Resonance Energy Transfer to Track the Motion of Lanthanide Ions-What Drives the Intermixing in Core-Shell Upconverting Nanoparticles?

The imagination of clearly separated core-shell structures is already outdated by the fact, that the nanoparticle core-shell structures remain in terms of efficiency behind their respective bulk material due to intermixing between core and shell dopant ions. In order to optimize the photoluminescence of core-shell UCNP the intermixing should be as small as possible and therefore, key parameters of this process need to be identified. In the present work the Ln(III) ion migration in the host lattices NaYF4 and NaGdF4 was monitored. These investigations have been performed by laser spectroscopy with help of lanthanide resonance energy transfer (LRET) between Eu(III) as donor and Pr(III) or Nd(III) as acceptor. The LRET is evaluated based on the Förster theory. The findings corroborate the literature and point out the migration of ions in the host lattices. Based on the introduced LRET model, the acceptor concentration in the surrounding of one donor depends clearly on the design of the applied core-shell-shell nanoparticles. In general, thinner intermediate insulating shells lead to higher acceptor concentration, stronger quenching of the Eu(III) donor and subsequently stronger sensitization of the Pr(III) or the Nd(III) acceptors. The choice of the host lattice as well as of the synthesis temperature are parameters to be considered for the intermixing process.

Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator.

Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm3+ or Er3+ as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < λ em < 480 nm (for Tm3+, three and four photon induced emission) or 525 nm < λ em < 545 nm (for Er3+, two photon induced emission), respectively. Especially for UCNPs containing Tm3+ a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (λ ex = 976 nm) in the presence of the Tm3+-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR.

Energy Transfer between Tm-Doped Upconverting Nanoparticles and a Small Organic Dye with Large Stokes Shift.

Lanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51%) despite the compromised luminescence due to surface quenching.

Divergent effects of norepinephrine, dopamine and substance P on the activation, differentiation and effector functions of human cytotoxic T lymphocytes.

BACKGROUND: Neurotransmitters are important regulators of the immune system, with very distinct and varying effects on different leukocyte subsets. So far little is known about the impact of signals mediated by neurotransmitters on the function of CD8+ T lymphocytes. Therefore, we investigated the influence of norepinephrine, dopamine and substance P on the key tasks of CD8+ T lymphocytes: activation, migration, extravasation and cytotoxicity. RESULTS: The activation of naïve CD8+ T lymphocytes by CD3/CD28 cross-linking was inhibited by norepinephrine and dopamine, which was caused by a downregulation of interleukin (IL)-2 expression via Erk1/2 and NF-kappaB inhibition. Furthermore, all of the investigated neurotransmitters increased the spontaneous migratory activity of naïve CD8+ T lymphocytes with dopamine being the strongest inducer. In contrast, activated CD8+ T lymphocytes showed a reduced migratory activity in the presence of norepinephrine and substance P. With regard to extravasation we found norepinephrine to induce adhesion of activated CD8+ T cells: norepinephrine increased the interleukin-8 release from endothelium, which in turn had effect on the activated CXCR1+ CD8+ T cells. At last, release of cytotoxic granules from activated cells in response to CD3 cross-linking was not influenced by any of the investigated neurotransmitters, as we have analyzed by measuring the beta-hexosamidase release. CONCLUSION: Neurotransmitters are specific modulators of CD8+ T lymphocytes not by inducing any new functions, but by fine-tuning their key tasks. The effect can be either stimulatory or suppressive depending on the activation status of the cells.

The inhibitory effect of norepinephrine on the migration of ES-2 ovarian carcinoma cells involves a Rap1-dependent pathway.

Our previous studies have shown that norepinephrine induces the migratory activity of human PC-3 prostate, SW 480 colon and MDA-MB-468 breast carcinoma cells. In contrast to these results, we show here that human ES-2 ovarian carcinoma cells have a reduced migratory activity after norepinephrine treatment. This inhibitory effect is possibly mediated by a cAMP-dependent activation of the small GTPase Rap1 via Epac. Furthermore, a key signalling event of the promigratory effect of norepinephrine in the above mentioned carcinoma cells is the activation of phospholipase C enzymes. In ES-2 cells, this part of the signalling cascade is constitutively active.

Neurotransmitter effects on tumor cells and leukocytes.

