Polyamines are widespread in living cells and play several important roles in both plants and animals. The polyamines spermine, spermidine and putrescine have been of primary interest, as they participate in cell growth and proliferation and thus are involved in health, disease and aging. Polyamines are also reported as secondary metabolites in stress response in plants. However, many of these functions have not been scientifically demonstrated. Thus, the objective of this research was to: (1) compare the antioxidant and anti-carcinogenic capacity of polyamines through various in vitro assays; (2) study the effect of ultrasound on secondary metabolite synthesis (polyamines) and maintenance of lettuce quality. Antioxidant capacity of polyamines was compared using two commonly used antioxidant capacity assays. The inhibitory effect of polyamines on cancer cell growth was investigated using murine breast cancer 4T1 cells and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay to monitor cell growth. Tyramine had the highest antioxidant capacity, followed by tryptamine, spermine, putrescine, and spermidine. Agmatine showed no antioxidant capacity. Spermine and spermidine inhibited the growth of 4T1 cells at IC50 of 6.0 µg/mL and 21.5 µg/mL, respectively. No anti-carcinogenic effects were observed in this cell system with putrescine. Abiotic stress application was conducted using sonication.Gas chromatographic analysis revealed that immediately after sonication, polyamine concentrations were not significantly different between unsonicated and sonicated lettuce samples.After three days recovery, the unsonicated lettuce leaves displayed significantly higher concentrations of putrescine and spermidine as compared to sonicated leaf tissue.This was also linked with a much higher quality of the lettuce leaves from sonicated tissue. This represents the first report of comparison of different polyamines for antioxidant capacity by two popular methods (ORAC and DPPH).For anti-carcinogenic activity, data were generated from one cell line indicating that the polyamines, but not putrescine, may prevent cell growth. Ultrasonication was found to be efficient in maintaining the quality of lettuce during storage, correspondingly, the polyamine levels in sonicated lettuce were decreased after 72 hours storage compared to control lettuce. Further studies are needed to ascertain the role of polyamines in cancer utilizing other cell lines. Microbial populations in sonicated and unsonicated lettuce after 72 hours recovery can also be tested to strengthen the impact of quality maintenance related to ultrasound treatment.
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The potential antioxidant and anticancer properties of polyamines and their response to high-intensity ultrasonication