Alzheimer's disease. Tangle disentanglement

Tolfenamic Acid: A Modifier of the Tau Protein and its Role in Cognition and Tauopathy

BACKGROUND

Tangles are deposits of hyperphosphorylated tau, which are found in multiple neurodegenerative disorders that are referred to as tauopathies, of which Alzheimer's disease (AD) is the most common. Tauopathies are clinically characterized by dementia and share common cortical lesions composed of aggregates of the protein tau.

OBJECTIVE

In this study, we explored the therapeutic potential of tolfenamic acid (TA), in modifying disease processes in a transgenic animal model that carries the human tau gene (hTau).

METHODS

Behavioral tests, Western blotting and Immunohistochemical analysis were used to demonstrate the efficacy of TA.

RESULTS

Treatment of TA improved improving spatial learning deficits and memory impairments in young and aged hTau mice. Western blot analysis of the hTau protein revealed reductions in total tau as well as in sitespecific hyperphosphorylation of tau in response to TA administration. Immunohistochemical analysis for phosphorylated tau protein revealed reduced staining in the frontal cortex, hippocampus, and striatum in animals treated with TA.

CONCLUSION

TA holds the potential as a disease-modifying agent for the treatment of tauopathies including AD.

Tolfenamic acid reduces tau and CDK5 levels: implications for dementia and tauopathies

Tau and its aggregates are linked to the pathology of Alzheimer's disease (AD) and other tauopathies and, therefore, are explored as therapeutic targets for such disorders. Tau belongs to a family of microtubule-associated proteins that promote microtubule assembly. When hyperphosphorylated, tau becomes prone to forming aggregates. Increased brain levels of hyperphosphorylated tau correlate with dementia. Specificity protein 1 (Sp1), a transcription factor elevated in AD, is responsible for the transcription of AD-related proteins including the amyloid precursor protein, tau, and its cyclin-dependent kinase-5 (CDK5) activators. Tolfenamic acid promotes the degradation of Sp1, our previous studies demonstrated its ability to down-regulate transcriptional targets of Sp1 like amyloid precursor protein and reduce amyloid beta (Aβ), the main component of AD plaques. In this study, we administered tolfenamic acid daily to hemizygous R1.40 transgenic mice for 34 days, and examined tau and CDK5 gene and protein expression within the brain. Our results demonstrate that tolfenamic acid lowers tau mRNA and protein, as well as the levels of its phosphorylated form and CDK5. Thus, we present a drug candidate that inhibits the transcription of multiple major intermediates in AD pathology, thereby helping uncover a new mechanism-based approach for targeting AD. A new approach for targeting Alzheimer's disease through a transcriptional based mechanism is presented. Tolfenamic acid lowers the levels of tau, which forms pathological aggregates in Alzheimer's disease and other tauopathies, by promoting the degradation of the transcription factor specificity protein 1 which regulates tau transcription.

Increased AβPP processing in familial Danish dementia patients

An autosomal dominant mutation in the BRI2/ITM2B gene causes Familial Danish Dementia (FDD). We have generated a mouse model of FDD, called FDDKI, genetically congruous to the human disease. These mice carry one mutant and one wild type Bri2/Itm2b allele, like FDD patients. Analysis of FDDKI mice and samples from human patients has shown that the Danish mutation causes loss of Bri2 protein. FDDKI mice show synaptic plasticity and memory impairments. BRI2 is a physiological interactor of amyloid-β protein precursor (AβPP), a gene associated with Alzheimer's disease, which inhibits processing of AβPP. AβPP/Bri2 complexes are reduced in synaptic membranes of FDDKI mice. Consequently, AβPP metabolites derived from processing of AβPP by β-, α-, and γ-secretases are increased in Danish dementia mice. AβPP haplodeficiency prevents memory and synaptic dysfunctions, consistent with a role for AβPP-metabolites in the pathogenesis of memory and synaptic deficits. This genetic suppression provides compelling evidence that AβPP and BRI2 functionally interact. Here, we have investigated whether AβPP processing is altered in FDD patients' brain samples. We find that the levels of several AβPP metabolites, including Aβ, are significantly increased in the brain sample derived from an FDD patient. Our data are consistent with the findings in FDDKI mice, and support the hypothesis that the neurological effects of the Danish form of BRI2 are caused by toxic AβPP metabolites, suggesting that Familial Danish and Alzheimer's dementias share common pathogenic mechanisms.

