Size and shape effects on the order-disorder phase transition in CoPt nanoparticles.

Chemically ordered bimetallic nanoparticles are promising candidates for magnetic-storage applications. However, the use of sub-10 nm nanomagnets requires further study of possible size effects on their physical properties. Here, the effects of size and morphology on the order-disorder phase transition temperature of CoPt nanoparticles (T(C)(NP)) have been investigated experimentally, using transmission electron microscopy, and theoretically, with canonical Monte Carlo simulations. For 2.4-3-nm particles, T(C)(NP) is found to be 325-175 degrees C lower than the bulk material transition temperature, consistent with our Monte Carlo simulations. Furthermore, we establish that T(C)(NP) is also sensitive to the shape of the nanoparticles, because only one dimension of the particle (that is, in-plane size or thickness) smaller than 3 nm is sufficient to induce a considerable depression of T(C)(NP). This work emphasizes the necessity of taking into account the three-dimensional morphology of nano-objects to understand and control their structural properties.

Investigation of the oxide shell forming on epsilon-Co nanocrystals.

This paper reports on the TEM characterization of the surface oxide layer forming on Co nanocrystals (NCs) prepared using a standard method [Puntes, V.F., Krishnan, K.M., Alivisatos, P., 2001. Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal epsilon-Co nanoparticles. Appl. Phys. Lett. 78 (15), 2187-2189]. Complementary transmission electron microscopy (TEM)-related techniques presented direct evidence of a 1.5-3nm CoO shell forming on epsilon-Co NCs. The crystalline structure of the Co NCs was confirmed by selected area diffraction study while the nature of the shell was probed by energy-loss near-edge spectroscopy and energy-filtered TEM. Based on these results, we comment on the detection of nanoscale feature with energy-filtered imaging.

Application of Targeted Mass Spectrometry for the Quantification of Sirtuins in the Central Nervous System.

Sirtuin proteins have a variety of intracellular targets, thereby regulating multiple biological pathways including neurodegeneration. However, relatively little is currently known about the role or expression of the 7 mammalian sirtuins in the central nervous system. Western blotting, PCR and ELISA are the main techniques currently used to measure sirtuin levels. To achieve sufficient sensitivity and selectivity in a multiplex-format, a targeted mass spectrometric assay was developed and validated for the quantification of all seven mammalian sirtuins (SIRT1-7). Quantification of all peptides was by multiple reaction monitoring (MRM) using three mass transitions per protein-specific peptide, two specific peptides for each sirtuin and a stable isotope labelled internal standard. The assay was applied to a variety of samples including cultured brain cells, mammalian brain tissue, CSF and plasma. All sirtuin peptides were detected in the human brain, with SIRT2 being the most abundant. Sirtuins were also detected in human CSF and plasma, and guinea pig and mouse tissues. In conclusion, we have successfully applied MRM mass spectrometry for the detection and quantification of sirtuin proteins in the central nervous system, paving the way for more quantitative and functional studies.

Therapeutic Approaches to ModulatingGlutathione Levels as a Pharmacological strategy in Alzheimer's Disease.

Accumulating evidence has suggested the involvement of oxidative stress in the pathogenesis of Alzheimer's disease (AD).The main endogenousantioxidant,glutathione (GSH),has been shown to decline with ageing and in several age-related degenerative diseases, including AD. Potential options for replenishing GSH levels as a therapeutic target to treat these conditions include the administration of GSH itself, and low toxicity forms of the limiting amino acid for GSH synthesis; cysteineHowever, passive GSH uptake is limited due to an unfavourable concentration gradient between the plasma and cytosol. Similarly, cysteine prodrugs have demonstrated limited efficacyto elevatedepleted GSH levels in several in vivo and in vitro models of disease.It has beensuggestedthat the decline in GSH levels in AD, may be associated with down regulation ofGSH homeostasis rather than substrate limitation. Cellular GSH homeostasis is regulatedby non-allosteric feedback inhibition exerted by GSH on glutamate cysteine ligase (GCL), which is responsible for the synthesis of the GSH precursor γ-glutamylcysteine (GGC). In conditions involving down regulated GSH homeostasis, GGC serves asa crucialrate-limiting substrate for GSH synthetase, the main enzyme responsible for condensing glycine with GGC to form the final thiol tripeptide, GSH. In this review, we focus on the therapeutic potential of GGC to elevate cellular GSH levels. We also discuss the efficacy of GGC prodrugs which would be taken up and converted by the unregulated GS to GSH,andthe administration of modified GSH compounds, such as GSH esters that could potentially overcome the concentration gradient that prohibits passive GSH uptake, in AD.

