N-Acetyl cysteine blunts proteotoxicity in a heat shock protein-dependent manner

Targeting HSP47 and HSP70: promising therapeutic approaches in liver fibrosis management

Liver fibrosis is a liver disease in which there is an excessive buildup of extracellular matrix proteins, including collagen. By regulating cytokine production and the inflammatory response, heat shock proteins (HSPs) contribute significantly to a wider spectrum of fibrotic illnesses, such as lung, liver, and idiopathic pulmonary fibrosis by aiding in the folding and assembly of freshly synthesized proteins, HSPs serve as chaperones. HSP70 is one of the key HSPs in avoiding protein aggregation which induces its action by sending unfolded and/or misfolded proteins to the ubiquitin–proteasome degradation pathway and antagonizing influence on epithelial-mesenchymal transition. HSP47, on the other hand, is crucial for boosting collagen synthesis, and deposition, and fostering the emergence of fibrotic disorders. The current review aims to provide light on how HSP70 and HSP47 affect hepatic fibrogenesis. Additionally, our review looks into new therapeutic approaches that target HSP70 and HSP47 and could potentially be used as drug candidates to treat liver fibrosis, especially in cases of comorbidities.

Association of heat shock protein A2 expression and sperm quality after N-acetyl-cysteine supplementation in astheno-terato-zoospermic infertile men

In infertile men, reduced expression of heat shock protein A2 (HSPA2) is related to reduced sperm quality and function. The present study has aimed to investigate the effects of N-acetyl-cysteine (NAC) supplementation on expression of heat shock protein A2 (HSPA2). In this study in continuation of previous study, semen samples from 50 astheno-terato-zoospermic men who have received NAC (600 mg/day) orally for three months were evaluated for expression HSPA2 using RT-PCR, and Western blot analysis. In addition, semen samples of these individuals were assessed for sperm parameters, DNA fragmentation (TUNEL), protamine deficiency (CMA3), lipid peroxidation index (MDA) and total antioxidant capacity (TCA). All assessment was carried out before and after NAC treatment. In addition to improved sperm parameters and aforementioned functional parameters, the presented results revealed the significant increase in relative expression levels of HSPA2 was obtained after using NAC treatment (p < .05). Correlation analysis also demonstrated that HSPA2 expression is significantly related to most of the assessed parameters. NAC may directly or indecently impose its beneficial effect through increased expression of HSPA2, which plays a potential role in proper folding of element needed to counteract stress condition in infertile individuals.

Putative neuroprotective pharmacotherapies to target the staged progression of mental illness

AIM

Neuropsychiatric disorders including depression, bipolar and schizophrenia frequently exhibit a neuroprogressive course from prodrome to chronicity. There are a range of agents exhibiting capacity to attenuate biological mechanisms associated with neuroprogression. This review will update the evidence for putative neuroprotective agents including clinical efficacy, mechanisms of action and limitations in current assessment tools, and identify novel agents with neuroprotective potential.

METHOD

Data for this review were sourced from online databases PUBMED, Embase and Web of Science. Only data published since 2012 were included in this review, no data were excluded based on language or publication origin.

RESULTS

Each of the agents reviewed inhibit one or multiple pathways of neuroprogression including: inflammatory gene expression and cytokine release, oxidative and nitrosative stress, mitochondrial dysfunction, neurotrophin dysregulation and apoptotic signalling. Some demonstrate clinical efficacy in preventing neural damage or loss, relapse or cognitive/functional decline. Agents include: the psychotropic medications lithium, second generation antipsychotics and antidepressants; other pharmacological agents such as minocycline, aspirin, cyclooxygenase-2 inhibitors, statins, ketamine and alpha-2-delta ligands; and others such as erythropoietin, oestrogen, leptin, N-acetylcysteine, curcumin, melatonin and ebselen.

CONCLUSIONS

Signals of evidence of clinical neuroprotection are evident for a number of candidate agents. Adjunctive use of multiple agents may present a viable avenue to clinical realization of neuroprotection. Definitive prospective studies of neuroprotection with multimodal assessment tools are required.

