Takashi Morihara

Curcumin Structure-Function, Bioavailability, and Efficacy in Models of Neuroinflammation and Alzheimer's Disease

Curcumin can reduce inflammation and neurodegeneration, but its chemical instability and metabolism raise concerns, including whether the more stable metabolite tetrahydrocurcumin (TC) may mediate efficacy. We examined the antioxidant, anti-inflammatory, or anti-amyloidogenic effects of dietary curcumin and TC, either administered chronically to aged Tg2576 APPsw mice or acutely to lipopolysaccharide (LPS)-injected wild-type mice. Despite dramatically higher drug plasma levels after TC compared with curcumin gavage, resulting brain levels of parent compounds were similar, correlating with reduction in LPS-stimulated inducible nitric-oxide synthase, nitrotyrosine, F2 isoprostanes, and carbonyls. In both the acute (LPS) and chronic inflammation (Tg2576), TC and curcumin similarly reduced interleukin-1β. Despite these similarities, only curcumin was effective in reducing amyloid plaque burden, insoluble β-amyloid peptide (Aβ), and carbonyls. TC had no impact on plaques or insoluble Aβ, but both reduced Tris-buffered saline-soluble Aβ and phospho-c-Jun NH2-terminal kinase (JNK). Curcumin but not TC prevented Aβ aggregation. The TC metabolite was detected in brain and plasma from mice chronically fed the parent compound. These data indicate that the dienone bridge present in curcumin, but not in TC, is necessary to reduce plaque deposition and protein oxidation in an Alzheimers model. Nevertheless, TC did reduce neuroinflammation and soluble Aβ, effects that may be attributable to limiting JNK-mediated transcription. Because of its favorable safety profile and the involvement of misfolded proteins, oxidative damage, and inflammation in multiple chronic degenerative diseases, these data relating curcumin dosing to the blood and tissue levels required for efficacy should help translation efforts from multiple successful preclinical models.

A molecular chaperone inducer protects neurons from ER stress

The endoplasmic reticulum (ER) stress response is a defense system for dealing with the accumulation of unfolded proteins in the ER lumen. Recent reports have shown that ER stress is involved in the pathology of some neurodegenerative diseases and cerebral ischemia. In a screen for compounds that induce the ER-mediated chaperone BiP (immunoglobulin heavy-chain binding protein)/GRP78 (78u2009kDa glucose-regulated protein), we identified BiP inducer X (BIX). BIX preferentially induced BiP with slight inductions of GRP94 (94u2009kDa glucose-regulated protein), calreticulin, and C/EBP homologous protein. The induction of BiP mRNA by BIX was mediated by activation of ER stress response elements upstream of the BiP gene, through the ATF6 (activating transcription factor 6) pathway. Pretreatment of neuroblastoma cells with BIX reduced cell death induced by ER stress. Intracerebroventricular pretreatment with BIX reduced the area of infarction due to focal cerebral ischemia in mice. In the penumbra of BIX-treated mice, ER stress-induced apoptosis was suppressed, leading to a reduction in the number of apoptotic cells. Considering these results together, it appears that BIX induces BiP to prevent neuronal death by ER stress, suggesting that it may be a potential therapeutic agent for cerebral diseases caused by ER stress.

Phosphorylation of tau at Ser214 mediates its interaction with 14-3-3 protein: implications for the mechanism of tau aggregation

The microtubule associated protein tau is a major component of neurofibrillary tangles in Alzheimer disease brain, however the neuropathological processes behind the formation of neurofibrillary tangles are still unclear. Previously, 14‐3‐3 proteins were reported to bind with tau. 14‐3‐3 Proteins usually bind their targets through specific serine/threonine –phosphorylated motifs. Therefore, the interaction of tau with 14‐3‐3 mediated by phosphorylation was investigated. In this study, we show that the phosphorylation of tau by either protein kinase A (PKA) or protein kinase B (PKB) enhances the binding of tau with 14‐3‐3 in vitro. The affinity between tau and 14‐3‐3 is increased 12‐ to 14‐fold by phosphorylation as determined by real time surface plasmon resonance studies. Mutational analyses revealed that Ser214 is critical for the phosphorylation‐mediated interaction of tau with 14‐3‐3. Finally, in vitro aggregation assays demonstrated that phosphorylation by PKA/PKB inhibits the formation of aggregates/filaments of tau induced by 14‐3‐3. As the phosphorylation at Ser214 is up‐regulated in fetal brain, tau’s interaction with 14‐3‐3 may have a significant role in the organization of the microtubule cytoskeleton in development. Also as the phosphorylation at Ser214 is up‐regulated in Alzheimer’s disease brain, tau’s interaction with 14‐3‐3 might be involved in the pathology of this disease.

