Potent Upregulation of Glutathione and NAD(P)H:Quinone Oxidoreductase 1 by Alpha-lipoic Acid in Human Neuroblastoma SH-SY5Y Cells: Protection Against Neurotoxicant-elicited Cytotoxicity

Neuroprotective potential of traditionally used medicinal plants of Manipur against rotenone-induced neurotoxicity in SH-SY5Y neuroblastoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Alternanthera sessilis (L.) R. Br. ex DC., Eryngium foetidum L., and Stephania japonica (Thunb.) Miers plants are traditionally used to treat various central nervous system disorders like paralysis, epilepsy, seizure, convulsion, chronic pain, headache, sleep disturbances, sprain, and mental disorders. However, their possible neuroprotective effects have not been evaluated experimentally so far.

AIM OF THE STUDY

The study aims to examine the neuroprotective potential of the three plants against cytotoxicity induced by rotenone in SH-SY5Y neuroblastoma cells and assess its plausible mechanisms of neuroprotection.

MATERIALS AND METHODS

The antioxidant properties of the plant extracts were determined chemically by DPPH and ABTS assay methods. The cytotoxicity of rotenone and the cytoprotective activities of the extracts were evaluated using MTT assays. Microtubule-associated protein 2 (MAP2) expression studies in cells were performed to assess neuronal survival after rotenone and extract treatments. Mitochondrial membrane potential and intracellular levels of reactive oxygen species were evaluated using Rhodamine 123 and DCF-DA dye, respectively. Catalase, glutathione peroxidase, and superoxide dismutase activities were also measured. Apoptotic nuclei were examined using DAPI staining. Liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS) analysis of the plant extracts was also performed.

RESULTS

The methanol extracts of A. sessilis, S. japonica, and E. foetidum showed excellent free radical scavenging activities. MAP2 expression studies show that A. sessilis and S. japonica have higher neuroprotective effects against rotenone-induced neurotoxicity in SH-SY5Y cells than E. foetidum. Pre-treating cells with the plant extracts reverses the rotenone-induced increase in intracellular ROS. The plant extracts could also restore the reduced mitochondrial membrane potential induced by rotenone treatment and reinstate rotenone-induced increases in catalase, glutathione peroxidase, and superoxide dismutase activities. All the extracts inhibited rotenone-induced changes in nuclear morphology and DNA condensation, an early event of cellular apoptosis. LC-QTOF-MS analysis of the plant extracts shows the presence of neuroprotective compounds.

CONCLUSIONS

The plant extracts showed neuroprotective activities against rotenone-treated SH-SY5Y cells through antioxidant and anti-apoptotic mechanisms. These findings support the ethnopharmacological uses of these plants in treating neurological disorders. They probably are a good source of neuroprotective compounds that could be further explored to develop treatment strategies for neurodegenerative diseases like Parkinson's disease.

Evaluating the Antioxidant Properties of the Ancient-Crop Tef (Eragrostis tef) Grain Extracts in THP-1 Monocytes

Tef (Eragrostis tef) is an orphan crop that is widely grown in East Africa, primarily in Ethiopia as a staple crop. It is becoming popular in the Western world owing to its nutritious and gluten-free grains and the forage quality of its biomass. Tef is also considered to have a high antioxidant capacity based on cell-free studies. However, the antioxidant activity of tef has never been validated using a physiologically relevant cell model. The purpose of this study was to investigate the antioxidant capacity of tef grain extracts using a mammalian cell model. We hypothesized that the tef grain extracts are capable of modulating the cellular antioxidant response via the modulation of glutathione (GSH) biosynthetic pathways. Therefore, we evaluated the antioxidant activity of purified tef grain extracts in the human acute monocytic leukemia (THP-1) cell line. Our findings revealed that the organic fraction of grain extracts increased the cellular GSH level, which was more evident for brown-colored tef than the ivory variety. Moreover, a brown-tef fraction increased the expressions of GSH-pathway genes, including γ-glutamate cysteine ligase catalytic (GCLC) and modifier (GCLM) subunits and glutathione reductase (GR), an enzyme that plays a key role in GSH biosynthesis, suggesting that tef extracts may modulate GSH metabolism. Several compounds were uniquely identified via mass spectrometry (MS) in GSH-modulating brown-tef samples, including 4-oxo-β-apo-13-carotenone, γ-linolenic acid (methyl ester), 4,4'-(2,3-dimethyl-1,4-butanediyl)bis-phenol (also referred to as 8,8'-lignan-4,4'-diol), and (3β)-3-[[2-[4-(Acetylamino)phenoxy]acetyl]oxy]olean-12-en-28-oic acid. Tef possesses antioxidant activity due to the presence of phytochemicals that can act as direct antioxidants, as well as modulators of antioxidant-response genes, indicating its potential role in alleviating diseases triggered by oxidative stresses. To the best of our knowledge, this is the first report revealing the antioxidant ability of tef extracts in a physiologically relevant human cell model.

Utilizing feline oral squamous cell carcinoma patients to develop NQO1-targeted therapy

Developing effective therapies for the treatment of advanced head-and-neck squamous cell carcinoma (HNSCC) remains a major challenge, and there is a limited landscape of effective targeted therapies on the horizon. NAD(P)H:quinone oxidoreductase 1 (NQO1) is a 2-electron reductase that is overexpressed in HNSCC and presents as a promising target for the treatment of HNSCC. Current NQO1-targeted drugs are hindered by their poor oxidative tolerability in human patients, underscoring a need for better preclinical screening for oxidative toxicities for NQO1-bioactivated small molecules. Herein, we describe our work to include felines and feline oral squamous cell carcinoma (FOSCC) patients in the preclinical assessment process to prioritize lead compounds with increased tolerability and efficacy prior to full human translation. Specifically, our data demonstrate that IB-DNQ, an NQO1-targeted small molecule, is well-tolerated in FOSCC patients and shows promising initial efficacy against FOSCC tumors in proof-of-concept single agent and radiotherapy combination cohorts. Furthermore, FOSCC tumors are amenable to evaluating a variety of target-inducible couplet hypotheses, evidenced herein with modulation of NQO1 levels with palliative radiotherapy. The use of felines and their naturally-occurring tumors provide an intriguing, often underutilized tool for preclinical drug development for NQO1-targeted approaches and has broader applications for the evaluation of other anticancer strategies.

