Effect of exogenous and endogenous nitric oxide on mitochondrial respiration of rat hepatocytes

Nitric oxide regulation of cellular metabolism: Adaptive tuning of cellular energy

Nitric oxide can interact with a wide range of proteins including many that are involved in metabolism. In this review we have summarized the effects of NO on glycolysis, fatty acid metabolism, the TCA cycle, and oxidative phosphorylation with reference to skeletal muscle. Low to moderate NO concentrations upregulate glucose and fatty acid oxidation, while higher NO concentrations shift cellular reliance toward a fully glycolytic phenotype. Moderate NO production directly inhibits pyruvate dehydrogenase activity, reducing glucose-derived carbon entry into the TCA cycle and subsequently increasing anaploretic reactions. NO directly inhibits aconitase activity, increasing reliance on glutamine for continued energy production. At higher or prolonged NO exposure, citrate accumulation can inhibit multiple ATP-producing pathways. Reduced TCA flux slows NADH/FADH entry into the ETC. NO can also inhibit the ETC directly, further limiting oxidative phosphorylation. Moderate NO production improves mitochondrial efficiency while improving O2 utilization increasing whole-body energy production. Long-term bioenergetic capacity may be increased because of NO-derived ROS, which participate in adaptive cellular redox signaling through AMPK, PCG1-α, HIF-1, and NF-κB. However, prolonged exposure or high concentrations of NO can result in membrane depolarization and opening of the MPT. In this way NO may serve as a biochemical rheostat matching energy supply with demand for optimal respiratory function.

Macrophage Reprogramming and Cancer Therapeutics: Role of iNOS-Derived NO

Nitric oxide and its production by iNOS is an established mechanism critical to tumor promotion or suppression. Macrophages have important roles in immunity, development, and progression of cancer and have a controversial role in pro- and antitumoral effects. The tumor microenvironment consists of tumor-associated macrophages (TAM), among other cell types that influence the fate of the growing tumor. Depending on the microenvironment and various cues, macrophages polarize into a continuum represented by the M1-like pro-inflammatory phenotype or the anti-inflammatory M2-like phenotype; these two are predominant, while there are subsets and intermediates. Manipulating their plasticity through programming or reprogramming of M2-like to M1-like phenotypes presents the opportunity to maximize tumoricidal defenses. The dual role of iNOS-derived NO also influences TAM activity by repolarization to tumoricidal M1-type phenotype. Regulatory pathways and immunomodulation achieve this through miRNA that may inhibit the immunosuppressive tumor microenvironment. This review summarizes the classical physiology of macrophages and polarization, iNOS activities, and evidence towards TAM reprogramming with current information in glioblastoma and melanoma models, and the immunomodulatory and therapeutic options using iNOS or NO-dependent strategies.

Plasmodium vivax Infection Alters Mitochondrial Metabolism in Human Monocytes

Monocytes play an important role in the host defense against Plasmodium vivax as the main source of inflammatory cytokines and mitochondrial reactive oxygen species (mROS). Here, we show that monocyte metabolism is altered during human P. vivax malaria, with mitochondria playing a major function in this switch. The process involves a reprograming in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. P. vivax infection results in dysregulated mitochondrial gene expression and in altered membrane potential leading to mROS increase rather than ATP production. When monocytes were incubated with P. vivax-infected reticulocytes, mitochondria colocalized with phagolysosomes containing parasites representing an important source mROS. Importantly, the mitochondrial enzyme superoxide dismutase 2 (SOD2) is simultaneously induced in monocytes from malaria patients. Taken together, the monocyte metabolic reprograming with an increased mROS production may contribute to protective responses against P. vivax while triggering immunomodulatory mechanisms to circumvent tissue damage. IMPORTANCE Plasmodium vivax is the most widely distributed causative agent of human malaria. To achieve parasite control, the human immune system develops a substantial inflammatory response that is also responsible for the symptoms of the disease. Among the cells involved in this response, monocytes play an important role. Here, we show that monocyte metabolism is altered during malaria, with its mitochondria playing a major function in this switch. This change involves a reprograming process in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. The resulting altered mitochondrial membrane potential leads to an increase in mitochondrial reactive oxygen species rather than ATP. These data suggest that agents that change metabolism should be investigated and used with caution during malaria.

Immunometabolism of Macrophages in Bacterial Infections

Macrophages are important effectors of tissue homeostasis, inflammation and host defense. They are equipped with an arsenal of pattern recognition receptors (PRRs) necessary to sense microbial- or danger-associated molecular patterns (MAMPs/DAMPs) and elicit rapid energetically costly innate immunity responses to protect the organism. The interaction between cellular metabolism and macrophage innate immunity is however not limited to answering the cell’s energy demands. Mounting evidence now indicate that in response to bacterial sensing, macrophages undergo metabolic adaptations that contribute to the induction of innate immunity signaling and/or macrophage polarization. In particular, intermediates of the glycolysis pathway, the Tricarboxylic Acid (TCA) cycle, mitochondrial respiration, amino acid and lipid metabolism directly interact with and modulate macrophage effectors at the epigenetic, transcriptional and post-translational levels. Interestingly, some intracellular bacterial pathogens usurp macrophage metabolic pathways to attenuate anti-bacterial defenses. In this review, we highlight recent evidence describing such host-bacterial immunometabolic interactions.

Nitric Oxide in Macrophage Immunometabolism: Hiding in Plain Sight

Nitric Oxide (NO) is a soluble endogenous gas with various biological functions like signaling, and working as an effector molecule or metabolic regulator. In response to inflammatory signals, immune myeloid cells, like macrophages, increase production of cytokines and NO, which is important for pathogen killing. Under these proinflammatory circumstances, called “M1”, macrophages undergo a series of metabolic changes including rewiring of their tricarboxylic acid (TCA) cycle. Here, we review findings indicating that NO, through its interaction with heme and non-heme metal containing proteins, together with components of the electron transport chain, functions not only as a regulator of cell respiration, but also a modulator of intracellular cell metabolism. Moreover, diverse effects of NO and NO-derived reactive nitrogen species (RNS) involve precise interactions with different targets depending on concentration, temporal, and spatial restrictions. Although the role of NO in macrophage reprogramming has been in evidence for some time, current models have largely minimized its importance. It has, therefore, been hiding in plain sight. A review of the chemical properties of NO, past biochemical studies, and recent publications, necessitates that mechanisms of macrophage TCA reprogramming during stimulation must be re-imagined and re-interpreted as mechanistic results of NO exposure. The revised model of metabolic rewiring we describe here incorporates many early findings regarding NO biochemistry and brings NO out of hiding and to the forefront of macrophages immunometabolism.

Regulation of cytochrome P450 enzyme activity and expression by nitric oxide in the context of inflammatory disease

Many hepatic cytochrome P450 enzymes and their associated drug metabolizing activities are down-regulated in disease states, and much of this has been associated with inflammatory cytokines and their signaling pathways. One such pathway is the induction of inducible nitric oxide synthase (NOS2) and generation of nitric oxide (NO) in many tissues and cells including the liver and hepatocytes. Experiments in the 1990s demonstrated that NO could bind to and inhibit P450 enzymes, and suggested that inhibition of NOS could attenuate, and NO generation could mimic, the down-regulation by inflammatory stimuli of not only P450 catalytic activities but also of mRNA expression and protein levels of certain P450 enzymes. This review will summarize and examine the evidence that NO functionally inhibits and down-regulates P450 enzymes in vivo and in vitro, with a particular focus on the mechanisms by which these effects are achieved.

