Destabilization of liposome membranes by the steroidal glycoalkaloid α-tomatine

The effect of the steroidal glycoalkaloid α-tomatine on the leakage of peroxidase from liposomes was studied. At pH 7.2, the optimum pH for disruption, tomatine had little effect at concentrations less than 10μM but was increasingly disruptive at concentrations of 10–100μM. Liposome destabilization was pH-dependent declining with decreasing pH until at pH 5 lysis was achieved only at tomatine concentrations of 500–1000μM. At all pH values tested (pH 5–8), tomatine caused significant disruption only if the membrane contained sterol. The extent of membrane damage was correlated with the concentration of sterol in the liposomes but not with the nature of the sterol or of the phospholipid. These findings are inconsistent with claims that surface glycosidases, which convert the glycoside to the aglycone, are prerequisites for tomatine action and that the aglycone is the active moiety.