Association between serum selenium species and 8-oxo-7,8-dihydro-2’deoxyguanosine levels: an Italian cross-sectional study

Introduction: Selenium (Se) is a metalloid present in trace amounts in the organism, with toxicological and nutritional properties depending on the dose and the species considered. Both organic and inorganic selenium species are involved in oxidoreduction reaction regulation and pathways. 8-oxo-7,8-dihydro-2’deoxyguanosine (8-oxodG) is a derivative of deoxyguanosine, used as biomarker of oxidative stress in urine. In this study, we aimed to assess total serum selenium levels along with its species in a population in Northern Italy and to evaluate the associations between selenium exposure with 8-oxodG levels. Material and methods: The present study consisted in a cross-sectional survey carried out in blood donors aged 30-60 years enrolled in the Transfusion Medicine Center ‘Casa del Dono’ of the AUSL-IRCCS of Reggio Emilia, Northern Italy, in the period April 2017-April 2019. Of 148 eligible subjects, 137 were eventually enrolled. They were all non-smokers, and not affected by any disease or clinical condition. Each participant gave urinary and blood samples in order to quantify selenium levels in these matrices; urinary samples were used to quantify cotinine and 8-oxodG levels, while speciation analysis was performed in serum samples. We performed spline regression analyses to assess the possible nonlinear associations of the different biomarkers of selenium exposure with 8-oxodG levels using a multivariable model adjusted for potential confounders. Results: Our population had a mean age of 47.4 years. Mean (standard deviation) level of serum selenium was 117.4±19.1 mcg/L, respectively. Association of serum selenium level with 8-oxodG levels adjusted for urinary creatinine was almost null. For what concerns selenium species, selenoprotein P-bound-Se showed a slightly inverted U-shaped association with 8-oxodG levels with a positive association until 90 mcg/L and negative above that amount. Selenomethionine-bound-Se, glutathione peroxidase-bound-Se, and selenocysteine-bound-Se were positively associate with 8-oxodG, though for the latter two the association was very imprecise. A negative association emerged for thioredoxin reductase-bound-Se. Total inorganic selenium along with the two inorganic species, i.e., selenite and selenate, were negatively and linearly associated with 8-oxodG levels. For Se-bound to human serum albumin-bound-Se the association was almost null. Conclusion: Our results suggest that even though total selenium exposure seems not associated with 8-oxodG, selected selenium species may largely differ in their association with this oxidative stress biomarker, thus strengthening the importance of selenium speciation analysis for the evaluation of selenium health effects.