This book is the outcome of a project; part funded by NMPB, on development of quality assessment parameters for selected Indian medicinal plants. The project involved standardization of 16 different medicinal plants, ten out of which have been covered in the first volume of this book series.
The quality assessment of medicinal plants becomes complex and challenging due to multiple end uses of each herb, lack of clear knowledge about the bio-active constituents, inherent phytochemical variations and non-availability of relevant reference standards. It is needless to say that the quality of the finished herbal products is directly dependent on the quality of the herbal raw material. In India, the entire herbal industry can be broadly classified into two groups, viz. traditional herbal industry (Ayurveda, Siddha and Unani medicine manufacturers) and modern herbal industry (manufacturers of standardized extracts, phytochemicals, oleoresins, cosmetics, nutraceuticals, etc.).
The quality assessment paradigms of both these types of herbal industries are very different. As a generalization, the traditional medicine manufacturers do not believe in the concept of active principles / marker compounds for quality assessment, as they believe that the entire herb or its preparation is "bio-active". On the other hand the modern herbal product manufacturers prefer to assess quality based on the content of specific secondary metabolites which are believed to be important for the overall biological effect of a given herb or its preparation. This book aims to serve mainly the later type of industry, as it utilizes a series of objectively verifiable quality assessment parameters.
In the international market also, natural products are often valued based on the content of specific active principles / secondary metabolites / marker compounds. In the recent years, several definitions have emerged for active compounds, bio-markers, markers, analytical markers etc. For the sake of simplicity, in this book, we have referred to these compounds as "desirable compounds" or "commercially pursued compounds". The higher the content of desirable compounds, the higher is the value of an herb or its preparation in the international market.
The task is challenging as till date there is no clear and general agreement as to which constituents should be considered as "desirable". There is a paucity of basic research which links the secondary metabolites with specific biological activities. For almost two decades (1970's to 1990's) there was a trend of isolation and characterization of secondary metabolites from medicinal plants with little or no regard to their bio-activity. During this period, a large number of phyto-constituents were reported without any knowledge about their utility. It is only when the international, peer reviewed, scientific journals started refusing to publish any research, where the isolated new constituents were not linked to any bio-activity, the trend started to change towards multi-disciplinary research involving both Phytochemistry and Pharmacology. Even today, for many Indian medicinal plants, the "desirable compounds" are not known. As a result, there is an uncertainty as to which compounds should be analyzed for a fair assessment of quality of such medicinal plants. For the purpose of this book, we have used the criterion that a phyto-compound should have preferably two in-vivo studies or a clinical study demonstrating efficacy in a particular condition for it to be considered as a "desirable compound". Due to the ADME related limitations of in-vitro phannacological methods, the compounds found to be active only in the in-vitro assays were not considered for this assessment.
Based on this criterion, we carefully studied the "Materials and Methods" section of the (available) published papers and short listed only those studies where an inference could be made linking specific phytochemicals with a particular bio-activity. It was felt that quality assessment of a herb can be much more reliable, if it is based on estimation of such desirable compounds rather than assay of any unique compound which may be only an analytical marker with little or no connection with bio-activity. In several research papers, we found that the test substance for biological evaluation was an extract or a fraction of the extract, but the investigators have inferred that the observed biological effect was on account of specific secondary metabolites simply because they were the major constituents of the test substance. We had to ignore such inferences as it is well known that very often it is the minor constituents which are responsible for the bio-activity. Thus, unless a proper bio-activity guided fractionation is conducted or a pure compound is isolated and biologically tested, it would continue to be a matter of speculation as to what makes the extract / fraction active. Further, we also observed that the compounds which tend to crystallize out easily from their respective extracts, are the ones generally, which have been studied in-vivo. In other words, what has been studied in-vivo is not necessarily the most important or the most bio-active constituent; instead these compounds have generally been only the "easiest option" to work with. Very few bio-activity guided fractionation studies were found in the published literature either because such information is often linked to patents and are thus confidential or because there is still not enough multi-disciplinary research occurring on Indian medicinal plants. Based on the literature compilation, we have proposed, at annexure III, the names of those compounds whose quantification could serve as a meaningful "Quality Assessment Criterion".
In the recent years, few research groups have developed and published quality standards for some of the Indian medicinal plants. Some of the official standards can be found in the Ayurvedic Pharmacopoeia of India (Volume I to Volume VII) and the Indian Pharmacopoeia 2010. Apart from these, several non-official standards are available in the Quality Standards of Indian Medicinal Plants (Volume 1 to 8) published by ICMR, Indian Herbal Pharmacopoeia, WHO monographs on Indian plants, British Herbal Pharmacopoeia, etc. However, since all these monographs have been developed by different groups, at different times and probably using different analytical methods, there are several variations in the proposed limits for many analytical parameters. In this book, the prevailing variability on analytical specifications, from various books of reference, has been highlighted and finally the specification closest to the one observed in our analysis has been recommended. In some rare cases, a new limit has been proposed as none of the available standards came close to the observed values for specific parameters. Our intention is not to contradict any prevailing standard, instead only to report the observed findings which hopefully will trigger further research leading to development of more realistic quality standards.
For this project, samples from different geographical regions (minimum four) were collected and analyzed using pre-validated methods (in our NABL accredited laboratories). During the course of this project, the expert committee of NMPB, responsible for reviewing the progress of the project, made several suggestions to improve the utility of this work which have also been included in this book. One of the suggestions was to provide more than one method of assay of desirable compounds such that all types of laboratories, having varying degrees of analytical instrumentation, can analyze the material. Wherever relevant, a correlation has been provided between different analytical techniques. In majority of the cases different analytical methods provided more or less similar results. Further, each of the HPLC methods described here were validated for specificity, precision, linearity, accuracy and ruggedness.
Most of the available quality standards provide criteria for "pass" or "fail". In this project, we have included the grading of raw material, which we hope would help the growers / farmers to classify their produce accordingly and earn better prices for higher quality produce.
Developing morphological descriptors of high quality raw material is important as it helps in identification of good quality raw material "in the field" itself, where one may not have ready access to a laboratory. Thus, an attempt has been made in this project to arrive at some generalized correlations between morphological characters and the assay of desirable compounds.
Based on the advice of reviewers and expert committee of NMPB, a brief section on regulatory status and Pharmacopoieal references, where ever known, has also been compiled. Information about research institutes which can authenticate the herbal raw material and suppliers details of reference standards used in estimation of desirable compounds has also been provided.
It is hoped that this book will help the readers from analytical laboratories involved in objective quality assessment of Indian medicinal plants. We encourage the readers to give us their feedback based on their analytical observations and experiences. We believe that quality assessment of complex natural products is an ever learning task and this feedback will help us significantly in improving our understanding of the quality of these Indian medicinal plants.
We are grateful to National Medicinal Plants Board for part funding this project. The basic knowledge gained during the course of this work empowered us to provide technical assistance in the development of official monographs, on some of the plants, to the Indian Pharmacopoeia, Ayurvedic Pharmacopoeia of India and United States Pharmacopoeia. |
