Iron Related Biomarkers Predict Disease Severity in a Cohort of Portuguese Adult Patients during COVID-19 Acute Infection

Large variability in COVID-19 clinical progression urges the need to find the most relevant biomarkers to predict patients' outcomes. We evaluated iron metabolism and immune response in 303 patients admitted to the main hospital of the northern region of Portugal with variable clinical pictures, from September to November 2020. One hundred and twenty-seven tested positive for SARS-CoV-2 and 176 tested negative. Iron-related laboratory parameters and cytokines were determined in blood samples collected soon after admission. Demographic data, comorbidities and clinical outcomes were recorded. Patients were assigned into five groups according to severity. Serum iron and transferrin levels at admission were lower in COVID-19-positive than in COVID-19-negative patients. The levels of interleukin (IL)-6 and monocyte chemoattractant protein 1 (MCP-1) were increased in COVID-19-positive patients. The lowest serum iron and transferrin levels at diagnosis were associated with the worst outcomes. Iron levels negatively correlated with IL-6 and higher levels of this cytokine were associated with a worse prognosis. Serum ferritin levels at diagnosis were higher in COVID-19-positive than in COVID-19-negative patients. Serum iron is the simplest laboratory test to be implemented as a predictor of disease progression in COVID-19-positive patients.

Distinct iron homeostasis in C57BL/6 and Balb/c mouse strains

C57BL/6 (BL6) and Balb/c mice exhibit prototypical Th1- and Th2-dominant immune predispositions, respectively. Iron is a proinflammatory metal ion; however, limited information is documented on the differences in iron homeostasis between BL6 and Balb/c strains. The objective of this study was to investigate the extent to which strain-level differences in these mice dictates the regulation of iron homeostasis during physiologic and inflammatory conditions. At basal levels, Balb/c mice displayed significantly higher levels of iron in systemic circulation and tissue compared to BL6 mice. Moreover, Balb/c mice had greater iron absorption as indicated by higher gene expressions of duodenal DcytB, DMT1, Fpn, SFT, and Heph. Similarly, hepatic Tf, TfR1, TfR2, and DMT1 expressions were augmented in Balb/c mice. Interestingly, there was no change in hepatic Hamp expression between the two strains, suggesting that the disparity in their maintenance of iron is independent of hepcidin. Additionally, the basal levels of intracellular labile iron pool in Balb/c intestinal epithelial cells, and bone marrow-derived macrophages and neutrophils, were higher compared to BL6 mice. When mice were challenged with lipopolysaccharide, the acute inflammatory response in BL6 mice was more pronounced than in Balb/c mice, as indicated by the more rapid development of hypoferremia and upregulation of serum IL-6 and TNF-α levels in BL6 mice. In conclusion, this study underscores that iron homeostasis is distinct between BL6 and Balb/c strains under both physiologic and inflammatory conditions.