Haemostasis-altering effects of Milos viper (Macrovipera schweizeri) venom

Haemotoxicity is one of the primary symptoms of viperid envenomation, manifesting in cardiovascular and haemostatic disturbances such as hypotension, haemorrhage, and coagulopathy. Bites by the Milos viper (Macrovipera schweizeri) have been reported to induce symptoms affecting the blood system, including fibrinogenolysis, erythrocytopenia, and venom-induced consumption coagulopathy. Consistent with these reports, its venom contains a variety of haemotoxic components and has been observed to exert strong procoagulant activity on human plasma. However, a more comprehensive analysis of the effects of Milos viper venom on haemostasis is currently lacking. Here, we present an in vitro evaluation of the haemostasis-altering properties of M. schweizeri venom. We conducted bioassays on key haematological targets to assess the thrombin-, plasmin-, coagulation Factor Xa-like, and haemolytic activities of Milos viper venom. A clear, positive concentration- dependent effect was observed in the thrombin-like and the plasmin-like activity assays, ranging from 1.6% to 77.4% and from 5.8% to 82.5%, respectively. The relatively comparable, pronounced activities detected at higher venom concentrations for these two haematological targets may align with the fibrinogenolysis and consumption coagulopathy described following M. schweizeri envenomation. Conversely, the assays revealed negligible Factor Xa-like and haemolytic activities. Our analysis provides a detailed overview of the haemostasis-altering potential of the toxin arsenal of M. schweizeri, shedding new light on its coagulotoxic effects.