Raymond Zinkowski

Longitudinal CSF and MRI biomarkers improve the diagnosis of mild cognitive impairment

The diagnosis of Alzheimers disease (AD) in patients with mild cognitive impairment (MCI) is limited because it is based on non-specific behavioral and neuroimaging findings. The lesions of Alzheimers disease: amyloid beta (Abeta) deposits, tau pathology and cellular oxidative damage, affect the hippocampus in the earlier stages causing memory impairment. In a 2-year longitudinal study of MCI patients and normal controls, we examined the hypothesis that cerebrospinal fluid (CSF) markers for these pathological features improve the diagnostic accuracy over memory and magnetic resonance imaging (MRI)-hippocampal volume evaluations. Relative to control, MCI patients showed decreased memory and hippocampal volumes and elevated CSF levels of hyperphosphorylated tau and isoprostane. These two CSF measures consistently improved the diagnostic accuracy over the memory measures and the isoprostane measure incremented the accuracy of the hippocampal volume achieving overall diagnostic accuracies of about 90%. Among MCI patients, over 2 years, longitudinal hippocampal volume losses were closely associated with increasing hyperphosphorylated tau and decreasing amyloid beta-42 levels. These results demonstrate that CSF biomarkers for AD contribute to the characterization of MCI.

Imaging and CSF Studies in the Preclinical Diagnosis of Alzheimer's Disease

Abstract:  It is widely believed that the path to early and effective treatment for Alzheimers disease (AD) requires the development of early diagnostic markers that are both sensitive and specific. To this aim, using longitudinal study designs, we and others have examined magnetic resonance imaging (MRI), 2‐fluoro‐2‐deoxy‐d‐glucose‐positron emission tomography (FDG/PET), and cerebrospinal fluid (CSF) biomarkers in cognitively normal elderly (NL) subjects and in patients with mild cognitive impairment (MCI). Such investigations have led to the often replicated findings that structural evidence of hippocampal atrophy as determined by MRI, as well as metabolic evidence from FDG‐PET scan of hippocampal damage, predicts the conversion from MCI to AD. In this article we present a growing body of evidence of even earlier diagnosis. Brain pathology can be detected in NL subjects and used to predict future transition to MCI. This prediction is enabled by examinations revealing reduced glucose metabolism in the hippocampal formation (hippocampus and entorhinal cortex [EC]) as well as by the rate of medial temporal lobe atrophy as determined by MRI. However, neither regional atrophy nor glucose metabolism reductions are specific for AD. These measures provide secondary not primary evidence for AD. Consequently, we will also summarize recent efforts to improve the diagnostic specificity by combining imaging with CSF biomarkers and most recently by evaluating amyloid imaging using PET. We conclude that the combined use of conventional imaging, that is MRI or FDG‐PET, with selected CSF biomarkers incrementally contributes to the early and specific diagnosis of AD. Moreover, selected combinations of imaging and CSF biomarkers measures are of importance in monitoring the course of AD and thus relevant to evaluating clinical trials.

MRI and CSF studies in the early diagnosis of Alzheimer's disease.

The main goal of our studies has been to use MRI, FDG‐PET, and CSF biomarkers to identify in cognitively normal elderly (NL) subjects and in patients with mild cognitive impairment (MCI), the earliest clinically detectable evidence for brain changes due to Alzheimers disease (AD). A second goal has been to describe the cross‐sectional and longitudinal interrelationships amongst anatomical, CSF and cognition measures in these patient groups. It is now well known that MRI‐determined hippocampal atrophy predicts the conversion from MCI to AD. In our summarized studies, we show that the conversion of NL subjects to MCI can also be predicted by reduced entorhinal cortex (EC) glucose metabolism, and by the rate of medial temporal lobe atrophy as determined by a semi‐automated regional boundary shift analysis (BSA‐R). However, whilst atrophy rates are predictive under research conditions, they are not specific for AD and cannot be used as primary evidence for AD. Consequently, we will also review our effort to improve the diagnostic specificity by evaluating the use of CSF biomarkers and to evaluate their performance in combination with neuroimaging. Neuropathology studies of normal ageing and MCI identify the hippocampal formation as an early locus of neuronal damage, tau protein pathology, elevated isoprostane levels, and deposition of amyloid beta 1‐42 (Aβ42). Many CSF studies of MCI and AD report elevated T‐tau levels (a marker of neuronal damage) and reduced Aβ42 levels (possibly due to increased plaque sequestration). However, CSF T‐tau and Aβ42 level elevations may not be specific to AD. Elevated isoprostane levels are also reported in AD and MCI but these too are not specific for AD. Importantly, it has been recently observed that CSF levels of P‐tau, tau hyperphosphorylated at threonine 231 (P‐tau231) are uniquely elevated in AD and elevations found in MCI are useful in predicting the conversion to AD. In our current MCI studies, we are examining the hypothesis that elevations in P‐tau231 are accurate and specific indicators of AD‐related changes in brain and cognition. In cross‐section and longitudinally, our results show that evaluations of the P‐tau231 level are highly correlated with reductions in the MRI hippocampal volume and by using CSF and MRI measures together one improves the separation of NL and MCI. The data suggests that by combining MRI and CSF measures, an early (sensitive) and more specific diagnosis of AD is at hand. Numerous studies show that neither T‐tau nor P‐tauX (X refers to all hyper‐phosphorylation site assays) levels are sensitive to the longitudinal progression of AD. The explanation for the failure to observe longitudinal changes is not known. One possibility is that brain‐derived proteins are diluted in the CSF compartment. We recently used MRI to estimate ventricular CSF volume and demonstrated that an MRI‐based adjustment for CSF volume dilution enables detection of a diagnostically useful longitudinal P‐tau231 elevation. Curiously, our most recent data show that the CSF isoprostane level does show significant longitudinal elevations in MCI in the absence of dilution correction. In summary, we conclude that the combined use of MRI and CSF incrementally contributes to the early diagnosis of AD and to monitor the course of AD. The interim results also suggest that a panel of CSF biomarkers can provide measures both sensitive to longitudinal change as well as measures that lend specificity to the AD diagnosis.

