Novel antiviral agents medicinal plant perspective Journal Applied Microbiology Jassim and ...

16 Pages·2003·0.59 MB·English

JournalofAppliedMicrobiology2003,95,412–427 doi:10.1046/j.1365-2672.2003.02026.x
A REVIEW
Novel antiviral agents: a medicinal plant perspective
S.A.A. Jassim and M.A. Naji
DepartmentofMicrobiology,ZayedComplexforHerbalResearchandTraditionalMedicine,GeneralAuthority
forHealthServicesofEmirateofAbuDhabi,AbuDhabi,UAE
2002/97:received4March2002,revised4April2003andaccepted16April2003
1. Summary, 412 6. Phyto-therapy and clinical trial, 419
2. Introduction, 412 7. Theeffectofsynergeticcombinationofmedicinalplants
2.1 Viral infection control, 413 in the potency of antiviral activity against selected
2.2 Overview of medicinal plants worldwide, 413 viruses, 421
3. Antiviral activity of herbal medicine against selected 8. Aspects of synergetic combination of medicinal plants
viruses, 413 with orthodox drugs for alleviating viral infection, 421
4. Marine herbs and antiviral activities, 414 9. Future prospects, 422
5. The common classes of antiviral compounds present in 10. Conclusion, 423
medicinal plants, 414 11. References, 423
capable of acting therapeutically in various viral infections
1. SUMMARY has raised optimism about the future of phyto-antiviral
agents. As this review illustrates, there are innumerable
Several hundred plant and herb species that have potential
potentially useful medicinal plants and herbs waiting to be
as novel antiviral agents have been studied, with surpris-
evaluated and exploited for therapeutic applications against
ingly little overlap. A wide variety of active phytochem-
genetically and functionally diverse viruses families such as
icals, including the flavonoids, terpenoids, lignans,
Retroviridae, Hepadnaviridae and Herpesviridae.
sulphides, polyphenolics, coumarins, saponins, furyl com-
pounds, alkaloids, polyines, thiophenes, proteins and
peptides have been identified. Some volatile essential oils 2. INTRODUCTION
of commonly used culinary herbs, spices and herbal teas
Viruses are obligate intracellular parasites, which contain
have also exhibited a high level of antiviral activity.
little more than bundles of gene strands of either RNA or
However, given the few classes of compounds investigated,
DNA,andmaybesurroundedbyalipid-containingenvelope
most of the pharmacopoeia of compounds in medicinal
(WagnerandHewlett1999).Yetvirusesarefarfromsimple.
plants with antiviral activity is still not known. Several of
Unlike bacterial cells, which are free-living entities, viruses
these phytochemicals have complementary and overlapping
utilize the host cell environment to propagate new viruses.
mechanisms of action, including antiviral effects by either
They use the reproductive machinery of cells they invade
inhibiting the formation of viral DNA or RNA or
causingailmentsasbenignasacommonwart,asirritatingas
inhibiting the activity of viral reproduction. Assay meth-
a cold, or as deadly as what is known as the bloody African
ods to determine antiviral activity include multiple-arm
fever.ThevirusesthatcauseLassafeverandEbolafeverand
trials, randomized crossover studies, and more compro-
the retrovirus that causes acquired immunodeficiency syn-
mised designs such as nonrandomized crossovers and pre-
drome(AIDS)areexamplesthatresearcherscallhotagents–
and post-treatment analyses. Methods are needed to link
viruses that spread easily, kill sometimes swiftly, and for
antiviral efficacy/potency- and laboratory-based research.
which there is no cure or vaccine (Peter 1994).
Nevertheless, the relative success achieved recently using
Viruses have numerous invasion strategies. Each strain of
medicinal plant/herb extracts of various species that are
virus has its own unique configuration of surface molecules
(Wagner and Hewlett 1999). These surface molecules work
Correspondenceto:SabahA.A.Jassim,HeadofMicrobiologyDepartment,Zayed
like keys in a lock, enabling viruses to enter into hosts by
ComplexforHerbalResearchandTraditionalMedicine,POBox29300,AbuDhabi,
UnitedArabEmirates(e-mail:[email protected]). precisely fitting the molecules on their surfaces to those on
ª2003TheSocietyforAppliedMicrobiology
NOVEL ANTIVIRAL AGENTS 413
the membranes of target cells. The success of viruses in Virtually all cultures around the globe have relied
evolution has been assured by four general attributes: historically, and continue to rely on medicinal plants for
genetic variation, variety in means of transmission, efficient primaryhealthcare.Thereiscurrentlyaworldwideupsurge
replication within hostcells,andtheability to persist in the in the use of herbal preparations and the active ingredients
host (Wagner and Hewlett 1999). As a consequence viruses isolated from medicinal plants in health care. Natural
have adapted to all forms of life and have occupied products from plants traditionally have provided the phar-
numerous (cid:1)ecological niches(cid:2) resulting in widespread dis- maceutical industry with one of its most important sources
eases in humans, livestock and plants. of (cid:1)lead(cid:2) compounds and up to 40% of modern drugs are
derived from natural sources, using either the natural
substance or a synthesized version.
2.1 Viral infection control
Control of viral infections, like any other kind of infection
3. ANTIVIRAL ACTIVITY OF HERBAL
control, can be affected either as a prophylactic (protective)
MEDICINE AGAINST SELECTED VIRUSES
measureortherapeutically,inordertocontrolandalleviatea
viral infection, which has already been established in the Manytraditionalmedicinalplantshavebeenreportedtohave
host.Unlikebacterial,fungalandparasiticinfections,viruses strongantiviralactivityandsomeofthemhavealreadybeen
are not autonomous organisms and therefore, require living used to treat animals and people who suffer from viral
cellsinwhichtoreplicate.Consequently,mostofthestepsin infection (Hudson 1990; Venkateswaran et al. 1987;Thyag-
theirreplicationinvolvenormalcellularmetabolicpathways, arajanet al.1988,1990).Researchinterestsforantiviralagent
andthismakesitdifficulttodesignatreatmenttoattackthe development was started after the Second World War in
virion directly, or its replication, without accompanying Europeandin1952theBootsdrugcompanyatNottingham,
adverse effects on the infected cells (Wagner and Hewlett England,examinedtheactionof288plantsagainstinfluenza
1999). Fortunately, we now know that many viruses have A virus in embryonated eggs. They found that 12 of them
unique features in their structure or in their replication suppressedvirusamplification(Chantrillet al.1952).During
cycles, and these constitute potential targets. In fact, the last 25 years, there have been numerous broad-based
successfulantiviral chemotherapy has been achieved against screening programmes initiated in different parts of the
the herpes virus with the development of acycloguanosine, globetoevaluatetheantiviralactivityofmedicinalplantsfor
soldas(cid:1)acyclovir(cid:2),becauseitinterfereswithcertainkeyviral invitroandinvivoassays.Canadianresearchersinthe1970s
enzymes that have distinctive affinities for different nucleo- reported antiviral activities against herpes simplex virus
tide analogues (Wagner and Hewlett 1999). Viral enzymes (HSV),poliovirustype1,coxsackievirusB5andechovirus7
playakeyroleintriggeringdisease.Ifviralenzymescouldbe from grape, apple, strawberry and other fruit juices (Kono-
neutralized, viral replication would not take place. The walchuk andSpeirs 1976a,b,1978a,b).
