Hepatoprotective Effect of Quercetin on Endoplasmic Reticulum Stress and Inflammation after Intense Exercise in Mice through Phosphoinositide 3-Kinase and Nuclear Factor-Kappa B

Revolutionizing Alzheimer's treatment: Harnessing human serum albumin for targeted drug delivery and therapy advancements

Alzheimer's disease (AD) is a neurodegenerative disorder initiated by amyloid-beta (Aβ) accumulation, leading to impaired cognitive function. Several delivery approaches have been improved for AD management. Among them, human serum albumin (HSA) is broadly employed for drug delivery and targeting the Aβ in AD owing to its biocompatibility, Aβ inhibitory effect, and nanoform, which showed blood-brain barrier (BBB) crossing ability via glycoprotein 60 (gp60) receptor and secreted protein acidic and rich in cysteine (SPARC) protein to transfer the drug molecules in the brain. Thus far, there is no previous review focusing on HSA and its drug delivery system in AD. Hence, the reviewed article aimed to critically compile the HSA therapeutic as well as drug delivery role in AD management. It also delivers information on how HSA-incorporated nanoparticles with surfaced embedded ligands such as TAT, GM1, and so on, not only improve BBB permeability but also increase neuron cell targetability in AD brain. Additionally, Aβ and tau pathology, including various metabolic markers likely BACE1 and BACE2, etc., are discussed. Besides, the molecular interaction of HSA with Aβ and its distinctive forms are critically reviewed that HSA can segregate Zn(II) and Cu(II) metal ions from Aβ owing to high affinity. Furthermore, the BBB drug delivery challenges in AD are addressed. Finally, the clinical formulation of HSA for the management of AD is critically discussed on how the HSA inhibits Aβ oligomer and fibril, while glycated HSA participates in amyloid plaque formation, i.e., β-structure sheet formation. This review report provides theoretical background on HSA-based AD drug delivery and makes suggestions for future prospect-related work.

Exercise enhances hepatic mitochondrial structure and function while preventing endoplasmic reticulum stress and metabolic dysfunction-associated steatotic liver disease in mice fed a high-fat diet

Metabolic dysfunction-associated steatotic liver disease (MASLD) has attracted increasing attention from the scientific community because of its severe but silent progression and the lack of specific treatment. Glucolipotoxicity triggers endoplasmic reticulum (ER) stress with decreased beta-oxidation and enhanced lipogenesis, promoting the onset of MASLD, whereas regular physical exercise can prevent MASLD by preserving ER and mitochondrial function. Thus, the hypothesis of this study was that high-intensity interval training (HIIT) could prevent the development of MASLD in high-fat (HF)-fed C57BL/6J mice by maintaining insulin sensitivity, preventing ER stress, and promoting beta-oxidation. Forty male C57BL/6J mice (3 months old) comprised 4 experimental groups: the control (C) diet group, the C diet + HIIT (C-HIIT) group, the HF diet group, and the HF diet + HIIT (HF-HIIT) group. HIIT sessions lasted 12 minutes and were performed 3 times weekly by trained mice. The diet and exercise protocols lasted for 10 weeks. The HIIT protocol prevented weight gain and maintained insulin sensitivity in the HF-HIIT group. A chronic HF diet increased ER stress-related gene and protein expression, but HIIT helped to maintain ER homeostasis, preserve mitochondrial ultrastructure, and maximize beta-oxidation. The increased sirtuin-1/peroxisome proliferator-activated receptor-gamma coactivator 1-alpha expression implies that HIIT enhanced mitochondrial biogenesis and yielded adequate mitochondrial dynamics. High hepatic fibronectin type III domain containing 5/irisin agreed with the antilipogenic and anti-inflammatory effects observed in the HF-HIIT group, reinforcing the antisteatotic effects of HIIT. Thus, we confirmed that practicing HIIT 3 times per week maintained insulin sensitivity, prevented ER stress, and enhanced hepatic beta-oxidation, impeding MASLD development in this mouse model even when consuming high energy intake from saturated fatty acids.

Protective effects of a chemically characterized extract from solanum torvum leaves on acetaminophen-induced liver injury

Distinct parts of Solanum torvum Swartz. (Solanaceae) are popularly used for a variety of therapeutic purposes. This study determined the phytochemical composition of a phenolic fraction of S. torvum leaf aqueous extract and investigated its antioxidant and liver-protective properties. A phenolic compound-enriched fraction, or phenolic fraction (STLAE-PF) of an infusion (STLAE) of S. torvum leaves, was tested in vitro (antagonism of H₂O₂ in cytotoxicity and DCF assays with HepG2/C3A cells), and in vivo for antioxidant activity and protective effects against acetaminophen (APAP)-induced liver injury in mice. Thirty-eight compounds (flavonoids, esters of hydroxycinnamic acid, and chlorogenic acid isomers) were tentatively identified (high-performance liquid chromatography coupled to high-resolution electrospray mass spectrometry) in the STLAE-PF fraction. In vitro assays in HepG2/C3A cells showed that STLAE-PF and some flavonoids contained in this phenolic fraction, at noncytotoxic levels, antagonized in a concentration-dependent manner the effects of a powerful oxidant agent (H₂O₂). In C57BL/6 mice, oral administration of STLAE (600 and 1,200 mg/kg bw) or STLAE-PF (300 mg/kg bw) prevented the rise in serum transaminases (ALT and AST), depletion of reduced glutathione (GSH) and elevation of thiobarbituric acid reactive species (TBARs) levels in the liver caused by APAP (600 mg/kg bw, i.p.). The hepatoprotective effects of STLAE-PF (300 mg/kg bw) against APAP-caused liver injury were comparable to those of N-acetyl-cysteine (NAC 300 or 600 mg/kg bw i.p.). These findings indicate that a phenolic fraction of S. torvum leaf extract (STLAE-PF) is a new phytotherapeutic agent potentially useful for preventing/treating liver injury caused by APAP overdosing.

