CHAPTER ONE
INTRODUCTION
1.1 Background
Clinical features similar to diabetes
mellitus were described about 3000 years ago by the Third Dynasty
Physicians of ancient Egyptian decent. The term "diabetes" was first
coined by a Greek doctor known as Araetus of Cappodocia (81-133AD).
Later, the word mellitus (honey sweet) was added by Thomas Willis, a
British in 1675 after rediscovering the sweetness of urine and blood of
patients, first noticed by the scholars of both ancient Indian and
Chinese decent. It was only in 1776 that Mathew Dobson an English doctor
first confirmed the presence of excess sugar in urine and blood as a
cause of their sweetness. In modern time, the history of diabetes
coincided with the emergence of experimental medicine. An important
milestone in the history of diabetes in 1857 by the French scientist
Claude Bernard is the establishment of the role of the liver in
glycogenesis, and the concept that diabetes is due to excess glucose
production. The role of the pancreas in pathogenesis of diabetes was
discovered by Mering and Minkowski of Austria in 1889. Later, this
discovery constituted the basis of insulin isolation and clinical use by
two Canadians, Banting and Best in 1921. Trials to prepare an orally
administrated hypoglycemic agent ended successfully by first marketing
of tolbutamide and carbutamide in 1955 (Ahmed, 2002).
Although there is paucity of data on the
prevalence of diabetes in Nigeria and other African countries,
available data suggests that diabetes is emerging as a major public
health problem in Africa, including Nigeria (Mbanya et al.,
1996). However, its prevalence and that of other non-communicable
diseases is on the rise in African communities due to the ageing of the
population and drastic life style changes accompanying urbanization and
westernization (Gwatkin et al., 1999). Diabetes is no longer
rare, and is higher in populations of African origin who have migrated
to Western countries compared to Caucasians living in the same countries
(Mbanya et al., 1999). Type 2 diabetes is the predominant
form, yet, a classification problem persists for a high proportion of
the patients (Elbagir et al., 1998). There are numerous reports
in populations of African ancestry, of clinical presentations of
diabetes, which do not easily fit with the definition criteria of the
main known types. Apart from classical type 1 and type 2 diabetes,
tropical diabetes and ketosis-prone atypical diabetes have been
described (Gautier et al., 2001). Moreover, diabetes mellitus
is associated with a high rate of long-term complications in populations
of African origin. Therefore, it will represent a growing burden of
health care systems of African countries, most of which already face
difficult economic conditions. However a prospective approach of this
burden and possible prevention strategies has been hindered by the
scarcity of data on diabetes in Africa. Thus, the design and
implementation of appropriate strategy for early diagnosis and
treatment, as well as population based primary prevention of diabetes in
these high-risk populations is therefore a public health priority.
There is an increasing demand for
medicinal plants and plant products as alternatives to orthodox
medicines especially in developing countries (Murray, 1998). The use of
plants and their natural products in Nigeria as either extract or
infusion is a widespread practice in the treatment and management of
diseases (Iwu, 1980). Medicinal plants contain accumulated natural
products, biologically active materials and ingredients which have
various effects. These active ingredients representing the value in use
are produced by biological synthesis in the plant in very small
concentrations of the dry material content of the plant (Hornok, 1992).
Some of these active ingredients accumulate in certain parts of the
plant like roots, stem, leaves, bark, fruits and flowers. It is only
those portions of these plants that contain active ingredients that are
used for therapeutic purposes. The part that contains the active
ingredient is taken in the form of extract, infusion and decoction
(Odebiyi and Sofowara, 1979).
1.2 Aim and Objectives of the Study
The aim of this study was to evaluate the biochemical and histological effects of Tapinanthus preussii
leaf aqueous and ethanolic extracts on streptozotocin induced diabetic
wistar rats in order to ascertain its hypoglycaemic potentials and
safety.
The objectives of the study were as follows:
- Determination of the elemental, proximate, phytochemical composition
and in vitro antioxidant activities of the crude aqueous and ethanolic
leaf extracts of Tapinanthus preussii.
- Evaluation of the acute toxicity profile of the crude aqueous and ethanolic leaf extracts of Tapinanthus preussii.
- A sub-chronic study on the effects of Tapinanthus preussii crude aqueous and ethanolic leaf extracts on some biochemical and haematological indices in normoglycaemic albino wistar rats.
- Evaluation of the antidiabetic effect of Tapinanthus preussii
crude aqueous and ethanolic leaf extracts as well as some biochemical
and haematological indices in streptozotocin induced diabetic albino
wistar rats.
- Histopathological studies on some vital organs of the normoglycaemic
and streptozotocin induced diabetic wistar rats treated with Tapinanthus preussii crude aqueous and ethanolic leaf extracts.
1.3 Justification
The incidence of diabetes is increasing in the world and is assuming epidemic proportions (Chougaleet al., 2007).
According to the world Health Organization the number of diabetics
which is about 160 thousand has doubled in the past few years and is
expected to double by the year 2025 (Eliziane et al., 2003).
Hence it is one of the most prevalent conditions with spontaneous
manifestations characterized by hyperglycemia, deranged metabolism of
carbohydrate, protein, fats, water and electrolytes predominantly
affecting the vasculature. Due to its high prevalence and potential
deleterious effect on the physical and psychological state of patients
which generally results in a morbid condition, it is therefore a major
medical concern (Halpern et al., 2000; Macedo et al., 2002). Hence the search for newer drugs is on the rise.
Although insulin and oral hypoglycaemic
agents are the mainstay of the management of diabetes, they have
prominent side effects (like gastrointestinal discomforts,
hepatotoxicity, lactic acidosis, anorexia etc) and fail to alter the
course of diabetic complications. The high cost of these hypoglycaemic
agents and their potential side effects have led to the focus on the use
of medicinal plants to manage this ravaging disorder. For centuries
people the world over have believed in the ability of herbs to treat
different illnesses. Hence the search for diabetes treatments has led to
the use of many herbs to help combat this disease that has afflicted
millions. The World Health Organization has estimated that one third of
the diabetic patients in the low income African families used
alternative medications especially herbal mixtures since they are
considered readily affordable, available and efficacious (Sarika et al.,
2006). Therefore the World Health Organization (WHO) has recommended
the use of alternative medicine for treating diabetes mellitus (WHO,
1980), hence providing an impetus for research in this area. Currently
the focus of research in diabetes includes discovering newer
antidiabetic agents as well as isolating the active compounds from
herbal sources that have been documented to have antidiabetic properties
described in some ancient texts (Tripathi, 1998).
According to ethno-botanical
information, more than eight hundred plants including the African
mistletoe are used as traditional remedies in one form or another for
the treatment of diabetes (Alarcon-Aguilara et al., 1998),
though only a few have been evaluated scientifically. Several
traditional plants have shown antidiabetic properties when assessed in
experimental models of diabetes though rarely in clinical studies. But
still these antidiabetic herbs have not gained enough momentum in
medicine due to absence of specific standardized raw materials and
extracts for formulation of phytomedicines as well as content uniformity
and therapeutic effectiveness. Hence it was worth while investigating
the hypoglycaemic effect as well as the lethal dose toxicity of Tapinanthus preussii
as reflected in some biochemical and haematological parameters in
normoglycaemic and streptozotocin induced diabetic wistar rats
(experimental model) since cellular and biochemical mechanisms are
involved in diabetes. This study may go a long way to elucidate the
mechanism of action of this widely used plant parasite, Tapinanthus preussii and therefore its safety and efficacy in alleviating diabetes.