CHAPTER ONE

1.0           INTRODUCTION AND LITERATURE REVIEW

       Africa is endowed with so many plants that can be used for medicinal purposes. In fact, out of the approximated 6400 plant species used in tropical Africa, more than 4,000 are used as medicinal plants (Stanley, 2009). So many medicinal plants have been used by traditional medicine practitioners in Nigeria for the treatment of different diseases. Traditional medicinal plants have positive role of in the prevention or control of some metabolic disorders like diabetes, heart diseases and certain types of cancers (Zhang, 1996).  One of the great advantages of these medicinal plants is that these are easily available and have no side effects (Mehta, 1982).

       Plants are living organisms belonging to the kingdom plantae. They include familiar organisms such as trees. They are typically characterized by their green colour, which include common groups such as trees, herbs, flowers and fern and algae. Worldwide trend towards the utilization of natural plant remedies has created an enormous need for information about the properties and uses of the medicinal plants. Medicinal plants play a major role in the health care sector of developing nations for the management of diseases. Thus herbal medicines have a prominent role to play in the pharmaceutical markets and health care sector of the 21st century (Annan and Houghton, 2007).

       In recent years, there has been a gradual revival of interest in the use of medicinal plants in developing countries because herbal medicines have been reported safe and without any adverse side effect especially when compared with synthetic drugs. Thus, a search for new drugs with better and cheaper substitutes from plant origin are a natural choice. The medicinal value of these plants lie in some chemical substances that produce a definite physiological action on the human body (Edeoga et al., 2005).

       Phytochemicals are bioactive chemical compounds found naturally in plants that protect against diseases. They are non nutritive compounds (secondary metabolite) that contribute to flavor colour. Many phytochemicals have antioxidant activity and reduce the risk of different diseases known, for example carotenoids (from carrots) and flavonoids (present in fruits and vegetables).

        Minerals are required by living organisms and can help to prevent occurrence of some diseases. Some sources state that sixteen chemical elements are required to support human biochemical processes by serving, structural and functional role as well as electrolyte.

       Trichilia prieureana is a medium-sized tree in the moist forest, more shrubby in gallery forests, drier forests and savanna regions (Lovett et al., 2006). It is a tree up to 20m high, often low-branched and sometimes with low buttresses. It has its bark pale brown and rather flaky. It is called Monkey apple (english) and Mtimaji. Its leaves are impari-pinnate with opposite leaflets with the rachis slighty winged. The fruits are hardly stalked with sub-globose capsule. Its seeds are dark brown, glossy and covered with a red aril.

1.1            Historical features of Trichilia prieureana

       The trichilia genus consist of about 70 species, mainly distributed in tropical America and Africa, of which 43 species occur in Brazil. Chemical studies have revealed the presence of limonoids as the main bioactive agents (champagne et al., 1992).

       Trichilia prieureana is a medium-sized tree in the forest, shrubby in gallery forests and savanna regions (Bolza et al., 1972). It is called monkey apple (english), banyunkikiet (senegal) and Urera (yoruba). T. prieureana belongs to the plantae family, the order ‘sapindales’ and meliaceae family.

       Trichilia prieureana is a medium-sized tree in the moist forest, more shrubby in gallery forests, drier forests and savanna regions; as a tree to 20 m high and 40 cm, often low-branched, sometimes with small buttresses. Its bark is pale brown and rather flaky with slash fibrous, contoured, slightly scented. Its leaves are impari-pinnate with opposite leaflets, the rachis slightly winged.

       The fruits are hardly stalked with a sub-globose capsule, 1.5 – 2.5 cm across, glabrous. Also, seeds are dark brown, glossy, for 1/3 – ¼ covered with a red fleshy aril. It is a shrub or small tree, 3–20 m high with bole buttressed and fluted, often low-branching, to 1–2 m girth carrying a dense spreading crown, or small and spherical, variable, in two subspecies, overlapping in distribution in the region.

       Trichilia prieureana is an evergreen shrub or small to medium-sized tree up to 30m tall. They are usually conspicuously fluted, up to 100cm in diameter. The bark surface is shallowly fissured, grayish brown, peeling off in thin flakes or rectangular strips with its inner bark pale yellow or pink; crown hemispherical, dense with young glabrous branches.

       The leaves alternate, imparipinnately compounds with 4 pairs of leaflets; stipules absent with petiole 10cm long; rachis 15cm long with petioules 2mm long; leaflets opposite, elliptical to ovate or obovate, cuneate at base, acuminate at apex, glabrous, pinnately veined; inflorescence an axillary panicle up to 10cm long, short-hairy; bracts ovate to triangular, up to 2.5mm long.

