Nitric oxide inhibits apoptosis by preventing increases in caspase-3-like activity via two distinct mechanisms

Nitric oxide (NO) has emerged as an important endogenous inhibitor of apoptosis, and here we report that NO prevents hepatocyte apoptosis initiated by the removal of growth factors or exposure to TNFalpha or anti-Fas antibody. We postulated that the mechanism of the inhibition of apoptosis by NO would include an effect on caspase-3-like protease activity. Caspase-3-like activity increased coincident with apoptosis due to all three stimuli, and treatment with the caspase-3-like protease inhibitor N-acetyl-Asp-Glu-Val-Asp-aldehyde inhibited both proteolytic activity and apoptosis. Endogenous or exogenous sources of NO prevented the increase in caspase-3-like activity in hepatocytes. Exposure of purified recombinant caspase-3 to an NO or NO+ donor inhibited proteolytic activity. Dithiothreitol (DTT), but not glutathione, reversed the inhibition of recombinant caspase-3 by NO. When lysates from cells stimulated to express inducible NO synthase or cells exposed to NO donors were incubated in DTT, caspase-3-like activity increased to about 55% of cells not exposed to a source of NO. Similarly, administration of an NO donor to rats treated with TNFalpha and D-galactosamine also prevented the increase in caspase-3-like activity as measured in liver homogenates. The effect of the NO donor was reversed by about 50% if the homogenate was incubated with DTT. TNFalpha-induced apoptosis and caspase-3-like activity were also reduced in cultured hepatocytes exposed to 8-bromo-cGMP, and both effects were inhibited by the cGMP-dependent kinase inhibitor KT5823. The suppression in caspase-3-like activity in hepatocytes exposed to an NO donor was partially blocked by an inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-1-one, (ODQ), while the incubation of these lysates in DTT almost completely restored caspase-3-like activity to the level of TNFalpha-treated controls. These data indicate that NO prevents apoptosis in hepatocytes by either directly or indirectly inhibiting caspase-3-like activation via a cGMP-dependent mechanism and by direct inhibition of caspase-3-like activity through protein S-nitrosylation.

Nitric oxide as a bioregulator of apoptosis

Nitric oxide (NO), synthesized from l-arginine by NO synthases, is a small, diffusible, highly reactive molecule with dichotomous regulatory roles under physiological and pathological conditions. NO can promote apoptosis (proapoptosis) in some cells, whereas it inhibits apoptosis (antiapoptosis) in other cells. This complexity is a consequence of the rate of NO production and the interaction with biological molecules such as iron, thiols, proteins, and reactive oxygen species. Long-lasting production of NO acts as a proapoptotic modulator by activating caspase family proteases through the release of mitochondrial cytochrome c into the cytosol, upregulation of p53 expression, activation of JNK/SAPK, and altering the expression of apoptosis-associated proteins including Bcl-2 family proteins. However, low or physiological concentrations of NO prevent cells from apoptosis induced by trophic factor withdrawal, Fas, TNFalpha, and lipopolysaccharide. The antiapoptotic mechanism can be understood via expression of protective genes such as heat shock proteins, Bcl-2 as well as direct inhibition of the apoptotic caspase family proteases by S-nitrosylation of the cysteine thiol. Our current understanding of the mechanisms by which NO exerts both pro- and antiapoptotic actions is discussed in this review article.

Nitric oxide protects cultured rat hepatocytes from tumor necrosis factor-alpha-induced apoptosis by inducing heat shock protein 70 expression

Nitric oxide (NO) and tumor necrosis factor-alpha (TNFalpha) play important roles in the pathogenesis of liver disease during acute inflammation. The present study was designed to elucidate the effect of NO pre-exposure on TNFalpha-induced hepatotoxicity. Pretreatment of primary cultures of rat hepatocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of heat shock protein 70 (HSP70) mRNA and protein, which was associated with thermotolerance and cytoprotection from TNFalpha+actinomycin D-induced hepatotoxicity and apoptosis. SNAP transiently changed the intracellular redox state by inducing glutathione (GSH) oxidation associated with the formation of S-nitrosoglutathione (GSNO). HSP70 mRNA was also induced by the GSH-oxidizing agent diamide and the GSH-conjugating agent N-ethylmaleimide, suggesting that NO induces HSP70 expression through GSH oxidation. The protective effect of SNAP pretreatment on TNFalpha-induced apoptosis correlated with the level of HSP70 expression. SNAP pretreatment inhibited reactive oxygen intermediate generation and lipid peroxidation effects that were reversed by blocking HSP70 expression using an antisense oligonucleotide to HSP70. Finally, endogenous NO formation, induced in hepatocytes stimulated with interferon-gamma and interleukin-1beta, led to the formation of GSNO and GSSG, induced HSP70, and attenuated TNFalpha-mediated cytotoxicity. These findings demonstrated that NO can induce resistance to TNFalpha-induced hepatotoxicity, possibly through the stimulation of HSP70 expression.

