GC-MS Analysis and Inhibitory Evaluation of Terminalia catappa Leaf Extracts on Major Enzymes Linked to Diabetes

Abstract

Terminalia catappa leaves are used in managing both diabetes mellitus and its complications in Southwest Nigeria. However, its inhibitory activity on enzymes implicated in diabetes is not very clear. This study investigated the in vitro inhibitory properties and mode of inhibition of T. catappa leaf extracts on enzymes associated with diabetes. The study also identified some bioactive compounds as well as their molecular interaction in the binding pocket of these enzymes. Standard enzyme inhibition and kinetics assays were performed to determine the inhibitory effects of aqueous extract (TCA) and ethanol extract (TCE) of T. catappa leaves on α-glucosidase and α-amylase activities. The phytoconstituents of TCA and TCE were determined using GC-MS. Molecular docking of the phytocompounds was performed using Autodock Vina. TCA and TCE were the most potent inhibitors of α-glucosidase (IC50 = 3.28 ± 0.47 mg/mL) and α-amylase (IC50 = 0.24 ± 0.08 mg/mL), respectively. Both extracts displayed a mixed mode of inhibition on α-amylase activity, while mixed and noncompetitive modes of inhibition were demonstrated by TCA and TCE, respectively, on α-glucosidase activity. The GC-MS analytic chromatogram revealed the presence of 24 and 22 compounds in TCE and TCA, respectively, which were identified mainly as phenolic compounds, terpenes/terpenoids, fatty acids, and other phytochemicals. The selected compounds exhibited favourable interactions with the enzymes compared with acarbose. Overall, the inhibitory effect of T. catappa on α-amylase and α-glucosidase may be ascribed to the synergistic action of its rich phenolic and terpene composition giving credence to the hypoglycaemic nature of T. catappa leaves.

Nauclea latifolia Sm. Leaf Extracts Extenuates Free Radicals, Inflammation, and Diabetes-Linked Enzymes

“…Higher β-carotene and lycopene content in NLE is as a result of their classification and structure making them more soluble in ethanol than water [22,23]. Previous studies have reported a higher phytochemical content in their ethanolic extracts than their aqueous thus corroborating the findings in this study [15,24]. Antioxidants scavenge free radicals which are products of metabolism.…”

“…The anti-inflammatory activity of this class of phytochemical has been well reported such as the erythrocyte membrane stabilising effect, cation-binding activity of tannins and wound healing properties of lycopene and β-carotene [36][37][38]. Boucherle et al [39] reported the presence of tannins in the leaf extract of N. latifolia buttressing findings 9 Oxidative Medicine and Cellular Longevity usually witnessed with synthetic inhibitors such as acarbose and voglibose [15,42]. This study revealed the promising inhibitory α-amylase and α-glucosidase potential of N. latifolia leaf extracts.…”

“…Alpha-Glucosidase (α-Glucosidase) Inhibitory Activity. α-Glucosidase inhibitory activity of the extracts was determined according to the method described by Iheagwam et al [15]. Briefly, 250 μL of each extract or acarbose at different concentrations (1-5 mg/mL) was incubated with 500 μL of 1.0 U/mL α-glucosidase solution in 100 mM phosphate buffer (pH 6.8) at 37°C for 15 min.…”

“…For α-glucosidase inhibition kinetics, the method described by Iheagwam et al [15] was adopted. Briefly, 250 μL of extract (5 mg/mL) was preincubated with 500 μL of α-glucosidase solution for 10 min at 25°C as inhibitor samples while 500 μL of α-glucosidase was preincubated with 250 μL of phosphate buffer (pH 6.9) in another set of tubes as noninhibitor samples.…”

“…An aliquot (250 μL) of 1% starch solution (dissolved in 100 mM phosphate buffer (pH 6.8)) was then added to the reaction mixture and incubated at 37°C for 1 h. One mL of DNS colour reagent was then added and boiled for 10 min. The absorbance of the resulting mixture was measured at 540 nm, and the inhibitory activity was expressed as a percentage of control without inhibitors [15]. The α-amylase inhibitory activity was calculated using equation (10):…”