Electroceutical Treatment of Pseudomonas aeruginosa Biofilms

Electroceutical wound dressings, especially those involving current flow with silver based electrodes, show promise for treating biofilm infections. However, their mechanism of action is poorly understood. We have developed an in vitro agar based model using a bioluminescent strain of Pseudomonas aeruginosa to measure loss of activity and killing when direct current was applied. Silver electrodes were overlaid with agar and lawn biofilms grown for 24 h. A 6 V battery with 1 kΩ ballast resistor was used to treat the biofilms for 1 h or 24 h. Loss of bioluminescence and a 4-log reduction in viable cells was achieved over the anode. Scanning electron microscopy showed damaged cells and disrupted biofilm architecture. The antimicrobial activity continued to spread from the anode for at least 2 days, even after turning off the current. Based on possible electrochemical ractions of silver electrodes in chlorine containing medium; pH measurements of the medium post treatment; the time delay between initiation of treatment and observed bactericidal effects; and the presence of chlorotyrosine in the cell lysates, hypochlorous acid is hypothesized to be the chemical agent responsible for the observed (destruction/killing/eradication) of these biofilm forming bacteria. Similar killing was obtained with gels containing only bovine synovial fluid or human serum. These results suggest that our in vitro model could serve as a platform for fundamental studies to explore the effects of electrochemical treatment on biofilms, complementing clinical studies with electroceutical dressings.

Molecular imaging of peroxynitrite with HKGreen-4 in live cells and tissues

Peroxynitrite (ONOO(-)), the product of a radical combination reaction of nitric oxide and superoxide, is a potent biological oxidant involved in a broad spectrum of physiological and pathological processes. Herein we report the development, characterization, and biological applications of a new fluorescent probe, HKGreen-4, for peroxynitrite detection and imaging. HKGreen-4 utilizes a peroxynitrite-triggered oxidative N-dearylation reaction to achieve an exceptionally sensitive and selective fluorescence turn-on response toward peroxynitrite in chemical systems and biological samples. We have thoroughly evaluated the utility of HKGreen-4 for intracellular peroxynitrite imaging and, more importantly, demonstrated that HKGreen-4 can be efficiently employed to visualize endogenous peroxynitrite generated in Escherichia coli-challenged macrophages and in live tissues from a mouse model of atherosclerosis. This probe should serve as a powerful molecular imaging tool to explore peroxynitrite biology under a variety of physiological and pathological contexts.

Kinetics of 3-chlorotyrosine formation and loss due to hypochlorous acid and chloramines

The persistent activation of innate immune cells in chronic inflammation is gaining recognition as a contributing factor in a number of human diseases. A distinguishing feature of activated leukocytes at sites of inflammation is their production of reactive species such as hypochlorous acid (HOCl). Investigating the role of reactive molecules such as HOCl in inflammation and human disease requires appropriate biomarkers. The preferred biomarker for HOCl, and by extension its synthesizing enzyme myeloperoxidase, is 3-chlorotyrosine. 3-Chlorotyrosine is a chemically stable product formed when HOCl, or an HOCl-generated chloramine, reacts with the tyrosine side chain and is readily measured by sensitive mass spectrometry methods. However, Whiteman and Spencer ((2008) Biochem. Biophys. Res. Commun., 371, 50 - 53.) noted that 3-chlorotyrosine is degraded by HOCl, calling into question its use as a biomarker. The kinetic rate constants for the reaction of 3-chlorotyrosine with HOCl, histidine chloramine, or lysine chloramine to form 3,5-dichlorotyrosine are reported. The kinetics of tyrosine chlorination in the context of a peptide with a nearby lysine residue was also determined and further supports the role of chloramines in the chlorination of protein-bound tyrosine residues. The likelihood of free and protein-bound 3,5-dichlorotyrosine occurring in vivo, given the reported rate constants, is discussed.