Nitric oxide reversibly inhibits seven members of the caspase family via S-nitrosylation

The caspases are a family of at least 10 human cysteine proteases that participate in cytokine maturation and in apoptotic signal transduction and execution mechanisms. Peptidic inhibitors of these enzymes are capable of blocking cytokine maturation and apoptosis, demonstrating their crucial roles in these processes. We have recently discovered that nitric oxide (NO), produced either extracellularly by NO donors or intracellularly by the inducible nitric oxide synthase, prevented apoptosis in hepatocytes. Caspase-3-like activity was found to be inhibited under these conditions. To investigate further the interaction between NO and caspases, we utilized purified human recombinant caspases and examined the effect of NO on enzymatic activities of different caspases. We report here that of the seven caspases studied, all were reversibly inhibited by NO. Dithiothreitol was able to reverse the NO inhibition, indicating direct S-nitrosylation of caspase catalytic cysteine residue by NO. Our results support the concept that NO is an endogenous regulator of caspase activity.

Funisitis and chorionic vasculitis: the histological counterpart of the fetal inflammatory response syndrome

OBJECTIVE

To determine whether there is a relationship between the presence of histological signs of inflammation in the extraplacental membranes and umbilical cord and the concentrations of fetal plasma interleukin-6 (IL-6).

METHODS

The study examined a cohort of patients who were admitted with preterm labor or preterm premature rupture of the membranes (PROM) and who underwent cordocentesis. Inclusion criteria included fetal plasma available for IL-6 determination, histological examination of the umbilical cord and placenta, and delivery within 48 h of the procedure. This last criterion was used to preserve a meaningful temporal relationship between fetal plasma IL-6 and the results of histological examination of the placenta. Fetal plasma IL-6 was determined by a high sensitivity ELISA. Forty-five patients were available for study: 18 patients had preterm labor with intact membranes and 27 had preterm PROM.

RESULTS

The incidence of funisitis was 44.4% (20/45): 27.8% (5/18) in patients with preterm labor and intact membranes and 55.6% (15/27) in patients with preterm PROM. The median values of fetal plasma IL-6 in patients with funisitis, chorioamnionitis without funisitis, and non-inflamed membranes were 51.4, 18.4 and 5.2 pg/ml, respectively. After log transformation of the fetal plasma IL-6 concentration, the means differed significantly from each other (ANOVA, p < 0.02). There was no difference in log fetal plasma IL-6 concentration between patients with funisitis and those with chorioamnionitis without funisitis. The difference in mean concentration of log fetal plasma IL-6 between patients with funisitis or chorionic vasculitis and those without inflammation was highly significant (post-hoc test, p = 0.01 and p < 0.01, respectively). Fetuses with fetal plasma IL-6 > 11 pg/ml had a significantly higher rate of histological signs of inflammation in the extra-placental membranes and umbilical cord than those with fetal plasma IL-6 < 11 pg/ml (funisitis: 55.6% (15/27) vs. 27.8% (5/18), p < 0.05; chorionic vasculitis: 55.6% (15/27) vs. 12.5% (2/16), p < 0.01; chorioamnionitis only: 25.9% (7/27) vs. 16.7% (3/18), p < 0.05; no inflammation: 18.5% (5/27) vs. 55.6% (10/18), p < 0.05, respectively). Fetuses with funisitis had significantly higher rates of clinical and histological chorioamnionitis, and neonatal infectious morbidity (proven + suspected sepsis) than fetuses without funisitis (40% (8/20) vs. 8% (2/25), 90% (18/20) vs. 36% (9/25), and 40% (8/20) vs. 4% (1/25), respectively; p < 0.01 for each). Fetuses with chorionic vasculitis had significantly higher rates of clinical and histological chorioamnionitis as well as neonatal infectious morbidity (proven + suspected sepsis) than fetuses without chorionic vasculitis (100% (17/17) vs. 42.3% (11/26), p < 0.01; 82.4% (14/17) vs. 50.0% (13/26), p = 0.05; and 41.2% (7/17) vs. 7.7% (2/26), p = 0.01).

