Venom is a type of zootoxin that is transferred in to the body of prey through bite or sting in a process called envenomation. Snake venom is a mixture of different chemicals with diverse biological and pharmacological activities. These chemicals, that are mainly proteins, constitute more than 90% of the dry weight of snake venom. These chemical components include proteases, L-amino acid oxidases, esterases, nucleases, hyaluronidase, phospholipase A2 (PLA2) and many others (Stábeli et al., 2012). Among these proteins some have enzymatic activity while others act as non-enzymatic proteins and peptides. These proteins usually act as toxins and depending upon their mode of action are categorized as myotoxins that affect muscle tissues, cytotoxins that affect body cells, hemotoxins that cause hemolysis, cardiotoxins that affect heart tissues and neurotoxins that affect nervous system (Gasanov et al., 2014; Ferraz et al., 2019).

Asian cobra, Naja naja, is among the most highly venomous snakes on earth causing high rates of morbidity and mortality particularly in tropical countries (Ranawaka et al., 2013). Cobra venom is also comprised of the two major fractions of toxic enzymatic and nonenzymatic proteins, the cytotoxins (Rudrammaji and Gowda, 1998; Thangam et al., 2012). Hydrolytic enzymes of PLA2, caseinolytic AMPase, hyaluronidase and ATPase combined with cytotoxic cobramines, neurotoxins, cardiotoxins and membranotoxins cause visible pathological anomalies on nervous, cardiac, hepatic, pulmonary and muscle tissues thus immobilizing and digesting the prey (Aird, 2002; Suzuki-Matsubara et al., 2016).

PLA2 is an important constituent of cobra snake venom (Friess et al., 2001) that paralyzes the prey by affecting its muscular and peripheral nervous system as well as by causing anticoagulation, hemolysis, platelet aggregation, edema and hypotension (Gasanov et al., 2014; López-Vales et al., 2008). It also hydrolyzes monomeric, micellar or lipid bilayer phase particularly acting on phospholipids present in micellar form and releases free fatty acids thus causing membrane damage. This leads to adverse pharmacological effects due to changes in structure of cell membranes (Dennis, 1983; Kini, 2003).

Anti-sera are useful in combating snake bite envenomation but are not effective in protecting local tissue damage due to hemorrhage necrosis and edema (Ushanandini et al., 2006). Antibodies produced in horses are the most important source of anti-venom products. However, the process is time consuming and requires low temperature storage conditions that cannot be maintained in rural areas of developing countries. Many snake bite victims may also develop sensitivity towards horse products due to severe side reactions upon treatment with antisera derived from horses (de Silva et al., 2016). The situation demands identification of alternative medicine without major side effects and low temperature storage requirements.

Medicinal plants have a traditional history of usage to treat snake bites and are still used in many rural areas of different countries due to easy availability, less expensive and less/no side effects. Based on their traditional use as anti-venom agents, medicinal plants can be selected for scientific investigation to search for bioactive compounds effective against snake venom (Samy et al., 2008; Fry, 2018). Vitex negundo L. is an important plant of family Lamiaceae that is used to treat snake envenomation in many Asian countries. In these areas leaves and roots of this plant are used as an antidote to snake venom (Jayaweera, 2006; Samy et al., 2008; Makhija and Khamar, 2010; Prakasha et al., 2010; Sri and Reddi, 2011). A few research studies are available regarding snake venom neutralizing studies of the plant (Alam and Gomes, 2003; Durairaj et al., 2014; Prasuna, 2018) but in all these studies mostly alcoholic or hydroalcoholic extracts of the plants are used. All parts of the plant are reported to have medicinal properties however, the leaves and roots are the most important parts used in traditional medicine (Vishwanathan and Basavaraju, 2010). The present study was designed to evaluate the PLA2 inhibitory potential of roots of this plant extracted in different non-polar and polar solvents.