During the last 10 years new evidence has come to light which shows that the biology of neurotransmitters has expanded beyond their traditional role as chemical messengers, which is the release from a neuron, diffusion across a synaptic cleft, binding to and stimulation of a post-synaptic cell. These external signaling substances of the nervous system have been found to exert a strong influence on cells of the immune system and tumor cells. The latter express neurotransmitter receptors and several studies demonstrate the involvement of neurotransmitters in tumor cell progression and metastasis development. Besides their impact on the migration of lymphocytes, which is of primary importance for an anti-tumor response, neurotransmitters comprise a multitude of other immunomodulatory properties, which differ depending on the cell type and cell function. To illuminate the interplay between the nervous system, the immune system and tumor cells, we herein summarize in vitro and in vivo experiments on the effects of neurotransmitters on the migratory activity, proliferation and survival of tumor cells, as well as on the function of leukocytes.

Phosphatidylinositol 3-kinase in the G protein-coupled receptor-induced chemokinesis and chemotaxis of MDA-MB-468 breast carcinoma cells: a comparison with leukocytes.

The polarization of tumor cells and leukocytes into a front end and a rear end is a crucial prerequisite for their autonomous, directed movement. Phosphatidylinositol 3-kinase (PI3K) is assumed to play an important role in this polarization process, whereas the results obtained with different cell types and different migration assays widely vary. Thus, we conducted a comparative study on the role of the PI3K in the locomotor activity and directionality of the migration of tumor cells on the example of MDA-MB-468 breast carcinoma cells in comparison with CTLs and neutrophil granulocytes. We used our well-established, collagen-based, three-dimensional migration assay for the investigation of the chemokinesis and chemotaxis of these cells. Our results show that the role of the PI3K in the regulation of migratory activity is distinct between the investigated cell types: the migration of CTLs and MDA-MB-468 cells was impaired by the inhibition of the PI3K with wortmannin, whereas neutrophil granulocytes were only slightly affected. However, neither cell type was impaired in the ability to respond chemotactically to gradients of ligands to G protein-coupled receptors. Thus, the PI3K contributes to the regulation of migratory activity but not to the directionality of migration of MDA-MB-468 breast carcinoma cells. As a further conclusion with regard to cancer treatment, the PI3K is not a suitable target for the inhibition of metastasis formation, because the migration of leukocytes is also affected, which leads to a dysfunction of the immune defense.

Analysis methods of human cell migration.

The autonomous migration of specialized cells is an essential characteristic in both physiological and pathological functions in the adult human organism. Leukocytes, fibroblasts, and stem cells, but also tumor cells, are thus the subject of intense investigation in a broad range of research fields. A wide spectrum of methods have therefore been established to analyze chemokinetic and chemotactic cell migration, ranging from easy-to-handle two-dimensional surface migration assays to highly specialized three-dimensional and intravital analysis methods. It is now manifest that the results obtained with these various migration assays substantially differ. This review therefore gives an overview of the migration assays which are currently in use, describes the methods, and critically enlightens the particular advantages and disadvantages of each method.

Inhibition of cell migration via G protein-coupled receptors to opioid peptides and angiotensin.

Neurotransmitters are stimulatory as well as inhibitory regulators of cell migration. Angiotensin is such an inhibitory regulator of the SDF-1-induced migration of cytotoxic T lymphocytes, as we have investigated by time-lapse videomicroscopy and computer-assisted cell tracking. For angiotensin II, the most effective form of angiotensin for the inhibition of migration, two G protein-coupled receptors are known, which both downregulate the activity of the adenylyl cyclase via activation of inhibitory G proteins. This downregulation of the enzymatic activity is a key signaling event for the inhibition of T lymphocyte and tumor cell migration, while stimulatory neurotransmitters--for example, norepinephrine--cause an activation of the adenylyl cyclase. Similar to angiotensin, the SDF-1-induced migration of cytotoxic T lymphocytes was inhibited by DAMGO, a specific agonist for the mu-opioid receptor, which is coupled to inhibitory G proteins, too. More interestingly, DAMGO downregulated the met-enkephalin-induced migration of MDA-MB-468 breast carcinoma cells. Met-enkephalin binds to the delta-opioid receptor and, with lower affinity, to the mu-opioid receptor. Since the delta-opioid receptor also activates inhibitory G proteins, the promigratory effect of met-enkephalin is caused by an intracellular signaling distinct from the engagement of each opioid receptor alone. In summary, the dual control of the adenylyl cyclase functions as an integrator of stimulatory and inhibitory signals for T lymphocyte and tumor cell migration, which are delivered by neurotransmitters and other signal substances that bind to G protein-coupled receptors.