Simultaneous inhibition of glutathione- and thioredoxin-dependent metabolism is necessary to potentiate 17AAG-induced cancer cell killing via oxidative stress

17-Allylamino-17-demethoxygeldanamycin (17AAG) is an experimental chemotherapeutic agent believed to form free radicals in vivo, and cancer cell resistance to 17AAG is believed to be a thiol-dependent process. Inhibitors of thiol-dependent hydroperoxide metabolism [L-buthionine-S,R-sulfoximine (BSO) and auranofin] were combined with the glucose metabolism inhibitor 2-deoxy-d-glucose (2DG) to determine if 17AAG-mediated cancer cell killing could be enhanced. When 2DG (20mM, 24h), BSO (1mM, 24h), and auranofin (500nM, 3h) were combined with 17AAG, cell killing was significantly enhanced in three human cancer cell lines (PC-3, SUM159, MDA-MB-231). Furthermore, the toxicity of this drug combination was significantly greater in SUM159 human breast cancer cells, relative to HMEC normal human breast epithelial cells. Increases in toxicity seen with this drug combination also correlated with increased glutathione (GSH) and thioredoxin (Trx) oxidation and depletion. Furthermore, treatment with the thiol antioxidant NAC (15mM, 24h) was able to significantly protect from drug-induced toxicity and ameliorate GSH oxidation, Trx oxidation, and Trx depletion. These data strongly support the hypothesis that simultaneous inhibition of GSH- and Trx-dependent metabolism is necessary to sensitize human breast and prostate cancer cells to 2DG+17AAG-mediated killing via enhancement of thiol-dependent oxidative stress. These results suggest that simultaneous targeting of both GSH and Trx metabolism could represent an effective strategy for chemosensitization in human cancer cells.

Transactivation of gene expression by NF-κB is dependent on thioredoxin reductase activity

The redox-sensitive transcription factor NF-κB mediates the expression of genes involved in inflammation and cell survival. Thioredoxin reductase-1 (TR1) and its substrate thioredoxin-1 act together to reduce oxidized cysteine residues within the DNA-binding domain of NF-κB and promote maximal DNA-binding activity in vitro. It is not clear, however, if NF-κB is regulated via this mechanism within living cells. The purpose of this study was to determine the mechanism of NF-κB modulation by TR1 in cells stimulated with the inflammatory cytokine tumor necrosis factor-α (TNF). In both control cells and cells depleted of TR1 activity through chemical inhibition or siRNA knockdown, TNF stimulation resulted in degradation of the cytoplasmic NF-κB inhibitor IκB-α and translocation of NF-κB to the nucleus. Similarly, the DNA-binding activity and redox state of NF-κB were unaffected by TR1 depletion. In contrast, NF-κB-mediated gene expression was markedly inhibited in cells lacking TR1 activity, suggesting that the transactivation potential of NF-κB is sensitive to changes in TR1 activity. Consistent with this concept, phosphorylation of the transactivation domain of NF-κB was inhibited in the presence of curcumin. Surprisingly, another TR1 inhibitor, 1-chloro-2,4-dinitrobenzene, had no effect, and siRNA knockdown of TR1 actually increased phosphorylation at this site. These results demonstrate that TR1 activity controls the transactivation potential of NF-κB and that more than one mechanism may mediate this effect.

Dietary selenium as a modulator of PCB 126-induced hepatotoxicity in male Sprague-Dawley rats

