Quercetin abrogates taxol-mediated signaling by inhibiting multiple kinases

Overview of biological effects of Quercetin on ovary

Over the last few decades, using natural products has been increased to treat different diseases. Today, great attention has been pointed toward the usage of natural products such as flavonoids, especially Quercetin (QUR), in the treatment of diseases. QUR as a natural antioxidant has been traditionally used to prevent or treat a variety of diseases such as cancer, cardiovascular disease, polycystic ovary syndrome (PCOS), obesity, chronic inflammation, and reproductive system dysfunction. Several studies demonstrated that QUR acts as an anti-inflammatory, anti-apoptotic, antioxidant, and anticancer agent. With this in view, in this study, we intended to describe an overview of the biological effects of QUR on the ovary. QUR improves the quality of oocytes and embryos. It affects the proliferation and apoptosis and decreases the oxidative stress in granulosa cells (GCs). Furthermore, QUR can be used as a complementary and alternative therapy in ovarian cancer and it has beneficial effects in the treatment of PCOS patients. It seems that QUR as a supplementary factor has different activities for the treatment of different disorders and it also has bidirectional activities. However, further investigations are needed for understanding the efficacy of QUR in the treatment and improvement of gynecological patients.

Modulation by hydroxytyrosol of oxidative stress and antitumor activities of paclitaxel in breast cancer

PURPOSE

The main objective of this study was to test the therapeutic potential of hydroxytyrosol and its combination with paclitaxel in breast cancer on oxidative stress status.

METHODS

Impact on proliferation rates of different chemotherapy administration patterns was assayed in MCF-7 and MDA-MB-231 breast cancer cell lines. Breast tumor-bearing rats were randomly assigned to Control, Hydroxytyrosol, Paclitaxel and Paclitaxel plus hydroxytyrosol groups, for 6 weeks. Tumor volume, cell proliferation and several systemic oxidative stress parameters were measured. Anti-proliferative activity in vitro experiments was correlated with in vivo experiments.

RESULTS

Combination group did significantly reduce tumor volume when compared with paclitaxel alone. Additionally, the combination improved the antioxidant status without compromising the antitumor activity of standard chemotherapy.

CONCLUSION

These findings reveal for the first time that hydroxytyrosol is an active partner in combined therapies with paclitaxel against breast cancer. Combination with hydroxytyrosol would also ensure a less oxidative impact of chemotherapeutic drugs that could potentially improve patient wellness.

Molecular Targets Underlying the Anticancer Effects of Quercetin: An Update

Quercetin, a medicinally important member of the flavonoid family, is one of the most prominent dietary antioxidants. It is present in a variety of foods—including fruits, vegetables, tea, wine, as well as other dietary supplements—and is responsible for various health benefits. Numerous pharmacological effects of quercetin include protection against diseases, such as osteoporosis, certain forms of malignant tumors, and pulmonary and cardiovascular disorders. Quercetin has the special ability of scavenging highly reactive species, such as hydrogen peroxide, superoxide anion, and hydroxyl radicals. These oxygen radicals are called reactive oxygen species, which can cause oxidative damage to cellular components, such as proteins, lipids, and deoxyribonucleic acid. Various oxygen radicals play important roles in pathophysiological and degenerative processes, such as aging. Subsequently, several studies have been performed to evaluate possible advantageous health effects of quercetin and to collect scientific evidence for these beneficial health claims. These studies also gather data in order to evaluate the exact mechanism(s) of action and toxicological effects of quercetin. The purpose of this review is to present and critically analyze molecular pathways underlying the anticancer effects of quercetin. Current limitations and future directions of research on this bioactive dietary polyphenol are also critically discussed.

Sub-chronic administration of LY294002 sensitizes cervical cancer cells to chemotherapy by enhancing mitochondrial JNK signaling