        The heartwood is pale pinkish brown to reddish brown and distinctly demarcated from the creamy white to pale yellow sapwood. The grain is wavy or straight, texture fine. The wood is moderately heavy, with a density of about 750kg/m3 at 12% moisture content. It air dries moderately well to with difficulty; the rates of shrinkage are moderately high.

       The wood is difficult to saw because of the presence of silica, which causes blunting of saw teeth and cutting edges. It planes satisfactorily, giving nice quarter-sawn surfaces. It polishes well. The nailing properties are good. The wood is moderately durable; it is susceptible to Lyctus attack. The heartwood is resistant to impregnation by preservatives, but the sapwood is moderately permeable. The wood dust may cause irritation to the respiratory tracts in wood workers.

       The flowers of Trichilia prieureana are unisexual, male and female flowers very similar in appearance, regular, greenish white, fragrant; pedicel up to 2 mm long; receptacle cylindrical, up to 1.5 mm long; calyx cup-shaped, lobes 2 mm long; petals free, narrowly obovate to narrowly oblong, stamens 6 mm long, fused completely into a tube, hairy inside; ovary superior, ovoid to globose, glabrous or slightly hairy, glabrous or slightly hairy, stigma head-shaped or distinctly lobed. Its male flowers with rudimentary ovary, female flowers with non-dehiscing anthers.

       Its fruit is an ovoid to globose capsule, often pink when ripe, dehiscent, up to 6-seeded. Seeds 10–17 mm × 7–12 mm, on a long funicle, seed coat partly fleshy and orange-red, remaining part glossy dark brown. Its seedlings undergoepigeal germination; with hypocotyl 4 cm long, epicotyl 3 cm long; cotyledons sessile, thick and fleshy, green.

       In Sierra Leone Trichilia prieureana flowers in January-March, and fruiting is from March onwards. The flowers are pollinated by insects such as bees. The fleshy seed coat has been recorded in Gabon as an important food for monkeys and birds such as hornbills and turacos early in the dry season.

       Trichilia comprises about 90 species, most of them in tropical America. In continental Africa 18 species occur, in Madagascar.Trichilia prieureana has an isolated position within the genus in Africa and has been placed in the section Moschoxylum. It is variable and 3 subspecies have been distinguished:

• Subsp. prieureana (synonym: Trichilia senegalensis C.DC.) occurring from Senegal to Nigeria, and characterized by usually 3-celled ovary, glabrous style and lobed stigma;
• subsp. vermoesenii J.J.de Wilde occurring from Côte d’Ivoire to Uganda and Angola, and characterized by usually incompletely 2-celled ovary, slightly hairy style but glabrous ovary, and head-shaped stigma;
• subsp. orientalis J.J.de Wilde occurring in southern DR Congo, Uganda, western Tanzania and northern Zambia, and characterized by usually incompletely 2-celled ovary, slightly hairy style and ovary, and head-shaped stigma;

       Trichilia prieureana occurs in lowland forest and riverine forest up to 1300 m altitude, up to 1500 m in Zambia, often as an understorey tree. In West Africa it prefers drier forest types, with subsp. prieureana usually found in savanna woodland and forest-savanna mosaic, and subsp. vermoesenii in the rainforest region.

In Uganda subsp. vermoesenii occurs in rainforest in higher-rainfall areas in the western part of the country, subsp. orientalis in savanna woodland and forest-savanna mosaic in the northern and eastern parts of the country (Keay, 1989).

       Trichilia prieureana does not suffer from genetic erosion because it is widespread and locally common, also in secondary forest. The 1000-seed weight is about 330 g. Seeds germinate 8-15 days after sowing. Logs split easily and therefore some care is needed during felling operations (Hawthorns et al., 2006).

       The often sinuous and fluted boles of Trichilia prieureana hamper its applicability in the peeling industry, and the presence of silica, which makes sawing difficult, and easy splitting of the wood are other drawbacks (White et al., 1997). Therefore, the prospects as a commercial timber tree seem to be poor, and Trichilia prieureana may remain an undesirable tree in exploited forest, as it has often been, like other Trichilia species.

1.2            Uses of Trichilia prieureana

       Trichilia prieureana has a wide range of uses. Its bark have medicinal purpose serving as antidotes for venomous stings and bites; laxatives, vermifuges. Also, the bark and root function as genital stimulants/depressants, help in stomach troubles and veneral diseases. The fruit is taken as food and the seed have naso-pharyngeal effect. The timber is of great importance in building, fuel and lighting (Neuwinger, 2000). Below are some other uses of T. prieureana:

1.           i.            The wood is used in Ethiopia for the construction of houses.
2.        ii.            In Tanzania, it is used for tool handles and spoons.
3.      iii.            The wood is suitable for heavy and light construction, railway sleepers, heavy and light flooring, joinery, interior trim, furniture works, cabinet work, sporting goods, toys, novelties, veneer, plywood, hardboard and particle board.
4.      iv.            It is used for firewood and charcoal production; it is efficient burning slowly and generating great heat.