The ying and yang of idebenone: Not too little, not too much - cell death in NQO1 deficient cells and the mouse retina

Idebenone has recently been investigated as a drug therapy for Leber's hereditary optic neuropathy (LHON), a rare genetic mitochondrial disease that causes rapid and progressive bilateral vision loss. Although several studies have shown that idebenone can promote vision recovery in patients with LHON, the evidence for the efficacy of idebenone is still limited. Idebenone failed to demonstrate superiority over placebo in the primary end-points of the only published randomised, double-blind, placebo-controlled trial. There appears to be a patient-specific response to idebenone with high variability in therapeutic outcomes. A recent study suggested that the cytosolic enzyme NAD(P)H: quinone acceptor oxidoreductase (NQO1) is the major enzyme involved in the activation of idebenone, and the beneficial effects of idebenone are dependent on the expression of NQO1. Here, we confirm the NQO1-dependent activity of idebenone, but we also show, for the first time, that the cytotoxicity of idebenone is linked to cellular expression of NQO1. Upon idebenone administration, cells deficient in NQO1 show a marked decrease in viability in comparison to NQO1 expressing cells, with idebenone causing ROS production and deleterious effects on ATP levels and cell viability. In addition, our data highlights that only cells expressing NQO1 can significantly activate idebenone, indicating that other proposed metabolic activation pathways, such as complex II and glycerol-3-phosphate dehydrogenase, do not play a significant role in idebenone activation. Furthermore, we provide evidence of idebenone-induced toxicity in the retina ex-vivo, which can be explained by the variation of NQO1 expression between different cell types in the mouse retina. Idebenone mediated cell rescue in the rotenone ex vivo model also indicated that this drug has a narrow therapeutic window. These findings will help to guide the development of future therapies and drug delivery strategies including intra-ocular administration. The specific dependence of idebenone activity on NQO1 may also explain the variation in patient outcomes in clinical trials.

Anti-inflammatory Effect of AZD6244 on Acrolein-Induced Neuroinflammation

Clinically, high levels of acrolein (a highly reactive α, β-unsaturated aldehyde) and acrolein adducts are detected in the brain of patients with CNS neurodegenerative diseases, including Alzheimer's disease and spinal cord injury. Our previous study supports this notion by showing acrolein as a neurotoxin in a Parkinsonian animal model. In the present study, the effect of AZD6244 (an ATP non-competitive MEK1/2 inhibitor) on acrolein-induced neuroinflammation was investigated using BV-2 cells and primary cultured microglia. Our immunostaining study showed that lipopolysaccharide (LPS, an inflammation inducer as a positive control) increased co-localized immunoreactivities of phosphorylated ERK and ED-1 (a biomarker of activated microglia) in the treated BV-2 cells. Similar elevation in co-localized immunoreactivities of phosphorylated ERK and ED-1 was detected in the acrolein-treated BV-2 cells. Furthermore, Western blot assay showed increases in phosphorylated ERK in BV-2 cells subjected to LPS (1 μg/mL) or acrolein (30 μM); these increases were blocked by AZD6244 (10 μM). At the same time, AZD6244 attenuated LPS-induced TNF-α (a pro-inflammatory cytokine) and cyclooxygenase-II (COX II, a pro-inflammatory enzyme). Consistently, AZD6244 reduced acrolein-induced elevations in COX-II mRNA and COX-II protein expression. In addition, AZD6244 inhibited acrolein-induced increases in activated caspase 1 (a biomarker of inflammasome activation) and heme oxygenase-1 (a redox-regulated chaperone protein) in BV-2 cells. Using a transwell migration assay, AZD6244 attenuated acrolein (5 μM)-induced migration of BV-2 cells and primary cultured microglia. In conclusion, our study shows that acrolein is capable of inducing neuroinflammation which involved ERK activation in microglia. Furthermore, AZD6244 is capable of inhibiting acrolein-induced neuroinflammation. Our study suggests that ERK inhibition may be a neuroprotective target against acrolein-induced neuroinflammation in the CNS neurodegenerative diseases.

Alpha lipoic acid attenuates hypoxia-induced apoptosis, inflammation and mitochondrial oxidative stress via inhibition of TRPA1 channel in human glioblastoma cell line

Apoptosis, overload Ca²⁺ entry and oxidative stress are induced in neurons by hypoxia. Drug-resistant cancer cells are killed by hypoxic conditions. α-Lipoic acid (ALA) has antioxidant and pro-oxidant functions. The TRPA1 channel is activated by oxidative stress and pro-oxidant ALA may have a regulator role in the TRPA1 activity in the human glioblastoma (DBTRG) cells. The aim of this study was to evaluate if a combination therapy of ALA with a hypoxia can alter the effect of this hypoxia through TRPA1 activation in the DBTRG cells. The DBTRG cells were divided into four treatment groups as control, ALA (50 μM), and hypoxia and hypoxia + ALA. Hypoxia in the cells was induced by CoCl₂ (200 μM). Apoptosis, Annexin V, mitochondrial membrane depolarization (JC-1), reactive oxygen species (ROS) production, IL-1β, IL-18, caspase 3 and 9 values were increased through activation of TRPA1 (cinnamaldehyde) in the cells by the hypoxia induction, although cell viability, reduced glutathione and glutathione peroxidase values were decreased by the treatments. The values were modulated in the cells by TRPA1 blocker (AP18) and ALA treatments. Involvements of TRPA1 activity on values in the cells were also confirmed by patch-clamp and laser confocal microscopy analyses. In conclusion, apoptotic, inflammatory and oxidant effects of hypoxia were increased by activation of TRPA1, but its action on the values was decreased by the ALA treatment. ALA treatment could be used as an effective strategy in the treatment of hypoxia-induced oxidative stress, apoptosis and inflammation in the neurons.

