Glial activation and inflammation along the Alzheimer's disease continuum.

BACKGROUND: Neuronal and glial cell interaction is essential for synaptic homeostasis and may be affected in Alzheimer's disease (AD). We measured cerebrospinal fluid (CSF) neuronal and glia markers along the AD continuum, to reveal putative protective or harmful stage-dependent patterns of activation. METHODS: We included healthy controls (n = 36) and Aß-positive (Aß+) cases (as defined by pathological CSF amyloid beta 1-42 (Aß42)) with either subjective cognitive decline (SCD, n = 19), mild cognitive impairment (MCI, n = 39), or AD dementia (n = 27). The following CSF markers were measured: a microglial activation marker-soluble triggering receptor expressed on myeloid cells 2 (sTREM2), a marker of microglial inflammatory reaction-monocyte chemoattractant protein-1 (MCP-1), two astroglial activation markers-chitinase-3-like protein 1 (YKL-40) and clusterin, a neuron-microglia communication marker-fractalkine, and the CSF AD biomarkers (Aß42, phosphorylated tau (P-tau), total tau (T-tau)). Using ANOVA with planned comparisons, or Kruskal-Wallis tests with Dunn's pairwise comparisons, CSF levels were compared between clinical groups and between stages of biomarker severity using CSF biomarkers for classification based on amyloid pathology (A), tau pathology (T), and neurodegeneration (N) giving rise to the A/T/N score. RESULTS: Compared to healthy controls, sTREM2 was increased in SCD (p < .01), MCI (p < .05), and AD dementia cases (p < .001) and increased in AD dementia compared to MCI cases (p < .05). MCP-1 was increased in MCI (p < .05) and AD dementia compared to both healthy controls (p < .001) and SCD cases (p < .01). YKL-40 was increased in dementia compared to healthy controls (p < .01) and MCI (p < .05). All of the CSF activation markers were increased in subjects with pathological CSF T-tau (A+T-N+ and A+T+N+), compared to subjects without neurodegeneration (A-T-N- and A+T-N-). DISCUSSION: Microglial activation as indicated by increased sTREM2 is present already at the preclinical SCD stage; increased MCP-1 and astroglial activation markers (YKL-40 and clusterin) were noted only at the MCI and AD dementia stages, respectively, and in Aß+ cases (A+) with pathological T-tau (N+). Possible different effects of early and later glial activation need to be explored.

Isobaric Quantification of Cerebrospinal Fluid Amyloid-ß Peptides in Alzheimer's Disease: C-Terminal Truncation Relates to Early Measures of Neurodegeneration.

The amyloid beta (Aß) peptide is the main constituent of the plaques characteristic of Alzheimer's disease (AD). Measurement of Aß1-42 in cerebrospinal fluid (CSF) is a valuable marker in AD research, where low levels indicate AD. Although the use of immunoassays measuring Aß1-38 and Aß1-40 in addition to Aß1-42 has increased, quantitative assays of other Aß peptides remain rarely explored. We recently discovered novel Aß peptides in CSF using antibodies recognizing the Aß mid-domain region. Here we have developed a method using both Aß N-terminal and mid-domain antibodies for immunoprecipitation in combination with isobaric labeling and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for relative quantification of endogenous Aß peptides in CSF. The developed method was used in a pilot study to produce Aß peptide profiles from 38 CSF samples. Statistical comparison between CSF samples from 19 AD patients and 19 cognitively healthy controls revealed no significant differences at group level. A significant correlation was found between several larger C-terminally truncated Aß peptides and protein biomarkers for neuronal damage, particularly prominent in the control group. Comparison of the isobaric quantification with immunoassays measuring Aß1-38 or Aß1-40 showed good correlation (r(2) = 0.84 and 0.85, respectively) between the two analysis methods. The developed method could be used to assess disease-modifying therapies directed at Aß production or degradation.

Chronic hyperglycemia reduces substrate oxidation and impairs metabolic switching of human myotubes.

