Nanoliposomes Reduce Stroke Injury Following Middle Cerebral Artery Occlusion in Mice

BACKGROUND AND PURPOSE

Neuroprotective strategies for stroke remain inadequate. Nanoliposomes comprised of phosphatidylcholine, cholesterol, and monosialogangliosides (nanoliposomes) induced an antioxidant protective response in endothelial cells exposed to amyloid insults. We tested the hypotheses that nanoliposomes will preserve human neuroblastoma (SH-SY5Y) and human brain microvascular endothelial cells viability following oxygen-glucose deprivation (OGD)-reoxygenation and will reduce injury in mice following middle cerebral artery occlusion.

METHODS

SH-SY5Y and human brain microvascular endothelial cells were exposed to oxygen-glucose deprivation-reoxygenation (3 hours 0.5%-1% oxygen and glucose-free media followed by 20-hour ambient air/regular media) without or with nanoliposomes (300 µg/mL). Viability was measured (calcein-acetoxymethyl fluorescence) and protein expression of antioxidant proteins HO-1 (heme oxygenase-1), NQO1 (NAD[P]H quinone dehydrogenase 1), and SOD1 (superoxide dismutase 1) were measured by Western blot. C57BL/6J mice were treated with saline (n=8) or nanoliposomes (10 mg/mL lipid, 200 µL, n=7) while undergoing 60-minute middle cerebral artery occlusion followed by reperfusion. Day 2 postinjury neurological impairment score and infarction size were compared.

RESULTS

SH-SY5Y and human brain microvascular endothelial cells showed reduced viability post-oxygen-glucose deprivation-reoxygenation that was reversed by nanoliposomes. Nanoliposomes increased protein expressions of HO-1, NQO1 in both cell types and SOD1 in human brain microvascular endothelial cells. Nanoliposomes-treated mice showed reduced neurological impairment and brain infarct size (18.8±2% versus 27.3±2.3%, P=0.017) versus controls.

CONCLUSIONS

Nanoliposomes reduced stroke injury in mice subjected to middle cerebral artery occlusion likely through induction of an antioxidant protective response. Nanoliposome is a candidate novel agent for stroke.

Royal Jelly Protects against Epidermal Stress through Upregulation of the NQO1 Expression

Royal jelly (RJ) is secreted by honeybees and has been used as an apitherapy to obtain healthy skin since ancient times. However, the mechanism of the protective effects of RJ against skin aging and skin diseases caused by skin stress and its components have not been clarified. In this study, we attempted to understand the effect of RJ on epidermal function and observed that NAD(P)H quinone dehydrogenase 1 (NQO1) is significantly induced by RJ in keratinocytes. The expression of NQO1 was also increased in the 3D epidermal skin model. NQO1 is involved in antioxidation and detoxification metabolism, and we found that RJ protects against the epidermal stress caused by UVB and menadione through the upregulation of NQO1. We identified 10-hydroxy-2-decenoic acid (10H2DA), a major fatty acid in RJ, as an active compound in this reaction as it induced the expression of NQO1 and protected the skin against oxidative stress. We demonstrated that the protective effect of RJ against epidermal stress is mediated through the upregulation of NQO1 by 10H2DA.

β-Caryophyllene exerts protective antioxidant effects through the activation of NQO1 in the MPTP model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, caused by the selective death of dopaminergic neurons in the substantia nigra pars compacta. β-caryophyllene (BCP) is a phytocannabinoid with several pharmacological properties, producing anti-inflammatory and antihypertensive effects. In addition, BCP protects dopaminergic neurons from neuronal death induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), yet it remains unclear if this effect is due to its antioxidant activity. To assess whether this is the case, the effect of BCP on the expression and activity of NAD(P)H quinone oxidoreductase (NQO1) was evaluated in mice after the administration of MPTP. Male C57BL/6 J mice were divided into four groups, the first of which received saline solution i.p. in equivalent volume and served as a control group. The second group received MPTP. The second group received MPTP hydrochloride (5 mg/kg, i.p.) daily for seven consecutive days. The third group received BCP (10 mg/kg) for seven days, administered orally and finally, the fourth group received MPTP as described above and BCP for 7 days from the fourth day of MPTP administration. The results showed that BCP inhibits oxidative stress-induced cell death of dopaminergic neurons exposed to MPTP at the same time as it enhances the expression and enzymatic activity of NQO1. Also, the BCP treatment ameliorated motor dysfunction and protected the dopaminergic cells of the SNpc from damage induced by MPTP. Hence, BCP appears to achieve at least some of its antioxidant effects by augmenting NQO1 activity, which protects cells from MPTP toxicity. Accordingly, this phytocannabinoid may represent a promising pharmacological option to safeguard dopaminergic neurons and prevent the progression of PD.

Regulation of TBBPA-induced oxidative stress on mitochondrial apoptosis in L02 cells through the Nrf2 signaling pathway

Tetrabromobisphenol A (TBBPA) is a commonly used brominated flame retardant, which has a wide range of toxic effects on organisms. This study investigated the cytotoxic effects on human hepatocytes (L02 cells) after treated with 0, 5, 10, 20, and 40 μM of TBBPA. Results showed that TBBPA significantly increased intracellular reactive oxygen species (ROS), malondialdehyde (MDA) and the ratio of oxidized/reduced glutathione (GSSG/GSH) dose-dependently. TBBPA also decreased the cell mitochondrial membrane potential (MMP), caused the release of cytochrome C (Cyt C) to cytoplasm and promoted the expression of caspase-9 and caspase-3, and finally increased the level of apoptosis. The ROS inhibitor N-acetyl-L-cysteine (NAC) relieved the oxidative stress responses, and prevented the decrease of MMP and increase of apoptosis. In addition, TBBPA promoted the expression of antioxidant genes related to Nrf2, such as quinone oxidoreductase 1 (NQO1), catalase (CAT), and heme oxygenase 1 (HO-1). Oxidative stress initiated by TBBPA, activated mitochondrial apoptosis and Nrf2 pathway, and increased the degree of apoptosis in L02 cells.

NRH:quinone oxidoreductase 2 (NQO2) and glutaminase (GLS) both play a role in large extracellular vesicles (LEV) formation in preclinical LNCaP-C4-2B prostate cancer model of progressive metastasis

In the course of studies aimed at the role of oxidative stress in the development of metastatic potential in the LNCaP-C4-2B prostate cancer progression model system, we found a relative decrease in the level of expression of the cytoplasmic nicotinamide riboside: quinone oxidoreductase (NQO2) and an increase in the oxidative stress in C4-2B cells compared to that in LNCaP or its derivatives C4 and C4-2. It was also found that C4-2B cells specifically shed large extracellular vesicles (LEVs) suggesting that these LEVs and their cargo could participate in the establishment of the osseous metastases. The level of expression of caveolin-1 increased as the system progresses from LNCaP to C4-2B. Since NQO2 RNA levels were not changed in LNCaP, C4, C4-2, and C4-2B, we tested an altered cellular distribution hypothesis of NQO2 being compartmentalized in the membrane fractions of C4-2B cells which are rich in lipid rafts and caveolae. This was confirmed when the detergent resistant membrane fractions were probed on immunoblots. Moreover, when the LEVs were analyzed for membrane associated caveolin-1 as possible cargo, we noticed that the enzyme NQO2 was also a component of the cargo along with caveolin-1 as seen in double immunofluorescence studies. Molecular modeling studies showed that a caveolin-1 accessible site is present in NQO2. Specific interaction between NQO2 and caveolin-1 was confirmed using deletion constructs of caveolin-1 fused with glutathione S-transferase (GST). Interestingly, whole cell lysate and mitochondrial preparations of LNCaP, C4, C4-2, and C4-2B showed an increasing expression of glutaminase (GLS, kidney type). The extrusion of LEVs appears to be a specific property of the bone metastatic C4-2B cells and this process could be inhibited by a GLS specific inhibitor BPTES, suggesting the critical role of a functioning glutamine metabolism. Our results indicate that a high level of expression of caveolin-1 in C4-2B cells contributes to an interaction between caveolin-1 and NQO2 and to their packaging as cargo in the shed LEVs. These results suggest an important role of membrane associated oxidoreductases in the establishment of osseous metastases in prostate cancer.

Exenatide Increases IL-1RA Concentration and Induces Nrf-2‒Keap-1‒Regulated Antioxidant Enzymes: Relevance to β-Cell Function

PURPOSE

We previously demonstrated the anti-inflammatory and antioxidant effects of exenatide. We now hypothesized that exenatide also increases the plasma concentration of interleukin-1 receptor antagonist (IL-1RA), an endogenous anti-inflammatory protein, and modulates the nuclear factor erythroid 2‒related factor‒Kelchlike ECH-associated protein 1‒antioxidant response element (Nrf-2‒Keap-1‒ARE) system to induce key antioxidant enzymes to suppress inflammatory and oxidative stress.

METHODS

Twenty-four patients with obesity and type 2 diabetes receiving combined oral and insulin therapy were randomly assigned to receive either exenatide 10 μg or placebo twice a day for 12 weeks.