Quercetin Attenuates Copper-Induced Apoptotic Cell Death and Endoplasmic Reticulum Stress in SH-SY5Y Cells by Autophagic Modulation

An increase in anthropogenic activities results in metal contamination in the ecosystem which has proven to be a major health risk in humans, as they make entry into cellular organelles via agricultural products. Copper (Cu) is one such metal that acts as an essential cofactor for the activity of several enzymes, one being the cytochrome c oxidase. The increasing number of evidence suggests a substantial correlation of Cu overload with neurodegenerative disorders, including Parkinson's disease (PD). We aim to explore quercetin, a well-known polyphenol, as an alternative for combating Cu-induced toxicity in human neuroblastoma SH-SY5Y secondary cell lines. We observed that Cu increased intracellular reactive oxygen species (ROS) levels, triggered morphological deformities and condensation of nuclei, caused an imbalance in the mitochondrial membrane potential (MMP), and finally induced apoptotic cell deaths. We further investigated the effects of Cu in modulating the pro- and anti-apoptotic proteins, such as Bax, Bcl-2, etc. However, quercetin reversed these changes owing to its antioxidant and anti-apoptotic properties, resulting in autophagy induction as an outcome of upregulation of autophagosome-bound microtubules-associated protein light chain-3 (LC3II). Besides, we investigated the role of Cu in stimulating ER stress proteins, viz. PERK, CHOP, and the concomitant responses of quercetin in restoring the ER homeostasis in cellular organelles like mitochondria and ER, against Cu-induced toxic insults by modulating autophagic pathways. Overall, this research work proposes a remedial approach for Cu-mediated neurotoxicity through understanding the diverse molecular signaling inside a cell with an aim to develop effective therapeutics.

Melatonin reduces muscle damage, inflammation and oxidative stress induced by exhaustive exercise in people with overweight/obesity

BACKGROUND

Intense physical exercise leads to inflammation, oxidative stress and muscle damage, and these responses are of greater magnitude in people with obesity. Melatonin (MLT) is considered an endogenous antioxidant which may have beneficial effects against inflammation, oxidative stress and promote tissue repair after exercise. The aim of this study was to examine the effect of MLT on inflammatory parameters, oxidative stress and muscle damage in people with overweight/obesity after a high-intensity interval exercise (HIIE).

METHODS

A total of 23 subjects with obesity (9 men and 14 women) age: 33.26 ± 9.81 years, BMI: 37.75 ± 8.87 kg.m-2 were randomized to participate in two experimental sessions: HIIE + Placebo and HIIE + MLT (3 mg). The HIIE protocol corresponds to 8 intervals of 1 min (90% of the maximal aerobic power (MAP)) alternating with 2 min recovery (45% of the MAP). Blood samples were drawn before and 5 min after each exercise session.

RESULTS

MLT ingestion attenuated the increase of inflammation (C-reactive protein, white blood cells (P < 0.001, ηp2 = 0.45; for both) and Neutrophils (P < 0.01, ηp2 = 0.36)) and hepatic and muscle damage (Aspartate aminotransferase (P < 0.01, ηp2 = 0.25), Alanine aminotransferase (P < 0.01, ηp2 = 0.27) and Creatine kinase (P = 0.02, ηp2 = 0.23). MLT also attenuated the exercise induced lipid and protein peroxidation (i.e., Malondialdehyde (P = 0.03, ηp2 = 0.19) and AOPP (P < 0.001, ηp2 = 0.55)). Concerning the antioxidant status, MLT intake increased Thiol (P < 0.01, ηp2 = 0.26) and Catalase (P < 0.01, ηp2 = 0.32) and decreased Uric acid (P = 0.02, ηp2 = 0.2) and Total bilirubin (P < 0.01, ηp2 = 0.33).

CONCLUSIONS

MLT intake before HIIE reduced muscle damage by modulating oxidative stress and preventing overexpression of the pro-inflammatory mediators in people with obesity.

Quercetin Regulates Key Components of the Cellular Microenvironment during Early Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a health problem worldwide due to its high mortality rate, and the tumor microenvironment (TME) plays a key role in the HCC progression. The current ineffective therapies to fight the disease still warrant the development of preventive strategies. Quercetin has been shown to have different antitumor activities; however, its effect on TME components in preneoplastic lesions has not been fully investigated yet. Here, we aimed to evaluate the effect of quercetin (10 mg/kg) on TME components during the early stages of HCC progression induced in the rat. Histopathological and immunohistochemical analyses showed that quercetin decreases the size of preneoplastic lesions, glycogen and collagen accumulation, the expression of cancer stem cells and myofibroblasts markers, and that of the transporter ATP binding cassette subfamily C member 3 (ABCC3), a marker of HCC progression and multi-drug resistance. Our results strongly suggest that quercetin has the capability to reduce key components of TME, as well as the expression of ABCC3. Thus, quercetin can be an alternative treatment for inhibiting the growth of early HCC tumors.

