Gossypol effects on the structure and dynamics of phospholipid bilayers: A FT-IR study

Abstract

Gossypol (1,1′,6,6′,7,7′-hexahydroxy-5,5′-diisopropyl-3,3′-dimethyl[2,2′-binaphthalene]-8,8′dicarboxaldehyde) previously used as a male oral contraceptive is an amphiphilic compound. At low concentrations, it is expected that gossypol would intercalate into the phospholipid bilayers. To demonstrate this, we used a pressure-tuning Fourier-transform infrared spectroscopy (FT-IR) technique to detect structural and dynamic effects of gossypol at 5 μM on a model bilayer membrane of 1,2-dipalmitoyl- sn-glycerol-3-phosphocholine (DPPC). The results indicate that gossypol induced interdigitation of the DPPC hydrocarbon chains, thus decreasing their dynamics. A slight decrease in the hydrogen bonding of the DPPC C=O ester group, and a slight increase in hydration of the P=O group were observed, whereas there was no effect on the absorption spectra of the C N of the choline group. The results suggest that gossypol, at a low micromolar concentration, did not bind to the polar headgroups of DPPC. Rather it is likely that it intercalated between the polar headgroups of the adjacent phospholipids and remained on the surface of the lipid bilayers. This work forms a basis for further pressure-tuning FT-IR studies of gossypol effects on sperm plasma membrane lipids.