RCB-4, a Novel Cyclic Peptide, from Ricinus Communis with Anti-Trypanosoma Cruzi Activities

Introduction: Chagas disease and toxoplasmosis caused by parasites Trypanosoma cruzi and Toxoplasma gondii affect more than 28 million people in poor areas of Latin America. There is an urgent need for therapeutic options as the treatments are related to efficacy, lower costs, and shorter administration time. Encouraged by the need to discover valid targets and new treatment options, we evaluated castor seed compounds against T. cruzi and T. gondii, considering their effects against proliferation, infection, and ultrastructure. Methodology: castor seed extract was fractionated by Gel -filtration chromatography using the Sephadex G-50 resin, and a fraction with MW <10 kDa, denoted LMWF, was isolated. The effect of this fraction against T. cruzi and T. gondii was investigated. LMWF was repurified by HPLC-Reverse Phase chromatography using C-18 column. The major isolated peptide, with antiprotozoal activity, denoted RCB-4, was characterized by SDS-PAGE, mass spectrometry, and "in silico" studies. To understand the mechanism of action underlying RCB-4 against T. cruzi activity, we investigated ultrastructural changes by optical and electron microscopy. Results: RCB-4 is a cycle peptide with an MW of 2229.78 Dalton, and the sequence is "ARCCLVMPVPP- FACVKFCSSA." RCB-4 was resistant to trypsin, endo-Glu, and endo-Asp enzymes. It inhibited parasite growth by up to 50 % at 10 and 15 mu g/mL (4.48 mu M and 6.73 mu M), inside and outside the cells, respectively. Ultrastructural studies showed that trypomastigotes incubated with natural or synthetic RCB-4 could impair T. cruzi proliferation and cause ultrastructural alterations, such as Golgi apparatus disorganization and mitochondrial swelling. Conclusions: Cyclic peptides emerged as promising organic compounds with diverse pharmacological activities. They possess superior therapeutic value due to the particular structures conferring resistance to enzymatic degradation and higher bioavailability. Our data allow us to prospect using RCB-4 to combat the parasites T. cruzi and T. gondii.