Nonalcoholic fatty liver disease: The role of quercetin and its therapeutic implications

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease, affecting almost one-third of the general population and 75% of obese patients with type 2 diabetes. The aim of this article is to review the current evidence concerning the role of quercetin, a natural compound and flavonoid, and its possible therapeutic effects on this modern-day disease. Despite the fact that the exact pathophysiological mechanisms through which quercetin has a hepatoprotective effect on NAFLD are still not fully elucidated, this review clearly demonstrates that this flavonoid has potent antioxidative stress action and inhibitory effects on hepatocyte apoptosis, inflammation, and generation of reactive oxygen species, factors which are linked to the development of the disease. NAFLD is closely associated with increased dietary fat consumption, especially in Western countries. The hepatoprotective effect of quercetin against NAFLD merits serious consideration and further validation by future studies.

Quercetin ameliorates ochratoxin A-Induced immunotoxicity in broiler chickens by modulation of PI3K/AKT pathway

Ochratoxin A (OTA) is a fungal secondary metabolite produced by certain species of Aspergillus and Penicillium, and exerts immunosuppressive effect on humans and animals. Quercetin (QUE) is one of the flavonoids produced as a plant-secondary metabolite. The present study was designed to evaluate the efficacy of QUE against the immunotoxic hazard of OTA in broiler chickens. Forty one-day-old broiler chicks were randomly and equally allocated into four groups; control, OTA (0.5 mg/kg feed), QUE (0.5 g/kg feed) and OTA + QUE (0.5 mg/kg OTA + 0.5 g/kg QUE). The results revealed that dietary OTA induced a significant decrease in the antibody response to Newcastle Disease (ND), Infectious Bronchitis (IB) and Avian Influenza (AI) vaccination and in the lymphoproliferative response to Phytohemagglutinin-P (PHA-P). Ochratoxin A also induced oxidative stress and lipid peroxidation in the bursa of Fabricius, spleen and thymus tissues of chickens as demonstrated by decreased CAT and GSH levels and increased TBARS content. In addition, administration of OTA resulted in apoptosis, which was evident by the increased expression level of PTEN, Bax and Caspase-3 genes and decreased expression level of PI3K, AKT and Bcl-2 genes. Furthermore, exposure to OTA resulted in various pathological lesions in the bursa of Fabricius, spleen and thymus of chickens. On the other hand, administration of QUE ameliorated most of the immunotoxic effects of OTAby its immunomodulatory, antioxidant and anti-apoptotic activities. Taken together, the results suggested that QUE potentially alleviated the OTA-induced immunotoxicity in broiler chickens, probably through amelioration of oxidative stress and activation of the PI3K/AKT signaling pathway.

Quercetin and its role in modulating endoplasmic reticulum stress: A review

The endoplasmic reticulum (ER) is the place where proteins and lipids are biosynthesized and where transmembrane proteins are folded. Both pathological and physiological situations may disturb the function of the ER, resulting in ER stress. Under stress conditions, the cells initiate a defensive procedure known as the unfolded protein response (UPR). Cases of severe stress lead to autophagy and/or the induction of cell apoptosis. Many studies implicate ER stress as a major factor contributing to many diseases. Therefore, the modulation of ER stress pathways has become an attractive therapeutic target. Quercetin is a plant-derived metabolite belonging to the flavonoids class which presents a range of beneficial effects including anti-inflammatory, cardioprotective, anti-oxidant, anti-obesity, anti-carcinogenic, anti-atherosclerotic, anti-diabetic, anti-hypercholesterolemic, and anti-apoptotic activities. Quercetin also has anti-cancer activity, and can be used as an adjuvant to decrease resistance to cancer chemotherapy. Furthermore, the effect of quercetin can be increased with the help of nanotechnology. This review discusses the role of quercetin in the modulation of ER stress (and related diseases) and provides novel evidence for the beneficial use of quercetin in therapy.

Natural Phyto-Antioxidant Albumin Nanoagents to Treat Advanced Alzheimer's Disease

Phytotherapeutic approaches are of immense value in the treatment of advanced Alzheimer's disease (AD) because of their diverse biological components and potential multitarget mechanisms. In this study, quercetin, a natural neuroprotective flavonoid, was encapsulated in human serum albumin to obtain HSA@QC nanoparticles (HQ NPs) as a natural phyto-antioxidant albumin nanoagent for the treatment of advanced AD. HQ NPs showed excellent antioxidant effects and protected PC12 cells from H2O2-induced oxidative damage. The intranasal administration of HQ NPs in 11-month-old APP/PS1 mice, which represented advanced AD, effectively prevented the loss of body weight, increased survival rates, and significantly reduced oxidative stress, Aβ aggregation, neuronal apoptosis, and synaptic damage in the brain. It also ultimately reversed severely impaired cognitive function. In addition to their favorable anti-AD effects, HQ NPs exhibited excellent biosafety and biocompatibility owing to their natural composition and are expected to become an ideal choice for future drug development and clinical applications.

Senolytic agent Quercetin ameliorates intervertebral disc degeneration via the Nrf2/NF-κB axis

OBJECTIVE

Intervertebral disc degeneration (IDD) represents major cause of low back pain. Quercetin (QUE) is one of the approved senolytic agents. In this study, we evaluated the protective effects of QUE on IDD development and its underlying mechanism.

