Endogenous Modulators of NMDA Receptor Control Dendritic Field Expansion of Cortical Neurons

Impairments of N-methyl-D-aspartate receptor (NMDAR) activity have been implicated in several neuropsychiatric disorders, with pharmacological inhibition of NMDAR-mediated currents and associated neurobehavioral changes considered as a model of schizophrenia. We analyzed the effects of brief and long-term exposure of rat cortical cultures to the most prevalent endogenous modulators of NMDAR (kynurenic acid, pregnenolone sulfate, spermidine, and zinc) on neuronal viability, stimulation-induced release of glutamate, and dendritic morphology with synaptic density. Both, glutamate release and neuronal viability studies revealed no difference between the test and control groups. No differences were also observed in the number of dendritic branching and length, or density of synaptic connections and neuronal soma size. Comparison of the extent of dendritic projections and branching patterns, however, revealed enhanced distal arborization with the expansion of the dendritic area under prolonged treatment of cultures with physiological concentrations of NMDAR modulators, with differences reaching significance in spermidine and pregnenolone sulfate tests. Measurements of the density of glutamatergic synapses showed consistency across all neuronal groups, except those treated with pregnenolone sulfate, which showed a reduction of PSD-95-positive elements. Overall, our data suggest that constitutive glutamatergic activity mediated by NMDAR controls the dendritic field expansion and can influence the integrative properties of cortical neurons.

Autoantibodies targeting neuronal proteins as biomarkers for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are associated with the accumulation of a range of misfolded proteins across the central nervous system and related autoimmune responses, including the generation of antibodies and the activation of immune cells. Both innate and adaptive immunity become mobilized, leading to cellular and humoral effects. The role of humoral immunity in disease onset and progression remains to be elucidated with rising evidence suggestive of positive (protection, repair) and negative (injury, toxicity) outcomes. In this study, we review advances in research of neuron-targeting autoantibodies in the most prevalent NDDs. We discuss their biological origin, molecular diversity and changes in the course of diseases, consider their relevance to the initiation and progression of pathology as well as diagnostic and prognostic significance. It is suggested that the emerging autoimmune aspects of NDDs not only could facilitate the early detection but also might help to elucidate previously unknown facets of pathobiology with relevance to the development of precision medicine.

Interactions of 17β-Hydroxysteroid Dehydrogenase Type 10 and Cyclophilin D in Alzheimer's Disease

The nucleus-encoded 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10) regulates cyclophilin D (cypD) in the mitochondrial matrix. CypD regulates opening of mitochondrial permeability transition pores. Both mechanisms may be affected by amyloid β peptides accumulated in mitochondria in Alzheimer's disease (AD). In order to clarify changes occurring in brain mitochondria, we evaluated interactions of both mitochondrial proteins in vitro (by surface plasmon resonance biosensor) and detected levels of various complexes of 17β-HSD10 formed in vivo (by sandwich ELISA) in brain mitochondria isolated from the transgenic animal model of AD (homozygous McGill-R-Thy1-APP rats) and in cerebrospinal fluid samples of AD patients. By surface plasmon resonance biosensor, we observed the interaction of 17β-HSD10 and cypD in a direct real-time manner and determined, for the first time, the kinetic parameters of the interaction (ka 2.0 × 105 M1s-1, kd 5.8 × 104 s-1, and KD 3.5 × 10-10 M). In McGill-R-Thy1-APP rats compared to controls, levels of 17β-HSD10-cypD complexes were decreased and those of total amyloid β increased. Moreover, the levels of 17β-HSD10-cypD complexes were decreased in cerebrospinal fluid of individuals with AD (in mild cognitive impairment as well as dementia stages) or with Frontotemporal lobar degeneration (FTLD) compared to cognitively normal controls (the sensitivity of the complexes to AD dementia was 92.9%, that to FTLD 73.8%, the specificity to AD dementia equaled 91.7% in a comparison with the controls but only 26.2% with FTLD). Our results demonstrate the weakened ability of 17β-HSD10 to regulate cypD in the mitochondrial matrix probably via direct effects of amyloid β. Levels of 17β-HSD10-cypD complexes in cerebrospinal fluid seem to be the very sensitive indicator of mitochondrial dysfunction observed in neurodegeneration but unfortunately not specific to AD pathology. We do not recommend it as the new biomarker of AD.

