Seaweeds in medicine and pharmacy: A global perspective

KETO E. MSHIGENI

Department of Botany
University of Dar es Salaam
P.O. Box 35091
Dar es Salaam, Tanzania.

ABSTRACT

The term seaweed carries the connotation that the plants under discussion are useless and worthless. In this paper the author reviews the state of the art with respect to the utilisation of seaplants in various parts of the world, and shows that there are more uses of the plants most people realise. Indeed, he concludes that the term seaweed is inappropriate for the marine plants in question. He gives an outline of the utilisation of seaweeds in medicine, in pharmacy, and in various other applications, on a worldwide basis. He advocates that in Africa, seaweeds are a grossly under-exploited resource, and calls for scientists in the region, and in the Third World countries in general, to pursue a regional collaborative approach in the development of the seaweed resources. Finally, he appeals to donor agencies for financial assistance towards the realisation of goals pertaining to the development of the unique marine plant resources.

Introduction

Let me begin my presentation by taking your minds back to the beginning of things; and allow me to start with a quotation from the First Book of Moses in the Bible:

...And God - id, "Let the waters under the heavens be gathered together into one place and let the dry land appear". And it was so. God called the dry land Earth, and the waters that were gathered together, He called Seas. And God saw that it was good" (Genesis 1:9-10, Revised Standard Version).

Allow me to quote further from the same author, in order to drive home the subject of my presentation

...And-God said, "Let the waters bring forth swarms of living creatures...' So God created the great sea monsters, and every living creature that moves... And God saw that it was good. And God blessed them saying, 'Be fruitful and multiply, and fill the waters in the seas...' (Genesis 1:20- 22).

And the seaplants multiplied. In the region of the Atlantic Ocean known as the Sargasso Sea the floating community of Sargassum alone has been estimated to be 5 to 10 million tonnes, fresh weight (Chapman and Chapman, 1980).

The plants that will constitute the subject of this presentation, the seaweeds fall within the framework of the great sea monsters referred to in the book of Genesis. Some may actually attain a height of 30 to 40 metres. This exceeds the height of most of the tall trees found on land. The plants in the sea fall under two broad ecological divisions. The first embraces the tiny microscopic algae, the phytoplankton, which grow in a freely floating condition within the seawater mass. The second division comprises the macroscopic algae which, typically, grow attached to the seabed and other solid objects in the ocean. The latter are referred to as benthic algae. Seaweeds fall within the domain of the benthic algae.

Because we are, essentially, terrestrial mammals, and since many of us were born and raised in far inland localities, we never come to a full understanding of the usefulness and economic potential of the marine plants that are embraced under the term seaweed. The situation is aggravated by the fact that the term "weed", as stated above, carries the connotation of useless and worthless plants. But actually, the marine plants in question have innumerable uses to mankind.

Many seaweeds are edible. When used as food they not only supply the body with a wide range of vitamins and essential mineral elements (including iodine), but some are also rich in protein and digestible carbohydrates (Chapman and Chapman, 1980). The protein content of the blue-green alga Spirulina platensis is, for example, up to 60 -70% protein, on a dry weight basis. This is the highest protein level reported for any plant species (Leonard and Compere, 1967).

The use of seaweeds as food for man goes far back into antiquity. In a book published in China by Sze Teu about 600 B.C., it is stated that some seaweeds are a delicacy, fit for the most honourable guest, even for the King himself (Johnston, 1966). The most widespread uses of seaweeds for food are found among the inhabitants of Japan, Korea, China, Indonesia and Hawaii. The most commonly eaten marine plants arc species of Porphyra, Laminaria, Monostroma, and Undaria. Currently these arc produced largely through farming, and the annual crop production is incredibly high. For Laminaria, the 1983 production figure for China alone was 1.4 million tones, wet weight (or 230,000 tones dry). For Porphyra, the 1981 production figure in Japan alone was 340,000 tones, wet weight (Tseng and Fei, 1987). These seaweeds now constitute a multi- million dollar industry.

