Tokuhei Ikeda

Polyneuropathy caused by cobalt–chromium metallosis after total hip replacement

Although metal intoxication after arthroplasty causes various symptoms, polyneuropathy has never been the focus of clinical investigation. We report the case of a 56‐year‐old woman with metal neuropathy. She had metallosis after hip arthroplasty with a cobalt–chromium alloy prosthesis. She developed progressive sensory disturbance, hearing loss, and hypothyroidism. Sural nerve biopsy indicated axonopathy. After exchange arthroplasty, blood levels of cobalt and chromium decreased, and her symptoms improved. Cobalt or chromium can cause axonopathy. Muscle Nerve, 2010

Phenolic compounds prevent amyloid β-protein oligomerization and synaptic dysfunction by site-specific binding

Background: Epidemiological evidence suggests that consumption of phenolic compounds reduce the incidence of Alzheimer disease (AD). Results: Myricetin and rosmarinic acid reduced cellular and synaptic toxicities by inhibition of amyloid β-protein (Aβ) oligomerization. Myricetin promoted NMR changes of Aβ. Conclusion: Phenolic compounds are worthy therapeutic candidates for AD. Significance: Phenolic compounds blocked early assembly processes of Aβ through differently binding. Cerebral deposition of amyloid β protein (Aβ) is an invariant feature of Alzheimer disease (AD), and epidemiological evidence suggests that moderate consumption of foods enriched with phenolic compounds reduce the incidence of AD. We reported previously that the phenolic compounds myricetin (Myr) and rosmarinic acid (RA) inhibited Aβ aggregation in vitro and in vivo. To elucidate a mechanistic basis for these results, we analyzed the effects of five phenolic compounds in the Aβ aggregation process and in oligomer-induced synaptic toxicities. We now report that the phenolic compounds blocked Aβ oligomerization, and Myr promoted significant NMR chemical shift changes of monomeric Aβ. Both Myr and RA reduced cellular toxicity and synaptic dysfunction of the Aβ oligomers. These results suggest that Myr and RA may play key roles in blocking the toxicity and early assembly processes associated with Aβ through different binding.

Cross-seeding effects of amyloid β-protein and α-synuclein

J. Neurochem. (2012) 122, 883–890.

Familial Parkinson disease mutations influence α-Synuclein assembly

Lewy bodies composed of aggregates of α-synuclein (αS) in the brain are the main histopathological features of Lewy body diseases (LBD) such as Parkinsons disease and dementia with Lewy bodies. Mutations such as E46K, A30P and A53T in the αS gene cause autosomal dominant LBD in a number of kindreds. Although these mutations accelerate fibril formation, their precise effects at early stages of the αS aggregation process remain unknown. To answer this question, we examined the aggregation including monomer conformational dynamics and oligomerization of the E46K, A30P, A53T and A30P/A53T mutations and wild type (WT) using thioflavin S assay, circular dichroism spectroscopy, photo-induced cross-linking of unmodified proteins, electron microscopy, and atomic force microscopy. Relative to WT αS, E46K αS accelerated the kinetics of the secondary structure change and oligomerization, whereas A30P αS decelerated them. These effects were reflected in changes in average oligomer size. The mutant oligomers of E46K αS functioned as fibril seeds significantly more efficiently than those of WT αS, whereas the mutant oligomers of A30P αS were less efficient. Our results that mutations of familial LBD had opposite effects at early stages of αS assembly may provide new insight into the molecular mechanisms of LBD.

A Comparison of the Diagnostic Sensitivity of MRI, CBF-SPECT, FDG-PET and Cerebrospinal Fluid Biomarkers for Detecting Alzheimer's Disease in a Memory Clinic

Background/Aim: Magnetic resonance imaging (MRI), cerebral blood flow single photon emission computed tomography (CBF-SPECT), fluorodeoxyglucose-positron emission tomography (FDG-PET) and cerebrospinal fluid (CSF) biomarkers are used for the diagnosis of Alzheimer’s disease (AD). We aimed to reveal the relative sensitivity of these tools in a memory clinic setting. Methods: In 207 patients with probable AD in our memory clinic, medial temporal lobe atrophy on MRI, hypoperfusion/hypometabolism of the parietotemporal lobe and posterior cingulate gyrus in ethylcysteinate dimer-CBF-SPECT/FDG-PET, and abnormalities of CSF amyloid β-protein 1–42, total tau and phosphorylated tau were evaluated as findings characteristic of AD. Results: The AD findings were observed in 77.4% of all AD patients with MRI, 81.6% with CBF-SPECT, 93.1% with FDG-PET and 94.0% with CSF biomarkers. At the stage of Clinical Dementia Rating (CDR) 0.5, CSF biomarkers were the most sensitive (90.0%); at the stage of CDR 1, FDG-PET (96.7%) and CSF biomarkers (95.5%) were highly sensitive. At the stage of CDR 2, all tools showed high positive percentages. Conclusion: The diagnosis of AD was most often supported by CSF biomarkers and FDG-PET at the early stage of dementia (CDR 1) and by CSF biomarkers at the earlier stage (CDR 0.5).

Effect of melatonin on α-synuclein self-assembly and cytotoxicity

α-Synuclein (αS) assembly has been implicated as a critical step in the development of Lewy body diseases such as Parkinsons disease and dementia with Lewy bodies. Melatonin (Mel), a secretory product of the pineal gland, is known to have beneficial effects such as an antioxidant function and neuroprotection. To elucidate whether Mel has an antiassembly effect, here we used circular dichroism spectroscopy, photoinduced crosslinking of unmodified proteins, thioflavin S fluorescence, size exclusion chromatography, electron microscopy and atomic force microscopy to examine the effects of Mel on the αS assembly. We also examined the effects of Mel on αS-induced cytotoxicity by assaying 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide metabolism in αS-treated, primary neuronal cells. Initial studies revealed that Mel blocked αS fibril formation as well as destabilizing preformed αS fibrils. Subsequent evaluation of the assembly-stage specificity of the effect showed that Mel was able to inhibit protofibril formation, oligomerization, and secondary structure transitions. Importantly, Mel decreased αS-induced cytotoxicity. These data suggest a mechanism of action for Mel, inhibition of assembly of toxic polymers and protection of neurons from their effect.

