Extracellular Histones Induced Eryptotic Death in Human Erythrocytes.

BACKGROUND/AIMS: Circulating or extracellular histones (EHs) in the bloodstream act as a damage-associated-molecular-pattern (DAMP) agent that plays a critical role in the pathogenesis of many diseases such as sepsis and sterile inflammation. To date, not much information is available to describe the mechanistic relationship between human erythrocytes and the cytotoxicity of EHs, the protein members from a highly conserved histone family across species. The present study explored this key question with a hypothesis that EHs induce eryptosis. METHODS: Freshly isolated human red blood cells (RBCs) from healthy donors were treated with EHs or agents for positive controls in a physiological buffer for 3 or 24 h. After treatments, flow cytometry was employed to quantify surface phosphatidylserine (PS) exposure from annexin-V-RFP binding, cell shrinkage from flow cytometric forward scatter (FSC) analysis, Ca2+ rise by fluo-4, reactive oxygen species (ROS) production by H2DCFDA, and caspase-3 activation by FAM-DEVD-FMK measurement. Hemolysis and membarne permeabilization were estimated respectively from hemoglobin release into supernatant and calcein leakage from RBC ghosts. RESULTS: With positive controls for validation, EHs in the pathophsyiological range were found to accumulate annexin-V binding on cell surface, decrease FSC, upregulate ROS production, elevate Ca2+ influx and increase caspase-3 activity in a 3-h incubation. Of note, no RBC hemolysis and no calcein release from ghosts were obtained after EHs treatment for 24 h. Interestingly, external Ca2+ was not a prerequisite for the EHs-mediated ROS production and PS externalization. Also, the eryptotic hallmarks in the apoptotic RBCs were partially blocked by heparin and antibody (Ab) against Toll-like receptor 2 (TLR2). CONCLUSION: EHs act as a DAMP agent in the human RBCs that induces eryptosis. The cytotoxic effect is rapid as the hallmarks of eryptosis such as cell shrinkage, surface PS exposure, [Ca2+]i rise, ROS production and caspase-3 activation can be seen 3 h after treatment in a dose-dependent manner. The EHs' cytotoxic effects could be blocked by heparin and the Ab against TLR2.

An Aptamer Bio-barCode (ABC) assay using SPR, RNase H, and probes with RNA and gold-nanorods for anti-cancer drug screening.

With modifications to an ultra-sensitive bio-barcode (BBC) assay, we have developed a next generation aptamer-based bio-barcode (ABC) assay to detect cytochrome-c (Cyto-c), a cell death marker released from cancer cells, for anti-cancer drug screening. An aptamer is a short single-stranded DNA selected from a synthetic DNA library that is capable of binding to its target with high affinity and specificity based on its unique DNA sequence and 3D structure after folding. Similar to the BBC assay, Cyto-c is captured by a micro-magnetic particle (MMP) coated with capturing antibodies (Ab) and an aptamer specifically against Cyto-c to form sandwich structures ([MMP-Ab]-[Cyto-c]-[Aptamer]). After washing and melting, our aptamers, acting as a DNA bio-barcode, are released from the sandwiches and hybridized with the probes specially designed for RNase H for surface plasmon resonance (SPR) sensing. In an aptamer-probe duplex, RNase H digests the RNA in the probe and releases the intact aptamer for another round of hybridization and digestion. With signal enhancement effects from gold-nanorods (Au-NRs) on probes for SPR sensing, the detection limit was found to be 1 nM for the aptamer and 80 pM for Cyto-c. Without the time-consuming DNA amplification steps by PCR, the detection process of this new ABC assay can be completed within three hours. As a proof-of-concept, phenylarsine oxide was found to be a potent agent to kill liver cancer cells with multi-drug resistance at the nano-molar level. This approach thus provides a fast, sensitive and robust tool for anti-cancer drug screening.