Endogenous zinc nanoparticles in the rat olfactory epithelium are functionally significant

Enhancement of olfaction by femtomolar concentrations of zinc ions

Zinc is recognized as an important element for olfaction. Zinc nanoparticles enhance olfaction in response to odors; however, the mechanisms underlying this action remain unknown. Herein, the effect of zinc on olfactory receptors was deduced using electro-olfactogram (EOG) responses recorded from the isolated olfactory mucosae of bullfrogs (Rana catesbeiana) following the administration or chelation of zinc ions. Menthone and n-amyl acetate were used as odorants, whereas forskolin (an adenylate cyclase activator) and cholera toxin (a Gαolf activator) were used as intracellular signal transduction activators. The EOG responses provoked by the odorants and cholera toxin were suppressed by dithizone-mediated zinc ion chelation, and the EOG responses were recovered by administering non-chelated zinc. However, the EOG response to forskolin was not suppressed by dithizone. In contrast, the addition of femtomolar concentrations of zinc ions enhanced the EOG responses. The above-mentioned effects on EOG responses were examined by changing the concentration of zinc ions but not zinc nanoparticles. The results of this study suggest that Gαolf alone or both olfactory receptors and Gαolf likely require zinc ions for their activation.

The Role of Endogenous Metal Nanoparticles in Biological Systems

The blood and tissues of vertebrate animals and mammals contain small endogenous metal nanoparticles. These nanoparticles were observed to be composed of individual atoms of iron, copper, zinc, silver, gold, platinum, and other metals. Metal nanoparticles can bind proteins and produce proteinaceous particles called proteons. A small fraction of the entire pool of nanoparticles is usually linked with proteins to form proteons. These endogenous metal nanoparticles, along with engineered zinc and copper nanoparticles at subnanomolar levels, were shown to be lethal to cultured cancer cells. These nanoparticles appear to be elemental crystalline metal nanoparticles. It was discovered that zinc nanoparticles produce no odor response but increase the odor reaction if mixed with an odorant. Some other metal nanoparticles, including copper, silver, gold, and platinum nanoparticles, do not affect the responses to odorants. The sources of metal nanoparticles in animal blood and tissues may include dietary plants and gut microorganisms. The solid physiological and biochemical properties of metal nanoparticles reflect their importance in cell homeostasis and disease.