proteolytic processing of viral polyprotein precursors by a One hundred British Columbian medicinal plants were
viral proteinase is essential for maturation of the virus. screened for antiviral activity against seven viruses
Designingspecificinhibitorsforeachofviralproteaseisthus (McCutcheon et al. 1995). Twelve extracts were found to
adesirable objective. have antiviral activity at the concentrations tested. The
extractsofRosanutkanaandAmelanchieralnifoliawerevery
active against an enteric corona virus. A root extract of
2.2 Overview of medicinal plants worldwide
Potentilla arguta and a branch tip extract of Sambucus
There is currently a large and ever-expanding global racemosa completely inhibited respiratory syncytial virus
population base that prefers the use of natural products (RSV).AnextractofIpomopsisaggregatademonstratedgood
in treating and preventing medical problems. This has activity against parainfluenza virus type 3. A Lomatium
influenced many pharmaceutical companies to produce new dissectum root extract completely inhibited the cytopathic
antimicrobialformulationsextractedfromplantsorherbs. effects of rotavirus. In addition to these, extracts prepared
At present, plant and herb resources are unlimited, as far from Cardamine angulata, Conocephalum conicum, Lysichiton
as the search for useful phyto-chemicals is concerned; but americanum, Polypodium glycyrrhiza and Verbascum thapsus
theseresourcesaredwindlingfast,duetotheonwardmarch exhibited antiviral activity against herpes virus type 1.
of civilization. We have barely scraped the surface in our The extracts of 40 different plant species have been used
effortstoexploittheplantworldforantimicrobials(namely, in traditional medicine and were investigated for antiviral
antiviral,antibacterialandantifungalcompounds).Although activity against a DNA virus, human cytomegalovirus
a significant number of studies have used known purified (HCMV), and two RNA viruses, Ross River virus (RRV)
plant chemicals, very few screening programmes have been and poliovirus type 1, at noncytotoxic concentrations
initiated on crude plant materials. (Semple et al. 1998). The most active extracts were the
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
414 S.A.A. JASSIM AND M.A. NAJI
aerial parts of Pterocaulon sphacelatum (Asteraceae) and preclinical and clinical evaluation. Others show promising
roots of Dianella longifolia var. grandis (Liliaceae), which biological activities in in vitroand in vivo assays(Konig and
inhibited poliovirus type 1 at concentration of 52 and Wright 1996; Blunden 2001). The antiviral properties of
250 lg ml)1, respectively. The same authors concluded marine algae have been addressed (Chamorro et al. 1996;
that the extracts of Euphorbia australis (Euphorbiaceae) and Siddhanta et al. 1997; Berge et al. 1999; Nicoletti et al.
Scaevola spinescens (Goodeniaceae) were the most active 1999). Preclinical testing suggests that Spirulina, a unicel-
against HCMV whilst, extracts of Eremophila latrobei lular filamentous cyanobacteria (formerly called (cid:1)blue-green
subsp. glabra (Myoporaceae) and Pittosporum phylliraeoides algae(cid:2)), has several therapeutic attributes such as cholesterol
var. microcarpa (Pittosporaceae) exhibited antiviral activity regulation, immunological, antiviral and antimutagenic
against RRV. properties (Chamorro et al. 1996). Strain-specific anti-
The human rotavirus (HRV), RSV and influenza A virus influenzavirusinhibitoryactivity,basedonthereproduction
were susceptible to a liquid extract from Eleutherococcus of influenza viruses in tissue cultures, was reported for
senticosus roots. In contrast, the DNA viruses, adenovirus marine algae of the Bulgarian Black Sea coast (Serkedjieva
and HSV type 1 virus (HSV-1) were not inhibited by the et al.2000).WaterextractsfromHasleaostreariaandthered
same plant extract (Glatthaar-Saalmuller et al. 2001). They marine alga Polysiphonia denudata from the Bulgarian Black
concluded that the antiviral activity of Eleutherococcus Sea coast, respectively, inhibited the reproduction of HSV
senticosus extract is viral RNA dependant. in cell cultures andaffectedadsorption and the intracellular
Related studies also showed that influenza RNA was stages of viral replication as demonstrated by the reduction
inhibitedbyawater-solubleextractofSaniculaeuropaea(L.) of virus-induced cytopathic effect and viral infectivity
(Turan et al.1996).InalaterstudyofKaragozet al.(1999) (Berge et al. 1999; Serkedjieva 2000a). In addition, the
itwasshownthatanacidicfractionobtainedfromthecrude water-soluble fraction of Haslea ostrearia has delayed HIV-
extract of Sanicula europaea was the most active fraction in 1-induced syncitia formation on MT4 cells (Berge et al.
inhibiting human parainfluenza virus type 2 replication at 1999).
noncytotoxicconcentrations.Bycomparison,ethanolextrac- Theinhibitoryeffectofmarinealgaewasinvestigatedand
tion abolished the antiviral activity. The plausible explan- found that cyanovirin-N, an 11 kDa protein from blue-
ation is that the antiviral activity could (cid:1)disappear(cid:2) during greenalgairreversiblyinactivatedHIVandalsoabortedcell-
the course of fractionation. to-cell fusion and transmission of HIV, due to its high-
Another example, Myrcianthes cisplatensis showed in vitro affinity interaction with gp120 (De Clercq 2000). The
anti-RSV but not anti-HSV-1 or anti-adenovirus serotype presenceof various sulphated polysaccharide groupsextrac-
7 (DNA virus) (Kott et al. 1999). In contrast, other ted from seaweeds and alga have exhibited many biological
medicinal plants, for example Nepeta coerulea, Nepeta properties, for example anti-HIV and anti-HSV activities
nepetella, Nepeta tuberosa, Sanguisorba minor magnolii and and also the inhibition of viral adsorption processes (De
Dittrichia viscose showed clear antiviral activity against Clercq 2000; Schaeffer and Krylov 2000; Duarte et al.
DNA and RNA viruses, i.e. HSV-1 and VSV in addition 2001). It is well known that the presence of the sulphate
to poliovirus type 1 in the case of Dittrichia viscose (Abad group is necessary for antiviral activity, and potency
et al. 2000). The Azadirachta indica leaf extract was found increases with the degree of sulphation (Schaeffer and
to be active against a number of viruses such as smallpox Krylov 2000). Given the few classes of compounds inves-
(DNA), chicken pox (DNA), poxvirus (DNA), poliomye- tigatedthusfar,mostoftheantiretroviralactivityinalgaeis
litis (RNA) and herpes viruses (DNA) (Rao et al. 1969; unknown.
