轻度认知功能障碍和阿尔茨海默病患者血小板α和β分泌酶活性的变化

目的 研究轻度认知功能障碍(MCI)和阿尔茨海默病(AD)患者血小板α和β分泌酶活性及α分泌酶的产物sAPPα含量的变化.方法 对48例其他疾病老年对照者、42例MCI患者及40例AD患者分别进行神经功能评定,用荧光法测定各组患者血小板α和β分泌酶的活性,并用Western印迹检测血小板sAPPα含量.结果 对照组、MCI组和AD组患者α分泌酶活性分别为100.0％±10.6％、78.2％±9.4％和61.8％±7.2％,MCI和AD组与对照组相比均降低,差异有统计学意义(F=22.935,P=0.001)；AD组与MCI组相比亦明显降低,差异有统计学意义.对照组、MCI组和AD组β分泌酶的活性分别为100.0％士11.2％、145.8％士12.7％和189.8％士14.2％；MCI组和AD组均较对照组升高,差异有统计学意义(F=16.368,P=0.001),AD组较MCI组高,差异有统计学意义.sAPPα的含量MCI组和AD组与对照组相比均明显降低；AD组与MCI组相比亦显著降低,差异有统计学意义.结论 MCI组和AD组患者的α分泌酶活性及其产物sAPPα均较对照组降低,β分泌酶活性升高；α和β分泌酶活性改变可能在MCI和AD的发病过程中起着一定的作用,在MCI和AD的诊断中有一定的潜在价值.     

脑脊液Tau蛋白及β淀粉样蛋白水平对阿尔茨海默病和轻度认知障碍诊断的意义

目的 研究轻度认知损害(MCI)和阿尔茨海默病(AD)患者脑脊液Tau蛋白和β淀粉样蛋白1-42 (Aβ1-42)的含量及其诊断意义.方法 采用酶联免疫吸附法检测32例MCI,30例AD 和31名健康对照者(对照组)脑脊液中Tau蛋白和Aβ1-42的水平.结果 MCI组和AD组患者脑脊液中Tau蛋白浓度均高于正常组, Aβ1-42的浓度均低于正常组,差异均有统计学意义(P<0.05).MCI组和AD组患者脑脊液中Tau蛋白和Aβ1-42的浓度差异无统计学意义(P>0.05).结论 脑脊液中Tau蛋白和Aβ1-42的浓度对MCI和AD的诊断有应用价值,但不能用于MCI和AD鉴别诊断.     

MCI患者血清中Tau蛋白 Aβ1-42P-tau的检测价值分析

目的 探讨血清磷酸化Tau（P-tau）、β淀粉样蛋白1-42（Aβ1-42）以及Tau蛋白在轻度认知障碍（MCI）患者中的临床应用价值.方法 采用酶联免疫法测定主诉健忘组（SMC）30例,MCI患者30例,阿尔茨海默病组（AD）68例（轻度AD 24例,中度AD 22例,重度AD 22例）以及健康对照组35例血清中P-tau、Aβ1-42、Tau蛋白水平,并分析三种标记物与疾病的相关性.结果 与对照组及MCI组相比,MCI组、AD组MMSE评分显著上升,差异有统计学意义（P〈0.05）,重度AD组MMSE评分显著高于轻度、中度AD组,两两比较差异有统计学意义（P〈0.05）.与对照组相比,MCI组、AD组P-tau、Tau蛋白水平显著上升,且AD组高于MCI组,而Aβ1-42水平显著下降,且AD组下降幅度大于MCI组,差异有统计学意义（P〈0.05）.其中重度AD组P-tau、Tau蛋白水平高于轻度、中度AD组,而Aβ1-42水平低于轻、中度组,差异有统计学意义（P〈0.05）.SMC 组与对照组相比,各标记物水平差异无统计学意义（P〉0.05）.与单纯Tau蛋白、Aβ1-42、P-tau诊断相比,Tau蛋白、Aβ1-42、P-tau联合诊断的灵敏性、特异性、准确性显著增加,差异有统计学意义（P〈0.05）.结论 MCI病情发生及发展过程可能与血清P-tau、Aβ1-42、Tau蛋白水平异常有关,通过测定这三种标记物可有效预测MCI患者病情进展情况.     

