Dietary iron deficiency in the adult mouse increases brain endothelial uptake and blood-brain barrier transport of a high-affinity, anti-transferrin receptor antibody

Background and objectivesBrain capillary endothelial cells (BCECs) express transferrin receptor 1 (TfR1) to ensure sufficient iron transport into the brain across the blood-brain barrier (BBB). Our main objective was to examine adult mice subjected to dietary iron deficiency (ID) for possible changes in the content of TfR1 in BCECs and the influence thereof on the uptake and transport of high-affinity anti-transferrin receptor IgG1 antibodies (clone Ri7217). Material and methodsWe subjected adult, female mice to dietary ID for 8 weeks. Iron and copper were measured using inductively coupled plasma mass spectrometry (ICP-MS) in various tissues, including total brain and isolated brain capillaries. Possible effects of ID on cerebral angioarchitecture were estimated using 3D confocal microscopy of optically cleared brain samples with endothelium labelled using intravenous injection of wheat germ agglutinin with subsequent machine learning-based segmentation and vascular tracing. TfR1 was quantified using ELISA. Ri7217 antibodies were conjugated with 1 nm nanogold and brain uptake quantified using ICP-MS. ResultsID significantly reduced the iron content in isolated brain capillaries, liver, spleen, kidney, heart and skeletal muscles. ID increased the copper content in the brain. Analysis of cerebral cortex angioarchitecture revealed no changes following dietary ID except for a minor increase in tortuosity of small-caliber vessels. TfR1 protein was unchanged in the total brain and isolated brain capillaries. In contrast, uptake of nanogold-conjugated Ri7217 increased in the total brain, the supernatant fraction of isolated brain capillaries representing the post-vascular compartment, liver, spleen, and dissected retinae. ConclusionsTargeting TfR1 in ID revealed increased uptake and transport across the BBB of Ri7217 antibodies. Possibly the elevated transport of transferrin receptors through BCECs is due to the increased trafficking of transferrin receptor-containing vesicles in ID, which appeared to have no major effects on the brain angioarchitecture.