METHODS

Effects of senolytic agent QUE on the viability of nucleus pulposus cells (NPCs) were measured by CCK-8 assays and EdU staining. The senescence associated secreted phenotype (SASP) factors expressions were measured by qPCR, western blot, and ELISA; and NF-κB pathway was detected by immunofluorescence and western blot. Molecular docking was applied to predict the interacting protein of QUE; while Nrf2 was knocked down by siRNAs to confirm its role in QUE regulated senescence phenotype. X-ray, MRI, Hematoxylin-Eosin and Safranin O-Fast green staining were performed to evaluate the therapeutic effects of QUE on IDD in the puncture-induced rat model.

RESULTS

In in vitro experiments, QUE inhibited SASP factors expression and senescence phenotype in IL-1β-treated NPCs. Mechanistically, QUE suppressed IL-1β induced activation of the NF-κB pathway cascades; it was also demonstrated in molecular docking and knock down studies that QUE might bind to Keap1-Nrf2 complex to suppress NF-κB pathway. In vivo, QUE ameliorated the IDD process in the puncture-induced rat model.

CONCLUSIONS

Together the present work suggests that QUE inhibits SASP factors expression and senescence phenotype in NPCs and ameliorates the progression of IDD via the Nrf2/NF-κB axis, which supports senolytic agent QUE as a potential therapeutic agent for the treatment of IDD.

Quercetin and hydroxytyrosol as modulators of hepatic steatosis: A NAFLD-on-a-chip study

Organs-on-chip (OoCs) are catching on as a promising and valuable alternative to animal models, in line with the 3Rs initiative. OoCs enable the creation of three-dimensional (3D) tissue microenvironments with physiological and pathological relevance at unparalleled precision and complexity, offering new opportunities to model human diseases and to test the potential therapeutic effect of drugs, while overcoming the limited predictive accuracy of conventional 2D culture systems. Here, we present a liver-on-a-chip model to investigate the effects of two naturally occurring polyphenols, namely quercetin and hydroxytyrosol, on nonalcoholic fatty liver disease (NAFLD) using a high-content analysis readout methodology. NAFLD is currently the most common form of chronic liver disease; however, its complex pathogenesis is still far from being elucidated, and no definitive treatment has been established so far. In our experiments, we observed that both polyphenols seem to restrain the progression of the free fatty acid-induced hepatocellular steatosis, showing a cytoprotective effect due to their antioxidant and lipid-lowering properties. In conclusion, the findings of the present work could guide novel strategies to contrast the onset and progression of NAFLD.

Intensive Running Enhances NF-κB Activity in the Mice Liver and the Intervention Effects of Quercetin

Background: Emerging evidence has supported that intensive exercise induces weakened performance and immune and metabolic disorders. We systematically evaluated the effects of quercetin against hepatic inflammatory damage caused by repeated intensive exercise and explored the potential mechanism. Methods: Male BALB/c mice were administered quercetin (100 mg/kg BW) for four weeks, and performed a treadmill running protocol of 28 m/min, 5° slope, 90 min/day concurrently for the last seven days. Results: Quercetin administration reduced the leakage of aspartic acid and alanine aminotransferase and improved ultrastructural abnormalities such as swelling, and degeneration caused by high-intensity running in mice. Quercetin significantly decreased the hepatic and plasmatic levels of inflammatory cytokines IL-1β, IL-6, TNF-α, inducible nitric oxide synthase, cyclooxygenase-2 and intercellular adhesion molecule-1—provoked by over-exercise. Furthermore, diminished activation and nuclear translocation of NF-κB were found after quercetin treatment through inhibiting IKKα and Iκbα phosphorylation of intensive running mice. Conclusion: Quercetin offers protection for mouse livers against intensive sports-induced inflammatory injury, and the suppression of the NF-κB signal transduction pathway may play a role in its anti-inflammatory effects. Our findings broaden our understanding of natural phytochemicals as a promising strategy to prevent excessive exercise damage.

Regulation of the cerebrovascular smooth muscle cell phenotype by mitochondrial oxidative injury and endoplasmic reticulum stress in simulated microgravity rats via the PERK-eIF2α-ATF4-CHOP pathway

Microgravity exposure results in vascular remodeling and cardiovascular dysfunction. Here, the effects of mitochondrial oxidative stress on vascular smooth muscle cells (VSMCs) in rat cerebral arteries under microgravity simulated by hindlimb unweighting (HU) was studied. Endoplasmic reticulum (ER)-resident transmembrane sensor proteins and phenotypic markers of rat cerebral VSMCs were examined. In HU rats, CHOP expression was increased gradually, and the upregulation of the PERK-eIF2α-ATF4 pathway was the most pronounced in cerebral arteries. Furthermore, PERK/p-PERK signaling, CHOP, GRP78 and reactive oxygen species were augmented by PERK overexpression but attenuated by the mitochondria-targeting antioxidant MitoTEMPO. Meanwhile, p-PI3K, p-Akt and p-mTOR protein levels in VSMCs were increased in HU rat cerebral arteries. Compared with the control, HU rats exhibited lower α-SMA, calponin, SM-MHC and caldesmon protein levels but higher OPN and elastin levels in cerebral VSMCs. The cerebral VSMC phenotype transition from a contractile to synthetic phenotype in HU rats was augmented by PERK overexpression and 740Y-P but reversed by MitoTEMPO and the ER stress inhibitors tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid (4-PBA). In summary, mitochondrial oxidative stress and ER stress induced by simulated microgravity contribute to phenotype transition of cerebral VSMCs through the PERK-eIF2a-ATF4-CHOP pathway in a rat model.

