Ellagitannins As Active Constituents of Medicinal Plants

Home , Casuarictin, Chebulagic acid, Chebulinic acid, Corilagin, Geraniin

Review 117 Ellagitannins as Active Constituents of Medicinal Plants

Takuo Okuda'2, Takashi Yoshida', and Tsutomu Hatano' Faculty of Pharmaceutical Sciences, Okayama University, Tsushima, Okayama 700, Japan 2Addressfor correspondence

Received: September 17, 1988

regarded as intractable mixtures having unfavorable biological Abstract activities, regardless of the structural differences among each tannin, the recent isolation and structural determination of a Isolation and structure determination, ac- number of ellagitannins, including their oligomers among companied by measurement of various biological activities which agrimonlin was the first one (2, 3), aided by the progress of each isolated tannin, particularly of ellagitannins, have in analysis methods (4) and in screening procedures for biolog- brought about a marked change in the concept of tannins as ical activities of each tannin thus brought about a marked active constituents of medicinal plants. Their biological ac- change in the concept of tannins. Ellagic acid, which has re- tivities should now be discussed on the basis of the struc- cently been a topic of interest because of its anti-carcinogenic tural differences among each tannin, in a way similar to that activity (5), should be considered as a compound derived from of the other types of natural organic compounds. The anti- ellagitannins, since ellagic acid is mostly produced by a hy- tumor activity exclusively exhibited by several oligomeric el- drolysis of ellagitannins taking place during their extraction lagitannins, and their anti-HIV activities are examples of and the concentration of the extracts from plants, and is rarely such biological activities, The inhibitory activity against found in living plants (6). The discovery of marked anti-tumor lipid peroxidation, which is different in the strength among (7) and anti-HIV activities (8) specifically exhibited by several of tannins of various structures, is exhibited in general more the oligomeric hydrolyzable tannins among a number of tan- strongly by ellagitannins than by the other types of tannins nins screened, further demonstrated the necessity for a change of similar structures. The radical-scavenging activities of of the old concept of tannins. tannins as the mechanism of their inhibition, which is regarded to participate in several biological activities of tan- Biogenesis of Ellagitannins nins, have been supported by the ESR spectral measure- ments. Other biological activities, i.e., inhibition of The HHDP group in ellagitannins has been mutagenicity of carcinogens, inhibition of tumor promotion, presumed biogenetically to be produced by the C-C bond for- etc., have been found for tannins including ellagitannins. mation between two galloyl groups (9). Recent investigation of the seasonal changes in the structures of hydrolyzable tannins in Liquidainbarforinosana, revealed the formation of an I-IHDP group in several tannins, in place of two galloyl groups with the same locations on the glucopyranose ring in the tannin Introduction molecule found in the same plant in earlier seasons (10). Liquidambin, a compound which has a partly hydrated al- Ellagitannins belong to the group of hydrolyz- dehyde group and is regarded as an intermediate product in able tannins which, along with condensed tannins, comprisethe biosynthesis of C-glucosidic ellagitannins, has also been isolated (11). An example of a series of biosyntheses of several one of the two large groups of tannins, and have the hexahy- This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. droxydiphenoyl (HHDP) group, or a similar group derivabletypes of ellagitannins, supported by these findings, can be de- from the HHDP group, in their molecules, The number of el- picted as shown in Scheme 1. lagitannins hitherto isolated is by far larger than that of gallotannins, which constitute another group belonging to the The distribution of ellagitannins in plant hydrolyzable tannins, and are often present as complex mix- families which have been thus biosynthesized, is therefore fun- tures. Ellagitannins are generally different from the other typesdamentally the same as that of gallotannins (15). of tannins in that each of them can be isolated as a comparatively stable compound, as exemplified by geraniin which is a Tatmins Related to Ellagitannins crystalline tannin (1), and can be handled as a single compound of defined structure. This property of ellagitannins made it pos- There are a number of monomeric ellagitan- sible to measure the biological activities of each isolated tanninnins, in which the HHDP group (a) has been further of determined chemical structure, like those of each compoundmetabolized to the other aromatic groups (b)—(f) by structural belonging to the alkaloids, terpenoids, and steroids, etc., al-modifications such as oxidation, reduction, ring cleavage, and though it is also true that there are some properties common toC-O(C) oxidative coupling. These tannins are often regarded as most of tannins. Although tannins, in the past, were generally belonging to the ellagitannin group on the basis of their pre- 118 PlantaMedica 55(1989) Takuo Okuda et at

