BAG3 down-modulation sensitizes HPV18(+) HeLa cells to PEITC-induced apoptosis and restores p53

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BAG3 down-modulation by siRNA technology restored p53.

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Reduced BAG3 expression sensitized HeLa but not C33A (HPV-negative) cells to PEITC.

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Reduced BAG3 expression was associated with a decrease of E6 viral protein levels.

BAG3 is a multi-functional component of tumor cell pro-survival machinery, and its biological functions have been largely associated to proteasome system. Here, we show that BAG3 down-modulation resulted in reduced cell viability and enhanced PEITC-induced apoptosis largely more extensively in HeLa (HPV18⁺) rather than in C33A (HPV⁻) cervical carcinoma cell lines. Moreover, we demonstrate that BAG3 suppression led to a decrease of viral E6 oncoprotein and a concomitant recovery of p53 tumor suppressor, the best recognized target of E6 for proteasome degradation. E6 and p53 expression were modulated at protein level, since their respective mRNAs were unaffected. Taken together our findings reveal a novel role for BAG3 as host protein contributing to HPV18 E6-activated pro-survival strategies, and suggest a possible relevance of its expression levels in drug/radiotherapy-resistance of HPV18-bearing cervical carcinomas.

BAG3 protects bovine papillomavirus type 1-transformed equine fibroblasts against pro-death signals

In human cancer cells, BAG3 protein is known to sustain cell survival. Here, for the first time, we demonstrate the expression of BAG3 protein both in equine sarcoids in vivo and in EqS04b cells, a sarcoid-derived fully transformed cell line harbouring bovine papilloma virus (BPV)-1 genome. Evidence of a possible involvement of BAG3 in equine sarcoid carcinogenesis was obtained by immunohistochemistry analysis of tumour samples. We found that most tumour samples stained positive for BAG3, even though to a different grade, while normal dermal fibroblasts from healthy horses displayed very weak staining pattern for BAG3 expression. By siRNA technology, we demonstrate in EqS04b the role of BAG3 in counteracting basal as well as chemical-triggered pro-death signals. BAG3 down-modulation was indeed shown to promote cell death and cell cycle arrest in G₀/G₁. In addition, we found that BAG3 silencing sensitized EqS04b cells to phenethylisothiocyanate (PEITC), a promising cancer chemopreventive/chemotherapeutic agent present in edible cruciferous vegetables. Notably, such a pro-survival role of BAG3 was less marked in E. Derm cells, an equine BPV-negative fibroblast cell line taken as a normal counterpart. Altogether our findings might suggest a mutual cooperation between BAG3 and viral oncoproteins to sustain cell survival.

Structural characterization of tetranortriterpenes from Pseudrocedrela kotschyi and Trichilia emetica and study of their activity towards the chaperone Hsp90

Investigation of roots extracts Pseudrocedrela kotschyi and Trichilia emetica led to identification of 5 limonoid derivatives, Kotschyins D-H, and 11 known compounds. Their structures were elucidated by extensive 1D and 2D NMR experiments in conjunction with mass spectrometry. A surface plasmon resonance (SPR) approach was adopted to screen their Hsp90 binding capability and kotschyin D showed a significant affinity for the chaperone. Therefore, the characterization of the biological activity of kotschyin D by means of a panel of chemical and biological approaches, including limited proteolysis, molecular docking and biochemical and cellular assays, was performed. Our result indicated this compound as a type of client selective Hsp90 inhibitor, directly binding to the middle domain of the protein and possibly preventing its interaction with the activator of Hsp90 ATPase 1 (Aha1).

Effect of sesquiterpene lactone coronopilin on leukaemia cell population growth, cell type-specific induction of apoptosis and mitotic catastrophe

OBJECTIVES

The aim of this study was to investigate anti-leukaemic potential of coronopilin, a sesquiterpene lactone from Ambrosia arborescens, and to characterize mechanism(s) underlying its activity.

MATERIALS AND METHODS

The study was conducted on Jurkat and U937, two leukaemia-derived cell lines. Apoptosis and impairment of cell cycle progression were evaluated by flow cytometry and by microscopic analysis. Changes in protein expression and activation were evaluated by western blot analysis. Coronopilin-tubulin covalent adducts were demonstrated by mass spectrometry.

RESULTS

Coronopilin inhibited (IC(50) ≤ 20 μm) leukaemia cell population growth, but displayed poor cytotoxicity to normal white blood cells. On Jurkat cells, coronopilin exerted cell population growth inhibition activity, mainly by triggering caspase-dependent apoptosis. Conversely, in U937 cells, coronopilin's primary response was a robust arrest in G(2) /M. Marked increase in mitotic index and presence of activated cyclin B1/Cdk1 complex, phosphorylated histone H3 at Ser10, and hyperpolymerized tubulin indicated that cells accumulated in mitosis. Prolonged mitotic arrest ultimately resulted in U937 mitotic catastrophe, and dying cells exhibited the features of non-caspase-dependent death.

CONCLUSIONS

  This study demonstrated that coronopilin efficiently inhibited leukaemia cell population growth by triggering cell type-specific responses. Moreover, coronopilin-mediated cell population expansion inhibition was specific to neoplastic cells, as normal white blood cell viability was not significantly affected. Thus, coronopilin may represent an interesting new chemical scaffold upon which to develop new anti-leukaemic agents.

Abstract 3034: air (apoptosis-induced regulator) expression and its sequence localization in human genome

The aim of this study was to characterize a newly identified transcript named air (AX538681) whose genomic sequence is missing in human genome draft. air was identified as a differentially expressed cDNA in TNFα-stimulated Jurkat cells, transfected with a IkBα-hyperexpressing vector, versus control cells (Turco et al, 2007). Indeed air expression appeared to be induced by a pro-apoptotic stimulus and repressed by NF-κB activity.

Air cDNA was isolated by differential screening analysis of an expression library from Jurkat cells; its sequence (3.4kb long, 79% A/T rich) didn't show any similarity with annotated sequences except the homology with an EST (U74659) from human neuroblastoma cells and a 98% identity with traces from chimpanzee WGS database. This evidence suggested that air could belong to an un-sequenced region, whose secondary structure results in cloning instability.

Air sequence is detectable by Southern blot and PCR, providing the evidence of its presence in human genome (in press). air genomic 3’ and 5’ flanking regions (each one ∼2.2kb long) were isolated by vectorette PCR and sequenced to allow the synthesis of a probe (∼8kb long) suitable to perform a FISH assay. Preliminary experiments, performed on a thyroid cancer cell line, showed that air localize on Chr. 22. Moreover, we found that air transcript is longer than 3.4kb, since air 5’ flanking region is detectable by RT-PCR on total RNA (unpublished).

Four main putative ORFs were identified by ORF-Finder tool, but the aminoacidic sequence of three of them did not show any homology with conserved structural motifs while the fourth, localized on the new isolated 5’ transcript end, showed a transmembrane-like motif. Anyway, we don't exclude that air could be a long ncRNA (but it is not the Air described by Nagano et al, 2008), in fact, it is rich in stop codons, it's strongly predisposed to form stem loop secondary structures and its expression coincides with pro-apoptotic events (submitted).

