TOXICOLOGICAL ASSESSMENT OF THE METHANOL LEAF EXTRACT OF SECURINEGA VIROSA(ROXB EX. WILLD) IN WISTAR RATS

ABSTRACT

Securinega virosa is one of the African medicinal plants described as a true “cure all” among traditional practitioners. Different parts of Securinega virosa have been used in the management of different disorders in Nigeria and other parts of the world. There is therefore the need to establish the toxicity profile of Securinega virosa leaves. In this study, toxicological assessment of the methanol leaf extract of Securinega virosa was carried out in Wistar rats. Forty rats of either sex (20 males and 20 females) were divided into four groups of 10 rats (5 males and 5 females) each and kept in separate cages. The rats were administered with 250, 500 and 1000 mg/kg body weight of the extract daily for 28 days. The effect of the extract on body weight, haematolological and biochemical (renal function, liver function and lipid profile) parameters as well as histopathological studies of the organs (liver, kidney, spleen, lungs, brain, heart, stomach, uterus, ovaries and testes) was assessed. The oral and the intraperitoneal median lethal dose (LD50) values of the extract were estimated to be greater than 5000 mg/kg bodyweight and within the doses of the study, no mortality was observed in both acute and sub-acute toxicity studies. The extract had no significant (p˃0.05) effect on body weight. The haematological parameters measured were normal except a significant (p˃0.05) increase in platelets count observed at the dose of 1000 mg/kg body weight. There was a significant (p˃0.05) increase in liver biomarkers, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase in both male and female rats treated at doses of 500 and 1000 mg/kg body weight when compared with the control. There was also a significant (p˃0.05) increase in the serum urea and creatinine in these groups. Histopathological findings indicated that there were some levels of liver damage characterised by centrilobular necrosis peri-portal hepatocytic vacuolation and scattered inflammatory changes, kidney (glomerular damage and atrophy, tubular epithelial cell necrosis and vascular congestion), and brain (degeneration of nerve fibres, pyknosis and vacuolation) at doses of 500 and 1000 mg/kg body weight. Some levels of damage was also observed in the spleen (splenic congestion) and lungs (diffused areas of congestion and inflammation) of both male and female rats across all the doses administered. These findings suggest that the methanol leaf extract of Securinega virosa is practically non toxic following acute administration, however, it produced some levels of damage to the liver, kidney, heart, spleen, lungs and brain in Wistar rats following oral administration for 28 days.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background

In the absence of an efficient primary health care system, traditional medicine occupies a central place in the provision of health care, especially among rural communities of developing countries. The strong historical bond between plants and human health is well substantiated by plants species‟ diversity and related knowledge of their use as herbal medicines (Tibuti and Dhillion, 2003). In addition, it is attributable to the accessibility and affordability of herbal medicines (Steenkamp, 2003). The difficult economic conditions often limit access to the rather expensive conventional medicines that are available, with the result that people seek out less expensive alternative medicines such as herbal products (WHO, 2010).

A medicinal plant is any plant which in one or more of its parts contains substances that can be used for therapeutic purposes or which are precursors for the synthesis of therapeutic agents (Sofowora, 2008). The use of traditional medicine and medicinal plants in most developing countries, as a normative basis for the maintenance of good health, has been widely observed (Jordan et al., 2010).

A survey conducted by the World Health Organization (WHO) indicated that about 70-80% of the world populations rely on non-conventional medicine mainly of herbal sources in their primary healthcare (WHO, 2003). This is especially the case in developing countries where the cost of consulting a qualified medical doctor and the price of medication are beyond the means of most people (Dyson, 1998; Chan, 2003).

Different retrospective studies done over the last two decades indicated that the incidence of deaths occurring due to exposure to plants (as a proportion of total patients poisoned by traditional plant medicine) was about 1.5% in France, 5% in Belgium, 6.5% in Italy,7.2% in Switzerland and 6% in Turkey (Gaillard and Pepin, 1999). The total number of deaths due to exposure to plants throughout the world however, is very difficult to establish and must certainly be underestimated since all cases of such deaths were, from analytical and forensic points of view, not always well documented and thus, rarely published (Bent and Ko, 2007)

Despite the growing market demand for herbal medicines, there are still concerns associated with not only their use, but their safety.Many plants produce toxic secondary metabolites as natural defence from adverse conditions. In some toxicologically and medicinally relevant plant species like Digitalis purpurea, Hyoscyamus niger, Atropa belladonna, Physostigma venenosum, Podophyllum peltatumand Solanum nigrum, these toxic substances are not distinguished from therapeutically active ingredients (Mosihuzzaman, 2012).