N-Acetyl Cysteine Is Associated With Dopaminergic Improvement in Parkinson's Disease

This study assessed the biological and clinical effects in patients with Parkinson's disease (PD) of N-acetyl-cysteine (NAC), the prodrug to l-cysteine, a precursor to the natural biological antioxidant glutathione. Forty-two patients with PD were randomized to either weekly intravenous infusions of NAC (50 mg/kg) plus oral doses (500 mg twice per day) for 3 months or standard of care only. Participants received prebrain and postbrain imaging with ioflupane (DaTscan) to measure dopamine transporter (DAT) binding. In the NAC group, significantly increased DAT binding was found in the caudate and putamen (mean increase from 3.4% to 8.3%) compared with controls (P < 0.05), along with significantly improved PD symptoms (P < 0.0001). The results suggest NAC may positively affect the dopaminergic system in patients with PD, with corresponding positive clinical effects. Larger scale studies are warranted.

Role of HSP70 protein in human periodontal ligament cell function and physiology

OBJECTIVE

Heat pre-treatment of mechanically loaded human periodontal ligament cells (hPDL) dampens the inflammatory cellular response, as evidenced by a reduced expression of pro-inflammatory cytokines, inhibition of monocyte adhesion and osteoclastic differentiation. These findings imply heat shock proteins (HSP) as cell protective molecules acting in the PDL that are up-regulated upon ischemia caused by mechanical loading. HSP70 and its inhibition by VER155008 as the active agent in several pharmaceuticals are established targets and strategies, respectively, in the treatment of neoproliferative diseases. However, the effect of both players on periodontal remodeling in unknown. Therefore, we analyzed the role of HSP70 and its frequently used inhibitor VER155008 in the regulation of physiological hPDL cell functions and immune cell interaction.

MATERIALS AND METHODS

Fifth passage hPDL cells were cultured in the presence of 25μm HSP70 inactivating agent VER155008. At harvest, HSP70 expression, cell proliferation, and parameters of cell interaction, colony formation and wound healing were analyzed by means of real-time PCR, immunohistochemistry, Western blot, biochemical MTS assay, microscopy, and functional assays for monocyte adhesion and differentiation.

RESULTS

Basal HSP70 expression and hPDL cell morphology were not affected by HSP70 inhibitor VER155008. In contrast, cell proliferation, tissue defect healing, and colony formation were reduced significantly following HSP70 inhibition, whereas apoptosis and necrosis, monocyte adhesion and osteoclastic differentiation were markedly increased.

CONCLUSIONS

The present data indicate a regulatory role for HSP70 protein in hPDL cell biology.

CLINICAL RELEVANCE

These findings identify HSP70 as a promising target in the attempt to modify periodontal remodeling and point to potential periodontal side effects of HSP70 pharmaceutical usage.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

N-Acetyl Cysteine May Support Dopamine Neurons in Parkinson's Disease: Preliminary Clinical and Cell Line Data

Backgound

The purpose of this study was to assess the biological and clinical effects of n-acetyl-cysteine (NAC) in Parkinson’s disease (PD).

Methods

The overarching goal of this pilot study was to generate additional data about potentially protective properties of NAC in PD, using an in vitro and in vivo approach. In preparation for the clinical study we performed a cell tissue culture study with human embryonic stem cell (hESC)-derived midbrain dopamine (mDA) neurons that were treated with rotenone as a model for PD. The primary outcome in the cell tissue cultures was the number of cells that survived the insult with the neurotoxin rotenone. In the clinical study, patients continued their standard of care and were randomized to receive either daily NAC or were a waitlist control. Patients were evaluated before and after 3 months of receiving the NAC with DaTscan to measure dopamine transporter (DAT) binding and the Unified Parkinson’s Disease Rating Scale (UPDRS) to measure clinical symptoms.

Results

The cell line study showed that NAC exposure resulted in significantly more mDA neurons surviving after exposure to rotenone compared to no NAC, consistent with the protective effects of NAC previously observed. The clinical study showed significantly increased DAT binding in the caudate and putamen (mean increase ranging from 4.4% to 7.8%; p<0.05 for all values) in the PD group treated with NAC, and no measurable changes in the control group. UPDRS scores were also significantly improved in the NAC group (mean improvement of 12.9%, p = 0.01).

