Antioxidant Activities of Solanum Nigrum L. Leaf Extracts Determined in in vitro Cellular Models

Abstract

Several medicinal foods abound in traditional medicine with antioxidant potentials that could be of importance for the management of several diseases but with little or no scientific justification to substantiate their use. Thus, the objective of this study was the assessment of the antioxidant effect of two leave extracts of Solanum nigrum L. (SN), which is a medicinal plant member of the Solanaceae family, mainly used for soup preparation in different parts of the world. Then methanolic/water (80:20) (SN1) and water (SN2) leaves extracts were prepared. The total polyphenolic content and the concentration of phenolic acids and flavones compounds were determined. In order to verify whether examined extracts were able to restore the oxidative status, modified by glutamate in primary cultures of astrocytes, the study evaluated the glutathione levels, the intracellular oxidative stress, and the cytotoxicity of SN1 and SN2 extracts. Both extracts were able to quench the radical in an in vitro free cellular system and restore the oxidative status in in vitro primary cultures of rat astroglial cells exposed to glutamate. These extracts prevented the increase in glutamate uptake and inhibited glutamate excitotoxicity, which leads to cell damage and shows a notable antioxidant property.

Keywords: Solanum nigrum L. leave extracts; antioxidant activity; functional food; natural products.

Figure 1

Representative chromatogram of the dry extract reporting the retention time (RT) of gallic acid (1, 0.65 min), protocatechuic acid (2, 13.85 min), chlorogenic acid (3, 20.5 min), gentisic acid (4, 25.1 min), caffeic acid (5, 27.5 min), luteolin (6, 52.9 min), and apigenin (7, 70.95 min). Axis: x label minutes, y label absorbance unit.

Figure 2

Quenching of DPPH of SN1 and SN2 extracts at different concentrations (0.025-0.5-0.1-0.2-0.4 mg/mL), compared to Trolox (30 mM). Axis: x label: concentration, y label: quenching of DPPH expressed as a percentage. (* p < 0.05 and ** p < 0.001).

Figure 3

GSH levels in primary rat astroglial cell cultures at 14 DIV: exposed to glutamate 500 µM for 24 h. Bar 1: control. Bar 2: cell culture exposed 500 µM. Bar 3: cell culture exposed 500 µM plus SN1 0.5 mg/mL. Bar 4: cell culture exposed 500 µM plus SN1 1 mg/mL. Bar 5: cell culture exposed 500 µM plus SN2 0.5 mg/mL. Bar 6: cell culture exposed 500 µM plus SN2 1 mg/mL. Four replicates were carried out for each sample. (* p < 0.05 and ** p < 0.001). Axis: x label: concentration, y label: nmoli of GSH per mg of protein.

Figure 4

ROS levels in primary rat astroglial cell cultures at 14 DIV: exposed to glutamate 500 µM for 24 h. Bar 1: control. Bar 2: cell culture exposed 500 µM. Bar 3: cell culture exposed 500 µM plus SN1 0.5 mg/mL. Bar 4: cell culture exposed 500 µM plus SN1 1 mg/mL. Bar 5: cell culture exposed 500 µM plus SN2 0.5 mg/mL. Bar 6: cell culture exposed 500 µM plus SN2 1 mg/mL. Four replicates were carried out for each sample. (* p < 0.05 and ** p < 0.001). Axis: x label: concentrations, y label: percentage of fluorescence intensity per mg protein versus control.