Skeletal muscle of insulin resistant individuals is characterized by lower fasting lipid oxidation and reduced ability to switch between lipid and glucose oxidation. The purpose of the present study was to examine if chronic hyperglycemia would impair metabolic switching of myotubes. Human myotubes were treated with or without chronic hyperglycemia (20mmol/l glucose for 4 days), and metabolism of [(14)C]oleic acid (OA) and [(14)C]glucose was studied. Myotubes exposed to chronic hyperglycemia showed a significantly reduced OA uptake and oxidation to CO(2), whereas acid-soluble metabolites were increased compared to normoglycemic cells (5.5mmol/l glucose). Glucose suppressibility, the ability of acute glucose (5mmol/l) to suppress lipid oxidation, was 50% in normoglycemic cells and reduced to 21% by hyperglycemia. Adaptability, the capacity to increase lipid oxidation with increasing fatty acid availability, was not affected by hyperglycemia. Glucose uptake and oxidation were reduced by about 40% after hyperglycemia, and oxidation of glucose in presence of mitochondrial uncouplers showed that net and maximal oxidative capacities were significantly reduced. Hyperglycemia also abolished insulin-stimulated glucose uptake. Moreover, ATP concentration was reduced by 25% after hyperglycemia. However, none of the measured mitochondrial genes were downregulated nor was mitochondrial DNA content. Microarray and real-time RT-PCR showed that no genes were significantly regulated by chronic hyperglycemia. Addition of chronic lactate reduced both glucose and OA oxidation to the same extent as hyperglycemia. In conclusion, chronic hyperglycemia reduced substrate oxidation in skeletal muscle cells and impaired metabolic switching. The effect is most likely due to an induced mitochondrial dysfunction.

Sequential ADP-stimulated light transmission and multiple electrode aggregometry in patients taking aspirin and clopidogrel after non ST-elevation myocardial infarction.

BACKGROUND: Fast platelet function tests can identify weak clopidogrel responders, but data on variability over time in clopidogrel responsiveness in several clinical settings are lacking. We wanted to explore long-term variability of multiple electrode aggregometry (MEA) measurements and the agreement between MEA and light transmission aggregometry (LTA) in patients with non-ST elevation myocardial infarction (NSTEMI) treated with aspirin and clopidogrel. METHODS: Parallel MEA and LTA were performed at baseline and after 6 and 12 weeks in 31 patients treated with percutaneous coronary intervention after NSTEMI. Adenosine diphosphate (ADP) concentrations 2 µM, 6.5 µM and 10 µM were used. Parallel testings in both arterial and venous blood were performed at baseline. MEA and LTA cut-off levels were applied to discriminate aggregation values suggesting presence or absence of high platelet reactivity (HPR). RESULTS: Arterial and venous MEA and LTA aggregation were similar. Within-subject variability in both MEA and LTA aggregation throughout the study was moderate. According to MEA, eight patients had HPR at baseline (MEA aggregation > 47 U). Defining > 47% as the LTA aggregation HPR cut-off level, the same number of patients (eight) had HPR according to LTA. Of the 93 MEA/LTA observations 81 (87.1%) gave the same HPR classification. MEA vs. LTA agreement at baseline was slightly inferior to that obtained after 12 weeks. CONCLUSIONS: MEA and LTA aggregation in arterial and venous blood seem similar. Within-subject variability over time was moderate, and the agreement between LTA and MEA was good, and stable in most patients.

Increased Glycolysis and Higher Lactate Production in Hyperglycemic Myotubes.

Previous studies have shown that chronic hyperglycemia impairs glucose and fatty acid oxidation in cultured human myotubes. To further study the hyperglycemia-induced suppression of oxidation, lactate oxidation, mitochondrial function and glycolytic rate were evaluated. Further, we examined the intracellular content of reactive oxygen species (ROS), production of lactate and conducted pathway-ANOVA analysis on microarray data. In addition, the roles of the pentose phosphate pathway (PPP) and the hexosamine pathway were evaluated. Lactic acid oxidation was suppressed in hyperglycemic versus normoglycaemic myotubes. No changes in mitochondrial function or ROS concentration were observed. Pathway-ANOVA analysis indicated several upregulated pathways in hyperglycemic cells, including glycolysis and PPP. Functional studies showed that glycolysis and lactate production were higher in hyperglycemic than normoglycaemic cells. However, there were no indications of involvement of PPP or the hexosamine pathway. In conclusion, hyperglycemia reduced substrate oxidation while increasing glycolysis and lactate production in cultured human myotubes.

