The holothurins are a group of toxins originally isolated from the sea cucumber '' Actinopyga agassizii''. They are contained within clusters of sticky threads called

Cuvierian tubules Cuvierian tubules are clusters of fine tubes located at the base of the respiratory tree in some sea cucumbers in the genera ''Bohadschia'', ''Holothuria'' and ''Pearsonothuria'', all of which are included in the family Holothuriidae. The tubules ...

which are expelled from the sea cucumber as a mode of

self-defence Self-defense (self-defence primarily in Commonwealth English) is a countermeasure that involves defending the health and well-being of oneself from harm. The use of the right of self-defense as a legal justification for the use of force in ...

. The holothurins belong to the class of compounds known as saponins and are

anionic surfactants An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

which can cause red blood cells to

rupture Rupture may refer to: General * Rupture (engineering), a failure of tough ductile materials loaded in tension Anatomy and medicine * Abdominal hernia, formerly referred to as "a rupture" * Achilles tendon rupture * Rupture of membranes, a "wate ...

. The holothurins can be toxic to humans if ingested in high amounts.

Pharmacology

Effects on nerves

Holothurin is shown to have a blocking effect on nerves in desheathed bullfrog sciatic nerve and rat phrenic nerve preparations, and its potency can be compared to that of

cocaine Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Ameri ...

procaine Procaine is a local anesthetic drug of the amino ester group. It is most commonly used in dental procedures to numb the area around a tooth and is also used to reduce the pain of intramuscular injection of penicillin. Owing to the ubiquity ...

, and

physostigmine Physostigmine (also known as eserine from ''éséré'', the West African name for the Calabar bean) is a highly toxic parasympathomimetic alkaloid, specifically, a reversible cholinesterase inhibitor. It occurs naturally in the Calabar bean a ...

. Unlike the other mentioned blocking agents, the disrupting effect of holothurin appears to be quite irreversible upon washing. In another experiment on frog sciatic nerve, holothurin A is shown to be capable of destroying electrical excitability of a

node of Ranvier In neuroscience and anatomy, nodes of Ranvier ( ), also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, al ...

along with

basophilic Basophilic is a technical term used by pathologists. It describes the appearance of cells, tissues and cellular structures as seen through the microscope after a histological section has been stained with a basic dye. The most common such dye i ...

macromolecular material found in and near the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

of the node. In another experiment on rat phrenic nerve, the nerve-disrupting effect of holothurin A is found to be preventable when specific concentrations of physostigmine are present.

Other effects

Holothurin A and holothurin A1, along with other sea cucumber saponins, are found to reduce weight gain in mice. They improve glucose tolerance, reduce levels of lipids in blood and liver, and inhibit the absorption of lipids in the intestine. They also inhibit the activity of

pancreatic lipase Triglyceride lipases () are a family of lipolytic enzymes that hydrolyse ester linkages of triglycerides. Lipases are widely distributed in animals, plants and prokaryotes. At least three tissue-specific isozymes exist in higher vertebrates, p ...

, decrease the growth of white adipocytes, a factor which contributes to

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

, and stimulate the production of LXR-β nuclear receptor and ABCA1 protein. These findings suggest a possibility of the holothurins and other sea cucumber saponins being used in the development of

anti-obesity drug Anti-obesity medication or weight loss medications are pharmacological agents that reduce or control weight. These medications alter one of the fundamental processes of the human body, weight regulation, by altering either appetite, or absorp ...

. The holothurins are shown to have anti-melanogenic and anti-wrinkling effects on human skin by inhibiting

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

production in Melan-A cells and promoting collagen production in human dermal fibroblasts via the

ERK pathway The MAPK/ERK pathway (also known as the Ras-Raf-MEK-ERK pathway) is a chain of proteins in the cell that communicates a signal from a receptor on the surface of the cell to the DNA in the nucleus of the cell. The signal starts when a signaling ...

Pharmacology

Effects on nerves

Other effects

References

Further reading