1.2 Statement of Research Problem

Herbs and herb-derived medicines have played a crucial role in health and disease management for many centuries. In Ghana, Mali, Nigeria and Zambia, the first line of treatment for 60% of children with high fever resulting from malaria is the use of herbal medicines at home (WHO, 2012). The global demand for herbal medicinal products has increased significantly in recent years. It is estimated that, the world‟s population will be more than 7.5 billion in the next 10 to 15 years. This increase in population will occur mostly in the southern hemisphere, where approximately 80% of the population still relies on a traditional system of medicine based on herbal drugs for primary healthcare (WHO, 2012). Less than 10% of herbal products in the world market are truly standardized to known active components and strict quality control measures are not always diligently adhered to (Winston, 2007). This raises concern on their safety and implications for their use as medicines. Toxicity testing can reveal some of the risks that may be associated with the use of herbs, therefore avoiding potential harmful effects when used as medicine. Some plant-based drugs have been used for centuries and for some like cardiac glycosides, there is no alternative conventional medicine (Obidike and Salawu, 2013). Therefore, medicinal plants and their bioactive molecules are always in demand and are a central point of research. The earliest report of the toxicity of herbs originated from Galen, a Greek pharmacist and physician who showed that herbs do not contain only medicinally beneficial constituents, but may also be constituted with harmful substances (Cheng and Zhen, 2004).

The most important aspects during the usage of drugs from all sources are their quality, efficacy and safety. Assumptions have been made that the use of herbal drugs in humans is going on without any noticeable toxic effects (Sushma et al., 2012). The assumption is not based on scientific evidence but on the fact that herbs are often believed to be safe because they are „natural‟ (Glesler, 1992). A study carried out on 548 compounds marketed between 1975 to1999 showed that 10.2% were withdrawn or acquired a black box warning due to toxicity (Boone et al., 2005). This emphasizes the need to carry out toxicity testing on all drugs intended for human and animal consumption.

1.3 Justification of the Study

The primary aim of toxicological assessment of any herbal medicine is to identify adverse effects and to determine limits of exposure level at which such effects occur. An equally important objective of toxicity testing is the detection of toxic plant extracts or compounds derived thereof in the early (pre-clinical) and late (clinical) stages of drug discovery and development from plant sources. This will facilitate the identification of toxicants which can be discarded or modified during the process and create an opportunity for extensive evaluation of safer promising alternatives (Gamaniel, 2000).

One of the basic criteria set by WHO for the use of herbs as medicines is that they should be shown to be non-toxic (WHO, 2011). Although the use of ethno-medicine is widespread in Africa, most of the plants have not been thoroughly investigated for their toxicities (Sowemimo et al., 2007).Besides studies on quality and efficacy of herbal medicines, it is necessary to ensure the safety of a product and this entails toxicity testing. Toxicity testing of herbal drugs has also been found to have a lot of benefits (OECD, 2008). Notably, it is easy to identify the toxic effects and thus determine the limit of exposure levels especially to sensitive population. Once these toxicants are known they may be discarded or modified via dosage adjustment, chemical group or structural adjustments (Obidike and Salawu, 2013).

The leaves, stem bark and root bark extracts of Securinega virosa have been used in the management of different disorders in Nigeria (Magaji et al., 2014; Tanko et al., 2008). There is paucity of scientific information on the potential toxicity profile of the leaf extract of Securinega virosa. Toxicity data, are therefore required to predict the safety and effect of short and long term exposure to the plant because of its widespread use in the management of various disorders.

1.4 Aim of the Study

The aim of this study is to establish the toxicity profile of the methanol leaf extract of Securinega virosa in Wistar rats.

1.5 Specific Objectives

The specific objectives of the study were to:

1. determine the effect of methanol leaf extract of Securinega virosaon body weight changes in rats.

2. evaluate the effect of methanol leaf extract of Securinega virosaon some haematological parameters in rats.

3. evaluate the effect of methanol leaf extract of Securinega virosa on some biochemical parameters in rats.

4. assess the histological changes on some vital organs of rats exposed to methanol leaf extract of Securinega virosa.

1.6 Research Hypothesis

H0 (Null Hypothesis): The methanol leaf extract of Securinega virosadoes not produce toxic effects in Wistar rats.

Ha (Alternate Hypothesis): The methanol leaf extract of Securinega virosa produce toxic effects in Wistar rats.

The null hypothesis will be rejected if p-value is ˃ 0.05 and the alternative hypothesis will be accepted.