Levels of 17β-hydroxysteroid dehydrogenase type 10 in CSF are not a valuable biomarker for multiple sclerosis

Aim: We aimed to characterize the role of mitochondrial 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10) overexpression in multiple sclerosis (MS) and to evaluate its use as a biomarker. Materials & methods: We estimated levels of 17β-HSD10, amyloid β 1–42, cyclophilin D, 17β-HSD10-cyclophilin D complexes or 17β-HSD10-parkin complexes in cerebrospinal fluid (CSF) samples. Results: The increase in 17β-HSD10 levels or in 17β-HSD10-parkin complexes and links to leukocytes were found only in relapsing–remitting MS. The sensitivity of the biomarker was 64%, the specificity equaled 60–63% compared with controls. Conclusion: Increased CSF levels of 17β-HSD10 in later stages of MS could be interpreted via its upregulation in demyelinated neuronal axons. CSF levels of 17β-HSD10 are not the valuable biomarker for the early diagnosis or for the progression of MS.

Inhibitors of Acetylcholinesterase Derived from 7-Methoxytacrine and Their Effects on the Choline Transporter CHT1

BACKGROUND

Reversible acetylcholinesterase inhibitors are used in Alzheimer disease therapy. However, tacrine and its derivatives have severe side effects. Derivatives of the tacrine analogue 7-methoxytacrine (MEOTA) are less toxic.

METHODS

We evaluated new derivatives of 7-MEOTA (2 homodimers linked by 2 C4-C5 chains and 5 N-alkylated C4-C8 side chain derivatives) in vitro, using the rat hippocampal choline transporter CHT1.

RESULTS

Some derivatives were effective inhibitors of rat acetylcholinesterase and comparable with 7-MEOTA. All derivatives were able to inhibit CHT1, probably via quaternary ammonium, and this interaction could be involved in the enhancement of their detrimental side effects and/or in the attenuation of their promising effects. Under conditions of disrupted lipid rafts, the unfavorable effects of some derivatives were weakened. Only tacrine was probably able to stereospecifically interact with the naturally occurring amyloid-β isoform and to simultaneously stimulate CHT1. Some derivatives, when coincubated with amyloid β, did not influence CHT1. All derivatives also increased the fluidity of the cortical membranes.

CONCLUSION

The N-alkylated derivative of 7-MEOTA bearing from C4 side chains appears to be the most promising compound and should be evaluated in future in vivo research.

Changes in concentrations of tau-reactive antibodies are dependent on sex in Alzheimer's disease patients

The presence of pre-existing natural antibodies against Alzheimer's disease (AD) pathological proteins might interfere with immune responses to therapeutic vaccination with these proteins. We aimed to compare levels of antibodies in CSF and serum: We observed higher reactivity of natural tau-reactive antibodies towards phosphorylated bovine tau protein than to human recombinant (non-phosphorylated) tau protein. Males with MCI-AD had higher amounts of these antibodies than corresponding controls. Concentrations of antibodies were lower in females with the MCI-AD than in control females. These findings may have implications for tau vaccination trials.

Purification of Natural Antibodies Against Tau Protein by Affinity Chromatography

Natural antibodies are now widely studied for their therapeutical potential. Therefore, their isolation and subsequent characterization is desired. Here, we describe an isolation method for natural anti-tau antibodies from human plasma by utilization of affinity chromatography with epoxy-activated copolymer resin. The evalution of isolation efficiency and avidity of isolated antibodies is decribed by modified indirect ELISA assay.

Tau Oligomers in Sera of Patients with Alzheimer's Disease and Aged Controls

Although tau protein was long regarded as an intracellular protein with several functions inside the cell, new evidence has shown tau secretion into the extracellular space. The active secretion of tau could be a physiological response of neurons to increased intracellular amounts of tau during the progression of tau pathology. We looked for potential differences in the serum levels of toxic tau oligomers in regards to cognitive impairment of subjects. We detected tau oligomers in the serum of Alzheimer's disease (AD) patients, but they were also present to some extent in the serum of healthy older subjects where the levels positively correlated with aging (Spearman r = 0.26, p = 0.016). On the contrary, we found lower levels of tau oligomers in the serum of mild cognitive impairment (MCI) (p = 0.033) and MCI-AD (p = 0.006) patients. These results could suggest that clearance of extracellular tau proteins takes place, in part, in the periphery. In the case of MCI patients, the lower levels of tau oligomers could be the result of impaired clearance of tau protein from interstitium to blood and consequent accumulation of tau aggregates in the brain.