The Emerging Role of Hepatocellular eNOS in Non-alcoholic Fatty Liver Disease Development

Non-alcoholic fatty liver disease (NAFLD) is comprised of a spectrum of liver injury ranging from excess fat accumulation in the liver (steatosis), to steatohepatitis (NASH), to its end stage of cirrhosis. A hallmark of NAFLD progression is the decline in function of hepatic mitochondria, although the mechanisms remain unresolved. Given the important role endothelial nitric oxide synthase (eNOS) plays in mitochondrial dynamics in other tissues, it has emerged as a potential mediator of maintaining mitochondrial function in the liver. In this mini review, we summarize the most relevant findings that extends current understanding of eNOS as a regulator of mitochondrial biogenesis, and identifies a potential additional role in mitochondrial turnover and attenuating inflammation during NAFLD development and progression.

Nitric oxide orchestrates metabolic rewiring in M1 macrophages by targeting aconitase 2 and pyruvate dehydrogenase

Profound metabolic changes are characteristic of macrophages during classical activation and have been implicated in this phenotype. Here we demonstrate that nitric oxide (NO) produced by murine macrophages is responsible for TCA cycle alterations and citrate accumulation associated with polarization. ¹³C tracing and mitochondrial respiration experiments map NO-mediated suppression of metabolism to mitochondrial aconitase (ACO2). Moreover, we find that inflammatory macrophages reroute pyruvate away from pyruvate dehydrogenase (PDH) in an NO-dependent and hypoxia-inducible factor 1α (Hif1α)-independent manner, thereby promoting glutamine-based anaplerosis. Ultimately, NO accumulation leads to suppression and loss of mitochondrial electron transport chain (ETC) complexes. Our data reveal that macrophages metabolic rewiring, in vitro and in vivo, is dependent on NO targeting specific pathways, resulting in reduced production of inflammatory mediators. Our findings require modification to current models of macrophage biology and demonstrate that reprogramming of metabolism should be considered a result rather than a mediator of inflammatory polarization.

Production of inflammatory mediators by M1-polarized macrophages is thought to rely on suppression of mitochondrial metabolism in favor of glycolysis. Refining this concept, here the authors define metabolic targets of nitric oxide as responsible for the mitochondrial rewiring resulting from polarization.

Molecular Mechanisms of Nitric Oxide in Cancer Progression, Signal Transduction, and Metabolism

SIGNIFICANCE

Cancer is a complex disease, which not only involves the tumor but its microenvironment comprising different immune cells as well. Nitric oxide (NO) plays specific roles within tumor cells and the microenvironment and determines the rate of cancer progression, therapy efficacy, and patient prognosis. Recent Advances: Key understanding of the processes leading to dysregulated NO flux within the tumor microenvironment over the past decade has provided better understanding of the dichotomous role of NO in cancer and its importance in shaping the immune landscape. It is becoming increasingly evident that nitric oxide synthase 2 (NOS2)-mediated NO/reactive nitrogen oxide species (RNS) are heavily involved in cancer progression and metastasis in different types of tumor. More recent studies have found that NO from NOS2+ macrophages is required for cancer immunotherapy to be effective.

CRITICAL ISSUES

NO/RNS, unlike other molecules, are unique in their ability to target a plethora of oncogenic pathways during cancer progression. In this review, we subcategorize the different levels of NO produced by cells and shed light on the context-dependent temporal effects on cancer signaling and metabolic shift in the tumor microenvironment.

FUTURE DIRECTIONS

Understanding the source of NO and its spaciotemporal profile within the tumor microenvironment could help improve efficacy of cancer immunotherapies by improving tumor infiltration of immune cells for better tumor clearance.

Carbon Monoxide Poisoning Presenting as Non-Convulsive Status Epilepticus Treated with Hyperbaric Oxygen Therapy

Carbon monoxide (CO) poisoning is one of the most serious medical emergencies causing life-threatening conditions, including cardiovascular and neurological sequelae. Acute CO poisoning can lead to myocardial ischemia, ventricular arrhythmia, syncope, seizures, and coma. Seizures and other neurological complications in the early stages of presentation are related to severe intoxication in CO poisoning. In such situations, aggressive hyperbaric oxygen therapy is recommended. In CO poisoning, non-convulsive status epilepticus has rarely been observed following hyperbaric oxygen therapy (HBO₂). We report a case of CO poisoning presenting as non-convulsive status epilepticus treated with HBO₂. Mechanisms and implications for non-convulsive status epilepticus provocation during HBO₂ treatment are discussed.

Molecular detection of inflammation in cell models using hyperpolarized 13C-pyruvate

The detection and treatment monitoring of inflammatory states remain challenging in part due to the multifactorial mechanisms of immune activation and spectrum of clinical manifestations. Currently, diagnostic strategies tend to be subjective and limited quantitative tools exist to monitor optimal treatment strategies. Pro-inflammatory M1 polarized macrophages exhibit a distinct metabolic glycolytic phenotype compared to the continuum of M2 polarization states. In the present study, the distinct metabolic phenotypes of resting and activated macrophages were successfully characterized and quantified using hyperpolarized carbon-13 (¹³C) labeled pyruvate and its metabolic products, i.e. lactate, as a biomarker of resting, disease and treated states. Methods: Mouse macrophage J774A.1 cells were used as a model system in an NMR compatible bioreactor to facilitate dynamic hyperpolarized ¹³C measurements. The glycolytic metabolism of the cells in the quiescent or resting state were compared with macrophages stimulated by lipopolysaccharide, a classical M1 activator using hyperpolarized ¹³C labeled pyruvate. Additionally, the activated macrophages were also treated with a non-steroidal anti-inflammatory drug to assess the changes in hyperpolarized lactate signal. The hyperpolarized lactate signals were then correlated using biochemical and molecular assays. Results: We first validated our model system of inflammatory cells by the hallmarks of M1 polarization using steady state metabolic profiling with high resolution NMR in conjunction with nitric oxide Greiss assay, enzyme activity, and mRNA expression. Subsequently, we clearly showed that the cutting edge technology of hyperpolarized ¹³C NMR can be used to detect elevated lactate levels in M1 polarized macrophages in comparison to control and non-steroidal anti-inflammatory drug treated M2 states. Conclusion: Hyperpolarized ¹³C lactate has the potential to serve as a biomarker to non-invasively detect and quantify pro-inflammatory state of immune regulatory cells and its response to therapy.

Network integration of parallel metabolic and transcriptional data reveals metabolic modules that regulate macrophage polarization

Macrophage polarization involves a coordinated metabolic and transcriptional rewiring that is only partially understood. By using an integrated high-throughput transcriptional-metabolic profiling and analysis pipeline, we characterized systemic changes during murine macrophage M1 and M2 polarization. M2 polarization was found to activate glutamine catabolism and UDP-GlcNAc-associated modules. Correspondingly, glutamine deprivation or inhibition of N-glycosylation decreased M2 polarization and production of chemokine CCL22. In M1 macrophages, we identified a metabolic break at Idh, the enzyme that converts isocitrate to alpha-ketoglutarate, providing mechanistic explanation for TCA cycle fragmentation. (13)C-tracer studies suggested the presence of an active variant of the aspartate-arginosuccinate shunt that compensated for this break. Consistently, inhibition of aspartate-aminotransferase, a key enzyme of the shunt, inhibited nitric oxide and interleukin-6 production in M1 macrophages, while promoting mitochondrial respiration. This systems approach provides a highly integrated picture of the physiological modules supporting macrophage polarization, identifying potential pharmacologic control points for both macrophage phenotypes.

