Development of a method for oral administration of hydrophobic substances to Caenorhabditis elegans: pro-longevity effects of oral supplementation with lipid-soluble antioxidants.

Methods for quantitative oral administration of various substances to Caenorhabditis elegans are needed. Previously, we succeeded in oral administration of hydrophilic substances using liposomes. However, an adequate system for delivery of hydrophobic chemicals was not available. In this study, we developed a method for oral administration of lipid-soluble substances to C. elegans. γ-cyclodextrin (γCD), which delivers hydrophobic chemicals, was used to make micro-particles of inclusion compounds that can be ingested by bacteriophagous nematodes, which do not distinguish these micro-particles from their food bacteria. Successful oral delivery of the hydrophobic fluorescent reagent 3,3'-dioctadecyloxacarbocyanine perchlorate into the intestines of C. elegans was observed. Oral administration of the hydrophobic antioxidants tocotrienol, astaxanthin, or γ-tocopherol, prolonged the nematode lifespan; tocotrienol rendered them resistant to infection with the opportunistic pathogen Legionella pneumophila. In contrast, older conventional delivery methods that involve incorporation of chemicals into the nematode growth medium or pouring chemicals onto the plate produced weaker fluorescence and no longevity effects. Our method efficiently and quantitatively delivers hydrophobic solutes to nematodes, and a minimum effective dose was estimated. In combination with our liposome method, this γCD method expands the usefulness of C. elegans for the discovery of functional food factors and for screening drug candidates.