Conclusions

The results of this preliminary study demonstrate for the first time a potential direct effect of NAC on the dopamine system in PD patients, and this observation may be associated with positive clinical effects. A large-scale clinical trial to test the therapeutic efficacy of NAC in this population and to better elucidate the mechanism of action is warranted.

Trial Registration

ClinicalTrials.gov NCT02445651

Synergistic stress exacerbation in hippocampal neurons: Evidence favoring the dual-hit hypothesis of neurodegeneration

The dual-hit hypothesis of neurodegeneration states that severe stress sensitizes vulnerable cells to subsequent challenges so that the two hits are synergistic in their toxic effects. Although the hippocampus is vulnerable to a number of neurodegenerative disorders, there are no models of synergistic cell death in hippocampal neurons in response to combined proteotoxic and oxidative stressors, the two major characteristics of these diseases. Therefore, a relatively high-throughput dual-hit model of stress synergy was developed in primary hippocampal neurons. In order to increase the rigor of the study and strengthen the interpretations, three independent, unbiased viability assays were employed at multiple timepoints. Stress synergy was elicited when hippocampal neurons were treated with the proteasome inhibitor MG132 followed by exposure to the oxidative toxicant paraquat, but only after 48 h. MG132 and paraquat only elicited additive effects 24 h after the final hit and even loss of heat shock protein 70 activity and glutathione did not promote stress synergy at this early timepoint. Dual hits of MG132 elicited modest glutathione loss and slightly synergistic toxic effects 48 h after the second hit, but only at some concentrations and only according to two viability assays (metabolic fitness and cytoskeletal integrity). The thiol N-acetyl cysteine protected hippocampal neurons against dual MG132/MG132 hits but not dual MG132/paraquat hits. These findings support the view that proteotoxic and oxidative stress propel and propagate each other in hippocampal neurons, leading to synergistically toxic effects, but not as the default response and only after a delay. The neuronal stress synergy observed here lies in contrast to astrocytic responses to dual hits, because astrocytes that survive severe proteotoxic stress resist additional cell loss following second hits. In conclusion, a new model of hippocampal vulnerability was developed for the testing of therapies, because neuroprotective treatments that are effective against severe, synergistic stress are more likely to succeed in the clinic. © 2016 Wiley Periodicals, Inc.

Investigation of the therapeutic potential of N-acetyl cysteine and the tools used to define nigrostriatal degeneration in vivo

The glutathione precursor N-acetyl-L-cysteine (NAC) is currently being tested on Parkinson's patients for its neuroprotective properties. Our studies have shown that NAC can elicit protection in glutathione-independent manners in vitro. Thus, the goal of the present study was to establish an animal model of NAC-mediated protection in which to dissect the underlying mechanism. Mice were infused intrastriatally with the oxidative neurotoxicant 6-hydroxydopamine (6-OHDA; 4 μg) and administered NAC intraperitoneally (100mg/kg). NAC-treated animals exhibited higher levels of the dopaminergic terminal marker tyrosine hydroxylase (TH) in the striatum 10d after 6-OHDA. As TH expression is subject to stress-induced modulation, we infused the tracer FluoroGold into the striatum to retrogradely label nigrostriatal projection neurons. As expected, nigral FluoroGold staining and cell counts of FluoroGold(+) profiles were both more sensitive measures of nigrostriatal degeneration than measurements relying on TH alone. However, NAC failed to protect dopaminergic neurons 3 weeks following 6-OHDA, an effect verified by four measures: striatal TH levels, nigral TH levels, nigral TH(+) cell counts, and nigral FluoroGold levels. Some degree of mild toxicity of FluoroGold and NAC was evident, suggesting that caution must be exercised when relying on FluoroGold as a neuron-counting tool and when designing experiments with long-term delivery of NAC--such as clinical trials on patients with chronic disorders. Finally, the strengths and limitations of the tools used to define nigrostriatal degeneration are discussed.

