Review Traditional Herbal Medicines — the Role of Polyphenols
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Review Planta Medica 55(1989) 1 Traditional Herbal Medicines — TheRole of Polyphenols B. Haslam1'3, T. H. Lilley', Ya Cai1, R. Martin1, andD. Magnolato2 Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom 2NestléResearch Department, Nestlé Ltd., Vers-Chez-Les-Blancs, CH-1000, Lausanne, Switzerland Address for correspondence Received: September 17, 1988 Table 2 Some medicinal plants containing polyphenolic metabolites. Abstract 1. Three Paeony (Paeonia lactiflora): outer skin of the root, used to cure disor- The polyphenol composition of some tradi- ders of the bloodstream, including high blood pressure. Principal tional herbal remedies is reviewed. Polyphenols probably polyphenolic metabolite the gallotannin (1). 2. Bearberry (Arctostaphylos uva-urs,): dried leaves; infusions have a soothing act in such remedies by virtue of their astringent action and astringent effect which have value as a diuretic, in kidney disorders and ail- current views on the molecular basis of this property are ments of the bladder and urinary tract. Polyphenolic constituents have been outlined and discussed. described in detail by Haslam and Britton and include arbutin, various galloyl esters of arbutin and the gallotannin (1). 3. Agrimony (Agrimonia sp.): roots and dried aerial parts of the herb. Used as an astringent on the digestive system, a diuretic and as a haemostatic agent. The principal polyphenolic constituents include compounds (3—6). Introduction 4. Gerani Herba (Geranium maculatum, G. thunbergi,: dried rhizome and leaves, employed as an astringent, anti-haemorrhagic and anti-inflammatory From the earliest of times man has been de- agent. Geranin (7) is the principal crystalline polyphenol of Geranium pendent on plants as sources of food and sustenance, for mate- species. rials as diverse as paper for writing and wood for construction, 5. Meadowsweet (Filipendula ulmaria): aerial parts of plant — leaves and flow- and from particular plants he has derived substances ranging ers — used as an infusion. Used as a mild astringent in digestive problems from perfumes, essences and spices to medicines and drugs. and as a diuretic. Its major polyphenolic constituent is rugosin-D (8). 6. Raspberry (Rubus idaeus): leaves and fruit. Raspberry leaf tea made from an One of the earliest recorded uses of plants rich in polyphenols infusion of dried leaves is used as a mouth gargle and for children's stomach (tannins) was in the conversion of raw animal hides and skins disorders, It has a long tradition of use during pregnancy when taken regu- to durable, non-putrescible leathers. A number of traditional larly and liberally. The principal polyphenolic metabolite is sanguin H-6 (9). plant-derived folk medicines are likewise rich in polyphenols (1). The outer-skin of the root of the tree paeony (Paeonia lacti- flora), known as Mudan, is thus used medicinally to cure disor- ders of the bloodstream, including high blood pressure, and its usage dates back at least 2000 years. Its active principle is most HO_ODOH probably the gallotannin (1); other examples of plants rich in (2) (3) polyphenols which find use as traditional medicines are shown in Table 2. In the constant effort to improve not only the efficacy GO but also, in oriental eyes, the ethics of modern medical practice researchers are increasingly turning their attention to folk )H medicines as sources of new drugs and to investigate the chem- OH I 0 This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. Table1 Plant polyphenols: physiological and pharmacological properties. (4) I.L I-IOLJJOH 1. Foodstuffs and Beverages 02H (5) (a) Flavour, palatability and acceptability (Astringency) (b) Nutritional Value (c) Non-biological hazes, ageing of wines (d) Herbal teas — aesophogeal cancer o (e) Toxic effects— molluscicidal action 2. Herbal medicines H (a) Effects on vascular system—blood pressure and capillary action (b) Antiviral (antiherpetic) effects (c) Stomach disorders, dysentry, diarrhoea, haemorrhages 4 (d) Microbial toxicity — antiseptic action (6) (e) Dressing of burns and inflammations (f) Inhibition of direct acting mutagens 3. Chemical Defence in Plants Planta Medica 55(1989) F. Haslam et al. CO2 H 06-6 H HOL)OH 6 OH 06 H 06 6 Davdiin -2 HI 6 6 6 GO\oG Geraniin (7) / G 2x Galtotannins (1 ) 6 H j 2x 6H/ OH 0 c' Cast alagin Rugosin D () Vescala cm Sanguin H-6(9) This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. 