CONCLUSION

Fetal plasma IL-6 concentration is significantly associated with the presence of inflammatory lesions in the extraplacental membranes and umbilical cord. Fetuses with fetal plasma IL-6 > 11 pg/ml had a significantly higher rate of funisitis and/or chorionic vasculitis than fetuses with fetal plasma IL-6 < 11 pg/ml. These findings suggest that funisitis/chorionic vasculitis is the histological manifestation of the fetal inflammatory response syndrome.

Sphingosine 1-phosphate induces angiogenesis: its angiogenic action and signaling mechanism in human umbilical vein endothelial cells

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite abundantly stored in platelets and released upon platelet activation. Recently, S1P has been postulated for its potential roles in angiogenesis. In this study, we provided several lines of evidence showing that S1P has angiogenic activity. In vitro, S1P stimulated DNA synthesis and chemotactic motility of human umbilical vein endothelial cells (HUVECs) in a dose-dependent manner, reaching a near maximum at 1 microM. S1P also significantly induced tube formation of HUVECs on Matrigel. Matrigel plug assay in mice revealed that S1P promotes angiogenesis in vivo. In addition, exposure of HUVECs to S1P led to rapid activation of extracellular signal-regulated kinases (ERKs) and p38 mitogen-activated protein kinase (p38 MAPK) in a pertussis toxin (PTX)-sensitive manner. Notably, HUVEC migration and tube formation in response to S1P were completely blocked by pretreatment with PTX. Further, the MEK inhibitor U0126 markedly inhibited S1P-induced tube formation but S1P-induced migration was not affected by inhibition of ERK and p38 MAPK. Taken together, these results indicate that S1P induces angiogenesis predominantly via G(i) protein-coupled receptors in endothelial cells and suggest that S1P may act as an important modulator of platelet-induced angiogenesis.

Nitric oxide suppresses apoptosis via interrupting caspase activation and mitochondrial dysfunction in cultured hepatocytes

Nitric oxide (NO) is a potent inhibitor of apoptosis in many cell types, including hepatocytes. We and others have described NO-dependent decreases in caspase activity in cells undergoing apoptosis. However, previous work has not determined whether NO disrupts the proteolytic processing and thus the activation of pro-caspases. Here we report that NO suppresses proteolytic processing and activation of multiple pro-caspases in intact cells, including caspase-3 and caspase-8. We found that both exogenous NO as well as endogenously produced NO via adenoviral inducible NO synthase gene transfer protected hepatocytes from tumor necrosid factor (TNF) alpha plus actinomycin D (TNFalpha/ActD)-induced apoptosis. Affinity labeling with biotin-VAD-fmk of all active caspase species in TNFalpha-mediated apoptosis identified four newly labeled spots (activated caspases) present exclusively in TNFalpha/ActD-treated cells. Both NO and the caspase inhibitor, Ac-DEVD-CHO, prevented the appearance of the four newly labeled spots or active caspases. Immunoanalysis of affinity labeled caspases demonstrated that caspase-3 was the major effector caspase. Western blot analysis also identified the activation of caspase-8 in the TNFalpha/ActD-treated cells, and the activation was suppressed by NO. Furthermore, NO inhibited several other events associated with caspase activation in cells, including release of cytochrome c from mitochondria, decrease in mitochondrial transmembrane potential, and cleavage of poly(ADP-ribose) polymerase in TNFalpha/ActD-treated cells. These findings indicate the involvement of multiple caspases in TNFalpha-mediated apoptosis in hepatocytes and establish the capacity of NO to inhibit not only active caspases but also caspase activation.