Paired helical filaments contain small amounts of cholesterol, phosphatidylcholine and sphingolipids

By using qualitative and quantitative high-performance thin layer chromatography (hpTLC) we found lipids associated with purified Alzheimer's (AD) paired helical filaments (PHF) in an amount of 1.4+/-0.2% of the total anhydrous mass. Compared to normal brain tissue these lipids have an unusual lipid class composition. The most prominent lipid classes were phosphatidylcholine (PC), cholesterol (CH), galactocerebrosides (GC) and sphingomyelin (SM). In addition, the use of micro high-performance liquid chromatography (HPLC) in combination with matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) allowed the determination of the molecular species of the polar membrane lipid classes present in PHF. The lipid pattern of intracellular PHF shows many characteristics of the conserved lipid pattern previously described for extracellular amyloid fibrils, suggesting similarities in their pathway of formation.

Hypothalamic digoxin and brain function

BACKGROUND AND OBJECTIVES

The study assessed the biochemical differences between right hemispheric-dominant and left hemispheric-dominant individuals. The chemical hemispheric-dominance in various systemic and neuropsychiatric diseases was also studied.

METHODS

The isoprenoid metabolites, digoxin, dolichol and ubiquinone, glycoconjugate metabolism, free radical metabolism and the RBC membrane composition, were studied in individuals with differing hemispheric-dominance. The digoxin levels and RBC membrane Na+-K+ATPase activity were also studied in systemic and neuropsychiatric diseases.

RESULTS

The results showed that right hemispheric-dominant individuals had elevated digoxin levels, increased free radical production and reduced scavenging, increased tryptophan catabolites and reduced tyrosine catabolites, increased glycoconjugate levels and increased cholesterol : phospholipid ratio of RBC membranes. Left hemispheric-dominant individuals had the opposite patterns. This patterns could be correlated with various systemic and neuropsychiatric diseases.

CONCLUSION

Right hemispheric-dominance represents a hyperdigoxinaemic state with membrane sodium-potassium ATPase inhibition. Left hemispheric-dominance represents the reverse pattern with hypodigoxinaemia and membrane sodium-potassium ATPase stimulation. Hemispheric-dominance could predispose to various systemic and neuropsychiatric diseases.

Hypothalamic digoxin-mediated model for Parkinson's disease

The isoprenoid pathway produces four key metabolites important in cellular function--digoxin (endogenous membrane Na(+)-K+ ATPase inhibitor), dolichol (important in N-glycosylation of proteins), ubiquinone (free-radical scavenger), and cholesterol (component of cellular membranes). This study assessed the changes in the isoprenoid pathway and the consequences of its dysfunction in Parkinson's disease (PD). There was an elevation in plasma HMG CoA reductase activity, serum digoxin and dolichol levels, and a reduction in serum magnesium, RBC membrane Na(+)-K+ ATPase activity, and serum ubiquinone levels. Serum tryptophan, serotonin, strychnine, nicotine, and quinolinic acid were elevated, while tyrosine, morphine, dopamine, and noradrenaline were decreased. The total serum glycosaminoglycans (GAG) and glycosaminoglycan fractions (except chondroitin sulphates and hyaluronic acid), the activity of GAG degrading enzymes, carbohydrate residues of serum glycoproteins, the activity of glycohydrolase-beta galactosidase, and serum glycolipids were elevated. HDL cholesterol was reduced and free fatty acids increased. The RBC membrane glycosaminoglycans, hexose and fucose residues of glycoproteins and cholesterol were reduced, while phospholipid was increased. The activity of all serum free-radical scavenging enzymes, concentration of glutathione, alpha tocopherol, iron binding capacity, and ceruloplasmin decreased significantly in PD, while the concentration of serum lipid peroxidation products and nitric oxide increased. A dysfunctional isoprenoid pathway and related cascade are important in the pathogenesis of Parkinson's disease. A hypothalamic digoxin mediated model for Parkinson's disease is also postulated.

Hypothalamic digoxin, geomagnetic fields and human disease--a hypothesis

The human hypothalamus synthesis an endogenous membrane Na(+)-K(+) ATPase inhibitor, digoxin. A digoxin-mediated model for quantal perception of geomagnetic fields is proposed. External geomagnetic fields can produce membrane Na(+)-K(+) ATPase inhibition. The inhibition of Na(+)-K(+) ATPase can contribute to increase in intracellular calcium and decrease in magnesium, which can result in (1) defective neurotransmitter transport mechanism, (2) neuronal degeneration and apoptosis, (3) mitochondrial dysfunction, (4) defective golgi body function and protein processing dysfunction, (5) immune dysfunction and oncogenesis. Geomagnetic fields can thus regulate cellular function and contributing to the pathogenesis of disease.