RESULTS

Exenatide increased IL-1RA concentration by 61% (from 318 ± 53 to 456 ± 88 pg/mL; P < 0.05). Exenatide treatment also suppressed Keap-1 protein (P < 0.05) and increased messenger RNA expression of NQO-1, glutathione S-transferase PI, heme oxygenase-1, and p21 and increased NAD(P)H dehydrogenase [quinone] 1 protein (P < 0.05) in mononuclear cells.

CONCLUSIONS

Because IL-1RA protects, maintains, and stimulates β-cell function in humans and Nrf-2‒Keap-1‒ARE protects β cells in animals with experimental diabetes, these actions of exenatide may contribute to a potential protective effect on β cells in diabetes.

Chemopreventive glucosinolate accumulation in various broccoli and collard tissues: Microfluidic-based targeted transcriptomics for by-product valorization

Floret, leaf, and root tissues were harvested from broccoli and collard cultivars and extracted to determine their glucosinolate and hydrolysis product profiles using high performance liquid chromatography and gas chromotography. Quinone reductase inducing bioactivity, an estimate of anti-cancer chemopreventive potential, of the extracts was measured using a hepa1c1c7 murine cell line. Extracts from root tissues were significantly different from other tissues and contained high levels of gluconasturtiin and glucoerucin. Targeted gene expression analysis on glucosinolate biosynthesis revealed that broccoli root tissue has elevated gene expression of AOP2 and low expression of FMOGS-OX homologs, essentially the opposite of what was observed in broccoli florets, which accumulated high levels of glucoraphanin. Broccoli floret tissue has significantly higher nitrile formation (%) and epithionitrile specifier protein gene expression than other tissues. This study provides basic information of the glucosinolate metabolome and transcriptome for various tissues of Brassica oleracea that maybe utilized as potential byproducts for the nutraceutical market.

Cancer chemopreventive activity of compounds isolated from Waltheria indica

ETHNOPHARMACOLOGICAL RELEVANCE

Waltheria indica L. is traditionally used in several countries against inflammatory related diseases and cancer, mainly as a decoction of the aerial parts.

AIM OF THE STUDY

The transcription factor NF-κB is known to induce tumor promotion and progression and is considered a major player in inflammation-driven cancers. Therefore, inhibitors of this pathway possess cancer chemopreventive and chemotherapeutic activities. This study aimed first to confirm the use of Waltheria indica as a traditional anti-inflammatory remedy by assessing the NF-κB inhibitory activity and then to identify the major bioactive compounds. The isolated compounds were also tested for their QR inducing property, a complementary strategy in cancer chemoprevention able to target tumor initiation. Finally, the relevance of in vitro results was examined by investigating the occurrence of the active compounds in traditional preparations.

MATERIALS AND METHODS

Compounds were isolated from the dichloromethane extract of the aerial parts using flash chromatography and semi-preparative HPLC. NF-κB inhibitory activity of pure compounds from Waltheria indica was assessed using a luciferase reporter assay in HEK293 cells. Their QR inducing activity was also assessed in Hepa1c1c7 cells.

RESULTS

Twenty-nine compounds, of which 5 are new, were obtained from the dichloromethane extract and tested for their cancer chemoprevention activity. Eleven compounds inhibited NF-κB and/or induced QR in the low to mid µM range. Chrysosplenol E (20) was active in both tests. Two of the most potent NF-κB inhibitors, waltherione A (4) and waltherione C (5), as well as 20 were found in the traditional decoction, in which 4 and 5 were major compounds.

CONCLUSION

The presence of potent NF-κB inhibitors and QR inducing compounds in the decoction of the aerial parts of Waltheria indica supports its traditional use in inflammatory-related diseases and cancer chemoprevention.

NAD(P)H: quinone oxidoreductase 1 inducer activity of novel 4-aminoquinazoline derivatives

Fourteen novel 4-aminoquinazoline derivatives 2-15 were designed and synthesized. The structure of the newly synthesized compounds was established on the basis of elemental analyses, IR, (1)H-NMR, (13)C-NMR, and mass spectral data. The compounds were evaluated for their potential cytoprotective activity in murine Hepa1c1c7 cells. All of the synthesized compounds showed concentration-dependent ability to induce the cytoprotective enzyme

NAD(P)H

quinone oxidoreductase (NQO1) with potencies in the low- to sub-micromolar range. This approach offers an encouraging framework which may lead to the discovery of potent cytoprotective agents.

Synthesis, molecular modeling and NAD(P)H:quinone oxidoreductase 1 inducer activity of novel 2-phenylquinazolin-4-amine derivatives

Reactive oxygen species (ROS) play an integral role in the pathogenesis of most diseases. This work presents the design and synthesis of novel 2-phenylquinazolin-4-amine derivatives (2-12) and evaluation of their

NAD(P)H

quinone oxidoreductase 1 (NQO1) inducer activity in murine cells. Also, molecular docking of all the new compounds was performed to assess their ability to inhibit Keap1-Nrf2 protein-protein interaction through occupying the Keap1-Nrf2-binding domain which biologically leads to a consequent Nrf2 accumulation and enhanced gene expression of NQO1. Docking results showed that all compounds have the ability to interact with Keap1; however compound 7, the most active compound in this study, showed more interactions with key amino acids.

Endophytic fungi associated with Taxus fuana (West Himalayan Yew) of Pakistan: potential bio-resources for cancer chemopreventive agents

CONTEXT

Endophytic fungi, being a prolific source of bioactive secondary metabolites, are of great interest for natural product discovery.

OBJECTIVE

Isolation and partial characterization of endophytic fungi inhabiting the leaves and woody parts of Taxus fuana Nan Li & R.R. Mill. (Taxaceae) and evaluation of biological activity.

MATERIALS AND METHODS

Endophytic fungal isolates were identified by molecular analysis of internal transcribed spacer (ITS) regions of 18S rDNA. Extracts of the endophytic fungi cultured on potato dextrose agar and modified medium were evaluated using cancer chemoprevention bioassays [inhibition of TNF-α-induced NFκB, aromatase and inducible nitric oxide synthase (iNOS); induction of quinone reductase 1 (QR1)] and growth inhibition with MCF-7 cells.

RESULTS

Nine of 15 fungal isolates were identified as belonging to Epicoccum, Mucor, Penicillium, Chaetomium, Paraconiothriym, Plectania or Trichoderma. Five of the 15 extracts inhibited NFκB activity (IC₅₀ values ranging between 0.18 and 17 μg/mL) and five inhibited iNOS (IC₅₀ values ranging between 0.32 and 12.9 μg/mL). In the aromatase assay, only two isolates mediated inhibition (IC₅₀ values 12.2 and 10.5 μg/mL). With QR1 induction, three extracts exhibited significant activity (concentrations to double activity values ranging between 0.20 and 5.5 μg/mL), and five extracts inhibited the growth of MCF-7 cells (IC₅₀ values ranging from 0.56 to 17.5 μg/mL). Six active cultures were derived from woody parts of the plant material.

CONCLUSION

The endophytic fungi studied are capable of producing pharmacologically active natural compounds. In particular, isolates derived from the wood of Taxus fuana should be prioritized for the isolation and characterization of bioactive constituents.

Salidroside Suppresses HUVECs Cell Injury Induced by Oxidative Stress through Activating the Nrf2 Signaling Pathway

Oxidative stress plays an important role in the pathogenesis of cardiovascular diseases. Salidroside (SAL), one of the main effective constituents of Rhodiola rosea, has been reported to suppress oxidative stress-induced cardiomyocyte injury and necrosis by promoting transcription of nuclear factor E2-related factor 2 (Nrf2)-regulated genes such as heme oxygenase-1 (HO-1) and NAD(P)H dehydrogenase (quinone1) (NQO1). However, it has not been indicated whether SAL might ameliorate endothelial injury induced by oxidative stress. Here, our study demonstrated that SAL might suppress HUVEC cell injury induced by oxidative stress through activating the Nrf2 signaling pathway. The results of our study indicated that SAL decreased the levels of intercellular reactive oxygen species (ROS) and malondialdehyde (MDA), and improved the activities of superoxide dismutase (SOD) and catalase (CAT), resulting in protective effects against oxidative stress-induced cell damage in HUVECs. It suppressed oxidative stress damage by inducing Nrf2 nuclear translocation and activating the expression of Nrf2-regulated antioxidant enzyme genes such as HO-1 and NQO1 in HUVECs. Knockdown of Nrf2 with siRNA abolished the cytoprotective effects against oxidative stress, decreased the expression of Nrf2, HO-1, and NQO1, and inhibited the nucleus translocation of Nrf2 in HUVECs. This study is the first to demonstrate that SAL suppresses HUVECs cell injury induced by oxidative stress through activating the Nrf2 signaling pathway.

Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicity

Parkinson's disease (PD) is the second most common late-age onset neurodegenerative disease. Except for the symptomatic alleviating treatment, no disease modifying therapy is currently available. In this study, we investigated the potential neuroprotective role of hydroxytyrosol (HT), a major phenolic compound present in olive oil, against dopaminergic cell death. We found that HT effectively protected dopaminergic SH-SY5Y cells against dopamine (DA) and 6-hydroxydopamine (6-OHDA) induced cell death, but had no apparent effect on 1-methyl-4-phenylpyridinium (MPP(+))-induced cytotoxicity. Furthermore, we have shown that HT efficiently induced the expression of phase II detoxifying enzymes, including NAD(P)H quinone oxidoreductase 1 (NQO1). Using an NQO1 inhibitor, we revealed that increased NQO1 expression contributed to the protective effect of HT against dopaminergic cell death. Together, our findings suggest that HT has a protective effect against DA- and 6-OHDA-induced dopaminergic cell death, supporting the beneficial effect of olive oil in preventing DA-metabolism related dopaminergic neuron dysfunction.