Alpha-Lipoic Acid Downregulates IL-1β and IL-6 by DNA Hypermethylation in SK-N-BE Neuroblastoma Cells

Alpha-lipoic acid (ALA) is a pleiotropic molecule with antioxidant and anti-inflammatory properties, of which the effects are exerted through the modulation of NF-kB. This nuclear factor, in fact, modulates different inflammatory cytokines, including IL-1b and IL-6, in different tissues and cell types. We recently showed that IL-1b and IL-6 DNA methylation is modulated in the brain of Alzheimer's disease patients, and that IL-1b expression is associated to DNA methylation in the brain of patients with tuberous sclerosis complex. These results prompted us to ask whether ALA-induced repression of IL-1b and IL-6 was dependent on DNA methylation. Therefore, we profiled DNA methylation in the 5'-flanking region of the two aforementioned genes in SK-N-BE human neuroblastoma cells cultured in presence of ALA 0.5 mM. Our experimental data pointed out that the two promoters are hypermethylated in cells supplemented with ALA, both at CpG and non-CpG sites. Moreover, the observed hypermethylation is associated with decreased mRNA expression and decreased cytokine release. These results reinforce previous findings indicating that IL-1b and IL-6 undergo DNA methylation-dependent modulation in neural models and pave the road to study the epigenetic mechanisms triggered by ALA.

Parkinson's disease and pesticides: A meta-analysis of disease connection and genetic alterations

Parkinson's disease (PD) is a globally prevalent, multifactorial disorder that occurs due to interactions between genetic and environmental factors. Observational studies have shown a link between exposure to pesticides and the risk of PD. We performed this study to systemically review published case-control studies and estimate quantitatively the association between pesticide exposure and PD. We searched Medline (through PubMed) for eligible case-control studies. The association between pesticide exposure and PD risk or occurrence of certain genetic alterations, related to the pathogenesis of PD was presented as odds ratios (OR) and pooled under the random effects model, using the statistical add-in (MetaXL, version 5.0). The pooled result showed that exposure to pesticides is linked to PD (OR 1.46, 95% CI [1.21, 1.77]), but there was a significant heterogeneity among included studies. Exposure to pesticides increased the risk of alterations in different PD pathogenesis-related genes, such as GST (OR 1.97, 95% CI [1.41, 2.76]), PON-1 (OR 1.32, 95% CI [1.09, 1.6]), MDR1 (OR 2.06, 95% CI [1.58, 2.68]), and SNCA genes (OR 1.28, 95% CI [1.02, 1.37]). There was no statistically significant association between exposure to pesticides and alteration of CYP2D6 (OR 1.19, 95% CI [0.91, 1.54]), SLC6A3 (OR 0.74, 95% CI [0.55, 1]), MnSOD (OR 1.45, 95% CI [0.97, 2.16]), NQO1 (OR 1.35, 95% CI [0.91, 2.01]), and PON-2 genes (OR 0.88, 95% CI [0.53, 1.45]). In conclusion, this meta-analysis provides evidence that pesticide exposure is significantly associated with the risk of PD and alterations in genes involved in PD pathogenesis. However, the underlying mechanism of this association and the effect of the duration of exposure or the type of pesticides should be addressed by future research.

An increased need for dietary cysteine in support of glutathione synthesis may underlie the increased risk for mortality associated with low protein intake in the elderly

Restricted dietary intakes of protein or essential amino acids tend to slow aging and boost lifespan in rodents, presumably because they downregulate IGF-I/Akt/mTORC1 signaling that acts as a pacesetter for aging and promotes cancer induction. A recent analysis of the National Health and Nutrition Examination Survey (NHANES) III cohort has revealed that relatively low protein intakes in mid-life (under 10 % of calories) are indeed associated with decreased subsequent risk for mortality. However, in those over 65 at baseline, such low protein intakes were associated with increased risk for mortality. This finding accords well with other epidemiology correlating relatively high protein intakes with lower risk for loss of lean mass and bone density in the elderly. Increased efficiency of protein translation reflecting increased leucine intake and consequent greater mTORC1 activity may play a role in this effect; however, at present there is little solid evidence that leucine supplementation provides important long-term benefits to the elderly. Aside from its potential pro-anabolic impact, higher dietary protein intakes may protect the elderly in another way-by providing increased amino acid substrate for synthesis of key protective factors. There is growing evidence, in both rodents and humans, that glutathione synthesis declines with increasing age, likely reflecting diminished function of Nrf2-dependent inductive mechanisms that boost expression of glutamate cysteine ligase (GCL), rate-limiting for glutathione synthesis. Intracellular glutathione blunts the negative impact of reactive oxygen species (ROS) on cell health and functions both by acting as an oxidant scavenger and by opposing the pro-inflammatory influence of hydrogen peroxide on cell signaling. Fortunately, since GCL's K m for cysteine is close to intracellular cysteine levels, increased intakes of cysteine-achieved from whole proteins or via supplementation with N-acetylcysteine (NAC)-can achieve a compensatory increase in glutathione synthesis, such that more youthful tissue levels of this compound can be restored. Supplementation with phase 2 inducers-such as lipoic acid-can likewise increase glutathione levels by promoting increased GCL expression. In aging humans and/or rodents, NAC supplementation has exerted favorable effects on vascular health, muscle strength, bone density, cell-mediated immunity, markers of systemic inflammation, preservation of cognitive function, progression of neurodegeneration, and the clinical course of influenza-effects which could be expected to lessen mortality and stave off frailty. Hence, greater cysteine availability may explain much of the favorable impact of higher protein intakes on mortality and frailty risk in the elderly, and joint supplementation with NAC and lipoic acid could be notably protective in the elderly, particularly in those who follow plant-based diets relatively low in protein. It is less clear whether the lower arginine intake associated with low-protein diets has an adverse impact on vascular health.

