Assessment of Interactions between Transition Metals and Atmospheric Organics: Ascorbic Acid Depletion and Hydroxyl Radical Formation in Organic-Metal Mixtures.

Excessive oxidative stress has been recognized as an important cause of the adverse health effects associated with exposure to ambient particulate matter (PM). Transition metals (TMs) (e.g., iron (Fe) and copper (Cu)) are known catalysts in the formation of reactive oxygen species (ROS) in surrogate lung fluid containing antioxidants. Humic-like substances (HULIS), extracted from atmospheric aerosols, retain the compositional complexity of real-world samples. It contains mixtures of organics that chelate TMs and was used in this work to examine the roles of atmospheric organics in affecting ROS formation and antioxidant depletion by TMs. Two types of metal-binding organics known to be present in HULIS, oxygen-containing (i.e., carboxylic acids) and reduced-nitrogen-containing organics (i.e., imidazoles), were first investigated for their effects on the ascorbic acid depletion (denoted as OPAA) and hydroxyl radical formation (denoted as OP•OH) from both Fe(II) and Cu(II) in phosphate buffered saline (pH 7.40) containing ascorbic acid. Our results show that carboxylic acids enhance the OPAA and OP•OH by TMs while imidazoles suppress them. Similar experiments using three HULIS samples with distinctly different chemical compositions revealed complexity in metal-organics interactions. While ambient HULIS showed negligible impacts, two biomass burning source HULIS samples from rice straw and sugar cane leaf burning displayed unambiguous suppression or enhancement effects on OPAA and OP•OH by TMs. The effect was metal-specific and source HULIS-specific. The distinct behaviors of the three HULIS types can be explained by their different chemical compositions, for example, outstanding higher level of alkaloid compounds (e.g., imidazoles) in rice straw burning HULIS was consistent with the suppression effect exerted by this source of HULIS. In addition, we found OPAA and OP•OH are well-correlated while the proportion of OP•OH/OPAA by Cu is noticeably lower than that by Fe, indicating varying sensitivity of the metals to different OP end points. Our work highlights the importance and complexity of metal-organics interactions and the advantages of comeasurements of ROS generation and antioxidant depletion when assessing oxidative stress elicited by atmospheric PM.

A robust probe for lighting up intracellular telomerase via primer extension to open a nicked molecular beacon.

A nicked molecular beacon (MB)-functionalized probe has been designed for in situ imaging and detection of intracellular telomerase activity. The nick separates the MB into two segments: a shorter telomerase primer (TSP) sequence as a part of the 5'-end stem and a longer sequence to form a loop with one thiol-labeled 3'-end stem. The MB can be opened by substitutional hybridization of the telomerase-triggered stem elongation product, which leads to separation of the Cy5 at the 5'-end nick from the gold nanoparticle (AuNP) as the nanocarrier and thus inhibits the energy transfer from Cy5 to AuNP. Upon endocytosis of the probe, the TSP can be extended by intracellular telomerase at its 3' end to produce the telomeric repeated sequence, which leads to the inner chain substitution and thus turns on the fluorescence of Cy5. The probe provides a one-step incubation technique for quantification and monitoring of the telomerase activity in living cells. The practicality of the proposed approach for distinguishing tumor cells from normal cells and monitoring the decrease of telomerase activity during treatment with antitumor drugs demonstrates its potential in clinical diagnostic and therapeutic monitoring.

Smart vesicle kit for in situ monitoring of intracellular telomerase activity using a telomerase-responsive probe.

A smart vesicle kit was designed for in situ imaging and detection of cytoplasmic telomerase activity. The vesicle kit contained a telomerase primer (TSP) and a Cy5-tagged molecular beacon (MB) functionalized gold nanoparticle probe, which were encapsulated in liposome for intracellular delivery. After the vesicle kit was transfected into cytoplasm, the released TSP could be extended in the presence of telomerase to produce a telomeric repeated sequence at the 3' end, which was just complementary with the loop of MB assembled on probe surface. Thus, the MB was opened upon hybridization to switch the fluorescent state from "off" to "on". The fluorescence signal depended on telomerase activity, leading to a novel strategy for in situ imaging and quantitative detection of the cytoplasmic telomerase activity. The cytoplasmic telomerase activity was estimated to be 3.2 × 10(-11), 2.4 × 10(-11), and 8.6 × 10(-13) IU in each HeLa, BEL tumor and QSG normal cell, respectively, demonstrating the capability of this approach to distinguish tumor from normal cells. The proposed method could be employed for dynamic monitoring of the cytoplasmic telomerase activity in response to a telomerase-based drug, suggesting the potential application in discovery and screening of telomerase-targeted anticancer drugs.

Distributed adaptive sliding-mode control for 2-D plane vehicle platoon with prescribed performance and angle constraint.

This paper focuses on the distributed adaptive sliding-mode control problem for two-dimensional (2-D) plane vehicle platoon with prescribed performance, angle constraints, and actuator faults. The quadratic spacing policy (QSP) is first adopted for the 2-D plane vehicle platoon to adjust the inter-vehicle spacing. The spacing error can converge within a finite time to the small region predetermined by a new finite-time performance function (FTPF). Meanwhile, a new transformed error function is introduced to convert the FTPF-constrained spacing errors into equivalent unconstrained ones. Besides, the property of the invertible nonlinear mapping function is used for the original system with the angle constraint to get a new unconstrained system. Moreover, a new controller based on hyperbolic tangent function is designed to handle actuator faults occurring multiple times over a period. Furthermore, the stability and string stability of the 2-D plane vehicle platoon are achieved through sliding-mode control. Finally, the simulation results validate the effectiveness of the proposed techniques.