Chemo-sensitization is used to improve the efficacy of chemotherapeutic agents against cancers, and understanding the precise molecular mechanisms of chemo-sensitization could lead to safer and more effective approaches to treat cancer. We have previously demonstrated that mitochondrial c-Jun N-terminal Kinase (JNK) signaling is a critical component of cell death. Mitochondrial JNK signaling is coordinated on the scaffold protein Sab. In this work, we developed a sub-chronic chemo-sensitization model by exposing HeLa cells to low-dose (2 μM) LY294002. We found that this treatment increased Sab expression on mitochondria, an effect not observed in acute exposures. To examine the role of Sab in chemo-sensitization, we ectopically expressed and silenced Sab in HeLa cells. We found that elevating Sab levels in HeLa cells increased the efficacy of chemotherapeutic agents, paclitaxel and cisplatin, while silencing Sab decreased the sensitivity of cells towards these agents. The effect of Sab-mediated signaling appeared to be dependent upon mitogen dependent protein kinases (MAPKs) as ablation of Sab's MAPK-binding motifs prevented chemo-sensitization. These results suggest that mitochondrial JNK signaling is an adaptable signaling pathway that can be enhanced or restored in cancer cells to improve therapeutic efficacy.

Quantitative analysis of the TNF-α-induced phosphoproteome reveals AEG-1/MTDH/LYRIC as an IKKβ substrate

The inhibitor of the nuclear factor-κB (IκB) kinase (IKK) complex is a key regulator of the canonical NF-κB signalling cascade and is crucial for fundamental cellular functions, including stress and immune responses. The majority of IKK complex functions are attributed to NF-κB activation; however, there is increasing evidence for NF-κB pathway-independent signalling. Here we combine quantitative mass spectrometry with random forest bioinformatics to dissect the TNF-α-IKKβ-induced phosphoproteome in MCF-7 breast cancer cells. In total, we identify over 20,000 phosphorylation sites, of which ∼1% are regulated up on TNF-α stimulation. We identify various potential novel IKKβ substrates including kinases and regulators of cellular trafficking. Moreover, we show that one of the candidates, AEG-1/MTDH/LYRIC, is directly phosphorylated by IKKβ on serine 298. We provide evidence that IKKβ-mediated AEG-1 phosphorylation is essential for IκBα degradation as well as NF-κB-dependent gene expression and cell proliferation, which correlate with cancer patient survival in vivo.

Inflammatory cytokines such as TNF-α influence inflammation, apoptosis and tumour development through regulation of the kinase IKKβ. Krishnan and Nolte et al. apply quantitative proteomics to identify potential IKKβ targets, and reveal phosphorylation of AEG-1 by IKKβ as a mechanism controlling NF-κB signalling.

Quercetin attenuates cell apoptosis of oxidant-stressed SK-N-MC cells while suppressing up-regulation of the defensive element, HIF-1α

Evidence is emerging that reactive oxygen species (ROS)-induced oxidative stress has a crucial role in the pathogenesis of neurodegenerative diseases. To find the effective therapies for neurodegenerative diseases, evaluation of the relevant molecular mechanisms is necessary. In the current study, we investigated the effects of hydrogen peroxide (H2O2)-induced oxidative stress on SK-N-MC cell death with focus on HIF-1α, Foxo3a and Notch1 signaling factors. Our results revealed that H2O2 reduced viability of cells through up-regulation of p53 followed by increase in Bax/Bcl2 ratio. In addition, H2O2 increased intracellular levels of HIF-1α, Foxo-3a and Notch intracellular domain (NICD). However, Quercetin decreased cell contents of HIF-1α, Foxo-3a and NICD as well as pro-apoptotic factors including p53 and Bax compared to H2O2-treated cells. Additionally, we found that HIF-1α down-regulation reduced Foxo3a and NICD contents parallel to up-regulation of p53 and Bax and led to further vulnerability to oxidative stress-induced cell death. In contrast, Notch inhibition resulted in HIF-1α/Foxo3a signaling pathway up-regulation, suggesting the bidirectional crosstalk between HIF-1α and Notch1. These results collectively suggest that ROS are involved in activation of both the defensive and pro-apoptotic pathways encompassing HIF-1α and p53, respectively. Regarding the HIF-1α-mediated neuroprotection role, elucidation of the molecular mechanism would certainly be essential for effective drug design against neurodegenerative diseases.

