylcholinesterase and intelligence quotient in children: implications for neurotoxicity

Blood lead level (BLL) is insufficiently sensitive for early detection of Lead-induced neurotoxicity (LIN). This study determined the possible role of the combination of BLL, intelligent quotient (IQ) and erythrocyte acetylcholinesterase (AChE) activity in the early detection of LIN in Children. Apparently healthy children (n=309) from eight public primary schools in Ibadan, Nigeria were recruited and classified into: children with Elevated BLL (EBLL) and children with Acceptable BLL (control) based on CDC cut-off for childhood lead exposure. Neurological indices (speech, memory, cranial nerves and cerebellar functions), IQ, BLL and erythrocyte AChE activity were assessed using standard methods, Standard Progressive Matrices, AAS and HPLC respectively. Statistical analysis involved Student’s t-test, Pearson’s correlation and multivariate regression. p<0.05 was considered significant. There were 169 (54.7%) children with EBLL while there were 140 (45.3%) control children. Both groups exhibited normal speech, memory, cranial nerves and cerebellar functions. However, IQ was lower in EBLL children (85.9±11.6) compared with control (91.5±14.0) while BLL and AChE activity were higher in EBLL children (0.4±0.1 µmol/l; 117.5±25.5 µkat/l) compared with control (0.2±0.0 µmol/l; 59.4±10.2 µkat/l). BLL showed inverse correlation with IQ (r=–0.134, p=0.019) but positive correlation with AChE (r=0.978, p≤0.001). 16.2% of the observed variation in BLL could be accounted for by AChE using the equation; [BLL=–0.007+0.003 AChE] p<0.05. Elevated blood lead level is prevalent among the school children and appears to have adverse effect on their IQ. Erythrocyte AChE could be a promising marker for early recognition of significant environmental lead exposure and lead-induced neurotoxicity in children.

PECULIARITIES OF METABOLITES TOXICOKINETICS OF G-TYPE ORGANOPHOSPHORUS NERVE AGENTS IN BIO FLUIDS OF RATS SUBECTED TO ANTIDOTE THERAPY

The effect of the Pelixim antidote on the possibility to detect markers of G type nerve agents sarin and soman was studies in bio probes obtained in an acute in vivo experiment after exposure of rats to organophosphorus nerve agents in doses of 0.5LD50. It was found out that the intake of equitoxic doses of soman and sarin leads to a decrease of acetylcholinesterase erythrocyte membrane (AChE) activity for up to 7 days after exposure. The effect of Pelixim on the recovery of erythrocyte AChE activity is mostly pronounced a day after sarin poisoning. The fluoride regeneration of nerve agents from blood plasma protein adducts was possible for up to 7 days after soman poisoning without antidotal therapy and for 3 days after with antidotal therapy; in case of sarin intoxication, fluoride regeneration was possible for 3 days regardless of the use of antidotal therapy . The antidote strongly affected the excretion of hydrolytic metabolite of sarin О-isopropyl methylphosphonic acid (IMPA) and had no effect on the excretion of hydrolytic metabolite of soman О-pinacolyl methylphosphonic acid (PMPA). A day after poisoning and Pelixim injection, IMPA was detected in urine at a level of 15.3 ng/ml, whereas its level in the urine samples of animals in the absence of antidotal therapy was 55.0 ng/ml; 3 days after poisoning, IMPA was detected at a level of 4.9 ng/ml exclusively in the urine of animals subjected to antidotal therapy. The urine levels of PMPA in animals subjected and not subjected to antidotal therapy were respectively 44 and 53 ng/ml a day after poisoning and 12 and 14 ng/ml respectively 3 days after poisoning. Thus, the antidote impact on the excretion profile of hydrolytic metabolites is more significant for sarin than that of soman.

LABORATORY EXAMINATION IN NERVE AGENT INTOXICATION

Diagnosis of nerve agent intoxication is based on anamnestic data, clinical signs and laboratory examination. For acute poisoning, cholinesterase activity in the blood (erythrocyte AChE, plasma/serum BuChE) is sensitive, simple and most frequent laboratory examination performed in biochemical laboratories. Specialized examinations to precise treatment (reactivation test) or to make retrospective diagnosis (fluoride induced reactivation etc.) can be conducted. Other sophisticated methods are available, too.

