Ethnobotany

Shortly before the start of the 20th century (1896), the American botanist William Harshberger coined the term ‘ethnobotany’ – the study of plant use by humans.

It is usual for ethnobotanists to live with indigenous people, to share the everyday life of their community and, of course, to respect the underlying cultures. Ethnobotanists have a responsibility both to the scientific community and to the indigenous cultures. According to the above definition, ethnobotany focuses not only on medicinal plants, but also on other natural products derived from nature, such as:

This broad definition is still used today, but modern ethnobotanists face a multitude of other tasks and challenges (see below). Medicinal plants have always been one of the main research interests of ethnobotany and the study of these resources has also made significant contributions to the theoretical development of the field (Berlin 1992); however, the more anthropologically oriented fields of research are beyond the scope of this introductory chapter.

Ethnopharmacology

Ethnopharmacology as a specifically designated field of research has had a relatively short history. The term was first used in 1967 in the title of a book on hallucinogens (see Efron et al 1970). The field is nowadays much more broadly defined.

This definition draws attention to the bioscientific study of indigenous drugs but does not explicitly address the issue of searching for new drugs. Medicinal plants are an important element of indigenous medical systems in many parts of the world, and these resources are usually regarded as part of the traditional knowledge of a culture. Europe has for many years profited from the exchange of ideas with other continents, and many of the natural products and phytomedicines used today are derived from plants used in indigenous cultures. Examples of 18th century explorers who described indigenous plant use in detail are Richard Spruce (British), Hipolito Ruiz (Spanish) and Alexander von Humboldt (German), who co-discovered curare.

Ethnopharmacology and the convention on biological diversity (convention of RIO)

None of the studies discussed so far took the benefits for the providers (the states and their people) into account. This has changed in recent years. Ethnopharmacological and related research using the biological resources of a country are today based on agreements and permits, which in turn are based on international and bilateral treaties. The most important of these is the Convention of Rio or the Convention on Biological Diversity (see http://www.biodiv.org/chm/conv.htm), which looks in particular at the rights and responsibilities associated with biodiversity on an international level:

The basic principles of access are regulated in article 5:

The rights of indigenous peoples and other keepers of local knowledge are addressed in article 8j:

This and subsequent treaties significantly changed the basic conditions for ethnopharmacological research. Countries that provide the resources for natural product research and drug development now have well-defined rights. This specifically includes the sharing of any benefits that may accrue from the collaboration. Access to resources is addressed in article 15, which is crucial for an understanding of this and any other activity which may yield economically important products:

In the case of ethnopharmacological research, the needs and interests of the collaborating community become an essential part of the research, and in fact there is an inextricable link between cultural and biological diversity. This principle was first formulated at the 1st International Congress on Ethnobiology held in Belem (Brazil) in 1988. No generally agreed upon standards have so far been accepted, but the importance of obtaining the ‘prior informed consent’ of the informants has been stressed by numerous authors (e.g. Posey 2002).

Bioprospecting and ethnopharmacology

Studies dealing with medicinal and other useful plants and their bioactive compounds have used many concepts and methodologies. These are interdisciplinary or multidisciplinary studies, combining such diverse fields as anthropology, pharmacology, pharmacognosy or pharmaceutical biology, natural product chemistry, toxicology, clinical research, plant physiology and others. In order to analyse their strengths and weaknesses, and especially the outcomes of research, two different but closely related approaches can be distinguished: bioprospecting and ethnopharmacology (see Table 5.2).

Table 5.2 Ethnopharmacology and bioprospecting compared

Bioprospecting focuses on the development of new drugs for the huge markets of the northern hemisphere. Potentially highly profitable pharmaceutical products are developed, based on the biological and chemical diversity of the various ecosystems of the earth; this requires an enormous financial input. The research starts with the collection of biogenic samples (plants, fungi, other micro-organisms and animals), progresses through analysis of the chemical, biological and pharmacological activities to the development of drug templates or new drugs. A key process in this search is high-throughput screening systems such as those that have been established by major international pharmaceutical companies. Huge libraries of compounds (and sometimes extracts) are screened for biological activity against specific targets. Active natural products are only one of the many sources of material for these batteries of tests but serve as a starting point for drug development. Currently, some companies envision screening 500,000 samples a week against a single target; thus it becomes essential to have an enormous number of chemically diverse samples available.

The other approach may best be termed ethnopharmacological. Ethnobotanical studies generally result in the documentation of a rather limited set of well-documented useful plants, mostly medicinal, but also those known to be toxic or used in nutrition. In ethnopharmacology, an important goal is the development of improved preparations for use by local people. Thus it is essential to obtain information on the bioactive compounds from these plants, their relative contribution to the effects of the extract (including, for example, synergistic or antagonistic effects), the toxicological profile of the extract and its constituents. By restricting ethnopharmacology to the bioscientific study of indigenous uses, attention is drawn to the need for improving indigenous phytomedical systems, especially in developing countries. This requires research strategies for studying indigenous medicinal plants and their uses.