Air role in modulating cell apoptosis was investigated: air silencing in lymphoma, neuroblastoma and AML cells, treated with stressful stimuli, showed a significant (p<0.01) reduction of caspase 3 activation, mitochondrial membrane depolarization, cytochrome c release and appearance of apoptotic cells. At the same time, transfection of human PBMC with an air-hyperexpressing construct resulted in more than 25% appearance of apoptotic cells in respect to controls (Turco et al, 2007). Finally we found that air is also induced in pancreas carcinoma cell lines by ROS-inducing compounds (as PEITC and DEM). Since PEITC inhibits NF-κB activation, air induction by this agent is consistent with the suppressive effect of NF-κB on air expression (in press). We also observed air down-modulation in pancreatic AsPc1 cells treated with CDDP.

These findings identify air as a novel potential tool for enhancing cancer response to therapeutics.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3034. doi:10.1158/1538-7445.AM2011-3034

Pro-apoptotic and cytostatic activity of naturally occurring cardenolides

PURPOSE

Cardenoliddes are steroid glycosides which are known to exert cardiotonic effects by inhibiting the Na(+)/K(+)-ATPase. Several of these compounds have been shown also to possess anti-tumor potential. The aim of the present work was the characterization of the tumor cell growth inhibition activity of four cardenolides, isolated from Periploca graeca L., and the mechanisms underlying such an effect.

METHODS

The pro-apoptotic and cytostatic effect of the compounds was tested in U937 (monocytic leukemia) and PC3 (prostate adenocarcinoma). Characterization of apoptosis and cell cycle impairment was obtained by cytofluorimetry and WB.

RESULTS

Periplocymarin and periplocin were the most active compounds, periplocymarin being more effective than the reference compound ouabain. The reduction of cell number by these two cardenolides was due in PC3 cells mainly to the activation of caspase-dependent apoptotic pathways, while in U937 cells to the induction of cell cycle impairment without extensive cell death. Interestingly, periplocymarin, at cytostatic but non-cytotoxic doses, was shown to sensitize U937 cells to TRAIL.

CONCLUSIONS

Taken together, our data outline that cardiac glycosides are promising anticancer drugs and contribute to the identification of new natural cardiac glycosides to obtain chemically modified non-cardioactive/low toxic derivatives with enhanced anticancer potency.

Inhibition of the thioredoxin system is a basis for the antileukemic potential of 13-hydroxy-15-oxo-zoapatlin

The mammalian thioredoxin (Trx) system, composed of Trx, Trx reductase (TrxR), and NADPH, is the most important thiol system involved in the redox control of signaling and regulatory proteins in apoptosis and cell proliferation. Here we addressed the inhibition of the Trx system by 13-hydroxy-15-oxo-zoapatlin (OZ), a nor-kaurane diterpene previously shown to possess proapoptotic potential and to cause cell cycle arrest in leukemia cells. OZ was found, by both biochemical and mass spectrometry-based approaches, to target Trx1 and TrxR in a cell-free system. In particular, the formation of reversible OZ adducts to Trx1 Cys35, Cys62, and Cys73 was demonstrated. We next showed that OZ efficiently inhibited Trx and TrxR catalytic activity in Molt4 cells. The occurrence of oxidative modifications of Trx molecules was assessed by "redox Western blot" analyses. OZ-mediated Trx oxidation resulted in apoptosis signaling kinase-1 release and activation of downstream JNK and p38 pathways. By means of specific inhibitors of these two stress-activated protein kinases, we demonstrated that the JNK pathway plays a major role in determining the apoptotic fate of OZ-exposed cells, whereas p38 activation seems to be involved mainly in OZ-induced G2/M block.

13-Hydroxy-15-oxo-zoapatlin, an ent-kaurane diterpene, induces apoptosis in human leukemia cells, affecting thiol-mediated redox regulation

13-Hydroxy-15-oxo-zoapatlin (OZ), a nor-kaurane diterpene, was first described as a compound inhibiting the proliferation of human cancer cell lines. Successively, it was reported that OZ inhibits the G2 DNA damage checkpoint and causes mitotic arrest. To get more insight into the molecular mechanism(s) underlying the antitumor potential of OZ, we evaluated the proapoptotic activity of this molecule. OZ was found to induce hypodiploidia and phosphatidylserine externalization, two hallmarks of apoptosis; to disrupt mitochondrial membrane potential; and to trigger caspase-3 activation. OZ-induced cell death, mostly dependent upon the presence of the alpha,beta-carbonyl group, is strongly related to alterations in the cellular redox balance. The interaction of OZ with cellular components and proteins containing reactive thiols was evaluated by mass spectrometry-based approaches. A specific reactivity of this compound toward glutathione and thioredoxin was observed.

The activity of hsp90 alpha promoter is regulated by NF-kappa B transcription factors

Heat-shock proteins (HSP) 90 exert a relevant role in the survival and response to therapy of many neoplastic cell types. Here, we show that the promoter of hsp90alpha gene, that encodes the inducible form of HSP90, is regulated by nuclear factor-kappaB (NF-kappaB) activity. Indeed, we found that NF-kappaB factors bound to one of the two putative consensus sequences present in the hsp90alpha-flanking region; mutation of such motif hampered the phorbol-myristate-13-acetate-stimulated expression of a luciferase reporter gene under the control of the hsp90alpha promoter. Furthermore, the downmodulation of NF-kappaB (p65) levels by a specific small interfering (si) RNA resulted in reducing the levels of endogenous HSP90alpha protein. These findings disclose a previously unrecognized mechanism that contributes to connect NF-kappaB factors and HSPs in cell defence machinery.

Antiproliferative and pro-apoptotic activity of novel phenolic derivatives of resveratrol

Gloriosaols A-C, isolated from Yucca gloriosa (Agavaceae), are novel phenolic compounds structurally related to resveratrol. In the present study, we show that gloriosaols possess antiproliferative and pro-apoptotic activity on tumor cells of different histogenetic origin and that their cell growth inhibition potential is higher than that of resveratrol. Despite the close similarities in their structure, gloriosaols A-C exhibited different antiproliferative potency, as the EC(50) ascending order is: gloriosaol C, gloriosaol A, gloriosaol B. Further mechanisms of gloriosaol C cytotoxicity were elucidated in detail in U937 cells, the most sensitive of the cell lines tested. The effect of gloriosaol C on cell growth turned out to be strongly dependent upon the concentration. Gloriosaol C doses lower than the EC(50) value (8 mu-icroM) blocked the cell cycle in G(0)/G(1), with a concurrent decrease in the number of cells in the G(2)/M phases of the cell cycle. At higher doses, this arrest overlaps with the occurrence of apoptosis and necrosis. In the 10-25 microM range of doses, gloriosaol C caused cell death mainly by apoptosis, as measured by hypodiploidia induction, phosphatidyl serine externalization and disruption of mitochondrial transmembrane potential. A switch in the mode of death from apoptosis to necrosis occurred at doses of gloriosaol C higher than 30 microM. Gloriosaol C was found to induce production of reactive species dose-dependently, but also to counteract their elevation in stressed cells. Thus, the different fate of cells, that is cell cycle arrest or cell death, in response to different doses of gloriosaol C might be related to the extent of induced oxidative stress.

