Proceedings of a South Asian Conference held in Bangalore (India) from 13 to 15 December
2006, organized by Italian Association Amici di Raoul Follereau (AIFO/Italy) as
part of a joint project under COE (Italy), co-funded by Directorate General of
Development Cooperation (DGCS) of Italian Foreign Ministry.
The conference was held in Bangalore from 13 to 15 December 2006. Participants for
this conference came from Bangladesh, Bhutan, India, Nepal and Sri Lanka. The
conference in India was organised in collaboration with International People's Health
University (IPHU) of the People's Health Movement (PHM).
APPROACHES TOWARDS THE PRECLINICAL TESTING
AND STANDARDIZATION OF MEDICINAL PLANTS
T. J. BIRDI, S. BRIJESH , P. G. DASWANI, FOUNDATION FOR
MEDICAL RESEARCH, INDIA
Before the introduction of modern medicines, disease treatment was entirely
managed by herbal remedies. It is estimated that about 80% of the world
population residing in the vast rural areas of the developing and under developed
countries still rely mainly on medicinal plants. Medicinal plants are the only
affordable and accessible source of primary health care for them, especially in the
absence of access to modern medical facilities. Studies reveal that there are more
traditional medicine providers than the allopathic providers especially in the rural
areas (WHO 2002).
The use of traditional medicine has increased in developed countries also, mainly
due to the failure of modern medicine to provide effective treatment for chronic
diseases and emergence of multi-drug resistant bacteria and parasites. The
adverse effects of chemical drugs, questioning of the approaches and assumptions
of allopathic medicine, their increasing costs and greater public access to
information on traditional medicine has also led to an increase in interest in
alternative treatments (WHO 2002). Plant extracts have become a source of hope
as a wide group of medicinal plant preparations are available that have been used
over the centuries almost exclusively on the basis of empirical evidence. Hence, it
has become necessary to revisit the importance of these herbal medicines.
Increasing interest by multinational pharmaceutical companies and domestic
manufacturers of herbal-based medicines is contributing to a significant economic
growth of the global medicinal plants sector. However, a large proportion of
medicinal plant research is focused on nutraceuticals, chronic and metabolic
disorders (diabetes, cardiovascular, etc.) and other diseases like HIV/AIDS,
malaria, etc. Whereas, the common diseases of resource poor
communities such as diarrhoeal diseases and acute respiratory tract
infections (ARI) are often not addressed. Moreover, unlike the rural
communities who use fresh/dried plant material or their crude extracts, the
industry lays importance on isolation of active principles or standardized fractions
since crude extracts are not patentable. However, it is often seen that a crude
extract is more active compared to the isolated active fractions e.g. Cirriformia
tentaculata loses its activity upon fractionation with hexane (Kicklighter et al.
It is generally believed that standardization of the plant material is not required
when used by the rural communities for their primary health care. But, regardless
of whether the medicinal plant is to be used by local communities or by industry, a
systematic approach is required for a plant identified from traditional medicine, as
is done in modern medicine. It is necessary to focus on all aspects of medicinal
plant research: from cultivation, ethno-pharmacology, utilization, isolation and
identification of active constituents to efficacy evaluation, pharmacology, safety,
standardization, formulation and clinical evaluation. Animal toxicity studies are
required to establish the potential adverse effects.
Artuso (1997) has outlined the entire process which includes formulating an
appropriate strategy and he estimates that the entire process would take more
than 10–20 years. This approach is very demanding since there is an estimated
250,000 species of higher plants present on this earth (Ayensu and DeFilipps,
1978). However, this scenario would change with use of the high throughput
advanced screening methods that are available today. Another approach than
can prove to be a highly productive and cost effective in development
of safe, effective and acceptable therapeutic agents is reverse
pharmacology which is based on the documented therapeutic effects of
plants in ancient texts (Vaidya, 2006).
This paper will discuss the approaches that need to be considered while studying
medicinal plants. It focuses on aspects of the medicinal plant research: from
collection of plant material, to efficacy and safety evaluation through preclinical
studies and phytochemical standardization.
SOURCE OF PLANT MATERIAL
The prominent mode of obtaining medicinal plants is wild harvesting and most of
the industrial requirement is still met through wild collection (Lange 1998).
Though many medicinal plants are commonly available in the wild and can be
freely harvested, uncontrolled collection and sale of large quantities of plant
material from the forest can lead to destruction of many forest plants especially
the endemic species that have a restricted geographical distribution. For example,
medicinal plants like Curcuma caesia, Rauwolfia serpentina were reported to
occur abundantly (IUCN 1994) in central India. However, due to their growing
economic importance and rampant harvesting, these plants have now been
categorized as critically endangered (Prasad and Patnaik 1998). The present
deteriorating condition of medicinal plants in forests needs immediate attention
not only for conservation but also for propagation. Countries can protect their
biodiversity in medicinal plants by working with industry towards monitoring and
maintaining controlled non-destructive harvesting with habitat management.
