Analytical Techniques: Shedding Light upon Nanometer-Sized Secretory Vesicles

Single-Vesicle Electrochemistry Following Repetitive Stimulation Reveals a Mechanism for Plasticity Changes with Iron Deficiency

Deficiency of iron, the most abundant transition metal in the brain and important for neuronal activity, is known to affect synaptic plasticity, causing learning and memory deficits. How iron deficiency impacts plasticity by altering neurotransmission at the cellular level is not fully understood. We used electrochemical methods to study the effect of iron deficiency on plasticity with repetitive stimulation. We show that during iron deficiency, repetitive stimulation causes significant decrease in exocytotic release without changing vesicular content. This results in a lower fraction of release, opposite to the control group, upon repetitive stimulation. These changes were partially reversible by iron repletion. This finding suggests that iron deficiency has a negative effect on plasticity by decreasing the fraction of vesicular release in response to repetitive stimulation. This provides a putative mechanism for how iron deficiency modulates plasticity.

A multimodal electrochemical approach to measure the effect of zinc on vesicular content and exocytosis in a single cell model of ischemia

Zinc ion is essential for normal brain function that modulates synaptic activity and neuronal plasticity and it is associated with memory formation. Zinc is considered to be a contributing factor to the pathogenesis of ischemia, but the association between zinc and ischemia on vesicular exocytosis is unclear. In this study, we used a combination of chemical analysis methods and a cell model of ischemia/reperfusion to investigate exocytotic release and vesicular content, as well as the effect of zinc alteration on vesicular exocytosis. Oxygen–glucose deprivation and reperfusion (OGDR) was used as an in vitro model of ischemia in a model cell line. Exocytotic release and vesicular storage of catecholamine content were increased following OGDR, resulting in a higher fraction of release during exocytosis. However, zinc eliminated these increases following OGDR and the fraction of release remained unchanged. Understanding the consequences of zinc accumulation on vesicular exocytosis at the early stage of OGDR should aid in the development of therapeutic strategies to reduce ischemic brain injury. As the fraction released has been suggested to be related to presynaptic plasticity, insights are gained towards deciphering ischemia related memory impairment.

Combined electrochemistry and mass spectrometry imaging to interrogate the mechanism of action of modafinil, a cognition-enhancing drug, at the cellular and sub-cellular level

Modafinil is a mild psychostimulant-like drug enhancing wakefulness, improving attention and developing performance in various cognitive tasks, but its mechanism of action is not completely understood. This is the first combination of amperometry, electrochemical cytometry and mass spectrometry to interrogate the mechanism of action of a drug, here modafinil, at cellular and sub-cellular level. We employed single-cell amperometry (SCA) and intracellular vesicle impact electrochemical cytometry (IVIEC) to investigate the alterations in exocytotic release and vesicular catecholamine storage following modafinil treatment. The SCA results reveal that modafinil slows down the exocytosis process so that, the number of catecholamines released per exocytotic event is enhanced in the modafinil-treated cells. Also, IVIEC results offer an upregulation effect of modafinil on the vesicular catecholamine storage. Mass spectrometry imaging by time-of-flight secondary ion mass spectrometry (ToF-SIMS) illustrates that treatment with modafinil reduces the cylindrical-shaped phosphatidylcholine at the cellular membrane, while the high curvature lipids with conical structures such as phosphatidylethanolamine and phosphatidylinositol are elevated after modafinil treatment. Combining the results obtained by SCA, IVIEC and ToF-SIMS suggests that modafinil-treated cells release a larger portion of their vesicular content at least in part by changing the lipid composition of the cell membrane, suggesting regulation of cognition.