The pharmacology of tacrine at N-methyl-d-aspartate receptors

The mechanism of tacrine as a precognitive drug has been considered to be complex and not fully understood. It has been reported to involve a wide spectrum of targets involving cholinergic, gabaergic, nitrinergic and glutamatergic pathways. Here, we review the effect of tacrine and its derivatives on the NMDA receptors (NMDAR) with a focus on the mechanism of action and biological consequences related to the Alzheimer's disease treatment. Our findings indicate that effect of tacrine on glutamatergic neurons is both direct and indirect. Direct NMDAR antagonistic effect is often reported by in vitro studies; however, it is achieved by high tacrine concentrations which are not likely to occur under clinical conditions. The impact on memory and behavioral testing can be ascribed to indirect effects of tacrine caused by influencing the NMDAR-mediated currents via M1 receptor activation, which leads to inhibition of Ca²⁺-activated potassium channels. Such inhibition prevents membrane repolarization leading to prolonged NMDAR activation and subsequently to long term potentiation. Considering these findings, we can conclude that tacrine-derivatives with dual cholinesterase and NMDARs modulating activity may represent a promising approach in the drug development for diseases associated with cognitive dysfunction, such as the Alzheimer disease.

Levels of 17β-Hydroxysteroid Dehydrogenase Type 10 in Cerebrospinal Fluid of People with Mild Cognitive Impairment and Various Types of Dementias

BACKGROUND

Overexpression of the mitochondrial enzyme 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10, which is also known as the intracellular amyloid-β peptide (Aβ) binding protein) is observed in cortical or hippocampal regions of patients with Alzheimer's disease (AD). It appears that 17β-HSD10 may play a role in the pathogenesis of AD.

OBJECTIVE

We investigated the possibility that levels of 17β-HSD10 in cerebrospinal fluid could be a prospective biomarker of AD.

METHODS

We estimated the enzyme levels in 161 people (15 non-demented controls, 52 people with mild cognitive impairment (MCI), 35 people with probable AD, or 59 people with other types of dementia) and compared them with those of Aβ(1- 42), tau, and phospho-tau.

RESULTS

We found significantly higher levels of 17β-HSD10 in people with MCI due to AD (to 109.9% ), with AD (to 120.0% ), or with other types of dementia (to 110.9% ) when compared to the control group. The sensitivity of the new biomarker to AD was 80.0% , and the specificity was 73.3% (compared to controls) or 52.5-59.1% (compared to other types of dementia). Results of multiple linear regression and of correlation analysis revealed AD-mediated changes in links between 17β-HSD10 and Mini Mental State Examination score.

CONCLUSION

It seems that changes in 17β-HSD10 start many years before symptom onset, analogous to those in Aβ1 - 42, tau, or phospho-tau and that the levels are a relatively highly sensitive but unfortunately less specific biomarker of AD. A role of 17β-HSD10 overexpression in AD is discussed.

Rapamycin blocks the antidepressant effect of ketamine in task-dependent manner

OBJECTIVE

The aim of our study was to test whether ketamine produces an antidepressant effect in animal model of olfactory bulbectomy and assess the role of mammalian target of rapamycin (mTOR) pathway in ketamine's antidepressant effect.

METHODS

Bulbectomized (OBX) rats and sham controls were assigned to four subgroups according to the treatment they received (ketamine, saline, ketamine + rapamycin, and saline + rapamycin). The animals were subjected to open field (OF), elevated plus maze (EPM), passive avoidance (PA), Morris water maze (MWM), and Carousel maze (CM) tests. Blood samples were collected before and after drug administration for analysis of phosphorylated mTOR level. After behavioral testing, brains were removed for evaluation of brain-derived neurotrophic factor (BDNF) in prefrontal cortex (PFC) and hippocampus.

RESULTS

Ketamine normalized hyperactivity of OBX animals in EPM and increased the time spent in open arms. Rapamycin pretreatment resulted in elimination of ketamine effect in EPM test. In CM test, ketamine + rapamycin administration led to cognitive impairment not observed in saline-, ketamine-, or saline + rapamycin-treated OBX rats. Prefrontal BDNF content was significantly decreased, and level of mTOR was significantly elevated in OBX groups.

