Habit and Distribution of the Plant
The genus Althaea belongs to the family Malvaceae and includes 12 species, which are located mainly in Europe, with the exception of the Scandinavian countries, and the Near East (western and north Asia). They are cultivated mainly in Germany, France, Belgium, Spain, Italy, Hungary, and Russia, and have been introduced in North and South America.
The most important species of the genus is Althaea officinalis L. (marshmallow), densely gray-pubescent perennial up to 1.5-2 m, with stellate hairs. Leaves triangularovate, acute, crenate-serrate, undivided or palmately 3-5-lobed, often somewhat plicate. Flowers solitary or clustered in axillary inflorescences shorter than the substanding leaf. Epicalix segments linear-lanceolate. Sepals ovate, acute, curved over the fruit. Petals, 15-20 mm, very pale, lilac-pink, rarely deeper pink. Anthers are purplish red. Mericarps more or less densely covered with stellate hairs. The chromosome number is 2n = 42. The plant has a woody rootstock from which numerous roots arise, up to 30 cm in length.
The roots (Radix Althaea naturalis and mundata); the leaves (Folia Althaeae), and the flowers (Flores Althaeae) are used in medicine.
The drug Radix Althaea is mainly collected from cultivated plants at least 2 years old. The roots are dug up in the autumn, cut away from the cork, and dried, either whole or after slicing (mundata). The drug occurs in whitish, fibrous pieces about 15-20 cm long and 1-2 mm in diameter, or in small transverse slices. Odor, slight; taste, sweetish and mucilaginous. A transverse section shows a bark about 1-2 mm thick which is separated by a grayish, sinuate cambium from the white radiate wood. The section shows numerous mucilage cells, the content of which is colored a deep yellow by solution of sodium hydroxide.
Medically Important Compounds
On the basis of the organ-specific distribution of the compounds, the following drugs are used:
Radix Althaea contains from 5-10% to 20-35% of mucilage. The amount being season-dependent (); 30-38% starch, 11% pectin, 5-10% sugars, 2% betain, lecithin, phytosterin, and asparagine. The latter, which is the amide of aspartic (aminosuccinic) acid has no therapeutic value, 2% tannins, 1.5% fatty acids, 7% minerals, flavonoids, the coumarin scopoletin, and phenolic acids.
Flores Althaea contains 5-8% mucilage, 0.02% essential oil, asparagin, sugars, and flavonoids.
Several groups of compounds of Althaea plants, proved to be of medical importance, are described here.
Different plant species vary enormously in their soil and nutritive requirements, and this aspect has received considerable attention in medicinal plants. It is known that the content of polysaccharides and their composition in the plant is affected by several factors, for example, the locality where it is grown, the degree of the development stage, time of harvest, etc.
Variation in particle size results in different soils, ranging from clay via sand to gravel. Particle size is one factor influencing water-holding capacity, and Althaea officinalis, which produces mucilage as a water-retaining material, contains less mucilage when grown on soil with a high moisture content.
The production of mucilage coincides with the fermentative disintegration of starch. The mucilayer is deposited on the cell wall and the whole cell is filled with mucilage. All starch-containing cells of A. officinalis have the capacity to produce mucilage.
Based on the chemical property of the mucilage of Althaea plants, von Friedrichs (1919) found its components to be glucose and xylose. In 1946, Beauquesne (cited in Franz 1966) reported that is was made up of uronic acid, methylpentoses, and hexoses. Franz (1966) reported that crude mucilage of the roots contains glucan, an arabinogalactan, and an acidic polysaccharide -galacturonorhamnan. He observed that the neutral fraction was composed of 21% glucose, 52% galactose, and 27% arabinose. For the acidic polysaccharide, Franz reported a composition of 58% galacturonic acid, 39% rhamnose, 3% galactose, and trace amounts of glucose. He isolated α-(D-galactopyranosyluronic acid)-(1-2)-L-rhamnose as a partial hydrolysate of the acidic polysaccharide.
Recently, several reports have appeared on structural studies of mucilaginous polysaccharides isolated from A. officinalis plants, as well as from other related species and varieties.
Pharmacological Effects of Althaea Compounds
Althaea officinalis L. has been known as a medicinal plant since ancient times, when its roots, leaves, and flowers were used Althaea radix is a well-known antiphlogistic, emollient, and demulcent. The mucous material isolated from the roots of the marshmallow may be used as a crude drug in treatment of catarrh of the respiratory system, gastritis, ulcus ventriculi, various inflammations of the nasal and oral cavities, kidney pain, and tonsillitis.
The use of polysaccharide hydrocolloides in antitussive preparations such as cough drops, cough syrup, and cough lozenges is well documented. As a consequence of inflammatory events of the mucous membranes in the respiratory tract, the naturally occurring mucin layer is disturbed in its function. After medication with polysaccharide hydrocolloids, the mucin effect can be restored by forming a protective layer in order to desensitize the irritated peripheroceptors. Local inflammations are diminished by this effect, and as a consequence, the dry cough is reduced.
According to recent literature, some of the flavonoids found in Althaea show pronounced antiinflammatory activity, e.g., tiliroside, astragalin, and kaempferol, hypolaetin-8-O-glucoside and its aglycone. They may be a supporting factor for the anti-inflammatory effect of the mucilage present in the investigated materials.
It has been known for some time that, in animal experiments, a high polysaccharide diet reduces the blood level of both cholesterol and glucose. The mucilages of Althaea showed considerable anticomplementary activity and remarkable hypoglycemic activity.
Several herbal drugs including Althaea are at present considered as being potent in the area of immunestimulants. The polysaccharides were postulated to have an unspecific immune-modulation effect. Those containing uronic acid in their structure have better effect. The mixture of polysaccharides from the variety Russalka of Althaea officinalis L. has a strong immunostimulating effect to the humoral immune response and phagocytic activity.
Summary and Conclusion
The experiments on cultured tissue of Althaea officinalis were performed from the following two viewpoints:
1. The standardization problems concerning the chemical composition of Althaea polysaccharides and biological activity of plant extracts, due to varying plant origin, make the production of polysaccharides by cell cultures of Althaea plants desirable.
2. Plant tissue culture technique can be successfully employed to study the influence of various physical, nutritional, and hormonal factors on growth and production of polysaccharides, flavonoids, coumarins, and phenolic acids under controlled conditions.
Selections from the book: Medicinal and Aromatic Plants VII (1994)