Oxidative stress triggers cytokinesis failure in hepatocytes upon isolation

Primary hepatocytes are highly differentiated cells and proliferatively quiescent. However, the stress produced during liver digestion seems to activate cell cycle entry by proliferative/dedifferentiation programs that still remain unclear. The aim of this work was to assess whether the oxidative stress associated with hepatocyte isolation affects cell cycle and particularly cytokinesis, the final step of mitosis. Hepatocytes were isolated from C57BL/6 mice by collagenase perfusion in the absence and presence of N-acetyl cysteine (NAC). Polyploidy, cell cycle, and reactive oxygen species (ROS) were studied by flow cytometry (DNA, phospho-histone 3, and CellROX(®) Deep Red) and Western blotting (cyclins B1 and D1, and proliferating cell nuclear antigen). mRNA expression of cyclins A1, B1, B2, D1, and F by reverse transcription (RT)-PCR was also assessed. Glutathione levels were measured by mass spectrometry. Here we show that hepatocyte isolation enhanced cell cycle entry, increased hepatocyte binucleation, and caused marked glutathione oxidation. Addition of 5 mM NAC to the hepatocyte isolation media prevented glutathione depletion, partially blocked ROS production and cell cycle entry of hepatocytes, and avoided the blockade of mitosis progression, abrogating defective cytokinesis and diminishing the formation of binucleated hepatocytes during isolation. Therefore, addition of NAC to the isolation media decreased the generation of polyploid hepatocytes confirming that oxidative stress occurs during hepatocyte isolation and it is responsible, at least in part, for cytokinesis failure and hepatocyte binucleation.

Viability assays for cells in culture

Manual cell counts on a microscope are a sensitive means of assessing cellular viability but are time-consuming and therefore expensive. Computerized viability assays are expensive in terms of equipment but can be faster and more objective than manual cell counts. The present report describes the use of three such viability assays. Two of these assays are infrared and one is luminescent. Both infrared assays rely on a 16 bit Odyssey Imager. One infrared assay uses the DRAQ5 stain for nuclei combined with the Sapphire stain for cytosol and is visualized in the 700 nm channel. The other infrared assay, an In-Cell Western, uses antibodies against cytoskeletal proteins (α-tubulin or microtubule associated protein 2) and labels them in the 800 nm channel. The third viability assay is a commonly used luminescent assay for ATP, but we use a quarter of the recommended volume to save on cost. These measurements are all linear and correlate with the number of cells plated, but vary in sensitivity. All three assays circumvent time-consuming microscopy and sample the entire well, thereby reducing sampling error. Finally, all of the assays can easily be completed within one day of the end of the experiment, allowing greater numbers of experiments to be performed within short timeframes. However, they all rely on the assumption that cell numbers remain in proportion to signal strength after treatments, an assumption that is sometimes not met, especially for cellular ATP. Furthermore, if cells increase or decrease in size after treatment, this might affect signal strength without affecting cell number. We conclude that all viability assays, including manual counts, suffer from a number of caveats, but that computerized viability assays are well worth the initial investment. Using all three assays together yields a comprehensive view of cellular structure and function.

N-acetyl cysteine prevents synergistic, severe toxicity from two hits of oxidative stress

The two hit hypothesis of neurodegeneration states that cells that have been severely stressed once are more vulnerable to the negative impact of a second hit. In other words, the toxicity of two hits of severe stress may be synergistic in neurons. We previously developed a two hit model of proteotoxic neurodegeneration using the proteasome inhibitor MG132. In that study, we found that the potent antioxidant N-acetyl cysteine was able to protect against the toxicity associated with dual MG132 hits. N-acetyl cysteine has been shown to ameliorate cognitive deficits in Alzheimer's patients and to reduce the symptoms of blast injury in soldiers. These studies and many others in experimental models of neurodegeneration suggest that N-acetyl cysteine can protect neurons even when they are severely injured. In the present study, we tested the hypotheses that dual hits of hydrogen peroxide and paraquat would elicit synergistic neurodegeneration and that this extreme toxicity would be prevented by N-acetyl cysteine. The findings reveal for the first time that neuronal N2a cells are much more sensitive to oxidative stress from hydrogen peroxide treatment when they have been exposed previously to the same toxin. Two hits of hydrogen peroxide also caused severe loss of glutathione. N-acetyl cysteine attenuated the loss of glutathione and reduced the near-complete loss of cells after exposure to dual hydrogen peroxide hits. The present study supports the notion that N-acetyl cysteine can robustly protect against severe, unremitting oxidative stress in a glutathione-dependent manner.