Solanaceae - Alkaloids

Alkaloids

Solanaceae is known for having a diverse range of alkaloids. As far as humans are concerned, these alkaloids can be desirable, toxic, or both.

One of the most important groups of these compounds is called the tropane alkaloids. The term "tropane" comes from a genus in which they are found, Atropa (the belladonna genus). Atropa is named after the Greek Fate, Atropos, who cut the thread of life. This nomenclature reflects its toxicity and lethality.

Tropane alkaloids are also found in the Datura, Mandragora, and Brugmansia genera, as well as many others in the Solanaceae family. Chemically, the molecules of these compounds have a characteristic bicyclic structure and include atropine, scopolamine, and hyoscyamine. Pharmacologically, they are the most powerful known anticholinergics in existence, meaning they inhibit the neurological signals transmitted by the endogenous neurotransmitter, acetylcholine. Symptoms of overdose may include dry mouth, dilated pupils, ataxia, urinary retention, hallucinations, convulsions, coma, and death.

Despite the extreme toxicity of the tropanes, they are useful drugs when administered in extremely small dosages. They can reverse cholinergic poisoning, which can be caused by overexposure to pesticides and chemical warfare agents such as sarin and VX. More commonly, they can halt many types of allergic reactions. Atropine, a commonly used ophthalmological agent, dilates the pupils and thus facilitates examination of the interior of the eye. Scopolamine is used as an antiemetic against motion sickness or for people receiving chemotherapy. Atropine has a stimulant effect on the central nervous system and heart, whereas scopolamine has a sedative effect.

An infamous alkaloid derived from Solanaceae is nicotine. Like the tropanes, its pharmacology acts on cholinergic neurons, but with the opposite effect (it is an agonist as opposed to an antagonist). It has a higher specificity for nicotinic acetylcholine receptors than other ACh proteins. Nicotine occurs naturally in the Nicotiana or tobacco genus.

Another class of toxic substances found in this family are the glycoalkaloids, for example solanine which has occasionally been responsible for poisonings in people who ate berries from species such as Solanum nigrum or Solanum dulcamara, or green potatoes.

The chemical in chili peppers responsible for the burning sensation is capsaicin. Capsaicin affects only mammals, not birds. Pepper seeds can survive the digestive tract of birds; their fruit becomes brightly colored once its seeds are mature enough to germinate, thereby attracting the attention of birds who then distribute the seeds. Capsaicin extract is used to make pepper spray, a useful deterrent against aggressive mammals.