Prospecting the insect model, Galleria mellonella, for gut-related pathobiology

Abstract

Animal research has contributed immensely to medical and scientific advances over the last century, and continues to play important roles in enhancing our understanding of infectious and non-communicable disease development, and the search for treatments. The mouse, for example, shares ~95% of human genes and is the most widespread vertebrate model in use. Since the late 1980s, there has been several UK and EU directives (e.g., 2010/63/EU) to improve the welfare of animals considered essential for experimentation, and to link directly with the principle of the 3Rs, to Replace, Reduce and Refine animal use. Additionally, animal maintenance, husbandry, compliance with legislation and licencing, and staff training are costly and time-consuming. Hence, there is much to gain from developing alternative in vivo models and complementary in vitro, in chemico and in silico tools. Larvae of the wax moth Galleria mellonella represent one such surrogate to rodents, and have been used successfully to study microbial isolates for virulence traits, putative antibiotic therapies, and more recently, toxicological assessment. There is an abundance of practical and biological advantages to selecting G. mellonella over rodents and traditional non-mammalian fruit flies and nematodes (which are described in Chapter 1), but one area lacking in knowledge is their applicability for studies of gut pathobiology. Therefore, the aim of this thesis was to evaluate the usefulness and accuracy of G. mellonella larvae as a model for gut specific toxins and pathogens when administered through an oral route (gavage). A series of whole-organism (phenotype), cellular, biochemical, microbiological and microscopy methods were used to interrogate the gastrointestinal tract of G. mellonella in the absence and presence of chemicals and microbes known to cause gastropathy in rodents and humans. First, the transferability of the indomethacin restraint/ulcer assay was established in G. mellonella, with levels of tissue deterioration and enhanced leakiness reminiscent of rodents (Chapter 2). Second, the rearing of insects on nutraceuticals Cordyceps sinensis and bovine colostrum alleviated gut damage caused by indomethacin, and improved survival outcomes when challenged with the enteric pathogen Campylobacter jejuni (Chapter 3). Third, oral administration of shellfish poisoning toxins (okadaic acid and azaspiracids 1-3) to G. mellonella, interfered with tissue integrity and microbial stability of the gastrointestinal tract, and produced comparable LD50 levels to their rodent counterparts (Chapter 4). The results presented here go beyond establishing synonymous damage phenomena between G. mellonella larvae and vertebrates (Chapter 5), but adds new knowledge to the structure and function of the lepidopteran alimentary canal, the cytopathology of emerging marine toxins, and how diet invariably influences a host’s capacity to recover from subacute chemical and microbial disruptors.