THE POTENTIAL USE OF LOCAL MEDICINAL PLANTS IN DRUG RESEARCH

1.1 Introduction

Medicinal plants are considered a repository of numerous types of bioactive compounds possessing varied therapeutic properties. The therapeutic potential of plants has been well explored over a very long time period (Raina et al., 2014). Knowledge of the medicinal plants used in the drugs of traditional systems of medicine (TSM) has been of great significance, especially as a lead for the discovery of new singlemolecule medicines for modern system of medicine. To determine the chemical nature of such compounds, isolation of a substance in pure form using various separation techniques, chemical properties and spectral characteristics are a prerequisite for establishing its correct structure. Thus, medicinal plants are used in crude or purified form in the preparation of drugs in different systems.

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research hypothesis and questions, Limitations of the Study and Definition of technical terms.

1.2 Background of Study

Traditional medicinal practices have formed the basis of most of the early medicines followed by subsequent clinical, pharmacological and chemical studies (Butler, 2004). Probably the most famous and well known example to date would be the synthesis of the antiinflammatory agent, ‘acetylsalicyclic acid’ (aspirin) derived from the natural product and ‘salicin’ isolated from the bark of the willow tree Salix alba L. Investigation of Papaver somniferum L. (opium poppy) resulted in the isolation of several alkaloids including ‘morphine’, a commercially important drug, first reported in 1803. It was in the 1870s that crude morphine derived from the plant P. somniferum, was boiled in acetic anhydride to yield diacetylmorphine (heroin) and found to be readily converted to codeine (painkiller). Historically, it is documented that the Sumerians and Ancient Greeks used poppy extracts medicinally, whilst the Arabs described opium to be addictive. Digitalis purpurea L. (foxglove) had been traced back to Europe in the 10th century but it was not until the 1700s that the active constituent ‘digitoxin’, a cardiotonic glycoside was found to enhance cardiac conduction, thereby improving the strength of cardiac contractibility. ‘Digitoxin’ and its analogues have long been used in the management of congestive heart failure and have possible long term detrimental effects and are being replaced by other medicines in the treatment of “heart deficiency” (Der Marderosian and Beutler, 2002). The anti-malarial drug ‘quinine’ isolated from the bark of Cinchona succirubra Pav. ex Klotsch, had been used for centuries for the treatment of malaria, fever, indigestion, mouth and throat diseases and cancer. Formal use of the bark to treat malaria was established in the mid 1800s when the British began the worldwide cultivation of the plant. ‘Pilocarpine’ found in Pilocarpus jaborandi (Rutaceae) is an L-histidine-derived alkaloid, which has been used as a clinical drug in the treatment of chronic open-angle glaucoma and acute angle-closure glaucoma for over 100 years.

In 1994, an oral formulation of pilocarpine was approved by the FDA to treat dry mouth (xerostomia) which is a side effect of radiation therapy for head and neck cancers and also used to stimulate sweat glands to measure the concentrations of sodium and chloride (Aniszewski, 2007).

In countries like India, China and others with well-founded traditional systems of medicine, plant-based formulations occupy an important place in health management (Ramawat et al., 2009). Ethnobotanical and traditional usage of medicinal plants serves as a source of information for the isolation of active compounds, e.g. as direct therapeutic agents (D-tubocurarine from Chondrodendron tomentosum), as the starting drug for semisynthesis (diosgenin from Dioscorea floribunda), the model drug for new synthetic drugs (cocaine from Erythroxylum coca), for the synthesis of local anaesthetics and, lastly, as taxonomic markers for identification (Balunas & Kinghorn, 2005; Gurib-Fakim, 2006 and Wagle et al., 2007). Thus the ancient wisdom has been the basis of modern medicine and will remain as one important source of future medicine and therapeutics.

Historically, the majority of new drugs have been generated from natural products (secondary metabolites) and from compounds derived from natural products (Lahlou, 2007). Natural products have long been a thriving source for the discovery of new drugs due to their chemical diversity and ability to act on various biological targets (Bhutani and Gohil, 2010). Most natural products are compounds derived from primary metabolites such as amino acids, carbohydrates and fatty acids and are generally categorized as secondary metabolites. The biosynthesis and breakdown of proteins, fats, nucleic acids and carbohydrates, which are essential to all living organisms, is known as primary metabolism with the compounds involved in the pathways known as “primary metabolites”. Secondary metabolites are considered products of primary metabolism and are generally not involved in metabolic activity viz. alkaloids, phenolics, essential oils and terpenes, sterols, flavonoids, lignins, tannins, etc. (Ramawat et al., 2009).

The drug discovery process from plants is a laborious and time consuming process. The classical examples of drug discovery like morphine, quinine, digoxin, etc which replaced the extracts of their respective plants were mostly responsible for harbouring the idea that a single active ingredient must have been responsible for the bioactivity (Bhutani and Gohil, 2010). Once the medicinal plant is chosen for a single drug molecule based on a literature survey and known phytochemical relationships, the next step is its collection and botanical identification. The plant material is subjected to drying at ambient temperature in a shady place or in an oven with a controlled airflow and temperature. The dried or stabilised plant material should then be powdered to give a suitable mesh size and subjected to a suitable extraction process as per standard operating procedures.

Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Potential use of Local Medicinal Plants in Drug Research.

1.3 Statement of Problems

Investigation revealed that herbal plants can be easily contaminated during growth, processing and collection. Adulteration and heavy metal contamination are the two major problems reported in Herbal medicines. Therefore, it is necessary to improve the quality and quantity of bioactive compounds for developing new herbal drug and keep pace with other drug discovery efforts (Dash et al., 2001). Today, there are several medicinal plants and their bioactive agents have been scientifically and clinically evaluated by Investigators.

There are also challenges on obtaining plant feedstock to large scale phytochemicals production, mainly because of two factors: finding the right maturation stage of the plant and hormonal responses to environmental factors. Both of them can interfere on the production of the secondary metabolites. Besides that, there’s also the problem of certain species aren’t available globally or in extinction (De La Parra and Quave, 2017).

1.4 Aim and Objectives of Study

The aim of the study is to identify the Potential use of Local Medicinal Plants in Drug Research. In achieving this aim, the following specific objectives were laid out as follows:

1. To ascertain the usefulness of local medicinal plants in drug research
2. To examine the factors inhibiting drug research on local medicinal plants
3. To understand the knowledge of the medicinal plants as a future source of herbal drugs.

1.5 Research Questions

The study came up with research questions so as to be able to ascertain the above stated objectives. The specific research questions for the study are stated below as follows:

• Are there factors inhibiting drug research on local medicinal plants?
• What is the usefulness of local medicinal plants in drug research?
• What is the knowledge of the medicinal plants as a future source of herbal drugs?

1.6 Significance of Study

This study will be of immense benefit to researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

1.7 Scope of the Study

The study focuses on the Potential use of Local Medicinal Plants in Drug Research in Nigeria.

1.8 Limitations of the Study

During the course of this study, many things militated against its completion, some of which are:

1. Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
2. Research material: availability of research material is a major setback to the scope of the study.
3. Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
4. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection.