Abstract
Eleusine coracana is commonly found in the arid regions of Asia and Africa. The seeds are used locally in the management of various diseases such as diabetes, osteoporosis, anaemia, ulcer, depression and insomnia. This study was carried out to determine the antidiabetic activity of different fractions of Eleusine coracana seeds and identify compounds present in the active fractions. Proximate analysis, phytochemical screening and mineral analysis were carried out using standard methods. The powdered seed (5.5 kg) was extracted with methanol in a Soxhlet apparatus. The concentrated crude extract (100 g) was subjected to vacuum liquid chromatography using solvents of increasing polarity (n-nexane, dichloromethane, ethylacetate, 50% ethanol/ethyl, 100% methanol, 20% water/methanol, 50% water/methanol and water) to obtain different fractions. The median lethal dose was determined using Lorke’s method. Antioxidant screening, total phenols and flavonoid content determination were also carried out on the extract and fractions using 1,1, diphenyl 2 picryl hydrazyl (DPPH) free radical scavenging method, ferric reducing antioxidant power (FRAP) method, folin ciocateau and aluminium chloride test respectively. The crude extract and selected fractions at a dose of 200 and 400 mg/kg/day were screened for antidiabetic activity using streptozotocin-induced diabetic rats. The ethylacetate fraction was chromatographed to obtain fractions. Fractions with similar TLC profile were combined and selected combinations were further purified. The ethylacetate and n-hexane fraction were subjected to infrared spectroscopic (IR) analysis and Gas Chromatography-Mass Spectroscopic (GC-MS) analysis to determine the chemical constituent(s) present. The moisture content and total ash of the powdered seed were 0.38 ± 0.14 and 2.23 ± 0.13, respectively. Phytochemical screening revealed the presence of carbohydrates, proteins, xxiv alkaloids, flavonoids, tannins, reducing sugars, saponins, phenols and terpenoids. Mineral analysis revealed the presence of essential minerals such as calcium (362.20 ± 9.01), sodium (11.66 ± 1.17), potassium (19.72 ± 0.39), magnesium (1.06 ± 0.00) and zinc (0.35 ± 0.01). Heavy metals such as nickel and cadmium were not present in the sample while the others fell below WHO recommended limit for heavy metals. The median lethal dose was observed to be 5000 mg/kg/day, no mortality was observed after 24 hr and 14 days of monitoring. Antioxidant screening revealed that the 50% ethylacetate: methanol fraction had the highest antioxidant activity (IC50 = 29.65 μg/mL) as well as the highest total phenol (132.40 ± 0.51 mgGAE/g) content compared to the crude extract and fractions. The crude extract and fractions at 200 and 400 mg/kg/day dose were able to significantly (P < 0.05) reduce the blood glucose level of the diabetic rats at varying degrees compared to the diabetic untreated animals. Photomicrograph of the pancreas revealed that the crude extract and fractions reduced degenerative changes in the beta cells of islet of Langerhans at varying degrees compared to the diabetic untreated animals. At 400 mg/kg/day, the n-hexane fraction showed the least protective effect on the islets cells. IR spectroscopic analysis revealed that carbonyl groups are the major functional groups present in the tested samples. GC-MS analysis of the ethylacetate and n-hexane fractions revealed that the compounds contained in these fractions are non-polar, long chain fatty acids and esters, few alcohols, long chain saturated alkanes and unsaturated alkenes. This study has shown that the various fractions of Eleusine coracana can significantly reduce blood glucose level in diabetic rats and these fractions contain compounds which may attribute to their antidiabetic effect
