Changes in oxidative stress parameters and neurodegeneration markers in the brain of the senescence-accelerated mice SAMP-8

Oligomeric proanthocyanidins improve memory and enhance phosphorylation of vascular endothelial growth factor receptor-2 in senescence-accelerated mouse prone/8

Senescence-accelerated mouse prone/8 (SAMP8), a murine model of accelerated senescence, shows age-related deficits in learning and memory. We investigated the effect of oligomeric proanthocyanidins (oligomers) on memory impairment using the SAMP8 model involving the oral administration of oligomers for 5 weeks. To analyse memory improvement in SAMP8, we performed Morris water maze, object location and object recognition tests. The oral administration of oligomers improved spatial and object recognition impairment in SAMP8. Expressions of phosphorylated neurofilament-H (P-NF-H, axon marker), microtubule-associated proteins (MAP) 2a and 2b (MAP2; dendrite marker) and synaptophysin were increased in the brains of SAMP8-administered oligomers. In particular, the expression of P-NF-H was significantly elevated in the hippocampal CA1. This indicates that oligomers result in an increase in the densities of axons, dendrites and synapses. To investigate the protective mechanisms of oligomers against brain dysfunction with ageing, we carried out a receptor tyrosine kinase phosphorylation antibody array, and clarified that the administration of oligomers led to an increase in the phosphorylation of vascular endothelial growth factor receptor (VEGFR)-2, suggesting the neuroprotective role of oligomers. The phosphorylation of VEGFR-2 was more greatly increased in the hypothalamus and choroid plexus than in other brain regions of SAMP8. Memory in oligomer-treated mice was impaired by SU1498, a VEGFR-2-specific antagonist. Elucidating the relationship between memory impairment with ageing and VEGFR-2 signalling may provide new suggestions for protection against memory deficit in the ageing brain.

Proteomic study of neuron and astrocyte cultures from senescence-accelerated mouse SAMP8 reveals degenerative changes

Senescence-accelerated prone (SAMP) strain 8 mice suffer an earlier development of cognitive age-related pathologies and a shorter life span than conventional mice. Protein alterations in astrocytes, in addition to those in neurons, may contribute to neurodegenerative damage. We applied proteomics techniques to study cell-specific early markers of brain aging-related degeneration in SAMP8. The two-dimensional protein expression patterns of the SAMP8 neuron and astrocyte cultures were compared with those obtained from senescence-accelerated resistant mouse strain 1 cultures. Differentially expressed spots were identified by matrix-assisted laser desorption/ionization-time of flight peptide map fingerprinting and database search. Proteins belonged to cell pathways of energy metabolism, biosynthesis, cell transduction and signaling, stress response, and the maintenance of cytoskeletal functions. Most of the changes were cell type specific. However, there was a general increase in cell transduction, signaling, and stress-related proteins and a decrease in cytoskeletal proteins. In addition, neurons showed an increased expression of proteins involved in biosynthetic pathways. A number of the protein alterations have been previously reported in the brain tissue proteome of SAMP8, aged brain or Alzheimer's disease brain. Alterations in neuron and astrocyte proteoma indicated that both cell types are involved in the brain degenerative changes of SAMP8 mice. However, network analysis suggests that neuronal changes are more complex and have a greater influence.

An evaluation of the neuroprotective effects of melatonin in an in vitro experimental model of age-induced neuronal apoptosis

The neuroprotective effects of melatonin in an experimental model of aging-induced apoptosis have been examined. Cerebellar granule neurons show characteristics of apoptosis after 17 days in culture (DV). The addition of melatonin to neuronal cell cultures (100-500 mum) resulted in neuroprotective and antiapoptotic effects, which were revealed by nuclear condensed cell counting. In a thorough analysis by Western-blot of the potential pathways responsible for melatonin's neuroprotective effects, we found an increase in the activation of prosurvival Akt. Subsequently GSK3beta inhibition and an increase in p-FOXO1 phosphorylation occurred. In this model of aging, apoptosis was associated with an elevated DNA damage, as demonstrated by an increase in the activation of ataxia telangiectasia muted (ATM). Subsequently, downstream targets such as p53 were activated. Furthermore, the process of DNA damage was coupled to an increase in the expression of certain proteins involved in cell cycle regulation; these were cyclin D and the proapoptotic transcription factor E2F-1. We conclude that the antiapoptotic effects of melatonin were mediated by two potential mechanisms: by increasing the activity of prosurvival pathways via Akt and by the prevention of DNA damage (via ATM inhibition) followed by the reduction of cell cycle re-entry.

