Abstract
The global rise of antibiotic-resistant bacteria highlights the urgent need for alternative strategies to support host defense against infections. Bioactive plant-derived compounds, such as isothiocyanates, have gained attention due to their antimicrobial and immunomodulatory properties. Allyl-isothiocyanate (AITC), a hydrolysis product of glucosinolates found in Brassica vegetables, has demonstrated antimicrobial activity in vitro and the ability to modulate antimicrobial peptide (AMP) expression in cell culture models. However, its in vivo effects under metabolically challenging dietary conditions remain poorly understood. In this study, we investigated the impact of dietary AITC supplementation on immune responses and survival in Drosophila melanogaster exposed to a high-sucrose diet (HSD), a dietary condition known to impair metabolic health and immune function. Flies were fed a HSD with or without 0.25 mM AITC and subsequently subjected to oral infection with either Leuconostoc pseudomesenteroides or Pectobacterium carotovorum subsp. carotovorum, which preferentially activate the Toll and Imd signaling pathways, respectively. AMP expression was analyzed by qPCR and RNA sequencing, and physiological consequences were assessed by performing lifespan analysis. AITC did not affect the flies' feed intake or basal AMP expression under non-infected conditions. HSD significantly shortened the lifespan in both sexes, and AITC supplementation was not able to rescue this effect. Following oral infection of the flies, both HSD alone and HSD supplemented with AITC influenced the survival in a sex- and pathogen-specific manner, with AITC frequently exacerbating mortality rather than improving outcomes. While selected AMPs, particularly Attacin D, were modulated in a context-dependent manner, RNA sequencing revealed no consistent transcriptional changes in core Toll or Imd pathway components. Overall, our findings indicate that dietary AITC does not enhance host defense in Drosophila melanogaster under high-sugar conditions and that its effects on immunity and survival are strongly sex-specific. These results highlight the complexity of diet-immune interactions and caution against extrapolating in vitro antimicrobial effects to in vivo host protection.