Apoptosis inhibition in cancer cells: A novel molecular pathway that involves BAG3 protein

Stress-induced apoptosis regulates neoplasia pathogenesis and response to therapy. Indeed, cell transformation induces a stress response, that is overcome, in neoplastic cells, by alterations in apoptosis modulators; on the other hand, antineoplastic therapies largely trigger the apoptosis stress pathway, whose impairment results in resistance. Therefore, the study of the roles of apoptosis-modulating molecules in neoplasia development and response to therapy is of key relevance for our understanding of these processes. Among molecules that regulate apoptosis, a role is emerging for BAG3, a member of the BAG co-chaperone protein family. Proteins that share the BAG domain are characterized by their interaction with a variety of partners (heat shock proteins, steroid hormone receptors, Raf-1 and others), involved in regulating a number of cellular processes, including proliferation and apoptosis. BAG3, also known as CAIR-1 or Bis, forms a complex with the heat shock protein (Hsp) 70. This assists polypeptide folding, can mediate protein delivery to proteasome and is able to modulate apoptosis by interfering with cytochrome c release, apoptosome assembly and other events in the death process. It has been recently shown that, in human primary lymphoid and myeloblastic leukemias and other neoplastic cell types, BAG3 expression sustains cell survival and underlies resistance to therapy, through downmodulation of apoptosis. This review summarizes findings that assign an apoptotic role to BAG3 in some neoplastic cell types and identify the protein as a candidate target of therapy.

Sulfated triterpene derivatives from Fagonia arabica

Two new sulfated triterpenes (1, 6) and four new sulfated triterpene glycosides (2-5) have been isolated from the aerial parts of Fagonia arabica. Their structures were established by spectroscopic data analysis. Compounds 1/2 and 3/4 are sulfated derivatives of the rare sapogenins 3beta,27-dihydroxyolean-12-en-28-oic acid and 3beta,27-dihydroxyurs-12-en-28-oic acid, respectively. Compound 5 is an unusual disulfated oleanene derivative characterized by the occurrence of a 13,18-double bond, while compound 6 is the first reported naturally occurring saturated and sulfated pentacyclic triterpene of the taraxastane series with a C-20,28 lactone unit.

The antiapoptotic protein BAG3 is expressed in thyroid carcinomas and modulates apoptosis mediated by tumor necrosis factor-related apoptosis-inducing ligand

CONTEXT

We previously showed that BAG3 protein, a member of the BAG (Bcl-2-associated athanogene) co-chaperone family, modulates apoptosis in human leukemias. The expression of BAG3 in other tumor types has not been extensively investigated so far.

OBJECTIVE

The objective of this study was to analyze BAG3 expression in thyroid neoplastic cells and investigate its influence in cell apoptotic response to TNF-related apoptosis-inducing ligand (TRAIL).

DESIGN, SETTING, AND PATIENTS

We investigated BAG3 expression in human thyroid carcinoma cell lines, including NPA, and the effect of BAG3-specific small interfering RNA on TRAIL-induced apoptosis in NPA cells. Subsequently, we analyzed BAG3 expression in 30 benign lesions and 56 carcinomas from patients of the Naples Tumor Institute Fondazione Senatore Pascale.

MAIN OUTCOME MEASURES

The main outcome measures were: analysis of BAG3 protein in NPA cells by Western blot and immunocytochemistry; analysis of apoptosis in TRAIL-stimulated NPA cells by flow cytometry; and evaluation of BAG3 expression in specimens from thyroid lesions by immunohistochemistry.

RESULTS

BAG3 was expressed in human thyroid carcinoma cell lines; small interfering RNA-mediated downmodulation of its levels significantly (P < 0.0195) enhanced NPA cell apoptotic response to TRAIL. The protein was not detectable in 19 of 20 specimens of normal thyroid or goiters, whereas 54 of 56 analyzed carcinomas (15 follicular, 28 papillary, and 13 anaplastic) were clearly positive for BAG3 expression.

CONCLUSIONS

BAG3 downmodulates the apoptotic response to TRAIL in human neoplastic thyroid cells. The protein is specifically expressed in thyroid carcinomas and not in normal thyroid tissue or goiter.

Modulation of chondrocyte adhesion to collagen by echistatin

Primary chondrocytes from quail embryo epiphysis (quail epiphyseal chondrocytes, QEC) can grow either in suspension or in monolayer. In this study, the adhesion of QEC to collagen II was used as a model to study the regulation of the ligand-binding activity of integrin receptors that allows these cells to undergo a rapid transition from suspension to an adherent state. Preincubation of suspension QEC (QECSP) with the disintegrin echistatin increased by 40% their adhesion to collagen II. An inverse relationship between immobilized collagen density and echistatin-induced increase of chondrocyte adhesion was observed, thus suggesting that the disintegrin acts by increasing the ligand-binding affinity of collagen receptor(s). Further, echistatin activity does not appear to depend upon a direct binding of the disintegrin to collagen receptor(s). In fact, immobilized anti-beta1 antibodies, but not immobilized echistatin, served as effective binding sites for QECSP. Echistatin failed to stimulate chondrocyte adhesion to collagen in the presence of metabolic inhibitors, while an activating anti-beta1 antibody was still effective. Thus, echistatin may promote cell adhesion by interfering with energy-dependent signals that keep the collagen receptor(s) in a low-affinity state. Adhesion experiments performed in the presence of pharmacological inhibitors indicate that phosphatidyl inositol 3-kinase (PI3-K)/protein kinase C (PKC) and protein kinase A (PKA) pathways may transmit opposing signals on chondrocyte adhesion, and that collagen receptors are kept in a low-affinity state by PI3-kinase/PKC signalling. Since echistatin is a high-affinity ligand for alphavbeta3 integrin, the effect of the function-blocking anti-alphavbeta3 antibody LM609 was investigated. Like echistatin, LM609 stimulated chondrocyte adhesion to collagen and failed to support their attachment. Therefore, our data suggest that alphavbeta3-antagonists might regulate the binding activity of the beta1 collagen receptor, which in turn leads to the rapid transition of chondrocytes from suspension to an adherent state.

