Diabetes is becoming a pandemic disease despite the recent surge in new drugs to manage the condition. The limitations of currentlyavailable oral anti-diabetic agents either in terms of efficacy/safety coupled with the emergence of diabetes into a global epidemic have encouraged a concerted effort to search indigenous, inexpensive botanical sources to manage diabetes more efficiently. Chrysophyllumalbidum (Linn) belongs to Sapotaceae family and is commonly called African star apple. Its various usesas anti-oxidant, antimicrobial and anti-hyperlipidemic agents have been described in the literature.This study aimed at evaluating the nutritive and non-nutritive components and anti-diabetic properties of the edible portions (seed-shell pericarp, pulp and skin) of C. albidum fruit in streptozotocin-induced diabetic male albino rats.
The nutritive and non- nutritive components in seed-shell pericarp, pulp and skin of C. albidum fruit were analyzed using standard methods.In addition, the anti-diabetic capacity in different solvents of seed-shell pericarp, pulp and skin extracts of C. albidum fruit using alpha-amylase and alpha-glucosidase inhibitory assays were investigated. Furthermore, animal studies were conducted, consisting of sixty rats and divided into four groups. Diabetes was induced using 50mg/kg streptozotocin (i.p.), and a 70g/kg C. albidum fruit skin (CAFS) formulated diet was fed to streptozotocin-induced diabetic rats for 28 days to evaluate its anti-diabetic efficacy against glibenclamide (2.5mg/kg b.w.) as standard. Fasting blood glucose levels and body weights of rats were measured on weekly intervals starting with base line untill the end of treatment. Other biochemical parameters such as serum insulin, glycosylated haemoglobin, hepatic glycogen, plasma and liver lipid profile contents were evaluated at the end of treatment.Histopathological examinations of liver and pancreatic sections were also carried out.
Results of nutritive composition revealed that CAFS contained the highest content of copper (0.55mg/100g) and manganese (2.25mg/100g).  Also the non-nutritive contents of CAFSshowed the highest of saponin (0.41%), pectin (0.44%), cellulose (2.76%), arabinose (4854.79mg/100g) and starch (29.15%), compared with seed-shell pericarp and pulp. Hexane extract of CAFS exhibited the highest inhibitory activities on alpha-amylase (96.70%) and alpha-glucosidase (86.93%) at a concentration of 0.04mg/ml compared with other extracts studied. In vivo studies indicated that CAFS-treated rats had increased body weight from 216.94g to 226.88g and decreased fasting blood glucose from 289.11mg/dl to 122.66mg/dlbefore- and after- treatment respectively. Results of studies at the end of treatment revealed that CAFS-treatment significantly (p<0.05) increased levels of serum insulin (7.40µU/ml) and hepatic glycogen (9.63mg/g wet tissue) while it decreased glycosylated haemoglobin (5.45%), compared with diabetic (untreated) control group. CAFS-treatment reduced plasma and liver lipids except high density lipoprotein-cholesterol compared with diabetic-untreated group. These results were comparable with the standard drug-treated group. Histopathological analysis on liver and pancreas of CAFS-treatedgroup showed regenerative effects.

As a result of anti-hyperglycemicand anti-hyperlipidemic potentials of CAFS,it can be concluded that CAFS may have a considerable impact inpreventing the ill effects of diabetes and lipid disorders in experimental diabetes. Thus, CAFS could be used as therapeutic adjunct in the management of diabetes.

1.1 Background to the Study
Dietary control is vital in the management of diabetes. Reports from FAO (1998); WHO and FAO (2003) have shown that diets with low saturated fat, cholesterol and glycemic index as well as high contents of soluble fiber, vitamins and minerals are effective in the management of diabetes. Low glycemic foods contain sugars that digest and absorbed slowly into the blood and thus control blood sugar levels. The fiber-like substances such as gums and pectin reduced blood postprandial glucose levels (Jenkins et al., 1978; Ou et al., 2001) while diabetic subjects fed xanthan gum have lower fasting, postprandial serum glucose levels and total plasma cholesterol (Osilesi et al., 1985). Jenkins et al. (1978) reported that daily intake of 5–10 g of soluble fiber from different sources reduced serum cholesterol by 5–10%.  Fruits serve as one of the best sources of dietary fiber, minerals, Vitamins A, C and E and frequent intake of vegetables and fruits have demonstrated a lowered risk of diabetes, heart disease, hypertension, stroke and cancer (Southon, 2000; Wargovich, 2000). Fruits supply carbohydrates in the form of soluble sugars, cellulose and starch (Nahar et al., 1998) and serve as source of nutrient, appetizer and food supplement in a world faced with problem of food scarcity.