The protective effect of melatonin on smoke-induced vascular injury in rats and humans: a randomized controlled trial

Smoking is one of the most harmful lifestyles in the world. Very few studies have investigated the effects of melatonin in smoke-induced vascular injury. This study was designed to investigate whether melatonin could protect rats and humans from smoke-induced vascular injury. 32 male rats and a double-blind randomized controlled trial (RCT) containing 63 participants formed the subjects of this study. In rats, 10 mg/kg of melatonin was intraperitoneally injected. Blood samples and abdominal artery were harvested two weeks later. Melatonin decreased the expression of platelet endothelial cell adhesion molecule-1 (CD31), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and endothelin-1 (ET-1) compared with the smoke exposed group (P < 0.05), whereas endothelial nitric oxide synthase (eNOS), nuclear erythroid 2-related factor 2 (Nrf2), NAD(P)H quinone oxidoreductase 1 (NQO-1), catalytic glutamate cysteine ligase (GCLC) and heme oxygenase-1 (HO-1) recovered markedly (P < 0.05). In humans, 3 mg/day of melatonin was taken orally by the participants. Blood samples were drawn at baseline and after two weeks of treatment. Compared with the oral placebo group, melatonin decreased the concentration of fibrinogen (Fbg) (P = 0.04) and free fatty acids (FFA) (P = 0.04) in smokers, along with the decreased expression of ICAM-1, VCAM-1 and ET-1 (P = 0.004, P = 0.001, P < 0.0001, respectively). In contrast, Nrf2 and HO-1 expression were markedly increased (P = 0.0001, P = 0.0049, respectively) after smokers took melatonin orally. In summary, our present data suggest that melatonin could ameliorate smoke-induced vascular injury.

Implications of NQO1 in cancer therapy

NAD(P)H

quinone oxidoreductase (NQO1), an obligatory two-electron reductase, is a ubiquitous cytosolic enzyme that catalyzes the reduction of quinone substrates. The NQO1- mediated two-electron reduction of quinones can be either chemoprotection/detoxification or a chemotherapeutic response, depending on the target quinones. When toxic quinones are reduced by NQO1, they are conjugated with glutathione or glucuronic acid and excreted from the cells. Based on this protective effect of NQO1, the use of dietary compounds to induce the expression of NQO1 has emerged as a promising strategy for cancer prevention. On the other hand, NQO1-mediated two-electron reduction converts certain quinone compounds (such as mitomycin C, E09, RH1 and -lapachone) to cytotoxic agents, leading to cell death. It has been known that NQO1 is expressed at high levels in numerous human cancers, including breast, colon, cervix, lung, and pancreas, as compared with normal tissues. This implies that tumors can be preferentially damaged relative to normal tissue by cytotoxic quinone drugs. Importantly, NQO1 has been shown to stabilize many proteins, including p53 and p33ING1b, by inhibiting their proteasomal degradation. This review will summarize the biological roles of NQO1 in cancer, with emphasis on recent findings and the potential of NQO1 as a therapeutic target for the cancer therapy.

Unprecedent aminophysalin from Physalis angulata

The 95% ethanol extract of the whole plant of Physalis angulata Linn. afforded one new skeletal physalin named aminophysalin A (1) and one new naturally occurring 5β-hydroxy-6a-chloro-5,6-dihydrophysalin B (2), together with five known physalins (3-7). Their structures were elucidated through MS, IR, NMR spectroscopy analyses and X-ray crystallography. Aminophysalin A (1) had an absolutely unusual structural feature in the chemistry of physalins with a nitrogen atom. Compounds 1-7 were evaluated for quinone reductase activities in hepa 1c1c7 cells. Physalin H (6) showed strong quinone reductase induction activity with IR (Induction ratio, QR induction activity) value of 3.74±0.02, using 4-bromoflavone as a positive control substance (2.17±0.01, 10 μg/mL), while compounds 1, 2, 3, 5 showed weak quinone reductase induction activity.

Melatonin stimulates antioxidant enzymes and reduces oxidative stress in experimental traumatic brain injury: the Nrf2-ARE signaling pathway as a potential mechanism

The goal of this study was to evaluate the potential involvement of melatonin in the activation of the nuclear factor erythroid 2-related factor 2 and antioxidant-responsive element (Nrf2-ARE) signaling pathway and the modulation of antioxidant enzyme activity in an experimental model of traumatic brain injury (TBI). In experiment 1, ICR mice were divided into four groups: sham group, TBI group, TBI + vehicle group, and TBI + melatonin group (n = 38 per group). Melatonin (10mg/kg) was administered via an intraperitoneal (ip) injection at 0, 1, 2, 3, and 4h post-TBI. In experiment 2, Nrf2 wild-type (Nrf2(+/+) group) and Nrf2-knockout (Nrf2(-/-) group) mice received a TBI insult followed by melatonin administration (10mg/kg, ip) at the corresponding time points (n = 35 per group). The administration of melatonin after TBI significantly ameliorated the effects of the brain injury, such as oxidative stress, brain edema, and cortical neuronal degeneration. Melatonin markedly promoted the translocation of Nrf2 protein from the cytoplasm to the nucleus; increased the expression of Nrf2-ARE pathway-related downstream factors, including heme oxygenase-1 and

NAD(P)H

quinone oxidoreductase 1; and prevented the decline of antioxidant enzyme activities, including superoxide dismutase and glutathione peroxidase. Furthermore, knockout of Nrf2 partly reversed the neuroprotection of melatonin after TBI. In conclusion, melatonin administration may increase the activity of antioxidant enzymes and attenuate brain injury in a TBI model, potentially via mediation of the Nrf2-ARE pathway.

Correlation of Nrf2, NQO1, MRP1, cmyc and p53 in colorectal cancer and their relationships to clinicopathologic features and survival

Due to emergence of resistant tumor populations, prognosis for metastatic colorectal cancer (CRC) patients remains poor and five-year survival rate is still very low. To guide clinicians in selecting treatment option for CRC patients, reliable markers predictive of poor clinical outcome are desirable. This study analyzed the correlation of NF-E2-related factor 2 (Nrf2), NAD(P)H quinine oxidoreductase 1 (NQO1), multidrug resistant protein 1 (MRP1), cmyc and p53 in CRC and their relationships to Duke's stage and clinical prognosis. 76 specimens of CRC tissues were immunohistochemically investigated using Nrf2, NQO1, MRP1, cmyc and p53 antibodies. IHC stain showed that Nrf2, NQO1, MRP1, cmyc and p53 were highly expressed in CRC tissues compared with adjacent non-tumor tissues. Significant positive correlations were found between the expression of Nrf2 and that of NQO1, MRP1, cmyc and p53. Moreover, there was significant correlation between the high level of Nrf2, NQO1, MRP1, p53 expression and Duke's stage, as well as poor clinical prognosis. We confirmed that Nrf2, NQO1, MRP1, and p53 expression exhibits considerable heterogeneity according to CRC clinical stage and prognosis. Nrf2 is the most promising biomarker in identifying a poor prognostic group of CRC.

Estrogen receptor and PI3K/Akt signaling pathway involvement in S-(-)equol-induced activation of Nrf2/ARE in endothelial cells

S-(-)equol, a natural product of the isoflavone daidzein, has been reported to offer cytoprotective effects with respect to the cardiovascular system, but how this occurs is unclear. Interestingly, S-(-)equol is produced by the human gut, suggesting a role in physiological processes. We report that treatment of human umbilical vein endothelial cells and EA.hy926 cells with S-(-)equol induces ARE-luciferase reporter gene activity that is dose and time dependent. S-(-)equol (10-250 nM) increases nuclear factor-erythroid 2-related factor 2 (Nrf2) as well as gene products of Nrf2 target genes heme oxygenase-1 (HO-1) and NAD(P)H (nicotinamide-adenine-dinucleotide-phosphate) quinone oxidoreductase 1 (NQO1). Endothelial cells transfected with an HA-Nrf2 expression plasmid had elevated HA-Nrf2, HO-1, and NQO1 in response to S-(-)equol exposure. S-(-)equol treatment affected Nrf2 mRNA only slightly but significantly increased HO-1 and NQO1 mRNA. The pretreatment of cells with specific ER inhibitors or PI3K/Akt (ICI182,780 and LY294002) increased Nrf2, HO-1, and NQO1 protein, impaired nuclear translocation of HA-Nrf2, and decreased ARE-luciferase activity. Identical experiments were conducted with daidzein, which had effects similar to S-(-)equol. In addition, DPN treatment (an ERβ agonist) induced the ARE-luciferase reporter gene, promoting Nrf2 nuclear translocation. Cell pretreatment with an ERβ antagonist (PHTPP) impaired S-(-)equol-induced Nrf2 activation. Pre-incubation of cells followed by co-treatment with S-(-)equol significantly improved cell survival in response to H2O2 or tBHP and reduced apoptotic and TUNEL-positively-stained cells. Notably, the ability of S-(-)equol to protect against H2O2-induced cell apoptosis was attenuated in cells transfected with an siRNA against Nrf2. Thus, beneficial effects of S-(-)equol with respect to cytoprotective antioxidant gene activation may represent a novel strategy to prevent and treat cardiovascular diseases.

