In order to clarify the basis of neuronal toxicity exerted by the shortest active peptides of amyloid beta-protein (Ab), the toxic effects of Ab(31-35) and Ab(25-35) peptides on isolated rat brain mitochondria were investigated. The results show that exposure of isolated rat brain mitochondria to and Ab(25-35) peptides determines: (i) release of cytochrome c; (ii) mitochondrial swelling and (iii) a significant reduction in mitochondrial oxygen consumption. In contrast, the amplitude of these events resulted attenuated in isolated brain mitochondria exposed to the Ab(31-35)Met35 OX in which methionine-35 was oxidized to methionine sulfoxide. The Ab peptide derivative with norleucine substituting Met-35, i.e., Ab(31-35)Nle-35, had not effect on any of the biochemical parameters tested. We have further characterized the action of Ab(31-35) and Ab(25-35) peptides on neuronal cells.Taken together our result indicate that Ab(31-35) and Ab(25-35) peptides in non-aggregated form, i.e., predominantly monomeric, are strongly neurotoxic, having the ability to enter within the cells, determining mitochondrial damage with an evident trigger of apoptotic signals. Such a mechanism of toxicity seems to be dependent by the redox state of methionine-35.

The toxic behaviour of the two shorter sequences of the native Abeta amyloid peptide required for cytotoxicity i.e., Abeta(31-35) and Abeta(25-35) peptides, was studied. We have shown that Abeta(31-35) peptide induces neurotoxicity in undifferentiated PC 12 cell via an apoptotic cell death pathway, including caspase activation and DNA fragmentation. Abeta(25-35) peptide, like the shorter amyloid peptide has the ability to induce neurotoxicity, as evaluated by the MTS reduction assay and by adherent cell count, but the Abeta(25-35) peptide-induced neurotoxicity is not associated with any biochemical features of apoptosis. The differences observed between the neurotoxic properties of Abeta(31-35) and Abeta(25-35) peptides might result on their different ability to be internalised within the neuronal cells. Furthermore, this study reveals that the redox state of methionine residue, C-terminal in Abeta(31-35) and Abeta(25-35) peptides affect in a different way the toxic behaviour of these two short amyloid fragments. Taken together our results suggest that Abeta(31-35) peptide induces cell death by apoptosis, unlike the Abeta(25-35) peptide and that role played by methionine-35 in Abeta induced neurotoxicity might be related to the Abeta aggregation state.

No abstract

Neuroglobin is a neuron-specific hexacoordinated globin capable of binding various ligands, including O2, NO, and CO, the biological function of which is still uncertain. Various studies seem to indicate that neuroglobin is a neuroprotective agent when overexpressed, acting as a potent inhibitor of oxidative and nitrosative stress. In this study, we evaluated the pathophysiological response of the neuroglobin gene and protein expression in the cerebral tissue of rats sustaining traumatic brain injury of differing severity, while simultaneously measuring the oxidant/antioxidant balance. Two levels of trauma (mild and severe) were induced in anesthetized animals using the weight-drop model of diffuse axonal injury. Rats were then sacrificed at 6, 12, 24, 48, and 120 h after traumatic brain injury, and the gene and protein expression of neuroglobin and the concentrations of malondialdehyde (as a parameter representative of reactive oxygen species-mediated damage), nitrite + nitrate (indicative of NO metabolism), ascorbate, and glutathione (GSH) were determined in the brain tissue. Results indicated that mild traumatic brain injury, although causing a reversible increase in oxidative/nitrosative stress (increase in malondialdehyde and nitrite + nitrate) and an imbalance in antioxidants (decrease in ascorbate and GSH), did not induce any change in neuroglobin. Conversely, severe traumatic brain injury caused an over nine- and a fivefold increase in neuroglobin gene and protein expression, respectively, as well as a remarkable increase in oxidative/nitrosative stress and depletion of antioxidants. The results of this study, showing a lack of effect in mild traumatic brain injury as well as asynchronous time course changes in neuroglobin expression, oxidative/nitrosative stress, and antioxidants in severe traumatic brain injury, do not seem to support the role of neuroglobin as an endogenous neuroprotective antioxidant agent, at least under pathophysiological conditions.

The effect of lactate on O 2 binding properties of sperm whale and horse heart myoglobins (Mb) has been investigated at moderately acid pH (i.e. pH 6.5, a condition which may be achieved in vivo under a physical effort). Addition of lactate brings about a decrease of O 2 affinity (i.e. an increase of P 50 ) in sperm whale and horse heart myoglobins. Accordingly, lactate shows a different affinity for the deoxygenated and oxygenated form, behaving as a heterotropic modulator. The lactate effect on O 2 affinity appears to differ for sperm whale and horse heart Mb, ␦logP 50 being Ϸ1.0 and Ϸ0.4, respectively. From the kinetic viewpoint, the variation of O 2 affinity for both myoglobins can be attributed mainly to a decrease of the kinetic association rate constant for ligand binding.

No abstract

No abstract

No abstract