Kaii-a-Kamb et al. 1992). An extract of the cactus plant
Opuntia streptacantha inhibited intracellular DNA and
5. THE COMMON CLASS OF ANTIVIRAL
RNA virus replication and inactivated extracellular virus,
COMPOUNDS PRESENT IN MEDICINAL
such as HSV, equine herpes virus, pseudorabies virus and
PLANTS
influenza virus (Ahmad et al. 1996). The Bergenia ligulata,
Nerium indicum and Holoptelia integrifolia plants exhibited Thedevelopmentofviralresistancetowardsantiviralagents
considerable antiviral activities against influenza virus enhancestheneedforneweffectivecompoundsagainstviral
(RNA) and HSV (DNA) (Rajbhandari et al. 2001). infections. Medicinal plants have a variety of chemical
constituents,whichhavetheabilitytoinhibitthereplication
cycleofvarioustypesofDNAorRNAviruses.Compounds
4. MARINE HERBS AND ANTIVIRAL
from natural sources are of interest as possible sources to
ACTIVITIES
control viral infection. In this context various research
Natural product research is increasingly turning to marine groups in Asia, Far East, Europe and America have given
herbs as a source of natural products and is currently in particular attention to develop antiviral agents from their
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
NOVEL ANTIVIRAL AGENTS 415
nativetraditionalplantmedicines.Sometypicalexamplesof virus. Sakagami et al. (1995) have put forward a number
such medicines and their antiviral activities are shown in of possible mechanisms whereby polyphenols may exert
Table 1. their antiviral action. They suggested that the major part
Theantimicrobialactivitiesofplantoilsandextractshave of the antiviral activity in polyphenols probably derives
been recognized for many years. Recently, the oil of from their direct inactivation of the virus and/or from
Melaleuca alternifolia (tea tree) has gained widespread inhibition of the virus binding to the cells. They also
acceptance and it is now the principal antimicrobial noted that although polyphenols are known to inhibit viral
preservative in a range of pharmaceutical cosmetics for replication enzymes (such as RT for HIV and RNA
external use, such as face and hand washes, pimple gels, polymerase for influenza virus) and other enzymes (e.g.
vaginal creams, foot powders, shampoos, conditioners and poly(ADP-ribose) glycohydrolase), these effects seem to be
veterinaryskincareproducts(Coxet al.2001).Theantiviral rather nonspecific. The most pronounced in vitro selec-
action of essential oils of Melaleucaalternifolia and eucalyp- tivity of anti-influenza and anti-herpes type 1 and type 2
tus oil exhibited a high level of antiviral activity against action were confirmed against polyphenolic complexes
HSV-1 and HSV-2 in viral suspension tests (Schnitzler isolated from the Bulgarian medicinal plant Geranium
et al. 2001). The activities of anti-herpes components could sanguineum (L.) (Serkedjieva and Hay 1998; Serkedjieva
be the result of terpinen-4-ol (Cox et al. 2001). Italian and Ivancheva 1999). Although polyphenols were shown to
medicinalplantsandfoodmedicineswerereviewed(Pieroni have a broad antiviral spectrum in vitro, their correspond-
2000) and it was found that essential oil obtained from ing properties in vivo have not been well established
SantolinainsularishaddirectantiviraleffectsonbothHSV-1 (Sakagami et al. 1995).
and HSV-2 and also inhibited cell-to-cell transmission of A peptide isolated from the leaves of the Argentinean
both herpes types (De Logu et al. 2000). Sandalwood oil, plant Melia azedarach has a molecular weight of 5000–6000
the essential oil of Santalum album (L.), showed a dose- (Table 1), which may be common in many plants (Hudson
dependent effect against HSV-1 but not HSV-2 with no 1990).Thepeptidewasevaluatedwithmiceinoculatedwith
reported cytotoxicity (Benencia and Courreges 1999). HSV-1strain(Alcheet al.2000).Infectedanimalstreatedor
Recently the antiviral effect of black seed oil (BSO) from not with meliacine were observed carefully for the develop-
Nigella sativa was investigated using murine cytomegalovi- ment of stromal keratitis and the clinical scoring was
rus (MCMV) as a model (Salem and Hossain 2000). Their followed 14 days postinfection. It was found that meliacine
results show that BSO exhibited a striking antiviral effect exerted a strong antiviral action on HSV-1 induced ocular
against MCMV infection, which may be mediated by diseaseinmicewithnoevidenceoftoxiceffects.Therehave
increasing one’s innate immunity. also been reports of the beneficial effects of meliacine in
Polyphenols and the proanthocyanidins extracted from helping to control the Junin hemorrhagic fever virus by
Hamamelis virginiana bark and two new hydrolysable inhibiting the multiplication of Junin virus in vero cells
tannins, shephagenins A and B, isolated along with hippo- treated with the compound before infection or immediately
phaenin A and strictinin from the leaf extract of Shepherdia after virus adsorption (Castilla et al. 1998). It also inhibited
argentea, showed a remarkable inhibitory activity against the multiplication of foot andmouth disease virus in BHK-
HSV-1 (Erdelmeier et al. 1996) and HIV-1 reverse tran- 21 cells (Wachsman et al. 1998). Analysis of early events
scriptase(RT)(Yoshidaet al.1996).Theinhibitoryeffectof followinginfectiondemonstratedthatmeliacineblocksvirus
theShepherdiaargentealeafextractonHIV-1RTwasfound penetration by preventing the uncoating step, but the
to be caused by tannins, and their activities were stronger addition of meliacine at different times after infection
than that of ())epigallocatechin gallate as a positive control indicated that meliacine also interferes with the release of
(Yoshida et al. 1996). infectious particles and inhibits the low-pH-induced fusion
In an early study of plant viral infection, Cadman (1960) ofinfectedcells(Castillaet al.1998;Wachsmanet al.1998).
suggested that polyphenolic extracts of the leaf of Rubus Taken together, these results suggest that meliacine affects
idaeus (raspberry) probably act against most viruses by two events of the virus replicative cycle that require
clumping the virus particles together into complexes, membrane fusion: uncoating and budding. (Castilla et al.
which are largely noninfective. Hudson (1990) deduced 1998). Such chemicals might be useful therapeutically to
that viral inactivation in vitro is directly attributable to block the spread of virus as they prevent the initial
preferential binding of the polyphenol to the protein coat replication cycles.
