Redox Index of Cys-Thiol Residues of Serum Apolipoprotein E and Its Diagnostic Potential

We explored the proper index for estimating the redox status of Cys-thiol of serum apolipoprotein E (apoE), named “redox-IDX-apoE,” which is necessary to understand the redox biology of age-related diseases, such as atherosclerosis. The fractions of reduced form (red-), reversible oxidized form (roxi-), and irreversibly oxidized form (oxi-) apoE were measured by a band-shift assay. Candidates of redox-IDX-apoE were determined by calculating the values of these fractions and total apoE concentration. The ratios of roxi-apoE to total-apoE (roxi/total), red-apoE to roxi-apoE (red/roxi), and [red-apoE + oxi-apoE] to roxi-apoE ([red + oxi]/roxi) were independent of age and sex. Roxi/total showed significant negative correlations with serum triglyceride (TG) and HbA1c levels, while red/roxi and [red + oxi]/roxi showed significant positive correlations with them. However, red/roxi and [red + oxi]/roxi in the patients with atherosclerosis were significantly lower than those in control subjects, although serum TG and HbA1c levels in the patients were significantly higher than those in controls. The redox status of serum apoE-Cys-thiol is closely involved in the metabolism of TG-rich lipoproteins and glucose and may vary depending on the difference in pathological conditions. The appropriate usage of these ratios could be helpful in the diagnosis and prognosis of age-related diseases.