Glutamine attenuates acute lung injury by inhibition of high mobility group box protein-1 expression during sepsis

Heat shock protein 70 (HSP70) is reported as the main factor responsible for the beneficial effects of glutamine (GLN) and as a negative regulator of high mobility group box protein-1 (HMGB-1) expression. Our aim was to determine whether GLN attenuates acute lung injury (ALI) by the inhibition of HMGB-1 expression during sepsis. Male Sprague-Dawley rats were subjected to caecal ligation and puncture (CLP) to induce sepsis. GLN or saline was administered through tail vein 1 h after CLP. Then, quercetin (Q), an inhibitor of HSP70, was utilised to assess the role of the enhanced HSP70. We observed the survival of the subjects. At 24 h post-CLP, we measured lung HSP70, phosphorylated heat shock factor-1 (HSF-1-p) and HMGB-1 expressions, NF-kappaB DNA-binding activity and ALI occurrence. We also measured serum HSP70, IL-6 and HMGB-1 concentrations. GLN improved survival during sepsis. In GLN-treated rats, lung HSP70 and HSF-1-p expressions were enhanced, lung HMGB-1 expression and NF-kappaB DNA-binding activity were suppressed, and ALI was attenuated. Furthermore, in GLN-administered rats, serum HSP70 concentration was higher, and serum IL-6 and HMGB-1 concentrations were lower than those in non-treated rats. Q inhibited the enhancement of HSP70 and HSF-1-p expressions and abrogated the GLN-mediated benefits. In conclusion, GLN attenuated ALI and improved survival by the inhibition of HMGB-1 expression during sepsis in rats. These benefits were associated with the enhancement of HSP70 expression by GLN.

Apoptotic mechanism of paclitaxel-induced cell death in human head and neck tumor cell lines

BACKGROUND

Paclitaxel (taxol) is clinically used to treat various human tumors. However, the cellular and molecular mechanism regarding apoptotic effect of paclitaxel on head and neck squamous cell carcinoma (HNSCC) remains elusive.

METHODS

The apoptotic effect and the mechanism of paclitaxel on FaDu hypopharyngeal cancer cell line, OEC-M1 gingival cancer cell line, and OC3 betel quid chewing-related buccal cancer cell lines were investigated by morphological observations, cell viability assay, flow cytometry assay and Western blotting methods.

RESULTS

Rounded-up cell number increased with membrane blebbing as the treatment of paclitaxel (50-500 nM) increased from 24 to 48 h among these cell lines. In cell viability assay, cell surviving rate significantly decreased from 87 to 27% as the dosage and duration of paclitaxel treatment increased (P < 0.05). Flow-cytometry analysis further demonstrated that 50 nM paclitaxel induced G2/M phase cell arrest among these cell lines within 8 h treatment, and then G2/M phase cell fraction significantly decreased as subG1 phase cell fraction significantly increased after 24 h treatment (P < 0.05), suggesting that cells underwent apoptosis. Furthermore, the activated caspases-8, -9, -3, -6 and poly ADP-ribose polymerase cleavage could all be significantly detected in FaDu, OEC-M1 and OC3 cells (P < 0.05).

CONCLUSION

Paclitaxel activated cell cycle arrest and caspase protein expressions to induce apoptosis in HNSCC cell lines.

Multitargeted cancer prevention by quercetin

Quercetin is an anti-oxidative flavonoid widely distributed in the plant kingdom. Phenolic hydroxyl groups at the B-ring and the 3-position are responsible for its free radical-scavenging activity. Quercetin is commonly present as a glycoside and is converted to glucuronide/sulfate conjugates during intestinal absorption and only conjugated metabolites are therefore found in circulating blood. Although metabolic conversion attenuates its biological effects, active aglycone may be generated from the glucuronide conjugates by enhanced beta-glucuronidase activity during inflammation. With respect to its relationship with molecular targets relevant to cancer prevention, quercetin aglycone has been shown to interact with some receptors, particularly an aryl hydrocarbon receptor, which is involved in the development of cancers induced by certain chemicals. Quercetin aglycone has also been shown to modulate several signal transduction pathways involving MEK/ERK and Nrf2/keap1, which are associated with the processes of inflammation and carcinogenesis. Rodent studies have demonstrated that dietary administration of this flavonol prevents chemically induced carcinogenesis, especially in the colon, whilst epidemiological studies have indicated that an intake of quercetin may be associated with the prevention of lung cancer. Dietary quercetin is, therefore, a promising agent for cancer prevention and further research is warranted.