UDP-glucuronosyltransferase 1A compromises intracellular accumulation and anti-cancer effect of tanshinone IIA in human colon cancer cells

Background and Purpose

NAD(P)H: quinone oxidoreductase 1 (NQO1) mediated quinone reduction and subsequent UDP-glucuronosyltransferases (UGTs) catalyzed glucuronidation is the dominant metabolic pathway of tanshinone IIA (TSA), a promising anti-cancer agent. UGTs are positively expressed in various tumor tissues and play an important role in the metabolic elimination of TSA. This study aims to explore the role of UGT1A in determining the intracellular accumulation and the resultant apoptotic effect of TSA.

Experimental Approach

We examined TSA intracellular accumulation and glucuronidation in HT29 (UGT1A positive) and HCT116 (UGT1A negative) human colon cancer cell lines. We also examined TSA-mediated reactive oxygen species (ROS) production, cytotoxicity and apoptotic effect in HT29 and HCT116 cells to investigate whether UGT1A levels are directly associated with TSA anti-cancer effect. UGT1A siRNA or propofol, a UGT1A9 competitive inhibitor, was used to inhibit UGT1A expression or UGT1A9 activity.

Key Results

Multiple UGT1A isoforms are positively expressed in HT29 but not in HCT116 cells. Cellular S9 fractions prepared from HT29 cells exhibit strong glucuronidation activity towards TSA, which can be inhibited by propofol or UGT1A siRNA interference. TSA intracellular accumulation in HT29 cells is much lower than that in HCT116 cells, which correlates with high expression levels of UGT1A in HT29 cells. Consistently, TSA induces less intracellular ROS, cytotoxicity, and apoptotic effect in HT29 cells than those in HCT116 cells. Pretreatment of HT29 cells with UGT1A siRNA or propofol can decrease TSA glucuronidation and simultaneously improve its intracellular accumulation, as well as enhance TSA anti-cancer effect.

Conclusions and Implications

UGT1A can compromise TSA cytotoxicity via reducing its intracellular exposure and switching the NQO1-triggered redox cycle to metabolic elimination. Our study may shed a light in understanding the cellular pharmacokinetic and molecular mechanism by which UGTs determine the chemotherapy effects of drugs that are UGTs’ substrates.

A tissue homogenate method to prepare gram-scale Allium thiosulfinates and their disulfide conjugates with cysteine and glutathione

The health benefits of Allium vegetables are widely attributed to the enzyme-derived organosulfur compounds called thiosulfinates (TS). However, the lack of a suitable method to prepare TS in good yields has hampered the evaluation of their biological activities. This paper describe a simple enzymatic method using Allium tissue homogenates as a reaction system to prepare gram-scale TS, including those enriched in 1-propenyl groups, which are particularly difficult to obtain. This method is simple, easy to scale up, and requires no column purification step, making it suitable for practical large-scale production of Allium TS. The prepared TS were further utilized to prepare the disulfide conjugates with cysteine and glutathione (CySSR and GSSR, R = methyl, ethyl, propyl, 1-propenyl, and allyl), which are the presumptive metabolites of TS. Among all of the Allium CySSR and GSSR conjugates, the newly prepared glutathione conjugate with 1-propenyl TS, GSSPe, showed the most potent effect to induce quinone reductase (QR, a representative phase II enzyme) in murine hepatoma cells (Hepa 1c1c7) and inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated macrophage cells (RAW 264.7).

NAD(P)H:quinone oxidoreductase expression in Cyp1a-knockout and CYP1A-humanized mouse lines and its effect on bioactivation of the carcinogen aristolochic acid I

Aristolochic acid causes a specific nephropathy (AAN), Balkan endemic nephropathy, and urothelial malignancies. Using Western blotting suitable to determine protein expression, we investigated in several transgenic mouse lines expression of NAD(P)H:quinone oxidoreductase (NQO1)-the most efficient cytosolic enzyme that reductively activates aristolochic acid I (AAI). The mouse tissues used were from previous studies [Arlt et al., Chem. Res. Toxicol. 24 (2011) 1710; Stiborova et al., Toxicol. Sci. 125 (2012) 345], in which the role of microsomal cytochrome P450 (CYP) enzymes in AAI metabolism in vivo had been determined. We found that NQO1 levels in liver, kidney and lung of Cyp1a1⁻/⁻, Cyp1a2⁻/⁻ and Cyp1a1/1a2⁻/⁻ knockout mouse lines, as well as in two CYP1A-humanized mouse lines harboring functional human CYP1A1 and CYP1A2 and lacking the mouse Cyp1a1/1a2 orthologs, differed from NQO1 levels in wild-type mice. NQO1 protein and enzymic activity were induced in hepatic and renal cytosolic fractions isolated from AAI-pretreated mice, compared with those in untreated mice. Furthermore, this increase in hepatic NQO1 enzyme activity was associated with bioactivation of AAI and elevated AAI-DNA adduct levels in ex vivo incubations of cytosolic fractions with DNA and AAI. In conclusion, AAI appears to increase its own metabolic activation by inducing NQO1, thereby enhancing its own genotoxic potential.

Inhibition of ROS-induced apoptosis in endothelial cells by nitrone spin traps via induction of phase II enzymes and suppression of mitochondria-dependent pro-apoptotic signaling

Oxidative stress is the main etiological factor behind the pathogenesis of various diseases including inflammation, cancer, cardiovascular and neurodegenerative disorders. Due to the spin trapping abilities and various pharmacological properties of nitrones, their application as therapeutic agent has been gaining attention. Though the antioxidant properties of the nitrones are well known, the mechanism by which they modulate the cellular defense machinery against oxidative stress is not well investigated and requires further elucidation. Here, we have investigated the mechanisms of cytoprotection of the nitrone spin traps against oxidative stress in bovine aortic endothelial cells (BAEC). Cytoprotective properties of both the cyclic nitrone 5,5-dimethyl-pyrroline N-oxide (DMPO) and linear nitrone α-phenyl N-tert-butyl nitrone (PBN) against H₂O₂-induced cytotoxicity were investigated. Preincubation of BAEC with PBN or DMPO resulted in the inhibition of H₂O₂-mediated cytotoxicity and apoptosis. Nitrone-treatment resulted in the induction and restoration of phase II antioxidant enzymes via nuclear translocation of NF-E2-related factor 2 (Nrf-2) in oxidatively-challenged cells. Furthermore, the nitrones were found to inhibit the mitochondrial depolarization and subsequent activation of caspase-3 induced by H₂O₂. Significant down-regulation of the pro-apoptotic proteins p53 and Bax, and up-regulation of the anti-apoptotic proteins Bcl-2 and p-Bad were observed when the cells were preincubated with the nitrones prior to H₂O₂-treatment. It was also observed that Nrf-2 silencing completely abolished the protective effects of nitrones. Hence, these findings suggest that nitrones confer protection to the endothelial cells against oxidative stress by modulating phase II antioxidant enzymes and subsequently inhibiting mitochondria-dependent apoptotic cascade.

The plasma membrane redox enzyme NQO1 sustains cellular energetics and protects human neuroblastoma cells against metabolic and proteotoxic stress

The plasma membrane redox system (PMRS) of nicotinamide adenine dinucleotide (NADH)-related enzymes plays a key role in the maintenance of cellular energetics. During the aging process, neural cells are particularly sensitive to impaired energy metabolism and oxidative damage, but the involvement of the PMRS in these processes is unknown. Here, we used human neuroblastoma cells with either elevated or reduced levels of the PMRS enzyme NADH-quinone oxidoreductase 1 (NQO1) to investigate how the PMRS regulates neuronal stress responses. Cells with elevated NQO1 levels were more resistant to death induced by 2-deoxyglucose, potassium cyanide (energetic stress), and lactacystin (proteotoxic stress), but were not protected from being killed by H(2)O(2) and serum withdrawal. The NAD(+)(an oxidized form of NADH)/NADH ratio was maintained at a significantly higher level in cells overexpressing NQO1, consistent with enhanced levels of NQO1 activity. Levels of the neuroprotective transcription factors nuclear factor kappa-light-chain-enhancer of activated B cells and nuclear factor (erythroid-derived 2)-like 2, and the protein chaperone HSP70 were elevated in cells overexpressing NQO1. Cells in which NQO1 levels were decreased by RNA interference exhibited increased vulnerability to death induced by 2-deoxyglucose and lactacystin. Thus, a higher NAD(+)/NADH ratio and activation of adaptive stress response pathways are enhanced by the PMRS in neuroblastoma cells, enabling them to maintain redox homeostasis under conditions of energetic and proteotoxic stress. These findings have implications for the development of therapeutic interventions for neural tumors and neurodegenerative conditions.

