Transient increase in neuronal chloride concentration by neuroactive aminoacids released from glioma cells

Hyaluronan-Cholesterol Nanogels for the Enhancement of the Ocular Delivery of Therapeutics

The anatomy and physiology of the eye strongly limit the bioavailability of locally administered drugs. The entrapment of therapeutics into nanocarriers represents an effective strategy for the topical treatment of several ocular disorders, as they may protect the embedded molecules, enabling drug residence on the ocular surface and/or its penetration into different ocular compartments. The present work shows the activity of hyaluronan-cholesterol nanogels (NHs) as ocular permeation enhancers. Thanks to their bioadhesive properties, NHs firmly interact with the superficial corneal epithelium, without penetrating the stroma, thus modifying the transcorneal penetration of loaded therapeutics. Ex vivo transcorneal permeation experiments show that the permeation of hydrophilic drugs (i.e., tobramycin and diclofenac sodium salt), loaded in NHs, is significantly enhanced when compared to the free drug solutions. On the other side, the permeation of hydrophobic drugs (i.e., dexamethasone and piroxicam) is strongly dependent on the water solubility of the entrapped molecules. The obtained results suggest that NHs formulations can improve the ocular bioavailability of the instilled drugs by increasing their preocular retention time (hydrophobic drugs) or facilitating their permeation (hydrophilic drugs), thus opening the route for the application of HA-based NHs in the treatment of both anterior and posterior eye segment diseases.

Effectiveness of porous silicon nanoparticle treatment at inhibiting the migration of a heterogeneous glioma cell population

BACKGROUND

Approximately 80% of brain tumours are gliomas. Despite treatment, patient mortality remains high due to local metastasis and relapse. It has been shown that transferrin-functionalised porous silicon nanoparticles (Tf@pSiNPs) can inhibit the migration of U87 glioma cells. However, the underlying mechanisms and the effect of glioma cell heterogeneity, which is a hallmark of the disease, on the efficacy of Tf@pSiNPs remains to be addressed.

RESULTS

Here, we observed that Tf@pSiNPs inhibited heterogeneous patient-derived glioma cells' (WK1) migration across small perforations (3 μm) by approximately 30%. A phenotypical characterisation of the migrated subpopulations revealed that the majority of them were nestin and fibroblast growth factor receptor 1 positive, an indication of their cancer stem cell origin. The treatment did not inhibit cell migration across large perforations (8 μm), nor cytoskeleton formation. This is in agreement with our previous observations that cellular-volume regulation is a mediator of Tf@pSiNPs' cell migration inhibition. Since aquaporin 9 (AQP9) is closely linked to cellular-volume regulation, and is highly expressed in glioma, the effect of AQP9 expression on WK1 migration was investigated. We showed that WK1 migration is correlated to the differential expression patterns of AQP9. However, AQP9-silencing did not affect WK1 cell migration across perforations, nor the efficacy of cell migration inhibition mediated by Tf@pSiNPs, suggesting that AQP9 is not a mediator of the inhibition.

CONCLUSION

This in vitro investigation highlights the unique therapeutic potentials of Tf@pSiNPs against glioma cell migration and indicates further optimisations that are required to maximise its therapeutic efficacies.

HPLC Determination of Bioactive Sulfur Compounds, Amino Acids and Biogenic Amines in Biological Specimens

There is an increasing interest for analytical methods aimed to detect biological sulfur-containing amines, because of their involvement in human diseases and metabolic disorders. This work describes an improved HPLC method for the determination of sulfur containing amino acids and amines from different biological matrices. We optimized a pre-column derivatization procedure using dabsyl chloride, in which dabsylated products can be monitored spectrophotometrically at 460 nm. This method allows the simultaneous analysis of biogenic amines, amino acids and sulfo-amino compounds including carnosine, dopamine, epinephrine, glutathione, cysteine, taurine, lanthionine, and cystathionine in brain specimens, urines, plasma, and cell lysates. Moreover, the method is suitable for the study of physiological and non-physiological derivatives of taurine and glutathione such as hypotaurine, homotaurine, homocysteic acid and S-acetylglutathione. The present method displays good efficiency of derivatization, having the advantage to give rise to stable products compared to other derivatizing agents such as o-phthalaldehyde and dansyl chloride.With this method, we provide a tool to study sulfur cycle from a metabolic point of view in relation to the pattern of biological amino-compounds, allowing researchers to get a complete scenario of organic sulfur and amino metabolism in tissues and cells.