Oral glutamine enhances heat shock protein expression and improves survival following hyperthermia

No pharmacologic agent has shown benefit in treating heatstroke. Previous data indicate that enhanced heat shock protein 70 (HSP-70) expression can improve survival postexperimental heatstroke. Glutamine (GLN) can enhance HSP-70 expression in other injury models. This study assessed if orally administered GLN could enhance tissue HSP expression and could improve survival following whole body hyperthermia. Intestinal permeability and plasma endotoxin were assayed to determine if enhanced HSP expression correlated with improved organ function. GLN (0.65 g/kg) or an iso-nitrogenous control (Travasol; T) was given to rats via gavage twice daily for 5 days pre-heatstroke. Hyperthermia was performed in anesthetized rats by heating animals to 42 degrees C (rectal temperature) for 30 min. HSP-70 analyzed via Western blot. Gut permeability was measured 6 and 24 h post-hyperthermia. Plasma endotoxin was measured 24 h post-hyperthermia. Survival was analyzed for 5 days post-hyperthermia. GLN administration enhanced gut and lung HSP-70 post-hyperthermia. GLN administration led to significantly enhanced gut heat shock factor 1 (HSF-1) activation before heatstroke and at 1 h postheat stress. GLN decreased gut permeability at 6 and 24 h post-hyperthermia versus T. Plasma endotoxin also decreased in GLN-treated rats 24 h post-hyperthermia. Oral GLN therapy significantly improved survival (P < 0.05). Our results indicate that oral GLN can enhance tissue HSP-70 and HSF-1 activation post-hyperthermia. These results also indicate that enhanced HSP-70 may have functional significance as GLN-treated animals had decreased gut permeability, plasma endotoxin, and improve survival following lethal hyperthermia. Enhanced expression of HSP-70 may be an important mechanism leading to enhanced survival via GLN. These data indicate that oral GLN may useful in prevention of mortality from heatstroke in at risk populations.

Glutamine's protection against cellular injury is dependent on heat shock factor-1

Glutamine (GLN) has been shown to protect cells, tissues, and whole organisms from stress and injury. Enhanced expression of heat shock protein (HSP) has been hypothesized to be responsible for this protection. To date, there are no clear mechanistic data confirming this relationship. This study tested the hypothesis that GLN-mediated activation of the HSP pathway via heat shock factor-1 (HSF-1) is responsible for cellular protection. Wild-type HSF-1 (HSF-1(+/+)) and knockout (HSF-1(-/-)) mouse fibroblasts were used in all experiments. Cells were treated with GLN concentrations ranging from 0 to 16 mM and exposed to heat stress injury in a concurrent treatment model. Cell viability was assayed with phenazine methosulfate plus tetrazolium salt, HSP-70, HSP-25, and nuclear HSF-1 expression via Western blot analysis, and HSF-1/heat shock element (HSE) binding via EMSA. GLN significantly attenuated heat-stress induced cell death in HSF-1(+/+) cells in a dose-dependent manner; however, the survival benefit of GLN was lost in HSF-1(-/-) cells. GLN led to a dose-dependent increase in HSP-70 and HSP-25 expression after heat stress. No inducible HSP expression was observed in HSF-1(-/-) cells. GLN increased unphosphorylated HSF-1 in the nucleus before heat stress. This was accompanied by a GLN-mediated increase in HSF-1/HSE binding and nuclear content of phosphorylated HSF-1 after heat stress. This is the first demonstration that GLN-mediated cellular protection after heat-stress injury is related to HSF-1 expression and cellular capacity to activate an HSP response. Furthermore, the mechanism of GLN-mediated protection against injury appears to involve an increase in nuclear HSF-1 content before stress and increased HSF-1 promoter binding and phosphorylation.

Effects of HSP70.1/3 gene knockout on acute respiratory distress syndrome and the inflammatory response following sepsis

