The holothurins are a group of toxins originally isolated from the

sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

Actinopyga agassizii ''Actinopyga agassizii'', commonly known as the five-toothed sea cucumber or West Indian sea cucumber, is a species of sea cucumber in the family Holothuriidae. It was first described by German zoologist Emil Selenka in 1867. It is native to the ...

''. 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 tubule ...

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 tim ...

. The holothurins belong to the class of compounds known as

saponin Saponins (Latin ''sapon'', 'soap' + ''-in'', 'one of') are bitter-tasting, usually toxic plant-derived secondary metabolites. They are organic chemicals that become foamy when agitated in water and have high molecular weight. They are present ...

s 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 "water ...

. 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 The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals. It is the largest branch of the sacral plexus and runs alongside the hip joint and down the right lower limb. It is the longest and widest ...

and rat

phrenic nerve The phrenic nerve is a mixed nerve that originates from the C3–C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. In humans, t ...

preparations, and its potency can be compared to that of

cocaine Cocaine is a tropane alkaloid and central nervous system stimulant, derived primarily from the leaves of two South American coca plants, ''Erythroxylum coca'' and ''Erythroxylum novogranatense, E. novogranatense'', which are cultivated a ...

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 of ...

, 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 and ...

. 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 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 axonal domains that are high in sodium and potassium ion channels co ...

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 ...

macromolecular material found in and near the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

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 A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

. 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 Pancreatic lipases () are a protein family, 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 ...

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

obesity Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...

, and stimulate the production of LXR-β

nuclear receptor In the field of molecular biology, nuclear receptors are a class of proteins responsible for sensing steroids, thyroid hormones, vitamins, and certain other molecules. These intracellular receptors work with other proteins to regulate the ex ...

and

ABCA1 ATP-binding cassette transporter ABCA1 (member 1 of human transporter sub-family ABCA), also known as the ''cholesterol efflux regulatory protein'' (CERP) is a protein which in humans is encoded by the ''ABCA1'' gene. This transporter is a major ...

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 excess body fat. These medications alter one of the fundamental processes of the human body, weight regulation, by: reducing appetite and con ...

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

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

production in Melan-A cells and promoting

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

production in human dermal fibroblasts via the ERK pathway.

Pharmacology

Effects on nerves

Other effects

References

Further reading