Effect of dietary α-lipoic acid on the mRNA expression of genes involved in drug metabolism and antioxidation system in rat liver

In the present study, the mRNA levels of hepatic proteins involved in the drug metabolism of rats fed α-lipoic acid were evaluated by DNA microarray and real-time PCR analyses. Experimental diets containing 0, 0·1, 0·25 and 0·5 % (w/w) α-lipoic acid were fed to four groups of rats consisting of seven animals each for 21 d. DNA microarray analysis revealed that the diet containing 0·5 % α-lipoic acid significantly (P< 0·05) increased the mRNA levels of various phase I drug-metabolising enzymes up to 15-fold and phase II enzymes up to 52-fold in an isoenzyme-specific manner. α-Lipoic acid also up-regulated the mRNA levels of some members of the ATP-binding cassette transporter superfamily, presumed to be involved in the exportation of xenobiotics, up to 6·6-fold. In addition, we observed that α-lipoic acid increased the mRNA levels of many proteins involved in antioxidation, such as members of the thiol redox system (up to 5·5-fold), metallothioneins (up to 12-fold) and haeme oxygenase 1 (1·5-fold). These results were confirmed using real-time PCR analysis, and α-lipoic acid dose dependently increased the mRNA levels of various proteins involved in drug metabolism and antioxidation. Consistent with these observations, α-lipoic acid dose dependently increased the hepatic concentration of glutathione and the activities of glutathione reductase and glutathione transferase measured using 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates, but decreased the hepatic and serum concentrations of malondialdehyde. In conclusion, the present study unequivocally demonstrated that α-lipoic acid increases the mRNA expression of proteins involved in drug metabolism and antioxidation in the liver.

Fermented wheat powder induces the antioxidant and detoxifying system in primary rat hepatocytes

Many plants exhibit antioxidant properties which may be useful in the prevention of oxidative stress reactions, such as those mediated by the formation of free radical species in different pathological situations. In recent years a number of studies have shown that whole grain products in particular have strong antioxidant activity. Primary cultures of rat hepatocytes were used to investigate whether and how a fermented powder of wheat (Lisosan G) is able to modulate antioxidant and detoxifying enzymes, and whether or not it can activate Nrf2 transcription factor or inhibit NF-kB activation. All of the antioxidant and detoxifying enzymes studied were significantly up-regulated by 0.7 mg/ml Lisosan G treatment. In particular,

NAD(P)H

quinone oxidoreductase and heme oxygenase-1 were induced, although to different degrees, at the transcriptional, protein and/or activity levels by the treatment. As for the Nrf2 transcription factor, a partial translocation of its protein from the cytosol to the nucleus after 1 h of Lisosan G treatment was revealed by immunoblotting. Lisosan G was also observed to decrease H2O2-induced toxicity Taken together, these results show that this powder of wheat is an effective inducer of ARE/Nrf2-regulated antioxidant and detoxifying genes and has the potential to inhibit the translocation of NF-kB into the nucleus.

Management of the aging risk factor for Parkinson's disease

The aging risk factor for Parkinson's disease is described in terms of specific disease markers including mitochondrial and gene dysfunctions relevant to energy metabolism. This review details evidence for the ability of nutritional agents to manage these aging risk factors. The combination of alpha lipoic acid, acetyl-l-carnitine, coenzyme Q10, and melatonin supports energy metabolism via carbohydrate and fatty acid utilization, assists electron transport and adenosine triphosphate synthesis, counters oxidative and nitrosative stress, and raises defenses against protein misfolding, inflammatory stimuli, iron, and other endogenous or xenobiotic toxins. These effects are supported by gene expression via the antioxidant response element (ARE; Keap/Nrf2 pathway), and by peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1 alpha), a transcription coactivator, which regulates gene expression for energy metabolism and mitochondrial biogenesis, and maintains the structural integrity of mitochondria. The effectiveness and synergies of the combination against disease risks are discussed in relation to gene action, dopamine cell loss, and the accumulation and spread of pathology via misfolded alpha-synuclein. In addition there are potential synergies to support a neurorestorative role via glial derived neurotrophic factor expression.

Genistein inhibits TNF-α-induced endothelial inflammation through the protein kinase pathway A and improves vascular inflammation in C57BL/6 mice

Genistein, a soy isoflavone, has received wide attention for its potential to improve vascular function, but the mechanism of this effect is unclear. Here, we report that genistein at physiological concentrations (0.1 μM-5 μM) significantly inhibited TNF-α-induced adhesion of monocytes to human umbilical vein endothelial cells, a key event in the pathogenesis of atherosclerosis. Genistein also significantly suppressed TNF-α-induced production of adhesion molecules and chemokines such as sICAM-1, sVCAM-1, sE-Selectin, MCP-1 and IL-8, which play key role in the firm adhesion of monocytes to activated endothelial cells (ECs). Genistein at physiologically relevant concentrations didn't significantly induce antioxidant enzyme activities or scavenge free radicals. Further, blocking the estrogen receptors (ERs) in ECs didn't alter the preventive effect of genistein on endothelial inflammation. However, inhibition of protein kinase A (PKA) significantly attenuated the inhibitory effects of genistein on TNF-α-induced monocyte adhesion to ECs as well as the production of MCP-1 and IL-8. In animal study, dietary genistein significantly suppressed TNF-α-induced increase in circulating chemokines and adhesion molecules in C57BL/6 mice. Genistein treatment also reduced VCAM-1 and monocytes-derived F4/80-positive macrophages in the aorta of TNF-α-treated mice. In conclusion, genistein protects against TNF-α-induced vascular endothelial inflammation both in vitro and in vivo models. This anti-inflammatory effect of genistein is independent of the ER-mediated signaling machinery or antioxidant activity, but mediated via the PKA signaling pathway.