Effects of sex hormones on Alzheimer's disease-associated β-amyloid oligomer formation in vitro.

The folding of amyloid β-protein (Aβ) into oligomeric, protofibrillar, and fibrillar assemblies is hypothesized to be the key pathogenic event in Alzheimers disease (AD), with oligomeric assemblies thought to be the most neurotoxic. Inhibitors of oligomer formation, therefore, could be valuable therapeutics for patients with AD. Epidemiological studies have indicated that estrogen therapy reduces the risk of developing AD in women. Here, we examined the effects of estrogen (estrone (E1), estradiol (E2), and estriol (E3)) and related sexual steroids (androstenedione (AND) and testosterone (TES)) on the in vitro oligomer formation of Aβ(1-40) and Aβ(1-42) using a method of photo-induced cross-linking of unmodified proteins (PICUP) and electron microscopic studies. Estrogens (E1, E2, and E3) inhibited low-order Aβ oligomer formation, and among them, E3 had the strongest in vitro activity. Estrogen could be a potential therapeutic agent to prevent or delay AD progression, and further understanding of the fact that these very similar molecules have different anti-oligomeric effects would contribute to the development of new agents.

Phenolic compounds prevent the oligomerization of α‐synuclein and reduce synaptic toxicity

Lewy bodies, mainly composed of α‐synuclein (αS), are pathological hallmarks of Parkinsons disease and dementia with Lewy bodies. Epidemiological studies showed that green tea consumption or habitual intake of phenolic compounds reduced Parkinsons disease risk. We previously reported that phenolic compounds inhibited αS fibrillation and destabilized preformed αS fibrils. Cumulative evidence suggests that low‐order αS oligomers are neurotoxic and critical species in the pathogenesis of α‐synucleinopathies. To develop disease modifying therapies for α‐synucleinopathies, we examined effects of phenolic compounds (myricetin (Myr), curcumin, rosmarinic acid (RA), nordihydroguaiaretic acid, and ferulic acid) on αS oligomerization. Using methods such as photo‐induced cross‐linking of unmodified proteins, circular dichroism spectroscopy, the electron microscope, and the atomic force microscope, we showed that Myr and RA inhibited αS oligomerization and secondary structure conversion. The nuclear magnetic resonance analysis revealed that Myr directly bound to the N‐terminal region of αS, whereas direct binding of RA to monomeric αS was not detected. Electrophysiological assays for long‐term potentiation in mouse hippocampal slices revealed that Myr and RA ameliorated αS synaptic toxicity by inhibition of αS oligomerization. These results suggest that Myr and RA prevent the αS aggregation process, reducing the neurotoxicity of αS oligomers.

Exogenous amyloidogenic proteins function as seeds in amyloid β-protein aggregation

Amyloid β-protein (Aβ) aggregation is considered to be a critical step in the neurodegeneration of Alzheimers disease (AD). In addition to Aβ, many proteins aggregate into the amyloid state, in which they form elongated fibers with spines comprising stranded β-sheets. However, the cross-seeding effects of other protein aggregates on Aβ aggregation pathways are not completely clear. To investigate the cross-seeding effects of exogenous and human non-CNS amyloidogenic proteins on Aβ aggregation pathways, we examined whether and how sonicated fibrils of casein, fibroin, sericin, actin, and islet amyloid polypeptide affected Aβ40 and Aβ42 aggregation pathways using the thioflavin T assay and electron microscopy. Interestingly, the fibrillar seeds of all amyloidogenic proteins functioned as seeds. The cross-seeding effect of actin was stronger but that of fibroin was weaker than that of other proteins. Furthermore, our nuclear magnetic resonance spectroscopic studies identified the binding sites of Aβ with the amyloidogenic proteins. Our results indicate that the amyloidogenic proteins, including those contained in foods and cosmetics, contribute to Aβ aggregation by binding to Aβ, suggesting their possible roles in the propagation of Aβ amyloidosis.

Vitamin A has Anti-Oligomerization Effects on Amyloid-β In Vitro

Inhibition of amyloid-β (Aβ) aggregation is an attractive therapeutic strategy for treatment of Alzheimers disease (AD). We previously reported that vitamin A and β-carotene inhibit fibrillation of Aβ40 and Aβ42 (Ono et al, 2004, Exp Neurol). In this study, we firstly examined the effects of vitamin A (retinoic acid, retinol, and retinal), β-carotene, vitamin B2, vitamin B6, vitamin C, vitamin E, coenzyme Q10, and α-lipoic acid on oligomerization of Aβ40 and Aβ42 in vitro; vitamin A and β-carotene dose-dependently inhibited oligomerization of Aβ40 and Aβ42. Furthermore, retinoic acid decreased cellular toxicity by inhibition of Aβ42 oligomerization. Second, we analyzed how vitamin A inhibits Aβ aggregation by using fluorescence spectroscopy and thioflavin T assay with two Aβ fragments, Aβ1-16 and Aβ25-35. A fluorescence peak of retinoic acid was greatly restrained in the presence of Aβ25-35, and retinoic acid inhibited aggregation of Aβ25-35, but not of Aβ1-16, which suggest the specific binding of retinoic acid to the C-terminal portion of Aβ. Thus, vitamin A and β-carotene might be key molecules for prevention of AD.