Alzheimer's disease (AD) is characterized by progressive decline in cognition, memory and intellect. It has been hypothesized that amyloid-beta peptide (A-beta) may have a prominent role in neurodegeneration. Oxidative mechanisms have been implicated in this pathway. There is substantial evidence that inflammatory mechanisms, induced by tumour necrosis factor alpha (TNF-alpha), are also involved in AD. TNF-alpha activates receptors linked to multiple effector systems, including a sphingomyelin pathway and peroxide oxidation. We have determined the changes of neutral sphingomyelinase activity, sphingomyelin and ceramide contents, and the level of lipid peroxide products (conjugated dienes), in the cerebral cortex, hippocampus and cerebellum of rats within 3 h and 7 days of intracerebral injection of A-beta and TNF-alpha. A single injection of A-beta and TNF-alpha has been shown to increase the level of peroxide products in the hippocampus and cerebral cortex within 3 h and 7 days. Sphingomyelinase activity and ceramide levels have been found to increase 7 days after A-beta administration. We found that activation of the sphingomyelin pathway lies downstream from the oxidative stress.

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We studied hemolytic activity of gold nanoparticles added to the whole blood (ex vivo) and of nanoparticles coated and not coated with plasma components on erythrocytes in hypotonic medium (osmotic hemolysis) in vitro. Gold nanoparticles did not stimulate erythrocyte hemolysis after 4-h incubation with the whole blood ex vivo. Hemolysis tended to increase in the presence of small gold nanoparticles (5, 10, 20 nm) at the maximum concentration of 20 μM (by gold content) used in our study in comparison with the control. This tendency was detected during the 1st hour of the nanoparticles incubation with blood. Gold nanoparticles in the used concentrations (up to 20 μM of gold) coated with plasma components after preincubation with autologous plasma and nanoparticles without coating caused no osmotic hemolysis of erythrocytes in vitro.

We studied the effect of gold nanoparticles on ROS production by leukocytes. ROS production was detected by luminol-dependent chemiluminescence (LDCL) of human peripheral blood leukocytes stimulated with opsonized zymosan. Nanoparticle size was 5, 10 and 30 nm. Simultaneous addition of nanoparticles and opsonized zymosan showed that 5-nm nanoparticles inhibited LDCL intensity in comparison with the control, when LDCL recording was conducted in the presence of opsonized zymosan. Increasing nanoparticle size from 5 up to 30 nm enhanced LDCL intensity. Preincubation of gold nanoparticles with autologous blood plasma increased LDCL intensity. In the control (without gold nanoparticles), blood plasma produced no activating effect on LDCL. We found that the effect of gold nanoparticles on leukocyte LDCL depended on nanoparticle size: 10- and 30-nm nanoparticles inhibited LDCL intensity in comparison with the control (incubation in the absence of nanoparticles) irrespective of the duration of incubation, while 5-nm gold nanoparticles had no effect on LDCL intensity. Incubation of gold nanoparticles with autologous plasma increased LDCL intensity if nanoparticle size was 30 and 10 nm.

The signal transduction pathways triggering apoptotic mechanisms after ischemia/reperfusion may involve TNF-alpha secretion, ceramide generation, and initiation of lipid peroxidation. In the present study involvement of the TNF-alpha, sphingomyelin cycle, and lipid peroxidation in the initiation of apoptosis induced in liver cells by ischemia and reperfusion was investigated. Wistar rats were subjected to total liver ischemia (for 15, 30 min, and 1 h) followed by subsequent reperfusion. Ischemia caused sharp decrease of neutral sphingomyelinase activity. Activity of acidic sphingomyelinase initially decreased (during 15-30 min ischemia) but then increased (after 1 h of ischemic injury). Reperfusion of the ischemic lobe of the liver caused increase in neutral sphingomyelinase activity and decrease in acidic sphingomyelinase activity. A small amount of TNF-alpha detected by immunoblotting analysis was accumulated in the ischemic area of liver rapidly and the content of this cytokine dramatically increased after the reperfusion. TNF-alpha is known to induce free radical production. We found that the accumulation of TNF and increase of sphingomyelinase activity during the development of ischemic/reperfusion injury coincided with increase in content of lipid peroxidation products (conjugated dienes) and DNA degradation detected by gel electrophoresis. Recently it was shown that superoxide radicals are used as signaling molecules within the sphingomyelin pathway. This suggests the existence of cross-talk between the oxidation system and the sphingomyelin cycle in cells, which may have important implications for the initial phase and subsequent development of post-ischemic injury.