species contain cathartic anthraglycosides at
concentrations between 10% and 20%, though
somecontainlevelsof30%barbaloin.Asingle
A. veraplant from Sri Lanka was found to
contain 57% barbaloin in its exudate. Highest
concentrationsofbarbaloinarefoundinyoung
mature leaf exudates, decreasing in older
leaves toward the base of the plant.^7 The con-
centrations of anthraglycosides vary with the
types of aloe; aloin content ranges from 4.5%
to 25%. Other constituents include aloesin
and its aglycone aloesone (a chromone),^8 free
anthraquinones(e.g.,aloe-emodin),and resins.
The composition of aloe vera gel is still not
clear.Studiestodateindicatethatthegelconsists
ofmorethanonetypeofpolysaccharideandthat
their compositions vary from one season and
source to the next. While one study showed it to
containatleastfourdifferentpartiallyacetylated
linear glucomannans with (1,4)-glycosidic
linkages,^9 others revealed an acidic galactan,
mannan, glucomannan, arabinan, and/or gluco-
galactomannan. The ratios of hexoses in each
polysaccharide differ widelyamong the studies,
as do their molecular weights.10–13
Thepolysaccharidesconstitute0.2–0.3%of
the fresh gel (0.8–1.2% of dry matter content).
Postproduction autodegradation of the gluco-
mannan polysaccharides produces mainly
mannans. The gel polysaccharides, consisting
mainly of mannose and glucose in a 1 : 3 ratio,
candegradein48 hatroomtemperature,witha
decrease in glucose content and an increase in
mannose:glucose ratio to>10.^14
Other constituents reported inA. verain-
clude other polysaccharides, polypeptides,
steroids, chromones, lectins, organic acids,
enzymes, amino acids, saponins, and miner-
als.1,3–5,13,15–23 Carboxypeptidase, a serine
carboxypeptidase enzyme found inA. arbor-
escensand other species ofAloe, is suggested
to be a primary antithermic agent.
PHARMACOLOGY AND BIOLOGICAL
ACTIVITIES
Drug aloe and its purified form, aloin, have
cathartic properties through action on the
colon. They are extremely bitter and are con-
sidered the least desirable among the plant
purgative drugs (seecascaraandsenna) due
to their bitterness and their tendency to pro-
duce more griping and irritation (GOSSELIN;
MARTINDALE). Aloin induces secretion of elec-
trolytes and water in the intestinal lumen,
inhibiting reabsorption of electrolytes and
water from the large intestine, which thereby
increases intestinal volume via increased fill-
ing pressure, which in turn stimulates peristal-
sis (BLUMENTHAL1).
An alcoholic extract of drug aloe was re-
ported to show antitumor activity (JIANGSU).
Aloe-emodin (seebuckthorn) administered
intraperitoneally (i.p.) has shown antitumor
activity in immunodeficient mice andin vitro
cytoxicity against tumor cells.^24 A phthalate
(diethylhexylphthalate or DEHP), isolated
from A. vera, has shownin vitroactivity
against the growth of several human leukemic
cell lines.^25 Daily oral administration of the
fresh leaf pulp ofA. veraproduced cancer
chemopreventive activity in mice, in part by
inducing the phase II enzyme system and by
increasing levels of endogenous antioxidants
in the liver.^26 Antiviral (herpes simplextypes 1
and 2) activities were found from a methanolic
extract of the whole leaf ofA. vera.17,27,28In
laboratory studies, the leaf gel or extracts ofA.
veraleaf have shown diverse activities, in-
cluding in vitroantimicrobial and in vivo
hypocholesteremic, dermal protectant, wound
healing, burn healing, frostbite healing, anti-
ulcerogenic, anti-inflammatory, hypoglyce-
mic, and others.^17
A number of studies have explored the
immunoreactive or immunomodulatory activ-
ity of variousAloespecies.^17 The principle
immunoactive constituents identified in A.
veraare lectins29–31and polysaccharides; in
particular, acemannan15,17and a water-solu-
ble polysaccharide named aloeride.^15
Chromones isolated fromA. veraleaves
have shown anti-inflammatory^32 and antioxi-
dant activities.^33 FromA. arborescens, car-
boxypeptidase showed analgesic activity
(comparable with bromelain) and dermopro-
tectant activity against burns in rats.34,35Aloe (and aloe vera) 25