Natural antioxidants' effects on endoplasmic reticulum stress-related diseases

Endoplasmic reticulum (ER) stress is a normal molecular process induced by the over-accumulation of misfolded or unfolded proteins. ER stress induces the unfolded protein response (UPR), which reduces global protein synthesis, increases ER capacity and protein degradation, to restart ER homeostasis, allowing cell survival. However, the over-induction of UPR can also trigger inflammatory processes, tissue damage and cell death. ER stress is involved in several pathologies, like endothelial dysfunction, diabetes and heart, liver, kidney or neurological diseases. Although the progression of these diseases is the result of several pathological mechanisms, oxidative stress has been widely related to these pathologies. Moreover, ER stress can establish a progressive pathological cycle with oxidative stress. Therefore, the use of natural antioxidants, able to modulate both oxidative and ER stress, can be a new strategy to mitigate these diseases. This review is focused on the effects of natural antioxidant compounds on ER stress in endothelial dysfunction, diabetes and heart, liver, kidney or neurological diseases.

Flavonoids and gut health

Flavonoids are dietary non-nutrient bioactives with antioxidant and anti-inflammatory properties. Fruits, vegetables, nuts, legumes, and tea are rich in flavonoids. After consumption, flavonoids are extensively metabolized by the gut microbiota and host tissues. Flavonoid metabolism exhibits extensive variation between individuals. It is plausible that inter-individual differences in flavonoid metabolism impact the immune system. Pre-clinical studies have characterized direct and indirect mechanisms by which flavonoids modulate intestinal immune function. This includes modulation of T cell differentiation, alteration of gut microbiota, and modulation of cytokines. Defining the importance of these mechanisms to human chronic disease will improve dietary recommendations for the anti-inflammatory uses of flavonoids.

A systematic review on hepatoprotective activity of quercetin against various drugs and toxic agents: Evidence from preclinical studies

Quercetin is one of the most abundant flavonoids in human diet that has been reported to exhibit a wide range of pharmacological properties. The biochemical and molecular mechanisms involved in the hepatoprotective activity of quercetin were discussed in this review. Quercetin exhibited hepatoprotective activity against 2-butoxyethanol, acrylamide, acrylonitrile, aflatoxin B1, aroclor-1254, arsenic, sodium arsenite, azathioprine, cadmium chloride, carbon tetrachloride, chlorpyrifos, cyclosporine A, diazinon, dimethylnitrosamine, doxorubicin, epirubicin, ethanol, fenvalerate, isoniazide, rifampicin, lead acetate, lindane, D-galactosamine, methotrexate, methylmercury, nickel sulfate, paracetamol, perfluorooctanoic acid, polychlorinated biphenyls, pyrrolizidine alkaloid clivorine, rotenone, sodium fluoride, streptazotocin, tert-butyl hydroperoxide, thioacetamide, titanium dioxide, tumor necrosis factor-α, tripterygium glycoside, triptolide, ultraviolet A light, concavalin A, bisphenol, and ischemia-induced hepatotoxicity in various animal models due to its antioxidant, free radical-scavenging,anti-inflammatory, antiapoptotic, and cytochrome P450 2E1 (CYP2E1) inhibitory activities. In this review, we provide an overview of the possible mechanisms by which quercetin reduced the hepatotoxicity of different hepatotoxicants. This will help the toxicologists, pharmacologists, and chemists to develop new safer pharmaceutical products with quercetin and other hepatotoxicants.

Antioxidant and hepato-preventive effect of Citrus aurantium extract against carbon tetrachloride-induced hepatotoxicity in rats and characterisation of its bioactive compounds by HPLC-MS

The objective of this study is to explore the preventive effects of ethyl acetate fraction from Citrus aurantium leaf extract (EACA), associated with its phytochemical content, against the toxic impacts of acute exposure to carbon tetrachloride (CCl₄) in the liver of adult rats. HPLC analysis of ethyl acetate fraction from extract C. aurantium revealed eight compounds. Administration of a single dose of CCl₄ caused hepatoxicity as monitored by an increase in lipid peroxidation (thiobarbituric acid reactive substances) and in protein carbonyl level but a decrease in antioxidant markers in the liver tissue. The pre-treatment with EACA; significantly prevented the increased plasma levels of hepatic markers and lipid levels induced by CCl₄ in rats. Furthermore, this fraction ameliorated biochemical and histological parameters as compared to CCl₄-treated group. Our results suggest that C. aurantium contains promising substances to counteract the CCl₄ intoxication and can be efficient in the prevention of hepatotoxicity complications.

Genipin attenuates mitochondrial-dependent apoptosis, endoplasmic reticulum stress, and inflammation via the PI3K/AKT pathway in acute lung injury

