Bufadienolides from the Skin Secretions of the Neotropical Toad Rhinella alata (Anura: Bufonidae): Antiprotozoal Activity against Trypanosoma cruzi.

Candelario Rodriguez,Michelle Ng,Marcelino Gutiérrez,Roberto Ibáñez,Luis Mojica,Carmenza Spadafora,Armando A Durant-Archibold

doi:10.3390/molecules26144217

Abstract

Toads in the family Bufonidae contain bufadienolides in their venom, which are characterized by their chemical diversity and high pharmacological potential. American trypanosomiasis is a neglected disease that affects an estimated 8 million people in tropical and subtropical countries. In this research, we investigated the chemical composition and antitrypanosomal activity of toad venom from Rhinella alata collected in Panama. Structural determination using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy led to the identification of 10 bufadienolides. Compounds identified include the following: 16β-hydroxy-desacetyl-bufotalin-3-adipoyl-arginine ester (1), bufotalin (2), 16β-hydroxy-desacetyl-bufotalin-3-pimeloyl-arginine ester (3), bufotalin-3-pimeloyl-arginine ester (4), 16β-hydroxy-desacetyl-bufotalin-3-suberoyl-arginine ester (5), bufotalin-3-suberoyl-arginine ester (6), cinobufagin-3-adipoyl-arginine ester (7), cinobufagin-3-pimeloyl-arginine ester (8), cinobufagin-3-suberoyl-arginine ester (9), and cinobufagin (10). Among these, three new natural products, 1, 3, and 5, are described, and compounds 1–10 are reported for the first time in R. alata. The antitrypanosomal activity assessed in this study revealed that the presence of an arginyl-diacid attached to C-3, and a hydroxyl group at C-14 in the structure of bufadienolides that is important for their biological activity. Bufadienolides showed cytotoxic activity against epithelial kidney Vero cells; however, bufagins (2 and 10) displayed low mammalian cytotoxicity. Compounds 2 and 10 showed activity against the cancer cell lines MCF-7, NCI-H460, and SF-268.

Highlights

Compounds present in the venom of toads have shown potential as therapeutic agents for the treatment of human diseases such as cancer and cardiovascular diseases [1]
Comparisons of the nmR data of compound 1 with those of similar bufadienolides previously described confirmed the assignment of the structure of compound 1 [22,23]. 1H nmR spectra displayed a spin system conformed by the protons at δH 1.78 d (J = 15.0 Hz, H-15a), 2.56 dd (J = 7.8, 15.0 Hz, H-15b), 4.51 t (J = 7.8 Hz, H-16), and 2.76 d (J = 7.8 Hz, H-17) confirmed by COSY correlations
Based on the nmR spectra and mass spectrometry analysis (Figures S2–S9 and Table S1), the structure of compound 1 was elucidated as 16β-hydroxy-desacetyl-bufotalin-3-adipoyl-arginine ester

Summary

Introduction

Compounds present in the venom of toads have shown potential as therapeutic agents for the treatment of human diseases such as cancer and cardiovascular diseases [1]. Bufonid toads contain in their skin glands alkaloids, amines, peptides, proteins, and steroids, which are thought to play a defensive role against predators and pathogens [5,6] Among these metabolites, steroids have attracted greater attention due to their high chemical diversity and pharmacological potential. Bufotoxins containing succinyl, adipoyl, pimeloyl, suberoyl, and azelayl moieties linked to an arginine residue were isolated from the skin of B. gargarizans and evaluated against hepatic carcinoma cells SMMC-7721. All these compounds showed potent cytotoxic activity [9,10]. These bufagins were tested against trypomastigotes of Trypanosoma cruzi, where only hellebrigenin displayed growth inhibition [13]

Methods

Results

Conclusion