Targeting nitric oxide (NO) delivery in vivo. Design of a liver-selective NO donor prodrug that blocks tumor necrosis factor-alpha-induced apoptosis and toxicity in the liver

We have designed a drug that protects the liver from apoptotic cell death by organ-selective pharmacological generation of the bioregulatory agent, nitric oxide (NO). The discovery strategy involved three steps: identifying a diazeniumdiolate ion (R2N[N(O)NO]-, where R2N = pyrrolidinyl) that spontaneously decomposes to NO with a very short half-life (3 s) at physiological pH; converting this ion to a series of potential prodrug derivatives by covalent attachment of protecting groups that we postulated might be rapidly removed by enzymes prevalent in the liver; and screening the prodrug candidates in vitro and in vivo to select a lead and to confirm the desired activity. Of five cell types examined, only cultured hepatocytes metabolized O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) to NO, triggering cyclic guanosine 3',5'-monophosphate (cGMP) synthesis and protecting the hepatocytes from apoptotic cell death induced by treatment with tumor necrosis factor-alpha (TNF alpha) plus actinomycin D. In vivo, V-PYRRO/NO increased liver cGMP levels while minimally affecting systemic hemodynamics, protecting rats dosed with TNF alpha plus galactosamine from apoptosis and hepatotoxicity. The results illustrate the potential utility of diazeniumdiolates for targeting NO delivery in vivo and suggest a possible therapeutic strategy for hepatic disorders such as fulminant liver failure.

Nitric oxide activates skeletal and cardiac ryanodine receptors

The endothelial-derived relaxing factor, nitric oxide (NO.) has been shown to depress force in smooth and cardiac muscles through the activation of guanylyl cyclase and an increase in cGMP. In fast skeletal muscle, NO (i.e. NO-related compounds) elicits a modest decrease in developed force, but in contracting muscles NO increases force by a mechanism independent of cGMP. We now demonstrate an alternative mechanism whereby NO triggers Ca2+ release from skeletal and cardiac sarcoplasmic reticulum (SR). NO delivered in the form of NO gas, NONOates (a class of sulfur-free compounds capable of releasing NO), or S-nitrosothiols (R-SNO) oxidized or transnitrosylated regulatory thiols on the release channel (or ryanodine receptor, RyR), resulting in channel opening and Ca2+ release from skeletal and cardiac SR. The process was reversed by sulfhydryl reducing agents which promoted channel closure and Ca2+ reuptake by ATP-driven Ca2+ pumps. NO did not directly alter Ca(2+)-ATPase activity but increased the open probability of RyRs reconstituted in planar bilayers and inhibited [3H]-ryanodine binding to RyRs. The formation of peroxynitrite or thiyl radicals did not account for the reversible R-SNO-dependent activation of RyRs. Ca2+ release induced by nitric oxide free radicals (NO.) was potentiated by cysteine providing compelling evidence that NO. in the presence of O2 formed nitrosylated cysteine followed by the transnitrosation of regulatory thiols on the RyR to activate the channel. These findings demonstrate direct interactions of NO derivatives with RyRs and a new fundamental mechanism to regulate force in striated muscle.

Nitric oxide suppression of apoptosis occurs in association with an inhibition of Bcl-2 cleavage and cytochrome c release

It is now known that caspase-3-like protease activation can promote Bcl-2 cleavage and mitochondrial cytochrome c release and that these events can lead to further downstream caspase activation. NO has been proposed as a potent, endogenous inhibitor of caspase-3-like protease activity. Experiments were carried out to determine whether NO could interrupt Bcl-2 cleavage or cytochrome c release by the inhibition of caspase activity linking these events. NO inhibited the capacity of purified caspase-3 to cleave recombinant Bcl-2. Both Bcl-2 cleavage and cytochrome c release were inhibited in tumor necrosis factor alpha- and actinomycin D-treated MCF-7 cells exposed to NO donors. The NO-mediated inhibition of Bcl-2 cleavage and cytochrome c release occurred in association with an inhibition of apoptosis and caspase-3-like activation. Thus, NO suppresses a key step in the positive feedback amplification of apoptotic signaling by preventing Bcl-2 cleavage and cytochrome c release.

Molecular recognition of acute myeloid leukemia using aptamers

Cell surface proteins can play important roles in cancer pathogenesis. Comprehensive understanding of the surface protein expression patterns of tumor cells and, consequently, the pathogenesis of tumor cells, depends on molecular probes against these proteins. To be effectively used for tumor diagnosis, classification and therapy, such probes would be capable of specific binding to targeted tumor cells. Molecular aptamers, designer DNA/RNA probes, can address this challenge by recognizing proteins, peptides and other small molecules with high affinity and specificity. Through a process known as cell-SELEX, we used live acute myeloid leukemia (AML) cells to select a group of DNA aptamers that can recognize acute myeloid leukemia cells with dissociation constants (Kds) in the nanomolar range. Interestingly, one aptamer (KH1C12), compared with two control cell lines (K562 and NB4), showed significant selectivity to the target AML cell line (HL60) and could recognize the target cells within a complex mixture of normal bone marrow aspirates. The other two aptamers KK1B10 and KK1D04 recognize targets associated with monocytic differentiation. Our studies demonstrate that the selected aptamers can be used as a molecular tool for further understanding surface protein expression patterns on tumor cells and thus providing a foundation for effective molecular analysis of leukemia and its subcategories.