The protective effects of genipin against lipopolysaccharide (LPS)-induced acute lung injury (ALI) have been reported; however, the mechanism is unclear. Genipin performs its pharmacological effects via activation of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. In the present study, we aimed to determine whether the PI3K/AKT pathway is involved in the protective effects of genipin against mitochondrial-dependent apoptosis, endoplasmic reticulum stress (ERS), and inflammation in ALI. We constructed in vivo and in vitro models of LPS-induced ALI. PI3K/AKT signaling was inhibited using LY294002. Pretreatment with genipin increased AKT phosphorylation, indicating that PI3K/AKT signaling was upregulated. Genipin pretreatment prevented LPS-induced histopathological deterioration, increased pulmonary edema, and decreased oxygenation index, all of which were inhibited using LY294002. In addition, genipin pretreatment attenuated LPS-mediated mitochondrial apoptosis, as indicated by improved mitochondrial dysfunction, downregulation of BAX (BCL2 associated X, apoptosis regulator), upregulation of BCL2 (BCL2 apoptosis regulator), inhibited the release of cytochrome c, activation of caspase-3, and cell apoptosis. Genipin pretreatment inhibited the LPS-induced upregulation of AF4/FMR2 family member 4 (CHOP), glucose-regulated protein, 78 kDa (GRP78), and X-box binding protein 1 (XBP1) levels, indicating ERS suppression. Moreover, genipin pretreatment alleviated LPS-induced inflammation, indicating by blockade of nuclear factor kappa b (NF-κB) signaling activation and reduced tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 levels in the lung and bronchoalveolar lavage fluid. LY294002 could inhibit these genipin-induced protective effects against apoptosis, ERS, and inflammation. Thus, genipin significantly activates PI3K/AKT signaling to ameliorate mitochondria-dependent apoptosis, ERS, and inflammation in LPS-induced ALI.

Rapamycin Rescues Endoplasmic Reticulum Stress-Induced Dry Eye Syndrome in Mice

Purpose

To investigate whether rapamycin protects tear production and the ocular surface during endoplasmic reticulum (ER) stress-induced dry eye syndrome in mice.

Methods

Tunicamycin was injected intraperitoneally in BALB/c mice without or with rapamycin (TM or RM5 group). Peritoneal injection of PBS performed in vehicle group. Group without injection served as control. Blinking rate, fluorescein staining score (FSS), and phenol red thread tear production test were measured at 4 days, 1 week, and 2 weeks after treatment. Levels of inflammatory and angiogenic cytokines were measured by ELISA.

Results

Blinking rate and FSS were elevated, and tear production was decreased in TM group compared with controls (P < 0.05 for all), which was ameliorated by rapamycin at 1 and 2 weeks. Levels of inflammatory and angiogenic cytokines in the cornea and lacrimal glands were higher in the TM group than controls, and lower in the RM5 group than the TM group at 1 and 2 weeks (P < 0.05 for all).

Conclusion

Rapamycin protected tear production and the ocular surface against this dry eye syndrome by ameliorating ER stress-induced vascular damage and inflammation of lacrimal glands and the ocular surface.

The IRE1α-XBP1 pathway function in hypoxia-induced pulmonary vascular remodeling, is upregulated by quercetin, inhibits apoptosis and partially reverses the effect of quercetin in PASMCs

Hypoxia is a common cause of pulmonary vascular remodeling and endoplasmic reticulum stress (ERS). Upon ER stress, the unfolded protein response (UPR) which activates the IRE1α, PERK and ATF6 signaling pathways is activated to cope with ERS in mammalian cells; however, the role of the three UPR arms in pulmonary vascular remodeling has not been defined. The present study showed that GRP78, a marker of ERS, was upregulated in hypoxic pulmonary artery smooth muscle cells (PASMCs). Among the three arms of the UPR, the IRE1α pathway was noticeably upregulated in hypoxic PASMCs. An inhibitor of IRE1α/XBP1 pathway, 4u8c, inhibited hypoxia-induced cell proliferation and migration and increased cell apoptosis by downregulating PCNA and MMP9 and activating mitochondrial apoptosis by enhancing the expression of BAX, activating caspase-9 and caspase-3, and eventually cleaving PARP. Quercetin affects ERS in many cell types and was shown to relieve hypoxic pulmonary hypertension (HPH) in our previous study. We demonstrated that quercetin evoked excessive GRP78 expression in hypoxic PASMCs compared with hypoxia alone by evaluating the expression of GRP78. The expression of IRE1α and XBP1s, a cleavage form of XBP1u, was upregulated by quercetin in a dose-dependent manner. Pretreatment with 4u8c reversed the apoptosis-promoting effect of quercetin by inhibiting mitochondrial apoptosis. However, 4u8c amplified the effect of quercetin on proliferation and migration in hypoxic PASMCs. In conclusion, the study demonstrated that the IRE1α-XBP1 pathway is involved in the process of hypoxia-induced pulmonary vascular remodeling; 4u8c could restrain hypoxia-induced cell proliferation and migration and reverse the hypoxia-induced apoptosis arrest, while quercetin excited excessive ERS and the IRE1α pathway in hypoxic PASMCs and promoted apoptosis. Our data suggest that intervening the IRE1α-XBP1 pathway may be useful for hypoxia-induced pulmonary arterial hypertension therapy.

Coxsackievirus B3 Infection Triggers Autophagy through 3 Pathways of Endoplasmic Reticulum Stress

OBJECTIVE

Autophagy is a highly conserved intracellular degradation pathway. Many picornaviruses induce autophagy to benefit viral replication, but an understanding of how autophagy occurs remains incomplete. In this study, we explored whether coxsackievirus B3 (CVB3) infection induced autophagy through endoplasmic reticulum (ER) stress.

METHODS

In CVB3-infected HeLa cells, the specific molecules of ER stress and autophagy were detected using Western blotting, reverse transcription polymerase chain reaction (RT-PCR), and confocal microscopy. Then PKR-like ER protein kinase (PERK) inhibitor, inositol-requiring protein-1 (IRE1) inhibitor, or activating transcription factor-6 (ATF6) inhibitor worked on CVB3-infected cells, their effect on autophagy was assessed by Western blotting for detecting microtubule-associated protein light chain 3 (LC3).