Diabetes mellitus (DM) is a worldwide endemic disease in terms of occurrence, cost of medical care, and general complications (King et al., 1998). The metabo­lism of protein, carbohydrate and fat are affected in diabetic conditions, resulting in hyperglycemia. DM complication is mainly associated with a high risk of coronary heart disease (Giugliano et al., 1996), atherosclerosis, stroke and peripheral vascular disease. The incidence of DM world wide, is projected to increase from 4% in 1995 to 5.4% by the year 2025 (Mohamed et al., 2006), with the utmost increases set to occur in the devel­oping countries of Africa, Asia and South America (WHO, 2008).

According to WHO (1994) and American Diabetes Association (2008), diabetes mellitus can be classified into insulin-dependent diabetes mellitus, IDDM (type 1 diabetes mellitus) and non- insulin- dependent diabetes mellitus, NIDDM (type 2 diabetes mellitus). Insulin-dependent diabetes mellitus is caused by cellular-mediated autoimmune damage to beta cells of the pancreas, accounts for about 5% to 15% of diabetic cases and occurs mostly in children or adolescents (Ranjan and Ramanujam, 2002). Genetics and environmental factors are implicated in the formation of IDDM. Administration of exogenous insulin is thus required to avert ketosis and preserve life (Lokesh and Amit, 2006). Non- insulin- dependent diabetes mellitus starts as insulin resistance, accounts for 85-95% of cases globally and occurs usually in adults of 40 years and above (WHO Regional Office for the South-East Asia, 2009). It is associated with hyperglycemia and glycosuria. The risk factors increases with age, lack of physical activity, obesity and impaired glucose tolerance.

Insulin resistance occurs when glucose is not properly utilized by the cells leading to high blood glucose in circulation. To maintain blood glucose level, the kidney excretes exess blood glucose through the urine and glucosuria occurs with increased excretion of water and sodium when blood glucose level exceeds the renal threshold (160 - 180 mg/L). The failure to use glucose by the body cells, results to increase appetite (polyphagia) (Robinson et al., 1986). The summary of the symptoms of diabetes is shown in Figure 1.

Insulin resistance is associated with decreased glucose uptake and stimulation of muscle glycogen synthesis (Cline et al., 1999). In addition, alteration of  enzymatic activities like increased phosphatase activity and/or seryl phosphorylation of the insulin  receptor substrate by glycogen synthesis kinase 3 (GSK- 3), have also been reported in some cases of type 2 diabetes mellitus (Begum et al., 1991; Nadiv et al.,1994; Eldar-Finkelman and Krebs, 1997). Insulin resistance plays an important role in the etiology of many disorders including obesity, NIDDM, glucose intolerance, hypertension and other related disorders. It has been reported that autophosphorylation of insulin receptor kinase and subsequent phosphorylation of its principal substrate, IRS-1, are significantly lowered in insulin-responsive tissues of patient with severe obesity or NIDDM (Nadiv et al., 1992). Increased lipolysis and decreased lipogenesis occurred when there is a fall in circulated insulin leading to fatty acids release from adipose tissues and subsequently oxidized to ketone bodies in the liver. The rapid release of fatty acids into the blood leads to increase level of blood cholesterol and the formation of atherosclerosis (Khan and Ahmad, 1993). In diabetics, there is increase in excreted nitrogen through deamination, which is accompanied by cellular potassium excretion in urine when the muscle protein is broken down to support gluconeogenesis in the liver.

