Patients with nonalcoholic fatty liver disease have higher risk of colorectal adenoma after negative baseline colonoscopy.

AIM: The study aimed to determine whether nonalcoholic fatty liver disease (NAFLD) is an independent risk factor of adenoma after negative baseline colonoscopy. METHOD: A retrospective cohort study was conducted on 1522 health-check individuals who underwent two consecutive colonoscopies at Taipei Veterans General Hospital between 2003 and 2010. Those developing an adenoma after an initial negative baseline colonoscopy (adenoma group) were compared with those in whom the second colonoscopy was negative (nonadenoma group). Anthropometric measurements, biochemical tests and the presence of NAFLD were compared between the two groups. RESULTS: The adenoma group had a higher prevalence of NAFLD than the nonadenoma group (55.6% vs 38.8%; P < 0.05). On multivariate logistic regression analysis, NAFLD was an independent risk factor (OR = 1.45, 95% CI: 1.07-1.98) for adenoma formation after a negative baseline colonoscopy. The risk of colorectal adenoma increased when NAFLD patients had other morbidities including metabolic syndrome, hypertension or smoking (OR = 2.85, 4.03 and 4.17). CONCLUSION: NAFLD is an independent risk factor for colorectal adenoma formation after a negative baseline colonoscopy. The risk is higher in individuals with NAFLD and other comorbidities, such as hypertension, smoking or metabolic syndrome.

VEGF -460T → C polymorphism and its association with VEGF expression and outcome to FOLFOX-4 treatment in patients with colorectal carcinoma.

The -460T → C polymorphism of vascular endothelial growth factor (VEGF) gene significantly increases its promoter activity. A pilot study was conducted to assess the influence of this polymorphism on clinicopathological features of patients with colorectal carcinoma. In total, 228 patients were enrolled, including 100 with stage II/III colorectal carcinoma receiving curative surgery and 128 with metastatic disease. An excellent correlation in VEGF -460 genotypes based on white blood cells and tumor tissues existed, but there was no between-group difference in patients with or without colorectal carcinoma. A marked increase in intratumor and circulating VEGF levels were observed in patients with the T/C or C/C genotypes (P < 0.01), which was associated with increased extent of invasion, nodal involvement, poor histological differentiation, subsequent metastasis and shorter survival in stage II/III patients treated with curative surgery (P < 0.01). For patients with metastatic disease, this polymorphism was associated with a lower response rate to FOLFOX-4 (P = 0.03) and shorter survival (P < 0.001). By multivariate analysis, this polymorphism was identified as an independent prognostic factor (P = 0.01). These data suggest that -460T → C polymorphism of VEGF gene, by increasing VEGF expression and subsequent angiogenesis, could be a key determinant for increased tumor recurrence and a poor prognosis of patients with colorectal carcinoma. However, this study is exploratory and is not adjusted for multiple comparisons, requiring independent replication.

N-nitrosophenacetin: its synthesis, characterization, mutagenicity, and teratogenicity.

Reaction of phenacetin (CAS: 62-44-2; p-acetophenetidide) with nitrous fumes (N2O3) in glacial acetic acid at 0-5 degrees C yields N-nitrosophenacetin (NP), 2-nitrophenacetin, N-nitroso-2-nitrophenacetin (NNP), and other compounds. Both NP and NNP are fairly stable at low temperature (-30 degrees C) but extremely labile at ambient temperature. NP (median lethal dose to Sprague-Dawley rat: 21 mg/kg body wt) is 80 times more toxic than its parent compound phenacetin and is directly mutagenic to bacterial cells including Salmonella typhimurium and Sarcina lutea. The mutagenicity of NP is comparable to that of N-methyl-N'-nitro-N-nitrosoguanidine [(MNNG) CAS: 70-25-7; 1-methyl-3-nitro-1-nitrosoguanidine] and requires no microsomal metabolic activation. The teratogenic potential of NP was studied in White Leghorn chick embryos given a single dose of 5-15 micrograms/egg on day 6 of incubation. A low incidence of exencephaly and eyelid defect and a high incidence of feather and claw malformations were found in the treated group; no such malformed embryos were found in the control group. The teratogenicity of NP was found to be weaker than that of MNNG, but stronger than that of N-methyl-N-nitrosourea (CAS: 684-93-5), dimethylnitrosamine (CAS: 62-75-9; N-nitrosodimethylamine), and diethylnitrosamine (CAS: 15-18-5; N-nitrosodiethylamine).

