Jan Ricny

Structure and pathology of tau protein in Alzheimer disease.

Alzheimers disease (AD) is the most common type of dementia. In connection with the global trend of prolonging human life and the increasing number of elderly in the population, the AD becomes one of the most serious health and socioeconomic problems of the present. Tau protein promotes assembly and stabilizes microtubules, which contributes to the proper function of neuron. Alterations in the amount or the structure of tau protein can affect its role as a stabilizer of microtubules as well as some of the processes in which it is implicated. The molecular mechanisms governing tau aggregation are mainly represented by several posttranslational modifications that alter its structure and conformational state. Hence, abnormal phosphorylation and truncation of tau protein have gained attention as key mechanisms that become tau protein in a pathological entity. Evidences about the clinicopathological significance of phosphorylated and truncated tau have been documented during the progression of AD as well as their capacity to exert cytotoxicity when expressed in cell and animal models. This paper describes the normal structure and function of tau protein and its major alterations during its pathological aggregation in AD.

7-MEOTA–donepezil like compounds as cholinesterase inhibitors: Synthesis, pharmacological evaluation, molecular modeling and QSAR studies

A novel series of 7-methoxytacrine (7-MEOTA)-donepezil like compounds was synthesized and tested for their ability to inhibit electric eel acetylcholinesterase (EeAChE), human recombinant AChE (hAChE), equine serum butyrylcholinesterase (eqBChE) and human plasmatic BChE (hBChE). New hybrids consist of a 7-MEOTA unit, representing less toxic tacrine (THA) derivative, connected with analogues of N-benzylpiperazine moieties mimicking N-benzylpiperidine fragment from donepezil. 7-MEOTA-donepezil like compounds exerted mostly non-selective profile in inhibiting cholinesterases of different origin with IC50 ranging from micromolar to sub-micromolar concentration scale. Kinetic analysis confirmed mixed-type inhibition presuming that these inhibitors are capable to simultaneously bind peripheral anionic site (PAS) as well as catalytic anionic site (CAS) of AChE. Molecular modeling studies and QSAR studies were performed to rationalize studies from in vitro. Overall, 7-MEOTA-donepezil like derivatives can be considered as interesting candidates for Alzheimers disease treatment.

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 Alzheimers 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.

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 Alzheimers 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.

Lateralization of 17Beta-Hydroxysteroid Dehydrogenase Type 10 in Hippocampi of Demented and Psychotic People

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

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

ObjectiveThe 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.MethodsBulbectomized (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.ResultsKetamine 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.ConclusionsOBX 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.

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 Alzheimers 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.

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 Alzheimers 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.

Interactions between Amyloid-β and Tau in Cerebrospinal Fluid of People with Mild Cognitive Impairment and Alzheimer's Disease

BACKGROUND Despite the physiological sequestration of amyloid-β (Aβ) peptides by various carriers, interactions between peptides and protein tau appear to be pathological and involved in the development of Alzheimers disease (AD). A recent study reported increased Aβ-tau interactions in the neurons of AD patients. OBJECTIVE We investigated the possibility that levels of Aβ-tau complexes in cerebrospinal fluid could be a prospective biomarker of AD, with greater sensitivity and specificity than Aβ1-42, tau, or phospho-tau individually. METHODS By means of ELISA, we estimated levels of the complexes in 161 people (non-demented controls, people with mild cognitive impairment (MCI), probable AD or other types of dementia). RESULTS We found significant reductions in levels in people with MCI due to AD (down to 84.5%) or with AD (down to 80.5%) but not in other types of dementia. The sensitivity of the new biomarker to AD was 68.6%, the specificity 73.3% (compared to controls) or 59.1-66.1% (compared to other types of dementia). No significant correlations were observed between the complexes and the remaining biomarkers or between those and Mini-Mental State Examination score. CONCLUSION We suppose that attenuated levels of complexes in cerebrospinal fluid reflect the accumulation of Aβ bound to tau in AD neurons and that changes start many years before symptom onset, analogously to those in Aβ1-42, tau, or phospho-tau. Unfortunately, these complexes are not a significantly better biomarker of AD than current biomarkers.

Characterization of isolated tau-reactive antibodies from the IVIG product, plasma of patients with Alzheimer's disease and cognitively normal individuals

The presence of natural tau-reactive antibodies was reported in human blood. In this study, we isolated and characterized natural tau-reactive antibodies occurring in IVIG product Flebogamma, plasma of patients with Alzheimers disease (AD) and older cognitively normal persons (controls). Using blotting immunoassays and ELISA, we showed reactivity of antibodies obtained from IVIG and controls against a recombinant fragment of tau (155-421aa) and aggregates present in brains of AD patients. In contrast, antibodies isolated from plasma of AD patients reacted mainly with the recombinant full-length tau form and tau monomeric forms in brain tissue.