On the untapped potential of the CO molecule in plasma medicine and agriculture
Résumé
In plasma medicine and agriculture reactive species produced by non-thermal plasma
sources must play an important role. Many studies have been devoted on the effects of reactive
species such as O, O2
1Δg, OH, N, NO and NO2 species just to name a few. So far, the CO molecule
has been overlooked.
Carbon monoxide (CO) is well known for its toxic effects at high doses. The effects of CO
can be quantified via the percentage of carboxyhemoglobin (COHb) it forms in the blood. The
percentage of COHb in blood strongly depends on, not only the percentage of CO in air, but also
on the exposure time. CO is however also naturally produced at cellular level, mostly via the
catabolism of heme. At low doses, CO has therapeutic properties. Experimental studies found
several positive effects of CO such as anti-inflammatory, vasodilatory and anti-apoptotic effects.
It has also an influence on plants and promote the seed germination and increases the roots
formation [1].
In this contribution, we will shortly review the reactivity of CO at the molecular level and
its effects as a signaling molecule. It will be shown that CO triggers and competes with several
cellular receptors which are sensitive to the NO molecule as well.
Many studies have demonstrated over the years that plasmas are able to produced CO from the
dissociation of CO2 over a wide range of concentrations. Using glow discharges, dielectric barrier
discharges, nanosecond pulsed discharges or microwave plasmas, CO can be produced from ppm
range to several tens %. Plasmas are flexible sources allowing in situ production of CO and
alleviate the risks related to its storage. Additionally, plasmas produce other components of
biological relevance such as electric fields, heat, ultraviolet radiation, O, NO, NO2 and many other
reactive species. Synergic effects may therefore occur for the treatment of certain afflictions. For
instance, it has been demonstrated that high doses of NO have a pro-inflammatory action [2] while
exogenous CO can down regulates its effects [3]. Plasmas with CO2 admixtures as a source of CO
seem then promising in applications such as wound healing and seed germination.
References
[1] E. Carbone and C. Douat, Plasma Medicine, 8(1):93–120 (2018).
[2] Guzik TJ, Korbut R, Adamek-Guzik T. Nitric oxide and superoxide in inflammation and immune
regulation. J Physiol Pharmacol. 2003;54(4):469–87.
[3] Ingi T, Cheng J, Ronnett G V. Carbon Monoxide: An Endogenous Modulator of the Nitric Oxide–Cyclic
GMP Signaling System. Neuron. 1996;16(4):835–42.