In vitro apoptosis in the human hepatoma cell line induced by transforming growth factor beta 1.

The effect of transforming growth factor beta 1 (TGF-beta 1) on human hepatoma cells (Hep 3B) was studied. Cell death was observed when the serum starved Hep 3B cells were exposed to a very low concentration of TGF-beta 1. The half-maximal cytocidal concentration of TGF-beta 1 was around 20 pM. Cell death began approximately 24 h following treatment, with more than 80% of the cells dying after 48 h. In contrast, the control cells, which were cultured in serum-free condition, still gradually proliferated. Furthermore, the cytocidal effect of TGF-beta 1 on Hep 3B cells was not altered by either cycloheximide or actinomycin D. It was discovered, using diphenylamine assay, that TGF-beta 1 induced DNA fragmentation in Hep 3B cells. Using gel electrophoresis, the fragmented DNA could be displayed, and showed a characteristic stepladder pattern. Thus, it appeared that TGF-beta 1 induced a particular pathway in Hep 3B cells in which de novo protein synthesis was not actively involved, but endogenous nuclease was activated which cleaves cellular DNA and induces cell death.

Structures of hepatic nucleic acid-bound dyes in rats given the carcinogen N-methyl-4-aminoazobenzene.

Rats were given the hepatocarcinogenic dye N-methyl-4-aminoazobenzene labeled in the prime ring with tritium. The hepatic ribosomal RNA and DNA from these rats were hydrolyzed to uoe;d imce;psode-dye products. The major nucleoside-dye derivatives cochromatographed with synthetic N-(guanosin-8-yl)-and N-(deoxyguanosin-8-yl)-N-(methyl-4-aminoazobenzene, respectively, on cellulose and silica gel thin layers in several solvent systems. Additional evidence for the characterization of the hepatic RNA-nucleoside derivative was obtained through its degradation by alkali in air to N-methyl-4-aminoazobenzene and -4-aminoazobenzene, as previously described for N-(guanosin-8-yl)-N-methyl-4-aminoazobenzene. The same nucleoside derivatives were also derived from ribosomal RNA and DNA reacted in vitro with the carcinogenic electrophilic derivative N-benzoyloxy-N-methyl-4-aminoazobenzene, esterification of the N-hydroxy derivative, and reaction of the resultant electrophilic esters with DNA and RNA.

Aflatoxin B1-2,3-oxide as a probable intermediate in the covalent binding of aflatoxins B1 and B2 to rat liver DNA and ribosomal RNA in vivo.

Administration of[3H]aflatoxin B2 (2,3-dihydroaflatoxin B1)(AFB2) to male rats resulted in levels of hepatic DNA- and ribosomal(r)RNA-aflatoxin adducts that were about 1% of those for rats given [3H]aflatoxin B1(AFB1). The levels of hepatic protein-aflatoxin adducts were 35 to 70% as great for AFB2-treated as compared to AFB1-treated rats...

Reduced nicotinamide adenine dinucleotide phosphate-dependent formation of 2,3-dihydro-2,3-dihydroxyaflatoxin B1 from aflatoxin B1 by hepatic microsomes.