OH OH HOL o OH HO HO - H H OH 0 "H HO HO

HO__HO HO OH OH HH pentagalloyLgLucose (12) pedunculagin (13) liquidambin (11)

OH =HO5 OH HO 0 OH HO HOOH HO HO>H tellimagrandin 11 (13) casuarictin (13) casuarinin (13)

dimers HO HO OH OH

trimers HO,OH

,J—O 0 OH HO—('H o>IO HO HO OH OH Scheme 1 castaLagin (14)

sumable biogenetic relationship with the tannins having thetannin having the dehydrohexahydroxydiphenoyl (DHHDP) HHDP group, although there are tannins such as geraniin (1)group is mixed with ascorbic acid in so)ution at room tempera- having two or more of these types of groups, and/or a galloylture (25). group in a molecule. Some ellagitannins also have the other This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. bonding in their molecules, as those referred to in groups (i)— (iii) Condensates with catechins: Most of this (iv). The representative ellagitannins having the groups (a)—(Otype of ellagitannins are composed of C-glucosidic ellagitannins are shown in Scheme 2. and catechins, and the C-C bond is formed between C-I of the former and C-6 or C-8 of the latter (26). (i) C-Glucosides: Ellagitannins of this type might be biogenetically produced by a phenol-aldehyde coupl- (iv) Oligomers: Oligomeric ellagitannins ing as illustrated in Scheme 1. They include tannins such asexemplified by agrimoniin (2, 3), oenothein B (dimer) (27), castalagin (14) having a flavogalloyl group, which is regardedrugosin G (trimer) (28), and nobotanin K (tetramer) (29), etc., as a condensate through the C-C coupling between an HHDPare regarded as products of biosyntheses in which a valoneoyl and a galloyl group. group, or a dehydrodigalloyl group is formed between two molecules of monomeric or oligomeric hydrolyzable tannins (ii) Condensates with ascorbic acid: As- (Scheme 4). corgeraniin was found in several species of Geranium, Acer, Elaeocarpus. Rhus, and Cercidiphyllum genera (24) (Scheme 3). This type of tannin is easily formed in a high yield when a Ellagitannins as Active Constituents of Medicinal Plants Planta Medica 55(1989) 119

O=c cO HO—-—OH O—)_OH HO HO OH OH HOH/'OH (a) hexahydroxydiphenoyl (b) dehydrohexahydroxydiphenoyl (HHDP) group (DHHOP) group pedunca(agin (13), Igeraniin (1), terchebln (16), casuarictin (13), etc.] isoterchebin (17), etc.]

HOØOØ HOO[\OH HOHO OH OH (C) chebuloyl group (dl dehydrodigalloyl (DHDG) group [chebulagic acid (18), [agrimonic acid A (19), chebulinic acid (18)1 agrimonic acid B (19)]

I I

HO_(_OHO HO HO HO _-_\oH OH OH (e) vatoneoyt group (rugosins A, B, C (20), castavalonic acid (21), mediniltin A (22), etc.]

OC HO OH CO HO-ç----O HO

HO HO OH OH (f) gatlagyl group [punicalagin (23), punicalin (23)] Scheme 2 ascorgeraniin Scheme 3

Biological Activities of Ellagitannins 1. inhibitory effect on peroxidation of lipids and other co-existing substances, Biological activities of any isolable compound and radical-scavenging effect

should be examined for each compound, however, there are This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. some properties commonly found for ellagitannins. The prop- Inhibitory effects of tannins on the lipid perox- erty most easily noticed for many ellagitannins is their com-idation induced by ADP and ascorbic acid in rat liver mitochon- paratively mild property, which is weakly astringent on the ton-dna, and on that induced by ADP and NADPH in rat micro- gue, and is weakly irritating on the mucous membrane. The ex- somes, were strongly exhibited by some ellagitannins, such as tracts of medicinal plants containing ellagitannins, thereforepedunculagin and isoterchebin (30). This effect in condensed have been generally administered orally without marked un-tannins was somewhat lower, and that in the polyphenols of favorable responses. small molecules, except for (—)-epigallocatechin gallate (EGCG) which is the main component of so-called green tea tannin, was markedly lower. No positive correlation of the intensity of effect was observed between the inhibition of peroxidation in the experiment with ADP and ascorbic acid and the binding activity, as expressed by RA and RMB values of tannins (31). The experiments on the inhibition of peroxidation by the radical-chain reaction of methyl linoleate, initiated by ultraviolet irradiation of AIBN in solution, also showed similar results (32). These re- 120 PlantaMedica 55(1989) Takuo Okuda et at