CONCLUSIONS

OBX animals significantly differed from sham controls in most of the tests used. Treatment had more profound effect on OBX phenotype than controls. Pretreatment with rapamycin eliminated the anxiolytic and antidepressant effects of ketamine in task-dependent manner. The results indicate that ketamine + rapamycin application resulted in impaired stress responses manifested by cognitive deficits in active place avoidance (CM) test. Intensity of stressor (mild vs. severe) used in the behavioral tests had opposite effect on controls and on OBX animals.

High dietary advanced glycation end products are associated with poorer spatial learning and accelerated Aβ deposition in an Alzheimer mouse model

There is growing evidence of the involvement of advanced glycation end products (AGEs) in the pathogenesis of neurodegenerative processes including Alzheimer's disease (AD) and their function as a seed for the aggregation of Aβ, a hallmark feature of AD. AGEs are formed endogenously and exogenously during heating and irradiation of foods. We here examined the effect of a diet high in AGEs in the context of an irradiated diet on memory, insoluble Aβ₄₂, AGEs levels in hippocampus, on expression of the receptor for AGEs (RAGE), and on oxidative stress in the vasculature. We found that AD‐like model mice on high‐AGE diet due to irradiation had significantly poorer memory, higher hippocampal levels of insoluble Aβ₄₂ and AGEs as well as higher levels of oxidative stress on vascular walls, compared to littermates fed an isocaloric diet. These differences were not due to weight gain. The data were further supported by the overexpression of RAGE, which binds to Aβ₄₂ and regulates its transport across the blood–brain barrier, suggesting a mediating pathway. Because exposure to AGEs can be diminished, these insights provide an important simple noninvasive potential therapeutic strategy for alleviating a major lifestyle‐linked disease epidemic.

Identification and characterization of natural antibodies against tau protein in an intravenous immunoglobulin product

The latest therapeutic approaches to Alzheimer disease are using intravenous immunoglobulin (IVIG) products. Therefore, the detailed characterization of target-specific antibodies naturally occurring in IVIG products is beneficial. We have focused on characterization of antibodies isolated against tau protein, a biomarker of Alzheimer's disease, from Flebogamma IVIG product. The analysis of IgG subclass distribution indicated skewing toward IgG3 in anti-tau-enriched IgG fraction. The evaluation of their reactivity and avidity with several recombinant tau forms was performed by ELISA and blotting techniques. Truncated non-phosphorylated tau protein (amino acids 155-421) demonstrated the highest reactivity and avidity index. We provide the first detailed insight into the reactivity of isolated natural antibodies against tau protein.

Differences Between Tg2576 and Wild Type Mice in the NMDA Receptor-Nitric Oxide Pathway After Prolonged Application of a Diet High in Advanced Glycation End Products

It has been suggested that advanced glycation end (AGE) products, via cognate receptor activation, are implicated in several diseases, including Alzheimer's disease. The NMDA receptor-nitric oxide pathway appears to be influenced by AGE products and involved in the pathogenesis of this type of dementia. In this study, C57BL/6J (WT) and transgenic (Tg2576) mice expressing human mutant amyloid precursor protein were kept on prolonged (8 months) diets containing regular or high amounts of AGE products. After the decapitation of 11-months old mice, brain tissue analyses were performed [expressions of the NR1, NR2A and NR2B subunits of NMDA receptors, activities of neuronal, endothelial and inducible nitric oxide synthase (nNOS, eNOS and iNOS)]. Moreover, levels of malondialdehyde and of human amyloid β 1-42 were estimated. We found increased activity of nNOS in WT mice maintained on a high compared to regular AGE diet; however, no similar differences were found in Tg2576 mice. In addition, we observed an increase in NR1 expression in Tg2576 compared to WT mice, both kept on a diet high in AGE products. Correlation analyses performed on mice kept on the regular AGE diet supported close links between particular subunits (NR2A-NR2B, in WT as well as in Tg2576 mice), between subunits and synthase (NR2A/NR2B-nNOS, only in WT mice) or between particular synthases (nNOS-iNOS, only in WT). Correlation analysis also revealed differences between WT mice kept on both diets (changed correlations between NR2A/NR2B-nNOS, between nNOS-eNOS and between eNOS-iNOS). Malondialdehyde levels were increased in both Tg2576 groups when compared to the corresponding WT mice, but no effects of the diets were observed. Analogously, no significant effects of diets were found in the levels of soluble or insoluble amyloid β 1-42 in Tg2576 mice. Our results demonstrate that prolonged ingestion of AGE products can influence the NMDA receptor-nitric oxide pathway in the brain and that only WT mice, not Tg2576 mice, are able to maintain homeostasis among subunits and synthases or among particular synthases. The prolonged application of AGE products enhanced differences between 11-months old Tg2576 and WT mice regarding this pathway. Observed differences in the pathway between WT mice kept on regular or high AGE diets suggest that the prolonged application of a diet low in AGE products could have beneficial effects in older or diabetic people and perhaps also in people with Alzheimer's disease.