of the virus, whereas, in a systematic study of the antiviral The HRV genus is perhaps the most common cause of
activity of a very wide range of natural products Van den gastroenteritis with accompanying diarrhoea in infants and
Berghe et al. (1986) concluded that polyphenols act remains among the leading cause of early childhood death
principally by binding to the virus and/or the protein of worldwide(WagnerandHewlett1999).Anti-HRVandanti-
the host cell membrane and thus arrest absorption of the HSV-1 activities of hot water extracts from Stevia rebaudi-
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
416 S.A.A. JASSIM AND M.A. NAJI
m,alis,
un
Exampleofplantsource RutaceaeandUmbelliferae(Apiaceae) CamptothecaacuminateAtropabelladonaRutaceae,,(L.),SwainsonacanescensAstragaluslentiginosusCastanospermum,,australeAglaiaroxburghiana,CampanulaceaePanaxginsengAsteraceae,Apiaceae,(KoreanBidensChrysanthemumsibiricumginsengroots),sp.,AchyroclineflaccidaBostrychiamontagneiCedrelatubiflora,,,PrunellavulgarisSclerotiumglucanicumSteviarebaudiana,,,RhizophoramucronataAspiliaChenactisdouglasiiDyssodiaanthemidifolia,,,EcliptaalbaEriophyllumlanatum,AgastacherugosaEuphorbiagrantiiBarleriaprionitis,,,CalophyllumcerasiferumCal.inophyllumCal.teysmannii,,,CamelliasinensisGarciniamultifloraHelichrysum,,aureonitensMacluracochinchinensisMarkhamialutea,,,MonotesafricanusPterocaulonsphacelatum,,RhussuccedaneaScutellariabaicalensisSelaginella,,sinensisSophoramoorcroftianaSophoratomentosa,,,Tephrosisp.Acokantherasp.Anagallisarvensis,(Primulaceae),CannabissativaGeumjaponicumGlycyrrhizaglabra,,,GlycyrrhizaradixGlyptopetalumsclerocarpum,,GymnemasylvestreMaesalanceolataOleaeuropa,,,QuillajasaponariaRhusjavanicaStrophanthusgratus,, Amanoaaff.OblongifoliaJuniperuscommunisJusticia,,procumbensPodophyllumpeltatum,Kadsuramatsudai RhinacanthusnasutusAloebarbadensisAsterscaberCassiaangustifoliaDianella,,,longifoliaEuodiaroxburghianaGeumjaponicum,,,HamamelisvirginianaHypericumMelissaofficinalis,sp.,,PhyllanthusmyrtifoliusPhyllanthusurinariaPunica,,granatumRhamnusfrangulaRhamnuspurshianus,,,RheumofficinaleRhinacanthusnasutusShepherdiaargentea,,,Syzgiumaromatica,St.John’swort ClerodendrumInermeDianthuscaryophyllusGeloniummultiflor,,MomordicacharantiaPhytolaccaAmericanaSaponariaoffici,,TrichosantheskirilowiiTriticumaestivum,
compoundfrommedicinalplants* Mechanismvirustarget DNAandRNAgenomes.Interactionsrequiredlong-waveultraviolet(UVA,300–400nm)DNAandotherpolynucleotidesandvirionsproteins.InsomeinteractionsareenhancedbyUVAMembraneinteraction.PhototoxicactivityfrequentlyrequiresUVABlockingvirusbinding Membraneinteraction.PhototoxicactivityfrequentlyrequiresUVABlockingRNAsynthesis.ExhibitedHIV-inhibitoryactivity Membrane-mediatedmechanisms.InhibitionofviralDNAsynthesis Blockingvirusreplication BlockingHBVreplication BlockinginfluenzavirustypeAreplicationInhibitionofviralRNAandDNAreplication Interactionwithribosomefunctionintheinfectedcellandinhibitedviralproteinsynthesis
al
r
antivi one,orin,
SummaryofthemechanismofthemostactiveTable1 Classofcompound Furylcompounds:furocoumarinsandfuranochromones bAlkaloidsconstitute:-carbolines,furanoquinolines,camptothecin,atropine,caffeine,indolizidinesswainsonine,castanospermine,colchicines,vinblastinePolyacetylenes(polyines) Polysaccharides Thiophenes Flavonoids:amentoflavone,theaflavin,iridoids,phenylpropanoidglycosides,agathisflavone,robustaflavrhusflavanone,succedaneflavanone,chrysosplenolC,mcoumarins,galangin(3,5,7-trihydroxyflavone),baicalin Terpenoids:sesquiterpene,triterpenoids(moronicacid,ursolicacid,maslinicacidandsaponin) LignansPodophyllotoxinandrelatedlignans(cyclolignanolides),suchasthepeltatinsDibenzocyclooctadienelignanssuchasschizarinBandtaiwanschirinDRhinacanthinEandrhinacanthinFMiscellaneousphenoliccompounds:anthraquinonechrysophanicacid,cafficacid,eugeniin,hypericin,tannins(condensedpolymers),proanthocyanidins,salicylatesandquinines(naphthoquinones,naphthoquinonesandanthraquinonesinparticularaloeemodin) Proteinsandpeptides1.Singlechainribosome-inactivatingproteins
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NOVEL ANTIVIRAL AGENTS 417
ana and Achyrocline flaccida, respectively, have been exam-
PhytolaccaAmericanaMomordicacharantiaGeloniummultiflorumPokeweedantiviralproteins(PAP)(MRK29,InactivateinfectiveHIVandHIV-infectedcells,,MAP30andGAP31)PanaxginsengPanaxaginInhibittheHIV-1reversetranscriptaseVignaunguiculataAlpha-andbeta-antifungalproteinsInhibittheHIVreversetranscriptaseRicinuscommunisAbrusprecatoriusAdeniadigitata2.DimericcytotoxinsInteractionwithribosomefunction,,intheinfectedcellandinhibitviralproteinsynthesisCanavaliaensiformisLensculinarisPhaseolusvulgarisTriticumvulgaris3.LectinsViralmembraneinteractions,,,Nicotianaglutinosa4.AntiviralfactorMechanismofactionisnotknownMeliaazedarach5.MeliacineAffectvirusreplicativecycle etal.etal.etal.etal.etal.TakechiandTanaka(1981);Singh(1985);Singh(1988);Hudson(1990);Sydiskis(1991);Asano(1996);Erdelmeier(1996);Marchetti(1996);McCormicketal.etal.etal.etal.etal.etal.etal.etal.etal.(1996);Olivieri(1996);Pengsuparp(1996);Sendl(1996);Xu(1996);Yoshida(1996);Kernan(1997);Meyer(1997);Castilla(1998);etal.etal.etal.etal.etal.etal.etal.etal.Chen(1998);Clark(1998);Kernan(1998);Kurokawa(1998a);Sindambiwe(1998);Spino(1998);Garcia(1999);Kurokawa(1999);Linetal.etal.etal.etal.etal.etal.etal.etal.(1999);Liu(1999);Premanathan(1999b);Schreiber(1999);Semple(1999);Sotanaphun(1999);Xu(1999);Alche(2000);Bunyapraphatsara´etal.etal.etal.etal.etal.etal.etal.etal.