Cultivation of medicinal plants would seem as a commercially attractive option to
companies because they have greater control over supply of the plant material and
it is easier to control post-harvest treatment. Moreover, cultivation can reduce the
dependence on collection of plants from wild and thus have the potential to save
wild populations and conserve their genetic diversity.
Cultivation in kitchen gardens can lead to easy availability of medicinal plants and
can be an effective means of self reliance in supply of these plants for rural
communities. Communities can cultivate plants with multiple uses such as those
with both medicinal and commercial value (e.g. guava) or those, which are
indicated against multiple disease conditions (e.g. Nirgudi for worms, cough,
aches and pains; Adulsa for wet and dry cough; guava for viral/bacterial
diarrhoea, swollen gums and kidney infections) (Satyavati 1987).
The feasibility of cultivating medicinal plants would, however, depend on a
number of factors such as the ability of the species to thrive under mono culturing.
The economic viability will depend on the demand and market prices. Moreover,
cultivation of medicinal plants requires intensive care and management and the
conditions and duration required can vary depending on the quality of the
medicinal plant material required. Risks of contamination from pollution by
hazardous chemicals should be avoided. Moreover, introduction of non-
indigenous plant species into cultivation can lead to detrimental consequences on
the ecological balance of the region (Sharma et al. 2005).
A point that needs specific consideration is that cultivated plants are sometimes
considered qualitatively inferior to the wild collections. The medicinal properties
in plants are due to the combinations of secondary products. Different plants
would have different combinations of these secondary products that would often
be taxonomically distinct in individual plants resulting in unique medicinal
properties (Wink 1999). Secondary metabolites that are generally produced for
defense against predators, pathogens or competitors or for protection/adaptation
to environmental stress related to changes in soil conditions, temperature, water
status, light levels, UV exposure, and mineral nutrients in their natural habitats;
and are responsible for most of the biological activities. Therefore, the
secondary metabolites may not be expressed in optimum quantities
when cultivated under optimum conditions to obtain better vegetative
yields. For example, the wild ginseng roots are 5-10 times more valuable than
cultivated roots because the cultivated roots lack the characteristic shape of wild
roots (Robbins 1998). These beliefs were also reflected in the conclusion reached
through research on Arnica montana by the herbal company Weleda (Ellenberger
1998). Analysis of the biochemical properties of the cultivated plants showed
differences when compared with wild plants that grow in poor meadows with
acidic soils in mountainous areas of Europe. The rhizomes of the cultivated stocks
had lost much of Arnica’s characteristics, reducing its commercial potential.
SELECTION OF PLANTS
As per WHO guidelines (WHO 2003), the plant selected for collection should be
taxonomically same as recommended by the national pharmacopoeia or other
related documents. If a new plant is being selected for collection then it should be
properly identified and documented. The botanical identity, scientific name
including genus, species, subspecies or variety and family of the plant should be
recorded. If available, the local name should also be verified. Complete
taxonomical identification is an important factor during selection as taxonomy of
the plant species can play an important role in their biological activity. This was
observed in our study with two varieties of Zingiber officinale wherein one variety
showed immune enhancing properties while the other did not (unpublished data).
Information regarding environmental conditions, such as topography, geology,
soil, climate and vegetation at the collection site, should be obtained. Information
such as the geographical distribution of the plant, its abundance, whether it is
threatened or endangered, shrub/fast growing tree etc should also be obtained. It
is of immense importance that a voucher specimen be deposited in a national or
regional herbarium for authentication and further consultation by other
Several reviews have described approaches that can be used for selecting plants of
potential therapeutic interest (Verpoorte 2000, Phillipson and Anderson 1989,
Kinghorn 1994, Vlietinck and Vanden Berghe 1991, Farnsworth 1996, Farnsworth
and Bingel 1977). In general, the search for the medicinal plants can follow three
main routes: random, ethno (including ethnobotanical, ethnomedical and
ethnopharmacological) and ecological search (Fabricant and Farnsworth 2001).
Random search is extremely laborious and the success rate could be very low
(Basso et al. 2005). Nevertheless, important drugs such as taxol, derivatives of
camptothecin and homoharringtonine have been discovered by the National
Cancer Institute (NCI) in collaborations with the United States Department of
Agriculture (USDA) using this method (Cragg et al. 1999).
