The development of Galleria mellonella as a model to test the toxicity of food additives

Traditionally the in-vivo assessment of novel therapeutics and food additive toxicity has relied strongly upon the use of a variety of vertebrate species, such as mice, rats, guinea pigs and birds. However the use of mammalian models incurs large costs and raises issues of ethical acceptance. In the past decade alternative models showing striking metabolic similarities to mammalian models have been widely utilized as mini models in biological research. These alternative model systems include; Zebrafish, Caenorhabditis elagans, Drosophila melanogaster and Bombyx mori. A widely used alternative model is Galleria. mellonella larvae. G. mellonella fulfil many of the basic requirements of a useful animal infection model and have many advantages over other invertebrate systems. There are a lot of similarities between the insect and mammalian gastrointestinal tracts. Several xenobiotic metabolism enzymes and anti-oxidant enzymes are highly conserved between species. The insect fat body functions in drug metabolism in a similar way to the mammalian liver. In addition the insect immune system and mammalian innate immune system show vast similarities in the cellular and Humoral responses. The response of G. mellonella larvae to food additives was ascertained. In this study larvae of the greater wax moth were administered eight commonly used food additives by intra-haemocoel or force feeding. A strong correlation between the relative toxicity of the compounds was observed between HEp-2 cells and larvae force-fed or administered the compounds by intra-haemocoel challenge. In addition a positive correlation between the LD50 values obtained for the preservatives in rats and in G. mellonella larvae administered the compounds by feeding was established. The fungicidal ability of haemocytes form larvae administered commonly used food additives was ascertained. There were significant decreases seen in the fungicidal ability of haemocytes extracted from larvae administered sodium benzoate, sodium nitrate, potassium nitrate, however there was no significant changes seen in the fungicidal killing ability of haemocytes from larvae treated with potassium sorbate, potassium nitrite, caffeine, monosodium glutamate and creatine. Significant increases in catalase activity was seen in the haemolymph of larvae administered sodium benzoate. Significant increases in superoxide dismutase activity were seen in larvae exposed to potassium sorbate, potassium nitrate and monosodium glutamate. A Significant increase in alkaline phosphatase activity was seen in larvae challenged with monosodium glutamate, but no significant changes were seen in larvae challenged with creatine monohydrate. The metabolism of caffeine was analysed using RP-HPLC analysis. Caffeine levels in larval haemolymph were significantly reduced from t = 0 to t = 48. The metabolites theobromine and theophylline were detected in larvae administered caffeine. The effect of caffeine on larval movement and rate of pupation was also measured. Both processes saw significant reductions when compared to control larvae. Three proteomic studies were conducted to determine the proteomic response to potassium nitrate, caffeine and monosodium glutamate. All three studies revealed findings that were comparable to those of vertebrates