Tanshinone IIA, the key compound in Salvia miltiorrhiza, improves cognitive impairment by upregulating Aß-degrading enzymes in APP/PS1 mice.

In Alzheimer's disease (AD), amyloid-beta (Aß) plays a crucial role in pathogenesis. Clearing Aß from the brain is considered as a key therapeutic strategy. Previous studies indicated that Salvia miltiorrhiza (Danshen) could protect against AD. However, the main anti-AD components in Danshen and their specific mechanisms are not clear. In this study, pharmacological network analysis indicated that Tanshinone IIA (Tan IIA) was identified as the key active compound in Danshen contributing to protect against AD. Then, APP/PS1 double transgenic mice were employed to examine the neuroprotective effect of Tan IIA. APP/PS1 mice (age, 6 months) were administered (10 and 20 mg/kg) for 8 weeks. Tan IIA improved learning and anxiety behaviors in APP/PS1 mice. Furthermore, Tan IIA reduced oxidative stress, inhibited neuronal apoptosis, improved cholinergic nervous system and decreased endoplasmic reticulum stress in the brain of APP/PS1 mice. Moreover, Tan IIA treatment reduced the level of Aß. Molecular docking result showed that Tan IIA might block AD by upregulating Aß-degrading enzymes. Western blot results confirmed that the expressions of insulin degrading enzymes (IDE) and neprilysin (NEP) were significantly increased after Tan IIA treatment, which demonstrated that Tan IIA improved AD by increasing Aß-degrading enzymes.

Amyloid beta peptide-degrading microbial enzymes and its implication in drug design.

Alzheimer's disease (AD) is a chronic and progressive neurological brain disorder. AD pathophysiology is mainly represented by formation of neuritic plaques and neurofibrillary tangles (NFTs). Neuritic plaques are made up of amyloid beta (Aß) peptides, which play a central role in AD pathogenesis. In AD brain, Aß peptide accumulates due to overproduction, insufficient clearance and defective proteolytic degradation. The degradation and cleavage mechanism of Aß peptides by several human enzymes have been discussed previously. In the mean time, numerous experimental and bioinformatics reports indicated the significance of microbial enzymes having potential to degrade Aß peptides. Thus, there is a need to shift the focus toward the substrate specificity and structure-function relationship of Aß peptide-degrading microbial enzymes. Hence, in this review, we discussed in vitro and in silico studies of microbial enzymes viz. cysteine protease and zinc metallopeptidases having ability to degrade Aß peptides. In silico study showed that cysteine protease can cleave Aß peptide between Lys16-Cys17; similarly, several other enzymes also showed capability to degrade Aß peptide at different sites. Thus, this review paves the way to explore the role of microbial enzymes in Aß peptide degradation and to design new lead compounds for AD treatment.

Fish oil protects the blood-brain barrier integrity in a mouse model of Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is ranked as the most prevalent neurodegenerative disease. However, the exact molecular mechanisms underlying pathophysiological alterations in AD remain unclear, especially at the prodromal stage. The decreased proteolytic degradation of Aß, blood-brain barrier (BBB) disruption, and neuroinflammation are considered to play key roles in the course of AD. METHODS: Male APPswe/PS1dE9 C57BL/6 J double-transgenic (APP/PS1) mice in the age range from 1 month to 6 months and age-matched wild type mice were used in this study, intending to investigate the expression profiles of Aß-degrading enzymes for Aß degradation activities and zonula occludens-1 (zo-1) for BBB integrity at the prodromal stage. RESULTS: Our results showed that there were no significant genotype-related alterations in mRNA expression levels of 4 well-characterized Aß-degrading enzymes in APP/PS1 mice within the ages of 6 months. Interestingly, a significant decrease in zo-1 expression was observed in APP/PS1 mice starting from the age of 5 months, suggesting that BBB disrupt occurs at an early stage. Moreover, treatment of fish oil (FO) for 4 weeks remarkably increased zo-1 expression and significantly inhibited the glial activation and NF-κB activation in APP/PS1 mice. CONCLUSION: The results of our study suggest that FO supplement could be a potential therapeutic early intervention for AD through protecting the BBB integrity and suppressing glial and NF-κB activation.

Sodium tanshinone IIA sulfonate protects against Aß1-42-induced cellular toxicity by modulating Aß-degrading enzymes in HT22 cells.

