Resume of current research in medicinal plants in Botswana

J. BACON

Chemistry Department
University of Botswana
P/Bag 0022 Gaborone, Botswana

ABSTRACT

The potential for the economic development of medicinal plants use in Botswana has been shown to be very great. Experience gained during the last decade shows the necessity for proper management of resources, and a coherent unified strategy for research to reduce the possibility of exploitation of resources by external concerns. The grapple plant, Harpogophytum procumbens, serves as an excellent example of economic exploitation which has necessitated nationwide cooperation of research and government bodies. Following the lessons learned from the grapple plant, traditional remedies are now being closely examined with a more unified approach. Initially, only medicinal plants that have an immediate economic potential are being studied.

Introduction

In common with all African countries, Botswana has a strong tradition in the use of herbal remedies. As is frequently the case, it is difficult to separate traditional religion from therapeutic properties of administered medicines. The value of any drug is greatly enhanced by the power of suggestion, with the conclusion that any innocuous substance administered under the right conditions of suggestion and belief, can have dramatic healing effects. Belief in the power of a drug is not however, limited to traditional medicine. Clinical trials using placebos will always result in a percentage of cases responding to the "drug". For this reason, it is extremely difficult to study possible medicinal properties of plant species and correlate findings with traditional uses. This is clearly exemplified by the "grapple plant" (Harpogophytum procumbens), which, in recent years, has become Botswana's pre-eminent medicinal plant, known in Europe and the USA as "Devils Claw".

In this paper, the author describes the status of the art with respect to the exploitation of the grapple plant and the herbal tea plant (lippia) in Botswana, for medicinal applications.

The grapple plant

The grapple plant grows only under the semi-arid conditions, and is indigenous in the Kalahari desert and parts of Namibia and Angola. It is a typical desert plant in that it shows adaptation to restricted and sporadic rainfall. Much of the plant mass lies below ground level in the form of a parent tuber, storage tubers and roots. The leaf system is highly susceptible to available water, and in times of drought (which is frequent in the Kalahari) may be inconspicuous, making the plant very difficult to identify or collect. The fruiting body has an endocarp which resembles a grappling hook, from which the plant takes its common name. The storage tubers of the grapple plant have been known in Botswana traditional medicine for generations. However, in Namibia, the plant has almost become extinct, due to systematic destruction by the Namibian farmers. The fruiting body can inflict serious damage to animals, and farmers in Namibia regarded it a menace. Its survival in Botswana is probably explained by its use in traditional medicine, and hence its destruction a taboo.

Studies conducted in 1986 by Kgathi, confirm that the grapple was used in small amounts in traditional medicine. Producers of grapple for the European trade, confirmed that it could be used for stomach disorders in man and to heal wounds in animals. However, according to Taylor (1982), clinical trials in Germany indicated that 60% of arthritis cases can be healed by an extract of the grapple storage tubers, with no observable side effects, apart from the purgative effect. It therefore seems apparent, that traditional medicine has utilized the grapple for its purgative effect rather than for its proven anti-arthritic properties. One reason for this may be that the purgative effect is almost spontaneous, whereas the anti-arthritic properties are discerned over a much longer period of time. If this is indeed the case, then the converse must also be true, i.e., detrimental effects of medicinal plants may not be immediately obvious, such that physiological damage may occur days, weeks, or months after receiving treatment. Western medicine has of course learnt this the hard way as in the case of the drug "Thalidomide".

Although the exact mechanism of the therapeutic action of grapple on arthritic cases is not known, the active components of the storage tubers were identified as far back as 1962, by Lux and Tinmann, who identified iridoid glucosides. Bendul et al., (1979) modified the structure to produce an improved form, procumbide. In 1981, Vanhelen et al., proposed a mechanism for the anti-arthritic properties in which they suggested a conversion from harpogoside to harpagogenine. Research is still continuing in Germany as to the exact mechanism involved with these substances.

The case history of the economical development of the grapple plant serves as an excellent example of beneficial exploitation of natural resources and also possible detrimental exploitation of human resources. During the early 1980's 15-20 tones of dried grapple storage tubers were exported yearly from Botswana to Europe, mainly by Namibian and South African traders.