Homeostasis of selenium (Se), a critical antioxidant incorporated into amino acids and enzymes, is disrupted by exposure to aryl hydrocarbon receptor (AhR) agonists. Here we examined the importance of dietary Se in preventing the toxicity of the most toxic polychlorinated biphenyl congener, 3,3',4,4',5-pentachlorobiphenyl (PCB 126), a potent AhR agonist. Male Sprague-Dawley rats were fed a modified AIN-93 diet with differing dietary Se levels (0.02, 0.2, and 2 ppm). Following 3 weeks of acclimatization, rats from each dietary group were given a single ip injection of corn oil (vehicle), 0.2, 1, or 5 μmol/kg body weight PCB 126, followed 2 weeks later by euthanasia. PCB exposure caused dose-dependent increases in liver weight and at the highest PCB 126 dose decreases in whole body weight gains. Hepatic cytochrome P-450 (CYP1A1) activity was significantly increased even at the lowest dose of PCB 126, indicating potent AhR activation. PCB exposure diminished hepatic Se levels in a dose-dependent manner, and this was accompanied by diminished Se-dependent glutathione peroxidase activity. Both these effects were partially mitigated by Se supplementation. Conversely, thioredoxin (Trx) reductase activity and Trx oxidation state, although significantly diminished in the lowest dietary Se groups, were not affected by PCB exposure. In addition, PCB 126-induced changes in hepatic copper, iron, manganese, and zinc were observed. These results demonstrate that supplemental dietary Se was not able to completely prevent the toxicity caused by PCB 126 but was able to increase moderately the levels of several key antioxidants, thereby maintaining them roughly at normal levels.

Thioredoxin reductase-2 is essential for keeping low levels of H(2)O(2) emission from isolated heart mitochondria

Respiring mitochondria produce H(2)O(2) continuously. When production exceeds scavenging, H(2)O(2) emission occurs, endangering cell functions. The mitochondrial peroxidase peroxiredoxin-3 reduces H(2)O(2) to water using reducing equivalents from NADPH supplied by thioredoxin-2 (Trx2) and, ultimately, thioredoxin reductase-2 (TrxR2). Here, the contribution of this mitochondrial thioredoxin system to the control of H(2)O(2) emission was studied in isolated mitochondria and cardiomyocytes from mouse or guinea pig heart. Energization of mitochondria by the addition of glutamate/malate resulted in a 10-fold decrease in the ratio of oxidized to reduced Trx2. This shift in redox state was accompanied by an increase in NAD(P)H and was dependent on TrxR2 activity. Inhibition of TrxR2 in isolated mitochondria by auranofin resulted in increased H(2)O(2) emission, an effect that was seen under both forward and reverse electron transport. This effect was independent of changes in NAD(P)H or membrane potential. The effects of auranofin were reproduced in cardiomyocytes; superoxide and H(2)O(2) levels increased, but similarly, there was no effect on NAD(P)H or membrane potential. These data show that energization of mitochondria increases the antioxidant potential of the TrxR2/Trx2 system and that inhibition of TrxR2 results in increased H(2)O(2) emission through a mechanism that is independent of changes in other redox couples.

Nrf2-dependent sulfiredoxin-1 expression protects against cigarette smoke-induced oxidative stress in lungs

Oxidative stress results in protein oxidation and is involved in the pathogenesis of lung diseases such as chronic obstructive pulmonary disorder (COPD). Sulfiredoxin-1 (Srx1) catalyzes the reduction of cysteine sulfinic acid to sulfenic acid in oxidized proteins and protects them from inactivation. This study examined the mechanism of transcriptional regulation of Srx1 and its possible protective role during oxidative stress associated with COPD. Nrf2, a transcription factor known to influence susceptibility to pulmonary diseases, upregulates Srx1 expression during oxidative stress caused by cigarette smoke exposure in the lungs of mice. Disruption of Nrf2 signaling by genetic knockout in mice or RNAi in cells downregulated the expression of Srx1. In silico analysis of the 5'-promoter-flanking region of Srx1 identified multiple antioxidant-response elements (AREs) that are highly conserved. Reporter and chromatin-immunoprecipitation assays demonstrated that ARE1 at -228 is critical for the Nrf2-mediated response. Attenuation of Srx1 expression with RNAi potentiated the toxicity of hydrogen peroxide (H2O2), whereas overexpression of Srx1 protected against H2O2-mediated cell death in vitro. Immunoblot analysis revealed dramatic decreases in Srx1 expression in lungs from patients with COPD relative to nonemphysematous lungs together with a decline in Nrf2 protein. Thus, Srx1, a key Nrf2-regulated gene, contributes to protection against oxidative injury in the lung.

