COMPARATIVE PHARMACOGNOSTIC STUDIES OF THE LEAVES OF SOLANUM INCANUM LINN AND SOLANUM MELONGENA LINN (SOLANACEAE)

ABSTRACT

Solanum incanum Linn. and Solanum melongena Linn (Solanaceae) are both shrubs or trees found in the sub-Saharan Africa and the Middle East. Both are called „gauta‟ among the Hausa community of Northern Nigeria and „Tarku‟ among the Bura/Babar speaking people of Southern Borno of North Eastern Nigeria. They are widely used in traditional medicine for the treatment of pain related illnesses such as sore throat, angina, stomach-ache, colic, headache, painful menstruation, liver pain and pain caused by onchocerciasis, pleurisy, pneumonia and rheumatism. Microscopic, chemo-microscopic, quantitative evaluative and thin layer chromatographic (TLC) studies were carried out on the leaves of both plant species using standard pharmacognostic procedures. Elemental analysis using Instrumental Neutron Activation Analysis (INAA) technique was also carried out on the two plant species. Organoleptically, leaves of both plants were green in colour and distinct in odour, but S. incanum had a more bitter taste than S. melongena. Microscopically, leaves of both plants had predominantly anisocytic stomata of different sizes on the adaxial surface, while anomocytic stomata were predominant on the abaxial surfaces. Numerous non glandular stellate trichomes of different sizes were observed on the abaxial surface of both plants. Epidermal cells with wavy anticlinal walls were observed on both surfaces of the two plant species. Transversely, the leaves of both plants were dorsiventral with multilacunar vascular bundles. Calcium oxalate crystal (prism), starch grains (oval-shaped) and xylem vessels (spiral) were observed. Quantitative-leaf microscopy of the two plants had shown that S. melongena had a higher vein-islet termination number (4.80) than S. incanum (3.40). They also differ in their stomatal numbers and indices: 4.00 and 6.80 (upper epidermis) and 12.00 and 20.50 (lower epidermis) in S. melongena were higher than 2.00 and 3.70 (upper epidermis) and 8.00 and 13.30 (lower epidermis) in S. incanum respectively, but had the same palisade ratio (4.60) and vein-islet number (2.60). Chemomicroscopic studies showed that both plants had all features tested in common, namely cellulose, lignin, starch, tannins, mucilage, fats and fixed oils and calcium oxalate crystals were present, while calcium carbonate was absent. Physicochemical analysis (%w/w) revealed that water-soluble ash (10.2%) and water-soluble extractive value (19.2%) were higher in S. melongena than in S. incanum (8.4%) and (18%) respectively. While moisture content (4.1%), total ash (20.5%), acid-insoluble ash (7.0%) and alcohol-soluble extractives (12.4%) were found to be higher in S. incanum than in S. melongena (3.5%), (19.0%), (6.0%) and (9.6%) respectively. Quantitative estimation of alkaloids in the leaves of the two plants revealed that S. incanum (8.0%) had a slightly higher percentage of alkaloid than S. melongena (5.0%). The mineral element concentrations (ppm) of the leaf powder of the two plants were found to vary considerably. Generally, S. incanum was found to contain more mineral elements both in number and concentrations than S. melongena. Uranium (0.026+0.007) the potentially toxic element and Neodymium (11.000+3.000) were only present in S. incanum. The percentage yield of the ethanol extract obtained revealed that S. incanum (2.42%) had a higher percentage yield than S. melongena (1.29%). Phytochemical screening on the ethanol extracts of both plants showed that they had all the phytochemicals tested in common namely; alkaloids, carbohydrate, flavonoids, cardiac glycoside, tannins and saponins were present while anthraquinone was absent. Thin Layer Chromatographic analysis of the crude ethanol extract showed several numbers of spots with different Rf values. Chromatographic analysis of the alkaloid extract of S. incanum and S. melongena also showed several numbers of spots with different Rf values. The results of this study show that Solanum incanum and S. melongena possess some similar morphological, anatomical and phytochemical characteristics. They were found to differ in respect to their histological features, physicochemical parameters and elemental mineral contents. The result can be useful in setting some diagnostic indices for the differentiation, identification, authentication and the preparation of the monograph of the two plants.

CHAPTER ONE

1.0    INTRODUCTION

1.1 Pharmacognostic Studies

Pharmacognosy being concerned with the description and identification of a plant including its history, commerce, collection, preparation and storage is of fundamental importance particularly for pharmacopoeial identification and quality control purpose. Pharmacognosy is the study of medicine derived from natural source. It is the study of the physical, chemical, biochemical and biological properties of drug substances of natural origin. Pharmacognostic studies of plant drugs involves the sources of drug, the morphological character, histological characters, chemical constituents and their qualitative test, various physicochemical test and pharmacological action of the drug or the active constituents (Ghani, 1990). It also includes the commercial varieties, substitutes, adulterants and any other quality control of the drugs. Pharmacognostic studies ensure plant identity and lays down standardization parameters which helps in preventing adulterations (Chanda, 2014).

Authentication of medicinal plants is of paramount importance in ensuring quality and safety of crude drugs. Pharmacognostic study not only gives the authentication but also quality, purity and standard of the plant drug. An authentication and quality assessment of herbal material deals with the Pharmacognosy that is based on macroscopic and microscopic characters (Heinrich, 2000). According to WHO (1998), the macroscopical and microscopical description of a medicinal plant is the first step towards establishing the identity and the degree of purity of such material. The pharmacognostic parameters are reliable and inexpensive criteria for confirmation of the identity of crude drugs (Evans, 2006). Unlike taxonomic identification, pharmacognostic study includes parameters which help in identifying adulteration in dry powder form also, this is necessary because once the plant is dried and made into powder form, it loses its morphological identity and easily prone to adulteration (Chanda, 2014). The WHO assembly in number of resolutions has emphasized the need to ensure quality control of medicinal plant products by using modern techniques and applying suitable standards (Panchawat et al., 2010).