1-Methoxy-Canthin-6-One Induces c-Jun NH2-Terminal Kinase–Dependent Apoptosis and Synergizes with Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand Activity in Human Neoplastic Cells of Hematopoietic or Endodermal Origin

We investigated the effects of 1-methoxy-canthin-6-one, isolated from the medicinal plant Ailanthus altissima Swingle, on apoptosis in human leukemia (Jurkat), thyroid carcinoma (ARO and NPA), and hepatocellular carcinoma (HuH7) cell lines. Cultures incubated with the compound showed >50% of sub-G1 (hypodiploid) elements in flow cytometry analysis; the apoptosis-inducing activity was evident at <10 micromol/L and half-maximal at about 40 micromol/L 1-methoxy-canthin-6-one. The appearance of hypodiploid elements was preceded by mitochondrial membrane depolarization, mitochondrial release of cytochrome c, and Smac/DIABLO and procaspase-3 cleavage. We subsequently investigated the effect of 1-methoxy-canthin-6-one in combination with human recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in the four cell lines. Suboptimal concentrations (10 micromol/L 1-methoxy-canthin-6-one and 0.25 ng/mL TRAIL, respectively) of the two agents, unable to elicit apoptosis when used alone, induced mitochondrial depolarization, activation of caspase-3, and 45% to 85% of sub-G1 elements when added together to the cells. The synergism seemed to rely partly on the enhanced expression of TRAIL receptor 1 (TRAIL-R1; DR4), analyzed by immunofluorescence, by 1-methoxy-canthin-6-one. Cell incubation with 1-methoxy-canthin-6-one resulted in activating c-Jun NH2-terminal kinase (JNK), as revealed by Western blotting; induction of apoptosis and TRAIL-R1 up-regulation by 1-methoxy-canthin-6-one were >80% prevented by the addition of the JNK inhibitor (JNKI) SP600125JNKI, indicating that both effects were almost completely mediated by JNK activity. On the other hand, synergism with TRAIL was reduced by about 50%, suggesting that besides up-regulating TRAIL-R1, 1-methoxy-canthin-6-one could influence other factor(s) that participated in TRAIL-induced apoptosis. These findings indicate that 1-methoxy-canthin-6-one can represent a candidate for in vivo studies of monotherapies or combined antineoplastic therapies.

Cytotoxic furostanol saponins and a megastigmane glucoside from tribulus parvispinus

Two new furostanol saponins, (25R)-26-O-beta-D-glucopyranosyl-5alpha-furostan-2alpha,3beta,22alpha,26-tetraol 3-O-{beta-D-galactopyranosyl-(1-->2)-O-[beta-D-xylopyranosyl-(1-->3)]-O-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranoside} (1) and (25R)-26-O-beta-D-glucopyranosyl-5alpha-furostan-3beta,22alpha,26-triol 3-O-{beta-D-galactopyranosyl-(1-->2)-O-[beta-D-xylopyranosyl-(1-->3)]-O-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranoside} (2), and their O-methyl derivatives (3 and 4), and a new megastigmane glucoside, (6S,7E,9xi)-6,9,10-trihydroxy-4,7-megastigmadien-3-one 10-O-beta-D-glucopyranoside (6), along with one known spirostanol saponin, gitonin (5), and four known megastigmane glucosides were isolated from the aerial parts of Tribulus parvispinus. Their structures were established by detailed spectroscopic analysis. The cytotoxic activities of 1-6 against U937, MCF7, and HepG2 cells were evaluated. Compounds 2 (IC(50) 0.5 microM) and 5 (IC(50) 0.1 microM) showed the highest activity against U937 cells.

Adhesive properties of platelets from different animal species

The use of large animals (e.g., pig and sheep) in human medicine, and the need to develop new therapeutic strategies for domestic animal diseases related to platelet disorders, require better characterization of the physiology of animal platelets. In this study, the ability of platelets from buffaloes, horses, pigs and sheep to adhere to immobilized autologous fibrinogen was compared with that of human platelets. Blood samples were collected from the jugular vein of six healthy subjects of each species and platelet-rich plasma (PRP) was obtained by centrifugation. Platelets, isolated by further centrifugation of PRP, were washed by gel-filtration on Sepharose-2B, counted and added to the wells of 96-well plates pre-coated with autologous fibrinogen. After different times of incubation, non-adherent platelets were removed, and the number of adherent platelets was assessed by measuring endogenous acid phosphatase activity. Horse platelets showed the strongest ability to adhere to autologous immobilized fibrinogen, being 1.7-, 3.1- and 2.3-fold more active than human, buffalo and porcine platelets, respectively. Sheep platelets were unable to adhere to autologous immobilized fibrinogen. Platelet activation by adenosine 5-diphosphate (ADP) increased both human and animal platelet adhesive response. ADP-stimulated sheep platelets were able to adhere to autologous immobilized fibrinogen, albeit to a lesser extent than platelets from the other animal species. The observed interspecies variability in adhesive properties of platelets may reflect structural differences, or differences in the availability of the fibrinogen receptor (glycoprotein IIb/IIIa) on the platelet surface.

Site-specific atherosclerotic plaques in the carotid arteries of middle-aged women from southern Italy: associations with traditional risk factors and oxidation markers

BACKGROUND AND PURPOSE

Studies on cardiovascular disease have preferentially involved men because of the lower frequency of the disease in preelderly women. The aim of this analysis was to examine, with the use of a standardized ultrasound protocol, a cohort of women to differentiate early atherosclerotic lesions in different carotid segments in relation to traditional (lipoprotein abnormalities, high blood pressure, cigarette smoking) and nontraditional (oxidation markers) cardiovascular risk factors.

METHODS

More than 5000 clinically healthy, middle-aged women (n=5062; age range, 30 to 69 years) living in the area of Naples in southern Italy participated in the Progetto Atena, a population-based study on the etiology of cardiovascular disease and cancer in the female population. A subsample of 310 participants underwent high-resolution B-mode ultrasound to assess intima-media thickness of common carotid artery and carotid bifurcation.

RESULTS

Early atherosclerotic plaques (intima-media thickness >1.2 mm) were detected within the common carotid arteries in 37 women, in the carotid bifurcations in 77 women, and in both sites in 91 women. After age adjustment, common carotid plaques were found to be associated with higher systolic blood pressure (143 versus 138 mm Hg; P<0.05) and higher body mass index (29 versus 27 kg/m(2); P<0.01), while lesions at the carotid bifurcations were associated with higher LDL cholesterol (4.3 versus 3.8 mmol/L; P<0.01) and with smoking habit. Multivariate odds ratios for the presence of common carotid plaques were related to antibodies against oxidized LDL (odds ratio, 2.72; 95% CI, 1.46 to 5.07), and those for plaques at the bifurcation were related to lipid peroxides (odds ratio, 1.90; 95% CI, 1.04 to 3.47), and both relationships were independent of age, LDL cholesterol concentrations, body mass index, smoking habit, and systolic blood pressure.

CONCLUSIONS

In a cohort of clinically healthy, middle-aged women, we found a site-specific association of traditional risk factors and oxidation markers with early atherosclerotic lesions in arterial segments differing in geometry, shear stress, extracellular matrix composition, and cell type populations.

Echistatin inhibits pp125FAK autophosphorylation, paxillin phosphorylation and pp125FAK-paxillin interaction in fibronectin-adherent melanoma cells

Echistatin, a snake-venom RGD-containing protein, was previously shown to disrupt cell-matrix adhesion by a mechanism that involves the reduction of pp125FAK tyrosine phosphorylation levels. The aim of this study was to establish the sequence of events downstream pp125FAK dephosphorylation that could be responsible for echistatin-induced disassembly of actin cytoskeleton and focal adhesions in fibronectin-adherent B16-BL6 melanoma cells. The results obtained show that echistatin induces a decrease of both autophosphorylation and kinase activity of pp125FAK. One hour of cell exposure to echistatin caused a 39% decrease of pp125FAK Tyr397 phosphorylation and a 31% reduction of pp125FAK autophosphorylation activity as measured by immune-complex kinase assay. Furthermore, 1 h of cell treatment by echistatin produced a 63% decrease of paxillin phosphorylation, as well as a reduction in the amount of paxillin bound to pp125FAK. Immunofluorescence analysis of echistatin treated cells showed the concomitant disappearance of both paxillin and pp125FAK from focal adhesions. The reduction of paxillin phosphorylation may represent a critical step in the pathway by which disintegrins exert their biological activity, including the inhibition of experimental metastasis in vivo.

