After oxidation, zinc nanoparticles lose their ability to enhance responses to odorants

Abstract

Electrical responses of olfactory sensory neurons to odorants were examined in the presence of zinc nanoparticles of various sizes and degrees of oxidation. The zinc nanoparticles were prepared by the underwater electrical discharge method and analyzed by atomic force microscopy and X-ray photoelectron spectroscopy. Small (1.2 ± 0.3 nm) zinc nanoparticles significantly enhanced electrical responses of olfactory neurons to odorants. After oxidation, however, these small zinc nanoparticles were no longer capable of enhancing olfactory responses. Larger zinc oxide nanoparticles (15 nm and 70 nm) also did not modulate responses to odorants. Neither zinc nor zinc oxide nanoparticles produced olfactory responses when added without odorants. The enhancement of odorant responses by small zinc nanoparticles was explained by the creation of olfactory receptor dimers initiated by small zinc nanoparticles. The results of this work will clarify the mechanisms for the initial events in olfaction, as well as to provide new ways to alleviate anosmia related to the loss of olfactory receptors.

Endogenous zinc nanoparticles in the rat olfactory epithelium are functionally significant

“…Therefore, the presence of the zinc diffraction pattern and absence of the oxidized zinc lines assure the elemental zinc state in the olfactory and respiratory samples. The TEM images and non-oxidized nature of the endogenous zinc nanoparticles compare well with those of the engineered Zn nanoparticles 5 , 6 . Our results are in agreement with the TEM and electron diffraction of the crystals of electrodeposited zinc 50 and zinc nanowires 51 .…”

“…Subsequent studies have demonstrated that zinc nanoparticles function at the olfactory receptor level in the initial events of olfaction 3 , and a single metal nanoparticle binds two receptor molecules to form a dimer 4 . This olfactory enhancement was observed in young and mature mouse olfactory epithelial cultures, dissected rodent olfactory epithelium 2 , 3 , 5 , 6 , and live conscious dogs 7 , 8 .…”

“…Additionally, this criterion is validated by the fact that engineered zinc nanoparticles enhance odor-related brain activity in awake and anesthetized dogs 7 . Criterion (iii) is met since the enhancement of the odorant responses is not detected when engineered zinc nanoparticles are replaced by zinc ions 2 and oxidized engineered zinc nanoparticles 5 or removed by perfusion with ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) 58 . Thus, the physiological significance of endogenous zinc nanoparticles may be recognized considering these criteria.…”

“…In most cases, the distribution of zinc in the brain was studied by the methods that cannot discriminate between zinc ions and zinc metal particles 10 . We have demonstrated that engineered zinc, which enhanced olfactory responses to the odorant, exists in a nonoxidized elemental metal state and comprises round crystalline clusters of zinc atoms ~ 1.2 nm in diameter 5 .…”

Status of the Vibrational Theory of Olfaction

“…Na + has been shown to allosterically modulate several GPCRs, including opiate and dopamine receptors via a specific binding site between helices 1, 2, and 7 [61]. Zn 0 nanopartiles, specific to oxidation and size, have been shown to enhance olfaction in rodents and canines [62][63][64][65][66] and have been shown to inhibit certain rodent ORs through competitive binding [67]; circumstantially, it should be noted that large concentrations of zinc have been found in specific areas of the brain [68][69][70][71]. Ionic copper has been shown to be vital for the robust activation of thiol-detecting olfactory receptors [72][73][74].…”