Microbiome Response Can Serve as Early Warning to Nerve Gas Exposure

Researchers report that the mammalian microbiome can act as a sentinel due to its high responsiveness to exposure. Their research article (“Poisoning with Soman, an Organophosphorus Nerve Agent, Alters Fecal Bacterial Biota and Urine Metabolites: a case for Novel Signatures for Asymptomatic Nerve Agent Exposure”) appears in Applied and Environmental Microbiology.

“The experimental pathophysiology of organophosphorus (OP) chemical exposure has been extensively reported. Here, we describe an altered fecal bacterial biota and urine metabolome that follows intoxication with soman, a lipophilic G class chemical warfare nerve agent. Non-anaesthetized Sprague-Dawley male rats were subcutaneously administered soman at 0.8 (sub-seizurogenic) or 1.0 (seizurogenic) of the median lethal dose (LD50) and evaluated for signs of toxicity. Animals were stratified based on seizing activity to evaluate effects of soman exposure on fecal bacterial biota and urine metabolites. Soman exposure reshaped fecal bacterial biota by altering Facklamia, Rhizobium, Bilophila, Enterobacter, and Morganella genera of the Firmicutes and Proteobacteria phyla, some of which are known to hydrolyze OPs. However, analogous changes were not observed in the bacterial biota of the ileum, which remained the same irrespective of dose or seizing status of animals after soman intoxication,” write the investigators.

“However, at 75 days post soman exposure, bacterial biota stabilized, and no differences were observed between groups. Interestingly, when considering just the seizing status of animals, we found that the urine metabolome was markedly different. Leukotriene C4, kynurenic acid, 5-hydroxyindoleacetic acid, norepinephrine, and aldosterone were excreted at much higher rates at 72 hours in seizing animals, consistent with early multi-organ involvement during soman poisoning. These findings demonstrate the feasibility of using the dysbiosis of fecal bacterial biota in combination with urine metabolome alterations as forensic evidence for pre-symptomatic OP exposure temporally to enable administration of neuroprotective therapies of the future.”

Soman is similar to sarin, an agent believed to have been released in Syria. Both are organophosphates, which are used in certain pesticides and nerve gases. They block the normal breakdown of the neurotransmitter, acetylcholine, causing overstimulation of nerves, muscles, and certain glands. In large doses, these compounds interfere with the mechanism that turns off nerve transmission, causing suffocation.

The investigators examined the microbiome for changes at 72 hours post exposure. “Our aim was to determine specific features of physiologic injury resulting from mild exposure to soman,” since these might provide warning symptoms and identify people needing treatment, says first author Derese Getnet, Ph.D., research scientist, Integrative Systems Biology Program, U.S. Army Center for Environmental Health Research, Fort Detrick, MD.

The most notable changes in the microbiome were the detection of the bacterial genera, Facklamia, Enterobacter, and Bilophila, and the beneficial-to-plants genus, Rhizobium. “It was very interesting to see Rhizobium grow in the presence of organophosphate since it is a known class of organism associated with bioremediation,” continues Dr. Getnet. Rhizobium is normally not associated with intestines, but the presence of organophosphate might have given it a brief advantage over competing microbes.

“These signatures of exposure are detectable for at least 72 hours following exposure, and they persist not only in symptomatic animals, but also in asymptomatic animals,” adds Dr. Getnet. “It should be possible to detect these changes before any symptoms develop, or if asymptomatic exposure has occurred.” He also noted that an advantage of this form of sampling is that it’s non-invasive, and that sites and subjects can be screened on a routine basis, absent specific knowledge of exposure.

This is important because during nerve agent attacks, it is difficult to determine the boundaries of the affected area, as well as who has been exposed. Additionally, the onset of symptoms is unpredictable, causing estimates of exposure based on symptoms to be inaccurate.

“The motivation behind this research is to identify novel signatures for nerve agents and organophosphate exposures that can quickly be adapted into the clinical pathology workflow of urine chemistry and microbiology, without the need to develop novel technology and clinical standards,” says Dr. Getnet. He explains that this work is “proof of concept” only, and more research will be necessary to determine the sensitivity of the sampling to each toxicant, as well as the signals for all of the different organophosphate pesticides and nerve agents.

To this end, there will be no need to develop novel platforms. Rather, existing technologies will simply need to be refined, according to Dr. Getnet.

These developments could be important for protecting civilians as well as the armed forces from nerve agents, or organophosphate toxicants. The work could also enable hospitals to determine whether a person has been exposed not only to nerve agents, but to organophosphate pesticides and to fire retardants, both of which can also be quite harmful.