Senescence-accelerated mouse (SAM) with special references to neurodegeneration models, SAMP8 and SAMP10 mice

The SAM strains, a group of related inbred strains consisting of senescence-prone inbred strains (SAMP) and senescence-resistant inbred strains (SAMR), have been successfully developed by selective inbreeding of the AKR/J strain of mice donated by the Jackson laboratory in 1968. The characteristic feature of aging common to the SAMP and SAMR is accelerated senescence and normal aging, respectively. Furthermore, SAMP and SAMR strains of mice manifest various pathobiological phenotypes spontaneously. Among SAMP strains, SAMP8 and SAMP10 mice show age-related behavioral deterioration such as deficits in learning and memory, emotional disorders (reduced anxiety-like behavior and depressive behavior) and altered circadian rhythm associated with certain pathological, biochemical and pharmacological changes. Here, the previous and recent literature on SAM mice are reviewed with an emphasis on SAMP8 and SAMP10 mice. A spontaneous model like SAM with distinct advantages over the gene-modified model is hoped by investigators to be used more widely as a biogerontological resource to explore the etiopathogenesis of accelerated senescence and neurodegenerative disorders.

Activation of Akt by lithium: pro-survival pathways in aging

The effects of lithium on senescence were investigated using the senescence-accelerated mouse prone 8 (SAMP8) mice and cultures of aging cerebellar granule cells. Our in vitro findings, using cerebellar granule neurons, demonstrate that lithium (1-10mM) exerts neuroprotective effects in young cultures (7-8 days) against LY294002-induced Akt inhibition. Furthermore, lithium (10mM) inhibits GSK-3beta activity by upregulating p-GSK-3beta (ser-9) and increases p-FOXO1 (Ser256) suggesting an effective anti-apoptotic effect. Our data also showed that lithium in aged cultures exerts anti-apoptotic effects via Akt activation and consequent inhibition of downstream targets regulated by this enzyme. Finally, the administration of lithium to senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) at 3 months of age also caused increased Akt activity and p-FoxO-1. These results demonstrate the effectiveness of lithium in preventing age-related neural loss and the potential therapeutic applications of lithium in treatment/prevention of neurological disease.

Long-term ginsenoside consumption prevents memory loss in aged SAMP8 mice by decreasing oxidative stress and up-regulating the plasticity-related proteins in hippocampus

Ginsenoside, the effective component of ginseng, has been reported to have a neuron protective effect, but the preventive effect on Alzheimer's disease (AD) related memory loss and the underlying mechanisms have not been well determined. The senescence-accelerated mouse (SAM) is a useful model of AD-related memory impairment. In the present study, SAMP8 mice aged 4 months were chronically treated with ginsenoside (3 dose groups were given ginsenoside in drinking water for 7 months). The three groups were treated with ginsenoside 50, 100 and 200 mg/kg per day, respectively. Placebo-treated aged mice and young ones (4 months old) were used as controls. In addition, SAMR1 mice were used as "normal aging" control. The beneficial role of ginsenoside was manifested in the prevention of memory loss in aged SAMP8 mice. The optimal dose of ginsenoside is 100 or 200 mg/kg per day. In ginsenoside treated groups, the Abeta level markedly decreased in hippocampus and antioxidase level significantly increased in serum. In addition, the plasticity-related proteins in hippocampus significantly increased in the two ginsenoside treated groups. The plasticity-related proteins were checked in the present study including postsynaptic density-95 (PSD-95), phosphor-N-methyl-D-aspartate receptor 1 (p-NMDAR1), phospho-calcium-calmodulin dependent kinase II (p-CaMKII), phospho-protein kinase A Catalyticbeta subunit (p-PKA Cbeta) and protein kinase Cgamma subunit (PKCgamma), phospho-CREB (p-CREB) and brain derived neurotrophic factor (BDNF) etc. These findings suggest that the increase of antioxidation and up-regulation of plasticity-related proteins in hippocampus may be one of the mechanisms of ginsenoside on the memory loss prevention in aged SAMP8 mice.