2,3-Dihydro-2,3-dihydroxyaflatoxin B1 (dihydrodiol) was formed as a major metabolite in the incubation of aflatoxin B1 with rat and hamster liver microsomes. The yield of the dihydrodiol was maximal at pH 6.5, was reduced nicotinmide adenine dinucleotide phosphate- and cytochrome P-450-dependent, and was increased 2- to 4-fold by pretreatment of the animals with phenobarbital; pretreatment with 3-methylcholanthrene did not alter the activity of rat hepatic microsomes. Inhibitors of epoxide hydrase did not lower the yield of the dihydrodiol in these systems. Negligible yields of the dihydrodiol were formed from aflatoxin B1 and rat liver microsomes in the presence of DNA. Little or no formation of the dihydrodiol was noted with microsomes from rat intestinal mucosa, kidney, or lung. These results further support the formation of aflatoxin B1 2,3-oxide as a major electrophilic metabolite of aflatoxin B1 in rat and hamster liver microsomal systems, since this highly reactive epoxide would be expected to hydrolyze readily to form the dihydrodiol.

N-substitution of carbon 8 in guanosine and deoxyguanosine by the carcinogen N-benzoyloxy-N-methyl-4-aminoazobenzene in vitro.

The major reaction products of the carcinogenic electrophile N-benzoyloxy-N-methyl-4-aminoazobenzene with guanosine or deoxyguanosine were characterized as N-(guanosin-8-yl)- and N-(DEOXYGUANOSIN-8-YL)-N-methyl-4-aminoazobenzene from the following chemical, radiochemical, and spectroscopic studies: (a) the presence of equimolar amounts of both N-methyl-4-aminoazobenzene (MAB) and guanosine or deoxyguanosine residues was shown by the 3H:14C ratios of the products from the reaction of (prime ring-3H)-N-benzoyloxy-N-methyl-4-aminoazobenzene with (8-14C)guanosine or (8-14C)deoxyguanosine and by the molecular weights of the trimethylsilyl derivatives of both products: (b) substitution of the dye residue on its amino nitrogen was indicated by the retention in the products of the 3H:14C ration of (CH2-3H + 14CH3)-N-BENZOYLOXY-N-methyl-4-aminoazobenzene and by the release of MAB on treatment of the nucleoside-dye derivatives with strong alkali in air; (c) substitution of the guanine residues in positon 7 or 8 was demonstrated by loss of 3H from (8-3H)guanosine or (8-3H)deoxyguanosine in the formation of the nucleoside-dye derivatives; (d) the stability of the products to mild alkali (as contrasted to the lability of 7-alkylguanosines) provided strong evidence that the substitution was in position 8 of the guanine residue; (e) direct evidence of 8-substitution came from the acid hydrolysis of guanosinyl- and deoxyguanosinyl-N-methyl-4-aminoazo benzene to N-(guan-8-yl)-N-methyl-4-aminoazobenze in up to 50% yield; (f) comparisons of the proton or 13C nuclear magnetic resonance spectra or both of N-(guan-8-yl)- N-methyl-4-aminoazobenzene, MAB, N-(guanosin-8-yl)-2-acetylaminofluorene, 2-acetylaminofluorene, guanosine, and 7 -methylguanosine with the spectra of the guanosine-MAB product further confirmed that substitution had occurred at position 8 of the guanosine residue. The new compound N-(guan-8-yl)-N-methyl-4-aminoazobenzene was synthesized. Attempts to devise an unambiguous synthesis of N-(GUANOSIN-8-YL)-N-methyl-4-aminoazobenzene were not successful.

Differential induction of c-fos and c-jun proto-oncogenes and AP-1 activity by tumor promoter 12-O-tetradecanoyl phorbol 13-acetate in cells at different stages of tumor promotion in vitro.