Also, T. prieureana has some medical applications and they include:

1.        i.            In West Africa, the bark is used to treat veneral diseases, fever, cough, constipation, poisoning and ascites and it also serves as aphrodisiac.
2.      ii.            In Central African Republic, a bark decoction is applied to scarification wounds and to treat pain caused by rheumatism and lumbago.
3.   iii.            Leaf, bark and roots are applied against anaemia and they are also applied against syphilis.
4.   iv.            Pulverized leaves are taken to treat stomach spasms.
5.      v.            Twigs are used as chew-sticks.
6.   vi.            A decoction of leafy twigs is taken to treat bronchitis and oedema.
7. The leaves and pounded leaves are used to treat gonorrhoea.
8. Root and bark are administered as enema to treat piles.
9.   ix.            Pulverized leaved are taken against ascariasis.
10.      x.            The seed is one of the ingredients of a preparation to treat goitre.
11.   xi.            It is used as a purgative.

1.3            Analyis of Trichilia prieureana as a medicinal plant

        Medicinal plants have bioactive compounds which are used for curing of various human diseases and also play an important role in healing. Phytochemicals have two categories, i.e, primary and secondary constituents. Primary constituents have chlorophyll, proteins, sugars and amino acids. Secondary constituents contain terpenoids and alkaloids.

        T. prieureana with their phytochemical properties are medicinal plants that have antifungal, antibacterial and anti-inflammation activities. The phytochemical analysis of plants the plant, T. prieureana is very important commercially and has great interest in pharmaceutical companies for the production of new drugs for curing of various diseases.

1.4 Phytochemicals

        Phytochemicals are chemical compounds that occur naturally in plants. Some are responsible for colour and other organoleptic properties such as the deep purple of blueberries and the smell of garlic. The term is generally used to refer to those chemicals that may have biological significance such as flavonoids but are not established as essential nutrients. These phytochemicals are naturally occurring in medicinal plants, leaves, vegetables and roots that have defense mechanism and protect from various diseases.

        Phytochemicals are present in virtually all of the fruits, vegetables, legumes (beans and peas), and grains we eat, so it is quite easy for most people to include them in their diet. For instance, a carrot contains more than a hundred phytochemicals. There are thousands of known phytochemicals, but only a few have been studied in detail.

        Phytochemicals are a plant’s way of protecting itself. They shield tender buds and spouts from predators and pollution. These protective compounds are passed along to us when we eat plant foods. Oxalate, saponin, cyanogenic glycoside, alkaloid, tannin and phytate are secondary metabolites used by some plants for defense and protection. They are beneficial chemicals with predator and parasite repelling effects.

        Phytochemicals, in the amounts consumed in a healthy diet, are likely to be helpful and are unlikely to cause any major problems. Some people assume that because phytochemical supplements come from “natural” sources, they must be safe and free from side effects, but this is not always true. Phytochemicals, in the amounts consumed in a healthy diet, are likely to be helpful and are unlikely to cause any major problems. Some people assume that because phytochemical supplements come from “natural” sources, they must be safe and free from side effects, but this is not always true. Phytochemicals are products of plant metabolism, mainly used by the plants for their defense. Hence attempts have been made to use them for therapeutic purposes. In humans and most animals, alkaloids and flavonoids have been observed to posses antidiuretic, antispasmodic, anti-inflammatory and analgesic effects.

        However, they inhibit certain mammalian enzymatic activities such as those of phosphodiesterase, prolonging the action of cyclic AMP. These phytochemicals can induce actions of glucagons and thyroid stimulatinghormone even when it is not needed.

        Phytochemicals have a number of functions. Antioxidant properties of plants help prevent damage that is associated with cancer, heart disease and other related human diseases. The presence of these phytochemicals has been attributed to the bioactive principles responsible for ethnopharmalological activities of most medicinal plant. This dictates why efforts have been expanded in studies aimed at elucidating their levels in medicinal plant. The medicinal values of plants and vegetables are dictated by their phytochemicals and other chemical constituents.

        The important bioactive components in plants are usually the secondary metabolites such as alkaloids, flavonoids, tannins and other phenolic compounds. Phytochemicals are products of plant metabolism, mainly used by the plants for their defense. Hence attempts have been made to use them for therapeutic purposes.

