Analytical evaluation of serum non-transferrin-bound iron and its relationships with oxidative stress and cardiac load in the general population.

Excessive iron accumulation provokes toxic effects, especially in the cardiovascular system. Under iron overload, labile free non-transferrin-bound iron (NTBI) can induce cardiovascular damage with increased oxidative stress. However, the significance of NTBI in individuals without iron overload and overt cardiovascular disease has not been investigated. We aimed to examine the distribution of serum NTBI and its relationship with oxidative stress and cardiac load under physiological conditions in the general population.We enrolled individuals undergoing an annual health check-up and measured serum NTBI and derivatives of reactive oxygen metabolites (d-ROM), an oxidative stress marker. In addition, we evaluated serum levels of B-type natriuretic peptide (BNP) to examine cardiac load. We excluded patients with anemia, renal dysfunction, cancer, active inflammatory disease, or a history of cardiovascular disease.A total of 1244 individuals (57.8 ± 11.8 years) were enrolled, all of whom had detectable serum NTBI. d-ROM and BNP showed significant trends across NTBI quartiles. Multivariable regression analysis revealed that serum iron and low-density lipoprotein cholesterol were positively associated with NTBI but that age, d-ROM, and BNP showed an inverse association with this measure. In logistic regression analysis, NTBI was independently associated with a combination of higher levels of both d-ROM and BNP than the upper quartiles after adjustment for possible confounding factors.Serum NTBI concentration is detectable in the general population and shows significant inverse associations with oxidative stress and cardiac load. These findings indicate that serum NTBI in physiological conditions does not necessarily reflect increased oxidative stress, in contrast to the implications of higher levels in states of iron overload or pathological conditions.