6 GG = 6—6 =HO)O HO OH HO HO. H OH HO HO OH depside OH hexahydroxydi phenoyl (11) Fig. 1 Polyphenolic metabolites based on gallic acid. Traditional Herbal Medicines— The Role ofPolyphenols Planta Medica 55(1989) 3 ical and biological basis of old remedies. Although the uses of Polyphenol (HzO)a +Macromolecule(H2O) polyphenols (tannins) as medicinal agents may be summarised under several headings (Table 1), many appear to devolve, at least in the first instance, on their astringent action. They thus [Polyphenol (H2O)b]fl -Macromolecule'(H2O) aid, for example, the healing of wounds, burns and inflamma- tion. In doing so the polyphenols act to produce an impervious Solution layer [polyphenol-protein and/or polysaccharide complex] 11. under which the natural healing processes can occur. Similar [Polyphenol]' Macromulecule (H2O) complexation processes probably take place internally; gut sec- retions are hindered thus protecting the underlying mucosa 11 from toxins and other irritants in the bowels. [ [Polyphenol],,Macromulecule (H2O)] Precipitate Studies of the reversible association of Fig. 2 Polyphenol complexation: reorganisation of water of solvation. polyphenols with proteins have a long history. One of the first scientific papers on this topic was that of Sir Humphry Davy in 1803. This early work (2) demonstrated some of the macro-bohydrate complexation have been hampered to a large extent scopic features of polyphenol complexation and it gave rise to by the unavailability of water-soluble polysaccharides with several, wholely empirical, definitions of the term vegetablesimilarly clearly defined molecular parameters of size and tannin. However until such times as structurally defined plantshape. Indeed the most satisfactory data have been obtained polyphenols became available the molecular mechanismsusing polysaccharides in the sohd phase —thechromato- which underly polyphenol-protein complexation were notgraphic gels Sephadex G-10, G-25 and G-50, and LH-20, and amenable to systematic investigation and were, in conse- cellulose acetate in membrane form (3). quence, poorly understood. In the past 10—15 years various studies of polyphenol complexation with both proteins and One of the key factors in this whole problem of polysaccharides have been conducted (3— 5). These investiga-polyphenol complexation is the role of the solvent water tions now permit a much more detailed picture of the molecular(Fig. 2). As Szent-Gyorgi once cryptically remarked "Biology processes involved to be outlined. has forgotten water, or never discovered it". Discussion The presence and influence of water is intui- tively accepted but invariably tacitly ignored. The structure of The association of polyphenols with proteinsthe aqueous media surrounding or included within molecules and polysaccharides is a specific example of the very important such as proteins, polysaccharides and polyphenols is neverthe- biological phenomenon of molecular recognition. The princi-less one of the most critical facets of their structure. The degree ples which underly molecular recognition may be analysed not of order of the solvent externally is generally proportional to its only in terms of the composition, structure and conformation ofproximity to hydrophilic groups on the substrate molecular both acceptor (host) and donor (guest) molecules but also insurface where water molecules are anchored by hydrogen terms of three idealised concepts. "Dye-mould" ("jig-saw")bonding to acceptor and donor fl.inctionalities (e.g. OH, CO, matching is essentially static with an exact fit of donor and ac-CONH, etc.). During the complexation process the reorganisa- ceptor molecules. "Key-lock" matching is time dependent since tion of the various solvation shells provides an important driv- the key (donor) invariably has to be manoeuvered into the locking force for the association of the polyphenol with the mac- (acceptor) to achieve the necessary precise fit. Finally "hand-romolecule, (Fig. 2). Given the presumed importance of these in-glove" matching of donor and acceptor is both time-depen-forces some detailed thought should be given in the future to the dent and dynamic. Donor and acceptor molecules are mobilehydrophilic and hydrophobic effects associated with phenolic and flexible and may assume a variety of shapes as complexa- nuclei. Accepting these various riders the critical facets of tion proceeds. In such situations, to bring about strong and ef- fective binding, it is imperative that many points of contact are Table3 Polyphenol-protein complexation (structure-activity relationships). ultimately established between donor and acceptor species. Such associative processes frequently exhibit strong coopera- 1.Complexation isdependent on protein type and pH. Association is essen- tive effects. Present evidence strongly indicates that polyphenol tially a surface phenomenon, maximised at or near the isoelectric point of This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.