脑老化糖基化终末产物上调BACE1活性促进Aβ生成

目的 探讨糖基化终末产物(AGEs)在β-淀粉样蛋白(Aβ)产生中分子机制.方法 以APPsw-N2a细胞为AD细胞模型,将细胞随机分为3组,空白对照组、AGEs组、AGEs+抗RAG抗体组.采用ELISA方法检测各组Aβ40和Aβ42的表达水平,并用荧光检测法检测BACE1的活性.结果 与对照组相比,AGEs组Aβ40、Aβ42表达水平及BACE1活性明显增加,差异有统计学意义(P＜0.01)；预先用抗RAG中和抗体(1∶100)1 h后,Aβ40,Aβ42表达水平及BACE1活性与AGEs组相比较明显减少,差异有统计学意义(P＜0.05).结论 AGEs可能通过上调BACE1的活性促使APPsw-N2a细胞Aβ生成增加,提示AGEs可能在AD发生、发展中起重要作用.     

轻度认知障碍患者认知水平与血清"淀粉样蛋白42磷酸化Tau同型半胱氨酸水平相关性分析

目的探讨轻度认知障碍患者认知水平与血清"淀粉样蛋白42、磷酸化Tau、同型半胱氨酸水平的相关性。方法选择2008-2011年济宁各社区近1 100例50~80岁的中老年人,筛选出MCI患者36例,并选取年龄、学历相匹配的健康对照组36例。检测MCI组与对照组的认知功能水平与血清Aβ-42、p-tan、Hcy水平,使用相关性分析MMSE水平与血清指标的关系。结果 2组患者性别比例、平均年龄、受教育年限方面比较差异无统计学意义(P0.05),对照组平均MMSE明显高于MCI组,差异有统计学意义(P≤0.05),MCI组平均Aβ-42、p-tan、Hcy水平明显高于对照组,差异有统计学意义(P≤0.05),MCI组及对照组的Aβ-42、p-tan、Hcy均与患者的MMSE得分呈相关性(P≤0.05),其中MMSE得分与Aβ-42、p-tan、Hcy为负相关。结论血清Aβ-42、p-tan、Hcy可指示认知功能水平。     

阿尔茨海默病患者脑脊液可溶性血小板衍生生长因子受体β与认知损害及脑脊液生物标志物的相关性研究

目的研究阿尔茨海默病(AD)患者脑脊液可溶性血小板衍生生长因子受体β(sPDGFRβ)浓度与认知损害程度及脑脊液生物标志物的相关性。方法选取2018年9月至2020年8月安徽医科大学附属省立医院神经内科收治的AD患者(AD组)50例,及同期住院的认知功能正常的对照组33例,对其完善神经心理学测评,依据临床痴呆量表(CDR)评分将AD患者分为轻度AD组和中重度AD组,比较3组的临床资料、认知功能。采用酶联免疫吸附法测定各组患者的脑脊液sPDGFRβ、脑脊液β-淀粉样蛋白(Aβ)1-42、脑脊液Aβ1-40、总tau蛋白(T-tau)及磷酸化tau蛋白(P-tau)含量,比较3组间差异。将AD组根据载脂蛋白E(ApoE)基因是否携带ε4基因分为ApoE4+组和ApoE4-组,比较组间脑脊液sPDGFRβ差异。并将轻度AD组和中重度AD组、对照组脑脊液sPDGFRβ与认知损害程度和脑脊液Aβ1-42、T-tau及P-tau含量进行相关分析。结果中重度AD组脑脊液sPDGFRβ浓度[(235.358±86.187)pg/ml]和轻度AD组脑脊液sPDGFRβ浓度[(219.301±69.711)pg/ml]高于对照组[(184.878±52.944)pg/ml],差异有统计学意义(F=3.90,P=0.024)。而在AD患者中,ApoE4+组脑脊液sPDGFRβ[(219.493±76.745)pg/ml]和ApoE4-组[(222.802±81.665)pg/ml]间差异无统计学意义(t=-0.13,P=0.900)。相关分析结果显示,轻度AD组脑脊液sPDGFRβ与脑脊液P-tau水平呈正相关(r=0.43,P=0.019),与Aβ1-42、T-tau水平、简易精神状态检查量表评分及蒙特利尔认知评估量表评分无相关性,而在中重度AD组和对照组中则均无相关性。结论脑脊液sPDGFRβ在AD患者中升高,并在早期与P-tau有关;周细胞损伤可能参与了AD患者脑内tau蛋白的磷酸化。     