The ethnobotanical, ethnomedical or ethnopharmacological approach uses
information obtained from ethnobotanical survey such as the geographical
distribution of the plant, its abundance, whether it is threatened or endangered,
shrub/fast growing tree, easily cultivable, easily identifiable (with minimum
varieties) etc. Information such as the season of collection, parts that are used and
whether those parts are seasonal/replenishable and if there is any reported
toxicity, are also required. The information can be obtained from traditional
medical practitioners and other people such as village elders and local women who
are traditional users of medicinal plants. Undertaking of an ethnobotanical survey
should be by a team of local botanists, traditional healers and medical
practitioners. While the traditional healers would identify medicinal plants for
treatment of different diseases, the botanist can carry out appropriate taxonomical
and botanical characterization of these medicinal plants, whereas the medical
practitioners would help in proper identification of the disease conditions (e.g.
differentiate between muscle pain and pain due to arthritis) and help in
understanding whether a treatment is curative or is alleviating the symptoms only
or whether it is a placebo effect.
Frequency of quote is an important indicator of the usage of the plants by the
community. However, information obtained from the community may not always
be reliable. It is possible that people may quote a particular plant more frequently
since it is easily available, easily recognizable or resembles a certain disease
feature e.g. seeds of Bixa orellana, which have a bright red arillus, are used in
herbal mixtures used for treating bloody diarrhoea (Kufer et al. 2005). People may
also quote plants about which they have gained information from personal
communication or books. In addition, publications on medicinal plants are often
compilations from other texts and seldom from personal experience, making
Ethnomedical information is available from ancient texts of different systems of
medicines such as Ayurveda, Unani, Kampo, and traditional Chinese medicine.
However, while using the ancient texts, one must consider the fact that the plants
may have evolved over a period of time resulting in changes in their
phytochemical composition and hence their medicinal properties and therefore
validation is required.
Nevertheless, the success rates of the ethno-based approaches are substantially
higher than those of random screening since the continued use of crude
preparations are, in fact, comparable to small scale clinical trials. Tests carried out
at the NCI for antineoplastic activity using this approach yielded positive activity
in the order of 2 to 5 times higher than random screening (Lewis and Elvin-Lewis
Plants with medicinal properties can also be selected using an ecological approach.
The absence of predation in areas infested with herbivores, for example, can
indicate the presence of toxic compounds. Selection can also be based on an
approach called zoopharmacognosy, a variation to the ecological approach, which
proposes the selection of plant species regularly ingested by animals, mostly
primates for reducing pain, microbial or worm infestations (Berry et al. 1995).
It has to be specifically understood that there are certain differences in approaches
when selecting plants for an industrial or a rural application. The rural community
requires medicinal plants for their primary health care and hence focuses more on
selection of plants for treatment of common diseases such as diarrhoea, malaria,
pneumonia, wound infections, etc. On the other hand, pharmaceutical industry
requires medicinal plants for formulation of herbal drugs for commercial gain and
hence focuses more on urban problems such as metabolic disorders, chronic
diseases, and multi-drug resistance among infectious pathogens. Whether for
rural community or for industrial application the selection of plant should be
based on its therapeutic efficacy in terms of its effect on the causative agent or on
the host. From the rural perspective, since the understanding of disease in terms
of causative agents is not possible in the community, it is important that the plant
formulation should address the common causative agents resulting in a given
symptom e.g. diarrhoea which is caused by various infectious agents including
bacteria, viruses and protozoa. The plants selected for utilization by rural
communities, should be able to control the respective diseases or else at least act
as a stop gap until further medical aid becomes available. Moreover, these plants
should be easily available so that the users of these medications can become self
COLLECTION OF MEDICINAL PLANTS
Good collection practices are necessary for the long term survival of wild
populations and their habitats. WHO guidelines (WHO 2003) can be followed
while collecting medicinal plant materials.
Medicinal plant materials should be collected in the proper season so
as to ensure the best possible quality of both the starting material as well as the
finished product. Seasonal variations can affect the chemical composition of the
plants and thus its biological activity. This was demonstrated in one of our studies
where the decoctions of Psidium guajava leaves collected in two different seasons
showed variable antibacterial activity against six bacterial strains, the November
collection being more active than the March collection (unpublished data). In
most cases, maximum accumulation of chemical constituents occurs at the time of
flowering which then declines at the beginning of the fruiting stage (Mendonca-
Filho 2006). The time of harvest should also depend on the plant part to be used
since it is well known that depending on the plant species the level of biologically
active constituents can vary in different parts at different stages of the plant
growth and development. For example, Kursar et al. (1999) found that younger
leaves of tropical rainforest plants contained secondary metabolites that were
either present in very little quantities or totally absent in matured leaves. The
extracts from these younger leaves showed better biological activity when tested
for anticancer activity or activity against Bacillus subtilis and Artemia salina
(brine shrimp). It also applies to other components in the plant material such as
the toxic components. Climatic conditions, e.g. light, rainfall, and temperature
(including daytime and nighttime temperature differences) also influence the
physical, chemical and biological qualities of medicinal plants. The water and
temperature stress related increase in the content of active constituents such as
the total phenolic compunds was shown by Nacif de Abreu and Mazzafera (2005)
in Hypericum brasilience. Hence the best time of collection should be determined
according to the levels of the biologically active constituents rather than the
Information such as the correct plant parts that are used (roots, leaves, fruits, etc.)