NAD(P)H:quinone oxidoreductase 1 (NQO1) competes with 20S proteasome for binding with C/EBPα leading to its stabilization and protection against radiation-induced myeloproliferative disease

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a flavoprotein that protects cells against radiation and chemical-induced oxidative stress. Disruption of NQO1 gene in mice leads to increased susceptibility to myeloproliferative disease. In this report, we demonstrate that NQO1 controls the stability of myeloid differentiation factor C/EBPα against 20S proteasomal degradation during radiation exposure stress. Co-immunoprecipitation studies showed that NQO1, C/EBPα, and 20S all interacted with each other. C/EBPα interaction with 20S led to the degradation of C/EBPα. NQO1 in presence of its cofactor NADH protected C/EBPα against 20S degradation. Deletion and site-directed mutagenesis demonstrated that NQO1 and 20S competed for the same binding region (268)SGAGAGKAKKSV(279) in C/EBPα. Mutagenesis studies also revealed that NQO1Y127/Y129 required for NADH binding is essential for NQO1 stabilization of C/EBPα. Exposure of mice and HL-60 cells to 3 Grays of γ-radiation led to increased NQO1 that stabilized C/EBPα against 20S proteasomal degradation. This mechanism of NQO1 regulation of C/EBPα may provide protection to bone marrow against adverse effects of radiation exposure. The studies have significance for human individuals carrying hetero- or homozygous NQO1P187S mutation and are deficient or lack NQO1 protein.

Dysregulation of glutathione homeostasis in neurodegenerative diseases

Dysregulation of glutathione homeostasis and alterations in glutathione-dependent enzyme activities are increasingly implicated in the induction and progression of neurodegenerative diseases, including Alzheimer’s, Parkinson’s and Huntington’s diseases, amyotrophic lateral sclerosis, and Friedreich’s ataxia. In this review background is provided on the steady-state synthesis, regulation, and transport of glutathione, with primary focus on the brain. A brief overview is presented on the distinct but vital roles of glutathione in cellular maintenance and survival, and on the functions of key glutathione-dependent enzymes. Major contributors to initiation and progression of neurodegenerative diseases are considered, including oxidative stress, protein misfolding, and protein aggregation. In each case examples of key regulatory mechanisms are identified that are sensitive to changes in glutathione redox status and/or in the activities of glutathione-dependent enzymes. Mechanisms of dysregulation of glutathione and/or glutathione-dependent enzymes are discussed that are implicated in pathogenesis of each neurodegenerative disease. Limitations in information or interpretation are identified, and possible avenues for further research are described with an aim to elucidating novel targets for therapeutic interventions. The pros and cons of administration of N-acetylcysteine or glutathione as therapeutic agents for neurodegenerative diseases, as well as the potential utility of serum glutathione as a biomarker, are critically evaluated.

Protein modification by acrolein: relevance to pathological conditions and inhibition by aldehyde sequestering agents

Acrolein (ACR) is a toxic and highly reactive α,β-unsaturated aldehyde widely distributed in the environment as a common pollutant and generated endogenously mainly by lipoxidation reactions. Its biological effects are due to its ability to react with the nucleophilic sites of proteins, to form covalently modified biomolecules which are thought to be involved as pathogenic factors in the onset and progression of many pathological conditions such as cardiovascular and neurodegenerative diseases. Functional impairment of structural proteins and enzymes by covalent modification (crosslinking) and triggering of key cell signalling systems are now well-recognized signs of cell and tissue damage induced by reactive carbonyl species (RCS). In this review, we mainly focus on the in vitro and in vivo evidence demonstrating the ability of ACR to covalently modify protein structures, in order to gain a deeper insight into the dysregulation of cellular and metabolic pathways caused by such modifications. In addition, by considering RCS and RCS-modified proteins as drug targets, this survey will provide an overview on the newly developed molecules specifically tested for direct or indirect ACR scavenging, and the more significant studies performed in the last years attesting the efficacy of compounds already recognized as promising aldehyde-sequestering agents.

Acrolein scavengers: reactivity, mechanism and impact on health

Acrolein (ACR) is an α,β-unsaturated aldehyde that exists extensively in the environment and (thermally processed) foods. It can also be generated through endogenous metabolism. Its high electrophilicity makes this aldehyde notorious for its facile reaction with biological nucleophiles, leading to the modification of proteins/DNA and depletion of glutathione. Recent studies also have revealed its roles in disturbing various cell signing pathways in biological systems. With growing evidences of ACR's implication in human diseases, strategies to eliminate its hazardous impacts are of great importance. One of the intervention strategies is the application of reactive scavengers to directly trap ACR. Some known ACR scavengers include sulfur (thiol)-containing and nitrogen (amino)-containing compounds as well as the newly emerging natural polyphenols. In this review, the interactions between ACR and its scavengers are highlighted. The discussion about ACR scavengers is mainly focused on their chemical reactivity, trapping mechanisms as well as their roles extended to biological relevance. In addition to their direct trapping effect on ACR, these scavengers might possess multiple functions and offer additional benefits against ACR-induced toxicity. A comprehensive understanding of the mechanism involved may help to establish ACR scavenging as a novel therapeutic intervention against human diseases that are associated with ACR and/or oxidative stress.

Dietary epicatechin promotes survival of obese diabetic mice and Drosophila melanogaster

The lifespan of diabetic patients is 7-8 y shorter than that of the general population because of hyperglycemia-induced vascular complications and damage to other organs such as the liver and skeletal muscle. Here, we investigated the effects of epicatechin, one of the major flavonoids in cocoa, on health-promoting effects in obese diabetic (db/db) mice (0.25% in drinking water for 15 wk) and Drosophila melanogaster (0.01-8 mmol/L in diet). Dietary intake of epicatechin promoted survival in the diabetic mice (50% mortality in diabetic control group vs. 8.4% in epicatechin group after 15 wk of treatment), whereas blood pressure, blood glucose, food intake, and body weight gain were not significantly altered. Pathological analysis showed that epicatechin administration reduced the degeneration of aortic vessels and blunted fat deposition and hydropic degeneration in the liver caused by diabetes. Epicatechin treatment caused changes in diabetic mice that are associated with a healthier and longer lifespan, including improved skeletal muscle stress output, reduced systematic inflammation markers and serum LDL cholesterol, increased hepatic antioxidant glutathione concentration and total superoxide dismutase activity, decreased circulating insulin-like growth factor-1 (from 303 ± 21 mg/L in the diabetic control group to 189 ± 21 mg/L in the epicatechin-treated group), and improved AMP-activated protein kinase-α activity in the liver and skeletal muscle. Consistently, epicatechin (0.1-8 mmol/L) also promoted survival and increased mean lifespan of Drosophila. Therefore, epicatechin may be a novel food-derived, antiaging compound.

