Bob Olsson

CSF and blood biomarkers for the diagnosis of Alzheimer's disease: a systematic review and meta-analysis

BACKGROUND Alzheimers disease biomarkers are important for early diagnosis in routine clinical practice and research. Three core CSF biomarkers for the diagnosis of Alzheimers disease (Aβ42, T-tau, and P-tau) have been assessed in numerous studies, and several other Alzheimers disease markers are emerging in the literature. However, there have been no comprehensive meta-analyses of their diagnostic performance. We systematically reviewed the literature for 15 biomarkers in both CSF and blood to assess which of these were most altered in Alzheimers disease. METHODS In this systematic review and meta-analysis, we screened PubMed and Web of Science for articles published between July 1, 1984, and June 30, 2014, about CSF and blood biomarkers reflecting neurodegeneration (T-tau, NFL, NSE, VLP-1, and HFABP), APP metabolism (Aβ42, Aβ40, Aβ38, sAPPα, and sAPPβ), tangle pathology (P-tau), blood-brain-barrier function (albumin ratio), and glial activation (YKL-40, MCP-1, and GFAP). Data were taken from cross-sectional cohort studies as well as from baseline measurements in longitudinal studies with clinical follow-up. Articles were excluded if they did not contain a cohort with Alzheimers disease and a control cohort, or a cohort with mild cognitive impairment due to Alzheimers disease and a stable mild cognitive impairment cohort. Data were extracted by ten authors and checked by two for accuracy. For quality assessment, modified QUADAS criteria were used. Biomarker performance was rated by random-effects meta-analysis based on the ratio between biomarker concentration in patients with Alzheimers disease and controls (fold change) or the ratio between biomarker concentration in those with mild cognitive impariment due to Alzheimers disease and those with stable mild cognitive impairment who had a follow-up time of at least 2 years and no further cognitive decline. FINDINGS Of 4521 records identified from PubMed and 624 from Web of Science, 231 articles comprising 15 699 patients with Alzheimers disease and 13 018 controls were included in this analysis. The core biomarkers differentiated Alzheimers disease from controls with good performance: CSF T-tau (average ratio 2·54, 95% CI 2·44-2·64, p<0·0001), P-tau (1·88, 1·79-1·97, p<0·0001), and Aβ42 (0·56, 0·55-0·58, p<0·0001). Differentiation between cohorts with mild cognitive impairment due to Alzheimers disease and those with stable mild cognitive impairment was also strong (average ratio 0·67 for CSF Aβ42, 1·72 for P-tau, and 1·76 for T-tau). Furthermore, CSF NFL (2·35, 1·90-2·91, p<0·0001) and plasma T-tau (1·95, 1·12-3·38, p=0·02) had large effect sizes when differentiating between controls and patients with Alzheimers disease, whereas those of CSF NSE, VLP-1, HFABP, and YKL-40 were moderate (average ratios 1·28-1·47). Other assessed biomarkers had only marginal effect sizes or did not differentiate between control and patient samples. INTERPRETATION The core CSF biomarkers of neurodegeneration (T-tau, P-tau, and Aβ42), CSF NFL, and plasma T-tau were strongly associated with Alzheimers disease and the core biomarkers were strongly associated with mild cognitive impairment due to Alzheimers disease. Emerging CSF biomarkers NSE, VLP-1, HFABP, and YKL-40 were moderately associated with Alzheimers disease, whereas plasma Aβ42 and Aβ40 were not. Due to their consistency, T-tau, P-tau, Aβ42, and NFL in CSF should be used in clinical practice and clinical research. FUNDING Swedish Research Council, Swedish State Support for Clinical Research, Alzheimers Association, Knut and Alice Wallenberg Foundation, Torsten Söderberg Foundation, Alzheimer Foundation (Sweden), European Research Council, and Biomedical Research Forum.

