Effect of malate on the development of rotenone-induced brain changes in Wistar and OXYS rats: An MRI study

Features of Postnatal Hippocampal Development in a Rat Model of Sporadic Alzheimer's Disease

Aging is the major risk factor of the most common (∼95% of cases) sporadic Alzheimer’s disease (AD). Accumulating data indicate middle age as a critical period for the relevant pathological processes, however, the question of when AD starts to develop remains open. It has been reported only recently that in the early postnatal period—when brain development is completing—preconditions for a decrease in cognitive abilities and for accelerated aging can form. Here, we hypothesized that specific features of early postnatal brain development may be considered some of the prerequisites of AD development at an advanced age. To test this hypothesis, we used OXYS rats, which are a suitable model of sporadic AD. The duration of gestation, litter size, and weight at birth were lower in OXYS rats compared to control Wistar rats. The shortened duration of gestation may result in developmental retardation. Indeed, we noted decreased locomotor activity and increased anxiety in OXYS rats already at a young age: possible signs of altered brain development. We demonstrated retardation of the peak of postnatal neurogenesis in the hippocampal dentate gyrus of OXYS rats. Delayed neuronal maturation led to alterations of mossy-fiber formation: a shortened suprapyramidal bundle and longer infrapyramidal bundle, less pronounced fasciculation of granule cells’ axons, and smaller size and irregular shape of nuclei in the CA3 pyramidal layer. These changes were accompanied by altered astrocytic migration. The observed features of early development may be considered some of the risk factors of the AD-like pathology that manifests itself in OXYS rats late in life.

The Rat Prefrontal-Cortex Transcriptome: Effects of Aging and Sporadic Alzheimer's Disease-Like Pathology

Alzheimer's disease (AD) is the most widespread late-life dementia and involves the prefrontal cortex, a vulnerable brain region implicated in memory, emotion, cognition, and decision-making behavior. To understand the molecular differences between the effects of aging and AD on the prefrontal cortex, this study characterized the age-dependent changes in gene expression in Wistar rats (control) and OXYS rats (rodents that simulate key characteristics of sporadic AD) using RNA sequencing. We found that major altered biological processes during aging in Wistar rats were associated with immune processes. Gene expression changes during development of AD-like pathology as well as at the preclinical stage were related to neuronal plasticity, catalytic activity, lipid and immune processes, and mitochondria. A comparison of genes between data sets "OXYS rats" and "human AD" revealed similarity in expression alterations of genes related primarily to mitochondrial function; immune, endocrine, and circulatory systems; signal transduction; neuronal and synaptic processes; hypoxia; and apoptosis. Expression changes in mitochondrial processes identified in OXYS rats by RNA sequencing were confirmed by ultrastructural neuronal organelle alterations and low activity of respiratory chain complexes I, IV, and V in cortical mitochondria, suggesting that mitochondrial dysfunction appears to mediate or possibly even initiate the development of AD.

Targeting of reactive isolevuglandins in mitochondrial dysfunction and inflammation

Inflammation is a major cause of morbidity and mortality in Western societies. Despite use of multiple drugs, both chronic and acute inflammation still represent major health burdens. Inflammation produces highly reactive dicarbonyl lipid peroxidation products such as isolevuglandins which covalently modify and cross-link proteins via lysine residues. Mitochondrial dysfunction has been associated with inflammation; however, its molecular mechanisms and pathophysiological role are still obscure. We hypothesized that inflammation-induced isolevuglandins contribute to mitochondrial dysfunction and mortality. To test this hypothesis, we have (a) investigated the mitochondrial dysfunction in response to synthetic 15-E2-isolevuglandin (IsoLG) and its adducts; (b) developed a new mitochondria-targeted scavenger of isolevuglandins by conjugating 2-hydroxybenzylamine to the lipophilic cation triphenylphosphonium, (4-(4-aminomethyl)-3-hydroxyphenoxy)butyl)-triphenylphosphonium (mito2HOBA); (c) tested if mito2HOBA protects from mitochondrial dysfunction and mortality using a lipopolysaccharide model of inflammation. Acute exposure to either IsoLG or IsoLG adducts with lysine, ethanolamine or phosphatidylethanolamine inhibits mitochondrial respiration and attenuates Complex I activity. Complex II function was much more resistant to IsoLG. We confirmed that mito2HOBA markedly accumulates in isolated mitochondria and it is highly reactive with IsoLGs. To test the role of mitochondrial IsoLGs, we studied the therapeutic potential of mito2HOBA in lipopolysaccharide mouse model of sepsis. Mito2HOBA supplementation in drinking water (0.1 g/L) to lipopolysaccharide treated mice increased survival by 3-fold, improved complex I-mediated respiration, and histopathological analyses supported mito2HOBA-mediated protection of renal cortex from cell injury. These data support the role of mitochondrial IsoLG in mitochondrial dysfunction and inflammation. We conclude that reducing mitochondrial IsoLGs may be a promising therapeutic target in inflammation and conditions associated with mitochondrial oxidative stress and dysfunction.

