Isolation and Function of Endogenous Zinc Nanoparticles in the Olfactory Epithelium

Abstract

The olfactory sensory neural system contains the highest levels of zinc found throughout the central nervous system. Zinc is one of many metals known to play a role in multiple facets of biology. Metal nanoparticles such as copper, gold, and zinc have been isolated from human and animal blood. The blood isolated zinc nanoparticles (ZnNPs) were unique in their ability to enhance the electrophysiological olfactory sensory neuron response to odorant by about threefold. Characterization of the physiochemical properties of ZnNPs determined that small (1.2±0.3 nm), non‐oxidized, primarily elemental, zinc nanoparticles were capable of olfaction enhancement. At low concentrations, ZnNPs added to odorant display a dose‐dependent, specific, and reversible effect. In conjunction with the enhancement of olfactory sensory neurons in the isolated rodent olfactory epithelium, cognitive processing of the sensory amplification is demonstrated by a significant increase of canine brain excitation in response to odorants resulted from the addition of ZnNPs. The presence of ZnNPs at the olfactory mucosa level has not been demonstrated. To evaluate the potential biological role ZnNPs have in the initial events of olfaction, the presence of ZnNPs in the olfactory and respiratory epithelia was examined by transmission electron microscopy (TEM). Detailed structures of nanoparticles were characterized by selected area diffraction. The physiological effects of nanoparticles were tested ex vivo by electroolfactogram (EOG). Zinc was identified in both the respiratory and olfactory filtrate samples. TEM demonstrated an organization of high homogeneity, crystalline structure, and within nanoparticle size range. The EOG responses to the epithelia filtrates mixed with odorant evoked higher olfactory responses compared to the response induced by odorant alone. These effects are similar to those produced by the engineered ZnNPs mixed with odorant. Calculation of the concentration of endogenous nanoparticles was performed using the relative EOG peaks as a function of engineered zinc concentration for a calibration curve. The calculated concentrations of ZnNPs in the olfactory epithelium and respiratory epithelium filtrates are 5.3×10−3 ± 5×10−4 nM and 2.7×10−3 ± 5×10−4 nM, respectively. The concentrations of ZnNPs in the olfactory epithelium and respiratory epithelia are 10.3 ± 1.0 nM and 7.9 ± 1.5 nM, respectively. The presence of ZnNPs within the olfactory and respiratory epithelia may have physiological significance. To determine the role of ZnNPs in olfaction, many questions still have to be answered. However, the presence of olfaction enhancing ZnNPs within the olfactory epithelium at the initial site of olfactory signaling suggests a physiological role in the initial events of olfaction at the receptor level. The confirmation of ZnNPs presence by TEM in combination with the electrophysiological enhancement of EOG provide support for this hypothesis.Support or Funding InformationSupported by grant from the National Institute of Standards and Technology: 70NANB14H324This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.