Evaluation of potential pro-survival pathways regulated by melatonin in a murine senescence model

We examined the effect of melatonin on pro-survival processes in three groups of mice. Untreated senescence-accelerated mice (SAMP8), melatonin-treated SAMP8 and untreated senescence-accelerated resistant mice (SAMR1) of 10 months old were studied. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) was supplied in the drinking water from the end of the first month until the end of the ninth month of life. Differences in the Akt/Erk1-2 pathway and downstream targets were examined and no significant changes were observed, except for beta-catenin. However, sirtuin 1 expression was significantly lower in SAMP8 than in SAMR1. In addition, acetylated p53 and NFkappaB expression were lower in SAMP8 than in SAMR1. These changes were prevented by melatonin. Moreover, the concentration/expression of alpha-secretase was lower and that of amyloid beta aggregates (Abeta) was higher in untreated SAMP8 than in SAMR1. Likewise, the levels of Bid were higher, whereas Bcl-2(XL) levels were lower in SAMP8 than in SAMR1. Melatonin reduced all these changes. We conclude that melatonin improves pro-survival signals and reduces pro-death signals in age-related impairments of neural processes.

Dysfunction of astrocytes in senescence-accelerated mice SAMP8 reduces their neuroprotective capacity

Early onset increases in oxidative stress and tau pathology are present in the brain of senescence-accelerated mice prone (SAMP8). Astrocytes play an essential role, both in determining the brain's susceptibility to oxidative damage and in protecting neurons. In this study, we examine changes in tau phosphorylation, oxidative stress and glutamate uptake in primary cultures of cortical astrocytes from neonatal SAMP8 mice and senescence-accelerated-resistant mice (SAMR1). We demonstrated an enhancement of abnormally phosphorylated tau in Ser(199) and Ser(396) in SAMP8 astrocytes compared with that of SAMR1 control mice. Gsk3beta and Cdk5 kinase activity, which regulate tau phosphorylation, was also increased in SAMP8 astrocytes. Inhibition of Gsk3beta by lithium or Cdk5 by roscovitine reduced tau phosphorylation at Ser(396). Moreover, we detected an increase in radical superoxide generation, which may be responsible for the corresponding increase in lipoperoxidation and protein oxidation. We also observed a reduced mitochondrial membrane potential in SAMP8 mouse astrocytes. Glutamate uptake in astrocytes is a critical neuroprotective mechanism. SAMP8 astrocytes showed a decreased glutamate uptake compared with those of SAMR1 controls. Interestingly, survival of SAMP8 or SAMR1 neurons cocultured with SAMP8 astrocytes was significantly reduced. Our results indicate that alterations in astrocyte cultures from SAMP8 mice are similar to those detected in whole brains of SAMP8 mice at 1-5 months. Moreover, our findings suggest that this in vitro preparation is suitable for studying the molecular and cellular processes underlying early aging in this murine model. In addition, our study supports the contention that astrocytes play a key role in neurodegeneration during the aging process.

Favorable effects of a prolonged treatment with melatonin on the level of oxidative damage and neurodegeneration in senescence-accelerated mice

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Beneficial effects of myocardial postconditioning are associated with reduced oxidative stress in a senescent mouse model

BACKGROUND

There is at present a tragic lack of organs available for transplantation. This has led to the harvesting of hearts from older donors. Unfortunately, hearts from such donors are much more sensitive to ischemic insult. Models such as "Senescence Accelerated Mouse" Prone 8 (SAM-P8) can help understand this sensitivity. New cardioprotective techniques such as postconditioning (PostC) could be of interest in this context. We studied (1) senescence in vessels and hearts and (2) the ability of the senescent heart to adapt to an ischemia-reperfusion (I/R) sequence in the context of PostC.

METHODS

Isolated working mouse hearts (8 months) were subjected to total ischemia, followed by 36 min of reperfusion; PostC was performed in the first minutes of reperfusion as three 10-sec sequences of I/R. Superoxide anion (O2.-) production was evaluated on heart and aorta cryosections with the dihydroethidium staining method. The collagen content in aortas was quantified.

RESULTS

The aortas of SAM-P8 mice showed a higher production of O2.- and a higher collagen content than did those of SAM-R1 mice (P<0.05). During reperfusion, SAM-P8 hearts showed the worst recovery of cardiac output. PostC significantly reduced reperfusion dysfunction (P<0.05) and was associated with a reduction in heart O2.- staining.

CONCLUSIONS

These results indicate that SAM-P8 presents a high degree of cardiovascular oxidative stress and a higher susceptibility to I/R injury, which confirms the senescence of the cardiovascular system in these animals. However, they remain sensitive to cardioprotection afforded by in vitro PostC.