The potential utilisation of seaweeds for food in Africa, Latin America and India is an issue which certainly deserves greater attention than has hitherto been the case. Indeed, it is remarkable how singularly little attention has been paid to the algae as food by the inhabitants of these regions.

Many seaweeds could also be developed for use as livestock feed supplements. This is by virtue of their rich content of vitamins and inorganic mineral nutrients, including many trace metals. Some seaweeds are also rich in protein. Indeed, the production of livestock meal supplements from seaweeds constitutes a well developed industry in Western Europe, and especially in Norway and Scotland. Over 20,000 tonnes of the seaweed Ascophyllum nodosum are produced as livestock feed supplements in Norway alone per annum (Jensen, 1978; Chapman and Chapman, 1980).

Considering that many countries in Africa support large population of cattle, goats, sheep, camels, and poultry, and considering the well-documented advantages of using seaweeds as livestock feed supplements (Levring et al., 1969; Chapman and Chapman, 1980), one can see the need for us to pay increasingly greater attention to our seaweed heritage. Seaweeds could also be used as an agricultural fertilizer. When used as manure, they supply the crop plants not only with a wide variety of inorganic mineral nutrients (including the essential trace metals), but also with valuable organic substances which serve as crop pesticides (Fenical, 1983), or as growth hormones (Augier, 1977; Mooney and Van Staden, 1984). Additionally, many seaweeds contain colloidal substances in their cell walls, which could help to bind the soil particles together, improving the crumb-like structure of the soil, and facilitating aeration (Chapman and Chapman, 1980). The use of seaweeds as manure actually goes back to the days of the ancient Chinese, the Vikings, and the Greeks. In France, it is documented that as long ago as 1681, a royal decree was issued, regulating the conditions under which seaweeds could be collected from the shore for application as manure (Aitken and Senn, 1965).

In the more recent times, seaweeds have been developed for the production of liquid agricultural fertilizers, which can be concentrated, and thus be transported more easily for application in the more inland regions. The liquid fertilisers can also be applied foliarly by spraying, with the use of air crafts, etc.

The liquid seaweed fertilizers are marketed under various commercial names, such as Maxicrop, Alginure, etc. (Chapman and Chapman, 1980; Abets and Young, 1983). It is now well documented that plants which are sprayed with the liquid seaweed extracts, not only produce significantly higher crop yields, but are also rendered free of attack by most of the common crop pests. They also become more drought resistant. The use of seaweed for the production of liquid fertilisers is thus now very popular, and is a multi- million dollar industry. Again, the use of seaweed as manure is something which Africa has, on the whole, neglected and to which we must now draw greater attention (Mshigeni, 1983).

Have I drifted away from the theme of the conference too far, and for too long? Yea, but with a purpose. If by using seaweed as food man gets adequate levels of protein, this means that we have freed him from kwashiorkor. If by eating seaweed man gets the essential vitamins, this means that we have freed him from beriberi, scurvy or other hypovitaminoses. If by eating seaweed man gets adequate levels of iodine, this means that we have freed him from goitre. Actually, in localities where seaweeds are regularly eaten as food, goitre is completely unknown. All this could be labelled preventive medicine. But even in curative medicine, there is a big hope in seaweeds.

The fact that there is such a wide range of medicinal products from the vascular plants on land, that two-thirds of our planet is covered with seawater, and that the ocean waters support a wider variety of plant, types than what we are used to seeing on land, one would expect many of the plants in the sea to possess chemical substances which could be used in curative medicine. This is, indeed, the case, as will now be elaborated.

Direct uses of seaweed as medicine

A survey of the literature indicates that the earliest records on the direct utilisation of seaweeds as medicine go back to the days of Emperor Shen Nung who, in 2700 B.C., documented medicinal uses of seaweeds in a Chinese herbal (Moi, 1987). The Chinese Materia Medica, published in the 8th Century A.D., (Chapman and Chapman, 1980), also lists many algae used in medicine (e.g., in the treatment of goitre, for wound-healing and for reducing hypertension, etc.).