Determination of mitochondrial metabolic phenotype through investigation of the intrinsic inhibition of succinate dehydrogenase

Many diseases are accompanied by systemic or organ metabolic abnormalities. Therefore, investigation of the roles of mitochondrial dysfunction in the pathogenesis of major diseases requires a methodology that reflects the characteristics of mitochondrial metabolism particular for the organ of origin. We provide evidence that for brain and heart mitochondria the intrinsic inhibition of succinate dehydrogenase (SDH) is a key mechanism for attenuation of mitochondrial respiration and energy production in response to the organ's energy needs. This mechanism also serves to minimize the production of reactive oxygen species when the organ is at rest. Changes in the organ's workloads are accompanied by changes in metabolites that are used by mitochondria as substrates and for modification of energy production at the SDH level. Measurement of the respiratory activity of mitochondria with various substrates and substrate mixtures and use of bovine serum albumin as an SDH inhibitor will be useful for evaluation of metabolic phenotype at the mitochondrial level.

Melatonin attenuates impairments of structural hippocampal neuroplasticity in OXYS rats during active progression of Alzheimer's disease-like pathology

Translational research on Alzheimer's disease (AD) has often focused on reducing the high cerebral levels of amyloid-β (Aβ) as a key characteristic of AD pathogenesis. There is, however, a growing body of evidence that synaptic dysfunction may be crucial for the development of the most common (sporadic) form of AD. The applicability of melatonin (mainly produced by the pineal gland) to the treatment of AD is actively evaluated, but usually, such studies are based on animal models of early-onset AD, which is responsible for only ~5% of AD cases. We have shown previously that in OXYS rats (an established model of sporadic AD), accumulation of toxic forms of Aβ in the brain occurs later than does the development of signs of neurodegenerative changes and synaptic failure. In this regard, recently, we uncovered beneficial neuroprotective effects of melatonin (prophylactic dietary supplementation) in OXYS rats. Our aim here was to evaluate, starting at the age of active progression of AD-like pathology in OXYS rats, the effects of long-term oral administration of melatonin on the structure of synapses and on neuronal and glial cells of the hippocampus. Melatonin significantly increased hippocampal synaptic density and the number of excitatory synapses, decreased the number of inhibitory synapses, and upregulated pre- and postsynaptic proteins (synapsin I and PSD-95, respectively). Furthermore, melatonin improved the ultrastructure of neuronal and glial cells and reduced glial density. Based on our past and present results, the repair of neuroplasticity by melatonin is a promising strategy against AD.

Senescence-accelerated OXYS rats: a model of age-related cognitive decline with relevance to abnormalities in Alzheimer disease