Development of nitric oxide synthase inhibitors for neurodegeneration and neuropathic pain

Nitric oxide (NO) is an important signaling molecule in the human body, playing a crucial role in cell and neuronal communication, regulation of blood pressure, and in immune activation. However, overproduction of NO by the neuronal isoform of nitric oxide synthase (nNOS) is one of the fundamental causes underlying neurodegenerative disorders and neuropathic pain. Therefore, developing small molecules for selective inhibition of nNOS over related isoforms (eNOS and iNOS) is therapeutically desirable. The aims of this review focus on the regulation and dysregulation of NO signaling, the role of NO in neurodegeneration and pain, the structure and mechanism of nNOS, and the use of this information to design selective inhibitors of this enzyme. Structure-based drug design, the bioavailability and pharmacokinetics of these inhibitors, and extensive target validation through animal studies are addressed.

Adenovirus-mediated eNOS expression augments liver injury after ischemia/reperfusion in mice

Hepatic ischemia/reperfusion (l/R) injury continues to be a critical problem. The role of nitric oxide in liver I/R injury is still controversial. This study examines the effect of endothelial nitric oxide synthase (eNOS) over-expression on hepatic function following I/R. Adenovirus expressing human eNOS (Ad-eNOS) was administered by tail vein injection into C57BL/6 mice. Control mice received either adenovirus expressing LacZ or vehicle only. Sixty minutes of total hepatic ischemia was performed 3 days after adenovirus treatment, and mice were sacrificed after 6 or 24 hrs of reperfusion to assess hepatic injury. eNOS over expression caused increased liver injury as evidenced by elevated AST and ALT levels and decreased hepatic ATP content. While necrosis was not pervasive in any group, TUNEL demonstrated significantly increased apoptosis in Ad-eNOS infected livers. Western blotting demonstrated increased levels of protein nitration and upregulation of the pro-apoptotic proteins bax and p53. Our data suggest that over-expression of eNOS is detrimental in the setting of hepatic I/R.

The spermatogenic effect of yacon extract and its constituents and their inhibition effect of testosterone metabolism

We screened the pharmacological effects of a 50% ethanol extract of Yacon tubers and leaves on spermatogenesis in rats. As a result, we found that Yacon tuber extracts increased sperm number and serum testosterone level in rats. It has been reported that the crude extract of Yacon tubers and leaves contain phenolic acids, such as, chlorogenic acid, ferulic acid and caffeic acid by HPLC/MS analysis. We were interested in the contributions made by phenolic acid, particularly chlorogenic acid of Yacon tuber extract to the spermatogenic activity. After administering Yacon tuber extract or chlorogenic acid to rats for 5 weeks, numbers of sperm in epididymis were increased by 34% and 20%, respectively. We also administered ferulic acid, which has been reported to be a metabolite of chlorogenic acid and a constituent of Yacon tuber extract to investigate its spermatogenic activity in rats. Yacon tuber extract and ferulic acid increased sperm numbers by 43% and 37%, respectively. And, Yacon tuber extract, and chlorogenic acid showed significantly inhibition effect of testoeterone degradation in rat liver homogenate. We considered that the spermatogenic effect of Yacon tuber extract might be related to phenolic compounds and their inhibitory effect of testosterone degradation. Yacon showed the possibility as ameliorable agents of infertility by sperm deficiency and late onset hypogonadism syndrome with low level of testosterone.

Immune-responsive gene 1 protein links metabolism to immunity by catalyzing itaconic acid production

Immunoresponsive gene 1 (Irg1) is highly expressed in mammalian macrophages during inflammation, but its biological function has not yet been elucidated. Here, we identify Irg1 as the gene coding for an enzyme producing itaconic acid (also known as methylenesuccinic acid) through the decarboxylation of cis-aconitate, a tricarboxylic acid cycle intermediate. Using a gain-and-loss-of-function approach in both mouse and human immune cells, we found Irg1 expression levels correlating with the amounts of itaconic acid, a metabolite previously proposed to have an antimicrobial effect. We purified IRG1 protein and identified its cis-aconitate decarboxylating activity in an enzymatic assay. Itaconic acid is an organic compound that inhibits isocitrate lyase, the key enzyme of the glyoxylate shunt, a pathway essential for bacterial growth under specific conditions. Here we show that itaconic acid inhibits the growth of bacteria expressing isocitrate lyase, such as Salmonella enterica and Mycobacterium tuberculosis. Furthermore, Irg1 gene silencing in macrophages resulted in significantly decreased intracellular itaconic acid levels as well as significantly reduced antimicrobial activity during bacterial infections. Taken together, our results demonstrate that IRG1 links cellular metabolism with immune defense by catalyzing itaconic acid production.

Hepatocytes determine the hypoxic microenvironment and radiosensitivity of colorectal cancer cells through production of nitric oxide that targets mitochondrial respiration

PURPOSE

To determine whether host hepatocytes may reverse hypoxic radioresistance through nitric oxide (NO)-induced oxygen sparing, in a model relevant to colorectal cancer (CRC) liver metastases.

METHODS AND MATERIALS

Hepatocytes and a panel of CRC cells were incubated in a tissue-mimetic coculture system with diffusion-limited oxygenation, and oxygen levels were monitored by an oxygen-sensing fluorescence probe. To activate endogenous NO production, cocultures were exposed to a cytokine mixture, and the expression of inducible nitric oxide synthase was analyzed by reverse transcription-polymerase chain reaction, Western blotting, and NO/nitrite production. The mitochondrial targets of NO were examined by enzymatic activity. To assess hypoxic radioresponse, cocultures were irradiated and reseeded for colonies.

RESULTS

Resting hepatocytes consumed 10-40 times more oxygen than mouse CT26 and human DLD-1, HT29, HCT116, and SW480 CRC cells, and thus seemed to be the major effectors of hypoxic conditioning. As a result, hepatocytes caused uniform radioprotection of tumor cells at a 1:1 ratio. Conversely, NO-producing hepatocytes radiosensitized all CRC cell lines more than 1.5-fold, similar to the effect of selective mitochondrial inhibitors. The radiosensitizing effect was associated with a respiratory self-arrest of hepatocytes at the level of aconitase and complex II, which resulted in profound reoxygenation of tumor cells through oxygen sparing. Nitric oxide-producing hepatocytes were at least 10 times more active than NO-producing macrophages to reverse hypoxia-induced radioresistance.

CONCLUSIONS

Hepatocytes were the major determinants of the hypoxic microenvironment and radioresponse of CRC cells in our model of metabolic hypoxia. We provide evidence that reoxygenation and radiosensitization of hypoxic CRC cells can be achieved through oxygen sparing induced by endogenous NO production in host hepatocytes.

Nitric oxide mediates interleukin-1 induced inhibition of glycosaminoglycan synthesis in rat articular cartilage

Interleek-1β (IL-1) is a key mediator of cartilage matrix degradation in osteoarthritis and rheumatoid arthritis. It was found that the IL-1-induced suppression of glycosaminoglycan (GAG) synthesis in rat articular cartilage occurred simultaneously with the accumulation of nitrite (a metabolite of nitric oxide (NO) in aqueous milieu) in the culture medium. NO-synthase inhibitors, L-NMMA and L-NIO, inhibited both these IL-1 effects. Dexamethasone suppressed GAG synthesis additively to IL-1, but did not alter nitrite accumulation. Three NO-donors (GEA 3175, SNAP and SIN-1) also had an inhibitory effect on cartilage GAG synthesis. Therefore, it is concluded that IL-1 induced suppression of GAG synthesis in rat articular cartilage is mediated by the production of NO.

Oxygen transport and mitochondrial function in porcine septic shock, cardiogenic shock, and hypoxaemia

INTRODUCTION

The relevance of tissue oxygenation in the pathogenesis of organ dysfunction during sepsis is controversial. We compared oxygen transport, lactate metabolism, and mitochondrial function in pigs with septic shock, cardiogenic shock, or hypoxic hypoxia.

