Biophysical parameters influencing secondary oxidants activation in human serum exposed to singlet oxygen

Modelling ROS formation in boreal lakes from interactions between dissolved organic matter and absorbed solar photon flux

Concentrations of dissolved organic matter (DOM) are increasing in a large number of lakes across the Northern hemisphere. This browning serves a dual role for biota by protecting against harmful ultraviolet radiation, while also absorbing photosynthetically active radiation. The photochemical activation of DOM and subsequent formation of reactive oxygen species (ROS) is a potentially harmful side effect, but can be difficult to measure directly in situ. In this study, we combine a data set of physico-chemical properties from 71 Nordic lakes with in vitro ROS formation quantum yields to predict ROS formations across a representative boreal ecosystem gradient. For the upper centimeter of the water column, we calculate ROS formations in the range of 7.93-12.56 μmol L^-1 h^-1. In the first meter, they range between 1.69 and 6.69 μmol L^-1 h^-1 and in the remaining depth the range is 0.01-0.46 μmol L^-1 h^-1. These ROS formations are comparable with previously field-measured hydrogen peroxide formation rates and likely affect both phyto- and zooplankton, as well as lake chemistry. Interestingly, wavelengths of the visible spectrum (>400 nm) contribute more than half of the overall ROS formation in surface-near water layers. The association between DOM and ROS formation was found to be two-fold. While DOM promotes ROS formation in the first centimeters of the water column, the shading effect of light attenuation overpowers this with increasing depth. In the context of water browning, our results indicate the emergence of an underestimated oxidative stress environment for lake biota in the upper centimeters of the water column.

Increased singlet oxygen-induced secondary ROS production in the serum of cancer patients

Photodynamic therapy (PDT) generates singlet oxygen ((1)O(2)) and Reactive Oxygen Species (ROS) that are counteracted by patient's defenses. As cancer treatments are among the most important PDT applications the aim of this pilot study was to determine whether the serum of cancer patients produces more or less secondary ROS or peroxides after a photoreaction as compared to healthy persons. Fifty-three volunteers and 105 cancer patients were recruited. The capacity of (1)O(2) or secondary oxidant production was found to be increased in 6 healthy donors and 36 cancer patients (23/69 women and 13/31 men p<0.007 and p<0.04) with a mean value of 1.52 as compared to 1.29 in the healthy subjects (p<0.05) when considering values higher than the normal range (norm=1±10%) or 1.1 vs. 0.85 (p<0.01) in the whole cohort. This increase correlated with a poor prognosis, TNM and SBR classification. Serum (1)O(2) deactivation capacity was impaired and secondary ROS were more produced during cancer progression. Although it is currently unclear whether this is the cause or effect of cancer, this finding may hold interest as a potential marker of cancer severity. It would also support the interest of PDT as an adjuvant for cancer treatment, even for aggressive tumors particularly when associated to surgery for bulk removal.