Kv1.3 activity perturbs the homeostatic properties of astrocytes in glioma

Glial cells actively maintain the homeostasis of brain parenchyma, regulating neuronal excitability and preserving the physiological composition of the extracellular milieu. Under pathological conditions, some functions of glial cells could be compromised, exacerbating the neurotoxic processes. We investigated if the homeostatic activities of astrocytes and microglia could be modulated by the voltage-gated K⁺ channel Kv1.3. To this end we used in vitro and in vivo systems to model cell-to-cell interactions in tumoral conditions, using a specific inhibitor of Kv1.3 channels, 5-(4-phenoxybutoxy) psoralen (PAP-1). We demonstrated that PAP-1 increases astrocytic glutamate uptake, reduces glioma-induced neurotoxicity, and decreases microglial migration and phagocytosis. We also found in a tumor blood brain barrier model that Kv1.3 activity is required for its integrity. The crucial role of Kv1.3 channels as modulators of glial cell activity was confirmed in a mouse model of glioma, where PAP-1 treatment reduces tumor volume only in the presence of active glutamate transporters GLT-1. In the same mouse model, PAP-1 reduces astrogliosis and microglial infiltration. PAP-1 also reduces tumor cell invasion. All these findings point to Kv1.3 channels as potential targets to re-instruct glial cells toward their homeostatic functions, in the context of brain tumors.

ATP release during cell swelling activates a Ca2+-dependent Cl- current by autocrine mechanism in mouse hippocampal microglia

Microglia cells, resident immune cells of the brain, survey brain parenchyma by dynamically extending and retracting their processes. Cl⁻ channels, activated in the cellular response to stretch/swelling, take part in several functions deeply connected with microglia physiology, including cell shape changes, proliferation, differentiation and migration. However, the molecular identity and functional properties of these Cl⁻ channels are largely unknown. We investigated the properties of swelling-activated currents in microglial from acute hippocampal slices of Cx3cr1^+/GFP mice by whole-cell patch-clamp and imaging techniques. The exposure of cells to a mild hypotonic medium, caused an outward rectifying current, developing in 5–10 minutes and reverting upon stimulus washout. This current, required for microglia ability to extend processes towards a damage signal, was carried mainly by Cl⁻ ions and dependent on intracellular Ca²⁺. Moreover, it involved swelling-induced ATP release. We identified a purine-dependent mechanism, likely constituting an amplification pathway of current activation: under hypotonic conditions, ATP release triggered the Ca²⁺-dependent activation of anionic channels by autocrine purine receptors stimulation. Our study on native microglia describes for the first time the functional properties of stretch/swelling-activated currents, representing a key element in microglia ability to monitor the brain parenchyma.

A role for intracellular zinc in glioma alteration of neuronal chloride equilibrium

Glioma patients commonly suffer from epileptic seizures. However, the mechanisms of glioma-associated epilepsy are far to be completely understood. Using glioma-neurons co-cultures, we found that tumor cells are able to deeply influence neuronal chloride homeostasis, by depolarizing the reversal potential of γ-aminobutyric acid (GABA)-evoked currents (EGABA). EGABA depolarizing shift is due to zinc-dependent reduction of neuronal KCC2 activity and requires glutamate release from glioma cells. Consistently, intracellular zinc loading rapidly depolarizes EGABA in mouse hippocampal neurons, through the Src/Trk pathway and this effect is promptly reverted upon zinc chelation. This study provides a possible molecular mechanism linking glioma invasion to excitation/inhibition imbalance and epileptic seizures, through the zinc-mediated disruption of neuronal chloride homeostasis.