METHODS

Thirty-two anaesthetized, ventilated pigs were randomized to faecal peritonitis (P), cardiac tamponade (CT), hypoxic hypoxia (HH) or controls. Systemic and regional blood flows, lactate, mitochondrial respiration, and tissue hypoxia-inducible factor 1 alpha (HIF-1α) were measured for 24 h.

RESULTS

Mortality was 50% in each intervention group. While systemic oxygen consumption (VO(2) ) was maintained in all groups, hepatic VO(2) tended to decrease in CT [0.84 (0.5-1.3) vs. 0.42 (0.06-0.8)/ml/min/kg; P = 0.06]. In P, fractional hepatic, celiac trunk, and portal vein blood flows, and especially renal blood flow [by 46 (14-91)%; P = 0.001] decreased. In CT, renal blood flow [by 50.4 (23-81)%; P = 0.004] and in HH, superior mesenteric blood flow decreased [by 38.9 (16-100)%, P = 0.009]. Hepatic lactate influx increased > 100% in P and HH, and > 200% in CT (all P < 0.02). Hepatic lactate uptake remained unchanged in P and HH and converted to release in CT. Mitochondrial respiration remained normal. Muscle adenosine triphosphate (ATP) concentrations decreased in P (5.9 ± 1.4 μmol/g wt vs. 2.8 ± 2.7 μmol/g wt, P = 0.04). HIF-1α expression was not detectable in any group.

CONCLUSION

We conclude that despite shock and renal hypoperfusion, tissue hypoxia is not a major pathophysiological issue in early and established faecal peritonitis. The reasons for reduced skeletal muscle tissue ATP levels in the presence of well-preserved in-vitro muscle mitochondrial respiration should be further investigated.

Sulfuretin protects against cytokine-induced beta-cell damage and prevents streptozotocin-induced diabetes

NF-kappaB activation has been implicated as a key signaling mechanism for pancreatic beta-cell damage. Sulfuretin is one of the main flavonoids produced by Rhus verniciflua, which is reported to inhibit the inflammatory response by suppressing the NF-kappaB pathway. Therefore, we isolated sulfuretin from Rhus verniciflua and evaluated if sulfuretin could inhibit cytokine- or streptozotocin-induced beta-cell damage. Rat insulinoma RINm5F cells and isolated rat islets were treated with IL-1 beta and IFN-gamma to induce cytotoxicity. Incubation of cells and islets with sulfuretin resulted in a significant reduction of cytokine-induced NF-gamma B activation and its downstream events, iNOS expression, and nitric oxide production. The cytotoxic effects of cytokines were completely abolished when cells or islets were pretreated with sulfuretin. The protective effect of sulfuretin was further demonstrated by normal insulin secretion of cytokine-treated islets in response to glucose. Treatment of mice with streptozotocin resulted in hyperglycemia and hypoinsulinemia, which was further evidenced by immunohistochemical staining of islets. However, the diabetogenic effects of streptozotocin were completely prevented when mice were pretreated with sulfuretin. The anti-diabetogenic effects of sulfuretin were also mediated by suppression of NF-kappaB activation. Collectively, these results indicate that sulfuretin may have therapeutic value in preventing beta-cell damage.

Topical application of dressing with amino acids improves cutaneous wound healing in aged rats

The principal goal in treating surgical and non-surgical wounds, in particular for aged skin, is the need for rapid closure of the lesion. Cutaneous wound healing processes involve four phases including an inflammatory response with the induction of pro-inflammatory cytokines. If inflammation develops in response to bacterial infection, it can create a problem for wound closure. Reduced inflammation accelerates wound closure with subsequent increased fibroblast function and collagen synthesis. On the contrary, prolonged chronic inflammation results in very limited wound healing. Using histological and immunohistochemical techniques, we investigated the effects of a new wound dressing called Vulnamin that contains four essential amino acids for collagen and elastin synthesis plus sodium ialuronate (Na-Ial), compared with Na-Ial alone, in closure of experimental cutaneous wounds of aged rats. Our results showed that the application of Vulnamin dressings modulated the inflammatory response with a reduction in the number of inflammatory cells and inducible nitric oxide synthase (iNOS) immunolocalisation, while increasing endothelial nitric oxide synthase (eNOS) and transforming growth factor-beta1 (TGF-beta1) immunolocalisation. Furthermore, the dressing increased the distribution density of fibroblasts and aided the synthesis of thin collagen fibers resulting in a reduction in healing time. The nutritive approach using this new wound dressing can provide an efficacious and safe strategy to accelerate wound healing in elderly subjects, simplifying therapeutic procedures and leading to an improved quality of life.

Endogenous nitric oxide can act as beneficial or deleterious in the hypoxic lung depending on the reoxygenation time

Nitric oxide (NO) has been implicated in many pathophysiological situations in the lung, including hypoxia/reoxygenation. This work seeks to clarify the current controversy concerning the double protective/toxic role of endogenous NO under hypoxia/reoxygenation situations in the lung by using a nitric oxide synthase (NOS) inhibitor, in a novel approach to address the problems raised from assaults under such circumstances. A follow-up study was conducted in Wistar rats submitted to hypoxia/reoxygenation (hypoxia for 30 min; reoxygenation of 0 h, 48 h, and 5 days), with or without prior treatment using the nonselective NOS inhibitor L-NAME (1.5 mM, in drinking water). Lipid peroxidation, apoptosis level, protein nitration, in situ NOS activity and NO production (NOx) were analyzed. This is the first work to focus on the time-course effects of L-NAME in the adult rat lung submitted to hypoxia/reoxygenation. The results showed that after L-NAME administration, in situ NOS activity was almost completely eliminated and consequently, NOx levels fell. Lipid peroxidation and the percentage of apoptotic cells rose at the earliest reoxygenation time (0 h), but decreased in the later period (48 h and 5 days). Also nitrated protein expression decreased at 48 h and 5 days posthypoxia. These results suggest that NOS-derived NO exerts two different effects on lung hypoxia/reoxygenation injury depending on the reoxygenation time: NO has a beneficial role just after the hypoxic stimulus and a deleterious effect in the later reoxygenation times. Moreover, we propose that this dual role of NO depends directly on the producer NOS isoform.

Nardostachys jatamansi extract protects against cytokine-induced β-cell damage and streptozotocin-induced diabetes

AIM: To investigate the anti-diabetogenic mechanism of Nardostachys jatamansi extract (NJE).

METHODS: Mice were injected with streptozotocin via a tail vein to induce diabetes. Rat insulinoma RINm5F cells and isolated rat islets were treated with interleukin-1β and interferon-γ to induce cytotoxicity.

RESULTS: Treatment of mice with streptozotocin resulted in hyperglycemia and hypoinsulinemia, which was confirmed by immunohistochemical staining of the islets. The diabetogenic effects of streptozotocin were completely abolished when mice were pretreated with NJE. Inhibition of streptozotocin-induced hyperglycemia by NJE was mediated by suppression of nuclear factor (NF)-κB activation. In addition, NJE protected against cytokine-mediated cytotoxicity. Incubation of RINm5F cells and islets with NJE resulted in a significant reduction in cytokine-induced NF-κB activation and downstream events, inducible nitric oxide synthase expression and nitric oxide production. The protective effect of NJE was further demonstrated by the normal insulin secretion of cytokine-treated islets in response to glucose.

CONCLUSION: NJE provided resistance to pancreatic β-cell damage from cytokine or streptozotocin treatment. The β-cell protective effect of NJE is mediated by suppressing NF-κB activation.