and whether these parts are seasonal or replenishable should be obtained. The
collection levels and the collection practices should also be known before initiating
collection. It is necessary that the collection practices employed should be non-
destructive. For example, while collecting roots, the main root should not be cut or
dug up or while collecting bark, the tree should not be girdled or completed
stripped of its bark. Parts that are not required or are decomposed and any foreign
matter such as soil or toxic weeds should be removed during collection.
Collection of medicinal plants should not be done from places that are prone to or
close to sources of contamination such as areas where high levels of pesticides or
other possible contaminants are used or found e.g. roadsides, drainages, mine
tailings, garbage dumps and industrial facilities which may produce toxic
chemicals or active pastures that may lead to microbial contamination. Quality
control ensures that the plant material is not contaminated with microbes,
pesticides, heavy metals or other toxic agents (Mendonça-Filho 2006) and that the
final product is of consistent high standard.
Rapid and safe transportation of the collected plant materials should be arranged
in advance. Handling of the plant material such as cleaning, drying and storage,
should be carried out by trained personnel.
PROCESSING OF PLANT MATERIALS AND THEIR PREPARATION
Preliminary processing of the plant material that can be done include elimination
of undesirable materials and contaminants, washing to remove soil, sorting and
cutting. It would be advisable to dry the plant materials prior to transportation if
the processing facilities are located away from the collection sites. Cross
contamination of the different collected plants or plant parts should be avoided
during transportation. The plant materials should be protected from conditions
that may cause deterioration such as rain, moistures, etc during or after
transportation till the processing begins. The plant material that needs to be used
fresh should be delivered as quickly as possible to the processing facility to prevent
microbial fermentation or thermal degradation.
Specific processing methods are often required, to reduce drying time, to detoxify
the inherent toxic constituents, to reduce side effects or to enhance therapeutic
effects. For example, the methods and temperatures used for drying may have a
considerable impact on the quality of the resulting medicinal plant materials.
Shade drying is the preferred method for drying plant material since it can
maintain or minimize loss of color of leaves and flowers; and the lower
temperatures can prevent the loss of volatile substances in the plant materials
(Ibanez et al. 2003, Bartram 1995). However, plants can be dried in a number of
other ways: in drying ovens/rooms and solar dryers, by indirect fire, baking,
lyophilization, microwave, or infrared devices. Pre-selection, peeling the skins of
roots and rhizomes, boiling in water, steaming, soaking, pickling, distillation,
fumigation, roasting, natural fermentation, treatment with lime and chopping are
some of the common processing practices. All processed medicinal plant materials
should be protected from contamination and decomposition as well as from
insects, rodents, birds and other pests, and from livestock and domestic animals.
Medicinal plant preparations can be prepared in several ways that usually vary
based upon the plant being used, and sometimes, the condition for which it is
being used. These preparations can be in the form of infusions, decoctions,
tinctures, macerations, fresh juices, etc. Some other methods include hot baths,
powdered plants, steam inhalation and even aromatherapy. Adherence to the
method of preparation as mentioned in the ancient texts or by
traditional practitioner is necessary depending on the form of preparation
or the plant used as they may hold important information for obtaining an
effective herbal preparation. A juice of a plant may be recommended instead of
decoction/powder if the active ingredients are volatile or thermo labile e.g. fresh
leaf juice of Adhatoda vasica is used for reducing blood glucose level of diabetic
patients (Ahmad et al. 2007). Sometimes, it is possible that due to the difficulty in
preparation of the extracts and the time required, whole fresh material (e.g.
leaves) or dried powder is used instead of the required extract for treatment. This
may lead to potential toxicity which would otherwise not be observed due to the
elimination of the toxic constituent during extraction. In this context, an example
that can be cited from our study is the extraction of negligible amounts of the toxic
component karanjin from the leaves of Pongamia pinnata in the aqueous
decoction (Brijesh et al. 2006).