Heat shock response has been implicated in attenuating NF-kappaB activation and inflammation following sepsis. Studies utilizing sublethal heat stress or chemical enhancers to induce in vivo HSP70 expression have demonstrated survival benefit after experimental sepsis. However, it is likely these methods of manipulating HSP70 expression have effects on other stress proteins. The aim of this study was to evaluate the role of specific deletion of HSP70.1/3 gene expression on ARDS, NF-kappaB activation, inflammatory cytokine expression, and survival following sepsis. To address this question, we induced sepsis in HSP70.1/3 KO and HSP70.1/3 WT mice via cecal ligation and puncture (CLP). We evaluated lung tissue NF-kappaB activation and TNF-alpha protein expression at 1 and 2 h, IL-6 protein expression at 1, 2, and 6, and lung histopathology 24 h after sepsis initiation. Survival was assessed for 5 days post-CLP. NF-kappaB activation in lung tissue was increased in HSP70.1/3((-/-)) mice at all time points after sepsis initiation. Deletion of HSP70.1/3 prolonged NF-kappaB binding/activation in lung tissue. Peak expression of lung TNF-alpha at 1 and 2 h was also significantly increased in HSP70.1/3((-/-)) mice. Expression of IL-6 was significantly increased at 2 and 6 h, and histopathology revealed a significant increase in lung injury in HSP70.1/3((-/-)) mice. Last, deletion of the HSP70 gene led to increased mortality 5 days after sepsis initiation. These data reveal that absence of HSP70 alone can significantly increase ARDS, activation of NF-kappaB, and inflammatory cytokine response. The specific absence of HSP70 gene expression also leads to increased mortality after septic insult.

Glutamine attenuates lung injury and improves survival after sepsis: Role of enhanced heat shock protein expression*

OBJECTIVE

Heat shock protein (HSP) expression is vital to cellular and tissue protection after stress or injury. However, application of this powerful tool in human disease has been limited, as known enhancers of HSPs are toxic and not clinically relevant. Glutamine (GLN) can enhance HSP expression in non-clinically relevant animal injury models. The aim of this study was to assess the ability of GLN to enhance pulmonary HSP expression, attenuate lung injury, and improve survival after sepsis in the rat.

DESIGN

Prospective, randomized, controlled animal trial.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

We utilized a rat model of cecal ligation and puncture to induce sepsis. GLN or saline was administered 1 hr after initiation of sepsis via single tail-vein injection. We analyzed heat shock factor-1 phosphorylation, HSP-70, and HSP-25 via Western blot. Tissue metabolism was assayed by magnetic resonance spectroscopy. Occurrence of lung injury was determined via histopathologic examination. An inhibitor of HSP expression, quercetin, was utilized to assess role of HSP expression in prevention of sepsis-related mortality.

MEASUREMENTS AND MAIN RESULTS

GLN, given after initiation of sepsis, enhanced pulmonary heat shock factor-1 phosphorylation, HSP-70, HSP-25, and attenuated lung injury after sepsis. Further, GLN improved indices of lung tissue metabolic function (adenosine 5-triphosphate/adenosine 5-diphosphate ratio, nicotinamide adenine dinucleotide) after sepsis. No significant effect of GLN on lung tissue-reduced glutathione was observed. GLN treatment led to a significant decrease in mortality (33% [6 of 18] GLN-treated rats vs. 78% [14 of 17] saline-treated rats). Administration of the HSP inhibitor quercetin blocked GLN-mediated enhancement of HSP expression and abrogated GLN's survival benefit.

CONCLUSIONS

GLN has been safely administered to critically ill patients and shown to improve outcome without clear understanding of the protective mechanism. Our results indicate GLN may prevent the occurrence of lung injury, lung tissue metabolic dysfunction, and mortality after sepsis via enhancement of deficient lung heat shock factor-1 phosphorylation/activation and HSP expression.

Glutamine attenuates endotoxin-induced lung metabolic dysfunction: Potential role of enhanced heat shock protein 70

OBJECTIVE

Septic shock leads to derangement of cellular metabolism. Enhanced heat shock protein 70 (HSP-70) can preserve cellular metabolism after other forms of cellular stress. Glutamine (GLN) can enhance lung HSP-70 expression after lethal endotoxemia. However, it is unknown whether GLN can enhance HSP-70 expression and attenuate lung metabolic dysfunction after sublethal endotoxemia. Our aim was to determine whether GLN could upregulate HSP-70 and attenuate metabolic dysfunction in lung tissue after sublethal endotoxemia.

METHODS

Sprague-Dawley rats were assigned to one of five groups. The first two groups were treated with Escherichia coli lipopolysaccharide (LPS; 1 mg/kg intravenously). GLN (0.75 g/kg intravenously) or balanced salt solution as a control was administered 5 min after LPS administration. The next two groups of rats were treated with quercetin (HSP-70 inhibitor; 400 mg/kg intraperitoneally) 6 h before LPS administration. The final group received no treatment. Lung tissue was harvested 24-h after LPS and analyzed with immunofluorescence and western blot for HSP-70. Tissue metabolites were quantified by 1H and 31P nuclear magnetic resonance spectroscopy.