Dietary genistein and equol (4′, 7 isoflavandiol) reduce oxidative stress and protect rats against focal cerebral ischemia

High soy diets reduce injury in rat models of focal cerebral ischemia and are proposed as alternatives to hormone replacement therapy for postmenopausal women. The present study tests the hypothesis that the major soy isoflavone genistein and the daidzein metabolite equol are neuroprotective in transient focal cerebral ischemia in male and ovariectomized (OVX) female rats by inhibiting oxidative stress. Genistein is the primary circulating soy isoflavone in humans, whereas equol is the primary circulating isoflavone in rats. Male and OVX female Sprague-Dawley rats were fed an isoflavone-reduced diet alone or supplemented with genistein (500 ppm) or equol (250 ppm) for 2 wk prior to 90-min transient middle cerebral artery occlusion followed by reperfusion under isoflurane anesthesia. Indices of oxidative stress were determined 24 h after reperfusion, and cerebral injury was evaluated 3 days after reperfusion. Genistein and equol significantly reduced infarct size in both sexes. Further studies in OVX female rats revealed that this neuroprotection was accompanied by a decrease in NAD(P)H oxidase activity and superoxide levels in the brain. In addition, equol reduced plasma thiobarbituric acid reactive substances, and neurological deficits up to 7 days after injury. There were no significant differences in cerebral blood flow among treatment groups. In conclusion, dietary soy isoflavones are neuroprotective in transient focal cerebral ischemia in male and OVX female rats. These isoflavones may protect the brain via increases in endogenous antioxidant mechanisms and reduced oxidative stress.

Sulforaphane and alpha-lipoic acid upregulate the expression of the pi class of glutathione S-transferase through c-jun and Nrf2 activation

The anticarcinogenic effect of dietary organosulfur compounds has been partly attributed to their modulation of the activity and expression of phase II detoxification enzymes. Our previous studies indicated that garlic allyl sulfides upregulate the expression of the pi class of glutathione S-transferase (GSTP) through the activator protein-1 pathway. Here, we examined the modulatory effect of sulforaphane (SFN) and alpha-lipoic acid (LA) or dihydrolipoic acid (DHLA) on GSTP expression in rat Clone 9 liver cells. Cells were treated with LA or DHLA (50-600 micromol/L) or SFN (0.2-5 micromol/L) for 24 h. Immunoblots and real-time PCR showed that SFN, LA, and DHLA dose dependently induced GSTP protein and mRNA expression. Compared with the induction by the garlic organosulfur compound diallyl trisulfide (DATS), the effectiveness was in the order of SFN > DATS > LA = DHLA. The increase in GSTP enzyme activity in cells treated with 5 micromol/L SFN, 50 micromol/L DATS, and 600 micromol/L LA and DHLA was 172, 75, 122, and 117%, respectively (P < 0.05). A reporter assay showed that the GSTP enhancer I (GPEI) was required for GSTP induction by the organosulfur compounds. Electromobility gel shift assays showed that the DNA binding of GPEI to nuclear proteins reached a maximum at 0.5-1 h after SFN, LA, and DHLA treatment. Super-shift assay revealed that the transcription factors c-jun and nuclear factor erythroid-2 related factor 2 (Nrf2) were bound to GPEI. These results suggest that SFN and LA in either its oxidized or reduced form upregulate the transcription of the GSTP gene by activating c-jun and Nrf2 binding to the enhancer element GPEI.

Potential utility of full-spectrum antioxidant therapy, citrulline, and dietary nitrate in the management of sickle cell disease

There is considerable evidence that oxidative stress and a loss of nitric oxide bioactivity are key mediators of the vasculopathies associated with sickle cell disease. A comprehensive nutraceutical strategy for mitigating the contribution of oxidative stress to pathogenesis - dubbed "full-spectrum antioxidant therapy" - may have utility in this syndrome. This strategy entails concurrent administration of phycocyanobilin - a phytochemical richly supplied by spirulina, shown to inhibit NADPH oxidase in a manner analogous to its chemical relatives biliverdin and bilirubin; high-dose folate - recently shown to quench peroxynitrite-derived radicals and restore coupling of NO synthase; N-acetylcysteine - for boosting intracellular glutathione levels; and a phase 2 inducer such as lipoic acid - to further promote glutathione synthesis while increasing expression of antioxidant enzymes. Suboptimal endothelial arginine levels, reflecting increased plasma arginase activity and elevated ADMA, contribute to the loss of NO bioactivity in sickle cell disease; supplementation with the arginine precursor citrulline may ameliorate this defect. Increased intakes of plant-derived nitrate have the potential to diminish the quenching of NO by plasma hemoglobin in sickle cell patients, while boosting systemic NO production independent of NO synthase activity. In addition to the well-documented utility of hydroxyurea - possibly a suboptimal strategy for life-long therapy owing to its mutagenic activity - rational pharmaceutical options for managing sickle cell disease include pentoxifylline and phosphodiesterase 5 inhibitors such as sildenafil.

