Effect of gangliosides on the copper-induced oxidation of human low-density lipoproteins

Antioxidant properties of ganglioside micelles

Antioxidant activity of gangliosides GM1 and GT1b in the Fenton type of reaction was investigated by EPR spectroscopy using DMPO as a spin trap. Hydroxyl radical spin adduct signal intensity was significantly reduced in the presence of gangliosides at their micellar concentrations. Mean micellar hydrodynamic diameter was not changed, whereas significant changes in negative Zeta potential values were observed as evidenced by Zetasizer Nano ZS. This study showed that the primary mode of ganglioside action was not due to direct scavenging of OH., but rather to the inhibition of hydroxyl radical formation. This phenomenon is related to the ability of ganglioside micelles to bind oppositely charged ferrous ions, thus reducing their concentration and consequently inhibiting OH. formation.

Effect of caffeine on oxidation susceptibility of human plasma low density lipoproteins

The effect of caffeine on oxidation susceptibility of low density lipoproteins (LDL) has been studied. LDL oxidation was induced by copper ions and an azo initiator. The conjugated dienes formation was followed spectrophotometrically and indicated the LDL oxidation status. Changes in LDL protein moiety during the lag phase, studied only in the experiments of copper induced oxidation, were followed using the intrinsic fluorescence spectroscopy. The decay of LDL fluorescence signal during initial stages of oxidation was slower in the presence of caffeine. Supported by the fluorescence quenching and polarization measurements, these results may indicate the protective role of caffeine against LDL oxidation in vitro. The results also indicate that the production of conjugated dienes in the propagation and decomposition phase of LDL oxidation is lower in the presence of caffeine, regardless of the initiation mechanism. These findings may have implications for the effect of caffeine on LDL in vivo.

Reduction of oxidative changes in human spermatozoa by exogenous gangliosides

The effect of exogenous gangliosides, the sialic acid-containing glycosphingolipids, on oxidative changes in human spermatozoa was investigated. The incorporation of disialogangliosides or trisialogangliosides (GD1b and GT1b, respectively) into the iron/ascorbate promoter system for induction of lipid peroxidation decreased the release of malondialdehyde (MDA) from peroxidizing spermatozoa. The application of monosialogangliosides and disialogangliosides (GM1 and GD1a, respectively) did not have any effect under identical experimental conditions. GT1b, at a micromolar concentration, significantly inhibited the production of MDA, a breakdown product of lipid peroxide decomposition in spermatozoa of normozoospermic infertile men (P < 0.001; n = 51). An enhanced generation of MDA exhibited by the sperm population from the low-density Percoll fraction containing defective and/or immature spermatozoa was significantly reduced in the presence of GT1b. These results and the experiments on the influence of iron-chelating agent ethylenediamine tetraacetic acid (EDTA) as well as ferrous ion concentration itself on lipid peroxidation support the hypothesis that the protective effect of ganglioside against MDA generation could be the result of its chelating activity. Furthermore, superoxide anion release of phorbol myristate acetate-stimulated spermatozoa was significantly reduced in the presence of 50 and 100 micromol l(-1) GD1b (P < 0.05) and GT1b (P < 0.005). The inhibitory effect of 100 micromol l(-1) GT1b on spermatozoa from infertile normozoospermic men was statistically significant (P < 0.001; n = 21) and did not depend on the initial superoxide anion production. In conclusion, the protective action of GD1b and GT1b could be related to both scavenging of free radicals and metal-chelating properties, which might have relevance in the protection against oxidation-induced processes in human spermatozoa.