Nitric oxide increases mitochondrial respiration in a cGMP-dependent manner in the callus from Arabidopsis thaliana

Nitric oxide (NO) acts as a key molecule in many physiological processes in plants. In this study, the roles of NO in mitochondrial respiration were investigated in the calli from wild-type Arabidopsis and NO associated 1 mutant (Atnoa1) which has a reduced endogenous NO level. Long-term exposure of wild-type Arabidopsis callus to sodium nitroprusside (SNP) increased mitochondrial respiration in both cytochrome and alternative pathways. In Atnoa1 callus, the capacity of both the cytochrome pathway and the alternative pathway was lower than that in wild-type callus. Further study indicated that NO enhanced the transcript abundance of genes encoding mitochondrial respiration-chain proteins as well as the protein expression of the NADH-ubiquinone reductase 75 kDa subunit and the alternative oxidase 1/2 in wild-type and Atnoa1 calli. 2-Phenyl-4,4,5,5-tetremethy-limidazolinone-1-oxyl-3-oxide (PTIO), a NO scavenger, inhibited the effects of NO in both calli. Co-incubation of callus with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor, also abolished NO effects. The membrane-permeable cGMP analog 8Br-cGMP mimicked NO effects. Moreover, the alternative pathway showed a higher sensitivity to the cellular cGMP changes than the cytochrome pathway did in gene transcription, protein expression and O(2) consumption. Taken together, NO could enhance mitochondrial respiration in both cytochrome and alternative pathways in a cGMP-dependent manner in Arabidopsis.

Gases in the mitochondria

Gasomodulators - nitric oxide, carbon monoxide and hydrogen sulphide - are important physiological mediators that have been implicated in disorders such as neurodegeneration and sepsis. Some of their biological functions involve the mitochondria. In particular, their inhibition of cytochrome c oxidase has received much attention as this can cause energy depletion and cytotoxicity. However, reports that cellular energy production and cell survival are maintained even in the presence of gasomodulators are not uncommon. In both cases, modulation of mitochondrial targets by the gasomodulators appears to be an important event. We provide an overview of the effects of the gasomodulators on the mitochondria.

Involvement of nitric oxide in 3-nitropropionic acid-induced depression of spinal reflexes in neonatal rat spinal cord in vitro

The objective of the present investigation is to study the involvement of nitric oxide (NO) in 3-nitropropionic acid (3-NPA)-induced depression of spinal reflexes. Experiments were conducted on preparations of hemisected spinal cord isolated from 4 to 8 day old rats. Stimulation of a dorsal root evoked reflex potentials (monosynaptic, MSR; polysynaptic, PSR) in the corresponding segmental ventral root. Superfusion of 3-NPA (3.4 mM) depressed the spinal reflexes in a time-dependent manner and the reflexes were abolished after 35 min. The time required to produce 50% depression of the reflexes (T-50) was 17.8+/-5.3 min for MSR and 17.5+/-2.1 min for PSR. L-NAME (Nomega-nitro-L-arginine methyl ester; 100 microM), a nitric oxide synthase inhibitor, antagonized the 3-NPA (3.4 mM)-induced depression of reflexes and increased the T-50 values (34 and 30 min for MSR and PSR, respectively) significantly (P<0.05). In addition, hemoglobin (Hb, 100 microM), a NO scavenger, blocked the 3-NPA-induced depression of reflexes significantly (P<0.05). T-50 values in Hb pretreated cords were 57 and 45 min for MSR and PSR, respectively which were greater than the cords pretreated with L-NAME. The nitrite (NO(2)(-)) content of the 3-NPA exposed cords was 84 microM/g of tissue which was significantly greater than the control (13 microM/g; P<0.05). Pretreatment of cords with L-NAME or Hb antagonized the 3-NPA-induced increase in NO(2)(-). The results indicate that NO produced by 3-NPA is involved in the 3-NPA-induced depression of spinal reflexes.

Differentiation of human osteosarcoma cells by isolated phlorotannins is subtly linked to COX-2, iNOS, MMPs, and MAPK signaling: implication for chronic articular disease

Arthritis is one of the most prevalent chronic inflammatory diseases, and it is characterized by structural and biochemical changes in major tissues of the joint, including degradation of the cartilage matrix, insufficient synthesis of extracellular matrix (ECM). Ecklonia cava (EC) is a member of the family of Laminariaceae, which is an edible marine brown alga with various bioactivities. In this study of the methanol extract of brown alga EC, the dieckol (1) and 1-(3',5'-dihydroxyphenoxy)-7-(2'',4'',6''-trihydroxyphenoxy) 2,4,9-trihydroxydibenzo-1,4,-dioxin (2) were isolated and characterized by NMR techniques with high yield. Phlorotannin derivatives (1, 2) promoted osteosarcoma differentiation by increasing alkaline phosphatase (ALP) activity, mineralization, total protein and collagen synthesis in human osteosarcoma cell (MG-63 cells), respectively. Furthermore, these phlorotannin derivatives (1, 2) inhibited mRNA gene and protein levels of matrix metalloproteinase (MMP-1, MMP-3, and MMP-13), iNOS and COX-2 in casein zymography, Western blot and reverse transcriptase-polymerase chain reaction (RT-PCR) assays. In addition, it was observed that the phlorotannins inhibited phosphorylation of JNK and p38 MAPK in human osteosarcoma cell. These results suggested the phlorotannin derivatives (1, 2) could promote cell differentiation, attenuate MMP-1, MMP-3, MMP-13 expressions, and inflammatory response via MAPK pathway in chronic articular diseases.

Nitric oxide inhibits the replication cycle of porcine parvovirus in vitro

This study investigated the inhibitory effect and mechanism of nitric oxide (NO) on porcine parvovirus (PPV) replication in PK-15 cells. The results showed that two NO-generating compounds, S-nitroso-l-acetylpenicillamine (SNAP) and l-arginine (LA), at a noncytotoxic concentration could reduce PPV replication in a dose-dependent manner and that this anti-PPV effect could be reversed by the NO synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME). By assaying the steps of the PPV life cycle, we also show that NO inhibits viral DNA and protein synthesis. This experiment provides a frame of reference for the study of the anti-viral mechanism of NO.

Autoinhibition of endothelial nitric oxide synthase (eNOS) in gut smooth muscle by nitric oxide

Nitric oxide in the gut is produced by nNOS in enteric neurons and by eNOS in smooth muscle cells. The eNOS in smooth muscle is activated by vasoactive intestinal peptide (VIP) released from enteric neurons. In the present study, we examined the effect of nitric oxide on VIP-induced eNOS activation in smooth muscle cells isolated from human intestine and rabbit stomach. NOS activity was measured as formation of the 1:1 co-product, l-citrulline from l-arginine. VIP caused an increase in l-citrulline production that was inhibited by NO in a concentration dependent manner (IC(50)~25 microM; maximal inhibition 72% at 100 microM NO). Basal l-citrulline production, however, was unaffected by NO. The effect was not mediated by cGMP/PKG since the PKG inhibitor KT5823 had no effect on eNOS autoinhibition. The autoinhibition was selective for NO since the co-product l-citrulline had no effect on VIP-induced NOS activation. Similar effects were obtained in rabbit gastric and human intestinal smooth muscle cells. The results suggest that NO produced in smooth muscle cells as a result of the activation of eNOS by VIP exerts an autoinhibitory restraint on eNOS thereby regulating the balance of the VIP/cAMP/PKA and NO/cGMP/PKG pathways that regulate the relaxation of gut smooth muscle.