In Mediterranean Europe, the Greek physician, Stephanopoli, discovered in 1775 that the red seaweed Alsidium helminthochorton, found on the rocky shores of Corsica, was an efficient vermifuge (Chapman and Chapman, 1960). The Hawaiians have also, from days immemorial, used the seaweed Hypnea nidifica for curing stomach ailments (Reed, 1906). In Indonesia, Hypnea musciformis was also used as a vermifuge from the very ancient times (Zaneveld, 1959).

In New Zealand, the Maori people traditionally harvested the seaweed Durvillea for use as medicine for the treatment of scabies, and also as a vermifuge (Schwimmer and Schwimmer, 1955). In Tonga, the inland pregnant women traditionally used to go to reside on the coast, in order to gather some particular seaweeds, which were believed to be beneficial to them in their pregnancy conditions (Lucas, 1936).

In latin America, South American Indians, from the ancient times, used to collect Sargassum bacciferum for use as a cure for goitre and kidney disorders (Schwimmer and Schwimmer, 1955). In many of the Caribbean Islands, and especially in Cuba, S. vulgare was also widely used as a vermifuge (Chapman and Chapman, 1980).

More recent studies by various scientists in different parts of the world, have revealed that there are more species of seaweeds which are used in traditional medicine than is generally conceived. In the Philippines, Ulva pertusa is used for wound healing. Other Philippine seaweeds used as medicine include Gracilaria lichenoides and Ulva lactuca (Nuqui, 1987). In Malaysia, Acetabularia major is commonly used for the treatment of gall stones, and Chondria armata is used as a vermifuge (Moi, 1987). In China and Hong Kong, species of Sargassum are commonly used for the cure of goitre, coughs, fever, and various tumours; Digenia simplex is used as a vermifuge; Lithothamnium pacificum is used as an expectorant, as a cough remedy, for reducing fever, and for the inhibition of tumours; and Caloglossa leprieuri is used as an antiheminthic agent (Tseng, 1983, Win Shin-Sun, 1987).

In the Mediterranean, in Western Europe, and in North America, Hypnea musciformis is used as a vermifuge; Palmaria palmata is also used as a vermifuge; Dictyopteris polypodioides is used for the cure of lung diseases; and Laminaria digitata was, in 1682, introduced by Dr. C.F. Sloan, for use as a cervical dilator, to facilitate baby delivery (Chapman and Chapman, 1980; Hale and Pion, 1972).

Other documented medicinal uses of seaweeds include their utilisation as an aphrodisiac (e.g., Porphyra sp. in the Philippines, under the name "gamet"); as a cure for menstrual troubles (e.g., Laminaria japonica in China) and also as a cure for syphilis, (e.g. Laminaria saccharina in China (Chapman and Chapman, 1980; Nuqui, 1987).

Curative medicinal substances in seaweeds

For many traditional practices, modern scientific and technological advances have, post facto, revealed that the ancients were, in fact, right. Most of the seaweeds (e.g., Sargassum spp.) which were traditionally used as a cure for goitre, have now been found to contain appreciable high levels of iodine, the curative substance (Chapman and Chapman, 1980). Digenia simplex, which was traditionally used as an anthelminthic agent, has been shown to contain kainic acid and allokainic acid (Levring et al., 1969). For Chondria armata, also used as a vermifuge, the curative substance has been found to be domoic acid. To-day one can buy medicinal drugs manufactured from fronds of Digenia, marketed under the trade name helminal, or digesan, for use against Ascaris lumbricoides.