The medicinal property of plants is closely related to the different classes of
phytoconstituents (such as essential oils, alkaloids, acids, steroids, tannins,
saponins, etc.) present in the plant, each of which would have a preferred effective
method of extraction, facilitating maximum yield in the preparation. For example,
preparing a decoction might extract a group of anti-inflammatory plant steroids to
treat arthritis and yet when the same plant is prepared in alcohol different
antibacterial alkaloids are extracted
Storage can also influence the physical appearance and chemical quality of plant
materials and hence it is necessary to maintain appropriate storage conditions so
as to increase their shelf life. It is customary to store the plant material in dried
form since preparations like decoctions/infusions can only be stored for a few
days. Dried plant materials can be stored in whole, crushed or powdered forms in
storage conditions that include use of cloth bags, clear glass bottles and plastic.
Plant materials that are used fresh should be stored under refrigeration, in jars or
sandboxes, or using enzymatic or other appropriate conservation methods.
However, they should be used as quickly as possible to avoid microbial
contamination. Shelf life of plant material is usually ignored due to the general
belief that the plant materials do not have an expiry date, however, dried plant
materials usually retain their activity for about six months only. It is observed that
the powdered plant material degrades faster than the whole or crushed plant
material (unpublished data). Different types of plastics can be used which prevent
absorption of moisture and oxidation of the plant material by preventing the
exchange of gasses to increase the shelf life of the plant material.
Biological screening is necessary to provide a scientific basis for validating the
traditional utilization of medicinal plants. A great number of screening programs
are ongoing worldwide for new plant based bioactive molecules. Several
researchers have worked on medicinal plants with activity against different
ailments. Preclinical pharmacological studies and randomized clinical trials form
an important part of the biological screening of medicinal plants. Preclinical
studies usually serve to verify the data on mechanisms of action reported in
animals or humans. However, a pharmacological effect observed in vitro or in
animal models, for both safety and efficacy needs to be reconfirmed by clinical
studies and the information obtained from the preclinical studies can form the
basis for further clinical trials. (Lipsky and Sharp 2001, Bleicher et al. 2003, Dove
2003, Kenakin 2003, Knowles and Gromo 2003, Verkman 2004).
Clinical studies are necessary to confirm the pharmacological effects of medicinal
plants before they can be integrated into conventional medical practice. Well-
established, randomized controlled clinical studies facilitate the acceptance of
herbal medicines in different regions and in people with different cultural
traditions. This would be especially true in case of some unrelated effects of
therapy contributing to efficacy that may be difficult to measure pre-clinically.
These studies should be carried out on the basis of information obtained from
official national compendia and relevant literature or traditional medical
practitioners. The general principles for the clinical studies that apply to
conventional drugs should be followed when testing a new herbal preparation, a
new indication for an existing formulation, or a significantly different dosage form
or route of administration (WHO 2000). Well recorded case reports can
contribute towards useful information at such times and put forward new
hypothesis and stimulate further study (Morris 1989). However, double blind
clinical trials may not be required when an extensive and detailed database of case
studies is available. Such a database is especially important when a particular
treatment is individualized.
The methods and guidelines used for clinical validation of modern medicines must
be applied to herbal products even though the latter has a holistic approach to
treatment. However, conventional concepts of clinical research design may be
difficult to apply when using clinical research to evaluate various systems and
practices of traditional medicine (WHO 2000). This could be due to the fact that
herbal remedies are individualized (each person has certain predispositions to
disease and susceptible to factors like environment, genetics, dietary and lifestyle)
therapies and hence depend on the proficiency (including the skills and
experience) of medical practitioners.
Clinical studies, in some cases, must be adapted to deal with the specifics of herbal
medicines. Single-case studies, as per the theories and concepts of traditional
medicine, for the evaluation of efficacy and randomization can allow for the
individualization of treatments. Methods such as randomization and use of
placebo may not always be possible. Patients previously treated with plant
preparation having a characteristic organoleptic property cannot be randomized
into control groups or a placebo may not be possible when the plant preparation
has a strong smell or taste as is the case of certain essential oils.
The number of patients required for undertaking clinical trial of medicinal plants
is large not only since the study design needs to be adequate and statistically
appropriate but also to cater to the control, confounders and placebo groups to
provide sufficient evidence for judging efficacy of the plant under study. The
increase in patient number also increases the time commitment and the expenses
Therefore only a limited number of plants can be subjected to clinical trials.
Hence, it is essential to undertake appropriate preclinical testing to short list
plants for clinical evaluation.
Preclinical testing helps in collection of important efficacy and safety data before
clinical trials can be carried out. The preclinical evaluation and authentication of
medicinal plants involves documentation and testing of their pharmacological
efficacy in vitro (cells) and in vivo systems and studies of toxicology, specificity,
biopharmaceutical properties and drug interactions.