ß-Amyloid (Aß) plays an important role in the pathogenesis of Alzheimer's disease (AD). However, there is still no effective Aß-targeting drugs for AD treatment. In this study, we explored the effect and mechanism of Sodium Tanshinone IIA Sulfonate (STS) on AD. Aß-treated HT22 cells, an immortalized mouse hippocampal neuronal cell line, were employed. Different dosages of STS (0.1, 1 and 10 µM) were selected. STS improved cell viability and protected against Aß-induced apoptosis in a dose-dependent manner. Furthermore, the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) were decreased, while the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were significantly increased after STS treatment. STS decreased the levels of phosphorylate PKR-like (p-PERK), phosphorylate eukaryotic initiation factor 2 (p-eIF2α), phosphorylate inositol-requiring enzyme (p-IRE1α), X-box binding protein 1 (XBP1) and binding immunoglobulin heavy chain protein (Bip), while increased protein disulfide isomerase (PDI) levels in Aß-treated HT22 cells. In addition, the levels of insulin degrading enzymes (IDE) and Nepterrilysin (NEP) (or call it CD10) were significantly increased after STS treatment. Taken together, these results indicated that STS might be effective in treating AD via increasing the levels of Aß-degrading enzymes.

Heterozygous CX3CR1 Deficiency in Microglia Restores Neuronal ß-Amyloid Clearance Pathways and Slows Progression of Alzheimer's Like-Disease in PS1-APP Mice.

CX3CR1 is a chemokine receptor expressed on microglia that binds Fractalkine (CX3CL1) and regulates microglial recruitment to sites of neuroinflammation. Full deletion of CX3CR1 in mouse models of Alzheimer's disease have opposing effects on amyloid-ß and tau pathologies raising concerns about the benefits of targeting CX3CR1 for treatment of this disease. Since most therapies achieve only partial blockade of their targets, we investigated the effects of partial CX3CR1 deficiency on the development and progression of amyloid-ß deposition in the PS1-APP Alzheimer's mouse model. We generated PS1-APP mice heterozygous for CX3CR1 (PS1-APP-CX3CR1+/-) and analyzed these mice for Alzheimer's-like pathology. We found that partial CX3CR1 deficiency was associated with a significant reduction in Aß levels and in senile-like plaque load in the brain as compared with age-matched PS1-APP mice. Reduced Aß level in the brain was associated with improved cognitive function. Levels of the neuronal-expressed Aß-degrading enzymes insulysin and matrix metalloproteinase 9, which are reduced in the brains of regular PS1-APP mice, were significantly higher in PS1-APP-CX3CR1+/- mice. Our data indicate that lowering CX3CR1 levels or partially inhibiting its activity in the brain may be a therapeutic strategy to increase neuronal Aß clearance, reduce Aß levels and delay progression of Alzheimer's-Like disease. Our findings also suggest a novel pathway where microglial CX3CR1 can regulates gene expression in neurons.

Neuroprotective mechanism of Kai Xin San: upregulation of hippocampal insulin-degrading enzyme protein expression and acceleration of amyloid-beta degradation.

Kai Xin San is a Chinese herbal formula composed of Radix Ginseng, Poria, Radix Polygalae and Acorus Tatarinowii Rhizome. It has been used in China for many years for treating amnesia. Kai Xin San ameliorates amyloid-ß (Aß)-induced cognitive dysfunction and is neuroprotective in vivo, but its precise mechanism remains unclear. Expression of insulin-degrading enzyme (IDE), which degrades Aß, is strongly correlated with cognitive function. Here, we injected rats with exogenous Aß42 (200 µM, 5 µL) into the hippocampus and subsequently administered Kai Xin San (0.54 or 1.08 g/kg/d) intragastrically for 21 consecutive days. Hematoxylin-eosin and Nissl staining revealed that Kai Xin San protected neurons against Aß-induced damage. Furthermore, enzyme-linked immunosorbent assay, western blot and polymerase chain reaction results showed that Kai Xin San decreased Aß42 protein levels and increased expression of IDE protein, but not mRNA, in the hippocampus. Our findings reveal that Kai Xin San facilitates hippocampal Aß degradation and increases IDE expression, which leads, at least in part, to the alleviation of hippocampal neuron injury in rats.

Clearance of cerebral Aß in Alzheimer's disease: reassessing the role of microglia and monocytes.

Deficiency in cerebral amyloid ß-protein (Aß) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer's disease (AD). Accumulation of misfolded Aß in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aß is a complex process mediated by various systems and cell types, including vascular transport across the blood-brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aß fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aß pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aß burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aß-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aß clearance with an emphasis on the role of peripheral monocytes and macrophages in Aß removal.