Nitrogen oxide-induced autoprotection in isolated rat hepatocytes

Pretreatment of rat hepatocytes with low-dose nitrogen oxide (addition of SNAP in vitro or induction of nitric oxide synthase in vitro or in vivo) imparts resistance to killing and decrease in aconitase and mitochondrial electron transfer from a second exposure to a higher dose of SNAP. Induction of this resistance is prevented by cycloheximide, indicating upregulation of protective protein(s). Ferritin levels are increased as are non-heme iron-NO EPR signals. Tin-protoporphyrin (SnPP) prevents protection, suggesting involvement of hsp32 (heme oxygenase) and/or guanylyl cyclase (GC). Cross-resistance to H2O2 killing is also observed, which is also prevented by cycloheximide and SnPP. Thus, hepatocytes possess inducible protective mechanisms against nitrogen oxide and reactive oxygen toxicity.

Loss and degradation of enzyme-bound heme induced by cellular nitric oxide synthesis

We report here that, like nonheme iron, protein-bound intracellular heme iron is also a target for destruction by endogenously produced nitric oxide (NO). In isolated rat hepatocytes NO synthesis results in substantial (approximately 60%) and comparable loss of catalase and cytochrome P450 as well as total microsomal heme, and decreased heme synthetic (delta-aminolevulinate synthetase and ferrochelatase) and increased degradative (heme oxygenase) enzymatic activities. The effect is reversible, and intact cytochrome P450 apoproteins are still present, as judged by heme reconstitution of isolated microsomes. The effects on delta-aminolevulinate synthetase and heme oxygenase are likely to be secondary to heme liberation, while the effects on ferrochelatase appear to be a direct effect of NO, perhaps destruction of its nonheme iron-sulfur center.

Nitric oxide prevents tumor necrosis factor alpha-induced rat hepatocyte apoptosis by the interruption of mitochondrial apoptotic signaling through S-nitrosylation of caspase-8

Mitochondrial cytochrome c release plays a critical role in apoptotic signal cascade after the activation of cell surface death receptors. We investigated the role played by nitric oxide (NO) in mitochondrial apoptotic signaling in tumor necrosis factor alpha (TNF-alpha) plus actinomycin D (TNF-alpha/ActD)-induced apoptosis. NO produced either by S-nitroso-N-acetyl-DL-penicillamine (SNAP) or inducible NO synthase (iNOS) prevented TNF-alpha/ActD-induced apoptosis in hepatocytes and also inhibited both caspase-8-like (IETDase) and caspase-3-like protease (DEVDase) activity as well as mitochondrial cytochrome c release. Recombinant human (rh) caspase-8 induced the cleavage of the cytochrome c-effluxing factor Bid and cytochrome c release from purified mitochondria in the reconstitution system with Bid(+/+) cytosol, but not with Bid(-/-) cytosol. The addition of SNAP and the caspase-8 inhibitor Ac-IETD-fmk inhibited caspase-8-dependent Bid cleavage and cytochrome c release. The inhibitory effect of NO on caspase-8 was reversed by dithiothreitol (DTT). Furthermore, rh-caspase-8 was found to be modified by S-nitrosylation with 1.7 moles of NO bound per mole of enzyme. Treatment of hepatocytes with interleukin 1beta (IL-1beta) plus interferon gamma (IFN-gamma), which induced iNOS expression and NO production, suppressed TNF-alpha/ActD-induced Bid cleavage and mitochondrial cytochrome c release. The NOS inhibitor N(G)-monomethyl-L-arginine (NMA) inhibited the protective effects of IL-1beta and IFN-gamma. The liver-specific NO donor V-PYRRO/NO also inhibited in vivo elevation of IETDase activity, Bid cleavage, and mitochondrial cytochrome c release in the livers of rats injected with TNF-alpha plus D-galactosamine. Our results indicate that one mechanism by which NO protects hepatocytes from TNF-alpha/ActD-induced apoptosis is via the interruption of mitochondrial apoptotic signaling through S-nitrosylation of caspase-8.