The preclinical studies help in determining the therapeutic effect of the plant in
question and also elucidate the efficacy and/or the mechanism of action including
cell interactions, cell-environment interactions, intracellular activity, and genetic
studies. Plants with novel and/or multiple mechanism(s) of action can also be
identified. The advantage of these studies is that one can easily study and compare
the efficacy of different plants in a cost effective manner and design rational drug
combinations. This requires proper designing of screening assays that have
significant impacts on the outcome of the overall drug discovery process. The
selected assay should be able to mimic the in vivo dynamics as far as possible with
high sensitivity and specificity.
The basis for designing a screening assay is the identification of valid target. An
estimated 30-40% of experimental drugs fail due to an inappropriate target
(Butcher 2003) and hence it is important to develop new screening assays with
newer and more appropriate targets. It is crucial to establish the role of the target
in question in the cause or symptoms of a disease (Williams 2003).
Pharmacological manipulation of the target should consistently lead to desired
phenotypic changes. The desired changes must also be reproducible in at least one
relevant animal model (Drews 2003). Emphasis has to be placed on assessment of
assay quality and validation of the parameters being used.
Assay formats employed in screening can be either cell-based or biochemical.
Though the logistics of cell-based assays are more challenging than with
biochemical assays due to requirement of significant investments in cell culture
infrastructure (Moore and Rees 2001), the current trend in drug discovery is
clearly shifting towards cell-based assays. Cell-based screening has multiple
advantages. It can provide biologically more relevant information on the nature of
the activity (Moore and Rees 2001, Johnston and Johnston 2002). In addition,
information regarding cellular membrane permeability and cytotoxicity can also
Approaches that are commonly used for studying the pharmacological effects of
medicinal plants are: use of single bioassay for screening multiple plants and use
of multiple bioassays for studying single plant. The latter approach has been used
widely for metabolic diseases. Unfortunately, when screening plants for infectious
diseases the assay system is often limited to testing for antimicrobial activity.
However, this approach is not always appropriate. Plants can exhibit their efficacy
against infectious diseases by mechanisms other than antimicrobial activity. When
screening plants for immuno-enhancing properties, often synthetic antigens and
immunological assays are used which do not have any biological relevance to
disease(s) in question.
The importance of using relevant and where necessary multiple bioassays for
screening medicinal plants for infectious diseases is highlighted in our studies.
Decoctions of two plants viz. Cyperus rotundus (unpublished data) and P. pinnata
(Brijesh et al. 2006) were screened for their antidiarrhoeal activity. The different
bioassays used were: antibacterial, antigiardial and antirotaviral assay; adherence
to and invasion of bacterial pathogens to epithelial cells; ganglioside monosialic
acid-enzyme linked immunosorbent assay for E. coli heat labile toxin (LT) and
cholera toxin (CT); and suckling mouse assay for E. coli heat stable toxin (ST).
These assays in addition to the antimicrobial action screened the plants for
colonization (adherence and invasion) and enterotoxins – the two most important
features of diarrhoeal pathogenicity and thus define the possible mechanism(s) of
action of C. rotundus and P. pinnata in infectious diarrhoea. It was observed that
though both plants did not have marked antimicrobial action, they were effective
antidiarrhoeal agents with different mechanism(s) of action. CT and LT were
affected though there was no effect on ST. P. pinnata inhibited bacterial
adherence to epithelial cells whereas C. rotundus inhibited both bacterial
adherence to and invasion of epithelial cells. These results showed that the
antidiarrhoeal activity of the plant could be due to its action on various
parameters other than just the antimicrobial activity. Different plants can show
activity in different assays determining their usefulness in different forms of
diarrhoea. The study highlighted the necessity of looking at different parameters
and not just concentrating on singular assays like antimicrobial activity for
determining the biological efficacy of plants.
Limitations of preclinical studies
1. Suitable pharmacological models have not yet been developed for many
common diseases with unknown, or multi-factorial origins (Hamburger and
2. Some compounds which show good activity in vitro may be metabolized in
vivo into inactive metabolites. Alternatively, extracts may only show in vivo
activity due to the metabolism of inactive compounds into active forms
3. The pharmacological investigation of drug interactions in multi-compound
preparations is difficult due to the presence of constituents from several plants
where some plants may show less specific activity and some plants may have
been added to reduce the toxicity of the more therapeutically effective plants
(Taylor et al. 2001).
