NANO-GOLD AND NANO-ZINC OXIDE: EFFECT ON GUSTATORY RECEPTOR GENES IN FLIES

Drinking colloidal gold as elixir of life is an age-old practice worldwide. A large body of data containing patients' experiences after intake of colloidal gold for long duration would be available in the medical records of hospitals. ZnO has been approved by FDA for topical use and not for oral intake. Drosophila melanogaster (wild type) strains were fed with physiologically relevant concentrations of nano-gold and nano-ZnO along with appropriate controls. Citrate-capped nano-gold (average particle size is 15-20 nm) synthesized by reducing hydrogen tetrachloroaurate with 1% trisodium citrate and custom-made nano-ZnO, purchased from M K Implex, Canada (average particle size 50nm) were used as treatments. Microarray studies revealed that fly trehalose receptor genes, Tre and Tre1, are both unaffected after nano-gold and nano-ZnO treatment. Gr64 subfamily members (encoding sugar receptors like glucose, sucrose, and maltose), for example, Gr64a-b become downregulated, but Gr64c, Gr64d, Gr64f remain unaltered in case of both the treatments. Among bitter receptor genes, Gr66a is the most well studied and shows significant downregulation by nano-gold and not by nano-ZnO. Ppk11 and Ppk19 are gustatory ion channel genes which modulate salt perception. Ppk11 was found to be downregulated by both nano-gold and nano-ZnO, while ppk19 expression is suppressed by nano-gold treatment but not by nano-ZnO. The effects of these two nanoparticles on pheromone receptors (Gr32a, Gr39a, and Gr68a) and CO2 receptors (Gr21a and Gr63a) are presented. To the best of our knowledge, this is the first report on the effect of pure nanoparticles on gustation. Data has been analyzed in the light of the age-old tradition of oral administration of the nano-gold viz-a-viz topical use of nano-ZnO. These results would have far reaching implications in the design of nano-gold mediated oral drug delivery of cancer and other drugs as well as nano-ZnO coated drugs/cosmetics and nano-ZnO carrier based drug delivery in skins and in other topical applications.