TAT-mediated PRDX6 protein transduction protects against eye lens epithelial cell death and delays lens opacity

A diminished level of endogenous antioxidant in cells/tissues is associated with reduced resistance to oxidative stress. Peroxiredoxin 6 (PRDX6), a protective molecule, regulates gene expression/function by controlling reactive oxygen species (ROS) levels. Using PRDX6 protein linked to TAT, the transduction domain from human immunodeficiency virus type 1 TAT protein, we demonstrated that PRDX6 was transduced into lens epithelial cells derived from rat or mouse lenses. The protein was biologically active, negatively regulating apoptosis and delaying progression of cataractogenesis by attenuating deleterious signaling. Lens epithelial cells from cataractous lenses bore elevated levels of ROS and were susceptible to oxidative stress. These cells harbored increased levels of active transforming growth factor (TGF)-beta 1 and of alpha-smooth muscle actin and beta ig-h3, markers for cataractogenesis. Importantly, cataractous lenses showed a 10-fold reduction in PRDX6 expression, whereas TGF-beta1 mRNA and protein levels were elevated. The changes were reversed, and cataractogenesis was delayed when PRDX6 was supplied. Results suggest that delivery of PRDX6 can postpone cataractogenesis, and this should be an effective approach to delaying cataracts and other degenerative diseases that are associated with increased ROS.

Increased permeability of blood-brain barrier on the hippocampus of a murine model of senescence

SAMP8 mice show several indicative characteristics of accelerated aging and have been used to study the physiological and physiopathological processes that take place during senescence. There is some controversy about the presence of a functional blood-brain barrier (BBB) disturbance on these animals, which could be related to the oxidative stress or the amyloidosis present in their brain. In order to elucidate BBB status in the hippocampus of SAMP8 mice, in this study we have determined the extravasation from brain microvessels of endogenous IgG in SAMP8 mice aged 3, 7 and 12 months and in age-matched control SAMR1 mice. Immunohistochemistry, confocal microscopy and an imaging methodology specially designed to quantify IgG extravasation have been used. The choroid plexus was analyzed as a control for positive extravasation in SAMP8 and SAMR1 mice and, as expected, in all studied ages high IgG immunoreactivity was observed in both strains. We have found significantly higher levels of IgG extravasation in the hippocampus of 12-month-old SAMP8 mice compared to SAMR1 mice, indicating an increased permeability of BBB in aged senescence-accelerated mice.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

Changes of brain activity in the aged SAMP mouse

This study investigates characteristics of aging in the central nervous system of the senescence accelerated prone mice (SAMP8). We examined 3 and 10-months old senescence-accelerated-prone mice (SAMP8) for functional and molecular changes in their brains, specifically in the hippocampus and somatosensory cortex. There was no statistically significant increase in the apoptosis indicators as revealed by Western Blotting for BAD and TUNEL experiments. However, the functional magnetic resonance imaging showed an increase in the area of BOLD images from the 3-month old to the 10-months old SAMP mice upon the application of tail stimulus. These results demonstrated a lack of neuronal deaths but an increase in the activated brain area with age.

Low molecular proanthocyanidin dietary biofactor Oligonol: Its modulation of oxidative stress, bioefficacy, neuroprotection, food application and chemoprevention potentials

Interdisciplinary research endeavors are directed at understanding the molecular mechanisms of neurodegenerative and chronic diseases that affect human lifestyle. Hence the potential for developing medicinal herb-derived and food plant-derived prophylactic agents directed at neurological, metabolic, cardiovascular and psychiatric disorders abounds. Oligonol is a novel technology product emanating from the oligomerization of polyphenols, typically proanthocyanidin from a variety of fruits (grapes, apples, persimmons etc.) that has optimized bioavailability. It is an optimized phenolic product containing catechin-type monomers and oligomeric proanthocyanidins, the easily absorbed forms. Typically the constituents of Oligonol are 15-20% monomers, 8-12% dimers and 5-10% trimers. Supplementation of mice with Oligonol prior to the administration of ferric-nitrilotriacetic complex (a Fenton chemistry model) significantly reduced the extent of lipid peroxidation in the kidney, brain and liver. Oligonol triggers apoptosis in the MCF-7 and MDA-MB-231 breast cancer cells through modulation of the pro-apoptotic Bcl-2 family of proteins and the MEK/ERK signaling pathway, an observation suggesting its important chemopreventive effects. The senescence-accelerated strain of mice (SAM) are models of senescence acceleration and geriatric disorders which exhibit learning and memory deficits and enhanced production or defective control of oxidative stress leading.