Muscadines grapes (Vitis rotundafolia) are rich in phenolic compounds and antioxidants. Studies on grape extracts have shown that several of these compounds possess cytotoxic effects against various human cancer cells. The goal of this research is to (1) determine the cytotoxicity of human lung cancer cells against a gradient concentration of grape pericarp and seed extracts, (2) identify differentially expressed proteins in cancer cells treated with the grape extracts, and (3) determine biosynthetic pathways associated with the inhibition of cancer cell growth.
Seed and pericarp extracts were prepared separately and incubated with A209 human lung cancer cell lines for varying durations. The cells were harvested and tested for viability at 24 and 48 hours to determine the cell growth inhibition. Total proteins were isolated from both control and treated cells and resolved using 2-dimensional electrophoresis. The gels were scanned to detect differentially expressed proteins. Protein spots were eluted and subjected to LC-MS/MS for peptide sequences. The peptides were matched to protein sequences in the human database, which mapped the proteins' functions.
A total of 38 proteins were identified with significantly altered expression in the cell lines treated with the extracts. Pericarp and seed extracts showed different responses on the protein abundance. Further analysis revealed that various proteins including disulfide-isomerase, thioredoxin, enolase, and peroxiredoxin were low in abundance in the lung cancer cells treated with grape extracts for 48 hours. The proteins mentioned serve a specific purpose attributing to the treatment of lung cancer cells. Thioredoxin plays a significant role in breast cancer cell lines because it inhibits apoptosis and stimulates cell growth. Enolase was found to be positively correlated with tumor size and venous invasion. Disulfide-isomerase has roles in protein folding and forming disulfide bonds and is abundant in metastasized breast cancer cells. Peroxidase is a molecular chaperone that is overexpressed in cancer cell lines. It was observed that the suppression of this protein resulted from an increase in the peroxide-induced cytotoxicity of the cells. This data shows the antiproliferative effect of muscadine extract on the downregulation of these proteins that play a major role in the metabolism of the cancer cells.
These findings suggest that the proteins involved in the formation of the cytoskeleton, cell signaling, and cellular integrity were significantly affected when the cells were treated with muscadine extracts. This research provides insight into the discovery of potential protein biomarkers for the onset of human cancers.