Blood was drawn from healthy volunteers, and lithium/heparin tubes were used to remove the clot by centrifugation. The plasma was aliquoted and incubated with the desired compounds for 24h at 37°C, at final concentrations of 5.83 µM for RADA, 3.12 µM for RADA-IM, 3.76 µM for RADA-KGHK and 3.52 µM for RADA-GHK. The samples were prepared under sterile conditions following the protocol previously described . The samples were collected at six time points (0, 1, 2, 3, 6 and 24h) for determining stability in water solutions, and at eleven time points (0, 10, 20, 30, 40, 50 and 60 min., and 2, 3, 6 and 24h) for determining stability in human plasma. The analysis was performed by HPLC using Phenomenex Luna C18(2) columns (5 µm, 100Å 4.6 x 250 mm) monitored by a PDA detector. For calculations, peak areas were compared to a calibration curve calculated by Shimadzu LCsolution Software. Additional peak detection was performed by LC-MS mass spectrometry using a Kromasil C8 column (5µm, 90Å 1.0 x 250 mm). Details of the peptide stability procedure are described in the Supplementary Data.