A two-stage (initiation and promotion) model of chemical transformation of mouse embryonic fibroblasts was used to elucidate the molecular mechanisms of tumor promotion in vitro. C3H10T1/2 cells which had been initiated with a subcarcinogenic dose (0.5 micrograms ml-1) of benzo[a]pyrene (B[a]P) were isolated after 12-O-tetradecanoyl phorbol 13-acetate (TPA) treatment lasting 12, 24 or 36 days. These series of partially promoted cells were designated T-12, T-24 and T-36 cells. T-12 and T-24 cells exhibited higher anchorage-independent growth on soft agar in the presence of TPA than did the initiated or T-36 cells. Cytosolic protein kinase C (PKC) in the resting state was slightly depleted in T-24 and T-36 cells. Proteolytic down-regulation of membrane-bound PKC was enhanced in T-12 cells compared with the initiated cells after 3 h of TPA treatment. Induction of c-fos and c-jun proto-oncogene expression increased two- to threefold in T-12 cells. Moreover, the basal level of c-fos mRNA progressively increased in T-12, T-24 and T-36 cells. As compared with other cell types, T-12 cells had the highest AP-1 DNA-binding activity at both the basal level and at 30 min after TPA treatment. These results indicate that deregulation of the TPA-induced cellular responses occurs in the cells at various stages of tumor promotion, and might be associated with transforming processes.

Differential regulation of p53, c-Myc, Bcl-2 and Bax protein expression during apoptosis induced by widely divergent stimuli in human hepatoblastoma cells.

Apoptosis of HepG2 cells triggered by various agents is characterized in an attempt to delineate the common apoptosis signaling pathway in human hepatoma cells. Several hallmarks of apoptosis, including DNA laddering, chromatin condensation and fragmentation, and an apoptosis specific cleavage of 28S and 18S ribosomal RNA were observed after treatment with curcumin. Curcumin treatment however did not alter the expression levels of Bcl-2 and Bax proteins. p53 protein accumulated slowly and decreased abruptly after reaching the maximum. Conversely, c-Myc protein decreased initially and subsequently increased preceding the onset of apoptosis. The accumulation of p53 protein is not due to increased levels of p53 mRNA and does not result in growth arrest. Staurosporine, quinacrine, ultraviolet irradiation, hydrogen peroxide, and cyclohexamide are all capable of triggering apoptosis in HepG2 cells. While most of these agents affect the expression levels of p53 and c-Myc similarly, none of them altered the expression levels of the Bcl-2 and Bax proteins. In conclusion, these data suggest that p53 and c-Myc may play a more important role in the apoptosis signaling pathway in HepG2 cells, than the bcl-2 gene family.

Curcumin, an antioxidant and anti-tumor promoter, induces apoptosis in human leukemia cells.

Curcumin, widely used as a spice and coloring agent in food, possesses potent antioxidant, anti-inflammatory and anti-tumor promoting activities. In the present study, curcumin was found to induce apoptotic cell death in promyelocytic leukemia HL-60 cells at concentrations as low as 3.5 micrograms/ml. The apoptosis-inducing activity of curcumin appeared in a dose- and time-dependent manner. Flow cytometric analysis showed that the hypodiploid DNA peak of propidium iodide-stained nuclei appeared at 4 h after 7 micrograms/ml curcumin treatment. The apoptosis-inducing activity of curcumin was not affected by cycloheximide, actinomycin D, EGTA, W7 (calmodulin inhibitor), sodium orthovanadate, or genistein. By contrast, an endonuclease inhibitor ZnSO4 and proteinase inhibitor N-tosyl-L-lysine chloro-methyl ketone (TLCK) could markedly abrogate apoptosis induced by curcumin, whereas 12-O-tetradecanoylphorbol-13-acetate (TPA) had a partial effect. The antioxidants, N-acetyl-L-cysteine (NAC), L-ascorbic acid, alpha-tocopherol, catalase and superoxide dismutase, all effectively prevented curcumin-induced apoptosis. This result suggested that curcumin-induced cell death was mediated by reactive oxygen species. Immunoblot analysis showed that the level of the antiapoptotic protein Bcl-2 was decreased to 30% after 6 h treatment with curcumin, and was subsequently reduced to 20% by a further 6 h treatment. Furthermore, overexpression of bcl-2 in HL-60 cells resulted in a delay of curcumin-treated cells entering into apoptosis, suggesting that bcl-2 plays a crucial role in the early stage of curcumin-triggered apoptotic cell death.

Pronounced activation of protein kinase C, ornithine decarboxylase and c-jun proto-oncogene by paraquat-generated active oxygen species in WI-38 human lung cells.