RNAi-mediated silencing of nuclear factor erythroid-2-related factor 2 gene expression in non-small cell lung cancer inhibits tumor growth and increases efficacy of chemotherapy

Nuclear factor erythroid-2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that regulates the expression of electrophile and xenobiotic detoxification enzymes and efflux proteins, which confer cytoprotection against oxidative stress and apoptosis in normal cells. Loss of function mutations in the Nrf2 inhibitor, Kelch-like ECH-associated protein (Keap1), results in constitutive activation of Nrf2 function in non-small cell lung cancer. In this study, we show that constitutive activation of Nrf2 in lung cancer cells promotes tumorigenicity and contributes to chemoresistance by up-regulation of glutathione, thioredoxin, and the drug efflux pathways involved in detoxification of electrophiles and broad spectrum of drugs. RNAi-mediated reduction of Nrf2 expression in lung cancer cells induces generation of reactive oxygen species, suppresses tumor growth, and results in increased sensitivity to chemotherapeutic drug-induced cell death in vitro and in vivo. Inhibiting Nrf2 expression using naked siRNA duplexes in combination with carboplatin significantly inhibits tumor growth in a subcutaneous model of lung cancer. Thus, targeting Nrf2 activity in lung cancers, particularly those with Keap1 mutations, could be a promising strategy to inhibit tumor growth and circumvent chemoresistance.

Oxidation and nuclear localization of thioredoxin-1 in sparse cell cultures

Reactive oxygen species (ROS) were once viewed only as mediators of toxicity, but it is now recognized that they also contribute to redox signaling through oxidation of specific cysteine thiols on regulatory proteins. Cells in sparse cultures have increased ROS relative to confluent cultures, but it is not known whether protein redox states are affected under these conditions. The purpose of the present study was to determine whether culture conditions affect the redox state of thioredoxin-1 (Trx1), the protein responsible for reducing most oxidized proteins in the cytoplasm and nucleus. The results showed that Trx1 was more oxidized in sparse HeLa cell cultures than in confluent cells. The glutathione pool was also more oxidized, demonstrating that both of the major cellular redox regulating systems were affected by culture density. In addition, the total amount of Trx1 protein was lower and the subcellular distribution of Trx1 was different in sparse cells. Trx1 in sparse cultures was predominantly nuclear whereas it was predominantly cytoplasmic in confluent cultures. This localization pattern was not unique to HeLa cells as it was also observed in A549, Cos-1 and HEK293 cells. These findings demonstrate that Trx1 is subject to changes in expression, redox state and subcellular localization with changing culture density, indicating that the redox environments of the cytoplasm and the nucleus are distinct and have different requirements under different culture conditions.

Redox-regulation of Erk1/2-directed phosphatase by reactive oxygen species: role in signaling TPA-induced growth arrest in ML-1 cells

Extracellular signal-regulated kinase (Erk)1/2 activity signals myeloid cell differentiation induced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Previously, we reported that Erk1/2 activation (phosphorylation) induced by TPA required reactive oxygen species (ROS) as a second messenger. Here, we hypothesized that ROS generated in response to TPA inhibit Erk1/2-directed phosphatase activity, which leads to an increase phosphorylation of Erk1/2 to signal p21(WAF1/Cip1)-mediated growth arrest in ML-1 cells. Incubation of ML-1 cells with TPA resulted in a marked accumulation of phosphorylated Erk1/2, and is subsequent to H2O2 generation. Interestingly, post-TPA-treatment with N-acetylcysteine (NAC) stimulated a marked and a rapid dephosphorylation of Erk1/2, suggesting a regeneration of Erk1/2-directed phospahatase activity by NAC. ROS generation in ML-1 cells induced by TPA was suggested to occur in the mitochondrial electron transport chain (METC) based on the following observations: (i) undifferentiated ML-1 cells not only lack p67-phox and but also express a low level of p47-phox key components required for NADPH oxidase enzymatic activity, (ii) pretreatment with DPI, an inhibitor of NADH- and NADPH-dependent enzymes, or rhein, an inhibitor of complex I, blocked the ROS generation, and (iii) examination of the microarray analysis data and Western blot analysis data revealed an induction of MnSOD expression at both mRNA and protein levels in response to TPA. MnSOD is a key member of the mitochondrial defense system against mitochondrial-derived superoxide. Together, this study suggested that TPA stimulated ROS generation as a second messenger to activate Erk1/2 via a redox-mediated inhibition of Erk1/2-directed phosphatase in ML-1 cells.

