Model Combustion-Generated Particulate Matter Containing Persistent Free Radicals Redox Cycle to Produce Reactive Oxygen Species

Abstract

Particular matter (PM) is emitted during thermal decomposition of waste. During this process, aromatic compounds chemisorb to the surface of metal-oxide-containing PM, forming a surface-stabilized environmentally persistent free radical (EPFR). We hypothesized that EPFR-containing PM redox cycle to produce ROS and that this redox cycle is maintained in biological environments. To test our hypothesis, we incubated model EPFRs with the fluorescent probe dihydrorhodamine (DHR). Marked increases in DHR fluorescence were observed. Using a more specific assay, hydroxyl radicals (•OH) were also detected, and their level was further increased by co-treatment with thiols or ascorbic acid (AA), known components of epithelial lining fluid. Next, we incubated our model EPFR in bronchoalveolar lavage fluid (BALF) or serum. Detection of EPFRs and •OH verified that PM generate ROS in biological fluids. Moreover, incubation of pulmonary epithelial cells with EPFR-containing PM increased •OH levels compared to PM lacking EPFRs. Finally, measurements of oxidant injury in neonatal rats exposed to EPFRs by inhalation suggested that EPFRs induce an oxidant injury within lung lining fluid and that the lung responds by increasing antioxidant levels. In summary, our EPFR-containing PM redox cycle to produce ROS, and these ROS are maintained in biological fluids and environments. Moreover, these ROS may modulate toxic responses of PM in biological tissues such as the lung.

Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

“…7 The critical environmental implication of this work lies in the observation that the clay system, when contaminated, in the absence of any biological components, can form EPFRs at concentrations close to those found in real contaminated soils at ambient temperature, which has wide ranging environmental and human health implications, especially when humidity is relatively low.…”

“…4,5 Organochlorinated contaminants, formed as products and by-products of such remediation processes, are not only toxic in their own right, but the intermediate reactions leading to their formation are also of major concern to environmental safety. 6,7 In particular, these intermediate processes result in the formation of surface-stabilized environmentally persistent free radicals (EPFRs). 2,8,9 Traditionally, EPFRs have been misidentified as molecular pollutants in soils and particulate matter.…”

“…This can occur in three steps: 1) EPFRs reduce molecular oxygen to superoxide, 2) the superoxide, through disproportion, forms hydrogen peroxide; 3) the reduced metal species formed via EPFR formation participate in Fenton chemistry which, in turn, generates ROS. 7 EPFRs have recently been found at elevated concentrations in numerous soil/sediment samples from a range of pentachlorophenol-polluted Superfund sites. 13,14 A detailed top-down study found that the EPFRs were almost solely associated with the clay/humic soil fraction.…”

Environmentally Persistent Free Radicals Cause Apoptosis in HL-1 Cardiomyocytes

“…Since DCB230 contains an EPFR that generates hydroxyl radical (OH − ) in biological and other solutions (13, 21), while its synthesis precursors silica and silica CuO do not (13), α-tocopherol was used to determine whether DCB230’s cytotoxicity was radical dependent. Treatment with 25 μg/ml or 100 μg/ml DCB230 significantly reduced HL-1 cell survival during an 8 hour incubation (Fig.…”

“…DCB230 is an environmentally-relevant pollutant particle that produces an electron paramagnetic resonance spectrum indicative of an oxygen centered semi-quinone radical (6, 16). Our group reported that DCB230 produces large numbers of hydroxyl radicals in saline, biological fluids (bronchoalveolar lavage fluid) and cultures of pulmonary epithelial cells (13). Control particles (<200 nm) consisted of Cab-O-sil EH-5 silica beads (Cabot, Alpharetta, Georgia), or CuO-coated (5%) silica beads (CuO/Si; 0.2 μm mean diameter) that do not contain EPFRs.…”