Sodium Sensing in Neurons with a Dendrimer-Based Nanoprobe

Department of Cell Biology and Morphology, University of Lausanne, Rue du Bugnon 9, CH-1005 Lausanne, Switzerland.
ACS Nano (Impact Factor: 12.88). 02/2012; 6(2):1176-87. DOI: 10.1021/nn203822t
Source: PubMed


Ion imaging is a powerful methodology to assess fundamental biological processes in live cells. The limited efficiency of some ion-sensing probes and their fast leakage from cells are important restrictions to this approach. In this study, we present a novel strategy based on the use of dendrimer nanoparticles to obtain better intracellular retention of fluorescent probes and perform prolonged fluorescence imaging of intracellular ion dynamics. A new sodium-sensitive nanoprobe was generated by encapsulating a sodium dye in a PAMAM dendrimer nanocontainer. This nanoprobe is very stable and has high sodium sensitivity and selectivity. When loaded in neurons in live brain tissue, it homogenously fills the entire cell volume, including small processes, and stays for long durations, with no detectable alterations of cell functional properties. We demonstrate the suitability of this new sodium nanosensor for monitoring physiological sodium responses such as those occurring during neuronal activity.

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    • "This nanoprobe homogenously filled the entire cell volume and remained for a long duration without detectable alterations of functional cellular properties when it was loaded in neurons in live brain tissue. The same principle can be applied to other existing fluorescent dyes, generating new applications for live fluorescent imaging.198In addition to their straight forward assembly, dendrimer based nanoprobes are promising for the noninvasive visualization of brain tumors with uncompromised BBB, providing the possibility for real-time optical-image-guided brain tumor resection during surgery. "
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    ABSTRACT: This review gives concise information about the dendrimers, properties, synthesis and application in drug delivery, diagnosis and therapy. Due to their unique architecture these have improved physical and chemical properties. They show high solubility, miscibility and reactivity due to their terminal groups. Dendrimers have well defined size, shape, molecular weight and monodispersity. These properties make the dendrimers a suitable carrier in drug delivery application. Dendrimers are unimolecular miceller in nature and due to this enhances the solubility of poorly soluble drugs. Their compatibility with DNA, heparin and polyanions make them more versatile. Dendrimers, also referred as modern day polymers, they offer much more good properties than the conventional polymers. Due to their multivalent and mono disperse character dendrimers have stimulated wide interest in the field of chemistry biology, especially in applications like drug delivery, gene therapy and chemotherapy. Self assembly produces a faster means of generating nanoscopic functional and structural systems. But their actual utility in drug delivery can be assessed only after deep understanding of factors affecting their properties and their behavior in vivo. Key words: Dendrimers PAMAM PPI Synthesis Divergent Convergent Cosmetics
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    ABSTRACT: Stimulus-dependent elevation of intracellular Ca(2+) ([Ca(2+)](i)) affects the expression of numerous genes--a phenomenon known as excitation-transcription coupling. Recently, we found that increases in [Na(+)](i) trigger c-Fos expression via a novel Ca(2+) (i)-independent pathway. In the present study, we identified ubiquitous and tissue-specific [Na(+)](i)/[K(+)](i)-sensitive transcriptomes by comparative analysis of differentially expressed genes in vascular smooth muscle cells from rat aorta (RVSMC), the human adenocarcinoma cell line HeLa, and human umbilical vein endothelial cells (HUVEC). To augment [Na(+)](i) and reduce [K(+)](i), cells were treated for 3 hrs with the Na(+),K(+)-ATPase inhibitor ouabain or placed for the same time in the K(+)-free medium. Employing Affymetrix-based technology, we detected changes in expression levels of 684, 737 and 1839 transcripts in HeLa, HUVEC and RVSMC, respectively, that were highly correlated between two treatments (p<0.0001; R(2)>0.62). Among these Na(+) (i)/K(+) (i)-sensitive genes, 80 transcripts were common for all three types of cells. To establish if changes in gene expression are dependent on increases in [Ca(2+)](i), we performed identical experiments in Ca(2+)-free media supplemented with extracellular and intracellular Ca(2+) chelators. Surprisingly, this procedure elevated rather than decreased the number of ubiquitous and cell-type specific Na(+) (i)/K(+) (i)-sensitive genes. Among the ubiquitous Na(+) (i)/K(+) (i)-sensitive genes whose expression was regulated independently of the presence of Ca(2+) chelators by more than 3-fold, we discovered several transcription factors (Fos, Jun, Hes1, Nfkbia), interleukin-6, protein phosphatase 1 regulatory subunit, dual specificity phosphatase (Dusp8), prostaglandin-endoperoxide synthase 2, cyclin L1, whereas expression of metallopeptidase Adamts1, adrenomedulin, Dups1, Dusp10 and Dusp16 was detected exclusively in Ca(2+)-depleted cells. Overall, our findings indicate that Ca(2+) (i)-independent mechanisms of excitation-transcription coupling are involved in transcriptomic alterations triggered by elevation of the [Na(+)](i)/[K(+)](i) ratio. There results likely have profound implications for normal and pathological regulation of mammalian cells, including sustained excitation of neuronal cells, intensive exercise and ischemia-triggered disorders.
    Full-text · Article · May 2012 · PLoS ONE
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    ABSTRACT: Dendrimers are characterized, among other quite interesting properties, by heterogeneity of zones inside their molecules and for a high local concentration of functionalities. These two particularly properties of dendrimers confer them a potential selective and sensitive recognition of guest molecules. On the other side, semiconductor nanoparticles (quantum dots), which are highly fluorescent nanomaterials, can be conjugated with numerous molecules including dendrimers, just by chemically modification of their surface. The coupling of dendrimers and quantum dots result in hybrids organic/inorganic nanocomposites, which can alter the charge, functionality and reactivity, based, for example, in the fluorescence changes induced by molecular recognition at their surfaces. This can simultaneously enhance the stability and dispersion of the nanocomposites. Here we review the advantages of dendrimers modified quantum dots as nanoprobes, to investigate their feasibility to be used as analytical tool in a wide variety of ions and molecules.
    Full-text · Chapter · Jan 2013
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