Multiple signal transduction pathways alterations during nerve agent toxicity.

Nerve agent toxicity is primarily due to the synaptic build up of toxic levels of acetylcholine. The acute lethal effects of the nerve agents are generally attributed to respiratory failure caused by a combination of effects at both central and peripheral levels and are further complicated by copious secretions, muscle fasciculations, and convulsions. In addition to this, a range of non cholinergic effects have been observed. The development of effective treatment to block multiple effects resulting from nerve agent exposure is hampered by a limited understanding of the molecular changes responsible for their persistent effects. Excessive accumulation of acetylcholine leads to activation nicotinic and muscarinic acetylcholine receptors, these receptors activate diverse kind of cellular responses by distinct signaling pathways. Metabolism of cyclic nucleotides, membrane phospholipids, activation of a multitude of protein kinases and the induction of transcription factors are the key biochemical steps and pathways that have been investigated. This review will focus on the effects of nerve agents on signal transduction pathways; particularly, MAP kinases, protein kinase C isozymes, calcium calmodulin dependent protein kinase II (CaMKII) and on cytoskeletal proteins, calpain, and certain transcription factors and discusses how such changes may be involved in nerve agent induced neurotoxicity. Alterations in these key brain proteins could explain the neurological impairments following nerve agent exposure. A better understanding of the whole picture may lead to new pharmacological interventions aimed to improve or modulate those signal transduction pathways affected during nerve agent poisoning or associated pathologies that are responsible for neuronal disturbances.

Gene expression and phosphoprotein profile of certain key neuronal signaling proteins following soman intoxication.

Nerve agents irreversibly inhibit acetylcholinesterase (AChE), leading to cholinergic crisis and death at acute exposure levels. The complexity, delayed onset, and persistent nature of nerve agent induced CNS effects need to be elucidated to block their multiple effects. In the present study gene expression and phosphoprotein profile of certain key neuronal proteins were studied after soman exposure. Quantitative real time PCR analysis of c-Fos, Bax, CREB and caspase 3 genes in the hippocampus, cortex and cerebellum showed that only c-Fos and Bax mRNA expression was increased significantly. Western blot analysis also confirmed the induction of c-Fos at early time points both at 0.5 and 1.0 LD(50) dose of soman exposure. Acute soman exposure caused perturbations in the phosphorylation status of ERK, JNK, p38 MAPK, CREB, c-Jun and NF-κB in all the three brain regions. The primary target for soman toxicity, AChE was inhibited in blood and brain up to 90%. Therapeutic treatment comprising of HI-6, atropine and diazepam has completely protected animals from death and reactivated soman inhibited AChE up to 40% in the plasma and RBC. This therapeutic regime also reduced soman induced Bax expression to near control levels, but could not reverse the soman induced changes in c-Fos expression and phosphorylation levels completely. Results suggest that exposure to soman caused persistent changes in these key brain proteins, which could lead to the development of complex neurotoxic effects and there is an urgent need for development of better drugs to stop multiple effects of nerve agents poisoning.

Regional alterations of JNK3 and CaMKIIα subunit expression in the rat brain after soman poisoning.

Calcium/calmodulin-dependent protein kinase II (CaMKII) and c-Jun N-terminal kinases (JNKs) exert numerous and diverse functions in the brain. However, their role in nerve agent poisoning is poorly understood. In the present study, rats were exposed to soman (80 µg/kg) subcutaneously to study the changes in the protein levels of calcium/calmodulin-dependent protein kinase II alpha subunit (CaMKIIα) and JNK3 and activities of acetylcholinestarase (AChE) and CaMKII in the rat brain. Western blot analysis revealed that significant changes were found in both the protein kinases expression. Immunoreactivity levels of neural specific JNK3 isoform increased from 2.5 hours to 30 days after soman exposure in cerebral cortex, hippocampus, striatum and thalamus regions and decreased in the case of cerebellum. CaMKIIα expression levels were also increased from 2.5 hours to 30 days after soman exposure in cerebral cortex, hippocampus, thalamus and down regulated in cerebellum. AChE activity remained inhibited in plasma and brain up to 3 days post exposure. CaMKII activity was increased in cerebrum and decreased in cerebellum. Results suggest that altered expression of both the protein kinases play a role in nerve agent-induced long-term neurotoxic effects.