Neurofilament ELISA validation

BACKGROUND

Neurofilament proteins (Nf) are highly specific biomarkers for neuronal death and axonal degeneration. As these markers become more widely used, an inter-laboratory validation study is required to identify assay criteria for high quality performance.

METHODS

The UmanDiagnostics NF-light (R)enzyme-linked immunoabsorbent assays (ELISA) for the neurofilament light chain (NfL, 68kDa) was used to test the intra-assay and inter-laboratory coefficient of variation (CV) between 35 laboratories worldwide on 15 cerebrospinal fluid (CSF) samples. Critical factors, such as sample transport and storage, analytical delays, reaction temperature and time, the laboratories' accuracy and preparation of standards were documented and used for the statistical analyses.

RESULTS

The intra-laboratory CV averaged 3.3% and the inter-laboratory CV 59%. The results from the test laboratories correlated with those from the reference laboratory (R=0.60, p<0.0001). Correcting for critical factors improved the strength of the correlation. Differences in the accuracy of standard preparation were identified as the most critical factor. Correcting for the error introduced by variation in the protein standards improved the correlation to R=0.98, p<0.0001 with an averaged inter-laboratory CV of 14%. The corrected overall inter-rater agreement was subtantial (0.6) according to Fleiss' multi-rater kappa and Gwet's AC1 statistics.

CONCLUSION

This multi-center validation study identified the lack of preparation of accurate and consistent protein standards as the main reason for a poor inter-laboratory CV. This issue is also relevant to other protein biomarkers based on this type of assay and will need to be solved in order to achieve an acceptable level of analytical accuracy. The raw data of this study is available online.

Lateralization of 17beta-hydroxysteroid dehydrogenase type 10 in hippocampi of demented and psychotic people

OBJECTIVE

The multifunctional mitochondrial enzyme 17beta-hydroxysteroid dehydrogenase type 10 could play a role in the development of Alzheimer disease via its high-affinity binding to amyloid-beta peptides and its overexpression.

METHODS

We evaluated the specificity of alterations in mRNA/enzyme expression levels in human right and left hippocampi.

RESULTS

We observed a trend towards right/left laterality in nondemented nonpsychotic controls; however, the degree of asymmetry was higher for mRNA when compared to enzyme expression levels. In Alzheimer disease and schizophrenia, significant shifts to left/right asymmetry were found and the changes were associated with more marked increases in mRNA/enzyme expression in the left hemisphere. On the other hand, no alterations were observed in people with multi-infarct dementia.

CONCLUSION

Our results support studies reporting an impairment of mitochondria in Alzheimer disease or schizophrenia and a higher vulnerability of the dominant hemisphere to pathological processes. Overexpression of the enzyme could be used to distinguish Alzheimer disease from multi-infarct dementia.

Effect of inhaled steroids on cholinergic transmission in human isolated bronchi

Steroids have been found to facilitate cholinergic transmission in skeletal muscle, but possible effects in airways smooth muscles have not been studied. Therefore, choline acetyltransferase (CAT) activity, tissue content of stored acetylcholine and release of newly-synthesized [3H]acetylcholine were were measured in freshly-dissected human bronchi. All lung tissue was obtained from patients with lung cancer at thoracotomy. Group I bronchi were obtained from patients who also suffered from chronic obstructive bronchitis and had been treated for at least 6 weeks before surgery with daily doses of four puffs of flusinolid. Group II bronchi were obtained from patients who did not suffer from chronic obstructive airways disease and had not been treated with steroids. Neither CAT activity (3.1 nmol.h-1.mg protein-1) nor acetylcholine tissue content (260 pmol.100 mg-1), or electrically evoked [3H]acetylcholine release (about 2,000 dpm.100 mg-1) differed in the two groups. This cross sectional study indicates that inhaled steroids do not change cholinergic transmission beyond the level observed in the airways obtained from patients with lung cancer who do not suffer from chronic airways disease and have not been treated with inhaled steroids. This suggests that inhaled steroids can be given chronically without the induction of a facilitatory side-effect on cholinergic transmission within the airways.