Reduction of glucose metabolism in brain is one of the main features of Alzheimer's disease. Thiamine (vitamin B1)-dependent processes are critical in glucose metabolism and have been found to be impaired in brains from patients with Alzheimer's disease. However, thiamine treatment exerts little beneficial effect in these patients. Here, we tested the effect of benfotiamine, a thiamine derivative with better bioavailability than thiamine, on cognitive impairment and pathology alterations in a mouse model of Alzheimer's disease, the amyloid precursor protein/presenilin-1 transgenic mouse. We show that after a chronic 8 week treatment, benfotiamine dose-dependently enhanced the spatial memory of amyloid precursor protein/presenilin-1 mice in the Morris water maze test. Furthermore, benfotiamine effectively reduced both amyloid plaque numbers and phosphorylated tau levels in cortical areas of the transgenic mice brains. Unexpectedly, these effects were not mimicked by another lipophilic thiamine derivative, fursultiamine, although both benfotiamine and fursultiamine were effective in increasing the levels of free thiamine in the brain. Most notably, benfotiamine, but not fursultiamine, significantly elevated the phosphorylation level of glycogen synthase kinase-3alpha and -3beta, and reduced their enzymatic activities in the amyloid precursor protein/presenilin-1 transgenic brain. Therefore, in the animal Alzheimer's disease model, benfotiamine appears to improve the cognitive function and reduce amyloid deposition via thiamine-independent mechanisms, which are likely to include the suppression of glycogen synthase kinase-3 activities. These results suggest that, unlike many other thiamine-related drugs, benfotiamine may be beneficial for clinical Alzheimer's disease treatment.
In February 2016, the World Health Organization declared a Public Health Emergency of International Concern on Zika Virus (ZIKV), because of its association with severe fetal anomalies of congenitally infected humans. This has led to urgent efforts by academic, federal, and industry research groups to improve our understanding of the pathogenesis of ZIKV and to develop detection methods, therapeutic strategies, and vaccines. Although we still do not have the entire picture of the pathogenesis of ZIKV, extensive research has been conducted on related pathogenic flaviviruses (i.e., dengue virus, West Nile virus, and yellow fever virus). Binding to glycosaminoglycans (GAGs) through its envelope protein is the first step in successful host cell invasion of dengue virus. In this study, we examined ZIKV envelope protein (ZIKV E) binding to GAGs in a real time interaction study using surface plasmon resonance (SPR) to explore the role of GAGs in host cell entry of ZIKV into placenta and brain. ZIKV E strongly binds (K = 443 nM) pharmaceutical heparin (HP), a highly sulfated GAG, and binds with lower avidity to less sulfated GAGs, suggesting that the ZIKV E-GAG interaction may be electrostatically driven. Using SPR competition assays with various chain length HP oligosaccharides (from 4 to 18 saccharide units in length), we observed that ZIKV E preferentially binds to longer HP oligosaccharides (with 8-18 saccharides). Next, we examined GAGs prepared from human placentas to determine if they bound ZIKV E, possibly mediating placental cell invasion of ZIKV. Compositional analysis of these GAGs as well as SPR binding studies showed that both chondroitin sulfate and heparan sulfate GAGs, present on the placenta, showed low-micromolar interactions with ZIKV E. Both porcine brain CS and HS also showed micromolar binding with ZIKV E. Moreover, heparan sulfate with a higher TriS content, the dominant repeating unit of HP, shows a high affinity for ZIKV E. These results suggest that GAGs may be utilized as attachment factors for host cell entry of Zika virus as they do in other pathogenic flaviviruses. They may also assist us in advancing our understanding of the pathogenesis of ZIKV and guide us in designing therapeutics to combat ZIKV with more insight.
Tau aggregates into paired helical filaments within neurons, a pathological hallmark of Alzheimer's disease. Heparin promotes tau aggregation and recently has been shown to be involved in the cellular uptake of tau aggregates. Although the tau-heparin interaction has been extensively studied, little is known about the glycan determinants of this interaction. Here, we used surface plasmon resonance (SPR) and NMR spectroscopy to characterize the interaction between two tau fragments, K18 and K19, and several polysaccharides, including heparin, heparin oligosaccharides, chemically modified heparin, and related glycans. Using a heparin-immobilized chip, SPR revealed that tau K18 and K19 bind heparin with a K of 0.2 and 70 μM, respectively. In SPR competition experiments, N-desulfation and 2-O-desulfation had no effect on heparin binding to K18, whereas 6-O-desulfation severely reduced binding, suggesting a critical role for 6-O-sulfation in the tau-heparin interaction. The tau-heparin interaction became stronger with longer-chain heparin oligosaccharides. As expected for an electrostatics-driven interaction, a moderate amount of salt (0.3 M NaCl) abolished binding. NMR showed the largest chemical-shift perturbation (CSP) in R2 in tau K18, which was absent in K19, revealing differential binding sites in K18 and K19 to heparin. Dermatan sulfate binding produced minimal CSP, whereas dermatan disulfate, with the additional 6-O-sulfo group, induced much larger CSP. 2-O-desulfated heparin induced much larger CSP in K18 than 6-O-desulfated heparin. Our data demonstrate a crucial role for the 6-O-sulfo group in the tau-heparin interaction, which to our knowledge has not been reported before.
Prion‐like transcellular spreading of tau in Alzheimer's Disease (AD) is mediated by tau binding to cell surface heparan sulfate (HS). However, the structural determinants for tau–HS interaction are not well understood. Microarray and SPR assays of structurally defined HS oligosaccharides show that a rare 3‐O‐sulfation (3‐O‐S) of HS significantly enhances tau binding. In Hs3st1−/− (HS 3‐O‐sulfotransferase‐1 knockout) cells, reduced 3‐O‐S levels of HS diminished both cell surface binding and internalization of tau. In a cell culture, the addition of a 3‐O‐S HS 12‐mer reduced both tau cell surface binding and cellular uptake. NMR titrations mapped 3‐O‐S binding sites to the microtubule binding repeat 2 (R2) and proline‐rich region 2 (PRR2) of tau. Tau is only the seventh protein currently known to recognize HS 3‐O‐sulfation. Our work demonstrates that this rare 3‐O‐sulfation enhances tau–HS binding and likely the transcellular spread of tau, providing a novel target for disease‐modifying treatment of AD and other tauopathies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.