High-throughput library screening identifies two novel NQO1 inducers in human lung cells

Many phytochemicals possess antioxidant and cancer-preventive properties, some putatively through antioxidant response element-mediated phase II metabolism, entailing mutagen/oxidant quenching. In our recent studies, however, most candidate phytochemical agents were not potent in inducing phase II genes in normal human lung cells. In this study, we applied a messenger RNA (mRNA)-specific gene expression-based high throughput in vitro screening approach to discover new, potent plant-derived phase II inducing chemopreventive agents. Primary normal human bronchial epithelial (NHBE) cells and immortalized human bronchial epithelial cells (HBECs) were exposed to 800 individual compounds in the MicroSource Natural Products Library. At a level achievable in humans by diet (1.0 μM), 2,3-dihydroxy-4-methoxy-4'-ethoxybenzophenone (DMEBP), triacetylresveratrol (TRES), ivermectin, sanguinarine sulfate, and daunorubicin induced reduced nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 (NQO1) mRNA and protein expression in NHBE cells. DMEBP and TRES were the most attractive agents as coupling potency and low toxicity for induction of NQO1 (mRNA level, ≥3- to 10.8-fold that of control; protein level, ≥ two- to fourfold that of control). Induction of glutathione S-transferase pi mRNA expression was modest, and none was apparent for glutathione S-transferase pi protein expression. Measurements of reactive oxygen species and glutathione/oxidized glutathione ratio showed an antioxidant effect for DMEBP, but no definite effect was found for TRES in NHBE cells. Exposure of NHBE cells to H(2)O(2) induced nuclear translocation of nuclear factor erythroid 2-related factor 2, but this translocation was not significantly inhibited by TRES and DMEBP. These studies show that potency and low toxicity may align for two potential NQO1-inducing agents, DMEBP and TRES.

Dyrk1a activates antioxidant NQO1 expression through an ERK1/2-Nrf2 dependent mechanism

BACKGROUND AND AIMS

Among cardiovascular risk factor, people with Down syndrome have a lower plasma homocysteine level. In a previous study, we have shown that DYRK1A (dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1a), a serine/threonine kinase found on human chromosome 21, is implicated on homocysteine metabolism regulation. Indeed, mice that overexpress in liver this kinase have a lower plasma homocysteine level concomitant with an increased hepatic S-adenosyhomocysteine hydrolase (SAHH) activity, which depends on the activation of NAD(P)H:quinone oxidoreductase-1 (NQO1). Since NQO1 gene transcription is under the control of NRF2 and AhR, the aim of the present study was to analyze the effect of DYRK1A overexpression in mice onto NRF2 and AhR signaling pathways.

METHODS

Effects of DYRK1A overexpression were examined in mice overexpressing Dyrk1a treated with an inhibitor, harmine, by real-time quantitative reverse-transcription polymerase reaction and western blotting.

RESULTS

We found that overexpression of DYRK1A increases the nuclear NRF2 quantity, concomitant with the activation of ERK1/2. We also show that the overexpression of Dyrk1a has no effect on PI3K/AKT activation, and AhR signaling pathway in liver of mice.

CONCLUSIONS

Our results reveal a link between DYRK1A and NRF2 signaling pathway.

Suppression of pre adipocyte differentiation and promotion of adipocyte death by anti-HIV drugs

In the present study, we investigated the ability of anti-HIV drugs to interfere with normal cell cycle progression and to induce oxidative stress by perturbing the redox environment. Our results provide evidence that anti-HIV drugs have a differential effect on adipocyte cell cycle and differentiation, being able to modify the response to oxidative stress through an increase of reactive oxygen species (ROS) that compromises the induction of phase-2 and antioxidant enzymes. In detail, saquinavir, efavirenz, and stavudine exert antiadipogenic influences on the model 3T3-L1 cell line, perturbing the oxidative response and inducing of apoptosis. When considered together, the effects of anti-HIV drugs on 3T3-L1 pre adipocytes are distinct but commonly antiadipogenic, thus suggesting another additional possible mechanism by which antiretroviral therapies could contribute to lipoatrophy.

Upregulation of chemoprotective enzymes and glutathione by Nigella sativa (black seed) and thymoquinone in CCl4-intoxicated rats

To examine the hepatoprotective activities of Nigella sativa (Ns) and thymoquinone (TQ) against carbon tetrachloride (CCl(4))-induced hepatotoxicity, the effects of water extract of Ns seeds (50 mg/kg) or TQ (5 mg/kg in corn oil) by gavage for 5 days on detoxifying enzymes and glutathione were compared in healthy and CCl(4)-challenged (1 mL/kg in corn oil, intraperitoneally [ip], a single dose) rats. Both Ns and TQ countered the elevations in serum alanine aminotransferase activity, oxidized glutathione level, and stress ratio caused by CCl(4). Both Ns and TQ ameliorated the reductions in the activities and messenger RNA (mRNA) levels of glutathione S-transferase, NAD(P)H-quinone oxidoreductase, and microsomal epoxide hydrolase, as well as the reductions in reduced glutathione and cysteine levels produced by CCl(4). In many instances, Ns was much superior to TQ in providing protection against the damaging effects caused by CCl(4). This protection could be attributed to the induction of chemoprotective enzymes probably through increasing transcription.

Nrf2-dependent induction of NQO1 in mouse aortic endothelial cells overexpressing catalase

Overexpression of catalase has been shown to accelerate benzo(a)pyrene (BaP) detoxification in mouse aortic endothelial cells (MAECs). NAD(P)H:quinone oxidoreductase-1 (NQO1) is an enzyme that catalyzes BaP-quinone detoxification. Aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor-2 (Nrf2) are transcription factors that control NQO1 expression. Here, we investigated the effects of catalase overexpression on NQO1, Nrf2, and AhR expression. The levels of NQO1 mRNA and protein were comparable in MAECs isolated from wild-type and transgenic mice that overexpress human catalase (hCatTg). BaP treatment increased NQO1 mRNA and protein levels in both groups, with a significantly greater induction in hCatTg MAECs than in wild-type cells. BaP-induced NQO1 promoter activity was dramatically higher in hCatTg MAECs than in wild-type cells. Our data also showed that the basal level of AhR and the BaP-induced level of Nrf2 were significantly higher in hCatTg MAECs than in wild-type cells. Inhibition of specificity protein-1 (Sp1) binding to the AhR promoter region by mithramycin A reversed the enhancing effect of catalase overexpression on AhR expression. Knockdown of AhR by RNA interference diminished BaP-induced expression of Nrf2 and NQO1. Knockdown of Nrf2 significantly decreased NQO1 mRNA and protein levels in cells with or without BaP treatment. NQO1 promoter activity was abrogated by mutation of the Nrf2-binding site in this promoter. In contrast, mutation of the AhR-binding site in the NQO1 promoter did not affect the promoter activity. These results suggest that catalase overexpression upregulates BaP-induced NQO1 expression by enhancing the Sp1-AhR-Nrf2 signaling cascade.

Nrf2-mediated adaptive response to cadmium-induced toxicity involves protein kinase C delta in human 1321N1 astrocytoma cells

Cadmium (Cd) is a toxic heavy metal, and exposure to Cd causes a range of changes within the cell. At high concentrations, Cd causes damage to cells via a range of mechanisms. At low concentrations, Cd can stimulate expression of genes that are part of an adaptive response. In this study, we have used the astrocytoma cell line 1321N1 as a model to investigate the induction of protective enzymes in response to Cd. We have shown that expression of NAD(P)H:quinone oxidoreductase and haem oxygenase enzymes are induced as the protein level by -fold and -fold, and in response to 5 and 10 μM Cd. Levels of NQO1 and HO1 mRNA are also increased by -fold and -fold following 24h exposure to 5 and 10 μM cadmium. An increase in the nuclear accumulation of the transcription factor Nrf2 was also observed following Cd treatment. Through the use of the protein kinase C inhibitor bisindolylmaleimide (VIII) acetate we have demonstrated the involvement PKC in the Nrf2-mediated response of 1321N1 cells to 5-10 μM Cd. We have also shown through the used of 10 μM rottlerin that PKCδ is the isoform responsible for mediating this response.

Chokeberry (Aronia melanocarpa) juice modulates 7,12-dimethylbenz[a]anthracene induced hepatic but not mammary gland phase I and II enzymes in female rats

Chokeberry is a rich source of procyanidins known to have several types of biological activity including anticarcinogenic potential in experimental models. In this study we examined the effect of chokeberry juice on the hepatic and mammary gland carcinogen metabolizing enzyme expression altered by the polycyclic aromatic hydrocarbon, 7,12-dimethylbenz[a]anthracene (DMBA). Sprague-Dawley rats were gavaged with chokeberry juice (8 ml/kg b.w.) for 28 consecutive days. DMBA was administered i.p. on the 27th and the 28th days. Pretreatment with chokeberry juice reduced the activity of CYP1A1 and increased that of CYP2B involved in metabolic activation/detoxication of DMBA in rat liver, as well as expression and activity of phase II enzymes. Chokeberry juice had no effect on these parameters in the mammary gland and DMBA induced DNA damage in rat blood cells. These results together with our earlier observations indicate that metabolic alterations induced by chokeberry feeding are tissue specific and depend on the class of carcinogen.