Thioredoxin reductase-1 knock down does not result in thioredoxin-1 oxidation

The active site of thioredoxin-1 (Trx1) is oxidized in cells with increased reactive oxygen species (ROS) and is reduced by thioredoxin reductase-1 (TrxR1). The purpose of the present study was to determine the extent to which the redox state of Trx1 is sensitive to changes in these opposing reactions. Trx1 redox state and ROS generation were measured in cells exposed to the TrxR1 inhibitors aurothioglucose (ATG) and monomethylarsonous acid (MMA(III)) and in cells depleted of TrxR1 activity by siRNA knock down. The results showed that all three treatments inhibited TrxR1 activity to similar extents (90% inhibition), but that only MMA(III) exposure resulted in oxidation of Trx1. Similarly, ROS levels were elevated in response to MMA(III), but not in response to ATG or TrxR1 siRNA. Therefore, TrxR1 inhibition alone was not sufficient to oxidize Trx1, suggesting that Trx1-independent pathways should be considered when evaluating pharmacological and toxicological mechanisms involving TrxR1 inhibition.

The effects of glutaredoxin and copper activation pathways on the disulfide and stability of Cu,Zn superoxide dismutase

Mutations in Cu,Zn superoxide dismutase (SOD1) can cause amyotrophic lateral sclerosis (ALS) through mechanisms proposed to involve SOD1 misfolding, but the intracellular factors that modulate folding and stability of SOD1 are largely unknown. By using yeast and mammalian expression systems, we demonstrate here that SOD1 stability is governed by post-translational modification factors that target the SOD1 disulfide. Oxidation of the human SOD1 disulfide in vivo was found to involve both the copper chaperone for SOD1 (CCS) and the CCS-independent pathway for copper activation. When both copper pathways were blocked, wild type SOD1 stably accumulated in yeast cells with a reduced disulfide, whereas ALS SOD1 mutants A4V, G93A, and G37R were degraded. We describe here an unprecedented role for the thiol oxidoreductase glutaredoxin in reducing the SOD1 disulfide and destabilizing ALS mutants. Specifically, the major cytosolic glutaredoxin of yeast was seen to reduce the intramolecular disulfide of ALS SOD1 mutant A4V SOD1 in vivo and in vitro. By comparison, glutaredoxin was less reactive toward the disulfide of wild type SOD1. The apo-form of A4V SOD1 was highly reactive with glutaredoxin but not SOD1 containing both copper and zinc. Glutaredoxin therefore preferentially targets the immature form of ALS mutant SOD1 lacking metal co-factors. Overall, these studies implicate a critical balance between cellular reductants such as glutaredoxin and copper activation pathways in controlling the disulfide and stability of SOD1 in vivo.