Paraquat (methyl viologen, PQ) is a widely used herbicide that produces oxygen-derived free radicals and severely injures human lungs. In this study we examined the effects of PQ on the protein kinase C (PKC), ornithine decarboxylase (ODC) and c-jun oncogene expression in WI-38 human lung cells. Exposure of cells to 25-200 microM PQ resulted in an increase of [3H]phorbol dibutyrate (PDBu) binding and PKC redistribution in a dose-dependent manner. Interestingly, a superoxide dismutase mimic, 4-hydroxyl-2,2,6,6-tetramethyl-piperidine-1-oxyl (Tempol, 2.5 mM) and catalase (400 micrograms/ml) could significantly reduce the PQ-stimulated increase of phorbol ester binding and particular PKC phosphorylating activity, but dimethylsulfoxide (DMSO, 1.5%), an effective .OH trapping agent, failed to prevent this stimulation. In addition, an endogenous substrate of PKC, 80 kDa protein, was found to be highly phosphorylated in intact WI-38 cells treated with 50 microM PQ. The increase of phosphorylated proteins could be completely or partly abolished by Tempol or catalase, but only the phosphorylation of 80 kDa protein was diminished by protein kinase C inhibitor, 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7). A maximal peak of ODC activity was observed at 6 h of treatment with 50 microM PQ. PQ induced activity was reduced at the following rates, Tempol 85%, DMSO 80% and catalase 45%, but H-7 failed to do so. Furthermore, we found that the level of c-jun mRNA was transiently increased by PQ and the peak appeared at 1 h of treatment. When correlated with the PKC result, Tempol, catalase and H-7 all effectively blocked PQ-elicited c-jun transcript expression, but DMSO only exhibited a weakly inhibitory effect. We therefore propose that superoxide anion (O2- and H2O2 generated by PQ could activate PKC and lead to induction of c-jun gene expression; on the other hand, O2- and .OH might trigger other kinase pathways to elevate ODC activity. Finally, the sequential expression of c-jun oncogene and ODC may cooperate to relieve the oxidative damages elicited by PQ.

Suppression of transcription factor NF-kappaB activity by Bcl-2 protein in NIH3T3 cells: implication of a novel NF-kappaB p50-Bcl-2 complex for the anti-apoptotic function of Bcl-2.

Bcl-2 can suppress apoptosis by controlling genes that encode proteins required for programmed cell death and by interference with peroxidative damage. Overexpression of Bcl-2 in NIH3T3 cells can prevent GSNO-induced (S-nitrosoglutathione-induced) apoptosis. The experimental results indicated that activation of NF-kappaB by GSNO is involved in inducing apoptosis. Surprisingly, we found that Bcl-2 delayed the release of IkB by formation of a Bcl-2-NF-kappaB complex (p50-p65-IkappaB) in the cytoplasm during cell apoptosis. Furthermore, a novel Bcl-2-p50 complex was found in the nucleus. These features were only observed in Bcl-2-transfected cells but not in the parental NIH3T3 cells. Overexpression of Bcl-2 suppressed the levels of c-myc, a target gene of NF-kappaB, and influenced the DNA-binding activity of NF-kappaB during GSNOinduced apoptosis. We suggest that the Bcl-2-p50 complex inhibits NF-kappaB DNA-binding activity by competing with the p65-p50 heterodimer for the DNA-binding site in the nucleus. Finally, it has been demonstrated that the anti-apoptotic potential of Bcl-2 may be attributed to its complexing with p50 in the nucleus that leads to blockage of nuclear gene expression.

Proliferation arrest and induction of CDK inhibitors p21 and p27 by depleting the calcium store in cultured C6 glioma cells.

