Author:
Abigail Meyer
Mentor:
Dr. Christine Priano
Abstract:
Peppers of the genus Piper are commonly used as spices and traditional medicines. The aim of this study was to identify total phenolic content and antioxidant, cytotoxic, antiviral, and antibacterial activities of extracts from seven commercial sources of P. nigrum, P. guineense, and P. borbonense. Crude extracts were prepared in different solvents from dried crushed seeds for each sample. Total phenolic compounds and antioxidant capacities were determined using the Folin-Ciocalteu assay and the 2,2′-azino-bis -ABTS assay. The cytotoxicity in different cell lines and viral entry inhibition by aqueous extracts were explored using the XTT colorimetric assay and the SARS-CoV-2 Delta variant pseudoviral model. Antibacterial activity was determined by growing Escherichia coli and Bacillis subtilis in microplate cultures in the presence or absence of each aqueous extract and monitoring growth by spectrophotometry. Variations in total phenolic content and antioxidant capacity between samples and extraction solvents were observed. Samples with high total phenolics exhibited the highest antioxidant capacity. The SARS-CoV-2 Delta variant pseudoviral model in HeLa ACE-2 cells showed half-maximal effective concentrations (EC50 values) between 0.7 and 3.7 mg/mL. The half-maximal cytotoxic concentration and EC50 ratio (selective index) showed promising viral entry inhibition in four of seven extracts with selective indexes between 8.2 and 14.9. Aqueous extracts from P. borbonense showed the best antiviral selectivity. The cytotoxicity in Caco-2 cells showed that most of the aqueous extracts did not decrease cell viability, with no dose-response observed. Whereas P. guineense and P. borbonense extracts inhibited growth of B. subtilis, there was no activity observed against E. coli. Differential results are possibly due to differences in bacterial cell wall structure. Samples of P. borbonense that exhibited the highest suppression of B. subtilis growth had relatively high phenolic content and antiviral activity. The data collectively support a scientific basis for traditional health benefits of Piper extracts and warrant further investigation into the actions of specific phenolic compounds present in these extracts and their potential biological activities.