(2000);Kwon(2000);Li(2000a,b;Sanchez(2000);Ye(2000);Zheng(2000);Craig(2001);D’CruzandUckun(2001);Duarte(2001);etal.etal.etal.etal.etal.etal.etal.Jacobson(2001);Jiratchariyakul(2001);Kuo(2001);Ma(2001);Meragelman(2001);NgandWang(2001);Semple(2001);Shirataki(2001);etal.Takahashi(2001). aefepocmtaAcaernsBnvirpvTkma(dwomdrabfldoiras(iiHinmnnnrhWRotuteoasnnnrnxeanfiincfareoaeoaiRorPhrrhcsecleehhaeoSpleopescGTTltdrdviherAnomauapliulemtaocntdniieianMtvituiissdoVsiortawclhA-easscvbbomnihsshhnPngsaint.yeeee,nrCncnehtcsrnc(dt,eer-aiiuceasnneeldisnrshn)owGelytduott,a1iacoat1ocvdnuereVsisonseoedsaHetactnnnpsirn9eimaiiie,taesdgitflhadanerrtnpdntydtoacbBepyis9nnrhnlgopxtotbrrpyhgIacnvaawglotdortsunmeeeobi9aogedbcMhoV3daoioetaooiicpescmstinmacyahtilmrasircliscrvmttsehpfltbahay-thoeybtobm,atbtdwfstiuotaietOsperonipibnheerhiasddcafmsllapieahnietanetnauipamocxnofoocaedctvo)iarbtnhaenieLtlnnHdnhesddedtpco.tmgiucccogd.lpeyuovuiriiibepridzltehiamceTnentuteosdidblveeHoneeiBln(nntahboecouhnaomdlreobhilslnen2eidcprrweioivcoslnyo.x-fldbaaarem-uoodnprvlefomsyIatnaeio0rwtidli4alidtrplcpstu1sielontsVtnsneyiirreileadydm0teerktehsicahlticv-die9oliuwisrMnrbasdbeegyacocs0oscctamdlnapoi(sisaeB9tilestlcsslctlhemailftso)pMets.Reebei-ndyeossme9.pwrofcctiilmblnRpterfci1nsepcliroltosrcfiriw;opyrAnnt2slafnrsbvnruhsiioTso9ooooptMkobnhieae.oRmttTda.4velfecmwiaboidPulme9mfngorhtinociwfrealnldhvetidUcnmohdhuftlki9uoanelprpeiritssntpenoecteebheupetlvlgieaktalymt)afehidhoaepphonzensistclftlr(aige.etoalcrnnantahtr.enuApmeegstordntodiotraemtfhtdhodattnasestc,oeaidpndhifrehtntcmaftihBPto,ontopeeacbtuoStnoogdhmohaidtifevieahta,sraRngl)enrfluroblaomnbetopfutdhspvesseehsiottlfeevaeei1cteeonngvurretabMoeroueagsecibrochsinnvnioorda9cparfimaavoissofrnmovinrtdeaerkolaeideoeomlhtnin9iiiteryaeseffPeuticandoeclieiitdeonioimcfrnone8aeadagarnrennstv(gninges(ccpnayltofrbngaidaatMr)cetpivMgrasgusoephreehvvlc(yo.lnggmltcalllecouyp.noisR,ecrBwlorute.ieeoitcblrebigolewafrhsotcxoodoTOtopyynslWpast2uhRahioditfriosMttuldfn,athecupanrilhsveomb0cunbiioityaeahLuwevpMfnosontznniviemceecidhtiu0ranideafmeactsecge.rocedpneTdhooedeosstdicthni1mieetntdyalogdhder)ahtnpadtluraanieyarapte)tclTi-edeehthcre,oeoh(tpnetd.geiinnocscpfhh4oracaPhshblisaefetob(deauihtsgfeTsynfpvnuc/tuprale,sehgnRttoeierri-eshplMynsrneietoeoreiordirHalhotveepathdtcrmhaacbiHsnMoalwgtrecinsuofmtnocavioaetniroafierydarhaoTewetemtoreshInniaklidnnneheaftRchrivdonlueVigpnlsPoraeastpoasve.tee-wlncitsoiy(s.edenmaaaheesnsVrtxiite,ct)i4dAn-dteh1flpgaote.ggtActofinuoes.ehtma1cPnktoptb9vcaaurfrnbwPrlaabtiftetvrohccaITciratoogrytate9ialaliihaaaaasnoecIhcee)iirottOtiahanrnnieaamivlhrcc6nnrlnon,sIdhhheehabhuullnnyogymrrroitklatssltaiBlli)tnnnlnnddyygaeeeeeeeeeea---sssssss----)tttft.,l,l
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
418 S.A.A. JASSIM AND M.A. NAJI
applied in human therapy, as described in the review by anti-HSV-2 activity in contrast with a synthetized morin
Havsteen (1983) and are now being increasingly used as pentaacetate that was inactive (Bunyapraphatsara et al.
prototypes for the development of specific drug therapies 2000). This would suggest that free hydroxyl groups are
(Berger et al. 1992). required for anti-HSV-activity, as demonstrated previously
The antiviral activities of bioflavonoids extracted from for the antiviral activity of other flavonoids (Hudson 1990;
medicinal plants have been evaluated (Beladi et al. 1977; Bunyapraphatsara et al. 2000). Such studies clearly indicate
Tsuchiyaet al.1985).Theblackteaflavonoid,theaflavinisa that antiviral activity varies with the compound and the
well-knownantioxidantwithfreeradical-scavengingactivity virus. It is premature to speculate further on chemical
and it was able to neutralize bovine rotavirus and bovine requirements, as the majority of studies that utilized
corona virus infections (Clark et al. 1998). different compounds were inadvertently designed to exam-
The flavonoid chrysosplenol C is one of a group of ine primarily the flavonoids inhibitory activity against viral
compounds known to be a potent and specific inhibitor of enzymes. The mechanisms of binding the flavonoids
picornavirusesandrhinoviruses,themostfrequentcausative extracted from medicinal plants received less attention.
agents of the common cold (Semple et al. 1999). The However,onestageofviralreplicationthatmaybeinhibited
Dianella longifolia and Pterocaulon sphacelatum, were found by flavonoids is viral DNA synthesis. For example, SP-303
to contain flavonoid chrysosplenol C and anthraquinone exhibited strong activity against herpes virus (HSV-1 and
chrysophanicacid,respectively,whichinhibitthereplication HSV-2) (Barnard et al. 1993). Most of the potent anti-HIV
of poliovirus types 2 and 3 (Picornaviridae) in vitro (Semple flavonoidssuchasBA,quercentinandmyricetinhaveshown
et al.1999,2001;Table1).Recently,newflavonolglycoside inhibitory activity not only against the virus-associated RT
– the iridoid glycosides and three phenylpropanoid glyco- butalsoagainstcellularDNAorRNApolymerase(Onoand
sides,namedluteosideA,luteosideBandluteosideC–were Nakane 1990). The fact that the RT plays a very important
isolated from Barleria prionitis and from the roots of the roleincontrollingthereplicationofHIVmakesitoneofthe
medicinalplantMarkhamialutea,respectively,andshownto most attractive targets in the development of anti-AIDS
have potent in vitro activity against RSV (Chen et al. 1998; drugs. The inhibition of DNA and RNA polymerase by
Kernan et al. 1998). In another study, five groups of these flavonoids was extensively analysed to elucidate the
biflavonoids (amentoflavone, agathisflavone, robustaflavone, inhibition mechanism(s) by Ono and Nakane (1990). Once
rhusflavanone and succedaneflavanone) were isolated from again the degree of inhibition also varied depending on the
medicinal plants of Rhus succedanea and Garcinia multiflora, flavonoid.
