Sex and Diet Biased Effect of L-DOPA on Iron Accumulation in the Ventral Midbrain

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra, a region within the ventral midbrain known to accumulate iron. While L-3,4-dihydroxyphenylalanine (L-DOPA) remains the gold standard treatment for PD, its impact on brain iron homeostasis, particularly under varying systemic iron conditions, remains poorly understood. In this study, we investigate how dietary iron status and anti-PD treatments influence brain iron accumulation and regulation in the ventral midbrain, with a focus on sex-specific differences. Male and female Long-Evans rats were placed on iron-adequate (IA), iron-deficient (ID), or iron-repletion (IR) diets from postnatal day (PND) 21 for eight weeks. In the final three weeks, animals received daily subcutaneous injections of L-DOPA, selegiline, or vehicle. Our findings revealed that L-DOPA treatment in IR males significantly increased brain iron levels in the ventral midbrain, whereas females showed no such effect. This sex-specific accumulation was accompanied by the upregulation of iron uptake protein transferrin receptor 1 (TfR1), increased ferroportin (FPN1), and reduced expression of the iron storage protein ferritin heavy chain (FTH1), indicating disrupted iron homeostasis. Furthermore, L-DOPA-treated males on the IR diet exhibited elevated glial fibrillary acidic protein (GFAP) and lipocalin-2 (LCN2), suggesting enhanced oxidative stress and astrocyte activation. Consistent with this, antioxidant enzymes catalase (CAT) and superoxide dismutase 2 (SOD2) were significantly decreased in L-DOPA-treated males on the IR diet, highlighting increased vulnerability to oxidative damage. In contrast, selegiline did not significantly alter brain iron levels or iron-regulatory protein expression, regardless of diet or sex. These findings demonstrate that systemic iron repletion after deficiency sensitizes the male brain to L-DOPA-induced iron accumulation, potentially increasing susceptibility to neurodegeneration. This study highlights the importance of considering that both dietary iron status and biological sex may impact PD treatment strategies.