Hypothalamic digoxin related membrane Na+-K+ ATPase inhibition and familial basal ganglia calcification

The isoprenoid pathway produces three key metabolites-digoxin (membrane sodium-potassium ATPase inhibitor and regulator of intracellular calcium-magnesium ratios), dolichol (regulator of N-glycosylation of proteins) and ubiquinone (free radical scavenger). The pathway was assessed in a rare and specific type of familial basal ganglia calcification described. The family had a coexistence of basal ganglia calcification (six out of 10 cases), schizophrenia, Parkinson's disease, Alzheimer's disease, rheumatoid arthritis, systemic tumours and syndrome X and were all right hemispheric dominant. The isoprenoid pathway was also studied for comparison in right hemispheric dominant, bihemispheric dominant and left hemispheric dominant individuals. The isoprenoid pathway was upregulated with increased digoxin synthesis in familial basal ganglia calcification. Membrane sodium-potassium ATPase inhibition can lead on to increase in intracellular calcium and calcification of the basal ganglia. There was increase in tryptophan catabolites and a reduction in tyrosine catabolites. There was also an increase in dolichol and glycoconjugate levels with reduced lysosomal stability in these patients. The ubiquinone levels were low and free radical levels increased. The cholesterol-phospholipid ratio was increased and glycoconjugate level of the RBC membrane reduced in these group of patients. No significance difference was noted in family members with and without basal ganglia calcification. This findings were correlated with the pathogenesis of syndrome X, immune mediated diseases, degenerations, tumours and psychiatric disorders noted in the familial basal ganglia calcification described. The biochemical patterns obtained in familial basal ganglia calcification correlated with those in right hemispheric dominance.

Hypothalamic digoxin, hemispheric dominance and the acquired immunodeficiency syndrome

OBJECTIVES

Hypothalamic digoxin, an isoprenoidal metabolite, is an endogenous regulator of membrane Na(+)-K(+) ATPase activity, immune activation and synaptic neurotransmission. The objective of this study was to assess the role of hypothalamic digoxin and hemispheric dominance in the pathogenesis of the acquired immunodeficiency syndrome (AIDS) and in the genesis of sexual orientation.

METHODS

The isoprenoid-pathway-related cascade - (i) isoprenoidal metabolites - digoxin, dolichol and ubiquinone, (ii) tryptophan/tyrosine catabolic patterns, (iii) glycoconjugate metabolism, (iv) free radical metabolism and (v) membrane composition were assessed in AIDS (CDC stage - group IV - subgroup C), individuals with differing hemispheric dominance as well as in individuals with differing sexual orientation. Statistical analysis was done by Student's t test with modified degrees of freedom.

RESULTS

The HMG CoA reductase activity was increased with increased digoxin and dolichol levels and reduced ubiquinone levels in AIDS. The membrane Na(+)-K(+) ATPase activity and serum magnesium levels were reduced. The tryptophan catabolites (serotonin, quinolinic acid, nicotine and strychnine) were increased and the tyrosine catabolites (morphine, dopamine and noradrenaline) were reduced. The serum glycoconjugate metabolites were increased and lysosomal stability was reduced in AIDS. There was reduced incorporation of glycoconjugates into membranes and an increased membrane cholesterol:phospholipid ratio. Lipid peroxidation products and NO were increased while free radical scavenging enzymes and reduced glutathione were reduced. The biochemical patterns obtained in AIDS correlated with those obtained in right-hemispheric dominance and homosexuals/bisexual states.

CONCLUSIONS

Hypothalamic digoxin and right-hemispheric dominance is important in the predisposition to AIDS as well as homosexual/bisexual states.

Effect of human neuronal tau on denaturation and reactivation of rabbit muscle D-glyceraldehyde-3-phosphate dehydrogenase

Human neuronal tau-40 (htau-40) has been used to study denaturation and renaturation of rabbit muscle D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12). Inactivation of GAPDH incubated with tau was more distinguishably detected than that of control GAPDH during thermal and guanidine hydrochloride (GdnHCl) denaturation. However, tau did not influence the activity of GAPDH at room temperature or in solution without GdnHCl. A marked change in both the emission intensity and emission maximum of the intrinsic fluorescence at 335 nm of GAPDH with tau was observed when GdnHCl concentration was 0.8 M, but that of the control without tau occurred in 1.2 M GdnHCl. The first-order rate of the decrease in the fluorescence intensity of the enzyme with tau was approximately twice as great as that of GAPDH without tau. Kinetics of inactivation of GAPDH with tau in 0.2 M GdnHCl was a monophasic procedure, instead of the biphasic procedure followed by the control, as described before [He, Zhao, Yan and Li (1993) Biochim. Biophys. Acta 1163, 315-320]. Similar results were obtained when the enzyme was thermally denatured at 45 degrees C. It revealed that tau bound to the denatured GAPDH but not the native molecule. On the other hand, tau suppressed refolding and reactivation of GAPDH when this enzyme was reactivated by dilution of GdnHCl solution. Furthermore, tau improved the aggregation of the non-native GAPDH in solutions. It suggested that tau acted in an anti-chaperone-like manner towards GAPDH in vitro. However, tau lost that function when it was aggregated or phosphorylated by neuronal cdc2-like protein kinase. It showed that tau's anti-chaperone-like function depended on its native conformation.