RESULTS

CVB3 infection induced ER stress, and ER stress sensors PERK/eIF2α, IRE1/XBP1, and ATF6 were activated. CVB3 infection increased the accumulation of green fluorescent protein (GFP)-LC3 punctuation and induced the conversion from LC3-I to phosphatidylethanolamine-conjugated LC3-1 (LC3-II). CVB3 infection still decreased the expression of mammalian target of rapamycin (mTOR) and p-mTOR. Inhibition of PERK, IRE1, or ATF6 significantly decreased the ratio of LC3-II to LC3-I in CVB3-infected HeLa cells.

CONCLUSION

CVB3 infection induced autophagy through ER stress in HeLa cells, and PERK, IRE1, and ATF6a pathways participated in the regulation of autophagy. Our data suggested that ER stress may inhibit mTOR signaling pathway to induce autophagy during CVB3 infection.

Quercetin ameliorates HFD-induced NAFLD by promoting hepatic VLDL assembly and lipophagy via the IRE1a/XBP1s pathway

The consumption of a quercetin-rich diet has been well-established as a feasible method against non-alcoholic fatty liver disease (NAFLD); however, the molecular mechanisms underlying the progression of NAFLD and its intervention by quercetin remain largely obscure. Male Sprague-Dawley rats fed high-fat diet (HFD), and HepG2 cells stimulated with free fatty acid, were treated with quercetin and various pharmacological reagents to explore the effect of signaling pathways involved in endoplasmic reticulum stress on very low-density lipoprotein (VLDL) assembly and lipophagy. Quercetin intake decreased hepatic TG content by 39%, with a 1.5-fold increase in VLDL, and up-regulated spliced X-box binding protein 1 (XBP1s) expression compared with the HFD group. Thapsigargin or STF-083010 (an IRE1α endonuclease inhibitor) decreased VLDL content in a dose-dependent manner, partially counteracting the protective effects of quercetin, 4-PBA or APY-29 (an IRE1α endonuclease activator). Additionally, microsomal TG-transfer protein complex expression was increased with quercetin-treated and down-regulated by STF-083010. Moreover, quercetin increased co-localization of lysosomes with lipid droplets (LDs) accompanied by decreased p62 accumulation. STF-083010 partially abolished the effect of quercetin on LDs autophagy in an mTOR-independent manner. Collectively, these findings demonstrate that hepatic VLDL assembly and lipophagy are the main targets of quercetin against NAFLD via the IRE1a/XBP1s pathway.

Establishment of pancreatic microenvironment model of ER stress: Quercetin attenuates β-cell apoptosis by invoking nitric oxide-cGMP signaling in endothelial cells

The involvement of endoplasmic reticulum (ER) stress in endothelial dysfunction and diabetes-associated complications has been well documented. Inhibition of ER stress represents a promising therapeutic strategy to attenuate endothelial dysfunction in diabetes. Recent attention has focused on the development of small molecule inhibitors of ER stress to maintain endothelial homeostasis in diabetes. Here we have developed a reliable, robust co-culture system that allows a study on the endothelial cells and pancreatic β-cells crosstalk under ER stress and validated using a known ER stress modulator, quercetin. Furthermore, sensitizing of endothelial cells by quercetin (25 μM) confers protection of pancreatic β-cells against ER stress through nitric oxide (NO^∙) signaling. In addition, increased intracellular insulin and NO^∙-mediated cyclic 3',5'-guanosine monophosphate (cGMP) levels in pancreatic β-cells further confirmed the mechanism of protection under co-culture system. In addition, the potential protein targets of quercetin against ER stress in the endothelial cells were investigated through proteomic profiling and its phosphoprotein targets through Bioplex analysis. On the whole, the developed in vitro co-culture set up can serve as a platform to study the signaling network between the endothelial and pancreatic β-cells as well as provides a mechanistic insight for the validation of novel ER stress modulators.

Chronic consumption of quercetin reduces erythrocytes oxidative damage: Evaluation at resting and after eccentric exercise in humans

The polyphenolic flavonoid quercetin has been shown to be a powerful antioxidant, in vitro and in murine models. However, its effect on redox status has been poorly examined in humans, particularly in combination with strenuous exercise. We hypothesized that quercetin supplementation would beneficially affect redox homeostasis in healthy individuals undergoing eccentric exercise. To test this hypothesis, the effects of chronic consumption of quercetin on glutathione system (reduced, oxidized, and reduced to oxidized glutathione ratio), oxidative damage [thiobarbituric acid reactive substances (TBARs)], antioxidant enzymatic network (catalase, glutathione peroxidase, superoxide dismutase) and resistance to lysis, were investigated in erythrocytes, a traditional model widely used to study the effects of oxidative stress as well as the protective effects of antioxidants. In a two weeks controlled, randomized, crossover, intervention trial, 14 individuals ingested 2 caps (1 g/d) of quercetin or placebo. Blood samples were collected before, after 2 weeks of supplementation and after a bout of eccentric exercise. Quercetin, reduced significantly erythrocytes lipid peroxidation levels and the susceptibility to hemolysis induced by the free radical generator AAPH, while no differences in antioxidant enzyme activities and glutathione homeostasis were found between the two groups. After a single bout of eccentric exercise, quercetin supplementation improved redox status as assessed by reduced/oxidized glutathione ratio analysis and reduced TBARs levels both in erythrocytes and plasma. In conclusion, our study provides evidences that chronic quercetin supplementation has antioxidant potential prior to and after a strenuous eccentric exercise thus making the erythrocytes capable to better cope with an oxidative insult.