Immobilised echistatin promotes platelet adhesion and protein tyrosine phosphorylation

Echistatin, a 5000-Da disintegrin, is a strong competitive inhibitor of platelet alpha(IIb)beta(3) binding to fibrinogen. In addition to its antiplatelet activity, echistatin also exhibits activating properties by inducing a switch of alpha(IIb)beta(3) conformation towards an active state. However, soluble echistatin, which is a monomeric ligand, provides only receptor affinity modulation, but it is unable to activate integrin-dependent intracellular signals. Since proteins may exhibit a multivalent functionality as a result of their absorption to a substrate, in this study we evaluated whether immobilised echistatin is able to stimulate platelet adhesion and signalling. The immobilisation process led to an increase of echistatin affinity for integrin(s) expressed on resting platelets. Unlike the soluble form, immobilised echistatin bound at comparable extent either unstimulated or ADP-activated platelets. Furthermore, echistatin presented in this manner was effective in stimulating integrin-dependent protein tyrosine phosphorylation. Platelets adhering to immobilised echistatin showed a pattern of total tyrosine phosphorylated proteins resembling that of fibrinogen-attached platelets. In particular, solid-phase echistatin induced a strong phosphorylation of tyrosine kinases pp72(syk) and pp125(FAK). Inhibitors of platelet signalling, such as apyrase, prostaglandin E(1), cytochalasin D and bisindolylmaleimide, while not affecting platelet adhesion to immobilised echistatin, abolished pp125(FAK) phosphorylation. This suggests that signals activating protein kinase C function, dense granule secretion and cytoskeleton assembly might be involved in echistatin-induced pp125(FAK) phosphorylation.

H(2)O(2) activity on platelet adhesion to fibrinogen and protein tyrosine phosphorylation

Platelets represent a target of reactive oxygen species produced under oxidative stress conditions. Controversial data on the effect of these species on platelet functions have been reported so far. In this study we evaluated the effect of a wide range of H(2)O(2) concentrations on platelet adhesion to immobilized fibrinogen and on pp72(syk) and pp125(FAK) tyrosine phosphorylation. Our results demonstrate that: (1) H(2)O(2) does not affect the adhesion of unstimulated or apyrase-treated platelets to immobilized fibrinogen; (2) H(2)O(2) does not affect pp72(syk) phosphorylation induced by platelet adhesion to fibrinogen-coated dishes; (3) H(2)O(2) reduces, in a dose-dependent fashion, pp125(FAK) phosphorylation of fibrinogen-adherent platelets; (4) concentrations of H(2)O(2) near to physiological values (10-12 microM) are able to strengthen the subthreshold activation of pp125(FAK) induced by epinephrine in apyrase-treated platelets; (5) H(2)O(2) doses higher than 0.1 mM inhibit ADP-induced platelet aggregation and dense granule secretion. The ability of H(2)O(2) to modulate pp125(FAK) phosphorylation suggests a role of this molecule in physiological hemostasis as well as in thrombus generation.

The mycotoxin fumonisin B1 inhibits integrin-mediated cell-matrix adhesion

Fumonisin B1 (FB1), a mycotoxin produced by the corn fungus Fusarium moniliforme, causes a variety of animal diseases and is a suspected human carcinogen. The FB1 molecule bears remarkable structural resemblance to the long-chain sphingoid base backbones of sphingolipids. The toxicity and carcinogenicity of FB1 has been ascribed to its ability to inhibit ceramide synthase, a key enzyme in the metabolism of complex sphingolipids. In this study we have investigated whether the exposure of B16-BL6 mouse melanoma cells to FB1 affects cell growth and integrin-mediated cell matrix adhesion. Cell treatment with the highest tested dose (75 microM) of FB1 for 72 h induced an about 20% inhibition of cell growth. FB1 strongly affected B16-BL6 cell adhesion to immobilized fibronectin, by causing a dose-dependent inhibition of cell attachment to this substrate. FB1 also inhibited in a dose-dependent manner the adhesion of B16-BL6 cells to the immobilized anti-fibronectin receptor antibody, whereas it affected only to a low extent cell attachment to concanavalin A. Our results demonstrate that FB1 treatment alters integrin adhesive activity, thus affecting all cellular integrin-dependent functions.

Effect of N-acetyl-cysteine on lymphomonocyte glutathione and response to interferon treatment in C-virus chronic hepatitis

BACKGROUND/AIM

Much controversy exists concerning effect of N-acetyl-cysteine, a precursor of glutathione, on the response to interferon treatment in patients with C-virus chronic hepatitis. The aim of this study was to evaluate the efficacy of interferon therapy with and without oral N-acetyl-cysteine. We also measured glutathione concentrations in lymphomonocytes of 25 patients with chronic C-virus hepatitis before and after interferon treatment and correlated the results with treatment response.

METHODS

Glutathione was extracted from lymphomonocytes and measured with a modified high performance liquid chromatographic method in the 25 hepatitis patients and 12 healthy controls.

RESULTS/CONCLUSIONS

1) Hepatitis patients and controls had similar basal concentrations of lymphomonocytic glutathione; 2) neither interferon nor N-acetyl-cysteine significantly affected glutathione concentrations in patients; and 3) N-acetyl-cysteine did not affect response to interferon.

Croton ruizianus: platelet proaggregating activity of two new pregnane glycosides

The MeOH extract of the aerial parts of Croton ruizianus afforded two new pregnane glycosides 1 and 2, together with the morphinandienone alkaloids flavinantine (3) and O-methylflavinantine (4). Their structures were elucidated by NMR experiments including 1H-1H (1D TOCSY and 2D DQF-COSY) and 1H-13C (HSQC, HMBC) spectroscopy. The proaggregating activity of the MeOH extract and the isolates were evaluated. Although the MeOH extract and pregnane glycosides (at different doses) were found to promote platelet aggregation, flavinantine (3) and O-methylflavinantine (4) showed only slight activity. The ability of the MeOH extract and the four compounds to act synergistically with thrombin was also evaluated. All the tested compounds were successful in augmenting the aggregating effect of thrombin, although to different degrees.

Echistatin inhibits pp72syk and pp125FAK phosphorylation in fibrinogen-adherent platelets

The adhesion of ADP-stimulated platelets to immobilized fibrinogen induces the tyrosine phosphorylation of multiple proteins which include pp72syk and pp125FAK. The phosphorylation of these two proteins increases as function of time of platelet adhesion to fibrinogen; however, pp72syk results strongly phosphorylated already after 15 min, whereas pp125FAK reaches high levels of phosphorylation after 1 h of platelet adhesion. Phosphorylation of both proteins is only slightly detectable when platelets are held in suspension or when platelets are allowed to adhere to bovine serum albumin, a non-specific substrate. Echistatin, an Arg-Gly-Asp (RGD)-containing snake-venom protein, affects protein tyrosine phosphorylation promoted by platelet adhesion to fibrinogen, by causing an approximately 44% and 39% decrease of pp72syk and pp125FAK phosphorylation, respectively. The interaction of echistatin with fibrinogen receptor glycoprotein IIb-IIIa on platelet surface might be responsible for the block of integrin-mediated signaling cascade, including pp72syk and pp125FAK inactivation.

