The cytotoxic effect of slow Loris (nycticebus) venom, on human cancer cells

Within the Kingdom Mammalia, venom evolution is rare, occurring in only six orders. Arguably the most cryptic, and academically neglected venom occurs within primates among slow lorises (Nycticebus spp.). Venoms comprise novel biological compounds with a potential plethora of proteins and peptides available for utilisation in bio-medical research. We collected samples of slow loris saliva from eight captive-bred pygmy slow lorises (N. pygmaeus) at Paignton Zoo and Shaldon Wildlife Trust UK, given voluntarily as slow lorises chewed on Salimetrics children’s swabs. From January to March 2017, we employed MTT assays, and microscopy assessments to determine cell survival on human epidermal carcinoma cells (A431 line) after the application of concentrations of slow loris salivary venom. Cell survival from both male and female derived saliva was half that of untreated cells. Cytotoxic action is demonstrated in concentrations as low as 0.01% venom. Results demonstrate a cytotoxic effect with ensuing physiological damage on human cancer cells, demonstrating the cytotoxic action of slow loris saliva only, without the admixture of brachial gland exudate. We show that even captive-bred slow loris saliva harbours potentially dangerous substances, with functional applications towards slow loris husbandry. Knowledge of slow loris salivary venom increases understanding of the novel salivary composition and supports discussions of slow loris conservation by proposing a functional narrative to oppose the illegal pet trade, by contradicting their ‘cute and cuddly’ appeal. Evidence of salivary venom shows that cytotoxic effects can result even in the absence of a bite puncturing the skin, and further demonstrates their inappropriateness as pets