Ptaquiloside
Encyclopedia
Ptaquiloside, the major toxin
of bracken
, was first isolated in 1983, and its chemical
stereostructure was determined to be norsesquiterpene glucoside
of illudane type by Yamada and co-workers.
The carcinogenicity of ptaquiloside was proven in 1984, and furthermore, ptaquiloside was shown to be responsible for the characteristic biological effects of bracken, such as acute bracken poisoning, bright blindness in sheep, mutagen
icity, clastogenic
effects and genotoxicity.
In a weakly alkaline solution, ptaquiloside is gradually converted, with concomitant elimination of glucose
, into an unstable compound “dienone”, which is the activated form of ptaquiloside and acts as a powerful alkylating agent. The “dienone” alkylates the purine
bases (adenine
and guanine
) of DNA
, and then the alkylated purine parts are spontaneously removed from DNA: subsequently the cleavage of DNA occurs (DNA damage). Prakash and co-workers suggested ptaquiloside-induced carcinogenesis was initiated by the activation of the H-Ras oncogene
.
From the chemical and ecological viewpoints, quantitative analyses
of ptaquiloside in bracken were intensively performed worldwide. The ptaquiloside content of bracken proved to vary: for example, concentrations of ptaquiloside in the dried fronds of bracken were 0.1-0.6%.
In 2004, Danish scientist Lars Holm Rasmussen released a study showing the chemical can leach from the plant into the water supply
, which may explain an increase in the incidence of gastric and oesophageal cancers in humans in bracken-rich areas. In addition, cattle
are known to eat the young shoots and fronds, which can then cause cancer
in the cattle and affect their milk
, especially when untreated. Other livestock (sheep, horses) are known to develop cancers after ingestion of bracken.
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
of bracken
Bracken
Bracken are several species of large, coarse ferns of the genus Pteridium. Ferns are vascular plants that have alternating generations, large plants that produce spores and small plants that produce sex cells . Brackens are in the family Dennstaedtiaceae, which are noted for their large, highly...
, was first isolated in 1983, and its chemical
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
stereostructure was determined to be norsesquiterpene glucoside
Glucoside
A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes....
of illudane type by Yamada and co-workers.
The carcinogenicity of ptaquiloside was proven in 1984, and furthermore, ptaquiloside was shown to be responsible for the characteristic biological effects of bracken, such as acute bracken poisoning, bright blindness in sheep, mutagen
Mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...
icity, clastogenic
Clastogenic
Clastogenic is an adjective that describes the ability of an agent or process to act as a clastogen—an agent or process giving rise to or inducing disruption or breakages of chromosomes.-Biology:...
effects and genotoxicity.
In a weakly alkaline solution, ptaquiloside is gradually converted, with concomitant elimination of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, into an unstable compound “dienone”, which is the activated form of ptaquiloside and acts as a powerful alkylating agent. The “dienone” alkylates the purine
Purine
A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
bases (adenine
Adenine
Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
and guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...
) of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, and then the alkylated purine parts are spontaneously removed from DNA: subsequently the cleavage of DNA occurs (DNA damage). Prakash and co-workers suggested ptaquiloside-induced carcinogenesis was initiated by the activation of the H-Ras oncogene
Oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, they are often mutated or expressed at high levels.An oncogene is a gene found in the chromosomes of tumor cells whose activation is associated with the initial and continuing conversion of normal cells into cancer...
.
From the chemical and ecological viewpoints, quantitative analyses
Quantitative analysis (chemistry)
In chemistry, quantitative analysis is the determination of the absolute or relative abundance of one, several or all particular substance present in a sample....
of ptaquiloside in bracken were intensively performed worldwide. The ptaquiloside content of bracken proved to vary: for example, concentrations of ptaquiloside in the dried fronds of bracken were 0.1-0.6%.
In 2004, Danish scientist Lars Holm Rasmussen released a study showing the chemical can leach from the plant into the water supply
Water supply
Water supply is the provision of water by public utilities, commercial organisations, community endeavours or by individuals, usually via a system of pumps and pipes...
, which may explain an increase in the incidence of gastric and oesophageal cancers in humans in bracken-rich areas. In addition, cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
are known to eat the young shoots and fronds, which can then cause cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
in the cattle and affect their milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
, especially when untreated. Other livestock (sheep, horses) are known to develop cancers after ingestion of bracken.