Multicenter assessment of CSF- phosphorylated tau for the prediction of conversion of MCI

Background: The measurement of hyperphosphorylated tau (p-tau) in CSF has been proposed as a biomarker candidate for the prediction of Alzheimer disease (AD) in patients with mild cognitive impairment (MCI). However, a standard quantitative criterion of p-tau has not been evaluated. Objective: To assess in a multicenter study the predictive accuracy of an a priori defined criterion of tau phosphorylated at threonine 231 (p-tau231) for the prediction of conversion from MCI to AD during a short-term observation interval. Methods: The study included 43 MCI converters, 45 stable MCI (average follow-up interval = 1.5 years), and 57 healthy controls (at baseline only). Subjects were recruited at four international expert sites in a retrospective study design. Cox regression models stratified according to center were used to predict conversion status. Bootstrapped 95% CIs of classification accuracy were computed. Results: Levels of p-tau231 were a significant predictor of conversion (B = 0.026, p = 0.001), independent of age, gender, Mini-Mental State Examination, and ApoE genotype. For an a priori–defined cutoff point (27.32 pg/mL), sensitivity ranged between 66.7 and 100% and specificity between 66.7 and 77.8% among centers. The bootstrapped mean percentage of correctly classified cases was 79.95% (95% CI = 79.9 to 80.00%). Post hoc defined cutoff values yielded a mean bootstrapped classification accuracy of 80.45% (95% CI = 80.24 to 80.76%). Conclusions: An a priori defined cutoff value of p-tau231 yields relatively stable results across centers, suggesting a good feasibility of a standard criterion of p-tau231 for the prediction of Alzheimer disease.

Longitudinal cerebrospinal fluid tau load increases in mild cognitive impairment.

Cross-sectional cerebrospinal fluid (CSF) levels of tau and amyloid (A) beta (beta) are of diagnostic importance for Alzheimers disease (AD) and mild cognitive impairment (MCI). However, most longitudinal studies of tau fail to demonstrate progression. Because predominantly brain-derived proteins such as tau, have higher ventricle to lumbar ratios, we hypothesized that adjusting for the ventricular enlargement of AD would correct for the dilution of tau, and improve detection of longitudinal change. Abeta which is not exclusively brain derived, shows a ratio <1, and no benefit was expected from adjustment. In a 1 year longitudinal study of eight MCI and ten controls, we examined CSF levels of hyperphosphorylated (P) tau231, Abeta40, and Abeta42. In cross-section, MCI patients showed elevated Ptau231 and Abeta40 levels, and greater ventricular volumes. Longitudinally, only after adjusting for the ventricular volume and only for Ptau231, were increases seen in MCI. Further studies are warranted on mechanisms of tau clearance and on using imaging to interpret CSF studies.

Dissociation between CSF total tau and tau protein phosphorylated at threonine 231 in Creutzfeldt–Jakob disease

To study the potential diagnostic value of abnormally phosphorylated tau protein in Creutzfeldt-Jakob disease (CJD) compared to Alzheimers disease (AD), we determined levels of tau phosphorylated at threonine 231 (p-tau231) and of total tau (t-tau) in cerebrospinal fluid (CSF) of CJD patients, AD patients, and healthy controls (HC). CJD patients showed excessively high t-tau levels but relatively low p-tau(231) concentrations compared to the AD group. t-tau alone yielded the best diagnostic accuracy to differentiate between CJD and AD patients, when compared to p-tau231 and the p-tau231/t-tau ratio (97, 78, and 95% correctly allocated cases, respectively). Our findings indicate a dissociation in the direction of change in CSF levels of t-tau and p-tau231 in CJD when compared to AD.

The effects of normal aging and ApoE genotype on the levels of CSF biomarkers for Alzheimer's disease.

