New Antimicrobials Of Plant Origin
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New Antimicrobials of Plant Origin
INFECTIOUS DISEASE
Historic Use of Plants as Antimicrobials
The Development of Phytomedicines and the Ethnomedicinal Approach
PRESENT USE OF PLANTS AS ANTIMICROBIALS
Therapeutic Benefit
Economic Benefit
PLANTS WITH PROMISING ANTIINFECTIVE ACTIVITY
Garcinia kola, bitter kola (Guttiferae)
Aframomum melegueta (Zingiberaceae) Grains of Paradise
Xylopia aethiopica, Ethiopian Pepper (Abbibacceae)
Cryptolepis sanguinolenta Lindl. Schltr. (Periplocaceae)
Chasmanthera dependens Hoschst (Menispermaceae)
Nauclea latifolia Smith (Rubiaceae)
Araliopsis tabouensis (Rutaceae)
CONCLUSION
REFERENCES
Infectious diseases account for approximately one-half of all deaths in tropical countries. In industrialized nations, despite the progress made in the understanding of microbiology and their control, incidents of epidemics due to drug resistant microorganisms and the emergence of hitherto unknown disease-causing microbes, pose enormous public health concerns. Historically, plants have provided a good source of antiinfective agents; emetine, quinine, and berberine remain highly effective instruments in the fight against microbial infections. Phytomedicines derived from plants have shown great promise in the treatment of intractable infectious diseases including opportunistic AIDS infections. Plants containing protoberberines and related alkaloids, picralima-type indole alkaloids and garcinia biflavonones used in traditional African system of medicine, have been found to be active against a wide variety of micro-organisms. The profile of known drugs like Hydrastis canadensis (goldenseal), Garcinia kola (bitter kola), Polygonum sp., Aframomum melegueta (grains of paradise) will be used to illustrate the enormous potential of antiinfective agents from higher plants. Newer drugs such as Xylopia aethiopica, Araliopsis tabouensis, Cryptolepis sanguinolenta, Chasmanthera dependens and Nauclea species will be reviewed.
INFECTIOUS DISEASE
World wide, infectious disease is the number one cause of death accounting for approximately one-half of all deaths in tropical countries. Perhaps it is not surprising to see these statistics in developing nations, but what may be remarkable is that infectious disease mortality rates are actually increasing in developed countries, such as the United States. Death from infectious disease, ranked 5th in 1981, has become the 3rd leading cause of death in 1992, an increase of 58% (Pinner et al. 1996). It is estimated that infectious disease is the underlying cause of death in 8% of the deaths occurring in the US (Pinner et al. 1996). This is alarming given that it was once believed that we would eliminate infectious disease by the end of the millennium
. The increases are attributed to increases in respiratory tract infections and HIV/AIDS. Other contributing factors are an increase in antibiotic resistance in nosicomial and community acquired infections. Furthermore, the most dramatic increases are occurring in the 25-44 year old age group (Pinner et al. 1996).
These negative health trends call for a renewed interest in infectious disease in the medical and public health communities and renewed strategies on treatment and prevention. Proposed solutions are outlined by the CDC as a multi-pronged approach that includes: prevention, (such as vaccination); improved monitoring; and the development of new treatments. It is this last solution that would encompass the development of new antimicrobials (Fauci 1998).
Historic Use of Plants as Antimicrobials
Historically, plants have provided a source of inspiration for novel drug compounds, as plant derived medicines have made large contributions to human health and well-being. Their role is two fold in the development of new drugs: (1) they may become the base for the development of a medicine, a natural blueprint for the development of new drugs, or; (2) a phytomedicine to be used for the treatment of disease. There are numerous illustrations of plant derived drugs. Some selected examples, including those classified as antiinfective, are presented below.
The isoquinoline alkaloid emetine obtained from the underground part of Cephaelis ipecacuanha, and related species, has been used for many years as and amoebicidal drug as well as for the treatment of abscesses due to the spread of Escherichia histolytica infections. Another important drug of plant origin with a long history of use, is quinine. This alkaloid occurs naturally in the bark of Cinchona tree. Apart from its continued usefulness in the treatment of malaria, it can be also used to relieve nocturnal leg cramps. Currently, the widely prescribed drugs are analogs of quinine such as chloroquine. Some strains of malarial parasites have become resistant to the quinines, therefore antimalarial drugs with novel mode of action are required.
Similarly, higher plants have made important contributions in the areas beyond antiinfectives, such as cancer therapies. Early examples include the antileukaemic alkaloids, vinblatine and vincristine, which were both obtained from the Madagascan periwinkle (Catharanthus roseus syn. Vinca roseus) (Nelson 1982). Other cancer therapeutic agents include taxol, homoharringtonine and several derivatives of camptothein. For example, a well-known benzylisoquinoline alkaliod, papaverine, has been shown to have a potent inhibitory effect on the replication of several viruses including cytomegalovirus, measles and HIV (Turano et al. 1989). Most recently, three new atropisomeric naphthylisoquinoline alkaloid dimers, michellamines A, B, and C were isolated from a newly described species tropical liana Ancistrocladus korupensis from the rainforest of Cameroon. The three compounds showed potential anti-HIV with michellamine B being the most potent and abundant member of the series. These compounds were capable of complete inhibition of the cytopathic effects of HIV-1 and HIV-2 on human lymphoblastoid target cell in vitro (Boyd et al. 1994).
The Development of Phytomedicines and the Ethnomedicinal Approach