Compartmentation of Nrf-2 redox control: regulation of cytoplasmic activation by glutathione and DNA binding by thioredoxin-1

Nrf-2 is a redox-sensitive transcription factor that is activated by an oxidative signal in the cytoplasm but has a critical cysteine that must be reduced to bind to DNA in the nucleus. The glutathione (GSH) and thioredoxin (TRX) systems have overlapping functions in thiol/disulfide redox control in both the cytoplasm and the nucleus, and it is unclear whether these are redundant or have unique functions in control of Nrf-2-dependent signaling. To test whether GSH and Trx-1 have distinct functions in Nrf-2 signaling, we selectively modified GSH by metabolic manipulation and selectively modified Trx-1 expression by transient transfection. Cytoplasmic activation of Nrf-2 was measured by its nuclear translocation and nuclear activity of Nrf-2 was measured by expression of a luciferase reporter construct containing an ARE4 from glutamate cysteine ligase. Results showed that tert-butylhydroquinone (TBHQ), a transcriptional activator that functions through Nrf-2/ARE, promoted Nrf-2 nuclear translocation by a type I (thiylation) redox switch which was regulated by GSH not by Trx-1. In contrast, the ARE reporter was principally controlled by nuclear-targeted Trx-1 and not by GSH. The data show that the GSH and TRX systems have unique, compartmented functions in the control of transcriptional regulation by Nrf-2/ARE.

Thioredoxin and Its Role in Toxicology

Thioredoxins (Trx) are members of an evolutionarily conserved family of redox-active proteins containing a conserved active site dithiol motif. Trx supports diverse reduction reactions, including several of direct toxicologic interest, but relatively little information is available concerning the roles of Trx under specific toxicologic conditions. Accumulating evidence suggests that Trx serves a partially overlapping and highly complementary role to the glutathione (GSH) system in protecting against toxicity. GSH and Trx both function in the reduction of peroxides through the action of multiple GSH peroxidases and Trx peroxidases (peroxiredoxins), respectively. However, GSH is a small molecule that is present at millimolar concentrations, thereby providing a potential mechanism for elimination of alkylating electrophiles. In contrast, even though Trx is only present at micromolar or submicromolar concentrations, its dithiol motif makes it suited to reverse oxidative changes to proteins, including reduction of protein disulfides, methioninyl sulfoxides, and cysteinyl sulfenic acids. Moreover, Trx functions in redox-sensitive signal transduction, transcriptional activation of stress response genes, ribonucleotide reduction in synthesis of deoxyribonucleotides for DNA repair, and post-injury cell proliferation. Molecular studies show that the predominant cytoplasmic/nuclear form, Trx-1, and the mitochondrial form, Trx-2, both protect against oxidative stress, that both are essential for embryonic development, and that Trx-1 is inducible in response to oxidative stress. Because of the differences between GSH and Trx in distribution, catalytic activities and reactivities with electrophiles, particularly with the important role to be played by glutathione S-transferases, considerable research is needed to clarify their respective roles in protection against specific toxicologic conditions.

Redox potential of human thioredoxin 1 and identification of a second dithiol/disulfide motif

Thioredoxin (Trx1) is a redox-active protein containing two active site cysteines (Cys-32 and Cys-35) that cycle between the dithiol and disulfide forms as Trx1 reduces target proteins. Examination of the redox characteristics of this active site dithiol/disulfide couple is complicated by the presence of three additional non-active site cysteines. Using the redox Western blot technique and matrix assisted laser desorption ionization time-of-flight mass spectrometry mass spectrometry, we determined the midpoint potential (E0) of the Trx1 active site (-230 mV) and identified a second redox-active dithiol/disulfide (Cys-62 and Cys-69) in an alpha helix proximal to the active site, which formed under oxidizing conditions. This non-active site disulfide was not a substrate for reduction by thioredoxin reductase and delayed the reduction of the active site disulfide by thioredoxin reductase. Within actively growing THP1 cells, most of the active site of Trx1 was in the dithiol form, whereas the non-active site was totally in the dithiol form. The addition of increasing concentrations of diamide to these cells resulted in oxidation of the active site at fairly low concentrations and oxidation of the non-active site at higher concentrations. Taken together these results suggest that the Cys-62-Cys-69 disulfide could provide a means to transiently inhibit Trx1 activity under conditions of redox signaling or oxidative stress, allowing more time for the sensing and transmission of oxidative signals.