Impaired prepulse inhibition and habituation of acoustic startle response in Japanese patients with schizophrenia

Prepulse inhibition (PPI) and habituation of the acoustic startle reflex (ASR) are considered to be candidate endophenotypes of schizophrenia. However, to our knowledge, only one group has investigated these startle measures in Asian patients with schizophrenia. In the present study, we evaluated these startle measures in 51 Japanese patients with schizophrenia and compared them with those of 55 healthy age- and sex-matched Japanese controls. A human startle response monitoring system was used to deliver acoustic startle stimuli, and record and score the electromyographic activity of the orbicularis oculi muscle. The startle measures examined were mean magnitude of ASR to pulse alone trials in initial block (SR), habituation of ASR during the session (HAB), and PPI at prepulse intensities of 82 dB (PPI82), 86 dB (PPI86), and 90 dB (PPI90) sound pressure level. SR was not significantly different between the patients and controls. Patients displayed significantly reduced HAB and PPI for all prepulse intensities compared to controls. The greatest statistical difference in PPI between patients and controls was found with PPI86. This did not correlate with any clinical variable in each group. Our results indicate that PPI and habituation of ASR are impaired in Asian patients with schizophrenia.

SORL1 is genetically associated with Alzheimer disease in a Japanese population

A recent study reported that variants of the neuronal sortilin-related receptor gene (SORL1) increased the risk of late-onset Alzheimer disease (AD) in several populations. Here, we examined the risk effect in a large, well-characterized group of 437 late-onset AD patients and 451 control subjects in a Japanese population. Among eight single-nucleotide polymorphisms (SNPs) of the SORL1 gene for which association has been reported, we found a significant association for four of them, located between exon 24 and intron 37. This risk was evident in non-carriers of the apolipoprotein E-epsilon 4 allele, but not in its carriers. Our results support the evidence that genetic variants of SORL1 affect susceptibility to late-onset AD.

Association study of KIBRA gene with memory performance in a Japanese population

Abstract Objectives. Papassotiropoulos et al. (Science 314: p 475) discovered that a single nucleotide polymorphism (SNP) of the KIBRA gene (rs17070145) was associated with delayed recall performance in Caucasians. KIBRA is highly expressed in the brain and kidneys, and is reported to be involved in synaptic plasticity. Therefore, we first tried to replicate the association between the SNP and memory performance in a Japanese subjects. Methods. We examined the association between the SNP and memory performance measured by the Wechsler Memory Scale-Revised (WMS-R) in 187 healthy Japanese people. Results. The T allele carriers had significantly better verbal memory, attention/concentration and delayed recall performance than the C/C carriers (corrected P = 0.044, 0.047 and 0.0084, respectively). Furthermore, the C/T carriers and the T/T carriers had better delayed recall performance than the C/C carriers (post hoc P = 0.0017 and 0.0096). Conclusions. This data suggest that the C/C genotype might have an impact on memory performance in Asian populations as well as in Caucasian populations. Further investigation to clarify the association of the KIBRA gene with memory in other ethnic groups is warranted.

TATA Box-Binding Protein gene is associated with risk for schizophrenia, age at onset and prefrontal function

Schizophrenia is a common polygenic disease in distinct populations, while spinocerebellar ataxia type 17 (SCA17) is a rare autosomal dominant neurodegenerative disorder. Both diseases involve psychotic symptoms. SCA17 is caused by an expanded polyglutamine tract in the TATA box‐binding protein (TBP) gene. In the present study, we investigated the association between schizophrenia and CAG repeat length in common TBP alleles with fewer than 42 CAG repeats in a Japanese population (326 patients with schizophrenia and 116 healthy controls). We found that higher frequency of alleles with greater than 35 CAG repeats in patients with schizophrenia compared with that in controls (p = 0.042). We also examined the correlation between CAG repeats length and age at onset of schizophrenia. We observed a negative correlation between the number of CAG repeats in the chromosome with longer CAG repeats out of two chromosomes and age at onset of schizophrenia (p = 0.020). We further provided evidence that TBP genotypes with greater than 35 CAG repeats, which were enriched in patients with schizophrenia, were significantly associated with hypoactivation of the prefrontal cortex measured by near‐infrared spectroscopy during the tower of Hanoi, a task of executive function (right PFC; p = 0.015, left PFC; p = 0.010). These findings suggest possible associations of the genetic variations of the TBP gene with risk for schizophrenia, age at onset and prefrontal function.

