PHYTOCHEMICAL AND INHIBITION STUDIES OF GARCINIA KOLA HECKEL (GUTTIFERAE) SEED EXTRACTS ON SOME KEY ENZYMES INVOLVED WITH DIABETES

ABSTRACT

Garcinia kola is an Angiosperm belonging to the family Guttiferae. It is known in commerce as bitter kola. The plant seeds have been used in the treatment of a wide range of diseases including diabetes, and its importance in folkloric medicine as a purgative, mastcatory, aphrodisiac etc. is eminent. Diabetes mellitus is a metabolic disorder of multiple etiologies characterized by chronic hyperglycemia leading to severe complications such as neuropathy, nephropathy, retinopathy and foot ulcer. n-Hexane, ethyl acetate and methanol extracts were prepared successively in a soxhlet apparatus at 50ºC. Qualitative phytochemical screening was carried out. Column chromatographic analysis was carried out on the ethyl acetate extract and the structure of the isolated compound was elucidated via Gas Chromatography-Mass Spectrophotometry and Fourier Transformed-Infra Red spectroscopy. Pancreatic α-amylase and intestinal α-glucosidase were extracted from porcine pancrease and rat small intestine under specified conditions. Steroids/triterpenes, phenolics, flavonoids, cardiac glycosides, alkaloids, coumarins and phlobatannins were detected. Methanol, ethyl acetate and n-hexane extracts inhibited α-amylase with IC50 = 0.78 ± 0.32 mg/ml, 3.44 ± 3.46 mg/ml, 4.89 ± 4.62 and α-glucosidase IC50 = 2.67 ± 0.74 mg/ml, 1.68 ± 1.27 mg/ml, 10.29 ± 4.08 mg/ml respectively. The compound ZAAK was isolated from ethyl acetate extract. Fourier Transformed-Infrared spectra revealed the presence of carboxylic acid and an ester in ZAAK. Total ion chromatogram of ZAAK revealed three major peaks corresponding to ZAAK1 ZAAK2 and ZAAK3. The mass spectra identified ZAAK1 ZAAK2 and ZAAK3 as 1-pentadecanecarboxylic acid, (Z)-11-Octadecenoic acid and octadecanoic acid, 2-(2-hydroxyethoxy) ethyl ester respectively.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Medicinal Plants

Since ancient times, people have been exploring nature particularly plants in search of new drugs. This has resulted in the use of large number of medicinal plants with curative properties to treat various diseases (Verpoorte, 1998). Nearly 80% of the world’s population relies on traditional medicines for primary health care, most of which involve the use of plant extracts (Sandhya, et al., 2006). Medicinal plants are the richest bio-resources of drugs for traditional medicinal systems, modern medicines, nutraceuticals, food supplement, pharmaceuticals and precursors for synthetic drugs (Hammer et al., 1999).

Secondary metabolites are responsible for the medicinal activity of medicinal plants, hence, due to their large biological activities. These metabolites have been used for centuries in traditional medicine. These secondary metabolites can be classified into three chemically distinct groups viz: alkaloids, terpenoids, and phenolics (Mazid et al., 2011).

1.1.1 Alkaloids

Alkaloids are naturally occurring chemical compounds containing one or more nitrogen atoms (usually in a heterocyclic ring) and are basic in nature (Evans, 2009). Many alkaloids are toxic and often have a pharmacological effect, which makes them to be used as medications and recreational drugs (Guillermo and Victor, 1999).

1.1.2 Phenolics

Plants have limitless ability to synthesize aromatic secondary metabolites, most of which are phenols or their oxygen-substituted derivatives (Geissman, 1963). Important subclasses in this group of compounds include phenols, phenolic acids, quinones, flavonoids, tannins and coumarins. These groups of compounds show antimicrobial effect and serves as plant defense mechanisms against pathogenic microorganisms. They are synthesized by plants in response to microbial infection (Dixon et al., 1983) and are often found effective in vitro as antimicrobial substance against a wide array of microorganisms (Bennet and Wallsgrove, 1994). They also show anti-allergic, anti-inflammatory and anticancer activity (Spencer and Jeremy, 2008).

1.1.3 Terpenoids

The terpenoids form a large and structurally diverse family of natural products. They are derived from five-carbon isoprene units, and according to the number of isoprene molecules incorporated, they can be classified into hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30), tetraterpenes (C40), and polyterpenes such as rubber (Dewick, 2002). They occur widely in the leaves and fruits of higher plants, conifers, citrus and eucalyptus (Breitmaier, 2008). Vast majority of the different terpenes structures produced by plants as secondary metabolites are presumed to be involved in defense as toxins and feeding deterrents to a large number of plant feeding insects and mammals (Gershenzon and Croteau, 1991).

1.2 Plants in Traditional Medicine

Plants have formed the basis of sophisticated traditional medicine (TM) practices that have been used for thousands of years by people in China, India, and many other countries (Sneader, 2005). They are important source of medicines, especially in developing countries that still use plant-based TM for their healthcare (Salim et al., 2008). It has been extensively documented that plants still form the bases of traditional medicine system and that plant based system continue to play an essential role in healthcare for over 80% of the world population (WHO, 2002).

1.3 Plants in Modern Medicine

Modern medicine has benefited enormously from plants used in traditional medicine as a source of natural products (Kinghorn, 1992). An estimate showed that over 50% of the best selling pharmaceuticals in use today are derived from or mimics of natural products (Newman and Cragg, 2007).

In more recent history, the use of plants as medicines has involved the isolation of active compounds, beginning with the isolation of morphine 1 from opium poppy (Papaver somniferum) in the early 19th century (Samuelsson, 2004). Other early drugs from medicinal plants were also isolated due to drug discovery research of which some are still in use (Butler, 2004). Crude morphine (a pain reliever) was found to be readily converted to codeine 2 (painkiller) when boiled in acetic anhydride (Marderosian and Beutler, 2002). Digitoxin 3, a cardiotonic glycoside isolated from Digitalis purpurea L. (foxglove) enhances cardiac conduction (Marderosian and Beutler, 2002). The anti-malarial drug quinine 4 isolated from the bark of Cinchona succirubra has been used for centuries for the treatment of malaria fever (Marderosian and Beutler, 2002).