Recently there has been a rapidly growing awareness on the need for research to be undertaken on the uses of seaweeds for modern medicine. Many species of marine algae have now been screened, and also tested against the common disease-causing bacteria, fungi and protozoans. In these studies the test organisms included gram-positive bacteria such as Staphylococcus aureus and S. pneumoniae, gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosae and fungi such as Trichophyton mentagrophytes, and the yeast Candida albicans, as well as the protozoan, Trichomonas foetus.

These studies have revealed that many species of seaweeds are biologically active against many of the common disease pathogens. Amongst the Green Algae (or the Chlorophyta), the biologically active members include species of the genera Codium, Halimeda, Ulva, Cladophoropsis Caulerpa and Enteromorpha. Amongst the Phaeophyta (Brown Algae) the taxa with antimicrobial activity include species of Dictyopteris, Zonaria, Ecklonia, Durvillea, Dictyota, Sargassum and Turbinaria. Amongst the Rhodophyta (Red algae) microbial activity has been detected amongst the species of Chondria, Digenia, Laurencia, Caloglossa, Grateloupia, Hypnea and Murayella (Chapman and Chapman, 1980; Tseng, 1983; Baker, 1987; Sivapalan, 1987).

Many scholars are now going beyond the screening stage. They are actively involved in extracting and characterising the active substances responsible for suppressing the growth of, or totally destroying the disease-causing bacteria, fungi or the protozoans referred above. Members of this audience who wish to go deeper into this issue, are referred to the excellent works of (Fenical, 1980, 1983; Fenical and McConnell, 1983; Glombitza, 1977, 1979; Glombitza et al., 1982).

According to Fenical (1983), many seaweeds show the presence of a wide range of biologically active compounds, which are often quite unrelated to those of their terrestrial counterparts. Many blue-green algae, indeed, contain substances which show potent anti-leukemic activity. Extracts from Lyngbya majuscula have recently given rise to a novel powerful antibiotic, malyngolide (Fenical, 1983).

In their recent studies on species of Sargassum that were traditionally used in Chinese herbal medicine for the treatment of cancer, Yamamoto (1974), and Yamamoto et al. (1977, 1982) revealed that the extract from S. fulvellum was active against leukemia and sarcoma tumour cells implanted on mice. Extracts of S. thunbergii were also tested (Yamamoto et al., 1981). In both cases the extracts from the seaweed gave an inhibition ratio of up to 93.7%, which showed a very high promise as an anti-tumour agent. The author referred to above found the anti tumour component to be a polysaccharide, which was suggested to be either a sulphated peptidoglycuronoglycan, or a sulphated glycuronoglycan (Yamamoto et al., 1981, 1982).

Several other species of Sargassum have also been found to contain extracts which are very active against bacteria, including Staphylococcus aureus, Escherichia coli and Salmonella spp. The active anti-bacterial constituent of Sargassum kjellmanianum, has been found to be a cyclopentenone (Fenical, 1983), whose structure has been determined.

Other applications of seaweeds in medicine and pharmacy

Let us now consider the indirect uses of seaweeds in medicine and pharmacy. In addition to their vitamins, inorganic minerals, proteins, and the medicinal compounds discussed above, seaweeds also contain colloidal polysaccharides which are of great significance in industry and commerce. The best known of these is agar, a sulphated galactan which is extensively used in microbiological and public health laboratories, as a culture medium for bacteria and fungi.

The name agar is of Malaysian origin. It was the traditional name for the red seaweed Eucheuma, which the people of Malaysia harvested, dried, and boiled to produce a gel that was used for food. The significance of agar in medicine and pharmacy was not, however, realised in the western world until 1881, when Robert Koch introduced its use for the culture and isolation of pathogenic micro- organisms. Since then agar has become a necessity for every hospital and bacterial research laboratory. Agar is preferred to any other solid culture medium because it is relatively inert, and is not decomposed by most bacteria.

Today most of the agar supplies of the world are extracted from species of the red seaweeds Gracilaria, Gelidiella, Gelidium and Pterocladia, which are well represented on our African shorelines. Indeed, Madagascar exports the agarophyte, Gelidum madagascariense, to Japan.

