Date Published: January 28, 2019
Publisher: Public Library of Science
Author(s): Marcelo A. Strauch, Marcelo Amorim Tomaz, Marcos Monteiro-Machado, Bruno Lemos Cons, Fernando Chagas Patrão-Neto, Jhonatha da Mota Teixeira-Cruz, Matheus da Silva Tavares-Henriques, Pâmella Dourila Nogueira-Souza, Sara L. S. Gomes, Paulo R. R. Costa, Edgar Schaeffer, Alcides J. M. da Silva, Paulo A. Melo, José María Gutiérrez.
It is known that local tissue injuries incurred by snakebites are quickly instilled causing extensive, irreversible, tissue destruction that may include loss of limb function or even amputation. Such injuries are not completely neutralized by the available antivenins, which in general are focused on halting systemic effects. Therefore it is prudent to investigate the potential antiophidic effects of natural and synthetic compounds, perhaps combining them with serum therapy, to potentially attenuate or eliminate the adverse local and systemic effects of snake venom. This study assessed a group of quinones that are widely distributed in nature and constitute an important class of natural products that exhibit a range of biological activities. Of these quinones, lapachol is one of the most important compounds, having been first isolated in 1882 from the bark of Tabebuia avellanedae.
It was investigated the ability of lapachol and some new potential active analogues based on the 2-hydroxi-naphthoquinone scaffold to antagonize important activities of Bothrops venoms (Bothrops atrox and Bothrops jararaca) under different experimental protocols in vitro and in vivo. The bioassays used to test the compounds were: procoagulant, phospholipase A2, collagenase and proteolytic activities in vitro, venom-induced hemorrhage, edematogenic, and myotoxic effects in mice. Proteolytic and collagenase activities of Bothrops atrox venom were shown to be inhibited by lapachol and its analogues 3a, 3b, 3c, 3e. The inhibition of these enzymatic activities might help to explain the effects of the analogue 3a in vivo, which decreased skin hemorrhage induced by Bothrops venom. Lapachol and the synthetic analogues 3a and 3b did not inhibit the myotoxic activity induced by Bothrops atrox venom. The negative protective effect of these compounds against the myotoxicity can be partially explained by their lack of ability to effectively inhibit phospholipase A2 venom activity. Bothrops atrox venom also induced edema, which was significantly reduced by the analogue 3a.
This research using a natural quinone and some related synthetic quinone compounds has shown that they exhibit antivenom activity; especially the compound 3a. The data from 3a showed a decrease in inflammatory venom effects, presumably those that are metalloproteinase-derived. Its ability to counteract such snake venom activities contributes to the search for improving the management of venomous snakebites.
Snakebites occur worldwide causing disabling injuries and death with serious social impact, most often in Africa, Asia and Latin America [1,2]. This burden of human suffering caused by snakebite is ignored by most of the global health community and overlooked by development agencies and governments. Only in April 2009 this problem was included in the World Health Organization List of Neglected Tropical Diseases . Annually in the world it is estimated that more than two million ophidian accidents occur, resulting in 400,000 amputations and around 125,000 deaths [4–7]. Severe venom-induced tissue damage derives from a cocktail of pharmacologically active proteins and toxins, which exhibit various enzymatic and non-enzymatic properties [7,8]. Snakes from the Bothrops genus are responsible for the vast majority of ophidian accidents in Central and South Americas, and Bothrops atrox is the major representative of this genus in the Brazilian Amazon.
Bothrops jararaca and Bothrops atrox venoms were collected from 15–30 snakes above 4 years old belonging to the serpentarium of Instituto Vital Brazil, Niterói, Brazil; creatine kinase (CK) activity was determined using a CK NAC kit from BIOCLIN; adult male Swiss mice were provided by the Rodent Vivarium of the Institute of Microbiology Paulo de Góes–UFRJ (Federal University of Rio de Janeiro). Mice weighing 25.0 ± 1.0 g used for the study received water and food ad libitum and were kept under a natural light cycle. Lapachol was purchased from Sigma Aldrich, St.Louis, USA, and lapachol analogues were obtained by the Institute for Natural Products Research (Instituto de Pesquisas de Produtos Naturais Walter Mors–UFRJ). All compounds were used for assessing enzymatic activities (proteolytic, phospholipase and collagenase), and of the two most efficient ones, i.e. compounds 3a and 3b, the first was chosen to be tested in all in vivo and in vitro experiments due to higher availability. All protocols were approved by the Ethics Committee for the Use of Animals of the Federal University of Rio de Janeiro (CEUA-UFRJ-N° DFBCICB072-04/16, following the Guide for the Care and Use of Laboratory Animals, from the National Academy of Sciences, 2011), where all the procedures that could cause pain were performed under anesthesia.
This study demonstrated that some synthetic naphthoquinones structurally related to lapachol were able to antagonize some activities of Bothrops snake venoms. Naphthoquinones are compounds widespread in nature playing important physiological roles in animals and plants. Previous studies described that secondary metabolites bearing in their structure the 1,4- and 1,2-naphthoquinone moieties have been isolated from plants and exhibit interesting biological activities . In addition, lapachol (2-hydroxy-3-prenyl-1,4-naphthoquinone), found in Tabebuia species, showed to be active against the Walker-256 carcinoma and Yoshida Sarcoma cells [29, 41, 42].
In summary, some newly synthesized lapachol analogues exhibit a range of significant inhibition of enzymatic activities, suggesting potential therapeutic value against the local effects of crotalid venoms.