4. Some of the most common side effects are difficult to recognize in animal
models e.g. nausea, nervousness, lethargy, heartburn, headache, depression,
5. Extrapolation of in vitro dose to in vivo animal models and humans is difficult.
Toxicological evaluation of medicinal plants has often been neglected since
prolonged and apparently uneventful use usually is considered as a testimony of
its safety. However, a history of traditional usage is not always a reliable guarantee
of safety since it is difficult for traditional practitioners to detect or monitor
delayed effects (e.g. mutagenicity), rare adverse effects, and adverse effects arising
from long-term use (Ernst 1998) such as for food supplements and nutraceuticals
e.g. Glycyrrhiza glabra, which is used for conditions like bronchitis and peptic
ulcers causes not only hypertension, weight gain and hypokalaemia but also low
levels of aldosterone and anti-diuretic hormone on excessive or prolonged usage
(Newall et al. 1996). The use of herbal preparations may also lead to
hypersensitivity reactions ranging from transient dermatitis to anaphylactic shock
(Ernst 1998). Many widely used medicinal plants have been implicated as possible
causes of long-term disease manifestations such as liver and kidney diseases. The
widespread use of Scenecio, Crotalaria and Cynoglossum has been implicated in
the occurrence of liver lesions and tumours, lung and kidney diseases in certain
areas of Ethiopia (Addae-Mensah, 1992).
The absence of any such documentation, however, does not automatically rule out
the possibility of toxicity. It is possible that the plant treatment taken up for the
clinical trials may lead to some unanticipated/unknown/unrelated side effects e.g.
Psoralea corylifolia Linn. which is used for treating conditions like psoriasis,
leucoderma, and non-healing ulcers and wounds is known to cause
hepatosplenomegaly in experimental animals (CHEMEXCIL 1992). Hence it
becomes necessary to carry out toxicological studies, both short term and long
Toxicological studies should include tests such as acute, subchronic and special
toxicology that are impossible to detect clinically such as immunotoxicity,
genotoxicity, carcinogenicity and reproductive toxicity (Remirez 2006). These
tests help in the identification of possible target organs involved and the toxic
symptoms. Studies of special toxicology such as carcinogenesis are very important
if the plants contain compounds with known mutagenic or carcinogenic activities
(Chanabra et al. 2003).
Phytochemical studies of the plant preparations are necessary for standardization,
which helps in understanding the significance of phytoconstituents in terms of
their observed activities. Phytochemistry also helps in standardizing the herbal
preparations so as to get the optimal concentrations of known active constituents,
and in preserving their activities.
Standardization can be carried out by obtaining a chemical fingerprint/profile or
through bioactivity guided fractionation. Chemical fingerprints through
chromatographic techniques are more commonly used for standardization and are
obtained in terms of one or more marker compounds. It would be ideal to use the
active constituent in the plant as the marker compound; however, in cases where
active constituents are not known the marker compound can be independent of
the therapeutic activity. Furthermore, the plant extracts can also be standardized
to class of compounds e.g. ginsenosides in ginseng, kava lactones in kava, or
oxindole alkaloids in cat’s claw (Roman 2001). Such an approach would be suited
to situations where though the active constituents are not known they are
expected to belong to a particular class of compounds.
According to European Medicines Agency guidelines (EMEA 2005), quantification
of substances with known therapeutic activity or markers is obligatory. As per the
European Pharmacopoeia, marker compounds should be characteristic or unique
for the herbal material or herbal preparation, have an established chemical
structure, be present in the starting material as well as the finished product in
sufficient amounts, be accessible to quantification with common analytical
methods such as high-performance liquid chromatography (HPLC) or high-
performance thin layer chromatography (HPTLC), be sufficiently stable, and be
commercially available or able to be isolated by the company in its own laboratory.
Thin layer chromatography (TLC) and HPLC are the most commonly used
methods for obtaining chemical fingerprints and identification of the crude plant
extracts. However, there are several possibilities that may arise while using these
techniques for standardizing the crude extracts. It is possible that the plant
material collected from the same plant in two different seasons can show different
phytochemical fingerprint and therefore different biological activity or two plants
with identical taxonomy collected under same environmental conditions can show
different phytochemical fingerprint but similar biological activity. In such
situations comparisons of the phytochemical profiles as an indicator of important
constituents can act as a shortcut for identifying biologically active constituents.
DNA fingerprinting is another technique, which though still in its early years,
seems to be of immense potential in identification of medicinal plants, particularly
when profiling the genotypic differences (Vasudevan 2004). Apart from
identifying these genetic variations, it can also aid in identification of germplasms
of important or endangered plants for future cultivation or conservation.
Use of isolated compounds can result in better biological activity due to higher
concentrations, but it can also lead to potential side effects e.g. the active
constituent conessine isolated from Holarrhena antidysenterica, a plant
commonly used by Ayurvedic practitioners in the treatment of diarrhoea, was
found to be toxic to the central nervous system (CHEMEXCIL 1992). More recent
studies have also indicated at reduced biological activity with isolated active
constituents compared to crude extracts (Kicklighter et al. 2003).