While cerebrospinal fluid (CSF) biomarkers are of use in the prediction and diagnosis of Alzheimers disease our understanding of the background effects of age and the ApoE genotype is limited. Seventy-eight community-based normal volunteers (mean age 60+/-10 years, range 36-86) were examined to determine the relationships between CSF measures of total tau (T-tau), hyperphosphorylated tau (P-tau 231), amyloid beta (Abeta42/Abeta40 ratio), and isoprostane (IP) with age and ApoE genotype. The results showed that age by epsilon4 genotype interactions were found for P-tau231 (beta=1.82; p<0.05) and IP (beta=1.6; p<0.05). T-tau CSF concentration increased with age. The increasing CSF concentrations of P-tau and IP in epsilon4 carriers suggest that early tauopathy and oxidative stress may be related to the increased risk for AD. The data also suggest that T-tau changes are more age dependent than Abeta changes. The evidence that P-tau231 and IP are the earliest markers for the neuronal damage related to AD awaits longitudinal study.

Phosphorylated tau predicts rate of cognitive decline in MCI subjects: A comparative CSF study

A significant increase in hyperphosphorylated tau proteins (P-tau) in CSF has been shown in Alzheimer disease (AD), suggesting potential utility as biologic markers of AD.1 Different subtypes of P-tau proteins perform differently in the discrimination of primary dementia disorders from AD.2 Recently, we have shown that tau phosphorylated at threonine 231 (P-tau231P) correlates with cognitive decline in subjects with mild cognitive impairment (MCI),3 a group at risk for AD.4 Here, we examined in an exploratory study whether different P-tau epitopes differ in their accuracy to predict cognitive deterioration within subjects with MCI. Therefore, previously published results on P-tau231P are again presented briefly for comparison. Moreover, we wished to know whether a combination of different P-tau epitopes is superior to a single P-tau marker for the prediction of cognitive decline. Three P-tau subtypes were measured at baseline in 59 patients with MCI.4 Clinical follow-up was performed in all patients (mean interval 12.27 months, range 6 to 42 months). The mean (SD) age of the MCI patients (28 female) was 72.56 (7.6) years with a mean Mini-Mental State Examination (MMSE) score of 28.0 (1.9). There were 23 healthy control subjects (HC; 14 female; age 60.0 ± 10.1 years; MMSE 29.2 ± 0.7 points). Study subjects were recruited at two centers (Department of Psychiatry, Ludwig Maximilian University, Munich, Germany, and …

Phosphorylated tau 231, memory decline and medial temporal atrophy in normal elders

Little is known whether cerebrospinal fluid (CSF) biomarkers of Alzheimers disease (AD) can predict both memory decline and associated longitudinal medial temporal lobe (MTL) gray matter (GM) reductions in cognitively healthy individuals. Fifty-seven normal elderly subjects received comprehensive evaluation at baseline and 2 years later. The baseline phosphorylated tau(231) (p-tau(231)), total tau, the amyloid beta (Aβ) Aβ42/Aβ40, t-tau/Aβ42 and p-tau(231)/Aβ42 ratios were examined as predictors of memory change and reductions in the global and MTL GM, determined from T1-weighted MRI. Twenty out of 57 participants experienced reduced memory performance at follow-up. The group with decreased memory performance showed higher baseline p-tau(231) (Z=-2.2, p=0.03), lower Aβ42/Aβ40 (t=-2.2 [55], p=0.04) and greater longitudinal MTL GM reductions (t([52])=-2.70, p=0.01). Higher baseline p-tau(231) was also associated with the absolute decrease in memory scores (rho=-0.30, p=0.02) and with longitudinal MTL GM reduction (F([2,52])=4.4, p=0.04, age corrected). Our results indicate that in normal individuals, elevated p-tau(231), a marker of neurofibrillary pathology is related to both a decrease in declarative memory and progressive atrophy of the MTL, suggesting its diagnostic potential in preclinical stage.

Greater Specificity for Cerebrospinal Fluid P-tau231 over P-tau181 in the Differentiation of Healthy Controls from Alzheimer’s Disease

Cerebrospinal fluid (CSF) measures of phosphorylated-tau (P-tau) 231 and P-tau181 are two biomarkers for the identification of tau pathology as related to Alzheimers disease (AD). While both are pathologically validated, their relative diagnostic performances are not well known. This cross-sectional diagnostic study of 87 normal (NL) subjects and 28 AD subjects compared CSF P-tau231 with CSF P-tau181. Logistic regression modeling demonstrated that the P-tau231 was superior to the P-tau181 in the diagnostic classifications. At a fixed 85% sensitivity cutoff, the ROC analysis shows that P-tau231 has greater overall specificity than P-tau181. While both P-tau analytes demonstrated equivalent negative predictive accuracies, P-tau231 yielded significantly fewer false positives. Moreover, P-tau231, but not P-tau181, demonstrated sensitivity to the E4 genotype. A postmortem validation with 9 AD subjects confirmed the superiority of the CSF P-tau231 specificity. This study suggests that P-tau231 has the potential to improve the CSF tau biomarker diagnosis of AD.