Cerebrospinal Fluid Levels of Amyloid Beta 1-43 Mirror 1-42 in Relation to Imaging Biomarkers of Alzheimer's Disease.

Introduction: Amyloid beta 1-43 (Aß43), with its additional C-terminal threonine residue, is hypothesized to play a role in early Alzheimer's disease pathology possibly different from that of amyloid beta 1-42 (Aß42). Cerebrospinal fluid (CSF) Aß43 has been suggested as a potential novel biomarker for predicting conversion from mild cognitive impairment (MCI) to dementia in Alzheimer's disease. However, the relationship between CSF Aß43 and established imaging biomarkers of Alzheimer's disease has never been assessed. Materials and Methods: In this observational study, CSF Aß43 was measured with ELISA in 89 subjects; 34 with subjective cognitive decline (SCD), 51 with MCI, and four with resolution of previous cognitive complaints. All subjects underwent structural MRI; 40 subjects on a 3T and 50 on a 1.5T scanner. Forty subjects, including 24 with SCD and 12 with MCI, underwent 18F-Flutemetamol PET. Seventy-eight subjects were assessed with 18F-fluorodeoxyglucose PET (21 SCD/7 MCI and 11 SCD/39 MCI on two different scanners). Ten subjects with SCD and 39 with MCI also underwent diffusion tensor imaging. Results: Cerebrospinal fluid Aß43 was both alone and together with p-tau a significant predictor of the distinction between SCD and MCI. There was a marked difference in CSF Aß43 between subjects with 18F-Flutemetamol PET scans visually interpreted as negative (37 pg/ml, n = 27) and positive (15 pg/ml, n = 9), p < 0.001. Both CSF Aß43 and Aß42 were negatively correlated with standardized uptake value ratios for all analyzed regions; CSF Aß43 average rho -0.73, Aß42 -0.74. Both CSF Aß peptides correlated significantly with hippocampal volume, inferior parietal and frontal cortical thickness and axial diffusivity in the corticospinal tract. There was a trend toward CSF Aß42 being better correlated with cortical glucose metabolism. None of the studied correlations between CSF Aß43/42 and imaging biomarkers were significantly different for the two Aß peptides when controlling for multiple testing. Conclusion: Cerebrospinal fluid Aß43 appears to be strongly correlated with cerebral amyloid deposits in the same way as Aß42, even in non-demented patients with only subjective cognitive complaints. Regarding imaging biomarkers, there is no evidence from the present study that CSF Aß43 performs better than the classical CSF biomarker Aß42 for distinguishing SCD and MCI.

Identification of amyloid beta mid-domain fragments in human cerebrospinal fluid.

Amyloid beta (Aß) is a peptide derived from processing of the membrane bound amyloid precursor protein and is a main constituent in amyloid plaques in Alzheimer's disease (AD). The excess Aß in AD brain may be caused by altered Aß metabolism, including reduced enzymatic degradation. Our previous enzymatic study of Aß degradation revealed that intracellular enzymes produced several truncated Aß mid-domain fragments. We therefore generated an antibody to enable identification of these anticipated Aß species in cerebrospinal fluid (CSF). The produced antibody displayed affinity for the Aß mid-domain region and 36 N-terminally truncated Aß fragments were precipitated from human CSF and identified by liquid chromatography - mass spectrometry. 31 peptides were truncated from residue 18 up to 23, N-terminal truncation that have not previously been identified in CSF. The results show that the complexity of amyloid beta peptides circulating in the CSF is greater than previously suggested and we also demonstrate that the mid-domain antibody used can serve as an additional tool for mapping a more complete Aß degradation profile.