Alpha-lipoic acid induces elevated S-adenosylhomocysteine and depletes S-adenosylmethionine

Lipoic acid is a disulfhydryl-containing compound used in clinical medicine and in experimental models as an antioxidant. We developed a stable isotope dilution capillary gas chromatography/mass spectrometry assay for lipoic acid. We assayed a panel of the metabolites of transmethylation and transsulfuration 30 min after injecting 100 mg/kg lipoic acid in a rat model. Lipoic acid values rose 1000-fold in serum and 10-fold in liver. A methylated metabolite of lipoic acid was also detected but not quantitated. Lipoic acid injection caused a massive increase in serum S-adenosylhomocysteine and marked depletion of liver S-adenosylmethionine. Serum total cysteine was depleted but liver cysteine and glutathione were maintained. Serum total homocysteine doubled, with increases also in cystathionine, N,N-dimethylglycine, and alpha-aminobutyric acid. In contrast, after injection of 2-mercaptoethane sulfonic acid, serum total cysteine and homocysteine were markedly depleted and there were no effects on serum S-adenosylmethionine or S-adenosylhomocysteine. We conclude that large doses of lipoic acid displace sulfhydryls from binding sites, resulting in depletion of serum cysteine, but also pose a methylation burden with severe depletion of liver S-adenosylmethionine and massive release of S-adenosylhomocysteine. These changes may have previously unrecognized deleterious effects that should be investigated in both human disease and experimental models.

Rottlerin induces heme oxygenase-1 (HO-1) up-regulation through reactive oxygen species (ROS) dependent and PKC delta-independent pathway in human colon cancer HT29 cells

Heme oxygenase-1 (HO-1) is a cytoprotective enzyme activated by its substrate heme and diverse stimuli. The induction of HO-1 gene expression is one of the important events in cellular response to pro-oxidative and pro-inflammatory insults. In this study, the effect of rottlerin, a putative PKC delta inhibitor, on HO-1 expression in HT29 human colon cancer cells was investigated. Rottlerin-induced HO-1 at both protein and mRNA levels in a dose- and time-dependent manner. Rottlerin-mediated HO-1 induction was abrogated in the presence of N-acetylcysteine (NAC) or glutathione (GSH). Rottlerin induced nuclear translocation of NF-E2-related factor 2 (Nrf2) and increased antioxidant response element (ARE)-driven transcriptional activity. Additionally, rottlerin activated p38 mitogen-activated protein kinase (MAPK) and ERK. The pharmacological inhibition of ERK and p38 MAPK inhibited rottlerin-induced HO-1 up-regulation. However, suppression of protein kinase C delta (PKC delta) expression by siRNA or overexpression of WT-PKC delta did not abrogate the rottlerin-mediated induction of HO-1. These results suggest that rottlerin induces up-regulation of HO-1 via PKC delta-independent pathway. Taken together, the present study identified rottlerin as a novel inducer of HO-1 expression and identified the mechanisms involved in this process.

Cruciferous nutraceutical 3H-1,2-dithiole-3-thione protects human primary astrocytes against neurocytotoxicity elicited by MPTP, MPP(+), 6-OHDA, HNE and acrolein

Astrocytes possess important roles in maintaining normal brain function and providing trophic support to the neurons. They also suffer a range of toxic insults, being a chief target of prooxidants such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenylpyridinium (MPP(+)), 6-hydroxydopamine (6-OHDA), 4-hydroxy-2-nonenal (HNE), and acrolein. Recently, we have observed that the cellular antioxidants and phase 2 enzymes can be upregulated by 3H-1,2-dithiole-3-thione (D3T), a nutraceutical found in cruciferous vegetables, against many prooxidants in human neuroblastoma cell lines (SH-SY5Y). However, the regulation of the above cellular factors by D3T in astrocytes and their role in ameliorating the neurotoxic effects of the above neurotoxins have not been investigated. In this study, we show that incubation of human primary astrocytes with micromolar concentrations (5-100 microM) of D3T for 24 h resulted in significant increases in the levels of reduced glutathione (GSH), glutathione reductase (GR), and the phase 2 enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1). D3T treatment also caused time-dependent increases in mRNA expression of the gamma-glutamylcysteine ligase catalytic subunit (GCLC), GR, and of NQO1 in these cells. Pretreatment of astrocytes with D3T was found to afford remarkable protection against the neurocytotoxicity elicited by MPTP, MPP(+), 6-OHDA, HNE and acrolein. Taken together, this study demonstrates for the first time that in human astrocytes, the cruciferous nutraceutical D3T potently induces the cellular GSH system and the phase 2 enzyme NQO1, which is accompanied by dramatically increased resistance of these cells to the damage induced by various neurotoxicants. The results of this study may have important implications for the development of novel neuroprotective strategies.

Probing and preventing quantum dot-induced cytotoxicity with multimodal α-lipoic acid in multiple dimensions of the peripheral nervous system

Aim: Toxicity of nanoparticles developed for biomedical applications is extensively debated as no uniform guidelines are available for studying nanomaterial safety, resulting in conflicting data obtained from different cell types. This study demonstrates the varied toxicity of a selected type of nanoparticle, cadmium telluride quantum dots (QDs), in three increasingly complex cell models of the peripheral nervous system. Materials & methods: QD-induced cytotoxicity was assessed via cell viability assays and biomarkers of subcellular damage in PC12 cells and mixed primary dispersed dorsal root ganglia (DRG) cultures. Morphological analysis of neurite outgrowth was used to determine the viability of axotomized DRG explant cultures. Results & discussion: Cadmium telluride QDs and their core metals exert different degrees of toxicity in the three cell models, the primary dispersed DRGs being the most susceptible. α-lipoic acid is an effective, multimodal, cytoprotective agent that can act as an antioxidant, metal chelator and QD-surface modifier in these cell systems. Conclusion: Complex multicellular model systems, along with homogenous cell models, should be utilized in standard screening and monitoring procedures for evaluating nanomaterial safety.