OH Scheme 4

agrimonlin

I-F

oenothein B

I-I

-OH

'H This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

nobotanin 1< Ellagitannins as Active Constituents of Medicinal Plants Planta Medica 55(1989) 121 suits indicate that the inhibitory effects of ellagitannins againstThese anti-tumor effects may be due to the enhancement of the lipid peroxidation, which are stronger than those of the otherimmune response of the host animals through the actions on types of tannins, should be due to stronger radical-scavenging tumor cells and some immunocytes, as shown by several exper- effect of the HHDP group (33), although the effect of the galloyl iments (40). Orally administered oenothein B also inhibited the group cannot be underestimated. The ESR spectra of the mix-Ehrlich ascites tumor (40). It is noticeable that this kind of anti- ture in the latter experiment exhibited formation of stable free tumor effect was exclusively exhibited by a limited number of radicals on the polyphenolic group in the tannins of fairly large oligomeric ellagitannins, including the tetramer. molecules, thus confirming the mechanism of the inhibition of lipid peroxidation by tannins, which was induced by donation 6. Anti-HIV activity of a hydrogen radical to the peroxide radical of the lipids which were undergoing peroxidation (33). The ESR spectrum of gera- These dimeric ellagitannins also inhibited re- nun, which has an HHDP, a DHHDP, as well as a galloyl groupplication of human immunodeficiency viruses (HIV) (8). Oeno- in its molecule, showed preferential formation of a free radical them B, among these ellagitannins, most strongly inhibited the on the HHDP group (33). Inhibition by several tannins and re-virus growth at the concentrations 1 ig/mi and 10 .tglml. The lated polyphenols of the oxidative damage to eye lenses of mice, investigation of the mechanism of this inhibitory effect indi- which was induced by the increase of lipid peroxide with thecated that the antiviral activity of these ellagitannins maybe as- xanthine-xanthine oxidase system, was observed (34). The oralcribable to the inhibition of adsorption of HIV on the cells, and administration of geranlin and the geraniin-containing extractalso to other effects such as the inhibition of reverse transcrip- from Geranium thunbergii to rats was found to reduce the lipidtase activity (8). Mouse sera taken after the oral administration peroxide concentrations in serum and liver, which was raisedof oenothein B also inhibited replication of HIV and herpes by feeding the animals with peroxidized corn oil. The levels ofvirus, thus indicating that this dimeric eilagitannin may be ef- serum cholesterol, GOT, and GPT were also lowered (35). fectively used by oral administration (8).

2. Effects on arachidonate metabolism 7. Inhibition of mutagenicity of carcinogens Inhibition of 5-lipoxygenase in the arachido- Strong inhibitions of the mutagenicity of the nate metabolism in rat peritoneal polymorphonuclear leuko-carcinogens Trp-P-1, Trp-P-2, MNNG, and also of direct acting cytes was observed with comparatively low concentrations ofmutagens, N-OH-Trp-P-2 and benzopyrene diol epoxide, were ellagitannins, e.g., geraniin and corilagin (36). The mechanismexhibited in the Ames text by geraniin and other ellagitannins of this inhibition may have a correlation with that of the inhibi- (41). Positive correlations between the inhibitions of Trp-P-1 tion of lipid peroxidation described above. and Trp-P-2, and the binding activities of each tannin were observed, while this correlation was reversed in the inhibition of 3. Inhibition of autoxidation MNNG. Although the inhibition of benzopyrene diol epoxide by of ascorbic acid ellagic acid was stronger than that by tannins, several tannins, including ellagitannins, showed markedly stronger inhibition Autoxidation of ascorbic acid was strongly in- for the mutagenicity of N-OH-Trp-P-2 in the absence of enzyme, hibited by tannins (geranlin and tannic acid), while the inhibit- than that bypolyphenols of small molecules in a way analogous ory effects by polyphenols of small molecules were almost neg- to the inhibition for Trp-P-2, indicating that the inhibition of ligible (37). The inhibitory effect of geraniin was stronger thanthis type of mutagens by tannins is due to a direct action of the that of tannic acid. The superior effect by this ellagitannin maytannins (41). be attributable to the formation of more stable radicals (32). 8. Inhibition of tumor promotion

4. Reduction of co-existing substance In a two-stage carcinogenesis experiment in mouse skin treated with DMBA plus teleocidin, EGCG and Reduction of metallic ions, Cu2t Fe3, and Cr6 penta-O-galloyl-13-n-glucose showed marked inhibitions of to Cut Fe2t and Cr3, occurred in the presence of tannins attumor growth at the stage of tumor-promotion (42, 43). Inhibi- room temperature (38). This reducing property of tannins willtion of the activation of protein kinase C induced by teleocidin be attributable to the property of tannins by which they are eas- was observed. EGCG was also found to inhibit duodenum cancer which was produced in a similar way (44). Ellagitannins ily oxidized to presumable quinoids. This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. also inhibited the binding of E3111-TPA to a particulate fraction 5. Host-mediated anti-tumor activity of mouse skin in a preliminary screening of the inhibition of the of oligomeric ellagitannins tumor-promotion (43).

