Inhibitory effect of natural metal ion chelators on the autolysis of sea cucumber (Stichopus japonicus) and its mechanism

Live sea cucumbers (Stichopus japonicus) were stored in a solution containing oxalic acid and tea polyphenols as natural metal ion chelators. The inhibitory effects of these chelators on the autolysis phenomenon and the underlying mechanism of action were investigated for the first time by using scanning electron microscopy, differential scanning calorimetry, low-field nuclear magnetic resonance and confocal laser scanning microscopy. External stimuli cause autolysis through the release of calcium ions (Ca²⁺) from cells into the extracellular connective tissue, initiating activity of the matrix metalloprotease (MMP) in the sea cucumber body wall (SCBW). MMP subsequently degrades the microfibrillar networks, that support the interconnecting collagen fibres and the interfibrillar proteoglycan bridges linking the collagen fibrils, to release the water restricted within the interspaces between collagen fibres and collagen fibrils, ultimately causing mucoid degeneration of SCBW. The natural metal ion chelators significantly inhibited the activation of MMP by chelating Ca²⁺, consequently effectively preventing the autolysis of SCBW.

Keywords: Autolysis; Calcium ion (Ca(2+)); Matrix metalloprotease (MMP); Natural metal ion chelators; Sea cucumber (Stichopus japonicus).