Effect of active hexose correlated compound on the production of nitric oxide in hepatocytes

BACKGROUND

Active hexose correlated compound (AHCC) is a "complex compound" containing polysaccharides. AHCC has been reported to improve the prognosis of postoperative hepatocellular carcinoma patients. However, the molecular mechanism of this improvement is not fully understood. In the diseased liver, nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS) is considered to be a causal factor for various hepatopathies. In this study, the possibility of AHCC regulation of NO production by iNOS was pursued as a potential liver-protecting mechanism.

METHODS

Primary cultured rat hepatocytes were treated with interleukin-1beta (IL-1beta) in the presence or absence of AHCC. NO production, iNOS induction, and iNOS signal were analyzed.

RESULTS

IL-1beta stimulated iNOS induction through the activation of nuclear factor kappaB (NFkappaB), leading to NO production. The addition of AHCC inhibited NO production, showing >80% inhibition at 8 mg/mL. AHCC also decreased the levels of iNOS protein and mRNA. However, AHCC influenced neither the degradation of inhibitory protein kappaB (IkappaB) nor the activation of NFkappaB stimulated by IL-1beta. Transfection experiments with an iNOS promoter-luciferase construct (iNOS-Luc) revealed that AHCC had no effect on the transactivation activity of the iNOS promoter. By contrast, AHCC inhibited the activity of iNOS-Luc containing a 3'untranslated region (UTR) with adenosine and uridine (AU)-rich elements, which shows the stabilizing activity of iNOS mRNA.

CONCLUSIONS

Results indicated that AHCC inhibits the induction of iNOS at the level of transcription, causing a decrease in NO production in hepatocytes. AHCC seems to decrease the levels of iNOS mRNA by reducing mRNA stabilization rather than inhibiting its synthesis.

Role of nitric oxide in downregulation of cytochrome P450 1a1 and NADPH: Quinone oxidoreductase 1 by tumor necrosis factor-alpha and lipopolysaccharide

We previously demonstrated that tumor necrosis factor alpha (TNF-alpha) and lipopolysaccharide (LPS) downregulate aryl hydrocarbon receptor (AhR)-regulated genes, such as cytochrome P450 1a1 (Cyp1a1) and NADPH: quinone oxidoreductase 1 (Nqo1) gene expression, yet the mechanisms involved remain unknown. The correlation between the inflammation-mediated suppression of AhR-regulated genes and the TNF-alpha or LPS-induced nitric oxide (NO) production especially in murine hepatoma Hepa 1c1c7 cells has been questioned; therefore we investigated whether NO is involved in the modulation of Cyp1a1 and Nqo1 by TNF-alpha or LPS in Hepa 1c1c7 cells. A significant dose-dependent increase in the inducible nitric oxide synthase (NOS2) expression and NO production were observed by various concentrations of TNF-alpha (1, 5, and 10 ng/mL) and LPS (1 and 5 microg/mL) which was completely inhibited by a NOS2 inhibitor, L-N6-(1-iminoethyl) lysine (L-NIL) (1 mM). Furthermore, TNF-alpha and LPS significantly induced NOS2 expression. Both TNF-alpha and LPS repressed the beta-naphthoflavone (betaNF)-mediated induction of Cyp1a1 and Nqo1 at mRNA and activity levels. The downregulation of Cyp1a1, but not Nqo1, was significantly prevented by L-NIL. However, proxynitrite decomposer, iron tetrakis (N-methyl-4'-pyridyl) porphyrinato (FeTMPyP) (5 microM) did not affect TNF-alpha- and LPS-mediated downregulation of Cyp1a1 and Nqo1 at mRNA and activity levels. These results show that NO, but not peroxynitrite, may be involved in TNF-alpha- and LPS-mediated downregulation of Cyp1a1 without affecting the downregulation of Nqo1.

S-nitrosation of mitochondrial complex I depends on its structural conformation

Nitric oxide is known to cause persistent inhibition of mitochondrial respiration as a result of S-nitrosation of NADH: ubiquinone oxidoreductase (complex I) (Clementi, E., Brown, G. C., Feelisch, M., and Moncada, S. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 7631-7636). Little is known about whether such nitrosation occurs in physiological conditions and, if so, what are the possible cellular mechanisms. We have now found that the conformational state (active/deactive transition (Vinogradov, A. D. (1998) Biochim. Biophys. Acta 1364, 169-185)) of mitochondrial complex I is an important factor for the interaction of the enzyme with nitrosothiols and peroxynitrite. Only the deactivated, idle form of complex I was susceptible to inhibition by nitrosothiols and peroxynitrite. In contrast, the active form of the enzyme was insensitive to such treatment. Neither form of complex I was inhibited by nitric oxide itself. Our data suggest that the process of active/deactive transition plays an important role in the regulation of complex I activity and cellular respiration by nitric oxide. The implications of this finding for hypoxic or pathophysiological conditions in vivo are discussed.

The control of hepatic glycogen metabolism in an in vitro model of sepsis

Culturing hepatocytes with a combination of LPS, TNF-alpha, IL-1beta and IFN-gamma resulted in an inhibition of glucose output from glycogen and prevented the repletion of glycogen in freshly cultured cells. The reduced glycogen mobilisation correlated with the lower cell glycogen content and reduced rate of glycogen synthesis from [U-(14)C]glucose rather than alterations in either total phosphorylase or phosphorylase a activity. There was no change in the percentage of glycogen exported as glucose nor the production of lactate plus pyruvate indicating that redistribution of the Gluc-6-P cannot explain the failure of the liver to export glucose. Although changes in glycogen mobilisation correlated with NO production, inhibition of NO synthase by inclusion of L-NMMA in the culture medium failed to prevent the inhibition of either glycogen accumulation or mobilisation by the proinflammatory cytokines, precluding the involvement of NO in this response. LPS plus cytokine treatment had no effect on total glycogen synthase activity although the activity ratio was lowered, indicative of increased phosphorylation. The inhibition of glycogen synthesis correlated with a fall in the intracellular concentrations of Gluc-6-P and UDP-glucose and in the absence of measured changes in kinase activity, it is suggested that the fall in Gluc-6-P reduces both substrate supply and glycogen synthase phosphatase activity. The fall in Gluc-6-P coincided with a reduction in total glucokinase and hexokinase activity within the cells, but no significant change in either the translocation of glucokinase or glucose-6-phosphatase activity. This demonstrates direct cytokine effects on glycogen metabolism independent of changes in glucoregulatory hormones.

Inhibition of an iron-responsive element/iron regulatory protein-1 complex by ATP binding and hydrolysis

Iron regulatory protein-1 binding to the iron-responsive element of mRNA is sensitive to iron, oxidative stress, NO, and hypoxia. Each of these agents changes the level of intracellular ATP, suggesting a link between iron levels and cellular energy metabolism. Furthermore, restoration of iron regulatory protein-1 aconitase activity after NO removal has been shown to require mitochondrial ATP. We demonstrate here that the iron-responsive element-binding activity of iron regulatory protein is ATP-dependent in HepG2 cells. Iron cannot decrease iron regulatory protein binding activity in cell extracts if they are simultaneously treated with an uncoupler of oxidative phosphorylation. Physiologic concentrations of ATP inhibit iron-responsive element/iron regulatory protein binding in cell extracts and binding of iron-responsive element to recombinant iron regulatory protein-1. ADP has the same effect, in contrast to the nonhydrolyzable analog adenosine 5'-(beta,gamma-imido)triphosphate, indicating that in order to inhibit iron regulatory protein-1 binding activity, ATP must be hydrolyzed. Indeed, recombinant iron regulatory protein-1 binds ATP with a Kd of 86+/-17 microM in a filter-binding assay, and can be photo-crosslinked to azido-ATP. Upon binding, ATP is hydrolyzed. The kinetic parameters [Km=5.3 microM, Vmax=3.4 nmol.min(-1).(mg protein)(-1)] are consistent with those of a number of other ATP-hydrolyzing proteins, including the RNA-binding helicases. Although the iron-responsive element does not itself hydrolyze ATP, its presence enhances iron regulatory protein-1's ATPase activity, and ATP hydrolysis results in loss of the complex in gel shift assays.