阿尔茨海默病患者脑脊液中葡萄糖、真胰岛素、Aβ_(40)和Aβ_(42)测定

目的检测阿尔茨海默病(AD)患者脑脊液中葡萄糖、真胰岛素、Aβ40和Aβ42水平,探讨AD患者脑内胰岛素及β淀粉样蛋白(Aβ)相关性。方法随机选取35例对照组、48例AD患者,检验其脑脊液中葡萄糖、真胰岛素、Aβ40和Aβ42水平,将AD按轻、中重度分组后与对照组进行比较。结果AD患者各组脑脊液中葡萄糖与相应对照组比较,无显著性差异(P>0.05);AD各组Aβ40与对照组相比,无显著性差异(P>0.05);轻度AD组脑脊液真胰岛素与对照组比较,无显著性差异(P>0.05),中重度AD组真胰岛素较对照组降低,有显著性差异(P<0.05);AD组、轻度AD组Aβ42较对照组降低,有显著性差异(P<0.01);中重度AD组Aβ42较对照组降低,有极显著性差异(P<0.001)。结论AD患者脑脊液中胰岛素和Aβ42异常情况,与疾病的严重程度相关。     

胰岛素抵抗大鼠认知功能的变化及其脑组织Alzheimer样病变

目的研究胰岛素抵抗大鼠(IR)认知功能的变化及其脑组织胆碱乙酰转移酶(ChAT)的活性、β-淀粉样(Aβ42)、P-Tau(ser396)、淀粉样前体蛋白(APP),β-分泌酶(BACE1)及早老素(PS1)的表达,探讨胰岛素抵抗在阿尔茨海默病(AD)中可能的作用机制。方法从25只Wistar雄性大鼠中随机选取10只作为正常对照组(NC),以普通标准饲料+自来水喂养;余15只为模型组以普通标准饲料+10%果糖水连续喂养12周后筛选出IR大鼠13只;12周末用Morris水迷宫试验测定各组大鼠认知功能行为学改变,放免法检测血浆胰岛素水平,葡萄糖氧化酶法检测血浆葡萄糖水平,化学比色法测定ChAT的活性,免疫组化法检测APP、Aβ42,蛋白印迹法检测BACE1,PS1及P-Tau(ser396)蛋白表达水平。结果 IR组大鼠逃避潜伏期较NC组明显延长(P0.01);IR组血浆血糖、胰岛素水平及运用HOMA-IR计算的胰岛素抵抗指数均显著高于NC组(P0.01);IR组ChAT的活性较NC组明显降低(P0.01);与NC组相比,IR组APP、Aβ42平均光密度值明显升高,组间差异有统计学意义(P0.01);IR组大鼠脑组织中BACE1,PS1及P-tau(ser396)蛋白表达水平较NC组显著增高(P0.01)。结论胰岛素抵抗大鼠认知功能受损,其程度与ChAT的活性相关;胰岛素抵抗通过上调BACE1,PS1的活性,使Aβ生成增加,同时P-Tau蛋白表达增加,从而可能参与类AD病变的发生。     