Iridoid glucosides

In 1987, the National Institute of Research (NIR), concluded that in general, producers of grapple are poor people, and in the Kgalagadi district, only those who desperately needed cash were involved in grapple production, because they needed the cash to purchase their basic needs. However, the report also concluded that although the grapple was being produced as a cash crop, it appeared not to have a detrimental effect on production of subsistence crops and the farming activities. The main reason for this seems to be that harvesting of the grapple takes place during the dry season when subsistence crop production has virtually ceased. It is however, interesting to note that the report found that the majority of grapple producers were women, the socio-economic implications of which need to be examined.

In 1981/1982, the average income earned by a grapple producer in the Kgalagadi District was 97 pula. Even allowing for inflation, this sum is small, but the report concluded that it was significant, particularly if it was used for purchasing such basic needs as food and health care.

The economics involved in the grapple trade, are, at best bewildering, and show the need for legislation. It has been calculated (Kgathi, 1987) that one harvester can collect kilogramme of dry grapple in 6.5 hours for which he receives 2 pula, which, although very small, is comparable with the rate for farm workers. It is nevertheless below the minimum wage for manual workers. Both collectors and traders in grapple require permits, and to ensure sustained yields, a quota system is in operation. In order to sell the grapple to foreign traders, the local traders must have an export permit. On the export permit, the amount and value of the grapple is recorded. However, serious discrepancies between the amount bought from producers and the amount exported have occurred in recent years.

The 1987 NIR report notes that although the export prices are recorded in the export permit, they do not make sense, since they are almost equivalent to the prices at which the trader buys from the producers. The report concluded that the correct prices are not actually declared. According to Taylor (1982), a South African company was prepared to pay 4.50 pula per kg for dried grapple storage tubers. Allowing for inflation, this price can now be expected to be much higher.

In 1982 grapple tablets were on sale in U.S.A. and South Africa, at an average price of 5.60 pula per kg (Taylor, 1982). In 1987 grapple tablets manufactured in Europe were on sale, in Botswana, at 148.25 pula per kg. (Kgathi, 1987). In February 1990, the price is 213.25 pula per kg. There is no evidence to suggest that other ingredients are added to the tablets, suggesting that the dried tubers are simply sterilized and compressed into tablet form. Kgathi (1987) concludes that the difference between trader prices and producer prices is just too wide, even if one allows for transport costs. The report recommends that the government should look into this matter and work out possibilities for increasing the producer prices of grapple. It is also apparent that strategies should be developed to lessen the difference between the trader prices and the tablet manufacturers prices.

In 1989, a non-profit making organization for rural development (Thusano Lefatsheng) approached the Ministry of Agriculture for funds to develop marketing and sustained production of grapple in Botswana. Thusano is a commercial concern, involved in the development of Botswana's natural products. Profits from the company are ploughed back into rural development. Research within Thusano liaises closely with many institutions, including NIR/Agricultural Research Institutions and the University of Botswana, Chemistry Department. Thusano's involvement with the grapple plant has so far been restricted to research on sustained yields and some sale of the product to European markets.

Following discussions with representatives from the Ministry of Agriculture, an advisory committee has been set up by the Ministry, with representatives from various institutions involved in natural product research, parastatals and Ministry of finance. In principle, it has been concluded that the research operations of the various institutions should be coordinated by Thusano, with financial support from the government for the development of veld products.

The immediate aim of Thusano is to start the manufacture of grapple tablets for export. If this can be achieved, Thusano will be able to pay the producers competitive prices for their labour and profits can be re-invested into rural development projects. The primary aim is to remove the control of the marketing of grapple from individuals who do not re-invest in rural development.

The formation of the advisory committee for the development of natural products in Botswana is certainly a step in the right direction. If environmental/economical chemical/agricultural research bodies can coordinate their activities, then repetitions of the abuse of the grapple plant can be avoided. There is no doubt that a coherent research programme coordinated by Thusano will undoubtedly serve rural development far better than ad hoc research in the Chemistry Department of the University of Botswana. Thusano currently has a number of projects under development, and the Chemistry Department of the University of Botswana is actively engaged in research of some of these products.