Echistatin induces decrease of pp125FAK phosphorylation, disassembly of actin cytoskeleton and focal adhesions, and detachment of fibronectin-adherent melanoma cells

B16-BL6 mouse melanoma cells cultured on fibronectin-coated dishes were detached by treatment with echistatin, an RGD-containing disintegrin. Echistatin was active at micromolar concentrations and was not cytotoxic. Its effect was dose-dependent and reversible. Sequential morphological changes leading to rounding up of the cells were detected by phase-contrast microscopy and by immunofluorescence analysis. A dramatic reduction in the number and size of focal adhesions and loss of cytoplasmic actin filaments were observed well before cell detachment occurred. Echistatin treatment down-regulated the phosphorylation of pp125FAK in fibronectin-adherent cells in a dose- and time-dependent fashion. The reduction of pp125FAK phosphorylation preceded cell detachment and occurred even in the presence of orthovanadate, an inhibitor of protein tyrosine phosphatases. These results suggest that echistatin detaches cells from the fibronectin substratum by inducing a decrease of pp125FAK phosphorylation and that echistatin acts by inhibiting protein tyrosine kinase activity rather than activating protein tyrosine phosphatases.

Metal-ion catalyzed oxidation affects fibrinogen activity on platelet aggregation and adhesion

Exposure of fibrinogen to the Fe3+/ascorbate oxidative system resulted in structural modifications and altered functionality of the glycoprotein. The overnight treatment of fibrinogen by oxidants caused a 20-fold increase of carbonyl content with respect to the native protein. Formation of dityrosines as well as loss of tryptophan following fibrinogen oxidation were observed. The occurrence of conformational changes of the fibrinogen molecule as a consequence of the oxidative treatment was also established. Oxidized fibrinogen showed a distinct capability from the native molecule to mediate platelet aggregation and adhesion. The percentage of ADP-induced platelet aggregation decreased as a function of fibrinogen oxidative damage. Further, both unstimulated platelets and ADP-activated platelets showed a reduced ability to adhere to oxidized fibrinogen than to the native protein. These results suggest that oxidative treatment alters fibrinogen domains involved in the recognition and the binding of this molecule by the platelet receptor GP IIb/IIIa.

Vitamin E nutritional status and serum lipid pattern in normal weanling rabbits

In a 6-wk postweaning trial (Trial 1), 30 male New Zealand White rabbits were fed a starter diet with three different levels of all-rac-alpha-tocopheryl acetate (60, 160, or 260 mg/kg diet). Plasma concentrations of alpha-tocopherol and serum concentrations of total cholesterol, high density lipoprotein (HDL) cholesterol, and triglycerides were measured at 2, 4, and 6 wk. In a 20-wk postweaning trial (Trial 2), 48 male New Zealand White rabbits were divided into two groups; one group was fed a vitamin E-free diet, and the other was fed the same diet supplemented with 60 mg/kg of all-rac-alpha-tocopheryl acetate. Plasma concentrations of alpha-tocopherol and serum total cholesterol, HDL cholesterol, and triglycerides were measured at 2, 4, 6, and 20 wk. In Trial 1, split-plot ANOVA showed that dietary all-rac-alpha-tocopheryl acetate increased plasma alpha-tocopherol (P < .01); in addition, serum total cholesterol and triglycerides declined more rapidly (P < .01) and HDL cholesterol increased more rapidly (P < .005) in rabbits fed supplemental all-rac-alpha-tocopheryl acetate than in controls. The all-rac-alpha-tocopheryl acetate intake was significantly correlated with serum total cholesterol reduction and HDL cholesterol increase only when plasma alpha-tocopherol was relatively low (< 23.5 mumol/ L). In trial 2, the vitamin E-free diet caused an increase (P < .05) in total serum cholesterol and a reduction in HDL cholesterol (P < .05 at 6 wk and P < .01 at 20 wk). The overall results of this study suggest that vitamin E plays an important role in the regulation of serum concentrations of cholesterol and lipoproteins in weanling rabbits. Consequently, the maintenance of an adequate nutritional status of vitamin E in the postweaning period is important to avoid alterations of serum lipid pattern.

In vitro effect of avarone and avarol, a quinone/hydroquinone couple of marine origin, on platelet aggregation

We investigated the effect on human platelet aggregation of the naturally occurring quinone/hydroquinone couple, avarone and avarol. Avarone exerted antiplatelet activity both on platelet-rich plasma and, to a greater extent, on washed platelets. The quinone inhibited the platelet aggregatory process with all the agonists used. The highest inhibitory potency occurred with arachidonic acid or A23187 as stimulating agents. In the case of agonists such as adenosine 5' diphosphate, platelet-activating factor or U46619, the antiaggregatory effect was more pronounced on the second wave. Inhibition of the aggregatory process paralleled thromboxane B2 formation. Avarol also exerted antiplatelet activity, even though its inhibitory potency was much lower than that of avarone.

Erythrocyte enzymes catalyze 1-nitropyrene and 3-nitrofluoranthene nitroreduction

Nitroarenes are environmental contaminants produced during incomplete combustion processes. Nitroreduction, the most important pathway of nitroarene toxification, occurs mainly in the liver and intestine. In the present study, we show that human red cells may also possess the metabolic competence to reduce 1-nitropyrene (NP) and 3-nitrofluoranthene (NF), the nitroarenes chosen as model compounds, to their corresponding amino derivatives, 1-aminopyrene (AP) and 3-aminofluoranthene (AF). The requirement of the cofactor couple NADH/FMN suggests that erythrocyte nitroreductase activity occurs via one electron transfer. The presence of oxygen strongly inhibited the haemolysate-catalyzed nitroarene reduction, whether measured as amine formation or nitroarene disappearance. Intermediate reactive species, that bind covalently to haemoglobin and/or other erythrocyte proteins, are formed during nitroreduction catalyzed by human haemolysate. In fact, the reduced metabolites AP and AF were released after mild acid hydrolysis of red cell proteins exposed to NP and NF, thus suggesting that sulphinamide adducts have been formed.

Erythrocyte-mediated toxification of 1,8-dinitropyrene: I. Reduction

Nitroarenes are environmental contaminants produced during incomplete combustion processes. It has been reported that nitroreduction, the most important pathway of nitroarene toxification, occurs mainly in the liver and intestine. In the present study we have shown that red cells also possess the metabolic competence to reduce nitroarenes. In particular, 1,8-dinitropyrene, the nitroarene chosen as model compound, was reduced to the corresponding mono- and diamino-derivatives, 1-amino-8-nitropyrene and 1,8-diaminopyrene, by human lysate supplemented with cofactors.