尿液β淀粉样蛋白寡聚体检测在阿尔茨海默病和轻度认知损害中临床意义的初步探索

目的探索阿尔茨海默病(AD)患者尿液β淀粉样蛋白(Aβ)寡聚体水平及其临床意义。方法收集60例病例组研究对象:包括轻度认知损害(MCI)组28例、AD组15例、主观认知下降(SCD)组17例;另选择上海市宝山区友谊街道社区认知正常健康者(对照组)19例。收集患者临床信息以及尿液,利用脑脊液Aβ寡聚体检测ELISA试剂盒检测研究对象尿液Aβ寡聚体水平,比较组间差异;评价尿液Aβ寡聚体水平与MMSE量表、MoCA-B量表认知功能的相关性。由于MMSE量表相较于MoCA-B量表对MCI的灵敏度不高,因此将研究对象进行重新分组,分为:所有受试者组(79例)、对照+SCD+MCI组(64例)和AD组(15例)。结果 SCD组尿液Aβ寡聚体水平(0.026±0.011)ng·mL~(-1),较对照组(0.024±0.009) ng·mL~(-1)、MCI组(0.020±0.015) ng·mL~(-1)和AD组(0.019±0.013) ng·mL~(-1)增高;对照组和SCD组Aβ寡聚体水平与MCI组比较,差异均有统计学意义(P=0.035 0,P=0.012 2)。相关分析结果显示尿液Aβ寡聚体水平与MoCA-B量表评分具有显著相关性,MCI组(r=0.441 3,P=0.018 7),SCD+MCI组(r=0.381 9,P=0.0096)。相较于所有受试者组和对照+SCD+MCI组,AD组Aβ寡聚体水平与MMSE量表评分的相关系数较高(r=0.341 4,P=0.213 0)。结论利用脑脊液Aβ寡聚体检测试剂盒检测尿液Aβ寡聚体有效,尿液Aβ寡聚体作为一种新型的生物标志物有望应用于AD的早期筛查。     

轻度认知损害病人脑脊液白细胞介素-1和肿瘤坏死因子水平的研究

目的:为探讨炎性细胞因子在轻度认知损害(mild cognitive impairment,MCI)慢性炎性病理过程中的作用。方法:本研究采用双抗体夹心酶联免疫吸附实验(enzyme linked immunosorbent assay,ELISA)分别对AD对32例MCI病人与15例正常对照的脑脊液(cerebrospinal fluid,CSF)的自细胞介素IL-1β(Interleukin-1β,IL-1β)和肿瘤坏死因子α(tumor necrosis factors alpha,TNFα)的水平进行了测定。结果:MCI组与正常对照相比,MCI组病人CSF中IL-1β水平和TNFα水平明显升高。结论:上述结果表明,炎性细胞因子IL-1β和TNFα在MCI的神经变性过程起着重要的作用,炎症参与MCI向AD转化发病机制。观察MCI患者CSF的IL-1β水平和TNFα水平可以为早期诊断和治疗提供依据。     

Levels of beta-secretase BACE and alpha-secretase ADAM10 mRNAs in Alzheimer hippocampus

The amyloid cascade hypothesis suggests that amyloid precursor protein (APP) proteolytic processing is a key event in the pathogenesis of Alzheimer's disease (AD). The enzymes beta-site APP cleaving enzyme (BACE) and A disintegrin and metalloproteinase 10 (ADAM10) play an important role in APP proteolysis. We measured by real time quantitative polymerase chain reaction their mRNA levels in hippocampal and cerebellar sections from 13 AD and 12 control brains. BACE mRNA amounts were similar in patients and controls. In contrast, ADAM10 mRNA levels were twofold higher in AD samples, but without relationship to the severity of anatomical damage. The data do not support the hypothesis that alteration of BACE and ADAM10 expression are associated with development of late stages of AD.     

Impaired lipoprotein receptor-mediated peripheral binding of plasma amyloid-β is an early biomarker for mild cognitive impairment preceding Alzheimer's disease

Soluble circulating low density lipoprotein receptor-related protein-1 (sLRP) provides key plasma binding activity for Alzheimer's disease (AD) amyloid-β peptide (Aβ). sLRP normally binds 70-90% of plasma Aβ preventing free Aβ access to the brain. In AD, Aβ binding to sLRP is compromised by increased levels of oxidized sLRP which does not bind Aβ. Here, we determined plasma oxidized sLRP and Aβ40/42 sLRP-bound, other proteins-bound and free plasma fractions, cerebrospinal fluid (CSF) tau/Aβ42 ratios, and mini-mental state examination (MMSE) scores in patients with mild cognitive impairment (MCI) who progressed to AD (MCI-AD, n = 14), AD (n = 14) and neurologically healthy controls (n = 14) recruited from the G?teborg MCI study. In MCI-AD patients prior to conversion to AD and AD patients, the respective increases in oxidized sLRP and free plasma Aβ40 and Aβ42 levels were 4.9 and 3.7-fold, 1.8, and 1.7-fold and 4.3 and 3.3-fold (p < 0.05, ANOVA with Tuckey post-hoc test). In MCI-AD and AD patients increases in oxidized sLRP and free plasma Aβ40 and Aβ42 correlated with increases in CSF tau/Aβ42 ratios and reductions in MMSE scores (p < 0.05, Pearson analysis). A heterogeneous group of 'stable' MCI patients that was followed over 2-4 years (n = 24) had normal CSF tau/Aβ42 ratios but increased oxidized sLRP levels (p < 0.05, Student's t test). Data suggests that a deficient sLRP-Aβ binding might precede and correlate later in disease with an increase in the tau/Aβ42 CSF ratio and global cognitive decline in MCI individuals converting into AD, and therefore is an early biomarker for AD-type dementia.     

