Elucidation of Arthropod 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) Metabolic Protein Structure, and Investigation of Novel Metabolic Enzyme Inhibitor Targets to Control Blood-Feeding Arthropods, Using Stable Flies (Stomoxys calcitrans) as a Model

Blood-feeding arthropods are a common pest for livestock, particularly cattle, and can lead to approximately $2 billion of economic damage associated with direct feeding and disease pathogens or parasites transmitted by vectors during feeding. There are various biochemical pathways involved in the breakdown of the blood meal, and the pathways have been studied to find novel targets for inhibition of the enzymes involved. One of the most well-known is Nitisinone and its role of inhibiting 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) in the tyrosine degradation pathway. Within literature evidence, Nitisinone is an effective reversible chemical inhibitor for this well conserved pathway and has been utilized to limit insect populations. Experimentation in this project focused on Stomoxys calcitrans (stable fly) for the first time, successfully using topical and oral bioassays with Nitisinone added to bovine blood that was fed to flies, a small clinical study dosing calves with Nitisinone via intravenous and intramuscular injections with blood draws taken that was then fed to flies, and in combination with other chemistries. Designing and developing novel inhibitors specifically targeting blood-feeding insects is a needed next step. Stomoxys calcitrans (stable fly) and Haematobia irritans (horn fly) HPPD proteins were isolated for further investigation to obtain the first structural models for both proteins. Using these models, it may be possible to design a novel inhibitor to selectively inhibit blood-feeding flies.