Oxidative stress induced by the Fe2+/ascorbic acid system or model ischemia in vitro: effect of carvedilol and pyridoindole antioxidant SMe1EC2 in young and adult rat brain tissue

New effective strategies and new highly effective neuroprotective agents are being searched for the therapy of human stroke and cerebral ischemia. The compound SMe1EC2 is a new derivative of stobadine, with enhanced antioxidant properties compared to the maternal drug. Carvedilol, a non-selective beta-blocker, possesses besides its cardioprotective and vasculoprotective properties also an antioxidant effect. We compared the effect of carvedilol and SMe1EC2, antioxidants with a similar chemical structure, in two experimental models of oxidative stress in young and adult rat brain tissue. SMe1EC2 was found to improve the resistance of hippocampal neurons to ischemia in vitro in young and even in 18-month-old rats and inhibited formation of protein carbonyl groups induced by the Fe2+/ascorbic acid pro-oxidative system in brain cortex homogenates of young rats. Carvedilol exerted a protective effect only in the hippocampus of 2-month-old rats and that at the concentration 10-times higher than did SMe1EC2. The inhibitory effect of carvedilol on protein carbonyl formation induced by the pro-oxidative system was not proved in the cortex of either young or adult rats. An increased baseline level of the content of protein carbonyl groups in the adult versus young rat brain cortex confirmed age-related changes in neuronal tissue and may be due to increased production of reactive oxygen species and low antioxidant defense mechanisms in the adult rat brain. The results revealed the new pyridoindole SMe1EC2 to be more effective than carvedilol in neuroprotection of rat brain tissue in both experimental models involving oxidative stress

Low-dose proton radiation effects in a transgenic mouse model of Alzheimer’s disease – Implications for space travel

Space radiation represents a significant health risk for astronauts. Ground-based animal studies indicate that space radiation affects neuronal functions such as excitability, synaptic transmission, and plasticity, and it may accelerate the onset of Alzheimer's disease (AD). Although protons represent the main constituent in the space radiation spectrum, their effects on AD-related pathology have not been tested. We irradiated 3 month-old APP/PSEN1 transgenic (TG) and wild type (WT) mice with protons (150 MeV; 0.1-1.0 Gy; whole body) and evaluated functional and biochemical hallmarks of AD. We performed behavioral tests in the water maze (WM) before irradiation and in the WM and Barnes maze at 3 and 6 months post-irradiation to evaluate spatial learning and memory. We also performed electrophysiological recordings in vitro in hippocampal slices prepared 6 and 9 months post irradiation to evaluate excitatory synaptic transmission and plasticity. Next, we evaluated amyloid 3 (A(3) deposition in the contralateral hippocampus and adjacent cortex using immunohistochemistry. In cortical homogenates, we analyzed the levels of the presynaptic marker synaptophysin by Western blotting and measured pro-inflammatory cytokine levels (INF alpha, IL-beta, IL-6, CXCL10 and CCL2) by bead-based multiplex assay. TG mice performed significantly worse than WT mice in the WM. Irradiation of TG mice did not affect their behavioral performance, but reduced the amplitudes of population spikes and inhibited paired-pulse facilitation in CA1 neurons. These electrophysiological alterations in the TG mice were qualitatively different from those observed in WT mice, in which irradiation increased excitability and synaptic efficacy. Irradiation increased A beta deposition in the cortex of TG mice without affecting cytokine levels and increased synaptophysin expression in WT mice (but not in the TG mice). Although irradiation with protons increased A beta deposition, the complex functional and biochemical results indicate that irradiation effects are not synergistic to AD pathology

Fig 3 and S3Fig Input Output Curves at Max and Full Stimualtion intesities

I-O functions in CA1 neurons in slices from TG and WT mice 9 months post-irradiation

Cytokine levels in the cortex of TG and WT mice 9 months post-irradiation.

<p>Expression of CXCL10 and CCL2 was significantly higher in TG mice than in WT mice, but irradiation had no further effect on these cytokines. The differences in TNFα, IL-1β and IL-6 expression were not statistically significant (NS) in either TG or WT mice. TG mice: N = 6, 6, 5, 5 animals/radiation group; WT mice: N = 7, 8 animals/radiation group. Statistical analyses: 2-way ANOVA, genotype effect ††† <i>p</i><0.001, † <i>p</i><0.05. Data represent means ± SEM.</p

IHC analyses of Aβ deposits in TG mice 9 months post-irradiation.

<p>Top left panel: A representative illustration of a medial coronal section of the brain of a TG mouse divided into 3 areas of interest: hippocampus (HPC, dorsal cortex (DC) and ventral cortex (VC). The purple spots indicate the software’s built-in algorithm detection of amyloid plaques that was further visually confirmed by the experimenter. Top right panel: Original micrographs of cortical sections exposed to 0–1 Gy. Bottom panels: Relative numbers of plaque areas measured in the hippocampus and the dorsal cortex. Significant differences in Aβ deposition were detected between 0 vs 1 Gy groups in the DC and similar trends were observed in the HPC. TG mice only: N = 8, 7, 4 and 5 animals/radiation group. Statistical analyses: 1-way ANOVA, Post hoc * <i>p</i><0.05. Data represent means ± SEM.</p

Comparison of functional (behavioral and electrophysiological) effects of irradiation in TG and WT mice.

<p>Comparison of functional (behavioral and electrophysiological) effects of irradiation in TG and WT mice.</p

I-O functions in CA1 neurons in slices from TG and WT mice 9 months post-irradiation.

<p>(A) Radiation exposure did not significantly affect the presynaptic fiber volleys (pV) in either in TG or in WT mice. However, pV amplitudes were significantly elevated in TG controls when compared to WT controls. Inset: Original trace and measurement of pV amplitude is indicated with arrows. (B) Irradiation of WT mice (0.5 Gy) increased the slopes of the fEPSP by ~36% when compared to WT controls. In TG mice irradiated with 0.5 Gy, the fEPSP slopes tended to decrease indicating qualitatively different (and significant) radiation response from WT mice irradiated with 0.5 Gy. Inset: Original trace of the fEPSP recorded from the dendritic layer of CA1 neurons. Measurement of the initial linear slope of the fEPSP is indicated with a dashed line. (C) The synaptic efficacies in slices from non-irradiated WT control mice tended to be higher than TG controls, but the difference was not statistically significant (NS). The synaptic efficacy in WT mice was increased by irradiation at 0.5 Gy on average by ~39%. In TG mice, the synaptic efficacy was not affected by the exposure, but there was a statistically significant difference between slightly reduced efficacy in TG mice exposed to 0.5 Gy compared to WT mice irradiated with an equivalent dose. Inset: Original voltage trace indicating measurements of pV and fEPSP to compute synaptic efficacy for each slice. (D) Irradiation at 0.1 and 1 Gy significantly reduced the maximal PS amplitudes in TG mice by about ~35% indicating reduced output from CA1 neurons. When compared to WT controls, the PS amplitudes in TG control slices were significantly higher. Inset: Original voltage trace recorded from somatic layer of CA1 neurons and determination of the PS amplitude. TG mice: N = 12–13, 14–15, 7 and 10 slices <i>per</i> 0, 0.1, 0.5 and 1 Gy radiation group, respectively. WT mice: N = 16, 14 slices per 0 and 0.5 Gy radiation groups, respectively. Statistical analyses: Linear Mixed Models (LMM). Only post hoc tests are indicated: radiation effects * <i>p</i><0.05; genotype effects † <i>p</i><0.05, †† <i>p</i><0.01. Data represent means ± SEM.</p