Differential suppression of proliferation in MCF-7 and MDA-MB-231 breast cancer cells exposed to alpha-, gamma- and delta-tocotrienols is accompanied by altered expression of oxidative stress modulatory enzymes

Tocotrienols belong to the vitamin E family of chemicals known to have potent anti-proliferative and apoptotic activities against a variety of cancer cells with little to no comparable influence on the normal cells. Whether tocotrienols control the expression of phase II antioxidant enzymes in the context of their anti-carcinogenic mechanisms has not been investigated. The present studies were performed to test whether the differential growth inhibition resulting from exposure to α-, γ- and δ-tocotrienols in estrogen receptor-positive human MCF-7 and estrogen receptor-negative MDA-MB-231 breast cancer cells might be accompanied by changes in phase II antioxidant enzymes. Cell proliferation and clonogenicity in both cell lines were significantly inhibited by γ- and δ-tocotrienols with little affect when cells were similarly exposed to α-tocotrienol, at doses up to 10 μM. The expression and activity of several antioxidant enzymes in 10 μM tocotrienol-treated cells were determined by Western blot and biochemical assays. In MDA-MB-231 cells, δ- was more active than α- or γ-tocotrienols in up-regulating glutathione peroxidase; however, the three tocotrienols had comparable activity in inducing thioredoxin. In MCF-7 cells, expression of quinone reductase 2 and thioredoxin was increased by γ- and δ-tocotrienols, whereas quinone reductase 1 was unaffected by exposure to the tocotrienols. The tocotrienols also did not affect the expression and activity of superoxide dismutase in both MCF-7 and MDA-MB-231 cells, but increased catalase activity concomitant with slight reduction in the catalase expression. In MDA-MB-231 cells, treatment by tocotrienols led to several fold increase of NRF2 expression marked by corresponding decrease in KEAP1 levels. By contrast, no significant change in NRF2 and KEAP1 levels was observed in MCF-7 cells. These studies demonstrate that different tocotrienols show distinct and selective activity in regulating the NRF2-KEAP1, in coordination with the induced expression of cytoprotective oxidative stress modulatory genes and regulation of proliferation in breast cancer cells.

Induced expression of drug metabolizing enzymes by preventive agents: role of the antioxidant response element

Identifying agents that block tumor initiation is a goal of cancer prevention. The ability of a chemically varied group of agents to induce various drug metabolizing genes in livers of rats was examined. Sprague-Dawley rats were treated for 7 days with various agents in the diet or by gavage. The agents examined, which might be expected to respond via specific nuclear receptors (CAR, AhR) as well as antioxidant response elements (AREs), included Phase I/II inducers [5,6-benzoflavone (BF, 5000mg/kg diet), diallyl sulfide (DAS, 500mg/kg BW/day), ethoxyquin (EXO, 300mg/kg BW/day) and phenobarbital (PB, 500mg/kg diet)] or pure Phase II inducers [1,2-dithiol-3-thione (DTT, 500mg/kg diet), and cyclopentadithiolthione (CPDTT, 175mg/kg BW/day)]. Liver RNA expression was analyzed employing oligonucleotide microarrays. The agents yielded unique expression profiles. In genes with known AREs, the induction ratios (Levels Treated/Levels Controls) were: quinone oxidoreductase (BF, 8:1; DTT, 3.2:1; CPDTT, 3:1; DAS, 1.8:1; Exo, 1.7:1), glutatione transferase Pi (DTT, 36:1; CPDTT, 34:1; EXO, 8:1; DAS, 5:1; BF, 2.5:1), and aldehyde keto reductase 7A3 (AFAR) (DTT and CPDTT, 14:1; DAS, 6:1; EXO, 4:1; PB, 1.5:1). When the search included a wider variety of Phase II drug metabolizing enzymes, no clear pattern was observed. Agent induced gene expression and preventive activity in published carcinogen induced tumor models showed limited correlation; questioning whether measuring the induction of one or two genes (e.g., quinone reductase) is a surrogate for overall Phase II inducing (antioxidant) and potential anti-tumor activity.

Melatonin downregulates nuclear erythroid 2-related factor 2 and nuclear factor-kappaB during prevention of oxidative liver injury in a dimethylnitrosamine model

Melatonin has potent hepatoprotective effects as an antioxidant. However, the signaling pathway of melatonin in the induction of antioxidant enzymes against acute liver injury is not fully understood. The study aimed to determine whether melatonin could prevent dimethylnitrosamine (DMN)-induced liver injury through nuclear erythroid 2-related factor 2 (Nrf2) and inflammation. Liver injury was induced in rats by a single injection of DMN (30 mg/kg, i.p.). Melatonin treatment (50 mg/kg/daily, i.p.) was initiated 24 hr after DMN injection for 14 days, after which the rats were killed and samples were collected. Serum and antioxidant enzyme activities improved in melatonin-treated rats, compared with DMN-induced liver injury group (P < 0.01). Melatonin reduced the infiltration of inflammatory cells and necrosis in the liver, and increased the expression of NADPH: quinone oxidoreductase-1, heme oxygenase-1, and superoxide dismutase-2, which were decreased by DMN. Melatonin increased expression of novel transcription factor, Nrf2, and decreased expression of inflammatory mediators including tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and inducible nitric oxide synthase. The increased nuclear binding of nuclear factor-kappa B (NF-kappaB) in the DMN-induced liver injury group was inhibited by melatonin. Our results show that melatonin increases antioxidant enzymes and Nrf2 expression in parallel with the decrease of inflammatory mediators in DMN-induced liver injury, suggesting that melatonin may play a role of antioxidant defense via the Nrf2 pathway, by reducing inflammation by NF-kappaB inhibition.

Induction of chemoprotective phase 2 enzymes by ginseng and its components

Phase 2 detoxification enzymes protect against carcinogenesis and oxidative stress. Ginseng ( PANAX spp.) extracts and components were assayed for inducer activity of NQO1 (quinone reductase), a phase 2 enzyme, in Hepa1c1c7 cells. Ginseng extracts were analyzed for ginsenosides and panaxytriol. Korean red PANAX GINSENG extracts demonstrated the most potent phase 2 enzyme induction activity (76,900 U/g dried rhizome powder and 27,800 U/g for two similar preparations). The ginsenoside-enriched HT-1001 American ginseng ( PANAX QUINQUEFOLIUS) extract was the next most potent inducer, with activity of 15,900 U/g, followed by raw American ginseng root with activity of 8700 U/g. Neither a polysaccharide-enriched extract of American ginseng nor a commercial white PANAX GINSENG preparation showed any inducer activity. Pure ginsenosides showed no inducer activity. Protopanaxadiol and protopanaxatriol, deglycosylated ginsenoside metabolic derivatives, showed potent induction activity (approximately 500,000 U/g each). Synthetic panaxytriol was over 10-fold more potent (induction potency 5,760,000 U/g). There was no correlation between ginsenoside content and phase 2 enzyme induction. The most potent inducing red ginseng extract also had the highest panaxytriol content, 120.8 microg/g. We found that ginseng induced NQO1 and that polyacetylenes are the most active components.

Phenolic derivatives from soy flour ethanol extract are potent in vitro quinone reductase (QR) inducing agents

The fractionation of soy flour directed by a cellular bioassay for induction of phase 2 detoxification enzymes was used to identify quinone reductase (QR) inducing agents. A phospholipid-depleted, 80% methanol-partitioned isolate from a crude ethanol extract of soy flour was resolved using normal phase medium-pressure liquid chromatography (MPLC). Early eluting fractions were found to be the most potent QR inducing agents among the separated fractions. Fraction 2 was the most potent, doubling QR at <2 mug/mL. Further fractionation of this isolate led to the identification of several constituents. Fatty acids and sn-1 and sn-2 monoacylglycerols were identified, but were not highly potent QR inducers. Benzofuran-3-carbaldehyde, 4-hydroxybenzaldeyde, 4-ethoxybenzoic acid, 4-ethoxycinnamic acid, benzofuran-2-carboxylic ethyl ester, and ferulic acid ethyl ester (FAEE) were also identified as QR inducing constituents of this fraction. FAEE was the most potent of the identified constituents, doubling QR specific activity at 3.2 muM in the cellular bioassay.

Lipopolysaccharide-induced expression of NAD(P)H:quinone oxidoreductase 1 and heme oxygenase-1 protects against excessive inflammatory responses in human monocytes

Monocytes play a central role in the immunopathological effects of sepsis. This role is mediated by production of the cytokines TNF-alpha and IL-1beta. The transcription factor NF-E2-related factor 2 (Nrf2) regulates innate immune responses in various experimental disease models. Presently, the role of Nrf2-regulated genes in LPS-treated human monocytes is not well defined. Herein we show that Nrf2 mediates a significant regulation of LPS-induced inflammatory responses. Analysis of Nrf2-regulated gene expression in human monocytes showed that LPS induced the expression of the phase II detoxification gene NAD(P)H:quinone oxidoreductase 1 (NQO1). Furthermore, NQO1 mRNA or protein expression in response to LPS was regulated by Nrf2. Silencing Nrf2 expression in human monocytes inhibited LPS-induced NQO1 expression; however, in contrast, it significantly increased TNF and IL-1beta production. Silencing expression of NQO1 alone, or in combination with heme oxygenase-1 (HO-1) silencing, markedly increased LPS-induced TNF and IL-1beta expression. Additionally, overexpression of NQO1 and/or HO-1 inhibited LPS-induced TNF and IL-1beta expression. These results show for the first time that LPS induces NQO1 and HO-1 expression in human monocytes via Nrf2 to modulate their inflammatory responsiveness, thus providing novel potential therapeutic strategies for the treatment of sepsis.