Oxidation of nuclear thioredoxin during oxidative stress

Thioredoxin 1 (Trx1) is a key redox control system within the nucleus, yet little is known about the sensitivity of nuclear Trx1 to oxidative stress. The present study compared oxidant-induced changes in the redox states of nuclear Trx1, cytoplasmic Trx1, and cellular glutathione (GSH). Nuclear Trx1 was more reducing than cytoplasmic Trx1 and cellular GSH in proliferating cells. tert-Butylhydroperoxide caused an increase in the total amount of nuclear Trx1, but this was accompanied by a 60 mV oxidation. Thus, the increase in nuclear Trx1 levels did not correspond to an increase in the overall reducing capacity of Trx1 in the nucleus.

Glutathione and thioredoxin redox during differentiation in human colon epithelial (Caco-2) cells

Cellular redox, maintained by the glutathione (GSH)- and thioredoxin (Trx)-dependent systems, has been implicated in the regulation of a variety of biological processes. The redox state of the GSH system becomes oxidized when cells are induced to differentiate by chemical agents. The aim of this study was to determine the redox state of cellular GSH/glutathione disulfide (GSH/GSSG) and Trx as a consequence of progression from proliferation to contact inhibition and spontaneous differentiation in colon carcinoma (Caco-2) cells. Results showed a significant decrease in GSH concentration, accompanied by a 40-mV oxidation of the cellular GSH/GSSG redox state and a 28-mV oxidation of the extracellular cysteine/cystine redox state in association with confluency and increase in differentiation markers. The redox state of Trx did not change. Thus the two central cellular antioxidant and redox-regulating systems (GSH and Trx) were independently controlled. According to the Nernst equation, a 30-mV oxidation is associated with a 10-fold change in the reduced/oxidized ratio of a redox-sensitive dithiol motif. Therefore, the measured 40-mV oxidation of the cellular GSH/GSSG couple or the 28-mV oxidation of the extracellular cysteine/cystine couple should be sufficient to function in signaling or regulation of differentiation in Caco-2 cells.

Swimming behavior of the nudibranch Melibe leonina

Swimming in the nudibranch Melibe leonina consists of five types of movements that occur in the following sequence: (1) withdrawal, (2) lateral flattening, (3) a series of lateral flexions, (4) unrolling and swinging, and (5) termination. Melibe swims spontaneously, as well as in response to different types of aversive stimuli. In this study, swimming was elicited by contact with the tube feet of the predatory sea star Pycnopodia helianthoides, pinching with forceps, or application of a 1 M KCl solution. During an episode of swimming, the duration of swim cycles (2.7 +/- 0.2 s [mean +/- SEM], n = 29) and the amplitude of lateral flexions remained relatively constant. However, the latency between the application of a stimulus and initiation of swimming was more variable, as was the duration of an episode of swimming. For example, when touched with a single tube foot from a sea star (n = 32), the latency to swim was 7.0 +/- 2.4 s, and swimming continued for 53.7 +/- 9.4 s, whereas application of KCl resulted in a longer latency to swim (22.3 +/- 4.5 s) and more prolonged swimming episodes (174.9 +/- 32.1 s). Swimming individuals tended to move in a direction perpendicular to the long axis of the foot, which propelled them laterally when they were oriented with the oral hood toward the surface of the water. The results of this study indicate that swimming in Melibe, like that in several other molluscs, is a stereotyped fixed action pattern that can be reliably elicited in the laboratory. These characteristics, along with the large identifiable neurons typical of many molluscs, make swimming in this nudibranch amenable to neuroethological analyses.