Several oligomeric, hydrolyzable tannins, 9. Other biological activities among the more than fifty of those hitherto isolated, showed strong anti-tumor activity when they were injected in- Besides the inhibition of reverse transcriptase traperitoneally into mice at 4 days before inoculation of Sar-(8, 45), inhibition and also promotion, by diluted solutions of coma 180 cells, while the about 80 tannins of the other types, each tannin, of the activities of the other enzymes to various ex- including polyphenols of small molecules, screened were inac-tents depending on the structure of each tannin, have been ob- tive (7). Among the oligomeric, hydrolyzable tannins, coriarlinserved (46—48). Antihepatotoxic activities assayed utilizing A (39), rugosin E (28), and oenothein B (27), etc., which are di- CC14- and Gain-induced cytotoxicity in primary cultured rat meric ellagitannins, showed the strongest anti-tumor activity. hepatocyctes was revealed (49). Inhibitions of adrenalin- and Similar effects were observed for other types of tumors includ-ACTFI-induced lipolysis and also insulin-induced lipogenesis ing solid type tumors, during experiments with oenothein B.from glucose in fat cells of rat were also found (50—52). 122 Planta Medica 55(1989) Takuo Okuda et at

The change in the concept of tannins, initiated 27 Okuda,T., Yoshida, T., Hatano, T., Yazaki, K., Kira, H., Ikeda, Y. (1986) J. Chromatogr. 362, 375. by that of ellagitannins, still requires further experimental sup- 28 port including that of absorption and metabolism, and also of Okuda,T., Hatano, T., Ogawa, N. (1982) Chem. Pharm. Bull. 30, 4234. the unfavorable effects, for each tannin, now based on pure 29Yoshida,T., Hatano, T., Okuda, T. (1988) J. Chromatogr., in press. tannins of determined structures. 30Okuda,T., Kimura, Y., Yoshida, T., Hatano, T., Okuda, H., Arichi, S. (1983) Chem. Pharm. Bull. 31, 1625. 31Okuda,T., Mori, K., Hatano, T. (1985) Chem. Pharm. Bull. 33, 1424. Acknowledgements 32Fujita,Y., Komagoe, K., Uehara, I., Okuda, T., Yoshida, T. (1988) Yakugaku Zasshi 108, 528. The authors are grateful to Prof. Y. Fujita and Prof. Fujita, Y., Komagoe, K., Sasaki, Y., Uehara, I., Okuda, T., Yoshida, T. H. Hayatsu of Okayama University, (the late) Prof. S. Arichi of Kinki Uni- (1987) Yakugaku Zasshi 107,17. versity, Prof. H. Okuda of Ehime University, Dr. H. Fujiki of National Iwata, S., Fukaya, Y., Nakazawa, K., Okuda, T. (1987) J. Ocul. Phar- Cancer Center Research Institute, Dr. H. Koshiura, President of macol. 3, 227. Hokuriku University, Prof. T. Kurimura of Tottori University, Prof. T. Kimura, Y., Okuda, H., Mori, K., Okuda, T., Arichi, 5. (1984) Chem. Namba of Toyama Medical and Pharmaceutical University, (the late) Pharm. Bull. 32, 1866. Prof. H. Hikino of Tohoku University, and their co-workers, for their col- 36Kimura,Y., Okuda, H., Okuda, T., Arichi, 5. (1986) Planta Med. 337. laboration in measuring biological activities, and their mechanisms. Yoshida, T., Koyama, S., Okuda, T. (1981) Yakugaku Zasshi 101, 695. Okuda, T., Moti, K., Shiota, M., Ida, K. (1982) Yakugaku Zasshi 102, References 734. Hatano, T., Hattori, S., Okuda, T. (1986) Chem. Pharm. Bull. 34, 4092. Okuda, T., Yoshida, T., Hatano, T. (1982) J. Chem. Soc. 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