Exosomes Communicate Protective Messages during Oxidative Stress; Possible Role of Exosomal Shuttle RNA

Background Exosomes are small extracellular nanovesicles of endocytic origin that mediate different signals between cells, by surface interactions and by shuttling functional RNA from one cell to another. Exosomes are released by many cells including mast cells, dendritic cells, macrophages, epithelial cells and tumour cells. Exosomes differ compared to their donor cells, not only in size, but also in their RNA, protein and lipid composition. Methodology/Principal Findings In this study, we show that exosomes, released by mouse mast cells exposed to oxidative stress, differ in their mRNA content. Also, we show that these exosomes can influence the response of other cells to oxidative stress by providing recipient cells with a resistance against oxidative stress, observed as an attenuated loss of cell viability. Furthermore, Affymetrix microarray analysis revealed that the exosomal mRNA content not only differs between exosomes and donor cells, but also between exosomes derived from cells grown under different conditions; oxidative stress and normal conditions. Finally, we also show that exposure to UV-light affects the biological functions associated with exosomes released under oxidative stress. Conclusions/Significance These results argue that the exosomal shuttle of RNA is involved in cell-to-cell communication, by influencing the response of recipient cells to an external stress stimulus.

Recruitment of T cells into bone marrow of ITP patients possibly due to elevated expression of VLA-4 and CX3CR1

In idiopathic thrombocytopenic purpura (ITP), platelets are destroyed in the spleen, liver, and bone marrow (BM) by autoantibodies and cytotoxic T cells. In a DNA microarray screen of peripheral blood T cells, we found that VLA-4, CX3CR1, and CXCR4, involved in T-cell homing, had increased expression in ITP patients compared with controls. However, we only found increased protein expression of VLA-4 on T cells from peripheral blood by flow cytometry. To address a possible recruitment of T cells into the organs involved in platelet destruction, we analyzed T cells in BM. In BM, T-cell surface expression of VLA-4 and CX3CR1 was increased in ITP patients compared with controls. Furthermore, the number of CD3(+) T cells in BM, but not in blood, was increased in ITP patients compared with controls. This finding was confirmed by immunohistochemistry of BM biopsies. The number of regulatory T cells (CD4(+)/CD25(bright)) was decreased in the BM of ITP patients, whereas Fas expression was increased. In conclusion, ITP is associated with accumulation and activation of T cells in the BM. Recruitment of T cells into the target organ (eg, BM) is plausible and may be facilitated through increased VLA-4 and CX3CR1 expression. These molecules might serve as new treatment targets in ITP.

Cerebrospinal Fluid Microglial Markers in Alzheimer’s Disease: Elevated Chitotriosidase Activity but Lack of Diagnostic Utility

Activated microglial cells, which are the resident macrophages of the central nervous system, surround amyloid β-plaques in Alzheimer’s disease (AD) brains. Inflammation including microglial activation may contribute in AD pathogenesis, and biomarkers for this process may thus be of value to study AD pathogenesis and might facilitate development of therapies targeting these cells. We therefore examined cerebrospinal fluid (CSF) biomarkers in patients with AD, other dementias, mild cognitive impairment and in healthy controls. Samples were analyzed for markers with known association to macrophage activity, including chitotriosidase, YKL-40 (CHI3L1, HC gp-39) and chemokine CC motif ligand 2 (CCL2, MCP1). Patients with AD had higher chitotriosidase activity than controls and patients with stable mild cognitive impairment, consistent with the presence of activated microglial cells in AD brains, but with large overlaps between groups. CCL2 and YKL-40 concentrations did not differ among groups. Microglial markers are unlikely to be useful for AD diagnosis, but might be useful for identification of distinct subgroups of patients, and for the development and implementation of drugs targeting microglial pathology.

Microglial markers are elevated in the prodromal phase of Alzheimer's disease and vascular dementia.