Inhibitory effect of quercetin on titanium particle-induced endoplasmic reticulum stress (ERS)-related apoptosis and in vivoosteolysis

Wear particle induced periprosthetic osteolysis is the main cause of aseptic loosening of orthopedic implants. The aim of the present study is to determine the protective effect of quercetin (QUE) against titanium (Ti) particle induced endoplasmic reticulum stress (ERS) related apoptosis and osteolysis. In the present study, RAW264.7 cells were pretreated with different concentrations (40, 80, and 160 μmol/l) of QUE for 30 min and then treated with Ti particle (5 mg/ml) for 24 h. Cell viability and apoptosis were determined using MTT assay and Annexin V-FITC Apoptosis Detection Kit, respectively. Protein and mRNA expressions of ERS-related genes were examined by Western blot and real-time PCR, respectively. The release of inflammatory cytokines was detected by ELISA. Then, a mouse calvarial osteolysis model was established. Histological sections of calvaria were stained with Hematoxylin-Eosin (H&E) or tartrate-resistant acid phosphatase (TRAP). The results showed that Ti particle reduced cell viability and induced apoptosis in RAW264.7 macrophages. The cytotoxic effects of Ti particle were dramatically inhibited by QUE pretreatment. Interestingly, we found that QUE also significantly reduced Ti particle induced up-regulation of the expression levels of protein kinase RNA-like ER kinase (PERK), inositol-requiring enzyme-1 (IRE1), glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein homologous protein (CHOP), caspase-12, and caspase-3 and enhanced the down-regulation of Bcl-2. In addition, QUE decreased Ti particle-induced inflammatory cytokines release from RAW264.7 cells. Moreover, treatment with QUE markedly decreased osteoclast number. In a mouse calvarial osteolysis model, QUE inhibited Ti particle induced osteolysis in vivo by inhibiting osteoclast formation and expressions of ERS-related genes. In conclusion, QUE can protect RAW264.7 cells from Ti particle induced ERS-related apoptosis and suppress calvarial osteolysis in vivo.

Oxidative stress and inflammation: liver responses and adaptations to acute and regular exercise

The liver is remarkably important during exercise outcomes due to its contribution to detoxification, synthesis, and release of biomolecules, and energy supply to the exercising muscles. Recently, liver has been also shown to play an important role in redox status and inflammatory modulation during exercise. However, while several studies have described the adaptations of skeletal muscles to acute and chronic exercise, hepatic changes are still scarcely investigated. Indeed, acute intense exercise challenges the liver with increased reactive oxygen species (ROS) and inflammation onset, whereas regular training induces hepatic antioxidant and anti-inflammatory improvements. Acute and regular exercise protocols in combination with antioxidant and anti-inflammatory supplementation have been also tested to verify hepatic adaptations to exercise. Although positive results have been reported in some acute models, several studies have shown an increased exercise-related stress upon liver. A similar trend has been observed during training: while synergistic effects of training and antioxidant/anti-inflammatory supplementations have been occasionally found, others reported a blunting of relevant adaptations to exercise, following the patterns described in skeletal muscles. This review discusses current data regarding liver responses and adaptation to acute and regular exercise protocols alone or combined with antioxidant and anti-inflammatory supplementation. The understanding of the mechanisms behind these modulations is of interest for both exercise-related health and performance outcomes.

Levels of Hepatic Activating Transcription Factor 6 and Caspase-3 Are Downregulated in Mice after Excessive Training

Recently, we demonstrated that different running overtraining (OT) protocols with the same external load, but performed downhill (OTR/down), uphill (OTR/up), and without inclination (OTR), led to hepatic fat accumulation. As the disruption of endoplasmic reticulum (ER) homeostasis is linked to animal models of fatty liver disease, we investigated the effects of these OT models on the proteins related to ER stress (i.e., BiP, inositol-requiring enzyme 1, protein kinase RNA-like endoplasmic reticulum kinase, eIF2alpha, ATF6beta, and glucose-regulated protein 94) and apoptosis (C/EBP-homologous protein, Caspase-3, 4, and 12, Bax, and tumor necrosis factor receptor-associated factor 2) in livers of C57BL/6 mice. Also, aerobic training can attenuate cardiac ER stress and improve exercise capacity. Therefore, we investigated whether the decrease in performance induced by our OT protocols is linked to ER stress and apoptosis in mouse hearts. The rodents were divided into six groups: naïve (N, sedentary mice), control (CT, sedentary mice submitted to the performance evaluations), trained (TR), OTR/down, OTR/up, and OTR groups. Rotarod, incremental load, exhaustive, and grip force tests were used to evaluate performance. After the grip force test, the livers and cardiac muscles (i.e., left ventricle) were removed and used for immunoblotting. All of the OT protocols led to similar responses in the performance parameters and displayed significantly lower hepatic ATF6beta values compared to the N group. The OTR/down group exhibited lower liver cleaved caspase-3 values compared to the CT group. However, the other proteins related to ER stress and apoptosis were not modulated. Also, the cardiac proteins related to ER stress and apoptosis were not modulated in the experimental groups. In conclusion, the OT protocols decreased the levels of hepatic ATF6beta, and the OTR/down group decreased the levels of hepatic cleaved caspase-3. Also, the decrease in performance induced by our OT models is not associated with ER stress and apoptosis in mice hearts.