Lipia javanica

A herbal tea, marketed by Thusano is made from the dried leaves of Lippia javanica. The taste is variously described as that of 'mint' or 'vanilla'. In traditional medicine, the plant has a variety of recorded uses throughout the Southern Africa area. The reported uses of Lippia javanica according to Watt et.al. (1962), are as follows:

Xhosa: infusion of leaf and stem for coughs/colds and bronchial infections: disinfecting anthrax infected meal

Kwema: cough/cold remedy

Tswana: cough/cold remedy

Zulu: "gangergous rectis" measles, urticaria and rashes.

Zimbabwe: blackwater fever, malaria, dysentery.

Masai: red ointment for body decoration.

Lobedu: colds/nasal haemorrhage.

Shangana: cough remedy

Swati: influenza/colds

Nunguoi Bushmen: Malaria

Tswana: Insect repellent/insecticide

Early research concluded that flowering tops from Tanzania contained 0.4% of an oil rich in ocimene. The leaves contain an oil that yields 65 - 70% of a liquid of molecular formula C₁₀H₁₆O, which has an odour of lemons.

Research within the Department of Chemistry, University of Botswana, in conjunction with the Analytical Chemistry Laboratory of Utrecht University in The Netherlands, has shown that the essential oil yields a liquid of formula C₁₀H₁₆O. However, detailed analysis using various separation techniques and hyphenated techniques such as C₁₀H₁₆O and GC-F.T. etc., show the presence of three compounds of formula C₁₀H₁₆O.

The major component is 3,7-dimethyl-1,3-octadien-5-one, which is a monoterpene with two geometrical isomers as shown:

Figure

These compounds have previously been identified in Tagetes species, specifically, in Tagetes minuta, from which they take their trivial name Tagetones. The antimicrobial action is being studied by Hethely.

The other compound is also a highly unsaturated ketone with a proposed structure as shown below:

Figure

The decongestant effect of ketonic terpenes is well known (c.f. menthone, etc.) and so it is not surprising that these compounds have a calming effect on respiratory conditions. Similarly, the insect repellant properties of cyclic and acyclic monoterpenes has recently been reported (Wang et al 1985). The anti-microbial properties, however, are rather more difficult to explain on the basis of ketonic structures. However, tagetone exists in equilibrium with the enolic form. This can easily be shown by the temperature dependence of the infrared spectrum. At high temperatures, the carbonyl stretching vibration disappears and a hydroxyl stretching absorption appears instead.

Figure

The formation of an enol may explain the anti-microbial properties since enols are known to show disinfectant properties.

When heated, the above compounds readily polymerize by opening of the double bonds. However, it is suspected that in the case of cis-tagetone, the molecule may also aromatize. This reaction is also possible in the presence of ultra violet light.

The product, thymol, is of course a well known natural product (Thyme oil) and its phenolic nature gives it disinfecting properties.

Figure

The potential use of this plant is very promising. However, we feel sure that much of the chemical analysis may be a replication of work that has already been done and unpublished and/or is under investigation in other regional laboratories since there is insufficient liaison between the various groups undertaking research in the field of medicinal plants. Effective research to aid development can only be achieved by a coordinated approach, both nationally and internationally. For this reason, current research into medicinal plants is being restricted to plants which have an 'immediate' commercial potential.

Acknowledgements

I am indebted to the fullest cooperation of the following,: Dr. T. Tietema, National Institute of Research, Gaborone; F. Taylor, Veld Products, Gaborone; Thusano Lefatsheng, Gaborone; Prof. J. H. van der Maas, University of Utrecht, The Netherlands and Phillips Laboratories, The Netherlands.

Reference

Kgathi, D.L. (1987). NIR Research notes (24), University of Botswana.

Hwang, Y., Wu, K., Kumamoto, J., Axelroad, H. and Mulla, M.S. (1985). J. Chem. Ecol., 11, 1297-130.

Taylor, F.W. (1982). The Resource and its Commercial Utilization of Veldproducts, Plan No. T.B. 7/14/80-8, Ministry of Commerce and Industry Government Printer, Gaborone.

Watt, J.M. and Breyer-Brandwisk, M.G. (1962). The Medicinal and Poisonous Plants of Southern and Eastern Africa. 2nd Edn., Livingstone.