Phytochemicals are plant secondary metabolites that

Phytochemicals are plant secondary metabolites that possess many health benefits [8]. Their health benefits, including antidiabetic activities [9], are attributed to antioxidant activities and the inhibition of enzymes such as α-amylase, α-glucosidase and aldose reductase [10]. Brachystegia eurycoma Harms and Detarium microcarpum, both of the family Caesalpinioideae, are two underutilized leguminous tree crops that have both food and medicinal uses. For instance, in South-Eastern part of Nigeria, both seeds are used for thickening of traditional soups [11]. B. eurycoma is a very economically valuable tree crop mostly grown in the tropical rain forest of West Africa [12]. The nutrients composition of the seeds shows that they are a good source of nutrient supplement as earlier reported by some studies [11,13]. The seed flour has good water prolyl hydroxylase capacity, and so, is useful as functional agent in processed foods such as bakery products and meat formulations [12]. On the other hand, D. microcarpum is found mostly in savannah forest of dried type. It is a high yielding tree with large quantities of its fruits being left wasting every year in the field [14]. The seed is known to contain lipids, carbohydrates, proteins, crude fiber and the essential elements: Na, K, Mg, Ca, S, P and Fe [15]. In African ethno-medicine, both plants are used in the treatment of microbial infections such as syphilis, dysentery, bronchitis, leprosy, sore throat, pneumonia, diarrhea, malaria and tuberculosis, and other diseases such as asthma and inflammatory conditions [16,17]. Methanol extract of D. microcarpum leaf has also been reported to possess antidiabetic activity [18]. Although there are these reports on the health benefits of B. eurycoma and D. microcarpum, information on the ability of their seeds flours extracts to inhibit the activities of some key enzymes linked to the pathology and complications of T2D is scarce. Therefore, this study was designed to evaluate the inhibitory activity of the methanol extracts of B. eurycoma and D. microcarpum seeds flours against α-amylase, α-glucosidase, aldose reductase (AR) and lipid peroxidation, as well as determine their antioxidant properties in vitro.
Materials and methods
Results The IC50 of B. eurycoma and D. microcarpum seeds flour extracts on α-amylase, α-glucosidase, aldose reductase (AR) and Fe2+-induced lipid peroxidation are presented in Table 1. The results revealed that both plants were able to inhibit α-amylase, α-glucosidase and AR. Fig. 1a–c further depicted that their inhibitory pattern was dose-dependent. Consistently, the IC50 values of B. eurycoma on these three carbohydrate-metabolizing enzymes were lower than those of D. microcarpum; hence, B. eurycoma had stronger inhibitory activity than D. microcarpum. Similarly, both extracts inhibited Fe2+-induced lipid peroxidation in rat pancreas homogenate in a dose-dependent manner (Fig. 1d), with B. eurycoma being more effective than D. microcarpum, as indicated by its lower IC50 value. The results of the antioxidant activities of both extracts, as tested using DPPH and ABTS+ scavenging, and reducing power assays, are presented in Table 2. Both extracts exhibited DPPH scavenging activity in a dose-dependent manner. However, based on their IC50 values, B. eurycoma (5.05mg/mL) possessed a stronger DPPH scavenging ability than D. microcarpum (12.63mg/mL). Similarly, B. eurycoma had significantly (P<0.05) higher ABTS+ scavenging ability and reducing power than D. microcarpum. The antioxidant phytochemical composition of B. eurycoma and D. microcarpum on dry weight basis are presented in Table 3. The result showed that B. eurycoma had significantly (P<0.05) higher total phenolics, tannins, total flavonoids and total saponins contents than D. microcarpum.
Discussion In view of the attendant clinical side effects and high cost of synthetic oral hypoglycemic drugs available for the management of T2D, research focus has been on affordable natural products that can be used to manage postprandial hyperglycemia and diabetic complications with minimal side effects. The results obtained in this study (Table 1) revealed that extracts of B. eurycoma and D. microcarpum seeds flours were potent in inhibiting the activities of α-amylase, α-glucosidase and AR. Plant-derived inhibitors of carbohydrate-hydrolyzing enzymes can delay carbohydrate digestion, thereby leading to a reduction in the rate of glucose absorption, and consequently, reduce the rise in postprandial blood glucose [31]. Thus, the level of postprandial blood glucose depends partly on the activities of these enzymes mainly, α-amylase and α-glucosidase, that breakdown dietary starch and sugars into glucose [32]. α-Amylase, found in the saliva and pancreatic juice, is responsible for cleaving the α-1,4 bonds of starch releasing dextrin, maltose, and maltotriose [33]. Subsequently, the glycosidic linkages of these oligosaccharides are hydrolyzed by α-glucosidase present in the ciliary membrane of small intestine to produce glucose molecules which are then absorbed [34]. Hence, the inhibition of α-amylase and α-glucosidase activities represents one of the most effective approaches to control hyperglycaemia in type 2 diabetic patients [20].