Background: Nearly half of all non-dialysis chronic kidney disease (CKD) patients respond to iron therapy. Factors affecting anemia response to iron therapy are not well characterized. Oxidative stress (OS) is a recognized factor for anemia in CKD and promotes erythropoiesis stimulating agent (ESA) resistance; however, the influence in predicting response to intravenous (IV) iron has not been evaluated.
Methods: Patients (n = 47) with non-dialysis CKD stages 3 - 5 (mean eGFR: 26 ± 10.4 mL/min/1.73 m2) and iron-deficiency anemia (hemoglobin < 11 g/dL, transferrin saturation (TSAT) index < 20%, and/or ferritin < 100 ng/mL) received a single injection of 1,000 mg of ferric carboxymaltose (FCM) and were observed for 12 weeks. Based on erythropoietic response (defined as ⥠1 g/dL increase in hemoglobin level), patients were classified as responders or non-responders. Baseline conventional markers of iron status (TSAT and ferritin), inflammatory markers (C-reactive protein and IL-6), OS markers (oxidized LDL, protein carbonyl groups, erythrocyte superoxide dismutase, and glutathione peroxidase (GPx)), and catalase activity were measured.
Results: FCM resulted in a significant increase in hemoglobin, TSAT, and ferritin (10 ± 0.7 vs. 11.4 ± 1.3 g/dL, p < 0.0001; 14.6 ± 6.4% vs. 28.9 ± 10%, p < 0.0001; 67.8 ± 61.7 vs. 502.5 ± 263.3 ng/dL, p < 0.0001, respectively). Responders and non-responders were 34 (72%) and 13 (28%), respectively. Age, baseline hemoglobin, estimated glomerular filtration rate, parathyroid hormone, and use of ESA or angiotensin-modulating agents were similar in both groups. Responders showed a tendency towards lower TSAT than non-responders (13.6 ± 6.5% vs. 17.2 ± 5.6%, p = 0.06) but similar ferritin levels. Inflammatory markers were similar in both groups. eGPx activity was lower in non-responders compared to responders (103.1 ± 50.9 vs. 144.9 ± 63.1 U/g Hb, p = 0.01, respectively), although the other proteins, lipid oxidation markers, and enzymatic antioxidants did not differ between the two groups. In the multivariate adjusted model, odds (95% CI) for achieving erythropoietic response to FCM were 10.53 (1.25 - 88.16) in the third tertile of eGPX activity and 3.20 (0.56 - 18.0) in the second tertile compared to those in the lowest tertiles (p = 0.02).
Conclusions: Decreased eGPx activity has adverse influences on response to FCM, suggesting that impaired erythrocyte antioxidant defense may be involved in the response to iron therapy in CKD patients.