Reticuloendothelial system (RES) macrophage uptake pathway (RES macrophage pathway)

The reticuloendothelial system (RES) macrophage uptake pathway is the primary physiological mechanism for the processing and utilization of intravenous iron-carbohydrate complexes like ferric carboxymaltose. Upon administration, these stable complexes are recognized and internalized by macrophages, predominantly in the liver, spleen, and bone marrow, through endocytic processes. Inside the macrophage, the iron core is separated from its carbohydrate shell within lysosomes, allowing for a controlled release of iron that avoids the toxicity associated with free "labile" iron. This released iron is then either sequestered in ferritin for storage or transported across the cell membrane by the exporter ferroportin to bind with plasma transferrin, which delivers it to the bone marrow for hemoglobin synthesis. This pathway is critical for treating iron deficiency anemia in patients who cannot tolerate oral iron, though the administration of ferric carboxymaltose is notably linked to transient hypophosphatemia due to its secondary effects on fibroblast growth factor 23 (FGF23) signaling and renal phosphate handling.

Other names

Mononuclear phagocyte system (MPS)Macrophage iron recycling pathwayRES iron processingIntracellular iron-carbohydrate complex biodegradation pathway

Ferric carboxymaltose is a stable iron-carbohydrate complex that is internalized by macrophages of the reticuloendothelial system via endocytosis. Within the acidic environment of the macrophage lysosomes, the complex is degraded, releasing iron which is then either stored as ferritin or exported into the systemic circulation via the transporter ferroportin to bind with transferrin for delivery to erythroid precursor cells.