Of the several approaches applied, to lower and control the occurrence of diabetes, drug and diet therapies form the most popular approaches. The most common approach are the drug therapy with four distinct classes of oral hypoglycemic agents (biguanides, sulfonylureas, thiazolidinediones and alpha-glucosidase inhibitors) currently being recommended for use to treat NIDDM.  In dietary therapy, dietary modifications with adequate exercise are used to prevent excessive weight gain and obesity (Derek, 2001).  Intake of diets with low total and saturated fat, limited protein with replacement by complex carbohydrate and/or mono unsaturated fatty acids are the recommended diets for type 2 diabetes patients. Controlled diets will improve the metabolic control in diabetic subject and lower the risk of diabetes complications (Griver and Henry, 1994).

A large number of plants with hypoglycemic activity have been reported in different animal models. Aloe vera, Acacia arabica, Allium sativum L., Bombax ceiba L., Allium cepa, Brassicajuncea (L.) Cassia auriculata L., Caesalpinia bonducella (L.) and Musa sapientum L. are some of the scientifically validated antidiabetic plants (Modak et al., 2007).

Plant of Study

Chrysophyllum albidum (Linn), commonly called African star apple is a forest tree species of Sapotaceae family (Figure 2). It is widely distributed in Nigeria, Niger Republic and Uganda (Bada, 1997). C. albidum has various ethno-medicinal uses (Dalziel, 1937; Amusa et al., 2003) and across Nigeria, it is locally called ‘‘agbalumo’’ in South Western Nigeria and “udara” in South Eastern Nigeria. 

The fleshy pulp of C. albidum fruit is taken as snack, the seeds serve as a source of oil for various uses and the fruit is a good source of ascorbic acid (Adisa, 2000; Adepoju and Adeniji, 2012). C. albidum plants are rich in natural antioxidants and can thus support health by preventing oxidative stress related disease such as diabetics, cancer and coronary heart diseases (Burits and Bucar, 2002). The antioxidants content in vegetables and fruits has been associated with the diminished risk to chronic diseases by scavenging free radicals and prevent cells damage (Halliwell, 1994).

The antimicrobial and phytochemical screening of C. albidum seed cotyledon (Idowu et al., 2003; Okoli and Okere, 2010), leaves (Duyilemi and Lawal, 2009; Okoli and Okere, 2010; Kamba and Hassan 2011), root (Okoli and Okere, 2010), and stem bark (Adewoye et al., 2010; Kamba and Hassan 2011) have been investigated. In addition, the anti-hyperglycemic and hypolipidemic effects of C. albidum seed cotyledon ethanolic extract (Olorunnisola et al., 2008) and leaf ethanolic extract (Adebayo et al., 2010) have been reported. Adebayo et al., 2010, 2011a and 2011b, have reported the antiplatelet, antioxidant and hepatoprotective effects of C. albidum leaf while Onyeka et al. (2012) and Omotosho et al. (2013) reported the antifertility and antioxidant effects of C. albidum root bark and fruit juice.

Nwadinigwe (1982); Edem et al. (1984); Adisa (2000); Ige and Gbadamosi (2007); Ureigho (2010); Christopher and Dosunmu (2011); Oyebade et al. (2011); Adepoju and Adeniji (2012), have independently analyzed the nutritional contents of C. albidum pulp. Similarly, Ige and Gbadamosi (2007) analyzed the nutrient compositions of C. albidum fruit-peel (skin) and fruit juice. Ewansiha et al. (2011), analyzed C. albidum seed shell pericarp for its nutritional compositions while Ajewole and Adeyeye (1990), studied the physico-chemical characteristics and fatty acid composition of the seed. However, information on the nutrient contents of seed shell pericarp, fruit skin (peel) and fruit pulp of C. albidum are scanty in available literature. In addition, there is dearth of information on the efficacy of either of these edible portions of C. albidum fruit as remedy for the management of DM. Therefore, this study was design to investigate the nutrtitive and non-nutritive components and the antidiabetic potentials of the edible portions of C. albidum fruit.

