Grayanotoxins are a group of closely related toxins found in rhododendrons and other plants of the family Ericaceae. They can be found in honey made from their nectar and cause a very rare poisonous reaction called grayanotoxin poisoning, honey intoxication, or rhododendron poisoning. Grayanotoxin I (see below) is also known as andromedotoxin, acetylandromedol, rhodotoxin and asebotoxin; the systematic chemical name is: grayanotaxane-3,5,6,10,14,16-hexol 14-acetate. Grayanotoxins are named after Leucothoe grayana, a plant species from Japan, which is in turn named after 19th century American botanist Asa Gray.
Video Grayanotoxin
Chemical structure
Ac = acetyl
Grayanotoxins are polyhydroxylated cyclic diterpenes. They bind to specific sodium ion channels in cell membranes, the receptor sites involved in activation and inactivation. The grayanotoxin prevents inactivation, leaving excitable cells depolarized.
Maps Grayanotoxin
Poisoning
Nectar containing grayanotoxin can kill honeybees, though some seem to have resistance to it and can produce honey from the nectar (see below). According to a team of researchers from the UK and Ireland, worker bumblebees are not harmed, and may be preferable as pollinators because they transfer more pollen. So it may be advantageous to a plant to produce grayanotoxin in order to be pollinated by bumblebees.
Poisoning from grayanotoxins is rarely fatal in humans, but can be lethal for other animals. Physical symptoms from grayanotoxin poisoning occur after a dose-dependent latent period of minutes to three hours or so. Initial symptoms are excessive salivation, perspiration, vomiting, dizziness, weakness and paresthesia in the extremities and around the mouth, low blood pressure and sinus bradycardia. In higher doses symptoms can include loss of coordination, severe and progressive muscular weakness, electrocardiographic changes of bundle branch block and/or ST-segment elevations as seen in ischemic myocardial threat, bradycardia (and, paradoxically, ventricular tachycardia), and nodal rhythm or Wolff-Parkinson-White syndrome. Despite the potential cardiac problems the condition is rarely fatal and generally lasts less than a day. Medical intervention is not often needed but sometimes atropine therapy, vasopressors and other agents are used to mitigate symptoms.
Mad honey disease
Grayanotoxins can be found in honey produced from the nectar of plants such as Rhododendron ponticum that contains alkaloids that are poisonous to humans. Such honey is called 'mad honey'. Honey from Japan, Brazil, United States, Nepal, and British Columbia is most likely to be contaminated with grayanotoxins, although very rarely to toxic levels. In Nepal, this type of honey is used by the Gurung people both for its supposed medicinal and hallucinogenic properties.
Honey produced from the nectar of Andromeda polifolia contains high enough levels of grayanotoxin to cause full body paralysis and potentially fatal breathing difficulties due to diaphragm paralysis. Honey obtained from spoonwood and allied species such as sheep-laurel can also cause illness. The honey from Lestrimelitta limao also produces this paralyzing effect seen in the honey of A. polifolia and is also toxic to humans.
There have been famous episodes of inebriation of humans from consuming toxic honey throughout history. Xenophon, Aristotle, Strabo, Pliny the Elder, and Columella all document the results of eating this "maddening" honey, believed to be from the pollen and nectar of Rhododendron luteum and Rhododendron ponticum, which are found around the Black Sea. According to Xenophon, an invading Greek army was accidentally poisoned by harvesting and eating the local Asia Minor honey; they made a quick recovery with no fatalities. Having heard of this incident,, and realizing that foreign invaders would be ignorant of the dangers of the local honey, King Mithridates later used the honey as a deliberate poison when Pompey's army attacked the Heptakometes in Asia Minor in 69 BCE. The Roman soldiers became delirious and nauseated after being tricked into eating the toxic honey, at which point Mithridates's army attacked.
Honey containing grayanotoxin known as deli bal is still deliberately produced in the Caucasus region of Turkey. In the eighteenth century, this honey was exported to Europe to add to alcoholic drink to give it extra potency.
References
Source of the article : Wikipedia