Erythrocyte-mediated toxification of 1,8-dinitropyrene. II. Covalent bind to erythrocyte-proteins

In the present study we have shown that erythrocyte-catalyzed 1,8-dinitropyrene reduction occurs via formation of reactive intermediate species, which bind covalently to haemoglobin and other erythrocyte proteins. In fact after mild-acid hydrolysis of lysate proteins exposed to DNP, the reduced metabolites, 1-amino-8-nitropyrene and 1,8-diaminopyrene, were released, thus indicating the formation of sulphinamide adducts to proteins. These results suggest that haemoglobin adduct biomonitoring would be a useful method of controlling exposure to nitroarene in persons at risk.

Glutathione depletion induced in rat liver fractions by seven pesticides

Glutathione (GSH) plays a central role in the chemical detoxication. Xenobiotics which induce GSH depletion, either via GSH conjugation or via oxidation of GSH to glutathione disulfide (GSSG), alter the mechanism of natural cellular defence against toxicants. The aim of this study was to evaluate the ability of seven widely used pesticides (Alachlor, Atrazine, Benomyl, Captan, Linuron, Methyl Parathion and Propanil) and/or of their metabolites to deplete GSH in rat liver fractions. In our experimental conditions, Atrazine, Linuron and Propanil failed to interact with rat liver GSH. Conversely, Alachlor, Benomyl and Methyl Parthion were able to deplete GSH in rat liver, probably by forming GSH conjugates. The fungicide Captan rapidly reduced the rat liver concentration of GSH by converting it to the oxidized form GSSG. But a longer incubation of Captan with rat hepatic enzymes produced the formation of metabolites which depleted GSH via conjugation. Our results suggest that exposure to the pesticides Alachlor, Benomyl, Captan and Methyl Parathion may induce an alteration of natural mechanisms of defence against toxicants in mammals, including humans.

Arylation of sulfhydryl groups in vitro by the naturally occurring sesquiterpenoid benzoquinone avarone

Avarone (AQ) is a naturally occurring sesquiterpenoid benzoquinone possessing antileukaemic activity. Its reactivity towards glutathione (GSH) and protein sulfhydryl (SH) groups was investigated. The stoichiometry of AQ reaction with GSH at [GSH]/[AQ] ratios lower than unity proved to be 1:2 (thiol:quinone), consistent with the formation of the corresponding hydroquinone (avarol) as well as a quinone-thioether in the reaction. Conversely, when the [GSH]/[AG] ratio was higher than unity, a hydroquinone-thioether was the only reaction product. AQ/protein interaction was also investigated by using bovine serum albumin (BSA) as model compound. As observed with GSH, arylation rather than oxidation of SH groups appeared to be the mechanism responsible for the AQ-induced depletion of protein SH groups. However, AQ proved to be less effective in depleting BSA sulfhydryls than that of GSH. AQ disappearance after BSA addition was greater than expected on the basis of the total SH groups depleted, if a stoichiometric ratio 1:2 (thiol:quinone) was assumed. It also occurred in the presence of BSA with blocked SH groups, thus suggesting that AQ may react with other nucleophilic protein residues, such as amino or imino groups. When HepG2 cells were exposed to AQ, depletion of both protein SH groups and GSH occurred. However, in contrast to the above, AQ proved to be more effective, probably because of its lipophilic nature, in depleting protein SH groups than GSH. Also, in intact cells AQ appeared to arylate both SH and other nucleophilic groups in proteins. This mechanism may play a major role in AQ-induced cytotoxicity.

Simultaneous evaluation of vitamins A and E in human plasma by normal phase HPLC

The production of toxic oxidants such as H2O2; OH. and O2.- which follows aerobic metabolism is highly enhanced in aging, alcohol consumption and in a variety of degenerative diseases including neoplasias. Among the different antioxidant agents that in human organisms counterbalance the oxidative stress, which damages lipid, protein and DNA, are included beta-carotene, alpha-tocopherol, glutathione, ascorbate, ubiquinol and specific enzymes such as superoxide dismutase, catalase and glutathione peroxidase. In particular, vitamins A and E are the most important lipid-soluble antioxidants in human tissues protecting polyunsaturated fatty acid from peroxidation. In this paper we report an improved method, obtained after modification of a normal phase HPLC method, which allows the simple and rapid simultaneous evaluation of vitamins A and E in plasma. The separation of vitamins is achieved by eluting the HPLC column with a linear gradient from 1 to 5% isopropanol in n-hexane. The eluate is simultaneously monitored by U.V. and fluorescence detection to identify and quantify vitamins A and E, respectively.

Effect of avarol and avarone on in vitro-induced microsomal lipid peroxidation

Lipid peroxidation was employed as an experimental model to study the antioxidant properties of avarol, a sesquiterpenoid hydroquinone and of its quinone, avarone. In the NADPH- or ascorbate-linked lipid peroxidation, avarol and avarone were shown to be more effective as inhibitors than in the t-BuOOH-dependent peroxidative process. However, in all three systems employed avarol was a more powerful inhibitor than avarone. The chemical structure of avarol, having an easily donatable hydrogen atom and its kinetics of inhibition suggested that the hydroquinone acted mainly as a radical scavenger. Conversely avarone appeared to interfere mainly with the initiation phase of lipid peroxidation. However, avarol and the semiquinone intermediate may contribute to the inhibitory action of the quinone. In fact avarone reduction to avarol has been shown to occur in the presence of reducing agents such as ascorbate or Fe(II) and to be catalyzed by NADPH-supplemented microsomes.

Effect of avarol, avarone and nine of their natural and synthetic derivatives on microsomal drug-metabolizing enzymes

Avarol, a sesquiterpenoid hydroquinone, its quinone avarone, both main secondary metabolites from the marine sponge Dysidea avara and nine of their natural and synthetic derivatives were tested for ability to interact selectively with rat liver microsomal phenobarbital (PB)- or 3-methylcholanthrene (3-MC)-induced cytochrome (cyt.) P-450 isoenzymatic forms. Ethoxy- and pentoxyresorufin, aminopyrine and ethoxycoumarin were the specific substrates used for assaying cyt. P-450-dependent mono-oxygenase activities. All compounds were more effective in inhibiting the enzymatic activities measured in microsomes from PB-induced rat liver than those measured in microsomes from 3-MC-treated rats. Avarol and avarone, which were the most active inhibitors, act as mixed-type inhibitors of pentoxyresorufin-O-dealkylase activity. Mono- and diacetyl-derivatives of avarol, being deacetylated by rat liver microsomes, were almost as effective as the parent compound. Conversely, avarone derivatives, where one or two hydrogen atoms of the quinone ring have been substituted, were less effective inhibitors than the parent compound. The selective inhibition of PB-inducible cyt.P-450IIB by avarol and avarone was confirmed by their ability to inhibit the mutagenic activation of cyclophosphamide, as opposed to that of benzo[a]pyrene, which is activated mainly by the 3-MC-inducible cyt.P-450IA.