1.2 Statement of the Problem
Diet has a vital role in the causes and control of several obesity-associated chronic diseases, such as diabetes and cardiovascular diseases. Current research has increased on studying individual foods to understand their specific role(s) and the mechanisms of action in the diminished risk to diseases in humans. Diabetes has emerged into a global epidemic, inspite of the recent search in new drugs to manage and prevent the condition; its prevalence continues to soar with increased risks and diagnosis in both adult and children (Ludwig and Ebbeling, 2001). In addition, many synthetic hypoglycemic agents such as biguanides, sulfonylureas, α-glucosidase inhibitors and insulin, commonly used for the treatment of diabetes are expensive and associated with serious side effects (Gupta et al., 2010). Sulfonylureas (e.g., glibenclamide) cause severe hypoglycemia, biguanides (e.g., metformins) are unsafe for patients with kidney problem, while α-glucosidase inhibitors cause dose-related malabsorption, flatulence and abdominal bloating (Codario, 2005). In addition, these hypoglycemic agents are not effective in the control of hyperlipidemia condition, which usually accompanies the incidence of diabetes (Derek, 2001). These associated problems with the synthetic oral anti-diabetic agents in terms of inefficacy, non-safety coupled with the emergence of the disease into a global epidemy have necessitate the search for more efficient alternatives with little or no side effect (Ranjan and Ramanujam, 2002). The plant kingdom, thus become a target for the search to develop indigenous, inexpensive botanical sources by multinational drug and biologically active lead compounds (Evans, 1996).

Since ancient times, medicinal plants with various active principles and properties have been used by laymen and physicians to cure a variety of human diseases such as coronary heart disease, diabetes and cancer (Havsteen, 1984; Middleton et al., 2000). Medicinal plants offer exciting opportunity to develop them into novel therapeutics due to their multiple beneficial effects as manipulating carbohydrate metabolism by various mechanisms, enhancing glucose uptake and utilization, restoring integrity and prevention of pancreatic β-cells damage as well as the antioxidant properties. In Nigeria, the populace is unaware of the high nutritional and nutraceutical values of C. albidum fruit; it is however considered as snack for the low-income earners. This has resulted into an information gap of its utilization as a functional food for all and sundry.

1.3  Obective of the Study
The main objective is to evaluate the nutritive and non-nutritive components and antidiabetic properties of the edible portions of C. albidum fruit (seed-shell pericarp, pulp and skin) in streptozotocin-induced diabetic male albino rats.
The specific objectives are to:
1        determine the nutritive and non-nutritivecomponents of the edible portions of C. albidum fruit;
2        assess the potential capability of the edible portions of C. albidum fruit in improving glucose tolerance, insulin sensitivity and oxidative stress factors often associated with diabetes mellitus;
3        compare the antidiabetic potency of the edible portions of C. albidum fruit with that of referenced drug (glibenclamide) and
4        determine the atherogenic and coronary risk indices from the lipid profile of the edible portions of C. albidum fruit.

1.4  Research Questions
1        What are the nutritive and non-nutritive constituents of the edible portions of C. albidum fruit?
2        Can the edible portions of C. albidum fruit improve glucose tolerance, insulin sensitivity and oxidative stress factors often associated with diabetes mellitus?
3        Can the edible portions of C. albidum fruit be as potent as the referenced drug (glibenclamide) in the control of DM?
4        Will the atherogenic and coronary risk indices of the edible portions of C. albidum fruit be low or high?

1.5 Hypotheses
The null hypothesis and alternative hypothesis at p<0.05 are as stated below:
Ho1:The nutritive and non-nutritive components of C. albidum edible portions (seed-shell                          pericarp, pulp and skin) do not possess antihyperglycemic and hypolipidemic                                          properties.
  Ho2:The nutritive and non-nutritive components of C. albidum edible portions (seed-shell
            pericarp, pulp and skin) possess antihyperglycemic and hypolipidemic properties.

1.6 Significance of the Study

The result of this study would be of great significance to the scientific community because it would provide evidence-based information on C. albidum fruit for Nutritionists and Dietitians for dietary management of DM in various communities. C. albidum fruit is readily available in the West Africa sub-region, cheap and with adequate information on its contributions to dietary management of DM. The results would serve as basis for useful information gathering to Food scientists, Biochemists and Pharmacists to research further on the medicinal potentials of C. albidum fruit. Results would also provide valuable information for use in compiling the food composition table of Nigerian food staples. Results would create public awareness of the use of C. albidum fruit as remedy for the management of DM and improve its consumption when in season. Equally, the results would  draw positive attention to attract Scientists to do further investigations on the efficacy of the fruit as remedy for the management of diabetic vascular related complications and other nutritionally related diseases.

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