Nanoformulations with synthetic and plant-derived compounds for cattle tick control

Nanocarriers of acaricidal compounds improve the bioavailability, absorption, and tissue distribution of active ingredients, releasing them in a slow, targeted way and protecting them against premature degradation. Thus, this study aimed to develop formulations from solid lipid nanoparticles (SLN), or nanostructured lipid carriers (NLC) associated with cypermethrin (cip) + chlorpyrifos (chlo) and vegetable compounds (citral, menthol, or limonene). Particles were then characterised, and their efficacy was verified on R. microplus in comparison to nanoformulations without the plant-based compounds. Six different formulations were developed and characterised by dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). Formulations 1 (SLN+cyp+chlo+citral), 2 (SLN+cyp+chlo+menthol), 3 (SLN+cyp+chlo+limonene), 4 (NLC+cyp+chlo+citral), 5 (NLC+cyp+chlo+menthol) and 6 (NLC+cyp+chlo+limonene) had mean diameters from 286 to 304 nm; polydispersion from 0.16 to 0.18; zeta potential from -15.8 to -20 mV, concentration from 3.37 ± 0.24 × 10¹³ to 5.44 ± 0.18 × 10¹³ particles/mL and encapsulation efficiency (EE) > 98.01 % for all active ingredients. All formulations were evaluated for their acaricidal potential by the larval packet test (LPT) and compared with nanoformulations without the plant-based compounds. Formulations were also compared with positive (Colosso® at 512 µg/mL) and negative controls (distilled water and nanoparticles without active ingredients). The SLN (1, 2 and 3) and NLC (4, 5 and 6) formulations, at 7 µg/mL, resulted in 90.4 % , 75.9 % , 93.8 % , 100 % , 95.1 % and 72.7 % mortality. The data demonstrated that the addition of citral, menthol or limonene in the formulations improved their acaricide action against tick larvae. Except for formulation 4, for which it was not possible to determine lethal concentrations (LC). Formulations, 1, 2, 3, 5 and 6 reached LC₅₀ and LC₉₀ values of 3.3 and 7.2, 5.4 and 9.2, 4.0 and 8.1, 2.3 and 5.4 as well as 5.5 and 9.4 µg/mL, respectively. It was possible to encapsulate the active ingredients and characterise the lipid carrier systems. SLN and NLC protected the active ingredients against degradation in solution and increased the overall stability. A stabile solution is necessary for synthesizing commercial acaricidal products. It is hoped that these findings may contribute to new studies focused on the use of nanocarriers in tick formulations. By reducing the amount or concentration of active ingredients within commercial products, the risk of residues presents in food of animal origin or remaining in the environment is reduced. Nanocarriers help prevent these challenges, while still maintaining effective parasitic control. Utilizing a combination of natural and synthetic products can be part of integrated management solutions and can help overcome widespread acaricide resistance in populations of cattle ticks.