Aloin

Aloin is a bitter, lemon-yellow-colored compound isolated from the aloe plant. It is used as a stimulant-laxative, treating constipation by inducing bowel movements.^[1] The compound is present in the yellow aloe latex that exudes from under the surface of the plant's leaves, and is not found in the gel commonly used to treat skin conditions.

In May 2002, the US FDA issued a ruling that aloe laxatives are no longer generally recognized as safe (GRAS) and effective, meaning that aloin-containing products are no longer available over-the-counter in the United States.^[2]

Additional recommended knowledge

Essential Laboratory Skills Guide

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Structure and preparation

Aloin extracted from natural sources is a mixture of two diastereomers, termed aloin A (also called barbaloin) and aloin B (or isobarbaloin), which have similar chemical properties. Aloin is an anthraquinone glycoside, meaning that its anthraquinone skeleton has been modified by the addition of a sugar molecule. Anthraquinones are a common family of naturally occurring yellow, orange, and red pigments of which many have cathartic properties, attributes shared by aloin. Aloin is related to aloe emodin, which lacks a sugar group but shares aloin's biological properties.^[3]

Aloin is usually prepared by extraction from aloe latex, the bitter yellow exudate that seeps out from just underneath the skin of aloe leaves. The latex, also called 'aloe juice', is then dried and powdered to make the final product, often made into tablets or a beverage, though aloin does not have good stability in aqueous solutions. Products derived from the gel of the aloe plant do not contain appreciable amounts of aloin, and have not been proven effective for any disease or condition when taken orally.^[4]

Effects

Once ingested, aloin increases peristaltic contractions in the colon, which induces bowel movements. Aloin also prevents the colon from re-absorbing water from the gastrointestinal tract, which leads to softer stools.^[4] This effect is caused by aloin's opening of chloride channels of the colonic membrane. In higher doses, these effects may lead to electrolyte imbalance, diarrhea, and abdominal pain, which are common side-effects of the drug.^[4] Because aloin can potentially cause uterine contractions, pregnant women should avoid ingesting aloe products.^[5]

Legal status

Plant-derived remedies containing aloin and other anthraquinones have been used as traditional medicines since antiquity,^[6] but harsh side effects make aloin generally unsuitable for household or daily use. In 2002, the US FDA mandated that manufacturers reformulate or stop manufacturing over-the-counter products containing aloe because the agency did not receive necessary safety data.^[7][8]

References

• Aloin MSDS