ABSTRACT
This study was carried out to investigate the phytochemical constituents of the methanol extract of the stem (bark) of Alstonia boonei (MEAB), in vitro antioxidant activity of the extract and its possible antidiabetic and antioxidant potential using alloxan- induced diabetic rats as model. The qualitative analysis of the extract showed a wide range of phytochemicals, which could be physiologically potent in ameliorating several diseases. Quantitative phytochemical analysis revealed that the extract contains relatively high concentration on tannin (7.375±0.005mg/100g), flavonoid (6.176±0.003 mg/100g) and phenols (5.867±0.003 mg/100g). The quantitative result of antioxidant vitamins shows that vitamin C was highest (24.91±0.005mg/100g) compared to vitamin A (1.314±0.002µg/g) and vitamin E (0.886±0.002mg/100g). The methanol extract of Alstonia boonei scavenged 1, 1- diphenyl-2-picrylhydrazyl radical (DPPH.) in a concentration dependent manner with a correlation coefficient (R2) of 0.7066, indicating antioxidant activity with effective concentration that inhibits 50 percent of the radicals (EC50) of 12.33 ± 0.2µg/ml compared to ascorbic acid standard EC50 of 98 ± 0.02µg/ml. The superoxide radical scavenging activity was concentration-dependent with an EC50 of 7.03±0.42µg/ml compared with ascorbic acid and rutin standards with EC50 of 812.97±0.97µg/ml and 3.47 ± 0.6µg/ml respectively. The extract also showed hydroxyl radical scavenging activity with an EC50 of 42.75±0.02µg/ml compared to α- tocophenol standard with EC50 of 232.31 ± 6.97µg/ml. The nitric oxide radical scavenging activity shows that the extract scavenged nitric oxide radical in a concentration dependent manner with 500µg/ml being more effective than 500µg/ml of ascorbic acid standard. There was a significant increase (P > 0.05) in the serum glucose level in group 2 (diabetic untreated) compared to group 1 (normal control). Significant decrease (P < 0.05) in glucose serum concentration was recorded in all groups treated with the extract and the standard drug compared to group 2 (diabetic untreated) . There was a significant increase (P < 0.05) in urea, creatinine, sodium ion and chloride ion concentrations of group 2 (diabetic untreated) compared to group 1 (normal control). Significant decrease (P < 0.05) in urea, creatinine, sodium ion and chloride ion concentrations was recorded in all groups treated with the methanol extract and the standard drug(group 3 to 6) compared to group 2 (diabetic untreated). There was no significant increase (P > 0.05) in potassium ion concentration of group 2 when compared with group 1. There was a significant increase (P < 0.05) in the serum concentration of Aspartate aminotransferase, (AST), Alanine aminotransferase, (ALT) and Alkaline phosphatase, (ALP) of group 2 (diabetic untreated) when compared with group 1 and significantly reduced (P < 0.05) in all groups treated with the extract and standard drugs when compared to group 2. Serum superoxide and catalase activities were significantly (P < 0.5) reduced in group 2 (diabetic untreated) when compared to the normal control. Serum superoxide and catalase activities increased significantly (P < 0.05) in all groups treated with the extract and standard drugs when compared to group 2 (diabetic untreated). There was a significant increase (P < 0.05) in serum malondialdehyde (MDA) concentration of group 2 (diabetic untreated) and a significant reduction (P < 0.05) in all groups treated with the extract and the standard drug compare to group 2. These results suggest that methanol extract of the stem (bark) of Alstonia boonei (MEAB), possesses and antidiadetic and antioxidant potentials.
CHAPTER ONE
INTRODUCTION
Diabetes is one of the most challenging health problems in the twenty first century (Rahman et al., 2009). Diabetes currently afflicts 171 million people worldwide (Boden and Taggart, 2009). Normal non-diabetic patients maintain plasma glucose <100 mg/dl in the fasting and <135 mg/dl in the post prandial period (Rossetti et al., 2008). Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action or both (American Diabetes Association, 2009a). Diabetes mellitus is classified as type 1, type 2, with other specific examples and gestational diabetes (American Diabetes Association, 2008). Type 1 diabetes is known as insulin dependent diabetes or Juvenile-onset diabetes and type 2 diabetes is known as non-insulin dependent or adult onset diabetes (American Diabetes Association, 2009b). A slowly progressive form of type 1 diabetes was acknowledged as latent autoimmune diabetes in adults (LADA) by the World Health Organization (WHO) and American Diabetes Association (ADA) (Van Deutekom et al., 2008). Classification schemes define type 1 diabetes as a state of absolute insulin deficiency and type 2 as a state of insulin resistance combined with inadequate insulin secretion (Greenbaum et al., 2009). Type 1 diabetes is an autoimmune disease where auto reactive immune cells attack insulin producing β-cells, destroying insulin reserve leading to hyperglycemia (Eldor et al., 2009). The rate of loss of β-cell function is affected by factors like age at diagnosis, degree of metabolic control, immune status, genetics and marked inter-individual variation (Palmer, 2009). The symptoms of type 1 diabetes are significant weight loss and ketoacidosis (Ludvigsson et al., 2008). Diabetes Type 2 diabetes is a progressive disease characterized by declining β-cell function that in concert with insulin resistance, leads to loss of glycemic control and eventual diabetes complications (Nauck et al., 2009). Type 1.5 diabetes also known as latent autoimmune diabetes in adults (LADA) is an important form of diabetes although it is frequently under estimated (Mayer et al., 2007). Type 1.5 diabetes is also known as slowly progressive type I diabetes, autoimmune diabetes in adults with slowly progressive β-cell failure, autoimmune diabetes not requiring insulin at diagnosis, autoimmune diabetes in adults and type 1.5 diabetes (Dunn et al., 2008). Type 1.5 diabetes has a later onset and slower progression towards an absolute insulin requirement (Cernea et al., 2009). Type 1.5 diabetes occurs in about 10% of patients classified as type 2 diabetes and not initially requiring insulin (Agardh et al., 2009). Diagnosis of type 1.5 diabetes is difficult due to lack of defining features (Jasem et al., 2010).
1.1 Alstonia boonei