and exhibited various antiviral effects against a number of Theoligostilbenesisolatedfromtheorganicextractofthe
viruses including respiratory viruses (influenza A, influenza leaves of Hopea malibato was also investigated against HIV
B, parainfluenza type 3, RSV, adenovirus type 5 and and found that a new oligostilbene dibalanocarpol, together
measles) and herpes viruses (HSV-1, HSV-2, HCMV and with one known oligostilbene balanocarpol exhibited only
varicellazostervirus,VZV)(Linet al.1999).Amentoflavone modest HIV-inhibitory activity (Dai et al. 1998).
androbustaflavone,demonstratedsignificantactivityagainst The state of Sarawak, on the island of Borneo, Malaysia,
anti-HSV-1andanti-HSV-2withonlymoderateanti-HSV- is known internationally for its rich rainforests and has
2 from rhusflavanone. A significant anti-influenza A and B attracted the attention of scientists for their potential
activity was achieved by amentoflavone, robustaflavone and medicinal value. Species of the Calophyllum tree produce
agathisflavone. By comparison, rhusflavanone and succeda- active anti-HIV agents. This has intensified interest in the
neflavanonewerefoundtoproduceaselectiveanti-influenza State’s plant resources for scientific research (Chung
type B only. The inhibitory activities against measles and 1996). One approach has been taken to identify novel
VZV were demonstrated with rhusflavanone and succeda- inhibitors of HIV-1-RT by the screening of natural
neflavanone, respectively. In general, none of groups of compounds of the Calophyllum tree. The most extensive
biflavonoids exhibited anti-HCMV (Lin et al. 1999). screening effort, carried out by researchers was on
Baicalein (BA), a flavonoid compound purified from the inophyllum, calanolide A and coumarins isolated from
medicinal plant Scutellaria baicalensis Georgi, has been the terrestrial plants of Calophyllum inophyllum, Cal.
shown to possess anti-inflammatory and anti-HIV-1 activ- lanigerum, Cal. teysmannii latex and Cal. cerasiferum,
ities. BA may interfere with the interaction of HIV-1 respectively. They possess the most interesting natural
envelope proteins with chemokine co-receptors and block RT inhibitor (Taylor et al. 1994; Currens et al. 1996;
HIV-1 entry of target CD4 cells and BA could be used as a Pengsuparp et al. 1996; Spino et al. 1998). It was found
basis for developing novel anti-HIV-1 agent (Li et al. that both inophyllum (Taylor et al. 1994) and calanolide A
2000a). (Currens et al. 1996) represented a novel subclass of non-
Morin is another type of flavonoid group extracted nucleoside RT inhibitor and merited consideration for
from Maclura cochinchinensis that exhibited a powerful anti-HIV drug development.
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
NOVEL ANTIVIRAL AGENTS 419
Morethan200lignanshavebeenidentified,andtheyhave with a purified sample of aloe emodin (the common
a widespread distribution in the plant kingdom, including aglycones which may exist as anthraquinones), prepared
many medicinal plants some of which showed promising from aloin. It inactivated HSV-1, varicella zoster virus,
antiviral activities (Hudson 1990). Recently, a new class of pseudorabies virus, influenza virus in vitro, but not adeno-
lignansisolatedfromLarreatridentates,Rhinacanthusnasutus virus and rhinovirus (Sydiskis et al. 1991).
and Kadsura matsudai showed anti-HIV, anti-influenza and Ingeneral,theaforesaidantiviralactivityisattributableto
anti-hepatitis potencies, respectively. With their important the polyphenols, rosmarinic acid, and the low-molecular
clinical relevance, they do merit further investigation glycoside-forming compounds of chlorogenic acid and
(Gnabre et al. 1996; Kernan et al. 1997; Li et al. 2000b; caffeic acid, and their derivatives (Litvinenko et al. 1975).
Kuo et al. 2001).
Rhus javanica has been shown to exhibit anti-HSV-2
6. PHYTO-THERAPY AND CLINICAL TRIAL
activity and potentiate the anti-HSV activity of acyclovir
in vitro and in vivo (Nakano et al. 1999). Moronic acid, a The use of medicinal plants for the treatment of viral
simple triterpenoid keto acid with antimicrobial activity infections arguably has been based largely on historical and
(Hostettmann-Kaldas and Nakanishi 1979), purified from anecdotalevidence.InIndiatherearethreemajorsystemsof
the herbal extract of Rhus javanica showed oral therapeutic traditional medicine, namely, the Ayurvedic, Siddha, and
efficacy with respect to wild-type HSV- (type1 and type 2) Unani systems that have standard treatments for clinical
infected mice. There is no question about the efficacy of jaundice. These treatments consist of oral administration of
triterpenoids, in particular that of moronic acid, but it is one or more dried plant extracts, in the form of tablets or
not clear if this is due to a direct antiviral effect or whether capsules. Other cultures in different parts of the globe also
this reflects the known healing properties of this compound used plant extracts for the same purpose, e.g. licorice root
in nonviral mucosal lesions (Hudson 1990). One might also Glycyrhiza glabra in China.
suggest a role for interferon, which can be induced by The most common ingredients in the Indian systems are
triterpenoids (Hudson 1990). For example, the triterpene extracts of the genus Phyllanthus of the Euphorbiaceae
acids of Geum japonicum such as ursolic acid and maslinic family.Theplantsarewidelydistributedinmosttropicaland
acid showed potent inhibitory activity against HIV-1 subtropical countries, and have long been used in folk
protease (Xu et al. 1996). It may at least in part be medicine to treat diabetes, kidney and urinary bladder
attributed to interference with virus–cell binding, as in the disturbances,intestinalinfectionsandthetreatmentofviral,
case of triterpene glycyrrhizin (extracted from the licorice bacterial and parasitic infections (Calixto et al. 1998; San-
root Glycyrrhiza radix) (De Clercq 2000). Herpes infec- chez-Lamaret al.1999).Inrecentyearssubstantialprogress
tions are known to be relatively poor responders to onchemicalandpharmacologicalproperties,aswellasafew
interferon (Hudson 1990), so the question of exactly how clinicalstudiesofsomePhyllanthusspecieshavebeenmade.
