Antibacterial, antiproliferative and antioxidant activity of leaf extracts of selected Solanaceae species

Abstract Plants belonging to the Solanaceae family are generally used in Sudanese traditional medicine for the treatment of different ailments. This study aimed at the evaluation of in vitro antibacterial, antiproliferative and antioxidant activities of methanolic leaf extracts and steroidal glycoalkaloids fractions (SGAFs) of Solanum incanum L ., S. schimperianum Hochst , S. nigrum L. , Physalis lagascae Roem. & Schult. and Withania somnifera (L) Dunal. Methods: Antibacterial activity of the methanolic extracts and SGAFs was determined against two Gram-positive and two Gram-negative bacteria by microdilution method. Anti-proliferative activity was determined against human cell lines (MCF7 and MDA-MB-231, HT29 and HCT116) by the thiazolyl blue tetrazolium bromide (MTT) procedure. Antioxidant activity was evaluated by diphenyl 2 pycril hydrazil (DPPH) and 2,2′-azino-bis 3-ethylbenzthiazoline-6-sulphonic acid (ABTS) scavenging radical methods. Methanolic extract of S. schimperianum was analyzed using liquid chromatography coupled to an Orbitrap mass spectrometer with an electrospray ionization source (LC–MS). Results The sensitivity of Gram-positive and Gram-negative bacteria to each extract was variable (MIC values in the range of 15–> 1000 μg/mL). Only the methanolic extract of S. schimperianum leaf demonstrated interesting anti-proliferative activity against the human cell lines tested with IC 50 values in the range of 2.69 to 19.83 μg/mL while the highest activity from the SGAFs was obtained from W. somnifera leaf with IC 50 values in the range of 1.29 to 5.00 μg/mL. In both assays the SGAFs of all species demonstrated higher scavenging activity than their respective methanolic extracts. The SGAF of S. schimperianum displayed the strongest antioxidant activity in both assays with IC 50 value 3.5 ± 0.2 DPPH and 3.5 ± 0.3 ABTS  μg/mL. The correlation coefficient (R 2 ) between the antioxidant capacities and the total phenolic contents of the methanol extracts suggested that the phenolic compounds could not be the main contributor to the antioxidant capacities of leaves of these plants. Twelve known hydroxycinnamic acid amides (HCAAs) were tentatively identified from the methanolic extract of S. schimperianum leaf and N -caffeoyl agmatine appeared with the highest intensity. Moreover, the presence of steroid alkaloids was also detected and the presence of solanopubamine and solanocapsine as well as dehydro derivatives of the 3-amino steroid alkaloids was suggested.