Cellular non-heme iron content is a determinant of nitric oxide-mediated apoptosis, necrosis, and caspase inhibition

In this report, we tested the hypothesis that cellular content of non-heme iron determined whether cytotoxic levels of nitric oxide (NO) resulted in apoptosis versus necrosis. The consequences of NO exposure on cell viability were tested in RAW264.7 cells (a cell type with low non-heme iron levels) and hepatocytes (cells with high non-heme iron content). Whereas micromolar concentrations of the NO donor S-nitroso-N-acetyl-DL-penicillamine induced apoptosis in RAW264.7 cells, millimolar concentrations were required to induce necrosis in hepatocytes. Caspase-3 activation and cytochrome c release were evident in RAW264.7 cells, but only cytochrome c release was detectable in hepatocytes following high dose S-nitroso-N-acetyl-DL-penicillamine exposure. Pretreating RAW264.7 cells with FeSO(4) increased intracellular non-heme iron to levels similar to those measured in hepatocytes and delayed NO-induced cell death, which then occurred in the absence of caspase-3 activation. Iron loading was also associated with the formation of intracellular dinitrosyl-iron complexes (DNIC) upon NO exposure. Cytosolic preparations containing DNIC as well as pure preparations of DNIC suppressed caspase activity. These data suggest that non-heme iron content is a key factor in determining the consequence of NO on cell viability by regulating the chemical fate of NO.

Sphingosine 1-phosphate protects human umbilical vein endothelial cells from serum-deprived apoptosis by nitric oxide production

Sphingosine 1-phosphate (S1P) can prevent endothelial cell apoptosis. We investigated the molecular mechanisms and signaling pathways by which S1P protects endothelial cells from serum deprivation-induced apoptosis. We show here that human umbilical vein endothelial cells (HUVECs) undergo apoptosis associated with increased DEVDase activity, caspase-3 activation, cytochrome c release, and DNA fragmentation after 24 h of serum deprivation. These apoptotic markers were suppressed by the addition of S1P, the NO donor S-nitroso-N-acetylpenicillamine (100 micrometer), or caspase-3 inhibitor z-VAD-fmk. The protective effects of S1P were reversed by the nitric-oxide synthase (NOS) inhibitor N-monomethyl-l-arginine, but not by the soluble guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo[4,3-a]-quanoxaline-1-one, suggesting that NO, but not cGMP, is responsible for S1P protection from apoptosis. Furthermore, S1P increased NO production by enhancing Ca(2+)-sensitive NOS activity without changes in the eNOS protein level. S1P-mediated cell survival and NO production were suppressed significantly by pretreatment with antisense oligonucleotide of EDG-1 and partially by EDG-3 antisense. S1P-mediated NO production was suppressed by the addition of pertussis toxin, an inhibitor of G(i) proteins, the specific inhibitor of phospholipase C (PLC), and the Ca(2+) chelator BAPTA-AM. These findings indicate that S1P protects HUVECs from apoptosis through the activation of eNOS activity mainly through an EDG-1 and -3/G(i)/PLC/Ca(2+) signaling pathway.

Differential regulation of NO availability from macrophages and endothelial cells by the garlic component S-allyl cysteine

Garlic has been used as a traditional medicine for prevention and treatment of cardiovascular diseases. However, the molecular mechanism of garlic's pharmacological action has not been clearly elucidated. We examined here the effect of garlic extract and its major component, S-allyl cysteine (SAC), on nitric oxide (NO) production by macrophages and endothelial cells. The present study demonstrates that these reagents inhibited NO production through the suppression of iNOS mRNA and protein expression in the murine macrophage cell line RAW264.7, which had been stimulated with LPS and IFNgamma. The garlic extract also inhibited NO production in peritoneal macrophages, rat hepatocytes, and rat aortic smooth muscle cells stimulated with LPS plus cytokines, but it did not inhibit NO production in iNOS-transfected AKN-1 cells or iNOS enzyme activity. These reagents suppressed NF-kappaB activation and murine iNOS promoter activity in LPS and IFNgamma-stimulated RAW264.7 cells. In contrast, these reagents significantly increased cGMP production by eNOS in HUVEC without changes in activity, protein levels, and cellular distribution of eNOS. Finally, garlic extract and SAC both suppressed the production of hydroxyl radical, confirming their antioxidant activity. These data demonstrate that garlic extract and SAC, due to their antioxidant activity, differentially regulate NO production by inhibiting iNOS expression in macrophages while increasing NO in endothelial cells. Thus, this selective regulation may contribute to the anti-inflammatory effect and prevention of atherosclerosis by these reagents.