Senescence-accelerated OXYS rats are an experimental model of accelerated aging that was established from Wistar stock via selection for susceptibility to cataractogenic effects of a galactose-rich diet and via subsequent inbreeding of highly susceptible rats. Currently, we have the 102nd generation of OXYS rats with spontaneously developing cataract and accelerated senescence syndrome, which means early development of a phenotype similar to human geriatric disorders, including accelerated brain aging. In recent years, our group found strong evidence that OXYS rats are a promising model for studies of the mechanisms of brain aging and neurodegenerative processes similar to those seen in Alzheimer disease (AD). The manifestation of behavioral alterations and learning and memory deficits develop since the fourth week of age, i.e., simultaneously with first signs of neurodegeneration detectable on magnetic resonance imaging and under a light microscope. In addition, impaired long-term potentiation has been demonstrated in OXYS rats by the age of 3 months. With age, neurodegenerative changes in the brain of OXYS rats become amplified. We have shown that this deterioration happens against the background of overproduction of amyloid precursor protein (AβPP), accumulation of β-amyloid (Aβ), and hyperphosphorylation of the tau protein in the hippocampus and cortex. The development of AMD-like retinopathy in OXYS rats is also accompanied by increased accumulation of Aβ in the retina. These published data suggest that the OXYS strain may serve as a spontaneous rat model of AD-like pathology and could help to decipher the pathogenesis of AD.

Nox2-induced production of mitochondrial superoxide in angiotensin II-mediated endothelial oxidative stress and hypertension

AIMS

Angiotensin II (AngII)-induced superoxide (O2(•-)) production by the NADPH oxidases and mitochondria has been implicated in the pathogenesis of endothelial dysfunction and hypertension. In this work, we investigated the specific molecular mechanisms responsible for the stimulation of mitochondrial O2(•-) and its downstream targets using cultured human aortic endothelial cells and a mouse model of AngII-induced hypertension.

RESULTS

Western blot analysis showed that Nox2 and Nox4 were present in the cytoplasm but not in the mitochondria. Depletion of Nox2, but not Nox1, Nox4, or Nox5, using siRNA inhibits AngII-induced O2(•-) production in both mitochondria and cytoplasm. Nox2 depletion in gp91phox knockout mice inhibited AngII-induced cellular and mitochondrial O2(•-) and attenuated hypertension. Inhibition of mitochondrial reverse electron transfer with malonate, malate, or rotenone attenuated AngII-induced cytoplasmic and mitochondrial O2(•-) production. Inhibition of the mitochondrial ATP-sensitive potassium channel (mitoK(+)ATP) with 5-hydroxydecanoic acid or specific PKCɛ peptide antagonist (EAVSLKPT) reduced AngII-induced H2O2 in isolated mitochondria and diminished cytoplasmic O2(•-). The mitoK(+)ATP agonist diazoxide increased mitochondrial O2(•-), cytoplasmic c-Src phosphorylation and cytoplasmic O2(•-) suggesting feed-forward regulation of cellular O2(•-) by mitochondrial reactive oxygen species (ROS). Treatment of AngII-infused mice with malate reduced blood pressure and enhanced the antihypertensive effect of mitoTEMPO. Mitochondria-targeted H2O2 scavenger mitoEbselen attenuated redox-dependent c-Src and inhibited AngII-induced cellular O2(•-), diminished aortic H2O2, and reduced blood pressure in hypertensive mice.

INNOVATION AND CONCLUSIONS

These studies show that Nox2 stimulates mitochondrial ROS by activating reverse electron transfer and both mitochondrial O2(•-) and reverse electron transfer may represent new pharmacological targets for the treatment of hypertension.

The mitochondria-targeted antioxidant SkQ1 but not N-acetylcysteine reverses aging-related biomarkers in rats

Although antioxidants have been repeatedly tested in animal models and clinical studies, there is no evidence that antioxidants reduce already developed age-related decline. Recently we demonstrated that mitochondria-targeted antioxidant 10-(6'-plastoquinonyl) decyltriphenylphosphonium (SkQ1) delayed some manifestations of aging. Here we compared effects of SkQ1 and N-acetyl-L-cysteine (NAC) on age-dependent decline in blood levels of leukocytes, growth hormone (GH), insulin-like growth factor-1 (IGF-1), testosterone, dehydroepiandrosterone (DHEA) in Wistar and senescence-accelerated OXYS rats. When started late in life, supplementation with SkQ1 not only prevented age-related decline but also significantly reversed it. With NAC, all the observed effects were of the lower magnitude compared with SkQ1 (in spite of that dose of NAC was 16000 times higher). We suggest that supplementation with low doses of SkQ1 is a promising intervention to achieve a healthy ageing.