Tau promoter activity in neuronally differentiated P19 cells

Tau proteins are encoded by a single gene which is regulated by a unique promoter. The proximal 196 base pairs of the tau 5' flanking region confers tau protein with neuronal specific expression and nerve growth factor inducibility. We tested tau promoter activity in neuronally differentiated embryonal carcinoma cells, the P19 mouse blastoderm cell line. In these experiments, we examined the temporal expression pattern of the tau promoter and compared it to other viral and cellular promoters. Tau promoter activity increases significantly with differentiation, specifically during neurite initiation. In addition, tau promoter activity in neuronally differentiated P19 cells was significantly greater than all five of the other neuronal or non neuronal promoters tested. All other promoters displayed low levels of promoter activity throughout retinoic acid induced neuronal differentiation of P19 cells. Taken together, our results suggest that the tau promoter is a good choice for ectopic expression of exogenous genes in P19 cells, which serves as a differentiating neuronal model system.

Heparin-induced conformational change in microtubule-associated protein Tau as detected by chemical cross-linking and phosphopeptide mapping

In Alzheimer's disease, microtubule-associated protein tau becomes abnormally phosphorylated and aggregates into paired helical filaments. Sulfated glycosaminoglycans such as heparin and heparan sulfate were shown to accumulate in pretangle neurons, stimulate in vitro tau phosphorylation, and cause tau aggregation into paired helical filament-like filaments. The sulfated glycosaminoglycan-tau interaction was suggested to be the central event in the development of neuropathology in Alzheimer's disease brain (Goedert, M., Jakes, R., Spillantini, M. G., Hasegawa, M., Smith, M. J., and Crowther, R. A. (1996) Nature 383, 550-553). The biochemical mechanism by which sulfated glycosaminoglycans stimulate tau phosphorylation and cause tau aggregation remains unclear. In this study, disuccinimidyl suberate (DSS), a bifunctional chemical cross-linker, cross-linked tau dimers, tetramers, high molecular size aggregates, and two tau species of sizes 72 and 83 kDa in the presence of heparin. In the absence of heparin only dimeric tau was cross-linked by DSS. Fast protein liquid chromatography gel filtration revealed that 72- and 83-kDa species were formed by intramolecular cross-linking of tau by DSS. These observations indicate that heparin, in addition to causing aggregation, also induces a conformational change in tau in which reactive groups are unmasked or move closer leading to the DSS cross-linking of 72- and 83-kDa species. Heparin-induced structural changes in tau molecule depended on time of heparin exposure. Dimerization and tetramerization peaked at 48 h, whereas conformational change was completed within 30 min of heparin exposure. Heparin exposure beyond 48 h caused an abrupt aggregation of tau into high molecular size species. Heparin stimulated tau phosphorylation by neuronal cdc2-like kinase (NCLK) and cAMP-dependent protein kinase. Phosphopeptide mapping and phosphopeptide sequencing revealed that tau is phosphorylated by NCLK on Thr212 and Thr231 and by cAMP-dependent protein kinase on Ser262 only in the presence of heparin. Heparin stimulation of tau phosphorylation by NCLK showed dependence on time of heparin exposure and correlated with the heparin-induced conformational change of tau. Our data suggest that heparin-induced conformational change exposes new sites for phosphorylation within tau molecule.

Conformational changes and disease--serpins, prions and Alzheimer's

Some of the most perplexing disorders in medicine are each now known to arise from the conformational instability of an underlying protein. The consequence is a continuum of pathologies with typically a change in fold leading to ordered aggregation and tissue deposition. The serpins provide a structural prototype for these pathologies and give a perspective on the assessment of current proposals as to the conformational basis of both Alzheimer's disease and the transmissible prion encephalopathies.

Conformational disease

Several diverse disorders, including the prevalent dementias and encephalopathies, are now believed to arise from the same general disease mechanism. In each, there is abnormal unfolding and then aggregation of an underlying protein. The gradual accumulation of these aggregates and the acceleration of their formation by stress explain the characteristic late or episodic onset of the clinical disease. The understanding of these processes at the molecular level is opening prospects of more rational approaches to investigation and therapy.