Estimation of adenosine and its major metabolites in brain tissues of rats using high-performance thin-layer chromatography–densitometry

Carbon dots-sensitized amorphous MoSx photoanode: Sequential electrodeposition preparation and dual amplified photoelectrochemical aptasensing of adenosine

The design and fabrication of high visible-light activated photoelectrode are essential to precisely detect biomolecule in biological system. Herein, an ultrasensitive photoelectrochemical (PEC) aptasensor for specific recognition of adenosine is established based on carbon dots sensitized-amorphous molybdenum sulfide (a-MoS_x/CDs) photoanode and dual amplification strategy. The heterostructured photoanode achieved by sequential electrodeposition reveals significantly boosted photocurrent with good stability and repeatability under visible light illumination, giving the credit to highly activated visible light absorption, uniform coverage and good electric contact to the underlying substrate, as well as the energy-band alignment between the two components. By stepwisely immobilizing complementary DNA probe (NH₂-DNA) and adenosine aptamer (Apt), followed by methylene blue (MB) binding with the guanine base on Apt, a dual amplified self-powered PEC aptasensor for adenosine detection is constructed. Based on the co-sensitization effect of CDs and MB, ultrasensitive and high-affinitive determination of adenosine is realized over the concentration range of 0.01 nM-1000 nM at 0 V (vs. SCE), with satisfactory stability and reproducibility. The detection limit is as low as 3.3 pM, demonstrating a performance even surpassing most of the sensors reported so far. The prospective application of the co-sensitized a-MoS_x photoanode for ultrasensitive aptasensing is highlighted in this work.

High-performance thin-layer chromatography for the evaluation of voacamine intracellular concentration related to its cytotoxic effect

Previous investigations demonstrated that pretreatment with non-cytotoxic concentrations of voacamine had a chemosensitizing effect on cultured multidrug resistant osteosarcoma cells exposed to doxorubicin; whereas when used alone at high concentrations voacamine induced apoptosis-independent cell death on both sensitive and resistant cells. To gain insight into the mechanism of action of voacamine at the subcellular level, we developed an analytical high-performance thin-layer chromatography technique to assess the intracellular content of voacamine that could be correlated with the induction of cell death and consequent morphological and ultrastructural changes. The results of the quantitative analysis not only did allow us to measure both the amount of unmodified voacamine molecules (determined by the method) and the amount of molecules which reacted with cellular components (undetectable), but also to confirm the findings of our previous studies and support the validity of this method.

Fast-scan Cyclic Voltammetry for the Characterization of Rapid Adenosine Release

Adenosine is a signaling molecule and downstream product of ATP that acts as a neuromodulator. Adenosine regulates physiological processes, such as neurotransmission and blood flow, on a time scale of minutes to hours. Recent developments in electrochemical techniques, including fast-scan cyclic voltammetry (FSCV), have allowed direct detection of adenosine with sub-second temporal resolution. FSCV studies have revealed a novel mode of rapid signaling that lasts only a few seconds. This rapid release of adenosine can be evoked by electrical or mechanical stimulations or it can be observed spontaneously without stimulation. Adenosine signaling on this time scale is activity dependent; however, the mode of release is not fully understood. Rapid adenosine release modulates oxygen levels and evoked dopamine release, indicating that adenosine may have a rapid modulatory role. In this review, we outline how FSCV can be used to detect adenosine release, compare FSCV with other techniques used to measure adenosine, and present an overview of adenosine signaling that has been characterized using FSCV. These studies point to a rapid mode of adenosine modulation, whose mechanism and function will continue to be characterized in the future.

Characterization of spontaneous, transient adenosine release in the caudate-putamen and prefrontal cortex

Adenosine is a neuroprotective agent that inhibits neuronal activity and modulates neurotransmission. Previous research has shown adenosine gradually accumulates during pathologies such as stroke and regulates neurotransmission on the minute-to-hour time scale. Our lab developed a method using carbon-fiber microelectrodes to directly measure adenosine changes on a sub-second time scale with fast-scan cyclic voltammetry (FSCV). Recently, adenosine release lasting a couple of seconds has been found in murine spinal cord slices. In this study, we characterized spontaneous, transient adenosine release in vivo, in the caudate-putamen and prefrontal cortex of anesthetized rats. The average concentration of adenosine release was 0.17±0.01 µM in the caudate and 0.19±0.01 µM in the prefrontal cortex, although the range was large, from 0.04 to 3.2 µM. The average duration of spontaneous adenosine release was 2.9±0.1 seconds and 2.8±0.1 seconds in the caudate and prefrontal cortex, respectively. The concentration and number of transients detected do not change over a four hour period, suggesting spontaneous events are not caused by electrode implantation. The frequency of adenosine transients was higher in the prefrontal cortex than the caudate-putamen and was modulated by A1 receptors. The A1 antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine, 6 mg/kg i.p.) increased the frequency of spontaneous adenosine release, while the A1 agonist CPA (N(6)-cyclopentyladenosine, 1 mg/kg i.p.) decreased the frequency. These findings are a paradigm shift for understanding the time course of adenosine signaling, demonstrating that there is a rapid mode of adenosine signaling that could cause transient, local neuromodulation.

The mechanism of electrically stimulated adenosine release varies by brain region

Adenosine plays an important role in neuromodulation and neuroprotection. Recent identification of transient changes in adenosine concentration suggests adenosine may have a rapid modulatory role; however, the extent of these changes throughout the brain is not well understood. In this report, transient changes in adenosine evoked by one second, 60 Hz electrical stimulation trains were compared in the caudate-putamen, nucleus accumbens, hippocampus, and cortex. The concentration of evoked adenosine varies between brain regions, but there is less variation in the duration of signaling. The highest concentration of adenosine was evoked in the dorsal caudate-putamen (0.34 ± 0.08 μM), while the lowest concentration was in the secondary motor cortex (0.06 ± 0.02 μM). In all brain regions, adenosine release was activity-dependent. In the nucleus accumbens, hippocampus, and prefrontal cortex, this release was partly due to extracellular ATP breakdown. However, in the caudate-putamen, release was not due to ATP metabolism but was ionotropic glutamate receptor-dependent. The results demonstrate that transient, activity-dependent adenosine can be evoked in many brain regions but that the mechanism of formation and release varies by region.

Nafion-CNT coated carbon-fiber microelectrodes for enhanced detection of adenosine

Adenosine is a neuromodulator that regulates neurotransmission. Adenosine can be monitored using fast-scan cyclic voltammetry at carbon-fiber microelectrodes and ATP is a possible interferent in vivo because the electroactive moiety, adenine, is the same for both molecules. In this study, we investigated carbon-fiber microelectrodes coated with Nafion and carbon nanotubes (CNTs) to enhance the sensitivity of adenosine and decrease interference by ATP. Electrodes coated in 0.05 mg mL(-1) CNTs in Nafion had a 4.2 ± 0.2 fold increase in current for adenosine, twice as large as for Nafion alone. Nafion-CNT electrodes were 6 times more sensitive to adenosine than ATP. The Nafion-CNT coating did not slow the temporal response of the electrode. Comparing different purine bases shows that the presence of an amine group enhances sensitivity and that purines with carbonyl groups, such as guanine and hypoxanthine, do not have as great an enhancement after Nafion-CNT coating. The ribose group provides additional sensitivity enhancement for adenosine over adenine. The Nafion-CNT modified electrodes exhibited significantly more current for adenosine than ATP in brain slices. Therefore, Nafion-CNT modified electrodes are useful for sensitive, selective detection of adenosine in biological samples.