Simultaneous detection of vesicular content and exocytotic release with two electrodes in and at a single cell

We developed a technique employing two electrodes to simultaneously and dynamically monitor vesicular neurotransmitter storage and vesicular transmitter release in and at the same cell. To do this, two electrochemical techniques, single-cell amperometry (SCA) and intracellular vesicle impact electrochemical cytometry (IVIEC), were applied using two nanotip electrodes. With one electrode being placed on top of a cell measuring exocytotic release and the other electrode being inserted into the cytoplasm measuring vesicular transmitter storage, upon chemical stimulation, exocytosis is triggered and the amount of release and storage can be quantified simultaneously and compared. By using this technique, we made direct comparison between exocytotic release and vesicular storage, and investigated the dynamic changes of vesicular transmitter content before, during, and after chemical stimulation of PC12 cells, a neuroendocrine cell line. While confirming that exocytosis is partial, we suggest that chemical stimulation either induces a replenishment of the releasable pool with a subpool of vesicles having higher amount of transmitter storage, or triggers the vesicles within the same subpool to load more transiently at approximately 10–20 s. Thus, a time scale for vesicle reloading is determined. The effect of l-3,4-dihydroxyphenylalanine (l-DOPA), the precursor to dopamine, on the dynamic alteration of vesicular storage upon chemical stimulation for exocytosis was also studied. We found that l-DOPA incubation reduces the observed changes of vesicular storage in regular PC12 cells, which might be due to an increased capacity of vesicular transmitter loading caused by l-DOPA. Our data provide another mechanism for plasticity after stimulation via quantitative and dynamic changes in the exocytotic machinery.

Simultaneous measurements of IVIEC and SCA by two nanotip electrodes allows direct and dynamic comparison between vesicular transmitter content and vesicular transmitter release to shed light on stimulation-induced plasticity.

Recent Progress in Quantitatively Monitoring Vesicular Neurotransmitter Release and Storage With Micro/Nanoelectrodes

Exocytosis is one of the essential steps for chemical signal transmission between neurons. In this process, vesicles dock and fuse with the plasma membrane and release the stored neurotransmitters through fusion pores into the extracellular space, and all of these steps are governed with various molecules, such as proteins, ions, and even lipids. Quantitatively monitoring vesicular neurotransmitter release in exocytosis and initial neurotransmitter storage in individual vesicles is significant for the study of chemical signal transmission of the central nervous system (CNS) and neurological diseases. Electrochemistry with micro/nanoelectrodes exhibits great spatial-temporal resolution and high sensitivity. It can be used to examine the exocytotic kinetics from the aspect of neurotransmitters and quantify the neurotransmitter storage in individual vesicles. In this review, we first introduce the recent advances of single-cell amperometry (SCA) and the nanoscale interface between two immiscible electrolyte solutions (nanoITIES), which can monitor the quantity and release the kinetics of electrochemically and non-electrochemically active neurotransmitters, respectively. Then, the development and application of the vesicle impact electrochemical cytometry (VIEC) and intracellular vesicle impact electrochemical cytometry (IVIEC) and their combination with other advanced techniques can further explain the mechanism of neurotransmitter storage in vesicles before exocytosis. It has been proved that these electrochemical techniques have great potential in the field of neuroscience.

Multimodal Imaging Mass Spectrometry: Next Generation Molecular Mapping in Biology and Medicine

Imaging mass spectrometry has become a mature molecular mapping technology that is used for molecular discovery in many medical and biological systems. While powerful by itself, imaging mass spectrometry can be complemented by the addition of other orthogonal, chemically informative imaging technologies to maximize the information gained from a single experiment and enable deeper understanding of biological processes. Within this review, we describe MALDI, SIMS, and DESI imaging mass spectrometric technologies and how these have been integrated with other analytical modalities such as microscopy, transcriptomics, spectroscopy, and electrochemistry in a field termed multimodal imaging. We explore the future of this field and discuss forthcoming developments that will bring new insights to help unravel the molecular complexities of biological systems, from single cells to functional tissue structures and organs.