Evaluation of HI-6 oxime: potential use in protection of human acetylcholinesterase inhibited by antineoplastic drug irinotecan and its cyto/genotoxicity in vitro.

The function of acetylcholinesterase (AChE) is the rapid hydrolysis of the neurotransmitter acetylcholine (ACh), which is involved in the numerous cholinergic pathways in both the central and the peripheral nervous system. Therefore, AChE measurement is of high value for therapy management, especially during the course of intoxication with different chemicals or drugs that inhibit the enzyme. Pyridinium or bispyridinium aldoximes (oximes) are able to recover the activity of the inhibited enzyme. Since their adverse effects are not well elucidated, in this study the efficiency of HI-6 oxime in protection and/or reactivation of human erythrocyte AChE inhibited by the antineoplastic drug irinotecan as well as its cyto/genotoxicity in vitro were investigated. HI-6 was effective in protection of AChE and increased its activity up to 30%; the residual activity after irinotecan inhibition was 7%. Also, it reactivated the enzyme previously inhibited by 50% irinotecan (4.6 microg/ml) applied at 1/4 of the IC50 value. The tested concentrations of HI-6 exhibited acceptable genotoxicity towards white blood cells, as estimated by the alkaline comet assay, DNA diffusion assay and cytogenetic endpoints (structural chromosome aberrations and cytokinesis-block micronucleus assay). The results obtained warrant the further investigation of HI-6 in vivo, as well as its development for possible application in chemotherapy.

Induction of oxidative stress and acetylcholinesterase inhibition in organophosphorous pesticide manufacturing workers

Oxidative stress status and acetylcholinesterase (AChE) activity were studied in blood samples obtained from 45 organophosphorous (OP)-formulating pesticide workers with a minimum work history of 1 year in the age range of 23–55. Controls were age-matched workers of a food-making factory. They were evaluated for oxidative stress markers, including thiobarbituric acid-reactive substances (TBARS) indicator of lipid peroxidation (LPO), ferric-reducing ability of plasma (FRAP) indicator of total anti-oxidant capacity, total thiol (SH) groups and gamma glutamyl transpeptidase (GGT) levels in blood and AChE activity in erythrocytes. The results show marked inhibition of AChE activity, increased TBARS, decreased FRAP and decreased thiol group levels in workers. The reduction in activity of AChE correlated well with increased TBARS and decreased FRAP in OP formulators. It is concluded that OP-formulating workers are exposed to more oxidative stress. The measurement of erythrocyte AChE activity in pesticide workers who formulate OPs can be a good monitoring factor and is recommended to be performed in a regular manner.

Enzyme-based assay for quantification of paraoxon in blood of parathion poisoned patients

1 Paraoxon concentration was estimated by means of inhibition kinetics observed with electric eel acetylcholinesterase (AChE) which was determined by a modified Ellman procedure. In human plasma, paraoxon was stabilized by inactivation of paraoxonase with EDTA and aluminon and by inhibition of butyrylcholinesterase with ethopropazine. Paraoxon (1-50 ng) was recovered at 86+1.7% (mean+s.e.m.) in ether extracts from 0.5 ml samples of spiked stabilized plasma. It could be stored without loss at 7208C for at least 1 month. 2 The enzyme-based assay was applied to follow the paraoxon plasma concentrations in three suicidal patients with severe parathion poisoning. In poisoning with excessive doses and initial paraoxon concentrations above 500 nM, therapeutic obidoxime concentrations of approximately 10 mM failed to essentially reactivate erythrocyte AChE in vivo, while reactivat-ability ex vivo was nearly complete. With the plasma concentrations of paraoxon dropping below 100 nM, however, reactivation by obidoxime became signifi-cant. Unexpectedly, paraoxon levels occasionally re-increased during treatment and resulted in re-inhibition of AChE, bearing some resemblance to the Intermediate Syndrome. 3 The paraoxon concentrations measured fitted satisfactorily the values calculated from the kinetic constants previously obtained for AChE inhibition and obidoxime-induced reactivation in vitro. This indicates that diethylphosphoryloxime formation during obidoxime-induced reactivation does not markedly contribute to the re-inhibition of AChE as observed in vitro.