Problems associated with incorrect identification, substitution and adulteration of plant material, sometimes accidental, sometimes deliberate, had not gone unnoticed by those who use the plant materials. Ahmad et al., (2010) and Khan et al., (2000) observed that in herbal markets of India and Pakistan, sometimes entirely different taxa are being sold under the same local or common name. The most common error is one common vernacular name is given to two or more entirely different species (Dineshkumar, 2007). Therefore, systematic identification is becoming essential in order to produce standardized finished herbal products.

1.2 Standardization of Crude Drugs

According to World Health Organization, medicinal plants would be the best source to obtain a variety of drugs. Therefore, such plants should be investigated to better understand their properties, safety and efficacy (Nascimento et al., 2000).The plant-based, traditional medicine systems continues to play an essential role in health care, with about 80% of the world‟s inhabitants relying mainly on traditional medicines for their primary health care (Owolabi et al., 2007).

In the Western world, as people are becoming aware of the potency and side effects of synthetic drugs, there is an increasing interest in plant-based medications. The increase in demand for herbal medicines may lead to indiscriminate and unscientific collection, misidentification, and adulteration without any standards for quality of the material (Shazia et al., 2011). Medicinal plant materials are being adulterated in commerce due to many reasons such as similar morphological features, same name as written in classical text, presence of similar active principles in the substituted plant which may badly affect the therapeutic activity of the finished products (Chandima and Sirimal, 2012). Substitution or adulteration of a particular genuine drug with other species due to demand exceeding the supply of the original species, is rampant in the present trade scenario. As a result, proper authentication of the drug for safe administration as a herbal medicine assumes paramount significance (Lalitha et al., 2012).

According to Handa (2004), the majority of medicinal plants used by the herbal drug industry and local communities come from wild collection. The raw materials used by the drug industry and communities in large cities, towns and regions are generally procured through market channels and are sometimes found adulterated.

Standardization of herbal medicines is the process of prescribing a set of standards or inherent characteristics, constant parameters, definitive qualitative and quantitative values that carry an assurance of quality, efficacy, safety and reproducibility. It is the process of developing and agreeing upon technical standards. Specific standards are worked out by experimentation and observations, which would lead to the process of prescribing a set of characteristics exhibited by the particular herbal medicine. Hence standardization is a tool in the quality control process (Kunle et al., 2012).

Describing herbal drugs in a systematic manner is based on multiple approaches of pharmacognostic, taxonomic and chemical analysis, including documentation of their biological and geographical source, cultivation, collection, processing, morphological, microscopic and chemical characters (Shazia et al., 2011). Generally, all medicines, whether they are synthetic or of plant origin, should fulfil the basic requirements of being safe and effective (EMEA, 2005; WHO, 2002c).

1.3 Phytochemistry

Phytochemistry deals with the enormous different types of organic substances that are not only elaborated but also accumulated by plants. The detailed phytochemical study of an unknown plant may be accomplished right from extraction of plant materials to the elaborated study of their biological characteristics (Ashutosh, 2003).

Phytochemicals produced in plants that are mostly of therapeutic value are called secondary metabolites, they are complex organic molecules biosynthesized from primary plant metabolites in plant cells. Secondary metabolites are typically produced in a specific organ, tissue, or cell type at specific stages of development (e.g., during flower, fruit, seed or seedling development). They can be present in the plant in an active state or as a prodrug that becomes activated upon wounding, infection or in the body of an herbivore. Their concentration in a given plant often varies during a 24-hour period (Raver et al., 1999).

1.4 Statement of Research Problem

The similarity in form and morphology among the widely distributed plants in Nigeria has led to confusion and misunderstanding in identifying them as well as adulteration in forms of substitution with closely related species. The biggest problems in Nigeria with herbal medicine are a lack of standardization and safety regulations (Rapheal, 2011); this has also led to misunderstanding and adulteration when dealing with the plants.

1.5       Justification

The challenges of morphological and taxonomic identification of Solanum incanum and S. melongena was reported in the works of Lester and Hasan (1990). Both species of the genus Solanum are widely found in the African continent most especially in tropical regions. They are abundant in Nigeria and are mostly regarded as the same plant except for the difference in fruit physical appearance. This assumption has led to adulteration in form of substitution of the two plant species.

Both plants are widely consumed in Northern Nigeria, the leaves of Solanum incanum is mostly confused with the closely related S. melongena. They are used for the treatment of several disease conditions namely earache, menstrual pain, asthma, dyspepsia, allergic rhinitis, constipation (Burkill, 2000; Bello et al., 2005) in different parts of the world. Despite their widespread consumption and medicinal uses, these two plant species have not been standardized. Therefore, the need for standardization and establishment of their diagnostic and morphological characteristics to prevent adulteration in form of substitution by the users is paramount.

1.6 Aim and Objectives of the Research

Overall Aim

To establish the pharmacognostic standards of the leaves of both Solanum incanum and S. melongena with a view to ensure their quality and prevent their adulteration.

Objectives

  1. To evaluate some morphological and physical characters of the leaves of Solanum incanum and melongena.
  2. To determine and compare some of the elemental contents of the leaves of the two plants.
  3. To determine and compare some of the phytochemicals present in the leaves of the two plants.

1.7 Research Hypothesis

Solanum incanum and S. melongena possess similar and differing morphological, physical, elemental and phytochemical characteristics.