Direct Measurement of Total Vesicular Catecholamine Content with Electrochemical Microwell Arrays

We have designed and fabricated a microwell array chip (MWAC) to trap and detect the entire content of individual vesicles after disruption of the vesicular membrane by an applied electrical potential. To understand the mechanism of vesicle impact electrochemical cytometry (VIEC) in microwells, we simulated the rupture of the vesicles and subsequent diffusion of entrapped analytes. Two possibilities were tested: (i) the vesicle opens toward the electrode, and (ii) the vesicle opens away from the electrode. These two possibilities were simulated in the different microwells with varied depth and width. Experimental VIEC measurements of the number of molecules for each vesicle in the MWAC were compared to VIEC on a gold microdisk electrode as a control, and the quantified catecholamines between these two techniques was the same. We observed a prespike foot in a significant number of events (∼20%) and argue this supports the hypothesis that the vesicles rupture toward the electrode surface with a more complex mechanism including the formation of a stable pore intermediate. This study not only confirms that in standard VIEC experiments the whole content of the vesicle is oxidized and quantified at the surface of the microdisk electrode but actively verifies that the adsorbed vesicle on the surface of the electrode forms a pore in the vicinity of the electrode rather than away from it. The fabricated MWAC promotes our ability to quantify the content of vesicles accurately, which is fundamentally important in bioanalysis of the vesicles.

Platinum(II) Terpyridine Anticancer Complexes Possessing Multiple Mode of DNA Interaction and EGFR Inhibiting Activity

Platinum(II) terpyridine complexes has attracted increasing attention as they have displayed great potential as antitumor agents due to their high intercalation affinity with nucleic acids. Epidermal growth factor receptor (EGFR) is often overexpressed in various tumor cells, leading to uncontrolled growth of tumor, and is regarded as an important target for developing novel antitumor drugs. Herein, we report four platinum(II) terpyridine complexes bearing EGFR inhibiting 4-anilinoquinazoline derivatives as potent multi-targeting antiproliferation agents against a series of cancer cells. EGFR inhibition assay revealed that these complexes are highly potent EGFR inhibitors. But competitive DNA binding assay and docking simulations also suggested that these complexes exhibited multiple modes of DNA interaction, especially great affinity toward DNA minor groove. Finally, cellular uptake and distribution measurements by inductively coupled plasma mass spectrometry (ICP-MS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) demonstrated that both nucleus DNA and membrane proteins are important targets for their anticancer mechanisms. The complexes herein can therefore be regarded as promising multi-targeting anticancer agents.

Functional imaging of a model unicell: Spironucleus vortens as an anaerobic but aerotolerant flagellated protist

Advances in optical microscopy are continually narrowing the chasm in our appreciation of biological organization between the molecular and cellular levels, but many practical problems are still limiting. Observation is always limited by the rapid dynamics of ultrastructural modifications of intracellular components, and often by cell motility: imaging of the unicellular protist parasite of ornamental fish, Spironucleus vortens, has proved challenging. Autofluorescence of nicotinamide nucleotides and flavins in the 400-580 nm region of the visible spectrum, is the most useful indicator of cellular redox state and hence vitality. Fluorophores emitting in the red or near-infrared (i.e., phosphors) are less damaging and more penetrative than many routinely employed fluors. Mountants containing free radical scavengers minimize fluorophore photobleaching. Two-photon excitation provides a small focal spot, increased penetration, minimizes photon scattering and enables extended observations. Use of quantum dots clarifies the competition between endosomal uptake and exosomal extrusion. Rapid motility (161 μm/s) of the organism makes high resolution of ultrastructure difficult even at high scan speeds. Use of voltage-sensitive dyes determining transmembrane potentials of plasma membrane and hydrogenosomes (modified mitochondria) is also hindered by intracellular motion and controlled anesthesia perturbs membrane organization. Specificity of luminophore binding is always questionable; e.g. cationic lipophilic species widely used to measure membrane potentials also enter membrane-bounded neutral lipid droplet-filled organelles. This appears to be the case in S. vortens, where Coherent Anti-Stokes Raman Scattering (CARS) micro-spectroscopy unequivocally images the latter and simultaneous provides spectral identification at 2840 cm^-1. Secondary Harmonic Generation highlights the highly ordered structure of the flagella.