Neuroprotective effects of rosmarinic acid on ciguatoxin in primary human neurons.

Ciguatoxin (CTX), is a toxic compound produced by microalgae (dinoflagellate) Gambierdiscus spp., and is bio-accumulated and bio-transformed through the marine food chain causing neurological deficits. To determine the mechanism of CTX-mediated cytotoxicity in human neurons, we measured extracellular lactate dehydrogenase (LDH) activity, intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) and H2AX phosphorylation at serine 139 as a measure for DNA damage in primary cultures of human neurons treated with Pacific (P)-CTX-1B and P-CTX-3C. We found these marine toxins can induce a time and dose-dependent increase in extracellular LDH activity, with a concomitant decline in intracellular NAD(+) levels and increased DNA damage at the concentration range of 5-200 nM. We also showed that pre- and post-treatment with rosmarinic acid (RA), the active constituent of the Heliotropium foertherianum (Boraginaceae) can attenuate CTX-mediated neurotoxicity. These results further highlight the potential of RA in the treatment of CTX-induced neurological deficits.

Neuroprotective Effects of a Variety of Pomegranate Juice Extracts (PJE) Against the Excitotoxin Quinolinic Acid in Human Primary Neurons.

BACKGROUND: Quinolinic acid (QUIN) excitotoxicity is mediated by elevated intracellular Ca2+ levels, and nitric oxide (NO•) mediated oxidative stress leading to DNA damage, and cell death due to energy restriction. METHODS: We evaluated the effect of a series of pomegranate juice extracts (PJE), Helow, Malasi, Qusum, and Hamedh, with antioxidant properties on QUIN induced excitotoxicity on primary cultures of human neurons. RESULTS: We showed that Helow and Malasi can attenuate QUIN-induced excitotoxicity to a greater extent than Qusum and Hamedh from Oman. Similarly, both Helow and Malasi were able to attenuate QUIN-induced Ca2+ influx and nNOS activity to a greater extent compared to Qusum, and Hamedh. All extracts reduced the oxidative effects of increased NO• production, and hence preventing NAD+ depletion and cell death. CONCLUSION: In addition to the well-known antioxidant properties of these natural phytochemicals, the inhibitory effect of some of these compounds on specific excitotoxic processes such as calcium influx provides additional evidence for the beneficial health effects of PJE in excitable tissue, particularly within the CNS.

Excitotoxicity in the pathogenesis of autism.

Autism is a debilitating neurodevelopment disorder characterised by stereotyped interests and behaviours, and abnormalities in verbal and non-verbal communication. It is a multifactorial disorder resulting from interactions between genetic, environmental and immunological factors. Excitotoxicity and oxidative stress are potential mechanisms, which are likely to serve as a converging point to these risk factors. Substantial evidence suggests that excitotoxicity, oxidative stress and impaired mitochondrial function are the leading cause of neuronal dysfunction in autistic patients. Glutamate is the primary excitatory neurotransmitter produced in the CNS, and overactivity of glutamate and its receptors leads to excitotoxicity. The over excitatory action of glutamate, and the glutamatergic receptors NMDA and AMPA, leads to activation of enzymes that damage cellular structure, membrane permeability and electrochemical gradients. The role of excitotoxicity and the mechanism behind its action in autistic subjects is delineated in this review.

The role of polyphenols in the modulation of sirtuins and other pathways involved in Alzheimer's disease.

Alzheimer's disease (AD) is characterised by extracellular amyloid deposits, neurofibrillary tangles, synaptic loss, inflammation and extensive oxidative stress. Polyphenols, which include resveratrol, epigallocatechin gallate and curcumin, have gained considerable interest for their ability to reduce these hallmarks of disease and their potential to slow down cognitive decline. Although their antioxidant and free radical scavenging properties are well established, more recently polyphenols have been shown to produce other important effects including anti-amyloidogenic activity, cell signalling modulation, effects on telomere length and modulation of the sirtuin proteins. Brain accessible polyphenols with multiple effects on pathways involved in neurodegeneration and ageing may therefore prove efficacious in the treatment of age-related diseases such as AD, although the evidence for this so far is limited. This review aims to explore the known effects of polyphenols from various natural and synthetic sources on brain ageing and neurodegeneration, and to examine their multiple mechanisms of action, with an emphasis on the role that the sirtuin pathway may play and the implications this may have for the treatment of AD.