Oxidation of the glutathione/glutathione disulfide redox state is induced by cysteine deficiency in human colon carcinoma HT29 cells

Glutathione (GSH) has a central role in the maintenance of the thiol-disulfide redox state in mammalian cells. GSH synthesis can be physiologically limited by the availability of cysteine (Cys), and Cys and its precursors are variable in the human diet. The purpose of this study was to determine the effect of severe Cys deficiency and readdition of Cys on the redox state of the GSH/glutathione disulfide (GSSG) pool in human colon carcinoma HT29 cells. Cells were cultured in Cys- (and cystine-)limiting medium for 48 h followed by culture in medium containing either Cys or cystine for 24 h. GSH and GSSG were measured by HPLC. Cys limitation decreased cellular GSH and GSSG concentrations with an associated >80 mV oxidation of the GSH/GSSG redox state. Upon addition of either Cys or its disulfide cystine (CySS), redox of GSH/GSSG recovered in 4 h, whereas GSH concentration continued to increase over 12 h. Maximal GSH concentrations attained were 200% of control cell values. These results show that severe Cys deficiency can have marked effects on cellular redox state but that redox recovers rapidly upon resupply. The magnitude of oxidation during Cys limitation in this cell model is sufficient to result in a >100-fold change in the reduced/oxidized ratio of redox-sensitive dithiol/disulfide motifs in proteins. If redox changes occur in vivo in association with variations in dietary Cys and its precursors, these changes could have important physiologic effects through altered redox signaling and control of cell proliferation and apoptosis.

S-Adenosylmethionine, cytokines, and alcoholic liver disease

Hepatic deficiency of S-adenosylmethionine (AdoMet) is a critical acquired metabolic abnormality in alcoholic liver disease (ALD) and in many experimental models of hepatotoxicity. Subnormal AdoMet, elevated serum tumor necrosis factor (TNF), and endotoxemia (LPS) are hallmarks of ALD and experimental liver injury. AdoMet deficiency is attributed to its subnormal synthesis, but mechanisms for increased TNF are not known. AdoMet deficiency may affect the critical balance of proinflammatory (e.g., TNF) and antiinflammatory [e.g., interleukin (IL)-10] cytokines. Rats maintained on a choline-deficient diet with limited amounts of methionine (MCD diet) developed AdoMet deficiency. When challenged with LPS, rats fed MCD diet had significantly increased serum TNF levels and worse liver injury compared with findings for controls. Exogenous AdoMet attenuated liver injury and serum TNF levels. Results of in vitro studies with the use of RAW 264.7 cells demonstrated that exogenous AdoMet supplementation lowered LPS-induced TNF formation in a dose-dependent manner, and AdoMet deficiency enhanced TNF secretion and TNF gene expression. AdoMet also dose-dependently decreased LPS-stimulated TNF production from monocytes obtained from patients with alcoholic hepatitis. Finally, AdoMet supplementation stimulated production of the antiinflammatory cytokine IL-10. Interleukin-10 plays a critical role in the modulation of TNF production, and IL-10 may inhibit hepatic fibrosis. This article will review (1) the role of AdoMet in ALD/liver injury, (2) the role of TNF/proinflammatory cytokines in ALD, (3) potential roles of AdoMet in TNF/proinflammatory cytokine regulation in ALD, and (4) conclusions and future directions.

Detection of salinity by the lobster, Homarus americanus

Changes in the heart rates of lobsters (Homarus americanus) were used as an indicator that the animals were capable of sensing a reduction in the salinity of the ambient seawater. The typical response to a gradual (1 to 2 ppt/min) reduction in salinity consisted of a rapid increase in heart rate at a mean threshold of 26.6 +/- 0.7 ppt, followed by a reduction in heart rate when the salinity reached 22.1 +/- 0.5 ppt. Animals with lesioned cardioregulatory nerves did not exhibit a cardiac response to changes in salinity. A cardiac response was elicited from lobsters exposed to isotonic chloride-free salines but not to isotonic sodium-, magnesium- or calcium-free salines. There was little change in the blood osmolarity of lobsters when bradycardia occurred, suggesting that the receptors involved are external. Furthermore, lobsters without antennae, antennules, or legs showed typical cardiac responses to low salinity, indicating the receptors are not located in these areas. Lobsters exposed to reductions in the salinity of the ambient seawater while both branchial chambers were perfused with full-strength seawater did not display a cardiac response until the external salinity reached 21.6 +/- 1.8 ppt. In contrast, when their branchial chambers were exposed to reductions in salinity while the external salinity was maintained at normal levels, changes in heart rate were rapidly elicited in response to very small reductions in salinity (down to 29.5 +/- 0.9 ppt in the branchial chamber and 31.5 +/- 0.3 ppt externally). We conclude that the primary receptors responsible for detecting reductions in salinity in H. americanus are located within or near the branchial chambers and are primarily sensitive to chloride ions.

