Reactive Oxygen Species in Physiologic and Pathologic Angiogenesis - Mechanical and Chemical Signaling in Angiogenesis - page 80

DBD plasma is generated at atmospheric pressure in air when short duration,
high voltage pulses are applied between two electrodes, with one electrode being
insulated to prevent an increase in current [ 177 , 178 ]. Depending on the applied
voltage, dielectric material and interelectrode distance, the DBD plasma charac-
teristics in air vary, including electron density, reduced electric field, gas tem-
perature, and active species concentration [ 178 ]. For living tissue treatment, a
floating electrode DBD (FE-DBD) is employed where an insulated high voltage
electrode acts as one electrode while the live tissue acts as the second electrode
[ 170 ]. Non-thermal DBD plasma produces a variety of biologically active reactive
species, in particular ROS [ 178 ]. Non-thermal DBD plasma has a g-factor (ROS
generated per electron volt) between 0.3 and 0.5 [ 179 ]. Thus, for every plasma
dose of 1 J/cm 2 , 1.88-3.13 9 10 16 ROS are produced in gas phase. Non-thermal
plasma devices, specifically DBD plasma, have great potential in medicine due to
their selectivity, portability, scalability, ease of operation, and low manufacturing
and maintenance costs.
5.2 DBD Plasma Induced Endothelial Cell Proliferation,
Migration, and Tube Formation
DBD plasma had previously been shown to kill bacteria and cancer cells using
high ROS doses [ 175 , 180 ]. However, we hypothesized that lower ROS doses from
the DBD plasma could induce angiogenesis via FGF-2 release. We had previously
studied altered FGF-2 release, storage, and cellular effect induced by ROS pro-
duction due to high glucose [ 39 , 181 ]. Others had also demonstrated that
mechanical forces, ionizing radiation, and pulsed electromagnetic fields lead to
angiogenesis via FGF-2 [ 69 - 71 , 182 - 184 ]. However, non-thermal plasma has
advantages over irradiation and electromagnetic fields in that the latter are pene-
trating and injure surrounding tissue, or they need an expensive setup to be safely
generated.
We initially demonstrated that while longer term plasma treatment induced
endothelial cell death via apoptosis, lower plasma doses (4.2 J/cm 2 ) led to FGF-2
release peaking 3 h after plasma treatment. This FGF-2 release then enhanced cell
proliferation, which was abrogated by an FGF-2 neutralizing antibody or ROS
inhibitors N-acetyl cysteine and sodium pyruvate [ 179 ]. We further showed that
plasma treatment enhanced endothelial cell 2- and 3-dimensional migration, again
through FGF-2 release via plasma-produced ROS. Using a collagen gel assay, we
demonstrated that plasma-produced ROS could induce endothelial cell tube
formation [ 185 ]. To ensure that plasma-produced ROS caused these effects, we
measured an increase in intracellular ROS about 1 h after plasma treatment, with
oxidative stress returning to baseline levels by 3 h. By analyzing each plasma-
produced ROS individually, hydroxyl radicals and hydrogen peroxide were iden-
tified as the key plasma-produced ROS responsible for the angiogenic effect [ 186 ].