Assessment of oxidative potential by hydrophilic and hydrophobic fractions of water-soluble PM2.5 and their mixture effects.

Transition metals (TMs) (e.g. copper (Cu) and iron (Fe)) and certain organic compounds are known active constituents causing oxidative potential (OP) by inhaled ambient fine particulate matter (PM2.5) in lung fluid. Humic-like substances (HULIS), isolated from atmospheric PM2.5, are largely metal-free and contain mixtures of organics that are capable of complexing TMs. TMs and HULIS co-exist in the water-extractable part of PM2.5. In this work, we used a solid phase extraction procedure to isolate the water-soluble TMs in the hydrophilic fraction (HPI) and HULIS in the hydrophobic fraction (HPO) and carried out this isolation procedure to a set of 32 real-world PM2.5 samples collected in Beijing and Hong Kong, China. We quantified two OP endpoints, namely hydroxyl radical formation (denoted as OP•OH) and ascorbic acid depletion (denoted as OPAA), by the two fractions separately and combined, as well as by the bulk water-soluble aerosols. OP•OH and OPAA were well-correlated in both separate fractions and their combined mixtures or bulk water-soluble aerosols. OP by HPI far exceeded that by HPO. On a per unit PM2.5 mass basis, the Hong Kong samples on average had a higher OPAA and OP•OH than the Beijing samples due to more water-soluble Cu. For HPI, Cu was a dominant OP•OH and OPAA contributor (>80%), although water-soluble Fe was present at a concentration approximately one order of magnitude higher. Suppression effects on OP•OH were observed through comparing the OP of the bulk water-soluble aerosol with that of HPI. Our work reveals the importance of monitoring PM2.5 chemical compositions (especially water-soluble redox active metals). Furthermore, we demonstrate the need to consider metal-organic interactions when evaluating the aggregate OP by PM2.5 from individual components or apportioning OP by PM2.5 to specific chemical components.

Dithiothreitol (DTT) concentration effect and its implications on the applicability of DTT assay to evaluate the oxidative potential of atmospheric aerosol samples.

The cell-free dithiothreitol (DTT) assay is widely used and the DTT consumption rate is interpreted to assess the oxidative potential (OP). Most researchers use an experimental procedure developed by Cho et al. (2005) while some adopt a procedure by Li et al. (2009). The key difference between the two procedures is the initial DTT concentration, 100 µM used in the former and 20 µM in the latter, raising an unaddressed issue of comparability. We examine in this work this issue using metal-free humic-like substance (HULIS) samples isolated from ambient aerosol and two metals (i.e. copper and manganese). We found that higher initial DTT concentrations led to higher DTT consumption rates for both HULIS and metals. For HULIS, the increase in DTT consumption rate was proportional to the initial DTT concentration (i.e., roughly by 5-fold), allowing correction of the concentration effect and direct comparison of results from the two protocols. However, the proportionality did not hold for the metals or metal-organic mixtures. The increase was much lower than the proportionality of 5 and metal concentration-dependent, specifically, 1.2-1.3 for Cu and from negligible to 2.0 for Mn. For six water extracts of ambient aerosol samples, in which HULIS and metals co-exist, the proportionality ranged from 1.3 to 2.2. This deviation from a linear dependence on initial DTT concentration, plausibly due to metal-DTT binding, impedes assessing and comparing OP of metals and metal-organic mixtures using different implementations of the DTT assay. Considering the different antioxidants concentrations in real human lung fluid, this work raises caution about using the DTT assay to assess metal-containing mixtures, such as ambient aerosol samples.

Effect of metal-organic interactions on the oxidative potential of mixtures of atmospheric humic-like substances and copper/manganese as investigated by the dithiothreitol assay.

Excessive generation of reactive oxygen species (ROS) and the corresponding oxidative stress has been recognized as one important cause for the adverse health effects associated with exposure to ambient particulate matter (PM). Transition metals and humic-like substances (HULIS) in PM have been separately demonstrated to contribute to the oxidative potential (OP) of PM, however, only few studies investigated the impact of their interactions on the measured OP and the effect is little understood. HULIS is an abundant fraction of water-soluble organic material in PM and serves to represent real-world PM organics. In this study, we applied a cell-free dithiothreitol (DTT) assay to quantify the OP, termed as OPDTT, by two representative transition metals (i.e., copper (Cu) and manganese (Mn)), HULIS, and mixtures of HULIS and metals in concentration levels relevant to those in human lung fluid resulting from PM inhalation. The organic-metal mixture effect was found to be metal-specific and concentration-specific, covering the possibility spectrum from being synergistic, additive to antagonistic. HULIS was observed to suppress OPDTT up to 10-20% by Cu at a concentration of 0.08 µM while had no discernable effect at 0.5 µM Cu. On the contrary, obvious enhancement of OPDTT was recorded in the mixtures of HULIS and Mn (e.g. up to ~2 times at 2.5 µM of Mn) while no mixture effects could be discerned at 0.5 µM Mn. Our work demonstrates the need for considering the metal-organic interactions and the complexity when evaluating the total OP of their mixtures, such as ambient PM samples. Further work in metal-PM organics interactions should be conducted using methods capable of measuring specific oxidants, in addition to the ability to deplete the reducing agent (i.e., DTT), in order to acquire a deeper mechanistic insight into the interactions.