Effect of rat liver cytosolic enzymes and cofactors on mutagenicity of 1-amino-8-nitropyrene

1-Amino-8-nitropyrene (1,8-ANP), a product of 1,8-dinitropyrene metabolism by either bacterial or mammalian enzymes, is weakly mutagenic to the 'classical nitroreductase'-deficient Salmonella tester strain TA98NR. The addition to the test system of rat liver cytosol without cofactors did not produce any effect on the 1,8-ANP mutagenic response toward TA98NR strain. Conversely, when both rat hepatic cytosol and NADPH (1 mM) were added to the mutagenicity assay, a 10-fold increase in 1,8-ANP mutagenic activity was observed. This suggests the involvement of rat hepatic cytosolic NADPH-dependent nitroreductase(s) in 1,8-ANP mutagenic activation. The addition to the mutagenesis assay of pentachlorophenol, an inhibitor of O-acetyltransferase and sulfotransferase, produced a dose-dependent decrease of 1,8-ANP mutagenic activation, whereas 2,6-dichloro-4-nitrophenol, a more specific inhibitor of sulfotransferase than O-acetyltransferase, did not affect the activation of 1,8-ANP to a mutagen at concentrations that selectively inhibit only bacterial sulfotransferase. This indicates that bacterial O-acetyltransferase but not sulfotransferase plays a role in the mutagenic activation of 1,8-ANP. Addition of acetyl co-enzyme A (AcCoA) and adenosine 3'-phosphate 5'-phosphosulfate (PAPS), cofactors for O-acetyl-transferase and sulfotransferase respectively, to the test system caused a dose-dependent inhibition of 1,8-ANP mutagenic activation by rat liver cytosol and NADPH, probably due to the formation of highly reactive O-acetoxy and N-sulfate ester derivatives of 1,8-ANP, which react with nucleophilic sites before reaching bacterial DNA. This hypothesis was confirmed by DNA covalent binding in in vitro experiments showing that both the cofactors AcCoA and PAPS enhanced the NADPH/rat liver cytosol-mediated covalent binding of 1,8-ANP to DNA from calf thymus 10- and 3-fold respectively. It seems likely that rat hepatic cytosolic nitroreductases activate 1,8-ANP to an N-hydroxyarylamine derivative which can be further metabolized to mutagenic species by either bacterial or mammalian O-acetyltransferase.

Effect of enzyme inducers on metabolism of 1-nitropyrene in human hepatoma cell line HepG2

We measured the response of HepG2 cells to the classic cytochrome (cyt.) P-450 inducers 3-methylcholanthrene (3-MC) and phenobarbital (PB), by evaluating oxidative and/or reductive metabolism of the nitroarenes, 1-NP and 1,6-dinitropyrene (1,6-DNP), in control and induced cells. In HepG2 cells, 3-MC induces ring-hydroxylation of 1-NP, whereas PB stimulates its nitroreduction. PB induces NADPH-cyt. c reductase, but does not affect other cytosolic and microsomal enzymes which contribute to 1-NP nitroreduction in these cells. However, PB-inducible nitroreductase activity seems to be associated primarily with cyt. P-450 isoenzymatic form(s), as indicated by the requirement for NADPH and the response to specific inhibitors such as alpha-naphthoflavone and CO.

Characterization of oxidative and reductive metabolism in vitro of nitrofluoranthenes by rat liver enzymes

Nitrofluoranthenes (NFs) are mutagenic and carcinogenic environmental pollutants found in incomplete combustion products and urban air particulate. We have studied both oxidative and reductive metabolism in vitro of different NF isomers mediated by subcellular rat liver fractions. Under aerobic conditions only ring hydroxylation of NFs by rat liver microsomes occurred and the isomeric position of the nitro group affected both the amount and the type of phenolic metabolites formed. Liver microsomes from 3-methylcholanthrene-induced rats were most effective in giving ring hydroxylated 7- and 8-nitrofluoranthene, whereas liver microsomes from phenobarbital-pretreated rats were the most active in metabolizing 1- and 3-nitrofluoranthene. Under anaerobic conditions, only reduction of NFs mediated by both cytosolic and microsomal rat liver enzymes occurred. Cofactor requirements and inhibition experiments indicated that the reductase activity in rat liver cytosolic fractions could be ascribed to DT-diaphorase, aldehyde oxidase and/or other unknown enzymes. The microsomal reductase activity was inhibited by oxygen, carbon monoxide, 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride and n-octylamine, and slightly by cytochrome c; flavin mononucleotide greatly enhanced this activity. 3-Nitrofluoranthene microsomal nitroreductase activity was increased by phenobarbital rat pretreatment and this increment correlated well with the content of cytochrome P450. These results indicate a participation of cytochrome P450 in the reductive metabolism of NFs by rat liver microsomes.

Characterization of the induction of rat hepatic microsomal drug-metabolizing enzymes by 1-nitropyrene metabolites, 1-aminopyrene and N-acetylaminopyrene

The effect of 1-aminopyrene (1-AP) and N-acetylaminopyrene (1-NAAP) on rat hepatic microsomal monooxygenase system was investigated. Both drugs increased the total content of cytochrome P-450 (cyt. P-450). The substrate specificity and the electrophoretic pattern of 1-AP and 1-NAAP induced cytochrome(s) were compared with those of the major forms of cyt. P-450 induced by 3-methylcholanthrene (3-MC) and phenobarbital (PB). The results suggest that the form of cyt. P-450 induced by 1-AP and 1-NAAP resembles that one induced by 3-MC. Furthermore the abilities of liver microsomes from control or differently induced rats to ring hydroxylate and to activate 1-nitropyrene (1-NP) metabolites to species mutagenic for bacteria were compared. It was observed that: (1) 1-NAAP is a good substrate for microsome-mediated ring hydroxylation, whereas 1-AP is oxygenated only at a low extent; (2) 3-MC, 1-AP and 1-NAAP-stimulated microsomes are more active than control or PB-ones to ring hydroxylate 1-NAAP. As phenolic derivatives of 1-NAAP show high mutagenic activity, these results indicate that 1-AP and 1-NAAP induce toxification pathways of 1-NP in similar way, even if in less extent, as compared to 3-MC.

Effect of liver enzyme inducers on metabolite excretion in rats treated with 1-nitropyrene

Non-induced and phenobarbital (PB) or methylcholanthrene (MC) pretreated rats were injected with 1-nitropyrene (1-NP). Mutagenic activity of urine and feces samples were compared by the Salmonella/microsome assay. The highest, indirect-acting mutagenicity was associated with urines from MC-induced rats; HPLC analysis of organic extracts of urine samples showed that the differences in mutagenic response can be ascribed to different amounts of hydroxy derivatives of N-acetylaminopyrene excreted. Monohydroxy derivatives of 1-NP, being detected in the HPLC profiles of urine from PB-induced rats only, could be responsible of the higher direct-acting mutagenic activity of these samples as compared to urine from non-induced or MC-induced rats. The excretion rate of aminopyrene, the main metabolite of 1-NP identified in rat feces samples, was not affected by inducer pretreatment.

Role of rat liver inducible enzymes in in vitro metabolic transformation of 1-nitropyrene

Liver enzymes (S9) of rats induced with various drugs differently affected the mutagenic response of 1-nitropyrene (1-NP) in vitro. The role of inducible enzymes in 1-NP conversion was evaluated by high-performance liquid chromatography (HPLC) analyses of 1-NP metabolites formed during incubation in vitro of the chemical with each S9 fraction. Methylcholanthrene (MC)-induced S9 preferentially results in 1-NP hydroxylation in position 6 or 8. Metabolic interconversions among 1-NP metabolites could be inferred from the HPLC patterns.