Monodictyochromes A and B, dimeric xanthone derivatives from the marine algicolous fungus Monodictys putredinis

Investigations of the marine-derived fungus Monodictys putredinis led to the isolation of two novel dimeric chromanones (1, 2) that consist of two uniquely modified xanthone-derived units. The structures were elucidated by extensive spectroscopic measurements including NOE experiments and CD analysis to deduce the configuration. The compounds (1, 2) were examined for their cancer chemopreventive potential and shown to inhibit cytochrome P450 1A activity with IC(50) values of 5.3 and 7.5 μM, respectively. In addition, both compounds displayed moderate activity as inducers of NAD(P)H:quinone reductase (QR) in cultured mouse Hepa 1c1c7 cells, with CD values (concentration required to double the specific activity of QR) of 22.1 and 24.8 μM, respectively. Compound 1 was slightly less potent than compound 2 in inhibiting aromatase activity, with IC(50) values of 24.4 and 16.5 μM.

Control of cellular redox status and upregulation of quinone reductase NQO1 via Nrf2 activation by alpha-lipoic acid in human leukemia HL-60 cells

alpha-Lipoic acid (LA) is a naturally-occurring micronutrient that has been actively investigated for the treatment and management of various chronic medical conditions including neurodegenerative diseases, diabetes and hepatic disorders. However, relatively few studies have examined the effects of LA as a chemopreventive agent, particularly in regard to its ability to modulate homeostasis of oxidoreductive state and to regulate detoxification enzymes such as quinone reductase NQO1 in LA-responsive cells. We tested the hypothesis that LA affects the intracellular redox status and induces NQO1 expression using the human promyelocytic HL-60 leukemia cells. We showed that treatment by LA maintains HL-60 cells in a relatively reduced state, supported by the dose/time-dependent increase in the activities of glutathione peroxidase and glutathione reductase and decrease in the activity of catalase. Moreover, LA significantly increased the activity and protein expression of NQO1. The induction of NQO1 was accompanied by the nuclear accumulation of transcription factor Nrf2, which was correlated with a decreased level of Nrf2 in the cytosol as well as the concomitant reduction in the expression of cytoplasmic repressor of Nrf2, Keap1.

Structure-activity relationships and organ specificity in the induction of GST and NQO1 by alkyl-aryl isothiocyanates

PURPOSE

To compare the ability of alkyl-aryl isothiocyanates (ITCs) to increase the activities of the Phase 2 detoxification enzymes NAD[P]H:quinone acceptor oxidoreductase 1 (NQO1) and glutathione S-transferases (GST) in rat tissues in vivo and in cells in vitro.

MATERIALS AND METHODS

Twelve alkyl-aryl ITCs and the fully-reduced derivative of benzyl ITC (cyclohexylmethyl ITC) were administered to rats each day for 5 days. The animals were then killed and organs harvested. The ITCs were also evaluated in a bladder cell line in culture. The activities of NQO1 and GST in the organs and cells were measured.

RESULTS

In vivo, the organ most susceptible to the inductive activity of the ITCs was the urinary bladder, with alpha-methylbenzyl ITC and cyclohexylmethyl ITC being the most effective. Inductive activity in the bladder in vivo did not, however, correlate with that in bladder cells in vitro.

CONCLUSIONS

Induction of Phase 2 enzymes increases resistance to chemical carcinogenesis. ITCs could therefore be valuable chemopreventative agents, and the specificity of these substances toward the urinary bladder suggest that they could be particularly useful for protecting against bladder cancer. In this regard, alpha-methylbenzyl ITC and cyclohexylmethyl ITC could be especially valuable.

In vitro activity of almond skin polyphenols for scavenging free radicals and inducing quinone reductase

Observational studies and clinical trials suggest nut intake, including almonds, is associated with an enhancement in antioxidant defense and a reduction in the risk of cancer and cardiovascular disease. Almond skins are rich in polyphenols (ASP) that may contribute to these putative benefits. To assess their potential mechanisms of action, we tested the in vitro effect of ASP extracted with methanol (M) or a gastrointestinal juice mimic (GI) alone or in combination with vitamins C (VC) or E (VE) (1-10 micromol/L) on scavenging free radicals and inducing quinone reductase (QR). Flavonoid profiles from ASP-M and -GI extracts were different from one another. ASP-GI was more potent in scavenging HOCl and ONOO (-) radicals than ASP-M. In contrast, ASP-M increased and ASP-GI decreased QR activity in Hepa1c1c7 cells. Adding VC or VE to ASP produced a combination- and dose-dependent action on radical scavenging and QR induction. In comparison to their independent actions, ASP-M plus VC were less potent in scavenging DPPH, HOCl, ONOO (-), and O 2 (-) (*). However, the interaction between ASP-GI plus VC promoted their radical scavenging activity. Combining ASP-M plus VC resulted in a synergistic interaction, inducing QR activity, but ASP-GI plus VC had an antagonistic effect. On the basis of their total phenolic content, the measures of total antioxidant activity of ASP-M and -GI were comparable. Thus, in vitro, ASP act as antioxidants and induce QR activity, but these actions are dependent upon their dose, method of extraction, and interaction with antioxidant vitamins.

Persistent induction of hepatic and pulmonary phase II enzymes by 3-methylcholanthrene in rats

We reported earlier that exposure of rats to 3-methylcholanthrene (MC) causes sustained induction of hepatic cytochrome P450 (CYP)1A expression for up to 45 days by mechanisms other than persistence of the parent MC (Moorthy, J. 2000. Pharmacology. Exp. Ther. 294, 313-322). The CYP1A genes are members of the Ah gene battery that also encode CYP1B1 and phase II enzymes such as glutathione S-transferase (GST-alpha), UDP glucuronyl transferase (UGT)1A, NAD(P)H (nicotinamide adenine dinucleotide phosphate, reduced):quinone oxidoreductase I (NQO1), aldehyde dehydrogenase (ALDH), etc. Therefore, in this investigation, we tested the hypothesis that MC elicits persistent induction of CYP1B1 and phase II genes, which are in part regulated by the Ah receptor (AHR). Female Sprague-Dawley rats were treated with MC (100 mumol/kg), ip, once daily for 4 days, and expression of CYP1B1 and several phase II (e.g., GST-alpha, NQO1) genes and their corresponding proteins were determined in lung and liver. The major finding was that MC persistently induced (3- to 10-fold) the expression of several phase II enzymes, including GST-alpha, NQO1, UGT1A1, ALDH, and epoxide hydrolase in both tissues for up to 28 days. However, MC did not elicit sustained induction of CYP1B1. Our results thus support the hypothesis that MC elicits coordinated and sustained induction of phase II genes presumably via persistent activation of the AHR, a phenomenon that may have implications for chemical-induced carcinogenesis and chemopreventive strategies in humans.

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.

Phytochemical profiling and phase II enzyme-inducing properties of Thunbergia laurifolia Lindl. (RC) extracts

Thunbergia laurifolia Lindl. (Acanthaceae) or Rang Chuet (RC) is described in traditional medicine for protection against dietary and environmental toxicants. This work, therefore, investigated RC's phytochemical profile, antimutagenic activity, and xenobiotic detoxification potential in its extracts. RC extracts were prepared by infusion with water, ethanol, acetone and subsequently assayed for major phytochemical constituents. Total phenolic content was 24.33, 5.65, and 1.42microg gallic acid equivalent (GAE) per mL for water, ethanol and acetone extract, respectively. HPLC analysis identified caffeic acid and apigenin as primary constituents of water extracts. Acetone and ethanol extracts contained primarily chlorophyll a and b, pheophorbide a, pheophytin a, and lutein. Treatment of Hepa 1C1C7 cells with standardized RC extracts resulted in a dose-dependent increase in QR specific activity for all extracts. Acetone extract (92microg GAE/mL) increased QR activity 2.8-fold, while ethanol (120microg GAE/mL) and water (1000microg GAE/mL) extracts increased QR activity by 1.35- and 1.56-fold, respectively. The RC extracts were subsequently assayed for mutagen and antimutagenic activity by bacterial reverse mutagenesis assay. All three RC extracts exhibited strong dose-dependent antimutagenic activity inhibiting 2-aminoanthracene induced mutagenesis up to 87% in Salmonella typhimurium TA 98. These results support the traditional medicinal use of RC for detoxification and suggest the potential role of both phenolic acids and natural chlorophyll constituents in modulating these effects.