The efficacy of crude extracts may be due to the synergism between the different
active constituents that may be present in the extract. Synergism can lead to
better activity as well as decrease in potential toxicity of some
individual constituents. Synergism can be due to the individual action of
different constituents present in the extract at multiple target sites/parameters.
This was observed in a study conducted by us on the antidiarrhoeal activity of P.
guajava (unpublished data). It was seen that the decoction of the dried leaves of
P. guajava showed antidiarrhoeal activity by showing antimicrobial activity
against five out of the six bacterial strains tested, Giardia lamblia and rotavirus. It
inhibited adherence to and invasion of the bacterial pathogens to the epithelial
cells. It also inhibited production and action of enterotoxins such as E. coli labile
toxin and cholera toxin. These results suggested that the different constituents
present in the decoction could be individually responsible for the different
activities observed against these parameters. Another mechanism by which these
constituents can show synergism is by having an additive effect against a single
target site/parameter. It was observed that the decoction of P. guajava leaves was
synergistically more active at a dilution of 1% than at 5% against the bacterial
adherence to epithelial cells. This effect could be due to the fact that the ratio of
constituents achieved at 1% was more optimal for activity than at 5%.
The modern analytical and isolation methods that are used for screening and
isolation of plant constituents are the chromatographic and spectroscopic
techniques such as TLC, thin layer electrophoresis, HPLC, nuclear magnetic
resonance, HPTLC etc. These techniques have proved very useful in isolation and
proper identification of the active constituents in the plant extracts.
It is necessary to devise simple techniques for standardization that can be used by
the rural community for identifying plants with good biological activity. Use of a
class of compounds, as mentioned earlier, as a surrogate marker is a potential
approach which can be used by the communities to identify plants with good
biological activity. For example, instead of a single polyphenol, tannins can be
used as a surrogate marker, which schoolchildren can estimate easily in their
laboratories. This approach has been attempted by us in collaboration with the
Foundation for Research in Community Health in their field project at Parinche,
Maharashtra. Tannin levels were estimated in aqueous decoctions of five different
collections of P. guajava leaves and compared them with their respective activities
against action of cholera toxin. It was observed that the decoctions with
∼10.5mg/ml tannin showed good activity with no further significant increase in
activity at higher tannin concentrations. However, below this level the activity was
significantly poorer (unpublished data). Hence, 10.5mg/ml tannin level may be
taken as a cut-off value for differentiating a P. guajava plant with good activity
from that with poor activity.
With the tremendous increase in the global use of medicinal plants, several
concerns regarding the efficacy and safety of the herbal medicines have also been
raised. Hence it has become necessary to standardize the efficacy and safety
measures so as to ensure supply of medicinal plant materials with good quality.
After proper botanical identification, WHO guidelines should be followed for
collecting plant material in terms of proper season and climatic conditions, correct
plant part, practices that are non-destructive and would prevent contamination
from soil, toxic weeds or microbes. Post collection, appropriate processing and
storage conditions are required to reduce drying time, detoxification to reduce
side effects and to enhance therapeutic value of the plant material and to improve
its shelf life.
Preclinical biological screening is important not only for establishing the
therapeutic efficacy of the medicinal plants but also to validate their historical
utilization by traditional healers and herbalists. This is especially important since
the plants may have evolved over a period of time leading to changes in their
chemical composition and thus the biological activity. Preclinical studies allow
comparison of efficacy of different plants and help in designing of rational drug
combinations. Toxicity studies need to be done even if the plants have a history of
long usage or do not have any documented toxicity, as they can lead to some
unrelated toxicity especially during long term treatment for chronic conditions or
when used as food supplements and nutraceuticals.
Phytochemical standardization for identification of the plant material can be
carried out by obtaining chemical fingerprint through chromatographic
techniques in terms of a known marker compound or through bioassay guided
fractionation and/or DNA fingerprinting techniques. Chromatographic and
spectroscopic techniques have proved very useful in isolation and proper
identification of active constituents in the plant extracts.
Though the pharmaceutical industry has been focusing on standardization of plant
materials when manufacturing herbal drugs, it is generally believed that
standardization is not required when used by rural community for their primary
health care. However, irrespective of whether the plant is being used by the
industry or by the rural community standardization of plant material is required
right from collection of the plant species to the formulation of the herbal drug. It is
necessary so that it minimizes batch-to-batch variation and meets standards of
quality, safety, and efficacy.
The Foundation for Medical Research, 84A, R. G. Thadani Marg, Worli, Mumbai –
400018, India. Email: email@example.com
The financial assistance of Sir Dorabji Tata Trust, Sir Ratan Tata Trust and
Department of Science and Technology, Ministry of Science and Technology,
Government of India (grant number 91283) is acknowledged.
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