Nitric oxide synthase inhibition in thoroughbred horses augments O2 extraction at rest and submaximal exercise, but not during short-term maximal exercise

REASON FOR PERFORMING STUDY

Work is required to establish the role of endogenous nitric oxide (NO) in metabolism of resting and exercising horses.

OBJECTIVES

To examine the effects of NO synthase inhibition on O2 extraction and anaerobic metabolism at rest, and during submaximal and maximal exertion.

METHODS

Placebo and NO synthase inhibition (with Nomega-nitro-L-arginine methyl ester [L-NAME] administered at 20 mg/kg bwt i.v.) studies were performed in random order, 7 days apart on 7 healthy, exercise-trained Thoroughbred horses at rest and during incremental exercise leading to 120 sec of maximal exertion at 14 m/sec on a 3.5% uphill grade.

RESULTS

At rest, NO synthase inhibition significantly augmented the arterial to mixed-venous blood O2 content gradient and O2 extraction as mixed-venous blood O2 tension and saturation decreased significantly. While NO synthase inhibition did not affect arterial blood-gas tensions in exercising horses, the exercise-induced increment in haemoglobin concentration and arterial O2 content was attenuated. In the L-NAME study, during submaximal exercise, mixed-venous blood O2 tension and haemoglobin-O2 saturation decreased to a greater extent causing O2 extraction to increase significantly. During maximal exertion, arterial hypoxaemia, desaturation of haemoglobin and hypercapnia of a similar magnitude developed in both treatments. Also, the changes in mixed-venous blood O2 tension and haemoglobin-O2 saturation, arterial to mixed-venous blood O2 content gradient, O2 extraction and markers of anaerobic metabolism (lactate and ammonia production, and metabolic acidosis) were not different from those in the placebo study.

CONCLUSION

Endogenous NO production augments O2 extraction at rest and during submaximal exertion, but not the during short-term maximal exercise. Also, NO synthase inhibition does not affect anaerobic metabolism at rest or during exertion.

POTENTIAL RELEVANCE

It is unlikely that endogenous NO release modifies aerobic or anaerobic metabolism in horses performing short-term maximal exertion.

Cranberry Juice Increases Antioxidant Status Without Affecting Cholesterol Homeostasis in Orchidectomized Rats

Oxidative stress and hypogonadism are linked to the increased incidence of cardiovascular disease in males. The objective of this research was to delineate whether drinking cranberry juice for 4 months affects antioxidant capacity and lipid profile in orchidectomized rats. Thirty-two 1-year-old male rats were randomized to two groups: a sham-control group (n = 8) and an orchidectomized group (n = 24). The orchidectomized group was divided into three groups of eight and assigned to one of the following treatments: orchidectomy, orchidectomy plus 27% cranberry juice, and orchidectomy plus 45% cranberry juice. At 120 days after initiation of the study, all rats were killed, blood was collected, and plasma was harvested for total antioxidant status, malondialdehyde, nitrate + nitrite, and superoxide dismutase (SOD) activity in liver, and concentrations of cholesterol and triglyceride in liver and in plasma. Orchidectomy depressed (P < .05) plasma antioxidant capacity and SOD activity, elevated (P < .05) nitrate + nitrite and malondialdehyde in plasma, and increased (P < .05) triglyceride and cholesterol values in liver and in plasma. Cranberry juice increased (P < .05) plasma antioxidant capacity and SOD activity and reduced (P < .05) nitrate + nitrite and malondialdehyde concentrations. Drinking cranberry juice did not affect cholesterol concentrations in liver and in plasma. Triglyceride concentration in plasma of orchidectomized rats that were drinking cranberry juice increased (P < .05), but its concentration in liver decreased (P < .05) to the level of shams. The protective effect of cranberry juice from oxidative damage may be mediated by a decrease in nitrate + nitrite and dose-dependent decrease in peroxidation.

Fe-S cluster proteins are intracellular targets for nitric oxide generated luminally at the gastro-oesophageal junction

In human, high concentrations of nitric oxide are generated at the gastro-oesophageal junction through entero-salivary recirculation of dietary nitrate. Nitric oxide is known to have a high affinity for Fe-S cluster proteins. The aim of this study is to investigate whether nitric oxide arising from the lumen diffuses into the adjacent tissue where it can interact with Fe-S proteins both in a rat animal model and human. An electron paramagnetic resonance detectable complex, dinitrosyl dithiolato iron complex (DNIC), was used as a biomarker for the interaction between Fe-S proteins and nitric oxide. The generation of the complex was evaluated in resected gastric tissue of nitrite-administered rat or biopsy specimens from human after nitrate ingestion. The activity of aconitase, one of the Fe-S cluster proteins, was also determined. The signal of the complex was observed at the rat gastro-oesophageal junction where luminal generation of nitric oxide from nitrite was maximal, and the intensity increased in a dose- and time-dependent manner. The appearance of the complex was accompanied by a significant inhibition of the aconitase activity at that site. The complex appeared in biopsy specimens from the gastro-oesophageal junction in three of five men after nitrate ingestion. Since DNIC is considered to be a decomposition product when Fe-S cluster proteins interact with nitric oxide, the appearance of the signal provides direct evidence that nitric oxide arising from the lumen can destroy such proteins. DNIC formation may represent the cellular mechanism responsible for the high prevalence of disease at the gastro-oesophageal junction.

Biological fate and clinical implications of arginine metabolism in tissue healing

Since its discovery in 1987, many biological roles (including wound healing) have been identified for nitric oxide (NO). The gas is produced by NO synthase using the dibasic amino acid L-arginine as a substrate. It has been established that a lack of dietary L-arginine delays experimental wound healing. Arginine can also be metabolized to urea and ornithine by arginase-1, a pathway that generates L-proline, a substrate for collagen synthesis, and polyamines, which stimulate cellular proliferation. Herein, we review subjects of interest in arginine metabolism, with emphasis on the biochemistry of wound NO production, relative NO synthase isoform activity in healing wounds, cellular contributions to NO production, and NO effects and mechanisms of action in wound healing.

Hyperhomocysteinemia alters cardiac substrate metabolism by impairing nitric oxide bioavailability through oxidative stress

BACKGROUND

Hyperhomocysteinemia (HHcy) has been considered a vascular disease associated with increased levels of oxidative stress that results in scavenging of NO. However, little is known of the impact of HHcy on cardiac function and especially myocardial metabolism.

METHODS AND RESULTS

L-Homocysteine was intravenously infused into conscious dogs, and the dogs were fed methionine to increase plasma homocysteine to 10 micromol/L for acute and 24 micromol/L for chronic HHcy. There was no significant change in hemodynamics with HHcy. Veratrine-induced, NO-dependent, coronary vasodilation (Bezold-Jarisch reflex) was reduced by 32% but was restored by simultaneous intravenous infusion of ascorbic acid or apocynin. Acute and chronic HHcy significantly increased uptake of glucose and lactate and decreased uptake of free fatty acid by the heart. HHcy significantly decreased bradykinin- or carbachol-induced reduction of myocardial oxygen consumption in vitro, and this effect was completely restored by coincubation with ascorbic acid, Tempol, or apocynin. Western blot analysis indicated an increase in Nox2 (82%) and a reduction in endothelial nitric oxide synthase (39%), phospho-endothelial nitric oxide synthase (39%), and superoxide dismutase-1 (45%). Microarray analysis of gene expression in heart tissue from chronic HHcy indicated a switch in cardiac phenotype to enzymes that metabolize glucose.

