Exposure to trans-anethole impairs reproduction and inhibits glutathione-S-transferase (GST) in engorged Rhipicephalus microplus female ticks (Acari: Ixodidae)

Abstract

Rhipicephalus microplus, the cattle tick, is a species of great importance to veterinary medicine and is responsible for massive economic losses in agriculture. In our study, engorged R. microplus females were exposed to the natural product trans-anethole in concentrations ranging from 1 to 50 μL/mL, a commercial pesticide (positive control), 5 % DMSO (solvent), and water control. We evaluated a series of endpoints related to survival, reproductive parameters, ovicidal activity, ovary histopathology, oxidative stress, and an in silico analysis (docking and molecular dynamics) of glutathione S-transferase (GST) inhibition. Exposure to 50 μL/mL trans-anethole caused mortality above 90 %, whereas in the positive control, this value was around 45 %. The mean lethal concentration (LC₅₀) estimated for trans-anethole in engorged R. microplus seven days after the exposure was LC₅₀ = 27.14 μL/mL. A concentration-dependent response was observed in the percentage of control (%C) in ticks treated with trans-anethole, reaching %C = 82.87 at 25 μL/mL. However, only the positive control presented an ovicidal effect against R. microplus. The most prevalent morphological alterations in the ovaries were basophilic granules in the cytoplasm, irregular oocyte shape, and fusion of yolk granules. The score of these alterations at 10 μL/mL trans-anethole was statistically equivalent to the positive control. Exposure to 10 μL/mL trans-anethole led to reduced GST activity. In silico analysis revealed inhibition of GST by trans-anethole with a MolDock score of −80.66. Collectively, our data showed that trans-anethole impairs the reproduction of R. microplus and is a promising bioactive compound for tick control.