triterpenoids work against virus infections in vivo remains Thyagarajan et al. (1988, 1990) reported that dried milled
unanswered. Phyllanthus amarus was successful in clearing hepatitis B
The phenolic compound eugeniin (ellagitannin) extracted surface antigen (HBsAg) from blood positive carriers in
fromGeumjaponicumandSyzygiumaromaticumdemonstra- Madras, India. Extracts of Phy. amarus, standardized to
tedclearlyitsanti-HSVactivity(TakechiandTanaka1981; contain20 mgofgeraniinperdose,hadnoeffectonlevelsof
Kurokawa et al. 1998a). A detailed analysis was made of HBsAgorHBeAgwhengiventhreetimesdailytohepatitisB
viral DNA synthesis, and eugeniin was found to inhibit the carriers from NewZealand for aperiod of 2 months(Milne
growth of acyclovir-phosphonoacetic acid-resistant HSV-1, et al.1994).ApowderofthePhy.amarusplantwascompared
thymidine kinase-deficient HSV-1 and wild HSV type 2, with placebo in patients with acute hepatitis B virus (HBV)
andEpstein–BarrvirusDNApolymerase.Oneofthemajor (Narendranathan et al. 1999). Fifty-six patients were rand-
target sites of inhibitory action of eugeniin is viral DNA omizedtoreceiveeithertheplacebo(28cases)orthedrug(28
synthesis (Kurokawa et al. 1998a; Liu et al. 1999). cases). The duration of the disease in the two groups was
DifferentkindsofanthraquinonesfromextractsofRheum compared by Cox’s proportional hazards analysis after
officinale, Aloe barbadensis (Aloe vera), Rhamnus frangula, adjusting for the variables that influence the duration of
Rhamnuspurshianus,andCassiaangustifoliawerefoundtobe jaundice.Theanalysis showedthatPhy.amaruspowder did
quite active against HSV-1 (Sydiskis et al. 1991). In not significantly reduce the duration of jaundice in HBV
contrast, anthraquinones were found inactive against vari- persons.
cella zoster virus, pseudorabies virus, influenza virus, In general the subsequent clinical results concerning the
adenovirus, poliovirus, semliki forest virus, coxsackievirus, use of Phyllanthus species for hepatitis has been conflicting
measles and rhinovirus (Van den Berghe et al. 1986; and this may have much to do with the extract standard-
Sydiskis et al. 1991). Nonetheless, progress has been made ization, species used and location harvested that resulted in
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
420 S.A.A. JASSIM AND M.A. NAJI
differentlevelsofactiveconstituentsinsamplesused(Wang 1987). This virus has often been used as a model for HBV,
et al.1994).Therefore,Wanget al.(1995)testedtheeffects asitspathogenesisinwoodchucksappearstobesimilartoits
of three different Phyllanthus species extracts on the human counterpart. The extract was found to inhibit the
serologic status of 123 patients with chronic hepatitis B. binding of both HBV and WHV surface antigens (HBsAg
Eleven patients received an extract of Phy. amarus (L.) and WHsAg) to their corresponding antibodies. In addition
provided by S.P. Thyagarajan, Madras, India. Forty-two the extract inhibited, in a dose-dependent manner, the
patients received Phy. niruri (L.), gathered from Hainan WHV DNA-polymerase activity in vitro. These reactions
Province in China, and 35 patients received an extract of could explain in part the beneficial effects of the extract in
Phy. urinaria (L.), which had been gathered in Henan patients.Thusantigen-antibody(immune)complexeswould
Province. Thirty-five control patients received no herbal be inhibited, and virus replication, which is normally
therapy.ThepatientsreceivingPhy.urinaria(L.)wereboth restricted to parenchymal cells of the liver, could be
more likely to lose detectable HBeAg from their serum and blocked. The extract found to be tolerated well by mice
morelikelytoseroconverthepatitisBe-antibodystatusfrom following intraperitoneal injections. The extract was tested
negative to positive than were patients given either of the in virus-carrier woodchucks. Intraperitoneal inoculations
other two preparations. The status of patients was not resulted in a gradual but impressive decrease in WHsAg,
changed with respect to HBsAg. which did not subsequently reappear. A similar result was
The literature is rife with contradictory conclusions of seeninanimalsthathadrecentlyacquiredtheinfection;the
anti-hepatitis B activity obtained from a variety of crude antigenconcentrationdroppeddramaticallyanddidnotrise
Phy. amarus extracts. In view of these discrepancies it is againafterstoppingthetreatment.Furthermore,serumviral
hardly surprising (but not explained) that Phy. amarus has DNA-polymeraseactivitydisappearedduringtreatmentand
no value as anti-HBV activity. Notwithstanding, with didnotreappear.Subsequenthistologyoftheliversrevealed
respect to the above reservations it is clear that some of only mild residual pathology in the treated animals, in
thesestudieswouldhavemissedmostofthe(cid:1)window(cid:2)period contrast to the usual severe pathology seen in untreated
for Phy. amarus anti-HBV activity. This emphasizes the carriers.
necessity of looking for concentration-dependant (cid:1)signifi- Thus, although the number of animals tested was quite
cant(cid:2)decreases in virus concentrations. In vitro Phy. amarus small, there was sufficient evidence from these studies to
at 1 mg ml)1 concentration inhibited the secretion of support the belief that Phy. niruri extracts can act
HBsAg for a period of 48 h. The plant suppresses HBV therapeutically against hepatitis B infections to halt the
mRNA transcription by a specific mechanism of action spread of virus and immune complexes and thus allow the
involvinginteractionsbetweenHBVenhancerIandC/EBP restoration of normal liver histology and functions.
alpha and beta transcription factors, which exhibit thera- Hepatitis C virus (HCV) is emerging as a serious
peutic potential in chronic HBV carriers (Lee et al. 1996; worldwide problem. The use of the botanical components
Ott et al. 1997). The disruption by Phy. amarus of HBV glycyrrhizin, catechin, silymarin and phytosterols, and the
polymerase activity, mRNA transcription, and replication antioxidants N-acetylcysteine and vitamin E were reviewed
supports its role as an antiviral agent (Lee et al. 1996). for their efficacy in treating chronic hepatitis and affecting
Phyllanthus niruri was also evaluated for anti-hepatitis liver damage (Patrick 1999). The potential of medicinal
activity (Thyagarajan et al. 1982; Hudson 1990) in more herbs Acacia nilotica, Boswellia carterii, Embelia schimperi,
detail against HBsAg positive sera (i.e. from chronic Piper cubeba, Quercus infectoria, Trachyspermum ammi and
hepatitis B carriers). It was found that the plant extract Syzygium aromaticumextractswereinvestigated in vitro and
(cid:1)inactivated(cid:2) HBsAg, the effect being faster at 37(cid:2)C than at a significant inhibiting activity against HCV protease were
4(cid:2)C. The toxicity studies for these extracts were performed reported (Hussein et al. 2000). More recently, five patients
in cell cultures and in mice and it was shown that the Phy. with chronic hepatitis C were treated for 1 year with
niruri extract had no toxic effect on vero cells or in mice Iscador(cid:3) Spezial (Weieda, Schwabisch, Germany), the
(Hudson 1990). A clinical trial was carried out with Phy. brandnameof anaqueousViscum albumextract.Theyields
niruri extract on a series of HBsAg positive carriers. They in HCV production was reduced about 6–20-fold in two
were given the extract or a placebo daily for 30 days patients along with normalization of liver function and
(Hudson 1990). A 90-day post-treatment has shown that improved life quality and there were no serious side effects
approximately two-thirds of the treated positive individuals (Tusenius et al. 2001).
