Medicinal plants are being widely used by people all over the world. People understand the strength of nature and its abilities to cure. Doctors and scientists are validating the wisdom of traditional use. Although a few of the remedies are strong, all can be used safely and without the side effects of drugs. These natural remedies can be used to cure problems rather than just mask symptoms and postpone the affects. A lot of the information about medicinal plants is in the form of their actions. Rather than saying a plant is used for insomnia, many references will state that it has the action "sedative" or "hypnotic". Properties and actions of medicinal plants describe the action of the plant on the body. Definitions of these actions and properties can be found in a companion volume entitled Herbal Property Dictionary.

In natural medicine, medicinal plants are often chosen to balance a person. There is usually a long list of plants available for a specific symptom. For example the problem is a headache. If the person is overly warm and over-stimulated, a cooling, sedative medicinal plant is chosen. If there is nervous agitation and a headache, a tonic action will be desired from those medicinal plants which are also helpful with headaches. This is where the same action is found in different cultures for the same medicinal plant. Over three-quarters of the world population relies mainly on plants and plant extracts for health care. More than 30% of the entire plant species, at one time or other was used for medicinal purposes. It is estimated that world market for plant derived drugs may account for about Rs.2, 00,000 crores. Presently, Indian contribution is less than Rs.2000 crores. Indian export of raw drugs has steadily grown at 26% to Rs.165 crores in 1994-1995 from Rs.130 crores in 1991-1992. The annual production of medicinal and aromatic plant's raw material is worth about Rs.200 crores. This is likely to touch US $1150 by the year 2000 and US $5 trillion by 2050. Of the 2, 50,000 higher plant species on earth, more than 80,000 are medicinal. India is one of the world's 12 biodiversity centers with the presence of over 45000 different plant species. India's diversity is unmatched due to the presence of 16 different agro-climatic zones, 10 vegetation zones, 25 biotic provinces and 426 biomes (habitats of specific species). Of these, about 15000-20000 plants have good medicinal value.

In India, drugs of herbal origin have been used in traditional systems of medicines such as Unani and Ayurveda since ancient times. The Ayurveda system of medicine uses about 700 species, Unani 700, Siddha 600, Amchi 600 and modern medicine around 30 species. Medicinal plants antioxidant activity is mainly due to the presence of secondary metabolites. Based on their biosynthetic origins, plant secondary metabolites can be divided into three major groups: flavonoids and allied phenol and polyphenolic compounds, terpenoids and nitrogen-containing alkaloids and sulphur-containing compounds.


Flavonoids

Flavonoids are a group of polyphenolic compounds, which are widely distributed throughout the plant kingdom. Many have low toxicity in mammals. Flavonoids exhibit several biological effects such as anti-inflammatory, anti-hepatotoxic and anti-ulcer actions. They also inhibit enzymes such as aldose reductase and xanthine oxidase. They are potent antioxidants and have free radical scavenging abilities. Many have antiviral actions and some of them provide protection against cardiovascular mortality. They have been shown to inhibit the growth of various cancer cell lines in vitro, and reduce tumour development in experimental animals.

Terpenoids

The term terpene refers to a hydrocarbon molecule, while terpenoid refers to a terpene that has been modified, for example by the addition of oxygen. Terpenes or isoprenoids, are one of the most diverse classes of secondary metabolites which play variety functional roles in plants as hormones (gibberellins, abscisic acid), photosynthetic pigments (phytol, carotenoids), electron carriers (ubiquinone, plastoquinone), mediators of polysaccharide assembly (polyprenyl phosphates), and structural components of membranes (phytosterols). More than 55,000 different terpenoids have been isolated, and this number has almost doubled each decade, many of which are of plant origin. Terpenoids are essential for plant growth, development, and general metabolism. Terpenoids are found in almost all plant species.

Alkaloids

Alkaloids are a diverse group of low molecular weight, nitrogen-containing compounds mostly derived from amino acids. Alkaloids are thought to play a defensive role in the plant against herbivores and pathogens. Plant-derived alkaloids currently in clinical use include analgesics, anti neoplastic agent, gout suppressant, muscle relaxants, antiviral, cytotoxic, antinociceptive, anticholinergic, antiinflammatory and DNA-binding activities and some of them have also been used in the treatment of Alzheimer?s disease, myasthenia gravis and myopathy. Purine alkaloids such as caffeine, theobromine, and theacrine are widely distributed in the plant kingdom. Caffeine, a nonselective adenosine A1 and A2A receptor antagonist, is the most widely used psychoactive substance in the world. Evidence demonstrates that caffeine and selective adenosine A2A antagonists interact with the neuronal systems involved in drug reinforcement, locomotors sensitization, and therapeutic effect in Parkinson's disease.

Some of the Most Widely Used Plants

Greater Ammi or Ammi majus Apiaceae also known as Bishop's weed or Honey plant is an annual or biennial herb which is extensively used in the treatment of leucoderma (vitiligo) and psoriasis. The compounds responsible for this are reported to be furocoumarins like ammoidin (xanthotoxin), ammidin (imperatorin) and majudin (bergapten) present in the seed. Xanthotoxin is marketed under the trade name "Ox soralen" which is administered orally in doses of 50 mg tad. or applied externally as 1% liniment followed by exposure of affected areas to sunlight or UV light for 2 hours. It is also used in "Suntan lotion". Meladinine is a by-product of Ammi majus processing, containing both xanthotoxin and imperatorin sold in various formulations increases pigmentation of normal skin and induces repigmentation in vitiligo. Imperatorin has antitumour activity. Fruit or seed causes photosensitization in fouls and sheep.