        Although phytochemicals are said to be useful to the human body, they may have some toxic effects as well, as seen in the case of alkaloids. Alkaloids are reported to have cytotoxic activity which may be used in treatment of cancer. Hence, it is desirable to know the phytochemical composition of the plant material before testing its efficacy for medicinal purpose.

       Phytochemicals are non-nutritive plant chemicals that have protective or disease preventive properties. They are nonessential nutrients, meaning that they are not required by the human body for sustaining life. It is well-known that plants produce these chemicals to protect themselves but recent research demonstrates that they can also protect humans against diseases. There are more than thousand known phytochemicals. Some of the well-known phytochemicals are lycopene in tomatoes, isoflavones in soy and flavanoids in fruits.

1.4.1 Mechanism of action of phytochemicals

       There are many phytochemicals and each works differently. These are some possible actions:

• Antioxidant – Most phytochemicals have antioxidant activity and protect our cells against oxidative damage and reduce the risk of developing certain types of cancer. Phytochemicals with antioxidant activity: allyl sulfides (onions, leeks, garlic), carotenoids (fruits, carrots), flavonoids (fruits, vegetables), polyphenols (tea, grapes).
• Hormonal action– Isoflavones, found in soy, imitate human estrogens and help to reduce menopausal symptoms and osteoporosis.
• Stimulation of enzymes – Indoles, which are found in cabbages, stimulates enzymes that make the estrogen less effective and could reduce the risk for breast cancer. Other phytochemicals, which interfere with enzymes, are protease inhibitors (soy and beans), terpenes (citrus fruits and cherries).
• Interference with DNA replication – Saponins found in beans interfere with the replication of cell DNA, thereby preventing the multiplication of cancer cells. Capsaicin, found in hot peppers, protects DNA from carcinogens.
• Anti-bacterial effect – The phytochemical allicin from garlic has anti-bacterial properties.
• Physical action – Some phytochemicals bind physically to cell walls thereby preventing the adhesion of pathogens to human cell walls. Proanthocyanidins are responsible for the anti-adhesion properties of cranberry. Consumption of cranberries will reduce the risk of urinary tract infectionsand will improve dental health.

     Foods containing phytochemicals are already part of our daily diet. In fact, most foods contain phytochemicals except for some refined foods such as sugar or alcohol. Some foods, such as whole grains, vegetables, beans, fruits and herbs, contain many phytochemicals.

       The easiest way to get more phytochemicals is to eat more fruit (blueberries, cranberries, cherries, apple,…) and vegetables (cauliflower, cabbage, carrots, broccoli,…). It is recommended take daily at least 5 to 9 servings of fruits or vegetable. Fruits and vegetables are also rich in minerals, vitamins and fibre and low in saturated fat.

       Phytochemicals are naturally present in many foods but it is expected that through bioengineering new plants will be developed, which will contain higher levels. This would make it easier to incorporate enough phytochemicals with our food.

1.4.2 Biological functions of phytochemicals

The term “phytochemicals” refers to a wide variety of compounds made by plants, but is mainly used to describe those compounds that may affect human health. Phytochemicals are found in plant-based foods such as fruits, vegetables, beans, and grains. Some phytochemicals have either antioxidant or hormone-like actions. There is some evidence that a diet rich in fruits, vegetables, and whole grains reduces the risk of certain types of cancer and other diseases. Some very important phytochemicals include:

       i.            Tannins

        Tannins are phenolic compounds, widely distributed in many species of plants where they play a role in protection from predators and perhaps also as pesticides and in regulating plant growth (Ferrel et al., 2006) and they coagulate gelatin and other proteins by binding to them and precipitating them (George et al., 2002). They also inhibit activities of some enzymes such as trypsin, chymotrypsin, amylase and lipase (Griffths, 1999).

        The tannin content of a particular herb has been speculated to account for the observed anti-inflammatory activity of the plant material. It exerts anti-inflammatory effects probably by inhibiting the release, synthesis and /or production of inflammatory cytokines and mediators, including prostaglandins, histamine, polypeptide kinins and so on (Ojewole, 2005).

        Tannins have astringent properties, hasten the healing of wounds and inflamed mucous membranes. These perhaps, could also explain why traditional medicine healers in Southeastern Nigeria often use herb in treating wounds and burns (Agoha, 1974). Tannins are also reported to have various physiological effects like anti-irritant, anti-scretolytic anti-parasitic and anti-microbial activities. Plants containing tannin are used to treat non-specific diarrhea and inflammation of the mouth (Ofokansi et al., 2005).