Microglia manage immunosurveillance and mediate inflammation, both suggested to be important in Alzheimers disease (AD). The aim of this study was to investigate if microglial markers could differentiate, firstly between AD and controls, and secondly between stable mild cognitive impairment (MCI) and those progressing to AD and vascular dementia (VaD). Furthermore, we investigated if these markers were sufficiently stable to be used in clinical trials. We quantified YKL-40 and sCD14 in cerebrospinal fluid (CSF) from 96 AD patients, 65 healthy controls, and 170 patients with MCI from baseline and over 5.7 years. For the stability analysis, two CSF samples were collected from 52 AD patients with a six-month interval in between. YKL-40, but not sCD14, was significantly elevated in AD compared with healthy controls (p = 0.003). Furthermore, YKL-40 and sCD14 were increased in MCI patients who converted to VaD (p = 0.029 and p = 0.008), but not to AD according to NINCDS-ADRDA. However, when stratified according to CSF levels of tau and Aβ42, YKL-40 was elevated in those with an AD-indicative profile compared with stable MCI with a normal profile (p = 0.037). In addition, YKL-40 and sCD14 were very stable in AD patients with good correlation between time-points (r = 0.94, p = 3.4 × 10-25; r = 0.77, p = 2.0 × 10-11) and the cortical damage marker T-tau. Thus, microglial markers are stable and may be used as safety markers for monitoring CNS inflammation and microglia activation in clinical trials. Moreover, YKL-40 differentiates between AD and controls and between stable MCI to AD and those that convert to AD and VaD.

Differences in gene expression and cytokine levels between newly diagnosed and chronic pediatric ITP

Immune thrombocytopenia (ITP) is an autoimmune disease where platelets are destroyed prematurely. In the majority of children the disease resolves, but in some it becomes chronic. To investigate whether these 2 phases of the disease are molecularly similar or separate entities we performed DNA microarray analysis (GEO accession number: GSE46922) of T-cells from newly diagnosed children and children with chronic ITP. We found complete separation of the gene expression profiles between the 2 phases of the disease. Furthermore, the gene expression levels of several cytokines differed between the 2 phases of the disease. This was also reflected in plasma with increased levels of interleukin (IL)-16 and TNF-related weak inducer of apoptosis and lower levels of IL-4 in newly diagnosed compared with chronic ITP. Thus, our data indicate that chronic ITP in childhood is a separate disease entity, dissimilar in many aspects to the newly diagnosed phase.

Disturbed apoptosis of T-cells in patients with active idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura (ITP) is an organ specific autoimmune disorder in which T-lymphocyte abnormalities have pathogenetic importance. In a DNA microarray screen of CD3+ T-lymphocytes from ITP patients and healthy controls we found an altered expression of genes associated with apoptosis, e.g. A20, caspase-8 and Bax. This together with our previous findings of increased gene expression of Fas, interferon-g and IL-2 receptor beta (IL2RB) indicated an altered activation induced cell death (AICD) of T-cells in ITP. Using a proliferation assay we found that CD3+ lymphocytes from ITP patients were significantly more resistant to dexamethasone induced suppression compared to normal lymphocytes. We also found that cultured CD3+ lymphocytes from ITP patients in remission were more susceptible to apoptosis both in the presence and absence of dexamethasone compared to cells from patient with active ITP and healthy controls, as indicated by increased staining of AnnexinV binding. Our findings suggest that apoptotic resistance of activated T-lymphocytes in patients with active ITP may lead to defective clearance of autoreactive T-lymphocytes through AICD, which might cause a continued immune destruction of platelets. Conversely, a loss of resistance to AICD in ITP patients in remission might be an important mechanism for the achievement of remission.

