Reptile Venom – A Rich Source of Bioactive Molecules With Potential Applications in Medicine

Reptile venom is a diverse mixture of toxin molecules that are excreted through a modified salivary gland into a delivery system consisting of specialised fangs, muscles and specialized cells or structures. This venom is then delivered to prey to immobilize and digest it.

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Front-fanged snakes (Elapidae, Colubridae and Viperidae) produce the most medically important venoms. Their venoms contain 3FTxs with diverse functions, but conserved structural scaffolds with subtle sequence differences in binding loops and conformations.

Venom Composition

Snake venom is one of nature’s most precious natural resources. It has been a vital part of the reptile’s survival, and has helped them evolve over time into highly effective predators and hunters. Its lethality, however, has also been a source of fascination and fear. Snakes, however, are careful not to use their venom unless they feel threatened or need to defend themselves. In fact, snakes will conserve their venom to ensure that it lasts them as long as possible.

The venom composition of snakes can be quite varied depending on the species and type of venom. The proteome of viperid snakes is dominated by enzyme toxins such as metalloproteinases, serine proteinases and modified phospholipases A2, whereas the venom of elapids tends to be primarily comprised of non-enzymatic, three-finger neurotoxic peptides.

Another significant component of snake venom is its disintegrins. These cysteine-rich peptides are generated by the post-translational cleavage of venom metalloproteases and act as a binding agent to platelet integrin receptors in prey. They can also induce apoptosis, thus enhancing the toxicity of other venom components. A notable example of a snake venom disintegrin is waglerin, which has four distinct isoforms in the venom of Tropidolaemus wagleri and makes up approximately 40% of the total venom protein content.

Toxins

Venoms contain a variety of lethally potent peptide and protein molecules with various bioactivities including neurotoxicity, haemotoxicity and cytotoxicity. The composition of reptile venoms is enormously varied both between different snake species and even within the same species, depending on factors such as environmental conditions, age and sex.

The venom proteins are grouped into families on the basis of their primary functional properties. In viperids, metalloproteinases, serine proteases and phospholipases A2 dominate the venom proteome, whereas in elapids non-enzymatic toxins such as three-finger proteins, cardiotoxins and modified phospholipases A2 are more prominent. The two charts below show averaged venom proteomes for the most well-studied genera at the genus level and reveal substantial compositional diversity. The large chart highlights that venoms from elapids generally contain nine protein families, while the smaller chart reveals that venoms from viperids generally contain seven protein families.

Some of these toxins have been used as medicines, for example batroxobin is an inhibitor of blood coagulation factor X, and haemocoagulase has antiplatelet activity. Moreover, many toxins target ion channels and represent important lead compounds in modern drug discovery efforts. In particular, the venom proteins CRiSP (cysteine-rich secretory protein), disintegrin and C-type lectin and C-type lectin-like proteins (CTL/SNACLEC) have great medicinal potential. However, the development of ex vivo pharmaceutical-grade venoms is challenging because of venom gland complexity and variable toxin expression.

Symptoms

A person who is bitten by a venomous snake should seek medical attention as soon as possible (call 911 or local EMS). Identifying the type of snake can help doctors know which antivenom to give and how much. The sooner the person gets antivenom, the sooner irreversible damage from the venom will be stopped.

Snake venoms are complex mixtures of chemicals that impact different parts of the body and cause specific symptoms. Venom from copperheads, cottonmouths and rattlesnakes contains neurotoxic chemicals that harm the nervous system, causing severe pain, sweating and breathing problems. It also thins the blood, causing bleeding at the bite site and around all body openings. This can lead to shock, loss of consciousness and death.

The venom from proteroglyphous snakes, including sea snakes, kraits and black and mambas, has more direct effects on the nervous system, causing respiratory paralysis that can lead to death without treatment. Other symptoms include vision problems, muscle weakness and numbness, vomiting, chills, and a drop in blood pressure that can cause fainting.

It is important to firmly bandage the limb involved and keep it still until medical help arrives. Do not try to suck out the bite or use ice on it. It is also a good idea to carry an adrenaline autoinjector such as an EpiPen(tm) or Anapen(tm), and follow an ASCIA allergy action plan if you have one, to treat severe allergic reactions such as anaphylaxis.

Treatment

Snake venom is a rich source of bioactive molecules with potential applications in medicine. Many of these compounds are currently used to treat a wide range of conditions including cancer, hypertension and thrombosis. Some venom components have also shown to be anti-inflammatory and have the ability to kill microorganisms. These compounds can be extracted from the venom of a variety of reptile species using sophisticated techniques such as reverse-phase high-performance liquid chromatography, mass spectrometry and next-generation sequencing15. These methods can be combined with X-ray crystallography, molecular modeling and bioinformatics to identify and understand the interactions of these peptides with proteins in complex environments.

For example, the discovery that venom from the South American pit viper jararaca (Bothrops jararaca) causes hypotension led to the development of the antihypertensive drug captopril. The same venom also contains several vasodilating peptides called three-finger toxins, which potentiate the action of bradykinin by inhibiting an enzyme that normally degrades it.

Another example is the cathelicidins, small cationic antimicrobial peptides that have been isolated from the venom of elapid snakes such as the cobra (Naja and other genera) and mamba (Dendroaspis and other genera). They exhibit strong antibacterial activity, but their toxic effects on human cells are relatively mild. The chemical structure of these peptides can be modified by rearranging the recognition motifs or by adding new amino acids. This allows them to be reduced in size for oral delivery while maintaining their affinity and specificity.