Pharmacognosy of Senna Leaves

Introduction of Drug:

Senna is a commonly found medication traditionally used by Arabian physicians primarily as a cathartic. The Arabic word ‘senna’ and the Hebrew word ‘Cassia’  meaning “peeled back” (with reference to its peelable bark) together gave this plant its name. The laxative effect exerted by senna is mainly attributed to the anthraquinones which includes dianthrone glycosides, sennosides A and B, sennosides C and D. The laxative effect is exerted by acting on the lower bowel and thereby increasing the peristaltic movements of the colon by irritating the colonic mucosa. Senna is suggested as a “stimulant laxative” during pregnancy and lactation.

Senna leaves

Biological Source Dried leaflets of Cassia senna (Cassia acutifolia) also known commercially as Alexandrian senna or khartoum senna and Cassia angustifolia, which is commercially known as Tinnevelly senna or Indian senna. Should not be confused with Cassia which is a common name for cinnamon.
Family Leguminosae
Geographical Source Cassia senna is aborigine of tropical Africa and Sudan while Cassia angustifolia is native to Arabia, Somalia, Sind and the Punjab (parts of India)
Morphology/Macroscopical Characters
  • Senna plants are low branching shrubs (3 feet) with a straight woody stem and yellow flowers.
  • Leaflets of senna have stout petiolules, entire margin lamina with an asymmetric base and an acute apex.
  • It has a characteristic odor (faint) and bitterish unpleasant taste.
Microscopic Characters
  • Senna leaflets have an isobilateral structure with straight walled epidermal cells.
  • Nonlignified, unicellular warty hairs (trichomes) (upto 260 µm long) are scattered on both the surfaces. These hairs are more abundant in Alexandrian senna with three epidermal cells between hairs, while in Tinnevelly senna it is less frequent with about six epidermal cells between hairs.
  • Paracytic stomata are present with Alexandrian senna having two subsidiary cells, while Indian senna has two or three subsidiary cells (in a ratio of 7:3).
  • Prismatic and cluster calcium oxalate crystals  can be observed.
  • Vein islet numbers for Alexandrian Senna is about 25-29.5 while that for Indian/Tinnevelly Senna is 19.5-22.5.
  • The transverse section contains upper and lower epidermis, upper and lower palisade cells with an inner mesophyll. The mesophyll contains vascular bundles,xylem, fiber groups, and calcium oxalate crystals. Below the midrib is the collenchyma.

Chemistry Senna contains the following:

  • Dianthrone glycosides (1.5% – 3%), Sennosides A and B (rhein dianthrones containing the aglycone Sennidin A and Sennidin B respectively), Sennosides C and D (gylcosides of heterodianthrones rhein and aloe emodin).
  • Free anthraquinones are also present and several other glycosides such as palmidin A and aloe-emodin dianthrone diglycosides are also present.
  • Senna also contains flavanols such as kaempferol (yellow color) and isorhamnetin. Traces of chrysophanic acid, saponin, salicylic acid and volatile oils have also been found.

Sennidin A and Sennidin B, 6-hydroxymusizin glucoside and tinnevellin glucoside- difference between Alexandrian and Indian Senna

Chemical Tests Difference between Alexandrian and Indian senna (Tinnevelly Senna)

  1. Treat powdered drug with acid solution and extract with ether. When the organic layer is treated with methanolic magnesium acetate solution Alexandrian Senna gives pink color in daylight, while Indian/Tinnevelly Senna gives orange color in daylight.
  2. The same solution above in UV light gives a pale greenish-orange color for Alexandrian Senna, while the Indian Senna gives a yellowish-green color.
  3. TLC test for both can be performed. Alexandrian senna contains 6-hydroxymusizin glycosides, while Indian Senna contains Tinnevellin glycoside.
Adulterants/Allied drugs/ Substitutes Allied drugs:

  • Arabian, Bombay and Mecca sennasobtained from wild plants of Cassia Angustifoliaresemble the leaflets of Tinnevelly senna but are of brownish-brownish green color and somewhat more elongated and narrower. Can be distinguished microscopically from other senna by their vein islet number.
  • Dog sennaderived from Cassia obovata have leaves obovate (ovate with the narrower end at the base) in shape and quite different from the official leaflets. Microscopically identified by the papillose cells of the lower epidermis.
  • Palthe senna obtained from Cassia auriculatacan be recognised by the long hair, absence of anthraquinone derivatives and the crimson color obtained on boiling it with chloral hydrate solution or with 80% H2SO4.

Substitutes and Adulterants

  • Argel leavesderived from Solenostemma arghel were mixed historically with senna leaflets. These days it is classified as an adulterant and can be identified microscopically by the presence of 2 or 3 celled hairs, each surrounded by about 5 subsidiary cells.
  • In Nigeria, Cassia podocarpa is officially substituted.
Uses Senna is a useful laxative for either occasional use or habitual constipation. It is a popular laxative specially amongst the elderly and is devoid of the astringent after effects as observed in Rhubarb. It is reviewed to be useful during pregnancy and lactation.
Other Notes (life cycle, extraction etc.)
Adverse Reactions Senna at times may cause little abdominal discomfort like cramping. Prolonged use can cause ‘laxative dependency syndrome’ resulting in poor bowel movement without the presence of a laxative and it also may cause alteration of electrolytes. Also overuse may result in colon pigmentation and reversible finger clubbing (enlarged finger ends and toe ends).

References:

  1. Trease and Evans’ Pharmacognosy, 16e (Evans, Trease and Evans Pharmacognosy)
    Elsevier: New York, 2009.
  2. Ara DerMarderosian, et. al. The Review of Natural Products 4th Edition.
  3. Kokate, C. K.; Gokhale, S. B.; Purohit, A. P. A textbook of Pharmacognosy, 29th ed.; Nirali Prakashan: Pune, 2009.

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