KIBRA genetic polymorphism influences episodic memory in Alzheimer's disease, but does not show association with disease in a Japanese cohort

Background/Aims: A single-nucleotide polymorphism (SNP) in the KIBRA gene, rs17070145, was reported to be significantly associated with episodic memory in cognitively normal cohorts. This observation has expanded genetic studies on KIBRA to Alzheimer’s disease (AD). Importantly, the association between KIBRA and episodic memory in AD has never been addressed. In this study, we investigated whether the KIBRA rs17070145 SNP influences AD episodic memory and the disease in a Japanese cohort. Methods: Blood samples from 346 AD patients and 375 normal cognitive controls were collected and genotyped for rs17070145. Episodic memory was measured in 32 AD patients, diagnosed for the first time, by use of the Rivermead Behavioral Memory Test (RBMT). Results: We found that KIBRA C allele carriers scored significantly lower than KIBRA non-C carriers on both RBMT total profile score (p = 0.042, effect size = 0.84) and RBMT total screening score (p < 0.001, effect size = 1.42). The KIBRA gene did not show association with AD in our Japanese cohort. Conclusion: Our results evidence a strong association between the KIBRA gene and episodic memory impairment in AD, but show no influence on AD in our Japanese cohort. We propose that KIBRA might have an effect similar to cognitive reserve.

Mild cognitive impairment and subjective cognitive impairment

Until a decade ago, the common understanding was that forgetfulness in the elderly is a physiological phenomenon and that all elderly people show memory loss to some extent, with considerable variations in the severity of memory loss between individuals. Commonly observed memory loss in the elderly was termed ‘benign senescent forgetfulness’, which was regarded as different from the pathological state of dementia. Kral described benign senescent forgetfulness as follows: (i) impossible to recall unimportant things and part of the experience; (ii) able to recall these forgotten things at other times and on other occasions; (iii) more memory loss with older things compared with recent things; and (iv) subjects recognize this forgetfulness and try to compensate for it by several means. In the 1980s, there was an interest in ‘age-associated memory impairment’ (AAMI), which was also regarded as different from Alzheimer’s disease, in which only memory function is disturbed without an affect on other cognitive functions. In those days, memory loss in the elderly was regarded as common and different from the pathological conditions leading to dementia, including Alzheimer’s disease. Recent findings in neuroscience do not necessarily support the notions described above, and it is conceived that memory loss in the elderly is not inevitable, because newer findings show fully functioning brain activity in the elderly. For example, there is no significant decrease in the number of neurons in the elderly brain, even though the size of the neurons is smaller, and there is no reduction in cerebral blood flow and cerebral glucose metabolism in the brain of healthy elderly people compared with the younger brain. Neurogenesis is observed in the dentate gyrus of the hippocampus of brains over 50 years of age. We have now abundant data that support the hypothesis that the human brain can function properly over 50 years of age if the elderly person is not affected by dementia. Furthermore, this new understanding has been accelerated by research into the pathogenesis of Alzheimer’s disease that explores possible means of intervention and prevention. Since 1996, drugs for the symptomatic treatment of Alzheimer’s disease have been used widely, including acetylcholinesterase inhibitors (donepezil, rivastigmine, and galantamine) and an N-methyl-D-aspartate (NMDA) antagonist (memantine), and we are now at the stage of developing disease-modifying drugs, which will give more benefit to the patients if administrated in earlier stages of the disease. Considering these situations, the initial stage, or even prestage, of the disease attracts more attention in research because it would be the period when the disease-modifying drugs would exert their maximum effect.

Association between CAG repeat length in the PPP2R2B gene and Alzheimer disease in the Japanese population

We analyzed the association between PPP2R2B gene CAG repeat length and Alzheimer disease (AD) susceptibility in the Japanese population. Blood samples were collected from 218 late-onset AD patients and 86 controls. DNA fragments containing the target CAG repeat region were amplified using polymerase chain reaction (PCR). PCR products were sequenced using ABI PRISM 310 genetic analyzer. The mean CAG repeat length did not differ significantly between the control and AD groups. In contrast, the frequency of CAG repeats shorter than 15 was significantly higher in AD group, specifically in the AD with APOE4 subgroup, than in the control group. The results suggest that CAG repeat lengths in the PPP2R2B gene may be potential genetic markers for AD susceptibility in the Japanese population.