C6 glioma - Ca2+ depletion - proliferation arrest morphology change - CDK inhibitor In this study, we investigated the role of the intracellular calcium store in modulating the cellular proliferation and the expression of cell cycle regulatory proteins in cultured C6 glioma cells. By means of microspectrofluorimetry and Ca(2+)-sensitive indicator fura-2, we found that the intracellular Ca2+ pump inhibitors, thapsigargin (TG) irreversibly and 2,5-ditert-butyl-hydroquinone (DBHQ) reversibly depleted the Ca(2+)-store accompanied with the induction of G0/G1 arrest, an increase in glial fibrillary acidic protein (GFAP) expression and morphological changes from a round flat shape to a differentiated spindle-shaped cell. The machinery underlying these changes induced by Ca(2+)-store depletion was investigated. The results indicated that Ca(2+)-store depletion caused an increased expression of p21 and p27 proteins (cyclin-dependent kinase inhibitors), with unchanged mutant p53 protein of C6 cells but reduced amounts of the cell cycle regulators: cyclin-dependent kinase 2 (CDK2), cdc2, cyclin C, cyclin D1, cyclin D3 and proliferating cell nuclear antigen (PCNA) in a time-dependent manner. These findings indicate a new function of the endoplasmic reticulum (ER) Ca2+ store in regulating cellular proliferation rate through altering the expression of p21 and p27 proteins. Moreover, cellular differentiation as revealed by spindle-shaped morphology and induced GFAP expression were also modulated by the ER Ca2+ store. The implication of this finding is that the abnormal growth of cancer cells such as C6 glioma cells may be derived from a signalling of the ER which can be manipulated by depleting the Ca2+ store.

Alternative activation of extracellular signal-regulated protein kinases in curcumin and arsenite-induced HSP70 gene expression in human colorectal carcinoma cells.

We have investigated the regulation mechanism of chemical stress-induced HSP70 gene expression in human colorectal carcinoma cells (COLO205 and HT29). Our data show that chemical treatments including sodium arsenite and curcumin, induced significant synthesis of HSP70 and its mRNA. The induced HSP70 gene expression appears to be increased at the transcriptional level. The increase in HSP70 gene expression by both chemicals is associated with an increase in HSF binding to HSE and induction of HSF1 di- or trimerization. Phosphorylation and activation of extracellular signal-regulated proteins (ERK1/2) were detected in sodium arsenite-treated COLO205 and HT29 cells, and the free radical scavenger N-acetyl-L-cysteine (NAC) was able to inhibit this ERK1/2 activation and HSP70 gene expression. MAPK blockade by the specific MEK1 inhibitor (PD98059) decreased the ability of sodium arsenite to increase HSP70 gene expression in a dose-dependent manner along with dephosphorylation of ERK1/2 proteins. In contrast to arsenite treatment, activation of ERK1/2 was not detected in curcumin-treated colorectal carcinoma cells, and NAC and PD98059 did not show any inhibitory effect on HSP70 gene expression induced by curcumin. Overexpression of a dominant negative mutant of mitogen-activated protein kinase kinase kinase 1 (MEKK1-DN) prevents arsenite-induced ERK1/2 phosphorylation and HSP70 protein synthesis. These results indicated that the ERK signaling pathway can participate in HSP70 gene expression induced by the prooxidant sodium arsenite, but not by the antioxidant curcumin.

Oxidation of LDL by nitric oxide and its modification by superoxides in macrophage and cell-free systems.

Oxidative modification of low density lipoproteins (LDL) can increase the atherogenicity of LDL. Here we demonstrate the potential role of nitric oxide (NO) in LDL modification. Dose-dependent alterations of LDL including an increase in electrophoretic mobility, generation of peroxides and degradation of apoprotein B occurred during incubation with NO. Sodium nitroprusside was also shown to increase the electromobility of LDL. Superoxide dismutase (SOD) and catalase did not affect this result. NO treatment also increases the negative charges on other lipoproteins. In addition, we have demonstrated that NO plays a protective role in macrophage or superoxide-induced LDL modification through its neutralizing action.

Induction of c-jun protooncogene expression by hydrogen peroxide through hydroxyl radical generation and p60SRC tyrosine kinase activation.