CONCLUSIONS

HHcy directly modulates substrate use by the heart independent of changes in hemodynamics or ventricular function by reducing NO bioavailability through the generation of superoxide. The progression of cardiac or coronary heart disease associated with HHcy should be evaluated in light of the impact of alterations in the regulation of cardiac metabolism and substrate use.

Involvement of nitric oxide in 3-nitropropionic acid-induced striatal toxicity in rats

The roles of nitric oxide (NO) in 3-nitropropionic acid (3-NPA)-induced toxicity were investigated using in vivo and in vitro models. Chronic 3-NPA administration (10 mg/kg) to rats produced selective striatal lesions that were associated with abnormal motor and EMG activities. In these animals, there was loss of glial fibrillary acidic protein (GFAP)-positive cells with extravasation of IgG in the lesion center, although microtubule-associated protein (MAP)-2-positive cells remained, indicating that astrocytes were involved. 3-NPA increased the NO(2)(-)/NO(3)(-) levels in microdialysates obtained from the striatum, thalamus and cerebellum. The basal NO(3)(-) level was much higher in the striatum than in the other areas. The NO(2)(-)/NO(3)(-) levels in the striatum were much higher in animals exhibiting abnormal muscular activity. Expression of endothelial NO synthase (eNOS), but not neuronal NOS (nNOS), was greatly increased in the striatum at 5 h after a second 3-NPA exposure, but not in other areas. In astrocyte cultures, the toxic effects of 3-NPA were associated with corresponding increases in the NO(2)(-) level, and this toxicity was attenuated by hemoglobin (Hb; 20 microM), which quenches NO. The NO(2)(-) generated by 3-NPA, even without cells, was also antagonized by Hb. 3-NPA, S-nitroso-n-acetyl-dl-penicillamine (SNAP) and sodium nitroprusside (SNP) all increased the NO current (detected by NO-sensitive electrodes) in concentration-dependent manners, and Hb significantly attenuated the NO generation induced by 3-NPA, SNAP or SNP. Taken together, these results suggest that 3-NPA generates NO both directly as a donor and indirectly by enhancing NOS expression to produce toxic effects on astrocytes and neuronal toxicity.

HEPATIC ISCHEMIA/REPERFUSION UPREGULATES THE SUSCEPTIBILITY OF HEPATOCYTES TO CONFER THE INDUCTION OF INDUCIBLE NITRIC OXIDE SYNTHASE GENE EXPRESSION

During hepatic ischemia/reperfusion (I/R), proinflammatory cytokines such as tumor necrosis factor alpha and interleukin (IL) 1beta stimulate the induction of inducible nitric oxide synthase (iNOS) in hepatocytes, followed by massive production of nitric oxide. We hypothesized that I/R upregulated the susceptibility of hepatocytes to confer the induction of iNOS gene expression. This study was designed to investigate whether cell susceptibility occurs in response to I/R and to delineate the mechanisms underlying the susceptibility. Hepatocytes were isolated from rats with hepatic I/R or sham, cultured, and treated with IL-1beta. The iNOS induction and its signal including inhibitor kappaB (IkappaB) kinase/nuclear factor kappaB (NF-kappaB) and Akt/type 1 interleukin 1 receptor (IL-1R1) were analyzed. Hepatocytes isolated from rats with I/R markedly increased the production of nitric oxide when stimulated by IL-1beta as compared with sham control. Ischemia/R also increased the levels of iNOS protein and its messenger RNA. Furthermore, I/R enhanced the activation of transcription factor NF-kappaB and the transactivation of iNOS promoter. However, I/R had no effects on the degradation of IkappaB and the nuclear translocation of p65 subunit of NF-kappaB. In contrast, I/R increased the phosphorylation of Akt and the upregulation of IL-1R1 induction, which is essential signal for the transcriptional activation of iNOS in addition to IkappaB kinase/NF-kappaB. These results demonstrate that I/R may augment hepatocyte susceptibility for the induction of iNOS gene expression through the enhancement of IL-1R1.

Cortex cinnamomi extract prevents streptozotocin- and cytokine-induced β-cell damage by inhibiting NF-κB

AIM: To clarify the mechanism underlying the anti-diabetic activities of cortex cinnamomi extract (CCE).

METHODS: To induce in vivo diabetes, mice were injected with streptozotocin (STZ) via a tail vein (100 mg STZ/kg body weight). To determine the effects of CCE, mice were administered CCE twice daily for 7 d by oral gavage starting 1 wk before the STZ injection. Blood glucose and plasma insulin concentration were measured as an index of diabetes. Also, to induce cytotoxicity of RINm5F cells, we treated with cytokines (IL-1β (2.0 ng/mL) and IFN-γ (100 U/mL)). Cell viability and nitric oxide production were measured colorimetrically. Inducible nitric oxide synthase (iNOS) mRNA and protein expression were determined by RT-PCR and Western blotting, respectively. The activation of NF-κB was assayed by using gel mobility shift assays of nuclear extracts.

RESULTS: Treatment of mice with STZ resulted in hyperglycemia and hypoinsulinemia, which was further evidenced by immunohistochemical staining of islets. However, the diabetogenic effects of STZ were completely prevented when mice were pretreated with CCE. The inhibitory effect of CCE on STZ-induced hyperglycemia was mediated through the suppression of iNOS expression. In rat insulinoma RINm5F cells, CCE completely protected against interleukin-1β and interferon-γ-mediated cytotoxicity. Moreover, RINm5F cells incubated with CCE showed significant reductions in interleukin-1β and interferon-γ-induced nitric oxide production and in iNOS mRNA and protein expression, and these findings correlated well with in vivo observations.

CONCLUSION: The molecular mechanism by which CCE inhibits iNOS gene expression appears to involve the inhibition of NF-κB activation. These results reveal the possible therapeutic value of CCE for the prevention of diabetes mellitus progression.

Demyelination: the role of reactive oxygen and nitrogen species

This review summarises the role that reactive oxygen and nitrogen species play in demyelination, such as that occurring in the inflammatory demyelinating disorders multiple sclerosis and Guillain-Barré syndrome. The concentrations of reactive oxygen and nitrogen species (e.g. superoxide, nitric oxide and peroxynitrite) can increase dramatically under conditions such as inflammation, and this can overwhelm the inherent antioxidant defences within lesions. Such oxidative and/or nitrative stress can damage the lipids, proteins and nucleic acids of cells and mitochondria, potentially causing cell death. Oligodendrocytes are more sensitive to oxidative and nitrative stress in vitro than are astrocytes and microglia, seemingly due to a diminished capacity for antioxidant defence, and the presence of raised risk factors, including a high iron content. Oxidative and nitrative stress might therefore result in vivo in selective oligodendrocyte death, and thereby demyelination. The reactive species may also damage the myelin sheath, promoting its attack by macrophages. Damage can occur directly by lipid peroxidation, and indirectly by the activation of proteases and phospholipase A2. Evidence for the existence of oxidative and nitrative stress within inflammatory demyelinating lesions includes the presence of both lipid and protein peroxides, and nitrotyrosine (a marker for peroxynitrite formation). The neurological deficit resulting from experimental autoimmune demyelinating disease has generally been reduced by trial therapies intended to diminish the concentration of reactive oxygen species. However, therapies aimed at diminishing reactive nitrogen species have had a more variable outcome, sometimes exacerbating disease.