Interactive Model

Iron clearance: the serial pathway

Iron exits the brain through a serial pathway: cell to ISF via ferroportin, ISF to CSF via glymphatic flow, CSF to periphery via drainage. Each step declines with age. Adjust parameters to see how comorbidities, genetics, and sex affect the trajectory.

Iron accumulation by compartment

All values normalized to young-adult baseline (1.0×). LIP baseline 0.8 µM (Kakhlon & Cabantchik 2002). ISF baseline ~1.0 µM (Singh 2014). Iron uptake ~0.5 mg/year (Hallgren & Sourander 1958). ISF rises faster than LIP because glymphatic clearance declines earlier (age 30) than ferroportin (age 40).

Mass balance

Net accumulation: ~0.5 mg/year

Healthy brains accumulate ~20 mg of iron between age 30 and 70. Most Fpn-exported iron (~85%) is recaptured by neighboring cells before reaching CSF.

Ferroptosis phases

When labile iron exceeds 1.2× baseline, cells enter Phase 1 (sublethal stress). Above 1.5×, Phase 2 triggers frank ferroptosis. Both thresholds are illustrative: no direct LIP threshold has been measured in human brain.

Clinical

The intervention window

Phase 1 is clinically silent but potentially measurable (MRI iron mapping, elevated CSF ferritin). Phase 2 is irreversible. The gap between them is the last opportunity for intervention.

Clearance pathway decline

Both export steps decline with age. Ferroportin: direction confirmed by Raha 2022 and Lupo 2022, but no annualized rate published. Glymphatic: derived from Patterson 2015 Aβ fractional turnover (~60% decline age 30–80), not iron-specific. Both rates (1%/yr Fpn, 1.2%/yr gly) are assumed linear approximations and may overestimate late-life decline.

Comorbidities

Disease effects stack

Hypertension reduces glymphatic flow by ~32% (Mortensen 2019). Diabetes by ~84% (Jiang 2017). Sleep disruption by ~36% (Xie 2013). These compound with age-related decline.

Cell-type Fpn export budget

Microglia make up only 10% of brain cells but contribute 25–50% of total Fpn-mediated iron export. Based on Bao 2021 back-calculation and cell-type expression ratios. Confidence: low-moderate (qualitative expression data, one direct measurement).

Cell biology

The microglial bottleneck

Hepcidin-induced Fpn internalization hits microglia hardest because they handle the most iron per cell. Chronic neuroinflammation suppresses the cell type most responsible for iron export.

Time to Phase 1

Age 68

Sublethal iron stress

Time to Phase 2

Age 89

Frank ferroptosis

Clearance at 70

52%

Relative to age 30

ISF iron at 70

1.33 µM

Baseline: 1.0 \u00B5M