Phytochemical Compositions and In vitro Assessments of Antioxidant and Antidiabetic Potentials of Fractions from Ehretia cymosa Thonn

Abstract

Background: Ehretia cymosa Thonn. is a popular medicinal plant used in different parts of West Africa for the treatment of various ailments including diabetes mellitus.

Objective: The current study investigates bioactive constituents and in vitro antioxidant and antidiabetic potentials of fractions from extract of E. cymosa.

Materials and methods: Phytochemical investigation and antioxidant assays were carried out using standard procedures. Antidiabetic potential was assessed by evaluating the inhibitory effects of the fractions on the activities of α-amylase and α-glucosidase, while bioactive constituent's identification was carried out using gas chromatography-mass spectrometric (GC-MS) analysis.

Results: The phytochemistry tests of the fractions revealed the presence of tannins, phenols, flavonoids, steroids, terpene, alkaloid, and cardiac glycosides. Methanol fraction shows higher phenolic (27.44 mg gallic acid/g) and flavonoid (235.31 mg quercetin/g) contents, while ethyl acetate fraction revealed higher proanthocyanidins (28.31 mg catechin/g). Methanol fraction displayed higher (P < 0.05) 1,1-diphenyl-2-picryl-hydrazyl (0.47 mg/mL), 2,2-azino-bis (3-ethylbenzothiazoline)-6-sulfonic acid (0.49 mg/mL), and hydroxyl radical (0.55 mg/mL) scavenging activities, while ethyl acetate exhibited strong metal chelating (0.61 mg/mL) and superoxide anion (1.68 mg/mL) scavenging activity. Methanol and ethyl acetate fractions displayed higher inhibition (P < 0.05) against α-glucosidase (0.60 mg/mL) and α-amylase (2.11 mg/mL), respectively. Methanol fraction also inhibited α-amylase and α-glucosidase in competitive and noncompetitive modes, respectively. The GC-MS chromatogram of the methanol fraction revealed 24 compounds, which include phytol (1.78%), stearic acid (1.02%), and 2-hexadecyloxirane (34.18%), which are known antidiabetic and antioxidant agents.

Conclusion: The results indicate E. cymosa leaves as source of active phytochemicals with therapeutic potentials in the management of diabetes.

Summary: E. cymosa fractions possess antioxidant and antidiabetic activities. Hence, it is a source of active phytochemicals with therapeutic potentials in the management of diabetesThe high flavonoid, phenolic, and proanthocyanidin contents of fractions from E. cymosa also contribute to its antioxidant and antidiabetic propertiesMethanol fraction of E. cymosa displayed better antidiabetic activities compared to acarbose as revealed by their half maximal inhibitory concentration valuesMethanol fraction of E. cymosa extract contains phytol, hexadecyl oxirane, and stearic acid, which are reported to possess antidiabetic and antioxidant potentials. Abbreviations used: ABTS: 2,2- Azino-bis (3-ethylbenzothiazoline)-6-sulfonic acid, DPPH: 1,1-diphenyl-2-picryl-hydrazyl, PMS: Phenazine methosulfate, NBT: Nitroblue tetrazolium, NADH: Nicotinamide adenine dinucleotide, TCA: Trichloroacetic acid, TBA: Thiobarbituric acid, DNS: Dinitrosalicylic acid.

Keywords: Ehretia cymosa; antioxidant; bioactive; diabetes; α-amylase; α-glucosidase.

Figure 1

2,2-azino-bis (3-ethylbenzothiazoline)-6-sulfonic acid radical scavenging effect of Ehretia cymosa leaves fractions. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05). ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 2

Hydroxyl (OH) radical scavenging effect of Ehretia cymosa leaves fraction. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05). ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 3

Metal chelating potential of Ehretia cymosa leaves fraction. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05). ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 4

Superoxide anion radical scavenging effect of Ehretia cymosa leaves fractions. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05). MBE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 5

1,1-diphenyl-2-picrylhydrazyl radical scavenging effect of Ehretia cymosa leaves fractions. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05), ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 6

Inhibitory potency of Ehretia cymosa leaves fractions against α-amylase activity. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05). ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 7

Inhibitory potency of Ehretia cymosa leaves fractions against α-glucosidase activity. The values are expressed as means ± standard error of the mean of triplicate determinations. Bars not sharing a common letter at the same concentration are significantly different (P < 0.05), ECE: Ehretia cymosa ethyl acetate fraction, ECM: Ehretia cymosa methanol fraction

Figure 8

Lineweaver–Burk plot of Ehretia cymosa methanol fraction eliciting noncompetitive Inhibition on α-glucosidase activity. Results represent mean ± standard error of the mean (n = 3); (P < 0.05). ECM: Ehretia cymosa methanol fraction

Figure 9

Lineweaver–Burk plot of Ehretia cymosa methanol fraction eliciting competitive Inhibition on α-amylase activity. Results represent mean ± standard error of the mean (n = 3); (P < 0.05). ECM: Ehretia cymosa methanol fraction

Figure 10

Gas chromatography-mass spectrometric chromatogram of Ehretia cymosa methanol fraction