LONG PEPPER Piper longum Piperaceae

Long pepper is a slender aromatic climber whose spike is widely used in ayurvedic and unani systems of medicine particularly for diseases of respiratory tract. Pipalarishta, Pippalyasava, Panchakola, Pippalayadilauha, and Lavana bhaskar churan are common ayurvedic preparations made out of the dry spikes of female types. Ittrifal fauladi, Angaruya-i-kabir and Majun khadar are well known unani preparations of long pepper. Its roots also have several medicinal uses. The root is useful in bronchitis, stomach ache, diseases of spleen and tumours. Fruit is useful in vata and kapha, asthma, bronchitis, abdominal complaints, fever, leucoderma, urinary discharges, tumours, piles, insomnia and tuberculosis. Root and fruit are used in gout and lumbago. The infusion of root is prescribed after parturition to induce the expulsion of placenta. The root and fruit decoction are used in acute and chronic bronchitis and cough. It contains the alkaloid piperine which has diverse pharmacological activities, including nerve depressant and antagonistic effect on electro- shock and chemo-shock seizures as well as muscular incoordination.

DATURA Datura metel Solanaceae

Downy datura or thorn apple is an erect branched under shrub that's intoxicating and narcotic properties have been made use of by man from ancient time. The plant and fruit are spasmolytic, anticancerous and anthelmintic. Leaves and seeds are inhaled in whooping cough, asthma and other respiratory diseases. Root, leaf and seed are febrifuge, antidiarrhoeal, anticatarrhal and are used in insanity, cerebral complications and skin diseases. Leaf is antitumour, antirheumatic and vermicide. Flower is antiasthamatic, anaesthetic and is employed in swellings and eruptions on face. For the rheumatic swellings of joints, lumbago, sciatica and neuralgia, warm leaf smeared with oil is used as a bandage or sometimes the leaf is made into a poultice and applied. The root boiled with milk is used in insanity. It is also an ingredient in the ayurvedic preparation Kanakasva used in bronchial troubles, and the Unani formulations "Roghan dhatura" used as massage oil for the paralysed part. The alkaloids of pharmaceutical interest present in the plant are hyoscyamine, hyoscine and meteloidine. Datura is the chief commercial source of hyoscine available from natural source. Hyoscine, in the form of hyoscine hydrobromide, is used as a pre-anaesthetic in surgery, child birth, ophthalmology and prevention of motion sickness.

Withania somnifera

Withania somnifera is one of the major herbal components of geriatric tonics mentioned in Indian systems of medicine. In the traditional system of medicine Ayurveda, this plant is claimed to have potent aphrodisiac rejuvenative and life prolonging properties. It has general animating and regenerative qualities and is used among others for the treatment of nervous exhaustion, memory elated conditions, insomnia, tiredness potency issues, skin problems and coughing. It improves learning ability and memory capacity. The traditional use of 'Ashwagandha' was to increase energy, youthful vigour, endurance, strength, health, nurture the time elements of the body, increase vital fluids, muscle fat, blood, lymph, and semen and cell production. It helps counteract chronic fatigue, weakness, dehydration, bone weakness, loose teeth, thirst, impotency, premature aging emaciation, debility, and convalescence and muscle tension. It helps invigorate the body by rejuvenating the reproductive organs, just as a tree is invigorated by feeding the roots.

Achyrocline satureioides (Less) DC (Asteraceae)

It is a medicinal plant symbol of Rio Grande do Sul state in Brazil. A new prenylated dibenzofuran, achyrofuran, a compound derived from A. satureioides significantly lowered blood glucose levels when administered orally at 20 mg/kg q.d [8]. The aqueous extract of the aerial parts of A. satureioides administered before bromobenzene (BB), at the dose of 300mg/kg, inhibited the increase of liver ALT and AST, whereas, the BB-induced liver shows increase of thiobarbituric acid reacting substances (TBARS) content. Also it significantly increases the depleted levels of liver glutathione and bile flow in rats. In addition, at the same dose, a significant increase in the bile flow of rats was found. The results obtained with the aqueous extract of A. satureioides support its use in popular medicine as a hepatoprotective and digestive agent, and the effects might be mediated through the antioxidant and choleretic activities.

Gongronema latifolium Endl. (Asclepiadaceae)

The origin of the plant is traced to Nigeria in West Africa. The aqueous extract of G. latifolium is able to significantly increase the activities of hepatic hexokinase and decrease the activities of glucokinase, but does not produce any change in the hepatic glycogen and both hepatic and blood glucose content of diabetic rats [64]. The effects of oral administration of aqueous and ethanolic leaf extracts increase the activity of superoxide dismutase and the level of reduced glutathione. The aqueous extract further increases the activity of glutathione reductase while the ethanolic extract causes a significant increase in the activity of glutathione peroxidase and glucose-6-phosphate dehydrogenase and a significant decrease in lipid peroxidation. These results suggest that the extracts from G. latifolium leaves could exert their antidiabetic activities through their antioxidant properties.

Plants and other natural products with known or unknown active compounds and/or known or unknown mechanisms of action against HIV and AIDS-related opportunistic infections A total of 30 plant species from 15 families were reported to have activities against HIV or HIV related sicknesses, and also against other diseases such as cancer, fungal infections, inflammation, and general microbial opportunistic infections. However, their active compounds or modes of actions were not well understood.

References

David Phillipson. Phytochemistry and medicinal plants. Phytochemistry 2001; 56

Breitmaier E. Terpenes: Flavors, Fragrances, Pharmaca, Pheromones; Wiley-VCH: Weinheim, Germany, 2006.

Daniel Seifu1, Freshet Assefa and Solomon M. Abay,Addis Ababa University, School of Medicine, Department of Biochemistry, Addis Ababa, Ethiopia.

Lee SE, Hwang HJ, Ha JS et al. screening of medicinal plant extracts for antioxidant activity. Life Sci 73



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