Acceleration of oxidative protein folding by curcumin through novel non-redox chemistry

Alleviating Neuroinflammation through Photothermal Conjugated Polymer Nanoparticles by Regulating Reactive Oxygen Species and Ca2+ Signaling

Neuroinflammation is one of the important manifestations of the amyloid β peptide (Aβ) protein-induced neurotoxic signaling pathway in which the aggregation of Aβ causes an increase in reactive oxygen species (ROS) and Ca²⁺ concentration. Here, near-infrared (NIR) photothermal-responsive conjugated polymer nanoparticles were designed to regulate ROS and Ca²⁺ signaling to alleviate neuroinflammation. Under 808 nm laser irradiation, the nanoparticles effectively penetrated the blood-brain barrier (BBB) and reduced the aggregation of Aβ and partially disaggregated the aggregates outside the cell, thereby reducing ROS content which downregulated the oxidative stress damage to cells. Meanwhile, the nanoparticles reduced the concentration of Ca²⁺ by inhibiting the transient receptor potential melastatin-related 2 (TRPM2) ion channel inside the cell. Ultimately, the concentration of inflammatory factor tumor necrosis factor-α was decreased. This study provides an effective strategy to reduce neuroinflammation by simultaneously regulating ROS and Ca²⁺ signaling.

Curcumin, a natural antioxidant, acts as a noncompetitive inhibitor of human RNase L in presence of its cofactor 2-5A in vitro

Ribonuclease L (RNase L) is an antiviral endoribonuclease of the innate immune system, which is induced and activated by viral infections, interferons, and double stranded RNA (dsRNA) in mammalian cells. Although, RNase L is generally protective against viral infections, abnormal RNase L expression and activity have been associated with a number of diseases. Here, we show that curcumin, a natural plant-derived anti-inflammatory active principle, inhibits RNase L activity; hence, it may be exploited for therapeutic interventions in case of pathological situations associated with excess activation of RNase L.

Natural products as promising drug candidates for the treatment of Alzheimer's disease: molecular mechanism aspect

Alzheimer’s disease (AD) is the most common neurodegenerative disorder to date, with no curative or preventive therapy. Histopathological hallmarks of AD include deposition of β-amyloid plaques and formation of neurofibrillary tangles. Extent studies on pathology of the disease have made important discoveries regarding mechanism of disease and potential therapeutic targets. Many cellular changes including oxidative stress, disruption of Ca2+ homeostasis, inflammation, metabolic disturbances, and accumulation of unfolded/misfolded proteins can lead to programmed cell death in AD. Despite intensive research, only five approved drugs are available for the management of AD. Hence, there is a need to look at alternative therapies. Use of natural products and culinary herbs in medicine has gained popularity in recent years. Several natural substances with neuroprotective effects have been widely studied. Most of these compounds have remarkable antioxidant properties and act mainly by scavenging free radical species. Some of them increase cell survival and improve cognition by directly affecting amyloidogenesis and programmed cell death pathways. Further studies on these natural products and their mechanism of action, parallel with the use of novel pharmaceutical drug design and delivery techniques, enable us to offer an addition to conventional medicine. This review discussed some natural products with potential neuroprotective properties against Aβ with respect to their mechanism of action.

Curcumin as a potential treatment for Alzheimer's disease: a study of the effects of curcumin on hippocampal expression of glial fibrillary acidic protein

Curcumin, an agent traditionally utilized for its preventative action against tumorigenesis, oxidation, inflammation, apoptosis and hyperlipemia, has also been used in the treatment of Alzheimer's disease (AD). Recent advances in the study of AD have revealed astrocytes (AS) as being key factors in the early pathophysiological changes in AD. Glial fibrillary acidic protein (GFAP), a marker specific to AS, is markedly more manifest during morphological modifications and neural degeneration signature during the onset of AD. Several studies investigating the functionality of curcumin have shown that it not only inhibits amyloid sedimentation but also accelerates the disaggregation of amyloid plaque. Thus, we are interested in the relationship between curcumin and spatial memory in AD. In this study, we intend to investigate the effects of curcumin in amyloid-β (Aβ(1-40)) induced AD rat models on both the behavioral and molecular levels, that is to say, on their spatial memory and on the expression of GFAP in their hippocampi. Our results were statistically significant, showing that the spatial memory of AD rats improved following curcumin treatment (p < 0.05), and that the expression of GFAP mRNA and the number of GFAP positive cells in the curcumin treated rats was decreased relative to the AD group rats (p < 0.05). Furthermore, the expression level of GFAP mRNA in hippocampal AS in the AD rats significantly increased when compared with that in the sham control (p < 0.05). Taken together, these results suggest that curcumin improves the spatial memory disorders (such disorders being symptomatic of AD) in Aβ(1-40)-induced rats by down regulating GFAP expression and suppressing AS activity.

Curcumin differentially regulates endoplasmic reticulum stress through transcriptional corepressor SMILE (small heterodimer partner-interacting leucine zipper protein)-mediated inhibition of CREBH (cAMP responsive element-binding protein H)

Curcumin (diferuloylmethane), a major active component of turmeric (Curcuma longa), is a natural polyphenolic compound. Herein the effect of curcumin on endoplasmic reticulum (ER) stress responsive gene expression was investigated. We report that curcumin induces transcriptional corepressor small heterodimer partner-interacting leucine zipper protein (SMILE) gene expression through liver kinase B1 (LKB1)/adenosine monophosphate-activated kinase (AMPK) signaling pathway and represses ER stress-responsive gene transcription in an ER-bound transcription factor specific manner. cAMP responsive element-binding protein H (CREBH) and activating transcription factor 6 (ATF6) are both ER-bound bZIP family transcription factors that are activated upon ER stress. Of interest, we observed that both curcumin treatment and SMILE overexpression only represses CREBH-mediated transactivation of the target gene but not ATF6-mediated transactivation. Knockdown of endogenous SMILE significantly releases the inhibitory effect of curcumin on CREBH transactivation. Intrinsic repressive activity of SMILE is observed in the Gal4 fusion system, and the intrinsic repressive domain is mapped to the C terminus of SMILE spanning amino acid residues 203-269, corresponding to the basic region leucine zipper (bZIP) domain. In vivo interaction assay revealed that through its bZIP domain, SMILE interacts with CREBH and inhibits its transcriptional activity. Interestingly, we observed that SMILE does not interact with ATF6. Furthermore, competition between SMILE and the coactivator peroxisome proliferator-activated receptor α (PGC-1α) on CREBH transactivation has been demonstrated in vitro and in vivo. Finally, chromatin immunoprecipitation assays revealed that curcumin decreases the binding of PGC-1α and CREBH on target gene promoter in a SMILE-dependent manner. Overall, for the first time we suggest a novel phenomenon that the curcumin/LKB1/AMPK/SMILE/PGC1α pathway differentially regulates ER stress-mediated gene transcription.

Disulfide-linked protein folding pathways

Determining the mechanism by which proteins attain their native structure is an important but difficult problem in basic biology. The study of protein folding is difficult because it involves the identification and characterization of folding intermediates that are only very transiently present. Disulfide bond formation is thermodynamically linked to protein folding. The availability of thiol trapping reagents and the relatively slow kinetics of disulfide bond formation have facilitated the isolation, purification, and characterization of disulfide-linked folding intermediates. As a result, the folding pathways of several disulfide-rich proteins are among the best known of any protein. This review discusses disulfide bond formation and its relationship to protein folding in vitro and in vivo.