Boral® 500 SC (sulfentrazone) induces accumulation of heme synthesis intermediates and changes in locomotor behavior and metabolic markers in Drosophila melanogaster

Abstract

Sulfentrazone (SULF) is an herbicide that inhibits protoporphyrinogen oxidase, which is essential for the biosynthesis of chlorophyll and heme. Its prolonged soil half-life, low effective concentration, and the conserved nature of the heme biosynthesis pathway suggest that SULF might significantly affect non-target organisms. This study evaluated the impact of the commercial formulation Boral® 500 SC (SULF) on Drosophila melanogaster when exposed to acute concentrations. Fruit flies were exposed to 10–300 mg/L of the herbicide for seven days, which resulted in dose- and time-dependent increases in mortality. Following these results, further evaluations were conducted on flies exposed to 30 and 150 mg/L on the fourth day of treatment. The exposed flies exhibited decreased climbing locomotor capacity (negative geotaxis assay) and reduced exploratory locomotor capacity (open field assay), suggesting an increased energy demand to counteract the herbicide's effects. This was evidenced by decreased weight, reduced energy-rich molecules, and increased total protein levels. Activation of the heme biosynthesis pathway was indicated by the accumulation of protoporphyrin IX, increased total heme in the head, and induction of the porphobilinogen synthase (PBGS) enzyme (δ-aminolevulinic acid dehydratase, δ-ALA-D, in mammals). Biochemical analysis showed increased thiobarbituric acid reactive species (TBARS) levels and superoxide dismutase (SOD) activity in flies exposed to 150 mg/L, and higher glutathione-S-transferase (GST) activity in the 150 mg/L Top group. Additionally, there was an increase in MTT reduction assay in flies from the 150 mg/L Bottom group. The study highlights that species with significant diurnal activity, such as pollinators, might be especially susceptible to SULF exposure due to accumulated protoporphyrin IX and pro-oxidative activity under light conditions.