Antimicrobial peptides in amniotic fluid: defensins, calprotectin and bacterial/permeability-increasing protein in patients with microbial invasion of the amniotic cavity, intra-amniotic inflammation, preterm labor and premature rupture of membranes

OBJECTIVE

Neutrophil defensins (HNP 1-3), bactericidal/permeability-increasing protein (BPI) and calprotectin (MRP8/14) are antimicrobial peptides stored in leukocytes that act as effector molecules of the innate immune response. The purpose of this study was to determine whether parturition, premature rupture of the membranes (PROM) and microbial invasion of the amniotic cavity (MIAC) are associated with changes in amniotic fluid concentrations of these antimicrobial peptides.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 333 patients in the following groups: group 1, mid-trimester with a subsequent normal pregnancy outcome (n = 84); group 2, preterm labor and intact membranes without MIAC who delivered at term (n = 36), or prematurely (n = 52) and preterm labor with MIAC (n = 26); group 3, preterm PROM with (n = 26) and without (n = 26) MIAC; and group 4, term with intact membranes in the absence of MIAC, in labor (n = 52) and not in labor (n = 31). The concentrations of HNP 1-3, BPI and calprotectin in amniotic fluid were determined by specific and sensitive immunoassays. Placentae of patients in both preterm labor with intact membranes and preterm PROM groups who delivered within 72 h of amniocentesis were examined. Non-parametric statistics, receiver-operating characteristic (ROC) curves and Cox regression models were used for analysis. A p value of < 0.05 was considered statistically significant.

RESULTS

Intra-amniotic infection was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin in both women with preterm labor and intact membranes, and women with preterm PROM. Preterm PROM was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin. Preterm parturition was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin, while parturition at term was associated with a significant increase in amniotic fluid concentrations of immunoreactive HNP 1-3. Among patients with preterm labor and intact membranes, elevation of amniotic fluid HNP 1-3, BPI and calprotectin concentrations was associated with intra-amniotic inflammation, histological chorioamnionitis and a shorter interval to delivery.

CONCLUSION

MIAC, preterm parturition and preterm PROM are associated with increased amniotic fluid concentrations of immunoreactive HNP 1-3, BPI and calprotectin. Moreover, elevated amniotic fluid concentrations of BPI, immunoreactive HNP 1-3 and calprotectin are associated with intra-amniotic inflammation, histological chorioamnionitis and shorter amniocentesis-to-delivery interval in patients presenting with preterm labor with intact membranes.

Nitric oxide down-regulates hepatocyte-inducible nitric oxide synthase gene expression

BACKGROUND

The expression of inducible nitric oxide synthase (iNOS) contributes to the systemic manifestations of sepsis.

OBJECTIVE

To determine whether nitric oxide (NO) can exert negative feedback regulation on iNOS gene expression.

SETTING

Molecular biology research laboratory of the department of surgery.

STUDY DESIGN

Isolated rat hepatocytes were cultured with a cytokine mix consisting of tumor necrosis factor alpha, interleukin 1 beta, and interferon gamma in the presence or absence of the NO donor S-nitroso-N-acetyl-D,L-penicillamine.

MAIN OUTCOME MEASURES

Nitrite and nitrate (NO2- and NO3-) levels were assayed. Hepatocyte iNOS messenger RNA and protein levels were assessed. Electromobility shift assays were performed for NF-kappa B DNA binding activity. Finally, iNOS enzyme activity was determined using high-performance liquid chromatography.

RESULTS

Cytokine mix-induced hepatocyte iNOS mRNA and protein production and the addition of the NO donor S-nitroso-N-acetyl-D,L-penicillamine markedly attenuated iNOS mRNA and protein levels. Gel shift assays of the nuclear extracts disclosed that decreased cytokine mix-induced DNA binding activity for NF-kappa B in a concentration-dependent manner. Finally, NO failed to significantly inhibit iNOS enzyme activity.

CONCLUSIONS

These data indicate that NO down-regulates iNOS gene transcription, and that the effect is mediated in part by inhibiting NF-kappa B activity. These results identify a novel negative feedback mechanism whereby NO down-regulates iNOS gene expression, possibly to limit overproduction during the septic response.