Calibration and functional analysis of three genetically encoded Cl(-)/pH sensors

Monitoring of the intracellular concentrations of Cl⁻ and H⁺ requires sensitive probes that allow reliable quantitative measurements without perturbation of cell functioning. For these purposes the most promising are genetically encoded fluorescent biosensors, which have become powerful tools for non-invasive intracellular monitoring of ions, molecules, and enzymatic activity. A ratiometric CFP/YFP-based construct with a relatively good sensitivity to Cl⁻ has been developed (Markova et al., 2008; Waseem et al., 2010). Recently, a combined Cl⁻/pH sensor (ClopHensor) opened the way for simultaneous ratiometric measurement of these two ions (Arosio et al., 2010). ClopHensor was obtained by fusion of a red-fluorescent protein (DsRed-monomer) to the E²GFP variant that contains a specific Cl⁻-binding site. This construct possesses pK_a = 6.8 for H⁺ and K_d in the 40–50 mM range for Cl⁻ at physiological pH (~7.3). As in the majority of cell types the intracellular Cl⁻ concentration ([Cl⁻]_i) is about 10 mM, the development of sensors with higher sensitivity is highly desirable. Here, we report the intracellular calibration and functional characterization of ClopHensor and its two derivatives: the membrane targeting PalmPalm-ClopHensor and the H148G/V224L mutant with improved Cl⁻ affinity, reduced pH dependence, and pK_a shifted to more alkaline values. For functional analysis, constructs were expressed in CHO cells and [Cl⁻]_i was changed by using pipettes with different Cl⁻ concentrations during whole-cell recordings. K_d values for Cl⁻ measured at 33°C and pH ~7.3 were, respectively, 39, 47, and 21 mM for ClopHensor, PalmPalm-ClopHensor, and the H148G/V224L mutant. PalmPalm-ClopHensor resolved responses to activation of Cl⁻-selective glycine receptor (GlyR) channels better than did ClopHensor. Our observations indicate that these different ClopHensor constructs are promising tools for non-invasive measurement of [Cl⁻]_i in various living cells.

Improved method for efficient imaging of intracellular Cl(-) with Cl-Sensor using conventional fluorescence setup

Chloride (Cl⁻) homeostasis is known to be fundamental for central nervous system functioning. Alterations in intracellular Cl⁻ concentration ([Cl⁻]_i) and changes in the efficacy of Cl⁻ extrusion are involved in numerous neurological disorders. Therefore, there is a strong need for studies of the dynamics of [Cl⁻]_i in different cell types under physiological conditions and during pathology. Several previous works reported having successfully achieved recording of [Cl⁻]_i using genetically encoded Cl-Sensor that is composed of the cyan fluorescent protein (CFP) and Cl⁻-sensitive mutant of the yellow fluorescent protein (YFP_Cl). However, all reported works were performed using specially designed setups with ultra-sensitive CCD cameras. Our multiple attempts to monitor Cl⁻-dependent fluorescence of Cl-Sensor using conventional epifluorescence microscopes did not yield successful results. In the present work, we have analysed the reason of our failures and found that they were caused by a strong inactivation of the YFP_Cl component of Cl-Sensor during excitation of the CFP with 430 nm light. Based on the obtained results, we reduced 20-fold the intensity of the 430 nm excitation and modified the recording protocol that allows now stable long-lasting ratiometric measurements of Cl-Sensor fluorescence in different cell types including cultured hippocampal neurons and their tiny dendrites and spines. Simultaneous imaging and patch clamp recording revealed that in mature neurons, the novel protocol allows detection of as little as 2 mM changes of [Cl⁻]_i from the resting level of 5–10 mM. We demonstrate also a usefulness of the developed [Cl⁻]_i measurement procedure for large scale screening of the activity of exogenously expressed potassium-chloride co-transporter KCC2, a major neuronal Cl⁻ extruder that is implicated in numerous neurological disorders and is a target for novel therapeutical treatments.