The importance of conserving such nature-derived products in the health care of the original keepers of such knowledge must be the main goal of truly interdisciplinary research. Ethnopharmacology may contribute to the development of new pharmaceutical products for the markets of the northern hemisphere, but this is only one of several targets. Truly multidisciplinary research on medicinal plants requires the inclusion of other methodologies from such fields as medical or pharmaceutical anthropology or sociology. Not only do we need a detailed understanding, incorporating social scientific and bioscientific methods, but we also need to support all means available of making better use of these products. It has been pointed out that the two approaches – ethnopharmacology and biodiversity prospecting – are not mutually exclusive and the two concepts as they are outlined here are rarely realized in such extreme forms. Instead, any discussion should specifically draw attention to particular strengths and roles of both approaches. In bioprospecting programmes, which are directed specifically towards infectious diseases, the use of ‘ethnobotanical’ information is very useful and promising (Lewis 2000). However, this is not necessarily the case in cancer chemotherapy, for example, where highly toxic plants are not used in traditional medicine because the dose cannot be controlled sufficiently well to ensure safety.

Examples of modern ethnopharmacological studies

A project focusing on the bioscientific study of indigenous uses of Hyptis verticillata (Lamiaceae) is a good example. This plant is prepared in different ways by the Lowland Mixe people of Oaxaca, Mexico, depending on the disease to be treated. For skin infections and inflammation, the plant is ground up with a little alcohol or the mashed leaves are applied directly to the affected part. However, for gastrointestinal problems, a tea is prepared using ‘a handful’ of fresh leaves (Heinrich 2001).

Phytochemical investigation using an inflammatory model as well as antibacterial activity led to the isolation of several lignans, rosmarinic acid and sideritoflavone (see Fig. 5.2). These compounds help to explain the rationale behind the indigenous uses. The lignans are known to have strong antibacterial activity, which was also corroborated in these studies, and both rosmarinic acid and sideritoflavone were shown to be active in anti-inflammatory models.

Fig. 5.1

Fig. 5.2

It was also possible to show that the lignans are only extracted to a very limited degree if the plant material is prepared as a tea, whereas relatively large amounts are extracted in a process mimicking the indigenous extraction with ‘aguardiente’ (40–70% ethanol). The more toxic lignans are thus present in much smaller quantities in the tea, reducing the health risk of this preparation.

The second example is drawn from ethnobotanical fieldwork in Eastern Guatemala with a Mayan-speaking people, the Chorti. The Chorti use the fruit of Ocimum micranthum Willd. (Lamiaceae) in the treatment of infectious and inflammatory eye diseases (Kufer et al, unpublished). The fruits are approximately 1 mm in diameter and hard, and several of these are applied directly into the eye. At first glance this seems an unlikely remedy for eye problems, but the rationale behind it becomes evident when considering the morphological and chemical make-up. The fruits are covered with a mucilaginous layer containing complex polysaccharides which form a soft layer around the fruit if it is put into water (Heinrich 1992). This layer may well have a cleansing effect, and polysaccharides are known to be useful in the treatment of inflammatory conditions and bacterial or viral infections. Although there are no pharmacological data from experimental studies available to corroborate this use, information on the histochemical structure of the fruit makes it likely that the treatment has some scientific basis.

The above two examples demonstrate the relevance of ethnopharmacology in relation to the scientific study of indigenous medical products. However, ethnopharmacology, as the science bridging the gap between natural sciences and anthropology, should also look at symbolic and cognitive aspects. People may select plants because of their specific pharmacological properties, but also because of the symbolic power they may believe is in a plant. Understanding these aspects requires cognitive and symbolic analysis of field data. Another example from field studies with the Mixe in Mexico can be used. At the end of a course of medical treatment, the patient is sometimes given a petal of Argemone mexicana L. (known to the Mixe as San Pedro Agats, Papaveraceae). This plant is known to contain a large number of biologically active alkaloids, including protopine. However, the yellow petals are presumably used, not because they exert a pharmacological effect (at this dose) but because they symbolize the bread of the Last Supper according to Christian mythology. Thus they are a powerful symbol for the end of the healing process (for other examples of symbolic and empirical forms of plant use see Heinrich 2010).

The role of ethnopharmacology can be extended beyond that defined previously. It looks not only at empirical aspects of indigenous and popular plant use, but also at the cognitive foundations of this use. Only if these issues are to be included will it truly be a interdisciplinary field of research (Bruhn & Holmstedt 1981:406). The key tasks of pharmaceutical researchers in this interdisciplinary process will be to:

This will result in a truly ethnopharmaceutical approach to medicinal plants which encompasses all subdisciplines of pharmacy and medicine. The value of integrating ethnobotanical with phytochemical and pharmacological studies has been clearly demonstrated. While, for example, the likelihood of developing new therapeutic agents for use in biomedicine is relatively low (although it is certainly much higher than with many other approaches), such studies confirm the therapeutic value and contribute to our general scientific knowledge about medicinal plants (Heinrich 2010).

Some plants have many side effects or are highly toxic. In an example from the Highlands of Mexico, Bah et al (1994) showed that a species popularly used there contains hepatotoxic pyrrolizidine alkaloids, which pose potential health risks. Although this information is available to the scientific community, the general public may not be aware of these risks. Such data must be summarized appropriately and made available to local people in regions where the plants are used. It is now essential to develop partnerships with institutions capable of translating these findings into an effective strategy.

Conclusion

The examples given in this chapter are intended to show the breadth of the contribution of ethnobotany and ethnopharmacology, from the study of indigenous, orally transmitted medical systems to drug development, and to illustrate that the pharmaceutical sciences may profit in many ways by including such approaches. It is also important to further consolidate local knowledge. Ethnopharmacology in this context will provide patients with access to some evidence-based forms of their own ‘traditional’ medicine, in developing countries in Africa, South and Central America, Asia and South-East Asia.