Isolation and characterization of anti-inflammatory peptides derived from trypsin hydrolysis of microalgae protein (Synechococcus sp. VDW)

The Synechococcus sp. VDW peptides were prepared by trypsin digestion, which was then purified by ultrafiltration with molecular weight cut off membranes of 10, 5 and 3 kDa. Among the fractions, the MW <3 kDa fraction exhibited high levels of inhibitory activity toward the NO radical scavenging activities with IC50 values of 34.51 ? 9.8 ?g/mL. The MW <3 kDa fraction was purified by reversed-phase HPLC to yield four fractions. The 30?40 min sub-fraction with maximum NO radical scavenging activity (77.50 ? 0.55%) was selected for further analysis by Q-TOF ESI mass spectrometry. Five isolated peptides with amino acid sequences of AILQSYSAGKTK; 1,265.69 Da, ALNKTHLIQTK; 1,265.74 Da, LLVHAPVK; 875.55 Da, IPDAHPVK; 875.48 Da, and VVVLRDGAVQQLGTPR; 1,706.97 Da were identified. The MW <3 kDa fraction showed no cytotoxicity toward RAW264.7 macrophage cells. Quantitative RT-PCR results showed that the MW <3 kDa fraction reduced gene expression of pro-inflammatory cytokines iNOS, TNF-?, COX-2, and IL-6. The peptides isolated from the MW <3 kDa fractions represent potential model peptides to develop natural anti-inflammation food-grade ingredients, drugs, and cosmetic products.