Dietary manipulation may provide protection against toxic substances such as nicotine and chemotherapy, study finds

A Monash University study has found that removing a single, essential, dietary amino acid provides tolerance to chemicals such as nicotine. Removing the amino acid could also potentially provide protection against physical traumas such as surgery or chemotherapy. The study by researchers from the School of Biological Sciences is published today in Open Biology and has wide ranging implications for improving health outcomes. The research team examined the relationship between dietary amino acids and stress tolerance using the common fruit fly, Drosophila melanogaster. Using a chemically defined medium for Drosophila, they found that restricting adult flies of a single essential amino acid generally protects against a lethal dose of the naturally occurring insecticide, nicotine. "This protection varied depending on the amino acid restricted, and the duration and intensity of its restriction," said study author Tahlia Fulton, a PhD candidate at the School of Biological Sciences. "Our study provides new insights into the physiological responses to restriction of individual amino acids that confer stress tolerance." "These findings may someday be the foundation of optimal pre-treatment diets for humans, pets, and livestock to eat before physical stress." Nutritionally adjusted diets promote stress tolerance in model systems, but the reasons are unknown. The full extent of these signalling interactions and the specific mechanisms by which each of the individual amino acids are detected are still being uncovered. However, in this study researchers found that transient deprivation of almost any essential amino acid increased nicotine resistance in Drosophila. Flies that were fed a diet that was missing isoleucine showed resistance to doses of nicotine between 0.33mg/mL – 1mg/mL when compared to complete diet controls. When the nicotine concentration fell below 0.17mg/mL, adult fly survival was compromised by dietary isoleucine omission, showing that the benefits of this diet for survival are only apparent when the flies are challenged with stronger nicotine stress. Though removing isoleucine from the diet long term reduces lifespan, removing isoleucine for a brief time had no cost to lifespan in flies. The protection is mediated by interactions between two known sensors of amino acids, GCN2 (General Control Non-derepressible 2) and mTORC1 (mechanistic Target Of Rapamycin Complex 1). "This study paves the way for a better understanding of the environmental factors that alter insect susceptibility to pesticides and could open opportunities for the use of diets to help patients recover from planned treatments with toxins such as chemotherapy," said Tahlia. Media