Another colloidal polysaccharide from seaweeds, which has a wide range of applications in industry and commerce, is carrageenan. This is also a sulphated galactan, extracted from red seaweeds such as Chondrus, Gigartina, Hypnea, Sarconema, and Eucheuma Since 1950, Tanzania has been involved in the export of several species of Eucheuma to Western Europe, where they are processed for carrageenan production. There are now serious efforts in the country, aimed at augmenting the export tonnage of Eucheuma through farming. The colloid from the seaweed, like agar referred to above, readily forms gels in hot water, and is thus referred to as a hydrocolloid.

Carrageenan and agar find innumerable applications in food products, cosmetics, and pharmaceutical industries, as gelling, thickening, emulsifying and stabilising agents. Many chocolate milks and infant food preparations, many medicinal syrups, many ointments ... contain varied proportions of agar or carrageenan. For a more thorough study of these applications, the reader is referred to the excellent works of Levring et al., (1969) and Chapman and Chapman (1980).

The Brown Seaweeds produce a different kind of hydrocolloid, algin, which is a polymer of guluronic and mannuronic acids. The tropical seaweeds containing exploitable quantities of algin include species of Sargassum, Turbinaria, Hormophysa and Cystoseira. In the temperate waters, the most important sources are species of Macrocystis, Laminaria, Ecklonia and Nereocystis. Algin is also extensively used as a gelling thickening, emulsifying and stabilizing agent in many branches of modern industry. These include the textile industries, the pharmaceutical industries, the breweries, and film industries, etc. Many medicinal substances are also delivered to the patients in the form of capsules which are coated with algin. Here again, the reader is referred to the detailed account on algin in the publications by Levring et al., (1969) and Chapman and Chapman (1980). The reader will, indeed, find that medical practitioners indirectly prescribe the use of seaweed colloids more frequently than they normally imagine. Perhaps many of our dentists are also not aware of the fact that dental industries also make very extensive uses of algin, in various dental preparations. Modern physicians additionally make frequent uses of algin as an adsorbent in wound dressing; as a haemostatic in brain and thoracic surgery (Schwimmer and Schurmmer 1955) and in many other medical practices.

Conclusions and recommendations

From what, has been outlined above, it is self evident that the plants discussed in this paper are not weeds in the real sense of the word. The name seaweed is certainly a misnomer for the seaplants it represents.

In this paper the thrust of the discussions has been on the utilisation of seaweeds in medicine and pharmacy. But it has also been shown that the plants could similarly be developed for use as food, fodder, manure, and as source of industrial colloids. To a small extent, there are a few localities in Africa where seaweeds are being exploited on a commercial scale (Mshigeni, 1983; 1987). But, by and large, Africa is a terra incognita with respect to the stage of exploration and mopping of her marine plant resources.

To make any significant step forward towards the development of our seaweed resources for medicine and pharmacy, our Third World institutions of higher learning, and our research and development centres, must attract more scientists into research on the biology, biomass ecology, biochemistry and microbiology of the marine plants in question, than is the case at present. Indeed, we need to pursue a multidisciplinary approach, involving botanists, chemists, medical doctors, sociologists, etc. Currently our progress is curtailed by the lack of an adequate number of well trained scientists, who are working full time on the subject. In view of the fact that most of the Third World countries share this problem, and considering that this could be most effectively solved through regional collaboration, and through the sharing of the human and other available resources, it is recommended that the Third World countries represented in this conference, consider the possibility of establishing a small international Task Force, to dig deeper into the issue of developing our vast, but neglected, marine plant resources. It is recommended also that the donor agencies represented at the conference also consider, favourably, requests for scholarship support, library support, and for the acquisition, of pieces of research equipment, which are so vital in the characterisation of some of the chemical substances contained by the seaplants.

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