Aβ3-10重复片段质粒免疫接种AD鼠后对脑内BACE1的影响

目的探讨Aβ3-10重复片段质粒免疫接种3月龄APPswe/PSEN1双转基因(AD)鼠脑内BACE1的影响。方法应用Aβ3-10重复片段质粒免疫3月龄APPswe/PSEN1双转基因鼠,同等剂量的PBS免疫对照组及C57BL/6J组小鼠,各组小鼠均在免疫后2、4、6次后通过RT-PCR法检测BACE1 m RNA水平,Western blotting法检测BACE1/GFAP/NF-κB蛋白水平,免疫组化法观察Aβ1-42脑内分布情况。水迷宫检测其行为学改变。结果在免疫2次后BACE1 m RNA表达水平C57BL/6J组Aβ3-10组对照组(F=4.649,P=0.021);免疫4次Aβ3-10组C57BL/6J组对照组(F=115.683,P=0.001);免疫6次C57BL/6J组Aβ3-10组对照组(F=86.600,P0.001)。BACE1的蛋白表达水平在免疫2、4、6次后C57BL/6J组Aβ3-10组对照组(F=432.843,P0.001;F=57.673,P0.001;F=26.550,P=0.001),NF-κB的蛋白表达水平在免疫2次后C57BL/6J组Aβ3-10组对照组(F=109.127,P0.001);免疫4,6次后Aβ3-10组C57BL/6J组对照组(F=30.301,P0.001;F=129.967,P0.001)。GFAP的蛋白表达水平在免疫2、4、6次后C57BL/6J组Aβ3-10组对照组(F=27.782,P=0.001;F=26.132,P=0.001;F=26.450,P=0.001);Aβ1-42在脑内的分布C57BL/6J组Aβ3-10组对照组(皮质:F=5.395,P=0.021;F=47.135,P=0.000;F=25.306,P=0.000,海马:F=11.023,P=0.002;F=14.936,P=0.001;F=50.132,P=0.000)。总潜伏期C57BL/6J组Aβ3-10组对照组(F=8.938,P=0.016;F=5.745,P=0.04;F=7.073,P=0.017)。结论 Aβ3-10重复片段质粒可以影响脑内BACE1的表达,影响Aβ产生,改善空间记忆能力。     

BACE1 mRNA expression in Alzheimer's disease postmortem brain tissue

β-site AβPP cleaving enzyme 1 (BACE1) catalyses the rate-limiting step for production of amyloid-β (Aβ) peptides, involved in the pathological cascade underlying Alzheimer's disease (AD). Elevated BACE1 protein levels and activity have been reported in AD postmortem brains. Our study explored whether this was due to elevated BACE1 mRNA expression. RNA was prepared from five brain regions in three study groups: controls, individuals with AD, and another neurodegenerative disease group affected by either Parkinson's disease (PD) or dementia with Lewy bodies (DLB). BACE1 mRNA levels were measured using quantitative realtime PCR (qPCR) and analyzed by qbasePLUS using validated stably-expressed reference genes. Expression of glial and neuronal markers (glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE), respectively) were also analyzed to quantify the changing activities of these cell populations in the tissue. BACE1 mRNA levels were significantly elevated in medial temporal and superior parietal gyri, compared to the PD/DLB and/or control groups. Superior frontal gryus BACE1 mRNA levels were significantly increased in the PD/DLB group, compared to AD and control groups. For the AD group, BACE1 mRNA changes were analyzed in the context of the reduced NSE mRNA, and strongly increased GFAP mRNA levels apparent as AD progressed (indicated by Braak stage). This analysis suggested that increased BACE1 mRNA expression in remaining neuronal cells may contribute to the increased BACE1 protein levels and activity found in brain regions affected by AD.     

