Introduction to Cascara and Its Primary Compounds
Cascara, also known by its Spanish name cascara sagrada or “sacred bark,” is derived from the aged bark of the Rhamnus purshiana tree, native to North America. Its use as a powerful yet gentle laxative was historically recognized by indigenous peoples and later adopted into Western medicine. The complex biological activity of cascara is not due to a single chemical but to a synergistic combination of constituents, with the most important being anthraquinone glycosides.
The Role of Cascarosides
The most pharmacologically significant constituents in cascara are the cascarosides, a group of anthraquinone glycosides, with cascarosides A, B, C, and D being the primary examples. These compounds are crucial for the herb's laxative action. They pass through the stomach and small intestine without being absorbed, reaching the large intestine where intestinal bacteria hydrolyze them into their active form, the aglycones. These active metabolites then directly stimulate the muscle contractions (peristalsis) of the colon and increase the secretion of water and electrolytes, which softens the stool and promotes bowel movement.
- Cascarosides A and B: These are the main glycosides derived from aloin.
- Cascarosides C and D: These are primary glycosides of 11-deoxyaloin or chrysaloin.
Free Anthraquinones and Their Impact
While cascarosides are the key players, cascara also contains smaller amounts of free anthraquinones, or aglycones, which are the products of cascaroside hydrolysis. Examples include emodin, aloe-emodin, and chrysophanol. It is these aglycones that are responsible for the irritating effect on the colon mucosa. This is why fresh cascara bark, containing higher levels of a more irritating form called anthranols, must be aged for at least one year before use. The aging process allows for the oxidation of these anthranols into the less aggressive anthraquinone derivatives.
Other Notable Compounds
Beyond the anthraquinones, cascara's chemical makeup is rounded out by several other constituents that contribute to its overall profile. These include:
- Dianthrones: These are dimmer forms of anthraquinones, such as palmidins A, B, and C.
- Tannins: These compounds are known for their astringent properties and are often present in herbal barks.
- Lipids, Volatile Oils, and Resins: These add to the bark's complex composition and characteristic properties.
Comparing Constituents: Cascara vs. Senna
Cascara and senna are both popular anthraquinone-containing herbal laxatives, but their chemical composition and effects differ. The comparison highlights cascara's unique blend of constituents, particularly its cascarosides, which lead to a generally milder action than senna.
| Feature | Cascara (Rhamnus purshiana) | Senna (Cassia species) |
|---|---|---|
| Primary Active Constituents | Cascarosides A, B, C, and D (hydroxyanthraquinone glycosides) | Sennosides A and B (dianthrone glycosides) |
| Mechanism of Action | Stimulates colonic peristalsis and increases fluid/electrolyte secretion, typically milder | Stronger stimulant action, more potent for bowel evacuation |
| Onset of Effect | Generally takes 6-12 hours for a bowel movement | Often quicker, sometimes with more pronounced cramping |
| Key Free Anthraquinones | Emodin, aloe-emodin, chrysophanol | Rhein, sennidin |
| Aging Requirement | Bark must be aged for at least one year to reduce harsh anthranol content | No specific aging process is required before use |
Proper Use and Safety Considerations
Given its potency, cascara should only be used in its aged form and is typically recommended for short-term use (less than a week) to address occasional constipation. Prolonged use can lead to dependency, electrolyte imbalances, and other adverse effects, including a harmless but noticeable pigmentation of the colon lining called melanosis coli. It is crucial to follow dosage guidelines and consult a healthcare provider for persistent issues.
Conclusion
The major constituents of cascara are a group of specialized anthraquinone glycosides, primarily cascarosides, which, along with free anthraquinones and other phytochemicals like tannins, contribute to its well-established laxative effects. The unique blend and proportion of these compounds give cascara its specific pharmacological profile, distinguishing it from other herbal laxatives. The practice of aging the bark is a vital step in mitigating the harshest effects of its fresh state. While a powerful and effective herbal remedy for constipation, an understanding of its constituents is key to appreciating its proper and safe application. Further clinical studies are needed to explore its mechanism and safety with contemporary validation.