RESULTS

GLN compared with balanced salt solution (BSS) administration in LPS-treated animals led to significant increases in lung HSP-70. Increased HSP-70 expression was observed in lung epithelial cells and macrophages. GLN significantly improved the ratio of adenosine triphosphate to adenosine diphosphate in the lung after LPS. Quercetin inhibited a GLN-mediated increase in lung HSP-70 and blocked a beneficial effect of GLN on the ratio of adenosine triphosphate to adenosine diphosphate after LPS.

CONCLUSIONS

A single dose of GLN can enhance HSP-70 in pulmonary epithelial cells and macrophages after sublethal endotoxemia. Further, GLN can attenuate endotoxin-induced lung metabolic dysfunction. GLN's beneficial effect on lung tissue after metabolic dysfunction caused by sublethal endotoxemia may be mediated in part by enhanced HSP-70.

Monastrol, a prototype anti-cancer drug that inhibits a mitotic kinesin, induces rapid bursts of axonal outgrowth from cultured postmitotic neurons

Terminally postmitotic neurons continue to express many of the kinesin-related proteins known to configure microtubules during mitosis. Drugs that inhibit these kinesins are being developed as anti-cancer agents with the hope that they will inhibit proliferation of tumor cells without having adverse effects on the nervous system. The prototype, termed monastrol, inhibits the kinesin known as Eg5, which is essential for maintaining separation of the half-spindles. Eg5 is also highly expressed in neurons, particularly during development. Exposure of cultured sympathetic neurons to monastrol for a few hours increased both the number and the growth rate of the axons. With additional time, the overall lengths of the axons were indistinguishable from controls. Sensory neurons showed a similar short-term increase in axonal growth rate. However, prolonged exposure resulted in shorter axons, suggesting that sensory neurons may be more sensitive to toxic effects of the drug. Nevertheless, the overall health of the cultures was still far more robust than cultures treated with taxol, a drug commonly used for anti-cancer therapy. On the basis of these results, we conclude that Eg5 normally generates forces that oppose axonal growth, presumably by partially suppressing the forward advance of microtubules. We speculate that local regulation of Eg5 could be a means by which neurons coordinate rapid bursts of axonal growth with appropriate environmental cues. The comparatively modest toxic effects on the neurons over time are a hopeful sign for clinicians interested in using anti-Eg5 drugs for cancer therapy.

The effect of short-term kaempferol exposure on reactive oxygen levels and integrity of human (HL-60) leukaemic cells

Flavonoids may be a principal contributor to the cancer preventative activity of fruit- and vegetable-rich diets and there is interest in their use as dietary supplements. However, there is potential conflict between the cytoprotective and cytotoxic activities of flavonoids, and their efficacy as anti-cancer agents is unresolved. Here, the integrity and survival of HL-60 promyelocytic leukaemia cells following short-term (90 min) exposure to the dietary abundant flavonoid kaempferol (1-100 microM) is reported. Supplementation initially decreased reactive oxygen levels but, paradoxically, a dose-dependent increase in single-strand DNA breakage occurred. However, there was no increase in oxidised DNA purines or membrane damage. Following a 24-h recovery period in non-kaempferol supplemented media, DNA single-strand breakage had declined and kaempferol exposed and control cultures possessed similar reactive oxygen levels. A reduction in (3)H-thymidine incorporation occurred with > or =10 microM kaempferol. One hundred micromolar kaempefrol increased the proportion of cells in G(2)-M phase, the proportion of cells with a sub-G(1) DNA content and enhanced 'active' caspase-3 expression but only induced a loss of mitochondrial membrane potential within a minority of cells. The relevance of induced DNA damage within a non-overtly oxidatively stressed environment to the disease preventative and therapeutic use of kaempferol is discussed.

