RNA adducts with Na2SeO4 and Na2SeO3 – Stability and structural features

Selenium compounds are widely available in dietary supplements and have been extensively studied for their antioxidant and anticancer properties. Low blood Se levels were found to be associated with an increased incidence and mortality from various types of cancers. Although many in vivo and clinical trials have been conducted using these compounds, their biochemical and chemical mechanisms of efficacy are the focus of much current research. This study was designed to examine the interaction of Na2SeO4 and Na2SeO3 with RNA in aqueous solution at physiological conditions, using a constant RNA concentration (6.25 mM) and various sodium selenate and sodium selenite/polynucleotide (phosphate) ratios of 1/80, 1/40, 1/20, 1/10, 1/5, 1/2 and 1/1. Fourier transform infrared, UV–Visible spectroscopic methods were used to determine the drug binding modes, the binding constants, and the stability of Na2SeO4 and Na2SeO3–RNA complexes in aqueous solution. Spectroscopic evidence showed that Na2SeO4 and Na2SeO3 bind to the major and minor grooves of RNA (via G, A and U bases) with some degree of the Se–phosphate (PO2) interaction for both compounds with overall binding constants of K(Na2SeO4–RNA) = 8.34 × 103 and K(Na2SeO3–RNA) = 4.57 × 103 M−1. The order of selenium salts–biopolymer stability was Na2SeO4–RNA > Na2SeO3–RNA. RNA aggregations occurred at higher selenium concentrations. No biopolymer conformational changes were observed upon Na2SeO4 and Na2SeO3 interactions, while RNA remains in the A-family structure.