Identifiable nitrergic neurons in the central nervous system of the nudibranch Melibe leonina localized with NADPH-diaphorase histochemistry and nitric oxide synthase immunoreactivity

Nitric oxide (NO) is a gaseous intercellular messenger produced by the enzyme nitric oxide synthase (NOS). In this study, we used two different techniques-nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and NOS immunocytochemistry-to demonstrate that NOS is present in a pair of identifiable cells in the central nervous system of the nudibranch Melibe leonina. In the Melibe brain, NADPH-d histochemistry revealed only a single pair of bilaterally symmetrical cells in the cerebropleural ganglia. NOS activity also was found in the neuropil of the cerebral, pedal, and buccal ganglia; in the tentacles of the oral hood; in the sensory end of the rhinophores; and in the epithelial tissue of the mouth, preputium, and glans penis. Immunocytochemistry using NOS antisera corroborated the results of the NADPH-d histochemistry by staining the same two cells in the cerebropleural ganglia. Each of these identifiable nitrergic neurons projects into the ipsilateral pedal ganglion. Because the pedal ganglia play a critical role in the control of locomotion, our results provide morphological evidence suggesting that NO may influence swimming or crawling in Melibe leonina.

Reversal of nonarteritic anterior ischemic optic neuropathy associated with coexisting primary antiphospholipid syndrome and Factor V Leiden mutation

PURPOSE

To report nonarteric anterior ischemic optic neuropathy (NAION) as an ocular manifestation in a woman with combined primary antiphospholipid syndrome and Factor V Leiden (FVL) mutation.

METHODS

Case report of a middle-aged woman with hematological investigations confirming the diagnosis of both primary antiphospholipid syndrome and Factor V Leiden mutation, who presented with visual disturbance in her left eye.

RESULTS

NAION was noted in her left eye. The patient was promptly treated with low molecular weight heparin, followed by warfarin, which resulted in the reversal of the ischemic optic neuropathy.

CONCLUSIONS

Primary antiphospholipid syndrome and coexisting Factor V Leiden mutation should be considered in the differential diagnosis of NAION. Prompt treatment with anticoagulants can result in the reversal of the ischemic process.

Diet and apoptosis

A range of compounds in or derived from the diet modulates apoptosis in cell cultures in vitro. These observations have important implications concerning the mechanisms whereby dietary components affect health. Proapoptotic compounds could protect against cancer by enhancing elimination of initiated, precancerous cells, and antiapoptotic compounds could promote tumor formation by inhibiting apoptosis in genetically damaged cells. Proapoptotic compounds could also contribute to age-related degenerative diseases by activating cell death in postmitotic cells or shifting the normal balance of mitosis and apoptosis in tissues with regenerative capacity. Many age-related diseases, for example macular degeneration and Parkinson's disease, appear to have oxidative stress as an underlying component that interacts with genetic, dietary, and environmental factors to determine relative risk in an individual. Oxidative stress activates apoptosis, and antioxidants protect against apoptosis in vitro; thus, a central role of dietary antioxidants may be to protect against apoptosis. However, little in vivo data are available to directly link diet with altered apoptosis as an underlying determinant of disease. Moreover, the possible antagonistic effects of different dietary components and the uncertainty about whether proapoptotic compounds that may protect against cancer could contribute to degenerative diseases and vice versa indicate that there is a great need for better in vivo assessment of apoptosis and that caution should be exercised when extrapolating in vitro data on apoptosis to in vivo dietary recommendations.