Biomarker-based dissection of neurodegenerative diseases

The diagnosis of neurodegenerative diseases within neurology and psychiatry are hampered by the difficulty in getting biopsies and thereby validating the diagnosis by pathological findings. Biomarkers for other types of disease have been readily adopted into the clinical practice where for instance troponins are standard tests when myocardial infarction is suspected. However, the use of biomarkers for neurodegeneration has not been fully incorporated into the clinical routine. With the development of cerebrospinal fluid (CSF) biomarkers that reflect pathological events within the central nervous system (CNS), important clinical diagnostic tools are becoming available. This review summarizes the most promising biomarker candidates that may be used to monitor different types of neurodegeneration and protein inclusions, as well as different types of metabolic changes, in living patients in relation to the clinical phenotype and disease progression over time. Our aim is to provide the reader with an updated lexicon on currently available biomarker candidates, how far they have come in development and how well they reflect pathogenic processes in different neurodegenerative diseases. Biomarkers for specific pathogenetic processes would also be valuable tools both to study disease pathogenesis directly in patients and to identify and monitor the effect of novel treatment strategies.

Identification of Adipocyte Genes Regulated by Caloric Intake

CONTEXT Changes in energy intake have marked and rapid effects on metabolic functions, and some of these effects may be due to changes in adipocyte gene expression that precede alterations in body weight. OBJECTIVE The aim of the study was to identify adipocyte genes regulated by changes in caloric intake independent of alterations in body weight. RESEARCH DESIGN AND METHODS Obese subjects given a very low-caloric diet followed by gradual reintroduction of ordinary food and healthy subjects subjected to overfeeding were investigated. Adipose tissue biopsies were taken at multiple time-points, and gene expression was measured by DNA microarray. Genes regulated in the obese subjects undergoing caloric restriction followed by refeeding were identified using two-way ANOVA corrected with Bonferroni. From these, genes regulated by caloric restriction and oppositely during the weight-stable refeeding phase were identified in the obese subjects. The genes that were also regulated, in the same direction as the refeeding phase, in the healthy subjects after overfeeding were defined as being regulated by caloric intake. Results were confirmed using real-time PCR or immunoassay. RESULTS Using a significance level of P < 0.05 for all comparisons, 52 genes were down-regulated, and 50 were up-regulated by caloric restriction and regulated in the opposite direction by refeeding and overfeeding. Among these were genes involved in lipogenesis (ACLY, ACACA, FASN, SCD), control of protein synthesis (4EBP1, 4EBP2), β-oxidation (CPT1B), and insulin resistance (PEDF, SPARC). CONCLUSIONS Metabolic genes involved in lipogenesis, protein synthesis, and insulin resistance are central in the transcriptional response of adipocytes to changes in caloric intake.

Association of sirtuin 1 (SIRT1) gene SNPs and transcript expression levels with severe obesity

Recent studies have reported associations of sirtuin 1 (SIRT1) single nucleotide polymorphisms (SNPs) to both obesity and BMI. This study was designed to investigate association between SIRT1 SNPs, SIRT1 gene expression and obesity. Case‐control analyses were performed using 1,533 obese subjects (896 adults, BMI >40 kg/m2 and 637 children, BMI >97th percentile for age and sex) and 1,237 nonobese controls, all French Caucasians. Two SNPs (in high linkage disequilibrium (LD), r2 = 0.96) were significantly associated with adult obesity, rs33957861 (P value = 0.003, odds ratio (OR) = 0.75, confidence interval (CI) = 0.61–0.92) and rs11599176 (P value: 0.006, OR = 0.74, CI = 0.61–0.90). Expression of SIRT1 mRNA was measured in BMI‐discordant siblings from 154 Swedish families. Transcript expression was significantly correlated to BMI in the lean siblings (r2 = 0.13, P value = 3.36 × 10−7) and lower SIRT1 expression was associated with obesity (P value = 1.56 × 10−35). There was also an association between four SNPs (rs11599176, rs12413112, rs33957861, and rs35689145) and BMI (P values: 4 × 10−4, 6 × 10−4, 4 × 10−4, and 2 × 10−3) with the rare allele associated with a lower BMI. However, no SNP was associated with SIRT1 transcript expression level. In summary, both SNPs and SIRT1 gene expression are associated with severe obesity.