The relationship of plasma Aβ levels to dementia in aging individuals with mild cognitive impairment

Amyloid β(Aβ) peptides are important components of plaques in Alzheimer's disease(AD). A decrease in the CSF concentration of Aβ40 and Aβ42 is a potential biomarker for incident AD. In contrast, studies on plasma Aβ40 and Aβ42 concentrations have yielded contradictory results. To explore the relationship between plasma Aβ40 and Aβ42 concentrations and AD in aging individuals with mild cognitive impairment (MCI), evaluate the sensitivity and the specificity of plasma Aβ and their ratio as a marker for progression to AD. We measured baseline concentrations of Aβ40 and Aβ42, and their ratio in plasma of patients carefully categorized clinically and neurochemically as having AD or other dementias from a cohort of patients with MCI (n=588) after 4-6 years of follow-up time. Plasma concentrations of Aβ40, Aβ42 were measured using a sandwich enzyme-linked immunosorbent assay technology. The association between plasma Aβ concentrations and the risk of dementia was assessed using Cox proportional hazard models. Optimal sensitivity and specificity of Aβ measurements were determined by ROC curve analysis. Plasma Aβ42 concentration and the Aβ42/Aβ40 ratio at baseline were significantly decreased in the MCI patients who developed AD as compared to cognitively stable MCI patients. The baseline concentrations of Aβ40 were similar in all MCI groups. The Aβ42/Aβ40 ratio was superior to Aβ42 concentration with regard to identify incipient AD in MCI. The ratio of Aβ42 to Aβ40 rather than absolute levels of the peptides can aid in the identification of incipient AD among MCI patients. A potential role of plasma Aβ concentrations as a marker of incipient dementia warrants further investigation.     

Platelets and Alzheimer&rsquo;s disease: Potential of APP as a biomarker

Platelets are the first peripheral source of amyloid precursor protein (APP). They possess the proteolytic machinery to produce Aβ and fragments similar to those produced in neurons, and thus offer an ex-vivo model to study APP processing and changes associated with Alzheimer’s disease (AD). Platelet process APP mostly through the α-secretase pathway to release soluble APP (sAPP). They produce small amounts of Aβ, predominantly Aβ₄₀ over Aβ₄₂. sAPP and Aβ are stored in α-granules and are released upon platelet activation by thrombin and collagen, and agents inducing platelet degranulation. A small proportion of full-length APP is present at the platelet surface and this increases by 3-fold upon platelet activation. Immunoblotting of platelet lysates detects APP as isoforms of 130 kDa and 106-110 kDa. The ratio of these of APP isoforms is significantly lower in patients with AD and mild cognitive impairment (MCI) than in healthy controls. This ratio follows a decrease that parallels cognitive decline and can predict conversion from MCI to AD. Alterations in the levels of α-secretase ADAM10 and in the enzymatic activities of α- and β-secretase observed in platelets of patients with AD are consistent with increased processing through the amyloidogenic pathway. β-APP cleaving enzyme activity is increased by 24% in platelet membranes of patients with MCI and by 17% in those with AD. Reports of changes in platelet APP expression with MCI and AD have been promising so far and merit further investigation as the search for blood biomarkers in AD, in particular at the prodromal stage, remains a priority and a challenge.     

