How Snake Venom Kills: Blood Clotting & Necrosis

Snake venoms contain proteases that break down proteins, causing tissue destruction and coagulation problems. These enzymes are named with the suffix '-ase' to indicate their protein-digesting function. The video explains how these same enzymes are used medically to dissolve blood clots, with patients requiring hospital monitoring. The cost of these treatments was historically very high (3000 euros per ampoule).

Snake venom consists of neurotoxins (attacking the nervous system and respiratory centers) and hemotoxins (damaging blood tissues and causing clotting). Venom is produced by glands in the head and injected through hollow fangs. Cobras can spray venom up to 2 meters. Snake venom contains approximately 20 enzymes with varying compositions. Despite being dangerous, venom enzymes have medical applications: proteinase enzymes show promise in cancer treatment research, while colin esterase can prevent heart attacks and strokes. The world's most venomous snakes include the Inland Taipan (110 mg venom, enough to kill 100 people), Eastern Brown Snake, Blue Banded Krait (16 times stronger than cobra), Taipan (kills 12,000 mice), Black Mamba (fastest land snake at 20 km/h), and others.

Venom compounds have significant therapeutic applications: hypertension is treated with medication derived from South American viper toxin, type 2 diabetes monitoring uses toxin from North American lizards, and hospitals are developing protocols using marine snail toxins for anesthesia. This demonstrates how venom research translates to human medicine.

Snake venom, a highly modified saliva containing hundreds of different toxins including neurotoxins, myotoxins, and hemotoxins, can be safely collected by stimulating the snake's venom glands and has significant medical applications; for example, the pro-coagulant proteins in Taipan venom can clot blood rapidly and are being researched for potential treatments of Hemophilia and other blood disorders, while anti-coagulant venoms from other snakes are being studied for stroke and hypertension prevention.

Snake venom, particularly from highly toxic snakes like the taipan, contains hemotoxins that prevent blood coagulation, causing internal hemorrhaging, loss of bodily control, respiratory difficulty, and convulsions; without immediate medical intervention, the victim experiences severe pain and death within hours as muscle cells dissolve and blood cells break down, turning urine red.

Venomous animals use four main types of venom to subdue prey or defend themselves: neurotoxins that paralyze by blocking nerve signals (like black mamba venom), hemotoxins that destroy blood clotting systems (like Russell's viper venom), cytotoxins that dissolve cells (like brown recluse spider venom), and myotoxins that destroy muscle tissue (like king brown snake venom); these venoms evolved through an ongoing evolutionary arms race over hundreds of millions of years, with approximately 15% of all animal species being venomous, yet they also provide valuable medical applications including blood pressure medications, diabetes treatments, and powerful painkillers.

This extensive section covers the three major classes of snake venom toxins. Neurotoxins are classified as presynaptic (blocking neurotransmitter release by binding to voltage-gated calcium channels) or postsynaptic (blocking neurotransmitter receptors), causing progressive paralysis, respiratory failure, and potentially death. The most potent neurotoxins are phospholipase A2 enzymes that attack cell membranes. Myotoxins are muscle-specific neurotoxins that cause progressive muscle paralysis by blocking sodium-potassium pumps, preventing muscle contraction. The most potent myotoxin is botrotoxin from the jararaca, five times more potent than the inland taipan's neurotoxin. Hemotoxins (hemorrhagins) are classified into coagulants (promoting blood clotting, causing rapid thrombosis and tissue death) and anticoagulants (preventing blood clotting, causing severe bleeding). The most dangerous hemotoxins are coagulants because they can cause rapid death from pulmonary embolism. Hemotoxins attack the 13-factor coagulation cascade, targeting fibrinogen, fibrin, and platelet aggregation.

Snake venom contains multiple toxin types: (1) Cytolytic toxins (hemotoxins) that destroy blood cells and cause tissue damage, (2) Neurotoxins that affect nerve function, (3) Cytotoxins that destroy cells, (4) Cardiotoxins that affect the heart, (5) Myotoxins that damage muscle tissue. Cobra venom is primarily neurotoxic, while viper venom is primarily cytolytic/hemotoxic. This classification is essential for understanding the different clinical presentations and treatment approaches for different snake bites.

Different venomous snakes produce venoms with fundamentally different mechanisms of action. King cobras produce neurotoxins that specifically target the nervous system, causing rapid paralysis and potentially fatal respiratory failure. In contrast, snakes like the rhino viper produce hemotoxins that affect the circulatory system and cause extensive tissue necrosis, resulting in extremely painful wounds that can lead to digit loss. This distinction explains why some snake bites cause immediate paralysis while others cause severe tissue damage requiring extensive medical intervention. The rhino viper is also one of the fastest striking snakes on the planet, capable of striking one and a half times its body length, and exhibits a unique caterpilling locomotion pattern. Understanding these differences is crucial for appropriate medical treatment and antivenom selection.

Snake venoms are classified into cytotoxins (destroying body cells causing necrosis), neurotoxins (affecting nervous system), and hemotoxins (affecting blood). Cytotoxins include cardiotoxins (Naja/cobra), myotoxins (bangarus), and nephrotoxins (vipers). Neurotoxins cause tetany by destroying acetylcholinesterase, leading to sustained muscle contraction, or paralysis by destroying acetylcholine receptors. Hemotoxins cause blood degeneration and red blood cell destruction. No venom is purely one type; they always have mixed effects.

The genes that create venom in snakes originated from genes that create digestive proteins. Gene duplication is a type of mutation where animals can be born with two sets of the same gene, allowing natural selection to alter one copy without affecting the original gene's function. Under environmental pressures, venomous animals co-opted these duplicated genes for producing deadly toxins.

Snake venom delivery systems evolved through recruitment of pre-existing structures. First, venom glands evolved from modified salivary glands. Second, grooved teeth (found in many venomous snakes) represent an intermediate stage where venom is delivered by chewing. In vipers and cobras, grooves deepened so much that teeth folded back on themselves, forming hypodermic needles. Each step increased delivery efficiency until reaching a threshold where function dramatically changed—this represents normal gradualism with threshold effects.

Manual annotation identified 166-130 toxin genes per species, with 12 conserved toxin groups in syntenic blocks. Differential expression analysis of venom-producing tissues showed 6,000 differentially expressed genes, but only 260-370 orthologous pairs showed distinct expression patterns. This suggests most duplicated toxin genes maintained original functions or underwent sub-functionalization, while neo-functionalization remains less common in this system.

Many venom toxins evolve through gene duplication and subsequent modification. The process involves duplicating a gene encoding a normal physiological body protein (often involved in key regulatory processes), then selectively expressing the duplicate copy in venom glands. Once recruited into venom glands, additional gene duplication often occurs coupled with protein neofunctionalization or subfunctionalization, resulting in large multi-locus gene families producing toxins with varied functional activities and potencies.

The traditional paradigm of venom evolution states that endophysiological genes undergo gene duplication, followed by changes in expression levels in the venom gland. One copy becomes fixed in the venom gland, and natural selection then drives structural changes toward increased toxicity. This process can repeat, with the newly formed toxin gene undergoing further duplication. This model was developed by researchers including Serebryakov starting in 1938 and later refined by Zou et al.