Nanoemulsions of Trichocline sinuata (Asteraceae) extracts as sunlight-activated insecticides

PAULINA CARDOSO SCHIAVI; ANALIA GURREIRO; MARCOS PASCUALI; SILVINA FAVIER; CLAUDIA ORTEGA; ELISA PETENATTI; MATÍAS FUNES

Villa Carlos Paz

Congreso; XIII ELAFOT; 2017

Despite the great advances reached in new drugs for phototherapy, natural products remain the main source of new phototoxic molecules [1]. In this context, center-west of Argentina flora, is still poorly studied as potentially font of phototoxic compounds. That is why isolation of new photoactive compounds or plant extracts, providing boundless opportunities to obtain insecticides with high phototoxic potential [2]. Chagas-Mazza is the only endemic disease transmitted by insects with epidemiological importance in Argentina due to the high number of infected people (25% of the total populations of Latin America at considerably higher risk to contracting it). Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, most transmission to humans are resulted from the contamination of vulnerable surfaces with the feces of infected vector Triatoma infestans knows as winchuka or vinchuca in Argentina. Natural compounds, such as coumarins, thiophenes, hypercin and chlorophyll [4] can act against a variety of noxious insects [3] when there are activated by light at specific wavelengths, they convert triplet oxygen (3O2) into singlet oxygen (1O2), which is a very strong oxidant. Nanoemulsios are being applied to enhance the solubility, transparence and bioavailability of hydrophobic compounds. Dispersions of hidrofobic sustrates in water are stabilized by an interfacial film of surfactant molecules having a droplet size smaller than 100 nm; then higher solubilization capacity and thermodynamic stability offers advantages over unstable dispersions. These nano-sized droplets are generated by ultrasonic cavitation leading an enormous increase in the interfacial areas that would influence the transport properties [5]. In order to evaluate the ability of T. sinuata (?árnica del campo?) dichloromethane extract nanoemulsions (DCMNE) as photoinsecticide against Triatoma infestans, profiles of dichloromethane extracts were realized employing spectroscopy and chromatographic technics. All extract presents the same UV spectra resembling to furanocoumarin compound (maximum absorbance at 309, 267 and 247 nm approximately). Using standard compounds, we determinate for HPLC-DAD that extracts are made of three majority furanocoumarins: xantotoxin, bergapten and trichoclin. The minority extract composition (finger print) was determinated employing CG-Ms finding a great number of furanocoumarins as dihidroxitrichoclin, psoralene, isopipinellin and other phototoxins as chromene and fenantrene. With these in main, nanoemulsions were dispersed over 30 nymphs of 4 º stages with microapplicator. The nymphs were placed in closed containers and exposed to natural sun light. Mortality was recorded every 24 hours up to 72 hours. The results were expressed as a mortality rate, being greater than 50% for DCMNE of T. sinuate. With the aim to determinate the photodynamic mechanism (Type I and II) by which DCMNE acts as photoinsecticide, we measure the production of reactive oxygen species. The photo-oxidation of L-tryptophan was studied following the decrease of the fluorescence intensity at 355 nm for generation of singlet oxygen (1O2). The production of superoxide radical (O2.-) was made employing nitroblue tetrazolium, irradiated with UVA ligth, and their absorbance at 560 nm was measured. This considerable body of data allows us to determine that DCMNE of T. sinuata acts as photoinsecticide against Triatoma infestans and the photochemical reactions involves are oxygen dependent. References[1] A.E.D. Bekhit, A.A. Bekhit, Natural Antiviral Compounds 2014, 7, 195. [2] R. Pavela, N. Vrchotova, Industrial Crops and Products, 2013, 43, 33.[3] G. Mougabure Cueto; M.I. Picollo, Acta Tropica 2015, 149, 70.[4]Mahmoud H. Abdel Kader, Photodynamic field control of malaria vector, schistosomiasis and agricultural pests, Photodiagnosis and Photodynamic Therapy. 2015, vol 12, p. 325?375[5] M. Tahir, A. Asif, A. Anwaar, A. Zaheer, Food Chemistry, 2017, 229, 790.