Effects of Cistanche deserticola on behavior and signs of cataract and retinopathy in senescence-accelerated OXYS rats

ETHNOPHARMACOLOGICAL RELEVANCE

Cistanche deserticola (СD) has been traditionally used in the Chinese medicine as a tonic, vasodilator and neuroprotective agent.

AIM OF THE STUDY

To investigate the effect of CD on the age-related behavior decline and cataract and retinopathy development in senescent accelerated OXYS rats.

MATERIALS AND METHODS

OXYS and Wistar (control) rats were supplemented with 15 mg CD on kg of body weight during 2 months from the age of 12 months. Behavioral responses of animals were assessed in the elevated plus-maze (EPM), open field (OF) and in a Morris water maze (MWM). Before and after CD treatment OXYS rats were examined by an ophthalmologist.

RESULTS

14-month-old OXYS rats had demonstrated considerably reduced activities in OF, increased anxiety in EPM, and manifestly impaired learning abilities in the MWM as compared to Wistar rats. Supplementation of CD had no effect on motor and exploratory activity of Wistar and OXYS rats in the OF, but it reduced their anxiety in the EPM compared to age-matched controls. CD significantly improved visual ability of the rats, reducing the severity of the developed signs of retinopathy and cataract while having no impact on OXYS rats' spatial memory in the MWM. CD-treated Wistar rats exhibited slower learning ability in the MWM task comparison to the control group. The effect of CD on the learning ability in OXYS and Wistar rats may be associated with differences in their redox homeostasis.

CONCLUSION

All in all, the findings suggest that CD improves the age-related behavioral decline, which makes it an attractive candidate for treatment of various neurodegenerative disorders. Primarily it demonstrated its ability to slow development and to reduce to some extent severity of pathological manifestations of cataract and retinopathy in OXYS rats, which makes it an attractive candidate for treatment of age-related eye diseases too.

Respiration and ROS production in brain and spinal cord mitochondria of transgenic rats with mutant G93a Cu/Zn-superoxide dismutase gene

Mitochondrial dysfunction is involved in the pathogenesis of motor neuron degeneration in the G93A mutant transgenic (tgmSOD1) animal model of ALS. However, it is unknown whether mitochondriopathy is a primary or secondary event. We isolated brain (BM) and spinal cord (SCM) mitochondria from 2 month old presymptomatic tgmSOD1 rats and studied respiration and generation of reactive oxygen species (ROS) using a new metabolic paradigm (Panov et al., Am. J. Physiol., Regul. Integr. Comp. Physiol., 2011). The yields of BM and SCM from tgmSOD1 rats were 27% and 58% lower than normal rats (WT). The rates of the State 3 and State 3U respiration of tgBM and tgSCM were normal with glutamate+pyruvate+malate as substrates but were inhibited with pyruvate+malate in tgBM and glutamate+malate in tgSCM. In tgSCM the State 4 respiration with all substrates was significantly (1.5-2 fold) increased as compared with WT-SCM. Western blot analysis showed that tgSCM had lower contents of complexes III (-60%) and IV (-35%), and the presence of mutated SOD1 protein in both tgBM and tgSCM. With glutamate+pyruvate+malate or succinate+glutamate+pyruvate+malate as substrates, tgBM and tgSCM generated 5-7 fold more ROS than normal mitochondria, and tgSCM generated two times more ROS than tgBM. We show that the major damaging ROS species in tgmSOD1 animals is H(2)O(2). It is known that mutated SOD1, damaged by H(2)O(2), associates with mitochondria, and we suggest that this further increases production of H(2)O(2). We also show that the total tissue calcium content remained normal in the brain but was diminished by 26% in the spinal cord of presymptomatic tgmSOD1 rats.

CONCLUSION

In tgSCM abnormally high rates of ROS generation, associated with reverse electron transport, result in accelerated mitochondriopathy, and the Ca(2+)-dependent excitotoxic death of motor neurons. Thus mitochondrial dysfunction is a key early element in pathogenesis of motor neuron degeneration in tgmSOD1 rats.