Flavonoids Induce Apoptosis in Human Leukemia U937 Cells Through Caspase- and Caspase-Calpain-Dependent Pathways

Flavonoids are polyphenolic phytochemicals that are ubiquitous in plants and present in the common human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. In this study we tested the apoptotic activity of 22 flavonoids and related compounds in leukemic U937 cells. Several flavones but none of the isoflavones or flavanones tested induced apoptotic cell death under these conditions, as determined by reduction in cell viability, flow cytometry, and oligonucleosomal DNA fragmentation. Structure-activity relationship showed that at least two hydroxylations in positions 3, 5, and 7 of the A ring were needed to induce apoptosis, whereas hydroxylation in 3' and/or 4' of the B ring enhanced proapoptotic activity. At lower concentrations, these compounds were also able to sensitize these cells to apoptosis induced by tumor necrosis factor-alpha. Regarding the mechanisms, galangin, luteolin, chrysin, and quercetin induced apoptosis in a way that required the activation of caspases 3 and 8, but not caspase 9. In contrast, an active role of calpains in addition to caspases was demonstrated in apoptosis induced by fisetin, apigenin, and 3,7-dihydroxyflavone. Our data show evidence of the proapoptotic properties of some flavonoids that could support their rational use as chemopreventive and therapeutic agents against carcinogenic disease.

Phosphatidylinositol promotes cholesterol transport and excretion

Administration of phosphatidylinositol (PI) to New Zealand White rabbits increases HDL negative charge and stimulates reverse cholesterol transport. Intravenously administered PI (10 mg/kg) associated almost exclusively with the HDL fraction in rabbits. PI promoted an increase in the hepatic uptake of plasma free cholesterol (FC) and a 21-fold increase in the biliary secretion of plasma-derived cholesterol. PI also increased cholesterol excretion into the feces by 2.5-fold. PI directly affects cellular cholesterol metabolism. In cholesterol-loaded macrophages, PI stimulated cholesterol mass efflux to lipid-poor reconstituted HDL. PI was about half as effective as cAMP at stimulating efflux, and the effects of cAMP and PI were additive. In cultured HepG2 cells, PI-enriched HDL also enhanced FC uptake from HDL by 3-fold and decreased cellular cholesterol synthesis and esterification. PI enrichment had no effect on the selective uptake of cholesterol esters or on the internalization of HDL particles. PI-dependent metabolic events were efficiently blocked by inhibitors of protein kinase C and the inositol signaling cascade. The data suggest that HDL-PI acts via cell surface ATP binding cassette transporters and signaling pathways to regulate both cellular and intravascular cholesterol homeostasis.

Direct interaction between survivin and Smac/DIABLO is essential for the anti-apoptotic activity of survivin during taxol-induced apoptosis

Survivin is a member of the inhibitor of apoptosis protein (IAP) family that has been implicated in both apoptosis inhibition and cell cycle control. However, its inhibitory mechanism and subcellular localization remain controversial. In this report, we provided evidence for the first time that Survivin physically interacts with Smac/DIABLO both in vitro and in vivo. A point mutation (D71R) in the baculovirus IAP repeat motif and a C-terminal deletion mutant (Surv-BIR) of Survivin fail to bind to Smac/DIABLO and abrogate its ability to inhibit apoptosis. The N-terminal of mature Smac/DIABLO is absolutely required for Survivin.Smac complex formation. Subcellular distributions of Survivin and Smac/DIABLO showed that they co-localized within the cytosol during interphase. In addition, Survivin was found to be incapable of binding to caspase. We also identified that the co-presence of Smac/DIABLO and XIAP was required for Survivin to inhibit caspase cleavage in a cell-free system. In conclusion, our results provide the first evidence that the interaction between Smac/DIABLO and Survivin is an essential step underling the inhibition of apoptosis induced by Taxol.

Mitochondrial function in response to cardiac ischemia-reperfusion after oral treatment with quercetin

Polyphenolic compounds present in red wines, such as the flavonol quercetin, are thought capable of cardioprotection through mechanisms not yet clearly defined. It has been established that mitochondria play a critical role in myocardial recovery from ischemia-reperfusion (I-R) damage, and in vitro experiments indicate that quercetin can exert a variety of direct effects on mitochondrial function. The effects of quercetin at concentrations typically found in 1-2 glasses of red wine on cardiac I-R and mitochondrial function in vivo are not known. Quercetin was administered to rats (0.033 mg/kg per day by gavage for 4 d). Isolated Langendorff perfused hearts were subjected to I-R, and cardiac functional parameters determined both before and after I-R. Mitochondria were isolated from post-I-R hearts and their function assessed. Compared to an untreated control group, quercetin treatment significantly decreased the impairment of cardiac function following I-R. This protective effect was associated with improved mitochondrial function after I-R. These results indicate that oral low dose quercetin is cardioprotective, possibly via a mechanism involving protection of mitochondrial function during I-R.