Core candidate neurochemical and imaging biomarkers of Alzheimer’s disease

BackgroundIn the earliest clinical stages of Alzheimer’s disease (AD) when symptoms are mild, clinical diagnosis can be difficult. AD pathology most likely precedes symptoms. Biomarkers can serve as early diagnostic indicators or as markers of preclinical pathologic change. Candidate biomarkers derived from structural and functional neuroimaging and those measured in cerebrospinal fluid (CSF) and plasma show the greatest promise. Unbiased exploratory approaches, eg, proteomics or cortical thickness analysis, could yield novel biomarkers. The objective of this article was to review recent progress in selected imaging and neurochemical biomarkers for early diagnosis, classification, progression, and prediction of AD.MethodsWe performed a survey of recent research, focusing on core biomarker candidates in AD.ResultsA number of in vivo neurochemistry and neuroimaging techniques, which can reliably assess aspects of physiology, pathology, chemistry, and neuroanatomy, hold promise as biomarkers. These neurobiologic measures appear to relate closely to pathophysiologic, neuropathologic, and clinical data, such as hyperphosphorylation of tau, amyloid beta (Aβ) metabolism, lipid peroxidation, pattern and rate of atrophy, loss of neuronal integrity, functional and cognitive decline, as well as risk of future decline. Current advances in the neuroimaging of mediotemporal, neocortical, and subcortical areas of the brain of mild cognitive impairment (MCI) and AD subjects are presented. CSF levels of Aβ42, tau, and hyperphosphorylated tau protein (p-tau) can distinguish subjects with MCI who are likely to progress to AD. They also show preclinical alterations that predict later development of early AD symptoms. Studies on plasma Aβ are not entirely consistent, but recent findings suggest that decreased plasma Aβ42 relative to Aβ40 might increase the risk of AD. Increased production of Aβ in aging is suggested by elevation of BACE1 protein and enzyme activity in the brain and CSF of subjects with MCI. CSF tau and p-tau are increased in MCI as well and show predictive value. Other biomarkers might indicate components of a cascade initiated by Aβ, such as oxidative stress or inflammation. These merit further study in MCI and earlier.ConclusionsA number of neuroimaging candidate markers are promising, such as hippocampus and entorhinal cortex volumes, basal forebrain nuclei, cortical thickness, deformation-based and voxel-based morphometry, structural and effective connectivity by using diffusion tensor imaging, tractography, and functional magnetic resonance imaging. CSF Aβ42, BACE1, total tau, and p-tau are substantially altered in MCI and clinical AD. Other interesting novel marker candidates derived from blood are being currently proposed (phase I). Biomarker discovery through proteomic approaches requires further research. Large-scale international controlled multicenter trials (such as the U.S., European, Australian, and Japanese Alzheimer’s Disease Neuroimaging Initiative and the German Dementia Network) are engaged in phase III development of the core feasible imaging and CSF biomarker candidates in AD. Biomarkers are in the process of implementation as primary outcome variables into regulatory guideline documents regarding study design and approval for compounds claiming disease modification.     

Characterization of plasma β‐secretase (BACE1) activity and soluble amyloid precursor proteins as potential biomarkers for Alzheimer's disease

Reduction in cerebrospinal fluid (CSF) amyloid β42 (Aβ42) and elevation in total tau and phospho‐thr181 tau consistently differentiate between Alzheimer's disease (AD) and age‐matched control subjects. In contrast, CSF β‐site APP‐cleaving enzyme activity (BACE1) and soluble amyloid precursor proteins α and β (sAPPα and sAPPβ) are without consistent patterns in AD subjects. Plasma sampling is much easier, with fewer side effects, and is readily applied in primary care centers, so we have developed and validated novel plasma BACE activity, sAPPβ, and sAPPα assays and investigated their ability to distinguish AD from age‐matched controls. Plasma BACE activity assay was sensitive and specific, with signal being immunodepleted with a specific BACE1 antibody and inhibited with a BACE1‐specific inhibitor. Plasma sAPPβ and sAPPα assays were specific, with signal diluting linearly, immunodepleted with specific antibodies, and at background levels in APP knockout mice. In rhesus monkeys, BACE1 but not γ‐secretase inhibitor led to significant lowering of plasma sAPPβ with concurrent elevation of plasma sAPPα. AD subjects showed a significant increase in plasma BACE1 activity, sAPPβ, sAPPα, and Aβ42 (P < 0.001) compared with age‐matched controls. In conclusion, plasma BACE activity and sAPP endpoints provide novel investigative biomarkers for AD diagnosis and potential pharmacodynamic biomarkers for secretase inhibitor studies. © 2012 Wiley Periodicals, Inc.