Florey Department of Neuroscience and Mental Health - Research Publications

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Author: Adlard, Paul × Author: Ayton, Scott × Author: Bush, Ashley × End date: 2014 × Start date: 2012 × Type: Journal Article ×

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    A comparison of ceruloplasmin to biological polyanions in promoting the oxidation of Fe2+ under physiologically relevant conditions
    Wong, BX ; Ayton, S ; Lam, LQ ; Lei, P ; Adlard, PA ; Bush, AI ; Duce, JA (ELSEVIER SCIENCE BV, 2014-12)
    BACKGROUND: Iron oxidation is thought to be predominantly handled enzymatically in the body, to minimize spontaneous combustion with oxygen and to facilitate cellular iron export by loading transferrin. This process may be impaired in disease, and requires more accurate analytical assays to interrogate enzymatic- and auto-oxidation within a physiologically relevant environment. METHOD: A new triplex ferroxidase activity assay has been developed that overcomes the previous assay limitations of measuring iron oxidation at a physiologically relevant pH and salinity. RESULTS: Revised enzymatic kinetics for ceruloplasmin (Vmax≈35μMFe(3+)/min/μM; Km≈15μM) are provided under physiological conditions, and inhibition by sodium azide (Ki for Ferric Gain 78.3μM, Ki for transferrin loading 8.1×10(4)μM) is quantified. We also used this assay to characterize the non-enzymatic oxidation of iron that proceeded linearly under physiological conditions. CONCLUSIONS AND GENERAL SIGNIFICANCE: These findings indicate that the requirement of an enzyme to oxidize iron may only be necessary under conditions of adverse pH or anionic strength, for example from hypoxia. In a normal physiological environment, Fe(3+) incorporation into transferrin would be sufficiently enabled by the biological polyanions that are prevalent within extracellular fluids.
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    Iron accumulation confers neurotoxicity to a vulnerable population of nigral neurons: implications for Parkinson's disease
    Ayton, S ; Lei, P ; Adlard, PA ; Volitakis, I ; Cherny, RA ; Bush, AI ; Finkelstein, DI (BMC, 2014-07-10)
    BACKGROUND: The substantia nigra (SN) midbrain nucleus is constitutively iron rich. Iron levels elevate further with age, and pathologically in Parkinson's disease (PD). Iron accumulation in PD SN involves dysfunction of ceruloplasmin (CP), which normally promotes iron export. We previously showed that ceruloplasmin knockout (CP KO) mice exhibit Parkinsonian neurodegeneration (~30% nigral loss) by 6 months, which is prevented by iron chelation. Here, we explored whether known iron-stressors of the SN (1) aging and (2) MPTP, would exaggerate the lesion severity of CP KO mice. FINDINGS: We show that while 5 month old CP KO mice exhibited nigral iron elevation and loss of SN neurons, surprisingly, aging CP KO mice to 14 months did not exacerbate iron elevation or SN neuronal loss. Unlike young mice, iron chelation therapy in CP KO mice between 9-14 months did not rescue neuronal loss. MPTP exaggerated iron elevation in young CP KO mice but did not increase cell death when compared to WTs. CONCLUSIONS: We conclude that there may exist a proportion of substantia nigra neurons that depend on CP for protection against iron neurotoxicity and could be protected by iron-based therapeutics. Death of the remaining neurons in Parkinson's disease is likely caused by parallel disease mechanisms, which may call for additional therapeutic options.
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    The effect of dopamine on MPTP-induced rotarod disability
    Ayton, S ; George, JL ; Adlard, PA ; Bush, AI ; Cherny, RA ; Finkelstein, DI (ELSEVIER IRELAND LTD, 2013-05-24)
    UNLABELLED: Dopamine depletion in Parkinson's disease (PD) results in bradykinesia and tremor. Therapeutic administration of the dopamine precursor, l-Dopa, alleviates these symptoms but dyskinesia's can manifest with chronic treatment. In the MPTP toxin mouse model of PD, lesion severity is often assessed by the rotarod behavioral assay. Dopamine depletion by MPTP is thought to induce rotarod behavioral decline. Here we surveyed rotarod behavior and striatal dopamine at timed intervals post-MPTP. Paradoxically, rotarod disability coincided with gradual striatal dopamine restoration. l-Dopa supplementation exacerbated rotarod disability, whereas dopamine antagonism restored performance. CONCLUSION: dopamine restoration, not depletion, precipitates rotarod disability after MPTP intoxication, and caution should be applied when using this assay for MPTP.
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    Ceruloplasmin dysfunction and therapeutic potential for Parkinson disease
    Ayton, S ; Lei, P ; Duce, JA ; Wong, BXW ; Sedjahtera, A ; Adlard, PA ; Bush, AI ; Finkelstein, DI (WILEY-BLACKWELL, 2013-04)
    Ceruloplasmin is an iron-export ferroxidase that is abundant in plasma and also expressed in glia. We found a ∼80% loss of ceruloplasmin ferroxidase activity in the substantia nigra of idiopathic Parkinson disease (PD) cases, which could contribute to the pro-oxidant iron accumulation that characterizes the pathology. Consistent with a role for ceruloplasmin in PD etiopathogenesis, ceruloplasmin knockout mice developed parkinsonism that was rescued by iron chelation. Additionally, peripheral infusion of ceruloplasmin attenuated neurodegeneration and nigral iron elevation in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model for PD. These findings show, in principle, that intravenous ceruloplasmin may have therapeutic potential in PD.