Bach1 Repression of Ferritin and Thioredoxin Reductase1 Is Heme-sensitive in Cells and in Vitro and Coordinates Expression with Heme Oxygenase1, β-Globin, and NADP(H) Quinone (Oxido) Reductase1

Ferritin gene transcription is regulated by heme as is ferritin mRNA translation, which is mediated by the well studied mRNA.IRE/IRP protein complex. The heme-sensitive DNA sequence in ferritin genes is the maf recognition/antioxidant response element present in several other genes that are induced by heme and repressed by Bach1. We now report that chromatin immunoprecipitated with Bach1 antiserum contains ferritin DNA sequences. In addition, overexpression of Bach1 protein in the transfected cells decreased ferritin expression, indicating insufficient endogenous Bach1 for full repression; decreasing Bach1 with antisense RNA increased ferritin expression. Thioredoxin reductase1, a gene that also contains a maf recognition/antioxidant response element but is less studied, responded similarly to ferritin, as did the positive controls heme oxygenase1 and NADP(H) quinone (oxido) reductase1. Bach1-DNA promoter interactions in cells were confirmed in vitro with soluble, recombinant Bach1 protein and revealed a quantitative range of Bach1/DNA stabilities: ferritin L approximately ferritin H approximately beta-globin, beta-globin approximately 2-fold >heme oxygenase1 = quinone reductase beta-globin approximately 4-fold >thioredoxin reductase1. Such results indicate the possibility that modulation of cellular Bach1 concentrations will have variable effects among the genes coordinately regulated by maf recognition/antioxidant response elements in iron/oxygen/antioxidant metabolism.

Upregulation of NAD(P)H:quinone oxidoreductase by radiation potentiates the effect of bioreductive beta-lapachone on cancer cells

We found that beta-lapachone (beta-lap), a novel bioreductive drug, caused rapid apoptosis and clonogenic cell death in A549 human lung epithelial cancer cells in vitro in a dose-dependent manner. The clonogenic cell death caused by beta-lap could be significantly inhibited by dicoumarol, an inhibitor of NAD(P)H:quinone oxido-reductase (NQO1), and also by siRNA for NQO1, demonstrating that NQO1-induced bioreduction of beta-lap is an essential step in beta-lap-induced cell death. Irradiation of A549 cells with 4 Gy caused a long-lasting upregulation of NQO1, thereby increasing NQO1-mediated beta-lap-induced cell deaths. Although the direct cause of beta-lap-induced apoptosis is not yet clear, beta-lap treatment reduced the expression of p53 and NF-kappaB, whereas it increased cytochrome C release, caspase-3 activity, and gammaH2AX foci formation. Importantly, beta-lap treatment immediately after irradiation enhanced radiation-induced cell death, indicating that beta-lap sensitizes cancer cells to radiation, in addition to directly killing some of the cells. The growth of A549 tumors induced in immunocompromised mice could be markedly suppressed by local radiation therapy when followed by beta-lap treatment. This is the first study to demonstrate that combined radiotherapy and beta-lap treatment can have a significant effect on human tumor xenografts.

Antigenotoxic effect of Xanthohumol in rat liver slices

Xanthohumol (XN), the principal prenylated flavonoid in the hop plant, Humulus lupulus L., is suggested to have cancer chemo-preventive activities. Its mechanisms of protection have been proposed to be inhibition of metabolic activation, induction of detoxifying enzymes and antioxidant activity. Our previous study showed that XN efficiently protected human hepatoma HepG2 cells against the genotoxic effects of two pro-carcinogens (2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and benzo(a)pyrene (BaP)) that are dependent on cytochrome P450 (CYP) mediated metabolic activation, and against genotoxic effects of the oxidative damage inducing tert-butyl hydroperoxide (tBOOH). In the present study, we investigated the antigenotoxic effects of XN in precision-cut rat liver slices. Using the comet assay, we detected that at non-cytotoxic concentrations (0.01-10 microM) XN completely prevented IQ and BaP-induced DNA damage. The protective effects of XN against tBOOH-induced DNA damage was less efficient; the maximal 50% reduction of DNA damage was observed at 0.1 microM XN. In rat microsomes, XN (0.001-10 microM) inhibited CYP1A activity (7-ethoxycoumarin (7EC) de-ethylation) in a concentration-dependent manner. Surprisingly, no inhibition of 7EC metabolism by XN was observed in rat liver slices. XN also did not have any influence on mRNA expression of the enzymes CYP1A2 and quinone reductase (QR). These results indicate that inhibition of metabolic activation of pro-carcinogens by CYP1A is not likely to be the mechanism of its antigenotoxic action. In conclusion, XN efficiently protects DNA against genotoxicity of IQ and BaP and against oxidative DNA damage. Although the mechanism of the protective effect of XN is unclear, our results indicate that XN exhibits antigenotoxic effects in fresh liver tissue and provide additional evidence for the cancer preventive potential of XN.

The Highly Expressed and Inducible Endogenous NAD(P)H:quinone Oxidoreductase 1 in Cardiovascular Cells Acts as a Potential Superoxide Scavenger

It has recently been demonstrated that purified NAD(P)H:quinone oxidoreductase 1 (NQO1) is able to scavenge superoxide (O2(.-)) though the rate of reaction of O2(.-) with NQO1 is much lower than the rate of enzymatic dismutation catalyzed by superoxide dismutase (SOD). This study was undertaken to determine if the endogenously expressed NQO1 in cardiovascular cells could scavenge O2(.-). We observed that NQO1 was highly expressed in cardiovascular cells, including rat aortic smooth muscle A10 and cardiac H9c2 cells, as well as normal human aortic smooth muscle and endothelial cells. NQO1, but not SOD in the cardiovascular cells was highly inducible by 3H-1,2-dithiole-3-thione (D3T). Cytosols from H9c2 and human aortic smooth muscle cells (HASMCs) were isolated to determine the O2(.-) scavenging ability of the endogenously expressed NQO1 by using pyrogallol autooxidation assay. We showed that cytosols from the above cells inhibited pyrogallol autooxidation in an NADPH or NADH-dependent manner. The NADH/NADPH-dependent inhibition of pyrogallol autooxidation by the cytosols was completely abolished by the NQO1-specific inhibitor, ES936, suggesting that the endogenously expressed NQO1 could scavenge O2(.-). In the presence of NADH/NADPH, cytosols from D3T-treated cells showed increased ability to scavenge O2(.-) as compared to cytosols from untreated cells. This increased ability to scavenge O2(.-) was also completely reversed by ES936. 5-(Diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide spin-trapping experiments using potassium superoxide as a O2(.-) generator further confirmed the ability of NQO1 from HASMCs to scavenge O2(.-). The spin-trapping experiments also showed that induction of NQO1 by D3T in HASMCs augmented the O2(.-) scavenging ability. Taken together, these results demonstrate that the highly expressed and inducible endogenous NQO1 in cardiovascular cells may act as a potential O2(.-) scavenger.

Aqueous extract from Spanish black radish (Raphanus sativus L. Var. niger) induces detoxification enzymes in the HepG2 human hepatoma cell line

Spanish black radish (Raphanus sativus L. var. niger) is a member of the Cruciferae family that also contains broccoli and Brussels sprouts, well-known to contain health-promoting constituents. Spanish black radishes (SBR) contain high concentrations of a glucosinolate unique to the radish family, glucoraphasatin, which represents >65% of the total glucosinolates present in SBR. The metabolites of glucosinolates, such as isothiocyanates, are implicated in health promotion, although it is unclear whether glucosinolates themselves elicit a similar response. The crude aqueous extract from 0.3 to 3 mg of dry SBR material increased the activity of the phase II detoxification enzyme quinone reductase in the human hepatoma HepG2 cell line with a maximal effect at a concentration of 1 mg/mL. Treatment of HepG2 cells with the crude aqueous extract of 1 mg of SBR per mL also significantly induced the expression of mRNA corresponding to the phase I detoxification enzymes: cytochrome P450 (CYP) 1A1, CYP1A2, and CYP1B1 as well as the phase II detoxification enzymes: quinone reductase, heme oxygenase 1, and thioredoxin reductase 1. Previous studies have shown that the myrosinase metabolites of different glucosinolates vary in their ability to induce detoxification enzymes. Here, we show that while glucoraphasatin addition was ineffective, the isothiocyanate metabolite of glucoraphasatin, 4-methylthio-3-butenyl isothiocyanate (MIBITC), significantly induced phase II detoxification enzymes at a concentration of 10 microM. These data demonstrate that the crude aqueous extract of SBR and the isothiocyanate metabolite of glucoraphasatin, MIBITC, are potent inducers of detoxification enzymes in the HepG2 cell line.

NRH:quinone oxidoreductase 2 and NAD(P)H:quinone oxidoreductase 1 protect tumor suppressor p53 against 20s proteasomal degradation leading to stabilization and activation of p53

Tumor suppressor p53 is either lost or mutated in several types of cancer. MDM2 interaction with p53 results in ubiquitination and 26S proteasomal degradation of p53. Chronic DNA damage leads to inactivation of MDM2, stabilization of p53, and apoptotic cell death. Here, we present a novel MDM2/ubiquitination-independent mechanism of stabilization and transient activation of p53. The present studies show that 20S proteasomes degrade p53. The 20S degradation of p53 was observed in ubiquitin-efficient and -deficient cells, indicating that this pathway of degradation did not require ubiquitination of p53. The cytosolic quinone oxidoreductases [NRH:quinone oxidoreductase 2 (NQO2) and NAD(P)H:quinone oxidoreductase 1 (NQO1)] interacted with p53 and protected p53 against 20S proteasomal degradation. Further studies revealed that acute exposure to radiation or chemical leads to induction of NQO1 and NQO2 that stabilizes and transiently activates p53 and downstream genes. These results suggest that stress-induced NQO1 and NQO2 transiently stabilize p53, which leads to protection against adverse effects of stressors.