Coordinated upregulation of a series of endogenous antioxidants and phase 2 enzymes as a novel strategy for protecting renal tubular cells from oxidative and electrophilic stress

In view of the crucial involvement of oxidative and electrophilic stress in various kidney disorders, this study was undertaken to test the hypothesis that pharmacologically-mediated coordinated upregulation of endogenous renal antioxidants and phase 2 enzymes is an effective strategy for renal protection. Notably, studies on the pharmacological inducibility of a series of antioxidants and phase 2 enzymes in renal tubular cells are lacking. Here we reported that incubation of normal rat kidney (NRK-52E) proximal tubular cells with low micromolar concentrations (10-50 microM) of the cruciferous nutraceutical, 1,2-dithiole-3-thione (D3T), led to a significant concentration-dependent induction of a wide spectrum of antioxidants and phase 2 enzymes, including catalase (CAT), reduced form of glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1 (NQO1), and heme oxygenase (HO). We further observed that D3T treatment also increased the protein and mRNA expression for CAT, gamma-glutamylcysteine ligase, GR, GST-A, GST-M, NQO1, and HO-1. Incubation of the renal tubular cells with H(2)O(2), SIN-1-derived peroxynitrite, or 4-hydroxy-2-nonenal led to concentration-dependent decreases in cell viability. Pretreatment of the renal tubular cells with 10-50 microM D3T afforded remarkable protection against the nephrocytotoxicity elicited by the above oxidative and electrophilic species. The D3T-mediated cytoprotection showed a concentration-dependent relationship. Taken together, this study for the first time comprehensively characterized the inducibility by a unique nutraceutical of a wide spectrum of antioxidative and phase 2 defenses in renal tubular cells at the levels of enzyme activity as well as protein and mRNA expression, and demonstrated that such a coordinated upregulation of cellular defenses led to remarkable protection of renal tubular cell from oxidative and electrophilic stress. Because of the crucial role of oxidative and electrophilic stress in inflammatory injury, D3T-mediated coordinated induction of endogenous antioxidative and phase 2 defenses may also serve as an important anti-inflammatory mechanism in kidneys.

Dopamine as a potent inducer of cellular glutathione and NAD(P)H:quinone oxidoreductase 1 in PC12 neuronal cells: a potential adaptive mechanism for dopaminergic neuroprotection

Dopamine auto-oxidation and the consequent formation of reactive oxygen species and electrophilic quinone molecules have been implicated in dopaminergic neuronal cell death in Parkinson's disease. We reported here that in PC12 dopaminergic neuronal cells dopamine at noncytotoxic concentrations (50-150 muM) potently induced cellular glutathione (GSH) and the phase 2 enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1), two critical cellular defenses in detoxification of ROS and electrophilic quinone molecules. Incubation of PC12 cells with dopamine also led to a marked increase in the mRNA levels for gamma-glutamylcysteine ligase catalytic subunit (GCLC) and NQO1. In addition, treatment of PC12 cells with dopamine resulted in a significant elevation of GSH content in the mitochondrial compartment. To determine whether treatment with dopamine at noncytotoxic concentrations, which upregulated the cellular defenses could protect the neuronal cells against subsequent lethal oxidative and electrophilic injury, PC12 cells were pretreated with dopamine (150 muM) for 24 h and then exposed to various cytotoxic concentrations of dopamine or 6-hydroxydopamine (6-OHDA). We found that pretreatment of PC12 cells with dopamine at a noncytotoxic concentration led to a remarkable protection against cytotoxicity caused by dopamine or 6-OHDA at lethal concentrations, as detected by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium reduction assay. In view of the critical roles of GSH and NQO1 in protecting against dopaminergic neuron degeneration, the above findings implicate that upregulation of both GSH and NQO1 by dopamine at noncytotoxic concentrations may serve as an important adaptive mechanism for dopaminergic neuroprotection.

Potent induction of total cellular GSH and NQO1 as well as mitochondrial GSH by 3H-1,2-dithiole-3-thione in SH-SY5Y neuroblastoma cells and primary human neurons: protection against neurocytotoxicity elicited by dopamine, 6-hydroxydopamine, 4-hydroxy-2-nonenal, or hydrogen peroxide

Evidence suggests oxidative and electrophilic stress as a major factor contributing to the neuronal cell death in neurodegenerative disorders, especially Parkinson's disease. Consistent with this concept, administration of exogenous antioxidants has been shown to be protective against oxidative/electrophilic neurodegeneration. However, whether induction of endogenous antioxidants and phase 2 enzymes by the unique chemoprotectant, 3H-1,2-dithiole-3-thione (D3T) in neuronal cells also affords protection against oxidative and electrophilic neurocytotoxicity has not been carefully investigated. In this study, we showed that incubation of SH-SY5Y neuroblastoma cells or primary human neurons with micromolar concentrations (10-100 microM) of D3T for 24 h resulted in significant increases in the levels of reduced glutathione (GSH) and NAD(P)H:quinone oxidoreductase 1 (NQO1), two crucial cellular defenses against oxidative and electrophilic stress. D3T treatment also caused increases in mRNA expression of gamma-glutamylcysteine ligase catalytic subunit and NQO1 in SH-SY5Y cells. In addition, D3T treatment of the neuronal cells also resulted in a marked elevation of GSH content in the mitochondrial compartment. To determine the protective effects of the D3T-induced cellular defenses on neurotoxicant-elicited cell injury, SH-SY5Y cells were pretreated with D3T for 24 h and then exposed to dopamine, 6-hydroxydopamine (6-OHDA), 4-hydroxy-2-nonenal (HNE), or H2O2, agents that are known to be involved in neuron degeneration. We observed that D3T-pretreatment of SH-SY5Y cells led to significant protection against the cytotoxicity elicited by the above neurotoxicants. Similar neurocytoprotective effects of D3T-pretreatment were also observed in primary human neurons exposed to 6-OHDA or HNE. Taken together, this study demonstrates that D3T potently induces neuronal cellular GSH and NQO1 as well as mitochondrial GSH, and that such upregulated endogenous defenses are accompanied by increased resistance to oxidative and electrophilic neurocytotoxicity.