Adenoviral transfer of the inducible nitric oxide synthase gene blocks endothelial cell apoptosis

BACKGROUND

We have previously reported that vascular inducible nitric oxide synthase (iNOS) gene transfer inhibits injury-induced intimal hyperplasia in vitro and in vivo. One mechanism by which NO may prevent intimal hyperplasia is by preserving the endothelium or promoting its regeneration. To study this possibility we examined the effect of iNOS gene transfer on endothelial cell (EC) proliferation and viability.

METHODS

An adenoviral vector (AdiNOS) containing the human iNOS cDNA was constructed and used to infect cultured sheep arterial ECs. NO production was measured, and the effects of continuous NO exposure on EC proliferation, viability, and apoptosis were evaluated.

RESULTS

AdiNOS-infected ECs produced 25- to 100-fold more NO than control (AdlacZ) infected cells as measured by nitrite accumulation. This increased NO synthesis did not inhibit EC proliferation as reflected by tritiated thymidine incorporation. Chromium 51 release assay revealed that EC viability was also unaffected by AdiNOS infection and NO synthesis. In addition, prolonged exposure to NO synthesis did not induce EC apoptosis. Instead, NO inhibited lipopolysaccharide-induced apoptosis in these cells by reducing caspase-3-like protease activity.

CONCLUSIONS

Vascular iNOS gene transfer, while inhibiting smooth muscle cell proliferation, does not impair EC mitogenesis or viability. Augmented NO synthesis may also protect ECs against apogenic stimuli such as lipopolysaccharide. Therefore iNOS gene transfer may promote endothelial regeneration and can perhaps accelerate vascular healing.

Involvement of Hofbauer cells and maternal T cells in villitis of unknown aetiology

AIMS

The nature of villitis of unknown aetiology (VUE) is intriguing in terms of its aetiology, origin of inflammatory cells and immunophenotype of T cells involved. The aim was to determine the origin of macrophages and the immunophenotype of T lymphocytes in VUE associated with various complications of pregnancy.

METHODS AND RESULTS

Placentas with VUE (n = 45) were studied by chromogenic in-situ hybridization (CISH) for Y chromosome (DYZ1) and immunohistochemistry for CD14, CD68, Ki67 (n = 10; all from male neonates) and a panel of T-cell antigens (CD3, CD4 and CD8) (n = 35). All of the placentas from male neonates showed CISH+ signals from Y chromosomes in the majority of macrophages, but not in lymphocytes, indicating that the macrophages were of fetal origin. Many macrophages of the affected chorionic villi were Ki67+, suggesting that they are hyperplastic Hofbauer cells. Among the lymphocytes, CD8+ T cells outnumbered CD4+ T cells in all placentas with different obstetrical conditions.

CONCLUSIONS

We define primary components of VUE as maternal CD8+ T cells and hyperplastic Hofbauer cells. We propose that VUE is a unique inflammatory reaction where the leucocytes from two hosts are key partners, analogous to either allograft rejection or graft-versus-host disease.

Upstream NF-kappaB site is required for the maximal expression of mouse inducible nitric oxide synthase gene in interferon-gamma plus lipopolysaccharide-induced RAW 264.7 macrophages

Transient transfection assays with various deletion mutants of the mouse inducible nitric oxide synthase (iNOS) promoter linked to a CAT reporter gene demonstrated that, besides the downstream NF-kappaB site, the region from -973 to -925 which contains a potential binding site for NF-kappaB (upstream NF-kappaB site) also mediated lipopolysaccharide (LPS)-inducibility in mouse macrophage cell line RAW 264.7. Site-specific mutation of three conserved nucleotides within the upstream NF-kappaB site abolished additional induction by LPS as well as maximal expression of iNOS by IFN-gamma plus LPS. In contrast, site-specific mutation of the downstream NF-kappaB site caused almost all reduction in expression of the reporter gene by LPS or LPS plus IFN-gamma. Electrophoretic mobility shift assays with the two NF-kappaB sites showed LPS-induced NF-kappaB binding to both probes and its higher affinity to the upstream NF-kappaB site. Taken together, these suggest that the upstream NF-kappaB site having enhancer function, besides the downstream NF-kappaB site as a core promoter, is essential for maximal expression of the iNOS gene.