cleared their HBV antigen. A study that followed indicated The potential of phyto-therapy for treatment of HIV
that in vivo, Phy. niruri eliminated hepatitis B in mammals positive patients was studied and recently in the USA a
within 3–6 weeks (Wang et al. 1995). Another study exam- phase I dose-escalating clinical trial of andrographolide
ined the effects of aqueous extracts of Phy. niruri on the extracted from Andrographis paniculata was conducted in 13
woodchuck hepatitis virus (WHV) (Venkateswaran et al. HIV positive patients and five HIV uninfected, healthy
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x
NOVEL ANTIVIRAL AGENTS 421
volunteers(Calabreseet al.2000).Theplannedregimenwas Terminalia chebula, showed a significant protective effect
5 mg kg)1bodyweightfor3 weeks,escalatingto10 mg kg)1 whenappliedtotheepithelialcellsindividually,butoverall,
bodyweight for 3 weeks, and to 20 mg kg)1 bodyweight for the synergism has indicated that the complete formula
afinal3 weeks.Attheendofthetrialtherewasasignificant maintained antiviral activity at a higher therapeutic index
rise in the mean CD4+ lymphocyte level of HIV subjects than the Terminalia chebula extract alone. In theory at least
after administration of 10 mg kg)1 andrographolide. There there is a possibility of synergism between two or more
were no statistically significant changes in mean plasma components, which together could provide useful antiviral
HIV-1 RNA levels throughout the trial. It was concluded activity (Hudson 1990). This may explain the success of
that andrographolide may inhibit HIV-induced cell cycle many medicinal plant extracts, which could be therapeutic-
disregulation,leadingtoariseinCD4+lymphocytelevelsin ally useful for several apparently unrelated syndromes by
HIV-1 infected individuals. virtue of the synergistic effects of two or more components
ItiswellknownthatHSVisanexampleofaclassiclatent that complement each other in vivo. It is also likely that
viral infection (Wagner and Hewlett 1999). A double-blind, some of the ingredients have restorative/activation func-
placebo-controlled,randomizedtrialwascarriedouttotreat tions, although these have not yet been defined.
66patientswithahistoryofrecurrentherpeslabialis(atleast Achemicalactivationofantiviralactivityfrompomegran-
four episodes per year) using a standardized balm mint ate (Punica granatum L.) rind, Viburnum plicatum (leaves or
cream, Lomaherpan(cid:3) (Natural Medicine Research, flowers), Camellia sinensis (tea leaves) or Acer pseudoplatanus
Emmenthal, Germany), prepared from Melissa officinalis (maple leaves) extracts was reported by using FeSO Æ7H O
4 2
(L.) leaves extract (Koytchev et al. 1999). The cream was (Jassim et al. 1995; Stewart et al. 1998). Furthermore, the
smeared on the affected area four times daily over 5 days. results by PCR revealed that this novel approach to restore
The tested formulation was found to be effective for the functionsofantiviralactivityhaveresultedinthecleavageof
treatment of herpes simplex labilalis without any cytotoxic viral RNA/DNA (Jassim et al. 1995).
sidereactions. Itremains tobefurtherinvestigatedwhether
the extract of Melissa officinalis (L.) leaves also has a
8. ASPECTS OF SYNERGETIC
therapeutic advantage to treat infections of genital mucosa,
COMBINATION OF MEDICINAL PLANTS
and HSV-2, which invades the sciatic nerve ganglia.
WITH ORTHODOX DRUGS FOR
ALLEVIATING VIRAL INFECTION
7. THE EFFECT OF SYNERGETIC
It is observed that patients in the Far East intentionally or
COMBINATION OF MEDICINAL PLANTS
unintentionally are incorporating orthodox medical drugs
IN THE POTENCY OF ANTIVIRAL ACTIVITY
into herbal medicinal preparations for alleviating their
AGAINST SELECTED VIRUSES
illnesses (Chan and Cheung 2000). The rationale for doing
Many medicinal plants/herbs are often prescribed in so is to reduce the side effects of orthodox medical drugs,
composite formulae according to traditional principles of and to produce synergistic effects for better treatment
treatment as an approach to neutralize or reduce toxicity of outcome. It has become apparent that not many of these
poisonous herbs (Xu and Chan 1994). Different combina- combinations are successful. Some of the over-the-counter
tions of plants can cause variations in therapeutic effects. medicinalplantproductscontainingorthodoxmedicaldrugs
Related studies showed that the dry Gingyo-san used in areavailabletothepublic.Inmostcasesthepharmacological
traditional antipyretic medicine for the treatment of the mechanisms of the combinations are not well-studied and
common cold and influenza virus infection has significantly exaggeratedadverseeffectsortherapeuticfailureshavebeen
reduced fever production and suppressed the rise in observed (Chan and Cheung 2000), although successful
interleukin (IL)-1 alpha caused by influenza infection treatments using combination of medicinal plant products
(Kurokawa et al. 1998b). Furthermore, the latter authors with orthodox drugs were also reported. In a clinical study
haveshownthatofthe10crudecomponentsofGingyo-san, Corina et al. (1999) examined the effect of extractants of
SaigaeTataricaeCornusimultaneouslyexhibitedantipyretic Romanianmedicinalplantsincombinationwithacyclovirin
and IL-1 alpha-regulatory activities. In a further study, a the treatment of 52 patients suffering herpetic keratitis.
multicomponentherbalformulaLedretan-96(Laboratoryof Better results andfaster healing of ulceration were obtained
Applied Pharmacology, State Institute, Staten Island, NY, using Actium lappa, Calendula officinalis and Geranium
USA)consistingof23individualcomponentsweretestedon robertianum extracts then with the usual acyclovir treatment
an epithelial tissue culture cell line (Madin-Darby Canine only. Amantadine hydrochloride is an accepted and well-
Kidney, MDCK) for its protective activity against cyto- studied selective inhibitor of influenza virus reproduction.
pathic effects caused by influenza A virus (Badmaev and Recently, a combined application of flowers of Verbascum
Nowakowski 2000). Of the 23 components tested, only one, thapsiforme(Scrophulariaceae)(FlosVerbasciinfusion,FVI)
ª2003TheSocietyforAppliedMicrobiology,JournalofAppliedMicrobiology,95,412–427,doi:10.1046/j.1365-2672.2003.02026.x