Nerve agents-sarin, soman, VX and Novichok-have become a health and security threat because they are not only being used in war but also by terrorists. The latest incident is the attempted assassination of a Russian double agent in the UK.
So, what is a nerve agent (gas)?
Nerve agents are a collection of different compounds that act in a similar manner as organophosphate insecticides to disrupt the nervous system.
The critical question is, how different is a nerve agent from the ordinary insecticide? Well, there are some similarities and a myriad of differences!
The organophosphate insecticides and nerve agents both contain a phosphorus moiety in their core structure and hence are organophosphorus compounds.
Organophosphorus compounds inhibit the enzyme acetylcholinesterase, preventing the normal breakdown of the neurotransmitter acetylcholine resulting in accumulation of the neurotransmitter in synapses. Increased acetylcholine in synapses causes overstimulation of cholinergic receptors, peripherally and centrally. Compared to insecticides, nerve agents are highly potent inhibitors of the acetylcholinesterase resulting in more severe forms of the cholinergic syndrome. The classical symptoms nerve agent poisoning are pinpoint pupils, sweating, drooling, tearing, vomiting, involuntary urination and defecation, seizures and death by asphyxiation.
Unlike the insecticides nerve agents are stable and easily dispersed in the environment to produce mass poisoning. And because of this, secondary poisoning of first responders is more likely with nerve agents than the organophosphorus pesticides. Appropriate personal protective equipments (PPE) is thus critical when treating nerve agent victims.
Nerve agents are not only small in nature but are also of high lipophilicity; factors that enhances their diffusion through biological membranes including the many layers of the skin.
Nerve agent also posses a high vapour pressure and are therefore readily vaporized or aerosolized. This property makes nerve agents toxic by inhalational route. They thus act fast and if exposure is substantial, death may occur within minutes.
Second generation nerve agents such as Novichok have been specifically designed to resist standard antidotal therapy. Unlike organophosphate insecticide poisoning where atropine is an effective antidote,with nerve gas attack atropine is difficult to administer safely. This is so because the therapeutic doses are close to the toxic dose at which patients suffer severe adverse effects such as tachyarrhythmias and thickening of the bronchial secretions. Advanced life support techniques including suctioning of bronchial secretions may be necessary in addition to atropine.
The other major difference between the organophosphates pesticides and nerve agents is in the time it takes enzyme-organophosphate complex to age (Aging is the chemical transformation of the complex that renders the enzyme permanently inactivated). The aging of organophosphate pesticides takes on average 48 hrs while it takes as little as 15 minutes in nerve agents. Aging process is important in determining the choice and success of antidotal therapy. For instance, aged acetylcholinesterase cannot be reactivated by oximes such as pralidoxime, better known as 2-PAM.
You may want to read more on Organophosphate poisoning @ www.poisonsense.com