The mechanisms of signal transduction of c-jun induction by hydrogen peroxide are elucidated in NIH3T3 cells by using trapping agents of hydroxyl free radical or inhibitors of various protein kinases. Pre-treatment of the cell with hydroxyl radical scavenger dimethyl sulfoxide (DMSO) abolishes the H2O2-induced c-jun expression. Hydroxyl radical generation can be detected and quantified in cells treated sequentially with DMSO and H2O2 for 30 min respectively by methane sulfinic acid (MSA) production, especially that from particulate fraction. Induction of c-jun by H2O2 is also dramatically reduced by pretreating the cells with biological antioxidant vit. E. Protein tyrosine kinase activity of membrane fraction is induced by H2O2 within 5 to 10 min, which can be prevented by DMSO pre-treatment. Inhibitor of non-receptor type tyrosine kinase, herbimycin A, has inhibitory effect on H2O2-induced c-jun expression while the inhibitor of receptor type tyrosine kinase, tyrphostin 23 or inhibitor of cyclic AMP dependent protein kinase, KT 5720, has not. TPA pre-treatment that depletes protein kinase C (PKC) has no influence on the c-jun induction by H2O2. Our results suggest that the highly reactive species HO is generated after H2O2 enter cells and mediate the signal responses of H2O2 including c-jun induction and the activation of p60src tyrosine kinase might be one of the molecular events associated with the c-jun induction pathway.

Suppression of inducible cyclooxygenase and nitric oxide synthase through activation of peroxisome proliferator-activated receptor-gamma by flavonoids in mouse macrophages.

Peroxisome proliferator-activated receptor (PPAR)gamma transcription factor has been implicated in anti-inflammatory response. Of the compounds tested, apigenin, chrysin, and kaempferol significantly stimulated PPAR gamma transcriptional activity in a transient reporter assay. In addition, these three flavonoids strongly enhanced the inhibition of inducible cyclooxygenase and inducible nitric oxide synthase promoter activities in lipopolysaccharide-activated macrophages which contain the PPAR gamma expression plasmids. However, these three flavonoids exhibited weak PPAR gamma agonist activities in an in vitro competitive binding assay. Limited protease digestion of PPAR gamma suggested these three flavonoids produced a conformational change in PPAR gamma and the conformation differs in the receptor bound to BRL49653 versus these three flavonoids. These results suggested that these three flavonoids might act as allosteric effectors and were able to bind to PPAR gamma and activate it, but its binding site might be different from the natural ligand BRL49653.

Induction of apoptosis by apigenin and related flavonoids through cytochrome c release and activation of caspase-9 and caspase-3 in leukaemia HL-60 cells.

The aim of this study was to investigate the mechanism of flavonoid-induced apoptosis in HL-60 leukaemic cells. Thus, the effect of structurally related flavonoids on cell viability, DNA fragmentation and caspase activity was assessed. Loss of membrane potential and reactive oxygen species generation were also monitored by flow cytometry. The structurally related flavonoids, such as apigenin, quercetin, myricetin, and kaempferol were able to induce apoptosis in human leukaemia HL-60 cells. Treatment with flavonoids (60 microM) caused a rapid induction of caspase-3 activity and stimulated proteolytic cleavage of poly-(ADP-ribose) polymerase (PARP). Furthermore, these flavonoids induced loss of mitochondrial transmembrane potential, elevation of reactive oxygen species (ROS) production, release of mitochondrial cytochrome c into the cytosol, and subsequent induction of procaspase-9 processing. The potency of these flavonoids on these features of apoptosis were in the order of: apigenin > quercetin > myricetin > kaempferol in HL-60 cells treated with 60 microM flavonoids. These results suggest that flavonoid-induced apoptosis is stimulated by the release of cytochrome c to the cytosol, by procaspase-9 processing, and through a caspase-3-dependent mechanism. The induction of apoptosis by flavonoids may be attributed to their cancer chemopreventive activity. Furthermore, the potency of flavonoids for inducing apoptosis may be dependent on the numbers of hydroxyl groups in the 2-phenyl group and on the absence of the 3-hydroxyl group. This provides new information on the structure-activity relationship of flavonoids.