Effects of Al3+ and related metals on membrane phase state and hydration: correlation with lipid oxidation

VERSTRAETEN, S. V.; OTEIZA, P. I.

ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS

ELSEVIER SCIENCE INC

Año: 2000 vol. 375 p. 340 - 346

0003-9861

The aim of the present study was to further understand how changes in membrane organization can lead to higher rates of lipid oxidation. We previously demonstrated that Al3+, Sc3+, Ga3+, Be3+, Y3+, and La3+ promote lipid packing and lateral phase separation. Using the probe Laurdan, we evaluated in liposomes if the higher rigidity of the membrane caused by Al3+ can alter membrane phase state and/or hydration, and the relation of this effect to Al3+-stimulated lipid oxidation. In liposomes of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylserine, Al3+ (10-100 microM) induced phase coexistence and displacement of Tm. In contrast, in liposomes of brain phosphatidylcholine and brain phosphatidylserine, Al3+ (10-200 microM) did not affect membrane phase state but increased Laurdan generalized polarization (GP = -0. 04 and 0.09 in the absence and presence of 200 microM Al3+, respectively). Sc3+, Ga3+, Be3+, Y3+, and La3+ also increased GP values, with an effect equivalent to a decrease in membrane temperature between 10 and 20 degrees C. GP values in the presence of the cations were significantly correlated (r2 = 0.98, P < 0.001) with their capacity to stimulate Fe2+-initiated lipid oxidation. Metal-promoted membrane dehydration did not correlate with ability to enhance lipid oxidation, indicating that dehydration of the phospholipid polar headgroup is not a mechanism involved in cation-mediated enhancement of Fe2+-initiated lipid oxidation. Results indicate that changes in membrane phospholipid phase state favoring the displacement to gel state can facilitate the propagation of lipid oxidation.